RÉSUMÉ

En raison de l'évolution rapide de l'industrie et de la croissance démographique, la pollution de l'environnement, l'accès à l'eau potable et le changement climatique deviennent des problèmes majeurs. Par conséquent, le développement d'énergies durables et les processus d'oxydation avancés attirent beaucoup d'attention. Diverses stratégies et solutions ont été développées pour produire de l'eau potable et de l'énergie verte. La photocatalyse a des applications potentielles pour la dépollution de l'eau et de l'air et la génération de combustibles solaires. Parmi les semiconducteurs photocatalytiques TiO 2 a été très étudié en raison de sa bonne activité photocatalytique, de sa stabilité et de son prix bas. Néanmoins, TiO 2 n'est actif que sous UV (ce qui ne représente qu'environ que 4% du spectre solaire). Cet inconvenient limite les applications du dioxide de titane en photocatalyse.

Les polymères conjugués émergent comme une nouvelle classe de photocatalyseurs. Ils ont reçu au cours des dernières années beaucoup d'attention car ils peuvent absorber la lumière visible grâce à leur système π délocalisé et possèdent les propriétés des matériaux semi-conducteurs.

Dans ce travail, nous avons synthétisé des nanostructures d'un polymère conjugué à savoir le polypyrrole (PPy). La polymérisation est induite dans des moules souples (mésophases hexagonales ou mésophases lamellaires). Ces mésophases sont constituées d'un système quaternaire (eau, huile, tensioactif et co-tensioactif). Les nanomatériaux synthétisés in situ peuvent être extraits facilement en ajoutant de l'éthanol et de l'eau.

La radiolyse est une technique de choix pour synthétiser des nanomatériaux. Cette technique a été utilisée pour synthétiser différentes nanoparticules mono-ou bi-métalliques et nanostructures de polypyrrole.

Les nanostructures de polypyrrole et les nanocomposites à base de PPy se sont révélées très actives pour la dépollution de l'eau et de l'air par photocatalyse sous lumière UV et visible.

Les nanomatériaux à base de PPy modifié avec des nanoparticules métalliques sont très prometteurs pour la génération d'hydrogène photocatalytique. D'autre part, les nanostructures de PPy sont très actives pour l'oxydation photocatalytique de l'eau sans cocatalyseurs.

Le plan de ce manuscrit est décrit brièvement ci-dessous :

Le chapitre 1 présente le processus de photocatalyse, y compris les mécanismes photocatalytiques de dégradation et de division (« splitting ») de l'eau en H 2 et O 2 . L'état de l'art sur la synthèse radiolytique et l'utilisation de moules souples (« soft templates ») pour la synthèse de nanomatériaux est présenté. La synthèse de diverses structures du polymère conjugué polypyrrole et les applications des nanostructures de PPy (PPy seul ou nanocomposites à base de polypyrrole) sont présentées.

Dans le chapitre 2, des procédures de synthèse de nanomatériaux à base de PPy sont décrites : synthèse de PPy dans des moules souples, synthèse radiolytique, synthèse de PPy-TiO 2 et modification de PPy et PPy-TiO 2 avec des nanoparticules métalliques (Pt, Ni et PtNi).

Ces photocatalyseurs ont été caractérisés par différentes techniques. Les tests photocatalytiques utilisés pour évaluer l'activité de ces matériaux ont également été présentés.

Au chapitre 3, la synthèse de nanostructures de PPy par méthode chimique dans des moules souples (mésophases hexagonales) (PPy-NS-c) et par radiolyse (PPy-NS-γ) est présentée ainsi que leurs applications pour la dégradation photocatalytique de polluants organiques (méthylorange et phénol pris comme polluants modèles). Les photocatalyseurs ont été caractérisés par spectroscopie infrarouge à transformée de Fourier (FT-IR), microscopie électronique à balayage (MEB), microscopie électronique à transmission (MET), spectroscopie d'absorption UV-Vis, etc. L'activité photocatalytique des différentes nanostructures à base de PPy a été étudiée et discutée. Ces nanostructures sont très actives pour le traitement de l'eau sous UV et lumière visible. Nous avons montré que la nanostructuration du PPy est un facteur important pour l'application de ce polymère en photocatalyse.

Dans le chapitre 4, nous présentons la préparation du nanocomposite PPy-TiO 2 et son application pour le traitement de l'eau et de l'air par photocatalyse (dégradation du MO et du phénol) et du traitement de l'air (dégradation du toluène). Le nanocomposite est très actif pour la dépollution, bien plus actif que le PPy ou le TiO 2 seuls. Nous avons ainsi développé un nanocomposite hybride organique-inorganique bon marché et très actif pour des applications en photocatalyse.

Le chapitre 5 présente la modification des nanostructures de PPy avec des nanoparticules mono-et bi-métalliques (Pt, Ni, PtNi) pour la production d'hydrogène par photocatalyse. L'effet de la nature des précurseurs métalliques et le taux de charge ont été étudiés. Nous avons montré que la teneur en co-catalyseurs est cruciale pour la génération de H 2 . Nos résultats indiquent que les polymères conjugués modifiés avec des nanoparticules mono-et bi-métalliques sont des photocatalyseurs prometteurs pour l'évolution de H 2 .

Le chapitre 6 décrit la préparation de différentes structures ternaires (composite PPy-TiO 2 modifié par des nanoparticules (NP) de Pt) en contrôlant les sites de dépôt des NP de Pt sur TiO 2 , PPy ou PPy-TiO 2 pour la génération photocatalytique de H 2 . L'effet de la teneur en Pt, la stabilité et le mécanisme photocatalytique ont été étudiés et discutés.

Enfin, au chapitre 7, une conclusion générale et quelques perspectives sont présentées.

En bref, nous avons souligné que les nanostructures PPy peuvent être obtenues à l'aide de moules souples et par radiolyse. Les nanomatériaux à base de PPy présentent des applications très prometteuses en photocatalyse pour la dépollution et la génération d'hydrogène et dans d'autres domaines comme la nanomédecine.

GENERAL INTRODUCTION

Owing to the fast-moving industry and growth of population, environmental pollution, access to clean water, and climate change are becoming main issues. Therefore, development of sustainable energies and advance oxidative processes are attracting much attention. Various strategies and solutions have been developed to yield potable water and green energy.

Photocatalysis is considered as a potential technology for environment depollution (such as water, air and soils remediation) and clean energy generation. Among the semiconductor photocatalysts, TiO 2 has attracted the greatest interest due to its low cost, non-toxicity and good photocatalytic activity. However, TiO 2 is only active under UV light, which limit its practical applications.

Conjugated polymers emerge as a new class of photocatalysts and have received in the recent years a lot of attention because they can absorb visible light owing to their delocalized π-system and possess properties of semiconductor materials.

In this work, we synthesized conjugated polymer polypyrrole (PPy) nanostructures in soft templates (hexagonal mesophases or lamellar mesophases). These mesophases are made of quaternary system (water, oil, surfactant and co-surfactant). The nanomaterials synthesized in situ can be extracted easily by adding ethanol and water.

Radiolysis is a powerful technique to synthesize nanomaterials. This technique has been used to synthesize different mono or bimetallic nanoparticles and polypyrrole nanostructures.

Polypyrrole nanostructures and PPy-based nanocomposites were found very active for photocatalytic water and air depollution. Modified PPy and PPy-based nanomaterials with metal nanoparticles are very promising for photocatalytic hydrogen generation and bare PPy nanostructures are very active for photocatalytic water oxidation without cocatalysts.

The outline of this manuscript is described briefly below:

Chapter 1 introduces photocatalysis process including the photocatalytic mechanisms for degradation and water splitting. The state of the art on radiolytic synthesis and the use of soft templates for synthesis of nanomaterials are presented. Synthesis of various conjugated polymers polypyrrole structures and applications of polypyrrole and polypyrrole-based nanocomposites were presented.

In chapter 2, synthesis procedures of PPy-based nanomaterials are described: synthesis of PPy in soft templates, radiolytic synthesis, synthesis of PPy-TiO 2 and modification of PPy and PPy-TiO 2 with metal nanoparticles (Pt, Ni and PtNi). These photocatalysts were characterized by different techniques. The photocatalytic tests used to evaluate the activity of these materials were also presented.

In Chapter 3, synthesis of PPy nanostructures by chemical method in soft templates (hexagonal mesophases) (PPy-NS-c) and by radiolysis (PPy-NS-γ), and their application in photocatalytic degradation of organic pollutants (methyl orange and phenol) are presented.

The photocatalysts were characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy etc. The photocatalytic activity of different PPy-based nanostructures was studied and discussed. We demonstrated that the nanostructuration of PPy is an important factor for their application in photocatalysis.

In Chapter 4, we present the preparation of PPy-TiO 2 nanocomposite and its application in photocatalytic water (MO and phenol degradation) and air treatment (toluene degradation).

This work provides a facile way to develop cheap and very active organic-inorganic hybrid nanocomposite materials for photocatalysis applications.

Chapter 5 presents modification of PPy nanostructures with mono (Pt, Ni) and bimetallic (PtNi) nanoparticles for photocatalytic hydrogen production application. The effect of the nature of the metal precursors and the loading ratio were studies. We show that the loading rate in co-catalysts is crucial for H 2 generation. Our results indicate that modified conjugated polymers with mono-and bimetallic nanoparticles are promising photocatalysts for H 2 evolution.

Chapter 6 describes the preparation of different ternary structures by controlling the deposition sites of Pt nanoparticles on TiO 2 , PPy and PPy-TiO 2 for photocatalytic H 2 generation. The loading rate effect, the stability and the photocatalytic mechanism were investigated and discussed.

Finally, in Chapter 7 a general conclusion and some perspectives are presented. In brief, we stressed that PPy nanostructures can be obtained using soft templates and radiolysis. PPy The environmental pollution and chemical wastes are causing more and more serious problems with the development of chemical technology. There are many persistent organic compounds that are highly toxic and harmful to human health and ecosystems in industrial wastewater from chemical plants. These compounds have low biodegradability, that is, they do not decompose naturally. Persistent organic pollutants remain in the environment for a long time and cause environmental pollution. Generally, the main water treatment methods are activated sludge treatment, activated carbon treatment and solid-liquid separation, however, with these methods it is difficult to completely decompose persistent organic pollutants (POPs). Currently, advanced oxidation processes (AOP) have attracted much attention as efficient technologies to remove POPs. Ozone or chloride are the most widely used reagent for this oxidation, which are not environmentally friendly in true sense, even they have saved lives since the end of the 19 th century. Photocatalysis is one of the most widely investigated AOP, and utilizes a solid semiconducting material as photocatalyst. 1,2 On the other hand, with global energy consumption increase, environmental contamination is getting worse. Over 85% of energy source comes from fossil fuels (such as coal, natural gas and oil), which involves fossil fuels burning leading to environmental issues and CO 2 emmission. 3 Therefore, renewable energies will be a more affordable option in the future owing to technology development. Solar energy is considered as a clean and sustainable energy source. Among the different techniques of solar energy conversion, solardriving water splitting is one of the most potential ways to convert solar to hydrogen (STH), a green fuel. There are three main methods for conversion of solar energy into chemical energy systems: photocatalysis, electrocatalysis and photoelectrocatalysis. Particularly, photocatalytic hydrogen production via water splitting presents a promising alternative for sustainable fuel production to meet the target hydrogen price of $ 2.00~4.00 kg -1 set by the United States Department of Energy due to its low operational cost. 4

Photocatalysis

Energy and environment issues related to the nonrenewable unclean energy sources, the remediation of hazardous wastes, and toxic air contaminants have received tremendous attention. In the past decades, many practical strategies have been investigated to treat wastewater: For example, biological technologies were developed to remove variable contaminants from wastewater. Nevertheless, these techniques are limited due to the secondary pollution, some of which even leads to the occurrence of health-threatening bacteria and soluble organic pollution that are difficult to remove. In addition, fossil fuels are still the main energy of global energy sources, which leads rise to environmental pollution and climate problems. 5 Therefore, development of sustainable materials for water treatment and future green fuel generation is of great significance. Photocatalysis, as a green technique, is a desirable way to convert solar light for depollution or generation of chemical energy. Indeed, depollution of organic dyes in wastewater by photocatalytic degradation and clean hydrogen fuel generation by photocatalytic water splitting hold great promise to moderate the environmental issues and energy shortage.

Generally, in the photocatalysis process, the semiconductor harvests incident light to generate charge carriers, when the photo energy is equal or higher than the band gap of the semiconductor. The photogenerated electron-hole pairs recombine or subsequently separate and transfer to the surface of semiconductor where the redox reactions take place. On the other hand, a large part of the charge carriers will recombine or undergo surface recombination, which extremely decreases the photocatalytic activity of catalysts (Figure

1.1a).

Many studies have focused on inorganic metal oxides (e.g., TiO 2 , 6, 7 BiVO 4 , 8 ZnO 9 ), (oxy)sulfides (e.g., CdS, 10 SnS 2 11 ), and (oxy)nitrides (such as InN, 12 GaN 13 ), which are often based on metal cations possessing d 0 and d 10 electronic configurations, but suffer from drawbacks such as large band gap, sometimes photocorrosion or self-oxidation. 14,15 In particular, titanium dioxide (TiO 2 ) has been the most widely used photocatalyst because of its nontoxicity, mechanical stability, high photocatalytic activity and low price. However, its large band gap (3. Significantly, the electronic band structures, morphologies, surface properties (such as porosity, shape) 24,25 and the other parameters (light intensity 26 , wavelength 27 , initial concentration 28 , catalyst loading rate 29 , pH 30 , oxidants/electron acceptor 31,32 ) also play important roles in photocatalytic system.

The mechanism of photocatalytic degradation of organic pollutants

In general, the photocatalytic process for a semiconductor material (in air or water, and excited with photons of equal or higher energy than the band gap) consists in four steps: (1) light harvesting, ( 2) charge (electrons (e -) and holes (h + )) generation and (3) separation, and

(4) redox reactions on the photocatalyst surface. The series of redox reactions is the following: 5 Photocatalyst + hν → h + + e - (a)

h + + H 2 O → • OH + H + (b) h + + OH -→ • OH (c) h + + organic pollutant → (organic pollutant) + (d) e -+ O 2 → O •- 2 (e) H + + O •- 2 → • OOH (f) 2 • OOH → O 2 +H 2 O 2 (g) H 2 O 2 + O •- 2 → • OH + OH -+O 2 (h) H 2 O 2 + hν → 2 • OH (i) Organic pollutant + ( • OH, h + , • OOH, O •- 2 ) → … →CO 2 + H 2 O (j)
The photocatalytic redox reaction relates to three main active species: hydroxyl radicals

( • OH) (E 0 ( • OH /OH -) = 1.83 V SHE ), holes (h + ) and superoxide radical (O •- 2 ) (E 0 ( • O •- 2 /O 2 ) = - 0.33 V SHE ).
• OH radicals are as being the initial oxidants in the degradation of pollutants in water phase. The production of • OH usually via two ways: (i) water and OH -are oxidized by generated holes; (ii) O 2 in the solution is reduced by the excited electrons to form superoxide radicals, and then these O •- 2 radicals (or • HO 2 depending on the pH), followed decomposition to generate • OH (formula e-h). On the other hand, h + is widely considered as an oxidant for direct degradation of organic pollutants. Organic pollutants will undergo different steps of oxidation, intermediates are formed, and in general the organic pollutants can be completely degraded in CO 2 and H 2 O at the end of the process, and this is called mineralization.

Significantly, photogenerated e --h + pairs are easy to recombine in the absence of the e - or h + scavengers. Therefore, the type of scavengers is also important factor for photocatalytic efficiency.

The mechanism of photocatalytic hydrogen generation

Overall water splitting (OWS) into H 2 and O 2 , as shown in equation 1, is an uphill chemical reaction with an associated increase in the Gibbs free energy (ΔG° = 237 kJ mol -1 ):

2 H 2 O → 2 H 2 + O 2 , E 0 (overall) = 1.23 V (1)
During water splitting, a semiconductor absorbs photons with energies equal or higher than its bandgap, e -in the semiconductor are generated from the VB to the CB (step 1). These e -and h + independently diffuse to the surface of the semiconductor particles (step 2) and subsequently participate in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on the photocatalyst surface (step 3) (see Figure 1.2), through the reactions given below as equations 2 and 3. Sacrificial reagents are used to evaluate the photocatalytic activity for water splitting.

H

+ + 2e -→ H 2 , E 0 (H 2 /H 2 O) = -0.41 V (νs NHE) (2) 2 H 2 O + 4 h + → 4 H + + O 2 , E 0 (H 2 O/O 2 ) = +0.82 V (νs NHE) (3)
Electron donors (alcohol) or holes scavengers (sulfide ion) and electron acceptors or electron scavengers (Ag + , Fe 3+ ) are added to produce H 2 and O 2 respectively. Electron donors employed in photocatalytic reduction are typically methanol, ethanol, isopropanol, triethanolamine (TEA), EDTA, etc. Methanol (CH 3 OH) is widely recognized as a good resource for high-purity hydrogen due to its low boiling point and high H/C ratio. In a wateralcohol mixture, methanol is a good hole scavenger and usually shows a better photocatalytic efficiency than other compounds. Using methanol as a sacrificial agent in the hydrogen production reaction, there are two purposes (i) to increase H 2 production and produce less toxic substances during the methanol degradation process. It has been reported that CH 3 OH is oxidized to HCHO, HCO 2 H, and finally mineralized to CO 2 (equations 4-6) 33,34 (Figure 1.3):

CH 3 OH !", %&'. HCHO + H 2 (4) HCHO + H 2 O !", %&'.
HCO 2 H + H 2 (5) HCO 2 H !", %&'.

CO 2 + H 2 (6) (ii) The oxidation potential of methanol is 0.02 V, which is lower than the corresponding value for water, E 0 O2/H2O = 1.23 V at pH = 0. In addition, photocatalytic activity of water splitting is usually estimated by the quantum efficiency:

Overall quantum yield (%) =

) * +,-./0 12 /"13"/4 5 6 -13/%,3/7 +,-./0 12 89%84/9' :!1'197

x 100 (H 2 )

Overall quantum yield (%) =

; * +,-./0 12 /"13"/4 < 6 -13/%,3/7 +,-./0 12 89%84/9' :!1'197

x 100 (O 2 )

Conjugated polymers (CPs)

In 2000, the noble prize in chemistry was awarded to A.G. MacDiarmid (University of Pennsylvania, Philadelphia, USA), A.J. Heeger (University of California ar Santa Barbara, USA) and H. Shirakawa (University of Tsukuba, Japan) for the discovery and development of conducting polymers. 35 Conjugated polymers (CPs), providing unique one-dimensional (1D) delocalized π- Among the family of CPs, polypyrrole (PPy) has been the most extensively investigated owing to its environmental stability, facile synthesis, excellent stability. Besides, nanostructured photocatalysts bear the potential to improve many of the weaknesses outlined above. For instance, electron-hole recombination may be reduced in nanosized photocatalysts due to short charge transfer distances, and reactant adsorption and product desorption can be enhanced due to the high surface area offered by nanostructures. 40

electrons

Synthesis of polypyrrole (PPy) nanostructures

Chemical polymerization usually provides powdery PPy and can be easily scaled up. PPy was firstly synthesized in 1912. 41 Generally, the polymerization of pyrrole monomers, Py, into PPy can be achieved by traditional chemical oxidation (e.g., K 2 S 2 O 8 , FeCl 3 , H 2 O 2 ) 42 and electrochemical methods. 43 Other polymerization methodologies have been investigated such as photo-induced synthesis 44 or radiolysis. 45 Although the polymerization technologies of chemical and electrochemical methods are quite different, the first step of polymerization corresponds to the preliminary oxidation of Py monomers into their ionic chemical methods.

In addition, nanostructured conjugated polymers are attractive as advanced materials due to their improved performance and versatile applications. By using chemical and electrochemical polymerization, zero-dimensional like nanoballs, one-dimensional structures such as nanorods, nanotubes and two-dimensional like nanobowls and nanoclips of PPy can be obtained using hard templates, soft templates or structure-guiding agents (such as methyl orange). 46

Chemical polymerization

Polymerization of Py occurs steadily in the presence of an oxidant (such as FeCl 3 or ammonium persulfate (APS) or H 2 O 2 ). 47,48 Halogens and organic electron acceptors were also used as oxidants to synthesize PPy. 49,50 Besides, there are many factors such as solvents, oxidants, initial Py/oxidant ratio, duration and temperatures, which can affect the yield and the conductivity of PPy. 51 For example, the optimized Fe(III)/Py ratio is 2.4 for a yield of PPy is about 100%. Changing the initial ratio of the reactants affects the yield, but not the chemical component or conductivity. 52 The shorter times of polymerization and lower temperatures, (0 o C ~ 5 o C), the better conductivity of PPy is obtained. 53 When the oxidant is FeCl 3 , the overall reaction is as follows: Nanostructures of different shapes can be obtained using templates or surfactants as explained in the next paragraphs.

PPy nanospheres

The main disadvantages of template and seeded growth synthetic routes are that the use of templates or seeds can add cost and complexity to the synthesis, and removing the template or seeds can affect the physical properties of the nanostructures. Emulsion and dispersion polymerizations often need external emulsifiers or stabilizers, which can be difficult to remove. Hong et al. reported a facile way to synthesize uniform nanometer-sized PPy based on water-soluble polymer and metal cations in aqueous solution without any surfactant or template (Figure 1.7a-c) 55 . The metal cation (Fe 3+ ) was used as an oxidizing agent to initiate the chemical oxidation polymerization of Py. This method does not require a temperature and pressure, and the facile process provides a great possibility for mass production of PPy NPs.

Liao et al synthesized water-dispersible PPy nanospheres with size of less than 100 nm without any template, surfactant, or functional dopant via introducing 2,4diaminodiphenylamine as initiator into a reaction mixture of Py monomer, oxidant, and hydrochloric acid (HCl) (Figure 1.7d-e). 56 When smaller acids are added, smaller size spherical PPy NSs are obtained. The size and morphologies of PPy NPs are also dependent on the initiator and oxidant concentrations. PPy hollow spheres providing some immediate advantages over their solid counterparts were used for various applications because of their relatively low densities. During the past decades, different synthetic methods were developed for the PPy hollow spheres preparation, however, the most efficient procedure has been based on template-assisted synthesis, e.g., polystyrene latex spheres (PS) 57,58 , SiO 2 spheres 59 , metal and metal derivative as template (such as Au, Fe, AgCl) [60][61][62] , PPy hollow spheres could be subsequently achieved via removal of the templates. For example, D. Su et al used poly (methyl methacrylate) (PMMA) NPs as template to synthesize PPy hollow spheres 63 . One dimensional nanowires and nanotubes have attracted much attention in recent years due to the high sensitivity to surface effects and a configured channel for carrying charge and exciton efficiently. 65 The unique geometrical advantages and properties promote the various applications of nanowires and nanotubes. Generally, synthesis of PPy nanotubes or nanowires is based on templates such as anodic aluminum oxide (AAO), 66 structure-guiding agent MO, 67 V 2 O 5 nanofibers. 68 For example, Zhang et al. synthesized one-dimensional PPy nanotubes by using FeCl 3 oxidant and V 2 O 5 nanofibers as the sacrificial template (Figure 1.9a-b and e-f) and the noble metal nanoparticles (Ag, Au, Pd etc.) were obtained on the surface of tubes spontaneously (Figure 1.9c-d). 68,69 Methyl organge (MO) as a simple and easily accessible structure-guiding agent to synthesize the PPy nanotubes was for the first time reported by Yang et al. in 2005. 70 MO with a planar hydrophobic section and hydrophilic edge group (-SO - 3 ) is soluble in water, and possesses anionic and no surfactant characteristic in aqueous solution due to the absence of critical micelle concentration. At room temperature (25 o C), MO can dimerize and form oligomers at a concentration of 1 mM and 5~10 mM, respectively. Complexation can be obtained when an organic compound (such as phenol or dye) and a flocculant (Fe 3+ or Al 3+ ) are together. In the work reported by Yang et al, FeCl 3 was used to suppress the electrostatic repulsions between MO aggregation and/or reacts with negatively charged aggregates of MO in solutions, and then destabilize the charged particles and build establish amorphous aggregates. 70 PPy hollow nanotubes in high yield by using FeCl 3 -MO reactive self-degraded template, which the outer and inner diameters are about 70 nm and 50 nm, respectively. Notably, when the oxidant FeCl 3 is replaced with ammonium peroxysulfate (APS), no tubular precipitates are observed when it is mixed with MO. Yan et al. reported synthesis of PPy nanotubes (PPy-NTs) with uniform diameters (~100 nm) by in situ chemical polymerization of Py with FeCl 3 and MO as oxidant and dopant, respectively. They showed that the diameter of the PPy-NTs can be controlled by adjusting the concentration of the reactants, the types of solvents and the reaction temperature (Figure 1.9 g-h). Granular PPy NPs were obtained in the absence of MO 71 .4.1.4 Other nanostructures of PPy Some new two-dimensional PPy nanostructures have been developed in recent years. Yang et al. reported PPy nanorings obtained by using a soft template ((CTA) 2 PdBr 4 complex), while the Pd complex was synthesized via the reduction reaction between PdBr -2 4 and the monomer (Py) (Figure 1.10a). 72 Liu et al. described for the first time synthesis of 2-D nanoclip structures of PPy by using an oxidative template composed of cetrimonium cations and peroxydisulfate anions in the presence of CTAB (Figure 1.10b). The diameter of the homogeneous nanoclips was in the 50~70 nm range. 73 Monodispersed nanobowl sheets of PPy were synthesized by using polystyrene spheres at the aqueous/air interface as template via chemical polymerization (Figure 1.10c). These PPy nanobowls can be easily lifted-off and deposited, in full size, on any flat substrate. 74 L.M. Santino presented a modified vaporphase synthesis of polypyrrole nanofibers (PPy), which can conformably coat 3D fibrillar substrates such as hard carbon papers, this facile polymerization method provides the opportunity to deposit PPy NSs onto many electrochemically active materials, but it may not be stable at high temperatures (Figure 1.10 d-e). Electropolymerization limits the reactions on the surface of the electrodes, and the PPy normally grow on the surface of the electrode as a film. In many instance, PPy NSs grow along with the orientation of the electric field to form special structures. 76 The mechanism of electropolymerized PPy is still controversial although many mechanisms have been proposed so far by Diaz, 77 Kim, 78 Pletcher 79 and Reynold. 80 Among them, Diaz's mechanism is the most frequently encountered in the literature. The reaction process of this mechanism is as follows: 77,81 In the first step, the oxidation of Py leads to a radical cation formation (Scheme 1) and several resonance forms of this cation are expressed in Scheme 2:

Two unpaired electron density in the α-position of dimerizes by resonance to form a dihydromer dication (Scheme 3), and the two protons loss leads to formation of a dimer (Scheme 4).

The bipyrrole is more easily oxidized due to the its lower oxidation potential than that of monomer (Scheme 5).

The resonance cation form reacts with a monomer to form the trimer dication, and then deprotonates to obtain the neutral trimer (Scheme 6). α-position and β-position can undergo of the trimer can react with the following trimer even β-position could not be accessible sterically and α-coupling will predominate (Scheme 7), the longer the length of the chain, the higher number of β-bands formed.

The propagation continues in the same order: oxidation, coupling and deprotonation until the final polymer product is obtained (Scheme 8). Indeed, Diaz is the first person to synthesize PPy by using electropolymerization. The method features a combination of several successive reactions such as radical cation formation, radical coupling and deprotonation. However, some steps like propagation and termination are hard to investigate. Besides, many electropolymerization parameters also influence the property of polymerization. 77,79

PPy nanowires and nanotubes

The electrochemical polymerization of Py favors formation of PPy bulk materials such as conductive films. D-H Nam successfully fabricated PPy nanowires with a one-step process by cathodic electropolymerization without templates and chemical additives. The electrochemically generated NO + was utilized to oxidize neutral Py monomers, making it possible to use oxidizable metal substrates such as Cu and Ni. The synthesized nanowires are directly deposited on the Cu substrate as a thin film and the kinetics of Py in cathodic electropolymerization is highly influenced by the radical cations reactivity. The results showed that PPy nanospheres initially deposited on the Cu substrate gradually changed to nanowire structures in the form of a thin film. The growth kinetics of PPy nanowires was studied by analyzing the effect of the electrolyte and synthetic time (Figure 1.12 a-c). 82 J. Xing et al. showed a facile approach to construct antimicrobial peptide functionalized PPy nanowire array conductive electrodes for bacterial environment electrical signal detection application (Figure 1.12 d-e). They introduced an antimicrobial peptide (AMP) immobilized PPy nanowire array conductive electrode (PNW-AMP) using facile electrochemical deposition and further molecular immobilizing process through the existing dopant (dopamine) as an anchor. 83 PPy nanotubes can be synthesized using sacrificial templates (α-Fe 2 O 3 nanowires grown on the steel substrate), and then α-Fe 2 O 3 nanowire template was removed by H 3 PO 4 solution at constant current of 5 mA cm -2 (Figure 1.12 f). acid, an anionic surfactant), 86 camphorsulfonic acid, 87 or polyelectrolyte 88 (Figure 1.13 b-g).

These surfactants coated on the surface of gas bubbles and resulted in forming "soap bubbles", which are negatively charged. They can assemble on the surface of working electrodes under a positive potential during electropolymerization. These microcontainers with diameters of 20~100 nm and thickness of 10~150 nm stand upright on the working electrode surface. Then, Y. Gao et al. developed a microdroplet template for the electrochemical synthesis of PPy microcontainers by combining the layer-by-layer technique (Figure 1. 13f). 89,90 In the synthesis process, Py was dispersed as microdroplets in aqueous LiClO 4 solution by sonication following assembled on the ITO electrode decorated with multilayers of poly(diallyldimethylammoiun chloride) and poly(styrenesulfonic acid) at a positive potential. Finally, the well-ordered PPy microcontaimers formed by the polymerization of the outermost layers of the droplets with the diameter of 1~10 µm, which are smaller than those of the microcontainers prepared by the "soap bubble" template strategy. Electrochemical polymerization provides many advantages compared to chemical methods. Firstly, the obtained product is an electroactive film, which attaches to the electrode surface and shows high conductivity; Secondly, it is easy to control the mass and the thickness of the film; Thirdly, the film can be controlled directly in the process of synthesis. 54 Using electrochemical polymerization, various complex structures can be achieved.

Polymerization by radiolysis

Radiolysis is the interaction of high energy radiation (γ-rays, X-rays, electrons or ions beams) with matter. It is a powerful method to synthesize metal, polymer and composite nanomaterials. The interaction of high-energy photons (γ-rays or X-rays) or atomic particles (electrons or ions beams) with polar solvents such as water generates free radicals (solvated electrons e - aq , H

H 2 O •+ + H 2 O à • OH + H 3 O + (equation 8) H 2 O * à H • + • OH, H 2 + O • (equation 9) e -+ n H 2 O à e -
aq (equation 10) DCM, CH 2 Cl 2 ) radiolysis. [94][95][96] Instead of using external oxidative (or reducing) chemicals to initiate polymerization as in the case of chemical method, the oxidative or deducing radicals formed by sovent radiolysis are used for polymerization. The team synthesized PEDOT polymers for the first time using γ radiolysis of water. 95 In this way, the synthetic procedure is easy and environmentally friendly. In other words, water is used as the solvent without addition of chemical oxidants, the oxidative radicals are induced by water radiolysis. b). The radiosynthesized PPy showed excellent thermal stability and electrical conductivity. 45 Wang et al. reported PPy NSs with uniform size about 30.5 nm through γ-ray irradiation in an acidic aqueous solution of Py, and the monodispersed PPy NPs showed high-efficient NIR photothermal conversion for cancer therapy (Figure 1.14c-d). 97 Radiolysis provides a facile way to synthesize PPy nanospheres (NSs).

In this PhD work, the radiolysis technique was used to synthesize PPy nanostructures as well as mono-and bimetallic nanoparticles on PPy. These nanostructures were used for photocatalytic water treatment and hydrogen generation. TEM images of silver/polypyrrole core/shell particles centrifuged. 100

Polypyrrole nanostructures for environment and energy applications

As we mentioned before, a great deal of effort has been devoted to increase the photocatalytic efficiency and extending the light absorption range of TiO 2 . Among these approaches, formation of semiconductor heterojunction is an efficient way to enhance the photocatalytic properties. According to the electronic affinity and bandgap of semiconductors, heterostructures can be divided into three types: type I (straddling gap), type II (staggered gap) and type III (broken gap) (Figure 1.16). 101 However, only formation of type II heterostructures is an effective way to decrease the recombination of charge carriers for enhanced photocatalytic degradation and water splitting activity. On the other hand, the formed heterostructures can effectively increase the utilization efficiency of solar energy owing to the synergetic absorption of different semiconductors.

PPy-based heterojunctions can play a pivotal way for photocatalysis application owing to the narrower band gap and broadened light absorption in the visible region. In addition, polyoxometaltates (POMs) (metal (Mo VI , Ta V , Mo V , W VI , V V , Mo V ) oxide polyanion clusters with linked together by shared oxygen atoms to form well-defined frameworks) have been widely investigated in photocatalysis. 121 However, investigation of PPy/POM-based photocatalysts for water depollution is rare. X. Xu et al. reported loading of PPy on TMCP/POM via a facile in situ polymerization process, and the PPy/CuSiW 12 enhanced its photocatalytic degradation of RhB and quantum yield (Figure 1.17 c-f). 122 for the first-time soft templates made by hexagonal or lamellar mesophases to synthezise PPy nanostructures and we studied their application in photocatalysis. Besides, we also synthesized PPy nanostructures by radiolytic polymerization and we studied their application for photocatalytic degradation of organic pollutants and for water oxidation.

Synthesis nanomaterials in soft templates

We used hexagonal mesophases composed of a quaternary system, namely surfactant, cosurfactant, oil and brine. 139,140 Here, the surfactant with hydrophilic head and hydrophobic tail group is used to reduce the interfacial tension and free energy. Depending on the nature of the polar head group, surfactants can be classified as nonionic (Triton X-100), anionic In order to understand the different structures of micelles that may form, it is necessary to introduce the critical packing parameter (CPP). CPP = V/α•L, where V and L are the volume and length of the tail group, respectively, α is the cross-sectional area of the head group. The interaction of surfactant head groups, tail groups, solvents and geometric factors controls the overall tendency to form different phases and structures in solution. For instance, when the CPP < 1/3, it tends to form a spherical micelle (Table 1.1) 142

Table 1.1 examples of self-assembled surfactant phase structures.

The structure of mesophase (hexagonal or lamellar) strongly depends on the concentration ratio of a mixed ternary-system (surfactant, water and oil) ( will result in self-assembly of the hexagonal mesophase. Co-surfactants help to balance the interaction between the hydrophilic groups of the surfactant molecules.

Besides, in most amphiphile-water systems, the formation of lamellar mesophase is almost inevitable. Double-chain surfactants usually form a lamellar phase when diluted with water, while single-chain detergents form a lamellar mesostructure under more concentrated conditions. 142 The ICP team in collaboration with Laurence Ramos (Université de Montpellier) has

shown that giant direct hexagonal mesophases made by a quaternary system (water, surfactant, cosurfactant, and oil) can be used as nanoreactors to synthesize nanostructured materials (metals, polymers, oxides) both in the aqueous and in the oil phases. 139,140,144 The mesophases consist in surfactant-stabilized oil-swollen tubes that are arranged on a triangular lattice in an aqueous medium (Table 1.1 and Figure 1.24). These mesophases are very stable in a large pH domain and can be doped with a large amount of precursors. 139 These mesophases can be easily swollen by enhancing the ratio O/W. 145 The polymerization takes place in the confined oil or water domain depending on the polymer, for example, the ICP team has developed a soft template mediated (hexagonal mesophase) controlled synthesis of PEDOT, PDPB, P3HT nanostructures with tunable morphology (the monomer EDOT, DPB or 3HT doped in the oil phase). [146][147][148] Oil-swollen hexagonal mesophase resulting from the surfactant mediated self-assembly of a quaternary mixture of water, surfactant, co-surfactant, and oil, are versatile templates to synthesize anisotropic nanomateriaks. For example, PDPB nanofibrous nextwork structures were developed in the oil tubes of the mesophases by photo-induced radical polymerization using a chemical initiator or by gamma irradiation, the diameter of the nanofibers can be varied from 5 to 25 nm in a controlled fashion, which is directly determined by the oil tube diameter of the doped mesophases. 147 Additionly, the cationic surfactant based hexagnol mesophases as templates for the preparation of PEDOT nanostructures in a simple chemical route were fabricated in our group. 146 In this PhD work, conjugated polymer nanostructures (PPy NSs) have been successfully

synthesized in soft templates formed by hexagonal or lamellar mesophases. PPy NSs are polymerized by chemical oxidation of Py (monomer doped in oil phase) using FeCl 3 as an oxidant. We also synthesized PPy NSs by radiolytic polymerization without templates. The synthesis steps are presented in the next experiment section. /H 2 O = +2.8 V NHE )), are also formed. To avoid competitive oxidation reactions which may limit or even prevent the reduction process of metals (in general), hydroxyl scavengers must be added in the solution prior to irradiation. Among these scavengers, primary or secondary alcohols (such as 2propanol) molecules or formate ions, which also react with hydrogen atoms, are generally used (equation 11).

(CH 3 ) 2 CHOH + HO • (or H • ) → (CH 3 ) 2 C • OH + H 2 O (equation 11)
Due to their redox potentials (E 0 (CH 3 ) 2 CO/(CH 3 ) 2 C • OH)) = -1.8 V NHE at pH 7, the alcohol radicals are almost as powerful reducing agents as H • radicals to reduce the metal ions (M + ).

Prior to irradiation, the solutions are degassed with nitrogen or argon to remove oxygen.

The reaction process is as follows (equation 12-14):

M n+ + e - aq → M 0 (equation 12) M n+ + H • → M 0 + H -(equation 13) M n+ + nR • → M 0 + nR' + nH + (equation 14)
In the case of metal nanoparticle synthesized by radiolysis, the nucleation and growth of the clusters depends on the dose rate, which fixes the reduction kinetics. Therfore, the dose rate is a very important parameter in radiolytic synthesis. The dose absorbed by the materials is expressed by Gray (1 Gy = 1 J/kg). At a low dose rate, the reduction reaction is slow and the association of M + with atoms is faster than the generation of reducing radicals.

Conversely, at high dose rate, the reduction of metal ions is faster and a large number of seeds are formed in the bulk (Figuree1.25a). 92 When two different metals are present in solution, competitive reactions between these tow metals will depend on the dose rate and metal precusors. At a low dose rate, electrons will transfer from less noble metal atoms to more noble metal ions, thus facilitating the formation of core-shell bimetallic nanoparticles (the more noble metal being in the core). On the contrary, at high dose rate, the process of electron transfer from the less noble metal to the more noble metal can be prevented (due to fast reduction process) yielding alloyed clusters (Figure 1.26). 149,150 Figure 1.25 Nucleation and growth of clusters generated by radiolytic radicals at high and low dose rates (a) 92 and the scheme of the influence of the dose rate on the competition between the intermetal electron transfer and the coalescence processes during the radiolytic reduction of mixed metal ion solutions (b). 149

CHAPTER II Experimental Part

In this chapter, we will present the synthesis procedures of PPy and PPy-based nanostructures and their characterization with different techniques (such as Fourier transform infrared, scanning electron microscopy, transmission electron microscopy etc.), the photocatalytic tests for water treatment and hydrogen generation.

Materials and reagents

All the reagents used for the experiments are shown in Table 2.1 and they were analytically pure, commercially available, and used without further purification. arranged on a triangular lattice in water and doped with Py monomer in water phases (in our case) were used as soft templates for the synthesis of PPy nanostructures. Formation of hexagonal mesophases was described in details in previous works [START_REF] Ghosh | [END_REF]40,146,147,151 . As shown in (iii) PPy-bulk was synthesized by chemical oxidation (using FeCl 3 as oxidant) in water without any surfactant nor irradiation. The ratio monomer/oxidant Py/ FeCl 3 = 1/2 (the same ratio as that used for synthesis of PPy-NS-c). After centrifugation of the suspensions, bulk-PPy PPy were washed several times with ethanol and dried in the oven at 60 °C.

Preparation of PPy NS -TiO 2 composite

PPy nanostructures (PPy NS ) were obtained by surfactant-mediated soft templating (lamellar mesophases) method: We used the synthetic protocol reported in our previous work with some modifications 152 . In short, first, the monomer pyrrole (100 µL) and 1.6 mg of the SDS surfactant were dissolved in 4 mL aqueous NaCl (0.1 M). Then 6 mL cyclohexane and 1 mL pentanol were then added to the solution, the obtained mesophase doped by monomer was labeled as A. The mesophase B was prepared: An aqueous solution (4 mL) containing 0.1 M FeCl 3 and SDS surfactant (1.6 mg) was added under stirring to cyclohexane (6 mL) and pentanol (1 mL). The achieved mixture (A+B) was vigorously stirred with vortex, and kept 12 h for complete polymerization. The polymerization takes place in the confined aqueous domain. The PPy nanostructures powder was extracted with a mixture ethanol and distilled water. 153 The composite PPy NS -TiO 2 was obtained by sonication (5 min) in ethanol followed by 2 h stirring (Figure 2.4a). PPy bulk was synthesized without any soft template (polymerization in water using FeCl 3 as oxidant). PPy bulk -TiO 2 was prepared with the sample procedure used for PPy NS -TiO 2 preparation.

3 mg catalysts were dispersed in 3 mL ethanol and then dip-coating on the ITO glasses for photoelectrochemical tests (Figure 2.4d)

1.2.3 Preparation of Ag-TiO 2 composite
Modification of TiO 2 with Ag NPs (Ag-TiO 2 ) was obtained by radiolytic reduction (using a panoramic gamma source) of Ag + on TiO 2 in suspension in water (containing 0.1 M of 2propanol as HO . scavenger) as reported in our previous work. 153,154 Here, Ag-TiO 2 plasmonic photocatalyst is taken as a model photocatalyst to be compared withPPy NSs and PPy NS -TiO 2 due to its good photocatalytic activity under visible light. The metal ions are reduced by solvated electrons and alcohol radicals induced by solvent radiolysis. 155 For each sample, 20 mg PPy-NSs were added into 25 mL of an aqueous solution containing 0.1 M of ethanol (added as HO . radical scavenger) 156 and the metallic precursors.

N 2 was bubbled for 15 minutes to remove oxygen. Then, the samples were exposed to 60 Co panoramic γ-source at a dose rate of 4 kGy•h -1 for 30 minutes (dose 2.0 kGy). After irradiation, the suspensions were centrifuged and washed with water (10 mL) for 3 times.

Then, the samples were dried at 50 o C for 2 h (Figure 2 According to the following equation, the conductivity (ρ, S•cm -1 ) was obtained:

ρ = ( > 39) × @ A ×𝑡) -1
where V is the voltage (V), I is the applied current (A) and t is the thickness of the films (cm). In TiO 2 based compounds, the electron mobility(𝜇 / ) is much higher than of holes.

Therefore, ∆𝜎(𝑡) is mainly due to excess electrons. ∆𝑛 / (𝑡) is the excess free electron number at time t. A (sensitivity factor) is time independent and relies on the conductivity of the semiconductor and the microwave frequency.

The primary data given by TRMC signals are its maximum value (I max ), which corresponds the quantity of the excess electrons generated by the laser pulse, and its decay I(t), which is owing to the decrease of excess electrons.

Photocatalytic tests

The photocatalytic activity of the synthesized PPy-based nanomaterials was evaluated for water and air depollution (organic molecules' degradation) and for hydrogen generation. as standard test molecule, and presents some advantages 157 :

-It does not undergo degradation by photolysis or catalysis.

-It presents an absorption band at 269 nm detectable by UV-visible spectroscopy.

-Its degradation mechanism is known and the principal intermediates are benzoquinone, hydroquinone, and catechol. 158 -It can be completely mineralized into CO 2 and H 2 O.

-It adsorbs very weakly at the surface of TiO 2 .

-It is a real pollutant of water.

Methyl orange is a toxic azo dye used in textile industry and toluene was used as a model air pollutant which usually occur indoors from the use of household products such as paints, thinners, adhesives and cigarette smoke. The degradation rate of pollutants (phenol, methyl orange and toluene) is expressed as

(C 0 -C)/C 0 × 100%)
, where C 0 is the initial concentration and C represents the present concentration of pollutants after every interval of 1 h.

The mineralization of phenol was measured by the total organic carbon (TOC) by using a Shimadzu TOC-LCSH.

These experiments were conducted in Poland in the team of A. Zaleska during my scientific stay in 2019 with a fellowship (PROM program).

Photocatalytic H 2 generation

We used methanol as a hole scavenger. Some works have reported that different sacrificial donors without H (such as N 2 S or I -) could enhance the yield of hydrogen during photocatalytic process. 159 However, their photocatalytic activities are not as efficient as methanol as a hole scavenger in our work. under UV and visible light [START_REF] Ghosh | [END_REF][168][169][170] . Novel organic polymeric based materials have recently made an upsurge in photocatalysis and solar energy conversion 171 . For example, g-C 3 N 4 is a thermally and chemically stable semiconducting material that was discovered to photocatalyze a wide variety of chemical reactions including the water splitting reaction [172][173][174][175][176] .

Recently, we developed an alternative radiolytic methodology to synthesize the conducting polymers either in aqueous solutions or in organic solvents thanks to the use of high-energy radiations 45,95,[177][178][179][180][181][182] . Also, the controlled synthesis in soft templates (made of hexagonal mesophases) of conjugated polymer nanostructures (CPNs) such as poly(diphenylbutadyine) (PDPB) 147 , poly(3,4-ethylenedioxythiophene) (PEDOT) 183 , and poly(3-hexylthiophene) (P3HT) 169 has been reported by our group. We have demonstrated for the first time in the literature that these CPNs are highly active photocatalysts under UV and visible light, and more interestingly that their photocatalytic activity under visible irradiation is higher than that of plasmonic TiO 2 (titania modified with silver nanoparticles) 170 . In all cases, the polymer nanostructures were synthesized in soft templates made by hexagonal mesophases. In spite of using various methodology (radiolysis or photochemical polymerization for PDPB or chemical oxidation for PEDOT and P3HT), polymerization has always been shown to proceed in the confined hydrophobic domain (oil cylinders) of the hexagonal mesophases 151 . The as-prepared nanometric sized polymeric material can be extracted from the hexagonal mesophases by simple addition of ethanol [START_REF] Ghosh | [END_REF]40,146,147 . Importantly, the beneficial role of the nanostructuration of the polymer for its photocatalytic activity in the visible region was clearly observed, since the bulk counterpart exhibited very low photocatalytic activity Here, we demonstrate for the first-time the high photocatalytic activity of bare polypyrrole nanostructures for water treatment. We show that PPy conjugated polymers are highly efficient for degradation of organic pollutants (phenol taken as a model pollutant) under both ultraviolet and visible light irradiation. We report on the synthesis of PPy nanostructures with three different approaches: i) in soft templates using swollen hexagonal mesophases by chemical oxidation (PPy-NS-c), ii) in the absence of any template by direct gamma irradiation synthesis (PPy-NS-γ), and iii) without any templates by chemical oxidation (PPy-bulk). PPy nanostructures are stable under photocatalytic cycling. The photocatalytic activities of these PPy structures were investigated and compared. The photocatalytic mechanism was also studied and discussed in details.

Results and discussions

Soft templates (swollen hexagonal mesophases) were used as to synthesize PPy nanostructures (PPy-NS-c). These mesophases consisted of oil-swollen surfactant tubes ordered on a triangular lattice in water 139,140 . The hydrophobic range of the mesophases can have a capacity of high concentrations (maximum 0.1 M) of PPy monomer, which is polymerized by oxidant FeCl 3 . The mechanism of chemical oxidation of Py leading to PPy is described in the literature 194 .

Other nanostructures of PPy were synthesized by radiolysis (PPy-NS-γ) 45 . Radiolysis of aqueous solution is an efficient way to polymerize monomers into polymers by oxidative hydroxyl radicals Reaction (1) 45 The FTIR spectra of PPy-NS-c, PPy-NS-γ and PPy-bulk (Figure 3.3a) have been compared to those of PPy reported in the literature. 45,[195][196][197][198] The major peaks in the 1400 to 1600 cm -1 region is related to the p conjugated polyene unit formation. The band located at 1420 cm -1 corresponds to the C-N stretching vibration from pyrrole ring, and the low intensity peak at 1550 cm -1 is ascribed to the C=C/ C-C stretching of PPy, whereas peak at 1677 cm water. The spectra are similar to that in the previous reports [199][200][201] . The spectrum of PPy-NS-γ exhibits short wavelength absorption edge at about 425 nm, and the optical band gap is estimated equal to 2.41 eV. While PPy-NS-c shows absorption at shorter wavelength at 300 nm. Obviously, PPy-NS-c exhibits a small absorption in the visible region (≥ 400 nm),

indicating that part of visible light can be transmitted through PPy solution. The peak at around 470 nm is due to the π-π * transitions 202 . Interestingly, there is a high absorption intensity from the visible region to near-IR region (700 nm~1000 nm), which is the characteristic of the polaronic and bipolaronic transitions 187,201 . PPy-bulk agglomerate into larger particles that cannot be dispersed in ethanol and other solvents.

The optical band gap energy (E g ) of PPy was estimated by Kubelka-Munk method. The corresponding E g can be determined by the linear portion of (αhν) n vs. (hν) plot, where α, h, ν and k are the absorption coefficient, Planck constant, and light frequency, respectively. The value of n is equal to 2 for the indirect bandgap and 1/2 for the direct bandgap. Furthermore, stability with cycling is another important factor for the applications in photocatalysis. In order to evaluate the stability of the conjugated polymer PPy nanostructures for practical application, the stability of PPy with cycling was studied. During the photocatalytic cycles, PPy NSs only shows a slight decrease trend, for example, the degradation rate of phenol is up to 87% at the fourth cycle (Figure 3.5a) and there is no difference of morphology after 4 cycles (Figure 3.5b-c). This small decrease is due to the loss of the photocatalyst during the tests, as the samples are centrifuged and washed for further use. These results demonstrate that the as-prepared PPy NSs are very promising for water treatment and other photocatalytic applications. Our study also proves that nanostructuration of CPs is a key factor for photocatalytic applications. However, conjugated polymer nanostructures are very active photocatalysts under UV and visible light, while the bulk polymer counterparts have no significant photoactivity. The difference of photocatalytic activity between nanostructures and bulk conjugated polymer has been assigned to (i) the presence of more defects in bulk polymers have led to higher electron-hole recombination, and (ii) decreasing size of the CPs results in higher surface area 151,170 . We investigated the electronic properties of the synthesized PPy structures to understand their original photocatalytic performance under ultraviolet and visible light. When a semiconductor absorbs photons with energy higher or equal to the that of the band gap, the excited electrons (e -) can be transmitted from the valence band (VB) to the conduction band (CB), leaving holes (h + ) in the VB. Consequently, the e -and h + , when they escape recombination, can migrate to the surface of the photocatalysts where they participate in redox reactions with adsorbed species. In the presence of dioxygen, e -react with it to come into being the oxidizing O 2

•-superoxide radicals (E 0 (O 2 /O 2 •-) = -0.33 V SHE ) (Eq.1) and h + may be trapped by H 2 O or HO -to produce hydroxyl radicals (HO • ) (Eq.2-4):

O 2 + e -®O 2 •-(1)
O 2

•-is highly reactive, so it can oxidize molecules and convert them to HO • by the following reactions:

O 2 •-+ H + ® HO 2 • (2) 2 HO 2 • ® H 2 O 2 + O 2 (3) H 2 O 2 + O 2 •-® HO • + O 2 + HO -(4) H 2 O 2 + h + ® 2 HO • (5)
While at the HOMO level, holes may react with HO -(or H 2 O) to produce oxidizing HO • free radicals:

H 2 O + h + ® HO • + H + (6)
These radicals are very active so that they can oxidize organic pollutants (such as phenol 2-propanol (0.1 M) was used as hole and HO • scavenger. radical. In addition, it was found that the rate of photocatalytic degradation increased with NaI (surface HO • radical scavenger) and tert-butanol (free HO • radical scavenger). The result also shows the surface HO • radicals are responsible for the degradation of phenol compared with free HO • radicals owing to the small detected quantity of HO • using Tris (hydroxymethy) aminomethane as a probe (Table 3 To further understand the photocatalytic activity of PPy nanostructures, their electronic properties were investigated. Figure 3.7d shows the cyclic voltammetry (CV) curve of PPy-NS-γ, PPy-NS-c and PPy-bulk, which was used to evaluate the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) energy levels from the ionization potential and the electronic affinity, and the band gap of PPy is calculated (Figure 3.7e-f, Table 3.3). Specifically, the primary oxidation (p-doping) process occurs at onset potentials of 0.07 V (PPy-NS-c) and 1.41 V (PPy-NS-γ), while reduction (n-doping) process Recently, in our group, CP nanostructures of PDPB, P3HT and PEDOT with small band gaps and high photocatalytic activity under visible light were developed 40,146,169 .

CHAPTER IV Composite TiO 2 -Polypyrrole Nanostructures for Water and Air Depollution

Semiconductor photocatalysts based on TiO 2 have attracted increasing attention for water and air treatment owing to the low cost of titania, its high photochemical properties, excellent stability and outstanding photocatalytic activity [211][212][213][214][215] . Nevertheless, the large band gap of TiO 2 (3.2 eV for anatase and 3.0 eV for rutile) induces a photocatalytic activity only under ultraviolet light (5% of the solar light), which limits its commercial applications in photocatalysis. Besides, high charge carrier recombination in TiO 2 also results in a poor photocatalytic activity. In order to improve its photocatalytic activity, numerous approaches have been developed such as noble metal loading 153,154,206,[216][217][218][219] , non-metal doping [220][221][222] , heterojunction construction 206,214,[223][224][225] or modification with conjugated polymers (CPs) 131,168,[226][227][228][229][230][231] . Organic-inorganic hybrid materials have attracted much attention in solar energy conversion and photocatalytic degradation of organic pollutants 232,233 . Among them, modification of TiO 2 with conjugated polymer nanostructures (CPNs) presents promising photocatalysis application under visible light. CPs with their unique extending π-π* electron system which can serve as stable photosensitizers inpouring the electrons into the conduction band (CB) of semiconductors 151,152,168,204,234 . For example, composite materials composed exhibit higher photocatalytic property in visible region contrary to their bulk counterpart, and this activity is much higher than that of plasmonic TiO 2 152, 183, 234, 235 . These CPNs are synthesized in soft templates formed by hexagonal or lamellar mesophases and polymerized by UV light or radiolysis 146,147,151 .

In this work, we modified commercial P25 TiO 2 with nanostructured PPy (PPy NS )

(prepared in soft templates formed by hexagonal mesophases) for photodegradation of organic pollutants (methyl orange and phenol as model water pollutants and toluene as air pollutant).

The nanocomposite shows an important increase of the photocatalytic performance under FTIR is used to analyze the chemical structures of as-prepared samples. wavelength, and the I max signal of PPy NS -TiO 2 is higher than that of TiO 2 at 450 nm and 500 nm excitation. The signal decay is also slower in the composite material, and this is related to longer life time of charge carriers due to less e --h + recombination or rapid electron trapping.

The signal intensity of PPy NS -TiO 2 at 500 nm is slightly lower than that obtained with 450 nm excitation. These results demonstrate the formation of heterojunction between PPy NS and TiO 2 , which induces electrons transfer from PPy NS to TiO 2 under visible light and extension of the life time of charge carriers under UV and visible light. MO and phenol were taken as model pollutants in water. The effect of the mass ratios between PPy NS and TiO 2 (PPy NS : TiO 2 = 0:1, 1:2, 1:1, 2:1, 1:0) for photocatalytic degradation of MO was investigated and the best mass ratio for photocatalytic activity is 1:1 (see in composite shows a good photocatalytic activity: 70% of degradation rate of MO is achieved after 4 h. This activity is much higher than that of bare PPy NS (18% degradation after 4 h) and also much higher than than of plasmonic TiO 2 (20% degradation after 5 h), and interestingly higher than that of PPy bulk -TiO 2 (41% degradation after 4 h) (see Figure 4.6b).

These photocatalysts were also tested for phenol degradation. In Table 4.1, we compare our photocatalytic results for water treatment with those previously reported with other materials. The photocatalytic activity of PPy NS and PPy NS -TiO 2 composite was evaluated for air treatment and toluene has been taken as model pollutant. In order to satisfy the practical application, the stability and reusability of the photocatalyst was investigated. The photocatalytic activity of PPy NS -TiO 2 is stable after 6 A huge number of defects could be aggregated at the contact interface of various solids and the energy levels of the interface are quasi-continuous, exhibiting alike properties to conductors. This contact interface can also produce low electric resistance Ohmic contact and serve as the center of charge carrier's recombination 250 .

CPs behave as classical organic semiconductors. The nanostructutration of a conjugated polymer is a pivotal factor for its photocatalytic activity. The morphology and size of the photocatalytic nanomaterials have an important effect on their photocatalytic performance, as demonstrated for TiO 2 for example 251,252 or for CP nanostructures 152,204,234 . The difference in the photocatalytic property between nano and bulk CPs may be owing to larger sizes, larger surface areas, and more defects in bulk CPs, which are responsible for the e --h + recombinations 152,204 .

Under UV irradiation, the photogenerated e -in the CB of TiO 2 can recombine with the h + in the highest occupied orbital (HOMO) of PPy NS via the intimate interface resulting in the separation of photogenerated charge carriers (see

Conclusions

We have prepared a highly photoactive PPy NS -TiO 2 nanocomposite under visible for environmental pollution remediation. PPy NS -TiO 2 presents a red-shift of the absorption band edge and a significant reduction of the band gap (1.95 eV). Our experiments demonstrate that for water and air treatment PPy nanostructures modified with TiO 2 exhibit under visible light higher photocatalytic activity than plasmonic TiO 2 , PPy NS and PPy bulk -TiO 2 . This enhancement of the photocatalytic activity is due to the nanostructuration of the CP and the heterojunction formation at the interface between PPy NS and TiO 2 , which promotes the seperation of photoinduced e -and h + .

Interstingly, the composite PPy NS -TiO 2 has much higher photocatalytic performance than PPy bulk -TiO 2 : Indeed, conjugated polymers nanostructuration is a pivotal factor for photocatalytic applications. Highest surface area and less number of defects in nanostructured polymers (which induce less electron-hole recombinations), lead to higher photocatalytic activity compared to their bulk conterparts 152,204,234 .

This work provides a facile way to develop cheap and very active organic-inorganic hybrid nanocomposite materials for air and water treatment. This stable nanocomposite can also find applications in self cleaning surfaces. Future works will also focus on its modifications with cocatalysts based on abondant elements for water splitting (see Chapter VI).

These results have been published in J. Environ. Chem. Eng. 254

CHAPTER V Polypyrrole Nanotructures Modified with Mono-and Bimetallic Nanoparticles for Photocatalytic H 2 Generation

Hydrogen is a clean, promising and environmental friendly energy source to solve the energy crisis and environmental pollution. The production of hydrogen through a photocatalytic water-splitting process (WSP) has attracted increasing attention. [255][256][257] Many studies have focused on inorganic metal oxides (e.g., TiO 2 , 6, 7 BiVO 4 , 8 ZnO 9 ), (oxy)sulfides (e.g., CdS, 10 SnS 2 11 ), and (oxy)nitrides (such as InN, 12 GaN 13 ), which are often based on metal cations possessing d 0 and d 10 electronic configurations, but generally confined by the relatively limited properties such as large band gap, photocorrosion and self-oxidation. 14,15 Our team has demonstrated that conjugated polymers (CPs) are very active for water and air treatment under UV and visible light. 148,152,183,234,254 However, the photocatalytic hydrogen evolution activity of CPs are weakened by their fast photogenerated electron-hole pairs recombination and low catalysis kinetics. Fortunately, CPs are also excellent conductive supports for stabilizing co-catalysts to enhance their properties or extend their functions. [258][259][260][261][262] Incorporation of metals into semiconductors has demonstrated to be a promising way to promote charge carrier separation and increase the active sites as well. 263 Noble metals with a low Fermi level can trap electrons from the conduction band (CB) of the semiconductor. Among these noble metals, Pt is the best candidate as co-catalyst for hydrogen production due to its largest work function. 264 However, because of high cost and scariness of platinum, its replacement by low cost and abundant catalysts (or co-catalysts) is desirable, but remains a great challenge. 265 Ni is also a very promising candidate as cocatalyst for H 2 production owing to its low-cost and high photocatalytic properties. 203,266,267 Ni nanoparticles do not only provide a large surface area and active sites, but also decrease the electron-hole recombination. 203,266 Besides, many studies focus on the decrease of the loading with this precious metal by alloying it with another metal of lower cost to increase the photocatalytic activity of the modified photocatalyst for hydrogen evolution, because formation of alloys can reduce the metal-metal interatomic distance, induce electronic effects, greatly increase the number of active sites and accelerate the mass transfer between the different active sites. 268 For example, strategies using Pd-Pt, 269,270 Ni-Pt 271, 272 or multi- The mesophases doped with Py, with FeCl 3 and the mesophase resulting from the mixing of the two previous ones were characterized by small angle X-ray scattering (SAXS) (see

Figure 5.1a).

All the three samples are lamellar phases, characterized by two peaks located at scattering vectors q 0 and 2q 0 ; The increase of the scattered intensity at small q is also typical of lamellar phases. The spacing (periodicity of the lamellar phase) d = 2π/ q 0 = 6.3 nm is the same for the three samples. We note that the lamellar phase containing the monomer is more ordered (second order peak sharper) than the other samples.

The electrochemical Mott-Schottky measurement was performed to obtain flat band potential which can be given by the intercepts of the extrapolated lines (Slope) (Figure 5.1b).

The carrier concentration (N A ) is determined by the equation 274 :

𝑁 X = ) /Y Z Y [ \31:/
, e is electron charge, ε r is the dilecectric constant (~ 10 for PPy), ε 0 is the free space (8.85x10 -14 Fcm -1 ). The N A of PtNi-PPy (17.7x10 19 m -3 ) is five times than PPy (3.5 x 10 19 m -3 ), indicating enhanced electronic conductivity, which will lead to decrease of charge carrier recombination and better electron transfer. 242,275,276 UV-Vis spectrum of PPy exhibits an absorption in the visible region (400 nm~700 nm)

and near-IR region (700 nm ~1000 nm) ( The Ni2p core-level spectrum shows the presence of metallic nickel, the component Ni2p 3/2 at 852.5 eV, alongside with its oxide, and hydroxide, which are expected as nickel is very sensitive to oxygen (Figure 5.6d). 203,266,279 Given the low loading levels of both Ni and Pt, especially in the case of PtNi-PPy-NSs (Figure 5.6e-f), the acquisition conditions were adjusted in order to have the best possible signal/noise ratio in detriment of spectral resolution.

Photocatalytic H 2 generation

The addition of co-catalyst (such as Pt, Ni-NiO, PtNi) NPs for photocatalytic hydrogen generation can reduce the activation energy of the reaction, provide an active site for proton reduction and H-H bond formation and decrease the recombination of charge carriers, resulting in an improvement of photocatalytic activity for hydrogen production. 203,266 In addition, the loading amount of the co-catalyst is also a crucial factor for hydrogen generation. Interestingly 0.05%Pt-PPy-NSs and 0.1%Pt-PPy-NSs present higher photocatalytic performance compared with nanostructures comprising higher loadings in Pt (0.3%, 0.5% and 1% loading rate). This indicates that higher photocatalytic activity is obtained with a very small amount of co-catalyst. The H 2 production rate with 0.2%Pt-PPy-NSs is 1400 µmol/h/g, and the H 2 production rates with 0.05%Pt-PPy-NSs and 0.1%Pt-PPy-NSs are 312 and 341 µmol/h/g, respectively. For loading larger than 0.2%, the H 2 production rate decreases dramatically, showing that an excess metal loading can induce a dramatic decrease of the photocatalytic activity. At high loading, metal nanoparticles can play the role of recombination centers, inducing a decrease in the photocatalytic activity. 206 It is worth mentioning that the nature of the metal precursors is one of the factors that may strongly affect the size, shape and/or the surface state of the metal nanoparticles, and therefore their activity as co-catalysts. and nickel formate (C 2 H 2 NiO 4 ), respectively (Table 5.1). Cui and co-workers investigated the influence of the metal precursor ligands on the selectivity of alloy particle shape and structures. 284 Therefore, the choice of the metal precursor is very important for the co-catalyst activity for hydrogen production. of the photocatalytic activity of semiconductors for hydrogen production. 203,266,288 In case of Ni-Pd/TiO 2 , the study of light absorption, charge-carrier dynamics, and photocatalytic activity revealed that the main role of the metal NPs is to act as catalytic sites for recombination of atomic hydrogen. Platinum is very efficient in electron scavenging and proton reduction, while Ni is a very good co-catalyst for H-H bond formation. 203,266,272,282 Water molecules are reduced by the electrons to produce H 2 (H 2 O + e -→ H 2 + OH -) in the presence of co-catalysts. Methanol was used as a hole scavenger: CH 3 OH reacts with the holes to give CO 2 and H 2 . This hole scavenging results in better charge carrier separation and leads to enhancement of light conversion quantum yield. 34 Platinum is known to be an efficient sink for electrons. 218 The presence of Pt-based nanoparticles decreases the charge carrier recombination, and therefore induces the increase of the quantum yield. The excited electrons migrate from PPy-NSs to the metal NPs, and then H + are reduced on the metal surface to promote the proton reduction to generate atomic hydrogen, while these atomic hydrogen recombine to produce the molecular hydrogen (Figure 5.8d). 298 The metal nanoparticles (such as Pt, Ni and Pt-Ni) not only serve as an electron sinks, but also provide effective proton reduction sites due to its relatively low over-potential. 203

Conclusions

In conclusion, polypyrrole nanostructures (NSs) as catalyst-support to stabilize monoand bimetallic nanoparticles presented highly efficient photocatalytic hydrogen evolution.

PPy NSs were successfully synthesized in soft templates formed by lamellar mesophases. 234, 148, 183 152 We have shown in Chapter V that conjugated polymers modified with mono-or bimetallic NPs as cocatalysts present a promising activity for green 1%Pt-(PPy-TiO 2 ) photocatalyst shows a significantly enhanced photocatalytic property for hydrogen generation (125.1 mmol h -1 g -1 and 3200 µmol/h/g under UV and visible light irradiation, respectively) compared with same loading rate of Pt NPs deposited on PPy (11.8 mmol h -1 g -1 under UV light and 70.9 µmol/h/g under visible light, respectively) and TiO 2 (24.2 mmol h -1 g -1 under UV and 454.2 µmol/h/g under visible light irradiation), respectively (Figure 6.7a). The higher photocatalytic activity of Pt NPs deposited on PPy-TiO 2 can be ascribed to the routes of electron transfer (e - PPy(LUMO) →Pt and e - PPy(LUMO) →TiO 2(CB) →Pt), compared with (Pt-PPy)-TiO 2 and (Pt-TiO 2 )-PPy. Our photocatalysts were compared with some modified photocatalysts reported in literature for hydrogen production in Table 6.1. Pt-(PPy-TiO 2 ) is very active for hydrogen production under both UV and visible light, and its performance is equal or even surpasses the literature reports 6,154,206,299,308,[324][325][326][327][328] for photocatalysts based on TiO 2 or PPy.

Monometallic

For practical applications, it is important to check the stability of the photocatalyst. The migration of electrons under visible light in the ternary photocatalysts can be explained by the proposed mechanism in

Conclusions

In

Self cleaning surfaces:

Nanostructures based on PPy exhibit high photocatalytic activity for water and air treatment. In particular, PPy-TiO 2 can be easily deposited on surfaces such as glass. We will study their hydrophobic properties and future work will also focus on their application in self cleaning surfaces.

Water treatment:

New composites based on PPy nanostructures will be developed for applications in water catalyst to simultaneously take advantage from the higher reaction rate of photo-Fenton and from the higher mineralization yield of photocatalysis in water treatment. In future collaboration, we will combine this inorganic material with CP nanostructures, which are very active in H 2 O 2 formation. 338 These Ti-LFO/CPNs composites can in-situ produce H 2 O 2 from water under visible light. The composite nanomaterials will integrate both catalytic functions of H 2 O 2 production from water and H 2 O 2 utilization for water depollution. Very active composite photocatalyts for water treatment will be developed.

Hydrogen generation:

CPs nanostructures modified with noble metal-free photocatalysts for photocatalytic hydrogen generation.

Generally, precious metal nanoparticles (such as Pt, Au and Ag nanoparticles) are used as effective cocatalysts to promote the photocatalytic H 2 production on semiconductors.

However, the high cost and low abundance of precious metals greatly limit their applications.

Among the noble metal-free cocatalyst, nickel-based cocatalysts have received much attention due to their low cost, high activity, and stability.

1

 1 Characterizations and discussions ......................................................................................................... 6.1.2 Photocatalytic H 2 generation .................................................................................................................. 6.2. Conclusions ........................................................................................................................................ CHAPTER VII ............................................................................................................................... General Conclusions and Perspectives ....................................................................................... 7.1. General conclusion: .................................................................................................................................... 7.2. Perspectives: ................................................................................................................................................. PUBLICATIONS ........................................................................................................................... REFERENCES ............................................................................................................................... ANNEX ............................................................................................................................................

1

 1 and PPy-based nanomaterials exhibit promising applications in photocatalysis and other related fields. Globle environmental and energy issues Environmental pollution and energy shortage problems are the two major issues in today's society.

  photocatalysis. Besides, high charge carrier recombination in TiO 2 also results in a poor photocatalytic activity (Figure1.1a-b). To overcome these limitations and extend its photocatalytic activity toward the visible region, a huge number of efforts have been made either via doping of TiO 2 with N 16 , C 17 or S18 or by its surface modification with metal

Figure 1 . 1 .

 11 Figure 1.1. Photocatalysis process of TiO 2 (left) and solar radiation spectrum (right).

Figure 1 . 2

 12 Figure 1.2 Schematic illustration of the main processes within the photocatalytic overall water-splitting reaction. 4

Figure 1 . 3 .

 13 Figure 1.3. Schematic illustration of the photocatalytic reduction of water in the presence of methanol. The oxidation of methanol (sacrificial donor) in this example by photogenerated holes and hydroxyl radicals could result in the formation of H 2 and other intermediates.34

  photocatalysis due to their excellent electrical, electrochemical, physicochemical, conducting and optical properties (Figure 1.4 a). Recently, π-conjugated polymer nanostructures (CPNs) emerge as a new class of catalysts for various photocatalytic applications like water splitting, CO 2 reduction, degradation of organic pollutants and organic transformations (Figure 1.4 b) 36 .

Figure 1 . 4 . 39 Figure 1 . 5 .

 143915 Figure 1.4. Various applications of CPs (a) and photocatalysis applications of CPs (b).36

Figure 1 .

 1 Figure 1.7 (a) Schematic diagram of synthesis process of water-soluble PPy. (b) SEM image of PPy nanoparticles. (c) Tilted and cross-section SEM images of the PPy nanoparticles stacked on a substrate (scale bar: 100 nm). 55 SEM images of polypyrrole nanospheres synthesized with the following acids: (d) CSA, (e)HClO 4 using 10 mol % 2,4-diaminodiphenylamine initiator.56

Figure 1 .

 1 8a is a schematic diagram which illustrates the synthesis of PPy hollow nanospheres. The PMMA can be washed away with acetone. SEM and TEM images showed the as prepared PPy retained the spherical shape of the templates with a homogeneous size distribution, without shrinkage or structural deformation (Figure 1.8b-c). X. Liu et al demonstrated a simple in situ synthetic method to obtain SiO 2 /PPy core-shell particles (Figure 1.8d). PPy hollow spheres can be achieved after removing the SiO 2 temple 64 (Figure 1.8e). The size and thickness of PPy hollow spheres are dependent on the size of SiO 2 and additive volume of Py monomer.

Figure 1 .

 1 Figure 1.8 (a) Schematic diagram of the synthesis of PPy hollow nanospheres. (b) FESEM images of asprepared PPy hollow nanospheres. (c) TEM image of as-prepared PPy hollow nanospheres; 63 (d) The formation mechanism of SiO 2 /polypyrrole core-shell structure particles and PPy hollow spheres; (e) TEM image of PPy hollow spheres.64

Figure 1 . 9

 19 Figure 1.9 Polypyrrole•Cl nanotubes: (a) SEM, as synthesized. (b) TEM, as synthesized showing hollow tube. Inset: TEM showing pore filled with V 2 O 5 . (c) TEM, Ag nanocomposite. Insets: coaxial cable of Ag and particle size distribution (d) TEM, Au nanocomposite; 68 SEM images of polypyrrole•Cl nanofibers synthesized in ethanol/FeCl 3 using V 2 O 5 as the seed. Prior to the reaction, V 2 O 5 was stirred in ethanol for (e) 30 min and (f) 12 h; 69 (g) SEM images of PPy-NTs obtained in the presence of MO, (h) TEM images of PPy-NTs obtained in the presence of MO. 71

71

 71

1

 1

75

 75

Figure 1 . 10

 110 Figure 1.10 Schematic diagram of the fabrication of PPy-Pd composite nanorings (a); 72 (b) SEM images of PPy•Cl nanoclips (scale bar, 1 µm; inset, digital picture of paper clips); 73 (c) SEM images of the PPy-CSA nanobowl sheet; 74 (d) SEM of unwashed PPy after vapor phase polymerization onto a hard carbon papersubstrate, (e) Upon washing in 6 M HCl and methanol, the fibers relax yet remain separated.75

84

 84

Figure 1 .

 1 Figure 1.12 (a) SEM images of the polypyrrole nanowires synthesized by cathodic electropolymerization at -0.6 V SCE for 10 min from an aqueous solution containing 0.2 M NaNO 3 and 0.8 M HNO 3 with concentrations of pyrrole 0.20 M, (b) at 0.25 M pyrrole and 0.8 M HNO 3 with 0.2 M NaNO 3 , (c) the changes in electrolyte color before and after cathodic electropolymerization at -0.6 V SCE for 10 min: (left) 0.025 M pyrrole, 0.2 M NaNO 3 and 0.8 M HNO 3 and (right) 0.2 M pyrrole, 0.2 M NaNO 3 and 0.8 M HNO 3 ; 82 (d) SEM image of constructed PPy nanowire electrode (PNW) surface. (e) SEM image of AMP immobilized PPy nanowire electrode (PNW-AMP) surface. Insets in (d) and (e) were high magnification images. 83 (f) high-magnification SEM image of polypyrrole nanotubes.84

Figure. 1 .

 1 Figure. 1.13 (a) ESEM images of PPy microsuckers deposited on different micropillars, including circular pillars, spindle pillars and hexagonal pillars; 85 SEM images of PPy microcontainers and microspheres synthesized by electrochemical polymerizations. (b) Microcontainers doped with camphorsulfonic acid; 86 (c) Microcontainers doped with poly (styrenesulfonic acid); 88 (d) Microcontainers doped with camphorsulfonic acid and prepared by the CV technique; 87 (e) Arranged microcontainers on patterned electrodes; (f) Microspheres doped with naphthalenesulfonic acid; 91 (g) Microcontainers prepared by electrochemical growth of PPy on LBL film modified electrode. 89

Figure 1 . 93 S

 193 Figure 1.13 Maine reactions during the three stages of water radiolysis at neutral pH under nitrogen atmosphere.93

Figure 1 . 14 .

 114 Figure 1.14. Cryo-TEM images of radio synthesized PPy (γ-PPy) at 72 kGy. (a) Nanostructures of γ-PPy; (b) full view of chaplets of γ-PPy; 45 TEM images of the products prepared from γ-ray radiation on an acidic aqueous solution of Py at different pH: a) pH = 1; b) pH = 0.8. 97

Figure 1 .

 1 Figure 1.15 (a) SEM of polypyrrole film on glass substrate for exposure of the monomer solution 72 h, 99 (b)

Figure 1 . 16

 116 Figure 1.16 Schematic energy band diagram of three types of semiconductor heterojunctions. 101

Figure 1 . 16 .

 116 Figure 1.16. NO removal (a) and NO 2 production (b) of BiOCl and BiOCl/PPy composites under visible light, 111 (c) Schematic of charge carriers transfer in BiOBr-PPy and BiOBr-Ag-PPy. 112

Figure 1 .

 1 Figure 1.17. (a) PPy/PEG-borate was electrodeposited onto the ZnO microrod arrays; (b) Degradation rates of methylene blue by photolysis under visible light. (c) Fundamental unit of CuSiW12; (d) 2D framework of CuSiW 12 ; (e) Photocatalytic efficiency of PPy/CuSiW 12 and (f) Diagram of the photocatalytic mechanism for PPy/CuSiW 12 under visible light. 122

Figure 1 . 18 .

 118 Figure 1.18. (a) The visible-induced photocatalytic activity of different samples; (b) Postulated mechanism of the visible light-induced photo-degradation of acetone with PPy-Ag-TiO 2 nanocomposites. 123 (c) Photodegradation of MO with different samples under simulated solar power for 180 min; (d) UV-vis adsorption spectra showing photo degradation of MO with TiO 2 -PDA/PPy/cotton under 1 kW m -2 illumination; (e) Pictures showing the color change of the MO solution containing TiO 2 -PDA/PPy/cotton. 124

Figure 1 .

 1 Figure 1.19. (a) The comparative data of H 2 generation rate after 60 min visible light illumination for bare PPy and PPy based nanohybrids. (b) Possible mechanism involved in the photocatalytic activity of Au/PPy NHs. 128 (c) Photocatalytic hydrogen generation in presence of pure PPy (black line), Cu/PPy-0.05 (red line) and Cu 2 O/PPy heterostructures (blue line) as catalysts after 75 min visible light irradiation. (d) p-n junction formation between p type PPy and n type Cu 2 O after contact. 129

(

  Sodium dodecyl sulfate, SDS), cationic (Cetyltrimethylammonium Bromide, CTAB) and amphoteric (Phosphatidylcholine, PC) (Figure 1.21). 141 Besides, critical micelle concentration (CMC) is another characteristic of surfactants, which tend to aggregate and form micelles at a particular concentration. In a W/O (W/O is the ratio water to oil volume) microemulsion, the hydrophobic tails of a surfactant molecule are oriented out from the micelle and the hydrophilic head group associate wihin the core (Figure 1.22a) and vice versa for a O/W microemulsion will produce normal micelles (Figure 1.22b). In our case, direct micelles (O/W microemulsion) are considered for polymer (PPy) preparation.

Figure 1 . 21 .Figure 1 . 22 .

 121122 Figure 1.21. The different types of surfactants

Figure 1 .

 1 23).The self-assembly of the hexagonal mesophase is shown in Figure1.24. A high concentration of surfactant (salt or salt-free) in water will cause micelle formation. Incorporating oil into micelles will form an unstable emulsion (oil droplets in water). Adding a small amount of cosurfactant (a small molecule alcohol that enters the air/oil interface as a surfactant molecule)

Figure 1 .

 1 Figure 1.23. A schematic phase diagram of surfactant-water-oil systems. 143

Figure 1 . 24

 124 Figure 1.24 Formation of hexagonal mesophases.

( i )

 i The as-prepared sample PPy-NS-γ was synthesized by radiolysis without any template and the color of the solution varied from a transparent solution (before irradiation) to a black solution (after irradiation). PPy-NS-γ are obtained by oxidation of the Py monomer by HO • radicals in water solution. The synthesis procedure was adapted from the ref.45 with few modifications. In brief, an aqueous solution containing 20 mM pyrrole was degassed with N 2 O for 20 min and irradiated with a 60 Co panoramic γ-source at a dose rate of 4.1 kG.h -1 . The used dose was 77 kGy. After drying in the oven at 50 o C, a black powder was obtained: PPy-NS-γ (Figrue 2.1a-b).

Figure 2 . 1 .

 21 Figure 2.1. The image of 60Co gamma source (a) and PPy Polymerization by radiolysis (b)

Figure 2 . 2 ,

 22 Figure 2.2, 7 µL Py was added to 2 mL of an aqueous solution containing 0.1 M NaCl, and 0.8 g SDS were introduced to the obtained solution. The mixture is vortexed for few minutes and then put in an oven at 50 o C for 1 h: A transparent viscous micellar solution (solution A) is obtained. 0.1 M FeCl 3 was dissolved in 2 mL of water. 0.8 g SDS is introduced in the solution and the mixture is mixed, vortexed and put in an oven at 50 o C for 1 h (solution B).Subsequently, 3 mL of cyclohexane was added to each micellar solution (solution A and B, respectively). The ratio monomer/oxidant Py/FeCl 3 was 1/2. After vortexed a few minutes, 400 µL n-pentanol (co-surfactant) were added dropwise. The mixtures were then vortexed until a transparent (A) and yellow translucent (B), birefringent gels (hexagonal mesophases) were obtained. Mixing A and B lead to a black gel (C). During the process, the color of the mesophases changed very fast from transparent to black (Figure2.3). The PPy nanostructures were extracted by addition of ethanol, which destabilizes the mesophase. After centrifugation of the suspensions, PPy nanostructures were washed several times with ethanol and dried in the oven at 60 °C: A black powder (D) was then obtained.

Figure 2 . 2

 22 Figure 2.2 The flow-process diagram of PPy-NS-c synthesis.

Figure 2 . 3

 23 Figure 2.3 Colour variation during the synthesis process in mesophases leading to PPy-NS-c.

Figure 2 .

 2 Figure 2.4 (a) Formation of PPy NS -TiO 2 composite in an ethanol-water aqueous solution; (b) SEM image of PPy NS ; (c) SEM image of PPy NS -TiO 2 ; (d) PPy NS and PPy NS -TiO 2 on glass for air treatment.

. 5 )

 5 . Different metal loadings were labeled as x%M-PPy-NSs, where x% indicates the percentage in mass of the metal with respect to the mass of PPy. The materials were collected by centrifugation. The supernatant was completely transparent indicating that all the metallic species were deposited on the PPy nanostructures.

Figure 2 . 5 .

 25 Figure 2.5. (a) Synthesis process of PPy-NSs using a soft template (a lamellar mesophase); (b) Doped mesophases with (i) FeCl 3 and (ii) Py; (iii) PPy-NSs in mesophase; (c) Radiolytic synthesis of metal nanoparticles on PPy NSs (the composite nanomaterials are labeled M-PPy-NSs).

1. 3 . 7 .

 37 photogenerated charge-carrier dynamics of the as-prepared samples under UV and visible light excitation. A pulsed and tunable laser source (200 ~ 2000 nm) equipped with an optical parametric oscillator (OPO; EKSPLA, NT342B) was used to excite the samples and a Gunn diode (30 GHz) was used to generate microwaves. TRMC technique measures the relative change ( ∆E(') :) in microwave power reflected from a semiconductor material during its

1. 3 .

 3 11 Photoelectrochemistry characterization Mott-Schottky (MS) plots measurement was carried out by using a typical three electrode setup (Pt wire and Ag/AgCl as counter and reference electrodes, respectively). PPy film on FTO as working electrode. The MS spectra were measured in the voltage window of 0.2 V~1.0 V in the dark (increment: 20 mV, frequency: 1 kHz). An aqueous solution of 1 M NaSO 4 was used as electrolyte.The photoelectrochemical performance of as-prepared samples were measured by Origalys workstation with a three-electrode system (the prepared sample electrode, Pt foil electrode and Ag/AgCl electrode were used as working electrode, counter electrode and reference electrode, respectively). The photoinduced current density with time (𝑖-t) curves were observed at a potential of -200 V (vs. Ag/AgCl). The electrochemical impedance spectroscope (EIS) measurements were conducted in 0.1 M Na 2 SO 4 solution. The working electrodes were prepared by a highly homogeneous sample film on FTO substrate. In details, 3 mg of sample powder was dispersed in 3 mL ethanol by stirring. Then, the solution was spread on the FTO substrate. Finally, the working electrodes were achieved after they dried at room temperature (Figure2.4d). EIS was recorded with AC voltage amplitude of 10 mV, and a frequency range from 0.1 Hz to 1000 Hz at 0.2 V (vs. Ag/AgCl).

1. 4 . 1

 41 Photocatalytic degradation of organic pollutants a. Model pollutants Water and air model pollutants were taken for this study: phenol, methyl orange and toluene. Phenol is one of the most employed test molecule. It has been proposed by Serpone et al.

7 )Figure 2 . 7 Figure 2 . 8

 72728 Figure 2.7 The equipment for the phenol and methyl orange degradation

Figure 2 . 9

 29 Figure 2.9 (a) the reactor for the toluene degradation, (b) the LEDs light source. (c-d) the sectional view of the reactor.

H 2

 2 photocatalyst was dispersed in 20 mL of a degassed aqueous solution with 25 vol % of methanol, as holes' scavenger. The samples were irradiated by an Oriel 300 W Xenon lamp with an infrared water filter for 5 h under stirring (Figure2.10). Every 1 h, 0.2 mL gas sample was taken by a syringe from the quartz reactor. The amount of H 2 was determined by gas chromatography (GC) using Shimadzu GC-14B.

Figure 2 . 10 .

 210 Figure 2.10. Photocatalytic hydrogen production reactor.

3. 1 . 1

 11 Characterizations of PPy nanostructures SEM images present for PPy-NS-c homogeneous spherical nanostructures with an average size of 40 nm (Figure 3.1a-b). Similar nanoparticles have been observed using TEM (Figure 3.2a-b). By contrast, PPy-NS-γ, synthesized by radiolysis, show nanoballs of uniform sizes of 400 nm (Figure 3.1c-d), which correspond to the TEM images of PPy-NS-γ (Figure 3.2c). In case of chemical polymerization without template, amorphous particles connected in nacklaces are obtained (PPy-bulk) (Figure 3.1e-f). Thanks to the confinement provided by the non-polar tubes of hexagonal mesophases used as soft template or γ-ray irradiation technique, we were able to control and direct the size and morphology of a variety of CPs, and hence to obtain polymer nanospheres.

Figure. 3 . 1

 31 Figure. 3.1 SEM images of PPy-NS-c (a-b), PPy-NS-γ (c-d), and PPy-bulk (e-f).

Figure 3 . 2 .

 32 Figure 3.2. (a-b) TEM images of PPy-NSs-c and (c) TEM image of PPy-NS-γ

- 1 could

 1 represent to C=N. The band of =C-H in plane-deformation vibration is situated at 1045 cm -1 . Furthermore, no significant difference exists between the nanostructures synthesized by chemical oxidation or by radiolysis. Compared with PPy-bulk, some bands of PPy-NS-c and PPy-NS-γ are slightly shifted. The occurrence of small peak at 3284 cm -1 could be assigned to presence of N-H stretching vibrations. The main absorption bands of PPy-bulk are similar to PPy-NS-c and PPy-NS-γ and are shown in Figure 3.3a. These spectra revealed that PPy was successfully synthesized by chemical oxidative method and by radiolysis.

Figure 3 .

 3 Figure 3.3b shows UV-vis spectra recorded for a dispersion of PPy nanostructures in

Figure 3 .

 3 3c-dpresents the Kubelka-Munk plots for PPy samples used to estimate the E g associated with the direct transitions. As a result, the E g of PPy-NS-γ and PPy-NS-c is about 1.94 eV and 2.01 eV. The results are quite similar to the band gap of PPy-NSs from CV calculation (Figure3.8d-e and Table3.3). The variation of the band gap values obtained by calculation by Kubelka-Munk and CV methods can be explained by numerous reasons, which include geometrical arrangement and electronic configuration of the constituting elements, charge imbalance, oxygen vacancies and defects on the polymer surface.

Figure 3 . 3

 33 Figure 3.3 (a) ATR-FTIR spectra of PPy-NS-c, PPy-NS-γ, PPy-bulk; (b) UV-Vis spectra of the PPy nanostructures (PPy-NS-c and PPy-NS-γ) in suspension. Kubelka-Munk plots and band gap energy estimation of PPy-NS-γ (c) and PPy-NS-c (d) for direct transition.

Figure 3 . 4 (

 34 Figure 3.4 (a) the dark adsorption and photolysis effect, (b) phenol degradation in the presence of different photocatalysts under UV and (c) visible light, (d) MO degradation of PPy-NS-c under UV light.

Figure 3 . 6 :

 36 Figure 3.6: (a) Photocatalytic activity of PPy-NS-c with cycling. (b) PPy-NS-c before photocatalytic cycles; (c) PPy after 4 photocatalytic cycles.

  207 and MO208, 209 ) to form CO 2 and H 2 O. Experiments were carried out in the presence of different scavengers in order to study the role of the free radicals during photocatalytic degradation process.In the absence of O 2 (experiments under N 2 atmosphere) the activity of PPy-NS-c for phenol degradation decreases from 100% to 15% under UV and from 22% to 8% under visible light irradiation after 5 h, respectively (Figure3.6a-b). This indicates that the present of O 2 is an important factor during the photocatalytic process.

Figure 3 .

 3 Figure 3.6 (a) The effect of oxygen about photodegradation of phenol in presence of PPy-NS-c under UV light and (b) visible light.

Figure 3 .

 3 Figure 3.7a shows the phenol degradation in the presence of PPy-NS-c using different electron scavengers under UV light. The experiments were conducted in the presence of Cu 2+

Figure 3 .

 3 7b shows that addition of 2-propanol does not affect the photodegradation rate (which is 85% after 5 h). Furthermore, to confirm the role of HO • and O 2 •-radicals, tert-butanol and NaI were used as free HO • and surface HO • radical scavengers, and benzoquinone was used as the O 2 •-radical scavengers 169 . As shown in Figure 3.7c, the rate of phenol degradation significantly decreases with benzoquinone (O 2 •-scavenger) addition indicating the crucial role of O 2 •-

  starts at -1.72 V (PPy-NS-c) and -0.38 V (PPy-NS-γ). The energy levels of the LUMO/HOMO, for PPy-NS-γ and PPy-NS-c were respectively determined: -4.18 eV/-5.97 eV and -2.84 eV/-5.16 eV. The band gap was estimated to be 1.79 eV and 2.32 eV, respectively, which are remarkably smaller than the band gap of TiO 2(3.20 eV). Actually, lower band gap implies the possibility of activation of the polymer nanostructures under visible light with potential application in optoelectronics, photocatalysis or eletrocatalysis.

Figure 3 . 7 :

 37 Figure 3.7: Photocatalytic degradation of phenol using PPy-NS-c in the presence of (a) different electron scavengers, (b) both electron and hole scavengers, and (c) superoxide and hydroxyl radical scavengers, (d) cyclic voltammetry of PPy recorded at 20 mV/s in acetonitrile and 0.1 M tetrabutylammonium perchlorate. Ferrocenium/ ferrocene (Fc/Fc + ) redox potential has been measured at the end of each experiment in order to calibrate the pseudo reference electrode (0.241 V νs. Ag in the present study). The energetic levels of PPy are obtained by the following equation: E HOMO (eV) = -(4.8 + E ox_onset -0.241) and E LOMO ( eV) = -(4.8 + E red_onset -0.241), (e) reduction curve of PPy-NS-c measured by electrochemistry, (f) possible photocatalytic mechanism with charge separation in PPy nanostructures with electron reducing oxygen and the hole oxidizing water.

  photocatalytic activity of the PPy nanostructures is close to that of plasmonic silver nanoparticles modified TiO 2 under visible light. Our experiments demonstrate that O 2 •-

of TiO 2

 2 photoactive under visible-light irradiation131 . Although there are already some investigations on photocatalytic performance of TiO 2 -PPy, some fundamental questions are still not answered. In previous studies, little attention was paid to the life time of photo-induced charge carriers and charge transfer route between TiO 2 and PPy nanostructures under ultraviolet and visible light, separately and the photocatalytic properties of TiO 2 -PPy nanocomposite for air treatment has not been reported.CPs present high mobility of charge carriers, narrow and tunable band gap, good stability and high absorption coefficients towards the visible region or near-infrared light. These excellent and special properties indicate that CPs are promising photosensitizers or photocatalysts under the solar light illumination. The ICP team has demonstrated in previous works that nanostructured CPs such as poly(diphenylbutadyine) PDPB, Poly(3,4ethylenedioxythiophene) PDOT, Poly(3-hexylthiophene) (P3HT) and polypyrrole (PPy),

4 . 1 .

 41 ultraviolet and visible light compared to bare TiO 2 and PPy NS, and most interestingly to PPy bulk -TiO 2 . The improved photocatalytic performance of PPy NS -TiO 2 is due to highest surface area and less defects in the nanostructure PPy and to the wide light absorption and increased charge separation efficiency owing to the heterojunction formation. The PPy NS -TiO 2 composite photocatalyst shows high stability and recyclability. The kinetics of charge carriers is also discussed. This work offers a facile and cheap way to fabricate the heterojunction in organic-inorganic hybrid materials interface, and the composite nanomaterial represents a promising photocatalyst for water treatment and indoor application such as air treatment. Results and discussions 4.1.1 Characterizations of PPy NS -TiO 2 composite The optical absorption properties of bare TiO 2 and PPy NS , and the composite PPy NS -TiO 2 were investigated by UV-Vis DRS. In Figure 4.1a, TiO 2 -P25 presents an absorption edge at 400 nm owing to the appearance of rutile, while the absorption edge of PPy NS -TiO 2 is located at 490 nm. The composite PPy NS -TiO 2 shows higher absorption in the visible range because of the interaction between PPy NS and TiO 2 in heterojunction leading to a red shift of the absorbance towards the visible region. The optical band gap (E g ) of as-prepared samples can be evaluated by DRS spectra (Kubelka-Munk method). The E g of PPy NS -TiO 2 and TiO 2 are 1.95 eV and 2.93 eV, respectively, which can be determined by the plots of (αhν) 1/2 vs hν (α ⎯ absorption coefficient; h ⎯ Planck constant; ν ⎯ light frequency) (Figure 4.1b) 236 . The band gap of PPy NS is about 2.01 eV, which was calculated in our previous work 152 .Figure 4.1a-b present that the broader light absorption and narrower band gap of PPy NS -TiO 2 than unmodified TiO 2 .

Figure 4 . 1

 41 Figure 4.1 (a) DRS spectra of composite PPy NS -TiO 2 and bare TiO 2 ; (b) Kubelka-Munk plots and band energy estimation of PPy NS -TiO 2 and TiO 2 , (c) FTIR spectra of TiO 2 , PPy NS and PPy NS -TiO 2 ; (d) X-ray diffraction pattern for TiO 2 and PPy NS -TiO 2 .

Figure 4 .

 4 1dpresents the typical spectrum of PPy NS -TiO 2 composite within the wavenumber range of 750 cm -1 ~ 1800 cm -1 . The broad peak at 3401 cm -1 ascribes to the O-H vibration of water molecular. The bands at 1556 cm -1 and 1459 cm -1 are assigned to the C=C and C-C stretching vibration of pyrrole ring, respectively. The peaks at 1182 cm -1 and 1047 cm -1 correspond to the N-C stretching band and =C-H in-plane deformation vibration237, 238 . The peak at 908 cm - 1 is due to C-H out-of-plane bending vibrations 228 . The wide absorption peak at 800 cm -1 to 500 cm -1 refers to the flexural vibration of Ti-O-Ti in TiO 2 and the weak peak at 1632 cm -1 is vibration of O-H in water, which absorbs on the TiO 2 surface 239 . The characteristic peaks of PPy NS -TiO 2 composite were shifted compared to neat PPy NS and TiO 2 indicating the interaction between PPy NS and TiO 2 .

Figure 4 .Figure 4 . 2 ,

 442 Figure 4.1e shows the XRD patterns of as-prepared samples. For pristine TiO 2 , the XRD patterns presents the characteristic diffraction peaks of both anatase and rutile. The PPy NS -

Figure 4 . 2

 42 Figure 4.2 TEM images of TiO 2 (a), PPy NS (b) and PPy NS -TiO 2 (c-d).

Figure 4 . 3

 43 Figure 4.3 XPS spectra of PPy NS -TiO 2 (a) Ti 2p of TiO 2 , (b) C 1s of PPy NS , (c) N 1s of PPy NS and O 1s of TiO 2 and SiO 2 .

Figure 4 . 4

 44 Figure 4.4 TRMC signals of PPy NS -TiO 2 at different excitation wavelengths: (a) 360 nm UV irradiation, (b) 420 nm, (c) 450 nm, and (d) 500 nm visible irradiation. The corresponding laser energy were 0.9, 2.3, 2.3 and 2.3 mJ•cm -2 , respectively.

Figure 4 .

 4 Figure 4.5a shows the photoinduced i-t curve of PPy NS -TiO 2 and TiO 2 photoanodes under UV-vis light irradiation. The photocurrent of PPy NS -TiO 2 photoanode was about 80 µA•cm -2 , which is 2 times higher than that of TiO 2 photoanode, indicating TiO 2 modification with PPy NS increases generation, separation and transfer of charge carriers leading to the enhanced photoelectrochemical property 125 . EIS Nyquist plots showed that PPy NS -TiO 2 exhibits a smaller semicircle compared to the TiO 2 (Figure 4.5b), suggesting that PPy NS may provide electron transfer channel for the PPy NS -TiO 2 /FTO photoanode, which increases the life time of electrons and ultimately enhances the photocatalytic activity 242, 243 .

Figure 4 . 5

 45 Figure 4.5 (a) photocurrent transient responses at a constant potential of -200 mV for TiO 2 and PPy NS -TiO 2 FTO electrodes under UV-vis light irradiation; (b) the EIS curve of PPy NS -TiO 2 and TiO 2 photoanodes under dark at the potential of 0.2 V vs Ag/AgCl in 0.1 M Na 2 SO 4 neutral electrolyte.

Figure 4 .

 4 Figure 4.7a). Figure 4.6 shows the degradation of methyl orange and phenol in aqueous solution. Under UV-vis light, the effective degradation of MO up to 100% takes place in 20 min in the presence of PPy NS -TiO 2 and PPy bulk -TiO 2 composite, while this total degradation is

Figure 4 .

 4 photocatalytic activity of bare TiO 2 ). The degradation rates of phenol are respectively: 55%, 25%, 15% and 10% with PPy NS -TiO 2, PPy bulk -TiO 2 , Ag-TiO 2 and bare PPy NS after 4 h irradiation under visible light (Figure 4.6d and Figure 4.7c). In Table 4.1, we compare our

Figure 4 . 6

 46 Figure 4.6 Photocatalytic degradation rate of MO (C 0 = 500 ppm) in the presence of as-prepared samples under UV (a) and visible light irradiation (b); photocatalytic degradation rate of phenol under UV (c) and visible light irradiation (d).

Figure 4 . 7

 47 Figure 4.7 (a) The effect of different mass ratios between PPy NS and TiO 2 (PPy NS : TiO 2 = 0:1, 1:2, 1:1, 2:1, 1:0) for photocatalytic MO degradation, (b) Photocatalytic degradation rate of MO (C 0 = 500 ppm) in the presence of PPy NS , (c) Photocatalytic degradation rate of phenol (C 0 = 500 ppm) in the presence of PPy NS .

Figure 4 . 8

 48 shows toluene degradation at different irradiation wavelength (375 nm, 415 nm and 465 nm). Under UV irradiation (λ = 375 nm), TiO 2 shows the best photocatalytic activity compared to PPy NS and PPy NS -TiO 2 : After 50 min., the degradation rate with TiO 2 is 100%, while with PPy NS and PPy NS -TiO 2 it is, 49% and 92% respectively. The photodegradation rate of PPy NS -TiO 2 is two times than pure PPy NS (Figure4.8a). More importantly, under visible light (λ = 415 and 465 nm), PPy NS -TiO 2 shows higher photocatalytic activity than PPy NS . The degradation rates of PPy NS -TiO 2 are 80% (λ = 415 nm) and 55% (λ = 465 nm) after 100 min, respectively, which is much higher than the photocatalytic activity of PPy NS (45% under λ = 415 nm and 33% under λ = 465 nm irradiation) (Figure4.8b-c). TiO 2 shows no photocatalytic activity under visible light.

Figure 4 . 8

 48 Figure 4.8 Photocatalytic activity of PPy NS and PPy NS -TiO 2 for the toluene degradation under (a) λ = 375 nm, (b) 415 nm, and (c) 465 nm irradiation, respectively.

Figure 4 .

 4 Figure 4.10 UV-vis spectra of MO with time evolution.

Figure 4 .

 4 Photogenerated h + located on the HOMO of PPy NS can participate in the oxidative reaction 132 . As a result, the redox reaction happens in the CB of TiO 2 (reductive reaction: A→ A -) and HOMO of PPy NS (oxidative reaction: D→D + ), and the effective charge separation can extend the lifetime of the generated e -and h + , and then enhance photocatalytic activity.

Figure 4 . 11

 411 Figure 4.11 Proposed photocatalytic mechanism for the PPy NS -TiO 2 system and charge transfer mechanisms under UV light (a), and under visible light irradiation (b).

5 . 1 .

 51 photocatalytic performance for hydrogen generation due to the efficient electron-hole pairs' separation contributed by nanosized Pt, Ni and Pt-Ni particles and extended absorption region by PPy NSs. The photocatalytic activity of the composite nanomaterials with various metal loadings was investigated for hydrogen generation under UV-visible light irradiation.

Figure 5 .

 5 1c). The peak at 470 nm is owing to the ππ* transitions. The corresponding band gap (E g ) of PPy was determined from the Kubelka-Munk function (Figure5.1d): The value of Eg of PPy was found to be 2.2 eV, which is similar to that of previous reports.152

Figure 5 . 1 .Figure 5 . 4 )

 5154 Figure 5.1. (a) SAXS of the mesophases doped with Py, FeCl 3 and the mesophase resulting from the mixing of the two other mesophases and containing PPy (induced by oxidation of Py by Fe 3+ ); (b) Mott-Schottky plot of PPy and PtNi-PPy; (c) UV-Vis spectrum of PPy, and (d) corresponding Kubelka-Munk plot.

Figure 5 . 2

 52 Figure 5.2 SEM images of PPy NSs.

Figure 5 . 3 .

 53 Figure 5.3. TEM images of 0.2%Pt-PPy-NSs (a-b), 5%Ni-PPy-NSs (c-d), 0.05%Pt0.05%Ni-PPy-NSs (e) and HAADF-STEM image of 0.05%Pt0.05%Ni-PPy (f).

Figure 5 . 4 . 6 . 5 . 5 .Figure 5 .

 546555 Figure 5.4. EDS corresponding to 0.05%Ni0.05%Pt-PPy.

Figure 5 . 5

 55 Figure 5.5 XPS spectra of wide region spectroscopy of PtNi-PPy-NSs.

Figure 5 .Figure 5 . 6

 556 Figure 5.6 XPS spectra of (a) C1s, (b) N1s in PtNi-PPy-NSs, (c) Pt 4f in Pt-PPy-NSs, (d) narrow scan spectrum of Ni 2p in Ni-PPy-NSs, (e) narrow scan spectrum of nickel states in PtNi-PPy-NSs and (f) narrow scan spectrum of Ni 2p in PtNi-PPy-NSs.

  282 5.1.2.1 Pt-PPy-NSs The photocatalytic H 2 generation efficiency of as-prepared samples was investigated in 25 vol.% methanol aqueous solution under UV-vis light. As shown in Figures 5.7a, with time increase, 0.2%Pt-PPy-NSs show a remarkable enhancement in the photocatalytic activity.

  photogenerated electrons in NiO/Ni structure migrate from the conduction band of the semiconductor to the Ni layer, and then transfer to the NiO layer, which leads to efficient charge carrier separation. Ni(OH) 2 as co-catalyst can also efficiently transport photogenerated electrons from the conduction band of the semiconductor to Ni(OH) 2 /Ni clusters leading to high photocatalytic activity for hydrogen generation.283

Figure 5 . 7

 57 Figure 5.7 (a) A comparison of the photocatalytic H 2 generation rate for different loading rates of PPy-NSs in Pt as indicated in the legend; (b) Hydrogen production with 0.2%Pt-PPy-NSs after 4 cycles of 5 h; (c) A comparison of the photocatalytic H 2 generation rate for different loading rates of Ni on PPy-NSs as indicated in the legend; (d) Hydrogen production with cycling in the presence of 5%Ni-PPy-NSs.

Figure 5 .

 5 Figure 5.8a and Figure 5.8b show the effect of the total metal loading on photocatalytic hydrogen production for sample with a fixed Pt: Ni ration of 1:1 and the catalytic activity strongly depends on the Ni/Pt ratio. The 0.1%PtNi-PPy-NSs exhibits the highest

Figure 5 . 8 (

 58 Figure 5.8 (a) Photocatalytic H 2 generation rate with the same loading rate for different samples. (b) The photocatalytic H 2 generation rate for different loading rate of Ni-Pt on PPy-NSs. (c) Hydrogen production with cycling in the presence of 0.1%PtNi-PPy-NSs. (d) Proposed photocatalytic mechanism for hydrogen generation.Metal NPs act as electron traps, and protons reduction catalysts.

  Pt, Ni-NiO and bimetallic Pt-Ni nanoparticles of homogeneous size and dispersion on the surface of PPy NSs were obtained by radiolytic reduction. Our work also demonstrated photocatalytic activity is very sensitive to the metal loading. 0.2%Pt-PPy-NSs presents the best activity compared with the other percentage loading rates. Modification with nickel-based nanoparticles gives also promising results for green hydrogen production. 5%Ni-PPy-NSs show enhanced photocatalytic performance due to the formation of the heterojunction between PPy and NiO-Ni nanoparticles. However, the phototocatalytic activity decreases slightly with time, probably because of Ni leaching. The choice of the metal precursors used in the NPs synthesis is important for the activity of the metal co-catalysts: The best activities were obtained using Ni and Pt acetylacetonates as precursors for the metalbased nanoparticles. The stability and the photocatalytic activity of Ni-based photocatalysts were much improved by alloying Ni with Pt.

H 2 Figure 6 . 1

 261 photocatalytic activity of the different Pt-modified PPy-TiO 2 composites for hydrogen generation under both ultraviolet and visible light irradiation. The results demonstrate that Pt-(PPy-TiO 2 ) structures exhibit markedly enhanced photocatalytic hydrogen production

Figure 6 .

 6 Figure 6.1c-d shows TEM images of the samples with Pt NPs synthesized on TiO 2 previous to the heterojunction with PPy: 2 nm Pt NPs uniformly deposited on the TiO 2 were observed. In addition, Pt NPs were found to deposit at the edges of TiO 2 by radiolytic reduction 314 and Pt NPs were not be observed on PPy.Figure 6.1e-f present TEM images of the samples with Pt NPs synthesis on PPy NSs previous to the heterojunction with TiO 2 : Pt NPs of homogeneous size were well dispersed on PPy, and no Pt NPs were observed on TiO 2 .

Figure 6 . 1 .

 61 Figure 6.1. TEM images of (a-b) Pt-(PPy-TiO 2 ), (c-d) (Pt--TiO 2 )-PPy, (e-f) (Pt-PPy)-TiO 2 .

Figure 6 . 2

 62 Figure 6.2 UV-vis absorption spectra (a) and Mott-Schottky plot of as-prepared samples (b);

Figure 6 . 4

 64 Figure 6.4 Pt 4f XPS spectra of the 1%Pt-(PPy-TiO 2 ) (a); Ti 2p (b), C 1s (c) and N 1s (d) of the (Pt-PPy)-TiO 2 , (Pt-TiO 2 )-PPy and Pt-(PPy-TiO 2 ), respectively; The mass ratio between PPy and TiO 2 was 1:4 for all the samples and the Pt loading is 1%.

Figure 6 . 5

 65 Figure 6.5 Photocurrent transient (a) and Nyquist plots of EIS (b) for (Pt-PPy)-TiO 2 , (Pt-TiO 2 )-PPy and Pt-(PPy-TiO 2 ) FTO electrodes under UV-vis light irradiation.

Figure 6 . 6 .

 66 Figure 6.6. The effect of different volume ration of methanol and water for hydrogen generation (a); Different scavengers of holes and mass ratio (insert graph) between PPy and TiO 2 for photocatalytic hydrogen generation (b); Hydrogen production with different loading rate of Pt NPs on PPy-TiO 2 in methanol-water mixture solution under both UV light (c) and visible light (d);

Figure 6 .

 6 Figure 6.7b shows that the photocatalyst Pt-(PPy-TiO 2 ) is stable with cycling.

Figure 6 . 7 .

 67 Figure 6.7. Hydrogen production with (Pt-PPy)-TiO 2 , (Pt-TiO 2 )-PPy and Pt-(PPy-TiO 2 ) in methanol-water mixture solution under UV light and visible irradiation (a); The photocatalytic hydrogen production of Pt-(PPy-TiO 2 ) with cycling in methanol-water mixture solution (b).

Figure 6 . 8 .

 68 Firstly, photocatalytic hydrogen generation involves three main steps: (i) light absorption, (ii) charge carriers generation and charge transfer to the surface of photocatalysts, and (iii) surface redox reactions.334 Here, PPy as a photosensitizer was used to absorb the incident light to generate e -and h + . Pt NPs used as a cocatalyst not only serve as e -sinks, but also provide proton reductive sites, and centers for H. radical recombination leading to H 2 formation.299 As shown in Figure6.8a, for (Pt-PPy)-TiO 2 system, the photogenerated electrons in the LUMO of PPy transfer to Pt NPs of PPy surface and also to TiO 2 CB. Then the protons can be reduced into H . on the surface of Pt much more efficiently than on bare TiO 2 . Pt NPs help also to form H-H bond to lead to H 2 . The oxidation of an electron donor (such as methanol) with h + happened on the HOMO of PPy (MeOH→3H 2 + CO 2 ).In the (Pt-TiO 2 )-PPy ternary system, PPy is introduced to create electrons from the HOMO to LUMO under visible light irradiation (Figure6.8b). The photo-induced electrons transfer from PPy to the TiO 2 CB due to the position of the PPy LUMO is much more negative than that of TiO 2 , and are eventually injected into the low Fermi level of Pt. As a result, rapid charge separation and slow charge recombination occurred, which results in a good photocatalytic activity. This electron transfer scheme is also illustrated in other ternary systems such as PPy-Ag-TiO 2 123 , TiO 2 /CuO/Cu 335 , In 2 O 3 -TiO 2 -Pt 336 . More interestingly, the Pt-(PPy-TiO 2 ) composite shows the best photocatalytic activity compared with (Pt-PPy)-TiO 2 and (Pt-TiO 2 )-PPy, because the active Pt sites coexist in both PPy and TiO 2 (as seen in Figure 6.1a-b). Figure 6.8c illustrates two efficient routes of electron transfer. The excited electrons from PPy LUMO migrate to the surface of PPy and TiO 2 , and then are trapped by Pt deposited on PPy and TiO 2 leading to very efficient separation of charge carriers. Furthermore, Pt NPs act as cocatalysts for H + reduction and as sites for H . recombination. The synergistic effect of the two electron transfer routes and formation of PPy-TiO 2 heterojunction facilitate the photocatalytic reaction process.

Figure 6 . 8

 68 Figure 6.8 Scheme representation of the electron transfer, migration and hydrogen production mechanism in the hybrid photocatalysts: (a) (1%Pt-PPy)-TiO 2 ; (b) (1%Pt-TiO 2 )-PPy; (c) 1%Pt-(PPy-TiO 2 ).

  photocatalysis.

  photocatalysts based on La 1-x Ti x FeO 3 modified with conjugated polymer nanostructures for water depollution. 337 N. Keller and his team synthesized a highly robust narrow band gap La 1-x Ti x FeO 3 dual catalyst (Ti-LFO) with combined photocatalytic and photoassisted Catalytic Wet Peroxide Oxidation (CWPO) activity under visible light. It yields full mineralization of refractory compounds in water at high reaction rates under pure visible light: The strategy of combining both photocatalysis and H 2 O 2 -mediated heterogeneous photo-Fenton advanced oxidation processes within one single heterogeneous catalyst allowed the dual La 1-x Ti x FeO 3

  photocatalytic activity for H 2 generation. Further studies are needed to synthesize CPs-based nanostructures modified with noble metal-free NPs and aboundant elements (Ni, Cu, Fe, Co or NiCu, NiFe, CuFe, CoNi, carbon dots etc.) for photocatalytic water splitting. For example, Ni-based bimetallic NPs modified PPy as photocatalysts show promising photocatalytic activity for H 2 generation (Annex 1).

Figure 7 . 1 .

 71 Figure 7.1. Photosystem II and nano-PDPB 338

Figure 7 . 2

 72 Figure 7.2 Photocatalytic process for water oxidation.

Figure 7 .

 7 2a-b show PPy particles with 0.4 µm diameters and good dispersion in water phase (Annex 2a-b). Photocatalytic activity of PPy nanostructures for water oxidation was conducted in pure water in the absence of sacrificial electron acceptor at neutral pH under visible light (λ≥435 nm) (Annex 2c). PPy nanostructures exhibit very high photocatalytic ability, and the O 2 production rapidly increases (220 µM after 70 min irradiation) under visible light irradiation, by contrast, no O 2 was not observed under dark condition, which indicates that O 2 are from light-driven water oxidation. When electron acceptor Na 2 S 2 O 8 (10 mM) was introduced in the solution, the O 2 production sharply increased (Annex 2d). This can be attribute to electron capture of Na 2 S 2 O 8 that leads to the efficient charge carrier separation. Alternate periods of irradiation and dark experiment demonstrates the photo respond for O 2 evolution during catalysis, and O 2 is not

  16

  , C17 or S18 or by its surface modification with metal nanoparticles (NPs) such as Ag19 , Au 20 , Pt, 21 Pd 22 NPs or heterojunction modification like Cu 2 O/TiO 2 , Bi 2 O 3 /TiO 2 and ZnMn 2 O 4 /TiO 2 .23 Additionally, the development of efficient, durable and cost-effective materials for photocatalytic applications and solar energy conversion is crucial for environmental applications and solar fuel production. These

	photocatalysts should at least satisfy the following conditions: (i) a strong and broad
	absorption in the visible region; (ii) high photogenerated charge carriers separation and
	transfer efficiency; (iii) appropriate energy level for redox reaction.

  54

  n C 4 H 5 N + (2+y)n FeCl 3 → (C 4 H 5 N) y+ n ny Cl -+ (2+y)n FeCl 2 + 2n HCl where y is the doping level of PPy and usually the value of y is between 0.200 and 0.33 for PPy. If oxygen is not counted, the reaction of Py with FeCl 3 can be presented as follows: 51 n C 4 H 5 N + 2.33n FeCl 3 → (C 4 H 5 N) + n +0.33Cl -+ 2.33n FelCl 2 + 2n HCl One chlorine atom can accept one e -from three Py unites to be a doped anion.

.13) (equations 7-10): 92 H

  • , HO • (homogeneously in the solution), H 3 O + and molecular recombination products (H 2 and H 2 O 2 ). These radicals can be used for reduction or oxidation reactions. 2 O à H 2 O •+ + e -and H 2 O * (equation 7)

	The process of free radical formation in the case of radiolysis of water is as follows
	(Figure 1

Figure 1.14a-

  HO • + HO -+ N 2 ). Py was polymerized into PPy due to the hydroxyl radicals produced by the radiolysis of water. The structures of PPy are spherical and chaplet-like (

	Cui et al. synthesized PPy NSs via γ-ray irradiation in the deionized water under N 2 O
	atmosphere without any templates. While hydroxyl radical is a very oxidative species, N 2 O
	was not only used as scavenger of hydrated electrons, but also produce more HO • (e -aq + N 2 O +
	H 2 O →

State of the art on soft template synthesis and metal nanoparticle synthesis by radiolysis

  TiO 2 /PPy modified with Pt NPs showed high photocatalytic efficiency for H 2 generation (1 mm H 2 g catalyst -1 h -1 wt% (Pt) -1 ) (Figure 1.20c-d). 131 PPy modified Pd-TiO 2 (TiO 2 -Pd-PPy) showed higher H 2 generation rate (601 µmol/h) than TiO 2 -Pd and TiO 2 . 132 To avoid the use of nobel metal NPs, some other catalysts were investigated for photocatalytic hydrogen production. CdS is one of the most efficient visible-light-driven photocatalysts due to its narrow band gap (2.4 eV) and its conduction band edge (more negative than the H 2 O/H 2 electrode potential). 133 Guo's group synthesized PPy/CdS photocatalyst by in situ chemical polymerization with different dopants (DBSNa, CTAB and TSNa). PPy/CdS doped by TSNa presented the best photocatalytic activity for H 2 generation without noble metals under visible light irradiation. 134 In addition, graphitic carbon nitride (g-C 3 N 4 ), a metal-free semiconductor photocatalyst, when modified with cocatalysts, is also an efficient visible light-driven watersplitting catalyst for hydrogen evolution. 135 Y. Sui et al. prepared highly dispersed conductive polymer PPy (1.5 wt%) on C 3 N 4 , which exhibited enhanced photocatalytic activity for H 2 evolution than pure C 3 N 4 from pure water under solar light. Scheme for photocatalytic activity of TiO 2 modified with Pt-polypyrrole nanocomposites; (b) H 2 evolution by using 0.5 g l -1 modified catalyst, 0.5 and 1.0 wt% Pt and polypyrrole, respectively, 75 ml aqueous methanol solution (2250 mmol). 130 (c) Electron transfer route of PPy-TiO 2 , TEM and SEM images of PPy-TiO 2 ; (d) Yield of H 2 production over time. Two solutions with different weight percent of Pt were tested.Nanostructured materials play a pivitol role in photocatalysis applications. Soft templates are used to synthesize different nanostructured polymers or metal nanoparticles.137, 138 We have introduced various methods to synthesize nanostructured PPy. In this PhD work, we used

	Both contained a total of 24 mg of TiO 2 /PPy-Pt nanocomposites and 6.4 mmol of TEA. 136
	1.6

136 Although conjugated polymer-based catalysts for photocatalytic hydrogen generation have achieved considerable development, the investigation of PPy-based photocatalysts is still scarce, for example, appropriate structures and sizes of PPy-based photocatalysts, suitable cocatalysts and optimized loading rate, reproducibility, decreasing or eliminating the use of rare and expensive elements etc.

Figure 1.20. (a)

Table 2 . 1

 21 The reagents used for the experiments

	Chemical Product	Chemical	Molar	Purity	Company
		Formula	mass
			(g/mol)
	Pyrrole (Py)	C 4 H 5 N	67.09	98%	Sigma-Aldrich
	Sodium dodecyl sulphate (SDS)	NaC 12 H 25 SO 4 288.372	98.5%	Sigma-Aldrich
	Cyclohexane	C 6 H 12	84.16	≥99%	Sigma-Aldrich
	Sodium Chloride	NaCl	58.44	≥99.5%	Sigma-Aldrich
	n-Pentanol	C 5 H 12 O	88.15	>99%	Honeywell
	Ethanol	C 2 H 6 O	46.06	≥99%	Sigma-Aldrich
	2-propanol	C 3 H 8 O	60.1	≥99%	Sigma-Aldrich
	Iron Chloride	FeCl 3	162.20	≥97%	Sigma-Aldrich

  To scavenge electrons and produce more oxidative HO˙ radicals, the aqueous solution is degassed with N 2 O: e -s + N 2 O + H 2 O→ HO • + HO -+ N 2 . Radiolytic polymerization of PPy is described in details (see Chapter I 1.4.3 ) 45 .

	H 2 O	MNOPQRPSRTU	HO˙, e -aq ,H˙, H 2 O 2 , H 3 O + , H 2	(1)

. Water radiolysis produces solvated electrons and radicals (HO˙ and H˙):

Table 3 .

 3

	Samples	Quality of catalyst	Phenol	Degradation rate (%)	Degradation rate (%)	Reference
		(mg)	(g/L)	UV	Visible light
	PPy-NS-c	3.4	1	100 (4.5 h)	10 (5 h)	This work
	PPy-NS-γ		1	80 (5 h)	20 (5 h)	This work
		3.4
	PDPB		1	82 (4.5 h)	70 (4.5 h)	40
		3.5
	P3HT	3.5	1	90 (3 h)	15 (4 h)	204
	PEDOT Spindle	3.5	1	100 (10 min)	100 (4 h)	183
	Ag-TiO 2	3.5	1	100 (25 min)	18 (4.5 h)	40
	N-doped TiO 2	300	0.05	99.6 (9 h)	99.2 (9 h)	205
	CuO/P25	3.5	1	100 (20 min)	22 (4 h)	154
	Ag@CuO
	(1:1)/P25	3.5	1	100 (15 min)	12 (4 h)	154
	Au 0.5% /P25	3.5	1	100 (20 min)	18 (4h)	206
	TiO 2	3.5	1	100 (1 h)	0	40

1. Photocatalytic degradation rate of phenol by using PPy NSs.

  to scavenge electrons (forming Cu + ). The photodegradation rate of phenol is decreased from 100 % to 87 % in the presence of CuSO 4 . Experiments with CuSO 4 show much lower degradation rates of phenol. Cu 2+ reacts with electrons to form Cu + , which competes with reaction(1). The presence of Cu 2+ leads to a decrease O 2•-production in the photocatalytic process, causing a decrease in the degradation kinetics.Other electron scavengers (1´10 -4 M of (NH 4 ) 2 O 8 and 1´10 -4 M of H 2 O 2 ) were added to the suspension to investigate the photocatalytic activity. After 5 h, the photocatalytic degradation of phenol was 20% and 35% in the presence of (NH 4 ) 2 O 8 and H 2 O 2 , respectively. These results indicate that addition of electron scavengers leads to lower photocatalytic degradation rate and Cu 2+ are the most active species for scavenging electrons compared to the (NH 4 ) 2 O 8 and H 2 O 2 .

Table 3 . 2

 32 Tris was used as a probe to detect the hydroxyl radical generation after photodegradation of phenol in the presence of PPy nanostructures after 5 h under UV and visible light.

	Materials	Irradation	Formalehyde concentration (µML -1 )
	PPy-NS-c	UV light	7.4
		Visible light	3.2

Table 3 . 3 .

 33 Determination of electrochemical data, ionization potentials, electronic affinity, energetic levels and electrochemical gap of PPy nanostructures and PPy-bulk from cyclic

	voltammograms.
	p-doping	n-doping	IP	EA	∆E
	E ox_onset (V)	E red_onset (V)
				E HOMO (eV)	E LUMO (eV)	(eV)
	PPy-NS-γ	1.41	-0.38	5.97	4.18	1.79
	PPy-NS-c	0.61	-1.72	5.16	2.84	2.32
	3.2. Conclusions
	PPy nanostructures were obtained by two different methods of polymerization: PPy-NS-

Table 4 . 1 .

 41 Comparison of this work with previously reported materials.

	Photocatalyst	Quality of catalyst	Pollutant	Degradation rate	Degradation rate (%) Visible	Reference
		(mg)		(%) UV light	light
	PPy NS -TiO 2	3	MO	100 (20 min)	70 (4 h) (λ>420 nm)	This work
	PPy NS -TiO 2	3	Phenol (50 ppm)	100 (20 min)	55 (4 h) (λ>420 nm)	This work
	PPy NS -TiO 2	3	Toluene (200 ppm)	90 (50 min)	80 (100 min) (λ=415 nm)	This work
	TiO 2 /PPy	40 -	MB (15 µM)	--	100 (80 min) (λ>400 nm)	Ref. 131
	MIP-PPy/TiO 2	200	MO (10 mg/L)	K = ln(Co/C)/t =	--	Ref. 105
				0.01504/min
	MIP RhB -PPy/TiO 2	100	RhB (10 mg/L)	--	K=0.0158/min (λ>400 nm)	Ref. 105
	Polypyrrole/TiO 2	150	RhB (10 mg/L)	--	97 (8 h), sunlight	Ref. 228
	Polypyrrole-TiO 2	450	MO (10 mg/L)	--	K=0.00913/min, sunlight	Ref. 192
	PPy@TS800	2000	MO (1 mg/L)	--	100 (50 min) sunlight	Ref. 244
	PANI/TiO 2	50	MB (1x10 -5 M)		100 (60 min) simulated solar	Ref. 245
					light
	PANI/TiO 2	50	RhB	--	90 (60 min) simulated solar	Ref. 245
					light
	TiO 2 @PoPD	25	RhB (50 mg/L)	--	K=0.1379/min Solar light	Ref. 246
	TiO 2 /P3HT	450	MO (10 mg/L)	--	88.5 (10 h) (λ>400 nm)	Ref. 247
	PANi/TiO 2 /SiO 2	1.5 cm x 0.8 cm	MO (1.5 mg/L)	--	K=0.021/min (λ>420 nm)	Ref. 248
	Ag@CuO/P25	3	Phenol (50 ppm)	100 (15 min)	22.5 (4 h) (λ>450 nm)	Ref. 249
	Ag-TiO 2	125	Phenol (0.21 mmol/L)	92 (60 min)	23 (λ>400 nm)	Ref. 153

  Our results show that PPy-NSs modified with metal nanoparticles prepared with platinum (II) acetylacetonate (Pt(C 5 H 7 O 2 ) 2 ) and nickel (II) acetylacetonate (Ni(C 5 H 7 O 2 ) 2 ), as metallic precursors exhibit higher photocatalytic properties compared with PPy-NSs modified prepared with potassium tetrachloroplatinate (II) (K 2 PtCl 4 )

Table 5 . 1 .

 51 Hydrogen production of 0.2%Pt-PPy and 5%Ni-PPy with different metallic precursors. after 5 cycles, the amount of H 2 has dropped by 33%. The small decrease of the photoactivity can be due to the leaching of Ni nanoparticles during the photocatalytic cycles. Indeed, Ni is a very efficient catalyst for many reactions, but it is known to leach in water.285

	Samples 0.2%Pt-PPy	Hydrogen	5%Ni-PPy		Hydrogen
		(µmol/h/g)			(µmol/h/g)
	Platinum(II)	1400	Nickel	(II)	289
	acetylacetonate		acetylacetonate
	Potassium	398	Nickel formate		200
	tetrachloroplatinate
	The stability of Ni-PPy-NSs with cycling was investigated. As shown in Figure 5.7d,

Table 5 . 2 .

 52 Comparison of this work with previously reported materials for H 2 generation:

	Photocatalyst	Scavenger Cocatalyst	Light source	Hydrogen	Reference
	TiO 2 /ALD-Pt	Ethanol	Pt	300 W Xe lamp	23 µL/h (AM 1.5)	J. Yoo, et al 289
	TiO 2 /NiS nanofiber	Methanol	NiS	350 W Xe lamp	655 µmol/h/g	F. Xu, et al
	2%Au/TiO 2	Methanol	Au	150 W CERAMICMetal-	500 µmol/h/g	F. Xu, et al
				Halide Lamp
	Ag-TiO 2 -Graphene	Methanol	Ag	300 W Xe lamp	129.5 µmol/h/g	F. Sheu, et al 292
	10%MoS 2 /CdS	Acetic	MoS 2	300 W Xe arc lamp	45 mmol/h/g	X. Yin, et al 293
		acid
	3%P3HT-g-C 3 N 4	S 2-+SO 2-3		300 W Xe lamp	5700 µmol/h/g	X. Zhang, et al 294
	1%Pt/PTh-20	ascorbic	Pt	300 W Xe arc lamp	2190 µmol/h/g	X. Zong, et al 295
		acid
	C 3 N 4 -2%PEDOT-1%Pt	TEA	Pt	300 W Xe lamp	320 µmol/h/g	Z. Xing, et al 296
	Pt/5 wt % g-PAN/g-C 3 N 4	TEOA	Pt	300 W Xe lamp	370 µmol/h/g	F. He, et al
	0.1%PtNi-PPy	CH 3 OH	Pt, Ni	300 W Xe lamp	664 µmol/h/g	X. Yuan, et al (This work)

Highly Promoted Photocatalytic Hydrogen Generation by Designed Structure of Nanoparticles Deposition on TiO 2 -Conjugated Polymer

  Pt-Ni-PPy exhibit higher activity compared to its monometallic counterparts in a low loading rate, and a synergetic effect is obtained. The presence of Pt leads to better electron scavenging and higher H. formation, while the association with Ni promotes H . recombination leading to higher H 2 generation. These nanostructures are also very stable with cycling. Metal nanoparticles (in particular noble metals Pt, Pd, Au) modified TiO 2 have been frequently used as co-catalysts to increase the photocatalytic hydrogen production of TiO 2 . 218 Noble metal NPs not only promote e -/h + separation because of the Schottky barrier effect, but also act as a good redox photocatalysts 311 and catalysts for H-H bond formation.

			CHAPTER VI
	These results have been published in J. Mater. Chem. A. 299 To date, numerous semiconductor photocatalysts have been synthesized and studied for
	photocatalytic hydrogen generation, especially, TiO 2 -based photocatalytic nanomaterials. TiO 2
	has prominently features over other inorganic semiconductors, such as earth abundance, good
	photocatalytic activity, photocorrosion resistance, chemical and thermal stability and low-
	cost 300, 301 . To overcome the drawbacks of TiO 2 (such as large band gap and only UV
	response), a significant number of routes have been explored. For example, self-doped TiO 2
	with Ti 3+ 302 , metal-free doped TiO 2	303-305 , surface modification with metal nanoparticles 266,
	306, 307 designed p-n junctions (g-C 3 N 4 -TiO 2	308, 309 ) and sensitization with conductive
	polymer 131, 310 . However, large Pt particles may act as recombination centers 312 .
	A promising way to increase the photocatalytic activity of TiO 2 -based photocatalyst is its
	combination with conjugated polymers, which have π-conjugated electron systems such as
	TiO 2 -based poly(benzothiadiazole) (BBT) 313 , poly(3-hexylthiophene) (P3HT) 247 , or
	polypyrrole (PPy) 131 . TiO 2 -conjugated composites with conjugated polymers present in
	general high absorption efficiency in the visible region, less electron-hole recombination, high
	charge carrier mobility, good stability and excellent biocompatibility.
	Conjugated polymer nanostructures emerge as a new class of photocatalysts very active
	under visible light.

Table 6 . 1 .

 61 Photocatalytic hydrogen production using PPy and TiO 2 based NSs.

	Samples	Solution	Hydrogen production	Hydrogen production	Reference
		(V scavenger /V water )	(mmol/h/g)	(µmol/h/g)
			UV	Visible light
	Pt-(PPy-TiO 2 )	Methanol (1/4)	125.1	3200	This work
	2wt%Pt-TiO 2	Ethanol (1/3)	16.7	-	Ref. 6
	0.5wt%Au-TiO 2	Methanol (1/4)	63	1050	Ref. 206
	Au@TiO 2 -0.2CdS	Na 2 S (0.25 M) +	-	1970	Ref. 325
		Na 2 SO 3 (0.35
		M)
	Ni-Pd/TiO 2	Methanol (1/1)	4.2	-	Ref. 306
	0.5-NiAu-TiO 2	Methanol (1/1)	3.2	-	Ref. 266

Acknowledgements

I sincerely appreciate my supervisor Hynd Remita for her patience, guidance of my research and caring of my daily life. Her kindness and support enables me to overcome many difficulties not only in research, but also in my life. She is very enthusiastic and full of a lot of good information, which helps me to master different useful skills for my research. I am grateful to Prof. Cassaignon Sophie and Prof. Keller Nicolas for their acceptance of being the reviewers of my thesis. I would like to thank Prof. Aukauloo Ally, and Prof. Johnny Deschamps for their acceptance of being the referees of my defense. It is my honor to invite the defense committee to attend my defense and I sincerely thank all of you. I would like to thank our collaborators Ally Aukauloo, Winfried Leibl, Fabrice Goubard, Pierre-Henri Aubert, Thanh-Tuân Bui, Diana Dragoe, Alexandre Dazzi, Ariane Deniset-Besseau, Patricia Beaunier, François Brisset, Samy Remita, Christope Colbeau-Justin, Isabelle Lampre, Mohammed Nawfal Ghazzal for their kind help and suggestions. I would like to thank my colleagues Mireille Benoit, Alexandre Demarque, Anais Lehoux, Maria Guadalupe, Marie Clément, Zhengpeng Cui, Dita Floresyona, Teseer Bahry, Sarah Al Gharib, Cong Wang, Jian Li, Qian Xu, Kairuo Zhu, Marija Kenzevic, Aisara Amanova, Ibrahim Abdellah and all the members of TEMiC group for their kind help and accompany and the people from ICP. They give me many help in my research and bring me a lot of fun in daily life. I would like to thank China Scholar Council (CSC) from my country for the fincial support. Lastly, I would like to say thanks to my family and my friends for their support, encouragement and kind help.

Acronyms list

POPs:

Persistent organic pollutants AOP:

CHAPTER II Experimental Part

min to disperse the aggregated nanoparticles. The prepared samples were exposed to γ-ray at the dose rate of 4kGy/h for 30 min (Figure 2.6c). The samples with different loading rate of Pt on PPy-TiO 2 were also synthesized labeled as x%Pt-(PPy-TiO 2 ).

For the photocatalytic tests the optimized mass ratio between PPy and TiO 2 was found to be 1/4.

Abstract:

Recently, π-conjugated polymer nanostructures (CPNs) emerge as a new class of catalysts for various photocatalytic applications such as water splitting, CO 2 reduction, water treatment (degradation of organic pollutants and heavy metals reduction). Among the family of CPs, polypyrrole PPy has been the most extensively investigated owing to its environmental stability, facile synthesis, excellent stability. In this thesis, PPy nanostructures were synthesized by different methods: chemical polymerization by soft templates (hexagonal or lamellar mesophases) and polymerization by radiolysis. These PPy nanostructures exhibit promising photocatalytic activity for organic pollutants (phenol and methyl organge) degradation under visible light and their activities are higher than that of PPy-bulk. Besides, we modified TiO 2 with nanostructured PPy for photodegradation of organic pollutants (methy orange and phenol as model water pollutants and toluene as air pollutant). The nanocomposite shows an important increase of the photocatalytic performance under UV and visible light compared to bare TiO 2 and PPy. This work offers a facile and cheap way to fabricate the heterojunction in organic-inorganic hybrid materials interface and the composite nanomaterials represents a promising photocatalyst for water treatment and indoor application. In another hand, green hydrogen production by photocatalytic water splitting offers a promising way to solve environment and energy issues. In this thesis, we have shown that modified conjugated polymer polypyrrole nanostructures with mono-and bimetallic (Pt, Ni, Pt-Ni) nanoparticles are very active for hydrogen generation, and that a synergistic effect is obtained by alloying Pt with Ni. Lastly, different ternary nanostructures based on PPy-TiO 2 composites with controlled active sites modification with Pt nanoparticles were developed ((Pt-PPy)-TiO 2 , (Pt-TiO 2 )-PPy and Pt-(PPy-TiO 2 )). The photocatalytic activity of Pt-(PPy-TiO 2 ) for hydrogen generation under UV and visible light is very high and drastically surpasses those of (Pt-PPy)-TiO 2 and (Pt-TiO 2 )-PPy.