Patricia Garcia-Muñoz

Fernando Fresno

Christophe Lefevre

Didier Robert

Nicolas Keller

Synergy Effect Between Photocatalysis and Heterogeneous PhotoFenton Catalysis on Ti-Doped LaFeO 3 Perovskite for High Efficiency Light-Assisted Water Treatment

A strategy combining both heterogenized photo-Fenton and photocatalysis advanced oxidation processes in a single dual catalyst is developed for simultaneously benefiting from the higher reaction rate of photo-Fenton and the higher mineralization yield of photocatalysis in water treatment, while overcoming the strong drawbacks still limiting their viability as single processes. We prepared via a facile Pechini sol-gel route a highly efficient and stable Ti-substituted LaFeO3 dual catalyst, active simultaneously as reusable photo-Fenton solid catalyst and photocatalyst in water treatment. The partial substitution of La by Ti ions in the crystalline network led to pure heterogeneous surface reactions with an increase in the catalyst robustness by more than two orders of magnitude, symbolized by the absence of any Fe release and the stability of catalytic performance with test cycles. It further strongly enhanced the reaction rates, due to both an increased availability of the photogenerated charge carriers at the surface and the electronic enrichment of surface Fe, and allowed full mineralization of the pollutant to be achieved at circumneutral pH through combined advanced oxidation processes.

Introduction

In addition to increasingly restrictive environmental govern regulations, the emergence of biorecalcitrant refractory pollutants in the water, the heterogeneity of the targets as well as the increase in the volume and concentration of polluted water streams, have created a strong interest for the elaboration of new sustainable and cost-effective water treatment technologies [1][2][3][4] . In this frame, Advanced Oxidation Processes (AOPs) -based on the generation of highly active HOx° oxidative radicals that react with the pollutant and further with the reaction intermediates to yield the substrate mineralization -, have been developed for removing a large class of refractory substances that cannot be treated through conventional mechanical, biological or physico-chemical water treatments 5,6 .

Among them, (i) the homogeneous Fenton process 7 , or its analogous heterogeneous Catalytic Wet Peroxide Oxidation (CWPO) 8 , -that are based on the catalytic decomposition of H2O2 in the presence of metallic ions, in most of the cases Fe -, and (ii) photocatalysis 9 , -that uses the redox surface properties developed by an adequately-irradiated semiconductor -, have aroused particular interest because of a high efficiency as well as relatively low investment/running costs, although they operate via different mechanisms and in different conditions. However, both processes still suffer from strong limitations that reduce their viability.

While heterogeneous semiconductor photocatalysis is an AOP that takes advantage of its ability to reach a total mineralization of a large variety of refractory organic substances and enables working within a large pH range, it unfortunately suffers from far lower reaction rates than homogeneous Fenton-like AOPs, and accordingly from far longer process durations 5,10,11 .

By contrast, the viability of the Fenton AOP is strongly reduced by the requirement to operate at acidic pH and by the complexation of Fe with short-chain acids that leads to the generation/precipitation of sludge, with the consequent continuous loss of active phase and the non-sustainable production of wastes 12 . Heterogeneizing the Fenton AOP by incorporating Fe in a catalytic body partially overcomes these issues, but at the expense of a strong reduction in the reaction rates in comparison to the homogeneous Fenton counterpart, with a drastic decrease of the process ability to reach a complete pollutant mineralization and a continuous Fe release to the water by leaching 7,12 . Furthermore, although performing CWPO under light in the so-called photo-assisted CWPO or heterogenized photo-Fenton process is a promising approach for increasing the catalyst reactivity by further boosting the rate-limiting Fe III ® Fe II conversion in the Fe III /Fe II redox cycle, the above-mentioned drawbacks still limit in a redhibitory way the viability of the heterogenized catalytic process 5,7,13 .

Therefore, a strategy consisting in combining both heterogenized photo-Fenton and photocatalysis AOPs within a unique catalyst is considered as a promising approach for simultaneously benefiting from a higher mineralization yield Please do not adjust margins Please do not adjust margins and a higher reaction rate, with as key-features that this unique dual catalyst works in similar reaction conditions as heterogeneous photocatalyst and Fe-based photo-Fenton catalyst without any loss of Fe active phase with time-on-run. Whereas physical mixtures of catalysts have been tested [14][15][16][17] , the design of a single catalyst combining both AOPs has been scarcely reported, notably using ZnFe2O4 spinel ferrite, natural Fe oxide or Ba-doped BiFeO3 perovskite [18][19][20] .

Here, we report on the use of Ti-substituted lanthanum ferrite (LaFeO3) perovskite catalysts in water treatment acting simultaneously in similar circumneutral pH reaction conditions as heterogeneized photo-Fenton catalyst and photocatalyst for achieving a complete mineralization of the substrate under UV-A light with strongly enhanced reaction rates, while improving the catalyst stability by totally inhibiting the Fe release to water. This new dual catalyst is based on the LaFeO3 semiconductor that is one of the most common ABO3 perovskite oxides studied in many research fields such as solid oxide fuel cells, optoelectronics, magnetism, gas sensors or heterogeneous thermal catalysis, for taking advantage of its A1-xA'xB1-yB'yO3±d composition versatility that allows notably its textural, structural or electronic properties to be modified, and as a result its redox and catalytic ability to be tuned through Aand/or B-site cationic partial substitution 21 . Its composition is consequently in agreement with the sustainability need currently in force that requires the use of cheap, abundant, and environmentally non-toxic elements in chemical processes 22 . While cation-doped LaFeO3 ferrites have been mainly used till now as photoFenton catalysts, their use also as photocatalysts remained scarce. Here, the removal of 4-chorophenol (4-CP) has been selected as test reaction in water under UV-A light, as 4-CP is a model molecule used in AOP studies as being representative of industrial waste-water refractory pollutants [23][24][25] , while some mineralization tests were also performed using the myclobutanil C15H17ClN4 triazole as antifungal substrate in order to broaden the scope of the work 26,27 .

Experimental part

Synthesis of Ti-substituted LaFeO3

La1-xTixFeO3 catalysts were prepared by modifying a sol-gel Pechini synthesis. La(NO3)3 lanthanum nitrate hexahydrate (108.3 g/L, 99.9%, Sigma Aldrich) and Fe(NO3)3 iron nitrate nonahydrate (133 g/L, 99.95%, Sigma Aldrich) were dissolved in stoichiometric amounts in distilled water (30 mL), and the metallic ions underwent complexation by subsequent addition of citric acid ((C6H8O7xH2O, 70 g/L, 99.5%, Sigma Aldrich) in a stoichiometric molar ratio with respect to the metallic ions.

A titanium source was introduced under stirring into the aqueous sol and the resulting suspensions were maintained at 80 °C for 48 h (2 °C/min heating rate) in order to induce the complete gel formation. The calcination of the dried gel was performed using a heating cycle as reported by Gosavi et al. 28 with heating rates of 5 °C/min, consisting in holding the temperature at 600 °C for 2 h, before subsequently maintaining a temperature plateau at 800 °C for 2 h.

In the synthesis of the P25-LFO catalyst, commercial TiO2 Aeroxide ©P25 powder (hydrophilic fumed titanium dioxide, ≥ 99.50%, Evonik, Germany) that consists of a mixture of anatase and rutile crystalline phases in 80/20 molar ratio, was used as titanium source.

In the synthesis of the SG-LFO catalyst, dried amorphous titania was used as titanium source. It was obtained according to a sol-gel synthesis method under basic conditions using titanium tetraisopropoxide (TTIP, 97%, Sigma-Aldrich) as precursor. In a typical synthesis, 17.8 g of TTIP was first added to a 40 mL ethanolic solution, before a similar volume of water was added dropwise to the solution. After rectification of the pH to 9 by adding ammonia (Carlo Erba, 30% aqueous solution), the solution was left under agitation at room temperature until a dry paste was obtained. The resulting powder was further dried at 110°C for 12 h to get the dried amorphous titania used as titanium source in the modified sol-gel Pechini synthesis.

Whatever the titanium source, the titanium added during the Pechini synthesis corresponded to a nominal amount of 10 wt.% in terms of TiO2 with respect to the theoretical amount of LaFeO3 perovskite obtained. Non-modified lanthanum ferrite powders have been synthesized as reference materials via the same protocol without any addition of titanium source, with a similar calcination procedure.

The stoichiometric reaction forming the LaFeO3 perovskite is as follows (Eq.1) 29 :

𝑳𝒂(𝑵𝑶 𝟑 ) 𝟑 𝒙𝟔𝑯 𝟐 𝑶 + 𝑭𝒆(𝑵𝑶 𝟑 ) 𝟑 𝒙𝟗𝑯 𝟐 𝑶 + 𝑪 𝟔 𝑯 𝟖 𝑶 𝟕 𝒙𝑯 𝟐 𝑶 → 𝑳𝒂𝑭𝒆𝑶 𝟑 + 𝟔𝑪𝑶 𝟐 + 𝟑𝑵 𝟐 + 𝒏𝑯 𝟐 𝑶 [Eq.1]
The reference titanium-free material was labelled as LFO, while the Ti-modified materials were labelled as P25-LFO and SG-LFO when using Aeroxide© TiO2 P25 and dried amorphous titania as titanium source, respectively.

Characterisation techniques

The reference X-ray diffraction (XRD) pattern have been recorded at room temperature in a θ/θ mode on a Brucker D8 Advance diffractometer equipped with a monochromatic copper radiation source (Kα = 1.54056 Å) with a scan step of 0.02°. Some patterns have been investigated by Rietveld refinement with the Fullprof software for which the modified Thompson-Cox-Hasting function was chosen to generate the line shape of the diffraction peaks. Instrumental broadening has been previously determined by measuring the scattering from corundum (NIST standard SRM 1976b) 30,31 .

Scanning electron microscopy (SEM) was performed in secondary electron mode on JEOL JSM-6700 F FEG microscope.

Transmission electron microscopy (TEM) was performed using a JEOL 2100F with a 0.2 nm point resolution. A copper grid covered by a holey carbon membrane was used for observation. The interplanar spacings were calculated using ImageJ software.

UV-vis diffuse reflectance spectra were acquired in a UV/Vis/NIR Perkin Elmer Lambda 1050 spectrometer, recording the reflectance between 250 and 800 nm. Band gaps were estimated from Tauc plots by representing (αhν) 2 vs. photon Please do not adjust margins Please do not adjust margins energy, where α= -Ln(Reflectance), in accordance with the direct semiconductor character of LaFeO3 32 .

Fluorescence spectra of the powdered samples were recorded in a Fluorescence Spectrometer Perkin Elmer LS55, using an excitation wavelength of 450 nm and a cut-off filter at 515 nm. Fluorescence lifetime measurements by timecorrelated single photon counting (TCSPC) were carried out with a Mini-t equipment from Edinburgh Instruments using as excitation source a laser diode (model EPL375) with a wavelength of 445.2 nm and a pulse width of 90.7 ps, at repetition rate of 1 MHz, and including a band pass filter at 600 ± 25 nm. The decay profiles were fitted to a bi-exponential decay curve, with lifetimes obtained as the average of both components, calculated as <τ>= [Σ(Aiτi 2 )]/ Σ(Ai τi), where Ai is the amplitude and τi the lifetime of each component.

X-ray photoelectron spectroscopy (XPS) analysis was performed on a ThermoVGMultilabESCA3000 spectrometer (Al Kα anode at hλ=1486.6 eV). The energy shift due to electrostatic charging was subtracted using the contamination sp 2 carbon C 1s band at 284.6 eV. Contributions with Doniach-Sunjic shape 33 and a S-shaped Shirley type background 34 were used.

Degradation test protocol

The 4-CP and myclobutanil degradation tests were performed in a batch beaker-type glass reactor at atmospheric pressure, at a constant temperature of 20°C ± 2°C (using a using cooling bath) and using H2O2 as main oxidant. In a typical reaction procedure, 50 mg of catalyst was dispersed under stirring in a 100 mL aqueous solution of 4-chlorophenol at concentration of 25 mg/L, corresponding to an initial organic carbon concentration of 14.8 ppm and to a catalyst load of 0.5 g/L. For the reactions with myclobutanil, starting concentration of 20 mg/L of the pollutant was selected. Prior to irradiation, the catalyst suspension has been stirred for 1h in the dark to ensure the establishment of the adsorption/desorption equilibrium. After adding H2O2 at the stoichiometric concentration corresponding to a complete mineralization of the initial pollutant (125 mg/L), or substoichiometric in some cases (31.25 and 62.50 mg/L), the tests were performed under UV-A (60 W/m 2 ; λ=365 nm, Philips 24W/10/4P lamps). At each time interval, 8 mL of solution has been sampled and then filtered through 0.20 μm porosity filter to remove the photocatalyst powder if any, before the concentration of 4-chlorophenol or myclobutanil was determined by UV-Visible spectrophotometry by following the disappearance of the main absorption peak at λ=224 nm 35 . Total Organic Carbon measurements were carried out using a Shimadzu TOC-L analyzer to determine the organic carbon load. H2O2 concentration was measured by colorimetric titration using the TiOSO4 method 36 and the Fe leached during time-course of reaction was quantified by the orthophenanthroline method 37 .

Tests with myclobutanil as substrate were performed following a similar test protocol, at a myclobutanil concentration of 20 mg/L. The myclobutanil concentration was determined by UV-visible spectrophotometry by monitoring the disappearance of the main absorption peak at λ=220 nm.

Results and discussion

Catalyst characterization

Figure 1 shows the XRD patterns of the pristine and Ti-modified LaFeO3 materials with their corresponding Rietveld refinement profiles. Table 1 andTable S1 show the refined cationic distribution in the LaFeO3 structure and the crystallographic data, respectively. The XRD patterns of the pristine catalyst exhibited the most intense diffraction peaks at 22.6°, 32.2°, 39.7°, 46.1°, 57.4° and 67.3° in 2θ, corresponding to the diffraction of the ( 100), ( 110), ( 111), ( 200), ( 210) and ( 220) planes of the LaFeO3 phase, respectively. α-Fe2O3 in small amount (11%) with a mean crystallite size of 35 nm was observed as extra phase. In the Ti-doped samples, independently of the Ti source, all the patterns can be indexed in the Pbnm orthorhombic unit cell of LaFeO3, with no change in terms of α-Fe2O3 additional phase. Neither La2O3 nor TiO2 are observed as extra phases. Elemental chemical analysis reveals a 3.2 at.% Ti content in the Ti-modified LaFeO3 catalyst prepared using the crystalline TiO2 nanopowder as precursor, further increased up to 4.0 at.% using the dried amorphous precursor, while the Ti/Fe molar ratio remains unchanged (Table 2). Please do not adjust margins

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The separate refinement of both Ti/Fe and Ti/La site occupations evidences that titanium atoms preferentially occupy exclusively the La A-site and substitute only the La atoms, so that the catalysts can be labelled as La1-xTixFeO3. A partial Ti ® La substitution rate of 5 at.% was achieved within the perovskite network in the A-site using the crystalline TiO2 nanopowder as titanium precursor, while it increases up to 11 at.% using the dried amorphous precursor (Table 1). The exclusive La A-site occupation is rather unexpected when considering the involved cationic sizes -(rFe+III)CN=6 = 0.64, (rLa+III)CN12 = 1.46 and (rTi+III)CN=6 = 0.76 38 . Both A-and B-site substitutions have been reported for the LaFeO3 structure depending on the doping element, although high valence metal ions usually occupy the Fe 3+ sites 39,40 . However, there is no empirical rule on the location of the substituting element depending on electronic or steric criterion, and many extrinsic parameters are known to affect the cationic distribution in oxides, like eg. the cooling rate or the synthesis temperature 41,42 . Here, we suggested that the partial substitution resulted from a temperature-driven solid-solid diffusion that is proposed to occur between the amorphous LaFeO3 network-before it crystallizes -and the TiO2 crystallites, allowing the Ti atoms to distribute in the LaFeO3 network. Consequently, replacing the well-crystallized TiO2 nanoparticles with a 22 nm average size by an amorphous network increased further the substitution rate by favouring the atomic titanium diffusion in the amorphous LaFeO3 perovskite network. In addition, this partial substitution hindered the growth of large crystallites during the temperature-driven crystallization at 800°C when compared to the undoped counterpart (20-21 nm vs. 46 nm), as previously observed for Li-or Cu-doped LaFeO3 materials 43,44 . An increase in the specific surface area from 8 to 28 m 2 /g was simultaneously observed for the P25-LFO catalyst as a result of the decrease in mean crystallite size, as shown in Table 2. However, the SG-LFO catalyst displayed a low specific surface area of 5 m 2 /g, although it displayed a smaller mean crystallite size of 20 nm. This was attributed to the existence of more grain boundaries within the SG-LFO materials compared to the P25-LFO counterpart.

While the SEM images shown in Figure S1 evidenced the overall powder morphology of the catalysts, the TEM images shown in Figure S2 and in Figure 2 confirmed the structural features of both the pristine LFO and the SG-LFO catalysts, respectively. Whether the

Catalyst

La site distribution [a] Fe site distribution [a] a-Fe2O3, % TiO2, % SG-LFO #1 [b] 0.88 0.12 1 12 0 SG-LFO #3 [b] 0.88 0.12 1 11 0 SG-LFO #3 [b] 0.88 0.12 1 12 0

La

[a] the determination of the cationic distribution within the structures was performed considering that titanium can move towards both cationic sites.

[b] SG-LFO #1 #3 and #5 correspond to the SG-LFO catalyst after tests #1, #3 and #5, respectively.

Catalyst

TiO2 precursor Fe (at.%) [a] Ti (at.%) [a] Ti/Fe molar ratio SBET (m 2 g -1 ) [b] D (nm) [c] [a] The iron and titanium contents in the catalysts were determined by Inductively coupled plasma optical emission spectroscopy (ICP-OES) carried out on an Optima 7000 DV spectrometer (Perkin Elmer), after a microwave-assisted acidic dissolution in aqua regia at 185°C under autogenic pressure.

[b] The Brunauer-Emmett-Teller (BET) specific surface area has been calculated from the N2 adsorption isotherm recorded on a Micrometrics Tristar 3000 using N2 as adsorbent at -196 °C with a prior outgassing at 250°C overnight to desorb the impurities or moisture.

[c] The mean crystallite size defined as the average size of the coherent diffracting domains, was derived from the whole XRD patterns after refinement and determined from the Scherrer equation with the usual assumption of spherical crystallites taking into account the intrinsic broadening of the peaks due to the instrumentation.

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Please do not adjust margins catalyst was doped or not with titanium, interplanar spacings of 0.39 nm, 0.28 nm and 0.23 nm consistent with the (110), ( 100) and ( 111) planes characteristic of the LaFeO3 structural crystallographic features were observed. The ability of La1-xTixFeO3 materials to be used as photocatalyst under UV-A light is confirmed by the UV-vis absorbance spectra, that reveals a broad absorption band in the UV-vis range, and a band-gap estimated graphically from Tauc plots at 2.1 eV whether the catalyst contained substitutional titanium or not (Figure 3). In order to shed light on the effects of Ti ® La substitution, further characterization of doped and undoped samples was performed. The fluorescence spectra displayed in the inset of Figure 4 showed an emission profile of LaFeO3 with a main contribution centered at ca. 485 nm, similarly to what has been reported for lanthanum ferrite 45 , which can be associated to the direct radiative de-excitation of electrons from high-energy levels within the conduction band to the valence band. 45,46 Lower intensity emission at energies lower than the band gap reflects excitonic photoluminescence which is usually associated with sub-band-gap transitions from electronic states related to surface defects or oxygen vacancies 46 .

Upon titanium doping, the positions of the emission bands remain, while some changes in the intensity are visible, depending on the involved feature. Thus, the high-energy emission is somewhat quenched in the presence of the dopant, which has been associated to a first approximation with decreased direct recombination rate due to improved charge separation within the semiconductor structure, and consequently with enhanced photocatalytic activity. 47,48 On the contrary, the reverse effect of doping is found on the intensity the sub-band-gap features, which can be related to a higher content of surface vacancies/defects in the doped systems. 46 Fluorescence lifetime should nevertheless give more accurate information than steady-state spectra about recombination kinetics. 49 The fluorescence decay curves for the different samples between 550 and 600 nm, corresponding to the band gap energy and shown in the main body of Figure 4, give fluorescence lifetimes of the same order as previously reported values for LaFeO3 and related structures. 47,50 As observed in the curves and the average lifetime values from curve fittings, the P25-LFO sample gives rise to a slightly higher lifetime than the pristine LFO ferrite, while the SG-LFO sample is characterized by a considerably longer fluorescence lifetime, indicative of slower radiative recombination kinetics, which can be ascribed to an enhanced charge separation and therefore a larger availability of photogenerated electrons and holes for the subsequent surface redox reactions 47,49,51 . Figure 5 shows the influence of the partial substitution of La ions by Ti ions in the LFO structure on the surface state of the SG-LFO catalyst. The XPS analysis revealed the presence of both cations as La 3+ and Fe 3+ ions at the surface of the pristine LFO and the SG-LFO catalyst. Indeed, the La 3d core level spectra recorded on the pristine LFO material exhibited a La 3d5/2-3/2 orbital doublet contribution at 833.4 eV and 850.1 eV, with a 16.7 eV spin orbit splitting 52-54 and a 3.8 eV multiplet splitting 55 , that is characteristic of La 3+ species. The binding energies of Fe 2p3/2-1/2 orbital doublet contribution at 710.3 eV and 723.7 eV, with a spin orbit coupling of 13.4 eV 54,55 and with the broad and low intensity shake-up satellite peak at about 718 eV characteristic of Fe 3+ 56,57 , confirmed the presence of Fe 3+ ions at the surface of the pristine LFO.

After the Ti ® La partial substitution in the LFO perovskite, the XPS Ti 2p profile of the SG-LFO catalyst displayed a single contribution, with the doublet related to Ti 2p3/2-1/2 spin-orbit components at 457.3 eV and 463.0 eV. This revealed the stabilization of Ti cations at the surface as lower oxidation state Ti 3+ in substitution of La 3+ in the perovskite structure 55 , or as Ti 4+ -O-M with a strongly lower binding energy than Ti 4+ in an usual TiO2 network environment (Figure 5) 58 . Further, this led Please do not adjust margins

Please do not adjust margins also to a slight downward (-0.7 eV) shift for the binding energies of the Fe 2p orbital doublet contribution at 709.7 eV and 723.2 eV, and simultaneous in a slight upward (+0.8 eV) shift for the La 3d orbital doublet contribution at 834.2 eV and 850.9 eV, both cations remaining present at the surface in the formal +3 oxidation state.

According to the electrostatic model, in the Ti-O-La configuration, the upward shift observed for La 3+ compared to the La-O-La reference configuration results from the higher electronegativity of Ti vs. La, that causes a O ® Ti shift of the electronic density, and consequently a La ® O shift of the La-O bond electronic density, that corresponds to a higher binding energy of La core electrons. So, oppositely, the downward shift of the Fe 3+ binding energy was assigned to an electronic enrichment of Fe cations, resulting in the lower binding energy of Fe core electrons.

In addition, by combining UV-vis diffuse reflectance and UPS data, it can be assumed that the partial cationic substitution did not significantly alter neither the potential of the conduction band edge, nor the valence band maximum, determined by UPS (He I, hl = 21.2 eV) at ca. 2.2 ± 0.1 eV vs. Fermi level whether the surface is modified or not by titanium (Figure S3).

Catalytic activity

Combined photo-assisted CWPO and photocatalysis

The evolution with time under irradiation of the main features followed during the reaction is shown in Figure 6. First, although the titanium-free LaFeO3 catalyst showed ability to decompose fully H2O2 and to remove 4-CP within 150 min of test, it only allowed a mineralization of 75% to be achieved. Further, the catalyst suffered from a strong iron leaching, with an iron release to the solution of 0.5 mg L -1 . The low stability of the catalyst resulted in a high contribution of the homogeneous photoFenton reaction to the H2O2 decomposition, and consequently to both 4-CP and TOC removal rates, so that the apparent kinetic rate constants obtained could not be ascribed to a pure heterogeneous process and were therefore overestimated. This homogeneous contribution was responsible for the low H2O2 efficiency value of 0.75, and the resulting uncomplete mineralization of the substrate, as typically observed in CWPO-like reactions. Indeed, iron in solution is known to react with the latest degradation intermediates, that are short-chain acids like oxalic, acetic or formic acids, to form highly stable iron complexes that photodegrade very slowly and consequently stop the reaction (Eq. 2) [59][60][61] .

[𝑭𝒆 𝟑6 (𝑹𝑪𝑶𝑶 8 )] 𝟐6 𝒉𝝊 < = 𝑭𝒆 𝟐6 + 𝑪𝑶 𝟐 + 𝑹 [Eq.2]
In the case of the La1-xTixFeO3 catalysts, the incorporation of titanium atoms into the perovskite network with the Ti ® La partial substitution increases considerably the robustness of the catalyst by more than two orders of magnitude. This was evidenced by a strong decrease in the iron release to 0.05 mg L - 1 for a 5% substitution (P25-LFO), and by a further reduction down to non-detectable level (below 0.001 mg L -1 , i.e. lower than 0.0009% relative to the catalyst Fe content) for the SG-LFO catalyst with a 11% substitution rate. This increase in stability is accompanied by a strong enhancement of the catalytic activity, more pronounced as the substitution rate increases. Thus the duration necessary for achieving a full removal of 4-CP is reduced to 120 min and 60 min on the P25-LFO and SG-LFO catalysts, respectively, while both catalysts achieve complete mineralization within 125 min and 90 min of reaction, respectively. This very good behaviour is reflected in a strong increase in the apparent kinetic constants for 4-CP degradation, TOC conversion and H2O2 decomposition (Table 3), The absence of any detectable release of iron demonstrates that the strong increase in the catalytic activity can be ascribed to pure heterogeneous surface reactions, without any homogeneous contribution. This journal is © The Royal Society of Chemistry 20xx

Please do not adjust margins Please do not adjust margins Further, both La1-xTixFeO3 catalysts exhibit a H2O2 efficiency x greater than 1, which reflects the fact that they allow full TOC conversion to be achieved at uncomplete H2O2 conversion. This evidences that the La1-xTixFeO3 catalysts can act as a dual catalyst, by working simultaneously as heterogenized photo-Fenton catalyst and photocatalyst. This dual behaviour was confirmed by the evolution of the TOC conversion with the H2O2 conversion shown in Figure 7A. While the curve obtained for the titanium-free LaFeO3 catalyst is distorted by the strong homogeneous Fenton contribution, the clear distribution of the whole data set for both catalysts above the unity diagonal confirms that the heterogeneous photo-Fenton process cannot be considered as the sole AOP operating for converting the TOC. Additional experiments performed using non-stoichiometric H2O2 doses underlined further that the TOC conversion is obtained simultaneously through both photo-Fenton and photocatalysis AOPs (Figure 7B). Indeed, complete TOC conversion was achieved following a zero-order kinetic and with a similar apparent kinetic rate constant independently of the H2O2 dose at 25% or 50%, while decomposition of H2O2 was already completed. This confirms that pure photocatalysis was taken place for allowing full TOC conversion to be obtained. Taking into account that the experiments were carried out using the stoichiometric amount of H2O2 to mineralize TOC, the linear curve with a unity slope reflects the implementation of an heterogenized photo-Fenton process with no occurrence of scavenging reactions.

Although the incorporation of Ti atoms into the LFO network strongly increases the activity in pure photocatalysis, -more pronounced as the Ti ® La partial substitution increases -, the activity remains far lower than that obtained using H2O2, (Figure 8, Table 4). This corroborates the fact that, in the combined AOPs, the dual La1-xTixFeO3 catalyst is acting predominantly as heterogeneous photo-Fenton catalyst at the beginning of the k(4-CP), min -1 [a] r0(TOC), mg L -1 min -1 [b] [Fe] leached, mg L -1 X(H2O2), % X(TOC), % x(H2O2) [c] LFO 0.010 0.020 0.12 0.5 100 75 0.75 P25-LFO 0.017 0.017 0.18 0.05 90 100 1.11 SG-LFO 0.043 0.033 0.28 <0.001 [d] 89 100 1.12 1-5# reuse of SG-LFO -33.3 ± 0.3 10 -3 0.28 ± 0.01 <0.001 [d] 100

[a] the H2O2 and 4-CP concentration evolution curves were fitted by a pseudo first-order kinetic as usually admitted, [b] the TOC concentration evolution curve was fitted with a zero-order kinetic model as usually admitted, [c] a theoretical x=1 efficiency of H2O2 use in Fenton-like processes reflects the fact that H2O2 and the formed radicals do not suffer any detrimental scavenger reactions, [d] the detection limit of Fe leached to the solution has been measured at 0.001 ppm Please do not adjust margins Please do not adjust margins process, so that high reaction rates can be obtained, while it subsequently operates as photocatalyst for mineralizing the short chain acids, and consequently allows full TOC conversion to be achieved by hindering the detrimental formation of stable Fe complexes. It is worth noting that, although the P25-LFO catalyst might take advantage from an enhanced surface area of 28 m 2 /g for exposing more surface iron active in the decomposition of H2O2, the specific surface area of the catalysts cannot be the key factor driving the catalytic activity, since the most active SG-LFO catalyst displays a low surface area of 5 m 2 /g. We propose therefore that a combination of surface and electronic modifications modulates the activity of La1-xTixFeO3 catalysts and leads the SG-LFO catalyst to exhibit the best catalytic results. On the one hand, electron-rich surface iron enables a faster H2O2 decomposition by the Fe surface sites, and therefore the production of higher concentrations of active radicals during the Fe III /Fe II redox cycle (Eqs. 3-5). We may assume that the photoassisted Fe 3+ to Fe 2+ reduction in (4) might be accompanied by a Ti 3+ to Ti 4+ oxidation as a plausible way of compensating the charge. The Ti 4+ species might further be reduced back to Ti 3+ by a photogenerated electron. Further, the degradation of the short-chain acids -and consequently the mineralization of the carboxylic acids -, might be favored by the electronic enrichment of the surface Fe according to Eq. 6, with the simultaneous Fe III ® Fe II surface reduction, known as the rate limiting step in the Fe redox cycle.

[𝑭𝒆 𝑰𝑰𝑰 (𝑹𝑪𝑶𝑶 8 )] 𝟐6 𝒉𝝊 → 𝑭𝒆 𝑰𝑰 + 𝑪𝑶 𝟐 + 𝑹 [Eq.6] On the other hand, the enhanced availability of the photogenerated charge carriers also enables a more efficient photocatalytic decomposition of H2O2, with the production of HO°x radicals (Eqs. 7-9), as well as a more efficient production of OH° radicals from adsorbed water (Eq. 10). The stabilization of Fe 3+ cations within the orthorhombic La1-xTixFeO3 nanocrystals -both in the bulk and at the surface, as revealed by XRD and XPS -explains the strong gain in the robustness of the substituted catalysts that leads essentially to the suppression of iron leaching. We cannot rule out that the α-Fe2O3 minority phase is subjected to a negligible Fe leaching 62,63 , nevertheless remaining below the detection threshold, so that its role in the catalytic performance can be discarded.

Finally, degradation of myclobutanil was studied in order to broaden the scope of the study and confirm further the interest of this new dual SG-LFO catalyst. Similarly, Table 5 clearly evidences the superiority of the SG-LFO catalyst in terms of both myclobutanil and TOC removal rates, as well as of catalyst robustness.

Stability tests of the SG-LFO catalyst

Considering the robustness of the SG-LFO catalyst in the first test cycle, its stability was further studied in terms of activity, Please do not adjust margins Please do not adjust margins iron release and structural features during recycling tests.

Actually, the refinement of the XRD patterns of the used catalysts reveals the structural stability of the La1-xTixFeO3 catalysts during recycling tests (Table 1, Figure S4 and Table S2). Thus, no extra-phase formation occurred under UV-A during the reaction, and no change in terms of Ti ® La substitution rate within the LaFeO3 network and of mean crystallite size has been observed. Regarding the activity, the results of recycling tests shown in Figure 9 and Table 3 demonstrate the very good stability and consequently the reusability of the SG-LFO catalyst. Indeed, apparent kinetic constants for 4-CP and TOC removal remained essentially unchanged after five consecutive runs, and the Fe release to the solution was below the detection threshold (ie. lower than 0.0009% relative to the catalyst Fe content).

Conclusions

To sum up, we have highlighted the interest of using a new and highly robust Ti-substituted LaFeO3 dual catalyst, active in water treatment as reusable heterogeneized photo-Fenton catalyst and photocatalyst. The La1-xTixFeO3 dual catalyst with a 11% substitution degree was prepared by modifying a facile Pechini sol-gel route using a dried amorphous titania as titanium source. The strategy combining both AOPs within a single dual catalyst allowed the La1-xTixFeO3 catalyst to simultaneously take advantage from the higher reaction rate of photo-assisted CWPO and the higher mineralization yield of photocatalysis. The partial Ti ® La cation substitution in the LaFeO3 perovskite network led to pure heterogeneous surface reactions with an increase in the catalyst robustness by more than two orders of magnitude, evidenced by the complete inhibition of the Fe release to water and the stability of the catalytic performance over five test cycles. It further strongly increased the reaction rates, due to both an enhanced availability of the photogenerated charge carriers at the surface and the electronic enrichment of the surface iron, and allowed full mineralization of the pollutant to be achieved at circumneutral pH through combined AOPs.

Forthcoming works are concerned with the use of solar light for taking advantage of the narrow band gap of the dual La1-xTixFeO3 catalysts, as well as with downsizing the La1-xTixFeO3 crystallites for increasing further the availability of Fe ions at the catalyst surface. conclusions section should come in this section at the end of the article, before the acknowledgements.

Figure 1 .

 1 Figure 1. Observed (black), calculated (red full line), and difference (blue full line) x-ray powder diffraction patterns of (a) LFO, (b) P25-LFO and (c) SG-LFO catalysts recorded on a D8 diffractometer (λ = 1.54056 Å). The positions of the Bragg reflections are represented by vertical bars, in blue for the reflexes indexed in the Pbnm orthorhombic unit cell of LaFeO3 and in green for those of the α-Fe2O3 extra phase.

Figure 2 .

 2 Figure 2. TEM images of the SG-LFO catalyst. The interplanar distances of 0.39 nm, 0.28 nm and 0.23 nm corresponded to the (110), (100) and (111) planes of the LFO structure, respectively.

Figure 3 .

 3 Figure 3. UV-vis diffuse reflectance spectra (a) and Tauc plots(b) of LFO, P25-LFO and SG-LFO catalysts. The numeric values in (b) indicate the band gap energies estimated from the Tauc plots.

  This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins

Figure 4 .

 4 Figure 4. Fluorescence decay curves of pristine and Ti-doped LaFeO3 samples between 575 and 625 nm. The green lines correspond to the decay curves fitted to each dataset. <τ> represents the average fluorescence lifetimes. The instrument response function (IRF) has been included for comparison. Inset: fluorescence spectra of the same samples; the signal marked with (*) corresponds to the lamp emission as confirmed by recording the emission spectra with different excitation wavelengths.

FIgure 5 .

 5 FIgure 5. XPS profiles recorded on both the Ti-free LFO and the SG-LFO catalysts, (A) wide scan survey spectrum, (B) La 3d, (C) Fe 2p and (D) Ti 2p orbitals.

Figure 6 .

 6 Figure 6. Evolution with time under irradiation of A) the relative 4-CP concentration, B) the relative TOC concentration, C) the H2O2 decomposition yield and D) the concentration of leached Fe in the solution, during the combined photo-Fenton and photocatalytic degradation of 4-CP over the pristine and the Ti-substituted LaFeO3 catalysts. Conditions: [4-CP]0 = 25 mg/L; [H2O2]0 = 125 mg/L; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 W m -2 .

Figure 7 .

 7 Figure 7. A) TOC conversion vs. H2O2 conversion for the combined photo-Fenton and photocatalytic degradation of 4-CP over the pristine and the Ti-substituted LaFeO3 catalysts. Conditions: [4-CP]0 = 25 mg/L; [H2O2]0 = 125 mg/L; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 W m -2 . B) Influence of the H2O2 dose on the relative TOC concentration time-evolution and the H2O2 conversion obtained on the SG-LFTO catalyst. Conditions: [4-CP]0 = 25 mg/L; [H2O2]0 = 31.25-125.00 mg/L, corresponding to the 25-100% range; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 W m -2 .

Table 3 .

 3 Kinetic rate constants of H2O2 decomposition, 4-CP oxidation, and mineralization though combined photo-Fenton and photocatalysis AOPs. Fe leached, H2O2 depletion percentage, TOC conversion and H2O2 efficiency parameters. Conditions: [4-CP]0 = 25 mg/L; [H2O2]0 = 125 mg/L; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 W m -2

Figure 8 .

 8 Figure 8. Time-evolution of both the C/C0 and TOC/TOC0 relative concentrations during the pure photocatalytic degradation of 4-CP over the pristine and the Ti-substituted LaFeO3 catalysts. Conditions: [4-CP]0 = 25 mg/L; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 Wm -2 .

Table 5 .

 5 Kinetic rate constants of myclobutanil oxidation and mineralization rate through the combined catalytic photo-Fenton and photocatalytic AOP over the pristine and the Ti-substituted LaFeO3 catalysts. The concentration of the leached Fe is also reported. Conditions: [myclobutanil]0 = 20 mg/L; [H2O2]0 = 125 mg/L; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 W m -2 the myclobutanil and the TOC concentration evolution curves were fitted by a pseudo first-order and a zero-order kinetic model as usually admitted; [b] the detection limit of Fe leached to the solution has been measured at 0.001 ppm Table 4. Kinetic rate constants of 4-CP oxidation and mineralization rate through pure photocatalysis. Operating conditions: [4-CP]0 = 25 mg/L; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 W m -the 4-CP concentration evolution curve was fitted by a pseudo firstorder kinetic as usually admitted, [b] the TOC concentration evolution curve was fitted with a zero-order kinetic model as usually admitted. This journal is © The Royal Society of Chemistry 20xx

Figure 9 .

 9 Figure 9. Catalyst recycling efficiency expressed in terms of time-evolution of both the C/C0 and TOC/TOC0 relative concentrations during 5 consecutive runs in the combined photo-Fenton and photocatalytic degradation of 4-CP with the reused SG-LFO catalyst. Conditions: [4-CP]0 = 25 mg/L; [H2O2]0 = 125 mg/L; T=25°C; [cat] = 0.5 g/L; UV-A irradiance of 60 W m -2 . The catalyst recovery was achieved by powder

Table 1 .

 1 Refined cationic distribution in the La1-xTixFeO3 perovskite catalysts and weight percentage of extra phases obtained after Rietveld refinement.

Table 2 .

 2 Main physico-chemical properties of the pristine and the Ti-substituted LaFeO3 perovskite catalysts.

  𝑳𝒂 𝟏8𝒙 𝑻𝒊 𝒙 𝑭𝒆 𝑰𝑰𝑰 𝑶 𝟑 + 𝑯 𝟐 𝑶 𝟐 𝑳𝒂 𝟏8𝒙 𝑻𝒊 𝒙 𝑭𝒆 𝑰𝑰 𝑶 𝟑 + 𝑯 𝟐 𝑶 𝟐 𝒉𝝊 → 𝑳𝒂 𝟏8𝒙 𝑻𝒊 𝒙 𝑭𝒆 𝑰𝑰𝑰 𝑶 𝟑 + 𝑯𝑶°+ 𝑶𝑯 8

		𝒉𝝊 → 𝑳𝒂 𝟏8𝒙 𝑻𝒊 𝒙 𝑭𝒆 𝑰𝑰 𝑶 𝟑 + 𝑯𝑶𝑶°+ 𝑯 6	[Eq.3]
	𝑳𝒂 𝟏8𝒙 𝑻𝒊 𝒙 𝑭𝒆 𝑰𝑰𝑰 𝑶 𝟑 → 𝒉𝝂	𝑳𝒂 𝟏8𝒙 𝑻𝒊 𝒙 𝑭𝒆 𝑰𝑰 𝑶 𝟑	[Eq.4]

[Eq.5]

  𝑳𝒂 𝟏8𝒙 𝑻𝒊 𝒙 𝑭𝒆𝑶 𝟑 → 𝒆 8 + 𝑯 𝟐 𝑶 𝟐 → 𝑯𝑶°+ 𝑶𝑯 8 𝒉 6 + 𝑯 𝟐 𝑶 𝟐 → 𝑯𝑶𝑶°+ 𝑯 6 𝒉 6 + 𝑯 𝟐 𝑶 → 𝑯𝑶°+ 𝑯 6

	𝒉𝝂	𝒆 8 + 𝒉 6	[Eq.7]
			[Eq.8]
			[Eq.9]

[Eq.10]

This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 3

This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 5

This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 9

Acknowledgements

The authors want to thank the European Fund for regional development (EFRE/FEDER) for funding the project PHOTOPUR which is performed within the framework of Interreg V program and Offensive Sciences call. F. Fresno thanks financial support from project SOLPAC: ENE2017-89170-R from the Ministry of Science, Innovation and Universities. T. Dintzer (ICPEES) and D. Ihiawakrim (IPCMS) are thanked for performing SEM and TEM characterization, respectively. V. Papaefthimiou and S. Zafeiratos (ICPEES) are thanked for performing XPS and UPS measurements.

Conflicts of interest

There are no conflicts to declare


Marisa Rico-Santacruz

Patricia García-Muñoz

Clément Marchal

Nelly Batail

Charlotte Pham

Didier Robert

Nicolas Keller

Coating-free TiO 2 @β-SiC alveolar foams as a ready-to-use composite photocatalyst with tunable adsorption properties for water treatment

Introduction

In wastewater treatment, photocatalysis is one of the advanced oxidation processes that have demonstrated its ability to degrade and mineralize biorecalcitrant refractory compounds that cannot be eliminated by conventional treatments, or at least to degrade them into readily biodegradable compounds [START_REF] Malato | Photocatalytic Treatment of Diuron by Solar Photocatalysis: Evaluation of Main Intermediates and Toxicity[END_REF][START_REF] Borges | Photocatalysis as a potential tertiary treatment of urban wastewater: new photocatalytic materials Clean[END_REF] . Photocatalysis is usually carried out at the lab scale with nanoparticle suspensions for taking advantage of a maximum irradiated and exposed surface for optimizing the degradation activity. However, the necessary implementation of timeconsuming and costly nanofiltration recovery steps for separating the powdery photocatalyst from the treated water, as well as safety issues related to its handling, make the process less viable for real applications and with a less secure environment for recycling and handling.

Therefore, in parallel to the implementation of approaches based on the advanced design of nanomaterials for enhancing the activity of powdery photocatalysts [START_REF] Li | Facile synthesis of cerium oxide nanoparticles decorated flower-like bismuth molybdate for enhanced photocatalytic activity toward organic pollutant degradation[END_REF][START_REF] Li | Facile construction of flower-like bismuth oxybromide/bismuth oxide formate p-n heterojunctions with significantly enhanced photocatalytic performance under visible light[END_REF][START_REF] Li | In situ construction of WO3 nanoparticles decorated Bi2MoO6 microspheres for boosting photocatalytic degradation of refractory pollutants[END_REF][START_REF] Li | In situ anion exchange strategy to construct flower-like BiOCl/BiOCOOH p-n heterojunctions for efficiently photocatalytic removal of aqueous toxic pollutants under solar irradiation[END_REF] , strategies dealing with the immobilization of photocatalysts -and more globally with the elaboration of macroscopic photocatalytic structuresare investigated for designing wastewater treatment processes allowing the photocatalysts to operate in a continuous mode. In this frame, among cellular monolithic solids, metallic and ceramic open-cell alveolar solid foams gained recently important interest for use as photocatalyst support in water treatment for taking advantage of a static mixer effect inside the reactor and of a better light transmission than honeycombor square-channel monoliths [START_REF] Masson | β-SiC alveolar foams as a structured photocatalytic support for the gas phase photocatalytic degradation of methylethylketone[END_REF][START_REF] Raupp | First-principles modeling, scaling laws and design of structured photocatalytic oxidation reactors for air purification[END_REF][START_REF] Ishiguro | Photocatalytic activity of Cu2+/TiO2-coated cordierite foam inactivates bacteriophages and Legionella pneumophila[END_REF][START_REF] Levchuk | Photocatalytic activity of TiO2 films immobilized on aluminum foam by atomic layer deposition technique[END_REF][START_REF] Martín-Sómer | Novel macroporous 3D photocatalytic foams for simultaneous wastewater disinfection and removal of contaminants of emerging concern[END_REF] . In addition, their open structure enables the photocatalyst to operate at ultra-low pressure drop [START_REF] Masson | β-SiC alveolar foams as a structured photocatalytic support for the gas phase photocatalytic degradation of methylethylketone[END_REF] .

Among ceramic foams, medium surface area self-bonded β-SiC foams gained a strong interest thanks to a high thermal and chemical stability that allow them to be submitted to a wide range of severe conditions during the photocatalyst immobilization step, the reaction itself or thermal/chemical regeneration steps (if required). Further, the β-SiC foam surface is composed of a thin amorphous nanolayer exposing a high density of oxygenated surface groups favoring the anchorage of photocatalysts [START_REF] Masson | β-SiC alveolar foams as a structured photocatalytic support for the gas phase photocatalytic degradation of methylethylketone[END_REF][START_REF] Raupp | First-principles modeling, scaling laws and design of structured photocatalytic oxidation reactors for air purification[END_REF][START_REF] Ishiguro | Photocatalytic activity of Cu2+/TiO2-coated cordierite foam inactivates bacteriophages and Legionella pneumophila[END_REF][START_REF] M'bra | Heterogeneous photodegradation of Pyrimethanil and its commercial formulation with TiO2 immobilized on SiC foams[END_REF] .

Binderless β-SiC alveolar foams have been already used as TiO2 support in water treatment [START_REF] Masson | β-SiC alveolar foams as a structured photocatalytic support for the gas phase photocatalytic degradation of methylethylketone[END_REF][START_REF] M'bra | Heterogeneous photodegradation of Pyrimethanil and its commercial formulation with TiO2 immobilized on SiC foams[END_REF][START_REF] Kouamé | β-SiC foams as a promising structured photocatalytic support for water and air detoxification[END_REF][START_REF] Plantard | TiO2-coated foams as a medium for solar catalysis[END_REF] . However, the preparation of the foam supported TiO2 photocatalysts requires immobilizing or synthesizing TiO2 onto the β-SiC support through separated post-synthesis process, so that the TiO2/β-SiC foams can suffer detrimental stability problems that could provoke a release of photocatalyst to the water. The resistance of the catalyst-support interface towards the strains derived from particle to particle and particle-fluid mechanical interactions in the reactor environment, remains indeed an essential quality criteria for a good support, in order to avoid the release of photocatalyst particles from the support. This work aimed at elaborating TiO2@β-SiC photocatalytic composite foams that gather the TiO2 photocatalyst and the β-SiC alveolar foam within a ready-to-use (coating-free) photocatalytic media, that consequently does not require the implementation of any post-synthesis immobilization or synthesis process at the foam surface. They were elaborated through a sequential multi-step carburization synthesis approach derived from the single carburization Shape Memory Synthesis (SMS) replica method developed by SICAT Catalyst for synthesizing pure self-bonded porous β-SiC foams from a preshaped polyurethane foam [START_REF] Rico-Santacruz | Alveolar TiO2-β-SiC photocatalytic composite foams with tunable properties for water treatment[END_REF][START_REF] Keller | A new TiO2β-SiC material for use as photocatalyst[END_REF] . Further, we aimed at controlling the adsorption properties of the ready-to-use TiO2@β-SiC composite foams towards the pollutant in water.

Diuron (C9H10Cl2N2O, 3-(3,4-dichlorophenyl)-1,1dimethylurea), one of the most used contact herbicides from the family of substituted phenylureas, has been taken as model substrate to degrade for evaluating the liquid phase photocatalytic activity of the TiO2@β-SiC composite foams under simulated solar light. Diuron is known to be degraded by photocatalysis via a well-admitted multi-pathway degradation route, involving mainly hydroxyl OH° radicals as active species [START_REF] López | Mechanisms of Direct and TiO2-Photocatalysed UV Degradation of Phenylurea Herbicides[END_REF][START_REF] Farré | Degradation of some biorecalcitrant pesticides This journal is[END_REF][START_REF] Katsumata | Photocatalytic degradation of diuron in aqueous solution by platinized TiO2[END_REF] , and consisting first in the attack of the alkyl function or in the chlorine substitution, followed by hydroxylation steps leading to the formation of acetic, formic and oxalic acid as last short-chain acid reaction intermediates [START_REF] Malato | Photocatalytic Treatment of Diuron by Solar Photocatalysis: Evaluation of Main Intermediates and Toxicity[END_REF][START_REF] Rico-Santacruz | Alveolar TiO2-β-SiC photocatalytic composite foams with tunable properties for water treatment[END_REF][START_REF] Fkiri | One-pot synthesis of lightly doped Zn1-x Cu x O and Au-Zn1-x Cu x O with solar light photocatalytic activity in liquid phase[END_REF][START_REF] Solís | Ozonation, photocatalysis and photocatalytic ozonation of diuron. Intermediates identification[END_REF] .

Experimental part

Synthesis of the TiO2@β-SiC photocatalytic composite foams

Alveolar shell/core TiO2@β-SiC composite foams with medium surface area were jointly developed at ICPEES and at the SICAT company (Strasbourg, France) according to a sequential multistep carburization SMS method, adapted from the single carburization SMS method owned by SICAT for synthesizing selfbonded porous β-SiC foams from a pre-shaped polyurethane foam [START_REF] Nguyen | Innovative porous SiC-based materials: From nanoscopic understandings to tunable carriers serving catalytic needs[END_REF] . This two-step carburization SMS replica approach schematized in Fig. 1 implements a sequential carburization strategy, in which a second carburization of the foam is performed at the surface of a β-SiC skeleton obtained during a first carburization step:

1. first, a pre-shaped precursor polyurethane foam was impregnated/infiltrated with a phenolic resin containing micronized (< 20 µm) metallic Si and carbon black powder. 2. the shaped green body obtained was dried overnight at 120°C and subsequently submitted to a first carburization reactive step under Ar atmosphere for 1 h at 1360°C. During the thermal treatment, the polyurethane was pyrolized giving almost no carbon yield, whereas the high carbon yield resin was pyrolized into amorphous carbon binding the carbon black and the Si powders together. Above 1000°C, the carbon skeleton was subsequently attacked by SiO vapors formed by reaction between Si and the residual traces of oxygen, whereas CO was allowed to carburize the metallic Si, yielding to the formation of β-SiC according to (1).

SiO(g) + 2C(s) ® SiC(s) + CO(g) (1)
3. the β-SiC skeleton foam was further impregnated by a Aeroxide® TiO2 P25 ethanolic suspension at 15 g/L by dipping the foam 50 times to get a 20 wt.% TiO2 content (with intermediate rinsing steps with ethanol solution). The impregnated β-SiC skeleton foam was dried at 100°C for 12 h. The impregnated β-SiC skeleton foam was dried at 100°C for 12 h. The TiO2 wt.% loading resulted from a preliminary study reported as Supporting Information S1. 4. the foam was further submitted to a second reactive carburization step at 1360°C for 1 h under Ar atmosphere Please do not adjust margins Please do not adjust margins for forming a TiC shell using residual unreacted carbon, according to (2).

TiO2(s) + 3C(s) ® TiC(s) + 2CO(g) (2)
5. finally, a thermal treatment in air was performed at temperatures between 550°C and 700°C for producing the final shell/core TiO2@β-SiC composite foams through the selective oxidation of the TiC skin into TiO2.

A reference β-SiC foam supported TiO2 catalyst with 15 wt.% of TiO2 has been prepared via the classical deposition method consisting in successive dippings of the foam into a 15 g/L TiO2 P25 ethanolic suspension, with intermediate rinsing steps with ethanol solution, drying at 100°C and final calcination treatment at 380°C. Prior deposition, the bare β-SiC foam was decarboned for 2 h at 700°C in air for removing residual unreacted carbon species by combustion. The TiO2 content of 15 wt.% relative to the total foam weight, was previously optimized [START_REF] Kouamé | β-SiC foams as a promising structured photocatalytic support for water and air detoxification[END_REF] and determined by weighting the TiO2/β-SiC foam.

Evaluation of the photocatalytic efficiency

The experiments were carried out within an Suntest XLS+ reaction chamber (Atlas Material Testing Technology BV, Gelnhausen, Germany) equipped with a Xenon arc lamp of 1700 W adjustable power and a Solar ID65 filter to limit the UV radiation at 300 nm for simulating solar exposition according to ICH Q1B guidelines. The runs were performed with simulated solar light at 250 Wm -2 (300-800 nm), which corresponds to an average solar radiation in a summer day in southern Europe (Fig. S2). The reaction volume was 100 mL and the starting concentration of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) 10 mgL -1 . At each time interval, 5 mL of solution has been sampled and then filtered through 0.20 μm porosity filter to remove the photocatalyst powder if any, before the concentration of Diuron has been determined by UV-Visible spectrophotometry (Cary100 scan Varian) by monitoring the disappearance of the main absorption peak at λ=248 nm, and Total Organic Carbon measurements were performed using a Shimadzu TOC-L analyzer to determine the organic carbon load.

Stability test of the photocatalytic composite foams

The stability test protocol is a two-step protocol consisting first in subjecting the foam to the reaction conditions and constraints of a photocatalytic test in pure distilled water. After 12 h under stirring with an applied irradiance of 60 W/m 2 , the foam was removed from the reactor before 4-chlorophenol as model substrate to degrade was added at 20 mg/L to the solution potentially containing the TiO2 nanoparticles released from the foam. A photocatalytic test is subsequently performed following the same reaction conditions and protocol than in the case of the Diuron substrate.

Characterisation techniques

X-ray diffraction (XRD) patterns were recorded on a D8 Advance Bruker diffractometer in a θ/θ mode and using the Kα1 radiation of a Cu anticathode (λ = 1.5406Å).

The surface area measurements have been carried out on a Micrometrics Tristar 3000 using N2 as adsorbent at -196°C with a prior outgassing at 200°C overnight to desorb the impurities or moisture. The Brunauer-Emmett-Teller (BET) specific surface area has been calculated from the N2 adsorption isotherm.

Scanning electron microscopy (SEM) was performed in secondary electron mode on JEOL JSM-6700 F FEG microscope.

Thermogravimetric analysis (TGA) was carried out on a 20% (v/v) O2/N2 mixture at a 40 mL/min flow rate at a 10°C/min heating rate in the 25-900°C range with a Q5000TA analyzer.

X-ray photoelectron spectroscopy (XPS) characterization was performed on a ThermoVGMultilabESCA3000

Results and discussion

Characterization of the TiO2@β-SiC composite foams

The main physico-chemical properties of the TiO2@β-SiC composite foams are shown in Table 1. The schematic diagram of the sequential two-step carburization SMS replica synthesis shows optical images of the pre-shaped alveolar polyurethane precursor and of the composite foam at different steps of the replica synthesis process (Fig. 1). It evidenced that the original macrostructural features of the alveolar foams were retained throughout the multi-step sequential carburization SMS replica process, going from the pre-shaped polyurethane foam to the ready-to-use TiO2@β-SiC composite foam (Table 1). Notably, both the alveolar open-cell structure and the cell size of the foam were maintained during each carburization step and the final calcination treatment. Similary to the reference β-SiC foams, the TiO2@β-SiC composite foams can be manufactured with adjustable shapes suitable for being adapted to the reactor geometry, and they have been prepared as 5 cm (d.) x 2 cm (h.) disks. The TiO2@β-SiC composite foams and the reference β-SiC foam displayed globally similar macroscopic features in terms of characteristic parameters, with a cell size of 5200 ± 400 µm, a window size of 2380 ± 400 µm and a strut diameter at 540 ± 50 µm, so that they exhibited a similar open porosity of ca. 0.91-0.94, and a similar geometrical surface area in the 440-620 m -1 range. One can thus stress that the reference TiO2/β-SiC foam and the newly developed TiO2@β-SiC composite foams show a similar light transmission profile through the foams [START_REF] Masson | β-SiC alveolar foams as a structured photocatalytic support for the gas phase photocatalytic degradation of methylethylketone[END_REF] .

The XRD patterns of the composite foams at different steps of the replica SMS are shown in Fig. 2A-B. They all exhibited the diffraction lines corresponding to the (111), ( 200), (202), (311) and (222) planes of the β-SiC polymorph in the fcc structure [START_REF] Shen | A novel twostage synthesis for 3Câ€"SiC nanowires by carbothermic reduction and their photoluminescence properties[END_REF] , that are similar to those of both the reference β-SiC foam and the β-SiC foam after the first carburization steps (labelled as Crich β-SiC foam considering the presence of residual unreacted carbon species, see later Fig. 5A). After the 2nd carburization step at 1360°C, the pattern revealed the TiC@β-SiC nature of the composite foam, with the diffraction lines corresponding to the (111), ( 200), ( 220), ( 311) and (222) planes of TiC in a fcc structure [START_REF] Keller | A new TiO2β-SiC material for use as photocatalyst[END_REF][START_REF] Baviera | Elaboration and structure of nanostructured TiC: a XRD and HRTEM study[END_REF] . The TiC@β-SiC composite foam contained as well a small amount of crystallized SiO2, evidenced by the presence of an additional peak at 22.0° characteristic of the diffraction of the (101) planes of crystallized SiO2. This could result from the inhomogeneity of the carbon distribution within the shaped infiltrated body -due to the inhomogeneity either of the foam coating or within the infiltration slurry -, that could lead to the existence of carbon-poor zones during the foam carburization, and therefore to local deficits in reductive carbon compared to the silicon species. The TiC@β-SiC composite foam can be considered as a shell/core foam, since the 2 nd carburization reaction occurred between the unreacted carbon species of the C-rich β-SiC foam and the TiO2 exclusively located at the skeleton foam surface. 101) and (110) planes of anatase (JCPDS card 21-1272) and rutile (JCPDS card 21-1276), respectively. At 550°C, the TiO2@β-SiC composite foams had an anatase:rutile ratio of 97:3, that decreased to 65:35 and 63:37 at 600°C and 700°C, respectively. Although the rutile content increased with increasing the calcination temperature, it remained lower than that of TiO2-β-SiC composite powders, that increased up to 70% when calcined at 600°C [START_REF] Keller | A new TiO2β-SiC material for use as photocatalyst[END_REF] . Indeed, whereas β-SiC can act as a thermal regulator to disperse the heat issued from the TiC oxidation thanks to its high thermal conductivity 25 , the continuous aspect of the self-bonded (ie. binder-less) foams is known to improve the heat transfer through the whole matrix [START_REF] Bracconi | A fundamental analysis of the influence of the geometrical properties on the effective thermal conductivity of open-cell foams[END_REF] . This explained as well that the calcination temperature did not impact on the TiO2 mean crystallite size, with a mean size around 11 nm.

The TiO2@β-SiC composite foams had a higher surface area within the 35-48 m 2 /g range when compared to that of the reference β-SiC foam at 25 m 2 /g. This probably resulted from the presence in the foams of residual unreacted carbon with Please do not adjust margins Please do not adjust margins adsorption properties. Indeed, increasing the calcination temperature from 550°C to 700°C caused a decrease in the surface area of the composites, attributed to the combustion of the residual carbon. At 700°C, the surface area might be explained by the possible formation of voids and cracks during the TiC to TiO2 oxidation, as reported in the case of TiO2-β-SiC composite powder systems [START_REF] Keller | A new TiO2β-SiC material for use as photocatalyst[END_REF] .

The heterogeneous nature of the TiO2@β-SiC composite foam surface compared to the surface of the bare β-SiC foam was evidenced in the SEM images of Fig. 3. Further, the shell/core nature of the TiO2@β-SiC composite foams was confirmed on the cross-section SEM images of a broken foam bridge, showing the existence of a thin skin located at the surface of a β-SiC core. EDS analysis carried out on the foam core revealed the absence of any titanium atoms, confirming its pure β-SiC nature, whereas both titanium and silicon elements were observed during the EDS analysis of the external skin, due to analysis depth in SEM (not shown). TEM images of the TiO2@β-SiC composite foam calcined at 550°C shown in Figure 4A evidenced the proximity of both β-SiC and anatase TiO2 crystallites in the photocatalyst, with interplanar spacings of 2.5 Å and 3.5 Å consistent with the (111) and ( 101) planes of β-SiC and anatase TiO2 phases, respectively. In addition, Figure 4B shows the residual presence of turbostratic carbon in the sample calcined at 550°C.

Dark adsorption experiments

The amount of residual unreacted carbon in the carbon-rich β-SiC skeleton foam after the 1 st carburization step and in the TiO2@β-SiC composite foams after calcination was determined by TGA experiments (Fig. 5A). The TGA profiles showed that the carbon-rich β-SiC skeleton foam contained 8 wt.% of excess carbon, whereas the calcination applied to the TiC@β-SiC composite after the 2 nd carburization of the foam for obtaining TiO2 from TiC directly influenced the amount of residual Please do not adjust margins Please do not adjust margins unreacted carbon remaining within the TiO2@β-SiC foams. A final calcination in air at 700°C was necessary for removing completely the residual carbon by combustion, whereas the TiO2@β-SiC composite foams calcined at 550°C and 600°C contained about 4 wt.% and 0.5 wt.% of unreacted carbon (Table 1). The small weight gain above 800°C corresponded to the high temperature surface oxidation of SiC into SiO2 as usually observed for SiC prepared via the SMS replica method. The evolution of the Diuron concentration during the dark adsorption period on the TiO2@β-SiC composite foams calcined at temperatures in the 550-700°C range is shown in Fig. 5B for a 10 mg/L initial Diuron concentration and in Fig. S4 for a large range of concentrations (5, 10 and 20 mg/L). The adsorption properties of the composite foams were strongly influenced by the final calcination temperature, in agreement with the TGA profiles. Indeed, no significant adsorption of Diuron was obtained on the composite foams calcined at 700°C, while about 20% and 80% adsorption of Diuron was achieved on the composite foams calcined at 550°C and 600°C for a 10 mg/L initial Diuron concentration.

Further, the influence of the amount of residual unreacted carbon in the composite on the adsorption profile was evidenced independently of the initial Diuron concentration (Fig. S4). The higher the amount of residual unreacted carbon in the composite foam, the higher the specific surface area developed by the foam and consequently the more pronounced the adsorption profile, and the higher the Diuron amount removed by adsorption whatever the initial concentration. So, the selection of the final calcination temperature (550-700°C range) appeared as an easy way to vary the amount of residual un-combusted carbon from 0 to 4 wt.%, and consequently, to tune the adsorption properties of the TiO2@β-SiC composite foams, as materialized in Fig. 5C.

Photocatalytic runs

Fig. 6A shows that the TiO2@β-SiC composite foams were active for degrading Diuron under solar light, whatever their adsorption properties, ie. whatever the remaining diuron concentration to be removed after the adsorption step -10, 8 or 2 mg/L for foams calcined at 700°C, 600°C and 550°C, respectively -. The higher the adsorption capacity, the faster the reduction of the diuron concentration in water. However, the kinetic rate constants were not compared to that achieved on the TiO2@β-SiC composite foam calcined at 700 °C, due to far different initial concentrations of Diuron to be degraded. Calcined at 700 °C, the composite foam exhibited a lower activity in terms of Diuron degradation than the reference TiO2/β-SiC foam prepared via impregnation and stabilization of TiO2 on a conventional β-SiC foam, with an apparent kinetic constant of 3 × 10 -3 min -1 vs. 14 × 10 -3 min -1 , respectively. By contrast, the superiority of the reference TiO2/β-SiC foam over the TiO2@β-SiC composite foam was less pronounced in terms of TOC removal, with a kinetic constant of 12 × 10 -3 mg/Lmin -1 vs. 9 × 10 -3 mg/Lmin -1 , respectively (Fig. 6B). This behavior might result from an enhanced degradation of the reaction intermediates on the composite foam compared to the reference foam counterpart.

Several groups evidenced that the Diuron degradation pathways were not affected when TiO2 was associated to fibers and SiO2 binder, or to Pt [START_REF] Katsumata | Photocatalytic degradation of diuron in aqueous solution by platinized TiO2[END_REF][START_REF] Madani | Photocatalytic degradation of diuron in aqueous solution in presence of two industrial titania catalysts, either as suspended powders or deposited on flexible industrial photoresistant papers[END_REF] . Matos et al. showed that associating TiO2 with carboned adsorbents did not modify the reaction mechanism and similar reaction intermediates were observed using 4-chlorophenol, phenol and 2,4-dichlorophenoxyacetic acid as model pollutants to degrade, compared to bare TiO2 (even if the product distribution might differ in some cases) [START_REF] Matos | Influence of activated carbon upon titania on aqueous photocatalytic consecutive runs of phenol photodegradation[END_REF][START_REF] Matos | Effect of the Type of Activated Carbons on the Photocatalytic Degradation of Aqueous Organic Pollutants by UV-Irradiated Titania[END_REF] . We thus proposed that the mechanism for the diuron photocatalytic degradation was not significantly influenced by the adsorption properties of the TiO2@β-SiC composite foams.

Finally, the stability of the TiO2@β-SiC-700 composite foam was evaluated by studying its ability to be reused, as well as by submitting the foam to a stability test procedure. First, the photocatalytic foam displayed a good reusability when performing several sequential runs, with apparent kinetic rate constants for Diuron degradation calculated in average as 2.9 × 10 -3 min -1 ± 0.1 × 10 -3 min -1 , respectively (Fig. 6C). Further, the implementation of the stability test procedure evidenced the superior stability of the TiO2@β-SiC composite foam when compared to the TiO2 supported β-SiC foam counterpart (Fig. 7). Indeed, after the first stirring treatment with the composite foams in pure water under UV-A, no 4-chlorophenol degradation was observed, whereas a degradation of 30% was obtained after of 150 min test in the case of the TiO2/β-SiC foam. Although it cannot be ruled out that the TiO2 nanoparticles potentially released from the composite foam displayed a lower photocatalytic activity than the TiO2 P25 released from its supported counterpart, the amount of TiO2 released from the supported photocatalyst has been estimated at 0.06 g/L using a calibration curve (Fig. S3), while by contrast remaining lower than 0.001 g/L in the case of the composite foam. The superior stability of the TiO2@β-SiC composite foam was proposed to result from the existence of Ti-O-Si cross linking bonds between the external TiO2 shell and the surface of the β-SiC skeleton core. Indeed, while the Ti2p orbital XPS spectra of the composite foam shows the typical Ti 2p3/2-Ti 2p1/2 doublet located at 458.3 eV and 464.0 eV with a spin-orbit splitting of 5.7 eV, ascribed to Ti 4+ (Ti-O) surface species in TiO2 observed in the case of bulk TiO2 powder and of the β-SiC foam supported TiO2 counterpart , a higher energy contribution was observed and assigned to Ti-O-Si bonds in agreement with the literature (Fig. 8) [START_REF] Sahu | Synthesis, analysis and characterization of ordered mesoporous TiO2/SBA-15 matrix: Effect of calcination temperature[END_REF][START_REF] Yin | Assembling of Composite of Ag/TiO2/Eu-MCM with Enhanced Photocatalytic Activity[END_REF][START_REF] Xia | TiO2 Coating of High Surface Area Silica Gel by Chemical Vapor Deposition of TiCl4 in a Fluidized-Bed Reactor[END_REF] .

Conclusions

Coating-free TiO2@β-SiC photocatalytic composite foams have been synthesized through a sequential multi-step SMS replica method, in which an external TiO2 layer was formed by the Please do not adjust margins Please do not adjust margins selective oxidation of an external TiC skin obtained by carburization of a TiO2 coating at the surface of a β-SiC skeleton foam synthesized from a pre-shaped polymer foam during a first carburization step. This ready-to-use shell/core alveolar media exposed as irradiated surface the TiO2 photocatalyst while the macroscopic structure was provided by the β-SiC alveolar foam, so that no post-synthesis immobilization or synthesis process of the active phase onto the foam support was necessary. Further, applying a final calcination treatment to the carbide foams (550-700°C) allowed the amount of residual unreacted carbon within the active shell/core TiO2@β-SiC composite foams to be tuned, and consequently their adsorption behaviour towards the Diuron pollutant in water to be tuned. The lower the calcination temperature, the more pronounced the adsorption profile of the composites and the higher the Diuron amount removed by adsorption on the residual unreacted carbon. The ready-to-use TiO2@β-SiC composite foams were active in the degradation of the Diuron pesticide in water, although remaining less efficient that the reference β-SiC supported foam TiO2 photocatalyst counterpart. However, they displayed a good reusability with test cycles and benefitted from an enhanced stability in terms of titania release to water.

Figure S1

For a preliminary study, TiO2@β-SiC composite foams were prepared with a TiO2 content of 11 wt.%, 20

wt.% and 33 wt.% on the β-SiC skeleton foam during the step 3 of the sequential multi-step carburization SMS method. The TiO2@β-SiC composite foams obtained after final calcination at 600°C displayed similar Diuron adsorption behavior in the dark indepently of the TiO2 content, as depicted in Fig. S1A. By contrast, Measurements have been performed using a wideband RPS900-W rapid portable spectroradiometer from International Light Technology.

Figure 1 .

 1 Figure 1. Schematic diagram of the sequential two-step carburization SMS replica synthesis of the shell/core TiO2@β-SiC composite foams.

Figure 2 .

 2 Figure 2. XRD patterns of the β-SiC-based foams at different steps of the synthesis protocol. (A) the bare alveolar β-SiC foam obtained through the classical SMS replica method, the C-rich β-SiC foam after the 1st carburization step and the shell/core TiC-β-SiC composite foam after the 2nd carburization step; (B) the TiO2β-SiC composite foams after calcination at 550°C, 600°C and 700°C. (*) most intense diffraction peak of crystallized SiO2 (JCPDS card 65-0466).

Figure 4 .

 4 Figure 4. TEM images of the TiO2@β-SiC composite foams calcined at 550°C. The (111) and (101) planes of β-SiC and anatase TiO2 have interplanar distances of 2.5 Å (JCPDS No. 00-029-1129) and 3.5 Å (JCPDS No.00-021-1272), respectively.

Figure 3 .

 3 Figure 3. SEM images of the (A) the bare β-SiC foam and (B) the TiO2@β-SiC composite foam after calcination at 550°C. Cross-section image of a broken foam bridge, evidencing the TiO2 skin and the β-SiC core.

Figure 5 .

 5 Figure 5. (A) TGA profiles of the C-rich β-SiC skeleton foam after the 1 st carburization step and of the TiO2@β-SiC composite foams after calcination ; (B) Dark adsorption experiments performed on the TiO2@β-SiC composite foams ; (C) Influence of the calcination temperature of the composite foams on both the wt.% of residual carbon and the wt.% of Diuron adsorption.

Figure 6 .

 6 Figure 6. (A) Diuron photodegradation kinetic and (B) mineralization kinetic obtained on the TiO2@β-SiC composite foams. Comparison with a reference TiO2(15wt.%)/β-SiC foam photocatalyst ; (C) Diuron photodegradation kinetics observed on the TiO2@β-SiC-700 composite foam with consecutive runs.

Figure 7 . 4 -

 74 Figure 7. 4-Chlorophenol photocatalytic degradation kinetics obtained during the stability test. Reaction conditions : [4-CP]0 = 20 mg/L; T=25°C; UV-A irradiance of 60 W m -2 .

Figure 8 .

 8 Figure 8. Ti 2p orbital XPS spectra recorded on the TiO2@β-SiC composite foams, in comparison to the β-SiC supported TiO2 counterpart and a reference TiO2 powder (Aeroxide© P25 from Evonik).

B

  This journal is © The Royal Society of Chemistry 20xx

Fig. S1B evidenced

  Fig. S1B evidenced the superiority of the composite foam with a 20 wt.% TiO2 content in terms of Diuron

Figure S1 ( A )

 A Figure S1 (A) Dark adsorption experiments performed on the TiO2@β-SiC composite foams with different

3 Figure S2 Figure S2 .

 3S2S2 Figure S2

Figure S3 .

 S3 Figure S3. Calibration curve expressing the influence of the TiO2 concentration on the apparent rate constant for the chlorophenol degradation (pseudo first order reaction). [4-CP]0 = 20 mg/L; T=25°C; UV-A irradiance of 60 W m -2 .

Figure

  Figure S4. A) Dark adsorption experiments performed on TiO2@β-SiC composite foams varying in terms of residual

Table 1 .

 1 Main physico-chemical properties of the TiO2@β-SiC composite foams.

		β-SiC	TiO2@β-SiC-550	TiO2@β-SiC-600	TiO2@β-SiC-700
	TiO2 crystallized phases (anatase/rutile)	-	97:3	65:35	63:37
	TiO2 mean crystallite size (anatase/rutile) (nm) a	-	11/-	12/10	12/11
	SBET surface area (m 2 /g)	25	48	38	35
	Residual carbon content (wt. %) b	0	4	0.5	0
	Mean cell size (φ) (μm)	5400 ± 700	5000± 600	5100± 500	5200± 400
	Window size (a) (μm)	2300 ± 575	2300± 300	2500± 500	2400± 400
	Bridge diameter (ds) (μm)	575 ± 80	510± 30	545± 50	530± 20
	Open porosity c	0.91± 0.05	0.94± 0.05	0.94± 0.05	0.94± 0.05
	Geometrical specific surface area (m -1 ) d	620 ± 200	460 ± 200	440 ± 200	453 ± 200

a determined from the XRD analysis by applying the Scherrer equation to the (101) and (110) peaks of anatase and rutile, respectively, with the classical assumption of spherical crystallites ; b the residual unreacted carbon content was determined by TGA analysis by evaluating the weight loss observed between 500°C and 800°C ; c measured by water displacement ; d derived from the model developed by Edouard and coll. using the open porosity and the mean strut diameter

[START_REF] Edouard | Pressure drop modeling on SOLID foam: State-of-the art correlation[END_REF][START_REF] Huu | Towards a more realistic modeling of solid foam: Use of the pentagonal dodecahedron geometry[END_REF]

. This journal is © The Royal Society of Chemistry 20xx

Please do not adjust margins Please do not adjust margins spectrometer (Al Kα anode at hλ = 1486.6 eV). The energy shift due to electrostatic charging was subtracted using the adventious sp2 carbon C 1s band at 284.6 eV.

Acknowledgements

The authors thank the French Agence Nationale de la Recherche (ANR) for funding the Project COPHOTOFE under reference ANR-13-ECOT-0010. The European Fund for regional development (EFRE/FEDER) is acknowledged for partially supporting the work, in the frame of the project PHOTOPUR, within the Program Interreg-V Rhin Supérieur and the Sciences Offensive Call.

Notes and references

Conflicts of interest

There are no conflicts to declare.

Supplementary material

Coating-free TiO2@β-SiC alveolar foams as ready-to-use composite photocatalyst with tunable adsorption properties for water treatment Marisa Rico-Santacruz Corresponding authors(*):garciamunoz@unistra.fr;nkeller@unistra.fr