Yik-Ken Ma

Stephen Chia

Jean-Louis Paillaud

T Jean Daou

Fitri Khoerunnisa

Zeinhom M El-Bahy

Tau Chuan Ling

Amal A Altalhi

Samy F Mahmoud

Eng-Poh Ng

Tau Chuan

SAPO-35 zeolite crystallized using novel structure-directing agent for catalytic conversion of levulinic acid into ethyl levulinate under non-microwave instant heating

Keywords: SAPO-35, zeolite, 1-propylpyridinium hydroxide, ethyl levulinate, non-microwave instant heating

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INTRODUCTION

Aluminophosphate (AlPO-n) is a class of zeolite material with neutral surface charge that is formed by strictly alternating [AlO4] -and [PO4] + monomer units [START_REF] Khoo | Ionothermal approach for synthesizing AlPO-5 with hexagonal thin-plate morphology influenced by various parameters at ambient pressure[END_REF]. By incorporating silicon (Si) atoms into the AlPO-n framework, it gives rise to the formation of acid sites in silicoaluminophosphates (SAPO-n) that are essential for broad industrial applications [START_REF] Liu | Eco-friendly synthesis of hierarchical SAPO-11 with fluoride ions for hydroisomerization of n-hexane[END_REF][START_REF] Calabrese | SAPO-34 based zeolite coatings for adsorption heat[END_REF][START_REF] Ng | Microwave-green synthesis of AlPO-n and SAPO-n (n = 5 and 18) nanosized crystals and their assembly in layers[END_REF]. These zeotypes have been proven as promising candidates as selective water adsorbents [START_REF] Ng | Selective capture of water using microporous adsorbents to increase the lifetime of lubricants[END_REF], and catalysts in the methanol-to-olefins (MTO) reaction [START_REF] An | Kinetics of steam regeneration of SAPO-34 zeolite catalyst in methanol-toolefins (MTO) process[END_REF], hydroisomerization of long-chain paraffin [START_REF] Yu | Optimization of the pore structure and acidity of SAPO-11 for highly efficient hydroisomerization on the long-chain alkane[END_REF][START_REF] Liu | Eco-friendly synthesis of hierarchical SAPO-11 with fluoride ions for hydroisomerization of n-hexane[END_REF], dewaxing [START_REF] Blasco | Changing the Si distribution in SAPO-11 by synthesis with surfactants improves the hydroisomerization/dewaxing properties[END_REF], isomerization [START_REF] Li | SAPO-11 with preferential growth along the a-direction as an improved active catalyst in long-alkane isomerization reaction[END_REF], hydrodeoxygenation (HDO) of vegetable oils [START_REF] Chen | Elucidation of the active phase in PtSn/SAPO-11for hydrodeoxygenation of methyl palmitate[END_REF], n-alkane cracking [START_REF] Chen | The production of renewable aviation fuel from waste cooking oil. Part II: catalytic hydrocracking/isomerization of hydroprocessed alkanes into jet fuel range products[END_REF], and oxidative dehydrogenation of ethane [START_REF] Marchese | Acid SAPO-34 catalysis for oxidative dehydrogenation of ethane[END_REF].

So far, there have been more than 50 types of SAPO-n with unique framework structures discovered and synthesized [START_REF] Yu | Insight into the construction of open-framework aluminophosphates[END_REF]. Among them, SAPO-35 (LEV topology) is one of the important SAPO-n materials. This small-pore zeotype material (3.6 × 4.8 Å 2 ) is made up of levyne cages that are connected through single six rings (S6R) and double six rings (D6R) where its adequate pore size and shape allow selective molecular diffusion and separation for linear hydrocarbons [START_REF] Pinilla-Herrero | Effect of framework topology of SAPO catalysts on selectivity and deactivation profile in the methanolto-olefins reaction[END_REF]. Nevertheless, the research into the synthesis and application of SAPO-35 is relatively scarce due to its rigid synthesis conditions. SAPO-35 zeolite was first synthesized at 200 °C for 7 days using quinuclidine as an organic template [START_REF] Lok | Crystalline Silicoaluminophosphates[END_REF]. Then, SAPO-35 was crystallized with the assistance of cyclohexylamine and hydrofluoric acid in a very narrow range of silicon concentration where SAPO-17 as 2 a competing phase was observed [START_REF] Lohse | Synthesis and characterization of the levynelike structure SAPO-35 prepared with cyclohexylamine as templating agent[END_REF]. Meanwhile, cobalt-aluminophosphate LEV molecular sieve named DAF-4 was also prepared using 2-methylcyclohexylamine organic template heating at 200 • C for 7 days [START_REF] Barrett | Rational design of a solid acid catalyst for the conversion of methanol to light alkenes: synthesis, structure and performance of DAF-4[END_REF].

Recently, the use of more reactive template, namely hexamethyleneimine has successfully reduced the crystallization time of SAPO-35 from 7 days to 98 h [START_REF] Venkatathri | Synthesis, characterization and catalytic properties of a LEV type silicoaluminophosphate molecular sieve, SAPO-35 from aqueous media using aluminum isopropoxide and hexamethyleneimine template[END_REF] and 24 h [START_REF] Pinilla-Herrero | Effect of framework topology of SAPO catalysts on selectivity and deactivation profile in the methanolto-olefins reaction[END_REF][START_REF] Siliveri | Investigation on the promoterinduced rapid non-aqueous media synthesis of SAPO-35 and methanol-to-olefin reaction[END_REF][START_REF] Huang | Utilization of SAPO-18 or SAPO-35 in the bifunctional catalyst for the direct conversion of syngas to light olefins[END_REF]. It is worth to note that the use of aliphatic aminic structure-directing agents so far still requires long heating times for crystallizing SAPO-35. Hence, seeking more reactive structure-directing agents for rapid crystallizing SAPO-35 with superior surface properties (e.g. high porosity, high framework Si content, high surface acidity) is worth to be further studied.

Herein, the use of N-heterocyclic pyridinium compound as a novel organic template for crystallizing SAPO-35 is reported. It is worth to mention here that unlike conventional synthesis route, the current system undergoes different crystallization route where SAPO-34 is first formed from the amorphous solid before intrazeolite transformation occurs forming SAPO-35. The catalytic behavior of SAPO-35 with high porosity and surface acidity is then investigated in esterification of levulinic acid into ethyl levulinate (a biofuel additive [START_REF] Heda | Highly efficient micro-meso acidic HUSY catalyst for one step conversion of wheat straw to ethyl levulinate (biofuel additive)[END_REF]) under nonmicrowave instant heating, where this mode of heating uses SiC heat superconductor to provide rapid and uniform heating, mimicking the microwave heating [START_REF] Obermayer | Design and performance validation of a conductively heated sealed-vessel reactor for organic synthesis[END_REF].

Experimental section

Synthesis of 1-propylpyridinium hydroxide ([PPy]OH) SDA solution

1-Propylpyridinium hydroxide ([PPy]OH) was prepared as follows as in Scheme 1. Typically, pyridine (58.708 g, 99.5%, Merck) and 1-bromopropane (136.925 g, 99%, Merck) in a molar ratio of 1:1.5 were first mixed in a 250-mL round bottom flask. Then, the mixture was heated in an oil bath at 70 °C for 18 h before being rotary evaporated at 90 °C to remove the non-reacted 1-bromopropane. The resulting 1-propylpyridinium bromide ([PPy]Br) ionic liquid was washed with 20 mL of acetone (Qrec) for five times before it was dried in an oven at 100 °C overnight. Yield 90.2%. 1 The 1-propylpyridinium hydroxide ([PPy]OH) template solution was prepared via ion-exchange of [PPy]Br using the Amberlyst® IRN-78 ion-exchange resin in hydroxide (OH -) form (Acros Organic). The Amberlyst IRN-78 ion exchange resin is an insoluble polymeric resin in yellowish microbeads form (diameter ca. 0.90 mm) that possess high porosity that provides large surface area enabling efficient ion exchange [START_REF] Heredia | Nitrate removal from groundwater using Amberlite IRN-78: modelling the system[END_REF]. Typically, 50.000 g of resin and 50.000 g of [PPy]Br were added into 50.000 g of distilled water before the ion-exchange process was initiated (16 h, 200 rpm). After the treatment, the resin was separated from the template solution using vacuum filtration. The %OH -conversion of the template solution was determined by titrating 1 mL of filtrate with 0.1 M of HCl. The ion exchange and titration process were repeated for several cycles until the %OH -reached at least 85%. Finally, the template solution was concentrated to 32.86% in water under oven evaporation (60 °C) before it was readily used as an organic template for the crystallization evolution study of SAPO-35.

Formation study of SAPO-35

SAPO-35 microporous solid was crystallized in the presence of [PPy] OH as the structure-directing agent. Typically, aluminum isopropoxide (0.625 g, 98%, Acros Organics) was dissolved in the [PPy]OH template solution (4.500 g, 89.7% OH -exchanged) under vigorous stirring (600 rpm, 30 min). Then, distilled water (0.835 g) and orthophosphoric acid (0.806 g, 85%, Merck) were mixed and slowly added dropwise into the solution to avoid the formation of large and dense particles; the addition process took about 30 min. Next, tetraethyl orthosilicate (0.277 g, 98%, Sigma-Aldrich) was added and the resulting mixture was further stirred for 5 min to produce a precursor hydrogel with a molar composition of 1Al2O3:2.33P2O5:3.34[PPy]2O:0.87SiO2148H2O. The precursor was then transferred into a 15-mL Teflon-lined stainless-steel autoclave, capped and subjected to hydrothermal treatment at 200 °C for different time intervals (0-21 h). The crystallization was interrupted, and the autoclave was cooled down to room temperature under running water. The precipitated solid was recovered using high-speed centrifugation (10000 rpm, 8 min) followed by washing with distilled water until pH 7 before the solid product was dried (80 °C, 14 h) and calcined (600 °C, 6 h, 1 °C/min) under air flow.

3

Characterization

The crystallinity and phase purity of the samples were confirmed by using a Bruker D8 AVANCE diffractometer (Cu Kα radiation, 2θ = 4-40°, λ = 0.15418 nm, 40 kV). The crystal size and morphology of the solid products were studied using a Leo Supra 50VP field emission scanning electron microscope (FESEM) operated at 30 kV. Prior to measurement, the sample was sputtered with gold to prevent charging. The functional groups of the samples were investigated using a PerkinElmer's System 2000 IR spectrometer. The spectra were recorded in the wavenumber of 1600-400 cm -1 using the KBr method (KBr:sample ratio = 50:1). The elemental analysis of sample was performed using the ICP-OES spectroscopy (Vista MPX, Varian Inc.). Prior to analysis, the sample (5 mg) was first stirred and dissolved in concentrated HF solution (47%, 5 mL) for 14 h before the resulting solution was top-up to 250 mL. Boric acid (1.000 g, Merck) was also added for minimizing the fluoride interference during the ICP-OES analysis. The porous properties of SAPO-35 was studied with a Micrometrics ASAP 2010 nitrogen adsorption analyzer. Prior to analysis, the powder sample was first outgassed at 250 °C for 4 h under vacuum before the adsorption analysis was initiated at -196 °C. The organic and inorganic moieties in the as-synthesized SAPO-35 sample were investigated using a PerkinElmer's TGA 4000 thermogravimeter (heating rate 20 °C/min) under air flow conditions. The amount and strength of surface acid of SAPO-35 were determined by the temperature program desorption analysis probed with NH3 (NH3-TPD). Before analysis, the sample (ca. 0.008 g) was first outgassed in a BELCAT-B analyzer (400 °C, 8 h, He flow). The system was then saturated with NH3 gas to allow adsorption before the desorption analysis acquisition was initiated from 50 to 700 °C at a heating rate of 10 °C/min.

Catalytic study

The catalytic biomass upgrading study was carried out via esterification of levulinic acid into ethyl levulinate using a novel nonmicrowave instant heating technique. Initially, 0.025 g of activated SAPO-35 zeolite (200 °C, 3 h), levulinic acid (0.040 g, 98%, Acros Organics) and ethanol (0.170 g, 99.7%, Acros Organics) in the molar ratios of 1:11 were added into a glass vial. The levulinic acid:ethanol molar ratio of 1:11 was selected because it gave the highest reaction conversion based on our catalytic reaction study and similar observation was also observed by Halder et al. [START_REF] Halder | Porous organic polymer as an efficient organocatalyst for the synthesis of biofuel ethyl levulinate[END_REF][START_REF] Mandi | Ruthenium nanoparticles supported over mesoporous TiO2 as an efficient bifunctional nanocatalyst for esterification of biomass-derived levulinic acid and transfer-hydrogenation reactions[END_REF] where high alcohol content is beneficial for high esterification reaction conversion.

The vial was sealed and instantly heated to the desired temperature (150-190 °C) for a specific time (0-60 min) under very fast stirring rate (800 rpm) using an Anton Paar's Monowave 50 non-microwave instant heating reactor; the system required less than 2 min to reach to the desired temperature. After the reaction, the solution was separated and injected into a GC-FID chromatograph (Agilent/HP6890 GC) and GC-MS (Agilent 7000 Series Triple Quad) for product identification and quantitative analyses, respectively; toluene was used as the internal standard. The GC data acquisition was performed using the ChemStation® software while the reaction conversion and selectivity are calculated using Equations ( 1) and ( 2) respectively:

𝐶𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 𝑜𝑓 𝑙𝑒𝑣𝑢𝑙𝑖𝑛𝑖𝑐 𝑎𝑐𝑖𝑑(%) = [ ( 𝐴 𝐿𝑒𝑣𝑢𝑙𝑖𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝐴 𝑇𝑜𝑙𝑢𝑒𝑛𝑒 ) 𝑡 0 -( 𝐴 𝐿𝑒𝑣𝑢𝑙𝑖𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝐴 𝑇𝑜𝑙𝑢𝑒𝑛𝑒 ) 𝑡 𝑖 ( 𝐴 𝐿𝑒𝑣𝑢𝑙𝑖𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝐴 𝑇𝑜𝑙𝑢𝑒𝑛𝑒 ) 𝑡 0
] × 100% (Equation 1)

𝑆𝑒𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 (%) = [ 𝐴 𝐸𝑡ℎ𝑦𝑙 𝑙𝑒𝑣𝑢𝑙𝑖𝑛𝑎𝑡𝑒 𝐴 𝑇𝑜𝑡𝑎𝑙 ] × 100% (Equation 2)
where 𝐴 𝐿𝑒𝑣𝑢𝑙𝑖𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 was the peak area of the limiting agent (levulinic acid), 𝐴 𝑇𝑜𝑙𝑢𝑒𝑛𝑒 was the peak area of the internal standard (toluene), 𝑡 0 and 𝑡 𝑖 were the reaction times at 0 h and i h respectively, 𝐴 𝑒𝑡ℎ𝑦𝑙 𝑙𝑒𝑣𝑢𝑙𝑖𝑛𝑎𝑡𝑒 was the peak area of the product (ethyl levulinate), and 𝐴 𝑡𝑜𝑡𝑎𝑙 was the total peak area of the products obtained (Figs. S1 andS2).

Results and discussion

Time-dependent crystallization study of SAPO-35

In the first 10 h of hydrothermal heating, no solid product was recovered upon centrifugation indicating that the reactants have undergone dissolution and the resulting precursor is in the induction stage. At this stage, the Si, Al and P reactants hydrolyze forming soluble monomers and oligomers [START_REF] Ng | Micro-to macroscopic observations of MnAlPO-5 nanocrystal growth in ionic-liquid media[END_REF]. At 16 h, the precursor solution turned cloudy and some solid was successfully collected indicating polymerization of inorganic species forming denser solid is taking place. Concurrently, the matter exchange between solid and liquid parts occurs, inducing nucleation process [START_REF] Wong | K-F zeolite nanocrystals synthesized from organic-template-free precursor mixture[END_REF].

Nevertheless, the solid is amorphous based on the detection of merely an XRD hump at 2θ = 17°-30° (Fig. 1a). According to FESEM microscopy analysis, this amorphous solid is composed of sub-micron sized particles (ca. 93 nm) having non-specific shape (Fig. 2a andb).

With crystallization time further extended for additional 2 h-18 h, the morphology of the solid drastically changed and fast crystallization of particles (ca. 1.7 μm) formed by smaller primary crystals with size ranging from 0.2 to 1.1 μm. Further heating the precursor solution to 20 h facilitates the intrazeolite transformation of SAPO-34 to SAPO-35 where the XRD peaks assigned to SAPO-35 emerge at the expense of the SAPO-34 XRD peaks (Fig. 1c). Thus, this suggested that the SAPO-34 crystals progressively dissolved in the mother liquor where its double-6-ring (D6R) secondary building units that are contained in the solution are served as a seed (or nuclei) for the growth of SAPO-35, viz. a more metastable crystalline phase [START_REF] Sogukkanli | Seed-directed synthesis of CON-type zeolite using tetraethylammonium hydroxide as a simple organic structural directing agent[END_REF][START_REF] Muraoka | Tracking the rearrangement of atomic configurations during the conversion of FAU zeolite to CHA zeolite[END_REF].

This phenomenon is also observed by the FESEM microscopy where the images of cubic-like (SAPO-34) and rhombohedra (SAPO-35) intergrown crystals are captured (Fig. 2e andf). The intrazeolite transformation occurs rapidly where the SAPO-34 crystalline phase completely disappears and transforms into SAPO-35 after 21 h of hydrothermal treatment (Fig. 1d). The XRD pattern of assynthesized SAPO-35 is indexed and compared with the theoretical generated XRD pattern (in red lines). It shows the XRD profile of SAPO-35 is well indexed to the standard diffraction pattern of trigonal LEV crystalline phase suggesting the sample is of very high purity [START_REF]Database of Zeolite Structures[END_REF]. The FESEM study also agrees with the XRD observation whereby rhombohedra crystals (ca. 1.3 μm) are formed, and the morphology of SAPO-35 synthesized in this work is identical to that reported in literature (Fig. 2g andh) [START_REF] Siliveri | Investigation on the promoterinduced rapid non-aqueous media synthesis of SAPO-35 and methanol-to-olefin reaction[END_REF][START_REF] Huang | Utilization of SAPO-18 or SAPO-35 in the bifunctional catalyst for the direct conversion of syngas to light olefins[END_REF]. One should note that the proposed method for synthesizing SAPO-35 is reproducible using different batch of [PPy]OH template solution (92.1% OH􀀀 exchanged). The crystallization time was also extended to 28 h. However, co-crystallization of SAPO-35 with SAPO-36 was observed explaining the metastability nature of SAPO-35. The HRTEM images of pure SAPO-35 are shown in Fig. 3. As seen, the SAPO-35 crystals possess rhombohedra shape and the crystallite size is ca. 1.3 μm which agrees with the FESEM analysis (Fig. 2h). Furthermore, a HRTEM image with a very high magnification shows that the interface of SAPO-35 solid is smooth with very sharp edge indicating the SAPO-35 crystals are well formed in the presence of [PPy]OH new templating system [START_REF] Appaturi | Selective synthesis of dioxolane biofuel additive via acetalization of glycerol and furfural enhanced by MCM-41-alanine bifunctional catalyst[END_REF].

The formation of SAPO-35 was also followed by using IR spectroscopy (1600-400 cm -1 ) where this technique can easily observe the change in the vibrations of framework and functional groups during the entire crystallization process [START_REF] Wong | Crystal growth study of K-F nanozeolite and its catalytic behavior in Aldol condensation of benzaldehyde and heptanal enhanced by microwave heating[END_REF]. The IR spectrum of crystallization time less than 16 h

was not recorded since no product was successfully collected. The IR spectrum of sample after 16 h of heating is shown in Fig. 4a where four amorphous characteristic broad absorption bands are detected: 1139 and 726 cm -1 are due to asymmetric and symmetric O-P-O stretching, respectively; 566 cm -1 is ascribed to bending of P-O in PO4; 484 cm -1 corresponds to Al-O bending mode [START_REF] Li | Facile synthesis of SAPO-34 with small crystal size for conversion of methanol to olefins[END_REF][START_REF] Van Heyden | Nanosized SAPO-34 synthesized from colloidal solutions[END_REF]. In addition, a very weak IR band due to double-6-ring (D6R) secondary building unit (SBU) also start to be observed at 628 cm -1 where this sub-unit is the basic and key component for the construction of AEI, CHA, EMT, FAU KFI, LEV and OFF-type zeolite frameworks [START_REF] Muraoka | Tracking the rearrangement of atomic configurations during the conversion of FAU zeolite to CHA zeolite[END_REF][START_REF] Van Heyden | Nanosized SAPO-34 synthesized from colloidal solutions[END_REF]. Thus, this indicates that the zeolite nucleation has occurred in the hydrogel precursor.

The IR spectrum pattern changes drastically when fast crystallization occurs after 18 h (Fig. 4b). As shown, the IR bands are becoming more resolved, and the IR pattern of this sample is identical to that of SAPO-34 [START_REF] Niu | Synthesis of highly selective and stable Co-Cr/SAPO-34 catalyst for the catalytic dehydration of ethanol to ethylene[END_REF]. The IR bands at 1227, 1110 and 1039 cm

Characterization of SAPO-35 zeolite catalyst

The as-synthesized SAPO-35 (sample crystallized at 21 h) was calcined at 550 °C prior being used in catalytic reaction study. This is to ensure that its porosity is free from occluded organic moiety for enabling molecular diffusion and accessibility. In this respect, the porous properties of SAPO-35 were first studied using the N2 adsorption-desorption technique at -196 °C. Fig. 6 shows the N2 adsorption-desorption isotherm and pore size distribution derived from non-local density functional theory (NLDFT) model. The sample exhibited type I adsorption isotherm with high and sharp knee at very low P/Po (Fig. 6a) confirming the presence of merely microporosity in the SAPO-35 solid (Fig. 6b) [START_REF] Sing | Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity[END_REF]. The SAPO-35 has an average pore size of 2.76 nm and high porosity (surface area = 526 m 2 /g, total pore volume = 0.26 cm 3 /g) where the large levyne cage and textural porosity of SAPO-35 contributes to its high surface area, large average pore size and high pore volume. Such features are appreciated in the catalytic application that require molecular accessibility [START_REF] Adam | Halide aided synergistic ring opening mechanism of epoxides and their cycloaddition to CO2 using MCM-41-imidazolium bromide catalyst[END_REF].

Besides high porosity, the Si content in SAPO-35 is important as it serves as the acid sites for a catalytic reaction [START_REF] Lyu | The regulation of Si distribution and surface acidity of SAPO-11 molecular sieve[END_REF]. Hence, the elemental analysis of SAPO-35 was carried out using the ICP-OES spectroscopy technique (Table 1). The data shows that the synthesized SAPO-35 has a chemical composition of Si0.207Al0.556P0.237O2. The Si/P and P/Al ratios of synthesized SAPO-35 are 0.87 and 0.43, respectively, with a Si/(Si + Al + P) ratio of 0.207 is recorded. Thus, it indicates that SAPO-35 has considerably high content of Si element as compared to the SAPO-35 previously synthesized using hexamethyleneimine, quinuclidine and cyclohexylamine [START_REF] Lohse | Synthesis and characterization of the levynelike structure SAPO-35 prepared with cyclohexylamine as templating agent[END_REF][START_REF] Siliveri | Investigation on the promoterinduced rapid non-aqueous media synthesis of SAPO-35 and methanol-to-olefin reaction[END_REF].

Surface acidity is a crucial factor controlling the intrinsic catalytic reactivity of a solid. Thus, the acidity of SAPO-35 was examined by NH3-TPD analysis whereby the peak area of the profile is associated with the number of acid sites and the peak position is related to the acid strength [START_REF] Choo | Deoxygenation of triolein to green diesel in the H2-free condition: effect of transition metal oxide supported on zeolite Y[END_REF]. As displayed in Fig. 7, the deconvoluted NH3-TPD profile reveals the presence of acidity with three different amounts and strengths in the [PPy]OHsynthesized SAPO-35, namely weak (0.25 mmol/g), mild (0.29 mmol/g) and strong (0.57 mmol/g) acid sites. The total acidity of SAPO-35 is calculated to be 1.10 mmol/g and the value is higher than that synthesized using conventional hexamethyleneimine template (0.89 mmol/g) [START_REF] Huang | Utilization of SAPO-18 or SAPO-35 in the bifunctional catalyst for the direct conversion of syngas to light olefins[END_REF].

Catalytic reaction study

Esterification of levulinic acid with ethanol under non-microwave instant heating conditions was chosen as a model reaction to evaluate the catalytic behavior of SAPO-35. The reaction was carried out at 150-190 °C from 0 to 60 min and the results are shown in Fig. 8. Without catalyst, the reaction is inactive where 8.5% of levulinic acid is converted into ethyl levulinate at 150 °C after 60 min. Notably, the conversion increases significantly when SAPO-35 catalyst is introduced. At 150 °C, the conversion is tremendously improved to 86.1% with the selectivity to ethyl levulinate remains 100% after 60 min of heating (Fig. 8a). The reaction temperature is further increased to 160 The catalytic activity of SAPO-35 is also compared with other homogeneous (HCl, H2SO4, acetic acid glacial) and heterogenous (SAPO- respectively. As seen, concentrated H2SO4 and HCl successfully convert all levulinic acid into ethyl levulinate whereas acetic acid only gives 70.3% conversion (Fig. 9). These three catalysts, however, are corrosive, harmful to the environment and not reusable. For SAPO-35, it achieves nearly complete conversion (96.3%) as compared to the corrosive H2SO4 and HCl. SAPO-35 also performs slightly better than other 8-membered ring zeolites-SAPO-34 (93.4%) and SAPO-18 (94.6%)-and 12-membered ring aluminosilicate zeolites (H-LTL: 80.2%, H-Y: 86.4%) thanks to its proper pore size that perfectly matches the size of reactants and large amount of surface acidity with medium-to-strong acid strength.

Proposed mechanism

The proposed reaction mechanism of SAPO-35 zeolite catalyst in esterification of levulinic acid with ethanol is shown in Fig. 10. Initially, the levulinic acid (2.49 × 1.78 × 5.98 Å 3 ) enters the micropores of SAPO-35 (3.6 × 4.8 Å 2 ) via head-on orientation. At high temperature, the micropore opening becomes larger due to "breathing" effect, hence facilitating efficient molecular entrance [START_REF] Georgieva | Triggered gate opening and breathing effects during selective CO2 adsorption by merlinoite zeolite[END_REF]. The levulinic acid then diffuses and adsorbs on

Catalyst reusability study

The catalyst recyclability of SAPO-35 was also studied at 190 °C for 20 min in order to determine its stability after ten subsequent reaction cycles.

Prior to the study, the used catalyst after the first cycle of reaction was washed with diethyl ether (15 mL × 3 times), air dried and reactivated (350 °C, 4 h) for subsequent uses. The results showed that the SAPO-35 catalyst after the tenth run of reaction recorded 89.2% of conversion where a decrease in the conversion could be due to slight coking after multiple cycles of reaction and slight catalyst loss during recovering process after the completion of catalytic reaction (Fig. 11) [START_REF] Shokouhimehr | Magnetically separable and sustainable nanostructured catalysts for heterogeneous reduction of nitroaromatics[END_REF]. Furthermore, the leaching test was also performed where the reactant mixture containing fresh SAPO-35 catalyst was first stirred at room temperature for 24 h. The solid catalyst was then separated from the liquid and the reactant mixture was reacted under similar reaction conditions (190 °C, 20 min). The GC analysis shows that the reaction only accounted for 11% of conversion. It hence indicates that negligible amount of Si species was detached out from the SAPO-35 framework. The stability of SAPO-35 framework structure after 10 cycles of reaction is further investigated using XRD technique. In general, the XRD peaks intensity slightly decreased but no amorphous hump is observed indicating that the SAPO-35 framework structure is stable after multiple cycles of reaction (Fig. S3). Thus, being not corrosive, reusable, easily handled and stored, this catalyst is considered green and environmentally friendly. In addition, the results indicate that the SAPO-35 molecular sieve serves not only as a good catalyst for producing ethyl levulinate biofuel additive but also offers as a promising material for other advanced applications (e.g. membrane separation, sensor). Comprehensive work on SAPO-35 zeolite in this aspect is in progress.

Conclusions

In conclusion, the synthesis and crystallization profiles of SAPO-35 zeolite has successfully been investigated using 1propylpyridinium hydroxide ([PPy]OH) as a structure-directing agent. By using this novel N-heterocyclic organic template, the crystallization time of SAPO-35 is shortened to 21 h as compared to that synthesized using conventional hexamethyleneimine-templating method. In addition, the current work also observes a different crystallization route of SAPO-35 involving dissolution of reactants, nucleation and crystal growth of SAPO-34, followed by intrazeolite transformation from SAPO-34 to SAPO-35. Unlike previous work, the SAPO-35 zeolite synthesized using of [PPy] OH template exhibits high porosity and acidity. The SAPO-35 solid is also active and selective in the catalytic conversion of levulinic acid into ethyl levulinate under non-microwave instant heating where excellent conversion (96.3%) and selectivity (100%) towards ethyl levulinate are achieved (190 °C, 20 min) with high catalyst recyclability. Hence, from the perspective of material science, the current work not only provides an insight into the roles of new pyridinium organic template on the crystallization of SAPO-n nanoporous material but also on designing solid catalyst with enhanced properties for green chemistry applications such as catalytic biofuel upgrading and molecular separation processes.

CRediT authorship contribution statement

Yik-Ken Ma: Writingoriginal draft, Investigation, Formal analysis, Data curation. Stephen Chia: Investigation, Formal analysis.

Jean-Louis

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Scheme 1 .

 1 Scheme 1. Synthesis route of 1-propylpyridinium hydroxide ([PPy]OH).

  H NMR (400 MHz, D2O): δ = 1.03 (3H, t, J = 7.4 Hz, pyridine N-CH2-CH2-CH3), 2.13 (2H, m, J = 7.3, pyridine N-CH2-CH2-CH3), 4.71 (2H, t, J = 7.25 Hz, pyridine N-CH2), 8.19 (2H, t, J = 6.5 Hz, pyridine N-CH═CH), 8.66 (1H, t, J = 7.75 Hz, pyridine N-CH═CH-CH), 8.98 (2H, d, J = 5.9 Hz, pyridine N═CH). FTIR (KBr disk) cm -1 : 1170 (C-N), 1489 (C═N), 1504 and 1633 (aromatic C═C), 2879 (𝐶 𝑠𝑝 3 -H), 3056 (𝐶 𝑠𝑝 2 -H), 3400 cm -1 (broad, O-H). Anal. Cacld. For C8H12NBr: C, 47.55%; H, 5.94%; N, 6.93%; found: C, 46.81%; H, 5.85%; N, 6.83%.

Fig. 1 .Fig. 2 .

 12 Fig. 1. XRD patterns of samples after (a) 16 h, (b) 18 h, (c) 20 h, and (d) 21 h. The theoretical LEV simulated XRD pattern is shown in red lines. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

  -1 are due to P-O-Al stretching, asymmetric O-P-O stretching and P-O stretching modes, respectively[START_REF] Van Heyden | Nanosized SAPO-34 synthesized from colloidal solutions[END_REF]. In addition, the signal at 641 cm -1 is assigned to D6R secondary building unit, whereas the bends of PO4, AlO4, SiO4 and T-O (T = Si, Al or P) are shown at 570, 531, 481 and 442 cm -1 , respectively[START_REF] Van Heyden | Nanosized SAPO-34 synthesized from colloidal solutions[END_REF][START_REF] Liu | Synthesis, characterization and catalytic properties of SAPO-34 synthesized using diethylamine as a template[END_REF]. When the crystallization is further extended to 20 and 21 h, intrazeolite transformation from CHA (SAPO-34) to LEV (SAPO-35) framework structure occurs where the IR bands of SAPO-34 in the low wavenumber region (760-490 cm -1 ) completely disappear and change to the IR pattern of SAPO-35 (Fig.4c and d): 752 cm -1 arising from symmetric O-P-O stretching; 688 cm -1 due to 4-membered ring; 643 cm -1 ascribed to D6R polyhedral unit and 559 cm -1 assigned to bending of T-O of TO4 unit[START_REF] Liu | Synthesis, characterization and catalytic properties of SAPO-34 synthesized using diethylamine as a template[END_REF]. The stretching vibration of aromatic carbon (C═C) and bending of C-H of pyridinium template are observed at 1492 cm -1 and 1456 cm -1 respectively[START_REF] Askari | Methanol conversion to light olefins over sonochemically prepared SAPO-34 nanocatalyst[END_REF].

Fig. 3 .

 3 Fig. 3. HRTEM images of as-synthesized SAPO-35 at (a) low and (b) high magnifications.

Fig. 4 .

 4 Fig. 4. IR spectra of samples after (a) 16 h, (b) 18 h, (c) 20 h and (d) 21 h.

Fig. 5 .

 5 Fig. 5. TGA/DTG of (a) pure [PPy]Br template, and (b) as -synthesized SAPO-35.

Fig. 6 .

 6 Fig. 6. (a) Nitrogen adsorption-desorption isotherm and (b) pore size distribution of SAPO-35.

Fig. 7 .

 7 Fig. 7. NH3-TPD profile of SAPO-35 crystallized using [PPy]OH at 200 °C for 21 h.

Fig. 8 .

 8 Fig. 8. Esterification of levulinic acid with ethanol catalyzed with SAPO-35 at (a) 150 °C, (b) 160 °C, (c) 170 •C, (d) 180 °C and (e) 190 °C under nonmicrowave instant heating. Reaction conditions: Mass of SAPO-35 catalyst = 0.025 g, levulinic acid = 0.33 mmol, ethanol = 3.67 mmol.

  •C, 170 °C, 180 •C and 190 °C in order to study the effect of reaction temperature where the reaction time is also varied. The reaction temperature was only studied until 190 °C because the reaction pressure will exceed 20 bar beyond 190 °C which will burst the reactor's pressure safety valve. As observed, the catalytic activity of SAPO-35 is enhanced with time and temperature where 79.4%, 88.8%, 93.5% and 96.3% of conversion are achieved after 20 min of reaction at 160 °C, 170 °C, 180 °C and 190 °C, respectively (Fig.8b-e)[START_REF] Ng | Hydrothermal synthesis of zeolite a from bamboo leaf biomass and its catalytic activity in cyanoethylation of methanol under autogenic pressure and air conditions[END_REF]. The catalytic reaction enhancement at high temperature is associated with several factors. First, the accessible Brønsted acid sites of SAPO-35 that take part in the esterification reaction where the active sites offer new reaction pathways by enhancing the electrophilicity of carbonyl carbon of levulinic acid via protonation. Second, the SAPO-35 molecular sieve provides an intriguing confinement environment (inner cage size: 6.3 × 7.3 Å 2 ) to the incoming reactants (ethanol: 2.03 × 2.57 × 1.82 Å 3 , levulinic acid: 2.49 × 1.78 × 5.98 Å 3 ) for the formation of stable transition intermediates, and product molecules (ethyl levulinate: 3.31 × 7.60 × 1.78 Å 3 )[START_REF] Ahmad | Morphological effects on catalytic performance of LTL zeolites in acylation of 2-methylfuran enhanced by non-microwave instant heating[END_REF][START_REF] Ginés-Molina | Selective conversion of glucose to 5-Hydroxymethylfurfural by using L-Type zeolites with different morphologies[END_REF], whereby structure "breathing" effect and molecular structure distortion allow diffusion for these organic molecules (via head-on orientation) even though their molecular dimensions are close to the pore diameter of SAPO-35 (3.6 × 4.8 Å 2 )[START_REF] Georgieva | Triggered gate opening and breathing effects during selective CO2 adsorption by merlinoite zeolite[END_REF][START_REF] Babic | Increasing the porosity of zeolites[END_REF]. Both effects become more significant especially the reaction is conducted at high temperature. Third, an increase in the reaction conversion is also associated with the chemical kinetics effect since the rate constant increases exponentially with temperature as described by Arrhenius equation[START_REF] Nandiwale | Environmentally benign catalytic process for esterification of renewable levulinic acid to various alkyl levulinates biodiesel[END_REF]. Meanwhile, the external surface is also important in the reaction but not as important as the micropores because the synthesized SAPO-35 has the micropore surface area (519 m 2 /g) larger than its external surface area (7 m 2 /g). From the catalytic study, the optimum reaction conditions are hence at 190 • C for 20 min of heating.

Fig. 9 .

 9 Fig. 9. Comparative catalytic study using different homogeneous and heterogeneous acid catalysts. Reaction conditions: temperature = 190 •C, time = 20min, levulinic acid = 0.33 mmol, ethanol = 3.67 mmol, catalyst = 7.70 μmol equivalent to 0.025 g of SAPO-35, 0.001 g of H2SO4, 0.001 g of HCl, 0.0005 g of CH3COOH, 0.0201 g of H-LTL, 0.088 g of H-Y, 0.020 g of SAPO-18 and 0.017 g of SAPO-34, number of experiments = 2.

the

  Brønsted acid site located in the micropore channels and/or at the external surface via electrostatic attraction force (Step 1). Then, the levulinic acid is activated by the Brønsted acid site to form a stabilized carbocation intermediate through delocalization of the positive charge on carbonyl carbon (Step 2) [47]. Meanwhile, the diffusion and adsorption of ethanol on the SAPO-35 surface also takes place via dipole interactions between O-H group of ethanol and the framework oxygen (Step 3), thus bringing it closer to carbocation and facilitates nucleophilic carbocation substitution by ethanol (Steps 4 and 5), yielding ethyl levulinate and water as the products (Step 6) [51]. After the reaction, the products molecules are released from the active sites and diffuse out from the zeolite pores. The active sites are available again to adsorb and react with subsequent incoming reactant molecules (Step 1).

Fig. 10 .

 10 Fig. 10. Possible mechanism of esterification reaction of levulinic acid with ethanol in the presence of SAPO-35 solid acid catalyst.

Fig. 11 .

 11 Fig. 11. Catalyst reusability study of SAPO-35 in esterification of levulinic acid with ethanol. Reaction conditions: temperature = 190 °C, time = 20 min, levulinic acid = 0.33 mmol, ethanol = 3.67 mmol, number of experiments = 2. The amounts of levulinic acid and ethanol used for the consecutive runs are normalized to the mass of SAPO-35 after recovery.

  Paillaud: Investigation, Formal analysis, Data curation. T. Jean Daou: Investigation, Formal analysis, Data curation. Fitri Khoerunnisa: Writingreview & editing, Data curation, Conceptualization. Zeinhom M. El-Bahy: Investigation, Formal analysis. Tau Chuan Ling: Writingreview & editing, Investigation. Amal A. Altalhi: Writingreview & editing, Investigation, Funding acquisition, Formal analysis. Samy F. Mahmoud: Data curation, Investigation. Eng-Poh Ng: Writingreview & editing, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Conceptualization.

Table 1

 1 Chemical composition and acidity of

	Sample	Product composition	Si/P ratio	P/Al ratio Si content	NH3-TPD acidity (mmol/g)
						Weak	Mild	Strong	Total
	SAPO-35	Si0.207Al0.556P0.237O2.000	0.87	0.43	0.207	0.25	0.29	0.57	1.10

  18, SAPO-34, H-LTL, H-Y) zeolite catalysts where similar molarity of catalyst is used to catalyze this reaction at 190 °C for 20 min. Note: The average crystal sizes of SAPO-18, SAPO-34, H-LTL (Si/Al = 3.2) and H-Y (Si/Al = 2.5) are ca. 3.21 × 0.10 μm 2 , 1.76 × 1.85 μm 2 , 4.16 × 2.07 μm 2 and 1.17 × 1.31 μm 2 ,

Acknowledgements

The financial assistance from RUI (1001/PKIMIA/8011128), Universiti Sains Malaysia, Malaysia is acknowledged. The authors would also like to extend their appreciation to Taif University Researchers Supporting Project (TURSP-2020/243), Taif University, Saudi Arabia for financial support.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.matchemphys.2022.126240.


Alexandre Holmes

Hugo Laval

Marc Schmutz

Sylvie Blanc

Joachim Allouche

Benjamin Watts

Guillaume Wantz

Natalie P Holmes

Kazuhiko Hirakawa

Elise Deniau

Sylvain Chambon

Christine Lartigau-Dagron
email: christine.lartigau-dagron@univ-pau.fr

Antoine Bousquet
email: antoine.bousquet@univ-pau.fr

Janus Organic Semiconductor Nanoparticles prepared by Simple Nanoprecipitation

Keywords: -conjugated materials, Janus nanoparticles, Photocatalysis, Photovoltaics

Nanoparticles of donor-acceptor organic semiconductors are produced by a onestep nanoprecipitation with a Janus morphology. Electron donor P3HT was blended with electron acceptor PC61BM in THF and then precipitated in water, firstly with surfactant, and secondly without surfactant. Cryo-TEM reveals an internal Janus structure at high magnification, for nanoparticles which have, in the past, been reported to have a molecularly intermixed morphology. Synchrotron-based scanning transmission X-ray microscopy (STXM) confirmed the segregation of the organic semiconductors and photoluminescence experiments showed an efficient electron transfer from P3HT to PC61BM. Organic field effect transistors (OFETs) were fabricated with these Janus nanoparticles and showed that the positive charges can be efficiently transported through thin films. This behaviour proves that the nanoparticles possess an electron-accepting face (the PC61BM face) able to transport electrons and a holeaccepting face (the P3HT face) for the conduction of holes. Finally, the deposition of silver via the photoreduction of a silver salt (AgNO3(aq)) was demonstrated, as a proof of concept. These experiments show the potential of the Janus nanoparticles for photovoltaics but also photocatalytic reactions in which reduction and oxidation reactions can occur at opposite sides of the nanoreactor (the individual Janus nanoparticles).

Introduction

The sun's photons provide the largest source of energy on earth and its exploitation will contribute to solve the world energy crisis without being detrimental for the environment. Indeed, photovoltaics (PV) technology allows the transformation of photons into electricity. [START_REF] Mazzio | The future of organic photovoltaics[END_REF][START_REF] Almora | Device Performance of Emerging Photovoltaic Materials (Version 2)[END_REF] Additionally, hydrogen (H2) production via photocatalytic water splitting has emerged as an attractive solution to store solar energy in a dispensable fuel that does not generate carbon dioxide (CO2), neither at the fabrication nor consumption stages. [START_REF] Fajrina | A critical review in strategies to improve photocatalytic water splitting towards hydrogen production[END_REF] Further, artificial photosynthesis is being developed to use sunlight to provide electrons for the reduction of CO2 in order to produce other solar fuels like ethanol. [START_REF] Singh | Design of an artificial photosynthetic system for production of alcohols in high concentration from CO 2[END_REF][START_REF] Cox | Artificial photosynthesis: understanding water splitting in nature[END_REF] The development of organic semiconductor nanoparticles has received significant consideration in the past three decades for these applications. [START_REF] Holmes | Organic semiconductor colloids: From the knowledge acquired in photovoltaics to the generation of solar hydrogen fuel[END_REF][START_REF] Kosco | Enhanced Photocatalytic Hydrogen Evolution from Organic Semiconductor Heterojunction Nanoparticles[END_REF][START_REF] Kosco | Generation of long-lived charges in organic semiconductor heterojunction nanoparticles for efficient photocatalytic hydrogen evolution[END_REF] Organic semiconductors, either polymers (mostly electron donor) or small molecules (fullerene derivatives or non-fullerene acceptors), can be dispersed in water to provide human and environmentally-friendly fabrication processes for organic photovoltaic (OPV) devices as an alternative to classical options which are typically using toxic organic solvent, such as chloroform and dichlorobenzene. [START_REF] Holmes | Review of Waterborne Organic Semiconductor Colloids for Photovoltaics[END_REF] Concerning solar fuels production, Pinaud et al. applied life cycle analysis to the production of H2, demonstrating that a colloidal system, in which the photocatalysts are in the form of nanoparticles (NPs) dispersed in water, would be the cheapest technology compared to planar photoelectrodes. [START_REF] Pinaud | Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry[END_REF] Self-assembly is a straightforward methodology to obtain organic nanoparticles dispersed in water. The driving force for the self-assembly is a decrease of surface energy, resulting in the segregation of all components towards an overall thermodynamic equilibrium. As a consequence, the morphology of a multicomponent nanoparticle evolves during segregation.

Moreover, it has been thoroughly documented that the donor/acceptor morphology is a critical parameter in the OPV field. [START_REF] Dou | 25th Anniversary Article: A Decade of Organic/Polymeric Photovoltaic Research[END_REF][START_REF] Hedley | Determining the optimum morphology in highperformance polymer-fullerene organic photovoltaic cells[END_REF][START_REF] Yoon | Progress in morphology control from fullerene to nonfullerene acceptors for scalable high-performance organic photovoltaics[END_REF] Nanoscale domain size that closely matches exciton diffusion length (approximately 10-20 nm) and conduction pathways for charges are both required to maximize performances.

A core-shell morphology is classically reported when miniemulsion is used for the nanoparticle preparation. [START_REF] Holmes | Organic semiconductor colloids: From the knowledge acquired in photovoltaics to the generation of solar hydrogen fuel[END_REF][START_REF] Holmes | Review of Waterborne Organic Semiconductor Colloids for Photovoltaics[END_REF] Donor and acceptor materials segregate in the miniemulsion hydrophobic droplets to minimize interface energy with water (or surfactant/water), while the organic solvent is slowly evaporating. Since the evaporation time is long, one of the components segregates to the core of the particles, while the other component forms the shell. Several organic semiconductor nanoparticle dispersions have been reported in the literature with a core-shell morphology such as TQ1:PC71BM, [START_REF] Holmes | Nano-pathways: Bridging the Divide Between Water-processable Nanoparticulate and Bulk Heterojunction Organic Photovoltaics[END_REF] P3HT:PC61BM, [START_REF] Holmes | Probing the origin of photocurrent in nanoparticulate organic photovoltaics[END_REF] P3HT:N2200 and TQ1:N2200. [START_REF] Barr | Nanomorphology of eco-friendly colloidal inks, relating non-fullerene acceptor surface energy to structure formation[END_REF] However, several studies reported device performance limitations due to this morphology, either for PV or H2 production, because after exciton dissociation, electrons or holes can be trapped in the core, without having the possibility to respectively reach the electrodes or the aqueous medium. [START_REF] Kosco | Enhanced Photocatalytic Hydrogen Evolution from Organic Semiconductor Heterojunction Nanoparticles[END_REF][START_REF] Ulum | The role of miscibility in polymer:fullerene nanoparticulate organic photovoltaic devices[END_REF][START_REF] Gehan | Multiscale active layer morphologies for organic photovoltaics through self-assembly of nanospheres[END_REF] Molecularly intermixed morphology is the second type of reported internal structure for organic semiconductor nanoparticles, which is mostly obtained via the nanoprecipitation methodology. [START_REF] Holmes | Review of Waterborne Organic Semiconductor Colloids for Photovoltaics[END_REF] During the nanoparticle formation, the rapid diffusion of the organic solvent (water/alcohol miscible) into the non-solvent leaves such little time for the donor and acceptor material to segregate, that a molecularly intermixed structure is obtained. This morphology was reported by different groups for P3HT:PC61BM (in ethanol), [START_REF] Darwis | Surfactant-free nanoparticulate organic photovoltaics[END_REF] P3HT:ICBA (in alcohols), [START_REF] Xie | Robot-based high-throughput engineering of alcoholic polymer: Fullerene nanoparticle inks for an eco-friendly processing of organic solar cells[END_REF] and PCDTBT:PC71BM (in water). [START_REF] Prunet | Aqueous PCDTBT:PC 71 BM Photovoltaic Inks Made by Nanoprecipitation[END_REF] The enhanced PV performances compared to the coreshell dispersion were attributed to better electron extraction. Kosco et al. recently showed that this intermixed morphology was also superior for hydrogen solar fuel production, improving the H2 evolution rate from 3,000 µmol h -1 g -1 to 28,000 µmol h -1 g -1 , compared to the coreshell morphology. [START_REF] Kosco | Enhanced Photocatalytic Hydrogen Evolution from Organic Semiconductor Heterojunction Nanoparticles[END_REF] In this report, we demonstrate the one-step formation of Janus nanoparticles, the simplest multifaced nanoparticle named after the two-faced Roman god, Janus, made of semiconducting organic materials via nanoprecipitation. Clear segregation between poly(3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) has been observed by cryogenic transmission electron microscopy (cryo-TEM) and synchrotron-based scanning transmission X-ray microscopy (STXM). Photoluminescence spectroscopy showed that the emission from the donor material is efficiently quenched. Organic field effect transistors (OFET) were prepared with Janus P3HT:PC61BM NP to demonstrate that the charges produced are efficiently transported to the electrodes. Finally, the deposition of silver via the photoreduction of a silver salt (AgNO3(aq)) was demonstrated. These results open the way to direct application in PV and in photocatalysis for the production of solar fuels.

Material and Methods

Nanoparticles synthesis

Commercial P3HT (50K Solaris) and PC61BM (Sigma) are first solubilized in tetrahydrofuran (THF) at 65°C for at least 2 hours. The aqueous phase is prepared by adding (if required) SDS or Pluronic F127 in MilliQ Water, and stirred few minutes. In a round bottom flask of 25 mL, 16 mL of the aqueous solution are injected (filtered on a cellulose filter of 0.45 µm in order to avoid any dust). Right before the addition of the organic solution, the aqueous medium is stirred at 650RPM, for at least 30 seconds, to ensure that the vortex is stable. Then, the organic solution (maintained at 65°C) is introduced quickly in the aqueous medium, under stirring, leading to the instantaneous formation of a red/purple dispersion. In order to eliminate THF, the stirring rate is reduced to 300 RPM, the dispersion is heated up to 70°C with a nitrogen airflow, for at least 1 hour (depending on the volume of organic solvent).

Dispersions stabilized with surfactant can be concentrated through centrifugal dialysis.

AmiconR ultra-15 Centrifugal Filter Devices (cutoff 100Kg.mol-1) are used. A volume up to 12 mL of the dispersion is added in the centrifugation tube, and then centrifugation using a Beckman Coulter Avanti J-30I centrifuge, at 6400 RPM (5,000 G) for 12 minutes in order to reduce the volume up to 200 µL. For dispersions using Pluronic F127, the dispersion is first cooled down to 0°C, and the centrifugation step is performed at 2°C, in order to efficiently remove the surfactant excess. This step was repeated for at least 3 times, with the addition of MilliQ water between washing steps.

Photodeposition

P3HT:PC61BM NPs (0.3 mg), stabilised by F127 (excess removed by centrifugal dialysis), AgNO3 (1 mg) and methanol (100 µL) were mixed in a 5.2 mL aqueous solution. The medium was then irradiated with a THORLABS M450LP1 lamp at 450 nm for 4 hours. Dialysis in extra pure water was performed in order to remove the excess of AgNO3 and methanol.

Characterization

Dynamic light scattering (DLS). The hydrodynamic diameters Dh and polydispersity (PDI) of particle dispersions were measured by DLS on a Nano-ZS zetasizer (Model ZEN3600 Malvern

Instruments) operating at an angle of 173°. Nano-ZS is equipped with a He-Ne 4.0 mW power laser operating at a wavelength of 633 nm. The particles were dispersed in deionized water at a concentration of 0.05 g.L -1 . The data were calculated using the cumulant analysis.

Cryogenic transmission electron microscopy (Cryo-TEM). A drop of 5 µL of the solutions was applied to a copper grid covered with a carbon film made hydrophilic using an ELMO glow discharge device (Cordouan Technologies, France). The grid was placed in a home-made vitrification apparatus at 22°C and 80% relative humidity before plunging into liquid ethane maintained at -190°C by liquid nitrogen. The grid was mounted on a cryo holder (Gatan 626, USA) and observed in a Tecnai G2 microscope (FEI, The Netherlands) at 200 kV. Images were acquired using an Eagle slow scan CCD camera (FEI).

Near Edge X-ray Absorption Fine Structure (NEXAFS) measurements of P3HT and PC61BM were performed on the PolLux beamline (X07DA) at the Swiss Light Source (SLS) synchrotron. Pristine films of P3HT and PC61BM were prepared by spin coating chloroform and chlorobenzene solutions, respectively, of each semiconductor material onto PEDOT:PSS coated glass substrates. 2 x 2 mm 2 sections were scored on the films using a scalpel, followed by floating off the film sections onto a D.I. water surface, which was made possible by dissolving the PEDOT:PSS sacrificial layer under the semiconductor material films. 2 x 2 mm 2 film sections were subsequently collected onto 300 mesh Cu grids (20 mm bar, 63 mm hole, 3 mm diameter, purchased from ProSciTech Pty Ltd) for NEXAFS measurements. The energy of the X-ray beam was varied between 278 and 390 eV, spanning the C K-edge region. Secondand third-order light was removed by an order sorting aperture and higher order suppressor.

Orthogonal energies were determined from NEXAFS spectra of pristine films of P3HT and PC61BM.

X-ray spectromicroscopy (STXM) measurements were performed on the PolLux beamline (X07DA) at the SLS synchrotron. Samples were prepared for STXM measurements by spin coating 2.5 μL of nanoparticle dispersions onto low stress silicon nitride (Si3N4) membrane windows (window dimensions 1 x 1 mm 2 , window thickness 30 nm, silicon frame dimensions 5 x 5 mm 2 , purchased from Silson, UK) at 3000 rpm, 1 min, low acceleration. Samples were air dried at room temperature. The samples on Si3N4 windows were loaded in the STXM sample chamber and rastered with respect to the X-ray beam. The transmitted X-ray beam is detected by a scintillator and a photomultiplier tube. The STXM Fresnel zone plate (Ni) had an outer most zone width of 25 nm, setting the spatial resolution limit of the measurement. Singular value decomposition (SVD) was used to fit a sum of the pristine material NEXAFS spectra to the measured blend spectrum of the nanoparticles, at each pixel, in the STXM images. Prior to SVD fitting, the pristine material NEXAFS spectra were normalized to film thickness. The method of reference-spectrum normalization constitutes dividing the real spectrum by a theoretical spectrum calculated based on the material's chemical formula using henke.lbl.gov/optical_constants/filter.html. The aXis2000 package was used to perform image analysis of STXM maps.

Correlative TEM enabled position-matched STXM-TEM images to be generated. Following STXM mapping at the Swiss Light Source, the Si3N4 substrates with deposited nanoparticles were transported back to the University of Newcastle (Australia) for TEM measurements on a JEOL 1200 EXII at an accelerating voltage of 80 kV.

UV-visible absorption spectra of P3HT:PC61BM nanoparticles were recorded on a Shimadzu UV-2450PC spectrophotometer. Emission Spectroscopy (Photoluminescence): The corrected steady-state luminescence spectra were measured between 520 and 800 nm at 2 nm resolution using a photon counting Edinburgh FLS920 fluorescence spectrometer equipped with a Xenon lamp. The concentrations of all compounds in MilliQ Water were adjusted to give an absorbance around 0.1 at the excitation wavelength (510 nm) in a 1 cm fluorescence quartz optical cell (Hellma).

OFET devices were fabricated base on a bottom-gate top-contact structure. N-doped Si wafers with 230 nm-thick thermally grown SiO2 were purchased from Fraunhofer IPMS. Substrates were cleaned by sequential ultrasonic treatments of 10 minutes at 50°C: acetone, ethanol and isopropanol. No passivation layers were used. Prior to deposition of the active layer, substrates were treated by UV-ozone for 15 minutes. The active layers were obtained by spin coating with a rotation speed of 1300 RPM, in order to have a homogeneous film formation. After deposition of the P3HT:PC61BM thin film, thermal evaporation of gold electrode was performed through a shadow mask to define the source and drain electrodes using ULVAC thermal evaporator.

Four kind of channel length (L) were defined: 50, 75, 100 and 125 µm for 1.5 mm channel width (W). OFET devices were connected from the back side to a copper plate using silver paste.

Auger electron spectroscopy (AES) were carried out with a JEOL JAMP 9500F Auger spectrometer nanoprobe (JEOL Ltd, Tokyo, Japan) equipped with a Schottky field emission gun working under UHV conditions (pressure < 2 .107 Pa). The AES spectra were recorded at a kinetic energy window from 0 to 800 eV by focusing the electron beam (size  10 nm, 20 keV, 5 nA) on target nanoparticles. The operating mode was a constant retarding ratio (CRR) mode for which the energy resolution (dE) linearly increases with the measured electron energy (E).

Result and Discussion

Nanoparticles synthesis

The nanoprecipitation technique relies on the miscibility of the organic solvent, in which the organic semiconductors are solubilized, and the aqueous phase acting as the anti-solvent, which can contain a surfactant. Upon addition of the solvent into the anti-solvent, a solvent displacement step occurs as the two are completely miscible, leading to the rapid precipitation of the hydrophobic materials into nanoparticles. This process is decomposed into three steps: nucleation, growth by accumulation and growth by coagulation. [START_REF] Martínez Rivas | Nanoprecipitation process: From encapsulation to drug delivery[END_REF] An efficient stirring is therefore required in order to have homogeneous nucleation and growth steps in the entire volume, leading to small, monodisperse and stable nanoparticles. [START_REF] Prunet | Aqueous PCDTBT:PC 71 BM Photovoltaic Inks Made by Nanoprecipitation[END_REF] As a starting point of this study, a dispersion of P3HT:PC61BM (1:1, mass equivalent) was prepared from a THF solution at 2 mg.mL -1 and a solvent/anti-solvent (THF/water) volume ratio of 1/8 (Entry 1, Erreur ! Source du renvoi introuvable.). The nanoprecipitation produced a colloidal dispersion with a mean particle hydrodynamic diameter, measured by DLS, of 100 nm. The dispersion was concentrated by centrifugal dialysis and the maximum solids content reached without irreversible aggregation was 1 mg.mL -1 . This low solids content will ultimately limit the use of this type of dispersion for solar cell fabrication where at least 20 mg.mL -1 solution concentrations are usually required. With the objective of increasing the solids content of the dispersion, sodium dodecyl sulphate (SDS) or Pluronic F127 surfactants were added to the formulation, in the anti-solvent (water).

Starting with the same photoactive materials concentration of 2 mg.mL -1 , and with a surfactant concentration of 3 mg.mL -1 , the mean particle diameter decreased to 80 nm (Entry 2 and 4, Table 1 for SDS and F127, respectively). The dispersion was then concentrated by the same centrifugation/filtration cycles and this time the solids content could be increased to over 10 mg.mL -1 without aggregation, due to the addition of surfactants (note that the concentration can be increased up to 60 mg.mL -1 without aggregation, but a concentration of 10 mg.mL -1 was more suited for cryo-TEM experiments, see Supplementary Information for the procedure).

This latter centrifugation/filtration step was also used to eliminate the excess of free surfactants from the dispersion (see Supplementary Information) in order to decrease their possible negative impact on the PV device performance (insulating behaviour, charge traps, recombination centres, etc.). [START_REF] Xie | Overcoming efficiency and stability limits in water-processing nanoparticular organic photovoltaics by minimizing microstructure defects[END_REF]

Nanoparticles morphology

The morphology of the nanoparticles was assessed by cryo-TEM in order to observe the structure in their native water-dispersed state. Due to its higher electron density (1.5 g.cm -3 ), PC61BM appears darker than P3HT (1.1 g.cm -3 ) [START_REF] Sun | Controlling PCBM aggregation in P3HT/PCBM film by a selective solvent vapor annealing[END_REF] in micrographs reported in Figure 1 (arrows).

For the three formulations defined above, i.e. without surfactant, or using SDS or F127 (Figure 1a-c), a Janus morphology was observed with P3HT and PC61BM clearly phase segregated from one another. A fine observation of the nanoparticles brings more information. First of all, the Janus domains are not completely pure and small dots of less than 10 nm are visible, meaning that nanodomains of PC61BM exist in the P3HT face and P3HT nanodomains exist in the PC61BM face (see additional cryo-TEM micrographs in Supplementary Information). Secondly, even though the mass ratio between P3HT and PC61BM is 1:1 and the volume ratio 1.36:1 (see calculation in Supplementary Information), the volume attributed to the P3HT bright areas appears much larger than the PC61BM dark areas. [START_REF] Sun | Controlling PCBM aggregation in P3HT/PCBM film by a selective solvent vapor annealing[END_REF] Finally, the crystallinity of P3HT domains can be observed in the bright face of the Janus nanoparticles for each sample (Supplementary Information Figure SI-8), with striped areas characteristic of lamellar stacking of regioregular P3HT polymer chains. [START_REF] Chaudhary | Highly aligned and crystalline poly(3-hexylthiophene) thin films by off-center spin coating for high performance organic field-effect transistors[END_REF] The formation of Janus-like nanoparticles via nanoprecipitation has already been reported in the literature for dispersions prepared from blends of two non-conjugated homopolymers such as PS/PI, PS/PB, PB/PLA. [START_REF] Yan | Nanoprecipitation as a simple and straightforward process to create complex polymeric colloidal morphologies[END_REF][START_REF] Sosa | Soft Multifaced and Patchy Colloids by Constrained Volume Self-Assembly[END_REF][START_REF] Higuchi | Spontaneous formation of polymer nanoparticles with inner micro-phase separation structures[END_REF] In each case, the two polymers self-organized into hemispherical domains in order to minimize the system (polymer-polymer-liquid) interfacial energy. The Janus morphology emerged because the two polymers had similar interfacial energies with the liquid phase and a low interfacial energy between themselves. Modelling studies confirmed that the formation of such nanoparticle morphology is intimately related to the interaction parameters between component A, component B and the liquid but also to the extremely quick formation of nanoparticles during the nucleation stage of the nanoprecipitation mechanism. [START_REF] Li | Structured Nanoparticles from the Self-Assembly of Polymer Blends through Rapid Solvent Exchange[END_REF] As soon as the organic phase diffuses through water, the active materials start to reach a supersaturated state, leading to the nucleation of active material all over the medium, as schematized in Erreur ! Source du renvoi introuvable.a. [START_REF] Martínez Rivas | Nanoprecipitation process: From encapsulation to drug delivery[END_REF][START_REF] Aubry | Nanoprecipitation of Polymethylmethacrylate by Solvent Shifting:1. Boundaries[END_REF][START_REF] Lepeltier | Nanoprecipitation and the "Ouzo effect": Application to drug delivery devices[END_REF][START_REF] Joye | Production of nanoparticles by anti-solvent precipitation for use in food systems[END_REF] Concerning the particles prepared without surfactant, the liquid phase is composed, at the nucleation stage, of a THF/water mixture (1/8 v, Table 1, Entry 1) with a surface tension already reported as γLiq = 44.2 mN.m -1 . [START_REF] Shen | Surface Tension Components Based Selection of Cosolvents for Efficient Liquid Phase Exfoliation of 2D Materials[END_REF] The contact angles between films of P3HT or PC61BM and a drop of THF/water mixture were measured and the solid/liquid surface tensions, γPCBM/Liq and γP3HT/Liq, were calculated (see Supplementary Information). These analyses show that PC61BM and P3HT have a similar solid/liquid surface tension, γPCBM/Liq = 15.2 mN.m -1 and γP3HT/Liq = 22.0 mN.m -1 , indicating that the nucleation is expected to occur simultaneously. [START_REF] Higuchi | Spontaneous formation of polymer nanoparticles with inner micro-phase separation structures[END_REF] The inner morphology of the nuclei has been modelled to be dependent on the ratio between γPCBM/Liq/γP3HT/PCBM and γP3HT/Liq/ γP3HT/PCBM. [START_REF] Li | Structured Nanoparticles from the Self-Assembly of Polymer Blends through Rapid Solvent Exchange[END_REF] From the dispersive and polar component of the surface tension of the materials, the interfacial tension between P3HT and PC61BM, γP3HT/PCBM, was calculated to be 13.6 mN.m -1 (see Supplementary Information) leading to a γPCBM/Liq/γP3HT/PCBM of 1.12 and γP3HT/Liq/ γP3HT/PCBM of 1.62. Since the difference between these two last values is rather small, the predicted morphology is Janus with a larger surface domain of P3HT. [START_REF] Li | Structured Nanoparticles from the Self-Assembly of Polymer Blends through Rapid Solvent Exchange[END_REF] The γPCBM/Liq/γP3HT/PCBM and γP3HT/Liq/γP3HT/PCBM were also calculated for the other aqueous phases used in this study (SDS, F127 solutions). The difference between both values (γPCBM/Liq/γP3HT/PCBM and γP3HT/Liq/ γP3HT/PCBM) is small for all the tested conditions (Table S5 in Supplementary Information) and should also give rise to a Janus morphology in accordance with the model and cryo-TEM results.

Once the concentration of active materials in the mixed organic phase decreases below the supersaturation state, a step of nuclei growth occurs, by accumulation of the solubilized active materials (Figure 2a). Due to the incompatibility between the active materials, P3HT is more likely to accumulate preferentially on a P3HT-rich "face" of the nuclei, and PC61BM on a PC61BM-rich face. Both steps of nucleation and growth occur extremely quickly. This was experimentally observed, with dynamic light scattering (DLS) analysis performed immediately after the addition of THF in water at t0 + 1 min., and after THF evaporation at t0 + 120 min.

(see Supplementary Information Figure SI-11) showing the same particles size. Adapted with Janus nanoparticle from Martinez Rivas et al. [START_REF] Martínez Rivas | Nanoprecipitation process: From encapsulation to drug delivery[END_REF] b) UV-visible spectra of P3HT and P3HT:PC61BM NPs for different nanoparticle size. c) Evolution of the photoluminescence quenching of P3HT (excitation at 510 nm) for different nanoparticle sizes, all stabilized with F127 (Entry 3, 4, 5, Table 1). The quenching percentage was calculated from the count ratio between the P3HT reference and corresponding P3HT:PC61BM nanoparticles, between 630 and 750 nm.

The TEM image in Figure 1d represents the formulation of Table 1 Entry 5 in which the initial active materials concentration [P3HT:PC61BM] was increased to 5 mg.mL -1 and the surfactant concentration [F127] was decreased to 0.5 mg.mL -1 in an attempt to produce larger nanoparticles. The mean hydrodynamic diameter of the spheres increased up to 131 nm (measured by DLS) and the TEM images showed the blend of small Janus nanoparticles with larger multifaced nanoparticles composed of one large P3HT domain and several PC61BM darker domains. We attributed this blend of morphologies to the coagulation of small Janus nanoparticles (Figure 2a) to give birth to large aggregates, this being induced by the increase of the active material/surfactant ratio. We believe that this step of growth by coagulation does not occur if collisions between Janus nanoparticles are impeded by the presence of a surfactant in sufficient concentration (Entry 2, 3, 4, Table 1) or if the solids content is low (Entry 1, Table 1). The nanoparticle size did not have a strong influence over the final material absorption, according to the UV-visible spectrum (Figure 2b). Only a slight increase of the shoulder at 600 nm can be observed for large nanoparticles, probably due to an increase of - stacking.

STXM measurements were performed at the PolLux beamline of the Swiss Light Source synchrotron (measurements details provided in the Supplementary Information) [START_REF] Raabe | PolLux: A new facility for soft x-ray spectromicroscopy at the Swiss Light Source[END_REF] to determine the morphology of the P3HT:PC61BM nanoparticles. STXM composition maps of P3HT:PC61BM (1:1) nanoparticles produced with and without surfactant (Entry 5 and 1 in Table 1) are presented in Figure 3. Although the observation was difficult due to the small nanoparticle size, no core@shell morphology was observed in the two sample types, consistent with the previous results reported for nanoparticles prepared via nanoprecipitation. Rather, several high contrast striped regions can be observed, indicative of alternating P3HT-rich and PC61BM-rich domains of Janus nanoparticles (framed in Figure 3), or agglomerations thereof.

The presence of Pluronic F127 does not influence the nanoparticle morphology (additional maps depicting the nanoparticle morphology are provided in Supplementary Information in a 2-color map mode, Figure SI-9).

Optoelectronic properties

In order to investigate the exciton dissociation efficiency, the Janus nanoparticles were characterized by photoluminescence and compared with pristine P3HT nanoparticles (Figure 2c and further spectra in Supplementary Information). All P3HT:PC61BM nanoparticles showed a strong decrease in the P3HT emission (excitation wavelength at 510 nm) of at least 86% due to ultrafast electron transfer from P3HT to PC61BM. The smallest nanoparticles (68 nm) quenched slightly more efficiently (94%) than the largest ones (86 and 89%), which is consistent with the existence of smaller material domains. When the particle diameter increases from 79 to 131 nm, the quenching is in the same range (86 and 89%). This is suggesting that the material domains size remains similar, which is explained by the formation mechanism via coagulation, detailed above and in Figure 2a, concerning the largest particles (131 nm). This important quenching behaviour indicates a high exciton dissociation rate within these particles.

This opens the way for the use of these dispersions in solar technologies, where donor-acceptor interfaces for exciton dissociation are needed.

As mentioned in the introduction, other research teams have reported an intermixed morphology for nanoparticles made via nanoprecipitation rather than the Janus morphology reported here. [START_REF] Darwis | Surfactant-free nanoparticulate organic photovoltaics[END_REF][START_REF] Xie | Robot-based high-throughput engineering of alcoholic polymer: Fullerene nanoparticle inks for an eco-friendly processing of organic solar cells[END_REF][START_REF] Prunet | Aqueous PCDTBT:PC 71 BM Photovoltaic Inks Made by Nanoprecipitation[END_REF][START_REF] Schwarz | Charge generation and morphology in P3HT : PCBM nanoparticles prepared by mini-emulsion and reprecipitation methods[END_REF] This difference can come from several factors. First of all, it is possible that these previous works actually produced Janus particles, but that the microscopic characterisation by microscopy was not performed with a sufficient spatial resolution to distinguish Janus from the intermixed morphology, or the two materials didn't show enough contrast (in TEM, SEM or AFM). Photoluminescence was also used to prove quenching.

However, PL is not a suitable technique to discriminate between intermixed or Janus morphology (at least when the size of the nanoparticles is below 100 nm). Secondly, previous works of nanoprecipitation did not use surfactant and hence aggregation by coagulation could have induced the creation of larger multidomain nanoparticles such as those shown in Figure 1d) and therefore obscured the small-scale morphology, especially when characterising large nanoparticles. Finally, some groups used ethanol rather than water as the anti-solvent so the solid/liquid values differ from those in the present study and may have produced a different morphology.

In order to probe the charge transport in these Janus NPs, organic field effect transistors have been prepared with P3HT:PC61BM NPs (F127, Table 1, entry 3) and following a bottom-gate top-contact architecture on Si/SiO2 wafers (n-doped Si/ SiO2/P3HT:PC61BM/Au). A reference P3HT:PC61BM device was casted from chlorobenzene. Both layers, deposited from NP or from organic solvent, were then annealed at 120°C for 10 minutes in glovebox. Details of transistors preparations and characterisation are given in SI.

Hole mobilities (µh+) were extracted from the transfer characteristic (IDS=f(VGS)) in the saturation regime [START_REF] Horowitz | Organic Field-Effect Transistors[END_REF] (Figure SI-14) for P3HT:PC61BM thin films casted from organic solvent as well as for P3HT:PC61BM NP assemblies. The devices show a hole mobility about 4.9 10 -5 cm 2 .V -1 .s -1 , against 3.2 10 -5 cm 2 .V -1 .s -1 for the reference samples casted from chlorobenzene and aqueous dispersions respectively. Therefore, the hole transport trough P3HT:PC61BM NP assemblies appears to be as efficient as in P3HT:PC61BM thin film casted from organic solvent.

However, the hole mobility in P3HT:PC61BM NP is one order of magnitude lower than the value obtained with only P3HT NP assemblies, casted from aqueous dispersions (µh+ = 1.2 10 - 4 cm².V -1 .s -1 ) see Figure SI-13). Such difference indicates that the presence of PCB61M hinders the conduction pathways of between P3HT domains, resulting in a lower hole mobility. More investigation must be performed to understand the impact of the size and thermal treatment of these P3HT:PC61BM Janus NPs on the charge transport since high and equilibrated mobilities are some of the conditions to achieve high performances organic photovoltaic devices. [START_REF] Morana | Organic Field-Effect Devices as Tool to Characterize the Bipolar Transport in Polymer-Fullerene Blends: The Case of P3HT-PCBM[END_REF][START_REF] Szymanski | Balanced Charge Transport Optimizes Industry-Relevant Ternary Polymer Solar Cells[END_REF] Finally, the potential for photocatalysis of these Janus nanoparticles was revealed via the successful elaboration of hybrid nanoparticles by photodeposition. For this purpose, the P3HT/PC61BM dispersions stabilized by F127 were irradiated at  = 450 nm in the presence of AgNO3(aq) and a sacrificial electron donor, methanol. The objective was to reduce Ag + with the photogenerated electrons coming from the Janus nanoparticles. Indeed, the laser irradiation (450 nm) absorbed by P3HT promotes the exciton dissociation (already proved by photoluminescence) and should produce electrons that are sufficiently reducing to transform Ag + into silver metal. As a consequence, silver metallic aggregates should deposit at the surface of the organic nanoparticles, as schematically represented on Figure 4a.

The presence of silver was first suggested by DLS, with an increase in the nanoparticle diameter, from 85 to 157 nm, after laser irradiation but also by an increase in the UV-Vis absorbance around 450 nm, classically attributed in literature to Ag nanoparticles (see Supporting Information Figure SI-15). [START_REF] Pacholski | Site-Specific Photodeposition of Silver on ZnO Nanorods[END_REF] For further evidence, nanoparticles were imaged via Cryo-TEM, and Figure 4b displays dark features corresponding to silver metal deposited on organic semiconductor nanoparticles in grey (for additional images see Supporting Information -16). Cryo-TEM contrast being dependant of the electron density, the presence of a high electron density material, such as silver metal, strongly decreases the contrast between the two organic semiconductors. As a consequence, the Janus morphology appears harder to identify with the presence of silver. However, when the contrast is high enough, the images shows that silver mainly covered the PCBM domains, consistent with the energetic mechanism driving the photodeposition process. The presence of the silver metal was formally identified by Auger analysis (Figure 4c). Two distinct areas, 1 and 2, were targeted for the Auger analysis on the sample, area 1 being silver free and area 2 deposited silver organic semiconductor nanoparticles. Several Auger elements were detected in the two spectra including sulphur (LVV transition at 130-160 eV), carbon (KLL transition at 180-290 eV) and oxygen (KLL transition at 455-530 eV), as expected for P3HT, PC61BM and F127 surfactant. However, only the area 2 revealed the presence of silver signal (MNN transition at 310-370 eV) attesting of the chemical detection of silver domains. [START_REF] Bera | Electron spectroscopic analysis of silver nanoparticles in a soda-glass matrix[END_REF][START_REF] Ambroziak | Cubic Silver Nanoparticles Fixed on TiO2 Nanotubes as Simple and Efficient Substrates for Surface Enhanced Raman Scattering[END_REF][START_REF] Ledeuil | New insights into micro/nanoscale combined probes (nanoAuger, μXPS) to characterize Ag/Au@SiO 2 core-shell assemblies[END_REF]

Conclusion

In summary, we report, for the first time, the preparation of Janus nanoparticles from organic semiconducting materials P3HT:PC61BM by a simple and one-step process, nanoprecipitation.

The conjugated materials were dissolved in THF and then precipitated in water containing a surfactant such as SDS or Pluronic F127, or without any surfactant. High resolution cryo-TEM allowed to identify this morphology which was further confirmed by STXM. This morphology is driven by a low difference between surface tensions ratios (γPCBM/Liq/γP3HT/PCBM and γP3HT/Liq/ γP3HT/PCBM) and in accordance with modelling reports. The nanoparticles absorb light from 200 to 650 nm and the PC61BM face effectively quenches the P3HT photoluminescence. Two sets of preliminary experiments were performed to reveal the potential use of these nanoparticles for photovoltaics or photocatalytic reactions. Firstly, OFETs were fabricated with P3HT:PC61BM Janus NP water-based dispersion and the mobilities measured were found to be close to that of P3HT:PC61BM OFET devices fabricated from traditional bulk heterojunction organic solutions, indicating efficient transport between the P3HT domains. These particles could be of high interest in PV as they present high exciton dissociation yield together with large charge percolation pathways provided by the Janus morphology. Secondly, we demonstrated that the irradiation of nanoparticles in the presence of a silver salt (AgNO3(aq)), could lead to the photodeposition of silver metal nanoparticles. We believe that such Janus morphology, with the two materials acting as the cathode and the anode, and in which H + or CO2 reduction can occur at one side of the nanoparticle and oxidation can take place at the other side, is a promising new candidate for photocatalysis.

Figure 1 .

 1 Figure 1. Cryo-TEM images of the nanoparticles a), b), c) and d) have been prepared from

Figure 2 .

 2 Figure 2. a) Scheme of the nanoparticle formation mechanism during nanoprecipitation,

Figure 3 .

 3 Figure 3. STXM fractional composition maps showing the concentration of P3HT (a) and PC61BM

Figure 4 .

 4 Figure 4. Schematic representation of silver photodeposition process from AgNO3 (aq),

Table 1 . P3HT:PC61BM nanoparticle dispersion characteristics.

 1

	Entry	Volume ratio	[P3HT:PC61BM] (mg.mL -1 )	Surfactant	[Surfactant] (mg.mL -1 )	[NPs] a (mg.mL -1 )	Dh b (nm)	PDI b
	1	1/8	2.0	None	-	1.00	100	0.10
	2		2.0	SDS	3.0	> 10	81	0.12
	3 4	1/4	1.0 2.0	F127	3.0	> 10 > 10	68 79	0.18 0.14
	5		5.0		0.5	> 10	131	0.08

a Final dispersion concentration used for cryo-TEM experiments; b Z-average hydrodynamic diameter and particle polydispersity obtained by DLS using cumulant analysis.

Acknowledgements

The authors thank E2S UPPA for funding the research. The PolLux end station at the Swiss Light Source synchrotron was financed by the German Minister für Bildung und Forschung (BMBF) through contracts 05K16WED and 05K19WE2. The authors acknowledge the support provided by the ANR through the WATER-PV project N°ANR-20-CE05-0002-01. The authors acknowledge the technical and scientific assistance of Sydney Microscopy & Microanalysis, the University of Sydney node of Microscopy Australia. We further thank the support of the University of Sydney Core Research Facilities. The University of Newcastle Electron Microscopy and X-ray (EMX) Unit is acknowledged for providing access to electron microscopes and associated expertise. The authors gratefully acknowledge Christophe Chassenieux from the Institute of Molecules and Macromolecules of Le Mans (IMMM, UMR 6283) for the fuitful discussions and financial support of a part of the Cryo-TEM measurements. The work at University of Tokyo has been supported by KAKENHI from JSPS (JP20H05660)

Data availability statement

The data sets generated and/or analysed during the present study are available from the corresponding author upon reasonable request.