Mohamad El-Roz
email: mohamad.elroz@ensicaen.fr.

Zeinab Haidar

Louwanda Lakiss

Joumana Toufaily

Frederic Thibault-Starzyk

L Reijnders

J Hazard

Mater

M Tashibi

C R Ngah

N Aziz

A Mansor

A Z Abdullah

L K Teong

A R Mohamed

Immobilization of TiO 2 nanoparticules on natural Luffa cylindrica fibers for photocatalytic applications

Keywords: [year], [vol], 00-00

TiO 2 /Luffa composites have been successfully prepared via a sol-gel method from the hydrolysis of a precursor of TiO 2 . The possibility to use Luffa fibers as biotemplate to self-support hierarchical TiO 2 macrostructures has been also tested with success. The photocatalysts used or prepared and the TiO 2 /Luffa composites were characterized by X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, FT-IR, and UV-visible spectroscopy. The photocatalytic activities have been investigated in the photodegradation of methanol, chosen as model molecules for VOCs in air. The reactions have been followed by IR-operando spectroscopy. TiO 2 /Luffa composites exhibited a good stability and photocatalytic activity under UV light irradiation, giving rise to a new generation of green photocatalysts, easy to shape and manufacture, for the photodegradation of organic pollutants.

Introduction

In the last few years TiO 2 has attracted much more attention due to its interesting properties as a semi-conductor: it is cheap, non toxic, photostable, resistant to photocorrosion and presents high photocatalytic activity to decompose a wide type of hazardous organic compounds that are present in air or water. Because of these notable characteristics, TiO 2 is the most well-known and frequently used catalyst in photocatalysis. Moreover, titanium dioxide nanostructures are also promising materials for various applications including photoelectronic, solar energy conversion, self-cleaning surfaces, etc. Although titanium dioxide is an ideal environmental photocatalyst, it has some drawbacks that limit its large-scale application especially when it is used in the nanosized form. For instance, the removal and recycling of the photocatalyst after the reaction process are very difficult. In addition titanium dioxide nanostructures dispersed in the reaction media could be hazardous, due to their potential inflammatory and cytotoxic effects [1]. In this context, immobilization of the photocatalysis on a specific support could be of great benefit. Several attempts have been already reported in the literature [2-22] and various techniques were successfully used to immobilize TiO 2 on different supporting materials such as SiO 2 glass beads [2], rings [3], and reactor tubular walls [4,5]; fiber-glass [6,7]; quartz [8,9]; zeolites [10,11]; perlite [12]; pumice [13]; alumina-based ceramic [14]; stainless steel [15,16]; aluminum [17]; polymeric membranes [18][19][20]; etc. Natural fibers were also found of great interest as supporting materials, and cotton conveniently adapted inside the 45 photoreactors [21][22][23]. These fibers are inexpensive, abundant, environmentally benign and renewable resources. Recently we have used Luffa sponge (aegyptica or cylindrica) to support freeorganic template zeolite materials, with high efficiency. It is a tropical annual climber vine plant (family Cucurbitaceae), with 50 fruits possessing a net-like fibrous vascular system (Luffa sponges). The struts of this natural sponge are characterized by microcellular architecture with continuous hollow microchannels (macropores with diameter of 10-20 m) which allow a good supporting of inorganic materials (Fig. 1). The network of the 55 Luffa fibers provides a tridimensional form for the support that allows a good penetration of the light and decreases the density of the fibers. Besides, the fibers nature makes the shaping of filters in different geometry and form easier. In addition, these fibers present a high stability in the synthesis media and support the 60 relatively high temperature (<170°C) and alkalinity of the synthesis media. Luffa sponges have also been applied as cell carriers in bioreactors [24], scaffolds for tissue engineering [25], for the development of biofiber-reinforced composites [26] and as biotemplate to self-support hierarchical zeolite macrostructures 65 for bio-inspired structured catalytic reactors [27]. Since researches on immobilized TiO 2 photocatalysts were mostly focused on the use of the commercial TiO 2 P25 or anatase phase, we focused on supporting TiO 2 anatase nanoparticles, by sol-gel method, on Luffa sponges as natural supports. The possibility to 70 use Luffa fibers as biotemplate to self-support hierarchical TiO 2 macrostructures will also be presented in this paper. The resulting TiO 2 /Luffa composite has been fully characterized and

Experimental part

Synthesis

Chemical treatment of Luffa fibers

Luffa fibers were obtained from a local specialty shop. They were washed with acetone in an ultrasonic bath at room temperature for 7 minutes. The fibers were then rinsed with water and dried at 60°C. After drying, the fibers were then treated in a sodium hydroxide solution (NaOH, 0.1M) at 80°C for 2 h. This treatment was done three times, in order to activate the cellulose fibers and remove the other constituents present between the fibers. After each step the fibers were filtered and washed with distilled water until reaching neutral pH.

Synthesis of TiO 2 photocatalysts supported on Luffa fibers

TiO 2 nanocrystals were prepared via a sol-gel process followed by hydrothermal treatment. Titanium (IV)-Etoxide (Ti(OEt) 4 , TTE 33% Alpha Aesar) was used as titanium source for the preparation of TiO 2 photocatalysts. Absolute ethanol (99%) was used as solvent. The temperature and synthesis time were optimized prior to the preparation of the composites. In a typical procedure, the reaction was carried out with the following composition: 10 TTE/ 45 C 2 H 5 OH/ 45 H 2 O vol.%. The treated fibers were first dispersed in a mixture of water and ethanol (50/50 vol.%; 90 ml). Then TTE has been added drop-wise to the treated fibers (m~500 mg) under vigorous stirring at ambient temperature. A white suspension was obtained. The resulting mixture (suspension + Luffa) was kept under stirring for 1 h. Then, the mixture was transferred in a Teflon-lined stainless steel autoclave and heated at different temperature (60-100 • C) from 1 to 48 h. After cooling down to room temperature, the TiO 2 /Luffa fibers were washed for 5-10 minutes in an ultrasonic bath in order to remove the weakly suspended particles. In order to show the possibility to use the Luffa support as biotemplate for hierarchical TiO 2 synthesis, a calcination of TiO 2 /Luffa composite has been performed at 500°C for 6h under air at atmospheric pressure.

Characterization

TiO 2 and TiO 2 /Luffa composites were characterized by X-ray diffraction (XRD; PANanalytical (X-Pert Pro) diffractometer with CuK1 source (=0.15406 nm, 40 kV, 30 mA)), thermal gravimetric analysis (SETARAM), Scanning Electron Microscope (SEM, Phillips CM 20) operating at 200kV), Nitrogen sorption measurements (Micromeritics ASAP 2020 micropore analyser) and by UV-Vis DR measurements (Thermoelectron evolution 500 UV-Vis spectrometer equipped with RSA-CU40 Diffuse Reflectance cell).

Photocatalytic application

The photocatalytic oxidation of methanol was followed by IR spectroscopy of the solid surface (IR-operando) and of the gas phase. TiO 2 /Luffa composites were pressed into self-supported wafers (Ø= 16 mm, m~40 mg/cm 2 ) (Fig. 1-c). IR spectra were 60 collected with a Nicolet 5700 FT-IR spectrometer (64 scans/spectrum) equipped with a MCT detector. The operando system was connected to a flow set-up. Gases were introduced into the lines (heated at 60°C) by mass flow controllers. The two gas mixtures, so called "activation" and "reaction" flows, could 65 be prepared and sent independently to the reactor cell. The "Sandwich" reactor-cell used in this study is an evolution of the operando cell which has proven its reliability over many years of operando studies. [29][30][31] It was made of a stainless steel cylinder that carries a toroidal sample holder in its centre, where the 70 catalyst self supporting wafer was placed. Tightness was obtained by Kalrez© O-rings, and the dead volume (typically defined as the residual space between each sample face and the windows) was reduced to about 0.4 ml by filling the empty space with KBr windows placed on each side of the sample holder. Analysis of 75 the surface was made possible without superposition of the gas phase signal and fluid dynamics was similar to that inside a honeycomb monolith. Gases were introduced on the sample by 1/8" OD pipe and collected on the opposite side of the sample holder. More details can be found in the following references 80 [29,31]. For this specific photocatalytic oxidation study, UV irradiation was carried out with a polychromatic light of a Xe-Hg lamp (LC8 spot light Hamamatsu, L10852, 200 W), by using a UV-light guide (A10014-50-0110) mounted at the entrance of a modified IR operando cell (Scheme S-1 in supporting 85 information) in order to establish a "homogeneous" irradiation. The intensity of the lamp was about 15 mW/cm 2 at =365 nm for a full irradiation capacity (100%) of the LC8 unit. It was difficult to calculate the intensity of the polychromatic irradiation. Therefore, the intensity values were presented in (%) of the lamp 90 capacity.

In such a configuration, at atmospheric pressure, a low partial pressure of VOC was established using a saturator at a carefully controlled temperature. The gas mixture composition was then fixed at 0.01 to 0.2 vol.% methanol, 20 vol.% O 2 in Ar and the 95 total flow was adjusted to 25 cm 3 /min. Analysis of the outlet gases was performed by means of a Nicolet 5700 FT-IR-gas spectrometer using a gas microcell. The photooxidation of methylene blue in water was also performed on TiO 2 /Luffa composite to show efficiency in dye 100 removal. Due to high absorption/adsorption capacity, photooxidation tests have been realized after absorption by using Luffa fibers as reference and the results of this part were reported in supplementary information. The photocatalytic activity was qualitatively estimated based on the color of the composites and In order to investigate the thermal stability and estimate the amount of TiO 2 recovery for the composites, thermal analyses have been performed. The samples were heated from 25 to 800 °C with a heating rate of 5 °C/min. Fig. 4 shows the thermogravimetric curves of pure TiO 2 (a), TiO 2 /Luffa composite (b) and plain Luffa (c) samples. For pure TiO 2 sample, one main weight loss of about ~8% appeared above 150 °C. This could be assigned to the desorption of water adsorbed on TiO 2 surface. An additional small weight loss occured progressively above 150 °C (insert of Fig. 4). This later could be ascribed to the dehydroxylation of TiOH groups at high temperature (150-400°C). The thermogravimetric curves of the plain Luffa fibers and TiO 2 /Luffa composites showed the same behaviour. Both were stable for below 250 °C. A weight loss appeared above this temperature, assigned to the degradation of the organic constituents of the fibers. The total weight loss observed for plain Luffa fibers was about 97.5 %. The residual 2.5 % of the weight corresponded to mineral compounds present in the fibers. For TiO 2 /Luffa composite, the total weight loss observed was ~93.9%. Based on the results obtained for plain Luffa fibers, the amount of TiO 2 deposited could be estimated to ~4% (TiO 2 (%)= 97.5-93.9=3.6%). It is noteworthy that the amount of water desorbed below 150°C was more pronounced for plain Luffa fibers than for the TiO 2 /Luffa sample. Such a result demonstrates that the plain Luffa fibers are more hydrophilic than the composites, which explains the high adsorption/absorption capacity of methylene blue by TiO 2 /Luffa (Fig. S.3, supplementary information). The reproducibility of this result has also been tested using different samples synthesized under the same conditions. The error on the TiO 2 amount was estimated below 2%. The effect of temperature on TiOH groups has also been studied by in-situ IR spectroscopy. Fig. 5 reports the IR spectra of the assynthesized TiO 2 sample under air and vacuum at different temperatures. For a temperature higher than 100 °C, a total disappearance of the band assigned to adsorbed water on TiO 2 surface at 1625 cm -1 has been observed. The broad band located at 3160 cm -1 also decreased. We assigned it to hydrogen bonding between neighbouring TiOH groups and/or to water adsorbed on TiOH groups. This decrease was due to water desorption for T<100°C and to TiOH dehydroxylation for a higher temperature 45 (TiOH … HOTi  TiOTi+H 2 O). These results are in a good agreement with the ATG results discussed above. The narrow bands at ~3720 and ~3670 cm -1 are assigned to Ti(III)OH and Ti(IV)OH bands respectively [29]. When the temperature increased (for 100°C<T<200°C), the intensity of the band at 50 3670 cm -1 decreased. This was accompanied by a low increase of the intensity of the band at 3720 cm -1 . This could be assigned to a reversible reduction of Ti(IV)OH group by adsorbed water at high temperature. In order to investigate the possibility of using Luffa fibers as biotemplate, a total combustion of the TiO 2 /Luffa composite was 60 performed at 500 °C for 6 hours under air. The SEM pictures of the calcined TiO 2 /Luffa composite show the formation of a negative replica of TiO 2 macro-microfibers Luffa sponge (TiO 2 -L) (Fig. 6). The replica resulted from TiO 2 /Luffa calcination confirms the high dispersion and uniform growth of TiO 2 on the The TiO 2 /Luffa composites and TiO 2 -L were also characterized by nitrogen sorption. For comparison, the TiO 2 powder prepared under the same conditions and plain Luffa fibers were also characterized (Fig. 7). The porous volume and the specific surface area are reported in table S-1 (see SI). The TiO 2 -L and the TiO 2 powder sample both display a type IV isotherm with hysteresis at relatively high pressure. The specific surface area of the 10 TiO 2 /Luffa composites is about 16 m 2 /g while that of TiO 2 powder synthesized under the same condition is 235 m 2 /g. The specific surface area of the plain Luffa fibres has been found lower than 1 m 2 /g (Table S-1). Such a result demonstrates that the 16 m 2 /g founded for TiO 2 /Luffa composite is related to the 15 surface area of the microporous TiO 2 particles immobilized on the Luffa. Taking into account the content of TiO 2 in TiO 2 /Luffa composite (~4%; see TG results), the specific surface area of TiO 2 supported on the Luffa fibres could be estimated to 400 m 2 /g (=16/0.04 m 2 /g). It is much higher than that of unsupported 20 and as-synthesized TiO 2 samples. Such a result confirms the high dispersion of TiO 2 particles on the Luffa fibers. It should be noted that several TiO 2 /Luffa samples have been prepared and characterized by nitrogen sorption to test the reproducibility. The results are similar and the error is estimated to ~3%. For TiO 2 -L, a significant decrease of the surface area could be observed in comparison with the as-synthesized TiO 2 . This decrease is explained by the agglomeration of TiO 2 nanoparticles after calcination. As a result the band gap energy (Eg) is found to be equal to 2.99 eV for TiO 2 -L, 3.07 eV for TiO 2 -P25 and 3.22 eV for TiO 2 pure anatase. Indeed, TiO 2 P25 is a mixture of 80% anatase and 20% rutile. This explains the low Eg compared to TiO 2 -anatase. On the 50 other hand, TiO 2 -L is a pure anatase as confirmed by XRD, which is contradictory with the Eg found. This result could be assigned to more defects in the TiO 2 structure (Ti(III), TiOH...) than for samples prepared without fibres.

photocatalytic applications

The newly elaborated TiO 2 /Luffa composites have first been tested in water purification. Methylene blue was used as a model molecule for dyes in water (see experimental part). Due to the different possible pathways of MB photodegradation (direct photolysis and/or photodegradation on TiO 2 surface) [32] and to the difficulty to have a quantitative study for the photoactivity of the composites in water, the results for water purification were shown as a preliminary qualitative analysis in the supplementary ). The photocatalytic activity of the replica TiO 2 -L samples has been also investigated and the results will be discussed in a separate paper. Herein we will discuss the photocatalytic activity of the TiO 2 /Luffa composite in the photodegradation of methanol as a model molecule for volatile organic compounds (VOCs) in air.

The photocatalytic degradation of methanol has been carried out under operando conditions. Fig. 9 presents the evolution of IR spectra of TiO 2 /Luffa surface during methanol photooxidation. It is impossible to follow the evolution of CH vibration band due to the saturation of the intensity in this region. As shown in this figure, only the band situated at 5370-4920 cm -1 , assigned to () H 2 O vibration mode disappears after irradiation. No modification of the bands between 5000 and 3200 cm -1 is observed. In addition a low amount of CO 2 is detected in the first few minutes of irradiation under dry air. This amount is assigned to the degradation of impurities adsorbed on TiO 2 /Luffa surface. These results show the high stability of the support under irradiation.

Methanol quantification has been performed from the IR spectra of the gas phase (Fig. 10) using the area of the band at 1090-950 cm -1 assigned to the (C-O) vibration mode of methanol. Methanol conversion has been estimated with the following formula:

Conversion (%) = (A 0 -A t )/A 0 *100 with:

A 0 = the band area of MeOH (in the gas phase) before photooxidation.

A t = the band area of MeOH during photooxidation at time "t".

The selectivity of MeOH transformation to CO 2 has been calculated using the band area for CO 2 measured during a complete and total photocombustion of 400 ppm of MeOH under high irradiation intensity (I 0 =100%), which corresponds to the full capacity of the lamp. The photocombustion is then 100 % selective (CO 2 production) and the observed CO 2 -band area corresponds to ~400 ppm of CO 2 . This result has been used for estimating CO 2 concentration during the photooxidation of MeOH under different conditions. The CO 2 -selectivity has been calculated as follows: The methanol photodegradation rate (V MeOH ) has also been calculated. It corresponds to the amount of methanol converted (n MeOH ) per second per gram of photocatalyst (g cat ). V MeOH has been calculated with the following formula: V MeOH = [n MeOH-converted (mmol)]/[m cat (g) x time (s)] (mmol/s/g cat ).

75

Due to the limitation of the irradiation on the external surface of TiO 2 /Luffa pellet, the V MeOH calculated are limit values. The influence of methanol concentration has also been studied.

The results are reported in Fig. 10 and shortlisted in Table 1. The new bands that appear during the photooxidation are assigned to 80 CO 2 (2400-2200 cm -1 ) and -C=O of carbonyl species (1820-1670 cm -1 ). As reported in previous works [32,34] an increase of concentration leads to a decrease of the CO 2 -selectivity of the reaction. It is important to note that the increase of the concentration increases the V MeOH of the photodegradation 85 reaction. This result could be assigned to the interaction of methanol in the gas phase with the active species adsorbed/formed on the photocatalyst surface. Table 1 Reactivity, selectivity and rate of methanol photooxidation reactions under polychromatic irradiation for different methanol concentrations using TiO2/Luffa composite as photocatalysts (Flow= 25 10 cm 3 /min, I0=25%, mpellet=90 mg mTiO2~ 3mg).(*) Values founded using TiO2-P25 as photocatalyst (mcat=20 mg) in the same conditions.

[MeOH] (ppm) A self supported TiO 2 -P25 has been used as reference. Contrarily to V MeOH which takes into account the weight of photocatalyst used, methanol conversion and CO 2 -selectivety values could not be compared directly in the case of TiO 2 /Luffa and TiO 2 -P25 (Table 1) due to the different content (or amount) of TiO 2 used.

In the case of TiO 2 /Luffa composite, the amount of TiO 2 is ~3mg (the weight of the TiO 2 /Luffa pellet, ~90mg with TiO 2 content 20 ~4%) while 20 mg of pure TiO 2 -P25 has been used to prepare the pellet. Therefore, the comparison of the photocatalytic activity of TiO 2 /Luffa with that of TiO 2 -P25 only aims at having an idea about the activity of the composite. This comparison could not be quantitative due to the different nature of the two photocatalysts 25 (e.g the internal shading effect in TiO 2 /Luffa pellet is much higher than in TiO 2 -P25 pellet). A high activity is observed with TiO 2 present on the TiO 2 /Luffa composite, with V MeOH values higher than 2.5 mmol/s/g cat . It is ~0.78 mmol/s/g cat for a total methanol mineralisation (100% 30 selectivity). The increase of the lamp intensity increases methanol conversion and CO 2 -selectivity of the photooxidation reaction.

The results are presented in table S-2 in SI. When the intensity of the lamp capacity is higher than 25% (which correspond to ~2.5 mW/cm 2 at 366nm), the conversion of 1900 ppm of methanol 35 reaches its maximum (~74%) with total methanol mineralisation and V MeOH ~3.8 mmol/s/g cat . In comparison, V MeOH was 3 to 4 times higher on TiO 2 /Luffa composite than on TiO 2 -P25 in the same reaction conditions (Table 1). These high values could be assigned to the high TiO 2 dispersion and to the high surface area 40 of TiO 2 on Luffa fibers, which increase the diffusion of methanol and the accessibility of active sites (S BET (TiO 2 in TiO 2 /Luffa composite)/ S BET (TiO 2 -P25)~7) .

Conclusion

TiO 2 nanoparticles were successfully immobilized on a support of 45 natural Luffa fibers by hydrothermal sol gel treatment. The net microstructures and hydroxyl groups of Luffa fibers provided a uniform dispersion of TiO 2 nanoparticles and a strong and complete recovery of the surface. The resulting TiO 2 /Luffa composites showed high stability and efficiency in the 50 photodegradation of methanol, model for VOCs in air. They also exhibited efficient removal of methylene blue from water. The photodegradation rate of methanol (V MeOH in mmol/s/g cat ) on the new elaborated TiO 2 /Luffa composite was 3 to 4 times higher than that on self supported TiO 2 -P25 used as reference. These 55 results could be explained by the high and uniform dispersion (high specific area) of TiO 2 supported on the Luffa support. This work showed that Luffa fibers are an ideal biosupport for photocatalytic applications of TiO 2 . The non compact form, tridimensional structure, mechanical and chemical stability and 60 low price of the newly elaborated composites make them very promising as green photocatalysts for air and/or water purification.

Associated content

The supporting information file contains:

-1 scheme for the sandwich reactor-IR cell modified for UV catalysis study.

-2 tables describing the different characteristics of the photocatalysts used in this work and their photocatalytic activity

Fig. 1

 1 Fig.1 Image of Luffa fruit (a) and TiO2/ Luffa composites (b-d): Face (c) and side (d) view of the pellet.

3 .

 3 Results and discussion3.1. Characterization of TiO 2 /Luffa compositesPrior to the preparation of the TiO 2 /Luffa composites, the sol-gel synthesis conditions of TiO 2 have been first optimized. Two parameters were considered: the synthesis time and the temperature. For further details, readers are invited to see the supporting information file. The synthesis of the TiO 2 /Luffa composites has been performed at 100 °C for 48 hours. The Xray diffraction pattern of the resulting TiO 2 /Luffa composite is reported in Fig.2. It shows in addition to the Bragg reflexions of the cellulose (L), the main constituent of the fibers, the Bragg reflections of the anatase TiO 2 phase (A). For comparison, the Xray diffraction pattern of the anatase phase and the plain Luffa fibers are also reported in this figure. The powder that has been recovered from the bottom of the autoclave after synthesis was also characterized by XRD. It shows the Bragg reflections of the anatase type phase. Such a result confirms the high cristallinity and purity of the composites prepared.

Fig. 2

 2 Fig.2 X-ray diffraction patterns for TiO2 samples (a) standard, (b) TiO2 powder recovered after the synthesis, (c) TiO2 deposited on Luffa fibers 25

Fig. 3 Fig. 3 4 |

 334 Fig.3shows the SEM images of the plain Luffa fibers (a-c) and TiO 2 /Luffa composite after ultrasonic treatment (d-f). As seen in this figure, the microfibers structure is completely preserved after the hydrothermal treatment and TiO 2 nanoparticles are uniformly30

Fig. 4

 4 Fig.4 Thermogravimetric curves of: (a) as-synthesized TiO2, (b) TiO2/Luffa and (c) Luffa. Insert: full scale of the thermogravimetric curves as-synthesized TiO2.

Fig. 5

 5 Fig.5 IR spectra of as-synthesized TiO2 at RT under air (a) and under vacuum (b-h) at RT 50°C (b), 75°C (d), 125°C (e), 200°C (f), 300°C(g) and 350°C (h).

65

  Luffa fibers. Moreover, it demonstrates the possibility to use Luffa fibers as a biotemplate to self-support hierarchical TiO 2 macrostructures. According to the XRD results, the negative replica TiO 2 -L is a pure anatase. It is noteworthy that the size of the resulting TiO 2 particles significantly increased in comparison 70 with TiO 2 /Luffa due to the aggregation of the particles during the calcination. This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00-00 | 5

Fig. 6

 6 Fig.6 Image (a) and SEM pictures of replica TiO2 Luffa sponges (TiO2-L) (b-e).

30 Fig. 7

 307 Fig.7 Nitrogen sorption isotherms adsorption (close symbols) and desorption (open symbols) at 77 K for : (a) Luffa fibers, (b) TiO₂/luffa composites, (c) TiO₂-L and (d) TiO2 powder (the TiO₂ powder recovered after the synthesis).It is difficult to investigate the UV-visible absorption of 35

Fig. 8

 8 Fig.8UV-vis spectra of (a) TiO2-P25, (b) TiO2-L and (c) TiO2-anatase.

  information part. The reason to include this part is to highlight the high capacity of the TiO 2 /Luffa composite in the removal of dyes from water as show in Fig. S.3. The irradiation of the filter recovered after purification shows an important color modification of the TiO 2 /Luffa composite from dark blue to light green which is not the case for plain Luffa fibers (Fig.S.4

Fig. 9

 9 Fig.9Evolution of the IR spectra of TiO2/Luffa surface during methanol photooxidation under operando conditions. (Flow= 25 cm 3 /min, MeOH/O2/Ar 400ppm/20%/79.99%, I0=25% ~2.5 mW/cm 2 at 366nm).

Fig. 10 A

 10 Fig.10 A) Evolution of the IR spectra of the gas phase during the photooxidation of methanol at different concentrations on TiO2/Luffa composite. (Flow= 25cm 3 /min, I0=25%). B) IR spectra of the gas phase before UV-irradiation of TiO2/Luffa composite pellet, at different 5

  70 under different light intensities. -Additional information related to the synthesis procedure (Figs. S.1 and S.2) and the capacity of the composites for the removal


Caroline Desombre
email: caroline.desombre@espe-lnf.fr.

Mathilde Lamotte

Mickaël Jury

French Teachers' General Attitude Toward Inclusion: The Indirect Effect of Teacher Efficacy

Keywords: Teacher efficacy, mainstream education, special educational needs, attitude toward inclusion, general teachers

French Teachers' General Attitude Toward Inclusion: The Indirect Effect of Teacher Efficacy

To promote diversity among schoolchildren, most European countries have legislated for the development of inclusive practices in their education system [START_REF] Ferguson | International trends in inclusive education: The continuing challenge to teach each one and everyone[END_REF][START_REF] Meijer | Special needs education in Europe: Inclusive policies and practices[END_REF][START_REF] Thomazet | L'intégration a des limites, pas l'école inclusive! [Integration has limits, not the inclusive school![END_REF]. These political measures aim to counteract the social exclusion of some children due to their ethnicity, religiosity, social status, gender, abilities, and notably those with Special Educational Needs (SEN, i.e., students who face learning problems or disabilities that make learning more difficult for them than for same-aged children without learning problems or disabilities). However, implementing such policy remains difficult [START_REF] Ferguson | International trends in inclusive education: The continuing challenge to teach each one and everyone[END_REF] and teachers' attitude toward inclusion could notably act as a barrier (De Boer, Spijl, & Minnaert, 2011). The purpose of the present paper is to specifically examine why general teachers (i.e., those who teach in mainstream education), in comparison with special education teachers (i.e., teachers who benefit from a specific training and teach students with SEN in mainstream or special education), are less favorable toward inclusion.

Based on previous research, we notably argue that general teachers' low sense of efficacy would prevent them from endorsing positive attitude toward inclusion. Such a hypothesis will be examined in a French context in which the inclusion of students with SEN is still particularly disputed (see [START_REF] Ebersold | Ecole inclusive pour les élèves en situation de handicap. Accessibilité, réussite scolaire et parcours individuels[END_REF][START_REF] Plaisance | Integration or inclusion[END_REF].

Teachers' Attitude Toward Inclusion

The World Conference on Special Needs Education in Salamanca defined the basis for inclusion [START_REF] Vislie | From integration to inclusion: Focusing global trends and changes in the western European societies[END_REF]. According to the Salamanca Declaration (United Nations Educational, Scientific and Cultural Organisation, 1994, p. ix), "regular schools with this inclusive orientation are the most effective means of combating discriminatory attitudes, creating welcoming communities, building an inclusive society and achieving education for all; moreover, they provide an effective education to the majority of children and improve the efficiency and ultimately the cost-effectiveness of the entire education". In other words, inclusion seems to promote positive attitude toward students with SEN and increase students' achievement (for a meta-analysis, see [START_REF] Ruijs | Effects of inclusion on students with and without special educational needs reviewed[END_REF].

In inclusive settings, students with SEN receive their entire academic curriculum in mainstream education, enrolled with students of their age groups. In such a system, schoolteachers are asked to meet the needs of all learners, that is, they should adapt their practices in order to help every student, including those with SEN, to reach his/her full potential. Therefore, the success of inclusion notably depends on teachers and their attitude toward inclusion [START_REF] Elliott | The effect of teachers' attitude toward inclusion on the practice and success levels of children with and without disabilities in physical education[END_REF][START_REF] Leatherman | Teachers' attitudes toward inclusion: Factors influencing classroom practice[END_REF]. Nonetheless, even if teachers' attitude toward inclusion was positive [START_REF] Scruggs | Teacher perceptions of mainstreaming/inclusion, 1958-1995: A research synthesis[END_REF], it does not mean that teachers are willing to accept "full inclusion" [START_REF] Avramidis | Teachers' attitudes toward integration/inclusion: A review of the literature[END_REF], much less agree to include a student with SEN within their own classroom [START_REF]General educators' attitudes toward students with mild disabilities and their use of instructional strategies: Implications for training[END_REF][START_REF] Ward | A question of attitudes: integrating children with disabilities into regular classrooms[END_REF].

A range of variables has been found to influence attitude toward inclusion (for reviews, see [START_REF] Avramidis | Teachers' attitudes toward integration/inclusion: A review of the literature[END_REF][START_REF] De Boer | Regular primary school teachers' attitudes towards inclusive education: A review of the literature[END_REF]. Thus, teachers' attitude seems to depend on the extent to which instructional practices should be modified to accommodate students' curricula [START_REF] Center | Teachers' attitudes toward the integration of disabled children into regular schools[END_REF] as well as the nature and severity of special educational needs. More precisely, teachers expect that students with emotional and behavioral difficulties as well as those with profound and multiple learning difficulties are the most difficult to include [START_REF] Avramidis | Student teachers' attitudes toward the inclusion of children with special educational needs in the ordinary school[END_REF][START_REF] Avramidis | Teachers' attitudes toward integration/inclusion: A review of the literature[END_REF]. In addition, attitude also varies as a function of educational policy in the country [START_REF] Savolainen | Understanding teachers' attitudes and self-efficacy in inclusive education: implications for pre-service and in-service teacher education[END_REF][START_REF] Takala | Inclusion seen by student teachers in special education: Differences among Finnish, Norwegian and Swedish students[END_REF], school resources or support for inclusive practices, including from the board [START_REF] Avramidis | Teachers' attitudes toward integration/inclusion: A review of the literature[END_REF][START_REF] Urton | Attitudes towards inclusion and self-efficacy of principals and teachers[END_REF]. Finally, teachers' attitude also appears to depend on teachers' characteristics. For examples, women and younger teachersin terms of age and experiences -have more favorable attitude toward inclusion (Alghazo & Naagar Gad, 2004[START_REF] Avramidis | Student teachers' attitudes toward the inclusion of children with special educational needs in the ordinary school[END_REF].

Concerning teachers' characteristics, literature has also identified a persistent difference in teachers' attitude based on their position. More precisely, and as evoked above, research has demonstrated that general teachers usually have less favorable attitude toward inclusion than their special education counterparts [START_REF] Mchatton | Purposeful preparation: Longitudinally exploring inclusion attitudes of general and special education pre-service teachers[END_REF][START_REF] Minke | Teachers' experiences with inclusive classrooms: Implications for special education reform[END_REF][START_REF] Shippen | Preservice teachers' perceptions of including students with disabilities[END_REF][START_REF] Tournaki | Do graduate teacher education programs change teachers' attitudes toward inclusion and efficacy beliefs[END_REF]. If several works of research have examined different ways to reduce this difference (see for an example [START_REF] Tournaki | Do graduate teacher education programs change teachers' attitudes toward inclusion and efficacy beliefs[END_REF], empirical research that specifically examines a psychological mechanism sustaining this difference has yet to be carried out. In the present paper, we propose to test teacher efficacy as a potential mediator of attitude toward inclusion.

Teacher Efficacy

Self-efficacy is defined as "beliefs in one's capabilities to organize and execute the courses of action required to produce given attainments" (Bandura, 1997, p. 3). According to [START_REF] Bandura | Self-efficacy: The exercise of control[END_REF], self-efficacy determines the organization and regulation of behavior. It leads people to choose activities that will enhance the acquisition of knowledge and skills. In education, teacher efficacy refers to "teachers' belief or conviction that they can influence how well students learn, even those who may be considered difficult or unmotivated" (Guskey & Passaro, 1994, p. 628). Several researchers point out the role of self-efficacy beliefs in engagement and choice of goals. In a school context, teachers with high efficacy are more engaged and persist longer in assisting students with learning difficulties [START_REF] Hoy | Teachers' self-efficacy beliefs[END_REF]. Efficacy also influences teaching behaviors and the use of didactic innovations in classrooms [START_REF] Holzberger | How teachers' self-efficacy is related to instructional quality: A longitudinal analysis[END_REF][START_REF] Schiefele | Teacher interests, mastery goals, and self-efficacy as predictors of instructional practices and student motivation[END_REF] for a review see [START_REF] Zee | Teacher self-efficacy and its effects on classroom processes, student academic adjustment, and teacher well-being: A synthesis of 40 years of research[END_REF]. [START_REF] Bandura | Self-efficacy: The exercise of control[END_REF] argued that one's sense of self-efficacy depends on four sources: mastery experiences, vicarious experiences, social persuasion, and somatic and emotional states (see also [START_REF] Fernandez | Overview of research on teacher self-efficacy in social cognitive perspective[END_REF]Morris, Uscher, & Chen, 2016). Mastery experiences are defined as a sense of satisfaction with one's past successful teaching experiences. Vicarious experiences are represented by models of success or failure observed in the actions of other teachers.

Social persuasion refers to self-efficacy judgments based on verbal stimulation of other important

people such as colleagues, supervisors and managers, as well as affective and emotional states represent the control of the activation level (i.e., fatigue, stress, anxiety, tension, mood), which in turn can directly affect judgments about teaching ability [START_REF] Fernandez | Overview of research on teacher self-efficacy in social cognitive perspective[END_REF].

In contrast, research has also identified that certain teacher-related parameters are usually associated with teacher efficacy. Thus, for examples, teaching experience and grade taught have been identified as antecedents of teacher efficacy (see [START_REF] Klassen | Effects on teachers' self-efficacy and job satisfaction: Teacher gender, years of experience, and job stress[END_REF]. As for teachers' attitude toward inclusion, research has also illustrated that teachers' position play a role in their sense of efficacy. Indeed, Buell and her colleagues (Buell, Hallam, Gamel-Mccormic, & Scheer, 1999) have demonstrated that special education teachers have a higher sense of efficacy than general teachers.

In the same way, [START_REF] Leyser | Changes in self-efficacy of prospective special and general education teachers: Implication for inclusive education[END_REF] illustrated that pre-service teachers majoring in special education already have a higher sense of efficacy than those majoring in general education.

As a result, and due to the consistent positive link observed between teacher efficacy and attitude toward inclusion [START_REF] Savolainen | Understanding teachers' attitudes and self-efficacy in inclusive education: implications for pre-service and in-service teacher education[END_REF]Soodak, Podell, & Lehmann, 1998;[START_REF] Urton | Attitudes towards inclusion and self-efficacy of principals and teachers[END_REF][START_REF] Weisel | School climate, sense of efficacy and Israeli teachers' attitudes toward inclusion of students with special needs[END_REF][START_REF] Yada | Japanese in-service teachers' attitudes toward inclusive education and self-efficacy for inclusive practices[END_REF], it seems reasonable to expect that general teachers' less favorable attitude toward inclusion in comparison with special education teachers [START_REF] Mchatton | Purposeful preparation: Longitudinally exploring inclusion attitudes of general and special education pre-service teachers[END_REF][START_REF] Minke | Teachers' experiences with inclusive classrooms: Implications for special education reform[END_REF][START_REF] Shippen | Preservice teachers' perceptions of including students with disabilities[END_REF][START_REF] Tournaki | Do graduate teacher education programs change teachers' attitudes toward inclusion and efficacy beliefs[END_REF] would be explained by the difference in efficacy [START_REF] Buell | A survey of general and special education teachers' perceptions and inservice needs concerning inclusion[END_REF][START_REF] Leyser | Changes in self-efficacy of prospective special and general education teachers: Implication for inclusive education[END_REF]. A correlational study was conducted in France in order to examine this hypothesis.

Inclusion in France

In France, the inclusion of students with SEN has been mandatory since 2005 (LOI n°2005-102) but only fully went into effect in 2013 (LOI n°2013-595). As a result, the current trends are towards more inclusive education (Desombre, 2009) and the number of students with SEN included in mainstream education have consistently increased over the last years (e.g., this number grew by 7.5% last year to reach a total of 300,815 included students, French Ministry of Education, 2017). However, as in others countries, inclusion faces barriers and general teachers continue to express concerns regarding the inclusion of students with SEN. Lack of training is one of the most frequently invoked reasons by general teachers to justify their attitude [START_REF] Rattaz | La scolarisation des enfants avec Troubles du spectre autistique (TSA) en France: l'expérience d'enseignants en classe ordinaire et spécialisée. [Students' with Autisitc Spectrum Disorders schooling in France: General and Special education teachers' experiences[END_REF]. Indeed, it should be acknowledged that until recently in France, training on instructing students with SEN was not a mandatory part of the 2-year teaching curriculum. Conversely, to become a special education teacher, general teachers had to pursue a 400-hour training program exclusively dedicated to inclusive behaviors (e.g., designing and using instructional and curricular adaptations). Since training is particularly linked to teacher efficacy [START_REF] Buell | A survey of general and special education teachers' perceptions and inservice needs concerning inclusion[END_REF][START_REF] Leyser | Changes in self-efficacy of prospective special and general education teachers: Implication for inclusive education[END_REF], we believe that such a discrepancy between general and special education teachers is particularly likely to explain French general teachers' attitude toward inclusion. Therefore, identifying a mechanism sustaining the obstacles to inclusion could be particularly helpful in furthering develop tools to overcome these barriers in France and throughout the world.

Method

Participants.

Five hundred and fifty-four teachers from three different areas of France participated voluntarily in this study. The sample included 113 men and 441 women with a mean age of 41.12 years (SD = 9.38). Four hundred and one participants were general teachers and 153 participants were special education teachers. Three hundred and one participants taught in elementary schools, and 253 taught post-elementary grades (middle school, high school and university). Overall, participants possessed a mean experience of 16.21 years (SD = 9.71) in their job.

General teachers were mostly women (i.e., 80.04%) who taught at elementary schools (i.e., 58.60%). Special education teachers were also mostly women (i.e., 78.43%) who taught primarily at post-elementary levels (i.e., 56.86%). General and special education teachers did not differ in terms of age or teaching experience (all ts < 1).

Material.

Teacher efficacy. The 15-item questionnaire developed by [START_REF] Gibson | Teacher efficacy: A construct validation[END_REF] validated in French by [START_REF] Dussault | L'échelle d'autoefficacité des enseignants: Validation canadienne-française du Teacher efficacy scale [The teachers self-efficacy scale: Canadian-French validation of the teacher efficacy scale[END_REF] was submitted to participants in order to assess their efficacy as teachers. Participants also indicated the extent to which they agreed with the items on a 5-point scale from 1, "Totally disagree", to 5, "Totally agree". Responses were projected across a measure of general efficacy and a measure of personal efficacy. Since the latter directly measured teacher's beliefs regarding his or her practices (e.g., "When a student faces difficulties in a task, I am usually able to adapt this task to his level of competence", "When students' grades improve, it is usually because I have found more efficient teaching practices"), this section of the scale was used as the measure of teacher efficacy. If ten items usually composed this measure, it should be noted that for a reliability reason, nine items were finally retained here (i.e., item #15 was excluded) to compute the mean score ( = .74, M = 3.48, SD = 0.52). However, replication of the analyses with the 10-item score did not change the results.

Attitude toward inclusion.

Participants completed a tool devised by [START_REF] Mahat | The development of a psychometrically-sound instrument to measure teachers' multidimensional attitudes toward inclusive education[END_REF]. This 18item scale assesses teachers' attitude toward inclusion (e.g., " I believe that an inclusive school is one that permits academic progression of all students regardless of their ability.", "I get irritated when I am unable to understand students with a disability.") on a 5-point scale from 1, "Totally disagree", to 5, "Totally agree". Reliability analysis was satisfactory ( = .88) and a mean score was computed (M = 3.90, SD = 0.61). Means, standard deviations and correlations between variables are displayed in Table 1. Note: Position is coded -0.5 for general teacher and +0.5 for special education teacher. Level of teaching is coded -0.5 for elementary school and +0.5 for above elementary. Gender is coded -0.5 for male and +0.5 for female. t p < .10, * p < .05, *** p < .001

Procedure.

Participants were invited by email to complete an online version of the questionnaire during the spring semester of the 2016-2017 school year. Participants were contacted through different national teachers' associations, the center for teacher training (i.e., "Ecole Supérieure du Professorat et de l'Education") as well as various education authorities (e.g., at a local and regional level).

Participants came from three different areas of France known to be representative of French diversity in terms of population density, economic activities and number of students with SEN. No information was collected regarding participants' geographical origin (e.g., neither school, nor city of origin).

The email sent out informed participants about the study's purpose as well as the way in which it would be conducted. Afterward, participants were invited to give their consent. At this time, they were informed that their participation was voluntary, that they could quit the study without consequences and that they would not receive any financial compensation for their participation. Once consent was given, participants were asked to fill in the measures of teacher's efficacy and attitude toward inclusion. At the end of the questionnaire, they completed demographic information and received more detailed information regarding the purpose of the study.

Statistical analysis.

The purpose of the present paper was to test the hypothesis that general teachers were less favorable toward inclusion than special education teachers because they experienced a lower sense of efficacy than special education teachers. Therefore, analyses of mediation were conducted following the guidelines provided by [START_REF] Preacher | SPSS and SAS procedures for estimating indirect effects in simple mediation models[END_REF]2008). More precisely, the confidence interval of the indirect effect (i.e., the mediating effect of teacher efficacy) was estimated following a bootstrapping method with a 5,000 bootstrap resamples. Such a method is particularly recommended when the presence of an indirect effect is tested [START_REF] Hayes | Beyond Baron and Kenny: Statistical mediation analysis in the new millennium[END_REF]. In the statistical model, teacher's position was contrast coded: -0.5 for general teachers and +0.5 for special education teachers (see [START_REF] Davis | Contrast coding in multiple regression analysis: Strengths, weaknesses, and utility of popular coding structures[END_REF].

In addition, since age, gender and teaching experiences are known to influence attitude toward inclusion in literature, preliminary analyses were conducted while controlling for the influence of these parameters. In said analyses, attitude toward inclusion and teacher efficacy were regressed on a model including teacher's position, age, gender (coded -0.5 for men and +0.5 for women), teaching experiences and teaching level (coded -0.5 for elementary schools and +0.5 for above elementary schools).

Finally, it is worth noting that in this research, no manipulations nor data exclusions were used. All variables analyzed are reported, and all data were collected before any analyses were conducted. All material and data can be accessed at: https://osf.io/fe4t7/.

Results

Preliminary analysis. As indicated above, preliminary analyses on attitude toward inclusion and teacher efficacy were conducted.

Regarding attitude, the overall model was significant, F(5, 532) = 14.99, p < .001, R 2 = .12, and the analysis revealed that teacher's position was the only significant predictor ( = . Regarding teacher efficacy, the overall model was also significant, F(5, 532) = 8.30, p < .001, R 2 = .07, and the analysis also indicated that teacher's position was the only significant predictor ( = .24, SE = .04, p < .001, 95% CIs [.16, .32]). As previously, neither age ( = .03, SE = .09, 95%

CIs [-.15, .21]), gender ( = -.00, SE = .04, 95% CIs [-.08, .08]), teaching experience ( = .07, SE = .09, 95% CIs [-.11, .25]), nor teaching level ( = .02, SE = .04, p = .59, 95% CIs [-.06, .10]) was related to teacher efficacy (all ps > .45). As a consequence, these parameters were not retained in the final models.

Main analysis. Firstly, results indicated that teachers' position predicted attitude toward inclusion,  = .34, SE = .04, t(552) = 8.55, p < .001, 95% CIs [.26, .42], R 2 = .12; General teachers (M = 3.77, SE = .03) expressed less favorable attitude toward inclusion than special education teachers (M = 4.24, SE = .05). Secondly, as expected, teachers' position predicted teacher efficacy,  = .25, SE = .04, t(552) = 6.05, p < .001, 95% CIs [.16, .33], R 2 = .06; General teachers (M = 3.40, SE = .03) expressed less confidence toward their teaching abilities than special education teachers (M = 3.69, SE = .04). Finally, teacher efficacy was positively related to attitude toward inclusion,  = .43, SE = .04, t(552) = 11.06, p < .001, 95% CIs [.35, .50], R 2 = .18; The more confident participants were about their teaching abilities, the more favorable they were to inclusion.

Results of the mediation analysis confirmed the indirect effect of teacher efficacy on the relationship between teachers' position and attitude toward inclusion,  = .09, 95% CIs [.05; .13]. In other words, special education teachers expressed more favorable attitude toward inclusion compared to general teachers, partly due to their higher perceived efficacy. Nonetheless, it should be noted that the direct effect of teachers' position on attitude remained significant,  = .25, SE = .04, t(551) = 6.56, p < .001, 95% CIs [.17, .32]. The results of the mediation analysis are displayed in Figure 1.

Two additional pieces of information should be noted. First, the instrument used here distinguishes between the three components of attitude (i.e., cognition, emotion and behavior).

However, since no hypotheses were formulated on these distinct dimensions, analyses were conducted on the general attitudinal score. For the sake of transparency, it is worth noting that replicating the analysis on each component separately showed the same results as those for the general attitudinal score. Secondly, due to unequal sample sizes, additional analyses using the "wec" package for R (te [START_REF] Te Grotenhuis | When size matters: advantages of weighted effect coding in observational studies[END_REF] and Welch t-tests (see [START_REF] Delacre | Why psychologists should by default use Welch's t-test instead of Student's t-test[END_REF] were conducted in order to avoid misinterpreting the findings. Results were unchanged and confirmed that teacher's position is associated with attitude toward inclusion (p < .001) and teacher efficacy (p < .001).

Note. Position is coded -0.5 for regular teachers and +0.5 for special education teachers. * p < .001

Discussion

The inclusion of students with SEN in mainstream education is a challenge in current education [START_REF] Ferguson | International trends in inclusive education: The continuing challenge to teach each one and everyone[END_REF]. Among the identified barriers, general teachers' attitude toward inclusion has received a great deal of attention in literature [START_REF] Avramidis | Teachers' attitudes toward integration/inclusion: A review of the literature[END_REF][START_REF] De Boer | Regular primary school teachers' attitudes towards inclusive education: A review of the literature[END_REF].

The goal of the present study was to test, in France, whether the usual difference observed between general and special education teachers in terms of attitude (toward inclusion) could be explained by their respective sense of efficacy.

Indeed, in view of previous results [START_REF] Buell | A survey of general and special education teachers' perceptions and inservice needs concerning inclusion[END_REF][START_REF] Leyser | Changes in self-efficacy of prospective special and general education teachers: Implication for inclusive education[END_REF][START_REF] Mchatton | Purposeful preparation: Longitudinally exploring inclusion attitudes of general and special education pre-service teachers[END_REF]al., 1996;[START_REF] Savolainen | Understanding teachers' attitudes and self-efficacy in inclusive education: implications for pre-service and in-service teacher education[END_REF][START_REF] Shippen | Preservice teachers' perceptions of including students with disabilities[END_REF][START_REF] Soodak | Teacher, student, and school attributes as predictors of teachers' responses to inclusion[END_REF][START_REF] Tournaki | Do graduate teacher education programs change teachers' attitudes toward inclusion and efficacy beliefs[END_REF][START_REF] Urton | Attitudes towards inclusion and self-efficacy of principals and teachers[END_REF][START_REF] Weisel | School climate, sense of efficacy and Israeli teachers' attitudes toward inclusion of students with special needs[END_REF][START_REF] Yada | Japanese in-service teachers' attitudes toward inclusive education and self-efficacy for inclusive practices[END_REF], we argue that general teachers would exhibit less favorable attitude toward inclusion than special education teachers because of their lower sense of efficacy. To investigate this hypothesis, general and special education teachers reported their attitude toward inclusion and their sense of efficacy. Our results confirmed our prediction. In other words, the present research supports the idea that efficacy is a key mechanism for explaining general teachers' less favorable attitude toward inclusion (in comparison with special education teachers). These results emphasize the importance of considering general teachers' efficacy in improving students with SEN inclusion since research showed the positive links that attitude and efficacy have respectively with behavioral intentions to include students with SEN and effective interventions toward these students [START_REF] Allinder | The relationship between efficacy and the instructional practices of special education teachers and consultants[END_REF][START_REF] Brownell | Teacher efficacy and perceived success in mainstreaming students with learning and behavior problems[END_REF][START_REF] Macfarlane | Teacher attitudes and behavior toward the inclusion of children with social, emotional and behavioral difficulties in mainstream schools: An application of the theory of planned behavior[END_REF][START_REF] Soodak | Teacher, student, and school attributes as predictors of teachers' responses to inclusion[END_REF][START_REF] Wertheim | Efficacy beliefs, background variables, and differentiated instruction of Israeli prospective teachers[END_REF][START_REF] Wilson | The impact of social cognitive and personality factors on teachers' reported inclusive behaviour[END_REF].

Amongst the four different sources of self-efficacy (see [START_REF] Fernandez | Overview of research on teacher self-efficacy in social cognitive perspective[END_REF][START_REF] Morris | Reconceptualizing the sources of teaching selfefficacy: A critical review of emerging literature[END_REF], [START_REF] Bandura | Self-efficacy: The exercise of control[END_REF] argued that mastery experience is the most powerful. Therefore, since inclusion is not yet generalized (at least in France), general teachers' lower confidence in their teaching practices (in comparison with special education teachers) may result from their being granted fewer experiences and opportunities to assess and improve their teaching practices with students with SEN. In addition, and as mentioned above, special education teachers in this country receive annual part-time training in addition to their initial curriculum. This training is designed to give them more resources to deal with students with SEN and may improve both their general and particular (i.e., for inclusive practices) sense of efficacy [START_REF] Chao | Improving teachers' self-efficacy in applying teaching and learning strategies and classroom management to students with special education needs in Hong Kong[END_REF][START_REF] Forlin | A system-wide professional learning approach about inclusion for teachers in Hong Kong[END_REF][START_REF] Lancaster | The design of inclusive education courses and the self-efficacy of preservice teacher education students[END_REF][START_REF] Leyser | Changes in self-efficacy of prospective special and general education teachers: Implication for inclusive education[END_REF]. Therefore, the differences found here may either translate a difference in training or a difference in terms of experience, or both. It bears mentioning some limitations of this work. First, in the present study, all measures were invoked variables. Therefore, causality cannot be established and results regarding the mediational analysis should be read cautiously. Though it does not make sense that attitude toward inclusion should influence sense of efficacy, such a possibility cannot be ruled out by our data. Second, research showed that attitude could vary according to the kind of attitude (i.e., general or specific, see [START_REF] Ajzen | The influence of attitudes on behavior[END_REF]. For example, as evoked above, a discrepancy exists between teachers' general attitude towards the concept of inclusion [START_REF] Scruggs | Teacher perceptions of mainstreaming/inclusion, 1958-1995: A research synthesis[END_REF], see also [START_REF] Abbott | Northern Ireland head teachers' perceptions of inclusion[END_REF] and their specific willingness to include a student with SEN in their classroom (deBettencourt, 1999, see also [START_REF] Florian | An examination of the practical problems associated with the implementation of inclusive education policies[END_REF]. In the present study, the used instrument was designed to measure general attitude toward inclusion [START_REF] Mahat | The development of a psychometrically-sound instrument to measure teachers' multidimensional attitudes toward inclusive education[END_REF]. Future research could examine if the indirect effect obtained here would vary depending on attitude type. Thirdly, it should also be acknowledged that even if efficacy acts as a mediator, the direct effect between teacher's position and attitude toward inclusion remains significant, leaving space for other potential mediators. Future studies should investigate these issues. Finally, it should be noted that the participants in the present study may not perfectly represent other French teachers. Indeed, since they deliberately chose to participate in a study about inclusion, it cannot be ruled out that these teachers already had a precise idea about inclusion (either positive or negative) that they would like to share.

Notwithstanding these limitations and research perspectives, the results of this study illustrate that to sustain an inclusive school system, general teachers must experience more confidence in their teaching practices. Therefore, in line with recent educational reforms in France, increasing the amounts of theoretical and practical knowledge received by pre-service teachers appears to be a relevant way to hone teachers' ability to teach in inclusive settings. Such curriculum modifications are undoubtedly steps forward to a more inclusive education despite the tangible effects still needing to be tested.

Figure 1 .

 1 Figure 1. Mediation analysis of teachers' attitude toward inclusion through teacher's efficacy (Position is coded -0.5 for general teachers and +0.5 for special education teachers. * p < .001).

Table 1

 1 Zero-order correlations between variables

		M	SD	1 ***	2 ***	3 ***	4 ***	5 ***	6 ***
	1. Teacher Efficacy	3.48	0.52	__ ***
	2. Attitude toward inclusion	3.90	0.61	.43 ***	__ *
	3. Position **	__	__	.25 ***	.34 ***	__ ***	*	*	***
	4. Level of teaching	__	__	.06 ***	.03 ***	.14 ***	__ ***
	5. Experience	16.21	9.71	.10 ***	-.01 ***	.01 ***	.08 t**	__ ***
	6. Age	41.12	9.38	.10 ***	.01 ***	.03 ***	.08 ***	.90 ***	__ **
	7. Gender	__	__	-.02 ***	.04 ***	-.02 *** -.26 *** -.09 *** -.10 ***

  To solve this issue, further research could first replicate the present findings while statistically controlling for teachers' previous experiences with students with SEN. Then, to examine the influence of the special education training program, a longitudinal study could also compare the evolution of general efficacy (throughout the program) of teachers who undergo the training program with that of teachers who do not benefit from the program but who have a similar profile in terms of age, teaching experience, level of teaching and experience with students with SEN.

This research was supported by the Ecole Supérieur du Professorat


Kawthar Ftouni

Louwanda Lakiss

Sébastien Thomas

Marco Daturi

Christian Fernandez

Philippe Bazin

Jaafar El Fallah

Mohamad El-Roz

Sébastien Thomas

Tio

Sebastien Thomas

TiO 2 /Zeolite Bifunctional (Photo)Catalysts for a Selective Conversion of Methanol to Dimethoxymethane: On the Role of Brønsted Acidity

come

Introduction

Designing new catalysts for selective methanol oxidation to valuable products such as dimethoxymethane (DMM), [START_REF] Fu | Selective Oxidation of Methanol to Dimethoxymethane Under Mild Conditions Over V 2 O 5 /TiO 2 With Enhanced Surface Acidity[END_REF] methyl formate (MF), 2 formaldehyde (FA), [START_REF] Hellier | VO x /Fe 2 O 3 Shell-Core Catalysts for the Selective Oxidation of Methanol to Formaldehyde[END_REF] or dimethyl ether (DME) [START_REF] Rownaghi | Selective Dehydration of Methanol to Dimethyl Ether on ZSM-5 Nanocrystals[END_REF] is of a high importance. Indeed, the demand for DMM has grown steadily in the last years owing to the remarkable growth of pharmaceutical industries. Due to its high chemical stability and low toxicity, DMM in fact is extensively used in cosmetic manufactures, as diesel fuel additive, as chemical intermediate and as an excellent solvent in perfume industries. [START_REF] Marrodań | High Pressure Oxidation of Dimethoxymethane[END_REF][START_REF] Zhu | Performance and Emission Characteristics of Diesel Engines Fueled with Diesel-Dimethoxymethane (DMM) Blends[END_REF][START_REF] Thavornprasert | One-pot 1,1-Dimethoxymethane Synthesis From Methanol: a Promising Pathway Over Bifunctional Catalysts[END_REF] At an industrial scale, DMM is produced from a homogeneous reaction of formaldehyde with methanol over acidic catalysts. [START_REF] Fuji | An Improved Method for Methoxymethylation of Alcohols under Mild Acidic Conditions[END_REF] However, this approach is very expensive. It involves a high reaction temperature and often causes equipment corrosion due to the presence of acidic catalysts. Therefore, a one-step selective oxidation of methanol to DMM is strongly recommended for economic and environmental reasons.

The selective oxidation of methanol to DMM may involve two steps: (1) oxidation of methanol to formaldehyde on redox sites and (2) condensation of formaldehyde produced with additional methanol to DMM on acidic sites. [START_REF] Liu | Selective One-Step Synthesis of Dimethoxymethane via Methanol or Dimethyl Ether Oxidation on H 3+n V n Mo 12-n PO 40 Keggin Structures[END_REF] Thus, bifunctional catalysts with redox and acidic characters are required for the reaction. In addition, the relative strengths of surface acidity and redox ability of a catalyst may be important in determining the reaction pathways as well as the selectivity.

Several catalysts such as supported Ruthenium [START_REF] Yuan | Performance and Characterization of Supported Rhenium Oxide Catalysts for Selective Oxidation of Methanol to Methylal[END_REF] and Rhenium oxides, [START_REF] Liu | Selective Oxidation of Methanol and Ethanol on Supported Ruthenium Oxide Clusters at Low Temperatures[END_REF] SbRe 2 O 6 , 12 heteropoly acids, [START_REF] Liu | Site Titration with Organic Bases During Catalysis: Selectivity Modifier and Structural Probe in Methanol Oxidation on Keggin Clusters[END_REF] Cu-ZSM-5, 14 V 2 O 5 /TiO 2 , [START_REF] Kaichev | Selective oxidation of Methanol to Form Dimethoxymethane and Methyl Formate Over a Monolayer V 2 O 5 /TiO 2 catalyst[END_REF] and VOx/TS-1, [START_REF] Heqin | Influence of Preparation Method on the Surface and Catalytic Properties of Sulfated Vanadia-Titania Catalysts for Partial Oxidation of Methanol[END_REF] etc. have been used for this procedure. Besides, the required reaction temperature is between 423 to more than 593 K.

Recently, we have reported that VO x /Beta zeolite can promote the DMM formation by a photocatalytic conversion of methanol at room temperature. [START_REF] El-Roz | High-Visible-Light Photoactivity of Plasma-Promoted Vanadium Clusters on Nanozeolites for Partial Photooxidation of Methanol[END_REF] However, the reaction was not selective and the DMM formation was related to the photocatalyst and the role of the support was indefinite.

Contrariwise to VO x based photocatalyst, no DMM was detected as a product of methanol photooxidation using pure titanium oxide as photocatalyst.

Despite the wide use of supports for enhancing photocatalytic activities, [START_REF] El-Roz | Immobilization of TiO 2 Nanoparticles on Luffa Cylindrical Fibers for Photocatalytic Applications[END_REF][START_REF] El-Roz | Ultra-Fast Framework Stabilization of Ge-Rich Zeolites by Low-Temperature Plasma Treatment[END_REF] the influence of these supports on the selectivity of the photocatalytic reaction is rarely assumed. This is mainly related to the fact that photocatalytic reactions mainly occur at near room temperature and under mild reaction conditions. In such conditions, only the photoactive sites are involved in the reaction.

We report herein the first example of a one-step DMM production from methanol photooxidation at room temperature over bifunctional TiO 2 /zeolite catalysts. We demonstrate that the selectivity of the photocatalytic reaction can be tuned and controlled by adjusting the reaction conditions and zeolite properties. In order to study the effect of zeolite type (supposed as support) on the selectivity of the reaction, several materials have been selected based on their acidity/basicity and porosity. The methanol photooxidations over TiO 2 combined with the different materials (porous, non-porous, acidic, basic) were performed under similar conditions. The reaction mechanism of methanol conversion to DMM is then proposed. Beta (Si/Al = 15), and purely siliceous MFI (Silicalite) zeolites were synthesized following the protocol reported in the references [20,21], respectively. g-alumina was prepared by heating a pseudoboehmite (Catapal B from Sasol) at 823 K for 5 h with a heating rate of 2 K/min under atmospheric condition. The acidic properties of the catalysts are determined by IR spectroscopy of adsorbed pyridine using a conventional glass cell. Infrared spectra are recorded on a Nicolet Magna 550-FT-IR spectrometer at 2 cm -1 optical resolution. Prior to the measurements, the catalysts are pressed into self-supporting discs (diameter: 1.6 cm, 20 mg cm 2 ) and pretreated in-situ under vacuum (10 -6 Torr) at 823 K (2 K /min) for 5 h. Pyridine is adsorbed at 373 K. After establishing a pressure of 1 Torr at equilibrium, the cell is evacuated at 523 K to remove the physisorbed species. The amount of pyridine adsorbed on the Brønsted (1545 cm -1 ) and Lewis (1454 cm -1 ) sites is determined by integrating their respective band areas using the following extinction coefficients: e (B)1545 = 1.35 and e (L)1454 = 1.5 cm.mol -1 for Py, respectively. [START_REF] Thibault-Starzyk | Situ Thermogravimetry in an Infrared Spectrometer: An Answer to Quantitative Spectroscopy of Adsorbed Species on Heterogeneous Catalysts[END_REF] For LZY-64-NH 4 + , the analysis was performed on two different samples: 1) LZY-64-NH 4 + pretreated in-situ under vacuum (10 -6 Torr) at 823 K (2 K /min) for 5 h, 2) LZY-64(H) which was calcined under air at 823 K (2 K /min) for 5 h and then pretreated in-situ under vacuum (10 -6 The catalysts were then pressed into self-supported wafers (Ø = 16 mm, m~10 mg/cm 2 ) with a thickness of about 65 ± 2 µm as measured by scanning electron microscopy (SEM, Tescan MIRA FEG).

Experimental part

The outlet gas phase evolution was followed by both IR spectroscopy and mass spectrometry. FTIR spectra of the outlet gas phase and of the surface were collected with a Nicolet 5700 FT-IR spectrometer (64 scans/spectrum) equipped with a MCT detector. The operando system was connected to a flow set-up. [START_REF] Wuttke | Discovering the Active Sites for C3 Separation in MIL-100(Fe) by Using Operando IR Spectroscopy[END_REF] Gases were introduced into the lines by mass flow controllers. The system allows the two gas mixtures, so-called "activation" and "reaction" flows, to be prepared and sent independently to the reactor cell. The "sandwich" type reactor-cell used in this study is described in reference [24]. It was made of a stainless-steel cylinder that carries a toroidal sample holder in its center, where the catalyst self-supporting wafer was placed. Tightness was obtained by O-rings, and the dead volume (typically defined as the residual space between each sample face and the windows)

was reduced to about 0.4 mL by filling the empty space with KBr windows placed on each side of the sample holder. The surface analysis was made possible without the superposition of the gas phase signal and fluid dynamics. Gases were introduced to the sample by 1/8-inch OD pipe and collected on the opposite side of the sample holder. For this specific photocatalytic oxidation study, UV irradiation was carried out with a polychromatic light of Xe-Hg lamps (LC8 spot light Hamamatsu, L10852, 200 W). It has been performed by using a UV-light guide (A10014-50-0110) mounted at the entrance of a modified operando IR cell to establish a homogeneous and similar irradiation on the different photocatalysts pellet surfaces. More details can be found in references [24] and [25]. In order to avoid any possible heating of the samples due to the IR emission of the lamp, a "Block infrared light" filter (Hamamatsu A9616-10) with a transmittance wavelength from 300 to 400 nm have been used in this work. The lamp irradiance was measured using ILT950 spectrilight spectroradiometer from International Light Technologies. All samples have been activated under dry synthetic air (in situ) at relatively low temperature (423 K) for 2h in order to preserve their original properties. The activation process was enough for removing the majority of adsorbed water.

The employed configuration allowed a low partial pressure of methanol to be achieved using a saturator at controlled temperature. The gas mixture composition was fixed then at 0.12 vol. % methanol and 20 vol. % O 2 in Ar and the total flow was adjusted to 20 cm 3 /min. The analysis of the outlet gases was performed by means of a Pfeiffer Omnistar mass spectrometer. Likewise, FT-IR spectra of the gas phase were collected using a gas microcell. The selectivity and the conversion were calculated using the calibration curves for the different products involved in the reaction. In this work, the light intensity of the lamp was adjusted in order to obtain a similar conversion around 35% (for preventing the effect of the mass transfer on the selectivity). The IR gas cell used in this work for analysing the reaction gas phase was previously calibrated with the different standard products expected from methanol photooxidation. This allows the determination of the concentration of the products in the gas phase. More experimental details are given in references (25-26). It should be noted that no deactivation of the catalyst is observed under the reaction conditions used in this study.

This agrees with our previous observation on methanol photooxidation on TiO 2 based photocatalyst at relatively low temperature. [START_REF] El-Roz | New Operando-IR Technique to Study the Photocatalytic Activity and Selectivity of TiO 2[END_REF] Each experiment was repeated at least twice and the average values are reported (error estimated lower than 10% on the different experiments).

Results and discussion

FTIR spectroscopy and mass spectrometry, connected on line with the operando IR reactor for analyzing the gas phase, complementarily allows the identification of the reaction products and the determination of reaction conversion and selectivity, calculated at the steady state (after stabilization for 2h). The conversion of methanol is calculated by using the n(OC) vibrational band of methanol at 1034 cm -1 . [START_REF] El-Roz | Operando Infrared (IR) Coupled to Steady-State Isotopic Transient Kinetic Analysis (SSITKA) for Photocatalysis: Reactivity and Mechanistic Studies[END_REF] As already mentioned in the experimental part, the conversions were maintained between 30 and 40% (by adjusting the lamp intensity) in order to reduce the effect of mass transfer on the selectivity. The IR spectra of the reaction gas phase, at the steady state, during methanol photooxidation on supported TiO 2 photocatalysts are assembled in Figure 1. The following products have been identified: Formaldehyde (FA), methylformate (MF), dimethyl ether (DME), dimethoxymethane (DMM), and carbon dioxide. A calibration (on IR and MS) of these products have been previously performed using standard products in order to calculate their selectivity. The selectivity of CO 2 was determined by using the n(CO 2 ) vibration band at 2300-2200 cm -1 (Figure 1).

A deconvolution of the IR spectra in the 1650-1850 cm -1 vibration region was necessary for determining the concentration of MF and FA using n(C=O) vibration bands at 1754 cm -1 and 1748 cm -1 , respectively. A deconvolution of the IR spectra in the 1650-1850 cm -1 region was necessary for determining the concentration of MF and FA using n(C=O) vibration bands at 1754 cm -1 and 1748 cm -1 , respectively. The overlapping of these bands makes the precise determination of the formaldehyde concentration a challenge. Therefore, the IR spectrum of the reaction gas phase at the steady state was first subtracted from the original spectrum of a pure MF standard (250 ppm/Ar) using Omnic software. A subtraction factor was applied until the disappearance of the characteristic IR bands of MF (see Figure 1-B). Using this factor, the MF formate concentration was then determined as a multiplicity of this factor (f) and the MF concentration (f x 250 ppm). The result was compared to that obtained from the mass spectrometer using the signal of MF at m/z = 60. Contrarily to the MS signals of FA, there is no contribution of other products at m/z = 60. The values obtained were in agreement with those determined by IR for MF and the concentration of FA was then determined on the deconvoluted spectrum using the intensity of the band at 1748 cm -1 (after MF subtraction). For DMM, the n(OC) vibration band at 1148 cm -1 and the MS signal at m/z = 75 have been used for calculating the selectivity. The so called "other compounds" added to some results represent minor species below the detection limits (e.g. formic acid or dimethyl ether in some cases) and complete the materials balance. It also accounts for the experimental error. and ZSM-5(N) supports, the only differences are their crystal size and Si/Al ratios (23 and 47, respectively). For comparison, self-supported (S.S.) TiO 2 wafer is also used as a reference. As shown in Figure 2, porosity has no impact on the selectivity; since silica and purely siliceous microporous

(B) (a) (b) (c) (d) (e) (f) (g) (h) (i) (j)
MFI zeolite (silicalite) showed similar results as the self-supported TiO 2 . g-alumina also shows similar results demonstrating that Lewis acidity has also no significant impact on the selectivity. Only zeolites with Brønsted acid sites have an important impact on the selectivity of the reaction. It should be noted, that there is no activity observed without TiO 2 and/or in the dark.

Based on our previous work, [START_REF] El-Roz | On the Mechanism of Methanol Photooxidation to Methylformate and Carbon Dioxide on TiO 2 : An Operando-FTIR Study[END_REF] the thermo-and/or photo-dissociation of the methanol is the first step of methanol photooxidation reaction on TiO 2 . After that, the first oxidation of the adsorbed methoxy species leads to the formation of FA. At a low methanol concentration (or conversion), FA desorption is promoted and this latter is detected as a main product of the reaction. Otherwise, a second oxidation of the adsorbed FA occurs and formal/formate species are then formed. These species are in a scrambling movement on the surface. [START_REF] El-Roz | Operando Infrared (IR) Coupled to Steady-State Isotopic Transient Kinetic Analysis (SSITKA) for Photocatalysis: Reactivity and Mechanistic Studies[END_REF][START_REF] El-Roz | On the Mechanism of Methanol Photooxidation to Methylformate and Carbon Dioxide on TiO 2 : An Operando-FTIR Study[END_REF] When these species come across a hole, an additional oxidation is promoted and yields to CO 2 . MF is the product of the crosslinking of the formyl species with adsorbed methoxy on an adjacent site. This product is promoted with the increase of methoxy concentration on TiO 2 surface. Indeed, the selectivity to MF can be tuned by adjusting the reaction conditions (e.g. methanol conversion or concentration) without need to change the photocatalyst.

However, DMM is exclusively formed with a high selectivity over bifunctional TiO 2 /zeolite catalysts with acid sites. As there is no formation of DMM on TiO 2 /Al 2 O 3 , the possible role of the Lewis site in the DMM formation can be eliminated. Consequently, the presence of the Brønsted acid sites is at the origin of the DMM formation which is in agreement with the previous results obtained on the thermal oxidation of methanol. Operando FTIR setup used in this work allows a time-resolve, simultaneous quantitative analysis of the photocatalyst surface species and the gas phase products. [START_REF] El-Roz | New Operando-IR Technique to Study the Photocatalytic Activity and Selectivity of TiO 2[END_REF] The low transparency of some zeolites toward IR in the 2500-1000 cm -1 vibration region makes the analysis of the IR data of the surface complex. Nevertheless, the IR results of the surface of some catalysts which demonstrate different selectivity were successfully treated and reported in Figure 3. Indeed, the low content of TiO 2 (10 wt.%) in addition to the high adsorption capacity of zeolites make difficult to distinguish between the adsorbed species on TiO 2 active sites and the products adsorbed on zeolites/supports. However, the comparison of the recorded IR data of the different samples reveals some interesting information.

New IR bands appear after the first minutes of irradiation. Two carbonyl vibration bands are observed in the case of TiO 2 /SiO 2 and TiO 2 /silicalite at 1736 and 1715 cm -1 , whereas only one band at 1715 cm -1 is observed in the case of TiO 2 /Beta. The band at 1715 cm -1 is assigned to the stretching vibration of the carbonyl of adsorbed formaldehyde [START_REF] Busca | FT-IR Study of the Adsorption and Transformation of Formaldehyde on Oxide Surfaces[END_REF] while the band at 1736 cm -1 is assigned to the stretching vibration of the carbonyl of adsorbed methylformate. Due to the different affinity of SiO 2 and silicalite vs. reaction products, the relative concentration of the adsorbed products is not the only factor affecting the intensity of the corresponding IR bands. However, the band intensity at 1715 cm - 1 observed in TiO 2 /Beta is 10 times higher than that observed for TiO 2 /SiO 2 and TiO 2 /silicalite. The bands at 1500-1300 cm -1 are mainly assigned to the adsorbed formaldehyde and related species. The decrease of the band at 1630 cm -1 in the case of TiO 2 /Beta is attributed to the desorption of residual water on the highly hydrophilic Beta zeolite.

As reported in Table 1, the difference in the surface area and microporous volumes between silicalite and Beta zeolites is not very significant. Basing on the gas phase data, the amount of produced FA and MF is more important on TiO 2 /silicalite than on TiO 2 /Beta. Therefore, in the case of Beta zeolite, the formaldehyde is probably an intermediate more than a final product. The low amount of adsorbed MF on Beta is mainly due to the low amount of this product. This can be explained by the low oxidation of FA into formyl as we can observe from the low IR band intensity of these species (broad band centered at ≈1570 cm -1 ) in the case of TiO 2 /Beta in respect to TiO 2 /SiO 2 and TiO 2 /Silicalite.

These results agree with the low amounts of CO 2 and MF obtained on TiO 2 /Beta(H) catalyst where formyl species are the common intermediates of these products. 27 ,30,31 Unfortunately, it was difficult to confirm this information by IR analysis of the surface during the reaction due to the saturation on bands intensity in the region of ammonium vibrations and the low transparency of these samples in IR. The evolution of the methanol, methylformate and dimethoxymethane in the gas phase was followed by IR and mass spectrometry. For comparison, the same experiment was realized on the same sample without any previous activation. The normalized results are presented in Figure 5. Figure 5-A represents the evolution of methanol in the gas phase before and after sending methanol through the reactor. The adsorption equilibrium of methanol is reached after 40 and 50 min (the minimum time required to detect methanol in the gas phase) on the non-activated and activated TiO 2 /LZY-64(NH 4 + ) samples, respectively. This difference in the equilibrium delay may be related to the increase of the adsorption capacity of TiO 2 /LZY-64(NH 4 + ) toward methanol after UV activation. Indeed, the oxidation of ammonium species generates Brønsted acid sites which increases the adsorption capacity. The evolution of the MF and DMM is reported in Figure 5-B. MF is detected in the first minutes of the reaction. This is in agreement with the fact that MF is selectively formed on TiO 2 surface and means that the affinity of the support toward MF is relatively low in respect to that of methanol and/or other products (e.g FA). However, an induction time of 100 minutes is observed for DMM on the non-activated sample. This delay is reduced to 40 minutes on the activated one. The The role of the heterogeneous bifunctional catalysts interface on the selectivity of the primary alcohol oxidation over metal/oxide catalysts was recently demonstrated. [START_REF] Kropp | Support Effect in Oxide Catalysis: Methanol Oxidation on Vanadia/Ceria[END_REF][START_REF] Zhao | Metal/Oxide Interfacial Effects on the Selective Oxidation of Primary Alcohols[END_REF] In our case, there are two possible ways for the formation of DMM over supported TiO 2 on acidic zeolites: i) DMM is formed at the TiO 2 /zeolite interface. This means that neighbor TiO 2 active sites and Brønsted acid sites on the external zeolite surface are required; or ii) DMM is formed in two consecutive steps: first, by the oxidation of methanol to FA on TiO 2 . Then, the produced FA is adsorbed/protonated on the Brønsted acid sites where it will be followed by condensation reactions with methanol. In order to elucidate these two hypotheses, methanol photooxidation was performed on two separated and superposed pellets, self-supported TiO 2 and Beta(H) (called TiO 2 +Beta), respectively. The two pellets are placed on the same samples holder in the operando cell. Therefore, the physical contact between the photocatalyst and the zeolite support is negligible compared to the mechanical mixture.

The result is presented in Figure 6. For comparison, methanol photooxidation under similar conditions has been performed over TiO 2 /Beta(H) (mechanical mixture) and TiO 2 supported on the as synthetized Beta (TiO 2 /Beta(a.s.)) sample (the organic template is not removed by calcination).

Contrary to the TiO 2 /LZY-64(NH 4 + ) sample, there is no formation of DMM observed using the as synthesized Beta zeolite. Therefore, we can discard the existence and creation of Brønsted acid sites during the photocatalytic reaction on this catalyst. For TiO 2 +Beta sample, a similar selectivity as for TiO 2 /Beta(H) prepared by solid state dispersion is observed. Consequently, the interface TiO 2 /zeolite has no consequence in the formation of DMM. This assumption means that the DMM formation is promoted even at room temperature on Brønsted acid sites in the presence of a stoichiometric amount of formaldehyde and methanol. Despite the important role of the Brønsted acid sites in the formation of DMM, the role of the Lewis sites cannot be excluded. A synergetic effect of the Brønsted/Lewis acid sites could be observed. [START_REF] Li | Brønsted/Lewis Acid Synergy in Dealuminated HY Zeolite: A Combined Solid-State NMR and Theoretical Calculation Study[END_REF][START_REF] Zheng | Acidic Properties and Structure-Activity Correlations of Solid Acid Catalysts Revealed by Solid-State NMR Spectroscopy[END_REF] As we mentioned above, the methanol conversion was maintained constant for all experiments. This justifies why the amount of the DMM formed and the Brønsted acidity of the samples are not dependent (Table 1). Other factors as the internal diffusion and/or the acidity strength might have an impact on the reaction rates but not on the selectivity. A separated study using steady state isotopic transient kinetic analysis (SSITKA) is in progress to determine the reaction parameters (e.g. diffusion constant, etc.) basing on the results obtained in this work. The effect of the temperature on the reaction selectivity has been investigated on TiO 2 /LZY-54(Na) and (B) TiO 2 /LZY-64(H) samples. The results are exposed in Figure 7. The increase of the temperature promotes the total oxidation versus the partial oxidation on TiO 2 /LZY-54(Na). This result agrees with the previous result obtained on self-supported TiO 2 photocatalyst. [START_REF] El-Roz | New Operando-IR Technique to Study the Photocatalytic Activity and Selectivity of TiO 2[END_REF] However, the increase of the temperature for TiO 2 /LZY64(H) has a dramatic effect on the formation of DMM, nevertheless, the formation of DME is promoted. As no DME is detected in the case of TiO 2 /LZY-54(Na), the acidic sites of the LZY64(H) are at the origin of the dehydration of methanol at a relatively high temperature. The dramatic decrease of DMM selectivity is not related to the total oxidation as we can understand from the low selectivity to CO 2 . Therefore, it is mainly due to the weak adsorption of formaldehyde when increasing the temperature. These results demonstrate that FA is an intermediate product of methanol photooxidation when a catalyst/support with Brønsted acidity is used and it is weakly adsorbed on the surface. The presence of the Brønsted active sites promotes the adsorption of formaldehyde, decreases its contact time with the photocatalyst surface, therefore its oxidation on the photocatalyst surface, and lead to the formation of DMM.

These results can be extrapolated for the thermo-catalytic oxidation of methanol and not only for the photocatalytic oxidation. In the thermal formation of DMM, a high temperature is required for the formation of FA on oxidant sites, while DMM can be formed with a high selectivity on the Brønsted acid sites at nearly room temperature. Based on the previous results, the mechanism of methanol photooxidation to dimethoxymethane can be proposed as follows: TiO 2 promotes the photooxidation of methanol to FA while zeolite promotes the adsorption and the protonation of methanol and/or formaldehyde on the Brønsted acid sites. A nucleophilic attack followed by a condensation reaction with methanol occurs and DMM is then formed (Scheme 1). This mechanism is in agreement with that reported recently in the literature. [START_REF] Liu | Highly Efficient and Stable Vanadia-Titania-Sulfate Catalysts for Methanol Oxidation to Methyl Formate: Synthesis and Mechanistic Study[END_REF][START_REF] Wang | Extra-Framework Aluminum-Assisted Initial C-C Bond Formation in Methanol-to-Olefins Conversion on Zeolite H-ZSM-5[END_REF] (1) CH3OH Despite that this work is intended to explain the selective methanol photooxidation, the obtained results can be extrapolated also to thermal catalysis. We can assume that a highly selective thermal oxidation of methanol to DMM is possible. However, the following conditions should be respected: a redox catalyst is necessary for selective methanol oxidation to FA (e.g. MoO x , Ag-based catalyst, TiO 2 or V 2 O 5 ). This reaction requires a relatively high temperature. In this step, a low methanol conversion is recommended to minimize the FA oxidation. The second step reaction can be held in the same reactor, however, a separate reactor (in series with the first one) containing a catalyst with Brønsted acid sites is recommended, and the condensation reaction is then promoted at near room temperature. As DMM is more stable than FA and MeOH, a loop configuration of the two reactors with recycling can be investigated in order to increase the yield of the reaction. In such a configuration, a heat exchanger between the two reactors is necessary to adjust the reaction temperature. Further work using different reactors configuration is required for demonstrating this hypothesis. In photocatalysis, there is no need to separate the two reactions as the reaction occurs at room temperature.

Conclusion

The mechanistic insights obtained by our investigations have shown that the selective oxidation of methanol to DMM involves first the oxidation of methanol to formaldehyde on redox sites and then the condensation of the produced formaldehyde with additional methanol to form DMM on acidic

TiO 2 -

 2 P25 (TiO 2 ) photocatalyst (Evonik Degussa) was used as received without any additional treatment. The different samples are prepared by solid state dispersion of 10 ± 2 wt.% TiO 2 with the different materials. SiO 2 (Ultrasil 7000, Evonik), commercial LZY-54 (Na + -form, UOP, Si/Al = 2.3), LZY-64 (NH 4 + -form, UOP, Si/Al = 2.3), a micron-sized ZSM-5(M) (Si/Al = 23, Clariant), and a nanometer-sized ZSM-5(N) (Si/Al = 47, Clariant) are used as supplied without any treatment.

  Specific surface area measured by BET; (b) microporous volume and (c) External surface area calculated using the t-plot method; (d) Brönsted and (e) Lewis acidity; (f) values calculated after the calcination of the ammonium form under air. (g) The particle sizes are determined according to SEM micrographs. The values between brackets correspond to the size of the aggregates.

Figure 1 /

 1 Figure 1/ (A) IR spectra of gas phase reaction (at steady state) during methanol photooxidation (at room temperature) over TiO 2 /oxides: (a) corresponds to the IR spectrum of methanol; (b) selfsupported TiO 2 ; (c) SiO 2 (used as reference); (d) Silicalite; (e) LZY-54(Na-form); (f) g-Al 2 O 3 ; (g) LZY-64(H-form); (h) ZSM-5 (N); (i) ZSM-5 (M); and (j) Beta(H). (B) IR spectra of methanol and possible products collected by sending them in Ar flow to the IR cell (except FA IR spectrum which is used from the data base of Omnic software). Reaction conditions: flow = 20 cm 3 /min; [methanol] = 1200 ppm; 20% O 2 /Ar; T = 298 K; TiO 2 /support = 10 ± 2 wt./wt. %; m cat = 20 ± 1 mg. Dotted lines correspond to the position of the characteristic IR bands of the identified products.

28

 28

Figure 2 /

 2 Figure 2/ Conversion and selectivity of methanol photooxidation over supported TiO 2 -P25 (prepared by solid state dispersion); (S.S.) corresponds to the self-supported TiO 2 . N.B. Irradiation adjusted in order to obtain a similar conversion (35 ± 5%). Reaction conditions: flow = 20 cm 3 /min; [methanol] = 1200 ppm; 20% O 2 /Ar; T = 298 K; m cat = 20 ± 1 mg; TiO 2 /support = 10 ± 2 wt./wt. %.

Figure 3 /

 3 Figure 3/ IR spectra of the adsorbed surface species on TiO 2 /SiO 2 (A), TiO 2 /Silicalite (B) and TiO 2 /Beta(H) (C) during the first minutes of irradiation (2 min/spectrum). The spectra were subtracted from the IR spectrum of the sample before irradiation. Reaction conditions: flow = 20 cm 3 /min; [methanol] = 1200 ppm; 20% O 2 /Ar; T = 298 K; m cat = 20 ± 1 mg; TiO 2 /support = 10 ± 2 wt./wt. %.

Figure 4 /

 4 Figure 4/ selectivity of methanol photooxidation on TiO 2 -P25 mixed with zeolite Y in different forms: sodium form (LZY-54(Na + ); ammonium form (LZY-64(NH 4 + )); and acidic form (LZY-64(H)). LZY-64(H) obtained after the calcination of LZY-64(NH 4 + ) at 550°C under vacuum. The conversion is also reported and maintained at around 30 ± 5%.

  photocatalytic reaction. In other words, a partial photocatalytic activation of TiO 2 /LZY-64(NH 4 + ) is

Figure 5 /

 5 Figure 5/ (A) Evolution of the characteristic IR band of methanol at 1033 cm -1 , in the gas phase during methanol photooxidation on TiO 2 -P25/LZY-64(NH 4 + ) (a) without activation and (b) after photoactivation by UV irradiation (lamp Hg-Xe; 200W). (B) Corresponding evolution of the MS intensities of (1) m/z = 60 (characteristic of MF) and (2) m/z = 75 (characteristic of DMM) during methanol photooxidation on the samples (a) and (b). t = 0 min corresponds to the time that methanol pass through the reaction flow. Reaction conditions: flow = 20 cm 3 /min; [methanol] = 1200 ppm; 20%O 2 /Ar; T = 298 K; mcat = 20 ± 1 mg; TiO 2 /support ratio = 10 ± 2 wt./wt. %.

Figure 6 /

 6 Figure 6/ Methanol photooxidation selectivity and conversion on TiO 2 -P25 mixed with as synthesized Beta zeolite (TiO 2 /Beta(a.s.)), with calcined Beta zeolite (TiO 2 /Beta (H)). TiO 2 +Beta corresponds to the sample where TiO 2 and Beta zeolite are prepared in two separated and superposed pellets (negligible physical contact between the two pellets (diameters = 16 mm)). Reaction conditions: flow

Figure 7 /

 7 Figure 7/ Evolution of the selectivity of the methanol photooxidation reaction over (A) TiO 2 /LZY-54(Na) and (B) TiO 2 /LZY-64(H) versus the temperature. The conversion was maintained at 30 ± 5% by adjusting the lamp intensity. Uncertainty ≈5%.

  Scheme 1. Main steps of the photocatalytic methanol oxidation, at room temperature, to dimethoxymethane over TiO 2 supported on zeolite support with Brønsted/Lewis acid sites.

Table 1 .

 1 The textural and the acidic properties of the different materials used in this work are summarized in the table 1.

Torr) at 823 K (2 K /min) for 5 h. The values for LZY-64(H) are reported between brackets in

Table 1 .

 1 Textural and acidic properties of the different materials used in this work.

	Sample	SiO	Silicalite LZY-54	ZSM-5	ZSM-5	LZY-64	Beta	g-
		2		(Na)	(M)	(N)	(H)	(H)
									alumina
	Si/Al lattice	/	/	2.3	23	47	2.3	15	/
	BET (m 2 .g -1 ) (a)	400	420	906	377	488	754	635	254
	V mic (cm 3 .g -1 ) (b)	/	0.17	0.34	0.18	0.17	0.34	0.25	/
	S ext (m 2 .g -1 ) (c)	/	125	60	9	75	60	164	243
	B Py (µmol.g -1 ) (d)	/	/	/		224	1320	274	/
					617
							(220) (f)
	L Py (µmol.g -1 ) (e)	/	/	/	91	67	45
							(690) (f)

/Zeolite Bifunctional (Photo)Catalysts for a Selective Conversion of Methanol to Dimethoxymethane: On the Role of Brønsted Acidity. Journal of Physical Chemistry C, 2018, 122 (51), pp.29359-29367. 10.1021/acs.jpcc.8b10092. hal-01963757

sites. In thermal catalysis, the reaction temperature required for this procedure is between 423 and 593 K. In this work we have demonstrated the possibility to produce dimethoxymethane by selective methanol photooxidation at room temperature. The results demonstrate that the condensation step occurs near room temperature (305-310 K) and there is no role of the photocatalyst in this step. This latter is involved in partial methanol photooxidation to formaldehyde. The high selectivity of DMM is explained by a simultaneous adsorption of produced formaldehyde, on the Brønsted sites of the support, preventing its oxidation on the photocatalyst surface. This is in agreement with the low selectivity obtained on the Brønsted-free support and on the self-supported TiO 2 . The increase of the temperature had a dramatic effect on dimethoxymethane formation. Therefore, we suggest that the best configuration of a setup for thermal selective methanol oxidation to dimethoxymethane would be obtained by using two connected batch reactors in a loop configuration: one with the redox catalyst at an optimized temperature, which promotes a selective partial oxidation of methanol to formaldehyde, while the second contains the catalyst with Brønsted acid sites (zeolite) at room temperature.

AUTHOR INFORMATION

Corresponding Author

*E-mail: mohamad.elroz@ensicaen.fr

Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.