Ka-Lun Wong

Mohamad El Roz

Lubomira Tosheva

Jean-Michel Goupil

Svetlana Mintova
email: svetlana.mintova@ensicaen.fr

Porous Materials Prepared by Co-condensation Synthesis Approach

Porous silica materials were prepared by a single step co-condensation synthesis approach using 3-mercaptopropyltrimethoxysilane (MPTS) as organo-functional compound and silica co-source. For comparison, MPTS-modified amorphous silica and pure microporous (Silicalite-1) samples were synthesized. The incorporation of MPTS into the silica structures was confirmed by 29 Si and 13 C Nuclear Magnetic Resonance (NMR) and Raman spectroscopy, while the presence of two types of pores was verified with nitrogen sorption and X-ray diffraction (XRD) measurements of as-synthesized and calcined materials.

The porous materials exhibited improved hydrophobicity in comparison with the samples prepared in the absence of MPTS. The presented method is simple and less toxic than the acid-meditated synthesis approach commonly applied for the preparation of hydrophobic zeolitic materials.

Introduction

Nanoporous materials with well-defined porous architecture are renowned for their traditional applications as catalysts, adsorbents and ion-exchangers [1][2][3][4][5]. Amongst them, the microporous (zeolites) and mesoporous molecular sieves (e.g. MCM-and SBA-type materials) are the two most intensively groups studied. The incorporation of organic moieties into their channels or anchored on their surfaces has provided them with distinctive properties for a broad range of applications such as immobilization of enzymes, drug delivery carriers, encapsulation of metal nanoparticles, etc. [6][7][8][9][10].

Nanoporous materials can be functionalized by different pathways, which are categorized in two groups: (i) post-synthesis and (ii) direct synthesis approaches [11][12].

Post-synthesis methods involve treatment on the initially prepared porous materials, using grafting of organofunctional compounds onto the pore walls via covalent bonds [13]. The grafting process is a reaction between suitable organic moieties with the surface silanol groups of the material. The direct synthesis method involves co-condensation of an organofunctional compound with inorganic precursors during synthesis in a single step [13,14].

Ordered mesoporous materials have amorphous pore walls of hydrophilic nature. The large number of surface hydroxyl groups available can readily be utilized for post-synthesis grafting. A wide range of organic groups have been grafted on the pore walls of mesoporous silicas such as amine, phenyl, thiol, isocyanate and urea [15][16][17][18][19]. The post-synthesis grafting of microporous materials tends to change only the external surface due to their smaller pore sizes compared to the pore size of mesoporous silicas. In this case, post-synthesis grafting may lead to pore blocking. Thus, only few reports have been published on the modification of zeolites by grafting [20,21].

Alternatively, functionalization of the zeolite inner surfaces can be achieved by cocondensation method using organically-substituted trialkoxysilane reagents, [R'-Si(OR)3], as a co-silica-source in addition to conventional silica sources. Pore blocking is not considered as a problem since the organic moieties become a part of the inorganic network structure.

Instead of quaternary ammonium cations usually used as template in zeolite syntheses, various zeolite phases have been synthesized using quaternary ammonium-functionalized organo-siliconates such as N-trimethoxysilyl-propyl-tri-N-butyl-ammonium [22,23]. The zeolite phases were successfully crystallized by co-condensation method and it was demonstrated that the majority of the organosilicon Si-C bonds were cleaved in the assynthesized zeolite, thus leaving only a small amount of alkylammonium moieties intact.

Ryoo and co-workers have used similar ammonium-functionalized organosilanes, but with longer alkyl chains for the preparation of zeolitic materials possessing microporous/mesoporous hierarchical structures [24,25]. Recently, the preparation of zeolitic materials with hierarchical porosity by co-condensation using alkyl-triethoxysilane was also reported [26]. The nano-crystal size and mesoporosity of the materials were found to be dependent on the alkyl chain and the amount of alkyl-alkoxysilanes added into the synthesis mixtures. Besides, the formation of hierarchical porosity in zeolitic materials by grafting of zeolite seeds with organosilanes larger than the micropore opening has been demonstrated [27,28]. The functionalization of the zeolite seeds perturb the zeolite crystal growth and hinder further agglomeration, which leads to the formation of secondary porosity in the mesopore range. For all materials, the hydrophobic-hydrophilic properties have not been studied in detail.

Organic-inorganic hybrid zeolite containing Si-CH2-Si bridges has been successfully synthesized using methylene-bridged organosilane as a silicon source [29,30]. However, long bridging organic groups other than methylene are unlikely to be incorporated into the crystalline framework. Davis and co-workers reported on the synthesis of organicfunctionalized molecular sieves (OFMSs) with shape-selective catalytic properties [31][32][33][34]. Pure silica zeolite Beta (BEA-type structure) in the presence of phenethyltrimethoxysilane and tetraethylammonium fluoride as structure-directing agent was also synthesized [33].

The aim of this work was to prepare porous materials by co-condensation method using 3-mercaptopropyltrimethoxysilane (MPTS) as template and silica source. Another objective was to prove the successful grafting and to evaluate the hydrophilicity/hydrophobicity of the functionalized MPTS porous sample compared to pure Silicalite-1 and amorphous silica.

Experimental

Preparation of porous samples

The amorphous colloidal silica (FD-SiO2) (Aldrich, SM-30, 30 wt. % in water) was freshly freeze-dried prior use.

Silicalite-1 was synthesized from a precursor solution prepared from freeze-dried colloidal silica and tetrapropylammonium hydroxide (TPAOH, Alfa Aesar, 1 M in water) with a molar composition of 9 TPAOH: 25 SiO2: 420 H2O. The freeze-dried silica was first mixed with TPAOH and stirred overnight at room temperature. The clear suspension obtained was transferred to a PTFE-lined autoclave and left to crystallize in a conventional oven at 140°C for 48 hours. The obtained crystalline colloidal suspension was purified using a high speed centrifugation followed by re-dispersion in distilled water in an ultrasonic bath.

The MPTS-functionalized Silicalite-1 (MPTS-Silicalite-1) sample was prepared similarly, except that the silica sources used were FD-SiO2 and MPTS (Alfa Aesar, 95 %).

Typically, FD-SiO2 was first mixed with TPAOH and stirred overnight at room temperature.

MPTS was then added in the solution and stirred for additional 2 hours. The molar composition of the mixture was the same as above with 22.5 SiO2 obtained from FD-SiO2 and 2.5 SiO2 added as MPTS. A clear purplish red (Burgundy) color solution was obtained and was subjected to crystallization at 140°C for 48 hours. The obtained crystalline suspension was recovered by filtration.

For the preparation of the MPTS functionalized silica (MPTS-SiO2), the FD-SiO2 was mixed with deionized water and stirred overnight at room temperature. After that, MPTS was added in the suspension (pH ~ 10) and stirred for additional 2 hours prior aging for 12 hours and heated at 140 °C for 48 hours. The suspension was filtrated and dried.

The removal of structure directing agent from as-synthesis samples has been performed by calcinations or by using a cold O2-plasma treatement The calcination process of the sample is consisted of heating from RT to 500 °C with a heating rate of 1.75°/min, kept at 500 °C for 5 hours and then cooled down to room temperature in 5 hours. Cold O2-plasma treatment has been performed at low pressure (350 Pa) without any temperature alteration as detailed in the reference [34].

Characterization methods

Powder X-ray diffraction (XRD) patterns of the samples were recorded using a STOE STADI-P diffractometer (Cu Kα, λ= 0.15406 nm), with 0.028 step size and 1s step time.

Electron micrographs of the samples were recorded on a Philips XL30 FEG scanning electron microscope (SEM). The chemical composition of the as prepared samples was determined by X-ray Fluorescence (XRF) analysis with a MagiX PHILIPS PW2540. In addition the amount of carbon, nitrogen and sulfur were determined using a Thermoquest NA2500 automatic apparatus. Solid state CP-MAS NMR spectra of the samples were recorded on a Bruker MSL 300 spectrometer using a 7 mm probe, operating at 59.6 MHz for 29 Si and 75.5 MHz for 13 C, respectively. Deconvolution and fitting of the NMR spectra were performed using the Winfit program [36]. The Raman spectra were measured at room temperature with a Bruker Equinox 55 FT-IR spectrometer equipped with an FRA106/S FT-Raman module. For the nitrogen (N2) adsorption measurements, the powder samples were calcined at 550 °C and outgassed at 350 °C prior analysis with a Micromeritics ASAP 2420 surface area analyzer. Thermal (TG/TGA) analyses were performed using a Setaram TGDSC 111 analyzer (heating rate of 5 °C min -1 ) in air.

The real-time in-situ FTIR spectroscopy studies of plasma treatment were performed on self-supporting wafers of zeolite MPTS-Silicalite 1 (~10 mg.cm -2 ) placed in the plasma reactor, where a desired gas composition was sustained at low pressure (350 Pa) after evacuation under vacuum for several minutes. The dielectric barrier discharge was ignited with a 50 Hz sinusoidal power supply (2 kV) between two electrodes fused to the IR cell.

During the experiments, the temperature increase due to the cold plasma process was below DT= 120 °C. The IR spectra were collected in transmission mode on a Bruker Vertex 80v equipped with a cryogenic MCT detector (4 cm -1 resolution, 8 scans, and acquisition time ~1.2 s). For a relative high amount of zeolite (>300 mg), the plasma treatment has been performed in an appropriate plasma reactor, without IR monitoring, and the treatment has been realised in the same condition wich cited above. The time of the treatment depend of the amount of zeolite, it is about 30 min for 300 mg.

The water mass gain rate upon exposure at constant temperature and relative humidity (RH) were used for a qualitative evaluation of the affinity of the pure silica and MPTSmodified samples towards water. The measurements were performed at 25 ºC using a CiSorp Water Sorption Analyzer (CI Electronics, UK). Calcined samples stored at ambient conditions were used in these measurements. The instrument allows two samples to be measured simultaneously. The samples were transferred from the vials to the instrument's chamber and the humidity was increased to 85%. The mass of the samples was recorded every 5-30 seconds over more than 5 hours.

Results and Discussion

General characterization

The crystalline nature of the Silicalite-1 and MPTS-Silicalite-1 samples was proven by X-ray diffraction (Fig. 1). Both samples exhibit diffraction patterns characteristic of the MFItype crystalline phase. Besides, a mesoporous phase in the MPTS-Silicalite-1 sample is seen by the presence of a relatively broad diffraction peak at low 2q (Fig. 1 b). The mesoporous peak at 1.8° 2q is not present in the XRD pattern of the amorphous MPTS-SiO2 and in the pure Silicalite-1 (Fig. 1). This can be explained by the co-condensation process occurring in the presence of MPTS as silica source and as template, leading to a high degree of framework cross-linking between the zeolite silica framework and the organosiloxane, thus resulting in the formation of both micro-and mesopores. In order to probe the porosity of these samples, calcination was carried out at 550 °C for 6 hours. No change in the crystallinity of the samples was measured however the mesoporosity was destroyed. Furthermore, the particle size and morphology in the calcined samples have not been changed.

In order to preserve the entire porosity of the MPTS-Silicalite-1 sample, a plasma treatment was carried out on this sample (see experimental section). Recently we have shown the efficiency of this process in the activation of microporous materials at relatively low temperature (<150 °C) [34]. This method could be useful for the thermally unstable materials.

In our case, this technique has been used in order to preserve the mesoporosity of MPTS-Silicalite 1, unstable after calcinations at high temperature. As show Figure 2, all the Bragg peaks are preserved after removal of the templates under plasma. Figure 3 present the evolution of IR spectra of MPTS-Silicalite 1 during O2-plasma treatment. A total disappearance of the C-H bands under plasma treatmentcould be observed after 10 min wich confirm the removing of the entire template and the liberation of zeolite porosity.

The morphological features of the samples revealed by SEM are shown in Figure 4. The Silicalite-1 consists of nanoparticles with almost spherical shape and a diameter of ca. 90 nm.

The organo-functionalized sample, MPTS-Silicalite-1, contain nanoparticles with a size below 50 nm which tend to form larger agglomerates with an ultimate size between 200 and 1000 nm. In contrast to the crystalline appearance of MPTS-Silicalite-1 and Silicalite-1, the functionalized amorphous silica (MPTS-SiO2) does not have any specific morphology and shape. The size and the shape of the MPTS-SiO2 fibers are determined by the conditions of drying.

Incorporation of MPTS in silica samples

The incorporation of MPTS in the samples was proven by analyzing the sulfur content, and the data are presented in Table 1 as amount of element per 1g of SiO2. In the as synthesized MPTS-SiO2 sample about 1.9 mmol MPTS is present, while in the MPTS-Silicalite-1 retained 4.1 mmol MPTS per gram silica. Only 0.9 mmol TPAOH was occluded in the MPTS-Silicalite-1, which is the same as in Silicalite-1 material.

The incorporation of MPTS in the samples was confirmed by both 29 Si and 13 C CP-MAS NMR spectra (Figures 5 and6). The 29 Si solid state NMR spectra of MPTS-Silicalite-1 and Silicalite-1 contain a main peak at -112 ppm and a weak peak at -102 ppm, which are attributed to Q 4 [Si(OSi)4] and Q 3 [Si(OSi)3OH] species, respectively [37,38]. Despite that the cross-polarizing technique is not quantitative, the intensity of the Q 4 peak is significantly higher than that of Q 3 , meaning that only a small amount of defect sites (Si-OH) were formed in the both samples. In addition, two well-resolved peaks at -68 and -55 ppm were found for the organo-functionalized sample (MPTS-Silicalite-1, Fig. 5b). These peaks are attributed to

T 3 [R-C-Si-(OSi)3] and T 2 [R-C-Si(OSi)2OH
] species, respectively. The T 2 and T 3 species confirm the presence of organosilane centers from the MPTS, and show that the Si-C bonds remain intact during the synthesis. This is an indication for the high degree of framework cross-linking between zeolite silica framework and the organosiloxane from the MPTS.

To identify the organic moieties attached to the zeolite framework, the solid state 13 C CP-MAS NMR measurements were carried out on the three samples. The resonance peaks at 62.7, 16.3, 11.3 and 10.1 ppm in the spectrum of pure Silicalite-1 can be attributed to the 13 C sites originated from the structure directing agent TPAOH (Figure 6 a) [39][40]. Additional peaks positioned at 35.5, 34.7, 14.0 and 13.0 ppm were only observed in the MPTS-Silicalite-1 sample. The most prominent peaks from the mercaptopropyl group at ~35 and 23.8 ppm are present. According to previous studies, peaks at 37-38 ppm are observed for organofunctionalized mesoporous silica prepared in alkaline solution, when quaternary ammonium compounds as structure directing agent and MPTS as organo-functional compound were used [41][42][43]. These peaks are tentatively assigned to the carbon closest to the S from disulfide group (RS-SR) or oxidized sulfur products. However, these peaks were not observed when samples were prepared in acidic medium or using neutral co-block polymers as structure directing agent [44][45]. In the case of the MPTS-SiO2 sample prepared in the absence of TPAOH, only the resonance peaks at 28.1 and 13.0 ppm identical to mesoporous silica functionalized with MPTS by post-synthesis grafting approach are seen (Figure 6 c) [37]. This leads to the suggestion that the SH thiol groups in the MPTS-Silicalite-1 sample are in strong interactions with the quaternary ammonium ions (TPA + ) after deprotonation in the aqueous base medium (Scheme 1). Therefore the resonance peaks at position 35.5 and 23.8 ppm could be due to C1 and C2 from S2 species, which are interacting with TPA + . The splitting of C1 peak into a doublet (35.5 ppm and 34.7 ppm) could be due to the conformational effects of the propyl chains incorporated in the zeolite channels. The two unresolved peaks at 14.0 and 13.0 ppm can be assigned to C3 resonance from both species (see Scheme 1).

The presence of the MPTS compound in the as-prepared MPTS-Silicalite-1 sample was further studied by the Raman spectroscopy. The spectra of Silicalite-1, MPTS-Silicalite-1 and MPTS-SiO2 samples are shown in Figure 7. In addition to the bands at 760, 1050, 1110, 1320 (doublet) and 1430 cm -1 , observed for Silicalite-1, the spectrum of MPTS-Silicalite-1 contains numerous bands. The bands at 650 and 740 cm -1 are assigned to νC-Si and νC-S stretching mode of the MPTS compound [46][47]. The bands at 1259 (doublet), 1302, and 1413 cm -1 are attributed to the C-H bending mode of the propyl chain of MPTS. These bands are slightly shifted in the MPTS-SiO2 sample in comparison with MPTS-Silicalite-1, thus proving that the MPTS is incorporated in the channels of the MPTS-Silicalite-1 sample. Raman spectroscopy is an excellent tool for detection of SH groups due to their relatively intensive Raman scattering, however, only a weak band at 2750 cm -1 which is due to the SH stretching mode is detected for the MPTS-Silicalite-1 sample (see the insert in Fig. 7), which is in a good agreement with the 13 C CP-MAS NMR results.

In summary, the NMR and Raman spectroscopies support the conclusion that TPAOH is present in the pores of Silicalite-1and MPTS-Silicalite-1 samples. In the case of MPTS-Silicalite-1, the TPAOH coexist with the organic moieties Si-R-, while the mercapto-propyl moieties are anchored to the surfaces of the MPTS-SiO2 sample. These statements are also supported by the chemical analysis data (see Table 1).

Thermal analyses (TG/TGA) of the samples were performed in oxidative conditions (Figure 8). The total weight losses of MPTS-SiO2, Silicalite-1 and MPTS-Silicalite-1 were 15.1, 15.5 and 26.4 wt. %, respectively (Table 2). The main weight loss near 300 °C is shifted to higher temperatures in the following order: MPTS-Silicalite-1 (310°C) < MPTS-SiO2 (320°C) < Silicalite-1 (345°C). Only the Silicalite-1 sample exhibits defined weight loss below 250°C. It can be ascribed to desorption of firmly bound water in addition to desorption of loosely bound water.

In the case of MPTS-SiO2 a small weight loss at 260 °C (1.5%) and a steep weight loss at 320 °C (5.5 %) were measured, followed by a broad weight loss (7 %) at 390 °C and 520 °C. According to the literature, [48][49] the weight loss at 320 °C arises from elution of sulfurcontaining molecules resulting from anchored propanethiol decomposition. Then propylene is evolved from the grafted alkyl chains, and dehydroxylation or desulphurization is occurred at higher temperature.

The weight losses of the Silicalite-1 sample (Figure 8 A,a) due to the degradation of the TPA + template are occurred at 345 °C (9 %) and 420 °C (3 %). After removal of the small amount of water below 200°C from MPTS-Silicalite-1 (1 %), a major weight loss at 310 °C (17 %) followed by two peaks at about 440 °C (2.1 %) and 570 °C (5.7 %) were measured.

The first step is from sulfur-containing molecules arising from propanethiol decomposition and then propylene is evolved from grafted alkyl chains.

The improved hydrophobicity of the MPTS-modified samples compared to pure silica was further confirmed by kinetics measurements at 85 % RH (Figure 9). It is well-known that Silicalite-1 is hydrophobic in nature as it doesn't contain aluminum. However, depending on the amount of structural defects, Silicalite-1 samples show a certain degree of hydrohilicity as well, and the effect is more pronounced for nanosized Silicalite-1 samples. Colloidal silica, on the other hand, is hydrophilic in nature. Thus, the mass change with time of FD-SiO2 is larger compared to that of Silicalite-1 (Fig. 9 a,b). The mass gain with time of both MPTS-SiO2 and MPTS-Silicalite-1 samples was less pronounced in comparison with the mass gain of corresponding non-modified samples. However, the decrease in mass gain was larger for the MPTS-SiO2 sample (from ca. 8.7% mass change for FD-SiO2 to ca. 2.2 % for MPTS-SiO2, Fig. 7 (d)) compared to the decrease for MPTS-Silicalite-1 (from ca. 5.4 % for Silicalite-1 to ca. 3.7 % for MPTS-Silicalite-1, Fig. 7 c). This can be explained by the pore structure of FD-SiO2 sample making the grafting procedure more efficient.

Textural properties

The porosity of the samples was studied by N2 adsorption; the measurements were carried out on calcined samples (Fig. 10). All isotherms contain hysteresis loop indicating the presence of mesopores. The hysteresis loop in the pure Silicalite-1 isotherm is related to the presence of mesopores and micropores in the agglomerates of nanosized particles with large external surface area. For the MPTS-Silicalite-1 sample after calcinations the shape of the isotherm changes to a nearly type I characteristic of microporous materials (see Fig. 10 b).

Moreover, the nitrogen uptake at low relative pressure (below 0.1 P/P0) was higher for the MPTS-Silicalite-1 in comparison with Silicalite-1indicating a higher microporosity of the former. The BET surface areas calculated from the range 0.05-0.25 P/P0 for the Silicalite-1 and MPTS-Silicalite-1 were 416 and 477 m 2 /g, respectively (Table 3). The microporous volume for all samples was determined by the a-plot method using a Silica-1000 as a reference non-porous material. The microporous volumes (Vmic) were 0.15 and 0.22 cm 3 g -1 for Silicalite-1 and MPTS-Silicalite-1, respectively. In the case of MPTS-SiO2, the isotherm was of type IV, and a micropore volume of 0.08 cm 3 g -1 and a BET surface area of 262 m 2 g -1 were determined.

Conclusions

Hydrophobic porous materials have been prepared by co-condensation method using 3mercaptopropyltrimethoxysilane (MPTS) as organo-functional compound and silica cosource. The incorporation of the organo-functional compounds into the zeolite framework has been proven by the NMR and Raman spectroscopy, and supported by TGA analysis. The presence of MPTS results in the formation of mesopores in the organo-functionalized samples. In addition, the MPTS-modified samples showed increased hydrophobicity according to TGA and water vapor sorption measurements. The method is simple and, compared to other methods for synthesis of hydrophobic zeolites such as the F route is less toxic and interesting for green chemistry applications.

Tables.

FiguresFigure 1 .Figure 2 .

 12 Figures

Figure 3 .

 3 Figure 3. Evolution of IR spectrum of MPTS-Silicalite-1 sample during O2-plasma treatment. Insert: IR spectra collected for the sample after 1 min (a) and 10 min (b) of O2-plasma treatment.

Figure 4 .

 4 Figure 4. SEM images of (a) Silicalite-1, (b) MPTS-Silicalite-1, and (c) MPTS-SiO2.

Figure 5 .

 5 Figure 5. 29 Si CP-MAS NMR spectra of (a) Silicalite-1, (b) MPTS-Silicalite-1, and (c) MPTS-SiO2.

Figure 6 .

 6 Figure 6. 13 C CP-MAS NMR spectra of (a) Silicalite-1, (b) MPTS-Silicalite-1, and (c) MPTS-SiO2.

Figure 7 .Figure 8 .Figure 9 .

 789 Figure 7. Raman spectra of (a) Silicalite-1, (b) MPTS-Silicalite-1, and (c) MPTS-SiO2.

Figure 10

 10 Figure 10 Nitrogen isotherms of (a) TPA-Silicalite-1, (b) MPTS-Silicalite-1 (calcined), (c) MPTS-Silicalite-1 (plasma) and (c) MPTS-SiO2.!!!!

Table 1 .

 1 Chemical composition of as synthesized samples.

	Sample	Elemental analysis		TPAOH	MPTS (S)
					(N)
		g g(SiO2) -1		mmol g(SiO2) -1
	Si	C	N	S
	FD SiO2
	0.467	nd	nd	nd
	MPTS-SiO2
	0.467	0.154	nd	0.061	-	1.9
	Silicalite-1
	0.467	0.109	0.013	nd	0.9	-
	MPTS-Silicalite-1
	0.467	0.37	0.013	0.13	0.9	4.1
	nd = non detected

Table 2 .

 2 TG/DTG data of as-synthesized samples.

	Sample	Temperature (°C) and weight loss (%)		Total weight
							loss at 800°C
							(%)
	MPTS-SiO2	200°C	260°C	320°C	380°C 520°C	15.1
		1.1%	1.5%	5.5%	7%
	Silicalite-1	200°C		345°C	420°C		15.5
		3.5%		9%	3%
	MPTS-Silicalite-1	200°C		310°C	440°C	560°C	26.4
		1%		17%	2.1%	5.7%

Table 3 .

 3 Textural properties of calcined samples determined by N2 sorption measurements.

	Sample	Vtotal (cm 3 g -1 )	Vmic (cm 3 g -1 )	SBET (m 2 g -1 )
	FD-SiO2	0.241	0.003	209
	MPTS-SiO2	0.208	0.080	262
	Silicalite-1	0.422	0.153	416
	MPTS-Silicalite-1	0.271	0.221	477
	(calcined)
	MPTS-Silicalite-1		0.150	379
	(plasma)	0.273
	Vtotal is determined at P/P0 = 0.99
	Vmic is determined from a-plot
	SBET is determined from the P/P0 range (0.05 -0.25)

  • Traitement Plasma Silicalite-1 TEAOH + 2.5 MPTS • Calciné four Silicalite-1 TEAOH + 2.5 MPTS Scheme 1Deprotonation of 3-mercaptopropyltrimethoxysilane in aqueous base.

	Si	H C 3 H	H C 2 H	H C 1 H	SH	OH -aqueous	Si	C 3 H H	C 2 H H	C 1 H H	S	-	+ H 2 O
			S1						S2

Porous materials prepared by co-condensation synthesis approach

Ka-Lun Wong, † Mohamad ElRoz, † Lubomira Tosheva, ‡ Jean-Michel Goupil, † and Svetlana Mintova †, * Hydrophobic porous materials have been prepared by co-condensation method using 3mercaptopropyltrimethoxysilane (MPTS) as organo-functional compound and silica cosource. The MPTS incorporated into the zeolite framework led to an increased hydrophobicity and formation of mesopores.

Silica source Template

Improved hydrophobicity MPTS


Mohamad El-Roz

Zeinab Haidar

Louwanda Lakiss

Joumana Toufaily

Frederic Thibault-Starzyk

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

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 selfsupport 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 UVvisible spectroscopy. The photocatalytic activities have been investigated in the photodegradation of methanol and methylene blue, chosen respectively as model molecules for VOCs in air and dyes in water. The photocatalytic reactions of methanol and methylene blue have been followed by IR-operando and UV-visible spectroscopy respectively. TiO 2 /Luffa composites show a high capacity to remove dyes from water. It exhibited also 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 its interesting properties as a semi-conductor: it is cheap, non toxic, photostable, resistant to photocorrosion and present 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 activities, solar energy conversion, self-cleaning surface, etc.

Although titanium dioxide is an ideal environmental photocatalyst, it has some drawbacks that limit their large scale application especially when it is used in the nanosized form. For instance, the removal and recycling of the photocatalysis after the reaction process are very difficult. In addition the titanium dioxide nanostructures that are dispersed in the reaction media could be hazardous, due to their potential inflammatory and cytotoxic effects [START_REF] Reijnders | hazard redcutoin for the application of titania nanoparticles in enverimental technology[END_REF]. In this context, the immobilization of the photocatalysis on a specific support could be of great benefit. Several attempts have been already reported in the literature and various techniques were successfully used to immobilize TiO 2 on different supporting materials such as SiO 2 glass beads [START_REF] Tashibi | Lifetime and Regeneration Studies of Various Supported TiO 2 Photocatalysts for the Degradation of Phenol under UV-C Light in a Batch Reactor[END_REF], rings [START_REF] Fernandez | Orange II photocatalysis on immobilised TiO 2 : Effect of the pH and H 2 O 2[END_REF], and reactor tubular walls [START_REF] Lee | Removal of paraquat dissolved in a photoreactor with TiO 2 immobilized on the glass-tubes of UV lamps[END_REF][START_REF] Nikolaki | Photocatalytical degradation of 1,3-dichloro-2-propanol aqueous solutions by using an immobilized TiO 2 photoreactor[END_REF]; fiber-glass [START_REF] Horikoshi | Photodecomposition of a nonylphenol polyethoxylate surfactant in a cylindrical photoreactor with TiO 2 immobilized fiberglass cloth[END_REF][START_REF] Aminian | Adsorption of TiO 2 Nanoparticles on Glass Fibers[END_REF]; quartz [START_REF] Martyanov | Comparative study of TiO 2 particles in powder form and as a thin nanostructured film on quartz[END_REF][START_REF] Antoniou | Application of immobilized titanium dioxide photocatalysts for the degradation of creatinine and phenol, model organic contaminants found in NASA's spacecrafts wastewater streams[END_REF]; zeolites [START_REF] Xu | Photoactivity of Titanium Dioxide Supported on MCM41, Zeolite X, and Zeolite Y[END_REF][START_REF] Li | Photodegradation of an azo dye using immobilized nanoparticles of TiO 2 supported by natural porous mineral[END_REF]; perlite [START_REF] Hosseini | Immobilization of TiO 2 on perlite granules for photocatalytic degradation of phenol[END_REF]; pumice [START_REF] Kansal | Studies on TiO 2 /ZnO photocatalysed degradation of lignin[END_REF]; alumina-based ceramic [START_REF] Xie | Origin of Photocatalytic Deactivation of TiO 2 Film Coated on Ceramic Substrate[END_REF]; stainless steel [START_REF] Shang | Structure and photocatalytic characteristics of TiO 2 film photocatalyst coated on stainless steel webnet[END_REF][START_REF] Kieda | Study of Transparent Visible-Light-Active TiO2 Self-Cleaning Surfaces-Effects of N-Doping Temperature and Thin Film Thickness[END_REF]; aluminum [START_REF] Chen | Photocatalytic decomposition of benzene with plasma sprayed TiO 2 -based coatings on foamed aluminum[END_REF]; polymeric membranes [START_REF] Bellobono | Pre-industrial experience in advanced oxidation and integral photodegradation of organics in potable waters and waste waters by PHOTOPERM TM membranes immobilizing titanium dioxide and promoting photocatalysts[END_REF][START_REF] Lei | Immobilization of TiO2 nanoparticles in polymeric substrates by chemical bonding for multicycle photodegradation of organic pollutants[END_REF][START_REF] Tsydenov | Toward the design of asymmetric photocatalytic membranes for hydrogen production: Preparation of TiO2-based membranes and their properties[END_REF], etc.

Moreover, natural fibers were also found of great interest as supporting materials and cotton conveniently adapted inside the photoreactors [START_REF] Liuxue | Photocatalytic activity of anatase thin films coated cotton fibers prepared via a microwave assisted liquid phase deposition process[END_REF][START_REF] Tryba | Immobilization of TiO 2 and Fe-C-TiO 2 photocatalysts on the cotton material for application in a flow photocatalytic reactor for decomposition of phenol in water[END_REF]. They are inexpensive, abundant, environmentally benign and renewable resources. Recently we have used Luffa sponge (aegyptica or cylindrica) to support free-organic template zeolite materials. It demonstrated a high efficiency. It is a tropical annual climber vine plant (family Cucurbitaceae), with 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 µm) which allow a good supporting of inorganic materials (Figure 1). The network of the Luffa fibers provides a tridimensional form for the support that allows a good penetration of the light and decrease the density of the fibers.

Besides, the fibers nature makes easier the shaping of filters in different geometry and form.

In addition, these fibers present a high stability in the synthesis media and support the relatively high temperature (<170°C) and alkalinity of the synthesis media. Luffa sponges have been also applied as cell carriers in bioreactors [START_REF] Pekdemir | Process intensification in wastewater treatment: ferrous iron removal by a sustainable membrane bioreactor system[END_REF], scaffolds for tissue engineering [START_REF] Chen | Loofa sponge as a scaffold for the culture of human hepatocyte cell line[END_REF], for the development of biofiber-reinforced composites [START_REF] Boynard | Aspects of alkali treatment of sponge gourd (Luffa cylindrica) fibers on the flexural properties of polyester matrix composites[END_REF] and as biotemplate to selfsupport hierarchical zeolite macrostructures for bio-inspired structured catalytic reactors [START_REF] Zampieri | Biotemplating of Luffa cylindrica sponges to self-supporting hierarchical zeolite macrostructures for bio-inspired structured catalytic reactors[END_REF].

Since researches on immobilized TiO 2 photocatalysts were mostly focused on the use of the commercial TiO 2 P25 or anatase phase, our aim focused then on supporting TiO 2 anatase nanoparticles on Luffa sponges as natural supports. The possibility to use Luffa fibers as biotemplate to self-support hierarchical TiO 2 macrostructures will be also presented in this paper. The resulting composite Luffa/TiO 2 has been fully characterized and investigated as photocatalyst for VOCs degradation in air and dye degradation in water.

Experimental section

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 treated with a sodium hydroxide solution (NaOH, 0.1M) at 80°C for 2 h. The process was repeated twice. The fibers were then treated in a sodium hydroxide solution (NaOH, 0.1M) at 80°C for 12 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 the 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 have been washed for 5-10 minutes in an ultrasonic bath in order to remove the weakly suspended particles.

Characterization

TiO 2 and TiO 2 /Luffa composites have been characterized by X-ray diffraction (XRD; PANanalytical (X-Pert Pro) diffractometer with CuKα1 source (λ=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 (Thermo-electron evolution 500 UV-Vis spectrometer equipped with RSA-CU40 Diffuse Reflectance cell).

Photocatalytic application

The photocatalytic oxidation of methanol has been followed by IR spectroscopy of the solid surface (IR-operando) and the gas phase. TiO 2 /Luffa composites and TiO 2 /Luffa mechanically mixed (5/95 wt.%) were pressed into self-supported wafers (Ø= 16 mm, m~40 mg/cm 2 ) (Figure 1-c). IR spectra were collected with a Nicolet 5700 FT-IR spectrometer (64 scans/spectrum) equipped with a MCT detector. The operando system is 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 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. [START_REF] Lesage | Studying the NO x -trap mechanism over a Pt-Rh/Ba/Al 2 O 3 catalyst by operando FT-IR spectroscopy[END_REF][START_REF] El-Roz | New Operando IR Technique to Study the Photocatalytic Activity and Selectivity of TiO2 Nanotubes in Air Purification: Influence of Temperature, UV Intensity, and VOC Concentration[END_REF] It is made of a stainless steel cylinder that carries a toroidal sample holder in its centre, where the catalyst self supporting wafer is placed. Tightness is obtained by Kalrez© O-rings, and the dead volume (typically defined as the residual space between each sample face and the windows) is 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 is made possible without superposition of the gas phase signal and fluid dynamics is similar to that inside a honeycomb monolith. Gases are 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 [START_REF] El-Roz | New Operando IR Technique to Study the Photocatalytic Activity and Selectivity of TiO2 Nanotubes in Air Purification: Influence of Temperature, UV Intensity, and VOC Concentration[END_REF][START_REF] Thibault-Starzyk | 2D-COS IR study of coking in xylene isomerisation on H-MFI zeolite[END_REF]. 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). It has been performed by using a UV-light guide (A10014-50-0110) mounted at the entrance of a modified IR operando cell (Scheme S-1 in supporting information) in order to establish a "homogeneous" irradiation.

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 total flow was adjusted to 25 cm 3 /min. The analysis of the outlet gases was performed by means of a Nicolet 5700 FT-IR-gas spectrometer using a gas microcell.

As mentioned above, the photooxidation of methylene blue has been also performed using TiO 2 /Luffa and TiO 2 replica of Luffa (calcined TiO 2 /Luffa). Due to the high dyes absorption/adsorption capacity of TiO 2 /Luffa, photooxidation tests have been realized after absorption by using Luffa fibers as reference and the results of this part are reported in supplementary information. The photocatalytic activity is qualitatively estimated based on the color of the composite and Luffa fibers after irradiation. For TiO 2 replica Luffa, the photooxidation activity has been estimated using TiO 2 -P25 (Degussa) and TiO 2 anatase (Mulhouse et Than) as references.

Results

Characterization of TiO 2 /Luffa composites

Prior 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 duration 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 X-ray diffraction pattern of the resulted TiO 2 /Luffa composite is reported in Figure 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 X-ray 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 the synthesis was also characterized by XRD. It showed the Bragg reflections of the anatase type phase. Such a result confirms the high cristallinity and purity of the composites prepared. In order to investigate the thermal stability and estimate the TiO 2 recovery amount of the elaborated composites, thermal analyses have been performed. The samples were heated from 25 to 800 °C with a heating rate of 5 °C/min. Figure 4 shows the thermogravimetric curves of the 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 the TiO 2 surface. An additional non pronounced weight loss occurs progressively above 150 °C (insert of Figure 4). This later could be ascribed to the dehydroxylation phenomena 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 behavior. They are both stable for a temperature below 250 °C. A weight loss appeared above 250 °C. This was 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 corresponds to mineral compounds present in the fibers. For TiO 2 /Luffa composite, the total weight loss observed was about ~93.9%. Based on the results obtained for the 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 the plain Luffa fibers than TiO 2 /Luffa sample. Such a result demonstrates that the plain Luffa fibers are more hydrophilic than the composites which explain the high adsorption/absorption capacity of methylene blue by TiO 2 /Luffa (Figure S.3, supplementary information). The reproducibility of this result has been also tested using different samples synthesized under the same conditions. The error on the TiO 2 amount was estimated below 2%.

The effect of the temperature on TiOH groups has been also studied by in-situ IR spectroscopy. Figure 5 reports the IR spectra of the as-synthesized 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. It is assigned to hydrogen bonding between neighboring TiOH groups and/or water adsorbed on TiOH groups. This decrease is due to water desorption for T<100°C and to TiOH dehydroxylation for a higher temperature (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 increases (for 100 °C <T<200 °C) the intensity of the band at 3670 cm -1 decreases. This latter is accompanied with 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 desorbed water under vacuum at high temperature.

In order to investigate the biotemplate effect of Luffa fibers, a total combustion of the TiO 2 /Luffa composite was performed at 500 °C for 6 hours. The SEM pictures of the calcined TiO 2 /Luffa composite showed the formation of TiO 2 macro-microfibers Luffa sponge negative replica (TiO 2 -L) (Figure 6). This confirms the high dispersion and homogenous growth of TiO 2 on the Luffa fibers. Moreover, it demonstrates the possibility to use Luffa fibers as biotemplate to self-support hierarchical TiO 2 macrostructures. According to the XRD results, the negative replica TiO 2 -L is a pure anatase and the size of TiO 2 particles significantly increased in comparison with TiO 2 /Luffa due to the aggregation of the particles during the calcination.

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 (Figure7). The porous volume and the specific surface area are reported in Band Gap Energy (E) = h*C/λ, where h is the Plank constant (6.626 x 10 -34 J. s), C is the speed of light (3.0 x 10 8 m/s) and λ is the minimum absorption wavelength.

As a result the band gap energy (Eg) was 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 other hand, the TiO 2 -L is a pure anatase as confirmed by XRD, which is contradictory with the Eg found.

This result could be explained by the doping phenomena that can occur at high temperature after calcination and the formation of « Ti-C » bond and/or a Ti(III)/Ti(IV) ratio higher than that in the TiO 2 anatase.

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 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 information part. Indeed, the high capacity of the TiO 2 /Luffa fibers in the adsorption/absorption of dyes (Figure S.3) competes with the photocatalytic phenomena and renders the study quiet difficult. The photocatalytic effect of TiO 2 /Luffa composite has been then observed after using the composite as filter to remove methylene blue. 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 of the plain Luffa fibers (Figure S.4). 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. For comparison, a mechanical mixing of TiO 2 and Luffa (TiO 2 +Luffa) with a similar ratio to that of TiO 2 /Luffa composite (4/96 wt.%) has been tested under the same conditions. For the mechanical mixture TiO 2 +Luffa, the photocatalytic activity is very low under the various conditions used. This low photoactivity could be assigned to the low and inhomogeneous dispersion of TiO 2 (surface area ~2 m 2 /g vs 16 m 2 /g for TiO 2 /Luffa). In addition, the support might have an internal filter effect which limits the irradiation of an important part of the powders. In the case of TiO 2 /Luffa this effect is less important due to the presence of the majority of TiO 2 on the surface of the support and to their high and homogenous dispersion. The turnover frequency (TOF) has been calculated as described in the reference [START_REF] Szczepankiewicz | Infrared Spectra of Photoinduced Species on Hydroxylated Titania Surfaces[END_REF][START_REF] Boudart | cinetique des reactions en catalyseheterogene[END_REF]. It corresponds to the number of molecules converted per second and per active site. As an upper limit of the number of active sites n sites, we can choose the maximum value of the surface density of titanol groups TiOH, equal to 5 10 18 OH/m 2 or 5 OH/nm 2 [START_REF] Herrmann | Fundamentals and misconceptions in photocatalysis[END_REF].

Therefore, n sites = 5 10 18 (OH/m 2 ) x S BET (m 2 /g) x m cat .

Due to the limitation of the irradiation on the external surface of TiO 2 /Luffa pellet (see experimental part), the TOF calculated is a limit value.

The effect of the concentration of methanol has also been studied. The results are reported in Figure 10 and shortlisted in Table 1. The new bands that appear during the photooxidation were assigned to CO 2 (2400-2200 cm -1 ) and -C=O of carbonyl species (1820-1670cm -1 ). As reported in the previous works [START_REF] Boudart | cinetique des reactions en catalyseheterogene[END_REF][START_REF] El-Roz | An Operando-IR study of photocatalytic reaction of methanol on new *BEA supported TiO 2 catalyst[END_REF] the increase of the concentration led to a decrease of the CO 2 -selectivity of the reaction. It is important to note that the increase of the concentration increases the TOF of the photodegradation reaction. This result could be assigned to the interaction of methanol in the gas phase with the active species adsorbed on the surface. These results showed a high reactivity for TiO 2 present on the TiO 2 /Luffa composite with a TOF value higher than 38 molecules per second per active sites. It was less than 1 for the TiO 2 -P25 mechanically mixed with the Luffa fibers with similar proportions than TiO 2 /Luffa composite. The increase of the lamp intensity increases the TOF and the selectivity of the photooxidation reaction. The results are presented in table S-2 in SI. When the intensity is higher than 25% (~2.5 mw/cm 2 at 366nm), the reaction TOF reaches its maximum (> 38.7 molecules per second per active site) with a high CO 2 -selectivity. This means that for intensity higher than 25% I 0 the absorption of TiO 2 /Luffa reaches its maximum and for a TOF~38 the methanol combustion is complete. The TOF values for TiO 2 /Luffa composite found to be 1.5 to 5 times higher than that observed when TiO 2 -P25 is used as a reference under the same reaction conditions (values obtained by calculation of the data reported in references [START_REF] El-Roz | New Operando IR Technique to Study the Photocatalytic Activity and Selectivity of TiO2 Nanotubes in Air Purification: Influence of Temperature, UV Intensity, and VOC Concentration[END_REF][START_REF] El-Roz | An Operando-IR study of photocatalytic reaction of methanol on new *BEA supported TiO 2 catalyst[END_REF]). These high values could be assigned to the high TiO 2 dispersion and the high surface area of TiO 2 deposited on the Luffa fibers (S BET (TiO 2 in TiO 2 /Luffa composite)/ S BET (TiO2-P25)~7) .

Finally the new elaborated TiO 2 /Luffa composites showed high efficiency in the removal and photodegradation of methylene blue molecule used as a model of dyes in water. They also exhibited efficient photocatalytic activity in the photodegradation of methanol, model for VOCs in air. Furthermore, their non compact form, tridimensional structure, mechanical and chemical stability and low price make them very promising as green photocatalysts, for water and/or air 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 under different light intensities.

-Additional information related to the synthesis procedure (Figures S.1 and S.2) and the photoactivity of the composites for the removal and degradation of methylene blue.

Graphical abstract

Immobilization of TiO 2 on natural Luffa cylindrica fibers for photocatalytic applications Mohamad El-Roz, Zeinab Haidar, Louwanda Al Lakiss, Joumana Toufaily, Frederic Thibault-Starzyk Tables Table 1. Reactivity, selectivity and turnover frequency of methanol photooxidation reactions under polychromatic irradiation for different methanol concentrations using TiO 2 /Luffa composite as photocatalysts (Flow= 25 cm 3 /min, I 0 =25%, m pellet =90 mg m TiO2 ~ 2.9mg).

(L) (L) (L) (L) (A) (L) (A) (L) (A) (A) (A) (A)
Relative intensity

Synthesis procedure

The sol gel synthesis conditions of TiO 2 have been optimized prior to the preparation of the TiO 2 /Luffa composites. Two parameters were considered: the synthesis time duration and the temperature. The X-ray diffraction patterns of the samples prepared at different temperatures for 48 hours are reported in Figure S1. It has been observed that the anatase phase begins to appear at 60 °C but with very low yield (Figure S1). For the samples that have been prepared at temperatures above 60 °C, the cristallinity and the yield were much higher. Thus the temperature that has been used for the preparation of the Luffa composites was 100 °C. It should be noted that higher temperature could affect the mechanical properties of Luffa fibers.

The synthesis time duration was also investigated in this study.

Figure 3

 3 Figure 3 shows the SEM images of the plain (a-c) and composite Luffa fibers after ultrasonic treatment (d-f). As seen at this figure, the microfibers structure was completely preserved after the hydrothermal treatment and TiO 2 nanoparticles were uniformly dispersed and grown on and trough the Luffa fibers. The fibers were completely covered and the radius of the TiO 2 nanoparticles was about 15-20 nm. Indeed, the net microstructures and hydroxyl groups of the Luffa fibers provided a homogeneous dispersion of TiO 2 nanoparticles, as well as a strong and complete recovery of the surface. Hydroxyl groups of cellulose may play a key role in the synthesis and growth of TiO 2 nanoparticles by condensation reaction (TiOH+HOC TiOC+H 2 O) and/or by hydrogen bonding.

Figure 9

 9 Figure 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 (ν+δ) H 2 O vibration mode disappeared after irradiation. Nomodification of the bands between 5000 and 3200 cm -1 was observed. In addition a low amount of CO 2 has been detected in the first few minutes of irradiation under dry air. This amount was assigned to the degradation of impurities adsorbed on TiO 2 /Luffa surface. These results show the high stability of the support under irradiation.

Figure 1 :

 1 Figures caption

Figure 2 :

 2 Figure 2: X-ray diffraction patterns for TiO 2 samples (a) standard, (b) TiO 2 powder recovered after the synthesis, (c) TiO 2 deposited on Luffa fibers (d) Luffa fibers.

Figure 3 :

 3 Figure 3: SEM pictures of treated Luffa fibers before (a-c) and after TiO 2 deposition (d-f).

Figure 4 :

 4 Figure 4: Thermogravimetric curves of: (a) as-synthesized TiO 2 , (b) TiO 2 /Luffa and (c) Luffa. Insert: full scale of the thermogravimetric curves as-synthesized TiO 2 .

Figure 5 :

 5 Figure 5: IR spectra of as-synthesized TiO 2 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).

Figure 6 :

 6 Figure 6: Image (a) and SEM pictures of replica TiO 2 Luffa sponges (TiO 2 -L) (b-e).

Figure 7 :

 7 Figure 7: Nitrogen sorption isotherms adsorption (close symbols) and desorption (open symbols) at 77 K for : (a) Luffa fibers, (b) TiO₂/luffa fibers, (c) TiO₂-L (the TiO₂ powder recovered after the synthesis) and (d) TiO 2 powder.

Figure 8 :

 8 Figure 8: UV-vis spectra of (a) TiO 2 -P25, (b) TiO 2 -L and (c) TiO 2 -anatase.

Figure 9 :

 9 Figure 9: Evolution of the IR spectra of TiO 2 /Luffa surface during methanol photooxidation under operando conditions. (Flow= 25cm 3 /min, MeOH/O 2 /Ar 400ppm/20%/79.99%, I 0 =25% ~2.5 m/cm 2 at 366nm).

Figure 10 :

 10 Figure 10: A) Evolution of the IR spectra of the gas phase during the photooxidation of methanol at different concentrations. (Flow= 25cm 3 /min, I 0 =25%). B) IR spectra of the gas phase before UV-irradiation of TiO 2 /Luffa composite pellet, at different methanol concentrations.

  FiguresFigure1

  Figure 3

Figure S. 2

 2 shows the X-ray diffraction patterns of the resulted samples obtained at 100 °C for different time durations. It has been observed that the the yield increases when the time duration increases. Indeed the anatase phase appears at 100 °C after 2 hours but the formation yield is very low (FigureS2).

Figure S1 .

 S1 Figure S1. X-ray diffraction patterns for anatase phase (a) and TiO 2 prepared for 48 hours at 100°C (b), 80°C (c), 60°C (d) and 35°C (e).

Figure S2 .Figure S3 .Figure S4 .

 S2S3S4 Figure S2. X-ray diffraction patterns for TiO 2 samples prepared at 100 °C for : (a) 48 h,(b) 12 h,(c) 7h,(d) 3 h,(e) 2 h, (f)1h .

table S -

 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 TiO 2 Luffa composites was about 16 m 2 /g while that of TiO 2 powder synthesized under the same condition was 235 m 2 /g. Taking into account the total amount of TiO 2 supported on Luffa fibers (~4%), the specific surface area of TiO 2 /Luffa could be estimated to 400 m 2 /g. It is much higher than that of pure TiO 2 . Such a result confirms the high dispersion of TiO 2 particles on the Luffa fibers. It is noteworthy that several TiO 2 /Luffa samples have been prepared and characterized by nitrogen sorption to test the reproducibility. The results were similar and the error was 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 could be explained by the agglomeration of TiO 2 nanoparticles after calcination.It is difficult to investigate the UV-visible absorption of TiO 2 /Luffa samples due to the low amount of TiO 2 supported. For this reason the UV-visible studies were performed on the TiO 2 powder samples (TiO 2 -P25, TiO 2 pure anatase and TiO 2 -L). The results are reported in Figure8. They showed minimum absorption wavelength at λ= 405, 416, and 380 nm for TiO 2 -P25, TiO 2 -L and TiO 2 anatase respectively. The band gap energy was calculated as follows:

Table S2 .

 S2 Reactivity, selectivity and turnover frequency of the photooxidation of 1900 ppm of methanol under different polychromatic irradiation intensities using TiO 2 /Luffa composite as photocatalysts (Flow= 25 cm 3 /min, I 0 =25%, m pellet =90 mg m TiO2 ~ 2.9mg).

	Figure 10
		A								B
	0.04 H 2 O I0 (%)	CH 3 OH [MeOH] CO 2 converted (ppm)	R 2 C=O	R 2 C=O CH 3 OH Conversion H 2 O (%)	0.04 CO 2 -selectivity (%)	TOF (molecules/s/active sites)
	25			1102					58	30			>30
									1900 ppm
									1400 ppm
									900 ppm
									400 ppm
	50	3500	3000	2500 1445	2000		1500	1000 71.6	3500 100	3000	2500	2000 >39	1500	1000
			Wavenumbers (cm	-1 )						Wavenumber (cm -1 )
	75			1433					75.4	100			>38
	100		1440					76	100			>38


Mohamad El-Roz

Philippe Bazin

‡ Tadeja

Birsa Čelič

Nataša Zabukovec Logar

Frederic Thibault-Starzyk

Pore occupancy changes water/ethanol separation in MOF -Quantitative map of coadsorption by IR

Keywords: FTIR spectroscopy, in-situ gravimetry, MIL-100(Fe), water-ethanol separation

The conventional distillation method to separate ethanol from water is energy-intensive and inefficient due to the presence of the azeotropic point of the binary system. Various processes have been proposed as potential separation techniques. Among them, preferential adsorptionbased separation is considered to be an efficient and energy-saving method for purification due to the easy regeneration under relatively mild conditions. In this work, the co-adsorption of gaseous water and ethanol on porous metal-organic framework (MIL-100(Fe)) in various proportions has been studied by coupling FTIR spectroscopy with in-situ gravimetry (AGIR).

The quantifications of co-adsorbed water and ethanol on the MIL-100(Fe) have been performed under different conditions (P/P0). Ethanol is preferentially adsorbed on MIL-100(Fe). Vaporliquid equilibrium of water/ethanol was altered when the pore volume of the MIL-100(Fe) was partially occupied. Our results suggest that the optimal conditions for the separation of H2O/EtOH on MIL-100(Fe) is at EtOH(P/Po)<0.05 with H2O(P/Po)<0.4 at room temperature.

Introduction

Separation of ethanol/water mixture is of great significance because the ethanol use as alternative to oil-based fuels and as a fuel additive. [START_REF] Hill | economic, and energetic costs and benefits of biodiesel and ethanol biofuels[END_REF][START_REF] Lively | Ethanol and water adsorption in methanol-derived ZIF-71[END_REF] The recent push for ethanol as an additive to gasoline has motivated the research interests in the production of anhydrous ethanol. [START_REF] Chum | Biomass and renewable fuels[END_REF][START_REF] Goldemberg | Ethanol for a Sustainable Energy Future[END_REF] In fact, water is always present in ethanol produced from the fermentation of biomass, and it is also found in ethanol produced via the catalytic hydration of ethylene. The conventional distillation method to separate ethanol from water is energy-intensive and inefficient due to the presence of the azeotropic point of the binary system (azeotrope at an 89.4:10.6 molar ratio, 78.2°C, and 1 atm of pressure), [START_REF] Treybal | Mass-transfer operations[END_REF] and only about 4 wt.% of water could be removed from ethanol by distillation. To circumvent these problems, various processes including liquid-liquid extraction, pervaporation, and adsorption in porous materials and molecule sieves have been proposed as potential separation techniques. [START_REF] Kumar | Anhydrous ethanol: a renewable resource of energy[END_REF] Among them, preferential adsorption-based separation is considered to be an efficient and energy-saving method for purification due to the easy regeneration under relatively mild conditions. [START_REF] Phan | Preferential Adsorption from Liquid Water-Ethanol Mixtures in Alumina Pores[END_REF][START_REF] Wang | Deconstructing Hydrogen-Bond Networks in Confined Nanoporous Materials: Implications for Alcohol-Water Separation[END_REF] Compared with traditional porous sorbents such as activated carbons and inorganic zeolites, metal organic frameworks (MOFs) materials have advantages for specific adsorption and separation. MOFs that are formed via coordination between metal centers and organic linkers possess extremely large surface areas and well-defined pores. They are predicted to be highly efficient for many potential applications in gas-separation membranes, [START_REF] Haldoupis | Efficient Calculation of Diffusion Limitations in Metal Organic Framework Materials: A Tool for Identifying Materials for Kinetic Separations[END_REF] selective gas adsorption, 10 hydrogen [START_REF] Murray | Hydrogen storage in metal-organic frameworks[END_REF] and CO 2 [START_REF] Millward | Metal-Organic Frameworks with Exceptionally High Capacity for Storage of Carbon Dioxide at Room Temperature[END_REF][START_REF] Soubeyrand-Lenoir | How Water Fosters a Remarkable 5-Fold Increase in Low-Pressure CO 2 Uptake within Mesoporous MIL-100(Fe)[END_REF][START_REF] Leclerc | Infrared study of the influence of reducible iron(III) metal sites on the adsorption of CO, CO 2 , propane, propene and propyne in the mesoporous metalorganic framework MIL-100[END_REF] storages, catalysis, [START_REF] Lee | Metal-organic framework materials as catalysts[END_REF] and sensing. [START_REF] Zacher | Thin films of metal-organic frameworks[END_REF] Diverse interactions between host frameworks and guest molecules, such as hydrogen-bonding, π-stacking, and van der Waals interactions, can be engaged to affect the selectivity and performance of adsorption. [START_REF] Serre | Role of Solvent-Host Interactions That Lead to Very Large Swelling of Hybrid Frameworks[END_REF] To date, progress has been made in the construction of porous framework materials with selective adsorption towards alcohols or water, [START_REF] Lively | Ethanol and water adsorption in methanol-derived ZIF-71[END_REF][START_REF] Zhang | Adsorption of C1-C4 Alcohols in Zeolitic Imidazolate Framework-8: Effects of Force Fields, Atomic Charges, and Framework Flexibility[END_REF][START_REF] Borjigin | microporous metalorganic framework with high stability for GC separation of alcohols from water[END_REF][21][START_REF] Nalaparaju | Molecular Understanding for the Adsorption of Water and Alcohols in Hydrophilic and Hydrophobic Zeolitic Metal-Organic Frameworks[END_REF] but the practical separation of alcohol/water mixtures, which is more complicated than single-component adsorption experiments, has rarely been explored. [START_REF] Ren | Targeted Functionalization of Porous Materials for Separation of Alcohol/Water Mixtures by Modular Assembly[END_REF] Based on density functional theory study, a combination of hydrogen bonding between the hydroxyl group in ethanol and MOF framework as well as van der Waals interactions between the ethanol alkyl chain with the phenyl ring in MOF were determined to be crucial for the alcohol-water separation in Zn-based MOF. [START_REF] Wang | Deconstructing Hydrogen-Bond Networks in Confined Nanoporous Materials: Implications for Alcohol-Water Separation[END_REF] In another computational study, the alterations of H-bond network together with water-alcohol separation were attributed to confiment effects in the silicalite-1 environment. [START_REF] De Lima | Mechanism of Alcohol-Water Separation in Metal-Organic Frameworks[END_REF] In this paper, our work is focused on the preferential adsorption on MIL-100(Fe) from gas water-ethanol mixtures. A new and successful approach has been used. It is based on the coupling infrared spectroscopy and in-situ gravimetry (AGIR). IR spectroscopy is a powerful and recognized technique to study the adsorbed species present on material surfaces (silica, zeolites, mesoporous materials, etc.). It allows one to quantify the adsorbates, e.g. water, and to characterize the active sites. [START_REF] El-Roz | Infrared study of the silica/silane reaction[END_REF] In-situ gravimetry permits to determine the mass adsorbed under different relative pressures. Therefore, a coupling of transmission IR spectroscopy with in-situ gravimetry is essential to determine the molar absorbance coefficients for the characteristic vibration bands of adsorbates, such as water and ethanol. Consequently, the quantification of water and ethanol co-adsorbed on the surface from different vapor water/ethanol mixtures and/or under different conditions becomes possible. Such a study allows highlighting the material performance not only for water/ethanol separation, but it also opens the way to study the adsorption of vapor mixtures on porous materials.

Experimental Section

Synthesis and characterization

An iron-based MOF material MIL-100(Fe) was synthesized hydrothermally from commercially available reagents. The final single crystalline phase was obtained after crystallization in Teflonlined autoclaves at 150 °C (5 days) from a mixture of reagents in following molar ratio: 3 Micromeritics 2020 volumetric adsorption analyzer. The isotherm shows type-I curves, the BET surface area is 1136 m 2 g -1 (p/p 0 = from 0.01 to 0.12) and the micropore volume estimated by the Dubinin-Astakhov equation is 0.38 cm 3 •g -1 , which is comparable with previously reported data. [START_REF] Surblé | Synthesis and catalytic properties of MIL-100(Fe), an iron(III) carboxylate with large pores[END_REF][START_REF] Birsa Čelič | Spectroscopic Evidence for the Structure Directing Role of the Solvent in the Synthesis of Two Iron Carboxylates[END_REF][START_REF] Seo | Large scale fluorine-free synthesis of hierarchically porous iron(III) trimesate MIL-100(Fe) with a zeolite MTN topology[END_REF] Additionally, the hydrothermal stability of MIL-100(Fe) material was tested by boiling in distilled water for different periods of time up to 24 hours under reflux. The structure did not change in water at ambient temperature not in boiling water for at least 24 hours, therefore the structure is very stable in water media.

AGIR technique

This technique developed recently in our laboratory allows measuring simultaneously the weight and IR spectra of a solid sample under gas flow, between room temperature and 773 K. The setup has been described in detail by Bazin et al. [START_REF] Bazin | Interaction of water and ammonium in NaHY zeolite as detected by combined IR and gravimetric analysis (AGIR)[END_REF] and has showed its interest in several works related to the quantification of adsorbed species on different materials. [START_REF] Bazin | Interaction of water and ammonium in NaHY zeolite as detected by combined IR and gravimetric analysis (AGIR)[END_REF][START_REF] Popov | Bio-oils Hydrodeoxygenation: Adsorption of Phenolic Molecules on Oxidic Catalyst Supports[END_REF][START_REF] Moulin | How to determine IR molar absorption coefficients of co-adsorbed species? Application to methanol adsorption for quantification of MgO basic sites[END_REF][START_REF] Stelmachowski | Speciation of adsorbed CO2 on metal oxides by a new 2-dimensional approach: 2D infrared inversion spectroscopy (2D IRIS)[END_REF] In this work, the AGIR was used to evaluate both water and ethanol adsorbed on MIL-100(Fe) sample at room temperature, versus the partial pressures water-ethanol vapor mixture. Analyses were carried out on self-supported pellets (2 cm² -20 mg). Infrared spectra of the sample were recorded with a Nicolet 6700 spectrometer equipped with a MCT detector (64 scans / 4 cm -1 resolution) within a broad spectral range [6000 -600 cm -1 ]. The infrared spectra and mass changes of the sample, for

Results

The porosity of MIL-100(Fe) originates from both 25 Å and 29 Å mesopores, which are accessible via 5.5 Å and 8.6 Å windows, respectively. [START_REF] Surblé | Synthesis and catalytic properties of MIL-100(Fe), an iron(III) carboxylate with large pores[END_REF] MIL-100(Fe) mesopores are easily accessible toward water and ethanol via the both windows, with a water and ethanol kinetic diameters equal to 2.68 Å and 4.5 Å, respectively. Therefore, the preferential water or ethanol adsorption depends of the interaction forces between these molecules and the MIL-100(Fe) surface.

Water and Ethanol isotherms on MIL-100(Fe) Therefore, optical isotherms of water and ethanol on MIL-100(Fe) are obtained by integration of the IR bands at 5210 cm -1 and at 877 cm -1 (Figures 3A-I and3B-I), respectively. The water isotherm is in good agreement with results previously published for MIL-100(Fe). [START_REF] Jeremias | MIL-100(Al, Fe) as water adsorbents for heat transformation purposes-a promising application[END_REF] At small relative pressures (p/p o <0.15), a first adsorption and cluster formation of water at the hydrophilic metal sites take place. [START_REF] Cělic | Study of Hydrothermal Stability and Water Sorption Characteristics of 3-Dimensional Zn-Based Trimesate[END_REF] The steep rise at 0.15<p/p o <0.50 has been soundly explained by the consecutive filling of, first, the 25 Å mesopores, then of the 29 Å mesopores. For ethanol, a type I isotherm is obtained. On the other hand, the in-situ gravimetry analysis shows the evolutions of mass gains (adsorbed mass) of MIL-100(Fe) during ethanol and water adsorptions (Figure S1). The adsorption isotherms and the optical isotherms have a totally similar shape. The Langmuir simulation of these isotherms provide total pore volume around 0.39 ± 0.02 cm 3 .g -1 and 0.35 ± 0.02 cm 3 .g -1 , estimated from ethanol and water gravimetric adsorption isotherms (using the specific volumic mass parameters), respectively (Figure S2). These values are in agreement with those obtained from the N 2 -adsorption isotherm (0.38 cm 3 /g), confirming a full pore accessibility of MIL-100(Fe) toward water and ethanol.

Based on the optical and gravimetric isotherms of pure water and pure ethanol, the molar absorption coefficients of the vibration bands at 5210 cm -1 and 877 cm -1 were then determined.

They were calculated from the relationship between the areas of the characteristic vibration bands of the adsorbates and their corresponding amounts (Figure 3). According to the Beer-Lamber law (equations 1), they are equals to the slopes of the curves for the IR band area evolution versus the corresponding amount of adsorbed molecules, taking into account the geometric area of the MIL-100(Fe) pellet. Consequently, the molar absorbance coefficient for (ν+δ)H 2 O and for (ν as )C-C-O (of ethanol), adsorbed on MIL-100(Fe), are found to be equal to 0.796 ± 5 10 -3 cm.µmol -1 and 0.726 ± 5 10 -3 cm.µmol -1 , respectively. Aν = ε ν.l.C = ε ν.l.n/V= ε ν.l.n/(s.l)= ε ν.n/s (equation 1)

With:

A (cm -1 ): IR band area of the band situated at ν-wavenumber; ε (µmol -1 .cm) ν: corresponding molar absorption coefficient; l (cm) : optical pathway (pellet thickness); Based on these results, the amounts of water and ethanol, co-adsorbed on MIL-100(Fe) from a water/ethanol vapor mixture, are then determined from the IR absorbance at 5210 cm -1 and 877 cm -1 , respectively (equation 2): In the region corresponding to a total pore occupation (zone c) the trend line follows the traditional vaporliquid equilibrium of the water-ethanol binary mixtures at room temperature. [START_REF] Baker | Equilibria in Ethanol-Water System at Pressures Less Than Atmospheric[END_REF] Therefore, in this region, the adsorbent (MIL100(Fe) has no significant effect. Vapor-liquid equilibrium is altered for partial pore occupations (a and b zones in Figure 8) showing the role of the MIL-100(Fe) surface in the preferential adsorption of ethanol. This variation can be assigned to the intermolecular interactions between the (phenyl) and oxy functions of the MIL-100(Fe) ligands with the ethyl and alcohol functions of the ethanol, respectively. In other hand, presence of water (in low concentration) could lead to the formation of new acid sites by the chemisorption of water clusters on the metal centres. [START_REF] Cělic | Study of Hydrothermal Stability and Water Sorption Characteristics of 3-Dimensional Zn-Based Trimesate[END_REF] These sites promote then the ethanol adsorption via hydrogen bonding with the alcohol function (the pK b of ethanol is higher than that of water).

(
Thus, at the interface between liquid and solid, the adjacent layers of dissimilar molecules are in force fields very different from those existing in the bulk liquid. Moreover, these long-range interactions would affect not only the molecular cohesive forces in the liquid phase but also the interfacial surface energy, and thus altering the vapor-liquid equilibrium (VLE) of the binary mixture. When the MIL-100(Fe) pores are almost occupied, the liquid-liquid interaction become dominant and the effect of the support on the bulk liquid (present on the pore) is insignificant. To conclude, these result indicate that the optimal condition for the separation of water/alcohols on MIL-100(Fe) is for EtOH(P/P o )<0.05 and H 2 O(P/P o )<0.4 (zone a in Figure 8).

Conclusion

In this work we have studied the preferential adsorption of water or ethanol from gas water-ethanol mixtures on MIL-100(Fe) by coupling in-situ gravimetry with infrared spectroscopy (AGIR). Coupling the transmission IR spectroscopy with in-situ gravimetry (AGIR) allowed determining molar absorbance coefficients for the characteristic vibration bands of water (at 5210 cm -1 ) and ethanol (at 877 cm -1 ). They were found to be equal to 0.796 cm.µmol - 1 and 0.726 cm.µmol -1 , respectively. Then, the quantification of water and ethanol co-adsorbed on the surface from different vapor water/ethanol mixtures was realized using this new approach.

We have shown that ethanol is preferentially adsorbed on MIL-100(Fe) for 0.0<H

each H 2 O

 2 /C 2 H 5 OH mixture investigated, were recorded after reaching the equilibrium, as indicated by the absence of change in the sample mass and infrared spectra. Additional indication for the occurrence of equilibrium was provided by a MS analyzer (Pfeiffer Omnistar GSD301), which was used for the monitoring of H 2 O/C 2 H 5 OH concentrations in the Ar outlet flow.

Figure 1 Figure 1 .

 11 Figure1shows the IR spectra of MIL-100(Fe) after water and ethanol (EtOH) adsorption, at

Figure 2 .

 2 Figure 2. Evolution of IR spectra of MIL-100

Figure 3 .

 3 Figure 3. Optical adsorption isotherms of water (AI) and

Figures (AII)

  Figures (AII) and (BII) represent the evolution of Aν versus

Figure 4 Figure 4 .

 44 Figure 4 displays the mass gains on a MIL-100(Fe) pellet during adsorption from various

Figure 5 . 6 .

 56 Figure 5. Evolution of adsorbed ethanol (A-I and B-I) and

Figure 6

 6 reveals that ethanol is preferentially adsorbed on MIL-100(Fe) for a 0.0<H 2 O(P/P o )<0.4, and for H 2 O(P/P o )>0.4 with EtOH(P/P o )>0.35. But these results could not exclude totally the adsorption of water (even in small amount) on MIL-100(Fe). We think that water is adsorbed (chemisorbed) on the Fe metal sites of MIL-100(Fe) but this adsorption become negligible compared to the adsorption of ethanol on the MOF surface.

Figure 6 .Figure 7 .Figure 7 .

 677 Figure 6. 2D cartography of the adsorbed water and ethanol

Figure 8 .

 8 Figure 8. Evolution of the adsorbed ethanol

  2 O(P/P o )<0.4 with 0.0<EtOH(P/P o )<1.0, or for H 2 O(P/P o )>0.4 with EtOH(P/P o )>0.35. The experimental results demonstrate that the vapor-liquid equilibrium of water-ethanol binary mixtures is altered when the pore volume of MIL-100(Fe) is partially occupied (for EtOH(P/P o )<0.05 and H 2 O(P/P o )<0.4). The approach (AGIR) proposed in this work is very promising to future studies of the co-adsorption of water ethanol on different types of porous materials.

ASSOCIATED CONTENT

Sun, J. K. ; Ji, M. ; Chen, C. ; Wang, W. G. ; Wang, P. ; Chen, R. P. ; Zhang, J. A chargepolarized porous metal-organic framework for gas chromatographic separation of alcohols from water, Chem. Commun. 2013, 49, 1624-1626.

Supporting Information. Evolution of the mass gain of MIL-100(Fe) during water (A) and ethanol (B) adsorption on MIL-100 (Fe) at 300 k. Estimation of the occupied micropores of MIL-100(Fe) by water and ethanol using Langmuir model. Evolution of the IR spectra of MIL-100 (Fe), in the region of (ν+δ)H 2 O and (ν) C-C for various partial pressure of water/ethanol mixtures. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

Corresponding Author E-mail: mohamad.elroz@ensicaen.fr

Fax: 0033 2 31 46 2732

Author Contributions ‡These authors contributed equally.

Table of Contents

New approach based on the coupling of FTIR spectroscopy with gravimetry has been used to study the co-adsorption of water and ethanol from water/ethanol mixtures on MIL-100(Fe). A preferential adsorption of ethanol was observed. The vapor-liquid equilibrium of water-ethanol binary mixtures is altered when the pore volume of MIL-100(Fe) is partially occupied (optimal condition for water/ethanol separation).