Lipophilic Balance of Clickable Mesoporous

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Tailoring the Hydrophilic/Lipophilic Balance of Clickable Mesoporous Organosilicas by the Copper-Catalyzed Azide-Alkyne Cycloaddition Click-Functionalization Achraf Noureddine, Philippe Trens, Guillaume Toquer, Xavier Cattoën, and Michel Wong Chi Man Langmuir, Just Accepted Manuscript • DOI: 10.1021/la503151w • Publication Date (Web): 26 Sep 2014 Downloaded from http://pubs.acs.org on October 1, 2014

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Tailoring the Hydrophilic/Lipophilic Balance of Clickable Mesoporous Organosilicas by the Copper-Catalyzed AzideAlkyne Cycloaddition Click-Functionalization Achraf Noureddine,1 Philippe Trens,1,* Guillaume Toquer,2 Xavier Cattoën1,3,* and Michel Wong Chi Man1 1

Institut Charles Gerhardt Montpellier (UMR 5253 CNRS-UM2-ENSCM-UM1), 8, rue de

l´école normale, 34296 Montpellier, France. Email: [email protected] 2

Institut de Chimie Séparative de Marcoule (UMR 5257 CEA-CNRS-UM2-ENSCM),

BP17171, 30207 Bagnols sur Cèze, France 3

Univ. Grenoble Alpes, Inst NEEL, F-38042 Grenoble, France and CNRS, Inst NEEL, F-

38042 Grenoble, France. E-mail: [email protected]

Abstract: We have designed and synthesized a clickable bridged silsesquioxane material featuring pendant alkyne chains as an aggregate of golf ball –like nanoparticles, as evidenced by SEM, TEM and SWAXS. Using the Copper-Catalyzed Azide-Alkyne Cycloaddition reaction with a range of organic azides of variable characteristics, we transformed this parent bridged silsesquioxane into new materials with tunable hydrophilic/lipophilic balance in high conversions while preserving the original morphology. N2, cyclohexane and water sorption experiments were used to quantify the affinity of these materials towards the sorbates through the determination of their Henry’s constants. This resulted in the following hydrophilic scale: M-OH>M-PEG>M-C6>M-Ph>M-F>M-C16, which was mostly confirmed by SWAXS measurements. Keywords: Mesoporous materials; functionalization; click chemistry; CuAAC; adsorption; organosilica.

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Introduction:

Organosilicas are attracting considerable attention owing to their wide range of application, which include catalysis,1 depollution,2-4 sensing, nanomedicine,5,

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electronics,

optics or as anti-scratch coatings.7 For most applications, tailoring the surface properties is of primary importance.8 Indeed, the density of silanol groups at the surface of the final material as well as the presence of hydrophilic or hydrophobic organic groups can alter dramatically the properties for the desired application.3,

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The introduction of a range of organic

functionalities has initially been performed using a post-functionalization strategy, by reacting organo(alkoxy)silanes with the material.10 However, this approach is known to result in a heterogeneous functionalization of the surface.11,

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Furthermore, it is limited to the

availability of organo(alkoxy)silanes. In another approach, the sol-gel co-condensation of organo(alkoxy)silanes with an (organo)silica precursor can lead to homogeneous dispersions of the functional organic groups within the matrix, but the textural properties depend importantly on the functionality that is introduced.10, 13 In order to circumvent these issues, several groups have used the Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) click post-functionalization approach,3,

4, 14-19

which is known to display a very wide functional

group tolerance, to involve moisture-stable functional molecules, and to occur under mild conditions with very high conversions.20 By co-condensing silicon tetraalkoxides or bridged organosilanes with clickable organosilanes, new organosilica materials ready for postfunctionalization can be produced. We recently introduced the preparation of organosilane 1 (Scheme 1) as a new precursor for clickable PMOs or mesoporous materials.21 These materials, which intrinsically exhibit the highest loading of clickable fragments for organosilicas can be derivatized with very high conversions (up to 90% ± 10%) with simple clickable organic molecules without altering their morphology.21 These features make them ideal platforms for studying the impact of post-functionalization on the surface properties and on the hydrophilic/hydrophobic balance. Sorption experiments represent the best strategy for determining the textural properties of porous or divided materials.22 Routinely, nitrogen is used as a probe in such experiments, the particular advantage of this sorbate being its low polarizability making it suitable for any kind of material as it does not favor any type of surface.23 However, difficulties may occur when adsorbing nitrogen at low temperature in hybrid materials as the frozen and pending organic content may prevent the diffusion of nitrogen in the pores. The main information gained when using N2 is related to the textural properties of the material of interest whereas surface 2 ACS Paragon Plus Environment

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chemistry can be investigated by using the same technique but with specific sorption probes.24 Indeed, sorbates with different affinities for hydrophilic or lipophilic surfaces may be used to characterize the hydrophilic or lipophilic character of the materials.25-31 More specifically, the affinity of a material for a sorbate can be characterized in the adsorption isotherm by the behavior at low p/p° values (0-0.01) which corresponds to the formation of the first monolayer on the surface. The comparison between sorbates such as low-polarizable N2, polar water or an apolar alkane would thus enable a good understanding of the surface properties. Furthermore, the adsorption of water or alkanes at room temperature will discard the diffusion issues mentioned above in the case of nitrogen at 77K. Despite the valuable information which can be drawn from these studies using a rather simple experimental setup, only few examples have been reported in literature for the study the surface modification of silica materials.26, 30, 32, 33 In order to draw a comparison between different organically modified siliceous materials, a family of materials with similar morphologies but fully functionalized with variable organic fragments should be used. To this aim, we decided to prepare a clickable mesoporous bridged silsesquioxane from organosilane 121 and to derivatize it with lipophilic (C6, C16, Ph), hydrophilic (OH, PEG) or both hydrophobic and lipophobic (F) moieties (Table 1) taking advantage of the wide scope, high conversions and preservation of the morphology offered by the CuAAC functionalization reaction. We present here the structural characterizations and the comparative N2, water and cyclohexane sorption studies of this family of materials.


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Experimental: Chemical and reagents: Bis(triethoxysilylpropyl)amine was purchased from ABCR. Calcium hydride, propargyl bromide, sodium ascorbate, hydrochloric acid 37%, ammonium hydroxide 27% were from Sigma Aldrich. Sodium N,N-diethyl dithiocarbamate, perfluorooctanoic acid, copper sulfate were from Alfa-Aesar. The reagents were used as purchased without any further purification. (Azidomethyl)benzene,

1-azidohexane,

1-azidohexadecane,

2-azidoethanol,

tetraethyleneglycol monoazide and 8-azido-1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane were synthesized according to published procedures. General: Solid state 13C and 29Si CP/MAS NMR experiments were recorded on a Varian VNMRS 300 MHz spectrometer using a two channel probe with 7.5 mm diameter-size ZrO2 rotors and TMS as reference for the chemical shifts. Scanning electron microscopy (SEM): The SEM images were obtained with a Hitachi S-4800 apparatus after platinum metallisation. TEM micrographs were obtained using a JEOL 1200 EX2 apparatus equipped with a SIS Olympus Quemesa 11 Mpixel camera. FTIR spectra were recorded using a Perkin100 spectrometer equipped with a mono internal reflexion ATR module. Raman spectra were recorded with a LabRAM ARAMIS (Horiba) spectrometer using a HeNe laser (633 nm). The small and wide angle X-ray scattering (SWAXS) experiments were conducted using a Guinier-Mering setup with a 2D image plate detector. The X-ray source was a molybdenum anode, which delivered a high-energy monochromatic beam (λ=0.71 Å, E=17.4 keV), providing structural information over scattering vectors q ranging from 0.01 to 3 Å−1. Helium flowed between the sample and the image plate to avoid air adsorption. The sample acquisition time was 3600s. The image azimuthal average was determined by the FIT2D software from ESRF (France). In order to normalize all spectra by the width of solid sample es, which depends on the material’s porosity, we determine it by using the experimental sample transmission Ts and the X-ray linear attenuation coefficient µs of the solid material from: ݁௦ = −

lnሺܶ௦ ሻ ߤ௦

The N2-sorption measurements were performed on an ASAP 2010 (Micromeritics) at 77.4 K. The different samples were activated for 5 hours at 40 °C prior to the analysis. The Henry's constants were calculated by determining the slope of the adsorption isotherms below p/p°=0.01. Prior to the vapour adsorption experiments cyclohexane (provided by Aldrich, purity >99.9%) was stored over an activated 3 Å molecular sieve. The deionized water 4 ACS Paragon Plus Environment

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reservoir was outgassed for 10 minutes under reduced pressure. The vapour sorption experiments were performed using a purpose-built adsorption apparatus already described.34 This set-up is based on gravimetric measurements, using a magnetic compensation balance provided by SETARAM, with a resolution better than 0.05 µg. The pressure in the sample cell can be recorded by two capacitive pressure gauges (0-10 Torr and 0-1000 Torr). The materials were activated for 5 hours at 313 K before adsorption. Vapour adsorption was performed at 313 K with a thermal stability of the sample better than 0.1 K. For each point on the adsorption isotherm obtained, the system was considered to have reached a state of thermodynamic equilibrium when the mass did not vary over a period of at least 600 s. As a consequence, diffusion issues as well as transient conformations of adsorbed phases could be discarded. When performed at longer equilibration times, the same sorption isotherms were obtained, thus validating the choice of 600 s as an equilibrium criterion. The exact time to reach equilibrium depended on the relative vapour pressure considered. Some adsorption steps took more than eight hours for completion. Synthesis of Clickable Mesoporous Bridged Silsesquioxane (M) In a round bottom flask, cetyltrimethylammonium bromide CTAB (2.6 g, 7.1 mmol) and perfluorooctanoic acid PFOA (0.2 g, 0.5 mmol) were dissolved in a water (153 mL) -NH4OH (25%wt, 21 mL) mixture under vigorous stirring at 70 °C. Precursor 121 (4.2 g, 9.0 mmol) was added and the mixture was kept for 24 h at 70 °C leading to a gel. The solvent was then evaporated to afford the material, which was then stirred in a mixture of 200 mL of ethanol and 10 mL of concentrated hydrochloric acid at 50 °C for 24 h, filtered and finally stirred overnight at RT in a mixture of 100 mL of ethanol and 5 mL of ammonium hydroxide (27%). The material was recovered by filtration, washed with ethanol until the filtrate became neutral and finally dried overnight at 70 °C. General procedure for the click reaction: M (120 mg, 0.5 mmol of alkyne functions) was incubated with the corresponding organic azide (1.5 mmol), copper sulphate (16 mg, 0.1 mmol) and sodium ascorbate (70 mg, 0.35 mmol) in a 1:1 water tert-butanol mixture (20 mL). The reaction mixture was stirred for 24 h at 25 °C. The functionalized material was recovered by centrifugation (16 500 rpm, 10 min) and washed twice with water, five times with sodium N,N-diethyl dithiocarbamate (0.1 M in methanol), methanol (x5), and acetone until the supernatant became clear. The powder was dried under reduced pressure overnight. The afforded functionalized material will be denoted M-R with R= C16, C6, Ph, OH, PEG, F according to the clicked moiety. 5 ACS Paragon Plus Environment

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Results and discussion

The parent clickable material (M) was synthesized by an ammonia-catalyzed sol-gel reaction in a concentrated solution of CTAB and PFOA (molar ratio 1/CTAB/PFOA/NH3/H2O = 1:0.79:0.06:31:1030), using a procedure similar to that previously described (Scheme 1).21 As evidenced by electron microscopies, the material was obtained as an assembly of nanospheres with diameters ranging from 20 to 30 nm (Figure 1). The chemical composition of M was ascertained by vibrational spectroscopies and solid-state NMR. In the FTIR spectrum (Figure S1), the presence of the Si-O-Si linkages was ascertained by the broad band at 1000-1150 cm-1, whereas the presence of the propargyl group was evidenced by the νC(sp)H at 3295 cm-1 (Figure 2). The C≡C stretching band was observed by Raman spectroscopy at about 2100 cm-1 (Figure S2). The solid-state

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C CP-MAS NMR

spectrum of M (Figure 3) is very similar to the spectrum of 1 in CDCl3 solution, with the noticeable exception of the signals at 18 and 58 ppm which correspond to the CH3 and CH2 atoms of the ethoxysilyl groups that disappear after the sol-gel reaction. A very high condensation at silicon (95%) was deduced from the

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Si NMR spectra (Figure S3), which

means that the structure is very well condensed. The nitrogen adsorption isotherm of the material before click reaction is shown in Figure 4. It is a classical type IV adsorption isotherm, as defined by the IUPAC.35 The main characteristics are the clear saturation plateau reached at p/p° = 0.85 and a broad hysteresis loop. This H2 type hysteresis loop is usually obtained with materials aggregated as small particles, the voids between particles having a size in the same order of magnitude than the particles themselves. This interpretation is fully consistent with what was observed by TEM and SEM (Figure 1). The pore size distribution (PSD) obtained for this material can be found in Figure S4. This PSD, obtained after BJH derivation of the desorption branch of the adsorption isotherm, shows a narrow pore size distribution centered around 4 nm. This result must be carefully considered. If this population of 4 nm pore diameter pores existed, it would be a striking feature, already apparent on the adsorption branch. In such a case, it would be possible to observe a marked sorbate uptake in a very small relative pressure range, as it occurs in the case of MCM-41 materials for instance.36 However, the adsorption branch only shows a gradual amount uptake in a wide range of relative pressure. In our case, this result is likely an artifact which can be classically attributed to the cavitation (also named as catastrophic


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desorption) of nitrogen from interconnected voids when the equilibrium pressure reaches 0.42 downwards.35 It is typically the case of aggregated mineral oxides such as ceria or zirconia.37 Additionally, after t-plot analysis, no microporosity was found in the parent material. Using small and wide angle X-ray scattering (SWAXS), it is possible to get complementary information about the structure of the material. For the parent material, the SAXS profile is compatible with an assembly of small dense nanospheres. The non-Porod regime (I(q) α q-3) that is displayed at intermediate q values indicates that the nanospheres have rough surfaces (Figure 5). The weak pseudo-Bragg peak observed at q≈0.55 Å−1 (corresponding distance 11.1 Å) might correspond to irregular repetitions of crater-like holes at the surface of the nanoparticles, which would confer nanoscale roughness to the material. Mesoporous material M was then functionalized using different organic azides (Table 1), with functions that may confer it a hydrophilic (OH, PEG), lipophilic (C6, C16, Ph) or both hydrophobic and lipophobic character (F). The CuAAC click reactions were performed at room temperature in a mixture of water and tert-butanol, yielding materials denoted as M-R, the suffix R indicating the grafted organic functions (Scheme 1). The extent of click reaction was analyzed by FTIR (Figure 2). Indeed, during a CuAAC reaction, the C(sp)-H bond of the terminal alkyne is converted into a Csp2-H bond in the triazole fragment, with a corresponding shift of the stretching vibration from 3295 cm-1 (m) to 3142 cm-1 (w). Whereas for all organic groups, the appearance of a weak Csp2-H band is observed at 3142 cm-1, the full vanishing of the C(sp)-H vibration at 3300 cm-1 is only visible in the case of the hydrophilic groups (PEG and OH). Therefore, despite precisely the same synthetic conditions used, the conversion of the alkynes into triazole does not proceed to the same extent, the highest conversions being observed with the hydrophilic azides, even with the long tetraethylene glycol group (12 C or O atoms). In addition, the decrease of the C≡C stretching band in Raman (2105 cm-1) compared to the C(sp3)-H band (2800-3000 cm-1) follows the same trend. The presence of the functional groups is mainly evidenced from the C(sp3)-H stretching region (2840-2960 cm-1). Moreover, the successful removal of the excess azide reactants is proven by the absence of peaks at 2100 cm-1, that would correspond to the strong vibration of the azide groups (Figure S1). Solid-state 13C CP-MAS NMR (Figure 3) confirms the information deduced from FTIR: the formation of the triazole linkers is evidenced by the appearance of signals at ca 125 and 145 ppm, while the intensity of the signals at 70-80 ppm, characteristic of the alkyne functions decreases. This decrease is more pronounced in the case of M-PEG and M-OH, though no quantitative information can be deduced from these spectra. The presence of the functional 7 ACS Paragon Plus Environment

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groups is evident for all materials except for M-F, with the appearance of intense signals at 125 ppm in the case of M-Ph (aromatic carbons) at 58 ppm for M-PEG or 30 ppm for M-C6 or M-C16 (carbons from the alkylene chains). It is noteworthy that the

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Si NMR spectra

(Figure S3) remain unaltered during the CuAAC reaction: no Q signal (-90 to -130 ppm) is observed, that is indicative of Si-C bond cleavage, and the shape of the T band remains unaltered. Therefore, we can suggest that under the CuAAC reaction conditions, no rearrangement occurs in the siloxane framework despite the densification of the structure. On the structural point of view, SEM micrographs show a preservation of the morphology of the material after the functionalization reaction. This is confirmed by SWAXS studies (Figure 5), with overall similar diffractogrammes, though for the functionalized materials, the medium angle region can be fitted as I(q) α q-n with n=3.8 except for the M-OH material with only n=3.5, compared to n = 3.0 in the case of M. This can be attributed to a reduced roughness after the grafting of the organic groups, the smallest CH2-CH2-OH yielding a material with still a noticeable roughness. After click reaction, interesting results are found from the N2-sorption experiments (Figure 4). In the case of the materials M-C6, M-OH, M-C16 and M-Ph the same shape is obtained. It can be deduced that the textural properties of these clicked materials are similar to that of the parent material. However, there is a difference in the extent of adsorption at saturation which decreases by a factor 2 in the case of M-C6. This decrease is even more pronounced in the case of M-OH, M-Ph and M-C16. Different interpretations can account for this observation, (i) coalescence of particles after click reaction which decreases the number of accessible interparticular voids, (ii) void accesses blocked by the clicked organic fragments. It must be noted that the hysteresis loops are very similar, in terms of shape but also in terms of relative pressure at which hysteresis occurs. This suggests that the accessible pores of the related materials retain their original structure. We mentioned that, when compared with the parent material, the hystereses of the clicked materials are less pronounced and the adsorbed amounts are lowered. This is especially the case for the materials M-F and M-PEG. In the latter case, adsorption is very limited and the hysteresis loop is absent. It can be deduced that the click reaction disables the interparticular voids. The nitrogen adsorption only takes place on the external surface of the particles assemblies leading to a poor specific area. M-F leads to the same interpretations. The H3-type hysteresis loop observed can be caused by the existence of some non-rigid aggregates of plate-like particles or assemblages of slit-shaped pores.24


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The affinity between nitrogen through its quadrupolar moment and the different materials can be expressed in terms of Henry's constants derived from the slope of the adsorption isotherms at very low relative pressure. These have been implemented in Table 2 along with textural parameters. Clear differences can be seen between Henry's constants. Interestingly, a wide range of Henry's constants is found, the parent material leading to the highest constant whereas M-PEG leads to a poor Henry's constant. The interpretation of these differences is not straightforward since it can be assumed that all the different materials still have some surface silanols left. These adsorption sites interact with nitrogen similarly to any mineral oxide. The material before click reaction, namely M, exhibits the higher Henry's constant which suggests a full accessibility to the most active surface sites, either on the silica surface or on the organic fragment. After click reaction, the Henry's constants are lowered, likely because the clicked molecule interacts at the expense of the hindered surface sites. The electric dipole polarizability of nitrogen is only 1.71 Å3, which makes this probe ideal for physisorption on any type of surface.38, 39 Indeed, this very low value will not really favor any surface site. However, finding such different Henry's constants values indicates that the nature of the surface of the clicked materials has been drastically modified. Based on these results, the prepared materials can be classified as hydrophilic (M-OH, M-PEG), hydrophobic (MC6, M-C16, M-Ph) and strongly hydrophobic (M-F). The click reaction producing these materials can be validated by adsorbing specific probes, favoring hydrogen bonding or only dispersion forces. Specifically, cyclohexane and water were chosen as sorbates to evaluate the surface properties of the modified materials. Before hand, it must be mentioned that nitrogen adsorption onto these materials already showed important differences in terms of adsorbed amounts at saturation. The adsorption isotherms of cyclohexane on the different materials are presented in Figure 6. Significant information can be deduced from two distinct regions: At high p/p° the uptake is an indication of the accessible pore volume, whereas at low p/p° the slope of the curve (Henry’s constant) outlines the sorbate-sorbent affinity. In fact, Henry's constants are not derived from the first adsorption site, but from adsorption taking place at relative pressure below p/p° = 0.01. The shape of the adsorption isotherms is rather similar, with significant maximum uptakes, but mainly differs in terms of affinity at low relative pressure. As already obtained with the adsorption of nitrogen, the highest interaction is obtained with the parent material. Having consistent results is very interesting since cyclohexane only interacts through dispersive interaction. Furthermore, clicking organic functions such as C6 or C16 does not render the 9 ACS Paragon Plus Environment

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material more lipophilic than the parent material. This could be due to the fact that clicking the organic functions is at the expense of interaction sites. Considering the clicked materials, it is clear that cyclohexane preferentially interacts with lipophilic clicked species such as C6. One would have expected a similar result with C16. However, the size of C16 likely prevents the quantitative adsorption of cyclohexane into the material. If we go into more details, we can observe that the adsorption isotherms of M and M-OH exhibit a slight knee which is the indication of some specific interactions. On the other hand, M-C6 and M-C16 lead to straight line which is indicative of a true Henry's behavior. These two clicked materials act as a solvent for cyclohexane and the adsorbed amount is proportional to the relative pressure. This means that according to the Henry's law, more sorbate is proportionally adsorbed as the pressure increases, according to pB = xB KB. In this classical expression, pB is the equilibrium pressure of the sorbate and xB is the molar fraction of a species B in the liquid phase. In our case, the liquid phase is the material and the species B stands for the sorbate. Cyclohexane interacts very poorly with M-PEG likely because of the structuration of the material, as already discussed with the adsorption of nitrogen. Its specific surface area is very low and consequently the active sites of M-PEG are very scarce. A high relative pressure is required for cyclohexane to adsorb in M-PEG. From p/p° = 0.2 upwards, M-PEG also acts as a solvent for cyclohexane. M-F exhibits a behavior very similar. However, the specific surface area of M-F is higher than that of M-PEG. It can be concluded that the fluorinated material results in a lipophobic material. The Henry's constants derived at low relative pressure confirm these findings (see Table 3). The original material, M, has a high specific surface area. This textural feature implies a large number of accessible surface sites and therefore a high Henry's constant. The click reaction with any organic molecule does not improve the affinity for cyclohexane. One reason is the specific surface areas of the clicked materials which are less than half of that of M. A second reason is the fact that M already has a large organic content. Since cyclohexane only interacts through dispersive interaction, it can be concluded that the behavior generally observed is closely related to that already discussed in the case of the adsorption of nitrogen. The Henry's constants are therefore sorted as in the case of those obtained with nitrogen. From this observation, it is interesting to focus on a polar sorbate such as water. The adsorption isotherms of water on the different materials are presented in Figure 7. The shape of the adsorption isotherms is quite similar from one system to another. However, it can be already noted that water has less affinity for M than cyclohexane has. As mentioned above, the parent material M has already an organic content. Even if few residual silanols are 10 ACS Paragon Plus Environment

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present, this material is poorly hydrophilic. At low relative pressure, the adsorption isotherm is rather flat, which indicates a low affinity between water and M. This shape can be compared to those obtained with clicked materials. In the case of M-OH and M-PEG, slight knees can be observed which suggests a higher affinity. This is confirmed in Table 3 in which the Henry's constants are gathered. Despite a very low surface area, M-PEG leads to a high constant as well as M-OH (62 and 113 mg.g-1 respectively). In the case of hydrophobic materials, unsurprisingly low Henry's constants are found. For instance, in the case of M-C6, the constant is 54 mg.g-1 whereas it is 62 mg.g-1 for M-PEG with a specific surface area 20 times lower. This comparison also holds true for the other hydrophobic clicked molecules MPh and M-C16. These materials can be sorted according to a hydrophilic scale: M-OH>M-PEG>M-C6>M-Ph>M-F>M-C16. It can be anticipated that obtaining nanoparticles of M-PEG with accessible surface sites would make this material the most hydrophilic of this series. By analyzing the wide angle zone of the SWAXS diffractogramme, (see Figure S5), we observe the correlation peaks of water at q from 1 to 2 Å−1 and we point out that the corresponding intensity due to the adsorbed water molecules from materials in normal condition might be correlated to the hydrophilic properties of material. Without any assumption on the specific surface or pore volume, a hydrophilic scale as following MOH>M-C6>M-PEG>M-Ph>M-C16>M-F was deduced, which is close to the above Henry’s constant order.

Conclusions The aims of this paper was firstly to design and characterize a clickable parent mesoporous bridged silsesquioxane, M which can be derivatized on-demand to afford a family of materials having different surface chemistry but featuring the same morphology. We demonstrated that the CuAAC click reaction could be used for this goal, thanks to its high conversions and excellent functional group tolerance. Indeed, we investigated the textural and adsorption properties of these materials with nitrogen, but also with water and cyclohexane. Nitrogen adsorption revealed that the different materials were made of aggregated nanoparticles, differing by the accessibility of their interparticular voids. This confirmed the electron microscopy and SWAXS results which already strongly suggested the occurrence of golf ball-like nanoparticles.


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The parent material showed a higher affinity for cyclohexane than towards water. This was explained by the high organic loading and the very few surface silanol left in this material. The resulting post-functionalized materials exhibited a preferential affinity for water or cyclohexane, depending on the clicked function. The quantification of the sorbate/sorbent affinity was obtained by means of Henry's constants. We obtained the following hydrophilic scale: M-OH>M-PEG>M-C6>M-Ph>M-F>M-C16. SWAXS measurements showed nearly the same trend. These results clearly demonstrate that the CuAAC click reaction offers a highly reliable route for tailoring the properties of mesoporous bridged silsesquioxanes, namely we could tune in the present studies the hydrophilic/lipophilic balance of such silica based materials by a simple chemical reaction. Beyond these fundamental aspects, the clicked materials could be envisaged in various technological issues. Amongst examples, applications may be found the industry of flat glasses. Indeed, a hydrophobic material will prevent the formation of water thin films on windscreens but it will favor the removal of water drops. On the other hand, a hydrophilic material may favor its wettability by the water content in air which will induce its self cleaning.

Supporting Information Available: FTIR, Raman and

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Si SSNMR spectra, BJH plot and

WAXS diffractogramms. This information is available free of charge via the Internet at http://pubs.acs.org/.

References 1. Zamboulis, A.; Moitra, N.; Moreau, J. J. E.; Cattoën, X.; Wong Chi Man, M., Hybrid materials: versatile matrices for supporting homogeneous catalysts. J. Mater. Chem. 2010, 20, (42), 9322-9338. 2. Mehdi, A., Self-assembly of layered functionalized hybrid materials. A good opportunity for extractive chemistry. J. Mater. Chem. 2010, 20, (42), 9281-9286. 3. Gao, J.; Zhang, X.; Xu, S.; Tan, F.; Li, X.; Zhang, Y.; Qu, Z.; Quan, X.; Liu, J., Clickable Periodic Mesoporous Organosilicas: Synthesis, Click Reactions, and Adsorption of Antibiotics. Chem. Eur. J. 2014, 20, (7), 1957-1963. 4. Gao, J.; Zhang, X.; Xu, S.; Liu, J.; Tan, F.; Li, X.; Qu, Z.; Zhang, Y.; Quan, X., Clickable SBA-15 to Screen Functional Groups for Adsorption of Antibiotics. Chem. Asian J. 2014, 9, (3), 908-914.


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5. Coti, K. K.; Belowich, M. E.; Liong, M.; Ambrogio, M. W.; Lau, Y. A.; Khatib, H. A.; Zink, J. I.; Khashab, N. M.; Stoddart, J. F., Mechanised nanoparticles for drug delivery. Nanoscale 2009, 1, (1), 16-39. 6. Croissant, J.; Cattoën, X.; Wong Chi Man, M.; Gallud, A.; Raehm, L.; Trens, P.; Maynadier, M.; Durand, J.-O., Biodegradable Ethylene-Bis(Propyl)Disulfide-Based Periodic Mesoporous Organosilica Nanorods and Nanospheres for Efficient In-Vitro Drug Delivery. Adv. Mater. 2014, DOI: 10.1002/adma.201401931. 7. Nicole, L.; Laberty-Robert, C.; Rozes, L.; Sanchez, C., Hybrid materials science: a promised land for the integrative design of multifunctional materials. Nanoscale 2014, 6, (12), 6267-6292. 8. Abu-Reziq, R.; Blum, J.; Avnir, D., Three-phase microemulsion/sol-gel system for aqueous catalysis with hydrophobic chemicals. Chem. Eur. J. 2004, 10, (4), 958-962. 9. Karimi, B.; Mobaraki, A.; Mirzaei, H. M.; Zareyee, D.; Vali, H., Improving the Selectivity toward Three-Component Biginelli versus Hantzsch Reactions by Controlling the Catalyst Hydrophobic/Hydrophilic Surface Balance. Chemcatchem 2014, 6, (1), 212-219. 10. Hoffmann, F.; Cornelius, M.; Morell, J.; Fröba, M., Silica-based mesoporous organicinorganic hybrid materials. Angew. Chem. Int. Ed. 2006, 45, (20), 3216-3251. 11. Brunel, D.; Cauvel, A.; Di Renzo, F.; Fajula, F.; Fubini, B.; Onida, B.; Garrone, E., Preferential grafting of alkoxysilane coupling agents on the hydrophobic portion of the surface of micelle-templated silica. New J. Chem. 2000, 24, (10), 807-813. 12. Sharma, K. K.; Anan, A.; Buckley, R. P.; Ouellette, W.; Asefa, T., Toward efficient nanoporous catalysts: Controlling site-isolation and concentration of grafted catalytic sites on nanoporous materials with solvents and colorimetric elucidation of their site-isolation. J. Am. Chem. Soc. 2008, 130, (1), 218-228. 13. Macquarrie, D. J., Direct preparation of organically modified MCM-type materials. Preparation and characterisation of aminopropyl-MCM and 2-cyanoethyl-MCM. Chem. Commun. 1996, (16), 1961-1962. 14. Cattoën, X.; Noureddine, A.; Croissant, J.; Moitra, N.; Bürglová, K.; Hodačová, J.; De los Cobos, O.; Lejeune, M.; Rossignol, F.; Toulemon, D.; Bégin-Colin, S.; Pichon, B.; Raehm, L.; Durand, J.-O.; Wong Chi Man, M., Click approaches in sol–gel chemistry. J. SolGel Sci. Technol. 2014, 70, (2), 245-253. 15. Nakazawa, J.; Smith, B. J.; Stack, T. D. P., Discrete Complexes Immobilized onto Click-SBA-15 Silica: Controllable Loadings and the Impact of Surface Coverage on Catalysis. J. Am. Chem. Soc. 2012, 134, (5), 2750-2759. 16. Nakazawa, J.; Stack, T. D. P., Controlled Loadings in a Mesoporous Material: Clickon Silica. J. Am. Chem. Soc. 2008, 130, (44), 14360-14361. 17. Malvi, B.; Sarkar, B. R.; Pati, D.; Mathew, R.; Ajithkumar, T. G.; Sen Gupta, S., "Clickable'' SBA-15 mesoporous materials: synthesis, characterization and their reaction with alkynes. J. Mater. Chem. 2009, 19, (10), 1409-1416.


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18. de los Cobos, O.; Fousseret, B.; Lejeune, M.; Rossignol, F.; Dutreilh-Colas, M.; Carrion, C.; Boissière, C.; Ribot, F.; Sanchez, C.; Cattoën, X.; Wong Chi Man, M.; Durand, J.-O., Tunable Multifunctional Mesoporous Silica Microdots Arrays by Combination of Inkjet Printing, EISA, and Click Chemistry. Chem. Mater. 2012, 24, (22), 4337-4342. 19. Moitra, N.; Trens, P.; Raehm, L.; Durand, J.-O.; Cattoën, X.; Wong Chi Man, M., Facile route to functionalized mesoporous silica nanoparticles by click chemistry. J. Mater. Chem. 2011, 21, (35), 13476-13482. 20. Meldal, M.; Tornøe, C. W., Cu-catalyzed azide-alkyne cycloaddition. Chem. Rev. 2008, 108, (8), 2952-3015. 21. Bürglová, K.; Noureddine, A.; Hodačová, J.; Toquer, G.; Cattoën, X.; Wong Chi Man, M., Suitable and General Method to Bridged Organosilanes with Pending Functions and Functional Mesoporous Organosilicas. Chem. Eur. J. 2014, 20, 10371-10382. 22. Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T., Reporting physisorption data for gas solid systems with special reference to the determination of surface area and porosity (recommendation 1984). Pure Appl. Chem. 1985, 57, (4), 603-619. 23. Trens, P.; Denoyel, R.; Glez, J. C., Comparative adsorption of argon and nitrogen for the characterisation of hydrophobized surfaces. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2004, 245, (1–3), 93-98. 24. Thommes, M., Physical Adsorption Characterization of Nanoporous Materials. Chem. Ing. Tech. 2010, 82, (7), 1059-1073. 25. Melnyk, I. V.; Goncharyk, V. P.; Kozhara, L. I.; Yurchenko, G. R.; Matkovsky, A. K.; Zub, Y. L.; Alonso, В., Sorption properties of porous spray-dried microspheres functionalized by phosphonic acid groups. Microporous Mesoporous Mater. 2012, 153, (0), 171-177. 26. Matsumoto, A.; Misran, H.; Tsutsumi, K., Adsorption characteristics of organosilica based mesoporous materials. Langmuir 2004, 20, (17), 7139-7145. 27. Gun’ko, V. M.; Yurchenko, G. R.; Turov, V. V.; Goncharuk, E. V.; Zarko, V. I.; Zabuga, A. G.; Matkovsky, A. K.; Oranska, O. I.; Leboda, R.; Skubiszewska-Zięba, J.; Janusz, W.; Phillips, G. J.; Mikhalovsky, S. V., Adsorption of polar and nonpolar compounds onto complex nanooxides with silica, alumina, and titania. J. Colloid Interface Sci. 2010, 348, (2), 546-558. 28. Rossi, P. F.; Busca, G.; Oliveri, G.; Vettor, A.; Milana, G., Surface reactivity of coals toward water and n-hexane and adsorption microcalorimetric study. Langmuir 1992, 8, (1), 104-108. 29. Yurchenko, G. R.; Matkovskii, A. K.; Mel’nik, I. V.; Dudarko, O. A.; Stolyarchuk, N. V.; Zub, Y. L.; Alonso, B., Adsorption properties of silica-based sorbents containing phosphonic acid residues. Colloid J. 2012, 74, (3), 386-390. 30. Zhao, X. S.; Lu, G. Q.; Hu, X., Characterization of the structural and surface properties of chemically modified MCM-41 material. Microporous Mesoporous Mater. 2000, 41, (1-3), 37-47. 14 ACS Paragon Plus Environment

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31. Qian, B.; Jiang, H.; Sun, Y.; Long, Y., Affinity Study of Organics on Siliceous Ferrierite Type Zeolite. Langmuir 2001, 17, (4), 1119-1125. 32. Tarasevich, Y. I.; Trofimchuk, A. K.; Legenchuk, A. V.; Ivanova, Z. G., Structural characteristics of silica gel modified with organosilicon compounds according to the data on the adsorption of water and n-hexane vapors. Colloid J. 2004, 66, (1), 78-83. 33. Ribeiro Carrott, M. M. L.; Candeias, A. J. E.; Carrott, P. J. M.; Ravikovitch, P. I.; Neimark, A. V.; Sequeira, A. D., Adsorption of nitrogen, neopentane, n-hexane, benzene and methanol for the evaluation of pore sizes in silica grades of MCM-41. Microporous Mesoporous Mater. 2001, 47, (2–3), 323-337. 34. Tanchoux, N.; Trens, P.; Maldonado, D.; Di Renzo, F.; Fajula, F., The adsorption of hexane over MCM-41 type materials. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2004, 246, (1–3), 1-8. 35. Rouquerol, F.; Rouquerol, J.; Sing, K. S. W., Adsorption by porous and divided solids. Plenum Press Ed.: San Diego, 1999. 36. Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S., Ordered mesoporous molecular sieves synthesized by a liquid crystal template mechanism. Nature 1992, 359, (6397), 710-712. 37. Trens, P.; J. Hudson, M.; Denoyel, R., Formation of mesoporous, zirconium(IV) oxides of controlled surface areas. J. Mater. Chem. 1998, 8, (9), 2147-2152. 38. Olney, T. N.; Cann, N. M.; Cooper, G.; Brion, C. E., Absolute scale determination for photoabsorption spectra and the calculation of molecular properties using dipole sum rules. Chem. Phys. 1997, 223, (1), 59-98. 39. Gregg, S. J.; Sing, K. S. W., Adsorption, Surface Area and Porosity. Academic Press Ed: London, 1982.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Scheme 1: Formation of the parent material M and its functionalization by CuAAC.


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A

B

C

D

E

F

G

H

Figure 1. Transmission electron micrograph of the parent material M (A); Scanning electron micrographs of M (B), M-F (C), M-OH (D), M-PEG (E), M-Ph (F), M-C6 (G), M-C16 (H). 17 ACS Paragon Plus Environment

Langmuir

3142 2 C(sp )-H

3300 C(sp)-H

M-C16

M-C6

M-Ph Transmittance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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M-PEG

M-OH

M-F

M 3500

3400

3300

3200

3100

3000

-1

Wavenumber (cm )

Figure 2. 3000-3500 cm-1 region of the FTIR spectra of the parent (M) and of the functionalized materials (M-R)


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145 125

78 71

22 11

M-C16

M-C6

M-Ph

M-PEG

M-OH

M-F

M

1

160

140

120

100

80

60

40

20

0

δ (ppm)

Figure 3. 13C solid-state CP-MAS NMR spectra of precursor 1, and of the parent (M) and functionalized materials (M-R).


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350 Raw

Adsorbed amount / cm3.g-1 (STP)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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M-C6

300

M-OH M-Ph M-C16

250

M-F M-PEG

200 150 100 50 0 0

0.2

0.4 0.6 Equilibrium relative pressure, p/p°

0.8

1

Figure 4. Nitrogen adsorption isotherms on the parent and on the functionalized materials.


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Figure 5. SWAXS on the parent and on the functionalized materials.


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80 M-OH M-C6 M-C16 M-PEG M M-F M-Ph

Adsorbed amount / mg.g-1

70 60 50 40 30 20 10 0 0

0.2


0.8

1

10 M M-OH M-C6 M-C16 M-Ph M-PEG M-F

9 8


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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7 6 5 4 3 2 1 0 0

0.005

0.01

0.015 0.02 0.025 0.03 Equilibrium relative pressure, p/p°

0.035

0.04

Figure 6. Adsorption isotherms of cyclohexane on the parent and on the functionalized materials at 313 K: full isotherm (a); zoom on the low relative pressure region (b).


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80 M-OH M-PEG M-C6 M-C16 M M-F M-Ph


70 60 50 40 30 20 10 0 0

0.2


0.8

1

0.02


0.08

0.1

4 M M-OH M-PEG M-C6 M-F M-Ph M-C16

3.5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3 2.5 2 1.5 1 0.5 0 0

Figure 7. Adsorption isotherms of water on the parent and on the functionalized materials at 313 K: full isotherm (a); zoom on the low relative pressure region (b).


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lipophilic N3

Azidomethyl benzene (Ph)

2-azidoethanol (OH)

1-azidohexane (C6) hydrophilic

1-azido hexadecane (C16)

Tetraethyleneglycol azide (PEG) hydrophobic and lipophobic

8-azido-1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane (F) Table 1: Organic azides clicked on the materials. The corresponding suffixes (R) are written in brackets.


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SBET / m2.g-1

Henry's constant / Uptake at cm3.g-1 saturation / cm3.g-1 475 340 4872 M 52 60 581 M-F 143 57 1570 M-OH 12 20 111 M-PEG 139 121 1355 M-Ph 221 190 1957 M-C6 166 58 528 M-C16 Table 2. Textural properties of the different materials and Henry's constants of nitrogen determined at 77 K.


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Adsorbate M-Ph M-F M-OH M-PEG M Cyclohexane 178 596

Lipophilic Balance of Clickable Mesoporous

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