Ion-Exchange Properties of Imidazolium-Grafted SBA-15 toward AuCl4

Jun 14, 2012 - Natalia Fattori, Camila M. Maroneze, Luiz P. da Costa, Mathias Strauss, Fernando A. Sigoli,. Italo O. Mazali, and Yoshitaka Gushikem*. ...
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Ion-Exchange Properties of Imidazolium-Grafted SBA-15 toward AuCl4− Anions and Their Conversion into Supported Gold Nanoparticles Natalia Fattori, Camila M. Maroneze, Luiz P. da Costa, Mathias Strauss, Fernando A. Sigoli, Italo O. Mazali, and Yoshitaka Gushikem* Institute of Chemistry, University of Campinas (UNICAMP), Post Office Box 6154, 13083-970 Campinas, São Paulo (SP), Brazil S Supporting Information *

ABSTRACT: Imidazolium groups were successfully prepared and grafted on the surface of SBA-15 mesoporous silica. The ionexchange properties of the functionalized porous solid (SBA-15/ R+Cl−) toward AuCl4− anions were evaluated through an ionexchange isotherm. The calculated values of the equilibrium constant (log β = 4.47) and the effective ion-exchange capacity (tQ = 0.79 mmol g−1) indicate that the AuCl4− species can be loaded and strongly retained on the functionalized surface as counterions of the imidazolium groups. Subsequently, solids containing different amounts of AuCl4− ions were submitted to a chemical reduction process with NaBH4, converting the anionic gold species into supported gold nanoparticles. The plasmon resonance bands, the X-ray diffraction patterns, and transmission electron microscopy images of the supported gold nanoparticles before and after thermal treatment at 973 K indicate that the metal nanostructures are highly dispersed and stabilized by the host environment.

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INTRODUCTION The use of porous solids in the development of nanotechnology has proven to be a powerful tool in the design of devices and nanoparticles (NPs) with unusual and remarkable properties for a wide field of applications, including catalysis,1,2 separation science,3 energy conversion,4 sensing,5 environmental remediation,6 and medical diagnosis.7 Most of the unique properties of such systems are related to quantum confinement effects and to the large surface/volume ratios that emerge when particles are in the nanometric size domain.8 The benefits achieved at the nano level and an ever-increasing number of applications for which nanomaterials can provide improved performance, when compared to their bulk counterparts, constitute the key driving force for current research efforts in materials science. Despite the desirable properties displayed by the NPs, structures in this size regime are not in a thermodynamically stable state and are likely to undergo aggregation and coalescence to minimize their high surface energies, losing important properties that are only achieved at the nano level. The fundamental role played by porous solids to the advances seen nowadays in this field is clearly associated with the possibilities offered by the porous network to act as an environment for the design, synthesis, manipulation, and stabilization of NPs.9,10 Among the porous solids suitable for such purposes, silicabased materials can be highlighted for the extraordinary versatility presented by this inorganic matrix, directly attributed © 2012 American Chemical Society

to the numerous possibilities of manipulating its porous structure and the variety of chemical modifications that can be performed on its surface, resulting in materials with a broad range of functionalities and properties.11−13 The combination between functional organic groups and the porous framework of silica results in hybrid systems whose properties combine, in a single solid, the porosity and mechanical stability of the robust inorganic support and the reactive features of the organic functional entities, which confer a suitable functionality and provide a smart basis for building diverse nanostructures. Among the devices developed by this approach, supported metal NPs on silica-based hosts 9,10,14−18 have shown remarkable catalytic properties, providing a very efficient approach to the production of chemicals, energy, and materials. The use of imidazolium ionic liquids as a solvent and stabilizing agent has proven to be a suitable fluid medium in the preparation of transition-metal NPs with narrow size distribution and different shapes.19,20 The successful application of such systems in catalysis and chemical sensing has also been described.21,22 Imidazolium-functionalized silica has also received great attention in the last few years, and studies in analytical chemistry have mostly been related to the development of chromatographic stationary phases,23 sorbents in solidReceived: April 3, 2012 Revised: June 11, 2012 Published: June 14, 2012 10281

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The mixtures were shaken for 5 h at 298 K in closed flasks. The solids were then separated by centrifugation, and the remaining amounts of gold in solution were determined by inductively coupled plasma− optical emission spectroscopy (ICP−OES). The quantities of exchanged anions were calculated as

phase extraction,24 and separation science. For instance, Vangeli et al. have shown that methyl-imidazolium-grafted silicas (MCM-41 and Vycor) can be successfully used in the selective adsorption of CO2 over CO, which is very important in the production of synthesis gas.25 The present work describes the preparation and properties of SBA-15 mesoporous silica21,22 presenting imidazolium entities chemically bound to the silica surface as a thin layer, resulting in a mesoporous solid with ion-exchange properties. Several studies in the literature report the ion-exchange properties of functionalized mesoporous silicas and their wide range of application in electrochemistry and adsorption.26−28 The ionexchange properties of the attached positively charged groups and the effectiveness toward AuCl4− anions uptake were investigated and applied in the preparation of highly stable supported gold NPs in the confined pore spaces. The effective uptake capacity for the anionic gold complex and the equilibrium constant for this reaction were calculated through ion-exchange isotherm data.

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Nf =

Ni − [AuCl4 −]V m

(2)

where Ni is the initial amount of Au in solution (in moles), [AuCl4−] is the equilibrium molar concentration of AuIII in the solution phase, V is the solution volume (in liters), and m is the mass (in grams) of SBA15/R+Cl−. On the basis of these data, the ion-exchange isotherm was obtained by plotting Nf versus [AuCl4−]. The ion-exchange reaction can be represented by eq 3 III

≡R+Cl−(s) + HAuCl4(aq) ⇌ ≡R+AuCl4−(s) + HCl(aq) β

(3)

−

where ≡R Cl represents the imidazolium groups bound to the SBA15 surface, (s) and (aq) indexes refer to solid and aqueous solution phases, and β is the equilibrium constant of this ion-exchange reaction. To provide a reliable calculation of the equilibrium constant (β) and the effective ion-exchange capacity (tQ), both parameters should be determined from the ion-exchange isotherm because it is known that great discrepancies between tQ and expected (maximum) capacity found by elemental analysis are often observed. The isotherm was properly fitted by the Langmuir equation, and the values of tQ and β were derived from the fitting. Preparation of Supported Gold NPs. The preparation of supported Au NPs was carried out in two simple steps: (a) adsorption of AuCl4− anions on the surface of SBA-15/R+Cl− through ionexchange reactions in the same experimental conditions of the isotherm discussed above, and (b) the solids SBA-15/R+AuCl4− were filtered and washed with bidistilled water and then immersed in 50.0 mL of 1.0 × 10−3 M aqueous NaBH4 solution under mechanical stirring for 30 min. The resulting solids (SBA-15/R+Cl−/Au) were filtered, washed with bidistilled water, and dried under vacuum. The thermal stability was evaluated by heating these samples under static air from room temperature to 973 K (10 K min−1), keeping the sample at this temperature for 1 h. Characterization. The amount of organic groups immobilized onto the SBA-15 surface was calculated on the basis of nitrogen content, determined by means of elemental analyses on a Perkin-Elmer 2400 elemental analyzer. A N2 adsorption−desorption isotherm was measured at 77 K on a Quantachrome Autosorb 1 instrument. The sample was previously outgassed at 353 K for 12 h. The Brunauer− Emmett−Teller (BET) method was employed to calculate the specific surface areas (SBET). A small-angle X-ray scattering (SAXS) measurement was performed using the D11A-SAXS1 beamline at the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, SP, Brazil. Data were collected between 0.14 and 4 nm−1, and the energy was set to 10 keV (λ = 0.077 nm). A diffuse reflectance spectrum was obtained on an ultraviolet−visible−near-infrared (UV−vis−NIR) Cary-5 2300 spectrometer equipped with a diffuse reflectance accessory. Solidstate cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS NMR) for 13C and 29Si was performed on a Bruker AC300/P spectrometer. 13C CP/MAS spectra were obtained using pulse sequences with a 4 ms contact time, an interval between pulses of 1 s, and an acquisition time of 0.041 s. 29Si CP/MAS spectra were obtained using pulse sequences with a 3 ms contact time, an interval between pulses of 2 s, and an acquisition time of 0.041 s. For these two measurements, the chemical shifts were calibrated against the tetramethylsilane (TMS) standard. Quantitative determinations of gold in solution were carried out by ICP−OES using a Perkin-Elmer 3000 DV instrument. Transmission electron microscopy (TEM) images were obtained on a Zeiss Libra 120 transmission electron microscope operating at 80 kV. The powders were ultrasonically suspended in water for 30 min, and the suspension was deposited on carbon-coated copper grids. Powder X-ray diffraction (XRD) measurements were obtained for the slightly pressed powders placed in a stainless-steel sample holder at room temperature using the +

EXPERIMENTAL SECTION

Synthesis of SBA-15. The ordered mesostructured SBA-15 silica sample (SBA-15) was synthesized according to a previously published procedure.29 In the preparation, 4.0 g of Pluronic P123 (Mav = 5800; EO20PO70EO20, Aldrich) was dissolved in 150 mL of 1.6 mol L−1 aqueous HCl solution at 313 K. Then, 8.5 g of tetraethylorthosilicate (TEOS, Acros, 98%) was added. The solution was kept under magnetic stirring for 5 min and then under static conditions at 313 K for 20 h. The mixture was then transferred into a Teflon-lined autoclave and treated at 373 K for 24 h. The solid product was recovered, washed with bidistilled water, and dried at 373 K. Calcination was carried out by slowly increasing the temperature from room temperature to 823 K (2 K min−1) and heating at 823 K for 6 h. Synthesis of Imidazolium Alkoxysilane (Si-Imi). The preparation of the imidazolium alkoxysilane (Si-Imi) was carried out in a single step according to the following procedure: in a round-bottomed flask with 6.00 mL of dry toluene, 4.93 mL of 3-(chloropropyl)trimethoxysilane (Aldrich, 99%) and 2.42 mL of 1-methylimidazole (Aldrich, 98%) were simultaneously added and the solution was stirred for 24 h at 333 K under a nitrogen atmosphere. After the set time, the reaction mixture was kept under static conditions until the complete separation of the resulting two immiscible liquid phases. The bottom fraction, which corresponds to the Si-Imi product, was physically separated and used in the surface functionalization of SBA-15. This reaction is schematically shown in eq 1.

Surface Functionalization of SBA-15 with Si-Imi. The chemical modification of the SBA-15 surface was carried out by the postgrafting procedure, as follows: 1.00 g of the previously synthesized SBA-15 was immersed into a solution containing 0.50 mL (≈2 mmol) of Si-Imi in 100 mL of dry ethanol. This mixture was kept under reflux for 24 h. The immobilization of the functional groups occurs through condensation reactions between the silanol groups (Si−OH) on the SBA-15 surface and the methoxy groups (−OCH3) of the Si-Imi alkoxysilane, with alcohol release. The product was then filtered and washed with ethanol in a Soxhlet extractor. Finally, the solid was filtered, washed with bidistilled water, and dried under vacuum at 323 K. The sample obtained will hereafter be designated as SBA-15/R+Cl−. Ion-Exchange Study. The ion-exchange isotherm of SBA-15/ R+Cl− toward the AuCl4− anionic complex was carried out by the batch technique. Precise weights (0.025 g) of SBA-15/R+Cl− were immersed in 25.0 mL of aqueous solutions containing different concentrations of tetrachloroauric(III) acid (HAuCl4·3H2O, Aldrich). 10282

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D12A-XRD1 beamline at LNLS (Brazil) with a radiation source of λ = 0.177 nm.

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RESULTS AND DISCUSSION The amount of organic groups on functionalized SBA-15/ R+Cl− was determined by elemental analyses. On the basis of

Figure 1. Nitrogen adsorption−desorption isotherms of (a) SBA-15 and (b) SBA-15/R+Cl−.

Figure 2. Ion-exchange isotherm of SBA-15/R+Cl− material toward AuCl4− anions: (● and ⊕) experimental data and () corresponding to the Langmuir fitting.

Figure 3. XRD patterns of (a) SBA-15/R+Cl−/Au1, (b) SBA-15/ R+Cl−/Au2, and (c) SBA-15/R+Cl−/Au3 as-prepared materials and after thermal treatment at 973 K.

the value of the N content (3.24 wt %), the degree of functionalization obtained for SBA-15/R+Cl− is 1.16 mmol g−1. To confirm the chemical modification of silica and to have structural information about the functional molecules bound to the matrix surfaces, 29Si and 13C CP/MAS NMR spectra of the modified samples were acquired (see Figure SI 1 of the Supporting Information). The 29Si NMR spectra (see Figure SI 1a of the Supporting Information) present signals related to both Q and T species.30 Q4, Q3, and Q2 units are attributed to Si atoms of the inorganic silica framework in the siloxane binding environment without hydroxyl groups [Si(OSi)4], isolated silanol group [Si(OSi)3OH], and geminal silanol groups [Si(OSi)2(OH)2], respectively. T1, T2, and T3 units refer to Si atoms bound to C atoms of the n-propyl bridge of the Si-Imi molecules attached to the surface in different configurations,31−33, such as CSi(OR)2(OSi), CSi(OR)(OSi)2, and CSi(OSi)3, respectively, with R = H or CH3.

13

C NMR spectrum for the functionalized silica (see Figure SI 1b of the Supporting Information) presents signals with specific chemical shifts [parts per million (ppm)] assigned according to the numbering shown in the figure. These results indicate that the functionalization step led to the expected configuration of the organic groups on the silica surface. The peak at ∼48 ppm (C1) is attributed to the C atom of −OCH3 groups that were not hydrolyzed during the functionalization processes.33 The C* marked peaks are related to residual synthesis solvent (ethanol) that was not eliminated during the drying step. The nitrogen adsorption−desorption isotherms for SBA-15 and SBA-15/R+Cl− are shown in Figure 1. As seen, both are type-IV isotherms, typical for mesoporous materials,34 indicating that the structure of SBA-15 is preserved after the surface modification. The observed hysteresis loops are characterized 10283

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Figure 4. TEM images of (a) SBA-15/R+Cl−/Au1, (b) SBA-15/R+Cl−/Au2, and (c) SBA-15/R+Cl−/Au3 as-prepared materials and (d, e, and f) TEM images after thermal treatment, respectively.

suggests that the functional groups are located within the mesopores. SAXS patterns were obtained (see Figure SI 2 of the Supporting Information) and show that mesoporous SBA-15 has a well-ordered two-dimensional mesostructure (P6mm), with three well-resolved peaks indexed as (100), (110), and (200). The calculated hexagonal cell parameter a is 11.67 and 11.65 nm for SBA-15 before and after gold NP formation.40 The mesoporous arrangement remained intact after gold incorporation, as demonstrated by the diffraction peaks at the same position. Furthermore, no decrease in intensity of diffraction peaks was observed, showing no structure collapse of the ordered phase. Ion-Exchange Equilibrium. The ability of cationic functional groups similar to imidazolium to retain metal chlorides (anionic complexes) through electrostatic interactions has been studied for some metal ions, such as Cu2+, Zn2+, Co2+, Fe3+, Cd2+, and Hg2+,32,33,41,42 generally focusing on the development

by parallel and nearly vertical branches (H1 type), associated with porous materials consisting of well-defined cylindrical-like pore channels and high degrees of pore size uniformity.35 For SBA-15/R+Cl−, a small shift to lower relative pressures in the capillary condensation step is observed, suggesting a decrease in the diameter of the pores. The nitrogen adsorption−desorption isotherms for SBA-15/ R+Cl− (Figure 1) do not show a two-step desorption branch (sub-step at a relative pressure of ca. 0.45), which means that no obstruction or blockage of the pores by the functional groups was observed. It suggests that the organic moieties may be present as a thin layer covering the silica surface.36,37 The calculated specific surface area for these samples decreased from 722 m2 g−1 for SBA-15 to 306 m2 g−1 for SBA-15/R+Cl−. Several studies in the literature report that inorganic surfaces modified with organic groups are generally followed by an expressive decrease in specific surface area.38,39 The lower surface area for SBA-15/R+Cl− is thus expected and 10284

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Figure 5. Schematic illustration showing the behavior of the supported Au NPs during thermal treatment.

Furthermore, ion-exchange processes can be carried out in ethanol as well.33,45 Preparation of Supported Au NPs. The possibility of converting the anionic AuCl4− species into gold NPs in the confined pore spaces was then evaluated through chemical reduction with NaBH4. The amounts of Au3+ ions (in weight percent) loaded by SBA-15/R+Cl− in three different equilibrium concentrations of AuCl4−, represented by the filled circles in the isotherm (Figure 2), are 1.8, 9.0, and 14.2%. These solids were then submitted to the reduction process and will be designated as SBA-15/R+Cl−/Au1, SBA-15/R+Cl−/Au2, and SBA-15/R+Cl−/Au3, respectively. The thermal stabilities of the confined Au NPs were evaluated by heating the samples at 973 K for 1 h in air. The diffuse reflectance spectroscopy (DRS) measurements of the samples before and after thermal treatment are shown in Figure SI 3 of the Supporting Information. All of the spectra of the as-prepared samples (see Figure SI 3a of the Supporting Information) show a broad and characteristic absorption band at ∼515 nm (surface plasmon resonance band), directly attributed to the formation of Au NPs.17,49−51 The absence of bands in the 600−800 nm range, typical of strong interparticle interactions or anisotropic particles,50,52−54 suggests that the gold NPs are sufficiently stabilized and that the nucleation occurs without aggregation or coalescence of the formed structures inside the cylindrical channels of SBA-15. After the thermal treatment, the plasmonic bands became more intense and the full width at half maximum (fwhm) is slightly decreased (see Figure SI 3 of the Supporting Information), showing that the size of Au NPs might have increased during the thermal treatment.55−58 However, the spectra display almost the same profile when compared to the samples before thermal treatment, suggesting a low tendency of coalescence during heating and also showing the low mobility of the Au NPs confined within the porous structure. The intensification of the plasmonic bands for the heated samples may be strongly related to an increase in the crystallinity of Au NPs.59 The XRD patterns (see Figure SI 4 of the Supporting Information) of SBA-15/R+Cl−/Au2 and SBA-15/R+Cl−/Au3 show the characteristic (111), (200), and (220) reflections of the face-centered cubic (FCC) structure of gold [Joint Committee on Powder Diffraction Standards (JCPDS) 040784]. The broadening of the diffraction peaks also indicates

of adsorbents applied in purification or decontamination processes. New stationary phases for high-performance anionexchange chromatography have also been developed on the basis of pyridinium43 and imidazolium derivatives44 grafted onto silica surfaces. In the present work, the anion-exchange properties of the imidazolium moieties attached on the silica surface allowed for a controlled loading of AuCl4− species throughout the porous structure. The ion-exchange isotherm for this reaction is shown in Figure 2. The adsorption process on porous solids involves the conformation of the organic functional groups on the surface, the diffusion of solvated ions/molecules, and the electrostatic repulsion in confined spaces.13 The effective ion-exchange capacity (tQ) may differ significantly from the experimental capacity found by elemental analyses (degree of functionalization),26,27,45,46 because it depends upon the stoichiometry of the interactions of the metal chloride with the active surface groups, the accessibility to sorption centers, the affinity between the anionic species and the charged functional group (given by the equilibrium constant, β), the nature of the solvent, and other factors. From the Langmuir fitting, the effective ion-exchange capacity tQ and the equilibrium constant β were calculated: tQ = 0.79 mmol g−1 and log β = 4.47 (±0.29). The value of tQ indicates that the saturation limit of the cationic imidazolium groups toward AuCl4− takes place when approximately 68% of the available chloride anions are exchanged by AuCl4−. This behavior is expected because the chloride anion is replaced by a much more voluminous anionic complex (AuCl4−) and also because of the fact that some sorption sites may be unavailable to the solution-phase reactants as a result of steric constraints. In addition, electrostatic repulsion between the anions on the solid−solution interface may play an important role, and some restrictions in capacity are observed when charged species are involved in the adsorption process.47,48 The high value of the equilibrium constant (log β = 4.47) provides evidence that the ion-exchange process is largely favored and guarantees that the AuCl4− ions are kept strongly retained on the SBA-15 surface functionalized with imidazolium groups. It should also be highlighted that, because the incorporation of the gold precursor is achieved through the ion-exchange process, carried out in water, residual ethanol on the SBA-15 substrate would not hinder this process. 10285

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and highlights the fundamental role played by the silica host to prevent Au NPs from sintering and, consequently, to stabilize the nanostructures prepared by this approach. This observation also confirms that the cationic organic molecules are dispersed within the channels, thus favoring the ion-exchange processes with no preferential adsorption or accumulation of the AuCl4− ions in specific regions within the porous structure.

that the Au particles are in the nanometer-size regime. In the case of SBA-15/R+Cl−/Au1, only the (111) reflection could be detected (see the inset in Figure SI 4 of the Supporting Information). Besides the low amount of gold in this sample (1.8 wt %), the possibility that extremely small particles have been formed in such conditions may have contributed to the observed profile. For the samples thermally treated, the XRD patterns of (111) reflections are shown in Figure 3. The diffraction peaks of the heated samples become sharper when compared to those of the as-prepared materials. Such observations can be associated with multiple effects, such as an increase in the crystallinity degree without changes on the crystallite size, particle growth by coalescence of some particles, and also a decrease in the number of lattice deformations and defects, which are very common in crystalline nanostructures. The thermal treatment effects were more pronounced for SBA15/R+Cl−/Au1. TEM images (Figure 4) of SBA-15/R+Cl−/Au1, SBA-15/ + − R Cl /Au2, and SBA-15/R+Cl−/Au3 before and after thermal treatment confirm the evidence pointed out before and show the structural changes observed by the UV−vis and XRD measurements. It can be clearly seen that the as-prepared supported Au NPs are well-distributed throughout the cylindrical channels of the hybrid mesoporous silicas (panels a−c of Figure 4). The confined environment of the host allows, independent of the amount of AuCl4− anions loaded by SBA-15/R+Cl−, for the formation of supported Au NPs highly dispersed within the porous structure. In the case of SBA-15/R+Cl−/Au1, the Au NPs are clearly much smaller than the samples with higher amounts of gold, as observed in the size histograms shown in Figure SI 5 of the Supporting Information. The maximum of each Au NP size distribution deduced from the fitting by the Gaussian curves is 1.5 nm (±0.46), 5.2 nm (±2.35), and 4.7 nm (±1.82) for the as-prepared materials SBA-15/R+Cl−/Au1, SBA-15/R+Cl−/Au2, and SBA-15/R+Cl−/Au3, respectively. After thermal treatment, it is possible to observe (panels d−f of Figure 4) for all samples that the supported Au NPs maintained their shape and were kept highly dispersed and stabilized by the host matrix. It is also possible to see in the micrographs that the smallest Au NPs in the sample SBA-15/ R+Cl−/Au1 show a more pronounced tendency toward growth during heating. The size histograms of Au NPs after thermal treatment are also shown in Figure SI 5 of the Supporting Information. In comparison to the as-prepared materials, all samples showed an evolution of particle size to higher values. The observed tendency of the smallest Au NPs (SBA-15/R+Cl−/Au1) to have lower thermal stability is thus expected and is strongly related to the behavior observed in the melting point of metal NPs that drastically decrease with a decreasing size of the nanostructures.60 Two possible mechanisms are known to be responsible for the metal NP growing process and can occur simultaneously: (i) Ostwald ripening and (ii) particle migration and coalescence.61−64 A schematic illustration that summarizes the discussion pointed out above is show in Figure 5. Although the particle growth takes place for all samples, the mean size of the Au NPs after heating is still below the mean pore size of SBA-15/R+Cl− (7.5 nm), determined by the density functional theory (DFT) method using nitrogen adsorption isotherm data. This fact is extremely important

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CONCLUSION Imidazolium functional groups were successfully prepared and chemically bound to the surface of SBA-15 mesoporous silica. The ion-exchange properties of the resulting material (SBA-15/ R+Cl−) toward AuCl4− ions allowed for a controlled and effective uptake of anionic gold species (up to 0.79 mmol g−1) throughout the porous structure. The high value of the equilibrium constant (log β = 4.47) for the ion-exchange reaction indicates that the anions (AuCl4−) are kept strongly retained on the surface as counterions of the imidazolium cationic groups. Supported gold NPs were prepared in the ordered channels of SBA-15/R+AuCl4− containing different amounts of AuCl4− anions by chemical reduction with NaBH4. The plasmon resonance bands in the UV−vis range, TEM images, and XRD patterns of the supported gold NPs before and after thermal treatment at 973 K demonstrate that the metal nanostructures are highly dispersed and stabilized on the host environment. Imidazolium-grafted SBA-15 and the proposed synthesis approach showed themselves to be very efficient and convenient for the preparation of uniform and stable supported gold NPs. The achieved synergy between the properties presented by the ordered porous framework and the reactive features of the organic entities certainly constitutes a powerful tool for the fabrication of similar nanostructures for numerous technological applications.

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ASSOCIATED CONTENT

S Supporting Information *

29

Si and 13C CP/MAS NMR spectra of functionalized SBA-15 (Figure SI 1), SAXS pattern of functionalized SBA-15 (Figure SI 2), diffuse reflectance spectra of supported Au NPs (Figure SI 3), XRD patterns of supported Au NPs (Figure SI 4), and normalized size histogram of Au NPs (Figure SI 5). This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +55-19-35213053. Fax: +55-19-35213023. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Natalia Fattori is indebted to FAPESP for a Ph.D. fellowship. Camila M. Maroneze, Luiz P. da Costa, and Mathias Strauss are indebted to CNPq/INCTBio and CAPES for postdoctoral and Ph.D. fellowships. Fernando A. Sigoli, Italo O. Mazali, and Yoshitaka Gushikem are indebted to CNPq and FAPESP for financial support and to Prof. C. H. Collins (IQ−UNICAMP, Brazil) for English revision. Contributions from Brazilian Synchrotron Light Laboratory (LNLS, Campinas, SP, Brazil) for XRD and SAXS measurements are also gratefully 10286

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acknowledged. This work is a contribution from the National Institute of Science and Innovation in Complex Functional Materials (INOMAT).

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