Ion-Exchange Properties of Imidazolium-Grafted SBA-15 toward AuCl 4 − 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, Sã o Paulo (SP), Brazil *S Supporting Information ABSTRACT: Imidazolium groups were successfully prepared and grafted on the surface of SBA-15 mesoporous silica. The ion- exchange properties of the functionalized porous solid (SBA-15/ R + Cl − ) toward AuCl 4 − anions were evaluated through an ion- exchange isotherm. The calculated values of the equilibrium constant (log β = 4.47) and the effective ion-exchange capacity (t Q = 0.79 mmol g −1 ) indicate that the AuCl 4 − species can be loaded and strongly retained on the functionalized surface as counterions of the imidazolium groups. Subsequently, solids containing different amounts of AuCl 4 − ions were submitted to a chemical reduction process with NaBH 4 , converting the anionic gold species into supported gold nanoparticles. The plasmon resonance bands, the X-ray diffraction patterns, and transmission electron micros- copy 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. ■ INTRODUCTION The use of porous solids in the development of nano- technology 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 environ- mental 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 counter- parts, 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, silica- based materials can be highlighted for the extraordinary versatility presented by this inorganic matrix, directly attributed 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 develop- ment of chromatographic stationary phases, 23 sorbents in solid- Received: April 3, 2012 Revised: June 11, 2012 Published: June 14, 2012 Article pubs.acs.org/Langmuir © 2012 American Chemical Society 10281 dx.doi.org/10.1021/la301374z | Langmuir 2012, 28, 10281−10288