Ion-Exchange Properties of Imidazolium-Grafted SBA-15 toward AuCl4- Anions and Their Conversion into Supported Gold Nanoparticles

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 AuCl4- anions were evaluated through an ion-exchange isotherm. The calculated values of the equilibrium constant (log beta = 4.47) and the effective ion-exchange capacity (t(Q) = 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.