Preventing sintering of Au and Ag nanoparticles in silica-based hybrid gels using phenyl spacer groups

Gold and silver metal salts were reduced in the presence of phenylethylthiol as capping agent to form metal nanoparticles of 2.1-2.4 nm diameter. These clusters were then added to a sol-gel process using phenyltriethoxysilane as a hybrid component to optimize the dispersion of the metal particles in the matrix. The encapsulated metal particles grow in the sol-gel process to an average diameter of 6 nm. This method permits a controlled variation of the materials' porosity by simply regulating the synthesis pH values. Optimized mixed micro-/mesoporous materials are obtained at pH = 6. The metal particles and the matrix are thermally stable, and catalyze CO oxidation.