Anisotropic growth of SiO2 and TiO2 mixed oxides onto Au nanostructures: highly thermal stability and enhanced reaction activity

Abstract

Eccentric Au@(SiO₂,TiO₂) core–shell nanostructure that consists of a 20 nm Au core coated with mixed SiO₂–TiO₂ oxides shell was fabricated by a facile sol–gel method. The prepared samples were characterized by means of TEM, EDS, FTIR, and N₂ adsorption–desorption isotherms. The results showed that incorporation of TiO₂ in SiO₂ shells led to the displacement of the Au particle from the center to eccentric positions. By tuning the nanostructure of Au core, the mixed oxides also exhibited anisotropic growth on smaller Au nanoparticles (10 nm) and Au nanorods. When used as the catalyst for the reduction of 4-nitrophenol, the mixed oxides coated catalysts exhibited significantly enhanced catalytic performance compared with the pure SiO₂ coated one. In particular, the calcined Au@(SiO₂,TiO₂) particles showed the highest catalytic activity due to the easy mass transfer, improved thermal stability and increased synergy effect of Au with TiO₂. Finally, a possible reaction mechanism for the reduction reaction on Au@(SiO₂,TiO₂) was also proposed.