A Facile Approach to TiO2 Colloidal Spheres Decorated with Au Nanoparticles Displaying Well-Defined Sizes and Uniform Dispersion

This paper describes a straightforward approach for the synthesis of hybrid materials composed of titanium dioxide (TiO2) colloidal spheres decorated with gold nanoparticles (Au NPs). In the reported method, monodisperse TiO2 colloidal spheres (similar to 220 nm in diameter) could be directly employed as templates for the nucleation and growth of Au NPs over their surface using AuCl4(aq)- as the Au precursor, ascorbic acid as the reducing agent, PVP as the stabilizer, and water as the solvent. The Au NPs presented a uniform distribution over the TiO2 surface. Interestingly, the size of the Au NPs could be controlled by performing sequential reduction steps with AuCl4(aq)-. This method could also be adapted for the production of TiO2 colloidal spheres decorated with other metal NPs including silver (Ag), palladium (Pd), and platinum (Pt). The catalytic activities of the TiO2-Au materials as a function of composition and NPs size were investigated toward the reduction of 4-nitrophenol to 4-aminophenol under ambient conditions. An increase of up to 10.3-fold was observed for TiO2-Au relative to TiO2. A surface-enhanced Raman scattering application for TiO2-Au was also demonstrated employing 4-mercaptopyridine as the probe molecule. The results presented herein indicate that our approach may serve as a platform for the synthesis of hybrid materials containing TiO2 and metal NPs displaying well-defined morphologies, compositions, and sizes. This can have important implications for the design of TiO2-based materials with improved performances for photocatalysis and photovoltaic applications.