Electrochemical methods for the preparation of gold-coated TiO2 nanoparticles with variable coverages

We report here the first electrochemical methods to prepare elemental Au(0)-coated TiO₂ nanoparticles with controllable coverages. First, Au substrates were cycled in a deoxygenated aqueous solution containing 0.1 N HCl and 1 mM TiO₂ nanoparticles from -0.28 to +1.22 V versus Ag/AgCl at 500 mV/s with different numbers of scans. The durations at the cathodic and anodic vertexes were 10 and 5 s, respectively. After this process, positively charged Au-coated TiO₂ nanoparticles were formed in the solutions. Then a cathodic overpotential of 0.6 V from the open circuit potential of ca. 0.82 V versus Ag/AgCl was applied under sonication to synthesize elemental Au(0)-coated TiO₂ nanoparticles. The coverage of Au shells in the elemental Au-coated TiO₂ nanoparticles is varied from 10% to 95% by increasing the number of scans from 10 to 50 in preparing the positively charged Au-coated TiO₂ nanoparticles. The extremely high coverage of 95% in this study is notable, as compared with other methods to prepare Au-coated TiO₂ nanoparticles.