Surface Modification of TiO₂ with Au Nanoclusters for Efficient Water Treatment and Hydrogen Generation under Visible Light

Small gold nanoparticles (Au-NPs) were used to modify the surface of titanium dioxide as visible-light absorbers and thermal redox active centers. Au-NPs were synthesized on commercial TiO₂ (P25) by reduction with tetrakis­(hydroxymethyl)­phosphonium chloride. The Au/P25 composites were characterized by different techniques including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). Time-resolved microwave conductivity (TRMC) was used to study the charge-carrier dynamics. The photocatalytic activity of Au/TiO₂ was evaluated for the degradations of phenol, 2-propanol, and acetic acid and for H₂ production from aqueous methanol solution. The modification of TiO₂-P25 with Au-NPs with preferential localization on the anatase phase led to an increase in its photocatalytic activity under UV and visible-light. TRMC signals showed the injection of electrons from Au-NPs into the conduction band of TiO₂ under visible-light excitation, as a result of the activation of the localized surface plasmon resonance (LSPR) of the Au-NPs. The action spectra (AS) correlated with the absorption spectra, confirming that the decomposition of acetic acid occurs by a photocatalytic mechanism. The modified TiO₂-P25 was also found to provide promising results for hydrogen generation under visible-light. The stability of these plasmonic photocatalysts was also investigated, and the results showed that they can be reused several times without appreciable loss of activity