Au-TiO_2 Nanocomposites and Efficient Photocatalytic Hydrogen Production under UV-Visible and Visible Light Illuminations: A Comparison of Different Crystalline Forms of TiO_2

摘要

Au_(～1 wt%)/TiO_(2(anatase or rutile or P25)) nanocomposites were prepared by the solvated metal atom dispersion (SMAD) method, and the as-prepared samples were characterized by diffuse reflectance UV-visible spectroscopy, powder XRD, BET surface analysis measurements, and transmission electron microscopy bright field imaging. The particle size of the embedded Au nanoparticles ranged from 1 to 10 nm. These Au/TiO_2 nanocomposites were used for photocatalytic hydrogen production in the presence of a sacrificial electron donor like ethanol or methanol under UV-visible and visible light illumination. These nanocomposites showed very good photocatalytic activity toward hydrogen production under UV-visible conditions, whereas under visible light illumination, there was considerably less hydrogen produced. Au/P25 gave a hydrogen evolution rate of 1600 μmol/h in the presence of ethanol (5 volume %) under UV-visible illumination. In the case of Au/TiO_2 prepared by the SMAD method, the presence of Au nanoparticles serves two purposes: as an electron sink gathering electrons from the conduction band (CB) of TiO_2 and as a reactive site for water/ethanol reduction to generate hydrogen gas. We also observed hydrogen production by water splitting in the absence of a sacrificial electron donor using Au/TiO_2 nanocomposites under UV-visible illumination.