Modification of gold nanoparticles with a hole-transferring cocatalyst: a new strategy for plasmonic water splitting under irradiation of visible light

Abstract

Plasmonic water splitting (H₂O → H₂ + 1/2O₂) over a metal-loaded metal oxide under irradiation of visible light is still difficult, although conversion of organic compounds over plasmonic photocatalysts has become popular. Acceleration of oxygen (O₂) production by water oxidation is the key for smooth water splitting. A chromium species was introduced to gold (Au)-loaded titanium(IV) oxide (Au/TiO₂) by using the photodeposition method. The morphology, structure and electronic state of the chromium species and Au/TiO₂ were analyzed by transmission electron microscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The results revealed that a very thin chromium hydroxide (Cr(OH)₃) layer was formed on Au nanoparticles, which made the state of Au slightly electron-rich. The Cr(OH)₃/Au/TiO₂ plasmonic photocatalyst exhibited reaction rates larger than those of reactions over Cr(OH)₃-free Au/TiO₂ towards both water oxidation and water splitting under irradiation of visible light. Oxidative deposition of PbO₂ revealed that plasmonic oxidation occurs on Cr(OH)₃/Au and that Cr(OH)₃ effectively works as the hole transfer cocatalyst. Based on the results, reaction mechanisms of plasmonic water oxidation and water splitting over Cr(OH)₃/Au/TiO₂ are proposed.