Metal-Cluster-Decorated TiO2 Nanotube Arrays: A Composite Heterostructure toward Versatile Photocatalytic and Photoelectrochemical Applications

Recent years have witnessed increasing interest in the solution-phase synthesis of atomically precise thiolate-protected gold clusters (Au-x); nonetheless, research on the photocatalytic properties of Au-x-semiconductor nanocomposites is still in its infancy. In this work, recently developed glutathione-capped gold clusters and highly ordered nanoporous layer-covered TiO2 nanotube arrays (NP-TNTAs) are employed as nanobuilding blocks for the construction of a well-defined Au-x/NP-TNTA heterostructure via a facile electrostatic self-assembly strategy. Versatile photocatalytic performances of the Au-x/NP-TNTA heterostructure which acts as a model catalyst, including photocatalytic oxidation of organic pollutant, photocatalytic reduction of aromatic nitro compounds and photoelectrochemical (PEC) water splitting under simulated solar light irradiation, are systematically exploited. It is found that synergistic interaction stemming from monodisperse coverage of Au-x clusters on NP-TNTAs in combination with hierarchical nanostructure of NP-TNTAs reinforce light absorption of Au-x/NP-TNTA heterostructure especially within visible region, hence contributing to the significantly enhanced photocatalytic and PEC water splitting performances. Moreover, photocatalytic and PEC mechanisms over Au-x/NP-TNTA heterostructure are elucidated and corresponding reaction models were presented. It is anticipated that this work could boost new insight for photocatalytic properties of metal-cluster-sensitized semiconductor nanocomposites.