Confined Au‐Pd Ensembles in Mesoporous TiO2 Spheres for the Photocatalytic Oxidation of Acetaldehyde

Titanium dioxide (TiO2) is the most widely used photocatalyst for environmental remediation and solar-fuel production, owing to its low cost, nontoxicity, and abundance. In TiO2-based photocatalysis, the photogenerated electrons and holes separate and migrate to the surface to be involved in the surface redox reactions. However, a high recombination rate of the photogenerated charge carriers leads to low photocatalytic efficiency. Various noble metals have been introduced to trap photogenerated electrons across the interface and, thus, improve the charge separation within the TiO2 semiconductor. In the case of metal/TiO2 composites, the photogenerated electrons are trapped by the metal, owing to the formation of a Schottky barrier at the metal/TiO2 interface, which inhibits electron-hole recombination and, thus, prolongs the lifetime of the charge carriers. In addition, the dispersed noble metal can also enhance reactant adsorption, as well as act as a co-catalyst to help the redox process by lowering the over-potential that arises from strong metal–support interactions. As a consequence, enhanced photocatalytic activities have been observed on the metal/TiO2 composites.