Sol–gel synthesis of defect-pyrochlore structured CsTaWO6 and the tribochemical influences on photocatalytic activity

Abstract

The semiconductor mixed oxide photocatalyst CsTaWO₆ was prepared via an aqueous sol–gel citrate route for the first time. The mild reaction conditions yield smaller primary particle sizes and larger specific surface areas than the conventional solid state reaction. The photocatalytic properties are determined using both photocatalytic terephthalic acid hydroxylation and photocatalytic hydrogen generation. All of the materials described herein generate hydrogen without the addition of a co-catalyst. Due to the initially agglomerated but porous morphology of the sol–gel-derived CsTaWO₆, tribochemical treatment via short term ball milling has a strong effect on the photocatalytic activities of these materials. Ball milling increases the surface area of the materials, leading to strongly improved activity for the generation of ˙OH radicals, but also generates surface defects in the materials. The defective sites act as electron traps, which depress the photocatalytic hydrogen evolution activity. However, by combining ball milling and photodeposition of Rh, highly improved hydrogen generation rates for CsTaWO₆ are achieved. The sol–gel citrate route finally leads to more active materials than the solid state reaction.