Cobalt Aluminate Spinel as a Cocatalyst for Photocatalytic Oxidation of Water: Significant Hole-Trapping Effect

Here we show that nanoparticulate CoAl2O4 spinel serves as an efficient cocatalyst for photocatalytic oxidation of water. The O2 evolution activity of CoAl2O4/g-C3N4 from an aqueous solution of AgNO3 under visible light irradiation was ∼10 times that of unmodified g-C3N4 and also exceeded that of an analogue modified with a well-known Co3O4 cocatalyst for each optimal preparation condition. Transient absorption spectroscopy indicated that the CoAl2O4 cocatalyst with Co2+ as the main cobalt species at the A site of the spinel possessed better hole-capturing properties than the Co3O4 cocatalyst, which was the main reason for the improved water-oxidation performance.