CuOx dispersion and reducibility on TiO2 and its impact on photocatalytic hydrogen evolution

Nanostructured CuOx/TiO2 (a mixture of Cu/Cu2O/CuO) was prepared by impregnation for enhancing photocatalytic hydrogen generation from an aqueous solution containing 10 v/v% methanol. At an optimum Cu loading of 0.5 wt% and a calcination temperature of 500 °C, the CuOx was present as relatively highly dispersed (0.90), fine deposits. At Cu loadings beyond 0.5 wt% a bimodal distribution of CuOx deposits appeared with the prevalence of larger Cu deposits increasing with increasing Cu content. A corresponding decrease in H2 generation was observed as Cu loading increased which was attributed to the increasing presence of the larger CuOx deposits. The particle calcination temperature (in air) was also found to affect CuOx/TiO2 activity with an optimum performance achieved at a temperature of 300 °C. Calcining the CuOx/TiO2 at 500 °C led to greater oxidation of the CuOx deposits (∼40%) to form more Cu2+ which corresponded to an almost proportional (42%) decrease in H2 generation. The findings demonstrate the importance of Cu dispersion and oxidation state in governing photocatalytic H2 generation by CuOx/TiO2.