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

Nanostructured CuO_x/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 CuO_x was present as relatively highly dispersed (0.90), fine deposits. At Cu loadings beyond 0.5 wt% a bimodal distribution of CuO_x 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 CuO_x deposits. The particle calcination temperature (in air) was also found to affect CuO_x/TiO₂ activity with an optimum performance achieved at a temperature of 300 °C. Calcining the CuO_x/TiO₂ at 500 °C led to greater oxidation of the CuO_x 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 CuO_x/TiO₂.