Synthesis of photocatalysts for the reduction of hexavalent chromium by modification of TiO2 with nanoparticles of Cu and/or CDS

In this work, TiO2-based composite photocatalysts were synthesized for the photoreduction of Cr(VI) by deposition of CdS and/or Cu nanoparticles. Oak leaf extract was used as a reducing agent for the synthesis of Cu nanoparticles. Although the deposited amount of Cu was small (~ 1.1 wt%), it resulted in a shift of the absorption edge to the visible region and a significantly higher efficiency compared to TiO2. Deposition of ~ 3 wt% CdS resulted also in a higher activity under the visible light compared to TiO2, but lower compared to Cu-TiO2. The best results were obtained with the ternary photocatalyst, probably due to the formation of a z-scheme in which the deposited Cu acts as a mediator for electron transfer between CdS and TiO2. The addition of citric acid as a hole "scavenger" allowed a further increase in activity, even in the case of TiO2.