Cu-doped CdS-TiO2 combined with upconverting particles for NIR-induced photocatalytic CO2 reduction

The influence of copper doping of cadmium sulfide on the activity in composites with TiO2 (anatase) for photocatalytic CO2 reduction was examined. CdS and (Cu,Cd)S were synthesized by the hydrothermal method and characterized using XRD, XPS, SEM, EDS, and XRF methods. It was found that copper doping is responsible for the shift of band edge potentials. The mechanisms of photocatalytic performance of the created heterojunctions were elucidated with photoelectrochemical, spectroelectrochemical and surface photovoltage techniques. The S-scheme heterojunction was recognized for both examined systems. The obtained composites were examined under Xe-lamp radiation in the gas phase revealing CO2 reduction to CO. Moreover, the photocatalytic performance under NIR irradiation was demonstrated with the use of the upconverting nanoparticles (UCPs) added to the photocatalytic system. It was found that Cu doping improved the photocatalytic performance of CdS/TiO2 in CO2 to CO conversion mainly through the increase of the photostability of the sulfide system.