Impact of tailoring of the defect states and the band gap towards extreme photocatalytic performance and photo-induced conductivity in cobalt doped ZnO QD

Abstract

Due to the advantages of tuning the electronic structure and reducing charge carrier recombination, metal doping into semiconductor metal oxides has been considered an efficient method for enhancing photocatalytic activity and photo-induced conductivity. In this paper, we focus on the effect of cobalt doping on the photocatalytic performance and photo-induced conductivity of ZnO QD. It was found that after Co doping, the photocatalytic activity of ZnO QD was remarkably higher than that of undoped ZnO QD when measured with methylene blue (MB) dye. The study showed that the complete degradation of the dye using 5 mol% cobalt doped ZnO QD occurred in just 6 min, which is 4 times faster than that of undoped ZnO QD. The extent of dye mineralization was supported by chemical oxygen demand (COD) study, which revealed that the dye was almost entirely mineralized. Furthermore, the photoconductivity and photosensitivity of 5 mol% doped Co doped ZnO QD were increased by 20 and 7 times, respectively, over that of undoped ZnO QD. The outstanding boost in photocatalytic activity and photoconductivity is caused by the tunable band gap mediated photo response, which increases light harvesting and thus the generation of a large number of electron hole pairs. Another possible explanation is that sub-energy levels formed between the conduction and valence bands act as a trap for electrons and holes, promoting charge separation by limiting photogenerated charge carrier recombination.