Enhanced Photocurrent Responses and Antiphotocorrosion Performance of CdS Hybrid Derived from Triple Heterojunction

The enhanced photocurrent responses and dramatic antiphotocorrosion performance of CdS hybrid were obtained by formation of triple heterojunction (TH), i.e., n-CdS/n-TiO2/p-BDD:n-TiO2 cube tubes were vertically grown on p-type boron-doped diamond (BDD) film. Then n-CdS nanoparticles (NPs) were randomly assembled onto the surface of TiO2 and BDD, forming a film of CdS NPs. This triple heterojunction CdS hybrid reveals 36.5% improvement of initial photocurrent and 78% reduction of photocorrosion rate in contrast with that of the coupled CdS/TiO2 hybrid, which has only single heterojunctions (SH). The mechanisms of TH on charge separation and transport during the photocatalytic reaction have been emphasized. Except for the CdS/TiO2 (n-n) heterojunction, another two p-n heterojunctions, i.e., p-BDD/n-CdS and p-BDD/n-TiO2 exist in the TH. The conduction band (CB) position of TiO2 is lower than the corresponding band positions of CdS and BDD, so TiO2 can act as an acceptor for the photogenerated electrons. Also, the valence band (VB) position of BDD is higher than those of CdS and TiO2, so BDD can act as a sink for the photogenerated holes. Under simulated solarlight, the photogenerated electrons on the conduction band (CB) of CdS flow to the CB of TiO2., whereas the photogenerated holes on valence band (VB) CdS and TiO2 inject to the VB of BDD. It promotes charge separation and leaves not enough holes on CdS to cause photoanodic corrosion, leading to the enhancement of photocurrent responses and the remarkable inhibited photocorrosion.