Double Z-Scheme g-C3N4/BiOI/CdS heterojunction with I3−/I− pairs for enhanced visible light photocatalytic performance

The g-C3N4/BiOI/CdS double Z-scheme heterojunction photocatalyst with I3−/I− redox pairs is prepared using simple calcination, solvothermal, and solution chemical deposition methods. The photocatalyst comprised mesoporous, thin g-C3N4 nanosheets loaded on flower-like microspheres of BiOI with CdS quantum dots. The g-C3N4/BiOI/CdS double Z-scheme heterojunction has abundant active sites and in situ redox I3−/I− mediators and shows quantum size effects, which are all conducive to enhancing the separation of photoinduced charges and increasing the photocatalytic degradation efficiency for bisphenol A, a model pollutant. Specifically, the heterojunction photocatalyst achieves a photocatalytic degradation efficiency for bisphenol A of 98.62% in 120 min and photocatalytic hydrogen production of 863.44 μmol h−1g−1 on exposure to visible light. The excellent visible-light photocatalytic performance is as a result of the Z-scheme heterojunction, which extends absorption to the visible light region, as well as the I3−/I− pairs, which accelerate photoinduced charge carrier transfer and separation, thus dramatically boosting the photocatalytic performance. In addition, the key role of the charge transfer across the indirect Z-scheme heterojunction has been elucidated and the transfer mechanism is confirmed based on the detection of intermediate I3− ions. Thus, this study provides guidelines for the design of indirect Z-scheme heterojunction photocatalysts.