Construction of S-scheme CdS/g-C3N4 heterojunctions with enhanced photocatalytic H2 evolution and Cr(VI) reduction performance

Abstract

Construction of heterojunctions is one of the most attractive approaches to synthesize highly active photocatalysts. In this work, we prepared CdS/g-C3N4 (CSCN) heterojunctions with different molar ratio of CdS/g-C3N4 via ball milling for photocatalytic hydrogen production and removal of Cr(VI). The successful construction of CSCN heterojunctions was proved by the various characterization methods. Formation of CSCN heterojunctions not only generates more vacancies to act as active site, but also accelerates the separation of photoinduced charge carriers, endowing with more electrons to participate in the photocatalytic reduction reaction. 2%CSCN sample was confirmed to hold the highest separation and transfer performance of photoinduced e−/h+ pairs by photoelectric tests. 2%CSCN samples exhibit the highest photocatalytic H2 evolution rate (680.04 μmol/g/h), which is 3.63-fold higher than that of the bare g-C3N4 (146.83 μmol/g/h). The activity of photocatalyst was further examined by removal of Cr(VI) experiment. The results show that the reduction efficiency of Cr(VI) on 2%CSCN is 2.46-fold of that of on the single g-C3N4, and the elimination rate of Cr(VI) on 2%CSCN can reach 64% after 1 h under simulated sunlight illumination. The improved photocatalytic performance can be ascribed to the creation of appropriate C vacancies and the widened light absorption range induced by CdS. A rational mechanism for enhanced photocatalytic activity was proposed to further understand the separation and transfer of photogenerated carriers produced by heterojunctions.