Nitrogen fixation is the second most important chemical process in nature next to photosynthesis. Herein, we report a novel g-C3N4/ZnSnCdS heterojunction photocatalyst prepared using the hydrothermal method that has an outstanding nitrogen photofixation ability under visible light. The as-prepared ZnSnCdS is the ternary metal sulfide Zn0.11Sn0.12Cd0.88S1.12 with many sulfur vacancies, not a mixture of ZnS, SnS2, and CdS. Strong electronic coupling, as evidenced by the ultraviolet–visible, X-ray photoelectron spectroscopy, photoluminescence, and electrochemical impedance spectra results, exists between two components in the g-C3N4/ZnSnCdS heterojunction photocatalysts, leading to more effective separation of photogenerated electron–hole pairs and faster interfacial charge transfer. The sulfur vacancies on ternary metal sulfide not only serve as active sites to adsorb and activate N2 molecules but also promote interfacial charge transfer from ZnSnCdS to N2 molecules, thus significantly improving the nitrogen photofixation ability. With the ZnSnCdS mass percentage of 80%, the as-prepared heterojunction photocatalyst exhibits the highest NH4 + generation rate under visible light, which is 33.2-fold and 1.6-fold greater than those of individual g-C3N4 and ZnSnCdS.

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Extending the application of photocatalytic oxidation technology to the anoxic removal of organic pollutants that exist under some oxygen-free conditions is attractive but challenging. In this study, oxygen functionalized S-P codoped g-C3N4 nanorods with outstanding visible light activity under anoxic conditions are synthesized using a hydrothermal post-treatment. S and P codoping inhibits the crystal growth of graphitic carbon nitride, enhances the SBET, decreases the band gap energy, and increases the separation efficiency of photogenerated electrons and holes, which increases the anoxic photocatalytic RhB degradation constant by approximately 6.5 times. Oxygen functionalization not only increases the adsorption ability of graphitic carbon nitride but also captures the photogenerated electrons to produce photogenerated holes for RhB degradation under anoxic conditions, leading to a doubling of the RhB degradation constant. This study provides new insight into the design and fabrication of anoxic photocatalysts.