Core-shell P-laden biochar/ZnO/g-C3N4 composite for enhanced photocatalytic degradation of atrazine and improved P slow-release performance

Technologies that can effectively address the environmental issues arisen from the use of agrochemicals and P fertilizers are needed for the development of green agriculture. Here, we reporta new core-shell P-laden biochar/ZnO/g-C3N4 composite (Pbi-ZnO-g-C3N4) used both as an efficient photocatalyst for degrading atrazine and a promising slow-release fertilizer for improving the P utilization efficiency. In comparison with P-laden biochar/ZnO (Pbi-ZnO), Pbi-ZnO-g-C3N4 exhibits enhanced photocatalytic activity with the maximum atrazine degradation efficiency of 85.3% after 260 min. Pbi-ZnO-g-C3N4 also shows superior P slow-release performance with the cumulative P release concentration of 216.40 g/L in 260 min. Besides, it is found that the coating of g-C3N4 on the surface of Pbi-ZnO improves the utilization of visible light and separation of photoinduced electron-hole pairs, producing more radicals (•OH and •O2-) under visible light irradiation. The mechanistic study reveals that Z-shaped heterojunction is formed between ZnO and g-C3N4 in Pbi-ZnO-g-C3N4, and biochar serves as an electron-transfer bridge that promotes the separation of electron-hole pairs. Finally, pot experiments reveal that the P utilization efficiency for pepper seedlings fertilized by Pbi-ZnO-g-C3N4 is higher than that by Pbi-ZnO. The application of Pbi-ZnO-g-C3N4 is beneficial for the growth of native soil microorganism.