Deposition of BiVO4 on the floating lightweight hollow sponge carbon nitride for efficient photocatalytic degradation of tetracycline by S-scheme heterojunction and the ecotoxicity assessment of the products

In this study, the floating lightweight hollow sponge carbon nitride containing BiVO₄ (BVO/LHSCN) was constructed using calcination and hydrothermal methods. Experiments and DFT theoretical calculations show that the S-scheme charge transfer path of BVO/LHSCN and its unique porous network floating structure achieve BVO/LHSCN excellent light capture ability, photogenerated carrier separation efficiency and recycling performance. After 180 min of illumination, BVO/LHSCN can degrade 94.9 % of tetracycline (TC), with a rate constant as high as 0.06235 min⁻¹, which was 4.35 times and 7.7 times higher than that of pure BVO (0.01433 min⁻¹) and LHSCN (0.00807 min⁻¹), respectively. After 5 cycles of experiment, BVO/LHSCN still exhibited excellent TC degradation performance, demonstrating outstanding stability. Subsequently, the site of TC attack was predicted by Fukui index, the intermediate product and degradation pathway during the TC degradation were analyzed by LC-MS. The possible ecological risks of the intermediate and final products were assessed, determining a low environmental risk in the degradation process of tetracycline. This study provides a novel method to improve the light-capturing ability of S-scheme heterojunction photocatalysts.