Enhanced catalytic activity of modified g-C3N4 heterojunction for photocatalytic degradation of methylene blue from wastewater

Rapid recombination of photoinduced charge carriers and poor photocatalytic degradation performance greatly hinder the large-scale application of g-C₃N₄ photocatalysis. Therefore, the g-C₃N₄ is modified by BiPO₄ to overcome its poor photocatalytic performance, which is investigated by methylene blue (MB) removal. The S scheme heterojunction is constructed by modifying g-C₃N₄ with BiPO₄, which can effectively preserve the redox activities of holes and electrons on VB and CB, exhibiting good photocatalytic activity. Therefore, the modified g-C₃N₄ exhibits excellent photocatalytic activity with efficient separation of the photoelectron-hole, compared to pure g-C₃N₄ and BiPO₄. The modified g-C₃N₄ exhibits large MB degradation removal of 96.7 %, which is significantly larger than the pure g-C₃N₄ (46.3 %) and BiPO₄ (3.3 %) owe to synergy, respectively. The photodegradation rate constant of the modified g-C₃N₄ is 4.8 and 43 times larger than that of the pure g-C₃N₄ and BiPO₄, respectively. The modified g-C₃N₄ still has large MB removal of 92.9 % after 5 cycles, indicating excellent stability and recyclability. The fractal density calculation of the modified g-C₃N₄ is investigated combined with LUMO and HOMO analysis. The MB photocatalytic degradation process follows the S scheme charge transfer mechanism, based on degradation mechanism analysis combined with semiconductor energy band and density functional theory calculation analysis. The MB photocatalytic degradation path is systemically analyzed based on MS-UPLC result analysis, which indicates that MB is finally decomposed into CO₂ and H₂O, achieving the degradation of MB.