Z-scheme heterojunction g-C3N4@PDA/BiOBr with biomimetic polydopamine as electron transfer mediators for enhanced visible-light driven degradation of sulfamethoxazole

Visible-light photocatalysis boosted by Z-scheme photocatalysts has been deemed as an economic and effective way in eliminating emerging antibiotics pollution. A Z-scheme heterojunction photocatalyst g-C3N4@PDA/ BiOBr (CNPB) was hereby facilely constructed through polydopamine (PDA) modification of g-C3N4 followed by deposition of BiOBr component via a solvothermal reaction. The structure, morphology, optical and photo-electrochemical properties etc. of CNPB were characterized and explored. The photocatalytic activity of CNPB was assessed on the degradation of sulfamethoxazole (SMX). CNPB manifested remarkably improved photocatalytic performance than the as-prepared g-C3N4, BiOBr and g-C3N4/BiOBr heterojunction in the degradation of SMX under visible light irradiation. SMX could be nearly completely degraded in 60 mins by CNPB, while the degradation rate of SMX under g-C3N4, BiOBr, g-C3N4/BiOBr heterojunction, and the "g-C3N4@PDA + BiOBr" mixture were 30%, 42%, 71%, and 47%, respectively. The highly enhanced photocatalytic efficiency of CNPB was attributed to the synergistic effect of improved light harvesting and accelerated transport and separation of photo-generated carriers in the Z-scheme structure with PDA as efficient electron transfer mediators. A Z-scheme charge transfer mechanism was confirmed by experiments on radical scavenging and electron spin resonance (ESR) signals trapping, which demonstrated that the h(+) and center dot O-2(-) were the major reactive species in oxidizing SMX. The degradation mechanism, main intermediates and reaction pathways were further explored. Besides, CNPB exhibited good stability and reusability in multiple uses. The construction of Z-scheme photocatalyst using biomimetic polydopamine as electron transfer mediators may provide an insight into designing new and efficient photocatalysts for environmental applications.