Photocatalyst degradation of binary pesticide/antibiotic mixtures by biochar/g-C3N4 for highly efficient water purification: Effects, mechanism and PVDF membrane application

A positive correlation between the degradation rates of pollutants and LUMO–HOMO gaps was revealed. • AZO degradation was conversely facilitated by coexisting pollutants with narrower LUMO–HOMO gaps. • Nearly all the degradation intermediates of AZO had lower toxicity than the parent compound did. • The BCN–PVDF membrane achieves excellent removal and self-cleaning performance. Pesticides and antibiotics from agricultural activities represent a major source of water pollution. While photocatalysis shows promise in eliminating individual pollutants, its behavior and degradation mechanisms in binary pollutant systems remain poorly understood. In this work, using biochar/g-C 3 N 4 as the photocatalyst, the k values for the degradation of typical pesticides and antibiotics, namely azoxystrobin (AZO), tetracycline (TC), ofloxacin (OFX), sulfadiazine (SDZ), and atrazine (ATR), were 0.14144, 0.14467, 0.24850, 0.03145, and 0.01337 min −1 , respectively. The -ln( k ) values were positively correlated with the LUMO–HOMO gaps of these pollutants. Interestingly, in AZO-based binary systems, the -ln( k ) value of AZO was negatively correlated with the LUMO–HOMO gaps of the coexisting pollutants. Through density functional theory (DFT) calculations and UHPLC-Q Exactive MS analysis, five key intermediates of AZO degradation were identified, most of which were predicted to be less toxic than the parent compound. To enable practical water purification application and facilitate catalyst recovery, a BCN–PVDF photocatalytic purification membrane was fabricated. Under continuous operation for 12 h, the membrane achieved nearly complete removal of TC and OFX, 91.17% removal of AZO, and over 73% removal of SDZ and ATR. It also exhibited excellent anti-fouling and self-cleaning performance. This work elucidates structure–activity relationships in photocatalytic degradation of organic pollutants, reveals interaction mechanisms in binary pollutant systems, and demonstrates a feasible pathway toward the practical purification treatment of complex wastewater containing mixed contaminants. Download: Download high-res image (143KB) Download: Download full-size image