Enhanced photocatalytic activity for tetracyclines degradation with Ag modified g-C3N4 composite under visible light

Tetracycline antibiotics (TCs) have high residual concentrations in the environment, which can cause serious problems with antibiotic resistance genes as well as bacterial resistance, and thus pose a threat to human health and ecosystem. The application of photocatalytic technology to degrade pollutants has received more and more attention due to its energy-saving and high-efficiency characteristics. In this work, special emphasis was placed on the degradation and mechanisms of three kinds of tetracycline antibiotics (including tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC)) by using novel Ag/g-C3N4 nano-sheets photocatalysts. The results showed that the heterojunction formed by the combination of g-C3N4 and Ag, being not only beneficial to supply more reaction active sites for catalytic reaction but also suppressing the recombination of photogenerated electron-holes pairs, can achieve 2-3 times the degradation efficiency of pure g-C3N4. The Ag(8%)/g-C3N4 sample showed the highest photocatalytic efficiency among these composites and the photocatalytic activities of TCs were improved with increasing pH. In addition, this work assessed the effects of TCs degradation intermediates on Escherichia coli (E. coli) activities and used TC as an example to infer the degradation pathway. The degradation mechanisms were also explored. It suggested that photogenerated holes were the main active species and the inhibition effect of degradation products on E. coli was significantly reduced compared with TCs. This proved again that the degradation of TCs by Ag/g-C3N4 was effective and reliable.