A 1D/2D Bi2O3/g-C3N4 step-scheme photocatalyst to activate peroxymonosulfate for the removal of tetracycline hydrochloride: insight into the mechanism, reactive sites, degradation pathway and ecotoxicity

A novel 1D/2D step-scheme Bi₂O₃/g-C₃N₄ was prepared using a simple reflux method. Bi₂O₃ photocatalysts showed lower photocatalytic activity for the degradation of tetracycline hydrochloride under visible light irradiation. After compositing with g-C₃N₄, the photocatalytic activity of Bi₂O₃ was enhanced obviously. The enhanced photocatalytic activity of the Bi₂O₃/g-C₃N₄ photocatalysts could be attributed to the high separation efficiency of carriers generated by the Bi₂O₃/g-C₃N₄ photocatalyst due to the formation of a step-scheme heterojunction, which inhibited the recombination of photogenerated electrons and holes. In order to further enhance the degradation efficiency of tetracycline hydrochloride, Bi₂O₃/g-C₃N₄ was used to activate peroxymonosulfate under visible-light irradiation. The influences of peroxymonosulfate dosage, pH value and tetracycline hydrochloride concentration on activating peroxymonosulfate to degrade tetracycline hydrochloride were investigated in detail. The mechanism of Bi₂O₃/g-C₃N₄ activating peroxymonosulfate was proved by radical quenching experiments and electron paramagnetic resonance analysis, which proved that the sulfate radical and hole dominated the degradation of tetracycline hydrochloride. The possible vulnerable sites and pathways of tetracycline hydrochloride were predicted via DFT calculations based on Fukui function and UPLC-MS. Toxicity Estimation Software predicts that the degradation processes of tetracycline hydrochloride could gradually reduce toxicity. This study could provide an efficient and green method for the subsequent treatment of antibiotic wastewater.