Sunlight degradation of tetracycline by Z-type BiOI/g-C3N4 photocatalyst synthesized via a simple two-step process: Response surface methods, degradation pathways, toxicity evaluation

Abstract

A method combining grinding and hydrothermal treatments was utilized to densely load three-dimensional BiOI onto two-dimensional g-C3N4, thereby preparing a BiOI/g-C3N4 photocatalyst with a Z-type heterojunction. Under varying climatic conditions throughout the year, 10%BiOI/g-C3N4 photocatalyst degraded 92.26 % of tetracycline (TC) under sunlight exposure in summer (sunny days) in 150 min, whereas it only degraded 47.33 % of TC under sunlight exposure in winter (cloudy days). The degradation parameters for TC by 10%BiOI/g-C3N4 were optimized using Response surface methods, establishing the optimal conditions for TC degradation (pollutant concentration of 10.94 mg/L, catalyst dosage of 31.34 mg, pH of 4.02), resulting in a degradation efficiency of 95.63 % for TC under the specified conditions. Employing HPLC-MS/MS and 3D EEM techniques, the degradation of TC primarily occurs due to the cleavage of its CC double bonds and CN bonds triggered by free radical attacks, and small molecular acids are produced during the degradation process. The impacts of TC solution treatment on plants were investigated, and the oxidative stress indicators MDA, SOD, POD, and CAT were assessed. The results demonstrated a decrease in all four indicators in plants cultured in TC degradation product solution, further affirming the applicability of 10%BiOI/g-C3N4 in practical scenarios.