Enhanced simulated sunlight photolysis of antibiotics on soil surfaces by biochar: Effects and mechanisms

The photocatalysis performance of biochar (BC) was often underestimate when it was employed to remediate antibiotic-contaminated soil. In our study, we adopted sawdust, rice husk, and tobacco straw to prepare biochar at three carbonization temperature (300 °C, 500 °C, and 700 °C) and explored the effect of biochar amendment on the sunlight photolysis of typical antibiotics tetracycline (TC), sulfamerazine (SM1), and enrofloxacin (ENR) on soil surfaces. The photolysis of three examined antibiotics in the surface layer of soil-biochar followed a quasi-first-order reaction kinetics model (R² > 0.9), and the photocatalytic activity of R500 (rice husk carbonized at 500 °C) was the most prominent, which reduces the half-life t_1/2 of TC, SM1 and ENR in red soil by 47.0%, 8.83% and 17.1%, respectively. The results of quenching experiments demonstrated that reactive oxygen species (ROS) ¹O₂ played a crucial role in promoting the degradation of TC and ENR while the ³DOM∗ greatly contributed to the photodegradation of SM1. A maximal degradation rates of TC and ENR could be observed at a neutral pH but the photolysis rate of SM1 peaked at a pH of 9. Both photolysis and indirect photolysis with the participation of ROS led to the degradation of three antibiotics in soil as suggested by analyzing of degradation pathways. The results of this study highlight the performance of biochar in photocatalysis by generating ROS, contributing to further research on biochar that could achieve in-situ remediation of antibiotic-contaminated soils.