Photocatalytic difference of amoxicillin and cefotaxime under visible light by mesoporous g-C3N4: Mechanism, degradation pathway and DFT calculation

beta-Lactam antibiotics are generally used for disease prevention in humans and animals. The antibiotics, which have been excreted into the surrounding environment, have caused serious concerns. In this study, mesoporous carbon nitride (MCN) was synthesized using a template-free method. The photocatalytic degradation of the two typical beta-lactam antibiotics, amoxicillin (AMX) and cefotaxime (CFX), was performed using MCN. Considering the complexity of the actual environment, four factors that may influence the photocatalytic degradation of AMX and CFX were studied, containing the initial antibiotics concentration, catalyst dosage, pH and humic acid (HA). The possible mechanism of photocatalysis was presented using ESR spectroscopy and free radical trapping experiments. Furthermore, rational photocatalytic degradation pathways were proposed through the combination of LC-Q-TOF-MS/MS and density functional theory (DFT). Toxicity Estimation Software Tool (TEST) was used to predicate the toxicity of the byproducts. This study identified the catalytic activity difference between AMX and CFX firstly and elucidated their degradation mechanisms. The new findings are very meaningful for optimizing the conditions of photocatalytic degradation of beta-lactam antibiotics. In addition, the results of wastewater test and stability experiments indicated that MCN has excellent performance. Therefore, MCN is a promising treatment material for the elimination of the antibiotic activity and mineralization of antibiotics under visible light.