Detailed mechanisms of amoxicillin decomposition in supercritical water by ReaxFF reactive molecular dynamics simulation

[Display omitted] •The ReaxFF MD simulation and experiments of amoxicillin SCWG were conducted.•The decomposition of amoxicillin in supercritical water includes three stages.•The detailed process of amoxicillin decomposition in SCW was revealed.•The dual effect of OH radicals on the amoxicillin decomposition in SCW was found.•Reaction networks for nitrogen and sulfur conversion in SCW were obtained. The abuse of antibiotics in China has aroused widespread concern, and the resistance genes of antibiotics in the natural environment seriously threaten human health. The supercritical water gasification (SCWG) technology is a clean and efficient technology for the treatment of antibiotic wastewater. In this paper, amoxicillin is selected as the representative antibiotic in wastewater, and the detailed mechanisms of amoxicillin decomposition in supercritical water (SCW) are studied by ReaxFF reactive molecular dynamics (MD) simulation. The results show that the decomposition process of amoxicillin in SCW includes carbon ring opening, carbon chain breaking and small molecular compounds conversion. The molecular vibration leads to the breaking of CN and CS bonds. The OH radical is vital to the ring opening of benzene ring and the breaking of carbon chain. However, the yield of NO increases with increasing OH radical concentrations. The ReacNetGenerator tool is used for the first time to analyze the migration path of nitrogen and sulfur in the SCWG system. It shows that H2 has a great effect on the transformation of sulfur, and OH radicals dominate the transformation of nitrogen. Decreasing the reaction time and the concentration of OH radicals result in inhibiting the NO production. This study will provide a theoretical guidance for understanding SCWG process of antibiotic-containing wastewater.