Highlight the plasma-generated reactive oxygen species（ROSs）dominant to degradation of emerging contaminants based on experiment and density functional theory

Abstract

This paper aims to deeply analyze the degradation mechanism of emerging contaminants by dielectric barrier discharge (DBD) plasma through experiments and simulations. It was confirmed that DBD plasma exhibits a high degradation effect on three emerging contaminants by the generated reactive oxygen species (ROSs). Increasing the output power leads to higher ROSs production and higher degradation rates of emerging contaminants. At an input power of 94.6 W, the degradation rates of sulfamethoxazole (SMX), bisphenol A (BPA) and ciprofloxacin (CIP) reach 94.5 %, 92.9 %, and 98.6 %, respectively. Trapping agent experiments were conducted to investigate the role of ROSs (·OH, ·O2–, and 1O2) in emerging contaminants degradation. Notably, capturing of 1O2 led to a decrease of up to 31 % in the degradation rate of BPA. Electron spin resonance (ESR) tests confirmed the involvement of various ROSs, especially 1O2, in the degradation process. Density functional theory (DFT) was employed to further explore the action mechanism of ROSs in the DBD plasma system. For SMX and BPA, the degradation is initiated by the dissociation of annular structures, while for CIP, annular structures are directly opened by ROSs. These findings highlight the importance of 1O2 and ·OH in the degradation process. Finally, the toxicity of intermediates produced by ROSs-dominate to degradation was declined. This work can provide new insights and unique guidance on the plasma degradation mechanism of emerging contaminants.