Regulating generation of radical and non-radical in plasma systems for selective degradation of persistent organic pollutants in water with high salinity resistance and slight environmental implication: Regulatory method and selective mechanism

The complexity of persistent organic pollutants (POPs) and high concentration of inorganic ion in practical wastewater pose great challenges to non-thermal plasma (NTP). How to treat POPs with high selectivity and high salt resistance is an important problem in the field of water treatment. This paper proposes for the first time to solve the above problems by regulating radicals and non-radicals. The regulated valence band level (2.38 V vs. NHE) of C₃N₄ by doping of B can effectively activate the generation of radicals. Cu doping of C₃N₄ can also provide more H₂O₂ catalytic sites for generation of non-radicals. The C₃N₄ allows NTP to activate persulfate efficiently and increase the radicals and non-radicals jointly. Sulfamethoxazole (SMX), bisphenol A (BPA) and methyl orange (MO) along with 13 other contaminants were selected as typical POPs. Based on experiments and theoretical calculations, the degradation effects, catalysis mechanism, water matrix, intermediate product toxicity and influencing factors were investigated. Research shows that the radical system has higher selectivity for hydroxyl and amine groups, while the non-radical system has higher selectivity for benzene ring. For the same pollutant, the radical system (99.3 %) often exhibits a better degradation effect versus non-radical system (78.2 %). However, non-radical systems show phenomenal adaptability to complex water matrix environments and lower intermediate toxicity in degradation process. This paper provides an important reference for regulating radicals and non-radicals to improve pollutant selectivity and salinity adaptability.