Highly efficient UV/H2O2 technology for the removal of nifedipine antibiotics: Kinetics, co-existing anions and degradation pathways

This study investigates the degradation of nifedipine (NIF) by using a novel and highly efficient ultraviolet light combined with hydrogen peroxide (UV/H 2 O 2 ). The degradation rate and degradation kinetics of NIF first increased and then remained constant as the H 2 O 2 dose increased, and the quasi-percolation threshold was an H 2 O 2 dose of 0.378 mmol/L. An increase in the initial pH and divalent anions (SO 4 2- and CO 3 2- ) resulted in a linear decrease of NIF (the R 2 of the initial pH, SO 4 2- and CO 3 2- was 0.6884, 0.9939 and 0.8589, respectively). The effect of monovalent anions was complex; Cl - and NO 3 - had opposite effects: low Cl - or high NO 3 - promoted degradation, and high Cl - or low NO 3 - inhibited the degradation of NIF. The degradation rate and kinetics constant of NIF via UV/H 2 O 2 were 99.94% and 1.45569 min -1 , respectively, and the NIF concentration = 5 mg/L, pH = 7, the H 2 O 2 dose = 0.52 mmol/L, T = 20 ℃ and the reaction time = 5 min. The ·OH was the primary key reactive oxygen species (ROS) and ·O 2 - was the secondary key ROS. There were 11 intermediate products (P345, P329, P329-2, P315, P301, P274, P271, P241, P200, P181 and P158) and 2 degradation pathways (dehydrogenation of NIF → P345 → P274 and dehydration of NIF → P329 → P315).