Highly efficient UV/H(2)O(2) 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).