Investigation of kinetics and mechanism for the degradation of antibiotic norfloxacin in wastewater by UV/H2O2

Abstract

• Inhibition effect order of cations: Cu 2+ > Ca 2+ > Mg 2+ • Inhibition effect order of anions: CO 3 2− > NO 3 − > SO 4 2− • ROS contribution rate order: •OH (72.56%) > 1 O 2 (24.24%) > other ROS (3.20%) • The active sites of norfloxacin in UV/H 2 O 2 degradation were the piperazine ring and F atom • Binding free energy of DNA gyrase A: norfloxacin (-11.8 kJ/mol) > P1 (-12.8 kJ/mol) This study investigates the degradation of norfloxacin by using UV combined with hydrogen peroxide (UV/H 2 O 2 ) with different cations and anions. The inhibition effect order of cations for degradation of norfloxacin was Cu 2+ > Ca 2+ > Mg 2+ , attributed to the forms of the coordination compounds between norfloxacin and the cations. The inhibition effect order of anions for degradation of norfloxacin was CO 3 2− > NO 3 − > SO 4 2− , attributed to the ability and efficiency of the anions to quench ·OH or H 2 O 2 . The order of the reactive oxygen species (ROS) contribution rate to the degradation of norfloxacin under UV/H 2 O 2 was ·OH (72.56%) > 1 O 2 (24.24%) > other ROS (3.20%) based on the trapping experiments and electron spin resonance (ESR) measurements. There were at least 8 kinds of intermediate products, with charge-to-mass ratio ( m/z ) of 294, 267, 333a, 333b, 347, 335, 351 and 317, which were formed by attacks at the piperazine ring and F atom active sites. The F atom was replaced with -OH via a substitution reaction, resulting in P1 ( m/z = 317) formation. The inhibition effect of P1 on DNA gyrase A was stronger than that of norfloxacin due to the binding free energy (the binding free energy of P1-DNA gyrase A was -12.8457 kJ/mol, and the binding free energy of norfloxacin-DNA gyrase A was -11.8488 kJ/mol).