Removal of norfloxacin using coupled synthesized nanoscale zero-valent iron (nZVI) with H2O2 system: Optimization of operating conditions and degradation pathway

Abstract

Abstract In this study, nanoscale zero-valent iron (nZVI) was synthesized in the laboratory by the borohydride reduction method. nZVI was characterized by transmission electron microscopy (TEM), scan electronic microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). In addition, the degradation performance of norfloxacin (NOR) in nZVI/H 2 O 2 Fenton-like system was investigated in detail under various experimental conditions. It was found that the removal of NOR depended on its initial concentration, initial pH, temperature, H 2 O 2 concentration and nZVI dose. At the ambient temperature, the degradation rate of NOR by nZVI/H 2 O 2 Fenton-like reaction under the acidic medium (pH = 3–4) was more than 95% within 40 min of the reaction time, and the mineralization degree was around 50% in terms of total organic carbon (TOC) measurement. Optimal temperature for NOR removal was 308 K, and higher temperature would cause useless decomposition of H 2 O 2 and consequently reduction of NOR degradation. The degradation rate and total removal efficiency of NOR were favored by increasing the nZVI and H 2 O 2 dosages. The optimal conditions for NOR degradation were: initial pH = 4.0, H 2 O 2 concentration = 20 mmol/L, nZVI dose = 100 mg/L, temperature = 308 K. The rate constants ( K ob s ) of NOR degradation could be fitted well with a pseudo-second-order kinetic equation. Several degradation intermediates of NOR were detected and confirmed, including C 15 H 20 FN 3 O ( m / z 278), C 9 H 11 FN 2 ( m / z 167), C 7 H 7 FN 2 ( m / z 139), and C 7 H 8 FN ( m / z 126), respectively. Based on the identified intermediates and the Gaussian quantum statistics molecular bonding energy calculation, the possible pathway for NOR degradation under nZVI/H 2 O 2 Fenton-like reaction was discussed.