CuNiN@C coupled with peroxymonosulfate as efficient catalytic system for the removal of norfloxacin by adsorption and catalysis

Abstract

In this study, calcined Cu-based metal-organic frameworks impregnated with nickel nitrate and pyrrole (CuNiN@C) with better stability and degradation performance was synthesized by doping of both Ni and N. Coupling with peroxymonosulfate (PMS), CuNiN@C worked as adsorptive bifunctional catalyst in effectively degradation of norfloxacin (NFX). Scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), transmission electron microscope (TEM), Selected area electron diffraction (SAED), High resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD) were applied for the preliminary characterization of the synthesized material to reveal the complete retention of the octahedral particle shape and successful doping of nitrogen. The results showed that over 80% NFX (5 mg/L) was degraded in 30 min with CuNiN@C (0.2 g/L) and PMS (2 mmol/L), and the reusability of CuNiN@C in four cycles did not significantly deteriorated, which was attributed to Ni doping. The mechanism of NFX degradation was separated into two parts: adsorption of CuNiN@C and activation of PMS. CuNiN@C adsorption followed a pseudo-second order rate model (R2 = 0.99), and nitrogen doping caused multiple electron-withdrawing functional groups in order to achieve chemisorption. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and N2 adsorption of both the pre-test and post-test CuNiN@C were adopted in the adsorption mechanism investigation. Meanwhile, as the activate sites of CuNiN@C, Cu and Ni responded to the PMS activation, and three radicals may be generated during the activation. Radical quenching experiments and Electron Paramagnetic Resonance (EPR) illustrated that the hydroxyl radical (OH) plays a major role in NFX oxidation, which was confirmed by the effect of pH value experiment. According to results of the liquid chromatograph linked to a mass spectrometer (LC-MS), possible degradation pathways are proposed: the substitution reactions and elimination reactions on both quinolone and benzene rings, the destruction of the piperazinyl group and the opening of the quinolone ring. This study provides new insight into the fabrication and application of the CuNiN@C/PMS system as antibiotic pollution remedy in aquatic environment.