Heterogeneous advanced oxidation processes (AOPs) activated by magnetic MFe2O4 (m = Fe, Zn, Mn, Mg or Cu) catalysts in water treatment

Abstract

Oxidative removal of sulfacetamide (SAM) was explored using (MFe2O4/PMS) AOP system. Parameters affecting degradation efficiency such as catalyst type, catalyst loading, oxidant dosage and initial pH were investigated. Fine nanosized MFe2O4 (M= Zn, Cu, Mn, Mg) synthesized with sol-gel method and a commercially purchased Fe3O4 were used as peroxymonosulfate (PMS) activator to induce radicals for SAM treatment. Both XRD and FTIR results indicated spinel ferrite structure in all five ferrite nanoparticles (FNPs). The use of Scherrer’s formula also confirmed that all the metal ferrites are nanosized. The presence of the respective metal ions required for catalytic PMS induction were confirmed with XPS characterisation. UV-vis spectra also indicated the absorbance of both ultraviolet (UV) and visible light in all five FNPs. Experiments conducted in the dark showed CuFe2O4 yielding the most promising result of 91% degradation efficiency with 0.4g/L and 0.3g/L of catalyst loading and PMS loading respectively. This is due to CuFe2O4 catalysis yielding a higher amount of sulfate radicals from the extra redox reaction seen in Equations 14 and 15. Elevated catalyst loading and PMS dosage are not desirable due to scavenging effects by metal ions and HSO5- respectively. Both catalyst loading and PMS dosage have to increase in tandem as they are limiting to each other. Optimum pH range is found to be from 7 to 9. The formation of hydrogen bond and metal precipitation could occur at conditions which are too acidic or alkaline respectively, resulting in lower degradation efficiency. The occurrence of metal leaching in the supernatant should be explored in future experiments to ensure the feasibility of using these metal catalyst for PMS activation for the treatment of SAM or other pharmaceuticals and personal care products (PPCPs).