Carbon doped Fe3O4 peroxidase-like nanozyme for mitigating the membrane fouling by NOM at neutral pH

Abstract

Oxidation is a widely used method in drinking water treatment to mitigate the membrane fouling caused by the natural organic matters (NOM) from the surface water during ultra-filtration (UF) and nano-filtration (NF) processes, and H2O2 is one of the common oxidants for it. However, the oxidation capability of H2O2 at neutral pH is lower, compared to the acidic and alkaline conditions. In order to improve the efficiency of NOM oxidation at neutral pH, a carbon-doped Fe3O4 peroxidase-like nanozyme (CFPN) was synthesized in this study and used as a high-performance catalyst for H2O2 to generate hydroxyl radical. The oxygen-containing groups on the carbon structure of CFPN can form an acidic microenvironment, allowing H2O2 to produce hydroxyl radical by catalysis in neutral conditions. The results of hydrophilicity analysis, zeta potential, high-performance liquid size exclusion chromatography (HPSEC), Fourier transform infrared spectrum (FTIR) and flux indicated that the hydroxyl radical can oxidize the hydrophobic matters of humic acid (HA) into hydrophilic matters by Fenton reaction or electrophilic addition reaction, which can mitigate the fouling of NF membranes. The results of the same test for the bovine serum albumin (BSA) indicated that the hydroxyl radical can mitigate the fouling of UF membranes by degrading the tertiary and secondary structures of BSA and partly oxidizing the side chain groups. In addition, two types of surface water samples were used to verify the above mechanism, and the results indicated that the hydroxyl radical treatment at neutral pH is a new viable and effective strategy to significantly mitigate the NOM fouling of UF and NF membranes.