Heterogeneous electro-Fenton catalytic FeOCl@NCNT/ceramic membrane filtration for in-situ membrane fouling control: Performance and mechanism

Abstract

Homogeneous electro-Fenton (EF) technique is effective to mitigate membrane fouling through oxidizing organic foulants by hydroxyl radicals (HO·), but suffers from acid pH working environment (2.5 ∼ 3.5), low iron recyclability, and iron sludge accumulation. Herein, we developed a heterogeneous EF catalytic membrane to overcome these problems. A FeOCl@NCNT-functionalized ceramic membrane (FeOCl@NCNT/CM) was prepared to control the membrane fouling caused by humic acid (HA). At near neutral pH (∼ 6.0), the membrane enabled the in-situ generation of HO·. It also imparted an effective regeneration of Fe(II) through cathodic reduction and the electron transfer to Fe(III) from pyrrolic-N. The continuously generated HO· could oxidize the HA on/in the membrane, thus effectively mitigating membrane fouling. Electrostatic repulsion also contributed to fouling control by reducing the adhesion of negatively charged HA on the membrane. In continuous electrification mode, the FeOCl@NCNT/CM showed a superior antifouling ability. The water flux of the membrane at an applied voltage of −2.2 V was 1.79 times as high as that without voltage. Both reversible and irreversible membrane fouling were greatly reduced, and the transition of membrane fouling mechanism from pore blockage to cake filtration was significantly delayed. In intermittent electrification mode, the membrane exhibited an excellent self-cleaning performance. The fouled membrane showed considerable water flux recovery ratios (> 95%) after the EF cleaning at −2.2 V. The excellent antifouling and self-cleaning properties, low energy consumption, good stability and reusability of the FeOCl@NCNT/CM make it promising for the in-situ control of membrane fouling in water treatment.