Laser-Induced Graphene-Based Thin Film Composite Nanofiltration Membrane with Electrochemical Fouling Cleaning

Abstract

Organic fouling remains a significant challenge for conventional nanofiltration (NF) membranes, which often require chemical cleaning, thereby increasing operational costs. Electroconductive membranes (ECMs) are a new generation of membranes that offer both electroconductive properties and filtration performance. However, NF-ECMs are the least explored to date. This study focuses on the fabrication of a laser-induced graphene (LIG)-based nanofiltration (LIG-NF) membrane to evaluate its performance in removing foulants, followed by an electrocleaning investigation. First, the LIG was fabricated on a carbon-rich substrate with a CO₂ laser, and then polysulfone (PSf) was coated on it. A top polyamide (PA) layer was incorporated and optimized for superior permselectivity; the resulting membrane was subsequently physicochemically and electrochemically characterized. The LIG-NF membrane exhibited salt rejections of ∼82% and ∼40% for bi- and monovalent salts, respectively, with a pure water permeability of 6 LMH bar^–1. This hydrophilic membrane demonstrated stable cyclic voltammetry over 25 scans. Furthermore, the fouling study showed an improvement in flux recovery from 85% to 100% when an external 5 V potential was applied for 5 min during electrocleaning, compared to the control. The cleaning was verified by impedance spectroscopy with charge transfer resistance measurements. A flux recovery of ∼99% was achieved in crossflow after multiple-cycle runs, demonstrating the process’s stability, scalability, and feasibility. The possible cleaning mechanism included a dominant role of electrostatic repulsion and radical-species-based degradation. This study demonstrates a novel class of fouling-resistant, electroconductive NF membranes that require no chemical cleaning, illustrating their potential as next-generation membranes for sustainable water treatment systems.