Suppressing polymerization-induced membrane fouling via current-modulated sequential pathway switching in PMS activation for complete dechlorination and mineralization of 4-chlorophenol

Current density modulates PMS activation pathways in the electrocatalytic membrane. • Sequential 1 O 2 , ETP, and radical oxidation achieves stepwise 4-CP degradation. • Polymerization-induced membrane fouling is suppressed during degradation. • Complete dechlorination and mineralization of 4-CP are simultaneously achieved. During peroxymonosulfate (PMS)-based advanced oxidation processes, uncontrolled generation of reactive oxygen species (ROS) causes phenolic substances to undergo polymerization reactions, which irreversibly block active sites and foul membrane catalytic systems. To address this, we develop a current-modulated pathway-switching strategy using a nitrogen-doped carbon quantum dots/g-C 3 N 4 nanosheet (NCQDs@CNNS) electrocatalytic membrane for complete dechlorination and mineralization of 4-chlorophenol (4-CP). By simply varying the applied current density (2, 0, and 8 mA cm −2 ), the peroxymonosulfate (PMS) activation pathway can be switched sequentially among singlet oxygen ( 1 O 2 ), direct electron transfer process (ETP), and free radicals (•OH and •SO 4 − ). Guided by theoretical calculations, the oxidation pathways are precisely tailored to the electronic structure of 4-CP and its intermediates, leading to a three-stage sequential degradation process: i) 1 O 2 first cleaves the aromatic ring without generating polymerizable phenoxy radicals; ii) ETP-triggered nucleophilic substitution then selectively dechlorinates the ring-opened intermediate; and iii) free radicals finally mineralize the residual chlorine-free aliphatic acids. This strategy completely avoids membrane fouling caused by polymerization reactions and can achieve a TOC removal efficiency of 99.3% and a dechlorination efficiency of 98.5% within 30 min, with an electrical energy per order (EEO) of 0.0026 kWh m −3 log −1 . This system maintains stable performance over five consecutive experimental cycles, and adapts well to various pH values, coexisting ions, natural organic substances, and actual water body substrates. This work provides a mechanistic strategy for the selective electrochemical regulation of oxidation pathways, which can simultaneously prevent fouling and thoroughly detoxify chlorophenolic wastewater. Download: Download high-res image (191KB) Download: Download full-size image