Constructing polyoxometalates-based electrocatalytic nanofiltration membranes for nitrite removal

Abstract

Nitrite-containing wastewater poses an imminent threat to both human health and ecosystems. Conventional methods like nitrification and denitrification rely heavily on chemical reagents, while emerging membrane separation has limitations in permselectivity. Here, a conductive membrane with both electroresponsive and electrocatalytic capabilities was developed by integrating Keggin-type polyoxometalates (POMs) through combining layer-by-layer self-assembly and interfacial polymerization. The pore size of the membranes remained largely unaffected by an electric field, but its Donnan effect was significantly enhanced, leading to a substantial increase in nitrite removal from 23.1% to an impressive 81%. Nitrite underwent a reductive degradation at the cathode, producing nitrogen-containing gases (8.3%), while oxidation at the anode yielded hypotoxic NO3− (11.3%), respectively exhibiting 79.9% rejection of NO2− and 83.1% rejection of NO3− under the electric field-enhanced Donnan effect. Therefore, the high-level total nitrogen removal was composed of three key components: 64.2% from direct NO2− rejection, 9.4% from oxidation-generated NO3− rejection, and 7.4% attributed to gas generation. Significantly, our work underscored the consistently robust structural stability of the POMs-based membrane under an electric field, maintaining an outstanding total nitrogen removal exceeding 75%. Consequently, this research introduced a promising electrochemical-membrane fusion approach for efficiently removing high-activity nitrite-containing wastewater, emphasizing the potential for environmental applications.