Dual Integration of Amine-Functionalized Carbon Dots Endowed Nanofiltration Membranes with Highly Efficient Biofouling/ Acid/chlorine Resistance for Effective Mg2+/Li+ Separation

Reports on nanofiltration (NF) membranes with acid/chlorine/biofouling resistance remain limited, resulting in a significant challenge. In this work, amine-functionalized carbon dots (Am-CDs) and nanocomposites (Am-CDs/ PL) were fabricated using citric acid and polyethyleneimine as precursors and coupling with Am-CDs on polylysine (PL) via catalysis. The Am-CDs were first integrated into the polyamide (PA) layer of a polyethersulfone substrate through interfacial polymerization (IP) (denoted as I-Am-CDs-M), and then the Am-CDs/PL was continuously grafted on the PA layer through secondary IP (denoted as II-Am-CDs-M). The pristine membrane was synchronously prepared by IP between trimesoyl chloride (TMC) and piperazine (PIP) for contrast (denoted as Contrast-M). The Am-CDs exhibited outstanding oxidase activity and acid/ClO- response performance. The dual integration of Am-CDs significantly improved the wettability and positive charge of the modified NF membranes, endowing them with excellent separation performance. Notably, I-Am-CDs-M and II-Am-CDs-M naturally inherited the oxidase activity of the Am-CDs, contributing to eminent anti-bacterial functionality. Furthermore, Am-CDs vested these membranes with good anti-acid and anti-chlorine performance through the generation of reversible C-NH3+ forms and the oxidization of some amines as nitryl groups and chlorination, respectively, which helped decrease the maintenance costs and prolonged the operational lifespan. II-Am-CDs-M was successfully applied for Mg2+/Li+ separation. This strategy provided a novel protocol for designing and fabricating NF membranes with highly efficient separation performance.