Vinyl Functionalization of Ti3C2T x MXene Enables Grafting of Sulfonated Polyelectrolytes for High Salt Rejection in Forward Osmosis Desalination

Abstract

MXene membranes are promising for aqueous separations but are fundamentally limited by swelling-induced loss of selectivity and structural instability. Here, we report, for the first time, vinyl functionalization of Ti3C2Tx MXene nanosheets, which enables subsequent grafting of anionic polyelectrolyte networks within the lamellar nanochannels. Vinyltriethoxysilane is covalently anchored onto Ti3C2Tx to introduce polymerizable vinyl groups, transforming the MXene into a reactive platform for interfacial polymer integration. Each of the four sulfonated monomers (sodium p-styrene sulfonate, ammonium p-styrene sulfonate, 2-acrylamido-2-methylpropanesulfonic acid (AmPS), and 3-sulfopropyl methacrylate potassium salt) is subsequently grafted and crosslinked separately within the nanochannels to form hydrated, ion-exchange polymer networks. This approach converts swelling-prone Ti3C2Tx galleries into anti-swelling, polymer-reinforced nanochannels with enhanced hydration and strong electrostatic exclusion. The optimized vinyl-functionalized MXene–AmPS membrane achieves near-complete salt rejection (99.20–99.86%) with a water permeance of 0.1142 L m–2 h–1 bar–1 under single-salt conditions and 99.92–99.99% rejection with 0.1134 L m–2 h–1 bar–1 under mixed-salt feeds simulating seawater. The membrane maintains ≈99.45% rejection over 13 regeneration cycles with >90% flux recovery. These findings establish vinyl functionalization-enabled polymer grafting as an effective strategy for engineering stable, ion-selective MXene nanochannels, delivering unprecedented desalination performance.