Harnessing phase engineered porous MXene-TiO2 in polyamide reverse osmosis membranes for enhanced short- and long chain PFAS removal from water

MXenes (2D transition metal nitrides, oxycarbides, carbonitrides, and carbides) hold promise in water treatment due to tunable surface chemistry and hydrophilic nature but restacking in aqueous environments and susceptibility to oxidation remain challenging. Here, we deliberately exploit partial oxidation of Ti 3 C 2 T x MXene to in situ grow TiO 2 nanoparticles on its surface, creating a porous, phase-engineered MXene-TiO 2 composite. The anatase:rutile ratio was adjusted through different hydrothermal process time (12, 18, and 24 h), after 18 h composition yielding the best balance of surface charge and structural stability. This composite was incorporated into the polyamide (PA) layer of a thin-film composite reverse osmosis (TFC RO) membrane at optimized loadings. Compared to the pristine membrane, the optimized membrane showed a 5.3-fold increase in permeance (reaching 21.8 ± 0.3 L m −2 h −1 bar −1 ). At environmentally relevant PFAS concentration, rejection of short-chain PFBA reached 96.9 ± 1.8% and of long-chain PFOA 98.8 ± 0.3%. Performance of fabricated membranes was tested in the presence of Ca 2+ , humic acid, their mixture, and cetyltrimethylammonium bromide (CTAB) in the background (maintaining >95% removal). ICP analysis after continuous filtration (10 days) detected no Ti in permeate, indicating strong integration or embedding and chemical bondings to membrane. Extended fouling tests demonstrated sustained permeance and rejection under realistic conditions. This work presents a practical route to overcome MXene restacking and oxidation, delivering a high-performance RO membrane for efficient PFAS removal under practical operating scenarios. • Phase-engineered MXene-TiO 2 composites synthesized via controlled partial oxidation • Optimized membrane reached 21.8 LMH/bar permeance and 98.8% PFOA rejection rate • PFBA rejection rate increased in the presence of Ca 2+ ions and CTAB • Co-presence of humic acid-Ca 2+ ions lead to severe fouling of unmodified membrane • Optimized membrane retained 94% of its initial permeance and rejection over 10 days