PANI-Ti3C2TX-doped QPPO membranes for enhanced separation of H+/metal cations and Li+/Mg2+

Conventional polymer anion exchange membranes (AEMs) suffer from the permeability-selectivity trade-off in diffusion dialysis (DD), limiting their efficiency in critical resource recovery scenarios (e.g., acid recycling and Li + extraction). To overcome this, this study incorporated polyaniline-modified MXene (PANI-Ti 3 C 2 T X ) nanosheets as transformative fillers into quaternized polyphenylene oxide (QPPO). The resulting PANI-Ti 3 C 2 T X -QPPO membranes enable dual-function DD for H + /metal cations and Li + /Mg 2+ separation. First, the as-prepared membranes exhibited enhanced microphase separation, yielding expanded hydrophilic domains (13.95–14.8 nm vs. 12.5 nm in pristine QPPO). Moreover, the 1.0 %-PANI-Ti 3 C 2 T X -QPPO membrane (with 1.0 wt% filler loading) achieved a peak ion exchange capacity of 1.75 mmol g −1 . For H + /metal cations separation: in HCl/FeCl 2 mixture, the H + dialysis coefficient ( U H ) reached 1.39–1.50 × 10 −2  m h −1 (2.7–2.9 times higher than the commercial TWDDA3S, 0.52 × 10 −2  m h −1 ); in HCl/AlCl 3 mixture, U H reached 1.50–1.53 × 10 −2  m h −1 , combined with exceptional selectivity ( S H/Al  = 1568.4–1805.8), outperforming both TWDDA3S ( U H  = 0.94 × 10 −2  m h −1 , S H/Al  = 1423.8) and pristine QPPO ( U H  = 1.27 × 10 −2  m h −1 , S H/Al  = 1117). Finally, for Li + /Mg 2+ separation, the membranes delivered enhanced Li  +  flux with competitive S Li/Mg (11.4–12.4) against TWDDA3S (11.4) and QPPO (11.8). This study demonstrates that PANI-Ti 3 C 2 T X and QPPO synergistically overcome the permeability-selectivity trade-off in polymer membranes.