Polyaniline-Encapsulated MIL-100 (Fe) MOF Composite as a Robust Modifier to Enhance the Performance of Nanofiltration Membranes for Desalination and Wastewater Treatment

Mixed matrix membranes (MMMs) are widely explored to overcome the permeability-selectivity trade-off that limits conventional nanofiltration membranes. In this work, poly(ether sulfone) (PES)-based nanofiltration MMMs were fabricated by incorporating a polyaniline (PANI)-encapsulated MIL-100(Fe) composite as a functional modifier. The synergistic integration of hydrophilic PANI and porous MIL-100 improved interfacial compatibility with the PES matrix, regulated pore structure, enhanced asymmetric morphology, and modified membrane surface charge. As a result, the water contact angle decreased from 81.11° (pristine PES) to 54.86°, indicating significantly improved hydrophilicity. The optimized membrane (M-3) exhibited a > 3-fold increase in pure water flux (13.36 to 48 L m^-2 h^-1) while maintaining high rejection of dyes (99% rose bengal and congo red; 90% methylene blue) and salts (63% NaCl; 75% MgSO₄), demonstrating balanced permeability and selectivity. The membrane also showed a strong antifouling performance with a flux recovery ratio of 84.93% and low irreversible fouling (15.06%) after simple hydraulic cleaning. Stable separation performance was maintained under elevated temperature (up to 65 °C), acidic pH, and varying salt concentrations (1000-2500 mg L^-1 NaCl), and over a continuous one-week operation. Compared with recently reported MMM nanofiltration membranes, the developed membrane demonstrates a favorable combination of high flux, effective dye-salt rejection, and antifouling stability. These results highlight the effectiveness of the PANI@MIL-100 composite in tuning the membrane structure and surface properties, offering a practical strategy for advanced wastewater treatment and low-pressure desalination applications.