Preparation of polyacrylonitrile mixed matrix ultrafiltration membranes doped with aminated MIL-125(Ti) and evaluation of their anti-fouling performance in oil-water separation

Mixed matrix ultrafiltration membranes based on polyacrylonitrile (PAN) and aminated MIL-125(Ti) (NH₂-MIL-125(Ti)) were fabricated by non-solvent induced phase separation for the treatment of oil-in-water emulsions. NH₂-MIL-125(Ti) nanoparticles with disc-like morphology and high crystallinity were successfully synthesized and incorporated into PAN at loadings of 0.5–5.0 wt%. Structural, chemical, wetting, mechanical, and thermal analyses confirmed successful MOF incorporation and showed that membrane hydrophilicity, porosity, surface area, and tensile strength improved up to an optimal filler loading of 2.0 wt%, whereas excessive loading caused partial aggregation and pore blockage. The optimized M3 membrane exhibited a water contact angle of 45.1°, BET surface area of 43.7 m²/g, tensile strength of 5.2 MPa, and pressure-normalized pure water flux of 552.1 ± 18.4 L·m⁻²·h⁻¹·bar⁻¹. During filtration of a 1000 mg/L soybean-oil-in-water emulsion, M3 maintained 99.7 ± 0.2% oil rejection, retained approximately 68% of its normalized flux after 60 min, achieved a first-cycle flux recovery ratio of 96.2%, and showed an irreversible fouling ratio of only 3.8%. The improved performance is attributed to the combined effects of enhanced surface hydration, additional water-transport pathways, and weaker oil adhesion at the hydrated MOF-containing interface. These results indicate that NH₂-MIL-125(Ti) is an effective functional filler for constructing high-flux and fouling-resistant PAN membranes for oily wastewater treatment.