Polysulfone mixed matrix membranes embedded with sub-25 nm NH2-MIL-101(Cr) for enhanced divalent salt separation and permeability.

Abstract

High-performance nanofiltration (NF) membranes are essential for sustainable water treatment but are often limited by the permeability-fouling trade-off. In this study, highly crystalline sub-25 nm NH₂-MIL-101(Cr) nanoparticles (19-21 nm), possessing a high BET surface area (1700.18 m² g^-1) and permanent pores (2.04 nm), were hydrothermally synthesized and incorporated into polysulfone (PSF) mixed matrix membranes via phase inversion. The uniform distribution of hydrophilic NH₂ groups enhanced membrane hydrophilicity, reducing the water contact angle from 76.2 ± 2° to 56.1 ± 2° at the optimum loading of 0.75 wt%. At 5 bar using a 2000 ppm feed solution, the optimized membrane achieved a water flux of 15.3 kg m^-2 h^-1, representing a 2.3-fold increase over pristine PSF, while maintaining high rejection of MgSO₄ (86.5%) and CaSO₄ (96.2%) through combined steric hindrance and Donnan exclusion mechanisms. Flux increased linearly with pressure up to 17.8 kg m^-2 h^-1 at 7.0 bar. Organic fouling tests with 10 ppm humic acid demonstrated excellent antifouling performance, with flux recovery ratios of 83.2% and 68.5% after the first and second alkaline cleaning cycles, respectively. These findings demonstrate that the PSF/NH₂-MIL-101(Cr) mixed matrix membrane effectively overcomes the permeability-fouling trade-off, offering a promising platform for high-performance and long-term desalination applications.