Rational design of a self-cleaning PES/UiO-66-NH2@g-C3N4 mixed-matrix membrane for high-efficiency oil–water separation

The continuous discharge of oil-laden wastewater poses a critical environmental and industrial challenge, necessitating the development of advanced membrane systems that simultaneously deliver high separation efficiency, strong fouling resistance, effective self-cleaning capability, and low energy consumption. In this study, a multifunctional mixed-matrix membrane based on polyethersulfone (PES), amino-functionalized UiO-66 metal–organic framework (UiO-66-NH 2 ), and graphitic carbon nitride (g-C 3 N 4 ) was rationally designed and fabricated via a controlled phase-inversion process, enabling a synergistic integration of adsorption and visible-light-driven photocatalytic functionalities. Comprehensive characterisation using FTIR, XRD, and SEM verified the effective incorporation and uniform dispersion of UiO-66-NH 2 and g-C 3 N 4 throughout the PES matrix. The resulting composite membrane exhibited markedly improved surface wettability, with a water contact angle of 58 ± 1.2° and an oil contact angle of 94 ± 1.5°, reflecting enhanced hydrophilicity and oleophobicity. Under optimized filtration conditions (0.5 MPa, 25 ± 1°C), the membrane achieved an oil rejection of 99.5 ± 0.3% and a permeate flux of 345.2 ± 10.8 L m⁻ 2 h⁻ 1 after 120 min, significantly surpassing pristine PES. Time-, dosage-, concentration-, and pressure-dependent studies revealed stable separation performance and suppressed fouling kinetics. Reusability assessments over ten cycles maintained a flux recovery ratio of 91.1 ± 1.3%, while oil rejection decreased moderately from 99.1 ± 0.4% to 92.8 ± 0.6%. Furthermore, long-term continuous filtration over 12 h exhibited stable operation, with flux retention of approximately 90%, oil rejection above 93.2 ± 0.7%, and a reduced specific energy demand of 0.82–0.91 kWh m⁻ 3 , highlighting the membrane’s promise for sustainable oily wastewater remediation.