Modulating Poly(ether Sulfone) Ultrafiltration Membrane Microstructure via Coagulation Bath Engineering for Enhanced Antifouling Performance

The coagulation bath plays a decisive role in determining membrane morphology and separation performance during the nonsolvent induced phase separation (NIPS) process. In this study, poly(ether sulfone) (PES) ultrafiltration membranes were fabricated using different coagulation media, including water, ethanol, saturated NaCl solution, and a hydrogel system, to investigate the relationship among phase inversion behavior, membrane morphology, and antifouling performance. The thermodynamic stability and phase separation kinetics of the casting system were analyzed through cloud-point measurements. The membrane morphology, pore structure, wettability, separation performance, and antifouling performance were systematically characterized. The results demonstrated that the coagulation medium significantly influenced the phase inversion pathway and membrane morphology. Rapid demixing in water produced membranes with relatively large pores and low porosity, whereas the hydrogel coagulation bath markedly retarded solvent-nonsolvent exchange, promoting the formation of a dense, uniform sponge-like structure with the highest porosity and the smallest average pore size. The membrane prepared via hydrogel-induced phase separation, designated as P-AG (coagulation bath: agarose hydrogel), exhibited a pure water flux of 73.3 L·m-2 h-1 and a water contact angle (WCA) of 58.75°. It showed the flux recovery ratio (FRR) values of 89.27% and 96.01% for bovine serum albumin (BSA) filtration and emulsion filtration, respectively, and had the lowest irreversible fouling resistance (Rir). Cyclic filtration tests further confirmed its excellent fouling reversibility and long-term operational stability. This work demonstrates that hydrogel-assisted phase inversion provides an effective strategy for tailoring membrane pore architecture. The proposed coagulation bath engineering approach offers new opportunities for developing antifouling membranes toward oily wastewater treatment.