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• Micro-patterned PES membranes exhibit underwater superoleophobic of 150 ± 2°. • Micro-patterned membranes have water permeance of 8036 L·h−1·m−2·bar−1. • Membranes show excellent oil-in-water emulsion separation efficiency. • Developed membranes demonstrate flux recovery ratio (FRR) of 99 % over three subsequent cycles. • Comprehensive separation mechanisms for oil removal are introduced and discussed. Developing polymeric membranes for oily wastewater treatment has attracted great interest over the last few years. However, the low permeance and poor fouling resistance are considered the most challenging issues. Introducing topographic patterns on the membrane surface to increase active area and surface roughness is one practical strategy for reducing membrane fouling. Here, isotropic polyethersulfone (PES) membranes with line patterns and continuous sponge-like porous structure were prepared using phase separation micro-molding processes. Various techniques were used to characterize the morphologies and physicochemical properties of the as-prepared membranes. The surface wettability of the membranes was evaluated by measuring contact angle of a water drop in air and of industrial crude oil under water. The as-prepared membranes separation and antifouling performance were assessed using water permeance, oil rejection, and flux recovery ratio after emulsion filtration. The results showed that the patterned PES membrane has superior hydrophilic and antifouling capabilities, with a lower static water contact angle (CA) of 32° as compared to a flat PES membrane (CA = 39°). Furthermore, the patterned membrane had pure water permeance (PWP) of 8036 ± 65 L·h−1·m−2·bar−1, which was ∼ 68 % greater than that of the flat PES membrane. This is mainly attributable to the discernible increase in the membrane pore size distribution and the enhancement in membrane surface hydrophilicity due to the increase in surface roughness as a result of micro-patterning. The patterned membranes showed superior separation efficiency (>99.0 %) and permeance (7031 ± 65 L·h−1·m−2·bar−1) for the oil-in-water emulsion of 0.1 g·L−1. At a higher concentration of crude oil-in-water emulsion (50 g·L−1), the patterned PES membranes achieved promising permeance of 90 L/h.m2.bar and 99.9 % rejection. Furthermore, the flux recovery ratio of the patterned membrane exceeded 91 % after three consecutive cycles of dead-end filtration and backwashing with water, demonstrating the benefit of using micro-patterned membranes for treating high concentration and industrial oil-in-water emulsions. [ABSTRACT FROM AUTHOR]

• Isotropic polyethersulfone (PES) membrane was successfully developed via the vapor-induced phase separation (VIPS) method. • The isotropic PES membrane demonstrated outstanding underwater superoleophobicity (OCA of crude oil, 145 ± 2.0) and oil-repellency properties. • The isotropic PES membrane has superior water permeability of 4721 L/h⋅m2⋅bar that is about 13.6 times higher than that recorded by anisotropic PES. • The isotropic PES membrane showed excellent oil-in-water emulsion separation efficiency (>98%) for different heavy oil concentrations. • The isotropic PES membrane showed durable oil-fouling repellency, which could be easily recycled with a flux a recovery ratio of 59.5% over three subsequent cycles. Isotropic polyethersulfone (PES) membrane for separation of oil-in-water nanoemulsion was successfully developed using non-solvent vapor-induced phase separation (VIPS). The surface and structural properties of the fabricated PES membranes were thoroughly characterized using various techniques. The membrane separation performance was evaluated in terms of permeate flux, oil rejection, antifouling capability, and water flux recovery. Remarkably improved surface hydrophilicity for isotropic PES membrane (contact angle, CA = 39°) compared to anisotropic PES membrane (CA = 70°), resulting in superior pure water permeance, attaining 4721 L/h⋅m2⋅bar at operating pressure of 0.5 bar. The isotropic PES membrane achieved superior crude oil-in-water nanoemulsion separation (permeance of 713 L/h⋅m2⋅bar and 100% rejection) at oil concentration of 1 g/L. At extremely high oil concentration of 50 g/L, the PES membrane was not completely fouled and showed permeance of 65 L/h⋅m2⋅bar and 98.2% rejection. Moreover, the flux recovery of the fouled isotropic PES membrane exceeded 59.5% over three subsequent cycles of filtration and back-washing with water. Overall, this study might provide substantial guidance for large-scale manufacturing and application of isotropic PES membrane in treating practically challenging emulsified oil-in-water nanoemulsion under harsh conditions. [ABSTRACT FROM AUTHOR]