Nano-armored super-hydrophilic antifouling membrane through dual counter-diffusion-induced process for separation of crude oil emulsion

Conventional superhydrophilic membrane surfaces effectively resist low-viscosity oil stains, but it is difficult to avoid crude oil adhesion. There is still room for improvement in the anti-fouling performance throughout the crude oil emulsion separation process. Using metal salts and phytic acid molecules as building blocks, a nano-armored superhydrophilic metal-phytic acid coordination self-assembled membrane (M−PA/CAM) is prepared with a dual counter-diffusion-induced strategy. Strong Lewis acid Fe³⁺ ions are easily coordinated with Lewis base phytic acid to form a three-dimensional cross-linked network. The addition of NaCl to the coagulation bath resulted in an increase in surface roughness. Therefore, the optimized Fe-PA/CAM have a high porosity of 60.9 % and a roughness of 182 nm, showing superhydrophilicity and underwater superoleophobicity. The pure water permeability is capable of reaching 805.9 L m⁻² h⁻¹ bar⁻¹. After 3.0 h of circulating filtration, a 1000 ppm crude oil-in-water emulsion can reach a recovery rate of 99 %. Compared with PA-Fe modified PVDF membranes prepared by impregnation and blending methods, the permeation attenuation rate of Fe-PA/CAM is reduced by more than 50 %. The coating had strong hydration capacity, verified by in-situ DRIFTS analysis of water adsorption kinetics. Both the Young's modulus and tensile strength exceeded PVDFM by 1.9 and 1.4 times respectively. The composite membrane exhibits chemical and mechanical stability and shows promise in actual oily wastewater treatment.