Superhydrophilic mixed matrix membranes by using strategy of internal and external coupling for oil-in-water emulsion separation

Abstract The intrinsic hydrophobicity of Poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HPF) membranes seriously hampers its application in the field of oily sewage treatment. The superhydrophilic surface transition of PVDF-HPF membranes can be achieved by the addition of inorganic nanoparticles. Nevertheless, the improvement of water remediation capacity may not be outstanding due to the addition of small or excessive amounts of nanomaterials. Herein, a highly active mixed matrix membranes (MMMs) were prepared by an internal and external coupling strategy of mixing and surface modification. Firstly, (3-mercaptopropyl) trimethoxysilane (KH590)-modified sodium bentonite (KNa-Bentonite) was used as nanofiller to prepare PVDF-HPF MMMs by phase inversion method. Subsequently, the assembly of plant-derived gallic acid (GA) and γ-aminopropyltriethoxysilane (APTES) couple KNa-Bentonite and polyethyleneimine (HPEI) as an intermediate component aims to constructed a nanostructured coating. The excellent superhydrophilicity could be achieved on PVDF-HPF MMMs by nanopapillae-like structures and sulfhydryl-quinone-amino covalent bridge. The optimal PVDF-HPF MMMs possessed favorable water flux (5966.31 ± 21 L·m−2·h−1 under 0.2 MPa, 266% higher than the pristine membrane), highly efficient separation ability for oil-in-water (O/W) emulsion (2369.5 ± 49 L·m−2·h−1) and operable antifouling performance (the flux recovery rate decreased by 10.24% after 10 cycles). Moreover, the oil rejection could be almost wholly restored after one month of standing at room temperature, indicating that the modified MMMs possessed good antioxidant property. The cost-effective strategy of internal and external coupling may offer new prospects for design and fabrication of super-wet membranes for O/W separation.