Reinforcing hydration layer on membrane surface via nano-capturing and hydrothermal crosslinking for fouling reduction

Polyvinylidene fluoride (PVDF)@Fe3O4 composite membranes were prepared by phase inversion, followed by crosslinking with hydrophilic silane-based prepolymers. The influences of Fe3O4 nanoparticles (NPs) on morphology, chemistry, hydrophilicity, electric charge and roughness of membrane surfaces were investigated by a number of characterization techniques. The results revealed that the dispersed Fe3O4 nanoparticles reduced the micropores of the composite membrane and maintained the membrane surface roughness. Meanwhile, the dispersed Fe3O4 enabled the membrane to capture more hydrophilic silane-based prepolymers, thereby leading to a robust, dense and zwitterionic characteristic hydration layer on the membrane surface. The reinforced hydration layer imparted the membrane surface with more stable water permeability and higher rejections to humic acid (HA), bovine serum albumin (BSA) and soybean oil during five cycles of cross-flow separation. According to the resistance-in-series model, the anti-oil-fouling mechanism of the membrane relied on manipulating the hydration layer on the membrane surface to prevent the foulants from approaching the membrane surface. The surface-immobilized Fe3O4 facilitated the hydration layer to repel HA and BSA to permeate through the membrane via chelation and adsorption, and then reduced the membrane internal fouling. Our findings provide a new strategy to construct antifouling membrane surfaces by properly tailoring the strength and thickness of the surface hydration layer.