Green dissolution-phase separation strategy for robust PVDF/PS membranes with improved membrane distillation performance

Membrane distillation (MD) suffers from challenges in industrial applications because of membrane wetting caused by hydrophobic decay. Although surface modifications such as nanoparticle loading or chemical grafting have been explored, weak interfacial adhesion and functional component detachment persists. This paper presents a novel dissolution-phase separation strategy for fabricating robust poly (vinylidene fluoride) (PVDF)/polystyrene (PS) composite membranes for MD. The hydrophobic PS microspheres and PVDF were dissolved in a PolarClean solvent to prepare a dilute solution. A PVDF base membrane was immersed in this solution and transferred to a water bath for phase separation, wherein the surface of the base membrane was dissolved in the PVDF/PS/PolarClean solution to form new PVDF/PS micro–nanostructures. The PS microspheres were entangled with molecular chains of PVDF and stably formed on the base membrane surface by controlling the solution temperature, immersion time, and concentrations of PVDF and PS in the dilute solution. The newly formed PVDF/PS micro/nanostructures significantly enhanced the antiwetting properties of the membrane. In contrast to conventional modification strategies, this method utilizes inherent hydrophobicity and micro/nanoscale structures of PVDF and PS for reinforcing the hydrophobicity of the resulting membrane, which significantly improves its stability. After 48 h of the MD process, the optimized PVDF/PS membrane exhibited a stable flux of 29.8 kg·m −2 ·h −1 and 23.1 kg·m −2 ·h −1 for 35 and 100 g/L saline water with all salt rejections above 99.9 %. In addition, the membrane demonstrated excellent performance in treating simulated dye wastewater, which maintains a high water flux above 20 kg m −2  h −1 with near-complete dye rejection and 99.9 % salt rejection.