Designing a novel integrated Janus membrane modified by PDMS/VTES for high salinity wastewater treatment

Membrane distillation technology is an important method for desalination, but it is susceptible to membrane contamination and wetting. In this study, PVDF membrane bottom surface was protected with polydimethylsiloxane (PDMS)-modified nonwoven fabric, and the membrane surface was hydrophilically modified with polymers formed from 1-vinyl-2-pyrrolidone (NVP) and vinyltriethoxysilane (VTES) to prepare the Janus membrane with hydrophilic and hydrophobic surfaces. By peeling off the PDMS-coated nonwoven fabric, part of the PDMS chains were transferred to the bottom surface of the PVDF membrane, which significantly improved the hydrophobicity of the bottom surface, and the hydrophobic contact angle of the membrane reached 152.0°. Since the casting liquid was put into a solidification bath containing hydrophilic modifier for simultaneous phase conversion into film and hydrophilic modification, the PVP-VTES was firmly anchored to the surface of the PVDF membrane through silane coupling, which resulted in excellent superhydrophilic stability of the membrane surface, and the hydrophilic contact angle reached 0°. Finally, the Janus membrane showed excellent performance in the separation of brine in DCMD. The membrane could reach a maximum flux of 43.0 kg·m −2 ·h −1 and a salt rejection rate of 99.9 % in the separation of 3.5 wt% NaCl solution. In the separation of complex salt solution, after three cycles of experiments, the salt rejection effect remained unchanged while the flux was still stable and maintained at 31.2 kg·m −2 ·h −1 . In the separation of 15 wt% NaCl solution, the membrane flux was maintained at 22.9 kg·m −2 ·h −1 after three cycles of experiment, and the salt rejection rate was still at 99.9 %. Therefore, this Janus membrane has high permeated flux and better anti-fouling properties, and it is an effective material for treating complex salt and high salinity wastewater.