Constructing anti-scaling and anti-wetting polyvinyl alcohol layers through spray-coating with improved water permeability in membrane distillation

Abstract

Membrane scaling and wetting severely hinder the implementation of membrane distillation (MD) in hypersaline wastewater treatment. In this study, Janus membranes with high water flux and anti-scaling/wetting capacities were successfully fabricated by spray-coating polyvinyl alcohol (PVA) layers on hydrophobic membrane substrates (SCJMs). The surface properties and wastewater treatment performances of SCJMs were systematically investigated and compared with those of Janus membranes fabricated via frame-coating methods (FCJMs). Compared with the FCJMs, the PVA layers formed on the SCJM surface were defect-free, more uniform in thickness, and had larger evaporation areas; consequently, they exhibited higher water fluxes. Further investigation of the flux-enhancement mechanisms of the SCJMs using Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and polarizing microscope analyses revealed that spray-coating promoted the crosslinking of PVA polymer networks and facilitated water molecule transport. In addition, although the PVA layer of the SCJMs exhibited higher crystallinity, the crystal particles were smaller in size, and the crystal domains exhibited a lower resistance to water transport compared to those of the FCJMs. Fabrication conditions such as spraying time and distance were also optimized to further enhance the performance of the SCJMs, which exhibited great potential for application in the efficient MD-based desalination of hypersaline wastewater.