Enhanced performance of superhydrophobic polyvinylidene fluoride membrane with sandpaper texture for highly saline water desalination in air-gap membrane distillation

Here, we report a simple and cost-effective process to fabricate a superhydrophobic Polyvinylidene Fluoride (PVDF) membrane. Four different PVDF membranes were investigated using sandpaper (SP), polydimethylsiloxane (PDMS), stainless steel mesh (SSM), and tempered glass as casting substrate in a non-solvent induced phase separation process. Sandpaper-like texture was replicated on a PVDF membrane using a PDMS template prepared via soft lithography technique. Interestingly, PDMS-based membrane reveals surface with textures depicting the lotus effect. The developed membranes were characterized in terms of their morphology, bulk properties, wetting behavior and MD performance. Among all the membranes developed, PDMS-based textured membrane showed excellent MD performance with high and stable salt rejection at 99.99%, and permeate flux reaching 21 kg m⁻² h⁻¹ after a 40-hour test using highly saline water (70 g/L NaCl) in Air-Gap Membrane Distillation (AGMD). Notably, the PVDF membranes developed in this study showed an increase in permeate flux with time due to a decrease in the air gap width as a result of membrane stretching. The textured PVDF membrane that was developed using sandpaper features offers a promising alternative for treating highly saline water in the MD system.