Hydrophilic surface coating on hydrophobic PTFE membrane for robust anti-oil-fouling membrane distillation

The hydrophobic membranes used in membrane distillation (MD) are inherently prone to fouling by hydrophobic contaminants due to the long-range hydrophobic-hydrophobic interaction, which limits the application of this promising technology. In this study, a novel dual-layer composite membrane was fabricated through eletrospinning a hydrophilic poly(vinyl alcohol) (PVA) coating on a commercial hydrophobic polytetrafluoroethylene (PTFE) membrane and then cross-linking with glutaraldehyde for robust anti-oil-fouling MD. The prepared composite membrane showed an asymmetric wettability, the coating surface was underwater oleophobic with underwater oil contact angle of 148.7° and the PTFE substrate surface was hydrophobic with in-air water contact angle of 134.5°. The test results of the adhesive force between an oil droplet and membrane surface exhibited that the fabricated membrane had a desirable surface to resist oil adhesion. Direct contact MD experiments were conducted using a saline emulsion with 1000 mg/L crude oil to compare the performance of the modified membrane and the pristine PTFE membrane. The results demonstrated that the modified membrane can present stable performance with robust resistance to oil-fouling compared to the pristine PTFE membrane. It is believed that the fabricated composite membrane has great potential to be applied in MD process with high concentration of hydrophobic organics.