Hierarchically-structured superhydrophobic POSS/PVDF composite membrane for anti-fouling and anti-wetting membrane distillation

Abstract

Membrane fouling and wetting were two unsolved issues for membrane distillation (MD), fostered an enduring pursuit of well-designed superhydrophobic membrane. In this work, a novel hierarchically-structured superhydrophobic membrane was prepared by grafting octavinyl-polyhedral oligomeric silsesquioxane (OVPOSS) onto polyvinylidene fluoride (PVDF) membrane via UV-induced thiol-ene click reaction after the hydroxylation and sulfhydrylation pretreatment. The POSS/PVDF membrane exhibited high roughness and superhydrophobicity, and the pore structure was optimized with smaller size but centralized distribution. For the fabricated superhydrophobic membrane with low sliding angle (about 7.5°), the maintaining of Cassie-Baxter state and the “slip effect” significantly mitigated membrane fouling and wetting, due to the retardation of the liquid invasion into the gas-solid interface. It was found that scaling was the leading fouling for the commercial PVDF membrane, and the interaction between Ca2+ and carboxyl was the main organic fouling mechanism. While for the POSS/PVDF membrane, organic fouling via hydrophobic-hydrophobic interaction was the main membrane fouling and the scaling was significantly alleviated. The fabricated POSS/PVDF composite membrane had significant superiority over commercial PVDF membrane, which showed promising potential in challenging wastewater treatment. Additionally, this work also offered a new and facile method for superhydrophobic membrane fabrication.