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

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 super hydrophobic membrane was prepared by grafting octavinyl-polyhedral oligomeric silsesquioxane (OVPOSS) onto polyvinylidene fluoride (PVDF) membrane via UV-induced thiolene 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 super hydrophobic 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.