Fabrication of superhydrophobic PVDF composite membranes using modified ZIF-8 for efficient and stable membrane distillation: Mitigating fouling and wetting
Membrane distillation (MD) represents a promising advance in wastewater purification, contributing to the mitigation of water scarcity. Hydrophobic poly(vinylidene fluoride) (PVDF) microporous membrane is susceptible to wetting by low surface tension substances, leading to fouling. To address this, PVDF membrane was superhydrophobically modified using modified ZIF-8 to obtain two composite membranes, AZ/PVDF and Z@C/PVDF. AZ/PVDF and Z@C/PVDF composite membranes were prepared by coating more dispersible APTES-ZIF-8 and ZIF-8@MWCNT, respectively, onto the surface of PVDF membrane. The hydrophobicity of the composite membranes was regulated by silane types, fluorination methods, and fluorination time, resulting in reduced surface roughness and increased surface energy. The contact angles of AZ/PVDF and Z@C/PVDF were 154.2 ± 3.4° and 156.8 ± 4.2°, respectively. Both AZ/PVDF and Z@C/PVDF membranes demonstrated outstanding mechanical, thermal, and chemical stability. AZ/PVDF and Z@C/PVDF membranes outperformed PVDF membrane, extending operation times by 2 h and 3 h, respectively, without obvious NaCl crystals. Furthermore, Z@C/PVDF membrane exhibited superior resistance to wetting by SDS than AZ/PVDF and PVDF membranes, treating pickle brine via the direct contact MD (DCMD) process with a recovery rate of 30.2 % within 10 h. Overall, this research offers a promising approach to fabricating superhydrophobic composite membranes for high-salt brine treatment via DCMD.
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