Preparation and Comparison of Merit Parameters of Hydrophobic Membranes on Metal Meshes Based on ZIF-8/PVDF and In Situ Formation of ZIF-8 by Secondary Growth and Electrochemical Synthesis

Abstract

Several hydrophobic membranes based on zeolitic imidazolate framework-8 (ZIF-8) on metallic meshes were prepared and compared. To assess whether the incorporation of PVDF would help improve merit parameters of the membranes for oil/water separation applications, two kinds of membranes were synthesized: polymeric membranes using polyvinylidene fluoride (PVDF) and non-polymeric membranes obtained by in situ growth of ZIF-8 on the membranes. Three polymeric and two in situ methods were used, determining and comparing their wettability, non-polar liquid flow, and critical water intrusion pressure. Additionally, the interface of ZIF-8/PVDF was investigated through computational simulations. The simulations predict excellent adhesion between ZIF-8 and PVDF, without the presence of interfacial cavities or microvoids. The adsorption isotherms of benzene, toluene and m-xylene (BTXs) on PVDF-ZIF-8 composites were calculated, indicating that BTXs are selectively adsorbed on ZIF-8 with negligible incorporation into the polymer phase, while ZIF-8 retains its high adsorption capacity in the composite. Encouraged by the computational results, several ZIF-8/PVDF membranes were prepared on metal meshes through three different synthesis strategies, referred as Immersion, Spray, and Sprinkling. Moreover, two non-polymeric type of membranes were prepared for comparison as well, obtained by in situ synthesis of ZIF-8 on the meshes, referred to as Secondary Growth and Electrochemical Anchoring. The static water-contact angle in air, flux of organic liquids, and critical inclusion pressure of water were measured and compared for the five methods. When globally analyzed, it is clear that the more hydrophobic the membrane, the higher the water pressure it supports, but at the cost of reducing the fluxes. The largest values of water pressure were obtained for a ZIF-8/PVDF membrane made with the sprinkling method, which consists of solid dispersion of ZIF-8 on the top of a PVDF coating, identified as a very promising preparation procedure.