Preparation and Comparison\nof Merit Parameters of\nHydrophobic Membranes on Metal Meshes Based on ZIF-8/PVDF and In Situ\nFormation of ZIF‑8 by Secondary Growth and Electrochemical\nSynthesis

Several hydrophobic membranes based on zeolitic imidazolate\nframework-8\n(ZIF-8) on metallic meshes were prepared and compared. To assess whether\nthe incorporation of polyvinylidene fluoride (PVDF) would help improve\nmerit parameters of the membranes for oil/water separation applications,\ntwo kinds of membranes were synthesized: polymeric membranes using\nPVDF and nonpolymeric membranes, determining and comparing their wettability,\nnonpolar liquid flow, and critical water intrusion pressure. Additionally,\nthe interface of ZIF-8/PVDF was investigated through computational\nsimulations. The simulations predict excellent adhesion between ZIF-8\nand PVDF, without the presence of interfacial cavities or microvoids.\nThe adsorption isotherms of benzene, toluene, and <i>m</i>-xylene (BTXs) on PVDF-ZIF-8 composites were calculated, indicating\nthat BTXs are selectively adsorbed on ZIF-8 with negligible incorporation\ninto the polymer phase, while ZIF-8 retains its high adsorption capacity\nin the composite. Encouraged by the computational results, several\nZIF-8-PVDF membranes were prepared on metal meshes through three different\nsynthesis strategies, referred to as immersion, spray, and sprinkling.\nMoreover, two nonpolymeric type of membranes were prepared for comparison\nas well, obtained by the <i>in situ</i> synthesis of ZIF-8\non the meshes, referred to as secondary growth and electrochemical\nanchoring. The static water-contact angle in air, the flux of organic\nliquids, and the critical inclusion pressure of water were measured\nand compared for the five methods. When globally analyzed, it is clear\nthat the more hydrophobic the membrane, the higher the water pressure\nit supports but at the cost of reducing the fluxes. The largest values\nof water pressure were obtained for a ZIF-8/PVDF membrane made with\nthe sprinkling method, which consists of a solid dispersion of ZIF-8\non top of a PVDF coating, identified as a very promising preparation\nprocedure.