Synthesis of ZIF-8 membrane via facile cathodic deposition in aqueous medium for propylene/propane separation

Abstract

Metal-organic frameworks (MOFs) are porous crystalline materials built by metal clusters coordinated to organic ligands. Synthesis of MOFs has attracted considerable attention in recent decades, owing to its potential for a wide range of applications such as gas separation, dye adsorption, and catalysis, etc. The development of MOF membranes further enhances the potential of this type of material in industrial applications. Membrane fabrication methods, including in-situ growth, seeded secondary growth, interfacial growth, and vapor-phase deposition, have been widely studied. However, most of these methods either require a complicated synthesis procedure or are timeconsuming. Recently, the electrochemical synthesis has emerged as a highly promising approach to fabricate MOF membranes in a scalable manner, because it allows shorter synthesis time, milder synthesis condition, continuous reaction, and crystal self-healing. In this thesis, for the first time, an aqueously cathodic deposition (ACD) approach was developed to fabricate ZIF-8 type of MOF membranes without the addition of any supporting electrolyte or modulator. The fabrication process used 100% water as the sole solvent, and a low-defect density membrane was obtained in only 60 min under room temperature without any pre-synthesis treatment. The membrane exhibited superior performance in C3H6/C3H8 separation with C3H6 permeance of 182 GPU and selectivity of 142, making it sit at the upper bound of permeance versus selectivity graph, outperforming the majority of the published data up to 2019. Notably, this approach used an extremely low current density (0.13 mA cm-2) operated under a facile apparatus setup, enabling an attractive method for environmentally friendly, energy-efficient, and scalable MOF membrane fabrications. This work demonstrates the enormous potential of aqueously electrochemical deposition of the MOF membrane in future research.