Efficient CO2/CH4 separation achieved by metal–organic framework crystal-glass composite membranes

Metal–organic framework (MOF) glass holds great promise for gas separation applications. However, the inherent low porosity of MOF glass poses a considerable challenge in improving membrane permeability. In this work, a self-supporting MOF crystal-glass composite (CGC) membrane was synthesized via an innovative blending and melting approach, in which ZIF-62 powder was converted into an amorphous glassy phase and ZIF-9 powder was partially flux-melted, effectively preventing the reorganization of Zn─N bonds within ZIF-62. Consequently, the composite component structure significantly enhances the porosity and permeability of the MOF glass membrane. Furthermore, the incorporation of cobalt into the membrane matrix has notably enhanced its adsorption affinity for CO₂, thereby boosting CO₂/CH₄ selectivity. The resultant a_g[(ZIF-9)_0.2/(ZIF-62)_0.8] membrane has demonstrated exceptional CO₂ permeability of 20,324 barrer and superior CO₂/CH₄ selectivity, both surpassing the 2018 upper bound. Thus, the innovative strategy for the design of MOF CGC membranes offers effective solutions to the challenges inherent in gas separation processes.