Preparation And Performance Investigation Of Zeolitic Imidazolate Framework Membranes

Metal-organic frameworks?MOFs?are a new type of porous crystalline material with diverse topological structure and abundant specific physical and chemical properties,which can be changed on their structure and properties through reasonable design.Therefore,MOF materials have shown a broad application prospect in adsorption,separation,catalysis and sensors.In recent decade,MOF membranes formed by self-assembly have been developed remarkably in the field of separation.Until now,the great progress in materials,synthesis methods and separation performance of MOF membranes have been achieved.However,considering from the perspective of industrial applications,the synthesis and separation performance of MOF membranes are still hard to meet the actual demand.The development of MOF membranes are into the bottleneck period.Based on the above consideration,in this paper,ZIF-8 was chosen as target MOF material,MOF membrane was studied from synthesis and separation performance.First of all,from the perspective of synthesis method,a new scalable synthesis methodcombining with membrane contactor and interface synthesis theory of MOF membrane has been proposed.The new method can get rid of low efficiency and high energy consumption fundamentally compared with the conventional methods,absolutely eliminate the possibility that MOF membranes are damaged in the process of installation,and enable the reaction solutions reused circularly.Using this method,we successfully synthesized continuous ZIF-8 membranes.The SEM,XRD,EDS and other characterization measurement were used to determine the morphology and structure of as-synthetized ZIF-8 membranes.By investigating the influence of precursor solution concentration ratio and synthetic time on the MOF membranes,we analyzed the film-forming mechanism of MOF membrane,provides theoretical support for the synthesis of followed other types of MOF membrane.In addition,in order to improve the separation performance of MOF membranes,polymer?polyvinylpyrrolidone,PVP?embedded ZIF-8membrane was synthesized successfully based on the new synthesis methods.The embedded polymer molecules into ZIF-8 crystals can effectively reduce the pore aperture of MOF and even eliminate nanometer-size grain boundary defects of MOF layers and enhance gas separation performance.Experimental results showed that after embedding of the PVP,the ZIF-8 particles became smaller,while the ZIF-8 crystaline structure remains unchanged,and ZIF-8 membranebecame denser.Through XRD,N2 adsorption test of PVP embedded ZIF-8 particles and the FTIR characterization of ZIF-8 composite membrane the embeddability of PVP was proved.Finally,single-component gas permeation test of PVP embedded ZIF-8membrane was carried out.The experimental results shown that the gas permeances of PVP embedded ZIF-8 membrane reduced to some extent compared with ZIF-8 membrane,but the H₂/CO2 separation selectivity was greatly increased.The ideal separation selectivity reached 52.71,which was much higher than those reported ZIF membranes.