Direct spraying approach for synthesis of ZIF-7 membranes by electrospray deposition

Zeolitic imidazolate frameworks (ZIFs) are promising materials for advanced membrane applications due to their desirable properties, which enable them to recognize specific target molecules based on the molecular sieving mechanism and/or adsorption affinity. However, their large scale commercial applications still remain a challenge because of the absence of a synthesis method that offers reproducibility, scalability, and cost-effectiveness. To this end, here we report our work of synthesizing supported zeolitic imidazolate framework ZIF-7 films and membranes in a facile and time-efficient manner at ambient pressure using a simple electrospray deposition technique. A governing parameter which dominantly affected the microstructures and crystal integrity of the membranes was deposition temperature while precursor flow rate and applied voltage to the precursor solution were important variables to obtain a stable spraying mode which is essential to have a uniform coating. Our method, which is an electrostatic force-assisted coating approach, has the following attractive advantages over conventional synthetic routes such as in situ and secondary growth methods: (1) dramatic reduction in synthesis time and precursor consumption, (2) simplification in the activation process, and (3) potential scalability. Furthermore, the membranes obtained under optimized conditions outperformed previously reported ZIF-7 membranes for H2/CO2 separation while showing rather noticeable improvement in H2 permeance which is roughly 4-10 times higher than the previous counterparts.