Zeolitic imidazolate frameworks (ZIFs) are an exciting new class of hybrid organic-inorganic materials, known as metal-organic frameworks (MOFs), due to their exceptional thermal and chemical stability1. Their regular microporous structure makes them promising for a variety of gas separations1-2.
To demonstrate this gas permeation performance in case of membranes, a general technique to fabricate a variety of ZIFs or MOFs membranes is required, thereby minimizing the time and resources required to develop a different method for each MOF3. We have previously reported a generally applicable thermal ligand modification technique which gives rise to continuous, well intergrown films and membranes in relatively short time (few hours as compared to days)4. Here we report a novel and general method for synthesizing MOF membranes. In this technique zinc nitrate solution is dropped on hot bare porous alumina support giving rise to metal modified supports (thermal metal modification). Zinc modified support promotes heterogeneous nucleation and growth and leads to continuous well intergrown films of ZIF-8. This technique offers certain advantages over the previously reported thermal ligand modification technique, wherein the necessity of ligand stability at high temperatures for thermal ligand modification is eliminated. Also it provides an environmentally greener route to membrane fabrication, due to reduced emissions from ligand decomposition at high temperature. Further, metal modification of support can be extended to the fabrication of any other ZIF membrane, or for any other MOF, in general. Here we investigate the gas permeation performance of a membrane grown on a zinc modified support as compared to a ligand modified support.
1. Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R. D.; Uribe-Romo, F. J.; Chae, H. K.; O'Keeffe, M.; Yaghi, O. M., Exceptional chemical and thermal stability of zeolitic imidazolate frameworks. Proceedings of the National Academy of Sciences of the United States of America 2006, 103 (27), 10186-10191.
2. Liu, Y. Y.; Hu, E. P.; Khan, E. A.; Lai, Z. P., Synthesis and characterization of ZIF-69 membranes and separation for CO2/CO mixture. Journal of Membrane Science 2010, 353 (1-2), 36-40.
3. Haldoupis, E.; Nair, S.; Sholl, D. S., Efficient Calculation of Diffusion Limitations in Metal Organic Framework Materials: A Tool for Identifying Materials for Kinetic Separations. Journal of the American Chemical Society 2010, 132 (21), 7528-7539.
4. McCarthy, M. C.; Varela-Guerrero, V.; Barnett, G. V.; Jeong, H. K., Synthesis of Zeolitic Imidazolate Framework Films and Membranes with Controlled Microstructures. Langmuir 2010, 26 (18), 14636-14641.