A purely green approach to low-cost mass production of zeolitic imidazolate frameworks

Although zeolitic imidazolate frameworks (ZIFs) have bright prospects in wide fields like gas storage/separation, catalysis and medicine, etc., their large-scale applications are bottlenecked by the absence of their low-cost commercial production technique. Here, we report an unconventional method suitable for environmentally friendly and low-cost mass-production of ZIFs. In this method, taking the synthesis of ZIF-8 as an example, ZnO was used instead of Zn(NO3)(2) in traditional solvent synthesis methods and CO2 was introduced to dissolve ZnO in aqueous solution of 2-methylimidazole (HMeim) and form water soluble salt ([ZnMeim](+)[MeimCOO](-)) at room temperature. Then, by removing CO2 through heating or vacuuming, Meim-ions are produced and instantaneously assemble with [ZnMeim](+)s to generate ZIF-8 without any byproduct. Due to the absence of strong acid anions (such as NO3- and Cl- et al.) in solution, the washing of filter cake required in the conventional approaches could be omitted and the filtrate containing only water and HMeim could be reused completely. This method is really green as no waste gas or liquid generates because CO2 and water could be recycled perfectly. It overcomes almost all bottlenecks occurred in commercial production of ZIF-8 when using traditional methods. A pilot plant was established for mass-production of ZIF-8 and hundreds kilograms of ZIF-8 was produced, which indicates that the new method is not only environmentally friendly but also low cost and commercial accessibility. It is expected that the new method would open an avenue for commercial applications of ZIFs. (c) 2021 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Although ZIFs have great potential in various fields, their large-scale applications are hindered by the lack of low-cost commercial production techniques. This study presents an unconventional method for environmentally friendly and low-cost mass-production of ZIFs. The method utilizes CO2 to dissolve ZnO in an aqueous solution and forms ZIF-8 without any byproducts. A pilot plant was established to produce hundreds of kilograms of ZIF-8, demonstrating the environmental friendliness, low cost, and commercial accessibility of the new method. It is expected to pave the way for commercial applications of ZIFs.