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 by-product. 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.