Fast synthesis of zeolitic imidazolate framework ZIF-94 using NaOH and recycling reagents

ZIF-94 is a zeolitic imidazolate framework with the same SOD type topology than ZIF-8 but with an aldehyde group functionalized organic ligand. This turns ZIF-94 less thermally stable than ZIF-8 but with interesting properties of water and carbon dioxide adsorption, making the former a material highly suitable for carbon capture technologies. In this work, an alternative procedure for the synthesis of ZIF-94 was developed based on the use of NaOH as deprotonator. Besides, the crystallization was carried out in a very short time (1–20 min) at room temperature while centrifuging at 10,000 rpm. This made possible the simultaneous crystallization and separation of the product material giving rise, together with the use of the inorganic deprotonator, to a very efficient process with crystallization yields higher than 65%. For the best conditions tested (crystallization-centrifugation time of 5 min), 66 ± 24 nm in particle size, highly crystalline ZIF-94 with 485 m2 g−1 of specific surface area was obtained at a crystallization yield of 66.9%. Similar properties were obtained for ZIF-94 when prepared from recycled reagents (solvent, ligand and Zn salt).