Optimized CO Capture of the Zeolitic Imidazolate Framework ZIF-8 Modified by Solvent-Assisted Ligand Exchange.

Zeolitic imidazolate frameworks, like ZIF-8 and related structures, have shown great potential for the capture of carbon dioxide. Modifying their structure by exchanging part of the constituent organic ligands is a proven method for enhancing the capacity to absorb CO. In this work, we performed solvent-assisted ligand exchange (SALE) on nanosized ZIF-8 (nZIF-8) with a series of functionalized imidazole derivatives (exchange percentages, after 24 h): 2-bromoimidazole (19%), 2-chloroimidazole (29%), 2-trifluoromethylbenzimidazole (4%), 2-mercaptobenzimidazole (4%), and 2-nitroimidazole (54%). The sodalite topology and porosity of nZIF-8 were maintained with all SALE modifications. Low-pressure CO adsorption of nZIF-8 (38.5 cm g) at STP was appreciably enhanced with all mixed-linker SALE products. Using halogenated (-Cl, -Br, and -CF) imidazole derivatives in a 24 h SALE treatment resulted in increases between 11 and 22% in CO adsorption, while the thiol (-SH)- and nitro (-NO)-functionalized SALE products led to 32 and 100% increases in CO uptakes, respectively. These CO uptakes were further optimized by varying the SALE treatment time. The SHbIm- and NOIm-exchanged SALE products of nZIF-8 show 87 and 98 cm g of CO uptakes after 60 and 120 h of SALE, respectively. These are record high CO adsorptions for all reported ZIF derivatives at low-pressure conditions.