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 2 . 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 2 adsorption of nZIF-8 (38.5 cm 3 g –1 ) at STP was appreciably enhanced with all mixed-linker SALE products. Using halogenated (−Cl, −Br, and −CF 3 ) imidazole derivatives in a 24 h SALE treatment resulted in increases between 11 and 22% in CO 2 adsorption, while the thiol (−SH)- and nitro (−NO 2 )-functionalized SALE products led to 32 and 100% increases in CO 2 uptakes, respectively. These CO 2 uptakes were further optimized by varying the SALE treatment time. The SHbIm- and NO 2 Im-exchanged SALE products of nZIF-8 show 87 and 98 cm 3 g –1 of CO 2 uptakes after 60 and 120 h of SALE, respectively. These are record high CO 2 adsorptions for all reported ZIF derivatives at low-pressure conditions.

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Direct mixing (de novo) and Solvent Assisted Ligand Exchange (SALE) are the main methods used for the synthesis of Mixed-Linker Zeolitic Imidazolate Frameworks (ML-ZIFs). ML-ZIFs with combined –NO2 and –Br/–Cl functionalities were prepared via both synthetic routes. Thereafter the CO2 uptake of the ML-ZIFs were compared, as well as their abilities to fixate CO2 with epoxide substrates. The de novo synthesis resulted in ML-ZIFs with SOD topologies, 60: 40 (–NO2: –Br/–Cl) functionality ratios, higher porosities, better thermal stability and higher CO2 uptake than equivalent SALE products. SALE resulted in smaller ML-ZIF crystallites, only ~ 10% incorporation of –Br/–Cl functionalized imidazolate linkers, and phase change during activation. ML-ZIF-7Cl, obtained from direct mixing, resulted in the highest CO2 uptake (90 cm3 g−1), in line with its higher porosity. ML-ZIF-7Cl, in combination with tetrabutylammonium bromide (TBAB), showed a high catalytic activity (TOF of 446 h−1) for the fixation of CO2 with propylene oxide and was reusable for up to 4 cycles without loss in activity. Graphical Abstract