Effect of Solvent Assisted Linker Exchange (SALE) and De Novo Synthetic Routes on CO 2 Uptake and Fixation by Mixed-Linker Zeolitic Imidazolate Frameworks

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 –NO 2 and –Br/–Cl functionalities were prepared via both synthetic routes. Thereafter the CO 2 uptake of the ML-ZIFs were compared, as well as their abilities to fixate CO 2 with epoxide substrates. The de novo synthesis resulted in ML-ZIFs with SOD topologies, 60: 40 (–NO 2 : –Br/–Cl) functionality ratios, higher porosities, better thermal stability and higher CO 2 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-7 Cl , obtained from direct mixing, resulted in the highest CO 2 uptake (90 cm 3 g −1 ), in line with its higher porosity. ML-ZIF-7 Cl , in combination with tetrabutylammonium bromide (TBAB), showed a high catalytic activity (TOF of 446 h −1 ) for the fixation of CO 2 with propylene oxide and was reusable for up to 4 cycles without loss in activity. Graphical Abstract