Effect of Solvent Assisted Linker Exchange (SALE) and De Novo Synthetic Routes on CO2 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 -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 similar to 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 CO2 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 CO2 with propylene oxide and was reusable for up to 4 cycles without loss in activity. [GRAPHICS] .