De novo syntheses of multi-linker Zn- and Co-based ZIFs with application in CO2 fixation

Zeolitic Imidazolate Frameworks (ZIFs) and ZIF derivatives can catalyze the fixation of CO2 with epoxide substrates. Herein, we report a De Novo (direct mixing) synthesis method to produce nano-sized Zn- and Co-based Multi-Linker ZIFs (termed as ML-ZIFs) with polar 2-mercaptoimidazolate (SHIm) and non-polar 2-methylimidazolate (mIm) linkers, characterized by PXRD, TGA, TEM, 1H NMR, N2 and CO2 isotherms. All the ML-ZIFs have sodalite (SOD) topologies with permanent porosity and thermal stability of up to 250 °C. Both Zn- and Co-based ML-ZIFs were efficient in the fixation of CO2 with epichlorohydrin (ECH) and propylene-oxide (PrO) substrates without co-catalyst, showing improved catalytic activity over their single-linker counterparts (ZIF-8 and ZIF-67). ML-ZIF 5Co (with Co metal center and Co(mIm)1.68(SHIm)0.32 composition) showed a maximum Turn-Over Frequency (TOF) of 893 and 787 h−1 for CO2 fixation with PrO and ECH, respectively.