Ultramicropore engineering of novel metal-organic frameworks for highly efficient CO2 capture

This thesis focuses on the synthesis and characterization of ultramicropore metal–organic frameworks (UM–MOFs) constructed from lanthanide (III) ions and carboxylate linker, specifically formate and oxalate. A series of compounds with the general formula [(CH3)2NH2][Ln)(HCOO)(C2O4)1.5]·0.3H2O (1Ln; Ln = Er3+, Tm3+, Yb3+, Lu3+), were successfully synthesized under solvothermal conditions. Structural characterization reveals that all compounds are isostructural, crystallizes in the orthorhombic system with space group Cmce. The coordination of lanthanide (III) centers with μ2-bidentate formate (HCOO–) and μ2-tetradentate oxalate (C2O42-) ligands results in square pyramid (sqp) topological networks, which in turn form the three dimensional (3D) anionic frameworks. In these frameworks, lattice water molecules and charge–balancing dimethylammonium cations, [(CH3)2NH2]+, are present in 1D ultramicroporous channels (~6 Å). The resultant UM–MOFs are noteworthy for their exceptional stability in a variety of organic solvent and aqueous conditions, as well as their great thermal stability (up to 300 °C). All compounds exhibit the S–shaped adsorption and desorption isotherms. The materials show temperature and pressure– responsive chemisorption behavior during CO2 sorption (up to 50 bar) following activation. The compounds demonstrate a CO2 adsorption maximum capacity of 22.46, 16.46, 34.89, and 45.79 cm3 g-1 at 298 K and 20 bar, for 1Er, 2Tm, 3Yn, and 4Lu respectively. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to better clarify the host–guest interactions and uncover the mechanism of CO2 binding inside the frameworks.