A Microporous Ni(II) Metal–Organic Framework Nanostructure with an Aspartate-Derived Tricarboxylate for Gas/Vapor Sorption and Size-Selective CO2 Chemical Fixation under Solvent-Free Conditions

A microporous metal–organic framework {[Ni4(μ3−OH)2(d-2,4-cbs)2(H2O)4]·5H2O}n (Ni-CBS) with a stable Ni4(μ3–OH)2 core has been solvothermally synthesized by using an aspartate-derived tricarboxylic acid, H3(d-2,4-cbs). A tapered microrod-like surface morphology of Ni-CBS is observed via field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Its crystallinity and thermal stability are analyzed using powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA), respectively. The nitrogen adsorption isotherm at 77 K validates the micron-size pores in the framework. The amine-functionalized framework is further utilized to study CO2 adsorption for a potent interaction between the framework and CO2 molecules with an isosteric heat of adsorption (Qst) value of 33.5 kJ mol–1 at zero loading. Further, the microporous nature of the framework is demonstrated through the encapsulation of various organic solvent molecules. With a high CO2 uptake value at room temperature (47.8 cm3g–1), Ni-CBS is found to be a competent heterogeneous catalyst for the formation of cyclic carbonates by fixing carbon dioxide chemically with epoxides of appropriate molecular dimensions. Furthermore, the catalytic behavior of Ni-CBS is compared with the previously reported isostructural Zn-CBS under solvent-free conditions, confirming more Lewis acid character of Zn(II) over Ni(II).