Effects of Alkali Metal (Li, Na, and K) Incorporation in NH2–MIL125(Ti) on the Performance of CO2 Adsorption

A series of titanium-based, metal⁻organic framework (MOF) materials, xM@NH₂-MIL125(Ti) (x is the alkali metal loading percentage during the synthesis; M = Li, Na, K), have been synthesized solvothermally. Alkali metal doping in the NH₂⁻MIL125(Ti) in situ solvothermal process demonstrated a vital modification of the material structure and surface morphology for the CO₂ adsorption capacity at ambient conditions. By changing the reactants' precursor, including different kinds of alkali metal, the morphology of xM@NH₂⁻MIL125(Ti) can be adjusted from a tetragonal plate through a circular plate to a truncated octahedron. The variation of the alkali metal loading results in substantial differences in the CO₂ adsorption. The properties of xM@NH₂⁻MIL125(Ti) were evaluated via functional group coordination using FT-IR, phase identification based on X-ray diffraction (XRD), surface morphology through scanning electron microscopy (SEM), as well as N₂ and CO₂ adsorption by physical gas adsorption analysis. This work reveals a new pathway to the modification of MOF materials for high-efficiency CO₂ adsorption.