Experimental investigation of CO2 adsorption capacities in bimetallic-doped UiO-66 and UiO-66-NH2 frameworks

A metal-organic framework (MOF) is a crystalline material that exhibits distinctive physical and chemical properties due to the coordination between metal ions and organic ligands. These properties, including a high surface area, adjustable porosity, and the ability to easily modify the chemical composition, collectively render MOFs advantageous for adsorption and separation applications. Introducing polar groups and bimetallic components into the MOF structure could significantly enhance CO2 adsorption performance. This article investigated the impact of integrating these two approaches on CO2 capture. Three Lewis acid metal ions (Al3+, Fe3+, and Cu2+) were doped into MOFs, specifically UiO-66 and UiO-66-NH2. A range of characterization techniques were employed to facilitate comparison and verification of the results, including N2 adsorption, powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. This study then evaluated CO2 adsorption at varying temperatures. The findings indicated that the Fe3+-doped samples exhibited the best performance irrespective of the presence of amino groups. Notably, the higher the concentration of metal dopants in UiO-66, the greater the adsorption capacity. UiO-66(Zr1 Fe1) exhibited the highest CO2 adsorption capacity of 2.22 mmol per gram of the modified MOF. In contrast, modified UiO-66-NH2 exhibited the opposite trend, where the lower the metal doping level, the higher the adsorption capacity. UiO-66-NH2(Zr5 Fe1) exhibited the highest adsorption capacity of 3.5 mmol/g.