Facile synthesis of bimetallic MIL-100(Fe, Al) for enhancing CO₂ Adsorption performance

Bimetallic metal-organic frameworks, having two different metal species in the framework metal sites, demonstrate higher effectiveness in CO₂ capture and separation performance than their monometallic counterpart. For this reason, a series of bimetallic MIL-100(Fe, Al) was synthesized using a hydrothermal reaction system in the presence of Fe and Al metal precursors with various molar ratios. The physicochemical characterizations of the products were influenced by adding Al species in the starting materials, inducing the successful incorporation of a certain amount of Al species inside the framework. The effect of Al incorporation was analyzed by inductively coupled plasma, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, NH₃-temperature program desorption, and a N₂ porosimetry. Among the investigated samples, MIL-100(Fe, Al)#2 showed the highest CO₂ adsorption capacity of 3.27 mmol g⁻¹ with an IAST-CO₂/N₂ selectivity of 76.5 at 25 °C and 1 bar. Compared to the MIL-100(Fe) parent sample, the results improved by approximately 26% for CO₂ uptake amount and by 1.5-fold for CO₂/N₂ selectivity due to the increment of micropore volume and presence of the new adsorptive sites of unsaturated metal sites (Al³⁺) and H⁺ from the bridges between tiny particles of AlOOH and –COOH groups. This facile synthetic route for bimetallic MOFs has the potential to enhance CO₂ adsorption performance.