Imidazolium Modified UiO‐67 Metal‐Organic Frameworks for CO₂ Adsorption

Abstract

This study investigates the CO₂ sorption properties of the Zirconium-based MOF UiO-67 and its imidazolium-functionalized derivatives (Im-UiO-67-X), focusing on the role of different ions (X = Br⁻, OAc⁻, NTf₂⁻) as counterpart to the positively charged imidazolium motifs. Imidazolium groups were introduced via side-chain functionalization of biphenyl dicarboxylate (bpd) linkers. The crystalline materials were synthesized using microwave-assisted methods and characterized by X-ray diffraction, N2 physisorption (77 K), CO₂ physisorption (298 K), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). CO₂ physisorption experiments (298 K) revealed that pristine UiO-67 exhibits the highest uptake capacity, correlating with its larger accessible surface area, whereas incorporation of imidazolium groups led to partial pore blocking and reduced capacity. Among the modified materials, however, the acetate counterion had the most beneficial effect, yielding an uptake capacity nearly comparable to unmodified UiO-67. DRIFTS studies further indicated that CO₂ chemisorption involves interactions with hydroxyl groups of the zirconia clusters. These findings underline the delicate balance between pore accessibility and adsorption capacity in imidazolium-functionalized MOFs. Beyond their potential for CO₂ capture, the ability of imidazolium groups to pre-activate CO₂ highlights promising opportunities for catalytic applications, such as CO₂ conversion and utilization in heterogeneous reaction environments.