Adsorption properties of M-UiO-66 (M = Zr(iv); Hf(iv) or Ce(iv)) with BDC or PDC linker

Abstract

The increasing CO₂ emissions and their direct impact on climate change due to the greenhouse effect are environmental issues that must be solved as soon as possible. Metal–organic frameworks (MOFs) are one class of crystalline adsorbent materials that are thought to have enormous potential in CO₂ capture applications. In this research, the effect of changing the metal center between Zr(IV), Ce(IV), and Hf(IV), and the linker between BDC and PDC has been fully studied. Thus, the six UiO-66 isoreticular derivatives have been synthesized and characterized by FTIR, PXRD, TGA, and N₂ adsorption. We also report the BET surface area, CO₂ adsorption capacities, kinetics, and the adsorption isosteric heat (Q_st) of the UiO-66 derivatives mentioned family. The CO₂ adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, Avrami's kinetic models, and the rate-limiting step with Boyd's film diffusion, interparticle diffusion, and intraparticle diffusion models. The isosteric heats of CO₂ adsorption using various MOFs are in the range 20–65 kJ mol⁻¹ observing differences in adsorption capacities between 1.15 and 4.72 mmol g⁻¹ at different temperatures due to the electrostatic interactions between CO₂ and extra-framework metal ions. The isosteric heat of adsorption calculation in this report, which accounts for the unexpectedly high heat released from Zr-UiO-66-PDC, is finally represented as an increase in the interaction of CO₂ with the PDC linker and an increase in Q_st with defects.