Carbon dioxide adsorption on MIL-100(M) (M = Cr, V, Sc) metal-organic frameworks: IR spectroscopic and thermodynamic studies

Abstract

[eng] Interaction between carbon dioxide and the coordinatively unsaturated Cr(III), V(III) and Sc(III) cationic centers in MIL-100(Cr), MIL-100(V) and MIL-100(Sc), respectively, was studied by means of variable-temperature infrared (VTIR) spectroscopy, a technique that affords determination of standard adsorption enthalpy (ΔH0) and entropy (ΔS0) from analysis of IR spectra recorded over a temperature range while simultaneously measuring equilibrium pressure inside a closed IR cell. ΔH0 was found to be −63, −54 and −48 kJ mol−1 for MIL-100(Cr), MIL-100(V) and MIL-100(Sc), respectively, which are among the highest values so far reported for CO2 adsorption on metal-organic frameworks containing open metal sites. Corresponding values for ΔS0 resulted to be −210, −198, and −178 J mol−1 K−1, thus showing a positive correlation between ΔH0 and ΔS0. The observed values of standard adsorption enthalpy are discussed in the broader context of corresponding data reported in the literature for the adsorption of carbon dioxide on other MOFs, as well as on zeolites.