Quantitative analysis of liquid-phase adsorption over chromium-containing metal–organic frameworks of MTN topology

Excess adsorption of cyclohexanone, cyclohexanol and tert-butanol over metal–organic frameworks Cr-MIL-100 and structurally close Cr-MIL-101 from n-hexane was measured at room temperature. Apparent adsorption equilibrium constants were calculated under the assumption of monolayer adsorption. Two types of adsorption centers turned out to be enough to build a model of experimental isotherms for cyclohexanone, cyclohexanol, and tert-butanol. The first type of centers is characterized by a high value of adsorption equilibrium constant, 1 × 103–3 × 103, and the fraction of such centers is ca. 0.2 for cyclohexanone and tert-butanol and ca. 0.4 for cyclohexanol. The second type of centers possesses a relatively low affinity to guest molecules (the adsorption equilibrium constant varies from 1.8 to 9) and occupies the rest of the surface of the adsorbent The centers with a strong affinity to oxygen-containing guests are associated with chromium atoms within MIL framework.