Gas Adsorption Properties of the Chromium-Based Metal Organic Framework MIL-101

Abstract

MIL-101, a chromium-based metal organic framework, is known to adsorb large amounts of green house gases such as CO 2 and CH 4 . Measurement, analysis, and modeling of the pure gas adsorption isotherms of desired gases are necessary for any attempt to use this framework for separation/storage applications. In an attempt to understand adsorption characteristics of this framework, pure gas adsorption properties of CO 2 and CH 4 along with C 3 H 8 , SF 6 , and Ar were measured at three temperatures 283, 319, and 351 K using a standard gravimetric method. The adsorbates were chosen based on their physical characteristics such as polarizability and quadrupole moment. Dual site Langmuir (DSL) isotherm proved to be useful for modeling adsorption of gases on this type of materials that are known to have heterogeneity. Active metal centers and sites inside the pores of supertetrahedra act as major locations for adsorption. Analysis of enthalpy of adsorption using the DSL model revealed that, for all gases, it initially decreases with loading and remains constant thereafter. For all gases considered, the enthalpies of adsorption were found to be lower than those on purely siliceous zeolite such as silicalite, suggesting that only moderate interaction exists between the gas and the MIL-101 framework. The enthalpy of adsorption at zero coverage and the logarithm of Henry's constant were found to be linear functions of polarizability of the adsorbate.

Effect of Textural Properties on the Adsorption and Desorption of Toluene on the Metal-Organic Frameworks HKUST-1 and MIL-101

“…In addition, there were eight small pockets of 5.3 Å around each cage (Chui et al 1999). However, the MIL-101 crystal had two kinds of pores with sizes of 12 Å and 16 × 14.5 Å estimated from its crystal structure (Férey et al 2005). Obviously, the pore sizes of the HKUST-1 crystal were smaller compared with the MIL-101 crystals.…”

“…The HKUST-1 crystal had three-dimensional inter-sectional pores with a window size of 9 Å and a cage size of 10.8 Å. In addition, there were eight small pockets of 5.3 Å around each cage (Chui et al 1999). However, the MIL-101 crystal had two kinds of pores with sizes of 12 Å and 16 × 14.5 Å estimated from its crystal structure (Férey et al 2005).…”

Ammonia adsorption and its effects on framework stability of MOF-5 and MOF-177

“…Millward and Yaghi [20] measured CO 2 uptake over various types of IRMOFs, and MOF-177 was proved to be the best adsorbent for CO 2 at elevated pressures and ambient temperatures. Chowdhury et al [21] performed CO 2 , CH 4 and SF 6 adsorption on MIL-101. Britt et al [22] employed Mg-MOF-74 for selective separation of CO 2 from CH 4 .…”

Heterogeneity of Adsorption Sites and Adsorption Kinetics of n-Hexane on Metal–Organic Framework MIL-101(Cr)

“…Table 3 lists the desorption activation energy E d of n-hexane corresponding to two types of adsorptive sites on the MIL-101 sample. The two desorption activation energies are 39.41 and 86.69 kJ·mol −1 , corresponding to the n-hexane desorption on the pore surfaces of framework and on the open Cr 3+ metal centers, respectively [38]. A comparison for the desorption activation energies of n-hexane on two types of adsorption sites indicates that the interaction between n-hexane and open Cr 3+ metal sites is much stronger than that between n-hexane and surfaces of framework pores.…”

“…This is a direct reflection of the surface energy heterogeneity on the MIL-101 frameworks for n-hexane adsorption. These two types of sites are considered to correspond to the pore surfaces of framework and open Cr 3+ metal centers [38]. The first desorption peak at lower temperature comes from n-hexane desorption from the pore surfaces of MIL-101, while the second at higher temperature is for n-hexane desorption from unsaturated Cr 3+ mental centers.…”