Trends in the Adsorption of Volatile Organic Compounds in a Large-Pore Metal−Organic Framework, IRMOF-1

Abstract

Metal-organic frameworks have been proposed as useful sorbents for the capture of a variety of compounds. In this work, inverse gas chromatography (IGC) utilizing micropacked capillary columns was used to probe the adsorption of more than 30 volatile organic compounds (VOCs) on IRMOF-1. In an attempt to study the effect of structural degradation upon VOC adsorption, multiple samples of IRMOF-1 with widely ranging properties were investigated. Trends in the differential enthalpies and equilibrium constants for the adsorption of VOCs were determined on the basis of the molecular properties of the adsorbate and the structural properties of the MOF sample. The results indicate that samples of IRMOF-1 that are affected by a moderate amount of structural degradation interact with adsorbed species more strongly than does a sample with fewer defects, resulting in higher heats of adsorption. Samples of IRMOF-1 with specific surface areas of around 1000 m(2)/g show heats of adsorption for alkanes that are higher than those estimated previously via Monte Carlo calculations. Although the data for nonpolar (and weakly polar) species showed many of the anticipated trends for the interactions with IRMOF-1, the equilibrium behavior of polar VOCs did not correlate well with the molecular properties of the adsorbate (i.e., vapor pressure and deformation polarizability), leaving some uncertainty about the nature of the interaction mechanism. The equilibrium data and the heats of adsorption were found to fit well to a small group of molecular descriptors through the application of the Abraham linear free-energy relationship, thus providing insight into the complex interactions between the MOF structure and the VOC compounds. Hydrogen bonding interactions were determined to be the primary contributors to specific interactions between adsorbates and the MOF surface. Size exclusion also seems to play a role in the adsorption of larger species. These results show that the interaction of VOCs with MOFs is more complex than previously assumed and that more work is needed to probe the mechanisms of these processes.

Metal‐Organic Frameworks: Harmful Gas Removal

“…The current adsorbents used to remove VOCs, such as carbonaceous adsorbents, zeolites, silicates, and polymeric resins, are limited by problems related to rigorous regeneration conditions, slow kinetics, low surface areas, and unacceptable stability. 28 Metal-organic framework materials have been proposed to remove VOCs, though compared to small molecules, such as H 2 , CH 4 , and CO 2 , only a limited number of studies reported about the adsorption of larger organic molecules in MOFs. A systematic study has been done by Luebbers et al 28 on the use of IRMOF-1 to adsorb a variety of VOCs, mainly alkanes, alkylbenzenes, and some common organic solvents.…”

“…28 Metal-organic framework materials have been proposed to remove VOCs, though compared to small molecules, such as H 2 , CH 4 , and CO 2 , only a limited number of studies reported about the adsorption of larger organic molecules in MOFs. A systematic study has been done by Luebbers et al 28 on the use of IRMOF-1 to adsorb a variety of VOCs, mainly alkanes, alkylbenzenes, and some common organic solvents. It was noted that the adsorption enthalpies vary linearly with the increase in chain length for a series of n-alkanes and alkylbenzenes.…”

“…These VOCs are a threat to human health, as well as to the environment, because of their involvement in photochemical pollution. 28 The fourth class of harmful gases to be discussed are the radioactive gases potentially emitted during nuclear fuel reprocessing and reactor operations. Radioactive Kr, Xe, and I are the most common radioactive gases potentially found in a typical off-gas from a nuclear power plant.…”

Topological Analysis of Void Space in Phosphate Frameworks: Assessing Storage Properties for the Environmentally Important Guest Molecules and Ions: CO2, H2O, UO2, PuO2, U, Pu, Sr2+, Cs+, CH4, and H2

“…In light of recent environmental concerns, much of the focus for guest incorporation within porous materials has centered on the storage of possible alternative fuels such as CH 4 and H 2 , 1-6 pollution-control reservoirs for CO 2 , [7][8][9] storage of dangerous waste products like volatile organic compounds [10][11][12] and radioactive waste, [13][14][15][16] or water adsorption for sanitation measures. [17][18][19] Initial assessment of the suitability of potential new materials for such encapsulation applications can reasonably focus on the analysis of void space within their crystalline solidstate frameworks.…”

High‐Separation Performance of Chromatographic Capillaries Coated with MOF‐5 by the Controlled SBU Approach

“…[4] To date, several investigations of MOF-based chromatography have been published, mainly addressing HPLC and packed-column applications. [5][6][7] However, capillary-based gas chromatography has only been addressed by the work of Gu and Yan, who deposited MIL-101 and ZIF-8 onto fusedsilica columns by evaporating the solvent from suspensions of MOFs, with which they separated xylene isomers and linear alkanes. [8,9] Of all of the established chromatographic capillaries, socalled PLOT columns (porous layer open tubular) coated with materials such as porous alumina or polystyrene, typically possessing pore sizes in the range of macro-and mesopores, come closest to the concept of an MOF-coated capillary, although their pore sizes are significantly larger than those of MOFs.…”