High Adsorption Capacities and Two-Step Adsorption of Polar Adsorbates on Copper–Benzene-1,3,5-tricarboxylate Metal–Organic Framework

Abstract

This work discusses the adsorption of polar and apolar molecules on the copper–benzene-1,3,5-tricarboxylate (Cu–BTC) metal–organic framework. Vapor phase adsorption isotherms of various polar adsorbates such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-hexanol, water, acetone, acetonitrile, tetrahydrofuran, and N,N-dimethylformamide, as well as some apolar adsorbates such as n-hexane, n-heptane, m-xylene, and cyclohexane, on the Cu–BTC framework are presented. We show that water exposure of the Cu–BTC framework has an adverse effect on the uptake capacity. However, with minimized water exposure, we find high adsorption capacities, exceeding 0.65 cm3/g for all adsorbates with the exception of water, and we show that small polar adsorbates exhibit a two-step adsorption behavior. This behavior is further studied using molecular simulation and proposed to occur due to the presence of the various Cu–BTC cages. The cages containing the exposed coordinatively unsaturated copper sites have a more polar character, while the other cages behave in a more apolar way, causing a two-step adsorption behavior depending on the character of the adsorbate.

Enhancement effect of lithium-doping functionalization on methanol adsorption in copper-based metal-organic framework

“…However, the adsorption over the entire pressure range should be overestimated by simulation due to the usage of idealized models in the calculations. The obtained results suggest that the simulation underestimates the adsorption at low pressures near the copper CUS, consistent with the discussion of methanol adsorption on Cu-BTC reported by Van Assche et al (2013), and the simulation model still needs to be refined by adequate experimental data. However, such a shortcoming of the simulations does not hinder the accurate description of the preferential binding sites as well as the electrostatic potentials in the following section.…”

“…Using a spherical cutoff radius of 13 Å in the simulations, Cu-BTC and Cu-BTC-Li were treated as rigid frameworks with all atoms frozen at their crystallographic positions. The assumption of rigidity is often made in the simulating adsorption on Cu-BTC (Jose Gutierrez-Sevillano et al, 2013;Van Assche et al, 2013), as the framework flexibility has been proved to be negligible on the adsorption of small gases (Skoulidas, 2004). In addition, Ewald summations were used to calculate Coulombic interactions between the adsorbate and framework atoms.…”

“…Van Assche et al (2013) reported the well-pronounced two-step adsorption isotherms of small alcohols (methanol and ethanol) on Cu-BTC, owing to the sequential adsorption behavior of the adsorbates. Jose et al (Jose Gutierrez-Sevillano et al, 2013) suggested the blockage of polar cages by using ionic liquids that could enhance the alcohol adsorption over Cu-BTC in aqueous mixtures.…”

The surface barrier phenomenon at the loading of metal-organic frameworks

“…27), which has to be augmented by the density of ethanol contained in the pores. This value amounts to 0.56 g per 1 g HKUST-1 MOF 38 . After activating the sample at 65°C in a flow of pure argon (with a flow rate is 100 ml min À 1 ) overnight, the uptake of the guest molecules was studied again with the QCM.…”

Removal of Confined Ionic Liquid from a Metal Organic Framework by Extraction with Molecular Solvents

“…[34][35][36][37] The present paper reports a systematic study of confined molecular solvents in a MOF. The solvents of interest are acetone, isopropanol, methanol, and the IL 1-ethyl-3-methylimidazolium ethyl sulfate (EMIM-ETS).…”