Methane Sorption in Nanoporous Metal−Organic Frameworks and First-Order Phase Transition of Confined Methane

Abstract

Nanoporous metal−organic frameworks (MOFs) are promising materials for methane sorption and storage. Using neutron powder diffraction, we have directly determined the methane sorption sites in two prototypical MOF materials: zeolitic imidazolate framework-8 (ZIF-8, Zn6(N2C4H5)12) and metal−organic framework-5 (MOF-5, Zn4O13(C8H4)3). The primary methane adsorption sites are associated with the organic linkers in ZIF-8 and the metal oxide clusters in MOF-5. Methane molecules on these primary sites possess well-defined orientations, implying relatively strong binding with the framework. With higher methane loading, extra methane molecules populate the secondary sites and are confined in the framework. The confined methanes are orientationally disordered and stabilized by the intermolecular interactions. Below 100 K a maximum of ∼18 and ∼24 methane molecules per formula unit can be stored in ZIF-8 and MOF-5, corresponding to ∼20 and ∼50 wt % storage capacities, respectively. An unusual reversible methane-induced structural phase transition in MOF-host lattice is observed at ∼60 K in both ZIF-8 and MOF-5 due to strong intermolecular interaction between confined methane molecules in the pores of the host lattice.

Understanding the adsorption mechanism of noble gases Kr and Xe in CPO-27-Ni, CPO-27-Mg, and ZIF-8

“…For comparison, the maximal uptake of methane CD 4 molecules was found to be 3 CD 4 molecules per Zn atom. 58 Also the experimentally determined positions for both Kr and Xe atoms correlate well with theoretically simulated positions for Ar atoms, 59 and results of grand canonical Monte Carlo simulations. 12 The adsorption of noble gases by MOFs is based on the polarizability of both possible adsorption sites of the MOF and the adsorbed noble gases.…”

Adsorption of CO2, CH4, and N2 on Zeolitic Imidazolate Frameworks: Experiments and Simulations

“…Our calculations agree with a recent experimental study in which the main adsorption sites for CH 4 in ZIF-8 were determined by neutron powder diffraction (NPD), difference Fourier, and Rietveld analysis. [32] We can superimpose the sites reported in Ref. [32] on the CH 4 adsorption sites in Figure 7 a.…”

van der Waals density functional study of CO2binding in zeolitic imidazolate frameworks

“…Experimental measurements have demonstrated a pronounced dependence on ZIF chemical compositions and structural topologies, for the equilibrium adsorptions of H 2 , CO 2 , CH 4 , N 2 , and CO gases and their mixtures 1,[7][8][9][10][11] . Neutron-scattering, spectroscopy measurements, and Monte-Carlo computer simulations [12][13][14] have provided important insights related to these results, by demonstrating that the gas molecules bind primarily in sites localized near the atoms in the imidazolate linkers in ZIF compounds 8,13,[15][16][17][18][19][20][21][22][23][24][25][26][27] . The magnitudes of the binding energies underlying the interactions between the gas species and ZIF linkers can be estimated based on the measured isosteric heat of adsorption, e.g.…”