Role of water molecules in the decomposition of HKUST-1: Evidence from adsorption, thermoanalytical, X-ray and neutron scattering measurements

Abstract

HKUST-1 is a strictly microporous crystalline metal organic framework with pore sizes of 5, 11, and 13.5 Å. Detailed gas adsorption measurements show that its adsorption capacity for water at 20 °C is higher than that for nitrogen at -196 °C, and far exceeds that for methane at 0 °C. Extended exposure to water vapour at high relative humidity, or consecutive adsorption-desorption cycling of water vapour, destroys both the MOF crystal structure and its adsorption capacity, after a reduced number (< 5) of cycles. Destruction proceeds through mesoporous defects that open within the crystal structure, as attested both by the development of hysteresis in the adsorption isotherms and by changes in the small angle X-ray scattering pattern. In the pristine crystal, the structure of the water in the micropores closely resembles that of bulk liquid water. Small angle neutron scattering demonstrates that water is adsorbed preferentially over methane, and that the size of the spherical cavities occupied by the adsorbed water molecules in the intact crystal is consistent with the known pore size structure in this system.

Elucidating the Drug Release from Metal–Organic Framework Nanocomposites via In Situ Synchrotron Microspectroscopy and Theoretical Modeling

“…10 However, HKUST-1 is a water-sensitive MOF, which degrades rapidly in the presence of humidity. [11][12] In this study, we demonstrate that 5-FU@HKUST-1 can be easily combined with a biocompatible polymer like polyurethane (PU) to fabricate the 5-FU@HKUST-1/PU composites that could suppress the burst effect. [13][14][15] The presence of a polymeric matrix can significantly enhance the aqueous stability of certain MOFs that have a huge potential for hosting a plethora of drug molecules, but suffer from poor water stability.…”

Graphene Oxide Protected Copper Benzene-1,3,5-Tricarboxylate for Clean Energy Gas Adsorption

“…Our previous work [ 9 ] revealed the destructive effect of water vapor on the structure of solvent-free HKUST-1. In order to study the influence of the GO as a potential protecting associate component under humid conditions, the behaviour of the pure HKUST-1 and the selected composite was investigated.…”

“…By contrast, activation at 110 °C removes all the water molecules, including those that decorate the “free” copper sites and are thus part of the crystal structure. The latter treatment leaves behind naked copper sites that are extremely vulnerable when re-exposed to water [ 9 ].…”

“…These are therefore released only at elevated temperatures, above 100 °C. As with HKUST_1, five different water binding sites were also recognised in the composite material [ 9 ]. The complete removal of the water during the activation leaves behind reactive Cu sites and easily accessible MOF porosity [ 9 ].…”

“…The release of the adsorbed solvent molecules from the entire pore volume, so-called activation, is required to achieve maximum adsorption capacity, which is essential in gas storage [ 8 ]. However, this activation significantly reduces the stability of the MOF in the presence of water vapor and challenges its application [ 9 ].…”