Fig 1. Example Metal Organic Framework (MOF). The yellow sphere represents the pore space within the crystal structure.
Metal-organic frameworks are crystalline solids with very high pore volumes and surface area, and as such, many are candidates for gas storage and gas separation. Theoretically the pore size can be calculated from X-ray diffraction and other scattering techniques.
However, gas sorption has the unique ability to directly probe the pore space thereby revealing additional information about the true nature of the material (is the porosity accessible?), and can additionally reveal structural changes in non-rigid materials. As such it can confirm the suitability, or not, of candidate materials for such gas storage applications.
Which instrument is used?
For this type of sample, the Autosorb iQ-MP and XR are normally used. These gas sorption analyzers feature both a fully integrated high vacuum system and very low pressure measuring capability required for measuring the adsorption process associated with micropore filling and can be used with a variety of suitable probe gases at a variety of temperatures.
These instruments are programmed to measure the gas adsorption isotherm from extremely low relative pressure (P/P0) up to near saturation (P/P0 = 1). In this way they automatically acquire the raw data from which the micropore distribution (size and volume) is calculated.
Which samples were analyzed?
As examples, a copper MOF and an indium soc- MOF with high adsorption capacity for hydrogen, carbon dioxide and methane were analyzed. The as-synthesized Cu-MOF had previously undergone methanol extraction and been evacuated to remove the solvent to reveal the thermally stable (up to 250°C), open pore structure.
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This information has been sourced, reviewed and adapted from materials provided by Quantachrome Instruments.
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