Simultaneous neutron powder diffraction and microwave dielectric studies of ammonia absorption in metal–organic framework systems

Abstract

Ammonia absorption has been investigated in metal-organic frameworks (UiO-67, HKUST-1 and CPO-27-Co) using custom-built apparatus that allows simultaneous neutron powder diffraction (NPD), microwave dielectric characterisation and out-gas mass spectroscopy of solid-state materials during ammonia adsorption. Deuterated ammonia was flowed through the sample and absorption monitored using mass flow meters and mass spectroscopy. Argon gas was then flowed through the ammoniated sample to cause ammonia desorption. Changes in structure found from NPD measurements were compared to changes in dielectric characteristics to differentiate physisorbed and metal-coordinated ammonia, as well as determine decomposition of sample materials. The results of these studies allow the identification of materials with useful ammonia storage properties and provides a new metric for the measurement of gas absorption within mesoporous solids.

Microwaves in Chemistry

“…New developments in microwave spectroscopy have been reviewed, including in dielectric measurements using cavity perturbation applied to the real-time measurement of ammonia storage in halide salts [71] and in metal-organic frameworks (MOFs) [72] for hydrogen storage applications. In microwave magnetic spectroscopy we have highlighted developments in electron paramagnetic resonance, with new methods using loop-gap resonators and dual mode cavities for simultaneous microwave heating [3], [80].…”

“…Recently we have developed instrumentation for the ISIS POLARIS neutron diffractometer at the UK's Science and Technology Facilities Council's Rutherford Appleton Laboratory, for real-time, simultaneous dielectric (microwave) and structural (neutron diffraction) characterization of absorption processes in solids [71], [72]. The aluminum cylindrical host cavity operates in its TM 010 mode at 2.45 GHz (internal diameter 92 mm, internal length 40 mm), with high electric field on its axis, where the sample is placed.…”

“…The system has been applied to the real-time measurement of ammonia storage in halide salts [71] and in metal-organic frameworks (MOFs) [72]. Ammonia is well known as a potential hydrogen storage material owing to is very high gravimetric (17.8 wt%) and volumetric (121 kg/m 3 ) H 2 density [73].…”

Simultaneous neutron powder diffraction and microwave characterisation at elevated temperatures

“…Such methods have been successfully used to investigate a range of samples, from simple compounds such as metal salts, 5,6 to complex systems such as metalorganic frameworks (MOFs). 7 MOFs are a class of porous crystalline materials which have been investigated for a range of applications including storage of alternative fuels, [8][9][10][11] gas separations, [12][13][14] chemical sensing, [15][16][17] and catalysis. [18][19][20] In order to create void spaces required for sorptionbased applications, adsorbed molecules, such as solvents from the synthesis and water from air, must be removed from the pores of the material.…”

ZIF-8 Degrades in Cell Media, Serum, and Some—But Not All—Common Laboratory Buffers

“…Over the preceding two decades, metal-organic frameworks (MOFs) have been proposed for a number of industrial applications in catalysis, [1][2] and separations [3][4][5] and have more recently emerged as promising materials for biological sensing 6 and drug delivery. [7][8][9] The applications for drug delivery have run from proposed systematic delivery of small molecules to the slow release of proteins in vivo.…”