In Situ Hyperfine Spectroscopy for Sensing Dihydrogen Isotopologues on the ZIF-8 Framework

Abstract

An in situ pulsed electron paramagnetic resonance spectroscopy approach based on three-pulse electron spin echo envelope modulation has been implemented to monitor the adsorption of deuterium (D₂) and deuterium hydride (HD) gases into the pores of ZIF-8 on a local microscopic scale within the environment of paramagnetic spin probes such as TEMPO radicals and Cu²⁺ ions. The desorption of D₂ could be followed up to a temperature of 40 K employing the TEMPO probe, where the majority of the gas has left the pores of ZIF-8. In contrast, H₂ gas was not detectable at 20 K with this technique due to the predominant para-hydrogen form. The approach utilizing TEMPO radicals can be used as reliable probes to sense weakly coupled D₂ or HD adsorbed into the pores of ZIF-8 without interference from the magnetically active ¹⁴N nuclei from the organic linker as we observed for HD adsorption on the Cu²⁺-doped ZIF-8 material.