Open-framework chalcogenides demonstrate potential to be applied in hydrogen generation from water owing to their porous structure and semiconducting property. Here, we report the hydration energetics study on of a series of alkali metal ion-exchanged chalcogenides (UCR-20s) using water adsorption calorimetry coupled with structural and spectroscopic analyses. Specifically, our study shows that water adsorption on Li+ and Na+ UCR-20s results in typical Type I isotherm suggesting microporosity, while hydration of K+, Rb+ and Cs+ UCR-20s leads to Type IV isotherms. The most exothermic near-zero coverage enthalpy of water adsorption are -57, -62, -52, -57, and -46 kJ per mole of water for Li+, Na+, K+, Rb+ and Cs+ UCR-20s, respectively, indicating relatively weak interactions between the extra-framework cations and water molecules. As the water uptake increases, the differential enthalpy of adsorption curves for Li+ and Na+-UCR-20s present no enthalpy plateau. In sharp contrast, the hydration energetics of K+, Rb+ and Cs+-UCR-20s appear to feature two plateaus, which strongly suggest different water – framework interaction mechanisms. We also compare the hydration mechanisms of these UCR-20s with that of alkali metal ion-exchanged zeolites A, which share a similar structure.

Confinement of water in ion-exchanged chalcogenide UCR-20

2019 Spring National Meeting

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