Unique adsorption and desorption behaviour of ammonia gas at heating temperature using the Prussian blue analogue Zn3[Co(CN)6

Abstract

Nanoparticles (NPs) of Zinc hexacynanocobaltate (ZnHCCo) were synthesised and characterized by analytical measurements. Thermogravimetric analysis revealed great thermal stability of the ZnHCCo NPs up to ~350 °C, even under ambient air conditions including water and oxygen. Ammonia (NH3) adsorption isotherms revealed that the ZnHCCo NPs exhibited a great adsorption capacity at room temperature. This was maintained at the heating temperatures 100–250 °C, in which the isotherm displayed special hysteresis curves in the adsorption/desorption processes. Based on these results, the ZnHCCo NPs were applied to NH3 gas adsorption/desorption in pressure (PSA) and temperature (TSA) swing adsorption processes by using a gas cell of FTIR, to confirm that both processes are possible. Characterisation before/after NH3 exposure, by in-situ FTIR and X-ray powder diffraction (PXRD) spectroscopy under dry or humid conditions, provided an understanding of the unique NH3 adsorption/desorption behaviour. The PXRD measurements suggested a crystal structure change of the ZnHCCo NPs after NH3 adsorption. Obtained results suggested a strong NH3 affinity of ZnHCCo, even though the structure was altered by the process. Owing to its high and unique ability, usage of non-rare metals, and cost-effectiveness of zinc, ZnHCCo shows a possibility as an adsorbent for NH3 in practical applications.