Influence of the Presence of Different Alkali Cations and the Amount of Fe(CN) 6 Vacancies on CO 2 Adsorption on Copper Hexacyanoferrates.

The CO ₂ adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogravimetric analysis. Compositions of prepared phases were verified by energy-dispersive X-ray spectroscopy, infra-red spectroscopy and powder X-ray diffraction. The influence of different alkali cations in the cubic Fm 3 m structures was investigated for nominal compositions A _{2 / 3} Cu[Fe(CN) ₆ ] _2/3 with A = vacant, Li, Na, K, Rb, Cs. The Rb and Cs compounds show the highest CO ₂ adsorption per unit cell, 3.3 molecules of CO ₂ at 20 C and 1 bar, while in terms of mmol/g the Na compound exhibits the highest adsorption capability, 3.8 mmol/g at 20 C and 1 bar. The fastest adsorption/desorption is exhibited by the A -cation free compound and the Li compound. The influence of the amount of Fe(CN) ₆ vacancies were assessed by determining the CO ₂ adsorption capabilities of Cu[Fe(CN) ₆ ] _1/2 ( Fm 3 m symmetry, nominally 50% vacancies), KCu[Fe(CN) ₆ ] _3/4 ( Fm 3 m symmetry, nominally 25% vacancies), and CsCu[Fe(CN) ₆ ] ( I -4 m 2 symmetry, nominally 0% vacancies). Higher adsorption was, as expected, shown on compounds with higher vacancy concentrations.
Competing Interests: The authors declare no conflict of interest.