Interpretation of the Role of Composition on the Inclusion Efficiency of Monovalent Cations into Cobalt Hexacyanoferrate

Abstract

Cobalt hexacyanoferrate of various compositions was prepared in flow mode and the role of the vacancy on the structure, thermogravimetric (TG) properties, and the adsorption efficiency was studied. The material, NayCo[Fe(CN)6]1−x⋅z H2O, with a minimum vacancy of x=0.014 to the highest x=0.47, was obtained. The TG‐differential scanning calorimetry (DSC) profile showed a distinct influence of the vacancy on the water release temperature. Materials with x>0.35 showed a smooth release of water at a relatively lower temperature. However, for the materials with x<0.35, water release took place in multiple steps, suggesting the existence of various forms of water. The FTIR profiles supported the existence of free and bonded water molecules. However, the materials with multiple water peaks in the FTIR spectra showed a shift of the major XRD peaks when heated at 285 °C in N2 atmosphere. Regarding the effect of the vacancy on the adsorption behavior, for NH4, the adsorption was found to be proportional to the number of Na atoms in the material, confirming the ion‐exchange process. On the contrary, the materials with low vacancy and high Na content showed nominal Cs adsorption capacity. Interestingly, the K adsorption capacity was found to be in between that of the other two ions. This means the ionic size decides the rate of placement into the interstitial sites. For larger ions like Cs, the ease of percolation via the vacancy decides the overall adsorption efficiency.

Self-Assembly and Properties of a Discrete Water-Soluble Prussian Blue Analogue FeII/CoIIICube: Confinement of a Water Molecule in Aqueous Solution

“…No reverse potassium-to-sodium ion exchange was observed upon the addition of excess NaClO 4 to the potassium cube. Despite the fact that some PBAs possess unique Cs + selectivity, 10,15,17,18 our cube shows a clear preference for K + . No spectroscopic changes were observed upon the addition of cesium salts to any of the cages, a feature that could be attributed to the relatively small size of the {Fe 2 Co 2 } faces of the cube (see the Supporting Information).…”

Molecular Approach to Alkali-Metal Encapsulation by a Prussian Blue Analogue FeII/CoIIICube in Aqueous Solution: A Kineticomechanistic Exchange Study

“…The cavity size of the structures indicated in Figures and clearly shows that an empty possibility is not feasible. Although the possible existence of encapsulated water clusters inside of the cubic structure cannot be ruled out, , proton exchange with the deuterated D 2 O solvent makes them undetectable by 1 H NMR. Nevertheless, the absence of any positive charge inside a highly negative cavity would point to a labile exchange of any Lewis base such as water.…”

Prussian Blue: A Safe Pigment with Zeolitic-Like Activity

“…However, ammonia removal is usually faced with selectivity concerns because the application area often contains chemical fertilizers or biomass matrices, making selectivity an important factor when choosing the adsorbent. Parajuli [78]. These important differences between PB and the indicated PBA have their origin in the switch of the metal in the ligand, the coordination metal, and the monovalent ion, that modify the crystal parameters.…”

“…Parajuli et al synthesized a PBA, copper hexacyanoferrate, capable of capturing dissolved NH4 + and NH3 simultaneously in the presence of high concentrations of potassium [77]. Zhang et al have prepared a PBA, a sodium salt of cobalt hexacyanoferrate, with an adsorption capacity for NH4 + higher than that of K + and Cs + [78]. These important differences between PB and the indicated PBA have their origin in the switch of the metal in the ligand, the coordination metal, and the monovalent ion, that modify the crystal parameters.…”