# Prussian Blue: A Safe Pigment with Zeolitic-Like Activity
## 4 Adsorption Properties of PB
### Adsorption of Cesium
This is an environmentally friendly, time-saving, and efficient ion extraction technique that has been proposed for the extraction of target ions in trace amounts electrochemically regulating the redox state of electroactive film to control ion adsorption and desorption processes reversibly [52]. Table 1 summarizes the most relevant adsorption properties of magnetic PB structures. An original, although rather complex, way to adsorb Cs\({}^{+}\) has been reported by [PERSON] et al. [53]. They prepared extruded liposomes hydrating the lipid with a hexaciazo-ferrate (III) salt. Then, the liposomes were treated with the antifungal polyene antibiotic amphotericin B (AmB) and with Mohr's salt ((NH\({}_{4}\))\({}_{2}\)Fe(SO\({}_{4}\))\({}_{2}\)\(\cdot\)6H\({}_{2}\)O). The salt entered the aqueous inner of the liposome through the channels formed by AmB in the bilayer and PB was formed inside the liposome. As main conclusion, the authors pointed out that the liposomes showed higher Cs\({}^{+}\) adsorption capacity than the PB nanoparticles in aqueous media. In order to enhance the adsorption properties of PB composites, usually formed by nanoparticles with cubic morphology, a three-dimensional hierarchical PB constructed by interconnected ultrathin nanosheets was prepared by [PERSON] et al. [54]. Nitrogen sorption analysis showed a drastic increase in the nitrogen adsorption-desorption isotherm of 3D hierarchical structures in comparison to cubic PB microcrystals. These results may indicate more exposed surface of nanosheets than cubic PB. The adsorption capacity of Cs\({}^{+}\) was about 200 mg/g. PBA have been used to regenerate nuclear-waste-contaminated soil. Cesium can interact with swelling 2:1 type clay. The oxygen atoms in the inner layer of 2:1 type clay usually binds with potassium. Cesium can replace potassium and interact with clay minerals, resulting in almost irreversible contamination of the soil [55]. First, is necessary to release Cs\({}^{+}\) from the clay, and then to adsorb the released Cs\({}^{+}\). [PERSON] et al. have used ionized chitosan that, similar to other cationic polyelectrolytes, increases the interlayer spacing of the clay, allowing desorption of Cs\({}^{+}\). Then, they utilized PBA functionalized magnetic microgels to adsorb Cs\({}^{+}\) from the solution after the treatment [56]. The microgels could be regenerated using NaOH (0.1 M) as desorb agent and recycled magnetically while keeping the adsorption capacity constant (149.70 mg/g) after multiple times of use. The reported studies about the adsorption of Cs by PB or PBA coincide in that this adsorption is a highly selective process that can be described by a pseudo-second-order kinetic model; this implies that the Cs\({}^{+}\) was chemisorbed and the adsorption rate of the PB composite depended on the active sites rather than the concentration of Cs\({}^{+}\) in the solution [39]. The equilibrium adsorption isotherm process can be explained in most of the cases by the Langmuir adsorption isotherm model [57]. However, a few studies pointed out that either the Freundlich adsorption isotherm model [58] or the Temkin model [59] agreed with the obtained isotherm [47; 60]. Having in mind that the adsorption process is depending on many factors (pH, adsorbent dose or equilibrium time, among others), such discrepancies do not appear as strange. The major weak point of PB is its instability in alkaline solutions, which causes hazardous cyanide contamination [5; 61]. The maximal concentration of total cyanide in drinking water is 0.07 mg/L according the guidelines established by WHO. To convert PB stable in alkaline solutions, [PERSON] et al. have added CuSO\({}_{4}\) to PB so that divalent copper ions act as a shielding element at a high concentration of hydroxide ions [62]. [PERSON] et al. observed that the Cs\({}^{+}\) were completely diffused onto the PB composite (aerogel formed by cellulose) [39]. This is a prerequisite for a good absorbent material.