# Prussian Blue: A Safe Pigment with Zeolitic-Like Activity
## 4 Adsorption Properties of PB
### Adsorption of Cesium  
First, the Chernobyl nuclear reactor disaster on 26 April 1986, and then the tsunami that caused the Fukushima nuclear accident on 11 March 2011 triggered a massive release of radioactive elements into the environment. The contamination by cesium isotopes, such as \({}^{134}\)Cs and \({}^{137}\)Cs, was one of the major environmental concerns. Whereas the half-live of the \({}^{134}\)Cs isotope is 2 years, the radioisotope \({}^{137}\)Cs has a long half-life (30.17 years). Cs is a strong emitter of gamma rays, which is a serious threat to health since due to its high solubility, high mobility, and easy incorporation into living organisms (it behaves similarly to K\({}^{+}\) and Na\({}^{+}\) in the biological behavior profile). Cs\({}^{+}\) may cause various human diseases. To date, methods such as chemical precipitation, extraction, volatilization, adsorption, and ion exchange have been proposed for cesium removal [21]. Adsorption and ion exchange both seem to be the most simple, economical, and effective techniques. One of the most important sorbents developed for the selective removal of Cs\({}^{+}\) are the nano- and microparticles formed by PB or PBA. As indicated previously, PB is an FDA-approved  
Figure 2: (**a**) Adsorption–desorption isotherm for BET surface area measurement. The hysteresis loop appearing at high \(P/P_{0}\) is characteristic of a type IV isotherm; (**b**) pore diameter. drug used in clinics for the treatment of radioactive exposure. The drug (trade name Radiogardase) consists of 500 mg of PB in gelatin capsules. The dose for adults is 3 g (six capsules) taken orally three times a day. The drug works by trapping Cs in the intestine, so that they can be passed out of the body in the stool rather than be readsorbed [22]. The proton/cation exchange, surface adsorption, and mechanical trapping within the crystal structure are the main mechanisms for decontamination of Cs by PB. For soluble PB, it has been reported that Cs\({}^{+}\) are adsorbed on PB via ion exchange with K\({}^{+}\) that are present in the cubic lattice of PB [23]. However, the Cs\({}^{+}\) sorption mechanism by the insoluble PB-based sorbents is not still elucidated. It is likely that the mechanism is composed by various independent phenomena: ion exchange, physical cesium ion entrapment, and physical sorption. The physical adsorption would imply the physical sorption of hydrated Cs\({}^{+}\) into the regular lattice spaces surrounded by the Fe\({}^{2+}\)-CN-Fe\({}^{3+}\) bonds. The ion-exchange mechanism needs the lattice to present defect sites, where Cs\({}^{+}\) is chemically adsorbed by means of proton exchange with proton elimination from the coordination water molecules [24]. The contribution of large defects in the adsorption of Cs\({}^{+}\) ions has also been demonstrated in PBA [25]. [PERSON] et al. have deduced that the Cs adsorption by KCu[Fe(CN\({}_{6}\)) was governed by three mechanisms: (a) mainly ion exchange between Cs\({}^{+}\) and K\({}^{+}\), (b) percolation of Cs\({}^{+}\) cations through vacancy sites from the surface, and (c) proton exchange with Cs\({}^{+}\) at the range of low K\({}^{+}\) incorporation [26]. The pioneering employment of PBA for cesium decontamination was proposed around twenty years ago by [PERSON] et al. using granular potassium cobalt hexacyanoferrate (K\({}_{2}\)[CoFe(CN)\({}_{6}\)] [27]. [PERSON] et al. verified that the adsorption capacity of insoluble PB was higher than that of soluble PB [24]. As indicated in the Introduction, the coordination water molecules are common in the structure of insoluble PB, and this could be the reason of this different adsorption ability between both types of PB. [PERSON] et al. observed that the adsorbed Cs\({}^{+}\) ions in PB were distributed homogenously along with the Fe ions throughout the PB nanoparticles according to the EDS mapping obtained from scanning transmission electron microscope images (STEM_HAADF images) using a high-angle annular dark field (HAADF) detector.