Prussian blue-functionalized magnetic nanoclusters for the removal of radioactive cesium from water

Radioactive cesium (¹³⁷Cs) is the most dangerous radioactive contaminant associated with nuclear fallout and radioactive liquid waste. In 2011, a large amount of radioactive cesium unfortunately leaked and spread over a large area of the water environment proximal to the nuclear accident sites at the Fukushima Daiichi nuclear power station. A variety of cesium adsorbents, including zeolites, calixarene, aluminum molybdophosphate, and metal ferrocyanide such as prussian blue(PB), were extensively investigated for their ability to remove ¹³⁷Cs from water. However, these adsorbents cannot be used in an open environment because there is no easy approach to collection after use.

Although various magnetic nanoparticle (MNPs) coated with PB were recently reported to treat ¹³⁷Cs-contaminated water because they can be magnetically separated from a water simply by application of an external magnet, the MNPs synthesized by a co-precipitation method tend to offer a poor magnetic separation properties and a low specific surface area for adsorption due to the poor size uniformity and crystallinity of MNPs. Furthermore, an interlayer such as poly(diallyldimethylammonium chloride) to coat the surface of MNP with PB using electrostatic interaction necessitate a multistep procedure and does not seem to be versatile enough because it is difficult to control the reproducibility and scale-up of the process.

In our paper of “Prussian blue-functionalized magnetic nanoclusters for the removal of radioactive Cesium from water”, PB-coated magnetic nanocluster (PB-MNC) with efficient removal performance of cesium and rapid magnetic separation property of the absorbent from water were prepared by simple reaction of magnetic nanocluster (MNC), synthesized via the hydrothermal method for uniform size, and good crystallinity of nanoparticles, with anionic [Fe(CN)₆]^4- under acidic conditions without an interlayer. These simple synthetic procedure developed in our paper allows the PB-MNC can be prepared on a large scale.

TEM images, XRD diffraction, and FTIR analysis indicated that MNC were successfully coated with PB. PB-MNC exhibited superparamagnetic behaviors with a saturation magnetization of 27.5 emu g–1. This value was higher than the corresponding values obtained from other magnetic cesium adsorbents. The adsorption of cesium onto the nanoparticle surfaces fit well to a Langmuir isotherm model with a maximum adsorption capacity of 45.87 mg/g, much higher than the adsorption capacities of other Prussian blue functionalized adsorbents. In addition, a high ¹³⁷Cs removal efficiency was obtained, exceeding 99.28% of the radioactive cesium present in an aqueous solution containing ¹³⁷Cs even in the presence of 3000 ppm competing ions such as K⁺ , Na⁺, Ca²⁺, and Mg²⁺. Therefore, PB-MNC demonstrated excellent potential for the treatment of ¹³⁷Cs-contaminated water