AsianScientist (Oct. 17, 2017) – By combining cellulose nanofibers with the same Prussian blue pigment used in the works of popular Edo-period artist Hokusai, researchers at the University of Tokyo have developed nanoparticles-based sponges that can decontaminate radioactive water and soil.
Removing radioactive materials such as cesium-134 and -137 from contaminated seawater or soil is challenging as there is a huge amount of similar substances with competing functions have to be removed.
Prussian blue (ferric hexacyanoferrate) has a jungle gym-like colloidal structure, and the size of its single cubic orifice, or opening, is a near-perfect match to the size of cesium ions. Therefore, it is prescribed as medication for patients exposed to radiation to selectively adsorb cesium. However, as Prussian blue is highly attracted to water, it is very difficult to recover once it is dissolved into the environment. For this reason, its use in the field for decontamination has been limited.
Taking a hint from the fact that Prussian blue in Hokusai’s woodblock prints do not lose their color even when wet from rain, a research team led by Professor Ichiro Sakata and Project Professor Bunshi Fugetsu at the University of Tokyo’s Nanotechnology Innovation Research Unit at the Policy Alternatives Research Institute, developed an insoluble nanoparticle by combining cellulose and Prussian blue.
“I was pondering about how Prussian blue immediately gets dissolved in water when I happened upon a Hokusai woodblock print, and how the indigo color remained firmly set in the paper, without bleeding, even after all these years,” said Fugetsu. “That revelation provided a clue for a solution.”
The scientists created this cellulose-Prussian blue combined nanoparticle by first preparing cellulose nanofibers using a process called TEMPO oxidization and adding ferric ions (III), then introduced a certain amount of hexacyanoferrate, which adhered to Prussian blue nanoparticles with a diameter ranging from 5–10 nanometers. The nanoparticles obtained in this way were highly resistant to water, and moreover, were capable of adsorbing 139 mg of radioactive cesium ion per gram.
Field studies on soil decontamination in Fukushima have been underway since last year. A highly effective approach has been to sow and allow plant seeds to germinate inside the sponge made from the nanoparticles, then getting the plants’ roots to take up cesium ions from the soil to the sponge. Water can significantly shorten decontamination times compared to soil, which usually requires extracting cesium from it with a solvent.
“The amount of research on cesium decontamination increased after the Chernobyl nuclear power plant accident, but a lot of the studies were limited to being academic and insufficient for practical application in Fukushima,” said study co-author Dr. Kiliyankil Vipin. “Our research offers practical applications and has high potential for decontamination on an industrial scale not only in Fukushima but also in other cesium-contaminated areas.”
The article can be found at: Vipin et al. (2017) Cellulose Nanofiber Backboned Prussian Blue Nanoparticles as Powerful Adsorbents for the Selective Elimination of Radioactive Cesium.
———
Source: University of Tokyo; Photo: Sakata & Mori Laboratory.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.
