Takao Lab, Laboratory for Zero-Carbon Energy,
Institute of Innovative Research, TokyoTech.

Tel & FAX: +81 3 5734 2968
E-mail: takao.k.ac[atmark]m.titech.ac.jp

Research Themes

1. Actinide Coordination Chemistry for Deeper Understanding of Their Migration Behavior in Geological Disposal of High-Level Radioactive Wastes

Since geological disposal of vitrified high-level radioactive wastes is currently considered, it is mandatory to well understand the migration behavior of radioactive nuclides (incl. actinides) in geosphere. The most realistic scenario for their leakage is underground water, where various kinds of organic and inorganic ligands are dissolved. The early actinides, U, Np and Pu, especially show rich redox chemistry, and therefore, their coordination chemistry in the aqueous solution will be highly complicated at a glance. However, we believe that some systematic trends arising from the 5f-electron series must be present and govern the complexation of the actinides. We intend to clarify such trends and to explore cutting-edge actinide chemistry from multiple viewpoints, i.e., various experimental techniques as well as computational chemistry.

Molecular structure of Th(IV) hexanuclear cluster with bridging gycine and oxo/hydroxo Ligands (left) and complexation behavior of Np(IV) under presence of formic acid (middle: pH dpendence of radial structure function derived from EXAFS, right: speciation diagram).
(Eur. J. Inorg. Chem. 2009, 4771-4775; Dalton Trans. 2012, 41, 12818-12823; Inorg. Chem. 2012, 51, 1336-1344.)


2. Ionic Liquid Opens Novel Aspects of Radioactive Waste Treatment and Decontamination Technologies

Ionic liquids (ILs) consist of only ionic species and possess unique properties, e.g., low melting points, negligibly low vapor pressure, moderately high ionic conductivity, and wide electrochemical windows. These traits make ILs attractive for green chemistry and various applications including nuclear engineering. We are developing preparation and purification methods of ILs to reduce their cost, and also investigating coordination and solution chemistry of various metal ions (incl. U) in ILs. The goal of our studies is development of an advanced separation technology for radionuclides and an efficient methodology for decontamination using ILs. Our currently on-going studies are, for instance, anybody-accessible method for IL preparation, rapid and efficient separation of platinum-group metals (Ru, Rh, Pd, which are cumbersome in the vitrification process), and decontamination of contaminated wood generated in the Fukushima accident.


Conceptual artwork of versatile and efficient IL preparation (left), main fields of actinide chemistry in ILs(middle), difference in color of several 3d-metal ions in aqueous and [emim]BF4 solutions (right).
(Bull. Chem. Soc. Jpn. 2014, 87, 974-981; Inorg. Chem. 2013, 52, 3459-3472; Inorg. Chem. 2012, 51, 4850-4854.)


3. Pioneering Peaceful and Effective Use of Depleted and Recovered Uranium Based on Its Coordination and Solution Chemistry

Depleted and recovered uranium are generated from nuclear fuel fabrication and spent fuel reprocessing, respectively. These uranium should not be regarded as wastes simply, but be properly used as resources. While the depleted and recovered uranium are considered to be applied for blanket fuels in fast breeder reactors and the fuels in light water reactors again, respectively, it could be promising to appropriately utilize isotope-independent chemical properties of uranium for other valuable purposes. To explore new chemical aspects and functionalities of uranium, we investigate catalytic activity of uranium complexes in organic syntheses and redox chemistry of uranium in ionic liquids for gaining fundamental knowledge towards wet batteries.


EXAFS study on diffrent uranyl(V) complexes (left) and redox non-innocent gha2- ligand in its uranyl(VI) complex.
(left: Inorg. Chem. 2009, 48, 9602-9604; right: Inorg. Chem., 2014, 53, 5772-5780.)