The University of Tokyo · Environmental Science
Professor Yoshio Takahashi's research lab focuses on environmental geochemistry and materials science, with a strong emphasis on the behavior and speciation of critical elements such as iron, manganese, and arsenic in natural and engineered systems. The lab investigates the transformation and bioavailability of these elements in soils, groundwater, and atmospheric dust, particularly under varying redox conditions. A key research direction involves using advanced spectroscopic techniques like XANES and XRD to understand the role of iron (hydr)oxides and clay minerals in sequestering or releasing contaminants. Additionally, the lab explores the synthesis and optical properties of novel crystalline glasses for nonlinear optical applications, especially those with ferroelectric and second-harmonic generation characteristics.
Figures are computed from collected data and may differ slightly.
The behavior of As in paddy fields is of great interest considering high As contents of groundwater in several Asian countries where rice is the main staple. We determined the concentrations of Fe, Mn, and As in soil, soil water, and groundwater samples collected at different depths down to 2 m in an experimental paddy field in Japan during the cycle of flooded and non-flooded periods. In addition, we measured the oxidation states of Fe, Mn, and As in situ in soil samples using X-ray absorption
Abstract. In the North Pacific, transport and deposition of mineral dust from Asia appear to be one of major sources of iron which can regulate growth of phytoplankton in the ocean. In this process, it is essential to identify chemical species of iron contained in Asian dust, because bioavailability of iron in the ocean is strongly influenced by the solubility of iron, which in turn is dependent on iron species in the dust. Here, we report that clay minerals (illite and chlorite) in the dusts ne
Transparent optical nonlinear crystallized glasses with the composition of 25La2O3 25B2O3 50GeO2, stoichiometric to ferroelectric stillwellite-type LaBGeO5 crystalline phase, have been prepared by a two-step heat-treatment (first heat treatment: T1=670 °C, t1=10 h, second heat-treatment: T2, t2), and their second harmonic (SH) intensities have been examined using the Maker fringe method. The samples obtained by heat treatments at T2=720∼725 °C for t2=3 h show only surface crystallization and exh
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