Determination of adsorption structure of hazardous chemical compounds by EXAFS measurements at various temperature conditions

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K17792
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Geochemistry/Cosmochemistry
• Research Institution: The University of Tokyo
• Principal Investigator: Tanaka Masato 東京大学, 大学院理学系研究科(理学部), 特任研究員 (60648195)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 有害元素 / 吸着構造 / EXAFS / Debye-Wallar因子 / 温度依存性 / ヒ素

Outline of Final Research Achievements

The adsorption structure of hazardous elements on minerals determines the distribution of the elements at the water-mineral interfaces. Thus, the determination of adsorption structures is important to understand the fate of hazardous elements in environments. In this study, we presented a method to determine the detail of adsorption structures by EXAFS measurements at several temperature conditions and analysis aided by quantum chemical calculation based molecular dynamic (ab initio MD) simulations. The key of this method is that temperature dependence of Debye-Waller(DW) factor differs by its bonding strength. We examined this method for arsenic compounds adsorbed on Fe/Al-(oxyhydr)oxide minerals system and confirmed that the degrees of change of DW factors in various temperatures for bidentate (BB) and monodentate (MM) adsorption structures were different. In addition, the degree for MM is larger than that for BB, which agrees with their bonding strengths.

Free Research Field

地球化学・環境化学・計算化学

Academic Significance and Societal Importance of the Research Achievements

本研究では、結合の強さによってDW因子の温度依存性が異なることに着目し、実際に鉄・アルミニウム水酸化鉱物へ吸着したヒ素化合物の吸着構造によって温度依存性が異なることが実測のEXAFSスペクトルとab initio MDシミュレーションの両方で確認された。本手法の有害元素化合物の吸着構造の詳細決定に対する有用性、またab initio MDシミュレーションがEXAFSスペクトル解析や予測に有効であることが示唆された。有害元素化合物の吸着構造を詳細に決定することにより、吸着量と吸着構造の関係を定量的に扱うことができ、分子レベルでの環境中における有害元素の移行挙動の解明につながる可能性がある。