Uptake of cations with high selectivity and capacity from aqueous solutions by redox-active ionic crystals

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K05742
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Functional solid state chemistry
• Research Institution: The University of Tokyo
• Principal Investigator: Uchida Sayaka 東京大学, 大学院総合文化研究科, 准教授 (10361510)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: イオン結晶 / 複合材料・物性 / 酸化還元 / イオン吸着

Outline of Final Research Achievements

Polyoxometalates (POMs) are nano-sized anionic metal-oxygen clusters of early transition metals with redox properties, which have been utilized as constituents of redox-active porous frameworks. In this work, we report redox-active porous ionic crystals based on Keggin-type POMs with highly-selective Cs+ adsorption property. The crystal possess closed pores, which are gaps between closely-packed oppositely-charged molecular ions, and Cs+ is selectively adsorbed among the alkali metal and alkaline earth metal cations via reduction of the crystal with ascorbic acid (reduction-induced Cs+ uptake). Despite the high selectivity to Cs+, there are several tasks to solve: Heating is needed and slow kinetics. In order to solve these tasks, Dawson-type POMs are employed because the molecular size and reduction potential are larger and higher, respectively, than those of Keggin-type POMs, which increase the pore volume and facilitate the reduction-induced Cs+ uptake.

Free Research Field

無機化学

Academic Significance and Societal Importance of the Research Achievements

東日本大震災に伴う福島第一原発の事故により放射性物質が環境中に放出され、特にセシウム137は半減期が約30年と長く、その除去が強く望まれている。セシウムは周期表の左下にある陽性の高い元素であるため、正電荷を持つ陽イオンとして環境中に存在するが、複数かつ高濃度の陽イオンを含む環境水から低濃度の放射性セシウムイオンを選択的に吸着除去するのは難しい。この課題に取り組むため、酸化還元活性を示すモリブデンを含むポリオキソメタレートを用い、多孔性イオン結晶を合成した。この化合物にビタミンC水溶液を加えるとポリオキソメタレートが還元され、この負電荷の中和のため、セシウムイオンが高選択的に吸着された。