Hydration and coordination structure of d-block metals formed by the confinement effect of carbon micropores

Abstract

We have studied the structure around a metal ion such as zinc and copper restricted in the micropores of carbon materials with the X-ray absorption fine structure (XAFS) technique and adsorption isotherm analyses. We succeeded in revealing the dehydrated structure of zinc ions confined in the micropores of activated carbon fibers (ACFs) and carbon nanotubes (CNTs) whose pore widths are below 1 nm. XAFS spectra and adsorption isotherms of zinc ions at 303 K strongly indicate that the dehydrated structure can be stably formed even in a micropore whose pore width is less than the diameter of a spherically hydrated zinc ion, where the dehydrated ions can be stabilized by the strong potential well of the carbon micropores. Also, we studied the local structure around a copper ion of copper acetate restricted in the micropore of two kinds of ACFs by the XAFS technique. The results obtained indicate the elongation of the Cu–Cu distance of the dinuclear copper complex because of the distortion or the reduction in the number of bridging carboxylates inside the micropore. We could understand the specific formation of hydration or coordination structure formed in micropores by using d-block elements as probe metal ions. [TANSO 2013 (No. 260) 297–305.]