Structure of hydrated cobalt ions confined in the nanospace of single-walled carbon nanotubes

The structure of hydrated Co ions confined in the nanospace of single-walled carbon nanotubes (SWNTs) has been studied using the X-ray absorption fine structure (XAFS) technique. Water adsorption isotherms on Co-impregnated SWNTs indicate a high affinity of Co ions to water molecules. The results of XAFS analysis provided the information on the proportion of dissolved species in nanospaces against the total amount of cobalt ions adsorbed on the open-pored SWNT. The structural information of the first shell around a Co ion was expressed in terms of the hydration number, Co-O distance and Debye-Waller factor. The actual coordination number and the interatomic distance of Co-O for the dissolved species were remarkably reduced compared to the bulk aqueous solution indicating the dehydration of water molecules from Co ions and a compact hydrated structure in the micropore of SWNTs.