61Ni synchrotron-radiation-based Mössbauer absorption spectroscopy of Ni nanoparticle composites

We obtained energy-domain ⁶¹Ni synchrotron-radiation-based Mössbauer absorption spectra of three materials that relate to nanoparticles: Ni₂(C₈O₆H₂) metal-organic frameworks (MOFs), Ni nanoparticles synthesized by complete heat decomposition of the MOFs, and the composites of Ni nanoparticles and the MOFs synthesized by partial decomposition of the MOFs. The ⁶¹Ni abundance of all the samples was not enriched but we were successfully able to obtain their spectra in 1 day or less, by using a highly efficient measurement system where the internal conversion electrons from energy standard ⁶¹Ni₈₆V₁₄ foil were detected. Although both nanoparticle constituent and MOF constituent in the composites included Ni atoms, the Mössbauer parameters of the Ni nanoparticle constituent could be evaluated; the magnetic hyperfine field of the Ni nanoparticle constituent in the composites was different from that of the Ni nanoparticles obtained by the complete heat decomposition. This difference implied that the 3 d and/or 4 s electron configuration of the nanoparticle constituent were affected by the MOF constituent in the composites.