Raman and XRD characterization of carbon structures in Fe-, Co-, and Ni-loaded woody charcoal: formation and growth of graphene-like layers

Abstract

To acquire a deeper understanding of the formation and growth mechanisms of graphitic carbon structures by metal catalysts, we prepared metal-loaded charcoal samples from Japanese cedar wood impregnated with Fe3+, Co2+, or Ni2+ at various carbonization conditions. The charcoal samples were examined using microscopic Raman and powder X-ray diffraction (XRD) techniques. The effects of the conditions on the ordering of sp2-carbon in the carbonization processes were compared with our previously reported data. The Gˊ(2D)-band is due to a double-resonance Raman scattering process and is attributed to graphitic structures. The Gˊ-band was observed in the Raman spectra of Fe-, Co-, and Ni-loaded charcoal synthesized at ≥650 °C and shifted to higher wavenumbers with increasing holding time (HT) at carbonization temperature (CT) and the heating rate. However, the occurrence of the Gˊ-band was not necessarily equivalent to that of the XRD peak at ~ 26.3° assigned to graphitic carbon (GLSs). The detection of XRD peaks assignable to the metal carbide corresponded to the formation of graphite-like structures (GLSs). GLSs imply multi-layer graphene-like structures. The formation of few-layer graphene-like structures was observed in the Fe-, Co-, and Ni-loaded charcoal carbonized in the CT range of 600–650 °C. The growth to GLSs occurred in the CT ranges of 600–650 °C, 700–750 °C, and 750–800 °C in the Fe-, Co-, and Ni-loaded charcoal, respectively. The formation temperatures of the few-layer graphene-like structures and those of GLSs were reduced by the HT extension. These temperatures were also lowered by the reduction of the heating rate.