Raman characterization of layer of graphene-like structures in 3d-transition metal-loaded charcoal by comparison with X-ray diffraction data

To evaluate the formation and changes in graphitic structures in transition-metal loaded charcoal, charcoal samples synthesized from Japanese cedar wood impregnated with 3d-transition metal (Cr, Mn, Fe, Co, Ni, Cu, Zn) ions were analyzed using microscopic Raman spectroscopy and powder X-ray diffractometry. The metal-loaded charcoal samples were carbonized at 650, 700, 750, 800, and 850 °C in downstream N₂ gas. The Raman Gˊ-band, which shows the structural ordering of carbon atoms, was observed in the Raman spectra of Fe-, Co-, and Ni-loaded charcoal. The Gˊ-bands occurred at ≤ 2670 cm^− 1 and shifted to 2700–2690 cm^− 1 with increasing carbonization temperature. The Gˊ-band observed in the higher wavenumbers (2700–2690 cm^− 1) range corresponded to an X-ray diffraction (XRD) peak at ∼ 26.3 ° assigned to the (002) plane of graphite-like structures. The high-wavenumber Gˊ-band also corresponded to the XRD detection of the carbide of the three metals. However, the XRD peak was not found for Co- and Ni-loaded charcoal samples exhibiting Gˊ-bands at ≤ 2670 cm^− 1.