Structural characterization of Nigerian coals by X-ray diffraction, Raman and FTIR spectroscopy

Abstract The structural parameters of six Nigerian coals were determined by X-ray diffraction, Raman and FTIR spectroscopy. This study reveals that the coals contain crystalline carbon of turbostratic structure with some amount of highly disordered amorphous carbon. The average lateral sizes ( L a ), stacking heights ( L c ) and interlayer spacing ( d 002 ) of the crystallite structures calculated from the X-ray intensities range from 16.47 to 25.70, 8.12 to 13.25 and 3.48 to 3.58 A, respectively. The L a values derived from the Raman spectra analyses using the classical linear relationship between 1/ L a and the D/G band ratio are higher (27.53–34.67 A) than values obtained from X-ray diffraction. The FTIR spectra of the coals show the presence of stretching vibrations of –OH bonds, aliphatic –CH, –CH 2 and –CH 3 absorptions, C C and –CH of aromatic structure, and C O stretching vibrations of carbonyl groups. A strong linear relationship exists between the coal structural parameters ( f a , d 002 , L c ) and the elemental carbon and volatile contents of the coal which reflects the dependency of the coals structure on their ranks.