A comprehensive analysis of various structural parameters of Indian coals with the aid of advanced analytical tools

An exhaustive structural analysis was carried out on three Indian coals (ranging from sub-bituminous to high volatile bituminous coal) using a range of advanced characterization tools. Detailed investigations were carried out using UV–Visible spectroscopy, X-ray diffraction, scanning electron microscopy coupled energy dispersive spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The X-ray and Raman peaks were deconvoluted and analyzed in details. Coal crystallites possess turbostratic structure, whose crystallite diameter and height increase with rank. The H/C ratio plotted against aromaticity exhibited a decreasing trend, confirming the graphitization of coal upon leaching. It is also found that, with the increase of coal rank, the dependency of I20/I26 on L a is saturated, due to the increase in average size of sp2 nanoclusters. In Raman spectra, the observed G peak (1585 cm−1) and the D2 band arises from graphitic lattices. In IR spectrum, two distinct peaks at 2850 and 2920 cm−1 are attributed to the symmetric and asymmetric –CH2 stretching vibrations. The intense peak at ~1620 cm−1, is either attributed to the aromatic ring stretching of C=C nucleus.