DIFFUSE REFLECTANCE SPECTRA OF COALS IN THE UV-VISIBLE AND NEAR-IR REGIONS

The electronic absorption spectra of various coal powders have been measured by diffuse reflectance spectrometry in the UV-visible and near-IR regions (285-2500 nm). The intensity of the broad absorption band in the visible and near-IR regions, which is attributed to the pi-pi* electronic transition of the polynuclear aromatic hydrocarbons, increases with the rank of coals. The absorption spectra are also changed by the solvent separation, maceral separation, and heat treatment. The energies of the absorption edges, which are close to the reported energy gaps of the coals obtained from their electrical conductivity, decrease with the coal rank in a reasonable way.