Structural Characterization of Hydrogen Peroxide-Oxidized Anthracites by X-ray Diffraction,Fourier Transform Infrared Spectroscopy,and Raman Spectra

Abstract

The structural characteristics of raw coal and hydrogen peroxide (H₂O₂)-oxidized coals were investigated using scanning electron microscopy, X-ray diffraction (XRD), Raman spectra, and Fourier transform infrared (FT-IR) spectroscopy. The results indicate that the derivative coals oxidized by H₂O₂ are improved noticeably in aromaticity and show an increase first and then a decrease up to the highest aromaticity at 24 h. The stacking layer number of crystalline carbon decreases and the aspect ratio (width versus stacking height) increases with an increase in oxidation time. The content of crystalline carbon shows the same change tendency as the aromaticity measured by XRD. The hydroxyl bands of oxidized coals become much stronger due to an increase in soluble fatty acids and alcohols as a result of the oxidation of the aromatic and aliphatic C-H bonds. In addition, the derivative coals display a decrease first and then an increase in the intensity of aliphatic C-H bond and present a diametrically opposite tendency in the aromatic C-H bonds with an increase in oxidation time. There is good agreement with the changes of aromaticity and crystalline carbon content as measured by XRD and Raman spectra. The particle size of oxidized coals (<200 nm in width) shows a significant decrease compared with that of raw coal (1 μm). This study reveals that the optimal oxidation time is ∼24 h for improving the aromaticity and crystalline carbon content of H₂O₂-oxidized coals. This process can help us obtain superfine crystalline carbon materials similar to graphite in structure.