The structural parameters of six coals were determined by X-ray diffraction (XRD), scanning electron microscope (SEM), and Raman and FTIR spectroscopy. The results reveal that the derivative coals prepared by calcination and HF acidification contain much crystalline carbon like graphite structure and are improved significantly in aromaticity, coal rank, and hydroxyl concentration. The increase of hydroxyl (OH) bonds is very beneficial to the surface modification of coal crystalline layers. In addition, the derivative coals have an obvious decrease of the aliphatic C–H content and a significant increase of the aromatic C–H content in FTIR spectra compared to that for the raw coal (AY). They are consistent with the changes of aromaticity and crystalline carbon measured by XRD and Raman spectra. With the increase of coal rank, the content of defect crystalline carbon and amorphous carbon decreases gradually from AY to the coal prepared by calcination and HF acidification (AY-C-HF). The particles of AY-C-HF with about 20 nm in thickness have better dispersibility with simultaneously a lot of pore space. The process of first calcination and then acidification can help us delaminate the aromatic layers in the coals and obtain the superfine crystalline carbon materials like graphite structure.

The structural characteristics of raw coal and hydrogen peroxide (H(2)O(2))-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 H(2)O(2) 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 H(2)O(2)-oxidized coals. This process can help us obtain superfine crystalline carbon materials similar to graphite in structure.

No abstract