The minerals in raw anthracite significantly limit the preparation of coal‐based graphene. Raw and demineralized anthracites were graphitized and coal‐based graphene was prepared by improved Hummers’ oxidation‐reduction method. The morphologies, crystal structures and spectroscopic characteristics of the products in various stages were characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy and Raman spectroscopy. The results show that demineralized or not, anthracite can be used to prepare graphene, but the minerals in anthracite physically inhibit the directional development of graphene sheets. And the residual high temperature conversion products of the minerals embedded between graphene sheets will lead to multiple irregular pore defects on the surface of graphene, which will have strongly unfavorable effects on the properties of coal‐based graphene materials. Demineralization of raw anthracite can reduce the defective pores and oxygen‐containing functional groups on the surface of coal‐based graphene and improves its morphology and properties.
Thirteen raw coal samples from Qinshui coalfield were prepared to produce coal-based graphene, and the raw coal, coal-based graphite, and coal-based graphene sheets (GS) were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy with energy dispersive spectrometer (SEM-EDS), and high-resolution transmission electron microscopy (HRTEM). The results show that the graphitization degree of coal-based graphite is positively linearly correlated with the reflectance of raw coal, has a low positive correlation with the content of inertinite, and has a low positive correlation with the content of vitrinite in raw coal. The crystallite width (La) and crystallite height (Lc) of coal-based graphite and graphene are positively linearly correlated with the reflectance of raw coal. La and Lc of coal-based graphite are distributed in 17.591–48.374 nm and 11.359–23.023 nm, respectively. After redox, La and Lc of coal-based graphene are distributed in 4.405 nm–6.243 nm and 0.804–1.144 nm, respectively. The defect degree (ID/IG) of coal-based graphene is higher than that of raw coal, demineralized coal, and coal-based graphite. The coal-based graphene is thin and transparent, and only contained carbon and oxygen. Combined with the parameters of XRD and HRTEM, it is calculated that the interlayer spacing (d002) of Qinshui-coal-based graphene is about 0.4007 nm and the number of layers (Nave) is about 5.
Coal-based graphene sheets (GS) and coal-based graphene quantum dots (GQDs) are usually prepared separately. In this paper, symbiosis of coal-based GS and coal-based GQDs was successfully prepared with our proposed preparation method by using three raw coals with different reflectance (collected from Qinshui coalfield, Shanxi Province) as carbon sources. The results showed that coal-based GS and coal-based GQDs can exist stably in the symbiosis and are distributed in different layers, and the GQDs are freely distributed between layers of GS. The average number of GS (N ave) in the three symbiosis is about 7 and the average interlayer spacing (d 002) is about 0.3887 nm. The average diameter of GQDs in the three symbiosis is about 4.255 nm and the average d 002 is about 0.230 nm. The average N ave of the three symbiosis was about 3 and the average d 002 is about 0.361 nm. The morphology and crystal parameters of symbiosis is more similar to that of graphene, the elements are only carbon and oxygen. In the prepared symbiosis, the higher the reflectance of raw coal, the smoother the lattice skeleton and the less vortex-layer structure of GS, and the larger the diameter and the denser the six membered ring of GQDs. The C and O functional groups of the prepared symbionts are similar. The higher the reflectance of coal, the higher the content of C–C/C=C. Under ultraviolet light, the prepared products all emit blue, and the higher the reflectance of coal, the higher the ultraviolet absorption, and the stronger the fluorescence intensity.
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