Coal-based Graphene Research Articles

Regulating Composition and Structure of Coal-based Graphene and Its Electrochemical Characteristics

Abstract Coal, a carbon-rich mineral with plentiful reserves, serves not only as a fuel but also as a raw material, presenting lower pollution emissions in the latter use. From a materials chemistry standpoint, coal is a viable raw material for graphene production. This study develops a promising and sustainable method to convert coal into graphene, leveraging its unique macromolecular aromatic structure and high carbon content. The investigation includes an analysis of the lateral size, morphology, and chemical composition of coal-derived graphene using techniques such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and optical microscopy. Results confirm that coal can effectively replace natural graphite flakes in graphene production, with the derived graphene featuring 3-6 exfoliated layers and an oxygen content below 5.5%. While the graphene from coal shares a similar morphology to that derived from graphite, it exhibits more structural defects. Interestingly, the macroscopic size of the coal does not influence the microscopic composition and structure of the graphene. However, the thermal reduction method for oxidized graphene proves more effective at repairing structural defects than chemical reduction. Employing coal-derived graphene as a supercapacitor electrode demonstrates excellent cycling stability and ultra-high capacitance storage capacity. The H-CG-325 shows the highest discharge area-specific capacitance across various current densities. At an increased current density of 10 A/g, the H-CG-325 maintains 80.6% of its initial capacitance of 79 F/g observed at 1 A/g. Electrochemical tests reveal that coal-based graphene holds significant potential as a supercapacitor material, indicating promising applications in energy storage and conversion.

The effects of crystal orientation and common coal impurities on electronic conductivity in copper–carbon composites

The electronic conduction properties of copper–graphene composite materials including common coal impurities are studied. Exploring the transport properties for three crystallographic orientations [(111), (110), and (100)] of copper in copper–graphene composites, a strong orientational dependence on electronic conductivity is shown. Graphene exhibits near-ideal registries for (111) and (110) orientations, forming a connected network between grains that enables efficient carrier transport. The influence of non-carbon elements: nitrogen (N), oxygen (O), and sulfur (S) in graphene, representing possible structures in coal-based graphene are investigated. N, O, and S in graphene negatively impact the composite’s electronic conductivity relative to pristine graphene. A new method is introduced for visualizing the spatial distribution of electrical conduction activity in materials using the square of the electronic charge density near the Fermi level, based on the work of Mott. We call this technique the N2 method.

Coal-based graphene derived from different coal ranks: exceptional sodium storage performance in sodium-ion batteries.

Coal is a premium carbon material precursor as anode materials for sodium-ion batteries (SIBs). Additionally, developing anode materials with large capacity and rapid charging performance is essential for the advancement of SIBs. Consequently, in this work, coal-based reduced graphene oxide (CrGO) was prepared as an anode materials for SIBs by a modified Hummers-high temperature thermal reduction method with different ranks of coal (coal-based graphite, CG) as a precursor. The CG prepared from higher-rank coal exhibits a higher degree of graphitization, and its graphene layers are easier to exfoliate. The unique microstructure of CrGO provides stability during the sodium storage process and exhibits fast ion capacitive adsorption behavior, enhancing reaction kinetics. CrGO, with an initial reversible capacity of up to 331 mA h g-1 at a current density of 0.03 A g-1, achieves a specific capacity of 75 mA h g-1, even at a high current density of 10 A g-1. Notably, CrGO also maintains a good specific capacity of 123 mA h g-1 after 1000 cycles at a current density of 1 A g-1, with a capacity retention rate of 91.8%. This study highlights the potential for using coal-derived materials in the development of high-performance anode materials for SIBs, promoting the green and high-value utilization of coal.

Cobalt/nitrogen co-doped carbon nanosheets from coal-based graphene quantum dots boosted oxygen reduction

We report on cobalt/nitrogen co-doped carbon nanosheets (Co/NCNs) as a highly efficient electrocatalyst for the oxygen reduction reaction (ORR). The Co/NCNs were synthesized through pyrolysis at 900 °C using coal-based graphene quantum dots that contain nitrogen as a source of both carbon and nitrogen, NaCl as a template, and trace amounts of cobalt salt as a metal source. The Co/NCNs-0.1 exhibited ORR activity that was equivalent to that of Pt/C, with a half-wave potential of 0.85 V and a limiting current density of 4.9 mA cm−2. Furthermore, the zinc-air battery incorporating Co/NCNs-0.1 demonstrated an open circuit voltage of 1.423 V, a maximum power density of 149 mW cm−2, and a specific capacity of 806.5 mAh g−1 at a current density of 20 mA cm−2. The results of density functional theory calculations indicate that metal Co, when protected by graphitic-N-doped carbon, holds a greater negative charge and exhibits a lower energy barrier compared to other types of nitrogen species. This property contributes to the catalytic activity of the ORR.

Chemical Structure Evolution of Thermally Altered Coal during the Preparation of Coal-Based Graphene and Division of Thermally Altered Zone: Based on FTIR and Raman.

A suite of coal samples near a diabase dike was collected to investigate the structural and functional group evolution of a series of carbon materials prepared from thermally altered coals, explore the influence of thermal metamorphism distance on the structure of coal and its carbon material products, and divide the thermally altered zones. Using Fourier transform infrared and Raman studies, it was found that after demineralization, the aromatic parameters f ar H and I of the coal structure slightly increase, while the aliphatic parameters CH2/CH3 and oxidation parameter 'C' slightly decrease, and the degree of order of the coal structure increases. Graphitization can greatly improve aromatic parameters, eliminate aliphatic structures, and enhance orderliness. However, after oxidation and reduction, the aromatic parameters and ordering degree of graphene decrease. Except for the sample closely attached to the dike, the coal-based graphene yield of the other samples first decreases and then stabilizes with the increase of distance from the dike, which is consistent with the trend of changes in the reflectance of raw coal. The thermally altered distance affects the structural changes of coal and carbon material products. The coal attached to the dike has been damaged and polluted, and the aromaticity and orderliness of the prepared carbon material products are relatively poor. The aromaticity and orderliness of coal-based products prepared from other thermally altered coals are relatively high and increase with the closer the thermally altered distance. Based on the characterized parameters of coal samples and products with distance from the dike, the sampling area is divided into four zones, including abnormally altered zone, normal altered zone, transition zone, and original coal zone. Among them, the yield and quality of coal-based graphene prepared from coal in the normal altered zone are the highest, an ideal raw material collection area for making coal-based graphene.

Coal-based graphene formation by CO2 laser scribing: Various structures and excellent electrochemical performance

The laser-induced technique is a cost-effective and environmentally-friendly method for upgrading coal into high value-added graphene materials. Here, laser-induced graphenes (LIGs) were prepared from different rank coals in one-step under vacuum conditions using a designed CO2 infrared laser device. The characteristics of laser-induced products were studied by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The electrochemical characteristics of coal-based laser-induced graphenes (C-LIGs) were examined in a three-electrode test system. Results show that subbituminous coal, bituminous coal, and low-metamorphic anthracite can form LIG with fewer layers after laser irradiation. The morphology of C-LIG is a layered porous structure. Corrugated folds can be observed at the edges of the C-LIG layer. There are only a few layers of graphene, with the majority of them concentrated in 2–10 layers. The most interesting result is that LIG prepared from low volatile bituminous coal has the highest crystallinity, the largest aromatic layer size, and the lowest average graphene layer number. Furthermore, LIG made from low volatile bituminous coal (LIG-ZJ) exhibits excellent electrical double-layer capacitive behavior, low equivalent series resistance (3.73 Ω), good rate capability, excellent cycling stability, greater Coulombic efficiency, and high mass specific capacitance. The LIG-ZJ electrode exhibits a high specific capacitance of 1879.92 F/g at 1 A/g, which is nearly ten times greater than that of most activated carbon electrodes reported. In addition, its power density and energy density can reach up to 924.07 kW/kg and 217.11 Wh/kg. These results indicate that coal-based laser-induced graphene has significant potential for application in the field of electrochemical energy storage.

Coal-based hard carbon anode for high-performance sodium ion batteries via coal-based graphene oxide as a multi-functional binder

Coal-based hard carbon for sodium ion batteries (SIBs) was successfully prepared using Shenfu bituminous coal (SFC) by one-step pyrolysis method. In the present work, we reported a novel method to fabricate carbon electrodes for SIBs from coal-based hard carbon with coal-based graphene oxide (CGO) as a multi-functional conductive binder to realize dual functional utilization of coal. As compared to traditional binder (CMC), electrodes with the CGO binder exhibits significantly increased reversible capacity and rate capability. This work provides a facile method for coal-based carbon materials used in SIBs.

Preparation of Coal-Based Graphene by Flash Joule Heating.

This study explores the production of flash graphene (AC-FG) from anthracite coal by using the flash Joule heating (FJH) method. This study demonstrates that AC-FG can be derived from anthracite coal by precisely controlling the system parameters, specifically the pulse voltage. The FJH process requires no catalyst. The produced material was characterized by using Raman, XRD, XPS, TG, SEM, TEM, and XPS techniques. The results reveal that the degree of graphitization of coal reaches its peak at 190 V. From an energy perspective, FJH provides a straightforward and cost-effective method for graphene preparation, offering a substantial avenue for the efficient utilization of coal resources and the cost-effective application of graphene.

A dual passivation strategy based on F/N co-doped coal-based graphene quantum dots for high-efficiency carbon-based perovskite solar cells

F/N-GQDs were used to synergistically passivate defects of perovskite layers, suppressing nonradiative recombination, optimizing energy level alignment, and improving hole extraction ability, greatly enhancing the photoelectric performance of C-PSCs.

Preparation and characteristic analysis of graphene based on coal macerals of different rank

Graphene is prepared using the improved Hummers redox method to study the preparation and structural characteristics of coal-based graphene from coal macerals of rank between 0.52 % and 1.98 %. The macerals are separated and enriched by hand sorting, sieving, and isopyknic gradient centrifugation. The crystal characteristics of the macerals, coal-based graphite, and graphene are characterized by XRD, Raman, SEM and TEM. The flake graphene with stable structure, good extensibility, different cell parameters and defects can be prepared from macerals. All the preparation yields are less than 4.0 %. The XRD data shows that after high-temperature graphitization, the layer spacing d002 of each sample is less than 0.3400 nm, and the lamellar crystallite sizes La and Lc are 7.70–21.09 nm and 11.53–16.94 nm, respectively. After the redox reaction, inertinite MLI-GS, YCWI-GS, and vitrinite GMDV-GS have the layer spacing d002, lamellar extendability La, stacking thickness Lc, and average stacking layer Nave that tend to be graphite-like structure. The microcrystalline structure is well developed and stable. Raman also confirmes that inertinite and high-rank vitrinite-derived graphene have fewer structural defects, good ordering, and a high degree of graphitization. The average values of ID/IG and AD/AG of maceral → coal-based graphite → graphene are 0.73 → 0.29 → 1.06, 2.12 → 0.40 → 1.62, indicating a relationship between the structural order: coal-based graphite > maceral > graphene, and between the degree of graphitization: coal-based graphite > graphene > maceral. The SEM and TEM dates show that inertinite tends to form a flat graphene structure with four–six layers, and has good light transmission. The graphene has few folds and warps, good layer extensibility, and high lattice order. The layer spacing at the edge is consistent with the d002 of XRD analysis. Vitrinite, cutinite, and barkinite derived graphene are similar to a kneaded paper balls. The layers are mixed with each other, forming more folds and ripples, and the peeling effect is poor. Only the high-rank GMDV-GS is clean like gauzy graphene, indicating that the micromorphological characteristics of graphene are related to the coal rank and macerals.

Ultrafast synthesis of novel coal-based graphene and its anticorrosion properties of epoxy/graphene nanocomposite coatings

Graphene has a wide range of applications in anti-corrosion coatings due to its excellent barrier, shielding, and mechanical properties. However, traditional graphene synthesis methods, including the production of graphene oxide (GO) using Homer's method and then its reduction in the form of reduced graphene oxide (rGO) are time-consuming, energy-consuming, and environmentally polluting, which limits their application in anti-corrosion coatings. This study leveraged the capabilities of flash Joule heating (FJH) to synthesize flash coal-based graphene (FCBG) from Taixi anthracite (TA) within 200 ms without pretreatments or chemical reagents. The FJH had the advantages of low energy consumption and being environmentally friendly. Compared with the rGO, the FCBG prepared by FJH was characterized by fewer defects, larger carbon sheets, and a turbostratic structure. Moreover, carbon steel Q235 was used as the substrate to prepare anti-corrosion coatings by mixing FCBG at different flash voltages with epoxy resin (EP). Based on this, the electrochemical performance of different coatings was compared before and after salt spray corrosion. The results demonstrated that the FCBG composite anti-corrosion coating (EP/FCBG190) prepared using EP and FCBG synthesized at 190 V in the FJH, displayed stronger corrosion resistance than the EP and rGO composite coating (EP/rGO). The FJH synthesis process provides a feasible route for improving the synthesis process of the anti-corrosion coatings and the high value-added utilization of coal.

Advantages of Structure and Electrochemical Properties of Graphene Prepared from Tectonically Deformed Coal.

Asa low-cost carbon-rich resource, coal has been widely used to prepare excellent electrochemical energy-storage carbon materials such as graphene. However, the different structures of carbon source will affect the performance of carbon materials. To explore the feasibility of preparing high-performance graphene from the carbon source affected by tectonic stress in coal, in this paper, series products of coal-based graphene are prepared by tectonically deformed coal (TDC) and normal structural coal (NSC). The structural parameters are characterized by HRTEM, XRD, Raman, and low-temperature CO2 and N2 adsorption, and the electrochemical performance of coal-based graphene lithium battery is tested by galvanostatic charge-discharge and cyclic voltammetry. The results show that tectonic stress makes the proportion of the medium-long aromatic fringes, preferred orientation degree (POD), and multilayer stacking in TDC aromatic fringes slightly higher than those in NSC. At the same temperature, the relatively large microcrystalline size, the high order degree, and more pore structures make the local molecular oriented (LMO) domain vertical height (d) and graphitization degree (G) of the coal-based graphite microcrystalline structure prepared by TDC better than those of NSC, which indicates that the carbon source in TDC contains more graphitizable carbon structures. This makes the graphene prepared by TDC not only possess perfectly ordered crystal planes but also relatively abundant nanochannels. High lithium-storage capacity and low charge-transfer resistance make the electrochemical performance of graphene prepared by TDC as an anode electrode material for lithium-ion batteries superior to that by NSC.

Optimization of perovskite/carbon interface performance using N-doped coal-based graphene quantum dots and its mechanism analysis

Optimizing the interfacial properties between perovskite and carbon electrodes has always been an important way to improve the photoelectric conversion efficiency (PCE) of carbon-based perovskite solar cells (C-PSCs) and facilitate their commercialization. In this paper, nitrogen-doped graphene quantum dots (N-GQDs) with fluorescent properties were successfully prepared using inexpensive coal as raw material by a facile and environmentally friendly chemical reagent oxidation. The results show that the electron-rich pyridinic nitrogen in N-GQDs can act as Lewis bases to form coordination bonds with uncoordinated lead ions by sharing electron pairs, thereby reducing the defect density and nonradiative recombination of photo-generated electron-hole, and extending lifetime of charge carriers. In addition, due to the passivation of N-GQDs, the hysteresis effect of the device is significantly reduced and the long-term stability is also improved. By optimizing the concentration, the PCE of C-PSCs achieved a maximum of 14.31%, which was improved by 20.25% compared with 11.90% of the pristine C-PSCs. This work provides a facile, environmentally friendly and efficient strategy for improving the overall performance of C-PSCs using inexpensive coal-based N-GQDs.

Coal-based graphene as a promoter of TiO2 catalytic activity for the photocatalytic degradation of organic dyes

Coal-based graphene as a promoter of TiO2 catalytic activity for the photocatalytic degradation of organic dyes

Preparation and Modification of Graphite-based and Coal-based Graphene and its Tribological Properties in Lubricants

Graphite-based graphene oxide (GO) and coal-based graphene oxide (GO/SiO2, which we call graphene oxide/SiO2 because the surface of the resulting coal-based GO is linked with SiO2 from the coal structure) were prepared by the conventional Hummers oxidation method and ultrasound-assisted Hummers oxidation method, respectively, using natural graphite powder and Xinjiang Wucaiwan coal as carbon sources. Furthermore, the structures of the two were studied comparatively. Afterwards, the two lamellar structure products were hydrophilically modified with octadecylamine and dicyclohexylcarbodiimide by a hydrothermal method. And then, added these products (graphite-based GO-ODA and coal-based GO/SiO2-ODA) to No.32 cycloalkyl base oils in order to comparatively investigated their tribological properties as lubricant additives. The results showed that the dispersion stability of coal-based GO/SiO2 in the lubricant was significantly better than that of graphite-based GO; meanwhile, the tribological performance of GO/SiO2-ODA in the lubricant better than that of graphite-based GO-ODA due to the surface linkage of coal-based GO/SiO2 with SiO2 particles. After 1 h - long grinding in a four-ball friction test, the lubricant friction coefficient of 0.03 wt% coal-based GO/SiO2-ODA oil reached a minimum of 0.118, which reduced 58.1% compared to pure base oil and reduced 2.8 times compared to the counterpart using graphite-based GO-ODA under the same experimental conditions.

Coal-based graphene as a promoter of TiO2 catalytic activity for the photocatalytic degradation of organic dyes

Graphene oxide (GO) obtained from coal-based graphite by the Hummers method was hydrothermally treated to obtain reduced GO (rGO). TiO2 was mixed with aqueous suspensions of GO and rGO and dried at 70 °C to obtain GO-TiO2 and rGO-TiO2 with 95 wt% TiO2. TiO2 was also combined with a GO suspension by hydrothermal treatment to obtain rGO-hTiO2 with 95 wt% TiO2. The three hybrids were used as catalysts for the photocatalytic degradation of rhodamine B (Rh B) and methyl orange (MO). Of the three materials, rGO-hTiO2 had the highest catalytic activity for the degradation of Rh B and MO under visible light irradiation. The reasons for having the best catalytic activity are that the incorporation of rGO into TiO2 helps increase its adsorption capacities for Rh B and MO as evidenced by adsorption in dark, and a narrowing of the TiO2 band gap as revealed by diffuse UV reflectance spectroscopy. This reduces the rate of recombination of electron-hole pairs by there being intimate contact between the TiO2 particles and rGO, forming Ti-O-C bonds as confirmed by XPS, with the TiO2 particles being uniformly decorated on the rGO sheets.

Enhanced oxygen reduction of porous N-doped carbon nanosheets with graphitic N and defects obtained from coal-based graphene quantum dots

Metal-free carbon-based electrocatalysts for oxygen reduction reaction (ORR) have received considerable attention owing to their abundance and low cost. However, designing carbon-based electrocatalysts with excellent performance in a facile manner remains a challenge. In this work, porous nitrogen-doped carbon nanosheet (PNCNs) catalysts with high contents of graphitic N and defects were readily prepared via a simple self-doping method, in which coal-based graphene quantum dots (GQDs) were used as the carbon and nitrogen resource. Based on the results, PNCNs-900 (obtained at 900 °C) displayed good ORR performance, with a half-wave potential (E1/2) of 0.80 V. It also exhibited high stability and methanol tolerance compared with commercial Pt/C. Experimental investigations and theoretical calculations prove that the increased ORR electrocatalytic activity of PNCNs-900 is due to the synergistic effect of a large number of defects and graphitic N. Furthermore, its higher electrocatalytic activity for ORR also benefits from the porous lamellar structure, which facilitates the mass transfer process. This study offers a novel approach for developing effective ORR catalysts and for the high value-added utilization of coal resources.

Study on the microstructure of the symbiosis of coal-based graphene and coal-based graphene quantum dots: preparation and characterization

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.

Effects of Coal Rank and Macerals on the Structure Characteristics of Coal-Based Graphene Materials from Anthracite in Qinshui Coalfield

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.

Construction of 2D-coal-based graphene/2D-bismuth vanadate compound for effective photocatalytic CO2 reduction to CH3OH

Scalable and sustainable photocatalytic technology can convert CO2 to valuable hydrocarbons, which requires highly efficient and inexpensive photocatalyst with a broad light absorption range, high stability and fast carrier separation efficiency. Herein, a nanostructure with 2D/2D conformation consisting of BiVO4 and coal-based graphene oxide (CGO) were fabricated by hydrothermal method, which achieves efficient photoreduction of CO2 to CH3OH. Surprisingly, this nanostructure exhibits a significantly enhanced photocurrent density (0.95 mA/cm2), good CO2 adsorption capacity (1.34 cm3/gSTP) and medium stability. Moreover, the optimized 10-CGO/BiVO4 composite shows moderate CO2 conversion activity with a CH3OH production of 537.78 μmol/g h under light irradiation, which is approximately 6.47 times higher than that of BiVO4 nanosheets. The enhanced photocatalytic activity can be attributed to the following three points: broadened visible light absorption ability, unique ultra-thin structure and abundant surface active sites; effective photocarriers separation efficiency and reduced interfacial resistance at their heterojunction between BiVO4 and CGO nanosheets; CGO as co-catalyst with an electron-transfer path coupling with CGO can expedite the separation speed of carriers of photocatalyst, reduce the interface resistance and enrich surface active sites. This work provides inspiration for high performance binary photocatalyst in solar-chemical energy conversion process.