Method for improving yield of coal-based graphene based on direct ultrasonic treatment

Abstract

The invention relates to the field of coal-based carbon materials in clean and efficient utilization of coal, in particular to a method for purifying the yield of coal-based graphene based on direct ultrasonic treatment. The preparation method comprises the following steps: by taking JJG bituminous coal as a raw material, sequentially performing crushing, grinding, acid pickling, water washing and drying treatment to obtain a powder sample with low-ash-content fine particles, then filling the powder sample into a graphite crucible with a hollow circular aperture, and treating by a tabletting tool to prepare sample slices; irradiating the whole sheet sample by laser in an out-of-focus and vacuum environment, and inducing to obtain a coal-based porous graphene material; the method comprises the following steps: preparing an ultrasonic solution (absolute ethyl alcohol (the purity is 99%) and ultrapure water according to a ratio of 2: 3), carrying out ultrasonic stripping treatment on a sample, carrying out ultrasonic dispersion, centrifuging, standing, taking an upper clear liquid sample and a lower clear liquid sample, drying and collecting to obtain the few-layer graphene material subjected to ultrasonic stripping. Product structure characterization finds that the number of layers of the coal-based porous graphene subjected to ultrasonic preparation is smaller, the pore connectivity is good, the interlayer spacing is large, the graphene yield is remarkably improved, and the great potential application value of the coal-based laser-induced graphene in the fields of biology, materials and the like is greatly improved; the method has important significance for further promoting the production of high-added-value carbon materials such as graphene by using coal as a carbon source.

Description

Technical Field

[0001] This invention relates to the field of coal-based carbon materials in the clean and efficient utilization of coal, specifically to a method for improving the yield of coal-based graphene based on direct ultrasonic treatment. Background Technology

[0002] Coal, as a vital energy source and chemical raw material, plays a crucial role in global economic development. Currently, coal is primarily consumed as fuel worldwide. Direct combustion of coal emits a range of greenhouse gases, causing severe environmental pollution. With continuous economic and social development and increasing awareness of energy conservation and emission reduction, expanding coal utilization methods and achieving clean and efficient coal use are essential for the sustainable development of the coal industry. Utilizing coal as a raw material to produce high-value-added chemical products and new materials is a key pathway to expanding and achieving clean and efficient coal utilization, and also a major way to reduce carbon emissions.

[0003] Graphene is a type of sp 2 Novel two-dimensional carbon materials, formed by a network of hybrid carbon atoms, exhibit excellent physicochemical properties (stable chemical structure, high carrier mobility, excellent electrical and thermal conductivity, good mechanical properties and flexibility, and ultra-large specific surface area, etc.), and have been widely used in optoelectronics, catalysis chemistry, medicine, and military fields, demonstrating superior performance. Generally, graphene is a single-layer structure, but in practical applications, structures with 10 or more layers are collectively referred to as graphene materials. Obtaining fewer layers (1-10 layers) (few-layer graphene) exhibits even better performance; therefore, this patent aims to solve a method to improve the yield of few-layer graphene. In the past few years, researchers have used direct laser technology to prepare porous graphene from graphene oxide, various polymers, and wood. Recently, Professor Tour's research at Rice University further verified that various carbon precursors, including fabrics and paper, can be converted into graphene using lasers. This new technology is highly scalable, enabling the preparation of graphene using a cost-effective and commercially viable carbon dioxide laser system under certain environmental conditions, thus making large-scale graphene production and commercialization possible. Coal is the cheapest and most abundant solid carbon material on Earth, with a carbon content generally exceeding 50%, and is rich in carbon and aromatic hydrocarbons, making it an ideal carbon source for the preparation of few-layer graphene. In previous explorations, our team has already used laser-induced graphene preparation technology to directly transform coal into porous graphene in a one-step process, laying a solid foundation for the preparation of few-layer graphene. Improving the performance of coal-based graphene is a significant breakthrough for future applications in the field of coal-based carbon materials. Summary of the Invention

[0004] This invention overcomes the shortcomings of existing coal-based graphene methods, such as low yield and high number of layers, by providing a method for improving the yield of coal-based graphene through direct ultrasonic treatment. Using Jiajiagou (JJG) bituminous coal as raw material, this invention first prepares coal-based graphene via a one-step laser-induced method, and then purifies it using ultrasonic exfoliation to obtain few-layer graphene material. This method is simple to operate, economical and environmentally friendly, significantly increases yield, and produces few-layer graphene with approximately 3-4 layers, exhibiting porous characteristics, good pore connectivity, and a large interlayer spacing.

[0005] To solve the above-mentioned technical problems, the technical solution adopted in this invention is as follows: a method for improving the yield of coal-based graphene based on direct ultrasonic treatment. Jiajiagou bituminous coal is used as raw material. It is successively ground and demineralized to obtain a deashed coal powder sample. Then, the sample is irradiated with a laser in a defocused and vacuum environment to obtain coal-based graphene material. The obtained coal-based graphene is further purified by ultrasonic exfoliation to obtain few-layer graphene.

[0006] Furthermore, the bituminous coal contains 60% vitrinite and 40% inertinite.

[0007] Furthermore, the particle size of the ground bituminous coal is below 200 mesh.

[0008] Preferably, the pickling method involves sequentially pickling with hydrochloric acid and hydrofluoric acid (national standard deashing method), with the concentrations of the two acids being 15% and 40%, respectively; each acid treatment is kept at a constant temperature of 60°C in a water bath for 8 hours; after pickling, the sample is washed with ultrapure water until the filtrate is neutral when tested with pH paper, and the drying temperature is 60°C for 24 hours.

[0009] Furthermore, the laser irradiation equipment used for laser-induced laser stimulation was independently built, primarily employing a commercially available 10.64μm wavelength infrared CO2 continuous laser with a rated power of 180W. The test conditions were a spot diameter of 8mm and a laser power density of 3.58W / mm². 2 The laser irradiation time is 120 seconds.

[0010] Furthermore, an ultrasonic solution was prepared for ultrasonic ablation treatment of the sample. The ultrasonic solution was prepared by mixing anhydrous ethanol (99% purity) and ultrapure water in a 2:3 ratio.

[0011] Further, after ultrasonic dispersion, centrifugation and settling were performed, and the supernatant and supernatant samples were collected and dried to obtain the few-layer graphene material after ultrasonic exfoliation. The ultrasonic dispersion temperature was set to 60℃, and the ultrasonic time was set to 20 min, 40 min, and 60 min; the centrifuge temperature was set to 30℃, the centrifugation speed to 3000 rpm, and the centrifugation time to 30 min; the settling time was 12 h.

[0012] In addition, the present invention also provides a few-layer graphene material prepared by the above-mentioned method for improving the yield of coal-based graphene through direct ultrasonic treatment.

[0013] The present invention also provides a few-layer graphene material prepared by the above-mentioned method of improving the yield of coal-based graphene through direct ultrasonic treatment, which has great potential for application in battery performance.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] This invention utilizes an advanced laser-induced irradiation method to convert bituminous coal into coal-based graphene in a one-step process. First, a certain yield of coal-based graphene material is obtained, and then few-layer graphene is obtained using ultrasonic exfoliation. The operation is simple, fast, pollution-free, and environmentally friendly. Structural characterization of the obtained few-layer graphene shows that it mainly consists of 3-4 layers with an interlayer spacing of 0.366-0.385 nm and exhibits a significant Raman 2D peak. Compared with laser-induced coal-based graphene pretreated with ultrasound, ultrasonic treatment significantly improves the purity of the graphene structure. Enhancing the performance of coal-based graphene represents a significant breakthrough for future applications in the field of coal-based carbon materials. Detailed Implementation

[0016] The present invention will be further described below with reference to specific embodiments.

[0017] Example 1

[0018] A method for improving the yield of coal-based graphene based on direct ultrasonic treatment includes the following detailed steps:

[0019] 1) Sample: The 0.5mm center sample of JJG after laser induction was selected as the test object, and 1.5g of sample was divided into three equal parts.

[0020] 2) Solution preparation: The solution is prepared by mixing 40% anhydrous ethanol (99% purity) and 60% ultrapure water per 100ml.

[0021] 3) Experimental conditions and procedures: Pour the three divided samples into the three prepared solutions, stir for 10 minutes, and then seal. Simultaneously, turn on the ultrasonic cleaning equipment and set the temperature to 60℃ (the instrument is a Jiangsu Kunshan Lichen research-grade ultrasonic instrument, model LC-MUC-100), the working frequency to 40kHz, and the power to 100W. When the water temperature reaches the set 60℃, place the three prepared solutions into the equipment and label them. Perform ultrasonication. After 20 minutes, remove one sample and place it in a fume hood to keep it dry. After 40 minutes, remove another sample and place it in the fume hood as well. After 60 minutes, remove the third sample and place it in the fume hood. Pour the samples into centrifuge tubes and place them in a centrifuge. Set the time to 30 minutes, the temperature to 30℃, and the speed to 3000 rpm, and centrifuge for 30 minutes. Let the ultrasonically dispersed samples stand for 12 hours (to allow the samples to settle and suspend). After standing, transfer the upper suspension (aqueous solution) of the sample into a glass dish using a pipette and label it as the supernatant. Similarly, transfer the slightly turbid precipitate into a glass dish using a pipette and label it as the subnatant. Figure 1 The supernatant and supernatant were placed in a forced-air drying oven at 60°C for 24 hours and then collected.

[0022] 4) The porous graphene products obtained before and after ultrasonic exfoliation were characterized by SEM, Raman, XRD and HRTEM to compare the differences in graphene structural features.

[0023] Figure 2 These are SEM images of coal samples before and after ultrasonic stripping under laser irradiation. The SEM images after ultrasonic treatment show that the layers are significantly thinner and the number of layers / packing density is reduced, and the arrangement is more straight.

[0024] Figure 3 The Raman spectra of the samples before and after ultrasonication are shown. Peak fitting results indicate that the G peak decreased significantly by about 3 times compared to the unexfoliated sample (the G peak is most sensitive to the two-phonon iTO vibration response, which can reflect that a lower G peak indicates fewer layers). Comparison at different times shows that under certain temperature and solution concentration conditions, ultrasonication for more than 40 minutes is sufficient for successful exfoliation, indicating that more graphene layers are present after ultrasonication. The G peak in Raman spectroscopy typically reflects the graphitization degree of carbon materials. A higher G peak indicates a higher degree of graphitization, meaning it is closer to graphite. Conversely, a lower G peak indicates a lower degree of graphitization, meaning it is closer to graphene. A key indicator for distinguishing between graphene and graphite in Raman spectroscopy is the symmetry of the 2D peaks. Graphite is asymmetrical, while graphene is relatively symmetrical. The graph shows that the G peak decreased after 20 minutes of ultrasonication, and at 40 and 60 minutes, the G peak stabilized at an intensity of approximately 144. After 40 minutes of ultrasonication, the I... 2D Than I GThe intensity increased from 0.73 before ultrasound to 0.88 after 40 minutes of ultrasound, demonstrating effective ablation compared to the control without ultrasound, resulting in a reduction in the number of layers. It is worth noting that I... D / I G The increase in chromatogram intensity (CPI) after ultrasonic exfoliation compared to before exfoliation (0.43-0.087) does not necessarily indicate an increase in defects. This is because ultrasonic exfoliation can only break the van der Waals forces between graphene layers but cannot destroy the C / C bonds of carbon atoms within the graphene layers. Therefore, ultrasonic exfoliation results in more thin, few-layer sheets and more edges, which can also indirectly reflect the exfoliation of more graphene.

[0025] Figure 4 The XRD patterns of the samples before and after ultrasound are shown. Peak fitting was performed, and calculations were performed using the Scherrer formula and Bragg's equation. The results show that the area ratio of the few-layer peaks increased by approximately 1 / 3 after JJG ultrasound compared to the area ratio without ultrasound. N ave The value also decreased accordingly, and the number of layers decreased significantly, further confirming that ultrasound effectively exfoliated the original multilayer graphene, resulting in a significant increase in yield.

[0026] The table shows the XRD results of JJG samples after fitting the peaks at different ultrasonic times.

[0027]

[0028]

[0029] Figure 5 The images show HRTEM images of the samples before and after ultrasonication. It is clear from the images that different ultrasonication times exhibit different morphological characteristics. Before ultrasonication, the graphene stacking is relatively severe. After 20 minutes of ultrasonication, the multilayered graphene sheets begin to thin, and more new edges are observed. After 40 minutes of ultrasonication, thinner, ridge-like graphene sheets are visible. After 60 minutes of ultrasonication, thin, multi-edge, few-layer graphene sheets are also observed. This clearly demonstrates that ultrasonic exfoliation significantly reduces the number of graphene layers and significantly increases the yield. Attached Figure Description

[0030] Figure 1 The supernatant and supernatant are the liquids after ultrasonic stripping of the JJG sample.

[0031] Figure 2 SEM images of coal samples before and after ultrasonic stripping under laser irradiation.

[0032] Figure 3 Raman spectra of coal samples before and after ultrasonic stripping under laser irradiation

[0033] Figure 4 The images show the XRD patterns of the coal samples before and after ultrasonic stripping under laser irradiation.

[0034] Figure 5 TEM spectra of coal samples before and after ultrasonic stripping under laser irradiation.

Claims

1. A method for improving the yield of coal-based graphene based on direct ultrasonic treatment, characterized in that, Using Jiajiagou low-volatile bituminous coal as raw material, coal-based graphene was prepared in one step based on laser-induced graphene technology after demineralization. Then, an ultrasonic solution was prepared to ultrasonically exfoliate the sample. After ultrasonic dispersion, the sample was centrifuged and allowed to stand. The supernatant and supernatant samples were dried and collected to obtain the ultrasonically exfoliated few-layer graphene material.

2. The method for improving the yield of coal-based graphene based on direct ultrasonic treatment according to claim 1, characterized in that, The demineralization process is carried out by acid washing. Specifically, 10g of coal sample, 300mL of ultrapure water, 50mL of hydrochloric acid and 40mL of hydrofluoric acid are weighed and thoroughly mixed with the coal sample. The mixture is then kept in a constant temperature water bath at 60℃ for 8 hours. After that, the mixture is filtered and rinsed with ultrapure water until it becomes neutral.

3. The method for improving the yield of coal-based graphene based on direct ultrasonic treatment according to claim 1, characterized in that, The laser-induced graphene technology is based on self-built equipment and uses commercial 10.64μm wavelength continuous CO2 infrared laser irradiation. The preparation process includes coal sample pretreatment, pelletizing, and laser irradiation.

4. The method for improving the yield of coal-based graphene based on direct ultrasonic treatment according to claim 1, characterized in that, The prepared ultrasonic solution is made of anhydrous ethanol (99% purity) and deionized water in a 2:3 ratio.

5. The method for improving the yield of coal-based graphene based on direct ultrasonic treatment according to claim 1, characterized in that, The ultrasonic dispersion temperature was set to 60℃, and the ultrasonic time was set to 20 min, 40 min, and 60 min; the centrifuge temperature was set to 30℃, the centrifugation speed to 3000 rpm, and the centrifugation time to 30 min; the settling time after centrifugation was 12 h.

6. A few-layer graphene material prepared according to any one of claims 1-9 based on a method for improving the yield of coal-based graphene through direct ultrasonic treatment.

7. The few-layer graphene material prepared by the method of improving the yield of coal-based graphene through direct ultrasonic treatment according to any one of claims 1-9 has great potential for application in battery performance.

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