Method for directly preparing coal-based graphene quantum dots through electrocatalytic oxidation depolymerization of coal water slurry

Abstract

The invention discloses a method for directly preparing coal-based graphene quantum dots through electrocatalytic oxidation depolymerization of coal water slurry, and belongs to the technical field of clean and efficient utilization of coal and preparation of coal-based nano materials. The method comprises the following steps: constructing a mixed electro-catalytic reaction system by taking coal water slurry as an anolyte and a potassium hydroxide solution as a catholyte; a pulse voltage electrolysis mode is adopted to realize selective bond breaking and controllable depolymerization of a coal macromolecular structure on a specific active site on the surface of the catalyst, so that the coal-based graphene quantum dots are directly prepared. The controllable preparation of the coal-based graphene quantum dots is realized by regulating and controlling the catalyst material, the concentration of the coal slurry solution, the reaction temperature and the pulse voltage parameters, and the highest yield of the coal-based graphene quantum dots can reach 20.1 wt%.

Description

Technical Field

[0001] This invention belongs to the field of clean and efficient utilization of coal and preparation of coal-based nanomaterials. Specifically, it relates to a method for preparing coal-based graphene quantum dots by using coal-water slurry as raw material and achieving highly selective depolymerization of coal macromolecules through electrocatalytic oxidation. Background Technology

[0002] Coal is one of my country's most abundant and widely distributed fossil energy resources, and will remain a crucial foundation for ensuring national energy security and socio-economic development for a considerable period. However, traditional coal utilization methods, primarily based on combustion, suffer from significant drawbacks such as low added value, low energy efficiency, and high pollutant and carbon emissions, making it difficult to meet the requirements of green and low-carbon development. Therefore, promoting the transformation of coal from a single fuel to a high-value-added carbon-based material precursor, and achieving clean, efficient, and refined utilization of coal resources, has become an important development direction in modern coal chemical industry and new materials fields.

[0003] From a molecular structure perspective, coal is a highly complex macromolecular organic polymer. Its basic structural units consist of polycyclic aromatic structures, aliphatic chain bridging bonds, and heteroatom functional groups, which are interconnected in three-dimensional space through various bridging bonds. If the macromolecular structure of coal can be directionally broken and selectively depolymerized, aromatic carbon structural units with controllable size and well-defined structure can be obtained, providing ideal precursors for the preparation of novel carbon-based nanomaterials such as carbon quantum dots and coal-based graphene quantum dots.

[0004] Coal-based graphene quantum dots, as zero-dimensional carbon nanomaterials with excellent optical, electrical, and chemical stability, have broad application prospects in fields such as fluorescent probes, bioimaging, sensors, and energy storage and conversion. Therefore, developing a green and efficient method for preparing coal-based graphene quantum dots using coal as a raw material is of great significance for enhancing the added value of coal resource utilization. Ye et al. (Ye R, Xiang C, Lin J, et al. Coal as an abundant source of graphene quantum dots. Nature Communications. 2013; 4: 2943) disclosed a method for directly preparing coal-based graphene quantum dots by chemically oxidizing coal using a mixed acid system composed of concentrated sulfuric acid and nitric acid.

[0005] Currently, the main methods for preparing coal-based carbon quantum dots or coal-based graphene quantum dots include liquid-phase chemical oxidation, hydrothermal methods (Xu S, Wang Y, Wu Y, Li M. Nitrogen and sulfur co-doped coal-based carbon quantum dots enhance the photocatalytic hydrogen evolution of Co-Fe-P derived from MOF. Surfaces and Interfaces. 2024; 44: 103576.), solvothermal methods (Li MY, Yu C, Hu C, Yang WB, Zhao CT, Wang S, Zhang MD, Zhao JZ, Wang XN, Qiu JS. Solvothermal conversion of coal into nitrogen-doped carbon dots with singletoxygen generation and high quantum yield. Chemical Engineering Journal. 2017;320: 570–575.), and electrochemical exfoliation methods (He MQ, Guo XR, Huang JZ, Shen HH, Zeng Q, Wang LS. Mass production of tunable multicolor graphene quantum dots from an energy resource of coke by a one-step (electrochemical exfoliation. Carbon. 2018; 140: 508–520), etc. However, the above preparation methods still have certain limitations. Liquid-phase chemical oxidation methods usually rely on strong acids or strong oxidants such as sulfuric acid and nitric acid. While achieving the breaking of the macromolecular structure of coal, they generally suffer from harsh reaction conditions, strong system corrosivity, and heavy waste liquid treatment burden. Moreover, the oxidation process lacks selectivity, and the aromatic structure in coal is prone to disordered breaking, which can easily lead to over-oxidation or structural destruction. The product size and structural distribution are wide and the controllability is poor. Hydrothermal and solvothermal methods usually need to be carried out under high temperature and high pressure conditions, with long reaction times, high energy consumption, and strict requirements on reaction equipment.While electrochemical stripping offers the advantage of relatively mild reaction conditions, existing methods largely rely on coal-derived carbon-based self-sacrificing electrodes (Bai R, Zhou X, Liu Q, et al. Self-supporting coal liquefaction residue electrode intensifies efficient coupling of hydrogen evolution and carbondots preparation. Chemical Engineering Journal. 2025; 504: 158975). These methods suffer from limitations such as a limited effective reaction interface, low mass transfer efficiency, and extremely high reaction voltage, making it difficult to fully utilize the structural advantages of coal as a dispersed phase precursor.

[0006] Overall, existing methods still struggle to balance structural controllability, energy consumption levels, and scalability. Summary of the Invention

[0007] To address the problems of harsh reaction conditions, poor structural controllability, high energy consumption, and difficulty in achieving large-scale preparation in existing methods for preparing coal-based carbon quantum dots or coal-based graphene quantum dots, this invention provides a method for the selective depolymerization of coal macromolecules under mild conditions, enabling the direct preparation of coal-based graphene quantum dots. By constructing a coal-water slurry electrochemical reaction system, selective bond breaking and depolymerization of coal macromolecules are achieved through anodic electrocatalytic oxidation, thereby directly obtaining coal-based graphene quantum dots.

[0008] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation and depolymerization of coal-water slurry is disclosed. The method uses coal-water slurry as the anolyte and potassium hydroxide solution as the catholyte to construct a mixed electrocatalytic reaction system. The anolyte coal-water slurry electrocatalytic oxidation reaction is carried out by pulse voltage electrolysis to directly obtain coal-based graphene quantum dots.

[0010] The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry involves an electrocatalytic oxidation reaction temperature of 30–60 °C; pulsed voltage electrolysis employs an alternating pulsed mode of high and low potentials, with the low potential ranging from -0.8 to 0 V. RHE The high potential is 1.0~1.5 V. RHEThe pulse width is 0.5 s, and the total electrolysis time is 12 h; the total electrolysis time refers to the cumulative electrolysis time from the start of electrolysis until the completion of multiple electrolysis cycles; preferably, the electrocatalytic oxidation reaction temperature is 40~60 ℃; the high potential of the pulse voltage is 1.0~1.4 V. RHE The low potential is -0.8 to -0.5 V. RHE .

[0011] The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation and depolymerization of coal-water slurry, wherein the concentration of the coal-water slurry is 10-60 g / L and the concentration of the potassium hydroxide solution is 0.5-6 mol / L; the cathode electrode of the electrocatalytic reaction system is a titanium felt electrode, and the anode electrode is any one of a platinum electrode, nickel electrode, iron electrode, lead electrode, palladium electrode, or copper electrode and their composite electrode; the composite electrode is a composite metal electrode, which is a composite metal electrode formed by alloying, composite coating, or co-deposition of at least two of the above metals, and can be a nickel-iron composite electrode, a platinum-nickel composite electrode, a palladium-nickel composite electrode, or a nickel-copper composite electrode; the area ratio of the anode electrode to the cathode electrode is 1:4; preferably, the concentration of the coal-water slurry is 20 g / L and the concentration of the potassium hydroxide solution is 4 mol / L; the cathode electrode of the electrocatalytic reaction system is a titanium felt electrode and the anode electrode is a copper electrode.

[0012] The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry includes the following steps for preparing the coal-water slurry: The coal raw material is pulverized and pretreated with DMF (N,N-dimethylformamide) solution for swelling. Then, it is washed sequentially with anhydrous ethanol and distilled water to remove residual DMF solution and ethanol from the coal. The treated coal raw material is then dried to obtain the swollen coal. Potassium hydroxide solution is added to the swollen coal, and after thorough stirring, an anode coal-water slurry electrolyte with uniformly dispersed coal particles is obtained.

[0013] The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry uses Heishan bituminous coal as the raw material. The coal raw material is crushed to 150 mesh, and the concentration of the coal raw material in DMF solution is 3 mL / g. The swelling treatment temperature is 30℃ for 12 h, the drying temperature is 80℃, and the drying time is 24 h. The concentration of potassium hydroxide solution is 0.5~6 mol / L; preferably, the concentration of potassium hydroxide solution is 4 mol / L.

[0014] The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry involves centrifuging the anolyte coal-water slurry reaction solution after the electrocatalytic oxidation reaction is completed to obtain solid residual coal and supernatant containing coal-based graphene quantum dots; the supernatant is then dialyzed until the dialysate is neutral.

[0015] The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry, wherein the dialysis bag used for dialysis has a molecular weight cutoff of 2000 Da, and dialysis is performed at a rotation speed of 200 r / min for a dialysis time of 72-120 h.

[0016] In the method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation and depolymerization of coal-water slurry, in order to ensure dialysis efficiency, deionized water is replaced every 2-4 hours during the first 48 hours of dialysis; thereafter, deionized water is replaced every 12 hours.

[0017] The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry includes the following steps:

[0018] (1) After the coal raw material is swollen and dispersed, an anode coal-water slurry electrolyte with uniformly dispersed coal particles is obtained;

[0019] (2) Install the anode and cathode electrodes in the electrolytic cell, and deliver the anode electrolyte and cathode electrolyte to the anode side and cathode side respectively through a peristaltic pump, and circulate or stir the coal-water slurry on the anode side to ensure uniform dispersion of coal particles; the flow rate of the peristaltic pump is 20 mL / min;

[0020] (3) Set the reaction temperature and perform pulsed voltage electrolysis in a two-electrode system to cause selective bond breaking and depolymerization of coal macromolecules at the anode through electrocatalytic oxidation, and obtain a reaction solution containing coal-based graphene quantum dots;

[0021] (4) Centrifuge the reaction solution to remove solid residual coal and take the supernatant; dialyze the supernatant; immerse the dialysis bag in a container of deionized water, and at the same time put a magnetic rotor in the deionized water and place it on a magnetic stirrer to complete the dialysis treatment under stirring conditions.

[0022] (5) After the dialysis solution is concentrated by rotary evaporation, it is then freeze-dried under vacuum and ground to obtain coal-based graphene quantum dot powder; the rotary evaporation concentration is carried out at 50~80 ℃ for 1 h, and the vacuum freeze-drying time is 12~72 h; preferably, the rotary evaporation concentration is carried out at 50 ℃ for 1 h, and the vacuum freeze-drying time is 48 h.

[0023] The method for directly preparing coal-based graphene quantum dots through electrocatalytic oxidation and depolymerization of coal-water slurry uses a copper electrode as the anode, a potassium hydroxide solution concentration of 4 mol / L, a coal-water slurry concentration of 20 g / L, a reaction temperature of 40 ℃, and a high potential of 1.1 V for pulse electrolysis. RHE The low potential is -0.8 V. RHE .

[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0025] (1) This invention directly uses coal molecules as reactants to prepare coal-based graphene quantum dots by selectively breaking bonds and depolymerizing them at specific active sites on the catalyst surface.

[0026] (2) Compared with the existing mixed acid system for preparing coal-based carbon quantum dots by liquid phase oxidation, the present invention does not require the use of corrosive and strong oxidizing acids, has a short reaction time and high product selectivity;

[0027] (3) Compared with the existing method for preparing coal-based carbon quantum dots by self-sacrificing electrode electrolytic stripping, the voltage used in this invention is only 1.0~1.5 V, which is much lower than the 2.0 V~5.0 V of the electrolytic stripping method. It has the advantages of low cell voltage and low energy consumption, and the product structure can be flexibly controlled.

[0028] (4) As an anode-side reaction of the electrocatalytic system, the present invention can be coupled with reactions such as hydrogen evolution, carbon dioxide reduction, and ammonia synthesis on the cathode side to construct a low-energy-consumption, high-value-added mixed electrocatalytic system.

[0029] (5) This invention can be applied to any type of coal and has strong versatility;

[0030] In summary, this invention provides a new universal technical approach for the clean and efficient conversion of coal resources into high-value-added carbon-based nanomaterials, characterized by mild reaction conditions, high product selectivity / tunable structure, low energy consumption, and environmental friendliness. Attached Figure Description

[0031] Figure 1 The image shows the appearance of the coal-based graphene quantum dots prepared in Example 1.

[0032] Figure 2 High-resolution transmission electron microscope (HRTEM) image of the coal-based graphene quantum dots prepared in Example 1;

[0033] Figure 3 High-resolution transmission electron microscope (HRTEM) image of coal-based graphene quantum dots prepared in Example 17;

[0034] Figure 4 TEM image of coal-based graphene quantum dots prepared in Example 17;

[0035] Figure 5 The fluorescence emission spectrum of the coal-based graphene quantum dots prepared in Example 17;

[0036] Figure 6 The graphs show the current density of the electrocatalytic system under different pulse high / low potential combinations in Examples 17-22 as a function of time. Detailed Implementation

[0037] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0038] Example 1

[0039] A method for directly preparing coal-based graphene quantum dots from coal via electrocatalytic oxidation and depolymerization of coal-water slurry includes the following steps:

[0040] (1) After crushing the black coal to 150 mesh, it was pretreated with DMF solution for swelling. The concentration of coal in DMF solution was 3 mL / g. The coal was swollen at 30 °C for 12 h. After swelling, it was washed with anhydrous ethanol and water in sequence, and then dried at 80 °C for 24 h to obtain swollen coal sample.

[0041] (2) Add 10 g of the swollen coal sample obtained in step (1) to 1 L of potassium hydroxide solution with a concentration of 0.5 mol / L, stir thoroughly to make the coal particles evenly dispersed, and prepare a coal-water slurry with a concentration of 10 g / L, which is used as the anode electrolyte; and use the potassium hydroxide solution with a concentration of 0.5 mol / L as the cathode electrolyte.

[0042] (3) The anode platinum electrode and the cathode titanium felt electrode are installed together in the electrolytic cell. An anion exchange membrane is set between them to realize the migration and conduction of anions and prevent the reactants from mixing directly. The reaction liquid flows continuously through the electrode surface in their respective channels.

[0043] The ratio of the electrode area of ​​the anode to the cathode is 1:4. The anode electrolyte and the cathode electrolyte are introduced into the electrolytic cell at a flow rate of 20 mL / min using a peristaltic pump, and the reaction solution on the anode side is circulated or stirred to ensure that the coal particles are evenly dispersed during the reaction.

[0044] (4) Turn on the water bath heating and control the reaction temperature at 30 ℃. Use a three-electrode system for pulse voltage electrolysis. The pulse electrolysis parameters are: high potential 1.0 V. RHE Low potential -0.8 V RHE The pulse width was 0.5 s, and the total electrolysis time was 12 h. After electrolysis, the reaction liquid on the anode side was centrifuged to remove unreacted solid coal residue and collect the supernatant containing coal-based graphene quantum dots.

[0045] (5) Transfer the obtained supernatant to a dialysis bag with a molecular weight cutoff of 2000 Da and place it in a container filled with deionized water for dialysis. During the dialysis process, keep the magnetic stirring at a speed of 200 r / min. Change the deionized water every 3 hours in the first 48 hours of the initial dialysis, and then change the deionized water every 12 hours until the dialysate is neutral.

[0046] (6) After dialysis, the coal-based graphene quantum dot solution was transferred to a round-bottom flask and concentrated by rotary evaporation at 50 °C for 1 h. The concentrated solution was then freeze-dried in a vacuum freeze dryer for 48 h. The resulting solid was ground to obtain dark brown powdered coal-based graphene quantum dots, as shown in the figure. Figure 1 As shown.

[0047] Based on the mass of the swollen coal sample added, the yield of coal-based graphene quantum dots was 4.3%. Characterization by transmission electron microscopy yielded the following results: Figure 2 As shown, the obtained coal-based graphene quantum dots exhibit a near-spherical structure with clear lattice fringes.

[0048] Example 2

[0049] A method for directly preparing coal-based graphene quantum dots from coal via electrocatalytic oxidation and depolymerization of coal-water slurry includes the following steps:

[0050] (1) Add 10 g of the swollen coal sample obtained in step (1) of Example 1 to 1 L of potassium hydroxide solution with a concentration of 1 mol / L, stir thoroughly to make the coal particles evenly dispersed, and prepare a coal-water slurry with a concentration of 10 g / L, which is used as the anode electrolyte; and use a potassium hydroxide solution with a concentration of 1 mol / L as the cathode electrolyte.

[0051] (2) The anode platinum electrode and the cathode titanium felt electrode are installed together in the electrolytic cell; the electrode area ratio of the anode to the cathode is 1:4; the anode electrolyte and the cathode electrolyte are introduced into the electrolytic cell by a peristaltic pump at a flow rate of 20 mL / min, and the reaction liquid on the anode side is circulated or stirred to ensure that the coal particles are evenly dispersed during the reaction.

[0052] (3) Turn on the water bath heating and control the reaction temperature at 30 ℃. Use a three-electrode system for pulse voltage electrolysis. The pulse electrolysis parameters are: high potential 1.0 V. RHE Low potential -0.8 V RHE The pulse width was 0.5 s, and the total electrolysis time was 12 h. After electrolysis, the reaction liquid on the anode side was centrifuged to remove unreacted solid coal residue and collect the supernatant containing coal-based graphene quantum dots.

[0053] (4) Transfer the obtained supernatant to a dialysis bag with a molecular weight cutoff of 2000 Da and place it in a container filled with deionized water for dialysis. During the dialysis process, keep the magnetic stirring at a speed of 200 r / min. Change the deionized water every 3 hours in the first 48 hours of the initial dialysis, and then change the deionized water every 12 hours until the dialysate is neutral.

[0054] (5) After dialysis, the coal-based graphene quantum dot solution was transferred to a round-bottom flask and concentrated by rotary evaporation at 50 °C for 1 h. The concentrated solution was then freeze-dried in a vacuum freeze dryer for 48 h. The resulting solid was ground to obtain dark brown powdered coal-based graphene quantum dots.

[0055] Based on the mass of the added swollen coal sample, the yield of the obtained coal-based graphene quantum dots was 6.7%.

[0056] Example 3

[0057] A method for directly preparing coal-based graphene quantum dots from coal via electrocatalytic oxidation and depolymerization of coal-water slurry includes the following steps:

[0058] (1) Add 10 g of the swollen coal sample obtained in step (1) of Example 1 to 1 L of potassium hydroxide solution with a concentration of 4 mol / L, stir thoroughly to disperse the coal particles evenly, and prepare a coal-water slurry with a concentration of 10 g / L, which is used as the anode electrolyte; and use the potassium hydroxide solution with a concentration of 4 mol / L as the cathode electrolyte.

[0059] (2) The anode platinum electrode and the cathode titanium felt electrode are installed together in the electrolytic cell; the electrode area ratio of the anode to the cathode is 1:4; the anode electrolyte and the cathode electrolyte are introduced into the electrolytic cell by a peristaltic pump at a flow rate of 20 mL / min, and the reaction liquid on the anode side is circulated or stirred to ensure that the coal particles are evenly dispersed during the reaction.

[0060] (3) Turn on the water bath heating and control the reaction temperature at 30 ℃. Use a three-electrode system for pulse voltage electrolysis. The pulse electrolysis parameters are: high potential 1.0 V. RHE Low potential -0.8 V RHE The pulse width was 0.5 s, and the total electrolysis time was 12 h. After electrolysis, the reaction liquid on the anode side was centrifuged to remove unreacted solid coal residue and collect the supernatant containing coal-based graphene quantum dots.

[0061] (4) Transfer the obtained supernatant to a dialysis bag with a molecular weight cutoff of 2000 Da and place it in a container filled with deionized water for dialysis. During the dialysis process, keep the magnetic stirring at a speed of 200 r / min. Change the deionized water every 3 hours in the first 48 hours of the initial dialysis, and then change the deionized water every 12 hours until the dialysate is neutral.

[0062] (5) After dialysis, the coal-based graphene quantum dot solution was transferred to a round-bottom flask and concentrated by rotary evaporation at 50 °C for 1 h. The concentrated solution was then freeze-dried in a vacuum freeze dryer for 48 h. The resulting solid was ground to obtain dark brown powdered coal-based graphene quantum dots.

[0063] Based on the mass of the added swollen coal sample, the yield of the obtained coal-based graphene quantum dots was 8.6%.

[0064] Example 4

[0065] The difference between this embodiment and Embodiment 3 is as follows: 10 g of the obtained swollen coal sample was added to 1 L of a 6 mol / L potassium hydroxide solution and stirred thoroughly to uniformly disperse the coal particles, thus preparing a 10 g / L coal-water slurry, which was used as the anolyte; the 6 mol / L potassium hydroxide solution was used as the catholyte; and the pulse electrolysis parameters were: high potential 1.0V. RHE Low potential -0.7 V RHE The pulse width was 0.5 s, and the total electrolysis time was 12 h; the yield of the obtained coal-based graphene quantum dots was 6.2%.

[0066] Example 5

[0067] The difference between this embodiment and Embodiment 3 is as follows: 20 g of the obtained swollen coal sample was added to 1 L of a 4 mol / L potassium hydroxide solution and stirred thoroughly to uniformly disperse the coal particles, thus preparing a 20 g / L coal-water slurry, which was used as the anolyte; the 4 mol / L potassium hydroxide solution was used as the catholyte; and the pulse electrolysis parameters were: high potential 1.0V. RHE Low potential -0.6 V RHE The pulse width was 0.5 s, and the total electrolysis time was 12 h; the yield of the obtained coal-based graphene quantum dots was 7.6%.

[0068] Example 6

[0069] The difference between this embodiment and Embodiment 3 is as follows: 40 g of the obtained swollen coal sample was added to 1 L of a 4 mol / L potassium hydroxide solution and stirred thoroughly to uniformly disperse the coal particles, thus preparing a 40 g / L coal-water slurry, which was used as the anolyte; the 4 mol / L potassium hydroxide solution was used as the catholyte; and the pulse electrolysis parameters were: high potential 1.0V. RHE Low potential -0.5 V RHE The pulse width was 0.5 s, and the total electrolysis time was 12 h; the yield of the obtained coal-based graphene quantum dots was 7.0%.

[0070] Example 7

[0071] The difference between this embodiment and Embodiment 3 is as follows: 60 g of the obtained swollen coal sample was added to 1 L of a 4 mol / L potassium hydroxide solution and stirred thoroughly to uniformly disperse the coal particles, thus preparing a 60 g / L coal-water slurry, which was used as the anolyte; the 4 mol / L potassium hydroxide solution was used as the catholyte; and the pulse electrolysis parameters were: high potential 1.0V. RHE Low potential -0.4 V RHE The pulse width was 0.5 s, and the total electrolysis time was 12 h; the yield of the obtained coal-based graphene quantum dots was 7.2%.

[0072] Example 8

[0073] The difference between this embodiment and Embodiment 3 is that: the anode electrode is an iron electrode, and 20 g of swollen coal sample is added to 1 L of potassium hydroxide solution with a concentration of 4 mol / L to prepare a coal-water slurry with a concentration of 20 g / L, which is used as the anode electrolyte; the potassium hydroxide solution with a concentration of 4 mol / L is used as the cathode electrolyte; the yield of the obtained coal-based graphene quantum dots is 6.8%.

[0074] Example 9

[0075] The difference between this embodiment and Embodiment 8 is that the anode electrode is a nickel electrode, and the yield of the obtained coal-based graphene quantum dots is 7.2%.

[0076] Example 10

[0077] The difference between this embodiment and Embodiment 8 is that the anode electrode is a palladium electrode, and the yield of the obtained coal-based graphene quantum dots is 7.5%.

[0078] Example 11

[0079] The difference between this embodiment and Embodiment 8 is that the anode electrode is a lead electrode, and the yield of the obtained coal-based graphene quantum dots is 8.1%.

[0080] Example 12

[0081] The difference between this embodiment and Embodiment 8 is that the anode electrode is a copper electrode, and the yield of the obtained coal-based graphene quantum dots is 9.5%.

[0082] Example 13

[0083] The difference between this embodiment and Embodiment 8 is that the anode electrode is a nickel-iron electrode, and the yield of the obtained coal-based graphene quantum dots is 7.5%.

[0084] Example 14

[0085] The difference between this embodiment and Example 12 is that the reaction temperature was controlled at 40 °C, and the yield of the obtained coal-based graphene quantum dots was 16.8%.

[0086] Example 15

[0087] The difference between this embodiment and Example 12 is that the reaction temperature was controlled at 50 °C, and the yield of the obtained coal-based graphene quantum dots was 13.6%.

[0088] Example 16

[0089] The difference between this embodiment and Example 12 is that the reaction temperature is controlled at 60 °C, and the yield of coal-based graphene quantum dots is 12.4%.

[0090] Example 17

[0091] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.1 V. RHE Low potential -0.8V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 20.1%.

[0092] Figure 3 The image shows a high-resolution transmission electron microscope (HRTEM) image of the coal-based graphene quantum dots prepared in Example 17. The inset shows lattice fringes with a corresponding interplanar spacing of approximately 0.21 nm and a photograph of the coal-based graphene quantum dot solution taken under 365 nm ultraviolet light. Figure 4 TEM image of the coal-based graphene quantum dots prepared in Example 17 (inset: particle size distribution). Characterized by transmission electron microscopy, the obtained coal-based graphene quantum dots exhibit a near-spherical structure and clear lattice fringes, with an interplanar spacing of approximately 0.21 nm, corresponding to the (100) interplanar spacing of graphene crystals. The particle size distribution is concentrated (average particle size approximately 1.33 nm), demonstrating structural uniformity and good fluorescence properties (e.g., ...). Figure 5 (As shown).

[0093] Example 18

[0094] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.1 V. RHE Low potential -0.7V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 15.1%.

[0095] Example 19

[0096] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.1 V. RHE Low potential -0.6V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 12.1%.

[0097] Example 20

[0098] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.1 V. RHE Low potential -0.5V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 10.3%.

[0099] Example 21

[0100] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.2 V. RHE Low potential -0.8V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 12.3%.

[0101] Example 22

[0102] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.3 V. RHE Low potential -0.8V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 10.1%.

[0103] Figure 6 The graphs shown are the current density versus time curves of the electrocatalytic system under different pulse high / low potential combinations in Examples 17-22. Figure 6 It can be seen that under the action of pulse voltage, the current density exhibits a reproducible periodic change over time and does not show an obvious decay trend, indicating that the system has good operational stability and can achieve continuous and stable reaction.

[0104] Example 23

[0105] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.4 V. RHE Low potential -0.8V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 13.7%.

[0106] Example 24

[0107] The difference between this embodiment and Embodiment 14 is that the pulse electrolysis parameters are: high potential 1.5 V. RHE Low potential -0.8V RHE With a pulse width of 0.5 s and a total electrolysis time of 12 h, the yield of coal-based graphene quantum dots was 7.7%.

[0108] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for directly preparing coal-based graphene quantum dots through electrocatalytic oxidation and depolymerization of coal-water slurry, characterized in that, A mixed electrocatalytic reaction system was constructed using coal-water slurry as the anode electrolyte and potassium hydroxide solution as the cathode electrolyte. The anode coal-water slurry electrocatalytic oxidation reaction was carried out by pulse voltage electrolysis to directly obtain coal-based graphene quantum dots.

2. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 1, characterized in that, The electrocatalytic oxidation reaction temperature is 30~60 ℃; the pulsed voltage electrolysis adopts a pulsed mode of alternating high and low potentials, wherein the low potential is -0.8~0 V. RHE The high potential is 1.0~1.5 V. RHE The pulse width is 0.5 s, and the total electrolysis time is 12 h.

3. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 1, characterized in that, The concentration of the coal-water slurry is 10~60 g / L, and the concentration of the potassium hydroxide solution is 0.5~6 mol / L; the cathode electrode of the electrocatalytic reaction system is a titanium felt electrode, and the anode electrode is any one of a platinum electrode, nickel electrode, iron electrode, lead electrode, palladium electrode or copper electrode, or any one of a composite metal electrode formed by combining at least two of the above metals; the area ratio of the anode electrode to the cathode electrode is 1:

4.

4. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 1, characterized in that, The preparation of coal-water slurry is as follows: the coal raw material is crushed, pretreated with DMF solution for swelling, and then washed with anhydrous ethanol and distilled water in sequence; the treated swollen coal is then dried to obtain the swollen coal used; potassium hydroxide solution is added to the swollen coal, and after thorough stirring, an anode coal-water slurry electrolyte with uniformly dispersed coal particles is obtained.

5. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 4, characterized in that, The coal raw material was Heishan bituminous coal, which was crushed to 150 mesh. The concentration of the coal raw material in the DMF solution was 3 mL / g. The swelling pretreatment temperature was 30 ℃ and the time was 12 h. The drying temperature was 80 ℃ and the drying time was 24 h. The concentration of potassium hydroxide solution was 0.5~6 mol / L.

6. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 1, characterized in that, After the electrocatalytic oxidation reaction is completed, the anolyte coal-water slurry reaction solution is centrifuged to obtain solid residual coal and supernatant containing coal-based graphene quantum dots; the supernatant is dialyzed until the dialysate is neutral.

7. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 6, characterized in that, The dialysis bag used for dialysis has a molecular weight cutoff of 2000 Da and is dialyzed at a rotation speed of 200 r / min for 72-120 h.

8. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 6, characterized in that, During the first 48 hours of dialysis, the deionized water was changed every 2 to 4 hours; thereafter, it was changed every 12 hours.

9. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 1, characterized in that, Includes the following steps: (1) After the coal raw material is swollen and dispersed, an anode coal-water slurry electrolyte with uniformly dispersed coal particles is obtained; (2) Install the anode and cathode electrodes in the electrolytic cell, and deliver the anode electrolyte and cathode electrolyte to the anode side and cathode side respectively through a peristaltic pump, and circulate or stir the coal-water slurry on the anode side; the flow rate of the peristaltic pump is 20 mL / min; (3) Set the reaction temperature and perform pulsed voltage electrolysis under a two-electrode system to obtain a reaction solution containing coal-based graphene quantum dots; (4) Centrifuge the reaction solution to remove solid residual coal and take the supernatant; dialyze the supernatant; immerse the dialysis bag in a container of deionized water, and at the same time put a magnetic rotor in the deionized water and place it on a magnetic stirrer to complete the dialysis treatment under stirring conditions. (5) After the dialysis solution is concentrated by rotary evaporation, it is then freeze-dried under vacuum and ground to obtain coal-based graphene quantum dot powder; the rotary evaporation concentration is carried out at 60~80 ℃ for 1 h, and the vacuum freeze-drying time is 12~72 h.

10. The method for directly preparing coal-based graphene quantum dots by electrocatalytic oxidation depolymerization of coal-water slurry according to claim 1 or 9, characterized in that, During pulse electrolysis, the anode electrode is a copper electrode, the concentration of potassium hydroxide solution is 4 mol / L, the concentration of coal-water slurry is 20 g / L, the reaction temperature is 40 ℃, and the high potential for pulse electrolysis is 1.1 V. RHE The low potential is -0.8 V. RHE .

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