In-situ doping-gradient quenching integrated preparation method of coal-based graphene quantum dots

Abstract

The invention provides an in-situ doping-gradient quenching integrated preparation method of coal-based graphene quantum dots, and relates to the technical field of graphene quantum dot preparation, and the method comprises the following steps: pretreating a coal raw material; mixing the pretreated coal raw material with a doping agent, and carrying out in-situ doping reaction, so that carboxyl of the doping agent and a coal aromatic ring are subjected to esterification reaction to form a C-O-X covalent bond; in the in-situ doping reaction process, gradient quenching treatment is synchronously carried out; according to the method, in-situ doping and gradient quenching are synchronously carried out, the steps of firstly preparing GQDs, then doping and independently cooling in a traditional method are omitted, the preparation steps are simplified, the production period is shortened, the yield is improved, an in-situ doping technology is adopted, a C-O-X covalent bond is formed through esterification of a doping agent carboxyl and a coal aromatic ring, doping elements are uniformly distributed in the GQDs, and the performance of the GQDs is improved. The segregation problem of post-doping is avoided, and the performance of the material is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of graphene quantum dot preparation technology, and in particular to an integrated method for in-situ doping and gradient quenching preparation of coal-based graphene quantum dots. Background Technology

[0002] Graphene quantum dots (GQDs) are a promising new type of carbon nanomaterial. With their excellent optical, electrical and chemical properties, they have shown broad application prospects in many fields such as bioimaging, sensors and optoelectronic devices. Currently, the preparation methods of GQDs are mainly divided into top-down methods, such as arc discharge method and laser ablation method, and bottom-up methods, such as chemical synthesis method and template method.

[0003] In the field of coal-based GQDs preparation, existing technologies have many obvious drawbacks: traditional post-doping methods involve doping after GQDs are formed, which makes it difficult for dopant elements to be uniformly distributed, easily leading to segregation and severely affecting material properties; the preparation process usually involves multiple independent steps, such as preparing GQDs first, then doping, and finally cooling, which is cumbersome and results in low yields, generally only 30%-40%; the control of parameters such as particle size and fluorescence wavelength of GQDs relies heavily on experience, resulting in poor precision and errors often exceeding 10nm and 15nm; furthermore, existing technologies have never considered the relationship between coal rank and quenching kinetics, making it impossible to optimize the preparation process according to the characteristics of different coal ranks, leading to resource waste and performance instability. Therefore, this invention proposes an integrated in-situ doping-gradient quenching preparation method for coal-based graphene quantum dots to solve the problems existing in the prior art. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes an integrated in-situ doping-gradient quenching method for preparing coal-based graphene quantum dots. This method simultaneously performs in-situ doping and gradient quenching, eliminating the need for the traditional steps of first preparing GQDs and then performing doping and separate cooling. This simplifies the preparation process, shortens the production cycle, and increases the yield.

[0005] To achieve the objectives of this invention, the following technical solution is employed: an integrated method for the in-situ doping and gradient quenching preparation of coal-based graphene quantum dots, comprising the following steps:

[0006] S1: Pre-treatment of coal raw materials;

[0007] S2: The pretreated coal raw material is mixed with the dopant and an in-situ doping reaction is carried out to make the carboxyl group of the dopant react with the aromatic ring of coal to form a COX covalent bond;

[0008] S3: During the in-situ doping reaction, gradient quenching is carried out simultaneously. The gradient quenching parameter optimization algorithm MGQ-GCOA for coal-based GQDs is used to control the particle size and fluorescence wavelength of GQDs.

[0009] S4: The product after gradient quenching is post-processed to obtain coal-based graphene quantum dots.

[0010] A further improvement is that, in S1, the coal raw material is one or a mixture of lignite, bituminous coal, and anthracite.

[0011] A further improvement is that, in S1, the pretreatment includes crushing, sieving, and drying, wherein the sieve mesh size is 50-100 mesh, the drying temperature is 80-100℃, and the drying time is 4-6 hours.

[0012] A further improvement is made in the following: In S2, the dopant is a carboxyl-containing compound, the mass ratio of coal raw material to dopant is 1:0.3-0.8, the temperature of the in-situ doping reaction is 180-250℃, the reaction pressure is 2-5MPa, the reaction time is 4-8 hours, and the reaction is carried out under an inert atmosphere, which is nitrogen or argon, and the gas flow rate is 50-200mL / min.

[0013] A further improvement is made in S3, where the variables of the coal-based GQDs gradient quenching parameter optimization algorithm MGQ-GCOA include coal rank parameter M, dopant concentration C, initial quenching temperature T0, temperature gradient change rate ΔT, quenching time t, target particle size D, and target fluorescence wavelength λ. The coal rank parameter M is set according to the type of coal: 1 for lignite, 2 for bituminous coal, and 3 for anthracite. The calculation logic is as follows: input the coal rank parameter M, dopant concentration C, target particle size D, and target fluorescence wavelength λ, calculate the initial quenching temperature T0, temperature gradient change rate ΔT, and quenching time t, and control the cooling system of the reactor to perform gradient quenching based on T0, ΔT, and t, thereby regulating the particle size and fluorescence wavelength of the GQDs.

[0014] A further improvement lies in the following: the formula for calculating the initial quenching temperature T0 is:

[0015] T0 = ​​a×M + b×C + c×D + d×λ + e

[0016] Where a, b, c, d, and e are constants obtained by fitting experimental data.

[0017] A further improvement lies in the formula for calculating the rate of change of the temperature gradient ΔT:

[0018] ΔT = f × T0 + g × D + h

[0019] Where f, g, and h are constants determined through experiments.

[0020] A further improvement lies in the following: the formula for calculating the quenching time t is:

[0021] t=i×ΔT+j×λ+k

[0022] Where i, j, and k are constants obtained through experimental fitting.

[0023] A further improvement is that S4 includes the following steps:

[0024] The material that has undergone gradient quenching is taken out and centrifuged to remove particulate impurities.

[0025] The supernatant was collected and dialyzed through a dialysis bag to remove residual solvent and unreacted dopants.

[0026] The dialysis solution was freeze-dried to obtain coal-based graphene quantum dots.

[0027] Further improvements include: during centrifugation, controlling the rotation speed to 8000-10000 r / min and the centrifugation time to 15-30 minutes; and during dialysis, the dialysis time to 24-48 hours.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention performs in-situ doping and gradient quenching simultaneously, eliminating the steps of preparing GQDs first and then doping and cooling separately in traditional methods. This simplifies the preparation process, shortens the production cycle, and improves the yield. Furthermore, by using in-situ doping technology, COX covalent bonds are formed by the esterification of the carboxyl group of the dopant with the aromatic ring of coal, so that the dopant element is uniformly distributed in the GQDs, avoiding the segregation problem of post-doping and effectively improving the performance of the material.

[0030] 2. The gradient quenching process of this invention, combined with an optimization algorithm, can accurately calculate various quenching parameters based on different coal ranks, dopant concentrations, and other parameters. This allows for precise control of the particle size and fluorescence wavelength of GQDs, with control errors within ±2nm and ±5nm, respectively. Furthermore, by linking coal rank with quenching kinetics, a more stable quenching path is obtained, resulting in more stable performance of the prepared GQDs and facilitating efficient utilization of different coal ranks. Attached Figure Description

[0031] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0032] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0033] Example 1

[0034] according to Figure 1 As shown, this embodiment proposes an integrated in-situ doping-gradient quenching preparation method for coal-based graphene quantum dots, including the following steps:

[0035] Coal raw material pretreatment: The coal raw material is crushed and sieved to obtain coal particles with a particle size of 50-100 mesh. Then, the coal particles are dried at 80-100℃ for 4-6 hours to remove moisture. This step provides dry and uniform coal raw material for the subsequent in-situ doping reaction, which is conducive to the full progress of the reaction.

[0036] In-situ doping reaction: Pretreated coal particles and carboxyl-containing dopants are added to a reactor at a mass ratio of 1:0.3-0.8, followed by the addition of an appropriate amount of solvent to ensure thorough dispersion of the coal particles and dopants. The reactor is sealed, heated to 180-250℃, and the reaction pressure is maintained at 2-5 MPa for 4-8 hours. During the reaction, the carboxyl groups of the dopants undergo esterification with the aromatic rings of the coal, forming COX covalent bonds (where X is the dopant element), achieving a uniform distribution of the dopant element within the coal structure. This step is closely integrated with the pretreatment step, allowing the pretreated coal particles to react more effectively with the dopants.

[0037] Synchronous gradient quenching: Immediately after the in-situ doping reaction, the materials in the reactor are subjected to gradient quenching. Gradient quenching is controlled by an optimized algorithm, specifically the Coal-based GQDs Gradient Quenching Parameter Optimization Algorithm (MGQ-GCOA), where the letters represent: M for Minerank, GQ for Graphene Quantum Dots, and GCOA for Gradient Cooling Optimization Algorithm. This algorithm is specifically designed for the gradient quenching process of coal-based GQDs. By comprehensively considering factors such as coal rank and dopant concentration, it can accurately calculate the parameters required for quenching, significantly improving the accuracy of controlling GQD particle size and fluorescence wavelength compared to traditional empirical control.

[0038] The variables in the algorithm include: M (coal rank parameter, set according to the type of coal, lignite is 1, bituminous coal is 2, and anthracite is 3); C (dopant concentration, in mol / L); T0 (initial quenching temperature, in °C); ΔT (temperature gradient change rate, in °C / s); t (quenching time, in s); D (target particle size, in nm); λ (target fluorescence wavelength, in nm).

[0039] The algorithm's calculation logic is as follows: First, input the coal rank parameter M, dopant concentration C, target particle size D, and target fluorescence wavelength λ. Then, calculate the initial quenching temperature T0 using the following formula: T0 = a × M + b × C + c × D + d × λ + e, where a, b, c, d, and e are constants obtained through fitting with a large amount of experimental data.

[0040] Then, the temperature gradient change rate ΔT is calculated based on the initial quenching temperature T0 and the target particle size D: ΔT = f × T0 + g × D + h, where f, g, and h are constants determined experimentally.

[0041] Finally, the quenching time t is calculated based on the temperature gradient change rate ΔT and the target fluorescence wavelength λ: t = i × ΔT + j × λ + k, where i, j, and k are constants, obtained through experimental fitting.

[0042] Based on the calculated T0, ΔT, and t, the cooling system of the reactor is controlled to perform gradient quenching, precisely regulating the particle size and fluorescence wavelength of the GQDs. This step is carried out simultaneously with the in-situ doping reaction and is processed immediately after the reaction, avoiding the influence of intermediate processes on the product, and is closely related to the previous step.

[0043] Post-processing: The material after gradient quenching is removed and centrifuged at 8000-10000 r / min for 15-30 minutes to remove larger particulate impurities. The supernatant is then dialyzed through a dialysis bag for 24-48 hours to remove residual solvent and unreacted dopants. Finally, the dialyzed solution is freeze-dried to obtain coal-based graphene quantum dots. This step purifies the product after gradient quenching to obtain pure coal-based graphene quantum dots and is the final step in the entire preparation process, forming a complete preparation flow together with the preceding steps.

[0044] Example 2

[0045] according to Figure 1 As shown, this embodiment proposes an integrated in-situ doping-gradient quenching preparation method for coal-based graphene quantum dots, including the following steps:

[0046] Lignite was selected as the raw material, and citric acid (containing carboxyl groups) was selected as the dopant.

[0047] Coal raw material pretreatment: The lignite is crushed, passed through an 80-mesh sieve to obtain lignite particles, and dried at 90℃ for 5 hours.

[0048] In-situ doping reaction: Pretreated lignite particles and citric acid were added to a reactor at a mass ratio of 1:0.5, with deionized water added as a solvent at a mass ratio of 1:10 (coal particles to deionized water). The reactor was sealed, heated to 220°C, and the reaction pressure was maintained at 3 MPa for 6 hours.

[0049] Synchronous gradient quenching: After the reaction, the MGQ-GCOA algorithm is used for gradient quenching control. Input parameters: coal rank M=1 (lignite), dopant concentration C=0.2mol / L, target particle size D=5nm, target fluorescence wavelength λ=450nm.

[0050] The algorithm calculates as follows:

[0051] T0=2×1+3×0.2+1×5+0.5×450+10=2+0.6+5+225+10=242.6℃

[0052] ΔT=0.1×242.6+0.5×5+1=24.26+2.5+1=27.76℃ / s

[0053] t=0.2×27.76+0.01×450+5=5.552+4.5+5=15.052s

[0054] Gradient quenching was performed based on the calculated values ​​of T0 = 242.6℃, ΔT = 27.76℃ / s, and t = 15.052s.

[0055] Post-processing: The quenched material was taken out and centrifuged at 9000 r / min for 20 minutes. The supernatant was collected and dialyzed for 36 hours using a dialysis bag with a molecular weight cutoff of 1000 Da. Then it was freeze-dried to obtain coal-based graphene quantum dots.

[0056] Example 3

[0057] according to Figure 1 As shown, this embodiment proposes an integrated in-situ doping-gradient quenching preparation method for coal-based graphene quantum dots, including the following steps:

[0058] Bituminous coal was selected as the raw material, and citric acid (containing carboxyl groups) was selected as the dopant.

[0059] Coal raw material pretreatment: The bituminous coal is crushed, passed through a 70-mesh sieve to obtain bituminous coal particles, and dried at 85℃ for 5 hours.

[0060] In-situ doping reaction: Pretreated bituminous coal particles and citric acid were added to a reactor at a mass ratio of 1:0.4, with deionized water added as a solvent at a mass ratio of 1:10 (coal particles to deionized water). The reactor was sealed, heated to 200℃, and the reaction pressure was maintained at 3.5 MPa for 5 hours.

[0061] Synchronous gradient quenching: After the reaction, the MGQ-GCOA algorithm is used for gradient quenching control. Input parameters: coal rank M=2 (bituminous coal), dopant concentration C=0.15mol / L, target particle size D=6nm, target fluorescence wavelength λ=460nm.

[0062] The algorithm calculates as follows:

[0063] T0=2×2+3×0.15+1×6+0.5×460+10=4+0.45+6+230+10=250.45℃

[0064] ΔT=0.1×250.45+0.5×6+1=25.045+3+1=29.045℃ / s

[0065] t=0.2×29.045+0.01×460+5=5.809+4.6+5=15.409s

[0066] Gradient quenching is performed according to the calculated parameters.

[0067] Post-processing: The quenched material was taken out and centrifuged at 8500 r / min for 25 minutes. The supernatant was collected and dialyzed for 30 hours using a dialysis bag with a molecular weight cutoff of 1000 Da. Then it was freeze-dried to obtain coal-based graphene quantum dots.

[0068] Example 4

[0069] according to Figure 1 As shown, this embodiment proposes an integrated in-situ doping-gradient quenching preparation method for coal-based graphene quantum dots, including the following steps:

[0070] Anthracite was selected as the raw material, and citric acid (containing carboxyl groups) was selected as the dopant.

[0071] Coal raw material pretreatment: The anthracite is crushed and passed through a 90-mesh sieve to obtain anthracite particles, which are then dried at 95℃ for 4.5 hours.

[0072] In-situ doping reaction: Pretreated anthracite particles and citric acid were added to a reactor at a mass ratio of 1:0.6, with deionized water added as a solvent at a mass ratio of 1:10 (coal particles to deionized water). The reactor was sealed, heated to 240℃, and the reaction pressure was maintained at 4 MPa for 7 hours.

[0073] Synchronous gradient quenching: After the reaction, the MGQ-GCOA algorithm is used for gradient quenching control. Input parameters: coal rank M=3 (anthracite), dopant concentration C=0.25mol / L, target particle size D=4nm, target fluorescence wavelength λ=440nm.

[0074] The algorithm calculates as follows:

[0075] T0=2×3+3×0.25+1×4+0.5×440+10=6+0.75+4+220+10=240.75℃

[0076] ΔT=0.1×240.75+0.5×4+1=24.075+2+1=27.075℃ / s

[0077] t=0.2×27.075+0.01×440+5=5.415+4.4+5=14.815s

[0078] Gradient quenching is performed according to the calculated parameters.

[0079] Post-processing: The quenched material was taken out and centrifuged at 9500 r / min for 18 minutes. The supernatant was collected and dialyzed for 40 hours using a dialysis bag with a molecular weight cutoff of 1000 Da. Then it was freeze-dried to obtain coal-based graphene quantum dots.

[0080] Validation data:

[0081] Yield: The coal-based GQDs prepared in Example 2 had a yield of 65%, in Example 3 it was 58%, and in Example 4 it was 52%, which were 25%, 18%, and 12% higher than the traditional method (average yield of 40%), respectively.

[0082] Doping uniformity: XPS detection showed that COX covalent bonds were present in the products of Examples 2, 3 and 4, and the doping elements were uniformly distributed in GQDs, with distribution uniformity reaching 90%, 88% and 85% or more, respectively.

[0083] Particle size: Detected by transmission electron microscopy, the average particle size of GQDs in Example 2 was 5.1 nm, with an error of 0.1 nm compared to the target particle size of 5 nm; the average particle size in Example 3 was 6.2 nm, with an error of 0.2 nm compared to the target particle size of 6 nm; and the average particle size in Example 4 was 4.1 nm, with an error of 0.1 nm compared to the target particle size of 4 nm. All of these were within the controllable error range.

[0084] Fluorescence wavelength: Detected by a fluorescence spectrophotometer, the fluorescence wavelength of GQDs in Example 2 was 448 nm, with an error of 2 nm compared to the target fluorescence wavelength of 450 nm; in Example 3 it was 459 nm, with an error of 1 nm compared to the target of 460 nm; and in Example 4 it was 442 nm, with an error of 2 nm compared to the target of 440 nm. All of these were within the control error range.

[0085] Electrical properties: The electrical properties of the products of Examples 2, 3 and 4 were tested, and their conductivity was increased by 10%, 8% and 6% respectively compared with GQDs prepared by conventional methods.

[0086] This integrated in-situ doping-gradient quenching method for preparing coal-based graphene quantum dots (GQDs) simultaneously performs in-situ doping and gradient quenching, eliminating the traditional steps of preparing GQDs first, then doping and separately cooling them. This simplifies the preparation process, shortens the production cycle, and increases the yield. Furthermore, the in-situ doping technology utilizes the esterification of the dopant carboxyl groups with the aromatic rings of coal to form COX covalent bonds, ensuring uniform distribution of the dopant element within the GQDs and avoiding segregation issues associated with post-doping, thus effectively improving material performance. Simultaneously, the gradient quenching process of this invention, combined with an optimization algorithm, can accurately calculate various quenching parameters based on different coal ranks, dopant concentrations, and other parameters. This allows for precise control of the GQD particle size and fluorescence wavelength, with control errors within ±2nm and ±5nm, respectively. Furthermore, by correlating coal rank with quenching kinetics, a more stable quenching path is obtained, resulting in more stable GQDs and facilitating efficient utilization of different coal ranks.

[0087] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An integrated method for in-situ doping and gradient quenching of coal-based graphene quantum dots, characterized in that: Includes the following steps: S1: Pre-treatment of coal raw materials; S2: The pretreated coal raw material is mixed with the dopant and an in-situ doping reaction is carried out to make the carboxyl group of the dopant react with the aromatic ring of coal to form a COX covalent bond; S3: During the in-situ doping reaction, gradient quenching is carried out simultaneously. The gradient quenching parameter optimization algorithm MGQ-GCOA for coal-based GQDs is used to control the particle size and fluorescence wavelength of GQDs. S4: The product after gradient quenching is post-processed to obtain coal-based graphene quantum dots.

2. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 1, characterized in that: In S1, the coal raw material is one or more of lignite, bituminous coal, and anthracite.

3. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 2, characterized in that: In step S1, the pretreatment includes crushing, sieving, and drying, wherein the sieve mesh size is 50-100 mesh, the drying temperature is 80-100℃, and the drying time is 4-6 hours.

4. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 1, characterized in that: In S2, the dopant is a carboxyl-containing compound, the mass ratio of coal raw material to dopant is 1:0.3-0.8, the in-situ doping reaction temperature is 180-250℃, the reaction pressure is 2-5MPa, the reaction time is 4-8 hours, and the reaction is carried out under an inert atmosphere, which is nitrogen or argon, with a gas flow rate of 50-200mL / min.

5. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 1, characterized in that: In S3, the variables of the coal-based GQDs gradient quenching parameter optimization algorithm MGQ-GCOA include coal rank parameter M, dopant concentration C, initial quenching temperature T0, temperature gradient change rate ΔT, quenching time t, target particle size D, and target fluorescence wavelength λ. The coal rank parameter M is set according to the type of coal: 1 for lignite, 2 for bituminous coal, and 3 for anthracite. The calculation logic is as follows: input the coal rank parameter M, dopant concentration C, target particle size D, and target fluorescence wavelength λ, calculate the initial quenching temperature T0, temperature gradient change rate ΔT, and quenching time t, and control the cooling system of the reactor to perform gradient quenching based on T0, ΔT, and t, thereby adjusting the particle size and fluorescence wavelength of the GQDs.

6. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 5, characterized in that: The formula for calculating the initial quenching temperature T0 is: T0 = ​​a×M + b×C + c×D + d×λ + e Where a, b, c, d, and e are constants obtained by fitting experimental data.

7. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 6, characterized in that: The formula for calculating the rate of change of the temperature gradient ΔT is: ΔT = f × T0 + g × D + h Where f, g, and h are constants determined through experiments.

8. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 7, characterized in that: The formula for calculating the quenching time t is: t=i×ΔT+j×λ+k Where i, j, and k are constants obtained through experimental fitting.

9. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 1, characterized in that: S4 includes the following steps: The material that has undergone gradient quenching is taken out and centrifuged to remove particulate impurities. The supernatant was collected and dialyzed through a dialysis bag to remove residual solvent and unreacted dopants. The dialysis solution was freeze-dried to obtain coal-based graphene quantum dots.

10. The in-situ doping-gradient quenching integrated preparation method for coal-based graphene quantum dots according to claim 9, characterized in that: During centrifugation, the rotation speed is controlled at 8000-10000 r / min, and the centrifugation time is 15-30 minutes; during dialysis, the dialysis time is 24-48 hours.

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