A method for efficiently preparing halogen-doped graphene quantum dots

Abstract

This invention provides an efficient method for preparing halogen-doped graphene quantum dots, comprising the following steps: adding 1,3,6-trinitropyrene to a polytetrafluoroethylene reactor, adding a halobenzene solvent, ultrasonically dispersing the mixture, and then carrying out a solvothermal reaction. After the reactor cools to room temperature, the solvent is removed by a rotary evaporator, finally obtaining graphene quantum dot powder. Using halobenzene as both solvent and dopant source enables one-step completion of doping and synthesis, avoiding the need for additional dopants and catalysts. The reaction system is simple, the process flow is greatly simplified, and the preparation cycle is significantly shortened.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to an efficient method for preparing halogen-doped zero-dimensional graphene quantum dots. Background Technology

[0002] Graphene quantum dots (GQDs), as zero-dimensional carbon-based nanomaterials, possess the excellent electrical conductivity, large specific surface area, and unique optical properties brought about by the quantum confinement effect of graphene, showing great application potential in optoelectronic devices, energy storage, and biomedicine. Halogen doping can effectively modulate the electronic structure of GQDs, significantly improving their fluorescence quantum yield, carrier mobility, and photocatalytic activity, and has become an important research direction for optimizing GQD performance.

[0003] Currently, the preparation methods for halogen-doped graphene crystallites (GQDs) are mainly divided into two categories: top-down and bottom-up methods. Top-down methods typically use large-size graphene or graphite as raw materials, cutting them into smaller GQDs through electrochemical exfoliation, laser ablation, or oxidative exfoliation. For example, Chinese invention patent CN 117361514A discloses a technical route for preparing GQDs using an electrochemical exfoliation method. The advantage of this type of method is the availability of raw materials, but it often faces problems such as poor product size uniformity, low yield, complex processes, and the potential introduction of structural defects.

[0004] Bottom-up methods utilize small-molecule carbon sources or biomass precursors as raw materials to assemble halogen-doped GQDs through chemical reactions. Representative methods include chemical vapor deposition, microwave-assisted synthesis, and hydrothermal / solvothermal methods. For example, one study synthesized halogen-doped GQDs via a hydrothermal reaction in the presence of concentrated sulfuric acid using 4-halogenated o-phenylenediamine as a precursor (Angewandte Chemie, 2025, 137(46): e202507405). Furthermore, a route for preparing GQDs using 1,3,6-trinitropyrene as a carbon source via a solvothermal method has also been reported in the literature. The hydrothermal / solvothermal method has been widely studied and applied among many bottom-up methods due to its relatively mild reaction conditions, simple equipment, and ease of control.

[0005] Currently, the preparation methods for halogen-doped graphene quantum dots (GQDs) are still in the exploratory stage, and existing technologies face many problems that urgently need to be solved. First, the doping process is usually quite complex. Most methods require the addition of exogenous halogen dopants such as halogenated aromatic hydrocarbons or halide salts, which not only increases raw material costs but may also introduce side reactions that affect the structural purity and optical properties of the product. Second, the reaction conditions are often harsh. Some processes require the use of strong acids such as concentrated sulfuric acid or concentrated nitric acid for oxidative exfoliation. The reaction process is violent and poses safety hazards, requiring high corrosion resistance of equipment, which is not conducive to industrial-scale production. Furthermore, existing methods often leave a large amount of unreacted precursors, inorganic salt catalysts, and byproducts in the reaction system. Extensive purification steps such as lengthy dialysis, centrifugation, or column chromatography are necessary to obtain pure GQDs, resulting in significant product loss and low overall yield. In addition, GQDs prepared by top-down methods often suffer from wide size distribution and irregular morphology, making it difficult to achieve precise control over optical properties. It is worth noting that existing research has largely focused on nitrogen and sulfur doping, with limited systematic reports on halogen doping, and a lack of simple and efficient preparation methods and studies on the mechanisms for regulating fluorescence performance. This invention addresses these issues by providing an efficient method for preparing halogen-doped graphene quantum dots that requires no external dopant, operates under mild conditions, is simple to operate, has high yield, and exhibits tunable fluorescence performance. Summary of the Invention

[0006] The purpose of this invention is to provide an efficient method for preparing halogen-doped graphene quantum dots.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An efficient method for preparing halogen-doped graphene quantum dots includes the following steps: 1) Weigh pyrene into a double-necked flask, add 68wt% concentrated nitric acid to carry out the nitration reaction, stir the solution thoroughly, and reflux at 80℃ for 24h. After cooling, add a large amount of distilled water to dilute, filter, wash with distilled water until neutral, and dry to obtain 1,3,6-trinitropyrene.

[0008] 2) Add 1,3,6-trinitropyrene to a polytetrafluoroethylene reactor and add halobenzene solvent. After ultrasonic dispersion for 10 minutes, carry out a solvothermal reaction. After the reactor is cooled to room temperature, the solvent is removed by a rotary evaporator to finally obtain graphene quantum dot powder.

[0009] Furthermore, the halobenzene in step (2) is a fluorobenzene, chlorobenzene, bromobenzene, iodobenzene, or a polysubstituted halobenzene such as dichlorobenzene.

[0010] Furthermore, in step (2), the mass ratio of 1,3,6-trinitropyrene to halobenzene is 1:20-1:200.

[0011] Furthermore, in step (2), the solvothermal reaction temperature is 180℃-240℃ and the reaction time is 8-24h.

[0012] Compared with existing technologies, this invention has the following significant technical advantages. This invention uses halobenzenes as both solvent and dopant source, achieving one-step doping and synthesis, avoiding the need for additional dopants and catalysts. The reaction system is simple, the process flow is greatly simplified, and the preparation cycle is significantly shortened. Unlike existing methods that require strong acid oxidation and stripping, the solvothermal reaction of this invention is carried out under relatively mild temperature conditions, resulting in high safety, low equipment requirements, and easier industrial-scale production. After the reaction, only rotary evaporation is needed to remove the solvent to obtain pure GQDs powder, eliminating the need for cumbersome post-processing steps such as dialysis and column chromatography. Examples show that the product yield can reach up to 98%, far exceeding existing methods. By selecting different types of halobenzenes, the fluorescence emission wavelength of GQDs can be systematically controlled, achieving controllable preparation of multicolor fluorescence from purple to orange, laying the foundation for its application in multicolor imaging and optoelectronic devices. This invention also reveals the regulation of the band structure of GQDs by halogen atoms, providing a theoretical basis for the design of GQDs' fluorescence performance. In addition, the raw materials used, pyrene and halobenzene, are common industrial chemicals with wide availability and low price, and have good economic benefits and prospects for industrial application.

[0013] This invention uses 1,3,6-trinitropyrene as a precursor, which has a well-defined aromatic ring structure and exhibits π-π stacking interactions with a similarly aromatic halobenzene solvent, which is beneficial for forming a regular two-dimensional graphene sheet structure. Attached Figure Description

[0014] Figure 1 The normalized fluorescence emission spectra of four halogen-doped graphene quantum dots (fluorine, chlorine, bromine, and iodine) prepared in Examples 1-4 of this invention are shown. The spectra reveal that chlorine-doped graphene quantum dots exhibit a main emission peak at 405 nm with a shoulder peak; bromine-doped graphene quantum dots have a maximum emission peak at 524 nm; iodine-doped graphene quantum dots have an emission peak at approximately 553 nm; and fluorine-doped graphene quantum dots exhibit a characteristic emission peak at 605 nm, along with a secondary emission band at 525 nm. With increasing halogen atomic number (chlorine, bromine, iodine), the fluorescence emission peaks of the graphene quantum dots show a significant redshift, i.e., the peak position gradually shifts from the blue-violet region to the orange-red region, while the fluorescence emission behavior of fluorine-doped graphene quantum dots does not follow this pattern. These phenomena indicate that halogen doping can play a crucial role in regulating the fluorescence emission of graphene quantum dots by modulating their band structure.

[0015] Figure 2These are fluorescence images of the graphene quantum dots prepared in Examples 1-4 of this invention under 365 nm ultraviolet light irradiation. From left to right, F-GQDs exhibit orange fluorescence, Cl-GQDs exhibit purple fluorescence, Br-GQDs exhibit green fluorescence, and I-GQDs exhibit yellow fluorescence. This figure visually demonstrates that by selecting different halobenzenes as solvents, the efficient and controllable preparation of multicolor fluorescence in graphene quantum dots can be achieved. Detailed Implementation

[0016] To make the above-mentioned features and advantages of the present invention more apparent and understandable, specific embodiments are described below in detail. Unless otherwise specified, the methods of the present invention are conventional methods in the art. Example 1

[0017] 4 g of pyrene was weighed into a double-necked flask, and 320 mL of 68 wt% concentrated nitric acid was added to initiate a nitration reaction. The solution was stirred thoroughly and refluxed at 80 °C for 24 h. After cooling, a large amount of distilled water was added for dilution, the mixture was filtered, and washed with distilled water until neutral before drying to obtain 1,3,6-trinitropyrene. 0.5 g of 1,3,6-trinitropyrene was weighed into a polytetrafluoroethylene reactor, and 25 mL of fluorobenzene solvent was added. After ultrasonic dispersion for 10 minutes, a solvothermal reaction was carried out at 200 °C for 16 h. After the reactor cooled to room temperature, the solvent was removed using a rotary evaporator, finally yielding 0.45 g of graphene quantum dot powder F-GQDs with orange fluorescence. Example 2

[0018] 4 g of pyrene was weighed into a double-necked flask, and 320 mL of 68 wt% concentrated nitric acid was added to initiate a nitration reaction. The solution was stirred thoroughly and refluxed at 80 °C for 24 h. After cooling, a large amount of distilled water was added for dilution, the mixture was filtered, and washed with distilled water until neutral before drying to obtain 1,3,6-trinitropyrene. 0.5 g of 1,3,6-trinitropyrene was weighed into a polytetrafluoroethylene reactor, and 25 mL of chlorobenzene solvent was added. After ultrasonic dispersion for 10 minutes, a solvothermal reaction was carried out at 200 °C for 16 h. After the reactor cooled to room temperature, the solvent was removed using a rotary evaporator, finally yielding 0.48 g of graphene quantum dot powder Cl-GQDs with purple fluorescence. Example 3

[0019] 4 g of pyrene was weighed into a double-necked flask, and 320 mL of 68 wt% concentrated nitric acid was added to initiate a nitration reaction. The solution was stirred thoroughly and refluxed at 80 °C for 24 h. After cooling, a large amount of distilled water was added for dilution, the mixture was filtered, and washed with distilled water until neutral before drying to obtain 1,3,6-trinitropyrene. 0.5 g of 1,3,6-trinitropyrene was weighed into a polytetrafluoroethylene reactor, and 25 mL of bromobenzene solvent was added. After ultrasonic dispersion for 10 minutes, a solvothermal reaction was carried out at 200 °C for 16 h. After the reactor cooled to room temperature, the solvent was removed using a rotary evaporator, finally yielding 0.48 g of green fluorescent graphene quantum dot powder Br-GQDs. Example 4

[0020] 4 g of pyrene was weighed into a double-necked flask, and 320 mL of 68 wt% concentrated nitric acid was added to initiate a nitration reaction. The solution was stirred thoroughly and refluxed at 80 °C for 24 h. After cooling, a large amount of distilled water was added for dilution, the mixture was filtered, and washed with distilled water until neutral before drying to obtain 1,3,6-trinitropyrene. 0.5 g of 1,3,6-trinitropyrene was weighed into a polytetrafluoroethylene reactor, and 25 mL of iodobenzene solvent was added. After ultrasonic dispersion for 10 minutes, a solvothermal reaction was carried out at 200 °C for 16 h. After the reactor cooled to room temperature, the solvent was removed using a rotary evaporator, finally yielding 0.49 g of graphene quantum dot powder I-GQDs with yellow fluorescence.

[0021] Comparative Example

[0022] 4 g of pyrene was weighed into a double-necked flask, and 320 mL of 68 wt% concentrated nitric acid was added to initiate a nitration reaction. The solution was stirred thoroughly and refluxed at 80 °C for 24 h. After cooling, a large amount of distilled water was added for dilution, the mixture was filtered, and after rinsing with distilled water until neutral, it was dried to obtain 1,3,6-trinitropyrene. 0.5 g of 1,3,6-trinitropyrene was weighed into a polytetrafluoroethylene reactor, and 25 mL of chloroform solvent was added. After ultrasonic dispersion for 10 minutes, a solvothermal reaction was carried out at 200 °C for 16 h. After the reactor cooled to room temperature, it was opened, revealing a large amount of unreacted trinitropyrene raw material mixed with the graphene quantum dot product, which was difficult to separate directly and required further purification by dialysis.

[0023] Example 2 uses chlorobenzene as a solvent. Chlorobenzene has an aromatic ring structure and has a strong π-π interaction with 1,3,6-trinitropyrene, which is beneficial to the dispersion and activation of the precursor.

[0024] The comparative example used chloroform as a solvent. Chloroform is a non-aromatic haloalkane and lacks π-π interaction with the pyrene ring. It has poor ability to dissolve and disperse precursors, resulting in a large amount of unreacted raw materials that are mixed with the product and difficult to separate.

[0025] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A highly efficient method for preparing halogen-doped graphene quantum dots, characterized in that, Includes the following steps: 1,3,6-trinitropyrene was added to a polytetrafluoroethylene reactor, along with a halobenzene solvent. After ultrasonic dispersion, a solvothermal reaction was carried out. After the reactor cooled to room temperature, the solvent was removed by a rotary evaporator, and finally, graphene quantum dot powder was obtained.

2. The efficient preparation method of halogen-doped graphene quantum dots according to claim 1, characterized in that: The preparation method of the 1,3,6-trinitropyrene includes: adding pyrene to 68wt% concentrated nitric acid for nitration reaction, stirring the solution thoroughly, refluxing at 80℃ for 24h, cooling, adding a large amount of distilled water for dilution, filtering, rinsing with distilled water until neutral, and drying to obtain 1,3,6-trinitropyrene.

3. The efficient preparation method of halogen-doped graphene quantum dots according to claim 1, characterized in that: The ultrasonic dispersion time is 10 minutes.

4. The efficient preparation method of halogen-doped graphene quantum dots according to claim 1, characterized in that: The halobenzene is one of fluorobenzene, chlorobenzene, bromobenzene, iodobenzene, and dichlorobenzene.

5. The efficient preparation method of halogen-doped graphene quantum dots according to claim 1, characterized in that: The mass ratio of 1,3,6-trinitropyrene to halobenzene is 1:20-1:

200.

6. The efficient preparation method of halogen-doped graphene quantum dots according to claim 1, characterized in that: The solvothermal reaction temperature is 180℃-240℃, and the reaction time is 8-24h.

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