Carbon quantum dot-carbon nitride composite photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of nano materials and photocatalysis, in particular to a carbon quantum dot-carbon nitride composite photocatalyst as well as a preparation method and application thereof. The composite photocatalyst is formed by tightly coupling carbon quantum dots of which the surfaces are rich in oxygen-containing functional groups and nitrogen-rich carbon nitride nanosheets of which the surfaces are rich in amino functional groups through hydrogen bond non-covalent acting force. According to the invention, hydrogen bond interface engineering is creatively combined with an advanced nitrogen-rich carbon nitride substrate; according to the preparation method, a high-efficiency photo-induced electron transmission and transfer channel is constructed, and the separation efficiency and surface reaction kinetics of photo-induced carriers are remarkably improved, so that the material shows remarkably enhanced catalytic activity and stability in photocatalytic hydrogen production application, and the preparation method is simple in process, readily available in raw materials and mild in conditions and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and photocatalysis, specifically to a carbon quantum dot-carbon nitride composite photocatalyst, its preparation method, and its application. Background Technology

[0002] With the energy crisis and environmental pollution becoming increasingly severe, the development of clean and sustainable energy technologies has become a global focus. Hydrogen energy, due to its high energy density and zero carbon emissions, is considered an ideal energy carrier. Photocatalytic water splitting technology can directly convert solar energy into hydrogen energy, showing broad application prospects.

[0003] Among numerous photocatalysts, graphitic carbon nitride (g-C3N4) has attracted considerable attention due to its suitable band structure, good chemical stability, and low cost. However, traditional g-C3N4 still suffers from problems such as a limited visible light response range and severe recombination of photogenerated carriers. To address these issues, researchers have developed nitrogen-rich carbon nitride materials with higher nitrogen content (such as C3N5), which are prepared by polymerizing precursors with higher nitrogen content (such as triazole compounds). Compared to pristine g-C3N4, C3N5 materials have a narrower band gap, enabling them to absorb longer wavelengths of visible light, thereby improving solar energy utilization. Furthermore, C3N5 nanosheets (CNNS) prepared via the molten salt method not only possess a two-dimensional ultrathin structure but also have enriched their framework and edges with more Lewis basic sites, such as primary amines (-NH2) and secondary amines (-NH-). This provides more active centers for catalytic reactions and also offers an ideal anchoring basis for surface functionalization through non-covalent interactions such as hydrogen bonding.

[0004] Meanwhile, carbon quantum dots (CQDs), as zero-dimensional carbon nanomaterials, are widely used as cocatalysts in photocatalytic systems due to their unique photoluminescence properties, excellent electronic conductivity, high specific surface area, and easy functionalization. Combining CQDs with carbon nitride-based materials allows CQDs to act as electron acceptors and transport mediators, effectively capturing and transferring photogenerated electrons from carbon nitride, thereby suppressing carrier recombination and improving overall photocatalytic efficiency.

[0005] In existing technologies, although there are research reports on the composite of CQDs with carbon nitride materials, the composite methods are mostly simple physical mixing or covalent modification. Physical mixing is difficult to achieve close interfacial contact and has limited electron transfer efficiency; although covalent modification can form stable connections, it often requires complex chemical reactions and may destroy the intrinsic structure of the material. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the present invention aims to provide a hydrogen-bonded carbon quantum dot-nitrogen-rich carbon nitride nanosheet composite photocatalyst, its preparation method, and its application, thereby solving the problems of severe carrier recombination and low catalytic efficiency in existing carbon nitride-based photocatalysts.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A carbon quantum dot-carbon nitride composite photocatalyst is disclosed, wherein the nitrogen-rich carbon nitride nanosheets are C3N5 nanosheets. Although there have been research reports on the composite of CQDs and carbon nitride materials, most of them are based on g-C3N4 rather than nitrogen-rich C3N5 nanosheets. The composite photocatalyst is formed by coupling carbon quantum dots and nitrogen-rich carbon nitride nanosheets through hydrogen bonding to form a heterojunction structure, wherein a dense hydrogen bond network is formed between the oxygen-containing functional groups on the surface of the carbon quantum dots and the amino sites on the surface of the carbon nitride nanosheets; the mass ratio of carbon quantum dots to nitrogen-rich carbon nitride nanosheets is 0.01-1:1.

[0008] A method for preparing a carbon quantum dot-carbon nitride composite photocatalyst (CQDs-CNNS), characterized by comprising the following steps: Carbon quantum dots (CQDs) were obtained by alkali-catalyzed acetone self-polymerization, in which NaOH was added to an acetone solution and stirred to react. After neutralization, carbon quantum dots (CQDs) were obtained.

[0009] 3-Amino-1,2,4-triazole was mixed with molten salt and calcined at high temperature to obtain nitrogen-rich carbon nitride nanosheets (CNNS).

[0010] The carbon quantum dots and nitrogen-rich carbon nitride nanosheets were dispersed separately in ethanol, mixed, and stirred to form a heterojunction through hydrogen bonding, thus obtaining a carbon quantum dot-carbon nitride composite photocatalyst.

[0011] In a preferred embodiment of the present invention, the mass ratio of 3-amino-1,2,4-triazole to molten salt is 1:1-3.

[0012] In a preferred embodiment of the present invention, the molten salt is LiCl and KCl, and the mass ratio of LiCl to KCl is 0.5-1:1.

[0013] In a preferred embodiment of the present invention, the mass-to-volume ratio of NaOH to acetone is 4g-10g:20mL-50mL, the neutralization reaction time is 1h-3h, and the pH is adjusted to 6.5-7.5.

[0014] In a preferred embodiment of the present invention, the high-temperature calcination temperature is 450℃-550℃, the high-temperature calcination time is 2h-4h, and the high-temperature calcination heating rate is 2℃ / min-6℃ / min.

[0015] In a preferred embodiment of the present invention, the temperature of the stirring reaction is 50℃-70℃, and the stirring reaction time is 5h-8h.

[0016] The application of the hydrogen-bonded carbon quantum dot-nitrogen-rich carbon nitride nanosheet composite photocatalyst described in this invention in photocatalytic water splitting for hydrogen production.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention proposes utilizing the naturally enriched amino sites on the surface of CNNS to form a dense hydrogen bond network with the oxygen-containing functional groups on the surface of CQDs. This hydrogen bond coupling strategy ensures tight interfacial contact between the two, enabling rapid electron transfer, while avoiding damage to the intrinsic structure of the material. It is a mild yet efficient new strategy for interface engineering.

[0018] 2. The carbon quantum dot-carbon nitride composite photocatalyst constructed in this invention has a hydrogen bond network that can significantly promote the rapid separation and transfer of photogenerated electrons and inhibit the recombination of photogenerated carriers, thereby achieving a significantly improved photocatalytic performance.

[0019] 3. The raw materials involved in this invention are all common chemical raw materials, which are inexpensive. The preparation process is a conventional chemical operation with mild conditions. No special and expensive equipment is required, which makes it easy to achieve large-scale production and has great potential for industrial application. Attached Figure Description

[0020] Figure 1 This is a TEM image of the hydrogen-bonded CQDs-CNNS heterojunction composite photocatalyst prepared in Example 1 of the present invention.

[0021] Figure 2 The above are comparative test results of the photocatalytic hydrogen production performance of the samples prepared in Example 1 and Comparative Examples 1-3 of this invention. Detailed Implementation

[0022] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0024] Example 1 A method for preparing a carbon quantum dot-carbon nitride composite photocatalyst includes the following steps: (1) Preparation of CQDs: 8 g of NaOH powder was added to 40 mL of acetone solution and stirred under vigorous magnetic stirring for 2 h until the milky white solution gradually turned into an orange solution. The mixture was then placed in air at room temperature and pressure for 5 days until the orange solution turned into an orange gel solid. Subsequently, a certain amount of 1 M dilute hydrochloric acid solution was added to adjust the pH value to neutral. The mixture was separated by centrifugation and washed 3 times with deionized water. Then it was dried at 100°C for 12 h. Finally, the remaining solid was collected and ground to obtain carbon quantum dot powder (i.e., CQDs).

[0025] (2) Preparation of CNNS: 5 g of 3-amino-1,2,4-triazole, 6.9 g of LiCl and 8.1 g of KCl were ground evenly and added to a mixture of 50 mL of deionized water and 20 mL of ethanol. The mixture was then placed in a constant temperature water bath and stirred continuously at 90°C until the water was completely evaporated. The mixture was then dried in a vacuum drying oven at 60°C for 12 h. Subsequently, the mixture in the beaker was transferred to a crucible and heated to 500°C at a heating rate of 5°C / min in a muffle furnace and held for 3 h. The powder after high-temperature calcination was collected and washed repeatedly with deionized water and ethanol three times. Finally, the powder was dried in a forced-air drying oven at 80°C for 12 h to obtain nitrogen-rich carbon nitride nanosheets (i.e., CNNS).

[0026] (3) Preparation of hydrogen-bonded CQDs-CNNS: First, 0.1 g of CQDs powder prepared in step (1) was weighed and dispersed in 50 mL of ethanol solution. Then, 1 g of CNNS powder prepared in step (2) was dispersed in 20 mL of ethanol solution. Finally, the two solutions were mixed and stirred continuously in a constant temperature water bath at 60 °C for 6 h. Finally, the resulting liquid was dried at 80 °C for 12 h to obtain a brown powder (i.e., CQDs-CNNS).

[0027] Example 2 A method for preparing a carbon quantum dot-carbon nitride composite photocatalyst includes the following steps: (1) Preparation of CQDs: 8 g of NaOH powder was added to 40 mL of acetone solution and stirred under vigorous magnetic stirring for 2 h until the milky white solution gradually turned into an orange solution. The mixture was then placed in air at room temperature and pressure for 5 days until the orange solution turned into an orange gel solid. Subsequently, a certain amount of 1 M dilute hydrochloric acid solution was added to adjust the pH value to neutral. The mixture was separated by centrifugation and washed 3 times with deionized water. Then it was dried at 100°C for 12 h. Finally, the remaining solid was collected and ground to obtain carbon quantum dot powder (i.e., CQDs).

[0028] (2) Preparation of CNNS: 5 g of 3-amino-1,2,4-triazole, 6.9 g of LiCl and 8.1 g of KCl were ground evenly and added to a mixture of 50 mL of deionized water and 20 mL of ethanol. The mixture was then placed in a constant temperature water bath and stirred continuously at 90°C until the water was completely evaporated. The mixture was then dried in a vacuum drying oven at 60°C for 12 h. Subsequently, the mixture in the beaker was transferred to a crucible and heated to 500°C at a heating rate of 5°C / min in a muffle furnace and held for 3 h. The powder after high-temperature calcination was collected and washed repeatedly with deionized water and ethanol three times. Finally, the powder was dried in a forced-air drying oven at 80°C for 12 h to obtain nitrogen-rich carbon nitride nanosheets (i.e., CNNS).

[0029] (3) Preparation of hydrogen-bonded CQDs-CNNS: First, 0.01 g of CQDs powder prepared in step (1) was weighed and dispersed in 50 mL of ethanol solution. Then, 1 g of CNNS powder prepared in step (2) was dispersed in 20 mL of ethanol solution. Finally, the two solutions were mixed and stirred continuously in a constant temperature water bath at 60 °C for 6 h. Finally, the resulting liquid was dried at 80 °C for 12 h to obtain a brown powder (i.e., CQDs-CNNS-1).

[0030] Example 3 A method for preparing a carbon quantum dot-carbon nitride composite photocatalyst includes the following steps: (1) Preparation of CQDs: 8 g of NaOH powder was added to 40 mL of acetone solution and stirred under vigorous magnetic stirring for 2 h until the milky white solution gradually turned into an orange solution. The mixture was then placed in air at room temperature and pressure for 5 days until the orange solution turned into an orange gel solid. Subsequently, a certain amount of 1 M dilute hydrochloric acid solution was added to adjust the pH value to neutral. The mixture was separated by centrifugation and washed 3 times with deionized water. Then it was dried at 100°C for 12 h. Finally, the remaining solid was collected and ground to obtain carbon quantum dot powder (i.e., CQDs).

[0031] (2) Preparation of CNNS: 5 g of 3-amino-1,2,4-triazole, 6.9 g of LiCl and 8.1 g of KCl were ground evenly and added to a mixture of 50 mL of deionized water and 20 mL of ethanol. The mixture was then placed in a constant temperature water bath and stirred continuously at 90°C until the water was completely evaporated. The mixture was then dried in a vacuum drying oven at 60°C for 12 h. Subsequently, the mixture in the beaker was transferred to a crucible and heated to 500°C at a heating rate of 5°C / min in a muffle furnace and held for 3 h. The powder after high-temperature calcination was collected and washed repeatedly with deionized water and ethanol three times. Finally, the powder was dried in a forced-air drying oven at 80°C for 12 h to obtain nitrogen-rich carbon nitride nanosheets (i.e., CNNS).

[0032] (3) Preparation of hydrogen-bonded CQDs-CNNS: First, 0.05 g of CQDs powder prepared in step (1) was weighed and dispersed in 50 mL of ethanol solution. Then, 1 g of CNNS powder prepared in step (2) was dispersed in 20 mL of ethanol solution. Finally, the two solutions were mixed and stirred continuously in a constant temperature water bath at 60 °C for 6 h. Finally, the resulting liquid was dried at 80 °C for 12 h to obtain a brown powder (i.e., CQDs-CNNS-5).

[0033] Example 4 A method for preparing a carbon quantum dot-carbon nitride composite photocatalyst includes the following steps: (1) Preparation of CQDs: 8 g of NaOH powder was added to 40 mL of acetone solution and stirred under vigorous magnetic stirring for 2 h until the milky white solution gradually turned into an orange solution. The mixture was then placed in air at room temperature and pressure for 5 days until the orange solution turned into an orange gel solid. Subsequently, a certain amount of 1 M dilute hydrochloric acid solution was added to adjust the pH value to neutral. The mixture was separated by centrifugation and washed 3 times with deionized water. Then it was dried at 100°C for 12 h. Finally, the remaining solid was collected and ground to obtain carbon quantum dot powder (i.e., CQDs).

[0034] (2) Preparation of CNNS: 5 g of 3-amino-1,2,4-triazole, 6.9 g of LiCl and 8.1 g of KCl were ground evenly and added to a mixture of 50 mL of deionized water and 20 mL of ethanol. The mixture was then placed in a constant temperature water bath and stirred continuously at 90°C until the water was completely evaporated. The mixture was then dried in a vacuum drying oven at 60°C for 12 h. Subsequently, the mixture in the beaker was transferred to a crucible and heated to 500°C at a heating rate of 5°C / min in a muffle furnace and held for 3 h. The powder after high-temperature calcination was collected and washed repeatedly with deionized water and ethanol three times. Finally, the powder was dried in a forced-air drying oven at 80°C for 12 h to obtain nitrogen-rich carbon nitride nanosheets (i.e., CNNS).

[0035] (3) Preparation of hydrogen-bonded CQDs-CNNS: First, 0.5 g of CQDs powder prepared in step (1) was weighed and dispersed in 50 mL of ethanol solution. Then, 1 g of CNNS powder prepared in step (2) was dispersed in 20 mL of ethanol solution. Finally, the two solutions were mixed and stirred continuously in a constant temperature water bath at 60 °C for 6 h. Finally, the resulting liquid was dried at 80 °C for 12 h to obtain a brown powder (i.e., CQDs-CNNS-50).

[0036] Example 5 A method for preparing a carbon quantum dot-carbon nitride composite photocatalyst includes the following steps: (1) Preparation of CQDs: 8 g of NaOH powder was added to 40 mL of acetone solution and stirred under vigorous magnetic stirring for 2 h until the milky white solution gradually turned into an orange solution. The mixture was then placed in air at room temperature and pressure for 5 days until the orange solution turned into an orange gel solid. Subsequently, a certain amount of 1 M dilute hydrochloric acid solution was added to adjust the pH value to neutral. The mixture was separated by centrifugation and washed 3 times with deionized water. Then it was dried at 100°C for 12 h. Finally, the remaining solid was collected and ground to obtain carbon quantum dot powder (i.e., CQDs).

[0037] (2) Preparation of CNNS: 5 g of 3-amino-1,2,4-triazole, 6.9 g of LiCl and 8.1 g of KCl were ground evenly and added to a mixture of 50 mL of deionized water and 20 mL of ethanol. The mixture was then placed in a constant temperature water bath and stirred continuously at 90°C until the water was completely evaporated. The mixture was then dried in a vacuum drying oven at 60°C for 12 h. Subsequently, the mixture in the beaker was transferred to a crucible and heated to 500°C at a heating rate of 5°C / min in a muffle furnace and held for 3 h. The powder after high-temperature calcination was collected and washed repeatedly with deionized water and ethanol three times. Finally, the powder was dried in a forced-air drying oven at 80°C for 12 h to obtain nitrogen-rich carbon nitride nanosheets (i.e., CNNS).

[0038] (3) Preparation of hydrogen-bonded CQDs-CNNS: First, 1 g of CQDs powder prepared in step (1) was weighed and dispersed in 50 mL of ethanol solution. Then, 1 g of CNNS powder prepared in step (2) was dispersed in 20 mL of ethanol solution. Finally, the two solutions were mixed and stirred continuously in a constant temperature water bath at 60 °C for 6 h. Finally, the resulting liquid was dried at 80 °C for 12 h to obtain a brown powder (i.e., CQDs-CNNS-100).

[0039] Comparative Example 1 A method for preparing a CQDs / CNNS composite photocatalyst using a physical mixing method includes the following steps: (1) Preparation of CQDs: 8 g of NaOH powder was added to 40 mL of acetone solution and stirred under vigorous magnetic stirring for 2 h until the milky white solution gradually turned into an orange solution. The mixture was then placed in air at room temperature and pressure for 5 days until the orange solution turned into an orange gel solid. Subsequently, a certain amount of 1 M dilute hydrochloric acid solution was added to adjust the pH value to neutral. The mixture was separated by centrifugation and washed 3 times with deionized water. Then it was dried at 100°C for 12 h. Finally, the remaining solid was collected and ground to obtain carbon quantum dot powder (i.e., CQDs).

[0040] (2) Preparation of CNNS: 5 g of 3-amino-1,2,4-triazole, 6.9 g of LiCl and 8.1 g of KCl were ground evenly and added to a mixture of 50 mL of deionized water and 20 mL of ethanol. The mixture was then placed in a constant temperature water bath and stirred continuously at 90°C until the water was completely evaporated. The mixture was then dried in a vacuum drying oven at 60°C for 12 h. Subsequently, the mixture in the beaker was transferred to a crucible and heated to 500°C at a heating rate of 5°C / min in a muffle furnace and held for 3 h. The powder after high-temperature calcination was collected and washed repeatedly with deionized water and ethanol three times. Finally, the powder was dried in a forced-air drying oven at 80°C for 12 h to obtain nitrogen-rich carbon nitride nanosheets (i.e., CNNS).

[0041] (3) Preparation of CQDs / CNNS composite photocatalyst by physical mixing method: 0.1 g of CQDs prepared in step (1) and 1 g of CNNS prepared in step (2) were added to 70 mL of ethanol solution and subjected to continuous magnetic stirring for 6 h. The liquid was then collected by centrifugation and dried in a forced-air drying oven at 80 ℃ for 12 h to obtain brown powder (i.e., CQDs / CNNS).

[0042] Comparative Example 2 A method for preparing a CQDs catalyst includes the following steps: 8 g of NaOH powder was added to 40 mL of acetone solution and stirred vigorously with a magnetic stirrer for 2 h until the milky white solution gradually turned into an orange solution. The mixture was then placed in air at room temperature and pressure for 5 days until the orange solution turned into an orange gel-like solid. Subsequently, a certain amount of 1 M dilute hydrochloric acid solution was added to adjust the pH to neutral. The mixture was separated by centrifugation and washed three times with deionized water. It was then dried at 100°C for 12 h. Finally, the remaining solid was collected and ground to obtain carbon quantum dot powder (i.e., CQDs).

[0043] Comparative Example 3 A method for preparing a CNNS catalyst includes the following steps: 5 g of 3-amino-1,2,4-triazole, 6.9 g of LiCl, and 8.1 g of KCl were ground evenly and added to a mixture of 50 mL of deionized water and 20 mL of ethanol. The mixture was then placed in a constant temperature water bath and stirred continuously at 90°C until the water was completely evaporated. The mixture was then dried in a vacuum drying oven at 60°C for 12 h. Subsequently, the mixture in the beaker was transferred to a crucible and heated to 500°C in a muffle furnace at a heating rate of 5°C / min for 3 h. The powder after high-temperature calcination was collected and washed three times repeatedly with deionized water and ethanol. Finally, it was dried in a forced-air drying oven at 80°C for 12 h to obtain nitrogen-rich carbon nitride nanosheets (CNNS).

[0044] Results Analysis Figure 1 The TEM image of the carbon quantum dot-carbon nitride composite photocatalyst CQDs-CNNS prepared in Example 1 of this invention clearly shows that a large number of tiny, black CQDs are loaded on the CNNS, proving that the hydrogen-bonded CQDs-CNNS composite photocatalyst was successfully prepared.

[0045] The CQDs-CNNS, CQDs / CNNS, CQDs, and CNNS photocatalysts prepared in Example 1 and Comparative Examples 1-3 were tested for their photocatalytic water splitting activity to produce hydrogen. The specific methods are as follows: In a top-illuminated photocatalytic reactor, 30 mg of photocatalyst powder was accurately weighed and ultrasonically dispersed in 80 mL of a deionized aqueous solution containing 20 vol% triethanolamine (TEOA) as a sacrificial agent. Then, an aqueous solution of H2PtCl6 was added to achieve a Pt loading of 3 wt%, and photodeposition was performed for 1 h under 300 W xenon lamp irradiation. Before irradiation, the reaction system was purged with high-purity N2 for 30 min to completely remove air. A 300 W xenon lamp was used as the light source, and the reaction temperature was maintained at approximately 6°C during the reaction using an external circulating condensate. The amount of H2 produced was detected online using a gas chromatograph every 1 h.

[0046] To verify the effectiveness of the technical solution described in this invention, we conducted a comparative test of photocatalytic hydrogen production performance, and the results are as follows: Figure 2 As shown, under the same test conditions, individual CQDs and CNNS exhibited low catalytic activity, with average hydrogen production rates of only 84 µmol g, respectively. -1 h -1 and 249µmol g -1 h -1 The CQDs / CNNS sample, prepared by a simple physical mixing method, showed an improved hydrogen production rate, reaching 594 µmol g. -1 h-1 However, the performance improvement was limited. Nevertheless, the CQDs-CNNS composite photocatalyst prepared using the hydrogen bonding method described in this invention achieved a significant performance improvement. Its average hydrogen production rate reached as high as 1631 µmol g / L. -1 h -1 These figures are approximately 19 times that of single CQDs and approximately 7 times that of single CNNS, respectively. More importantly, the activity of the catalyst in this invention is about 3 times that of the physically mixed CQDs / CNNS sample. This series of significant data comparisons powerfully demonstrates that this invention, by constructing a hydrogen-bonded interface, does not simply linearly add up the properties of the two materials, but rather produces a synergistic effect of "1+1>>2," highlighting the enormous advantages and significant progress of the hydrogen-bonded coupling strategy in constructing highly efficient heterojunction photocatalysts.

[0047] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0048] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A carbon quantum dot-carbon nitride composite photocatalyst, characterized in that, The composite photocatalyst is formed by coupling carbon quantum dots and nitrogen-rich carbon nitride nanosheets through hydrogen bonding to form a heterojunction structure, wherein a dense hydrogen bond network is formed between the oxygen-containing functional groups on the surface of the carbon quantum dots and the amino sites on the surface of the carbon nitride nanosheets. The mass ratio of carbon quantum dots to nitrogen-rich carbon nitride nanosheets is 0.01-1:

1.

2. The method for preparing the carbon quantum dot-carbon nitride composite photocatalyst according to claim 1, characterized in that, Includes the following steps: Carbon quantum dots were obtained by alkali-catalyzed acetone self-polymerization, in which NaOH was added to an acetone solution and stirred to react. After neutralization, carbon quantum dots were obtained. 3-Amino-1,2,4-triazole was mixed with molten salt and calcined at high temperature to obtain nitrogen-rich carbon nitride nanosheets; The carbon quantum dots and nitrogen-rich carbon nitride nanosheets were dispersed separately in ethanol, mixed, and stirred to form a heterojunction through hydrogen bonding, thus obtaining a hydrogen-bonded carbon quantum dot-nitrogen-rich carbon nitride nanosheet composite photocatalyst.

3. The method for preparing the carbon quantum dot-carbon nitride composite photocatalyst according to claim 2, characterized in that, The mass-to-volume ratio of NaOH to acetone is 4g-10g: 20mL-50mL, the neutralization reaction time is 1h-3h, and the pH is adjusted to 6.5-7.

5.

4. The method for preparing the carbon quantum dot-carbon nitride composite photocatalyst according to claim 2, characterized in that, The mass ratio of 3-amino-1,2,4-triazole to molten salt is 1:1-3.

5. The method for preparing the carbon quantum dot-carbon nitride composite photocatalyst according to claim 2, characterized in that, The molten salts are LiCl and KCl, with a mass ratio of LiCl to KCl of 0.5-1:

1.

6. The method for preparing the carbon quantum dot-carbon nitride composite photocatalyst according to claim 2, characterized in that, The high-temperature calcination temperature is 450℃-550℃, the high-temperature calcination time is 2h-4h, and the high-temperature calcination heating rate is 2℃ / min-6℃ / min.

7. The method for preparing the carbon quantum dot-carbon nitride composite photocatalyst according to claim 2, characterized in that, The temperature for the stirring reaction is 50℃-70℃, and the stirring reaction time is 5h-8h.

8. The application of the carbon quantum dot-carbon nitride composite photocatalyst according to claim 1 in photocatalytic water splitting for hydrogen production.

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