A nitrogen-vacancy-enriched carbon quantum dot / polymeric carbon nitride s-type heterojunction photocatalytic material, a preparation method therefor, and an application thereof

Abstract

This invention discloses a nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material, its preparation method, and its applications, belonging to the field of photocatalytic materials technology. The material is prepared by the following method: First, CQDs are hydrothermally synthesized using citric acid and urea as precursors, and g-C3N5 is thermally polymerized using 3-amino-1,2,4-triazole as a precursor; then, g-C3N5 is etched using dielectric barrier discharge plasma under an argon atmosphere to precisely introduce nitrogen vacancy defects, obtaining Nv-g-C3N5; finally, CQDs are selectively anchored to nitrogen vacancy sites through hydrothermal assembly, forming S-type heterojunction charge transfer channels. This invention achieves deep coupling of defect engineering and interface engineering through a synergistic strategy of plasma etching and hydrothermal assembly. The obtained CQDs / Nv-g-C3N5 exhibits significantly improved performance in visible light-driven two-electron oxygen reduction synthesis of hydrogen peroxide in a sacrificial agent-free pure water system, with a significantly increased H2O2 generation rate and good cycling stability, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, specifically to a nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material, its preparation method, and its application. Background Technology

[0002] Hydrogen peroxide (H2O2) is an important green oxidant and clean chemical with wide applications in environmental remediation, fine chemicals, and energy. Traditional industrial production of H2O2 mainly uses the anthraquinone process, which suffers from drawbacks such as high energy consumption, complex processes, and the generation of organic pollutants, making it difficult to meet the demands of green chemistry and sustainable development. This paper explores a new method for utilizing solar energy to drive photocatalytic two-electron oxygen reduction (2e2O2) reactions. - The direct synthesis of hydrogen peroxide using ORR (-ORR) has advantages such as mild reaction conditions, environmental friendliness, and high atom economy, and is regarded as a very promising green alternative technology route.

[0003] Polymerized carbon nitride (g-C3N5) possesses a narrow band gap and excellent visible light response characteristics, making it a promising candidate for photocatalysis of 2e⁻. - -ORR is an ideal candidate semiconductor material for preparing H2O2. However, single-component g-C3N5 has many intrinsic shortcomings: fast photogenerated carrier recombination rate, slow surface reaction kinetics, insufficient number of catalytic active sites, and weak oxygen molecule adsorption and activation ability, resulting in low photocatalytic quantum efficiency and product yield, making it difficult to achieve efficient and stable hydrogen peroxide synthesis.

[0004] Currently, defect engineering and heterojunction engineering are the mainstream modification strategies for optimizing the electronic structure of semiconductors and improving the efficiency of interfacial charge separation. Introducing defects such as nitrogen vacancies into materials can serve as electron trapping centers to suppress electron-hole recombination and as active sites to enhance the chemisorption and activation of oxygen molecules. Constructing S-scheme heterojunctions can achieve efficient charge separation while retaining the material's strong oxidation and reduction potentials, thereby improving the catalytic driving force and reaction selectivity of the oxygen reduction reaction.

[0005] Existing methods for constructing nitrogen vacancies often employ chemical reduction and high-temperature heat treatment, which generally suffer from problems such as difficulty in precisely controlling vacancy concentration, easy damage to the material's crystal framework, and easy introduction of impurity phases. Dielectric barrier discharge (DBD) plasma technology, as a mild non-thermal processing method, can perform "atomic-level" etching on the material surface while maintaining the integrity of the g-C3N5 host structure, achieving directional and controllable introduction of nitrogen vacancies. Meanwhile, carbon quantum dots (CQDs) possess excellent electron transport and optical properties; combining them with nitrogen-vacancy-modified g-C3N5 holds promise for significantly improving the efficiency of photocatalytic H2O2 production through the synergistic effects of defect trapping, interfacial coupling, and S-type charge transfer.

[0006] Current research and applications still face key technological bottlenecks: the lack of a controllable selective anchoring strategy between defect sites and CQDs makes it difficult to construct stable interfacial charge transport channels; and achieving high selectivity, high yield, and high stability of 2e in a sacrificial agent-free pure water system remains a challenge. - The ORR photocatalytic reaction still lacks efficient material structure design and reliable mechanism support. These problems severely limit the technological breakthrough and large-scale application of polymeric carbon nitride-based photocatalytic systems in the green synthesis of H2O2. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material, its preparation method, and its application. A two-step method combining DBD plasma etching and hydrothermal assembly is used to regulate defects and couple interfaces in g-C3N5, resulting in a nitrogen-vacancy-enriched CQDs / Nv-g-C3N5 composite photocatalytic material with selectively anchored carbon quantum dots. This significantly improves its visible light-driven 2e2O3 performance in a sacrificial agent-free pure water system. - -Photocatalytic activity and reaction selectivity of ORR in the synthesis of H2O2.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material includes the following steps:

[0010] S1, preparing carbon quantum dot solution;

[0011] S2, to prepare polymeric carbon nitride powder;

[0012] S3, polymeric carbon nitride powder is subjected to dielectric barrier discharge plasma etching to obtain nitrogen vacancy-enriched polymeric carbon nitride;

[0013] S4 involves mixing nitrogen-vacancy-enriched polymeric carbon nitride with a carbon quantum dot solution and carrying out a hydrothermal reaction to obtain a photocatalytic material.

[0014] Furthermore, in step S3, the conditions for dielectric barrier discharge plasma etching are: argon atmosphere, gas flow rate 300-350 mL / min, radio frequency electric field voltage 100-120 V, and processing time 4-6 min.

[0015] Furthermore, in step S4, the hydrothermal reaction conditions are: temperature 150-200℃, time 4-6h, and the mass-to-volume ratio of nitrogen-vacancy-enriched polymeric carbon nitride to carbon quantum dot solution is 0.2-0.5g:0.5-2mL.

[0016] Further, step S2 specifically involves heating the precursor 3-amino-1,2,4-triazole to 500-550℃ at a rate of 2.2-2.8℃ / min, calcining it for 3 hours, and then grinding it after cooling to obtain polymeric carbon nitride powder.

[0017] Further, step S1 specifically involves dissolving citric acid and urea in deionized water and reacting them hydrothermally at 150-200℃ for 4-7 hours to obtain a carbon quantum dot solution.

[0018] On the other hand, the present invention also provides a nitrogen-vacancy-enriched carbon quantum dot / polymeric carbon nitride S-type heterojunction photocatalytic material, which is obtained by the above preparation method. The photocatalytic material is CQDs / Nv-g-C3N5, which is formed by hydrothermal assembly of carbon quantum dots and nitrogen-vacancy-enriched polymeric carbon nitride to form an S-type heterojunction, wherein the carbon quantum dots are selectively anchored to nitrogen vacancy sites.

[0019] Furthermore, the nitrogen vacancies are introduced through dielectric barrier discharge plasma etching.

[0020] In another aspect, the present invention also provides the application of the above-mentioned nitrogen vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material in the photocatalytic synthesis of H2O2.

[0021] Furthermore, in a pure water system without sacrificial agents, H2O2 is synthesized through a two-electron oxygen reduction reaction under visible light irradiation using the aforementioned photocatalytic material as a catalyst.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) This invention employs a two-step synergistic strategy of dielectric barrier discharge (DBD) plasma etching and hydrothermal assembly. While maintaining the integrity of the g-C3N5 host framework, plasma etching precisely introduces nitrogen vacancy defects onto its surface. Subsequently, under thermodynamic drive, CQDs preferentially anchor to the nitrogen vacancy sites, constructing a stable S-shaped heterojunction charge transport channel dominated by nitrogen vacancies, thereby achieving deep coupling between defect engineering and interface engineering. This method overcomes the problems of difficult precise control of vacancy concentration, easy damage to the material framework, or introduction of impurities in existing vacancy construction technologies, and has significant advantages such as process controllability, good repeatability, and structural stability.

[0024] (2) The CQDs / Nv-g-C3N5 composite photocatalyst material prepared in this invention exhibits significantly improved performance in the visible light-driven two-electron oxygen reduction synthesis of H2O2 in a pure water system without sacrificial agents. Testing showed that its H2O2 generation rate can reach 283.52 μmol∙g. -1 ∙h -1It is approximately 8.78 times that of unmodified g-C3N5, and maintains good catalytic activity and structural stability after multiple cycles, demonstrating excellent photocatalytic efficiency and long-term reliability.

[0025] (3) This invention effectively enhances the chemical adsorption and activation capacity of oxygen molecules through the synergistic effect of nitrogen vacancies and carbon quantum dots, inhibits the recombination of photogenerated charge carriers, constructs an S-type charge transfer channel driven by a built-in electric field, and significantly improves the transfer efficiency of electrons to oxygen molecules and the two-electron reduction selectivity. This material not only performs excellently in pure water, but can also efficiently generate hydrogen peroxide in actual water bodies such as tap water and river water, and has good practical application adaptability and promotion prospects. Attached Figure Description

[0026] Figure 1 The unmodified g-C3N5 powder from Example 1;

[0027] Figure 2 The Nv-g-C3N5 powder after plasma treatment in Example 1;

[0028] Figure 3 The carbon quantum dot solution synthesized by hydrothermal method in Example 1;

[0029] Figure 4 The carbon quantum dot solution under ultraviolet light irradiation in Example 1;

[0030] Figure 5 The CQDs / Nv-g-C3N5 powder synthesized by hydrothermal assembly in Example 1;

[0031] Figure 6 This is the H2O2 standard curve corresponding to the KI colorimetric method in this invention;

[0032] Figure 7 This is a bar chart showing the hydrogen peroxide yields of g-C3N5, Nv-g-C3N5, CQDs / g-C3N5, and CQDs / Nv-g-C3N5 in this invention.

[0033] Figure 8 The hydrogen peroxide yield of CQDs / Nv-g-C3N5 for five cycles in this invention;

[0034] Figure 9 This is a bar chart showing the hydrogen peroxide yield of CQDs / Nv-g-C3N5 in pure water, tap water, and river water in this invention.

[0035] Figure 10 This is an HR-TEM image of CQDs / Nv-g-C3N5 in this invention;

[0036] Figure 11This is a diagram illustrating the photocatalytic electron transfer mechanism of CQDs / Nv-g-C3N5 in this invention. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0038] The preparation method of nitrogen-vacancy-enriched CQDs / Nv-g-C3N5 heterojunction photocatalytic material provided by the present invention includes the following specific steps:

[0039] S1, Preparation of carbon quantum dot solution:

[0040] Dissolve 3-5g of citric acid and 1-3g of urea in 10-15mL of deionized water and stir thoroughly until completely dissolved. Then transfer the solution to a 40-80mL polytetrafluoroethylene reactor and perform a hydrothermal reaction at 150-200℃ for 4-7 hours. After the reaction is complete, centrifuge the solution, take the supernatant suspension and dilute it 15-25 times to obtain a carbon quantum dot (CQDs) solution.

[0041] S2, Preparation of g-C3N5 powder:

[0042] The precursor 3-amino-1,2,4-triazole was added to a crucible, filling the crucible to 1 / 3–2 / 3 of its volume. The crucible was placed in a muffle furnace and heated to 500–550 °C at a rate of 2.2–2.8 °C / min. After calcination for 3 hours, the crucible was allowed to cool naturally and then ground until it was free of granules to obtain g-C3N5 powder.

[0043] S3, Plasma etching to prepare nitrogen-vacancy g-C3N5 (Nv-g-C3N5):

[0044] g-C3N5 powder was evenly spread in the middle region between the two poles of a quartz tube, with the powder volume not exceeding 1 / 3 of the quartz tube volume. Argon gas was first introduced to purge the tube for 1-2 minutes to remove the air inside. Then, plasma bombardment was carried out for 4-6 minutes under the conditions of argon flow rate of 300-350 mL / min and radio frequency electric field voltage of 100-120V to obtain nitrogen vacancy-enriched Nv-g-C3N5 powder.

[0045] S4, hydrothermal assembly preparation of CQDs / Nv-g-C3N5 composite photocatalyst material:

[0046] Mix 0.2-0.5g of Nv-g-C3N5 powder with 0.5-2mL of CQDs solution, add deionized water to a final volume of 8-15mL, and ultrasonically disperse for 10-20min. Then transfer the mixture to a 40-80mL polytetrafluoroethylene reactor and hydrothermally react at 150-200℃ for 4-6h. The resulting product is centrifuged and washed 2-3 times, and then dried in an oven at 65-85℃ for 20-24h to finally obtain the CQDs / Nv-g-C3N5 heterojunction photocatalytic material.

[0047] The CQDs / Nv-g-C3N5 prepared above is an S-type heterojunction photocatalytic material that can generate photo-generated electrons (e) under visible light irradiation. - With hole h + Photogenerated electrons are captured by nitrogen vacancies and efficiently transferred through S-type interface charge channels, selectively reducing dissolved oxygen to H2O2 via a two-electron oxygen reduction pathway, accompanied by the generation of ∙O2. - This material contains active species and can achieve efficient and stable photocatalytic generation of hydrogen peroxide in a sacrificial agent-free pure water system.

[0048] The following specific embodiments are provided for further explanation.

[0049] Example 1

[0050] The preparation method of the nitrogen-vacancy-enriched CQDs / Nv-g-C3N5 heterojunction photocatalytic material provided in this embodiment is as follows:

[0051] (1) Preparation of carbon quantum dot solution (CQDs):

[0052] Weigh 4g of citric acid and 2g of urea, add them to 12mL of deionized water and stir until completely dissolved. Transfer the solution to a 50mL polytetrafluoroethylene reactor and hydrothermally react at 180℃ for 5 hours. After natural cooling, centrifuge and dilute the supernatant suspension 20 times to obtain a carbon quantum dot solution.

[0053] (2) Preparation of g-C3N5 powder:

[0054] The precursor 3-amino-1,2,4-triazole was added to a crucible until it reached 2 / 3 of its volume. The crucible was then placed in a muffle furnace and heated to 500°C at a rate of 2.5°C / min, and calcined at this temperature for 3 hours. After cooling, the mixture was ground until it was free of granules to obtain g-C3N5 powder (e.g., ...). Figure 1 (As shown).

[0055] (3) Preparation of nitrogen vacancy g-C3N5 (Nv-g-C3N5):

[0056] g-C3N5 powder was evenly spread between the two electrodes of a quartz tube, filling the tube to 1 / 3 of its volume. The tube was first purged with argon gas for 1 min, followed by plasma bombardment for 5 min at an argon flow rate of 300 mL / min and a radio frequency voltage of 100 V, to obtain Nv-g-C3N5 powder (e.g., g-C3N5 powder). Figure 2 (As shown).

[0057] (4) Preparation of CQDs / Nv-g-C3N5 photocatalytic material:

[0058] Mix 0.3g of Nv-g-C3N5 powder with 1mL of CQDs solution, add deionized water to a final volume of 10mL, and sonicate for 15min. Transfer to a 50mL polytetrafluoroethylene reactor and hydrothermally react at 180℃ for 5h (the resulting carbon quantum dot solution is as shown in the image). Figure 3 As shown, the carbon quantum dot solution exhibits significant fluorescence under ultraviolet light irradiation, such as... Figure 4 (As shown). The product was centrifuged and washed three times, then dried in an oven at 75℃ for 24 hours to obtain CQDs / Nv-g-C3N5 photocatalytic material, as shown. Figure 5 As shown.

[0059] Example 2

[0060] The preparation method of the nitrogen-vacancy-enriched CQDs / Nv-g-C3N5 heterojunction photocatalytic material provided in this embodiment is as follows:

[0061] (1) Preparation of carbon quantum dot solution (CQDs):

[0062] Weigh 3g of citric acid and 1g of urea, add them to 10mL of deionized water and stir until completely dissolved. Transfer the solution to a 40mL polytetrafluoroethylene reactor and hydrothermally react at 150℃ for 4 hours. After natural cooling, centrifuge and dilute the supernatant suspension 15 times to obtain a carbon quantum dot solution.

[0063] (2) Preparation of g-C3N5 powder:

[0064] The precursor 3-amino-1,2,4-triazole was added to a crucible until it was 1 / 3 full, and then placed in a muffle furnace. The temperature was increased to 500℃ at 2.2℃ / min and calcined at this temperature for 3 hours. After cooling, it was ground until there were no particles, yielding g-C3N5 powder.

[0065] (3) Preparation of nitrogen vacancy g-C3N5 (Nv-g-C3N5):

[0066] g-C3N5 powder was evenly spread between the two electrodes of a quartz tube, filling one-third of the tube's volume. Argon gas was first introduced to purge the tube for 1 min, followed by plasma bombardment for 4 min at an argon flow rate of 300 mL / min and a radio frequency voltage of 100 V, yielding Nv-g-C3N5.

[0067] (4) Preparation of CQDs / Nv-g-C3N5 photocatalytic material:

[0068] Mix 0.2 g of Nv-g-C3N5 powder with 0.5 mL of CQDs solution, add deionized water to a final volume of 8 mL, and sonicate for 10 min. Transfer to a 40 mL polytetrafluoroethylene reactor and react hydrothermally at 150 °C for 4 h. Wash the product twice by centrifugation and dry in an oven at 65 °C for 20 h to obtain the CQDs / Nv-g-C3N5 photocatalytic material.

[0069] Example 3

[0070] The preparation method of the nitrogen-vacancy-enriched CQDs / Nv-g-C3N5 heterojunction photocatalytic material provided in this embodiment is as follows:

[0071] (1) Preparation of carbon quantum dot solution (CQDs):

[0072] Weigh 5g of citric acid and 3g of urea, add them to 15mL of deionized water and stir until completely dissolved. Transfer the solution to an 80mL polytetrafluoroethylene reactor and hydrothermally react at 200℃ for 7 hours. After natural cooling, centrifuge and dilute the supernatant suspension 25 times to obtain a carbon quantum dot solution.

[0073] (2) Preparation of g-C3N5 powder:

[0074] The precursor 3-amino-1,2,4-triazole was added to a crucible until it was 1 / 3 full, and then placed in a muffle furnace. The temperature was increased to 550°C at 2.8°C / min, and calcined at this temperature for 3 hours. After cooling, it was ground until there were no particles, yielding g-C3N5 powder.

[0075] (3) Preparation of nitrogen vacancy g-C3N5 (Nv-g-C3N5):

[0076] g-C3N5 powder was evenly spread between the two electrodes of a quartz tube, filling one-third of the tube's volume. Argon gas was first introduced to purge the tube for 2 minutes, followed by plasma bombardment for 6 minutes at an argon flow rate of 350 mL / min and a radio frequency voltage of 120 V, yielding Nv-g-C3N5.

[0077] (4) Preparation of CQDs / Nv-g-C3N5 photocatalytic material:

[0078] Mix 0.5 g of Nv-g-C3N5 powder with 2 mL of CQDs solution, add deionized water to a final volume of 15 mL, and sonicate for 20 min. Transfer to an 80 mL polytetrafluoroethylene reactor and react hydrothermally at 200 °C for 6 h. Wash the product three times by centrifugation and dry in an oven at 85 °C for 24 h to obtain the CQDs / Nv-g-C3N5 photocatalytic material.

[0079] The following performance tests are conducted using Example 1 as an example:

[0080] I. Performance Testing of Photocatalytic H2O2 Production

[0081] Take 0.05g of the photocatalytic material prepared in Example 1 and add it to 50mL of pure water (or tap water, river water). Disperse the mixture ultrasonically for 15min to obtain a uniform suspension. Transfer the suspension to a 100mL quartz reactor and place it in a photocatalytic reaction apparatus. Then, under continuous O2 priming, magnetically stir in the dark for 40min to reach adsorption-desorption equilibrium. Subsequently, place the reactor under a 300W xenon lamp source for vertical irradiation, with a distance of 10cm between the reactor and the light source, and continuously stir during the reaction. Take a 3mL sample every 30min, filter it through a 0.22μm filter membrane to remove the photocatalytic material, and determine the H2O2 concentration using the KI colorimetric method.

[0082] II. Determination of Hydrogen Peroxide Concentration by KI Colorimetric Method

[0083] Take 0.25 mL of the filtrate and add 1 mL of KI solution (0.1 M), 0.01 mL of ammonium molybdate solution (0.01 M), and 0.01 mL of H₂SO₄ solution (0.01 M) sequentially. During this process, the I₂ in the system... - Reduced to I3 by H2O2 - A characteristic absorption peak was generated at 350 nm. After reacting for 15 min, the absorbance was measured using a UV-Vis spectrophotometer, and the result was determined according to the H2O2 standard curve (e.g., ...). Figure 6 (As shown) Calculate the sample concentration.

[0084] III. Comparison of Photocatalytic Performance and Stability Testing

[0085] To verify the performance advantages of the material of the present invention, the photocatalytic hydrogen peroxide production performance of CQDs / Nv-g-C3N5 prepared in Example 1 was compared with that of pure g-C3N5, plasma-treated Nv-g-C3N5, and CQDs / g-C3N5 without nitrogen vacancies. The results are as follows: Figure 7 As shown. By Figure 7 It can be seen that the H2O2 generation rate of CQDs / Nv-g-C3N5 is significantly higher than that of the other comparative samples, indicating that nitrogen vacancy modification and S-type heterojunction structure can synergistically improve the photocatalytic hydrogen peroxide production performance.

[0086] The recycling performance of the CQDs / Nv-g-C3N5 obtained in Example 1 was tested by repeating the photocatalytic hydrogen peroxide production experiment five times. The results are as follows: Figure 8 As shown, the material maintains high catalytic activity after 5 cycles, indicating that the composite photocatalytic material possesses good structural and operational stability.

[0087] The CQDs / Nv-g-C3N5 prepared in Example 1 was placed in three different water quality systems—pure water, tap water, and river water—to test photocatalytic hydrogen peroxide production, examining the material's application potential in real-world water bodies. The results are as follows: Figure 9 As shown. By Figure 9 It can be seen that the material can still efficiently generate hydrogen peroxide in tap water and river water systems, and has strong adaptability to practical applications.

[0088] IV. Microstructure Characterization

[0089] The microstructure of CQDs / Nv-g-C3N5 prepared in Example 1 was characterized using high-resolution transmission electron microscopy, and the results are as follows: Figure 10 As shown. By Figure 10 As can be seen, carbon quantum dots are uniformly anchored on the surface of Nv-g-C3N5 with tight interfacial bonding and no obvious agglomeration, confirming the successful construction of a stable heterojunction structure.

[0090] V. Mechanism of photocatalytic H2O2 production

[0091] Visible light excitation of CQDs / Nv-g-C3N5 generates photogenerated electrons (e - ) and photogenerated holes (h + Photogenerated electrons are captured and enriched by nitrogen vacancies, carrying dissolved oxygen via the two-electron oxygen reduction pathway (2e). - -ORR) selectively reduces to H2O2: electrons reduce O2 to generate ∙O2 - Subsequently, ∙O2 - With the participation of protons, it is further converted into H2O2; photogenerated holes are used to maintain the charge balance at the interface and suppress side reactions that consume products.

[0092] In the CQDs / Nv-g-C3N5 system, nitrogen vacancies enhance the chemisorption and activation of O2, effectively suppressing photogenerated carrier recombination as electron traps. Together with CQDs, they construct an S-type charge transfer channel driven by a built-in electric field, accelerating the directional migration of interfacial electrons and providing more catalytically active sites, thereby significantly improving the efficiency of electron resorption and activation. - The transfer efficiency to O2 and 2e - -ORR selectivity ultimately enables highly efficient photocatalytic synthesis of H2O2 in a sacrificial agent-free pure water system. The photocatalytic electron transfer mechanism is as follows: Figure 11 As shown.

[0093] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material, characterized in that, Includes the following steps: S1, preparing carbon quantum dot solution; S2, to prepare polymeric carbon nitride powder; S3, polymeric carbon nitride powder is subjected to dielectric barrier discharge plasma etching to obtain nitrogen vacancy-enriched polymeric carbon nitride; S4 involves mixing nitrogen-vacancy-enriched polymeric carbon nitride with a carbon quantum dot solution and carrying out a hydrothermal reaction to obtain a photocatalytic material.

2. The preparation method according to claim 1, characterized in that, In step S3, the conditions for dielectric barrier discharge plasma etching are: argon atmosphere, gas flow rate 300-350 mL / min, radio frequency electric field voltage 100-120 V, and processing time 4-6 min.

3. The preparation method according to claim 1 or 2, characterized in that, In step S4, the hydrothermal reaction conditions are: temperature 150-200℃, time 4-6h, and the mass-to-volume ratio of nitrogen-vacancy-enriched polymeric carbon nitride to carbon quantum dot solution is 0.2-0.5g:0.5-2mL.

4. The preparation method according to claim 3, characterized in that, Step S2 specifically involves heating the precursor 3-amino-1,2,4-triazole to 500-550℃ at a rate of 2.2-2.8℃ / min, calcining it for 3 hours, and then grinding it after cooling to obtain polymeric carbon nitride powder.

5. The preparation method according to claim 3, characterized in that, Step S1 specifically involves dissolving citric acid and urea in deionized water and reacting them hydrothermally at 150-200℃ for 4-7 hours to obtain a carbon quantum dot solution.

6. A nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material, obtained by the preparation method according to any one of claims 1 to 5, characterized in that, The photocatalytic material is CQDs / Nv-g-C3N5, which is formed by hydrothermal assembly of carbon quantum dots and nitrogen-vacancy-enriched polymeric carbon nitride to form an S-shaped heterojunction, with the carbon quantum dots selectively anchored to the nitrogen vacancy sites.

7. The nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material according to claim 6, characterized in that, The nitrogen vacancies are introduced through dielectric barrier discharge plasma etching.

8. The application of a nitrogen-vacancy-enriched carbon quantum dot / polymerized carbon nitride S-type heterojunction photocatalytic material as described in claim 7 in the photocatalytic synthesis of H2O2.

9. The application according to claim 8, characterized in that, In a pure water system without sacrificial agents, H2O2 is synthesized through a two-electron oxygen reduction reaction under visible light irradiation using the aforementioned photocatalytic material as a catalyst.

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