RNCDs / g-C3N4 photocatalytic material with high hydrogen production activity as well as preparation method and application of RNCDs / g-C3N4 photocatalytic material

Abstract

The invention discloses an RNCDs / g-C3N4 photocatalytic material with high hydrogen production activity and a preparation method and application thereof.The preparation method comprises the following steps that bamboo reed, urea and hydrogen peroxide are added into deionized water to be subjected to a hydrothermal reaction, and carbon dots RNCDs are obtained; the preparation method comprises the following steps: calcining urea in vacuum under the protection of nitrogen to obtain g-C3N4; the preparation method comprises the following steps: dissolving g-C3N4 in deionized water, adding carbon dots, carrying out ultrasonic treatment until the carbon dots are completely dissolved, and calcining to obtain the RNCDs / g-C3N4 photocatalytic material. The waste bamboo reed biomass is used as a raw material, nitrogen-doped high-crystallinity carbon dots are prepared through a urea-assisted controllable hydrothermal method, then the nitrogen-doped high-crystallinity carbon dots are loaded on g-C3N4 nanosheets through an in-situ calcination method, the RNCDs / g-C3N4 photocatalytic material of a three-dimensional hierarchical structure is constructed, and the material shows excellent photocatalytic hydrogen evolution performance under visible light.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic hydrogen production technology, and more specifically, to a high hydrogen production activity RNCDs / g-C3N4 photocatalytic material, its preparation method, and its application. Background Technology

[0002] With the rapid depletion of fossil fuels, hydrogen, as a zero-pollution energy carrier, has become an ideal alternative to traditional carbon-based fuels due to its high energy density. The increasing demand for hydrogen has spurred the development of photocatalytic water splitting technology, which can effectively convert renewable solar energy into hydrogen, demonstrating good cost-effectiveness and environmental friendliness. However, pure photocatalysts, such as common graphitic carbon nitride (g-C3N4), are prone to photogenerated electron-hole recombination during photocatalytic hydrogen production, and their surface lacks effective hydrogen evolution active sites, ultimately resulting in poor photocatalytic hydrogen evolution activity in single-phase g-C3N4. Therefore, to address the low hydrogen production performance of photocatalysts, modification of the photocatalysts is necessary.

[0003] Carbon dots (CDs), as an emerging zero-dimensional carbon-based nanomaterial (Li et al., 2010), are widely used to enhance photocatalytic activity due to their excellent light-harvesting ability, electronic conductivity, and surface functionalization capabilities. Biomass-based carbon dots (BCDs) not only inherit the advantages of traditional CDs but also possess the characteristics of renewable raw materials and a green, low-carbon synthesis process. Their abundant surface functional groups (such as -OH and -COOH) can also serve as active sites to enhance interfacial charge transport, providing a new approach to reducing catalyst costs and promoting waste resource utilization.

[0004] When carbon dots are used as modifications on the surface of the photocatalyst g-C3N4 for photocatalytic hydrogen production, their photogenerated electron transfer efficiency is crucial to improving their photocatalytic hydrogen production activity.

[0005] Therefore, CDs must have a small particle size and be tightly bonded to the surface of the g-C3N4 host material, and be evenly distributed without agglomeration.

[0006] Currently, the main methods for synthesizing carbon dots include microwave-assisted synthesis, pyrolysis, and electrochemical oxidation. Most of these methods require very high temperatures, making them unsuitable for the milder field of photocatalysis. Therefore, among these methods, hydrothermal synthesis is currently the mainstream method for carbon dot preparation in photocatalysis. Combining carbon quantum dots (CDs) with g-C3N4 is an effective way to develop high-performance g-C3N4-based photocatalysts. However, the preparation process of these CDs / g-C3N4 composites is currently quite complex, and the mechanism for enhancing their photocatalytic performance is not yet fully understood. Therefore, further research is needed to improve their photocatalytic activity, but no relevant reports have been published yet. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned defects in the existing technology and provide a high hydrogen production activity RNCDs / g-C3N4 photocatalytic material, its preparation method and application. Using waste reed as biomass as raw material, nitrogen-doped high-crystallinity carbon dots (RNCDs) are prepared by urea-assisted controllable hydrothermal method, and then loaded onto g-C3N4 nanosheets by in-situ calcination to construct a three-dimensional hierarchical RNCDs / g-C3N4 photocatalytic material.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material includes the following steps: S1. Add Reed, urea and hydrogen peroxide to deionized water for hydrothermal reaction to obtain carbon dots RNCDs; S2. Urea is calcined under vacuum and nitrogen protection to obtain g-C3N4; S3. Dissolve g-C3N4 in deionized water, add the carbon dots, sonicate until completely dissolved, and then calcine to obtain the RNCDs / g-C3N4 photocatalytic material.

[0009] Optionally, the particle size of the carbon dots is 4.0~4.5 nm.

[0010] Optionally, step S1 specifically includes: washing and drying the reed shoots with ultrapure water, pulverizing and sieving them to obtain reed shoot powder; placing the reed shoot powder, urea, hydrogen peroxide and deionized water in a high-pressure reactor and hydrothermally reacting them at 180~200℃ for 10~12h; after the reaction is completed, cooling, centrifuging and filtering are performed in sequence, followed by rotary evaporation concentration and freeze drying to obtain the carbon dots.

[0011] Optionally, the drying temperature is 80~90℃; the drying time is 18~24h.

[0012] Optionally, the particle size of the reed powder is ≤100μm.

[0013] Optionally, the mass-volume ratio of the reed powder, urea, hydrogen peroxide, and deionized water is 5g:2g:1ml:60ml.

[0014] Optionally, the centrifugation speed is 4000 r / min; the centrifugation time is 3~5 min.

[0015] Optionally, the freeze-drying temperature is -45 to -40°C; the freeze-drying time is 10 to 12 hours.

[0016] Optionally, step S2 specifically includes: placing 3.00g of urea in a ceramic boat, placing it in a vacuum tube furnace, heating it to 520-550°C at a programmed heating rate of 5-10°C / min under a nitrogen atmosphere and calcining it at that temperature for 3 hours, then cooling it naturally and grinding it to obtain g-C3N4.

[0017] Optionally, in step S3, the mass-to-volume ratio of the g-C3N4 to the deionized water is 3g:20mL.

[0018] Optionally, in step S3, the mass ratio of the g-C3N4 to the carbon dots is 3g:0.5~0.9mg.

[0019] Optionally, in step S3, the calcination temperature is 520~550℃; the calcination time is 3h.

[0020] The present invention also discloses a high hydrogen production activity RNCDs / g-C3N4 photocatalytic material prepared by the preparation method described above.

[0021] The present invention also discloses the application of the highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material prepared by the above preparation method in photocatalytic hydrogen production.

[0022] Optionally, the application includes: dispersing 10 mg of RNCDs / g-C3N4 photocatalyst material into 100 mL of triethanolamine aqueous solution under vigorous stirring conditions, then adding 1 mL of platinum chloride solution to obtain a suspension; continuously purging the system with high-purity nitrogen gas at a flow rate of 50 mL / min for 30 min to establish an anaerobic environment, and irradiating it under 420 nm visible light for 5-120 min.

[0023] Optionally, the purity of the high-purity nitrogen gas is 99.999%.

[0024] Optionally, the concentration of the triethanolamine aqueous solution is 10 vol%.

[0025] Optionally, the concentration of the platinum chloride solution is 0.300 mol / L.

[0026] Implementing the embodiments of the present invention will have the following beneficial effects: This invention innovatively utilizes waste reeds and urea to develop a value-added pathway from biomass waste to high-performance photocatalytic materials. Through a urea-assisted hydrothermal and in-situ calcination strategy, a three-dimensional hierarchical RNCDs / g-C3N4 photocatalytic material was successfully constructed. This material exhibits excellent photocatalytic hydrogen evolution performance under visible light: the RNCDs / g-C3N4 photocatalytic material in Example 1 achieved an optimal hydrogen evolution rate of 4.33 mmol·g⁻¹. - ¹·h - ¹, which is 10 times that of the original g-C3N4. The significant performance improvement is due to: (1) efficient charge separation: RNCDs / g-C3N4 micro heterojunction drives the directional transfer of photogenerated charges and effectively suppresses recombination; (2) broadened light absorption: the quantum confinement effect of RNCDs significantly enhances the visible light capture range; (3) rich active sites: the introduction of RNCDs optimizes the specific surface area and electronic structure of the material. Structural characterization and photoelectrochemical analysis revealed the efficient interfacial charge transport mechanism, and the theory and experiment were in high agreement. It effectively addresses the core challenge of high-value conversion of waste biomass and contributes a key solution for developing low-cost, sustainable, high-performance metal-free photocatalysts for clean hydrogen production. The proposed synthesis strategy provides a promising approach for the recycling of biomass resources and provides key insights for designing advanced carbon-based nanomaterials for energy applications. Attached Figure Description

[0027] Figure 1 The preparation process of the RNCDs / g-C3N4 photocatalytic material in this embodiment is described.

[0028] Figure 2 This is a TEM image of the RNCDs / g-C3N4 photocatalytic material in this embodiment.

[0029] Figure 3 The XRD patterns of g-C3N4 and RNCDs / g-C3N4 in this embodiment are shown.

[0030] Figure 4 The infrared spectra of g-C3N4 and RNCDs / g-C3N4 in this embodiment are shown.

[0031] Figure 5 The images show the UV-Vis diffuse reflectance absorption spectra of g-C3N4 and RNCDs / g-C3N4 photocatalytic materials in this embodiment.

[0032] Figure 6 This is a high-resolution XPS spectrum of g-C3N4 and RNCDs / g-C3N4 in this embodiment.

[0033] Figure 7 The graph shows the photocatalytic hydrogen production performance of g-C3N4 and RNCDs / g-C3N4 photocatalytic materials in this embodiment.

[0034] Figure 8 This study examines the cycle stability of the hydrogen production performance of the RNCDs / g-C3N4 photocatalyst material with high hydrogen production activity in this embodiment.

[0035] Figure 9 This describes the mechanism of the RNCDs / g-C3N4 photocatalytic material in Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0037] Example 1 The preparation method of the highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material in this embodiment includes the following steps: S1. Wash the reed several times with ultrapure water, then dry it in an oven at 80℃ for 24 hours. Grind it into powder using a ball mill and sieve it to obtain reed powder with a particle size ≤100μm. Place 5g of reed powder, 2g of urea, 1ml of hydrogen peroxide and 60ml of deionized water in a 100ml high-pressure reactor lined with polytetrafluoroethylene and hydrothermally react at 200℃ for 12 hours. After the reaction, cool it, centrifuge it at 4000r / min for 3 minutes, filter it, and then concentrate it by rotary evaporation at 100℃ and freeze-dry it at -45℃ for 12 hours to obtain carbon dot RNCDs.

[0038] S2. Place 3.00g of urea in a porcelain boat, put it into a vacuum tube furnace, and calcine it at a programmed heating rate of 5°C / min to 550°C for 3 hours under a nitrogen atmosphere. Then, let it cool naturally and grind it to obtain g-C3N4.

[0039] S3. Weigh 3.00g of g-C3N4 and dissolve it in 20 mL of deionized water. Add 0.8mg of RNCDs, sonicate until completely dissolved, and then calcine at 550℃ in a muffle furnace for 3 hours. After natural cooling, grind to obtain RNCDs / g-C3N4 photocatalytic material.

[0040] The RNCDs / g-C3N4 photocatalyst material prepared above was used in photocatalytic hydrogen production. Specifically, under vigorous stirring, 10 mg of RNCDs / g-C3N4 photocatalyst material was dispersed in 100 mL of triethanolamine aqueous solution (10 vol%), and then 1 mL of platinum chloride solution (0.300 mol / L) was added to obtain a suspension. The system was continuously purged with high-purity nitrogen gas (99.999%) at a flow rate of 50 mL / min for 30 min to establish an anaerobic environment. The system was then irradiated with 420 nm visible light for 10 min to uniformly photodeposit Pt nanoparticles on the surface of g-C3N4.

[0041] During the photocatalytic reaction, 1 mL of headspace gas was collected every 60 min using a gas-tight syringe and injected into a gas chromatography system equipped with a TCD detector (5A molecular sieve column, Ar carrier gas, column temperature 80℃). The hydrogen concentration was quantitatively analyzed using the external standard method, and the hydrogen production rate was accurately calculated by combining the reactor headspace volume.

[0042] Figure 1 This describes the preparation process of the RNCDs / g-C3N4 photocatalytic material in this embodiment.

[0043] Figure 2 This is a TEM image of the RNCDs / g-C3N4 photocatalyst material in this embodiment. Figure 2 As can be clearly seen in image a, the g-C3N4 photocatalyst host material has a very thin nanosheet morphology, with many small, uniformly distributed, dark-colored particles on its surface, which can be attributed to RNCD nanoparticles. Further magnification of these small particles reveals… Figure 2 b shows that the RNCDs nanoparticles have a distinct core-shell structure with a size of 4.3 nm, and lattice fringes with a spacing of 0.22 nm can be observed, corresponding to the RNCDs plane, while the RNCDs outside the core have an amorphous structure.

[0044] Figure 3 The XRD patterns of g-C3N4 and RNCDs / g-C3N4 in this embodiment clearly show that the g-C3N4 sample exhibits a distinct characteristic peak at 27.3 degrees, corresponding to the interlayer stacking of g-C3N4 nanosheets. Compared to pure g-C3N4, the RNCDs / g-C3N4 sample modified with the additives shows an interlayer stacking peak of the same intensity at the same position, proving that the RNCD loading method achieved by this method is relatively mild and does not change the intrinsic crystal structure of g-C3N4.

[0045] Figure 4 The images show the infrared spectra of g-C3N4 and RNCDs / g-C3N4 in this embodiment. The infrared spectra reveal that g-C3N4 exhibits high activity at 810 cm⁻¹. -1A characteristic peak appears at 1200-1700 cm⁻¹, attributed to its triazine ring unit. Additionally, a characteristic peak appears at 1200-1700 cm⁻¹. -1 Multiple consecutive peaks appear nearby, belonging to the CN structure in g-C3N4. Additionally, at 3000-3500 cm⁻¹... -1 The range showed characteristic peaks corresponding to the terminal NH. Compared to g-C3N4, the carbon dot-modified RNCDs / g-C3N4 had the same infrared characteristic peaks, indicating that the additives were deposited on the surface of g-C3N4 without changing the internal structure of g-C3N4.

[0046] Figure 5 The images show the UV-Vis diffuse reflectance absorption spectra of the g-C3N4 and / or g-C3N4 photocatalysts in this embodiment. Compared to pure g-C3N4, all RNCDs-modified samples exhibit enhanced light absorption in the visible region. Furthermore, the figures show a distinct absorption peak around 370 nm for both g-C3N4 and RNCDs / g-C3N4, attributed to the local surface plasmon resonance (LSPR) effect of the RNCD nanoparticles, indicating successful deposition of the RNCD nanoparticles.

[0047] Figure 6 The figures show the high-resolution XPS spectra of g-C3N4 and RNCDs / g-C3N4 in this embodiment. As can be seen from the figures, both g-C3N4 and RNCDs / g-C3N4 exhibit distinct C 1s (~288 eV) and N 1s (~398 eV) characteristic peaks in their full XPS spectra, confirming that the composite material is mainly composed of carbon and nitrogen. This demonstrates that RNCDs were successfully integrated into the g-C3N4 nanosheets.

[0048] Figure 7 The image shows the photocatalytic hydrogen production performance of g-C3N4 and RNCDs / g-C3N4 photocatalytic materials in this embodiment. It can be seen that the photocatalytic hydrogen production performance of pure g-C3N4 is 0.4 mmol / h. -1 g -1 When RNCDs were deposited on g-C3N4, the photocatalytic hydrogen production performance of the RNCDs / g-C3N4 photocatalytic material was further significantly enhanced, reaching 4.3 mmol / h. -1 g -1 .

[0049] Figure 8 This study examines the cycle stability of the hydrogen production performance of the highly hydrogen-producing RNCDs / g-C3N4 photocatalyst material in this embodiment. Figure 8As can be seen, after four photocatalytic hydrogen production cycle experiments, the photocatalytic hydrogen production activity of the RNCDs / g-C3N4 photocatalyst did not decrease significantly, indicating that the highly active RNCDs / g-C3N4 material prepared in this invention has good cycle stability in photocatalytic hydrogen production applications.

[0050] Figure 9 The mechanism of the RNCDs / g-C3N4 photocatalytic material in Example 1 is illustrated. The photocatalytic hydrogen production process involves three steps: photoexcitation to generate electron-hole pairs, electron migration, and reactions occurring on the catalyst surface. Regarding light absorption, the band gap of RNCDs / g-C3N4 is narrowed due to the modification of carbon dots (NCDs). The band gap (Eg) determines the minimum energy of light that the material can absorb; a narrower band gap means the material can absorb lower-energy photons, i.e., longer wavelength light. The modification of RNCDs not only alters the band gap but also introduces intermediate energy levels, allowing electrons to transition from the valence band to these intermediate levels. The narrowing band gap leads to a redshift of the absorption edge, thereby enabling the utilization of longer wavelength visible light, extending the visible light utilization range to long wavelengths (≥500 nm). In terms of carrier separation, the ultrathin two-dimensional structure of the g-C3N4 nanosheets significantly shortens the migration path of conduction band electrons to the surface, effectively suppressing carrier recombination. The RNCDs anchored on the surface of g-C3N4 act as electron acceptors. Their unique electron affinity enables them to efficiently capture and directionally transfer conduction band electrons from CN nanosheets, achieving rapid dissociation of electron-hole pairs in the spatial dimension. This heterostructure, through the dual effects of band matching and interface coupling, synergistically optimizes the separation and utilization efficiency of photogenerated carriers, thereby significantly enhancing the photocatalytic hydrogen production activity of the composite system.

[0051] In the photocatalytic reaction, Pt acts as a co-catalyst (promoter) for H. + Reduction provides the active site, while triethanolamine (TEOA) is a sacrificial electron donor used to capture holes.

[0052] Example 2 The difference between this embodiment and Example 1 is that the amount of RNCDs added in the RNCDs / g-C3N4 photocatalytic material is 0.5 mg.

[0053] Example 3 The difference between this embodiment and Example 1 is that the amount of RNCDs added in the RNCDs / g-C3N4 photocatalytic material is 0.6 mg.

[0054] Example 4 The difference between this embodiment and Example 1 is that the amount of RNCDs added in the RNCDs / g-C3N4 photocatalytic material is 0.7 mg.

[0055] Example 5 The difference between this embodiment and Example 1 is that the amount of RNCDs added in the RNCDs / g-C3N4 photocatalytic material is 0.9 mg.

[0056] The hydrogen production performance of the RNCDs / g-C3N4 photocatalyst materials prepared in Examples 2-5 was tested. Combined with the test results of Example 1, it was found that when the RNCDs addition amounts were 0.5, 0.6, 0.7, 0.8, and 0.9 mg, the hydrogen production performance of the RNCDs / g-C3N4 photocatalyst was 1.58, 2.11, 2.65, 4.33, and 1.55 mmol h, respectively. -1 g -1 The results show that regardless of the concentration of RNCDs added, the hydrogen production performance of the RNCDs / g-C3N4 photocatalyst is always higher than that of g-C3N4, and its performance first increases and then decreases with increasing RNCD concentration. Therefore, the optimal RNCDs addition amount in the preparation process of the RNCDs / g-C3N4 photocatalyst is 0.8 mg.

[0057] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a high-hydrogen-producing RNCDs / g-C3N4 photocatalytic material, characterized in that, Includes the following steps: S1. Add Reed, urea and hydrogen peroxide to deionized water for hydrothermal reaction to obtain carbon dots RNCDs; S2. Urea is calcined under vacuum and nitrogen protection to obtain g-C3N4; S3. Dissolve g-C3N4 in deionized water, add the carbon dots, sonicate until completely dissolved, and then calcine to obtain the RNCDs / g-C3N4 photocatalytic material.

2. The method for preparing the highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material according to claim 1, characterized in that, The carbon dots have a particle size of 4.0~4.5 nm.

3. The method for preparing the highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material according to claim 1, characterized in that, Step S1 specifically includes: washing and drying the reed shoots with ultrapure water, pulverizing and sieving them to obtain reed shoot powder; placing the reed shoot powder, urea, hydrogen peroxide and deionized water in a high-pressure reactor and hydrothermally reacting them at 180~200℃ for 10~12h; after the reaction is completed, cooling, centrifuging and filtering are performed in sequence, followed by rotary evaporation concentration and freeze drying to obtain the carbon dots.

4. The method for preparing the highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material according to claim 3, characterized in that, The drying temperature is 80~90℃; the drying time is 18~24h; The particle size of the reed powder is ≤100μm; The mass-volume ratio of the reed powder, urea, hydrogen peroxide, and deionized water is 5g:2g:1ml:60ml; The centrifuge speed is 4000 r / min; the centrifuge time is 3~5 min; The freeze-drying temperature is -45 to -40°C; the freeze-drying time is 10 to 12 hours.

5. The method for preparing the highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material according to claim 1, characterized in that, Step S2 specifically includes: placing 3.00g of urea in a ceramic boat, placing it in a vacuum tube furnace, heating it to 520-550°C at a programmed heating rate of 5-10°C / min under a nitrogen atmosphere, calcining it at a constant temperature for 3 hours, then cooling it naturally, and grinding it to obtain g-C3N4.

6. The method for preparing the highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material according to claim 1, characterized in that, In step S3, the mass-to-volume ratio of the g-C3N4 to the deionized water is 3g:20mL; The mass ratio of the g-C3N4 to the carbon dots is 3g:0.5~0.9mg; The calcination temperature is 520~550℃; the calcination time is 3h.

7. A high-hydrogen-producing RNCDs / g-C3N4 photocatalytic material prepared by the preparation method according to any one of claims 1-6.

8. The application of a highly hydrogen-producing RNCDs / g-C3N4 photocatalytic material prepared by the preparation method according to any one of claims 1-6 in photocatalytic hydrogen production.

9. The application according to claim 8, characterized in that, The application includes: dispersing 10 mg of RNCDs / g-C3N4 photocatalyst material into 100 mL of triethanolamine aqueous solution under strong stirring conditions, then adding 1 mL of platinum chloride solution to obtain a suspension; continuously purging the system with high-purity nitrogen gas at a flow rate of 50 mL / min for 30 min to establish an anaerobic environment, and irradiating it under 420 nm visible light for 5-120 min.

10. The application according to claim 9, characterized in that, The purity of the high-purity nitrogen gas is 99.999%. The concentration of the triethanolamine aqueous solution is 10 vol%. The concentration of the platinum chloride solution is 0.300 mol / L.

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