A modified rod-like graphite phase carbon nitride material by molten salt method and a preparation method and application thereof

Abstract

This invention discloses a molten salt modified rod-shaped graphitic carbon nitride material, its preparation method, and its applications. This rod-shaped graphitic carbon nitride material possesses a suitable defect structure and a rod-shaped microstructure. In water splitting hydrogen production performance tests, the hydrogen production performance of this catalyst is significantly improved compared to the original g-C3N4. The catalyst achieves a maximum hydrogen production rate of 1.75 mmol·g⁻¹ in photocatalytic water splitting experiments. ‑1 ·h ‑1 In the photocatalytic half-water splitting experiment with the addition of trace amounts of sacrificial agent, the rate of hydrogen production reached a maximum of 4.39 mmol·g. ‑1 ·h ‑1 It has a promising application prospect in the photocatalytic water splitting hydrogen production industry. Its preparation method has the advantages of simple materials, simple process, low cost and easy control, which is conducive to industrial application.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, specifically to a molten salt modified rod-shaped graphitic carbon nitride material, its preparation method, and its application.

[0002] Background Introduction

[0003] With the severe depletion of fossil fuels and the increasingly serious environmental pollution problems worldwide, the importance of developing renewable and clean energy is widely recognized. Hydrogen is the cleanest energy fuel and an irreplaceable part of the future energy system. Since the first report of TiO2 photoelectrocatalytic water splitting in 1972, research on converting solar energy into hydrogen energy has attracted widespread attention. In the past, semiconductor photocatalysis was considered a promising method because it can generate hydrogen energy or degrade organic pollutants under visible light. Therefore, further research on highly stable and efficient semiconductor-based photocatalysts is fundamental to promoting the rapid development of hydrogen energy.

[0004] Graphitic carbon nitride (g-C3N4), a metal-free visible-light-responsive polymer, exhibits responsiveness under visible light, is inexpensive, possesses significant thermal and chemical stability, and is easy to synthesize. It has been widely used in research on hydrogen production, CO2 reduction, and the degradation of organic pollutants. Traditional g-C3N4 materials can be obtained through simple thermal polymerization of organic precursors such as thiourea, urea, dicyandiamide, and melamine. However, g-C3N4 obtained under these conditions suffers from low visible light utilization, small specific surface area, and severe recombination of photogenerated carriers, significantly inhibiting its photocatalytic activity. Therefore, a series of strategies to improve the photocatalytic performance of g-C3N4 have attracted extensive research, including nanostructure engineering, crystal structure design, metal / non-metal element doping, heterostructure design, and vacancy modification.

[0005] Among various modification methods, the construction of rod-shaped porous g-C3N4 materials has attracted widespread attention. Rod-shaped g-C3N4 is beneficial for enhancing light reflection / scattering and providing channels for directional electron transfer. Simultaneously, porous g-C3N4 has well-developed pores, a large specific surface area, and can expose abundant active sites while possessing low mass transfer resistance. Inspired by these structural advantages, the preparation of rod-shaped porous g-C3N4 is an effective way to improve photocatalytic performance using rod-shaped and porous structures. Furthermore, introducing specific point defects, such as carbon or nitrogen vacancies, into the g-C3N4 framework can modify surface properties, adjust the electronic structure, and act as electron trapping sites to promote the separation of photogenerated carriers, ultimately improving the photocatalytic quantum efficiency of g-C3N4. CN107473191A discloses a salt-assisted method for preparing three-dimensional graphitic carbon nitride with cyano groups. However, the precursor processing requires mixing a dissolved salt and graphitic carbon nitride as a precursor solution, followed by low-temperature freezing and freeze-drying to obtain the precursor, which undoubtedly increases costs in industrial applications. Secondly, the amount of alkali metal salt added is very large and cannot be recycled. Therefore, achieving a g-C3N4 photocatalyst with novel hierarchical structure and point defects while improving industrial production at low cost is a very ideal and challenging task. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a method and application for preparing modified rod-shaped graphitic carbon nitride materials using the molten salt method. The catalyst is a modified rod-shaped non-metallic polymer graphitic carbon nitride synthesized by the molten salt method. The preparation method is novel, uses a single material, and does not contain any metal elements, which greatly reduces the preparation cost of the catalyst. The obtained modified rod-shaped graphitic carbon nitride material has excellent visible light photocatalytic hydrogen production activity, excellent hydrogen production effect in photocatalytic half-water splitting systems, and good hydrogen production effect in whole-water splitting systems without the addition of sacrificial agents, which has good social benefits.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a rod-shaped graphitic carbon nitride material modified by molten salt method. The carbon nitride material has a rod-shaped microstructure, a smooth surface, and micropores.

[0009] This invention provides a method for preparing rod-shaped graphitic carbon nitride materials modified by molten salt method, comprising the following steps:

[0010] (1) Using nitrogen-containing precursors as raw materials, they are ground and compounded with alkali metal salts to obtain a mixture;

[0011] (2) Calcine the mixture obtained in step (1) to obtain the carbon nitride material;

[0012] The nitrogen-containing precursor is selected from melamine or urea, and the alkali metal salt is selected from KCl, Na2SO4 or K2SO4. The mass ratio of the nitrogen-containing precursor to the alkali metal salt in the mixture is 2.0:(0.015~2.5).

[0013] Furthermore, the method for preparing the mixture in step (1) is selected from any of the following:

[0014] 1) Melamine and KCl are mixed and then ground to obtain the S1 mixture;

[0015] 2) Melamine and K2SO4 are mixed and then ground to obtain S2 mixture;

[0016] 3) Melamine and Na2SO4 are mixed and then ground to obtain the S3 mixture;

[0017] 4) Mix urea and KCl and grind them to obtain the S4 mixture;

[0018] 5) Mix urea and K2SO4 and grind them to obtain the S5 mixture;

[0019] 6) Mix urea with Na2SO4 and grind them to obtain the S6 mixture.

[0020] Furthermore, in the S1 mixture, the mass ratio of melamine to KCl is 2.0:(2.5-1.5); in the S2 mixture, the mass ratio of melamine to K2SO4 is 2.0:(2.5-1.5); in the S3 mixture, the mass ratio of melamine to Na2SO4 is 2.0:(2.0-0.015); in the S4 mixture, the mass ratio of urea to KCl is 2.0:(2.5-1.5); in the S5 mixture, the mass ratio of urea to K2SO4 is 2.0:(2.5-1.5); and in the S6 mixture, the mass ratio of urea to Na2SO4 is 2.0:(2.0-0.015).

[0021] Preferably, in the S1 mixture, the ratio of melamine to KCl is 2.0g:2.0g.

[0022] Preferably, the S2 mixture has a melamine to K2SO4 ratio of 2.0g:2.0g.

[0023] Preferably, in the S3 mixture, the ratio of melamine to Na2SO4 is 2.0g:0.015g.

[0024] Preferably, the S4 mixture has a urea to KCl ratio of 2.0g:2.0g.

[0025] Preferably, in the S5 mixture, the ratio of urea to K2SO4 is 2.0g:2.0g.

[0026] Preferably, in the S6 mixture, the ratio of urea to Na2SO4 is 2.0g:0.015g.

[0027] Furthermore, in the process of forming a mixture of S1, S2, S3, S4, S5 or S6, the mixing of the nitrogen-containing precursor and the salt only requires grinding, excluding hydrothermal treatment.

[0028] Further, in step (2), the atmosphere during calcination is N2, Ar, or air; the calcination heating program is as follows: heating rate of 2.5–10 °C / min, final temperature of 450–550 °C, and final temperature holding time of 2–4 h. More specifically, the calcination heating rate is 2.5 °C / min, 5 °C / min, or 10 °C / min, the final temperature is 450 °C, 500 °C, or 550 °C, and the final temperature holding time is 2 h, 3 h, or 4 h. Preferably, the calcination heating program is: heating at 5 °C / min to a final temperature of 500 °C, and holding at 500 °C for 4 h. The thermal polymerization rate is an important factor affecting the crystal structure and defect distribution of carbon nitride. Similarly, the final temperature and the final temperature holding time are also important factors affecting the crystal structure of carbon nitride. Under the preferred calcination heating program, the hydrogen production performance of the obtained catalyst is further improved.

[0029] Furthermore, step (2) specifically involves:

[0030] SS1. Place a mixture in a ceramic boat or crucible, and then place it in a tube furnace or muffle furnace;

[0031] SS2. After introducing the atmosphere, calcination is carried out according to the calcination heating procedure. After calcination, the material is naturally cooled to room temperature to obtain the carbon nitride material.

[0032] As a general technical concept, the present invention also provides an application of the above-mentioned molten salt modified rod-shaped graphitic carbon nitride material in photocatalytic whole water splitting for hydrogen production and photocatalytic half water splitting for hydrogen production.

[0033] In a further improved application, the molten salt modified rod-shaped graphitic carbon nitride material is used for photocatalytic water splitting to produce hydrogen, comprising the following steps: ultrasonically dispersing the molten salt modified rod-shaped graphitic carbon nitride material in deionized water to remove dissolved oxygen, adding a co-catalyst and ultrasonically mixing evenly, evacuating the vacuum, and then starting the photocatalytic water splitting to produce hydrogen under visible light irradiation to obtain H2.

[0034] In a further improvement to the above application, when the molten salt modified rod-shaped graphitic carbon nitride material is used for photocatalytic water splitting to produce hydrogen, the deionized water used to remove dissolved oxygen is obtained by continuously purging pure nitrogen gas for 30 minutes; the ultrasonic treatment power of the molten salt modified rod-shaped graphitic carbon nitride dispersed in deionized water is 100W, and the ultrasonic treatment time is 30 minutes; the ratio of the molten salt modified rod-shaped porous graphitic carbon nitride to deionized water is 20mg:100mL; the ratio of the molten salt modified rod-shaped graphitic carbon nitride to the co-catalyst 2%wt H2PtCl6·6H2O solution is 20mg:500μL; the light source used in the photocatalytic reaction is a xenon lamp with a light power of 400W; the photocatalytic reaction is carried out under stirring conditions at a speed of 200rpm to 300rpm; and the temperature of the photocatalytic reaction is 5℃ to 7℃.

[0035] When the molten salt modified rod-shaped graphitic carbon nitride material is subjected to photocatalytic half-water splitting to produce hydrogen under conditions containing a sacrificial agent, the following steps are included: dispersing the molten salt modified rod-shaped graphitic carbon nitride in deionized water containing triethanolamine and removing dissolved oxygen, adding a co-catalyst and ultrasonically mixing evenly, evacuating the vacuum, and starting the photocatalytic water splitting to produce hydrogen under visible light irradiation to obtain H2.

[0036] When the molten salt modified rod-shaped graphitic carbon nitride material is used for photocatalytic partial water splitting to produce hydrogen, the ratio of the molten salt modified rod-shaped graphitic carbon nitride to deionized water is 20 mg: 100 mL; the ratio of the molten salt modified rod-shaped graphitic carbon nitride to triethanolamine (sacrificial agent) is 20 mg: 500 μL; the ratio of the molten salt modified rod-shaped graphitic carbon nitride to the co-catalyst 2% wt H2PtCl6·6H2O solution is 20 mg: 500 μL; the light source used in the photocatalytic reaction is a xenon lamp with a light power of 400 W; the photocatalytic reaction is carried out under stirring conditions at a speed of 200 rpm to 300 rpm; and the temperature of the photocatalytic reaction is 5℃ to 7℃.

[0037] The applicant conducted numerous experiments with alkali metal salts. The vast majority of these salts, or combinations thereof, failed to effectively modify carbon nitride, resulting in suboptimal catalytic hydrogen production performance. Furthermore, many of these catalysts lacked the ability to produce hydrogen through complete water splitting. The results showed that single-component KCl, Na₂SO₄, or K₂SO₄, as modifying ligands, effectively modified graphitic carbon nitride, achieving better catalytic hydrogen production performance. Further experiments revealed that more alkali metal as a modifying ligand does not necessarily lead to optimal hydrogen production. With Na₂SO₄ as the modifying ligand, the hydrogen production performance of 0.15 g Na₂SO₄-modified carbon nitride was significantly greater than that of 2.0 g Na₂SO₄-modified carbon nitride.

[0038] The technical solution provided by this invention has the following beneficial effects:

[0039] (1) The rod-shaped graphitic carbon nitride material modified by the molten salt method of the present invention has a rod-shaped structure with a smooth surface and micropores. This unique morphological structure can promote light reflection and scattering, provide internal and external active sites, and endow electron directional transfer channels, which is beneficial to provide more catalytic active sites and promote the separation and migration of photogenerated carriers, thereby improving its catalytic performance.

[0040] (2) This invention uses nitrogen-containing precursors and salts as raw materials. After grinding, the two are combined and no additional treatment is required. The modified catalyst can be directly prepared by thermal polymerization. Not only is the material cost low and the preparation method simple, but it also does not contain any metal elements, so it has little environmental pollution and is conducive to its promotion to large-scale production.

[0041] (3) The modified rod-shaped graphitic carbon nitride material prepared has significantly enhanced photocatalytic performance compared with pure g-C3N4. It not only has excellent hydrogen production performance in the photocatalytic half-water splitting experiment with added sacrificial agent, but also achieves good hydrogen evolution performance in the photocatalytic whole-water splitting experiment without added sacrificial agent. Attached Figure Description

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0043] Figure 1 The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 X-ray diffraction (XRD) patterns of the original graphitic carbon nitride (CN) obtained in Comparative Example 1.

[0044] Figure 2 The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 Fourier transform infrared (FTIR) spectra of the original graphitic carbon nitride (CN) obtained in Comparative Example 1.

[0045] Figure 3 The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MSNa2SO4 Electron paramagnetic resonance (EPR) spectra of pristine graphitic carbon nitride (CN) prepared in Comparative Example 1 and Comparative Example 2.

[0046] Figure 4 The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 Fluorescence emission spectra of the original graphitic carbon nitride (CN) prepared in Comparative Example 1 and Comparative Example 2.

[0047] Figure 5 The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 The rate of hydrogen production from the pristine carbon nitride (CN) prepared in Comparative Example 1 during the photocatalytic total water splitting experiment is shown in the graph.

[0048] Figure 6 The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 The rate of hydrogen production from the pristine carbon nitride (CN) prepared in Comparative Example 1 in the photocatalytic half-water splitting (0.5 vol.% triethanolamine) experiment is shown in the graph.

[0049] Figure 7 The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 Typical SEM images of the original graphitic carbon nitride C3N4 obtained in Comparative Example 1. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0051] All raw materials and instruments used in the following embodiments are commercially available. Unless otherwise specified, the processes and equipment used in these embodiments are conventional.

[0052] To more clearly describe the technical content of the present invention, the following description is provided in conjunction with specific embodiments.

[0053] CN-MS mentioned in the following embodimentsKCl This refers to KCl-modified rod-shaped graphitic carbon nitride materials, CN-MS K2SO4 This refers to K2SO4-modified rod-shaped graphitic carbon nitride materials, CN-MS Na2SO4 This refers to Na2SO4-modified rod-shaped graphitic carbon nitride materials.

[0054] Example 1

[0055] A method for preparing rod-shaped graphitic carbon nitride materials by molten salt method includes the following steps:

[0056] (1) Grind and mix 2g of melamine with 2.0g of KCl;

[0057] (2) Place the mixture obtained in step (1) in a tube furnace and heat it to 500°C at a heating rate of 2.5°C / min under an Ar atmosphere. Hold it at this temperature for 4 hours and then let it cool naturally to room temperature.

[0058] (3) After grinding and collecting the product obtained in step (2), rod-shaped graphitic carbon nitride material modified by molten salt method with KCl as the modifying salt is obtained and named CN-MS. KCl-2.0 .

[0059] In this embodiment, modified rod-shaped graphitic carbon nitride CN-MS with KCl addition amounts of 2.5 g and 1.5 g were also prepared. KCl-2.5 and CN-MS KCl-1.5 .

[0060] Comparative Example 1

[0061] A method for preparing pristine graphitic carbon nitride includes the following steps:

[0062] According to traditional methods, melamine is thermally polymerized under an Ar atmosphere to prepare graphitic carbon nitride. Specifically, 5g of melamine is placed in a boat, and under a N2 atmosphere, the temperature is increased to a final temperature of 550℃ at a rate of 2.5℃ / min. After holding at 550℃ for 4 hours, it is naturally cooled to room temperature. The resulting blocky sample is then ground to obtain a yellow powder, which is the original graphitic carbon nitride, named CN.

[0063] Example 2

[0064] A method for preparing rod-shaped graphitic carbon nitride materials by molten salt method includes the following steps:

[0065] (4) Grind and mix 2g of melamine with 2.0g of K2SO4;

[0066] (5) Place the mixture obtained in step (1) in a tube furnace and heat it to 500°C at a heating rate of 2.5°C / min under an Ar atmosphere. Hold it at this temperature for 4 hours and then let it cool naturally to room temperature.

[0067] (6) After grinding and collecting the product obtained in step (2), a rod-shaped graphitic carbon nitride material modified by molten salt method with K2SO4 as the modifying salt is obtained and named CN-MS. K2SO4-2.0 .

[0068] In this embodiment, modified rod-shaped graphitic carbon nitride CN-MS with K2SO4 addition amounts of 2.5 g and 1.5 g were also prepared. K2SO4-2.5 and CN-MS K2SO4-1.5 .

[0069] Example 3

[0070] A method for preparing rod-shaped graphitic carbon nitride materials by molten salt method includes the following steps:

[0071] (7) Grind and mix 2g of melamine with 0.015g of Na2SO4;

[0072] (8) Place the mixture obtained in step (1) in a tube furnace and heat it to 500°C at a heating rate of 2.5°C / min under an Ar atmosphere. Hold it at this temperature for 4 hours and then let it cool naturally to room temperature.

[0073] (9) After grinding and collecting the product obtained in step (2), a rod-shaped graphitic carbon nitride material modified by molten salt method with Na2SO4 as the modifying salt is obtained and named CN-MS. Na2SO4-0.015 .

[0074] In this embodiment, modified rod-shaped graphitic carbon nitride CN-MS were also prepared with Na2SO4 addition amounts of 1.5 g, 1.0 g, 0.5 g, 0.25 g, 0.15 g, and 0.1 g, respectively. Na2SO4-1.5 CN-MS Na2SO4-1.0 CN-MS Na2SO4-0.5 CN-MS Na2SO4-0.25 CN-MS Na2SO4-0.15 CN-MS Na2SO4-0.1 .

[0075] Example 4

[0076] In this embodiment, the preparation method is the same as in Example 1, except that melamine is replaced with the same mass of urea. In this embodiment, modified rod-shaped graphitic carbon nitride with KCl addition amounts of 2.0g, 2.5g, and 1.5g were prepared.

[0077] Example 5

[0078] In this embodiment, the preparation method is the same as in Example 1, except that melamine is replaced with the same mass of urea. In this embodiment, modified rod-shaped graphitic carbon nitride with K2SO4 addition amounts of 20 g, 2.5 g, and 1.5 g were prepared.

[0079] Example 6

[0080] In this embodiment, the preparation method is the same as in Example 1, except that melamine is replaced with the same mass of urea. In this embodiment, modified rod-shaped graphitic carbon nitride with Na2SO4 addition amounts of 0.015g, 1.5g, 1.0g, 0.5g, 0.25g, 0.15g, and 0.1g were prepared.

[0081] Figure 1 All the molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 X-ray diffraction patterns of the original graphitic carbon nitride (CN) prepared in Comparative Example 1 and Comparative Example 1. From... Figure 1 As can be seen, CN prepared from melamine exhibits typical carbon nitride diffraction peaks. The two diffraction peaks at 12.8° and 27.6° reflect the interlayer stacking of nitrogen-linked heptaazine units (1 0 0) and conjugated aryl groups (0 0 2) in the carbon nitride plane (JCPDS 87-1526). After adding KCl, K2SO4 or Na2SO4, the modified graphitic carbon nitride still exhibits typical diffraction peaks, but also shows some differences. Among them, the increased diffraction peak intensity of KCl-modified graphitic carbon nitride indicates that the degree of in-plane stacking of nitrogen-linked heptaazine units (1 0 0) and conjugated aryl groups (0 0 2) in this material is greater than that of graphitic carbon nitride. Conversely, the intensity of the diffraction peak in the K2SO4-modified catalyst is lower than that of graphitic carbon nitride, indicating a lower structural order. Furthermore, the intensity of the (1 0 0) diffraction peak in Na2SO4-modified carbon nitride increases significantly, while the intensity of the (0 0 2) diffraction peak is similar to that of graphitic carbon nitride, demonstrating that the heptaazine units in Na2SO4-modified carbon nitride are more ordered. X-ray diffraction characterization results demonstrate that the addition of different molten salts has a significant impact on the crystal structure of carbon nitride.

[0082] Figure 2 This invention demonstrates all the molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention. KCl CN-MS K2SO4 CN-MS Na2SO4 Fourier transform infrared spectra of the original graphitic carbon nitride prepared in Comparative Example 1 and Comparative Example 1. Figure 2 It can be seen that the rod-shaped graphitic carbon nitride modified by the molten salt method and the original graphitic carbon nitride exhibit the same basic characteristic peaks, proving that the molten salt method modification did not destroy the basic structure of carbon nitride. Among the diffraction peaks, 810 cm⁻¹... -1 The sharp peak at 1200–1700 cm⁻¹ belongs to the out-of-plane bending mode of the heptaazine ring. -1 The sharp peaks between 3000-3400 cm⁻¹ are related to the stretching vibrations of aromatic CN heterocycles, demonstrating the generation of the CNC bond extension network. -1 The broad absorption band within the range originates from the stretching vibration modes absorbed by the H2O molecule and the terminal amino group (-NHx). For KCl-modified graphitic carbon nitride, the band at 2156 cm⁻¹... -1 It exhibits cyano diffraction peaks, while K₂SO₄ or KCl-modified carbon nitride materials show peaks in the 1200–1700 cm⁻¹ range. -1 The tensile vibration peaks between the two are stronger than those of the original carbon nitride, but the molten salt modified carbon nitride material has a peak at 810 cm⁻¹. -1 The peak intensities at the flanks are all weaker than those of the original carbon nitride. This demonstrates that molten salt modification may lead to changes in the defect structure within carbon nitride materials.

[0083] Figure 7 This invention demonstrates the molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention. KCl CN-MS K2SO4 CN-MS Na2SO4 Typical SEM images of the original graphitic carbon nitride C3N4 prepared in Comparative Example 1 are shown. The carbon nitride materials prepared in Examples 1-3 have a rod-like shape, smooth surface, and micropores.

[0084] Figure 3 This invention demonstrates all the molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention. KCl CN-MS K2SO4 CN-MS Na2SO4 The EPR spectra of the original graphitic carbon nitride (CN) prepared in Comparative Example 1 and Comparative Example 2 are shown. The comparative test results show that the rod-shaped graphitic carbon nitride modified by the molten salt method and the original graphitic carbon nitride exhibit the same paramagnetic absorption signal, with a g value of 2.0046 for both. This is due to the sp... 2The -C group generates unpaired electrons of the same type. Furthermore, the Lorentz line intensity of the rod-shaped graphitic carbon nitride modified by the molten salt method is weaker than that of the original graphitic carbon nitride. This result suggests that molten salt modification of rod-shaped graphitic carbon nitride may lead to a more rational defect distribution within the material, as excessive defects become recombination centers for photogenerated electrons and holes, while a suitable defect structure distribution promotes photocatalytic reactions. The above characterization indicates that the vacancies in molten salt modified rod-shaped graphitic carbon nitride can be regulated by changing the type of molten salt, while excessive vacancies are detrimental to improving the hydrogen production performance of the modified catalyst. These test results demonstrate that the introduction of vacancies optimizes the electronic structure of molten salt modified rod-shaped graphitic carbon nitride, providing more electrons to participate in the photocatalytic reduction reaction.

[0085] Figure 4 All the molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl CN-MS K2SO4 CN-MS Na2SO4 The fluorescence excitation spectra of the original graphitic carbon nitride (CN) prepared in Comparative Example 1 are shown. The fluorescence excitation spectra show that the Na2SO4-modified carbon nitride material has a longer photogenerated electron lifetime, while the photogenerated electron lifetime of the KCl or K2SO4-modified carbon nitride materials is similar to that of the original carbon nitride material, and they do not have a photocatalytic performance advantage.

[0086] The deionized water used in Examples 7-8 was obtained by continuously purging pure nitrogen gas for 30 minutes.

[0087] Example 7

[0088] Application of a molten salt modified rod-shaped graphitic carbon nitride material in visible light photocatalytic water splitting for hydrogen production.

[0089] 20 mg of molten salt modified rod-shaped graphitic carbon nitride prepared in Examples 1, 2, and 3, and 20 mg of original graphitic carbon nitride prepared in Comparative Example 1 were respectively dispersed in 100 mL of deionized water after removing dissolved oxygen. 500 μL of 2% wt chloroplatinic acid hexahydrate (H₂PtCl₆·6H₂O) solution was added as a co-catalyst. After ultrasonic treatment at 100 W for 30 min, photodeposition was performed for 1 h. The system was then evacuated, and a 400 W xenon lamp was turned on for photo-irradiation. The amount of hydrogen produced was analyzed online using a gas chromatograph every 1 h.

[0090] The hydrogen production in the photocatalytic water splitting experiment of the molten salt modified rod-shaped graphitic carbon nitride prepared in Examples 1, 2, and 3 of this invention and the original graphitic carbon nitride prepared in Comparative Example 1 is as follows: Figure 5As shown in (ac), the experimental results indicate that the optimal hydrogen production rates of the tested photocatalysts, from highest to lowest, are as follows: CN-MS Na2SO4-0.015 CN-MS K2SO4-2.0 CN-MS KCl-2.0 >CN. Among them, CN-MS Na2SO4-0.015 It boasts optimal hydrogen production performance, with a maximum hydrogen production rate of 1.75 mmol·g⁻¹ achieved through photocatalytic water splitting. -1 ·h -1 The results were significantly higher than those of the original carbon nitride. This demonstrates the different effects of different molten salt types on the catalytic performance of carbon nitride materials.

[0091] Example 8

[0092] Application of a molten salt modified rod-shaped graphitic carbon nitride material in visible light photocatalytic half-water splitting for hydrogen production.

[0093] Take 20 mg of the molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 respectively. KCl-2.0 CN-MS K2SO4-2.0 CN-MS Na2SO4-0.015 The original graphitic carbon nitride prepared in Comparative Example 1 (20 mg) and 20 mg were dispersed in 100 mL of deionized water after removing dissolved oxygen. A 2% chloroplatinic acid hexahydrate solution (H₂PtCl₆·6H₂O) and 500 μL of triethanolamine were added as a co-catalyst and sacrificial agent, respectively. After ultrasonic treatment for 30 min, photodeposition was performed for 1 h. The system was then evacuated, and a xenon lamp was turned on for photo-irradiation. Hydrogen production was analyzed online using a gas chromatograph every 1 h, for a total of 5 h.

[0094] The molten salt modified rod-shaped graphitic carbon nitride (CN-MS) prepared in Examples 1, 2, and 3 of this invention KCl-2.0 CN-MS K2SO4-2.0 CN-MS Na2SO4-0.015 The hydrogen production of the original graphitic carbon nitride prepared in Example 1 and Comparative Example 1 during the photocatalytic half-water splitting experiment is as follows: Figure 6 As shown in the figure. Based on the comprehensive photocatalytic half-water splitting test results, the catalyst with the best overall water splitting and hydrogen evolution performance still exhibits the best half-water splitting and hydrogen evolution performance. The experimental results show that the KCl-modified rod-shaped graphitic carbon nitride material (CN-MS)... Na2SO4-0.015 The optimal hydrogen production rate achieved through photocatalytic half-water splitting is 4.39 mmol·g. -1 ·h -1 The nitridation concentration was higher than that of the original graphitic phase (0.51 mmol·g). -1 ·h -1Furthermore, the hydrogen production performance of rod-shaped graphitic carbon nitride modified by the molten salt method did not show a significant decrease during the five-hour test period, demonstrating its good stability in catalytic hydrogen production.

[0095] As can be seen from the above, the molten salt modified rod-shaped graphitic carbon nitride material of the present invention has the advantages of strong light absorption, low photogenerated electron-hole recombination rate, good photocatalytic performance, and good stability. It is a new type of carbon nitride photocatalytic material that can be widely used in photocatalytic water splitting to produce hydrogen and has a very good application prospect.

[0096] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A molten salt modified rod-shaped graphitic carbon nitride material, characterized in that, The carbon nitride material has a rod-shaped microstructure, a smooth surface, and micropores.

2. A method for preparing rod-shaped graphitic carbon nitride material modified by molten salt method, comprising the following steps: (1) Using nitrogen-containing precursors as raw materials, they are ground and compounded with alkali metal salts to obtain a mixture; (2) Calcine the mixture obtained in step (1) to obtain the carbon nitride material; The nitrogen-containing precursor is selected from melamine or urea, and the alkali metal salt is selected from KCl, Na2SO4 or K2SO4. The mass ratio of the nitrogen-containing precursor to the alkali metal salt in the mixture is 2.0:(0.015~2.5).

3. The preparation method according to claim 2, characterized in that, The method for preparing the mixture in step (1) is selected from any one of the following 1) to 6): 1) Melamine and KCl are mixed and then ground to obtain the S1 mixture; 2) Melamine and K2SO4 are mixed and then ground to obtain S2 mixture; 3) Melamine and Na2SO4 are mixed and then ground to obtain the S3 mixture; 4) Mix urea and KCl and grind them to obtain the S4 mixture; 5) Mix urea and K2SO4 and grind them to obtain the S5 mixture; 6) Mix urea with Na2SO4 and grind them to obtain the S6 mixture; In the S1 mixture, the mass ratio of melamine to KCl is 2.0:(2.5-1.5); in the S2 mixture, the mass ratio of melamine to K2SO4 is 2.0:(2.5-1.5); in the S3 mixture, the mass ratio of melamine to Na2SO4 is 2.0:(2.0-0.015); in the S4 mixture, the mass ratio of urea to KCl is 2.0:(2.5-1.5); in the S5 mixture, the mass ratio of urea to K2SO4 is 2.0:(2.5-1.5); and in the S6 mixture, the mass ratio of urea to Na2SO4 is 2.0:(2.0-0.015).

4. The preparation method according to claim 3, characterized in that, The S1 mixture has a melamine to KCl ratio of 2.0g:2.0g; the S2 mixture has a melamine to K2SO4 ratio of 2.0g:2.0g; the S3 mixture has a melamine to Na2SO4 ratio of 2.0g:0.015g; the S4 mixture has a urea to KCl ratio of 2.0g:2.0g; the S5 mixture has a urea to K2SO4 ratio of 2.0g:2.0g; and the S6 mixture has a urea to Na2SO4 ratio of 2.0g:0.015g.

5. The preparation method according to claim 3 or 4, characterized in that, In the process of forming a mixture of S1, S2, S3, S4, S5 or S6, the mixing of nitrogen-containing precursors and salts only requires grinding, excluding hydrothermal treatment.

6. The preparation method according to claim 2, characterized in that, In step (2), the atmosphere during calcination is N2, Ar or air; the calcination heating program is as follows: heating rate is 2.5-10℃ / min, final temperature is 450-550℃, and final temperature holding time is 2-4h.

7. The preparation method according to claim 6, characterized in that, The calcination heating rate is 2.5℃ / min, 5℃ / min or 10℃ / min, the final temperature is 450℃, 500℃ or 550℃, and the final temperature holding time is 2h, 3h or 4h.

8. The preparation method according to claim 6, characterized in that, Step (2) specifically involves: SS1. Place the mixture in a ceramic boat or crucible, and then place it in a tube furnace or muffle furnace; SS2. After introducing the atmosphere, calcination is carried out according to the calcination heating procedure. After calcination, the material is naturally cooled to room temperature to obtain the carbon nitride material.

9. The application of the molten salt modified rod-shaped graphitic carbon nitride material according to claim 1 or the molten salt modified rod-shaped graphitic carbon nitride material prepared by any one of claims 2 to 8 in visible light photocatalytic complete water splitting for hydrogen production or visible light photocatalytic partial water splitting for hydrogen production.

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