Three-dimensional carbon nitride photocatalyst with sharp tip structure and preparation method and application thereof

Abstract

This invention provides a three-dimensional carbon nitride photocatalyst with an advanced structure, its preparation method, and its application, relating to the field of photocatalyst technology. The preparation method includes: obtaining graphitic carbon nitride through thermal condensation and nitrogen-rich precursor polymerization; mixing the graphitic carbon nitride in a polyphenol solution, then adding Tris-HCl solution dropwise and stirring to react, causing the polyphenols to polymerize in situ on the surface of the graphitic carbon nitride to form a polyphenol coating; separating and drying the coating to obtain a composite intermediate; mixing and grinding the composite intermediate with molten salt, then calcining it under a protective atmosphere at 400-650℃ to obtain the three-dimensional carbon nitride photocatalyst with an advanced structure. The preparation method provided by this invention is green and environmentally friendly, using readily available and inexpensive raw materials. Simultaneously, the reaction conditions are mild, requiring no template agent. The resulting catalyst has an advanced structure and exhibits extremely high photocatalytic activity for water splitting to produce hydrogen and excellent stability at room temperature and pressure, showing promising application prospects and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, and in particular to a three-dimensional carbon nitride photocatalyst with an advanced structure, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, with its high calorific value and pollution-free combustion products, holds promise as an ideal energy source to replace fossil fuels. Photocatalytic water splitting using solar energy, through a suitable photocatalyst, can convert low-density solar energy into high-density chemical energy stored in hydrogen gas, showing broad application prospects. Therefore, developing a highly efficient and stable photocatalytic material is a current research focus. Graphitic carbon nitride (g-C3N4), as a metal-free organic polymer photocatalyst, has become a research hotspot due to its unique electronic structure, good physical and chemical stability, and ease of tunability.

[0003] Traditional one-step thermal polycondensation methods for preparing g-C3N4 suffer from poor mass transfer, leading to bulk formation, small specific surface area, and high carrier recombination rates, thus limiting the photocatalytic activity of g-C3N4. Constructing g-C3N4 with a pointed structure can not only promote light collection but also accelerate charge collection and facilitate interfacial charge transport. Furthermore, introducing carbon-based materials into g-C3N4 can further promote charge transfer, modulate its band structure, and improve photoresponse. However, since carbon materials are typically introduced through carbon source copolymerization, this can potentially lead to the formation of amorphous carbon within the g-C3N4 or disrupt its framework structure. Additionally, direct thermal polycondensation often results in incomplete polycondensation, easily introducing defects and reducing photocatalytic activity. Therefore, a solution is urgently needed to address these issues. Summary of the Invention

[0004] The purpose of this invention is to provide a three-dimensional carbon nitride photocatalyst with an advanced structure, its preparation method, and its application. The preparation method is green and environmentally friendly, and the raw materials are simple, readily available, and inexpensive. At the same time, the reaction conditions are mild and no template agent is required. The resulting catalyst has an advanced structure and exhibits extremely high photocatalytic activity and stability in water splitting to produce hydrogen at room temperature and pressure, showing good application prospects and economic benefits.

[0005] In a first aspect, the present invention provides a method for preparing a three-dimensional carbon nitride photocatalyst with an advanced structure, comprising: obtaining graphitic carbon nitride by thermal condensation and polyurethane enrichment of a nitrogen precursor; mixing the graphitic carbon nitride in a polyphenol solution and then adding Tris-HCl solution dropwise and stirring to react, so that the polyphenols are polymerized in situ on the surface of the graphitic carbon nitride to form a polyphenol coating, and separating and drying to obtain a composite intermediate; mixing and grinding the composite intermediate with molten salt, and then calcining it under a protective atmosphere at 400-650°C to obtain a three-dimensional carbon nitride photocatalyst with an advanced structure.

[0006] The preparation method provided by this invention is green and environmentally friendly, using readily available and inexpensive raw materials. At the same time, the reaction conditions are mild and do not require the use of template agents. The resulting photocatalyst has extremely high photocatalytic activity and long-term catalytic stability, and has good application prospects and economic benefits.

[0007] Optionally, the nitrogen-rich precursor includes one of melamine, dicyandiamide, urea, and thiourea.

[0008] Optionally, the nitrogen-rich precursor is calcined at 400-650°C in an inert atmosphere.

[0009] Optionally, the nitrogen-rich precursor is thermally polycondensed under an inert atmosphere for 2-10 hours.

[0010] Optionally, the mass ratio of polyphenol solute to graphite phase carbon nitride in the polyphenol solution is 1:(5-200).

[0011] Optionally, the polyphenol solute in the polyphenol solution includes one of tannic acid, dopamine, and gallic acid.

[0012] Optionally, the concentration of the Tris-HCl solution is 0.1-5.0 mol / L.

[0013] Optionally, the pH of the Tris-HCl solution is 8.5.

[0014] Optionally, the molten salt includes one of KCl-LiCl, KCl-NaCl, and KCl-NaCl-LiCl.

[0015] Optionally, the mass ratio of the composite intermediate to the molten salt is 1:(2-10).

[0016] Optionally, the protective atmosphere includes either a nitrogen atmosphere or an argon atmosphere.

[0017] Optionally, calcination can be carried out at 400-650℃ under a protective atmosphere for 2-10 hours.

[0018] Secondly, the present invention also provides a three-dimensional carbon nitride photocatalyst with a pointed structure prepared by any of the above-mentioned optional preparation methods.

[0019] Thirdly, the present invention also provides the application of a three-dimensional carbon nitride photocatalyst with a cutting-edge structure prepared by any of the above-mentioned optional preparation methods in photocatalytic water splitting for hydrogen production. Attached Figure Description

[0020] Figure 1 A flowchart illustrating a method for preparing a three-dimensional carbon nitride photocatalyst with an advanced structure, provided by this invention;

[0021] Figure 2 This is a bar chart showing the hydrogen production rate of the three-dimensional carbon nitride photocatalysts prepared in Examples 1 to 4 and Comparative Example 1 during the photocatalytic water hydrogen production reaction.

[0022] Figure 3 This is a bar chart showing the hydrogen production rate of the three-dimensional carbon nitride photocatalysts prepared in Examples 3, 5 to 7 of the present invention during the photocatalytic water hydrogen production reaction.

[0023] Figure 4 This is a SEM characterization image of the three-dimensional carbon nitride photocatalyst prepared in Example 3 of the present invention;

[0024] Figure 5 The image shows a TEM characterization of the three-dimensional carbon nitride photocatalyst prepared in Example 3 of this invention.

[0025] Figure 6 This is a graph showing the change in hydrogen production of the three-dimensional carbon nitride photocatalyst prepared in Example 3 of the present invention during photocatalytic hydrogen production;

[0026] Figure 7 The image shows a comparison of XRD characterization of the three-dimensional carbon nitride photocatalyst prepared in Example 3 of this invention before and after photocatalytic hydrogen production. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0028] See Figure 1 This invention provides a method for preparing a three-dimensional carbon nitride photocatalyst with an advanced structure, comprising:

[0029] S1. Graphitic carbon nitride is obtained by thermal condensation and nitrogen-rich precursor process.

[0030] S2. Graphite phase carbon nitride was mixed in a polyphenol solution and Tris-HCl solution was added dropwise and stirred to react. The mixture was then separated and dried to obtain the composite intermediate.

[0031] S3. The composite intermediate is mixed and ground with molten salt, and then calcined under a protective atmosphere at 400-650℃ to obtain a three-dimensional carbon nitride photocatalyst.

[0032] In fact, this invention synthesizes graphitic carbon nitride through thermal polycondensation, forms a polyphenol coating by in-situ polymerization of polyphenols on the surface of graphitic carbon nitride, and then further etches it with high-temperature molten salt to obtain a three-dimensional carbon nitride photocatalyst with a pointed structure, which has high photocatalytic activity and good cycle stability.

[0033] In fact, when polyphenols are mixed with graphitic carbon nitride, the polyphenols react with the amino groups on the surface of graphitic carbon nitride through functional groups such as hydroxyl groups, and undergo in-situ polymerization on the surface of graphitic carbon nitride. At the same time, the fluid environment created by high-temperature molten salt can effectively promote mass transfer, and the high-temperature molten salt environment promotes the formation of an expanded carbonized polyphenol coating. In addition, the molten salt fluid enters the carbonized expanded polyphenol coating and selectively etches the graphitic carbon nitride, which can effectively control the morphology of the photocatalyst, thereby increasing the active sites of the photocatalyst.

[0034] In some embodiments, the nitrogen-rich precursor used in step S1 includes one of melamine, dicyandiamide, urea, and thiourea. Furthermore, calcining the nitrogen-rich precursor in an inert atmosphere at 400-650°C for 2-10 hours in step S1 is beneficial for improving the thermal polycondensation effect.

[0035] In a further embodiment, in step S1, the nitrogen-rich precursor can be placed in a tube furnace, and after the tube furnace is purged with an inert atmosphere, the nitrogen-rich precursor is heated to 400-650°C at a rate of 1-10°C / min and held at that temperature for 2-10 hours.

[0036] In some embodiments, the mass ratio of polyphenol solute to graphite-phase carbon nitride in the polyphenol solution in step S2 is 1:(5-200), and the polyphenol solute in the polyphenol solution includes one of tannic acid, dopamine, and gallic acid. In fact, by selecting different polyphenols, different polyphenol layers can be polymerized on the surface of graphite-phase carbon nitride. The thickness of the polyphenol layer can be controlled by controlling the amount of polyphenol added and the polymerization time, thereby obtaining an expanded carbonized polyphenol layer after carbonization in molten salt.

[0037] In some embodiments, the concentration of the Tris-HCl solution used in step S2 is 0.1-5.0 mol / L, and the pH of the Tris-HCl solution is 8.5. In practice, the thickness of the formed polyphenol coating is controlled by adding the Tris-HCl solution dropwise to a mixture of graphitic carbon nitride and polyphenol solution, and by controlling the dropping time of the Tris-HCl solution. Specifically, the total dropping time of Tris-HCl can be 15-120 min.

[0038] In some embodiments, the molten salt used in step S3 includes one of KCl-LiCl, KCl-NaCl, and KCl-NaCl-LiCl. Furthermore, the mass ratio of the composite intermediate to the molten salt is 1:(2-10), and the protective atmosphere used is either a nitrogen atmosphere or an argon atmosphere. In some embodiments, calcination is performed in step S3 at 400-650°C under a protective atmosphere for 2-10 hours.

[0039] Example 1

[0040] This embodiment 1 provides a method for preparing a three-dimensional carbon nitride photocatalyst with an advanced structure, comprising the following steps:

[0041] S1. Place 2g of melamine in the furnace chamber of a tube furnace and purge with nitrogen for gas replacement. Heat the tube furnace to 550℃ at a rate of 10℃ / min and keep it at that temperature for 2 hours. After cooling to room temperature with the furnace, remove and grind to obtain graphite phase carbon nitride.

[0042] S2. Dissolve 3 mg of tannic acid in 70 mL of deionized water, add 0.3 g of graphitic carbon nitride to the above tannic acid aqueous solution, and stir for 0.5 h to obtain a mixed suspension; add 10 mL of Tris-HCl solution with pH 8.5 and concentration of 0.1 mol / L dropwise to the above mixed suspension, controlling the dropwise addition time to 60 min; stir continuously while adding Tris-HCl solution; after the dropwise addition is completed, filter and separate, wash with deionized water, and dry in an oven at 60℃ for 12 h to obtain the composite intermediate;

[0043] S3. After uniformly mixing and grinding the composite intermediate with molten salt (KCl and LiCl in a mass ratio of 2.25 to 2.75 of the composite intermediate), the mixture was transferred to a tube furnace and calcined at 550°C for 2 hours under a nitrogen atmosphere. After cooling to room temperature in the furnace, the mixture was removed, washed with deionized water, and dried in an oven at 60°C for 12 hours to obtain the three-dimensional carbon nitride-based photocatalyst (TCS-1).

[0044] Example 2

[0045] Example 2 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 1 is that in step S2, 6 mg of tannic acid is dissolved in 70 mL of deionized water, and the dropping time of the Tris-HCl solution is controlled to be 60 min. In step S4, the three-dimensional carbon nitride-based photocatalyst (TCS-2) is prepared.

[0046] Example 3

[0047] This embodiment 3 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from embodiment 1 is that in step S2, 12 mg of tannic acid is dissolved in 70 mL of deionized water, and the dropping time of the Tris-HCl solution is controlled to be 60 min. In step S4, the three-dimensional carbon nitride-based photocatalyst (TCS-4) is prepared.

[0048] Example 4

[0049] Example 4 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 1 is that in step S2, 24 mg of tannic acid is dissolved in 70 mL of deionized water, and the dropping time of the Tris-HCl solution is controlled to be 60 min. In S4, a three-dimensional carbon nitride-based photocatalyst (TCS-8) ​​is prepared.

[0050] Comparative Example 1

[0051] Comparative Example 1 provides a method for preparing a three-dimensional carbon nitride photocatalyst with an advanced structure. The difference from Example 1 is that tannic acid is not added in step S2, but 0.3g of graphitic carbon nitride is used in step S3 to prepare a three-dimensional carbon nitride-based photocatalyst (TCS-0).

[0052] Performance testing

[0053] The three-dimensional carbon nitride photocatalysts prepared in Examples 1 to 4 and Comparative Example 1 were subjected to photocatalytic water splitting to produce hydrogen, including the following steps: 50 mg of the photocatalyst was uniformly dispersed in a 10% (v / v) triethanolamine aqueous solution, and then 4 mL of chloroplatinic acid solution was added to bring the volume to 100 mL. After ultrasonic dispersion for 5 min, nitrogen was bubbled for 30 min to remove oxygen from the reaction environment. A 300 W xenon lamp was used as the light source for irradiation in the visible light range, and continuous stirring was maintained during the reaction. The hydrogen production rate was calculated using a gas chromatograph (TCD detector, nitrogen as carrier gas), and the results are as follows. Figure 2 As shown.

[0054] from Figure 2 As can be seen from Examples 1 to 4 of this invention, the photocatalysts prepared exhibit good catalytic activity, with hydrogen production rates of 10-12 mmol / g·h. Furthermore, compared to Comparative Example 1, it can be seen that the photocatalytic activity is significantly increased by polymerizing and carbonizing the graphitic carbon nitride surface with tannic acid, followed by molten salt etching to form a three-dimensional pointed structure. Additionally, Examples 1 to 4 show that the photocatalyst with the best activity is obtained when the mass ratio of tannic acid to graphitic carbon nitride is 4%.

[0055] Example 5

[0056] Example 5 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 3 is that the Tris-HCl solution is added for 30 minutes in step S2.

[0057] Example 6

[0058] Example 6 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 3 is that the Tris-HCl solution is added for 90 minutes in step S2.

[0059] Example 7

[0060] Example 7 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 3 is that the Tris-HCl solution is added for 120 min in step S2.

[0061] Performance testing

[0062] The three-dimensional carbon nitride photocatalysts prepared in Examples 3, 5 to 7 were subjected to photocatalytic water splitting to produce hydrogen, and the hydrogen production rate was calculated as follows: Figure 3 As shown. From Figure 3 As can be seen, controlling the dropping time of Tris-HCl has a significant impact on the thickness of the polytannic acid coating polymerized on the graphitic carbon nitride surface, which in turn affects the catalytic activity of the prepared photocatalyst.

[0063] Example 8

[0064] Example 8 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 1 is that in step S2, 0.5 mg of dopamine is dissolved in 70 mL of deionized water, and the dropping time of the Tris-HCl solution is controlled to be 30 min. In step S4, a three-dimensional carbon nitride-based photocatalyst (DCS-0.5) is prepared.

[0065] Example 9

[0066] Example 9 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 1 is that in step S2, 1 mg of dopamine is dissolved in 70 mL of deionized water, and the dropping time of the Tris-HCl solution is controlled to be 30 min. In step S4, the three-dimensional carbon nitride-based photocatalyst (DCS-1) is prepared.

[0067] Example 10

[0068] Example 10 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 1 is that in step S2, 2 mg of dopamine is dissolved in 70 mL of deionized water, and the dropping time of the Tris-HCl solution is controlled to be 30 min. In step S4, a three-dimensional carbon nitride-based photocatalyst (DCS-2) is prepared.

[0069] Example 11

[0070] Example 11 provides a method for preparing a three-dimensional carbon nitride photocatalyst with a cutting-edge structure. The difference from Example 1 is that in step S2, 4 mg of dopamine is dissolved in 70 mL of deionized water, and the dropping time of the Tris-HCl solution is controlled to be 30 min. In step S4, a three-dimensional carbon nitride-based photocatalyst (DCS-4) is prepared.

[0071] Morphological representation

[0072] The three-dimensional carbon nitride photocatalyst (TCS-4) prepared in Example 3 was characterized by SEM and TEM, as shown below. Figure 4 and Figure 5 As shown. From Figure 4 The SEM images show that TCS-4 has a three-dimensional sea urchin-like structure. Figure 5 The TEM image shows that its surface has a uniform and neatly arranged needle-like structure, and the needle-like structure is long and thin, which is beneficial to increasing the specific surface area and the number of surface active sites of the catalyst.

[0073] Performance testing

[0074] The three-dimensional carbon nitride photocatalyst (TCS-4) prepared in Example 3 was tested for photocatalytic water splitting to produce hydrogen. The hourly hydrogen production was measured for four cycles, each lasting 4 hours, for a total of 16 hours. The changes in hydrogen production during each cycle are shown below. Figure 6 As shown, the XRD characterization of TCS-4 before and after the periodic photocatalytic reaction is as follows. Figure 7 As shown.

[0075] from Figure 6 As can be seen from the data, the three-dimensional carbon nitride photocatalyst prepared in Example 3 exhibits superior photocatalytic hydrogen production activity, and its catalytic activity does not decrease significantly after 16 hours of continuous reaction. This indicates that the photocatalyst is a relatively stable photocatalyst that can maintain long-term photocatalytic performance. Meanwhile, from... Figure 7 As can be seen, the characteristic diffraction peaks and peak positions of the catalyst did not change significantly before and after 16 hours of photocatalytic reaction, which further illustrates that the catalyst can maintain good structural stability during the catalytic reaction.

[0076] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for preparing a three-dimensional carbon nitride photocatalyst with an advanced structure, characterized in that, include: Graphitic carbon nitride was obtained by thermally condensing nitrogen-rich precursors. Graphite-phase carbon nitride was mixed in a polyphenol solution and then Tris-HCl solution was added dropwise with stirring to allow the polyphenols to polymerize in situ on the surface of the graphite-phase carbon nitride to form a polyphenol coating. The coating was then separated and dried to obtain a composite intermediate. The composite intermediate was mixed with molten salt and ground, and then calcined at 400-650℃ under a protective atmosphere to obtain a three-dimensional carbon nitride photocatalyst with a cutting-edge structure.

2. The preparation method according to claim 1, characterized in that: The nitrogen-rich precursor includes one of melamine, dicyandiamide, urea, and thiourea; and / or, the nitrogen-rich precursor is calcined at 400-650°C in an inert atmosphere; and / or, the nitrogen-rich precursor is thermally polycondensed in an inert atmosphere for 2-10 hours.

3. The preparation method according to claim 1, characterized in that: The mass ratio of polyphenol solute to graphite phase carbon nitride in the polyphenol solution is 1:(5-200); and / or, the polyphenol solute in the polyphenol solution includes one of tannic acid, dopamine, and gallic acid; and / or, the concentration of the Tris-HCl solution is 0.1-5.0 mol / L; and / or, the pH of the Tris-HCl solution is 8.

5.

4. The preparation method according to claim 1, characterized in that: The molten salt includes one of KCl-LiCl, KCl-NaCl, and KCl-NaCl-LiCl; and / or, the mass ratio of the composite intermediate to the molten salt is 1:(2-10); and / or, the protective atmosphere includes one of nitrogen atmosphere and argon atmosphere; and / or, calcination is carried out at a protective atmosphere of 400-650℃ for 2-10 hours.

5. A three-dimensional carbon nitride photocatalyst with a pointed structure prepared by the preparation method according to any one of claims 1 to 4.

6. The application of a three-dimensional carbon nitride photocatalyst with a pointed structure prepared by any one of claims 1 to 4 in photocatalytic water splitting for hydrogen production.

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