Porous bismuth vanadate nanorod loaded flaky cobalt-doped graphite phase carbon nitride catalyst as well as preparation and application thereof

Abstract

The invention provides a photo-anode catalyst of porous bismuth vanadate nanorod loaded flaky cobalt-doped graphite phase carbon nitride, a preparation method of the photo-anode catalyst and application of the photo-anode catalyst in the field of hydrogen production by photoelectrocatalytic cracking of water. The Co: CN nanosheet is tightly loaded on the surface of BiVO4 in a spin-coating annealing manner; by changing the ratio of Co to CN, the energy band structure of the Co: CN nanosheet is precisely regulated and controlled, and the Co: CN / BiVO4 heterostructure is successfully constructed. The ultrathin flaky Co: CN has more negative conduction potential and enhanced light absorption capacity, and BiVO4 can drive photo-induced electrons to be transmitted to a photocathode. On the basis of integrating the advantages of g-C3N4 and BiVO4, the heterojunction structure can effectively shorten the transmission path of current carriers, improve the separation efficiency of photo-induced electrons-holes and realize efficient hydrogen production by water splitting. The synthesis method is simple and easy to operate, clear in process thought and clear in steps, and provides possibility for future commercial application.

Description

Technical Field

[0001] The present invention belongs to the field of nanocomposite materials, and more specifically, relates to a porous bismuth vanadate nanorod-loaded flake cobalt-doped graphite-phase carbon nitride photoelectrocatalytic material capable of efficiently and selectively photoelectrocatalytically splitting water to produce hydrogen, and its application. Background Art

[0002] The energy problem is the primary problem that needs to be solved in this century. However, the proven fossil energy reserves are gradually approaching exhaustion, and it is expected that by the end of this century, fossil energy will be completely exhausted, which will pose a major obstacle to future sustainable development. In recent years, photoelectrocatalytic hydrogen production technology has attracted much attention because of its ability to efficiently convert solar energy into directly usable chemical energy. This technology not only achieves efficient energy conversion, but also provides a convenient way of energy storage. Although photoelectrocatalytic research has gone through half a century of development, due to its low efficiency, lack of stability and other problems, this technology is still difficult to achieve large-scale industrial application. Therefore, the development of efficient and stable photoelectrocatalysts has become a key scientific issue that needs to be overcome urgently.

[0003] Bismuth vanadate (BiVO4) is an advanced photoanode material with a band edge position that matches the water redox potential, thus possessing excellent photoelectrocatalytic potential. However, its practical application faces several inherent challenges, such as low carrier mobility, fast electron-hole recombination rate, and sluggish surface reaction kinetics. These problems result in its actual photocurrent density being far lower than the theoretical value. Due to the intrinsic properties of the Bi element, the BiVO4 surface has a large number of trap states, which leads to a large number of carrier recombination. To address this problem, filling the surface trap states is an effective strategy. Two-dimensional sheet materials are believed to be able to fill surface trap states well due to their strong radial carrier transport properties and excellent water molecule adsorption capacity.

[0004] Graphitic carbon nitride (CN) is a two-dimensional polymer semiconductor material composed of carbon and nitrogen. Its unique photoelectrochemical properties and low cost have led to its widespread application in photoelectrocatalysis. To significantly enhance the PEC performance of CN, material properties are often optimized by introducing functional groups. This modification strategy not only provides ample reactive sites but also further optimizes the kinetics of photogenerated charge carriers by regulating their energy levels, promoting their rapid migration and efficient separation, thereby enhancing overall PEC efficiency.

[0005] Studies have shown that BiVO4 can be combined with CN to form a type II heterojunction for water splitting. However, due to the mismatch between the energy band positions of CN and BiVO4, CN fails to fill surface trap states, resulting in low photoelectrocatalytic efficiency. How to construct an excellent type II heterojunction between the two through band modulation to achieve efficient PEC water splitting remains a challenge. Summary of the Invention

[0006] To address the above technical problems, the first objective of the present invention is to provide a novel method for synthesizing graphite-phase carbon nitride nanosheets doped with Co atoms, wherein carbon nitride serves as a carrier and Co is loaded onto the carbon nitride surface by in-situ growth (Co:CN). The second objective of the present invention is to provide a method for preparing the aforementioned Co:CN nanosheets loaded on BiVO4, the core point of which is to convert Co:CN into Co:CN / BiVO4 by spin coating annealing, comprising the following steps: Step S1: Preparation of ultrathin flake graphite-phase carbon nitride (CN): 1.1 Melamine was used as the raw material and prepared by a multiple calcination method. Specifically, melamine (mass: 10 g) was placed in a covered porcelain crucible and heated to 550°C at a heating rate of 5°C / min, maintained for 4 hours, and then cooled naturally. After the reaction was completed, the sample was collected.

[0007] 1.2 The sample prepared in step 1.1 was placed in a covered porcelain crucible for secondary calcination. The sample was heated to 450°C at a heating rate of 2.5°C / min, maintained for 2 hours, and then cooled naturally. This process was repeated three times. After the reaction was completed, the sample was collected to obtain ultrathin flake graphite phase carbon nitride.

[0008] Step S2: Preparation of Co:CN catalyst by hydrothermal method: 2.1 Disperse 2 g of the CN sample prepared in Step 1.22 in 75 mL of anhydrous ethanol. Add 25 mL of an aqueous solution containing 1.48 g of Co(NO₃)₂·6H₂O. Alternately stir and sonicate four times, each for 30 minutes. The resulting mixture is then stirred, immersed, and evaporated to dryness at 60°C. The collected sample is heated to 350°C under argon at a rate of 2°C / min and annealed for 2 hours. This collected sample is the Co:CN.

[0009] Step S3: preparing BiVO4 photoanode by electroplating: 3.1 3.32 g of KI was dissolved in 50 mL of deionized water, and the pH of the solution was precisely adjusted to around 1.7 using HNO3. Subsequently, 0.9702 g of Bi(NO3)3·5H2O was added and stirred until a clear solution was formed. Next, 0.52 g of p-benzoquinone was dissolved in 20 mL of anhydrous ethanol and quickly added to the clear solution. The reaction was maintained under high-speed stirring for 3 minutes. Subsequently, BiOI thin films (1 × 1 cm in size) were prepared at room temperature by potential-controlled cathodic deposition. 2), using Ag / AgCl as the reference electrode, set the potential to -0.1 V, and deposit for 180 seconds. The resulting film was collected and washed.

[0010] 3.2 The BiOI film obtained in 3.1 was converted into a BiVO4 film. A 0.4 mol / L vanadium acetylacetonate solution was impregnated on the BiOI electrode (50 μL / cm 2 ) and heated to 450°C in air at a rate of 2°C / min for 2 hours. The resulting BiVO4 electrode was then immersed in a 1 mol / L sodium hydroxide solution for 10 minutes while gently stirring to remove excess V2O5, and then rinsed with deionized water.

[0011] Step S4: Preparation of Co:CN / BiVO4 catalyst by spin coating annealing method: 4.1 Disperse 100 mg of Co:CN in 20 mL of anhydrous ethanol to form a homogeneous suspension. Subsequently, spin-coat the suspension onto the BVO surface at 2,500 rpm for 1 minute. Repeat this process several times. Anneal the resulting sample in a nitrogen atmosphere at 350°C for 1 hour at a heating rate of 10°C / min. After cooling, collect the Co:CN / BVO sample.

[0012] The third object of the present invention is to provide the application of Co:CN / BiVO4 in PEC water splitting. Specifically, under visible light irradiation (300 W xenon lamp), the H2 generation rate of the Co:CN nanosheet-supported BiVO4 catalyst is as high as 15.236 μmol cm -1 h -1 , which has potential application prospects in the field of photoelectrocatalytic hydrogen production.

[0013] Compared with existing composite functional photoelectrocatalytic materials, the present invention has the following advantages: (1) The present invention uses a simple and novel method to in-situ grow cobalt atoms in ultrathin carbon nitride nanosheets, which significantly improves the light absorption capacity of the carbon nitride nanosheets without destroying their intrinsic structure.

[0014] (2) The present invention grows cobalt-doped carbon nitride nanosheets on porous bismuth vanadate nanorods, successfully constructing a type II heterojunction without changing the basic structure and basic properties of bismuth vanadate and g-C3N4. This structure not only maintains the high reduction driving force of BiVO4 conduction band electrons, but also significantly improves the light absorption capacity of BiVO4 in the visible light region with the loading of Co:CN nanosheets. In addition, thanks to the electron transport mechanism of the type II heterojunction, the recombination efficiency of the photogenerated carriers of the photoanode material obtained after loading the Co:CN nanosheets is reduced, thereby greatly improving the PEC catalytic activity of the photoanode material.

[0015] (3) The preparation process of the present invention is simple, the preparation conditions are mild, and it is convenient for large-scale production. It has good application prospects in the field of PEC water splitting to produce hydrogen, and can provide a technical reference for the preparation of other heterojunction structure photoanode materials.

[0016] (4) The porous bismuth vanadate nanorods loaded with sheet-like cobalt-doped graphite-phase carbon nitride catalyst of the present invention do not require any sacrificial agent or promoter to be added in the preparation of hydrogen, which greatly saves economic costs and does not put any environmental pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a scanning electron microscope photograph of the porous bismuth vanadate nanorod-supported flaky cobalt-doped graphite-phase carbon nitride catalyst of the present invention.

[0018] Figure 2 The present invention provides an X-ray diffraction spectrum of the porous bismuth vanadate nanorod-supported flaky cobalt-doped graphite-phase carbon nitride catalyst.

[0019] Figure 3 The present invention provides an ultraviolet-visible diffuse reflectance spectrum of the porous bismuth vanadate nanorod-supported flaky cobalt-doped graphite-phase carbon nitride catalyst.

[0020] Figure 4 The electrochemical spectrum of the porous bismuth vanadate nanorod-loaded sheet-shaped cobalt-doped graphite phase carbon nitride catalyst of the present invention is shown.

[0021] Figure 5 This is a comparison chart of the rates of hydrogen generation by splitting water using the porous bismuth vanadate nanorod-supported flaky cobalt-doped graphite-phase carbon nitride catalyst of the present invention.

[0022] The porous bismuth vanadate nanorod-supported sheet-shaped cobalt-doped graphite-phase carbon nitride catalyst of the present invention is described in detail below with reference to the accompanying drawings. The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to these embodiments. Example

[0023] Step S1: Preparation of ultrathin flake graphite-phase carbon nitride (CN): 1.1 Melamine was used as the raw material and prepared by the calcination method. Specifically, melamine (mass: 10 g) was placed in a covered porcelain crucible and heated to 550°C at a heating rate of 5°C / min, maintained for 4 hours, and then cooled naturally. After the reaction was completed, the sample was collected.

[0024] 1.2 The sample prepared in step 1.1 was placed in a covered porcelain crucible for secondary calcination. The sample was heated to 450°C at a heating rate of 2.5°C / min, maintained for 2 hours, and then cooled naturally. This process was repeated three times. After the reaction was completed, the sample was collected to obtain ultrathin flake graphite phase carbon nitride.

[0025] Step S2: Preparation of Co:CN catalyst by hydrothermal method: 2.1 Disperse 2 g of the CN sample prepared in Step 1.22 in 75 mL of anhydrous ethanol. Add 25 mL of an aqueous solution containing 1.48 g of Co(NO₃)₂·6H₂O. Alternately stir and sonicate four times, each for 30 minutes. The resulting mixture is then stirred, immersed, and evaporated to dryness at 60°C. The collected sample is heated to 350°C under argon at a rate of 2°C / min and annealed for 2 hours. This collected sample is the Co:CN.

[0026] Step S3: preparing BiVO4 photoanode by electroplating: 3.1 3.32 g of KI was dissolved in 50 mL of deionized water, and the pH of the solution was precisely adjusted to around 1.7 using HNO3. Subsequently, 0.9702 g of Bi(NO3)3·5H2O was added and stirred until a clear solution was formed. Next, 0.52 g of p-benzoquinone was dissolved in 20 mL of anhydrous ethanol and quickly added to the clear solution. The reaction was maintained under high-speed stirring for 3 minutes. Subsequently, BiOI thin films (1 × 1 cm in size) were prepared at room temperature by potential-controlled cathodic deposition. 2 ), using Ag / AgCl as the reference electrode, set the potential to -0.1 V, and deposit for 180 seconds. The resulting film was collected and washed.

[0027] 3.2 The BiOI film obtained in 3.1 was converted into a BiVO4 film. A 0.4 mol / L vanadium acetylacetonate solution was impregnated on the BiOI electrode (50 μL / cm 2 ) and heated to 450°C in air at a rate of 2°C / min for 2 hours. The resulting BiVO4 electrode was then immersed in a 1 mol / L sodium hydroxide solution for 10 minutes while gently stirring to remove excess V2O5, and then rinsed with deionized water.

[0028] Step S4: Preparation of Co:CN / BiVO4 catalyst by spin coating annealing method: 4.1 Disperse 100 mg of Co:CN in 20 mL of anhydrous ethanol to form a homogeneous suspension. Subsequently, spin-coat the suspension onto the BVO surface at 2,500 rpm for 1 minute. Repeat this process several times. Anneal the resulting sample in a nitrogen atmosphere at 350°C for 1 hour at a heating rate of 10°C / min. After cooling, collect the Co:CN / BVO sample.

[0029] Figure 1 This is a scanning electron microscope photograph of the porous bismuth vanadate nanorods supported on a sheet-like cobalt-doped graphite-phase carbon nitride catalyst of the present invention. It can be seen that the cobalt-doped graphite-phase carbon nitride is successfully supported on the bismuth vanadate.

[0030] Figure 2 The X-ray diffraction pattern of the porous bismuth vanadate nanorods supported on the flake-shaped cobalt-doped graphite carbon nitride catalyst of the present invention is shown in FIG. It can be seen that the loading of the cobalt-doped graphite carbon nitride does not affect the crystal structure of the bismuth vanadate.

[0031] Figure 3 This is the UV-visible diffuse reflectance spectrum of the porous bismuth vanadate nanorods supported on a cobalt-doped graphitic carbon nitride catalyst. It clearly shows that the light absorption capacity of the cobalt-doped graphitic carbon nitride is significantly superior to that of undoped graphitic carbon nitride. After the cobalt-doped graphitic carbon nitride is successfully loaded, the light absorption capacity of the porous bismuth vanadate nanorods is significantly enhanced.

[0032] Figure 4 The electrochemical spectrum of the porous bismuth vanadate nanorod-supported flake cobalt-doped graphitic carbon nitride catalyst of the present invention is shown in Figure 1. It can be clearly observed that various electrochemical properties of the porous bismuth vanadate nanorod-supported flake cobalt-doped graphitic carbon nitride catalyst are significantly improved compared to the original bismuth vanadate.

[0033] Figure 5 This is a comparison chart of the hydrogen generation rate of water splitting by the porous bismuth vanadate nanorods supported on the cobalt-doped graphite carbon nitride catalyst of the present invention. It can be seen that after loading the cobalt-doped graphite carbon nitride, the hydrogen generation rate of the photoanode material can reach 15.236 μmol cm -1 h -1 .

Claims

1. A method for synthesizing Co:CN nanosheets loaded on BiVO4, characterized by: The steps include: (1) Ultrathin flake graphite-phase carbon nitride (CN) was prepared by multiple calcination using melamine as raw material; (2) The CN sample prepared in step (1) is dispersed in anhydrous ethanol, and then a Co(NO3)2·6H2O aqueous solution is added thereto, and the mixture is alternately stirred and ultrasonicated to react; after the reaction is completed, the mixture is immersed and evaporated to dryness, and the collected sample is annealed to obtain a new graphite phase carbon nitride nanosheet doped with Co atoms, wherein carbon nitride is used as a carrier and Co is loaded on the surface of the carbon nitride by in situ growth (Co:CN); (3) Preparation of BiVO4 photoanode by electroplating; (4) Preparation of Co:CN / BiVO4 catalyst by spin coating annealing method.

2. The method for synthesizing Co:CN nanosheets loaded on BiVO4 according to claim 1, wherein: The prepared CN sample was placed in a covered porcelain crucible for secondary calcination, heated to 450°C at a heating rate of 2.5°C / min, maintained for 2 hours, and then cooled naturally, and the process was repeated three times; after the reaction was completed, the sample was collected, which was ultra-thin flake graphite phase carbon nitride.

3. The method for synthesizing Co:CN nanosheets loaded on BiVO4 according to claim 1, wherein: In step (2), the mixed aqueous solution of CN and Co(NO3)2·6H2O was alternately stirred and ultrasonicated for a total of 4 times, each time for 30 minutes. The resulting mixed solution was then stirred, impregnated, and evaporated to dryness at 60°C.

4. The method for synthesizing Co:CN nanosheets loaded on BiVO4 according to claim 1, wherein: In step (3), 0.52 g of p-benzoquinone was dissolved in 20 mL of anhydrous ethanol and quickly added to the reaction system, and the reaction was maintained for 3 minutes under high-speed stirring conditions.

5. The method for synthesizing Co:CN nanosheets loaded on BiVO4 according to claim 1, characterized in that: In step (3), a 0.4 mol / L vanadium acetylacetonate solution is impregnated on the BiOI electrode (the amount is 50 μL / cm 2 ).

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