C / C-based tungsten nitride / bismuth tungstate composite material and preparation method and application thereof

Abstract

The invention discloses a C / C-based tungsten nitride / bismuth tungstate composite material and a preparation method and application thereof.The preparation method comprises the steps that WN and Bi2WO6 are placed in the same beaker, then an isopropanol solution is added, stirring is conducted till the WN and the Bi2WO6 are evenly dispersed, then iodine is added, stirring continues to be conducted till the mixture is even, and a deposition solution is obtained; the preparation method comprises the following steps: pre-treating a C / C substrate, fixing the pre-treated C / C substrate on a negative electrode of hydrothermal electrophoretic deposition equipment, then putting the pre-treated C / C substrate in a deposition solution F, heating a hydrothermal deposition kettle, applying voltage to carry out electrophoretic deposition, putting a self-supporting sample after deposition into a drying oven for drying to finally obtain a C / C-WN / Bi2WO6 photoelectrode material, and synthesizing a WN / Bi2WO6 heterojunction on the C / C substrate to be used as a photoanode. Tungsten nitride is used as the electron transport layer, photo-induced electrons generated by light absorption of bismuth tungstate can be transmitted to the C / C substrate and then transmitted to the photocathode, the structure is beneficial to reduction of recombination of photo-induced carriers, and then the photoelectrocatalysis performance of bismuth tungstate is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, relates to photocatalytic materials, and particularly relates to a C / C-based tungsten nitride / bismuth tungstate composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of the economy, the demand for energy has been continuously climbing, and the current energy mainly relies on fossil fuels. This dependence has led to serious energy and environmental crises, posing a threat to the sustainable development of mankind. Therefore, transforming the energy structure and actively developing clean and renewable energy have become an urgent issue faced globally. As a technology for converting solar energy into chemical energy, photocatalysis generates hydrogen by catalyzing water decomposition, effectively reducing our dependence on fossil energy and alleviating environmental pollution, and thus has become the focus of global research. In this technology, the energy band structure of the photoanode directly affects the light absorption and charge separation efficiency. Therefore, selecting a suitable photoanode is the key factor determining the performance of photocatalytic water splitting.

[0003] Bismuth tungstate (Bi2WO6) is an Aurivillius-type oxide, which has a typical layered structure, a relatively narrow bandgap (about 2.7 eV), and band edges suitable for water splitting. At the same time, the tungstate ion structure is stable and not prone to photocorrosion. These advantages have made it a research focus in the field of semiconductor photocatalytic water splitting materials in recent years. However, bismuth tungstate still has problems such as a small absorption part of the solar spectrum, poor charge transport, and high recombination of photo-generated electron-hole pairs, which limit its application in the field of photocatalysis.

[0004] Tungsten nitride (WN), as a metal-like compound, has an electronic structure between that of a metal and a semiconductor, and usually exhibits an extremely narrow bandgap (close to zero bandgap) or metal-like continuous energy band characteristics, which endows it with high conductivity and fast carrier migration ability. However, this quasi-metallic property results in its light absorption mainly depending on the plasma effect or interband transition, and the direct capture efficiency of visible light is relatively low. To overcome this limitation, researchers often combine it with narrow-bandgap semiconductor materials to achieve efficient separation and utilization of photo-generated carriers through energy band matching at the heterojunction interface, and at the same time enhance the photoelectric response ability of the system by virtue of the wide spectral absorption characteristics of the semiconductor. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a C / C-based tungsten nitride / bismuth tungstate composite material, a preparation method thereof, and an application thereof. This material has high conductivity and excellent photocatalytic performance, and is used for photocatalysis to achieve efficient water splitting.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions to be implemented:

[0007] A preparation method of a C / C-based tungsten nitride / tungstate bismuth composite material, comprising the following steps:

[0008] Step 1: Dissolve 0.10 - 0.21 mmol of ammonium tungstate in 40 - 70 mL of water to prepare solution A, dissolve 2 - 5 mmol of bismuth acetate in 5 - 10 mL of acetic acid to prepare solution B. Drop solution A into solution B, stir until uniform, then gradually add ammonia water to adjust the pH to 8, let it stand for 6 - 12 h, perform suction filtration separation, washing, drying, grinding, and then place it in a muffle furnace and calcine at 500 - 700 °C for 4 - 6 h. After cooling to room temperature, obtain powder C;

[0009] Step 2: Take sodium tungstate and citric acid according to a molar ratio of 1:(2 - 10), dissolve sodium tungstate and citric acid in deionized water according to a solid-liquid ratio of 1:(70 - 100) g / mL, stir to obtain a clear solution, transfer the solution to a water bath pot and carry out water bath at 60 - 90 °C for 4 - 7 h. After cooling, perform suction filtration washing and drying on the solution, and then calcine in an air atmosphere at 400 - 600 °C for 4 - 6 h to obtain powder D;

[0010] Step 3: Charge powder D and melamine according to a mass ratio of 1:(2 - 4), grind and mix the mixed powder, put it into an alumina boat, place it in a tubular furnace, heat it to 800 - 1000 °C in an Ar atmosphere and maintain for 2 - 4 h. After cooling to room temperature, obtain powder E;

[0011] Step 4: Weigh 0.15 - 0.2 g of powder C and E respectively and place them in the same beaker, then add 150 - 200 mL of isopropanol solution, stir until evenly dispersed, then add 0.3 - 0.4 g of iodine, and continue to stir until uniform to obtain deposition solution F;

[0012] Step 5: Pretreat the C / C substrate and fix it at the negative electrode of a hydrothermal electrophoresis deposition device, then place it in deposition solution F, heat the hydrothermal deposition kettle and apply voltage for electrophoresis deposition for 1 - 20 min. Put the deposited self-supporting sample into an oven for drying, and finally obtain the C / C-WN / Bi2WO6 photoanode material.

[0013] The present invention also has the following technical features:

[0014] Preferably, the washing in Step 1 and Step 2 is to perform suction filtration washing with deionized water and absolute ethanol successively for 2 - 5 times.

[0015] Preferably, the drying in Step 1, Step 2 and Step 5 is to place it in an oven and dry at 120 - 160 °C for 10 - 16 h.

[0016] Preferably, the process of pre-treating the C / C substrate in step five includes: calcining in a muffle furnace at 300-350 °C for 1-2 h, cooling and then placing it in a reagent mixture of acetone, deionized water and absolute ethanol with a volume ratio of 1:(1-2):(1-2) for ultrasonic treatment for 1 h, and then drying at 60-90 °C for 1-3 h.

[0017] Preferably, during the electrophoretic deposition process in step five, the heating temperature is 80-160 °C and the applied voltage is 15-30 V.

[0018] The present invention also protects a C / C-based tungsten nitride / bismuth tungstate composite material prepared by the method as described above and its application as a photoanode in the process of photoelectrocatalysis.

[0019] Compared with the prior art, the present invention has the following technical effects:

[0020] The present invention synthesizes a C / C-based tungsten nitride / bismuth tungstate photoanode material, and this system synergistically enhances the efficiency through a hierarchical structure: the C / C carrier serves as a conductive framework to improve the charge transfer efficiency; the intermediate WN layer accelerates electron transfer by virtue of its metalloid characteristics and reduces the hydrogen evolution energy barrier; the outer Bi2WO6 utilizes its narrow bandgap to capture visible light, forms a heterojunction with WN, promotes the migration of photogenerated electrons to WN and the enrichment of holes on the surface, and significantly inhibits recombination. The three aspects take into account light absorption - charge separation - catalytic reaction, making the entire system have excellent photoelectrocatalytic performance;

[0021] The present invention uses C / C as a carrier, which has the advantages of high conductivity, strong binding energy, large specific surface area, corrosion resistance and stable performance, which is beneficial to increasing the number of active sites of the catalytic material and improving the photoelectric performance of the catalytic material;

[0022] The present invention uses a hydrothermal electrophoretic deposition technique, which is easy to control, can precisely synthesize in a directional manner, and has a very wide application range. Description of the Drawings

[0023] Figure 1 X-ray diffraction analysis diagram of the WN / Bi2WO6 mixed powder prepared in Example 1;

[0024] Figure 2 Scanning diagram of the C / C-WN / Bi2WO6 prepared in Example 1;

[0025] Figure 3 LSV diagram of the C / C-WN / Bi2WO6 prepared in Examples 1-3 in a solution with pH = 9.5 under simulated sunlight;

[0026] Figure 4 Impedance fitting curve of the C / C-WN / Bi2WO6 prepared in Example 1 in a solution with pH = 9.5 under simulated sunlight;

[0027] Figure 5 The applied bias photoelectrochemical conversion efficiency (ABPE) of the C / C-WN / Bi2WO6 prepared in Example 1 as a photoelectrode in a solution with pH = 9.5 under simulated sunlight. Specific implementation mode

[0028] The following further elaborates on the specific content of the present invention in conjunction with examples.

[0029] Example 1

[0030] This example provides a method for preparing a C / C-based tungsten nitride / tungstic acid bismuth composite material, including the following steps:

[0031] Step 1: Dissolve 0.313 g of ammonium tungstate in 60 mL of water to prepare solution A, and stir it at room temperature for 1 h at a rotation speed of 300 rmp until it is fully dissolved. Dissolve 0.965 g of bismuth acetate in 5 mL of analytical pure acetic acid to prepare solution B, and heat it to 60 °C and stir it for 1 h at a rotation speed of 300 rmp until it is fully dissolved. Then, drop solution A at a rate of 3 drops / s, stir until it is uniform, and then gradually add ammonia water to adjust the pH to 8. Let it stand for 6 h, filter and wash it 3 times successively with deionized water and absolute ethanol, and then recover the solid. Place the solid in an oven and dry it at 160 °C for 12 h, grind it to obtain a powder, place the powder in a muffle furnace and calcine it at 500 °C for 4 h, and after cooling to room temperature, obtain powder C;

[0032] Step 2: Dissolve 0.33 g of sodium tungstate and 0.576 g of citric acid in 80 mL of deionized water and stir until it is clear. Transfer the solution to a water bath and heat it at 80 °C for 6 h. After cooling, filter and wash the solution 3 times successively with deionized water and absolute ethanol, and then recover the solid. Place the solid in an oven and dry it at 160 °C for 12 h, grind it to obtain a powder, and then calcine it at 400 °C for 4 h in an air atmosphere to obtain powder D;

[0033] Step 3: Put 0.3 g of powder D and 1 g of melamine into an alumina boat after grinding and mixing evenly, place it in a tubular furnace, heat it to 900 °C in an Ar atmosphere and maintain it for 2 hours, and after cooling to room temperature, obtain powder E;

[0034] Step 4: Weigh 0.15 g of powder C and E respectively and place them in the same beaker, then add 150 mL of isopropanol solution, stir until it is evenly dispersed, add 0.3 g of iodine, and continue to stir until it is uniform to obtain deposition solution F;

[0035] Step 5: Calcinate the C / C substrate in a muffle furnace at 300 °C for 2 h. After cooling, place it in a reagent with a volume ratio of 1:1:1 of acetone, deionized water, and absolute ethanol and ultrasonicate for 1 h. Dry it at 60 °C for 2 h and then fix it at the negative electrode of a hydrothermal electrophoresis deposition device. Subsequently, place it in deposition solution F. After heating the hydrothermal deposition kettle to a deposition temperature of 80 °C, apply a voltage of 15 V for electrophoresis deposition for 3 min. Put the deposited self-supporting sample in an oven to dry, and finally obtain the C / C-WN / Bi2WO6 photoanode material.

[0036] Figure 1 Figure 4 is the X-ray diffraction analysis pattern of the WN / Bi2WO6 mixed powder prepared in Example 1. It can be seen from the figure that the main phases of the prepared mixed powder are Bi2WO6 and WN. The characteristic peaks at 28.12°, 47.04°, and 56.62° correspond to the (131), (202), and (133) crystal planes of Bi2WO6 (PDF#39-0256), respectively, and the characteristic peaks at 31.25°, 35.62°, and 48.2° correspond to the (001), (100), and (101) crystal planes of WN (PDF#25-1256), respectively. This indicates that the WN / Bi2WO6 composite is successfully prepared;

[0037] Figure 2 Figure 8 is the scanning electron microscope image of the C / C-WN / Bi2WO6 prepared in Example 1. It can be seen from the figure that a large amount of WN / Bi2WO6 heterostructures are loaded on the surface of the carbon fiber, providing a large number of active sites and exposing a large specific surface area;

[0038] Figure 3 Figure 12 is the linear sweep voltammetry (LSV) curves of the C / C-WN / Bi2WO6 prepared in Examples 1-3 in a solution with pH = 9.5 under simulated sunlight. It can be seen that the synthesized self-supporting electrodes all have a large photocurrent density at 1.23 V vs. RHE, indicating that this system has excellent photocatalytic water splitting performance;

[0039] Figure 4 Figure 16 is the impedance fitting curve of the C / C-WN / Bi2WO6 prepared in Example 1 in a solution with pH = 9.5 under simulated sunlight, indicating the good conductivity of this system;

[0040] Figure 5 Figure 20 is the incident photon-to-current conversion efficiency (IPCE) curve of the C / C-WN / Bi2WO6 photoanode prepared in Example 1 in a solution with pH = 9.5 under simulated sunlight, indicating the good photoelectric conversion efficiency of this system.

[0041] Example 2

[0042] This example provides a preparation method of a C / C-based tungsten nitride / tungsten bismuthate composite material, including the following steps:

[0043] Step 1: Dissolve 0.470 g of ammonium tungstate in 60 mL of water, and stir at room temperature for 1 h at a rotation speed of 400 rmp to completely dissolve it to prepare solution A. Dissolve 1.39 g of bismuth acetate in 5 mL of analytical pure acetic acid, heat to 70 °C and stir for 1 h at a rotation speed of 400 rmp to completely dissolve it to prepare solution B. Then, drop solution A into solution B at a rate of 5 drops / s, stir until uniform, and then gradually add ammonia water to adjust the pH to 8. Let it stand for 12 h, recover the solid by suction filtration and washing twice with deionized water and absolute ethanol in sequence. Place the solid in an oven and dry it at 140 °C for 14 h. Grind it to obtain a powder. Place the powder in a muffle furnace and calcine it at 600 °C for 4 h. After cooling to room temperature, obtain powder C;

[0044] Step 2: Dissolve 0.33 g of sodium tungstate and 0.430 g of citric acid in 65 mL of deionized water and stir until clear. Transfer the solution to a water bath and water bath at 90 °C for 5 h. After cooling, recover the solid by suction filtration and washing twice with deionized water and absolute ethanol in sequence. Place the solid in an oven and dry it at 140 °C for 14 h. Grind it to obtain a powder. Then, calcine it at 500 °C for 4 h in an air atmosphere to obtain powder D;

[0045] Step 3: Grind 0.3 g of powder D and 1.2 g of melamine and mix them evenly, put them into an alumina boat, place them in a tube furnace, heat up to 800 °C in an Ar atmosphere and maintain for 3 h. After cooling to room temperature, obtain powder E;

[0046] Step 4: Weigh 0.2 g of powder C and E respectively and place them in the same beaker. Then add 180 mL of isopropanol solution, stir until evenly dispersed, add 0.4 g of iodine, and continue to stir until uniform to obtain deposition solution F;

[0047] Step 5: Calcinate the C / C substrate in a muffle furnace at 350 °C for 1 h. After cooling, place it in a reagent with a volume ratio of acetone, deionized water and absolute ethanol of 1:2:2 and ultrasonicate for 1 h. Dry it at 90 °C for 1 h and then fix it at the negative electrode of a hydrothermal electrophoresis deposition device. Then place it in deposition solution F. Heat the hydrothermal deposition kettle to the deposition temperature of 100 °C, and then apply a voltage of 20 V for electrophoresis deposition for 1 min. Place the deposited self-supporting sample in an oven to dry, and finally obtain the C / C-WN / Bi2WO6 photoanode material.

[0048] Example 3

[0049] This example provides a preparation method of a C / C-based tungsten nitride / tungstic acid bismuth composite material, including the following steps:

[0050] Step 1: Dissolve 0.313 g of ammonium tungstate in 70 mL of water to prepare solution A, and stir it at room temperature for 1 h at a speed of 400 rmp until it is fully dissolved. Dissolve 0.772 g of bismuth acetate in 8 mL of analytical pure acetic acid to prepare solution B, and heat it to 80 °C and stir for 1 h at a speed of 400 rmp until it is fully dissolved. Then, add solution A dropwise to solution B at a rate of 5 drops / s, stir until it is uniform, and then gradually add ammonia water to adjust the pH to 8. Let it stand for 6 h, filter and wash it 5 times successively with deionized water and absolute ethanol, and then recover the solid. Place the solid in an oven and dry it at 150 °C for 10 h, grind it to obtain a powder, place the powder in a muffle furnace and calcine it at 600 °C for 6 h, and cool it to room temperature to obtain powder C;

[0051] Step 2: Dissolve 0.33 g of sodium tungstate and 2.15 g of citric acid in 250 mL of deionized water and stir until it is clear. Transfer the solution to a water bath and heat it at 70 °C for 4 h. After cooling, filter and wash the solution 5 times successively with deionized water and absolute ethanol, and then recover the solid. Place the solid in an oven and dry it at 150 °C for 10 h, grind it to obtain a powder, and then calcine it at 600 °C for 5 h in an air atmosphere to obtain powder D;

[0052] Step 3: Grind 0.25 g of powder D and 1 g of melamine evenly and put them into an alumina boat, place it in a tubular furnace, heat it to 1000 °C in an Ar atmosphere and maintain it for 4 hours, and cool it to room temperature to obtain powder E;

[0053] Step 4: Weigh 0.17 g of powder C and E respectively and place them in the same beaker, then add 200 mL of isopropanol solution, stir until it is evenly dispersed, add 0.3 g of iodine, and continue to stir until it is uniform to obtain deposition solution F;

[0054] Step 5: Calcinate the C / C substrate in a muffle furnace at 330 °C for 1.5 h, cool it, place it in a reagent with a volume ratio of acetone, deionized water and absolute ethanol of 1:1.5:1.5 and ultrasonicate it for 1 h, dry it at 60 °C for 2 h, then fix it at the negative electrode of a hydrothermal electrophoresis deposition device, and then place it in deposition solution F. Heat the hydrothermal deposition kettle to the deposition temperature of 120 °C, and then apply a voltage of 25 V for electrophoresis deposition for 8 min. Place the deposited self-supporting sample in an oven to dry, and finally obtain the C / C-WN / Bi2WO6 photoanode material.

[0055] Example 4

[0056] This example provides a preparation method of a C / C-based tungsten nitride / tungstic acid bismuth composite material, including the following steps:

[0057] Step 1: Dissolve 0.640 g of ammonium tungstate in 50 mL of water, and stir at room temperature for 1 h at a rotation speed of 350 rmp to fully dissolve it to prepare solution A. Dissolve 1.93 g of bismuth acetate in 6 mL of analytical pure acetic acid, heat it to 80 °C and stir for 1 h at a rotation speed of 350 rmp to fully dissolve it to prepare solution B. Then, drop solution A into solution B at a rate of 2 drops / s, stir until uniform, and then gradually add ammonia water to adjust the pH to 8. Let it stand for 10 h, filter and wash the solid 3 times successively with deionized water and absolute ethanol, and then recover the solid. Place the solid in an oven and dry it at 120 °C for 16 h. After grinding, obtain a powder. Place the powder in a muffle furnace and calcine it at 700 °C for 5 h. After cooling to room temperature, obtain powder C;

[0058] Step 2: Dissolve 0.33 g of sodium tungstate and 0.576 g of citric acid in 63 mL of deionized water and stir until clear. Transfer the solution to a water bath and water bath at 60 °C for 7 h. After cooling, filter and wash the solution 3 times successively with deionized water and absolute ethanol, and then recover the solid. Place the solid in an oven and dry it at 140 °C for 14 h. After grinding, obtain a powder. Then, calcine it at 400 °C for 6 h in an air atmosphere to obtain powder D;

[0059] Step 3: Grind and mix 0.3 g of powder D and 0.6 g of melamine powder, put them into an alumina porcelain boat, place it in a tubular furnace, heat it to 900 °C in an Ar atmosphere and maintain it for 3 hours. After cooling to room temperature, obtain powder E;

[0060] Step 4: Weigh 0.2 g of powder C and E respectively and place them in the same beaker. Then add 170 mL of isopropanol solution, stir until evenly dispersed, add 0.35 g of iodine, and continue to stir until uniform to obtain deposition solution F;

[0061] Step 5: Calcinate the C / C substrate in a muffle furnace at 300 °C for 2 h. After cooling, place it in a reagent with a volume ratio of acetone, deionized water and absolute ethanol of 1:1:1 and ultrasonicate for 1 h. Dry it at 70 °C for 3 h and then fix it at the negative electrode of the hydrothermal electrophoresis deposition equipment. Then place it in deposition solution F. After heating the hydrothermal deposition kettle to the deposition temperature of 160 °C, apply a voltage of 30 V for electrophoresis deposition for 20 min. Place the deposited self-supporting sample in an oven to dry, and finally obtain the C / C-WN / Bi2WO6 photoanode material.

[0062] Those of ordinary skill in the art will realize that the embodiments described herein are for helping readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A method for preparing a C / C-based tungsten nitride / bismuth tungstate composite material, characterized in that: The following steps are involved: Step 1, dissolve 0.10-0.21mmol ammonium tungstate in 40-70mL water to prepare solution A, dissolve 2-5mmol bismuth acetate in 5-10mL acetic acid to prepare solution B, drop solution A into solution B, stir until uniform, add ammonia water dropwise to adjust the pH to 8, let stand for 6-12h, filter, separate, wash, dry, grind, place in a muffle furnace at 500-700°C and calcine for 4-6h, and cool to room temperature to obtain powder C; Step 2: Sodium tungstate and citric acid are taken in a molar ratio of 1:(2-10), and the sodium tungstate and citric acid are dissolved in deionized water at a solid-liquid ratio of 1:(70-100) g / mL, and stirred to obtain a clear solution. The solution is transferred to a water bath pot and water bathed at 60-90°C for 4-7 hours. After cooling, the solution is filtered, separated, washed, dried, and calcined at 400-600°C in an air atmosphere for 4-6 hours to obtain powder D; Step 3, powder D and melamine are mixed in a mass ratio of 1: (2-4), the mixed powder is ground and mixed, and put into an alumina porcelain boat, placed in a tube furnace under an Ar atmosphere, heated to 800-1000° C. and maintained for 2-4 hours, and cooled to room temperature to obtain powder E; Step 4: Weigh 0.15-0.2 g of powders C and E respectively and place them in the same beaker, then add 150-200 mL of isopropanol solution, stir until evenly dispersed, then add 0.3-0.4 g of iodine, continue stirring until evenly dispersed to obtain a deposition solution F; Step 5: Pre-treat the C / C substrate and fix it on the negative electrode of the hydrothermal electrophoretic deposition equipment, then place it in the deposition solution F, heat the hydrothermal deposition kettle and apply voltage for electrophoretic deposition for 1 to 20 minutes, place the deposited self-supporting sample in an oven and dry it, and finally obtain the C / C-WN / Bi2WO6 photoelectrode material.

2. The method for preparing the C / C-based tungsten nitride / bismuth tungstate composite material according to claim 1, characterized in that: The washing in step 1 and step 2 is performed by filtering and washing with deionized water and anhydrous ethanol in sequence for 2 to 5 times.

3. The method for preparing the C / C-based tungsten nitride / bismuth tungstate composite material according to claim 1, characterized in that: The drying described in step 1, step 2 and step 5 is to place in an oven and dry at 120-160° C. for 10-16 hours.

4. The method for preparing the C / C-based tungsten nitride / bismuth tungstate composite material according to claim 1, characterized in that: The C / C substrate pretreatment process described in step 5 includes: calcining at 300-350°C in a muffle furnace for 1-2 hours, placing it in a reagent mixed with acetone, deionized water and anhydrous ethanol in a volume ratio of 1:(1-2):(1-2) for 1 hour after cooling, and then drying it at 60-90°C for 1-3 hours.

5. The method for preparing the C / C-based tungsten nitride / bismuth tungstate composite material according to claim 1, characterized in that: During the electrophoretic deposition process described in step five, the heating temperature is 80-160° C. and the applied voltage is 15-30V.

6. A C / C-based tungsten nitride / bismuth tungstate composite material prepared by the method according to any one of claims 1 to 5.

7. Use of the C / C-based tungsten nitride / bismuth tungstate composite material as claimed in claim 6 as a photoanode in a photoelectrocatalytic process.

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