A sheet-shaped sulfur and nitrogen-containing carbon nitride / tubular copper-doped phosphorus and nitrogen-containing carbon nitride heterojunction, a preparation method and application thereof

Abstract

This invention provides a sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-nitride homo-heterojunction, its preparation method, and its application. The preparation method is as follows: S1. Calcining trithiocyanate to obtain sheet-like sulfur-containing carbon nitride; dissolving copper acetate and melamine in water, then adding concentrated phosphoric acid and stirring until homogeneous, and obtaining a tubular copper-doped phosphorus-nitride precursor using a hydrothermal method; S2. Dispersing the tubular copper-doped phosphorus-nitride precursor and sheet-like sulfur-containing carbon nitride in ethanol or an ethanol-water solution, ultrasonicating, stirring, drying, and then performing a second calcination to obtain the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-nitride homo-heterojunction. The prepared sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-nitride homo-heterojunction is sensitive to visible light response, has high photocatalytic hydrogen production activity, and the preparation method is simple, easy to operate, and has good reproducibility.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic hydrogen production technology, specifically to a sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction, its preparation method, and its application. Background Technology

[0002] With rapid societal development, energy consumption and environmental pollution have become two major challenges facing humanity. In response, the global scientific community has focused on research into sustainable green new energy sources such as solar, wind, and geothermal energy. Among these, solar energy, as the most abundant energy source, is experiencing rapid development in photocatalysis technology. To date, various photocatalysts have been developed and widely used in areas such as pollutant degradation, carbon dioxide reduction, and photocatalytic water splitting for hydrogen and oxygen production. Hydrogen, in particular, has attracted significant attention due to its significant advantages: it is green and pollution-free, has high energy density, and is recyclable. Hydrogen combustion produces only water, which can then be reused to produce more hydrogen, thus achieving a sustainable energy cycle. Based on this characteristic, the use of solar energy for photocatalytic water splitting to produce hydrogen has become a research hotspot in recent years.

[0003] Among numerous photocatalysts, graphitic carbon nitride (g-C3N4) stands out as a promising visible-light-responsive semiconductor catalyst due to its suitable bandgap, non-toxicity, simple and low-cost preparation method, and good chemical stability. g-C3N4 possesses properties such as resistance to acids and alkalis, resistance to photocorrosion, and easy control over its structure and performance. However, its bandgap is 2.7 eV, corresponding to a critical absorption wavelength of approximately 460 nm, resulting in relatively low utilization efficiency of visible light. Furthermore, g-C3N4 catalytic materials also suffer from high energy for generating photogenerated carriers, small specific surface area, low quantum efficiency, and severe photogenerated electron-hole recombination, hindering its large-scale application in environmental and energy fields.

[0004] There is an urgent need to develop new carbon nitride materials to improve their photocatalytic performance. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention provides a sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction, its preparation method and application. The prepared sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction is sensitive to visible light response, has high photocatalytic hydrogen production activity, and the preparation method is simple, easy to operate and has good reproducibility.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides a method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions, comprising the following steps: S1. Calcining trithiocyanate yields flake-shaped sulfur-containing carbon nitride; copper acetate and melamine are dissolved in water, then concentrated phosphoric acid is added and stirred until homogeneous, and tubular copper-phosphorus-doped carbon nitride precursor is obtained by hydrothermal method; S2. Disperse the tubular copper-doped carbon nitride precursor and the sheet-like sulfur-containing carbon nitride in ethanol or an aqueous ethanol solution, sonicate, stir, dry, and then calcine a second time to obtain a sheet-like sulfur-containing carbon nitride / tubular copper-doped carbon nitride homo-heterojunction.

[0007] According to the above scheme, the calcination process conditions in step S1 are: calcination temperature of 500-600 ℃ and holding time of 1-4 h.

[0008] According to the above scheme, the calcination atmosphere in step S1 is air or nitrogen.

[0009] According to the above scheme, in step S1, the temperature is increased to 500-600 ℃ at a rate of 5-20 ℃ / min.

[0010] According to the above scheme, in step S1, the phosphoric acid content in the concentrated phosphoric acid is not less than 85%. Based on the amount of 85% concentrated phosphoric acid used being 5-20 mL, the mass-volume ratio of copper acetate, melamine and concentrated phosphoric acid is (0.2-0.8 g): (2-4 g): (5-20 mL).

[0011] According to the above scheme, in the hydrothermal reaction system in step S1, copper acetate, melamine and concentrated phosphoric acid are added, and the concentration of phosphoric acid is not less than 10%.

[0012] According to the above scheme, in step S1, the hydrothermal reaction temperature is 120-180 ℃ and the time is 12-24 h. After the hydrothermal reaction, the tubular copper-doped phosphorus nitride carbon precursor is obtained by drying.

[0013] According to the above scheme, in step S1, with melamine used at a rate of 2-4 g, the amount of trithiocyanate used is 0.5-2.5 g.

[0014] According to the above scheme, in step S2, the ethanol content in the ethanol aqueous solution is not less than 50%.

[0015] According to the above scheme, in step S2, the ultrasonic treatment is performed for 10-30 minutes, the stirring is performed for 2-4 hours, the drying temperature is 60-100 ℃, and the drying time is 6-10 hours.

[0016] According to the above scheme, the temperature of the secondary calcination in step S2 is 500-600 ℃, and the holding time is 1-3 h.

[0017] According to the above scheme, the atmosphere for secondary calcination is nitrogen or air.

[0018] According to the above scheme, the heating rate for the second calcination is 5-10 ℃ / min.

[0019] Secondly, the present invention provides sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-containing carbon nitride homo-heterojunctions prepared by the above preparation method.

[0020] Thirdly, the present invention provides the application of the above-mentioned sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-containing carbon nitride homo-heterojunction in photocatalytic hydrogen production.

[0021] The principle of this invention is as follows: This invention involves fully dispersing sheet-like sulfur-containing carbon nitride and tubular copper-phosphorus-doped precursors in ethanol or an aqueous ethanol solution, followed by ultrasonication, stirring, and drying, and then obtaining a sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction through secondary calcination. On the one hand, during the secondary calcination process, the sheet-like material becomes thinner, and the tubular copper-doped carbon nitride disperses between the sheet-like sulfur-containing carbon nitride, forming an irregular stack. The tubular structure is dispersed due to the presence of the sheet-like structure, increasing the specific surface area of ​​the material and providing more active sites. On the other hand, the difference in electronic band structure between the sheet-like sulfur-containing carbon nitride and the tubular copper-doped carbon nitride drives the directional transfer of photogenerated electrons and holes at the heterojunction interface. The homo-heterojunction of the sheet-like sulfur-containing carbon nitride and the tubular copper-doped carbon nitride synergistically optimizes the light absorption and carrier separation efficiency of the material, promoting electron-hole separation. At the same time, by finely controlling the band structure and surface active site distribution of the homo-heterojunction through element doping strategy, the visible light response range is broadened and the interface charge is efficiently migrated, thereby significantly enhancing its photocatalytic performance.

[0022] The beneficial effects of this invention are: 1. The sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus carbon nitride homo-heterojunction material of the present invention has strong light absorption capacity, high photocatalytic hydrogen production activity, and excellent cycle stability, and has good application prospects for photocatalytic hydrogen production.

[0023] 2. The preparation method of the homo-heterojunction of sheet-like sulfur-containing carbon nitride and tubular copper-phosphorus-doped carbon nitride of the present invention is simple, easy to operate, has good repeatability, high safety, and low cost. Attached Figure Description

[0024] Figure 1 This is a comparison diagram of the photocatalytic hydrogen production effects of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunctions of Examples 1-3 and the photocatalytic materials prepared in Comparative Examples 1-4. Figure 2 This is a TEM image of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-nitride homo-heterojunction of Example 1 of the present invention. Figure 3The PL spectra of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction of Example 1 of the present invention and the photocatalytic materials prepared in Comparative Examples 1-4 are shown. Figure 4 Impedance test diagrams of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction of Example 1 of the present invention and the photocatalytic materials prepared in Comparative Examples 1-4; Figure 5 This is a test diagram of the stability of the continuous 20-hour photocatalytic hydrogen production cycle of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction of Example 1 of the present invention. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] In the following examples, the concentration of concentrated phosphoric acid is 85%.

[0027] Example 1 This embodiment provides a sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction, the specific preparation method of which is as follows: 1) Weigh 2g of trithiocyanate (purity 95wt%), spread the trithiocyanate powder evenly in the crucible, place it in the central area of ​​the muffle furnace, and calcine it at room temperature at a heating rate of 5℃ / min to 550℃ for 2h. After naturally cooling to room temperature, grind it into powder to obtain flake sulfur-containing carbon nitride (SCN). 2) Disperse 0.04 g of copper acetate and 2 g of melamine in water, add 10 mL of concentrated phosphoric acid and stir thoroughly. The hydrothermal temperature is 180℃ and the hydrothermal time is 24 h. After drying, a tubular copper-phosphorus carbon nitride precursor is obtained. 3) 0.1 g of flake-shaped sulfur-containing carbon nitride (SCN) and 0.4 g of tubular copper-doped phosphorus-nitride precursor were dispersed in an ethanol-water solution (ethanol to water volume ratio of 1:1), then sonicated for 30 min, stirred for 4 h, and dried. The product was then subjected to a second calcination (calcined at room temperature at a heating rate of 5 °C / min to 550 °C for 2 h) to obtain flake-shaped sulfur-containing carbon nitride / tubular copper-doped phosphorus-nitride homo-heterojunctions. The resulting product was denoted as SCN / Cu,P-TCN.

[0028] Example 2 This embodiment provides a sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction, the specific preparation method of which is as follows: 1) Weigh 2 g of trithiocyanate (purity 95 wt%), spread the trithiocyanate powder evenly in the crucible, place it in the central area of ​​the muffle furnace, and calcine it at room temperature to 550 ℃ at a heating rate of 5 ℃ / min for 2 h. After naturally cooling to room temperature, grind it into powder to obtain flake sulfur-containing carbon nitride (SCN). 2) Disperse 0.02 g of copper acetate and 2 g of melamine in water, add 5 mL of concentrated phosphoric acid and stir thoroughly. The hydrothermal temperature is 180 ℃ and the hydrothermal time is 20 h. After drying, a tubular copper-phosphorus carbon nitride precursor is obtained. 3) 0.1 g of flake-shaped sulfur-containing carbon nitride (SCN) and 0.4 g of tubular copper-doped phosphorus-nitride precursor were dispersed in an ethanol-water solution (ethanol to water volume ratio of 1:1), then sonicated for 30 min, stirred for 4 h, and dried. The product was then calcined twice (calcined at room temperature at a heating rate of 5 ℃ / min to 520℃ for 2 h) to obtain flake-shaped sulfur-containing carbon nitride / tubular copper-doped phosphorus-nitride homo-heterojunctions. The product was denoted as SCN / Cu,P-TCN-2.

[0029] Example 3 This embodiment provides a sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction, the specific preparation method of which is as follows: 1) Weigh 2 g of trithiocyanate (purity 95 wt%), spread the trithiocyanate powder evenly in the crucible, place it in the central area of ​​the muffle furnace, and calcine it at room temperature to 550 ℃ at a heating rate of 5 ℃ / min for 2 h. After naturally cooling to room temperature, grind it into powder to obtain flake sulfur-containing carbon nitride (SCN). 2) Disperse 0.08 g of copper acetate and 2 g of melamine in water, add 10 mL of concentrated phosphoric acid and stir thoroughly. The hydrothermal temperature is 180 ℃ and the hydrothermal time is 24 h. After drying, a tubular copper-phosphorus carbon nitride precursor is obtained. 3) 0.1 g of flake-shaped sulfur-containing carbon nitride (SCN) and 0.4 g of tubular copper-doped phosphorus-nitride precursor were dispersed in an ethanol-water solution (ethanol to water volume ratio of 1:1), then sonicated for 30 min, stirred for 4 h, and dried. The product was then calcined twice (calcined at room temperature at a heating rate of 5 ℃ / min to 520℃ for 2 h) to obtain flake-shaped sulfur-containing carbon nitride / tubular copper-doped phosphorus-nitride homo-heterojunctions. The product was denoted as SCN / Cu,P-TCN-3.

[0030] Comparative Example 1 This comparative example provides a sulfur-containing carbon nitride material, and the specific preparation method is as follows: 1) Weigh out 2g of trithiocyanate (purity 95wt%) and set aside; 2) The solid trithiocyanate was spread evenly in the crucible and placed in the central area of ​​the muffle furnace. It was heated to 550°C at a heating rate of 5°C / min at room temperature for 2 hours. After natural cooling to room temperature, it was ground into powder to obtain sulfur-containing carbon nitride material, denoted as SCN.

[0031] Comparative Example 2 This comparative example provides a carbon nitride material, and the specific preparation method is as follows: 1) Weigh out 2g of melamine and set aside; 2) Melamine is spread evenly in a crucible and placed in the central area of ​​a muffle furnace. It is heated to 550°C at a heating rate of 5°C / min at room temperature for 2 hours. After natural cooling to room temperature, it is ground into powder to obtain carbon sulfur nitride material, denoted as CN.

[0032] Comparative Example 3 This comparative example provides a copper-phosphorus-doped carbon nitride material, and the specific preparation method is as follows: 1) Disperse 0.04 g of copper acetate and 2 g of melamine in water, add 10 mL of concentrated phosphoric acid and stir thoroughly. The hydrothermal temperature is 180℃ and the hydrothermal time is 24 h to obtain a tubular copper-doped phosphorus carbon nitride precursor. 2) The tubular copper-phosphorus carbon nitride precursor was spread in a ceramic boat and placed in the constant temperature zone of a tube furnace. It was calcined at room temperature to 550°C at a heating rate of 5°C / min for 2 hours. After naturally cooling to room temperature, it was ground into powder to obtain the tubular copper-phosphorus carbon nitride material, denoted as Cu,P-TCN.

[0033] Comparative Example 4 This comparative example provides a sheet-like sulfur-containing carbon nitride / tubular carbon nitride homo-heterojunction material, and the specific preparation method is as follows: 1) Weigh 2g of trithiocyanate (purity 95wt%), spread the solid trithiocyanate evenly in a crucible, place it in the central area of ​​a muffle furnace, and calcine it at room temperature to 550℃ at a heating rate of 5℃ / min for 2 hours. After naturally cooling to room temperature, grind it into powder to obtain flake-shaped sulfur-containing carbon nitride (SCN) for later use. 2) Disperse 2g of melamine in water, and perform hydrothermal treatment at 180℃ for 24 hours to obtain a tubular precursor; 3) Disperse 0.1g of flake-shaped sulfur-containing carbon nitride and 0.4g of tubular precursor into an ethanol-water solution (ethanol to water volume ratio of 1:1), then sonicate for 30min, stir for 4h, and dry. Then, calcine twice (calcine at room temperature at a heating rate of 5℃ / min to 500℃ for 4h) to obtain sulfur-containing carbon nitride / tubular carbon nitride homo-heterojunctions. The resulting product is denoted as SCN / TCN.

[0034] Photocatalytic hydrogen production performance test: 10 mg of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction prepared in Examples 1-3 and the photocatalyst materials prepared in Comparative Examples 1-4 were added to 5 portions of 50 mL deionized water containing 10 wt% triethanolamine. H2PtCl4 solution was added to each solution (based on the 3 wt% Pt loading of 10 mg of photocatalyst, H2PtCl4 acts as a co-catalyst in the photocatalytic system). After ultrasonic dispersion of the mixed solution for 30 min, it was irradiated for 4 h in a photoreactor (Labsolar-6A, light source: a 300W xenon lamp with a 420 nm cutoff filter) for testing. The visible light photocatalytic hydrogen production effects of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction in Examples 1-3 and the photocatalyst materials prepared in Comparative Examples 1-4 are shown in Table 1 and 2, respectively. Figure 1 As shown.

[0035] Table 1. Visible light photocatalytic hydrogen production effects of sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunctions in Examples 1-3 and Comparative Examples 1-4.

[0036] The photocatalytic hydrogen production performance of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-containing carbon nitride homo-heterojunctions prepared in Examples 1-3 was significantly higher than that of Comparative Examples 1-4. The highest photocatalytic hydrogen production rate was 9272.4 μmol / g / h in Example 1, which was nearly 2.9 times that of Comparative Example 1, 32 times that of Comparative Example 2, nearly 8.5 times that of Comparative Example 3, and 2.26 times that of Comparative Example 4.

[0037] Figure 2 The image shown is a TEM image of the sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction prepared in Example 1. It can be seen that the sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction is an irregular stack of sheet and tubular structures aggregated together. The tubular structure is dispersed due to the presence of the sheet-like structure, resulting in a completely hollow interior with extremely thin walls. Some interlocking sheet-like flocculent bodies are present on both sides of the tube, exhibiting a loose, porous, cotton-candy-like texture. It is lightweight and composed of numerous interconnected thin sheets with rich pore structures, resulting in a large specific surface area that effectively improves photon absorption. This is beneficial for photocatalytic hydrogen production.

[0038] Figure 3The steady-state photoluminescence (PL) spectra of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction (SCN / Cu,P-TCN) prepared in Example 1 and the photocatalytic materials (CN, SCN, Cu,P-TCN, SCN / TCN) of Comparative Examples 1-4 are shown under excitation light at a wavelength of 400 nm. The PL emission peak intensity of SCN / Cu,P-TCN is significantly lower than that of CN, SCN, SCN / TCN, and Cu,P-TCN, indicating that the separation efficiency of photogenerated electrons and holes of SCN / Cu,P-TCN prepared in Example 1 is significantly better than that of the photocatalytic materials (CN, SCN, SCN / TCN, Cu,P-TCN) of Comparative Examples 1-4. This is mainly because sulfur atoms and copper and phosphorus atoms replace the bridging N atoms, resulting in the formation of delocalized π bonds between the newly doped atoms and the aromatic rings, thereby increasing the conductivity of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction and facilitating electron transfer. The improved photogenerated carrier separation efficiency in SCN / Cu,P-TCN may be due to the increased specific surface area of ​​the samples after secondary calcination in a tubular furnace, which simultaneously forms a homo-heterojunction. This shortens the transport distance of photogenerated carriers, making it easier for photogenerated electrons to reach the sample surface and suppressing their recombination with photogenerated holes. The PL emission peak of SCN / Cu,P-TCN shows a significant redshift compared to the other four samples, and the band gap of SCN / Cu,P-TCN is reduced, which is beneficial to improving the photocatalytic hydrogen production efficiency.

[0039] Figure 4 Electrochemical impedance spectroscopy (EIS) charts are shown for the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-containing carbon nitride homo-heterojunction (SCN / Cu, P-TCN) prepared in Example 1 and the photocatalytic materials (CN, SCN, Cu, P-TCN, SCN / TCN) of Comparative Examples 1-4. The semi-circle radii show a specific order: CN > SCN / TCN > Cu, P-TCN > SCN > SCN / Cu, P-TCN. This indicates that SCN / Cu, P-TCN, with its homojunction structure, exhibits the lowest impedance. Impedance primarily reflects the efficiency of photogenerated charge carriers (electrons and holes) separation and transfer to the surface to participate in the reaction: low impedance indicates low charge transfer resistance, allowing photogenerated holes and electrons to be injected more smoothly from the electrode surface into the electrolyte, participating in the oxidation or reduction reaction of water, thereby improving photocatalytic efficiency. Low charge transfer resistance accelerates the surface reaction to consume holes, which helps suppress the recombination of photogenerated electrons and holes inside or on the surface of the material, allowing more charge carriers to be used for the target reaction. Both elemental doping and homogeneous structure construction can effectively reduce impedance, which is beneficial to promoting carrier migration and thus improving photocatalytic activity.

[0040] Cyclic stability of hydrogen production catalytically generated by the sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction prepared in Example 1 was tested: 10 mg of the sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction prepared in Example 1 was added to 50 mL of deionized water containing 10 wt% triethanolamine, and H2PtCl4 solution was added (based on the mass fraction of Pt loaded on 10 mg of photocatalyst being 3 wt%). After ultrasonic dispersion of the mixed solution for 30 min, cyclic hydrogen production stability was tested in a photoreactor (Labsolar-6A, with a 300W xenon lamp with a 420 nm cutoff filter as the light source). The test was stopped every 4 h, and 5 cycles were conducted for a total of 20 h. The cyclic stability test results of the sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction prepared in Example 1 for continuous 20 h of photocatalytic hydrogen production are shown in the figure below. Figure 5 As shown in the figure, the sulfur-containing carbon nitride / tubular copper-phosphorus carbon nitride homo-heterojunction exhibits good cycling stability.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction, characterized in that, Includes the following steps: S1. Calcining trithiocyanate yields flake-shaped sulfur-containing carbon nitride; copper acetate and melamine are dissolved in water, then concentrated phosphoric acid is added and stirred until homogeneous, and tubular copper-phosphorus-doped carbon nitride precursor is obtained by hydrothermal method; S2. Disperse the tubular copper-doped carbon nitride precursor and the sheet-like sulfur-containing carbon nitride in ethanol or an aqueous ethanol solution, sonicate, stir, dry, and then calcine a second time to obtain a sheet-like sulfur-containing carbon nitride / tubular copper-doped carbon nitride homo-heterojunction.

2. The method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions according to claim 1, characterized in that, The calcination process conditions in step S1 are: calcination temperature of 500-600 ℃ and holding time of 1-4 h.

3. The method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions according to claim 1, characterized in that, In step S1, the phosphoric acid content in the concentrated phosphoric acid is not less than 85%. Based on the amount of 85% concentrated phosphoric acid used being 5-20 mL, the mass-volume ratio of copper acetate, melamine, and concentrated phosphoric acid is (0.2-0.8 g): (2-4 g): (5-20 mL).

4. The method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions according to claim 3, characterized in that, In step S1, a hydrothermal reaction system containing copper acetate, melamine, and concentrated phosphoric acid was added, with the concentration of phosphoric acid not less than 10%.

5. The method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions according to claim 1, characterized in that, In step S1, the hydrothermal reaction temperature is 120-180 ℃ and the time is 12-24 h. After the hydrothermal reaction, the tubular copper-doped phosphorus nitride precursor is obtained by drying.

6. The method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions according to claim 3, characterized in that, In step S1, based on the amount of melamine used being 2-4 g, the amount of trithiocyanate used is 0.5-2.5 g.

7. The method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions according to claim 1, characterized in that, In step S2, sonicate for 10-30 min, stir for 2-4 h, dry at 60-100 ℃, and dry for 6-10 h.

8. The method for preparing sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunctions according to claim 1, characterized in that, In step S2, the temperature of the secondary calcination is 500-600 ℃, and the holding time is 1-3 h.

9. A sheet-like sulfur-containing carbon nitride / tubular copper-phosphorus-doped carbon nitride homo-heterojunction, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the sheet-like sulfur-containing carbon nitride / tubular copper-doped phosphorus-doped carbon nitride homo-heterojunction as described in claim 9 in photocatalytic hydrogen production.

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