A graphite phase carbon nitride film and preparation method thereof

Abstract

The present invention relates to a graphite phase carbon nitride film and a preparation method thereof, and belongs to the field of photoelectrode technology. The preparation method of the graphite phase carbon nitride film comprises the following steps: adding melamine and cyanuric acid to water and stirring to obtain a CM supramolecular precursor; adding the CM supramolecular precursor to an iodine-acetone solution to obtain an electrolyte, adopting an electrophoresis method, using FTO as a cathode and an anode, preparing a CM supramolecular precursor film; calcining the CM supramolecular precursor film and melamine under the protection of an inert gas to obtain a graphite phase carbon nitride film. The present invention directly converts the CM supramolecular precursor film prepared by the electrophoresis method into a graphite phase carbon nitride film, greatly increasing the contact between the graphite phase carbon nitride and the substrate, and simultaneously selecting a graphite phase carbon nitride film with a relatively good crystallinity through calcination at different temperatures, so that it exhibits excellent photoelectric properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectrodes, and in particular relates to a graphite phase carbon nitride film and a preparation method thereof. Background Art

[0002] In the process of energy transfer of graphite carbon nitride thin films, most of them are prepared by first preparing graphite carbon nitride powder and then loading it on a carrier for transfer. Some of them also use a precursor method to prepare thin films for energy transfer. At present, the main methods for loading graphite carbon nitride thin films include the doctor blade method, electrophoresis method and vapor deposition method. However, the above methods have problems such as weak bonding between the material and the substrate and uneven film, which affect the transfer process of photogenerated charges and thus affect the material's effective use of solar energy. Currently, most of the research on the contact problem between carbon nitride and the substrate is to load graphite carbon nitride materials on other semiconductor materials (such as TiO2, Fe2O3, BiWO4, etc.) to increase charge transfer, but there is less research on photoelectrodes based on graphite carbon nitride. The main methods for preparing graphite carbon nitride thin film photoelectrodes include electrophoretic deposition method, doctor blade method, vapor deposition method, etc. Although these methods are based on pure graphite phase carbon nitride as the research object, the problems of such methods such as the loose contact between graphite phase carbon nitride and the substrate and the thin film are too limited in the application of graphite phase carbon nitride photoelectrodes. For example, the electrophoretic deposition method is based on the generation of graphite phase carbon nitride. It is easy to load a layer of graphite phase carbon nitride film on the substrate at a voltage of 300V, which has the advantages of being green and environmentally friendly. However, the graphite phase carbon nitride is simply adsorbed on the surface of the carrier, which results in only weak adsorption between the graphite phase carbon nitride and the substrate, and the transport of carriers generated after the graphite phase carbon nitride is excited by light is affected. At 1.23V vs.RHE, the photocurrent density in 1M KOH solution is only 1.0μA / cm 2 In 2018, Menny Shalom's group used CM supramolecular precursors and ethylene glycol to mix and grind to prepare CM supramolecular precursor films, and then prepared graphite carbon nitride films by calcining under nitrogen. This method used a seeding method to increase the contact between the generated graphite carbon nitride film and the substrate, but the photocurrent density in 1M KOH solution at 1.23V vs. RHE was only 3.0μA / cm 2 , indicating that the force between graphite phase carbon nitride and the matrix is ​​still weak. In 2022, Zheng Jinyou's team loaded a layer of graphite phase carbon nitride film on FTO by adding melamine to the glass bottle and covering the bottle mouth with FTO. However, since the graphite phase carbon nitride film loaded on FTO is only 27nm, it seriously affects the film's ability to absorb light. Therefore, the photocurrent density in 0.5M Na2SO4 solution at 1.23Vvs.RHE is only 0.72μA / cm 2 .

[0003] Furthermore, the poor crystallinity of carbon nitride can lead to severe recombination of photogenerated electrons and holes, and low carrier mobility. Research on the crystallinity of graphite-phase carbon nitride currently primarily focuses on the crystallinity of graphite-phase carbon nitride powder. For example, in 2016, Wang Xinchen's team used a molten salt method to synthesize highly crystalline graphite-phase carbon nitride powder. This increased crystallinity significantly reduces the migration resistance of photogenerated electrons and inhibits the recombination of photogenerated electrons and holes. Therefore, research on the crystallinity of graphite-phase carbon nitride is essential. However, reports on the crystallinity of carbon nitride films are scarce. Summary of the Invention

[0004] The purpose of the present invention is to provide a graphite phase carbon nitride film to solve the problem of poor contact between the existing graphite phase carbon nitride and the substrate, and at the same time explore the influence of temperature on the crystallinity and photoelectric properties of graphite phase carbon nitride.

[0005] The second object of the present invention is to provide a method for preparing a graphite phase carbon nitride film.

[0006] In order to achieve the above objectives, the technical solution adopted by the present invention is:

[0007] A method for preparing a graphite phase carbon nitride film comprises the following steps:

[0008] Step 1): Preparation of CM supramolecular precursor: Melamine and cyanuric acid are added to water and stirred to obtain a CM supramolecular precursor;

[0009] Step 2): Preparation of CM supramolecular precursor film: adding the CM supramolecular precursor obtained in step 1) to an iodine-acetone solution to obtain an electrolyte, and using an electrophoresis method with FTO as the cathode and anode to deposit the CM supramolecular precursor film at the anode;

[0010] Step 3): Preparation of graphite carbon nitride film: The CM supramolecular precursor film obtained in step 2) is calcined with melamine under the protection of an inert gas to obtain the graphite carbon nitride film.

[0011] Furthermore, the molar ratio of melamine to cyanuric acid in step 1) is 1:1; the mass of melamine added per mL of water is 0.0168 g; in the iodine-acetone solution in step 2), the mass of iodine added per mL of acetone solution is 0.1 to 0.17 g, and the mass of CM supramolecular precursor added per mL of iodine-acetone solution is 0.67 to 1 mg.

[0012] Furthermore, the calcination temperature in step 3) is 500-580° C., the heating rate is 3-5° C. / min, and the calcination time is 2-6 h.

[0013] Furthermore, the electrophoresis time in step 2) is 5 to 30 minutes.

[0014] Furthermore, the preparation method of the electrolyte described in step 2) is: adding the CM supramolecular precursor to an iodine-acetone solution, obtaining a dispersion after ultrasonication, and centrifuging the dispersion to obtain a turbid liquid; the centrifugal speed is 500-1000 r / min.

[0015] Furthermore, the distance between the cathode and the anode in step 2) is 2 to 4 cm; and the voltage of the electrophoresis method is a DC voltage of 100 V.

[0016] Furthermore, the preparation method of the CM supramolecular precursor described in step 1) is: adding melamine and cyanuric acid to water and stirring, centrifuging to obtain a precipitate, washing the precipitate with water and anhydrous ethanol, and vacuum drying to obtain the product; the vacuum degree is 0.06-0.08 MPa, and the drying temperature is 60-80°C.

[0017] Furthermore, the inert gas in step 3) is nitrogen or argon.

[0018] A graphite phase carbon nitride film is prepared by the above-mentioned method for preparing the graphite phase carbon nitride film.

[0019] The graphite phase carbon nitride film as described above is used in photoelectrocatalytic oxygen evolution.

[0020] Beneficial effects of the present invention:

[0021] The graphite phase carbon nitride film and preparation method thereof of the present invention adopt an electrophoresis method plus a gas phase protection method to prepare the graphite phase carbon nitride film. First, a CM supramolecular precursor is electrophoresed on FTO so that the CM supramolecular precursor is tightly adsorbed on the FTO, so that the graphite phase carbon nitride formed during the high-temperature calcination process is in closer contact with the substrate.

[0022] The present invention's graphite-phase carbon nitride film and preparation method thereof first utilize an electrophoretic method to prepare a CM supramolecular precursor film, which is then converted into a graphite-phase carbon nitride film through high-temperature calcination. By directly converting the electrophoretically prepared CM supramolecular precursor film into a graphite-phase carbon nitride film, the present invention significantly increases contact between the graphite-phase carbon nitride and the substrate. Furthermore, through calcination at different temperatures, graphite-phase carbon nitride films with superior crystallinity are selected, resulting in excellent photoelectric properties.

[0023] The advantage of using an iodine-acetone solution during the electrophoresis process of the graphite-phase carbon nitride film and its preparation method of the present invention is that acetone has a large electrochemical window, and the generation of gas from the electrolysis of acetone during the electrophoresis process does not affect the density of the CM supramolecular precursor film. Iodine increases the conductivity of the CM supramolecular precursor, thereby achieving a desired thickness of the CM supramolecular precursor film at a low voltage.

[0024] The graphite phase carbon nitride film and preparation method thereof of the present invention have the advantage of adding melamine during the calcination process. Since the CM supramolecular precursor is easily vaporized at high temperature, it is separated from the FTO surface, resulting in the inability to form a graphite phase carbon nitride film on the FTO surface. However, melamine will first vaporize at a certain temperature to fill the entire confined space, thereby inhibiting the volatilization of the CM supramolecular precursor, and ultimately allowing the CM supramolecular precursor to form a graphite phase carbon nitride film on the original FTO surface.

[0025] The graphite phase carbon nitride film and preparation method thereof of the present invention prepare CM supramolecular precursor films of different thicknesses by using different electrophoresis times, explore the influence of different calcination temperatures on the crystallinity and performance of the graphite phase carbon nitride film by using different calcination temperatures, and then select graphite phase carbon nitride films with relatively excellent photoelectric properties. The influence of calcination atmosphere on the photoelectric properties of the graphite phase carbon nitride film is explored by using different calcination atmospheres. It is finally found that the graphite phase carbon nitride film prepared under an electrophoresis time of 20 minutes, a calcination temperature of 550°C, and a nitrogen atmosphere has the best photoelectric performance, with a photocurrent density of 45μA / cm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 (a) is a schematic diagram of the CM supramolecular precursor film in Example 1;

[0027] Figure 1 (b) is a schematic diagram of the graphite phase carbon nitride film in Example 1;

[0028] Figure 1 (c) is a schematic diagram of the graphite phase carbon nitride film in Comparative Example 1;

[0029] Figure 1 (d) Schematic diagram of graphitic carbon nitride film prepared without adding CM supramolecular precursor film;

[0030] Figure 2 (a) is the XRD pattern of the graphite phase carbon nitride film of Example 1, Example 2, Example 3, and Example 4;

[0031] Figure 2 (b) is the XRD pattern of the graphite phase carbon nitride films of Example 1, Example 7, Example 8, and Example 9;

[0032] Figure 2 (c) is the XRD pattern of the graphite phase carbon nitride films of Example 1, Example 10, and Example 11;

[0033] Figure 2 (d) is the XRD pattern of the graphite phase carbon nitride films of Example 1 and Example 12;

[0034] Figure 3 (a) is a schematic diagram of the FT-IR spectra of the CM supramolecular precursor and graphitic carbon nitride film in Example 1;

[0035] Figure 3 (b) is the XPS image of the graphite phase carbon nitride film in Example 1;

[0036] Figure 3 (c) is the XPS graph of C1s of the graphite phase carbon nitride film in Example 1;

[0037] Figure 3 (d) is the XPS graph of N1s of the graphite phase carbon nitride film in Example 1;

[0038] Figure 4 (ac) are SEM images of the graphite phase carbon nitride film in Example 2;

[0039] Figure 4 (d-f) are SEM images of the graphite phase carbon nitride film in Example 3;

[0040] Figure 4 (gi) is the SEM image of the graphite phase carbon nitride film in Example 1;

[0041] Figure 4 (jl) is a SEM image of the graphite phase carbon nitride film in Example 4;

[0042] Figure 4 (mp) is the EDS analysis of the graphite phase carbon nitride film in Example 1;

[0043] Figure 5 (a) is a UV-vis image of the graphite phase carbon nitride films of Example 1, Example 2, Example 3, and Example 4;

[0044] Figure 5 (b) is the Tauc plot of the graphite phase carbon nitride films of Example 1, Example 2, and Example 3;

[0045] Figure 5 (c) is the PL spectrum of the graphite phase carbon nitride films of Example 1, Example 2, and Example 3;

[0046] Figure 5 (d) is the MS curve of the graphite phase carbon nitride film of Example 1, Example 2, and Example 3;

[0047] Figure 5 (e) is a diagram showing the band gap and band edge positions of the graphite phase carbon nitride films of Examples 1, 2, and 3;

[0048] Figure 6 (a) is a UV-vis image of the graphite phase carbon nitride films of Example 1, Example 7, Example 8, and Example 9;

[0049] Figure 6 (b) is the Tauc plot of the graphite carbon nitride films of Example 1, Example 7, Example 8, and Example 9;

[0050] Figure 6 (c) is the PL spectrum of the graphite phase carbon nitride films of Example 1, Example 7, Example 8, and Example 9;

[0051] Figure 6 (d) is the MS curve of the graphite phase carbon nitride film of Example 1, Example 7, Example 8, and Example 9;

[0052] Figure 6 (e) is a diagram showing the band gap and band edge positions of the graphite phase carbon nitride films of Examples 1, 7, 8, and 9;

[0053] Figure 7 (a) is the UV-vis image of the graphite phase carbon nitride film of Example 1 and Example 12;

[0054] Figure 7 (b) Tauc plots of the graphite-phase carbon nitride films of Examples 1 and 12;

[0055] Figure 7 (c) is the PL spectrum of the graphite phase carbon nitride film of Example 1 and Example 12;

[0056] Figure 7 (d) is the MS curve of the graphite phase carbon nitride film of Example 1 and Example 12;

[0057] Figure 7 (e) is a diagram showing the band gap and band edge positions of the graphite phase carbon nitride films of Examples 1 and 12;

[0058] Figure 8 (a) is the LSV curve of the graphite phase carbon nitride film of Example 1, Example 2, Example 3, and Example 4;

[0059] Figure 8(b) is the IT diagram of the graphite carbon nitride films of Example 1, Example 2, Example 3, and Example 4 under alternating light and dark conditions, with 1 sun and 20 seconds of alternating light and dark conditions respectively;

[0060] Figure 8 (c) is the EIS graph of the graphite phase carbon nitride films of Example 1, Example 2, Example 3, and Example 4;

[0061] Figure 9 (a) is the LSV curve of the graphite phase carbon nitride film of Example 1, Example 7, Example 8, and Example 9;

[0062] Figure 9 (b) is the IT diagram of the graphite carbon nitride films of Example 1, Example 7, Example 8, and Example 9 under alternating light and dark conditions, 1 sun, and 20 seconds of alternating light and dark conditions respectively;

[0063] Figure 9 (c) is the EIS graph of the graphite phase carbon nitride films of Example 1, Example 7, Example 8, and Example 9;

[0064] Figure 10 (a) is the LSV curve of the graphite phase carbon nitride film of Example 1 and Example 12;

[0065] Figure 10 (b) is the IT diagram of the graphite carbon nitride films of Example 1 and Example 12 under alternating light and dark conditions, 1 sun, and 20 seconds of alternating light and dark.

[0066] Figure 10 (c) is the EIS graph of the graphite phase carbon nitride films of Example 1 and Example 12;

[0067] Figure 11 This is a flow chart of the preparation process of graphite phase carbon nitride film. DETAILED DESCRIPTION

[0068] The present invention will be further described below with reference to the embodiments of the present invention and the accompanying drawings.

[0069] Example 1

[0070] The graphite carbon nitride film of this example was prepared by adding 1.26 g of melamine and 1.29 g of cyanuric acid to 75 mL of deionized water and stirring for 12 hours. The precipitate was collected and washed twice with deionized water and twice with anhydrous ethanol to remove excess impurities. The washed precipitate was then dried in a vacuum drying oven at 60°C overnight to obtain a CM supramolecular precursor.

[0071] 30 mg of the CM supramolecular precursor was added to 30 mL of iodine-acetone solution and sonicated for 1 hour to completely disperse the CM supramolecular precursor, resulting in a dispersion. The dispersion was then poured into a 50 mL centrifuge tube and centrifuged at 500 rpm for 10 minutes to remove larger particles. The supernatant was used as the electrolyte and electrophoresed for 20 minutes at 100 V DC with FTO as the cathode and anode. A CM supramolecular precursor thin film, designated CM / FTO, was obtained on the anode. The iodine-acetone solution was prepared by dissolving 5 mg of elemental iodine in 30 mL of acetone solution until the elemental iodine was completely dissolved. The distance between the cathode and anode was 2 cm.

[0072] CM / FTO was placed in the middle end of a quartz boat, and 500 mg of melamine was placed at the other end of the quartz boat. After covering and sealing with aluminum foil, the quartz boat was placed in a tube furnace and heated to 550°C at a heating rate of 3°C / min under a nitrogen atmosphere. After calcination for 4 hours, a graphite phase carbon nitride film was obtained, which was recorded as CN / FTO.

[0073] The graphite phase carbon nitride film (g-C3N4 film) of Example 1 was prepared by the above method. The graphite phase carbon nitride film of Example 1 had the best photoelectric performance, with a photocurrent density of 45 μA / cm 2 The OER performance of the prepared graphite phase carbon nitride thin film electrode was analyzed using the Donghua electrochemical workstation. The specific test method is: a three-electrode test system, with Pt sheet as the counter electrode, Ag / AgCl electrode as the reference electrode, CN / FTO as the working electrode, and 0.5M Na2SO4 solution (PH=7) as the electrolyte; the light source is a Chinese teaching light source, using a 300W xenon lamp as the light source, and adjusting the power density of the photoelectrode surface to 100MW / cm under a simulated AM 1.5G filter. 2 All tests were performed with Ag / AgCl as the reference electrode, and the final potential was the reversible hydrogen standard electrode potential (RHE), which is converted to E RHE =E Ag / AgCl +0.059PH+0.197.

[0074] The graphite phase carbon nitride film prepared in Example 1 is as follows Figure 1 As shown in (b), melamine first vaporizes and fills the entire confined space, thereby inhibiting the volatilization of the CM supramolecular precursor, and finally the CM supramolecular precursor forms a graphite phase carbon nitride film on the original FTO surface. When melamine is not placed in the calcined CM supramolecular precursor film, Figure 1 (c) It can be seen that no dense graphite phase carbon nitride film is formed on the original FTO surface; Figure 1(d) It can be seen that when only 500 mg of melamine and blank FTO are placed, no dense graphite-phase carbon nitride film is formed on the blank FTO at 550 °C, indicating that melamine can effectively prevent the volatilization of the CM supramolecular precursor in this process.

[0075] Example 2

[0076] The graphite carbon nitride film of this example was prepared by adding 1.26 g of melamine and 1.29 g of cyanuric acid to 75 mL of deionized water and stirring for 12 hours. The precipitate was collected and washed twice with deionized water and twice with anhydrous ethanol to remove excess impurities. The washed precipitate was then dried in a vacuum drying oven at 60°C overnight to obtain a CM supramolecular precursor.

[0077] 30 mg of the CM supramolecular precursor was added to 30 mL of iodine-acetone solution and sonicated for 1 hour to completely disperse the CM supramolecular precursor, resulting in a dispersion. The dispersion was then poured into a 50 mL centrifuge tube and centrifuged at 500 rpm for 10 minutes to remove larger particles. The supernatant was used as the electrolyte and electrophoresed for 20 minutes at 100 V DC with FTO as the cathode and anode. A CM supramolecular precursor thin film, designated CM / FTO, was obtained on the anode. The iodine-acetone solution was prepared by dissolving 5 mg of elemental iodine in 30 mL of acetone solution until the elemental iodine was completely dissolved. The distance between the cathode and anode was 2 cm.

[0078] CM / FTO was placed in the middle end of a quartz boat, and 500 mg of melamine was placed at the other end of the quartz boat. After covering and sealing with aluminum foil, the quartz boat was placed in a tube furnace and heated to 500°C at a heating rate of 3°C / min under a nitrogen atmosphere. After calcination for 4 hours, a graphite phase carbon nitride film was obtained, which was recorded as CN / FTO.

[0079] The graphite phase carbon nitride film of Example 2 was prepared by the above method. The photocurrent density of the graphite phase carbon nitride film of Example 2 was 24 μA / cm 2 .

[0080] Example 3

[0081] The graphite carbon nitride film of this example was prepared by adding 1.26 g of melamine and 1.29 g of cyanuric acid to 75 mL of deionized water and stirring for 12 hours. The precipitate was collected and washed twice with deionized water and twice with anhydrous ethanol to remove excess impurities. The washed precipitate was then dried in a vacuum drying oven at 60°C overnight to obtain a CM supramolecular precursor.

[0082] 30 mg of the CM supramolecular precursor was added to 30 mL of iodine-acetone solution and sonicated for 1 hour to completely disperse the CM supramolecular precursor, resulting in a dispersion. The dispersion was then poured into a 50 mL centrifuge tube and centrifuged at 500 rpm for 10 minutes to remove larger particles. The supernatant was used as the electrolyte and electrophoresed for 20 minutes at 100 V DC with FTO as the cathode and anode. A CM supramolecular precursor thin film, designated CM / FTO, was obtained on the anode. The iodine-acetone solution was prepared by dissolving 5 mg of elemental iodine in 30 mL of acetone solution until the elemental iodine was completely dissolved. The distance between the cathode and anode was 2 cm.

[0083] Place CM / FTO at one end of a quartz boat, and 500 mg of melamine at the other end of the quartz boat. After covering and sealing with aluminum foil, place the quartz boat in a tube furnace and heat it to 520°C at a heating rate of 3°C / min under a nitrogen atmosphere. After calcining for 4 hours, a graphite phase carbon nitride film was obtained, which was recorded as CN / FTO.

[0084] The graphite phase carbon nitride film of Example 3 was prepared by the above method. The photocurrent density of the graphite phase carbon nitride film of Example 3 was 30 μA / cm 2 .

[0085] Example 4

[0086] The graphite carbon nitride film of this example was prepared by adding 1.26 g of melamine and 1.29 g of cyanuric acid to 75 mL of deionized water and stirring for 12 hours. The precipitate was collected and washed twice with deionized water and twice with anhydrous ethanol to remove excess impurities. The washed precipitate was then dried in a vacuum drying oven at 60°C overnight to obtain a CM supramolecular precursor.

[0087] 30 mg of the CM supramolecular precursor was added to 30 mL of iodine-acetone solution and sonicated for 1 hour to completely disperse the CM supramolecular precursor, resulting in a dispersion. The dispersion was then poured into a 50 mL centrifuge tube and centrifuged at 500 rpm for 10 minutes to remove larger particles. The supernatant was used as the electrolyte and electrophoresed for 20 minutes at 100 V DC with FTO as the cathode and anode. A CM supramolecular precursor thin film, designated CM / FTO, was obtained on the anode. The iodine-acetone solution was prepared by weighing 5 mg of elemental iodine and adding it to 30 mL of acetone solution until the iodine was completely dissolved. The distance between the cathode and anode electrodes was 2 cm.

[0088] CM / FTO was placed in the middle end of a quartz boat, and 500 mg of melamine was placed at the other end of the quartz boat. After covering and sealing with aluminum foil, the quartz boat was placed in a tube furnace and heated to 580°C at a heating rate of 3°C / min under a nitrogen atmosphere. After calcination for 4 hours, a graphite phase carbon nitride film was obtained, which was recorded as CN / FTO.

[0089] The graphite carbon nitride film of Example 4 was prepared by the above method. When the calcination temperature was 580° C., the conductive surface of FTO was destroyed and no photocurrent could be obtained.

[0090] Example 5

[0091] The graphite carbon nitride film of this example was prepared by adding 1.26 g of melamine and 1.29 g of cyanuric acid to 75 mL of deionized water and stirring for 12 hours. The precipitate was collected and washed twice with deionized water and twice with anhydrous ethanol to remove excess impurities. The washed precipitate was then dried in a vacuum drying oven at 70°C overnight to obtain a CM supramolecular precursor.

[0092] 20 mg of the CM supramolecular precursor was added to 30 mL of iodine-acetone solution and sonicated for 1 hour to completely disperse the CM supramolecular precursor, resulting in a dispersion. The dispersion was then poured into a 50 mL centrifuge tube and centrifuged at 300 rpm for 10 minutes to remove larger particles. The supernatant was used as the electrolyte and electrophoresed for 20 minutes at 100 V DC with FTO as the cathode and anode. A CM supramolecular precursor thin film, designated CM / FTO, was obtained on the anode. The iodine-acetone solution was prepared by weighing 3 mg of elemental iodine and adding it to 30 mL of acetone solution until the iodine was completely dissolved. The distance between the cathode and anode was 3 cm.

[0093] CM / FTO was placed in the middle end of a quartz boat, and 500 mg of melamine was placed at the other end of the quartz boat. After covering and sealing with aluminum foil, the quartz boat was placed in a tube furnace and heated to 550°C at a heating rate of 5°C / min under a nitrogen atmosphere. After calcination for 4 hours, a graphite phase carbon nitride film was obtained, which was recorded as CN / FTO.

[0094] Example 6

[0095] The graphite carbon nitride film of this example was prepared by adding 1.26 g of melamine and 1.29 g of cyanuric acid to 75 mL of deionized water and stirring for 12 hours. The precipitate was collected and washed twice with deionized water and twice with anhydrous ethanol to remove excess impurities. The washed precipitate was then dried in a vacuum drying oven at 80°C overnight to obtain a CM supramolecular precursor.

[0096] 25 mg of the CM supramolecular precursor was added to 30 mL of iodine-acetone solution and sonicated for 1 hour to completely disperse the CM supramolecular precursor, resulting in a dispersion. The dispersion was then poured into a 50 mL centrifuge tube and centrifuged at 800 rpm for 10 minutes to remove larger particles. The supernatant was used as the electrolyte and electrophoresed for 20 minutes at 100 V DC with FTO as the cathode and anode to obtain a CM supramolecular precursor film, designated CM / FTO. The iodine-acetone solution was prepared by weighing 4 mg of elemental iodine and adding it to 30 mL of acetone solution until the iodine completely dissolved. The distance between the cathode and anode electrodes was 4 cm.

[0097] CM / FTO was placed in the middle end of a quartz boat, and 500 mg of melamine was placed at the other end of the quartz boat. After covering and sealing with aluminum foil, the quartz boat was placed in a tube furnace and heated to 550°C at a heating rate of 4°C / min under a nitrogen atmosphere. After calcination for 4 hours, a graphite phase carbon nitride film was obtained, which was recorded as CN / FTO.

[0098] The preparation method of the graphite phase carbon nitride film of Examples 7 to 12 of the present application is roughly the same as the preparation method of the graphite phase carbon nitride film of Example 1. The difference is that the electrophoresis time, calcination temperature, calcination time, and calcination atmosphere of Examples 7 to 12 are different from those of Example 1. The electrophoresis time, calcination temperature, calcination time, and calcination atmosphere of Examples 7 to 12 are shown in Table 1.

[0099] Table 1 Electrophoresis time, calcination temperature, calcination time, calcination atmosphere of Examples 7 to 12

[0100] Electrophoresis time (min) Calcination temperature (℃) Calcination time (h) Calcination atmosphere Example 7 5 550 4 Nitrogen Example 8 10 550 4 Nitrogen Example 9 30 550 4 Nitrogen Example 10 20 550 2 Nitrogen Example 11 20 550 6 Nitrogen Example 12 20 550 4 Argon

[0101] XRD is used for qualitative analysis of samples. Figure 2 As shown, the XRD pattern shows (100) and (002) peaks at 13.2° and 27.6° in addition to the six peaks of FTO, indicating the successful synthesis of CN / FTO without other impurities. Figure 2 In (a), as the calcination temperature increases, the crystallinity of CN / FTO increases accordingly. However, when the temperature rises to 580 °C, the conductive material on the FTO surface (FTO doped with SnO2) is destroyed, resulting in a weakening of the FTO peak. Figure 2 In (b), as the amount of CM supramolecular precursor film increases, the characteristic peak XRD of carbon nitride shows an increasing trend, indicating that the thickness of CN / FTO increases. Secondly, the crystallinity of CN / FTO is explored by different calcination times, such as Figure 2As shown in (c), with the increase of calcination time, the (002) characteristic peak of CN / FTO shows an increasing trend, but the difference between calcination for 6h and calcination for 4h is not much. Therefore, the crystallinity of CN / FTO under different inert atmospheres was explored at 550℃, electrophoresis for 20min, and calcination for 4h. Figure 2 As shown in (d), the crystallinity of CN / FTO in nitrogen atmosphere is much better than that in argon atmosphere. In summary, the crystallinity of CN / FTO prepared by electrophoresis for 20 min, calcination for 4 h in N2 atmosphere is the best, which is conducive to photoelectrocatalytic reaction.

[0102] FT-IR and XPS analysis were further performed on CN / FTO calcined at 550℃. Figure 3 As shown in (a), at 800 cm -1 The vibration is caused by the breathing vibration of tri-S-triazine unit, 1200~1600cm -1 The vibration caused by the hybrid ring of CN / FTO is 3000~3200cm -1 The vibration at is caused by the NH and OH bonds adsorbed in the air. Figure 3 (b) shows that the photoanode contains only C and N elements. Figure 3 (c) is the C1s XPS spectrum, and the XPS spectra at 281.7 eV and 284.7 eV correspond to the CC and C=NC coordinated N1s, respectively. Figure 3 The four peaks at 396.7 eV, 398.3 eV and 399.4 eV in (d) correspond to C=NC, N-(C)3 and NH coordination, respectively. Their FT-IR spectrum and XPS spectrum are consistent with XRD, indicating the successful preparation of CN / FTO.

[0103] In order to explore the effect of different temperatures on the structure and elements of CN / FTO, scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) tests were performed on CN / FTO at different temperatures. Figure 4 As shown. CN / FTO obtained by calcination at different temperatures has the same structure, which is composed of a dendritic structure composed of upright flake structures and spheres. This structure has a large void and specific surface area, which is conducive to the refraction of light and thus increases the absorption of light. In addition, the porous structure of CN / FTO may be caused by the sublimation of iodine during the heating process. Among them, EDS analysis of CN / FTO calcined at 550℃ was performed, as shown Figure 4 As shown in (m~p), the CN / FTO contains only carbon and nitrogen elements, and no iodine element exists, which proves that the prepared CN / FTO has a high purity.

[0104] CN / FTO shows light absorption within 480nm. CN / FTO prepared by calcination at 500℃ and 520℃ show the same absorption edge, while the absorption edge of CN / FTO prepared by calcination at 550℃ shows a slight red shift and a significant red shift at 580℃. According to the UV-vis spectrum and Tauc equation fitting, as shown in Figure 5 As shown in (b), the band gaps at 500°C, 520°C, and 550°C are 2.78 eV, 2.78 eV, and 2.76 eV, respectively. This demonstrates that as the crystallinity of CN / FTO increases, the semiconductor band gap decreases, which is beneficial for expanding the semiconductor material's absorption range of visible light.

[0105] For carbon nitride materials, the high recombination rate of photogenerated electrons and holes is also one of the defects that limit its application. Therefore, the recombination of carriers is suppressed by improving the crystallinity of CN / FTO. Figure 5 As shown in (c), with the increase of crystallinity of CN / FTO, the defects in the CN / FTO body are reduced, the recombination of carriers is suppressed, the separation of photogenerated electrons and holes is promoted, and the performance of the semiconductor material is improved.

[0106] Combining the results of UV-vis spectrum and Mott-Schottky diagram, the energy band diagram of CN / FTO calcined at different temperatures was calculated, such as Figure 5 (e) The results show that CN / FTO with different crystallinity has different energy band positions, which in turn affects the photoelectrocatalytic performance.

[0107] The thickness of CN / FTO plays a crucial role in the absorption of light. The thicker the film, the higher the absorption of visible light. Figure 6 As shown in (a), with the increase of electrophoresis time, the thickness of the supramolecular precursor film gradually increases, which increases the absorption intensity of CN / FTO to light. However, the light absorption intensity when the electrophoresis time is 30 min is less than that of 20 min. This may be because the electrophoresis time is too long, which causes the supramolecular precursor film to fall off, making the thickness of the supramolecular precursor film less than that of the supramolecular precursor film after 20 min electrophoresis. As a result, the thickness of CN / FTO prepared after 30 min electrophoresis is less than that of CN / FTO prepared after 20 min electrophoresis. According to the UV-vis spectrum and Tauc equation fitting, as shown in Figure 6 As shown in (b), the band gap widths for electrophoresis times of 5 min, 10 min, 20 min, and 30 min are 2.65 eV, 2.73 V, 2.76 eV, and 2.71 eV, respectively. As the thickness of CN / FTO increases, the number of internal defect states increases, which reduces the recombination rate of photogenerated electrons and holes in CN / FTO. Figure 6 (c) shown.

[0108] Combining the results of UV-vis spectrum and Mott-Schottky diagram, the energy band diagram of CN / FTO calcined at different temperatures was calculated, such as Figure 6 (e) shown.

[0109] In order to explore the effect of calcination atmosphere on the preparation of CN / FTO, CM / FTO was calcined in nitrogen and argon inert atmospheres. Figure 7 As shown in Figure 2, compared with N2 atmosphere, the UV-vis DRS of CN / FTO under calcination in Ar atmosphere has a significant red shift, indicating that the argon component is beneficial to reducing the band gap width of CN / FTO, as shown in Figure 2. Figure 7 (a) and Figure 7 As shown in (b), calcination under argon causes carbon vacancies in CN / FTO, accompanied by the generation of more amino groups, making it a recombination site for photogenerated electrons and holes, as shown in Figure 7 (c) shown.

[0110] Combining the results of UV-vis spectrum and Mott-Schottky diagram, the energy band diagram of CN / FTO calcined at different temperatures was calculated, such as Figure 7 As shown in (e), the results show that although CN / FTO prepared under argon reduces the semiconductor band gap width and increases the absorption range of ultraviolet and visible light, it will produce more amino radicals, which intensifies the recombination of photogenerated electrons and holes.

[0111] Photoelectrochemical tests of CN / FTO prepared at different temperatures Figure 8 As shown. Figure 8 As can be seen from (a), the photocurrent density of CN / FTO increases with the increase of preparation temperature in the range of 500-550℃, and is 45μA / cm at 1.23V vs.RHE. 2 、30μA / cm 2 , 24μA / cm 2 However, during the preparation of CN / FTO calcined at 580℃, the SnO2 doped on the FTO surface was destroyed, making it impossible to measure. Figure 8 (b) shown.

[0112] EIS test is usually used to characterize the transfer resistance of semiconductor material interface. The smaller the arc radius of semiconductor material, the smaller the interface transfer resistance. We tested the CN / FTO interface transfer resistance under 1 sun intensity and 1.23V vs. RHE. Figure 8As shown in (c), with the increase of temperature, the EIS arc radius decreases, indicating that the higher the temperature, the smaller the interface transfer resistance. The results show that the improvement of CN / FTO crystallinity helps to improve the interface transfer resistance of CN / FTO, expand the ultraviolet-visible light absorption range and reduce the recombination rate of photoelectrons and holes, thereby increasing the photocurrent density.

[0113] Different thicknesses of CN / FTO mainly affect the migration distance of carriers within the material. The carriers generated by CN / FTO have a specific survival time. When CN / FTO is too thin, although it will not affect the large migration of carriers, it will affect the absorption intensity of CN / FTO to light, thereby generating fewer photogenerated electrons and holes, thereby affecting the photoelectrocatalytic performance. If CN / FTO is too thick, the carriers will be "inactivated" before reaching the surface, thereby affecting the photoelectrocatalytic performance. Therefore, CM supramolecular precursor films of different thicknesses were prepared by different electrophoresis times to explore their effects. The performance of CN / FTO of different thicknesses is shown in Figure 2. Figure 9 As shown, from Figure 9 (a) It can be seen that with the increase of CN / FTO thickness, the photocurrent of CN / FTO gradually increases. Among them, the photocurrent density of CN / FTO prepared after electrophoresis for 20 min is the largest at 1.23 V vs. RHE, which is 45 μA / cm 2 ,like Figure 9 (b) shown.

[0114] The interfacial charge transfer resistance of CN / FTO with different thicknesses is shown in Figure 2. Figure 3 and Figure 9 As shown in (c), it can be seen from the figure that at 20 min, the interface charge transfer resistance of CN / FTO is the smallest, and it has a good photoelectric response, which is consistent with the Figure 9 (a) and Figure 9 (b) Corroboration.

[0115] The photoelectrocatalytic performance of CN / FTO prepared by calcining in different atmospheres is very different. Although CN / FTO prepared by calcining in argon has a larger UV-visible light absorption edge, thereby generating more photogenerated electrons and holes. However, due to the generation of more amino groups inside the prepared CN / FTO in argon atmosphere, the recombination of photogenerated electrons and holes is heavier. Figure 10 As shown in the figure, the photoanode performance of CN / FTO prepared under nitrogen is better than that prepared under argon. The photoanode performance of CN / FTO prepared under nitrogen and argon is 45μA / cm at 1.23V vs.RHE respectively. 2 and 29 μA / cm 2 .

[0116] The interfacial charge transfer resistance of CN / FTO with different thicknesses is shown in Figure 2. Figure 10 As shown in (c), it can be seen from the figure that the interface charge transfer resistance of CN / FTO prepared under nitrogen atmosphere is better than that of CN / FTO prepared under argon atmosphere, and has better photoelectric response. Figure 10 (a) and Figure 10 (b) Corroboration.

[0117] Comparative Example 1

[0118] The graphite carbon nitride film of Comparative Example 1 was prepared by adding 1.26 g of melamine and 1.29 g of cyanuric acid to 75 mL of deionized water and stirring for 12 hours. The precipitate was collected and washed twice with deionized water and twice with anhydrous ethanol to remove excess impurities. The washed precipitate was then dried in a vacuum drying oven at 60°C overnight to obtain a CM supramolecular precursor.

[0119] 30 mg of the CM supramolecular precursor was added to 30 mL of iodine-acetone solution and sonicated for 1 hour to completely disperse the CM supramolecular precursor, resulting in a dispersion. The dispersion was then poured into a 50 mL centrifuge tube and centrifuged at 500 rpm for 10 minutes to remove larger particles. The supernatant was used as the electrolyte and electrophoresed for 20 minutes at 100 V DC with FTO as the cathode and anode to obtain a CM supramolecular precursor thin film, designated CM / FTO. The iodine-acetone solution was prepared by weighing 5 mg of elemental iodine and adding it to 30 mL of acetone solution until the iodine completely dissolved. The distance between the cathode and anode electrodes was 2 cm.

[0120] The CM / FTO prepared by electrophoresis for 20 minutes was placed in a quartz boat and sealed with aluminum foil. The quartz boat was placed in a tube furnace and heated to 550°C at a heating rate of 3°C / min under a nitrogen atmosphere. After calcination for 4 hours, a graphite phase carbon nitride film was obtained. The graphite phase carbon nitride film prepared in Comparative Example 1 was as follows: Figure 1 (c) shown.

Claims

1. A method for preparing a graphite phase carbon nitride film, characterized in that: The following steps are involved: Step 1): Preparation of CM supramolecular precursor: Melamine and cyanuric acid are added to water and stirred to obtain a CM supramolecular precursor; Step 2): Preparation of CM supramolecular precursor film: adding the CM supramolecular precursor obtained in step 1) to an iodine-acetone solution to obtain an electrolyte, and using an electrophoresis method with FTO as the cathode and anode to deposit the CM supramolecular precursor film at the anode; Step 3): Preparation of graphite carbon nitride film: calcining the CM supramolecular precursor film obtained in step 2) with melamine under the protection of an inert gas to obtain; The calcination temperature in step 3) is 500-550° C., the heating rate in step 3-5° C. / min, and the calcination time is 2-6 hours; the electrophoresis time in step 2) is 5-30 minutes.

2. The method for preparing a graphite phase carbon nitride film according to claim 1, wherein: The molar ratio of melamine to cyanuric acid in step 1) is 1:1; the mass of melamine added per mL of water is 0.0168 g; in the iodine-acetone solution in step 2), the mass of iodine added per mL of acetone solution is 0.1 to 0.17 g, and the mass of CM supramolecular precursor added per mL of iodine-acetone solution is 0.67 to 1 mg.

3. The method for preparing a graphite phase carbon nitride film according to claim 1, wherein: The preparation method of the electrolyte described in step 2) is as follows: adding the CM supramolecular precursor to an iodine-acetone solution, ultrasonically obtaining a dispersion, centrifuging the dispersion and taking the turbid liquid; the centrifugal speed is 500-1000 r / min.

4. The method for preparing a graphite phase carbon nitride film according to claim 1, wherein: The distance between the cathode and the anode in step 2) is 2 to 4 cm; the voltage of the electrophoresis method is a DC voltage of 100 V.

5. The method for preparing a graphite phase carbon nitride film according to claim 1, wherein: The preparation method of the CM supramolecular precursor described in step 1) is as follows: melamine and cyanuric acid are added to water and stirred, centrifuged to obtain a precipitate, the precipitate is washed with water and anhydrous ethanol, and vacuum dried; the vacuum degree is 0.06-0.08 MPa, and the drying temperature is 60-80°C.

6. The method for preparing a graphite phase carbon nitride film according to claim 1, wherein: The inert gas in step 3) is nitrogen or argon.

7. A graphite phase carbon nitride film, characterized in that: The graphite phase carbon nitride film is prepared by the method for preparing the graphite phase carbon nitride film according to any one of claims 1 to 6.

8. A use of the graphite phase carbon nitride film according to claim 7, characterized in that: The graphite phase carbon nitride film is used in photoelectrocatalytic oxygen evolution.

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