Preparation method of carboxyl-modified polymer carbon nitride thin film electrode

Abstract

The present invention provides a method for modifying a polymer carbon nitride thin film electrode. Dicyandiamide and cyanuric acid are mixed and ground evenly as a precursor, and then it is evenly spread on the bottom of a heat-resistant carrier. The FTO conductive layer is directly placed flat upward on the precursor and wrapped with materials such as tin foil, and then the heat-resistant carrier is placed in a heating device. Under the protection of an atmosphere, the heating device is heated to 550<supgt;o< / supgt;C and maintained for 2 h and then cooled to room temperature. The polymer carbon nitride thin film electrode can be obtained. Then, the prepared polymer carbon nitride thin film electrode is placed in an ethanol solution containing different amounts of guanidine hydrochloride, and after treatment by the solvothermal method, the carboxyl-modified polymer carbon nitride thin film electrode can be prepared. The polymer carbon nitride thin film prepared by this method has good uniformity and high repeatability, and the photoelectrochemical performance is significantly improved compared with that of the polymer carbon nitride thin film before modification.

Description

Technical Field

[0001] The present invention relates to the field of thin film modification technology and photoelectrochemistry, and specifically relates to a method for modifying a polymer carbon nitride thin film electrode. Background Art

[0002] Photoelectrochemical water splitting technology is one of the effective ways to solve the world's energy problems. Among semiconductor materials used as photoanodes, polymer carbon nitride (CN) has received extensive attention from domestic and foreign researchers as a photoanode due to its moderate bandgap (2.7 eV), suitable positions of the conduction band and valence band that are easy to regulate, and stable physical and chemical properties. However, the currently prepared polymer carbon nitride thin film electrodes have problems such as poor conductivity and severe charge recombination, resulting in poor optoelectronic performance, which affects the application of CN in the field of photoelectrochemistry. Introducing functional groups on the surface of polymer carbon nitride thin film electrodes can regulate their surface electronic structure and thus improve the photoelectrochemical performance of CN ( Sustainable Energy Fuels , 2020, 4, 485 - 503). For example, research shows that the introduction of carboxyl groups can regulate the affinity on the surface of the catalyst, and the electron-withdrawing carboxyl groups can also effectively lower the position of the conduction band and improve the separation efficiency of electrons and holes. Currently, the post-treatment method is generally used to prepare carboxyl-modified polymer carbon nitride in powder form. 1. Polymer carbon nitride powder is treated in a nitric acid aqueous solution and then heat-treated; 2. refluxed in a nitric acid aqueous solution at a certain temperature. ( Chemical Engineering Journal , 2021, 414:128810; Applied Catalysis B: Environmental , 2020, 266, 118590; InfoMat . 2022; 4(1):e12273) However, since the binding property between polymer carbon nitride and the substrate will be fatally affected in an aqueous solution and high-temperature environment, the thin film often falls off. Therefore, in the present invention, a polymer carbon nitride thin film is first prepared by chemical vapor deposition technology, and then a carboxyl-modified polymer carbon nitride thin film is obtained by solvothermal post-treatment in an alcohol solution of guanidine hydrochloride. The recombination rate of photogenerated electrons and holes of the modified thin film is reduced, and the injection efficiency is improved, thereby improving its photoelectrochemical performance. The photoelectrochemical performance of the modified thin film is much higher than that of the untreated polymer carbon nitride. Summary of the Invention

[0003] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a method for modifying a polymer carbon nitride thin film electrode with a simple process. Through solvation treatment with guanidine hydrochloride, hydroxyl groups are generated on the polymer carbon nitride, reducing the recombination efficiency of photogenerated electrons and holes, enhancing the optoelectronic performance of the electrode, and expanding the application of polymer carbon nitride thin film electrodes in the field of photoelectrochemistry.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions, which specifically include the following steps:

[0005] (1) Mix dicyandiamide and cyanuric acid and grind them evenly, then use the gas-phase deposition method with the mixture as a precursor to prepare a polymer carbon nitride thin film electrode;

[0006] (2) Place the prepared polymer carbon nitride thin film electrode into the inner lining of a reaction kettle containing a certain amount of guanidine hydrochloride solution;

[0007] (3) Heat the heating device to a certain temperature and react for a certain time to obtain the modified polymer carbon nitride thin film electrode.

[0008] In the step (1), the heat-resistant carrier in the gas-phase deposition process is a porcelain boat, a corundum boat or a quartz boat.

[0009] The heat-resistant carrier is subjected to a sealing treatment.

[0010] In the step (1), the heat treatment atmosphere in the gas-phase deposition method includes N 2 , Ar.

[0011] In the step (1), in the gas-phase deposition method, the temperature is raised to 500 - 600 °C at a heating rate of 2 - 8 °C / min.

[0012] The mass ratio of the dicyandiamide to the cyanuric acid is 2:0.6 - 1.2.

[0013] In the step (2), the concentration of the guanidine hydrochloride solution is between 0.5 - 5 mol / L.

[0014] The solvent of the solution is ethanol or methanol.

[0015] The reaction temperature is 140 °C - 200 °C, and the reaction time is 1 - 24 hours.

[0016] The polymer carbon nitride thin film electrode is a carboxyl-modified polymer carbon nitride thin film electrode.

[0017] Compared with the prior art, the advantages of the present invention are as follows:

[0018] The present invention uses guanidine hydrochloride as a solvent and alcohol as a solution to perform solvothermal post-treatment on the polymer carbon nitride thin film, so that the polymer carbon nitride thin film obtains carboxyl groups, improves the injection efficiency, reduces the photogenerated electron-hole recombination rate, and improves the photoelectrochemical performance. The present invention can perform modification treatment on the prepared thin film, and its modified photoelectrochemical performance is much higher than that of the untreated polymer carbon nitride before. The present invention provides a method for modifying an in-situ deposited polymer carbon nitride thin film electrode, with a simple process and low cost. Description of the Drawings

[0019] Figure 1Shown are the X-ray diffraction spectra of the polymer carbon nitride thin film electrodes prepared on the FTO surface at 550 °C in Example 1 and Example 2, compared with those after modification with guanidine hydrochloride.

[0020] Figure 2 Shown are the tracing diagrams of the polymer carbon nitride thin film electrodes prepared on the FTO surface at 550 °C in Example 1 and Example 2, and the scanning electron microscope images after modification with guanidine hydrochloride.

[0021] Figure 3 Shown is the photocurrent performance diagram of the polymer carbon nitride thin film electrodes prepared on the FTO surface at 550 °C in Example 1 and Example 2 after modification with guanidine hydrochloride.

[0022] Figure 4 Shown are the X-ray photoelectron spectra (O 1s) of the polymer carbon nitride thin films (CN) prepared on the FTO surface at 550 °C in Example 1 and Example 2 and those after modification (CN-GH).

[0023] Figure 5 Shown are the fluorescence emission spectra of the polymer carbon nitride thin films (CN) prepared on the FTO surface at 550 °C in Example 1 and Example 2 and those after modification (CN-GH).

[0024] Figure 6 Shown is the process diagram of the present invention. Detailed implementation manners

[0025] A method for preparing and modifying a polymer carbon nitride thin film electrode of the present invention includes the following steps:

[0026] First step: Mix and grind the polymer carbon nitride precursor evenly, and then spread it evenly on the bottom of the heat-resistant carrier; Second step: Place the substrate directly on top of the precursor and wrap it with materials such as tin foil, and then place the heat-resistant carrier in the heating device;

[0027] Third step: Heat the heating device to 550 °C and keep it for 2 hours, then cool it to room temperature to obtain the polymer carbon nitride thin film electrode;

[0028] Fourth step: Dissolve different amounts of guanidine hydrochloride in ethanol, and put the prepared polymer carbon nitride thin film electrode and the solution into a reaction kettle with a polytetrafluoroethylene inner liner;

[0029] Fifth step: Place the reaction kettle in a hydrothermal box, heat it to 180 °C and keep it for 8 hours, then cool it to room temperature to obtain the modified polymer carbon nitride thin film electrode.

[0030] The prepared thin film is polymer carbon nitride.

[0031] The substrate material is fluorine-doped tin oxide (FTO), etc.

[0032] The heating device is a tube furnace, a hydrothermal box, etc.

[0033] The schematic diagram of the preparation process of the present invention is as Figure 6 shown. Except as otherwise specified, all raw materials used are of analytical purity.

[0034] Example 1

[0035] Weigh 2.66 g of dicyandiamide and 1.33 g of cyanuric acid at room temperature, mix the two, place the mixture in a mortar and grind and mix evenly to obtain a carbon nitride precursor; then evenly spread the precursor on the bottom of a ceramic crucible and place the FTO substrate on it; then wrap the ceramic crucible containing the precursor with tin foil and place it in a tube furnace; finally, heat the precursor to 550 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and hold for 2 hours, and after the reaction is completed, naturally cool to room temperature, and a polymer carbon nitride thin film electrode is formed on the FTO substrate.

[0036] Example 2

[0037] Weigh 2.66 g of dicyandiamide and 1.33 g of cyanuric acid at room temperature, mix the two, place the mixture in a mortar and grind and mix evenly to obtain a carbon nitride precursor; then evenly spread the precursor on the bottom of a ceramic crucible and place the FTO substrate on it; then wrap the ceramic crucible containing the precursor with tin foil and place it in a tube furnace; then, heat the precursor to 550 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and hold for 2 hours, and after the reaction is completed, naturally cool to room temperature, and a polymer carbon nitride thin film is formed on the FTO substrate. Place the prepared thin film in a reaction kettle with a polytetrafluoroethylene inner liner, and the inner liner contains an ethanol solution dissolved with 0.65 g of guanidine hydrochloride; finally, heat the heating device to 180 °C and hold for 8 h. After the reaction is completed, naturally cool to room temperature, and a modified polymer carbon nitride thin film electrode is obtained.

[0038] Example 3

[0039] Weigh 2.66 g of dicyandiamide and 1.33 g of cyanuric acid at room temperature, mix the two, and place the mixture in a mortar for grinding and mixing evenly to obtain a carbon nitride precursor; then evenly spread the precursor on the bottom of a ceramic crucible and place the FTO substrate on it; then wrap the ceramic crucible containing the precursor with tin foil and place it in a tube furnace; then, under an argon atmosphere, heat the precursor to 550 °C at a heating rate of 5 °C / min and hold for 2 hours. After the reaction is completed, cool it naturally to room temperature. A polymer carbon nitride film is formed on the FTO substrate. Place the prepared film in a reaction kettle with a polytetrafluoroethylene inner liner, and the inner liner contains an ethanol solution in which 0.65 g of guanidine hydrochloride is dissolved; finally, raise the temperature of the heating device to 180 °C and hold for 8 h. After the reaction is completed, cool it naturally to room temperature to obtain a modified polymer carbon nitride film electrode.

[0040] Example 4

[0041] Weigh 2.66 g of dicyandiamide and 1.33 g of cyanuric acid at room temperature, mix the two, and place the mixture in a mortar for grinding and mixing evenly to obtain a carbon nitride precursor; then evenly spread the precursor on the bottom of a ceramic crucible and place the FTO substrate on it; then wrap the ceramic crucible containing the precursor with tin foil and place it in a tube furnace; then, under an argon atmosphere, heat the precursor to 550 °C at a heating rate of 5 °C / min and hold for 2 hours. After the reaction is completed, cool it naturally to room temperature. A polymer carbon nitride film is formed on the FTO substrate. Place the prepared film in a reaction kettle with a polytetrafluoroethylene inner liner, and the inner liner contains an ethanol solution in which 0.5 g of guanidine hydrochloride is dissolved; finally, raise the temperature of the heating device to 180 °C and hold for 8 h. After the reaction is completed, cool it naturally to room temperature to obtain a modified polymer carbon nitride film electrode.

[0042] Example 5

[0043] Weigh 2.66 g of dicyandiamide and 1.33 g of cyanuric acid at room temperature, mix the two, and place the mixture in a mortar for grinding and mixing evenly to obtain a carbon nitride precursor; then evenly spread the precursor on the bottom of a ceramic crucible and place the FTO substrate on it; then wrap the ceramic crucible containing the precursor with tin foil and place it in a tube furnace; then, under an argon atmosphere, heat the precursor to 550 °C at a heating rate of 5 °C / min and hold for 2 hours. After the reaction is completed, cool it naturally to room temperature. A polymer carbon nitride film is formed on the FTO substrate. Place the prepared film in a reaction kettle with a polytetrafluoroethylene inner liner, and the inner liner contains an ethanol solution in which 0.75 g of guanidine hydrochloride is dissolved; finally, raise the temperature of the heating device to 180 °C and hold for 8 h. After the reaction is completed, cool it naturally to room temperature to obtain a modified polymer carbon nitride film electrode.

[0044] Example 6

[0045] Weigh 2.66 g of dicyandiamide and 1.33 g of cyanuric acid at room temperature and mix the two. Place the mixture in a mortar and grind and mix evenly to obtain a carbon nitride precursor. Then, evenly spread the precursor on the bottom of a ceramic crucible and place the FTO substrate on it. After that, wrap the ceramic crucible containing the precursor with tin foil and place it in a tube furnace. Then, heat the precursor to 550 °C at a heating rate of 5 °C / min in an argon atmosphere and hold for 2 hours. After the reaction is completed, naturally cool to room temperature, and a polymer film will be formed on the FTO substrate. Place the prepared film in a reaction kettle with a polytetrafluoroethylene inner liner, and the inner liner contains an ethanol solution in which 0.8 g of guanidine hydrochloride is dissolved. Finally, raise the temperature of the heating device to 180 °C and hold for 8 h. After the reaction is completed, naturally cool to room temperature to obtain a modified polymer carbon nitride film electrode.

[0046] Example 7

[0047] The method and steps are the same as those in Example 6, except that the amount of guanidine hydrochloride used is 0.7 g, and a polymer carbon nitride film electrode is prepared.

[0048] Table 1 Relationship table between the amount of guanidine hydrochloride solute used and the improvement efficiency of photocurrent density

[0049]

Claims

1. A preparation method of a carboxyl-modified polymer carbon nitride thin film electrode, characterized in that: It includes the following steps: (1) Mix dicyandiamide and cyanuric acid and grind them evenly, and then use the gas-phase deposition method with the mixture as a precursor to prepare a polymer carbon nitride thin film electrode; (2) Place the prepared polymer carbon nitride thin film electrode in a reaction kettle with a polytetrafluoroethylene inner liner, where the inner liner contains an ethanol solution dissolved with 0.65 g of guanidine hydrochloride; finally, heat the heating device to 180 °C and keep it for 8 h to obtain the modified polymer carbon nitride thin film electrode.

2. The preparation method of the carboxyl-modified polymer carbon nitride thin film electrode according to claim 1, characterized in that: The heat-resistant carrier in the gas-phase deposition process in step (1) is a porcelain boat, a corundum boat or a quartz boat.

3. The preparation method of the carboxyl-modified polymer carbon nitride thin film electrode according to claim 2, characterized in that: The heat-resistant carrier is subjected to a sealing treatment.

4. The preparation method of the carboxyl-modified polymer carbon nitride thin film electrode according to claim 1, characterized in that: In the gas-phase deposition method in step (1), the heat treatment atmosphere includes N 2 , Ar.

5. The preparation method of the carboxyl-modified polymer carbon nitride thin film electrode according to claim 1, characterized in that: In the gas-phase deposition method in step (1), the temperature is raised to 500 - 600 °C at a heating rate of 2 - 8 °C / min.

6. The preparation method of the carboxyl-modified polymer carbon nitride thin film electrode according to claim 1, characterized in that: The mass ratio of dicyandiamide to cyanuric acid is 2:0.6 - 1.2.

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