1. A preparation method of a self-capture carbon nitride film is characterized in that dicyanodiamine and bicarbonate or carbonate powder are dissolved in a solvent and dried to obtain precursor powder; and putting the precursor powder into a crucible, covering the crucible with the pretreated substrate, heating to 500-600 ℃, and calcining for 4-5 hours to obtain the self-capture carbon nitride film.

2. The preparation method according to claim 1, wherein the mass ratio of dicyanodiamine to the bicarbonate or carbonate powder is 3-5: 1.

3. The method according to claim 1 or 2, wherein the bicarbonate is one or more of sodium bicarbonate, potassium bicarbonate or calcium bicarbonate; the carbonate is potassium carbonate.

4. The method according to claim 2, wherein the mass ratio of dicyanodiamine to the bicarbonate or carbonate powder is 4: 1.

5. The method according to claim 3, wherein the bicarbonate is potassium bicarbonate.

6. The method according to claim 1, wherein the temperature is raised to 500 ℃ to 600 ℃ at a temperature raising rate of 2.5 ℃/min.

7. The self-trapping carbon nitride film prepared by the preparation method of any one of claims 1 to 6.

8. A self-trapping photoanode comprising an electrically conductive substrate coated with the self-trapping carbon nitride film of claim 7.

9. The capture photoanode of claim 8, wherein the conductive substrate is FTO conductive glass.

10. Use of the self-trapping carbon nitride film of claim 7 or the self-trapping photoanode of any one of claims 8 to 9 in the protection of marine photocathodes.

Background

Electrochemical protection is a common means for marine corrosion protection, and is mainly divided into two methods, namely a cathode protection method of a sacrificial anode and an external direct current power supply method, but the former method has the problem of environmental pollution caused by cation dissolution, and the latter method needs larger economic expenditure, particularly for the protection of offshore and offshore island reef facilities. The photoelectric effect is utilized to carry out cathode protection, which has good natural advantages, and the main principle is that after the semiconductor material is irradiated by light, photo-generated electrons are transited from a valence band to a conduction band, and then the photo-generated electrons act on protected metal through an external lead, so that the cathode polarization of the protected metal is lower than the self-corrosion potential of the protected metal, and the protection is generated.

The carbon nitride material is widely applied to the fields of photocatalytic water splitting, photodegradation pollutants and photoelectrochemical cathode protection because of the advantages of low cost, controllable band gap, environmental friendliness and the like. Research shows that the valence band potential of the carbon nitride material is about 1.4V (vs NHE, pH 7), theoretically, the carbon nitride material can meet the requirement of oxidizing seawater, and can be directly applied to cathodic protection in a seawater environment. Taking photocathode protection as an example (other photocatalytically decomposing water, CO)₂Reduction of N₂Similar problems also exist in the fields of reduction and the like), most laboratory researches adopt hole trapping agents (sodium hydroxide, sodium sulfite and sodium sulfide) to improve the photoelectric separation efficiency, so that the protection of metal is realized, however, the practical application environment is quite different from the laboratory environment, similar hole trapping agents do not exist, and the method is not in line with the practical situation of on-site protection in the marine environment.

Disclosure of Invention

The present invention is directed to overcoming the above-mentioned deficiencies and drawbacks of the prior art and providing a self-trapping carbon nitride film.

The second purpose of the invention is to provide the application of the self-trapping carbon nitride film.

The above object of the present invention is achieved by the following technical solutions:

dissolving dicyanodiamine and bicarbonate or carbonate powder in a solvent, and drying to obtain precursor powder; and putting the precursor powder into a crucible, covering the crucible with the pretreated substrate, heating to 500-600 ℃, and calcining for 4-5 hours to obtain the self-capture carbon nitride film.

According to the method, bicarbonate or carbonate is introduced into the carbon nitride material through one-step vapor deposition, the bicarbonate is heated at a high temperature to generate the carbonate, the carbonate auxiliary agent promotes the optical absorption of the carbon nitride material, and the carbonate auxiliary agent plays an important role in delaying the irradiation recombination of electrons and holes; the modified carbon nitride film has the self-capturing characteristic, so that the consumption of photo-generated holes is promoted, the photoelectric conversion efficiency is obviously improved, and meanwhile, the coupling potential of the self-capturing carbon nitride film and 316 stainless steel generates cathode polarization during illumination, so that the metal is fully protected; OH generated by hydrolysis of the self-trapping carbon nitride film^-Endows the self-trapping cavity performance of the composite material, enables the composite material to show long-acting stable photoelectrochemical cathode protection performance in a seawater environment, and can realize in-situ protection without adding a cavity trapping agent.

Preferably, the mass ratio of dicyandiamide to bicarbonate or carbonate powder is 3-5: 1.

Further preferably, the bicarbonate is one or more of sodium bicarbonate, potassium bicarbonate or calcium bicarbonate; the carbonate is potassium carbonate.

Further preferably, the mass ratio of dicyanodiamine to bicarbonate or carbonate powder is 4: 1.

Further preferably, the bicarbonate is potassium bicarbonate.

Preferably, the solvent is deionized water.

Preferably, the temperature is raised to 500-600 ℃ at a rate of 2.5 ℃/min.

The invention also claims the self-capture carbon nitride film prepared by any one of the preparation methods.

The invention also provides a self-capture photoelectric anode which comprises a conductive substrate, wherein the self-capture carbon nitride film is coated on the conductive substrate. The preparation method of the self-capture photoelectric anode comprises the steps of replacing a substrate material with a conductive substrate in the process of preparing the self-capture carbon nitride film, placing the pretreated conductive substrate with the conductive surface facing downwards in a crucible with precursor powder for vapor deposition, and thus obtaining the self-capture photoelectric anode.

Preferably, the conductive substrate is FTO conductive glass; the pretreatment is that the FTO conductive glass is placed in 30mL acetone solution for ultrasonic cleaning for 30min, and then deionized water is adopted for repeated washing, and drying is carried out at room temperature.

The invention aims at the actual situation that the existing laboratory-made photocathode protection system excessively depends on a hole trapping agent to enhance the photoelectric separation efficiency and seriously does not accord with the in-situ protection in the marine environment. The carbon nitride film with self-trapping performance is constructed by utilizing a vapor deposition technology and is applied to photoelectrochemical cathodic protection of metal. OH generated by hydrolysis of the film^-Endows the material with self-trapping cavity performance, and leads the material to show long-acting stable photoelectrochemistry cathode protection performance in seawater environment (long-acting for 8 hours, and the performance retention rate reaches 80%).

Therefore, the invention also provides the application of the self-capture carbon nitride film or the self-capture photo-anode in the protection of the marine photo-cathode, namely the application in marine corrosion prevention.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, bicarbonate or carbonate is introduced into the carbon nitride material through a vapor deposition technology, the carbonate auxiliary agent promotes optical absorption of the carbon nitride material, delays irradiation recombination of electrons and holes, promotes consumption of photoproduction holes, remarkably improves photoelectric conversion efficiency, and prepares the carbon nitride film with self-capture performance, and OH generated by hydrolysis of the film^-Endows the self-trapping cavity performance of the photoelectric material, and leads the photoelectric material to show long-acting stable photoelectricity in the seawater environmentChemical cathodic protection performance (long-acting for 8 hours, and the performance retention rate reaches 80%). When the photoanode film material with the self-capture function is applied to a photocathode protection system in a seawater environment, the in-situ protection can be realized without adding a hole capture agent, and the photoanode film material is long-acting and stable, so that the foundation is laid for future industrialization.

Drawings

FIG. 1 is an XRD spectrum of a carbon nitride thin film material. Wherein CN is the carbon nitride film, S-CN is the self-capture carbon nitride film.

Fig. 2 shows an ultraviolet spectrum and a fluorescence emission spectrum of the carbon nitride thin film. Wherein, a) a UV-vis spectrum; b) photoluminescence spectroscopy.

FIG. 3 shows the photo-induced current density curves (a, b) and photo-induced open circuit potential variation curves (c, d) of the carbon nitride film in 3.5 wt% NaCl electrolyte (without hole trapping agent).

FIG. 4 is a graph of the corrosion protection performance of a self-trapping carbon nitride film against metal materials. a) The photoelectrochemical cathode protection performance of the carbon nitride film material in the marine environment; b) long-acting photoelectrochemical cathodic protection of self-trapping films.

FIG. 5 shows a self-trapping carbon nitride film (S-CN-KHCO)₃) Photoelectrochemical cathodic protection in extreme pH marine environments; b) the pH of the self-trapping film changes during the open and dark tests.

Detailed Description

The invention is further described with reference to the drawings and the following detailed description, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Unless otherwise indicated, reagents and materials used in the following examples are commercially available.

Example 1

A preparation method of a self-trapping carbon nitride film comprises the following steps:

s1, pretreating FTO conductive glass, placing the FTO conductive glass in 30mL of acetone solution, ultrasonically cleaning for 30min, repeatedly washing with deionized water, and drying at room temperature;

s2, dissolving dicyandiamide and sodium bicarbonate powder in 50mL of deionized water according to the mass ratio of 4:1, and evaporating to dryness (magnetic stirring and heating) at 90 ℃ to obtain precursor powder;

s3, placing the FTO pretreated in the step S1 in an alumina crucible with a cover and precursor powder with the conductive surface facing downwards, then placing the alumina crucible in a muffle furnace, and calcining at 550 ℃ for 4h at a heating rate of 2.5 ℃/min to obtain the self-trapping carbon nitride film.

Example 2

A preparation method of a self-trapping carbon nitride film comprises the following steps:

s1, pretreating FTO conductive glass, placing the FTO conductive glass in 30mL of acetone solution, ultrasonically cleaning for 30min, repeatedly washing with deionized water, and drying at room temperature;

s2, dissolving dicyandiamide and potassium bicarbonate powder in 50mL of deionized water according to a ratio (mass ratio) of 4:1, and evaporating to dryness (magnetic stirring and heating) at 90 ℃ to obtain precursor powder;

s3, placing the FTO pretreated in the step S1 in an alumina crucible with a cover and precursor powder with the conductive surface facing downwards, then placing the alumina crucible in a muffle furnace, and calcining at 550 ℃ for 4h at a heating rate of 2.5 ℃/min to obtain the self-trapping carbon nitride film.

Example 3

A preparation method of a self-trapping carbon nitride film comprises the following steps:

s1, pretreating FTO conductive glass, placing the FTO conductive glass in 30mL of acetone solution, ultrasonically cleaning for 30min, repeatedly washing with deionized water, and drying at room temperature;

s2, dissolving dicyandiamide and calcium bicarbonate powder in 50mL of deionized water according to a ratio (mass ratio) of 4:1, and evaporating to dryness (magnetic stirring and heating) at 90 ℃ to obtain precursor powder;

s3, placing the FTO pretreated in the step S1 in an alumina crucible with a cover and precursor powder with the conductive surface facing downwards, then placing the alumina crucible in a muffle furnace, and calcining at 550 ℃ for 4h at a heating rate of 2.5 ℃/min to obtain the self-trapping carbon nitride film.

Example 4

A method for producing a self-trapping carbon nitride thin film, substantially the same as in example 2, except that potassium hydrogencarbonate in step S2 was replaced with potassium carbonate, and carbonate was directly added.

Test example 1

XRD tests of the carbon nitride thin film materials prepared in examples 1-3 were carried out, and XRD patterns (CN: carbon nitride thin film, S-CN: self-trapping carbon nitride thin film) of the carbon nitride thin film materials are shown in FIG. 1, and it can be seen that characteristic peaks of S-CN and CN show almost the same characteristic peaks, which shows that the structure of the carbon nitride material is not changed by introducing the bicarbonate, and at the same time, a series of carbon nitride thin film materials on the surface of FTO are successfully obtained.

Test example 2

The optical information of the self-trapping carbon nitride films of examples 1-3 was explored by ultraviolet spectroscopy and fluorescence emission spectroscopy of potassium, sodium and calcium bicarbonate. As shown in FIG. 2, the carbonate auxiliary agent promotes the optical absorption of the carbon nitride material, the absorption wavelength is broadened to 500-600nm, and the band gap is shortened to 2.36-2.47 eV. In addition, the self-trapping film shows a weaker fluorescence emission peak, indicating that the carbonate promoter plays an important role in delaying the radiative recombination of electrons and holes.

Test example 3

A3.5 wt% NaCl electrolyte is used to simulate the marine environment, and no hole trapping agent is added in all test processes. Electrochemical tests all adopt a three-electrode system (Ag/AgCl is used as a reference electrode, a Pt sheet is used as a counter electrode), a CHI600e electrochemical workstation records the photoelectrochemical properties of the carbon nitride film, and a Porphy xenon lamp (PLS-SXE300/300UV) is used for simulating sunlight.

A photoinduced current density test is carried out to explore the photoelectric conversion efficiency of the carbon nitride series materials in a seawater environment. As a result, as shown in FIG. 3, a carbon nitride film (CN) was drop-coated_coating) Shows obvious p-type semiconductor characteristics (-3 muA/cm)²Negative current after light irradiation), vapor deposition of the prepared film (CN)_tvd) Exhibit weak n-type semiconductor characteristics (3 muA/cm)²Generating a forward current upon illumination). In comparison, S-CN showed significantn-type semiconductor features, the photo-induced current density increased to 8 times that of CN. Accordingly, the same trend was shown for the photo-potential of CN, with an anodic polarization of the photo-potential of about 29mV for drop-coated carbon nitride films and a cathodic polarization of 300mV for S-CN. The result shows that the self-trapping characteristic promotes the consumption of the photo-generated holes and obviously improves the photoelectric conversion efficiency.

Test example 4

The corrosion protection performance of the self-capture carbon nitride film on metal materials is researched by coupling 316 stainless steel with the self-capture carbon nitride film and taking an open-circuit potential as a cathodic protection evaluation mode and simulating the marine environment electrolyte with 3.5 wt% of NaCl.

As a result, as shown in FIG. 4, the coupling potential of the drop-coated carbon nitride material and 316 stainless steel is polarized anodically (electrons flow from 316 stainless steel to carbon nitride material) upon illumination, indicating that this process promotes corrosion of 316 stainless steel; and the coupling potential of the self-capture carbon nitride film and 316 stainless steel generates cathode polarization in illumination, and the polarization potential reaches 300mV, which indicates that the self-capture carbon nitride film provides sufficient protection for metal. It is worth mentioning that the self-trapping film is 316 stainless steel which can provide long-term protection for 8 hours, and the performance retention rate can still maintain about 80% after 8 hours. The direct use of carbonate as an additive (example 4) provided superior photocathode protection for 316 stainless steel (superior to pure carbon nitride materials, although less than bicarbonate as an additive), confirming that carbonate also has the property of imparting self-trapping properties to carbon nitride materials.

Test example 5

The self-capture film is placed in different pH test environments, the open circuit potential drop during illumination is used as an evaluation index, the pH of the self-capture film is monitored during open/dark under a neutral condition, the relation between the pH and the potential is explored, and the self-capture characteristic of the film material is verified.

As a result, as shown in fig. 5a, the self-trapping thin film shows stable n-type semiconductor characteristics in both strongly acidic and strongly alkaline electrolytes, and shows a photo-induced open circuit potential performance far superior to that under the strongly alkaline condition. This phenomenon indicates that the pH of the electrolyte has a large influence on the photoelectric properties of the material, namely: the more alkaline the product isLarge, the more negative its cathodic polarization termination potential and the greater the photoinduced potential drop. In other words, the more basic, the more strongly the photocathode protective properties. As shown in fig. 5b, the self-trapping carbon nitride material was irradiated in a neutral electrolyte environment (pH 7) for a while, and then its pH increased significantly, and was returned to neutral after being shielded from light for a while. This phenomenon indicates that the process of illumination enhances the alkalinity of the electrolyte, i.e., OH exists during the process of illumination and light shielding^-Generation and disappearance of the cell. This phenomenon confirms the self-trapping properties of the carbon nitride film, namely: hydrolysis of carbonate to OH upon irradiation^-OH formed by hydrolysis^-The consumption of the holes is promoted, and therefore, the excellent photoelectric cathode protection performance in a seawater environment is realized.