A simple and scalable preparation method for double Z-type heterojunction photoanode film and its application in marine engineering

Abstract

The present application provides a simple and scalable preparation method for a double Z-type heterojunction photoanode film and its marine engineering application. The preparation method is as follows: (1) solution preparation: dissolving indium salt and cadmium salt in deionized water to form a first solution; dissolving vanadate and molybdate in warm water to form a second solution; (2) precipitation method: slowly adding the second solution to the first solution, adjusting the pH to obtain a precipitate, washing and drying, and calcining at high temperature to obtain InVO4–CdMoO4 nanoparticles; (3) ion layer deposition method: immersing the InVO4–CdMoO4 nanoparticles in a cadmium salt solution and a Na2S solution in sequence, and generating CdS through multiple cycles of deposition to obtain an InVO4–CdMoO4–CdS double Z-type heterostructure. The double Z-type heterojunction photoanode film prepared by the co-precipitation and ion layer deposition method of the present invention can provide multiple, directional charge separation channels through CdMoO4 as an "electron trap" and "recombination center", effectively improving the cyclic stability of the photoanode photoelectric reaction and enhancing the durability of marine engineering structures.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion inhibition of marine engineering structural metal materials, and specifically relates to a simple and scalable preparation method of a double Z-type heterojunction photoanode film and its marine engineering application. Background Art

[0002] Marine infrastructure is exposed to extreme operating environments for extended periods, facing multiple corrosion threats. Critical structures such as offshore energy installations, underwater transportation systems, and cross-sea transportation facilities are subject to the synergistic effects of electrochemical corrosion, localized pitting, and biocorrosion in complex marine conditions. This material degradation process not only results in a loss of structural integrity but can also trigger unexpected safety incidents, profoundly impacting marine ecosystems and energy supply systems. International research indicates that maintenance costs associated with corrosion account for over 40% of the total lifecycle cost of marine engineering.

[0003] Currently, mainstream protection technologies fall into two categories: electrochemical protection and coating protection. While the sacrificial anode method of electrochemical protection is simple to implement, it faces challenges in deep-sea environments, including difficulty replacing the anodes and unstable protection. The impressed current method faces energy supply challenges, especially in waters far from land, and its operating costs remain high. While widely used, coating protection is subject to issues such as aging failure and pitting corrosion caused by localized damage.

[0004] As an emerging green anti-corrosion method, photocathodic protection technology has demonstrated unique advantages in the field of marine engineering anti-corrosion in recent years. This technology utilizes the photoelectric effect of semiconductor materials to achieve cathodic polarization protection of metal structures through the migration of photogenerated electrons, while avoiding the problems of traditional sacrificial anode material consumption and high energy consumption of external current systems. Current research is mainly focused on the optimization of photoanode materials. Among them, TiO2-based materials have become the research basis due to their good chemical stability, but their wide bandgap characteristics limit the utilization rate of sunlight; narrow bandgap semiconductors such as BiVO4 and WO3 can absorb visible light, but they face problems such as high carrier recombination rate and photocorrosion. To improve performance, researchers have developed a variety of heterojunction structures to enhance charge separation efficiency through band matching.

[0005] In photocathode protection systems, photoanodes are typically designed with heterojunction structures to enhance light absorption and charge separation performance. Current research focuses primarily on type II heterojunction systems. While this structure can effectively promote the spatial separation of photogenerated carriers, it inevitably weakens the redox ability of the semiconductor, resulting in insufficient reduction potential for photogenerated electrons, making it difficult to meet the cathodic protection requirements for carbon steel structures in marine engineering. In comparison, the Z-type heterojunction system has significant advantages in maintaining strong redox capabilities and, in theory, can effectively protect carbon steel. However, this structure suffers from severe electron-hole recombination at the interface, causing the photocurrent output to decay rapidly over time and poor stability of the protection potential, ultimately affecting the overall protection effect. This performance degradation problem severely restricts the application prospects of Z-type heterojunctions in practical engineering.

[0006] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0007] The purpose of the present invention is to provide a simple and scalable preparation method of a double Z-type heterojunction photoanode film and its marine engineering application, so as to help solve or improve the problems of poor stability of existing photoanode materials and unsatisfactory photocathode protection effect.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a simple and scalable method for preparing a double Z-type heterojunction photoanode film and its marine engineering application, comprising the following steps:

[0009] (1) Solution preparation: dissolve indium salt and cadmium salt in deionized water to form a first solution; dissolve vanadate and molybdate in warm water (60°C) to avoid hydrolysis and precipitation of vanadate to form a second solution;

[0010] (2) Preparation by precipitation method: slowly add the second solution obtained in step (1) to the first solution obtained in step (1), and control the stirring speed to 300–500 rpm, add a strong alkaline solution dropwise, adjust the pH to 7.5–8.5, and form a suspension; and stir the suspension at 60–80°C for 1–8 hours to promote uniform growth of particles, and then alternately centrifuge and wash with deionized water and anhydrous ethanol to remove impurities; after drying the precipitate, calcinate it at high temperature (450–550°C) to obtain InVO4–CdMoO4 nanoparticles;

[0011] (3) Ion layer deposition method: Immerse the InVO4–CdMoO4 nanoparticles obtained in step (2) in a cadmium salt solution and stir for 1–2 minutes to allow Cd 2+ Adsorbed on the surface of the material, and washed with deionized water to remove the adsorbed Cd 2+; The above particles are then transferred to a Na2S solution, stirred for 1–2 minutes, and rinsed with deionized water. This completes one deposition cycle to generate CdS. Repeat this step 1–20 times to obtain InVO4–CdMoO4–CdS.

[0012] Preferably, in the precipitation method, the pH is controlled at 7.5-8.5, the calcination temperature is controlled at 450-550° C., and the calcination time is 1-24 h.

[0013] Preferably, the cadmium salt is a water-soluble organic salt or inorganic salt of cadmium; and the indium salt is a water-soluble organic salt or inorganic salt of indium.

[0014] Preferably, the cadmium salt is at least one of cadmium nitrate, cadmium chloride, cadmium acetate and cadmium citrate.

[0015] Preferably, the indium salt is at least one of indium nitrate, indium chloride, indium acetate and indium citrate; the vanadate is at least one of sodium vanadate and potassium vanadate; the molybdate is at least one of sodium molybdate and potassium molybdate; and the strong alkaline solution is at least one of NaOH or KOH.

[0016] Preferably, in step (1), the molar ratio of cadmium in the cadmium salt to indium in the indium salt is 1:8-8:1; the molar ratio of vanadate to cadmium is 1:1; and the molar ratio of molybdate to indium salt is 1:1.

[0017] The present invention also provides a double Z-type heterojunction photoanode film, which adopts the following technical solution: a double Z-type heterojunction photoanode film, wherein the double Z-type heterojunction photoanode film is prepared by the method described above.

[0018] The present invention also provides an application of the double Z-type heterojunction photoanode film as described above, which adopts the following technical solution: application of the double Z-type heterojunction photoanode film as described above in corrosion protection of metal materials of marine engineering structures.

[0019] Preferably, the marine engineering structural metal material is located in an environment such as the atmosphere, seawater or wet soil.

[0020] Beneficial effects:

[0021] The preparation method of the double Z-type heterojunction photoanode film of the present invention designs a precipitation method and an ion layer deposition method to optimize the nanomaterial preparation method. By introducing a third semiconductor material, two Z-type charge migration paths are formed, providing multiple, directional charge separation channels, avoiding the recombination of photogenerated charges at the semiconductor interface, and improving the cyclic stability of the heterojunction.

[0022] The double Z-type heterojunction structure contained in the double Z-type heterojunction photoanode film of the present invention can effectively solve or alleviate the problem that the photoanode materials used for photocathode protection in the prior art have poor anti-corrosion effects on metals used in marine construction projects, and can achieve efficient photocathode protection of marine engineering structures and improve the durability of marine engineering structures. This is because InVO4, CdMoO4 and CdS have matching band structures. The photogenerated electrons of InVO4 and CdS can spontaneously select and transfer to the valence band of CdMoO4 for recombination. CdMoO4 plays a key role as an "electron trap" and "recombination center", effectively inhibiting the recombination of photogenerated charges of InVO4 and CdS. This is the key bridge for realizing the double Z-type charge transfer path. This structural design fully utilizes the energy band advantages of the three materials, realizes efficient separation of photogenerated charges, maximum retention of strong redox ability and wide spectrum absorption, thereby obtaining efficient and stable photocathode protection performance.

[0023] The double Z-type heterojunction photoanode film of the present invention can shift the corrosion potential of carbon steel negatively by 0.35V under light; the long-term open-circuit potential curve and the potential change curve after multiple intermittent light cycles both show that the double Z-type composite photoanode film of the present invention has good stability and can provide long-term stable protection; the EIS spectrum shows that the double Z-type heterojunction photoanode film of the present invention effectively improves the separation efficiency of photogenerated electron-hole pairs; the ESR spectrum shows that the invented double Z-type heterojunction photoanode film has stronger redox activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0025] Figure 1 The electrochemical impedance spectroscopy (EIS) curves of the CdMoO4 photoanode film of Comparative Example 1, the InVO4–CdMoO4 photoanode film of Comparative Example 2, and the double Z-type heterojunction photoanode film of Example 1 under the light-on condition are shown;

[0026] Figure 2 Mott-Schottky (MS) curves of the InVO4–CdMoO4 photoanode film of Comparative Example 2 and the double Z-type heterojunction photoanode film of Example 1;

[0027] Figure 3 The UV-Vis absorption curves of the CdMoO4 photoanode film of Comparative Example 3, the InVO4–CdMoO4 photoanode film of Comparative Example 4, and the double Z-type heterojunction photoanode film of Example 2 are shown;

[0028] Figure 4The potentiodynamic polarization curve of the double Z-type heterojunction photoanode film coupled with steel bars (carbon steel) of Example 2 was measured in a seawater (3.5wt% NaCl solution) environment under the condition of light on;

[0029] Figure 5 Electron spin resonance (ESR) curves of the CdMoO4 photoanode film of Comparative Example 5, the InVO4–CdMoO4 photoanode film of Comparative Example 6, and the double Z-type heterojunction photoanode film of Example 3;

[0030] Figure 6 The potential change curves of the InVO4-CdMoO4 photoanode film of comparative example 7 and the double Z-type heterojunction photoanode film of example 4 after multiple intermittent illumination cycles. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0032] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0033] Aiming at the problems of poor stability of existing photoanode materials and unsatisfactory photocathode protection effect, the present invention provides a method for preparing a double Z-type heterojunction photoanode film.

[0034] The method for preparing a double Z-type heterojunction photoanode film according to an embodiment of the present invention comprises the following steps: (1) preparing a solution: dissolving an indium salt and a cadmium salt in deionized water to form a first solution; dissolving a vanadate and a molybdate in warm water (60°C) to avoid hydrolysis and precipitation of the vanadate, to form a second solution;

[0035] (2) Preparation by precipitation method: slowly add the second solution obtained in step (1) to the first solution obtained in step (1), and control the stirring speed to 300–500 rpm, add a strong alkaline solution dropwise, adjust the pH to 7.5–8.5, and form a suspension; and stir and age the suspension at 60–80°C for 1–8 hours to promote uniform growth of particles, and then alternately centrifuge and wash with deionized water and anhydrous ethanol to remove impurities; after drying the precipitate, calcinate it at high temperature (450–550°C) to obtain InVO4–CdMoO4 nanoparticles;

[0036] (3) Ion layer deposition method: Immerse the InVO4–CdMoO4 nanoparticles obtained in step (2) in a cadmium salt solution and stir for 1–2 minutes to allow Cd 2+Adsorbed on the surface of the material, and washed with deionized water to remove the adsorbed Cd 2+ ; The above particles are then transferred to a Na2S solution, stirred for 1-2 minutes, and rinsed with deionized water to complete a deposition cycle to generate CdS. Repeating this step 1-20 times can obtain InVO4-CdMoO4-CdS, which is a double Z-type heterojunction photoanode.

[0037] The method for preparing a double Z-shaped heterojunction photoanode film in this embodiment of the present invention combines three semiconductor materials (InVO4, CdMoO4, and CdS) to form two Z-shaped charge migration pathways. This provides multiple, directional charge separation channels, prevents the recombination of photogenerated charges at the semiconductor interface, and improves the heterojunction's cycling stability. This enables efficient and stable photocathodic protection of marine engineering steel structures, enhancing their durability.

[0038] Preferably, in the precipitation method, the pH is controlled at 7.5-8.5, the calcination temperature is controlled at 450-550° C., and the calcination time is 1-24 h.

[0039] Preferably, the cadmium salt is an organic salt or an inorganic salt of water-soluble cadmium;

[0040] The indium salt is an organic salt or an inorganic salt of water-soluble indium.

[0041] Preferably, the cadmium salt is at least one of cadmium nitrate, cadmium chloride, cadmium acetate and cadmium citrate.

[0042] Preferably, the indium salt is at least one of indium nitrate, indium chloride, indium acetate and indium citrate; the vanadate is at least one of sodium vanadate and potassium vanadate; and the molybdate is at least one of sodium molybdate and potassium molybdate.

[0043] Preferably, in step (1), the molar ratio of cadmium in the cadmium salt to indium in the indium salt is 1:8-8:1; and the molar ratio of vanadate and molybdate to the cadmium and indium salts in step (1) is 1:1.

[0044] In a preferred embodiment of the method for preparing a double Z-type heterojunction photoanode film of the present invention, the pH of the precipitation method is controlled at 7.5–8.5 (for example, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4 or 8.5), the aging time is selected from 1–8h (for example, 1h, 2h, 4h, 6h or 8h), the aging temperature is selected from 60–80°C (for example, 60°C, 65°C, 70°C, 75°C or 80°C), the calcination temperature is selected from 450–550°C (for example, 450°C, 480°C, 500°C, 520°C or 55°C), the calcination time is 1–24h, and the number of ion layer depositions is selected from 1–20 times (for example, 1 time, 5 times, 10 times, 15 times or 20 times).

[0045] In a preferred embodiment of the method for preparing the double Z-type heterojunction photoanode film of the present invention, the cadmium salt is a water-soluble organic salt or inorganic salt of cadmium; and the indium salt is a water-soluble organic salt or inorganic salt of indium.

[0046] In a preferred embodiment of the preparation method of the double Z-type heterojunction photoanode film of the present invention, the cadmium salt is at least one of cadmium nitrate, cadmium chloride, cadmium acetate and cadmium citrate; the indium salt is at least one of indium nitrate, indium chloride, indium acetate and indium citrate; the vanadate is at least one of sodium vanadate and potassium vanadate; and the molybdate is at least one of sodium molybdate and potassium molybdate.

[0047] In a preferred embodiment of the method for preparing a double Z-type heterojunction photoanode film of the present invention, in step (1), the molar ratio of cadmium in the cadmium salt to indium in the indium salt is 1:8–8:1 (for example, 1:1, 1:2, 1:5, 1:6, 1:8, 8:1, 6:1, 4:1 or 2:1).

[0048] Preferably, in the first solution, the concentration of the cadmium salt and the indium salt is 1mmol / L–1mol / L (for example, 1mmol / L, 10mmol / L, 50mmol / L, 100mmol / L, 300mmol / L, 500mmol / L, 800mmol / L or 1mol / L); the concentration of the vanadate and the molybdate is 1mmol / L–1mol / L (for example, 1mmol / L, 10mmol / L, 50mmol / L, 100mmol / L, 300mmol / L, 500mmol / L, 800mmol / L or 1mol / L) and the molar ratio with the cadmium salt and the indium salt in step (1) is 1:1. The concentration of the cadmium salt in step (3) is 1 mmol / L–1 mol / L (e.g., 1 mmol / L, 10 mmol / L, 50 mmol / L, 100 mmol / L, 300 mmol / L, 500 mmol / L, 800 mmol / L, or 1 mol / L) and the concentration of Na2S in step (3) is 1 mmol / L–1 mol / L (e.g., 1 mmol / L, 10 mmol / L, 50 mmol / L, 100 mmol / L, 300 mmol / L, 500 mmol / L, 800 mmol / L, or 1 mol / L).

[0049] The present invention further proposes a double Z-type heterojunction photoanode film. The double Z-type heterojunction photoanode film in the embodiment of the present invention is prepared by the method described above.

[0050] The double Z-type heterojunction structure contained in the double Z-type heterojunction photoanode film of the present invention can effectively solve or alleviate the problem that the photoanode materials used for photocathode protection in the prior art have poor anti-corrosion effects on metals used in marine construction projects, realize efficient photocathode protection of marine engineering structures, and improve the durability of marine engineering structures. This is because InVO4, CdMoO4 and CdS have matching band structures. The photogenerated electrons of InVO4 and CdMoO4 can spontaneously select and transfer to the valence band of CdS for recombination. CdS plays a key role as an "electron trap" and "recombination center", effectively inhibiting the recombination of photogenerated charges of InVO4 and CdMoO4. This is the key bridge for realizing the double Z-type charge transfer path. This structural design makes full use of the energy band advantages of the three materials, realizes efficient separation of photogenerated charges, maximum retention of strong redox ability and wide spectrum absorption, thereby obtaining efficient and stable photocathode protection performance.

[0051] The present invention also proposes an application of a double Z-type heterojunction photoanode film, and the application of the double Z-type heterojunction photoanode film in the corrosion protection of metal materials in marine engineering structures.

[0052] In the preferred embodiment of the application described above, the marine engineering structure metal material is located in seawater or wet soil. The double Z-type heterojunction photoanode film of the present invention can provide effective photocathode protection in the atmosphere, seawater and wet soil.

[0053] The double Z-type heterojunction photoanode film of the present invention, its preparation method and application are described in detail below through specific examples.

[0054] Example 1

[0055] The method for preparing the double Z-type heterojunction photoanode film of this embodiment includes the following steps:

[0056] (1) Solution preparation: Dissolve indium chloride and cadmium nitrate in deionized water to form a first solution with concentrations of 1 mmol / L and 8 mmol / L, respectively; dissolve sodium vanadate and potassium molybdate in warm water (60°C) to avoid hydrolysis and precipitation of vanadate to form a second solution with concentrations of 1 mmol / L and 8 mmol / L, respectively;

[0057] (2) Preparation by precipitation method: the second solution obtained in step (1) is slowly added to the first solution obtained in step (1), and the stirring speed is controlled at 300 rpm, and a strong alkaline solution is added dropwise to adjust the pH to 7.5 to form a suspension; the suspension is stirred and aged at 60°C for 8 hours to promote uniform growth of particles, and then alternately centrifuged and washed with deionized water and anhydrous ethanol to remove impurity ions; after drying the precipitate, it is calcined at a high temperature of 450°C for 12 hours to obtain InVO4–CdMoO4 nanoparticles;

[0058] (3) Ion layer deposition method: Immerse the InVO4–CdMoO4 nanoparticles obtained in step (2) in 1 mmol / L cadmium acetate solution and stir for 2 minutes to allow Cd 2+ The particles are adsorbed on the surface of the material and rinsed with deionized water to remove the adsorbed Cd²⁺. The particles are then transferred to a 1 mmol / L Na2S solution, stirred for 2 minutes, and rinsed with deionized water. This completes one deposition cycle to generate CdS. This step is repeated 20 times to obtain InVO4–CdMoO4–CdS, which is the double Z-type heterojunction photoanode film of this embodiment.

[0059] Example 2

[0060] The method for preparing the double Z-type heterojunction photoanode film of this embodiment includes the following steps:

[0061] (1) Solution preparation: Indium acetate and cadmium chloride were dissolved in deionized water to form a first solution with concentrations of 8 mol / L and 1 mol / L, respectively; potassium vanadate and sodium molybdate were dissolved in warm water (60°C) to avoid hydrolysis and precipitation of vanadates to form a second solution with concentrations of 8 mol / L and 1 mol / L, respectively;

[0062] (2) Preparation by precipitation method: the second solution obtained in step (1) is slowly added to the first solution obtained in step (1), and the stirring speed is controlled at 500 rpm, and a strong alkaline solution is added dropwise to adjust the pH to 8.5 to form a suspension; the suspension is stirred and aged at 80°C for 1 hour to promote uniform growth of particles, and then alternately centrifuged and washed with deionized water and anhydrous ethanol to remove impurity ions; after drying the precipitate, it is calcined at a high temperature of 550°C for 24 hours to obtain InVO4–CdMoO4 nanoparticles;

[0063] (3) Ion layer deposition method: Immerse the InVO4–CdMoO4 nanoparticles obtained in step (2) in 500mmol / L cadmium acetate solution and stir for 2 minutes to allow Cd 2+ Adsorbed on the surface of the material, and washed with deionized water to remove the adsorbed Cd 2+ ; The above particles are then transferred to a 50 mmol / L Na2S solution, stirred for 1 minute, and rinsed with deionized water to complete a deposition cycle to generate CdS. This step is repeated 5 times to obtain InVO4–CdMoO4–CdS, which is the double Z-type heterojunction photoanode film of this embodiment.

[0064] Example 3

[0065] The method for preparing the double Z-type heterojunction photoanode film of this embodiment includes the following steps:

[0066] (1) Solution preparation: Indium acetate and cadmium chloride were dissolved in deionized water to form a first solution with concentrations of 500 mmol / L and 500 mmol / L, respectively; potassium vanadate and sodium molybdate were dissolved in warm water (60°C) to avoid hydrolysis and precipitation of vanadates to form a second solution with concentrations of 500 mmol / L and 500 mmol / L, respectively;

[0067] (2) Preparation by precipitation method: the second solution obtained in step (1) is slowly added to the first solution obtained in step (1), and the stirring speed is controlled at 500 rpm, and a strong alkaline solution is added dropwise to adjust the pH to 8 to form a suspension; the suspension is stirred and aged at 75°C for 8 hours to promote uniform growth of particles, and then alternately centrifuged and washed with deionized water and anhydrous ethanol to remove impurity ions; after drying the precipitate, it is calcined at a high temperature of 500°C for 10 hours to obtain InVO4–CdMoO4 nanoparticles;

[0068] (3) Ion layer deposition method: Immerse the InVO4–CdMoO4 nanoparticles obtained in step (2) in 500mmol / L cadmium citrate solution and stir for 1 minute to allow Cd 2+ Adsorbed on the surface of the material, and washed with deionized water to remove the adsorbed Cd 2+ ; The above particles are then transferred to a 1 mmol / L Na2S solution, stirred for 1 minute, and rinsed with deionized water, completing a deposition cycle to generate CdS. Repeating this step once can obtain InVO4–CdMoO4–CdS, which is the double Z-type heterojunction photoanode film of this embodiment.

[0069] Example 4

[0070] The method for preparing the double Z-type heterojunction photoanode film of this embodiment includes the following steps:

[0071] (1) Solution preparation: Dissolve cadmium acetate and cadmium acetate in deionized water to form a first solution with concentrations of 100 mmol / L and 500 mmol / L, respectively; dissolve potassium vanadate and potassium molybdate in warm water (60°C) to avoid hydrolysis and precipitation of vanadate to form a second solution with concentrations of 100 mmol / L and 500 mmol / L, respectively;

[0072] (2) Preparation by precipitation method: the second solution obtained in step (1) is slowly added to the first solution obtained in step (1), and the stirring speed is controlled at 300 rpm, and a strong alkaline solution is added dropwise to adjust the pH to 8.3 to form a suspension; the suspension is stirred and aged at 70°C for 4 hours to promote uniform growth of particles, and then alternately centrifuged and washed with deionized water and anhydrous ethanol to remove impurity ions; after drying the precipitate, it is calcined at a high temperature of 480°C for 8 hours to obtain InVO4–CdMoO4 nanoparticles;

[0073] (3) Ion layer deposition method: Immerse the InVO4–CdMoO4 nanoparticles obtained in step (2) in 500mmol / L cadmium chloride solution and stir for 1 minute to allow Cd 2+ Adsorbed on the surface of the material, and washed with deionized water to remove the adsorbed Cd 2+ ; The above particles are then transferred to a 500 mmol / L Na2S solution, stirred for 2 minutes, and rinsed with deionized water, completing a deposition cycle to generate CdS. This step is repeated 15 times to obtain InVO4–CdMoO4–CdS, which is the double Z-type heterojunction photoanode film of this embodiment.

[0074] Comparative Example 1

[0075] The only difference between the preparation method of the CdMoO4 photoanode film in this comparative example and that in Example 1 is that in step (1), no indium salt is added to the first solution, and no vanadate is added to the second solution; step (3) is omitted; and the rest is consistent with Example 1.

[0076] Comparative Example 2

[0077] The preparation method of the InVO4-CdMoO4 photoanode film in this comparative example differs from that in Example 1 only in that step (3) is omitted; the rest is consistent with Example 1.

[0078] Comparative Example 3

[0079] The only difference between the preparation method of the CdMoO4 photoanode film in this comparative example and that in Example 2 is that: in step (1), no indium salt is added to the first solution, and no vanadate is added to the second solution; step (3) is omitted; and the rest is consistent with Example 2.

[0080] Comparative Example 4

[0081] The only difference between the preparation method of the InVO4-CdMoO4 photoanode film in this comparative example and that in Example 2 is that step (3) is omitted; the rest is consistent with Example 2.

[0082] Comparative Example 5

[0083] The only difference between the preparation method of the CdMoO4 photoanode film in this comparative example and that in Example 3 is that in step (1), no indium salt is added to the first solution, and no vanadate is added to the second solution; step (3) is omitted; and the rest is consistent with Example 3.

[0084] Comparative Example 6

[0085] The only difference between the preparation method of the InVO4-CdMoO4 photoanode film in this comparative example and that in Example 2 is that step (3) is omitted; the rest is consistent with Example 3.

[0086] Comparative Example 7

[0087] The preparation method of the InVO4-CdMoO4 photoanode film in this comparative example differs from that in Example 4 only in that step (3) is omitted; the rest are consistent with Example 4.

[0088] Experimental example

[0089] 1. The double Z-type heterojunction photoanode film (InVO4-CdMoO4-CdS composite film) of Example 1, the CdMoO4 photoanode film of Comparative Example 1, and the InVO4-CdMoO4 photoanode film of Comparative Example 2 were placed under light conditions for AC impedance testing and Mott-Schottky testing:

[0090] Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (MS) measurements were performed using an electrochemical workstation (Gamry Interface 5000E). The tests were conducted in a dual-electrolytic cell system, using a DuPont proton exchange membrane as the ion exchange channel, a 3.5wt% NaCl solution as the electrolyte, and a 300W xenon lamp (PLS-SXE 300) as the simulated light source. The test connection used a traditional three-electrode system, with a photoanode as the working electrode (WE), a saturated calomel electrode (SCE) as the reference electrode (RE), and a platinum electrode as the counter electrode (CE).

[0091] The AC impedance curve under light conditions is as follows Figure 1 shown; from Figure 1 It can be seen that the impedance arc radius of the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) of Example 1 under the on-state condition is much smaller than that of the CdMoO4 photoanode film in Comparative Example 1 and the InVO4–CdMoO4 photoanode film in Comparative Example 2, indicating that the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) of Example 1 has the smallest impedance value under the on-state condition. This indicates that the double Z-type heterostructure has better electron transfer capability and higher separation efficiency of photogenerated electron-hole pairs.

[0092] The results of the Mott-Schottky (MS) test are as follows: Figure 2 shown; from Figure 2It can be seen that the slopes of the Mott-Schottky plots for both the InVO4–CdMoO4 photoanode film of Comparative Example 2 and the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) of Example 1 are positive, indicating that they are both n-type semiconductors. Furthermore, the flat band potential of the InVO4–CdMoO4 photoanode film of Comparative Example 2 is at -0.68V, while the flat band potential of the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) of Example 1 shifts positively to -0.78V, indicating that the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) retains a relatively low conduction band potential. This suggests that the construction of the double Z-type heterojunction in the photoanode film of Example 1 further modulates the energy level structure of the InVO4–CdMoO4 heterojunction.

[0093] 2. The UV-visible light absorption of the double Z-type heterojunction photoanode film (InVO4-CdMoO4-CdS composite film) of Example 2, the CdMoO4 photoanode film of Comparative Example 3, and the InVO4-CdMoO4 photoanode film of Comparative Example 4 were tested:

[0094] Ultraviolet-visible absorption (UV-Vis) curves were measured using a TU-1901 double-beam UV-visible spectrophotometer. The wavelength range was set to 200 nm–1000 nm, and glass was used for baseline calibration before testing.

[0095] UV-visible light absorption test results are as follows Figure 3 shown; from Figure 3 It can be seen that the light absorption threshold of the CdMoO4 photoanode film in Comparative Example 3 is 377nm; the light absorption threshold of the InVO4–CdMoO4 photoanode film in Comparative Example 4 is 540nm; while the light absorption threshold of the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) in Example 2 is widened to 621nm, with the largest light absorption range. This indicates that the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) in Example 2 has the strongest light absorption capability and improves the utilization efficiency of visible light.

[0096] 3. After coupling the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) of Example 2 with steel bars (carbon steel, represented by Q235 CS in the figure), a potentiodynamic polarization curve test was performed under light conditions:

[0097] Potentiodynamic polarization curve tests were performed using a PARSTAT 4000A electrochemical workstation. During the test, a photoanode-coupled metal electrode was used as the working electrode (WE), a saturated calomel electrode (SCE) was used as the reference electrode (RE), and a platinum electrode was used as the counter electrode (CE).

[0098] The test results are as follows Figure 4 shown; from Figure 4 It can be seen that the self-corrosion potential of the steel bar (Q235) is -0.69 V; the corrosion potential after coupling with the double Z-type heterojunction photoanode (InVO4–CdMoO4–CdS composite film) of Example 2 shifts negatively to -0.98 V under light irradiation, indicating that the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) of Example 2 can provide better photoelectric cathode protection effect for the steel bar.

[0099] 4. Electron spin resonance tests were performed on the double Z-type heterojunction photoanode film (InVO4-CdMoO4-CdS composite film) of Example 3, the CdMoO4 photoanode film of Comparative Example 5, and the InVO4-CdMoO4 photoanode film of Comparative Example 6:

[0100] Electron spin resonance (ESR) measurements were performed using a Magnettech ESR 5000 instrument at room temperature and DMPO as the capture agent.

[0101] The test results are as follows Figure 5 shown; from Figure 5 It can be seen that the CdMoO4 photoanode film of Comparative Example 5 can capture free radicals, but the signal intensity generated is weak; this shows that the InVO4–CdMoO4 photoanode film of Comparative Example 6 can also capture free radicals, and the signal intensity is relatively strong. In contrast, the double Z-type heterojunction photoanode (InVO4–CdMoO4–CdS composite film) of Example 2 exhibits the strongest ESR signal, indicating that the scavenger in the double Z-type heterojunction photoanode (InVO4–CdMoO4–CdS composite film) of Example 2 can capture the most free radicals. This shows that the construction of the double Z-type heterojunction achieves efficient separation of photogenerated electrons and holes while retaining stronger redox capacity.

[0102] 5. In seawater (using 3.5wt% NaCl solution to simulate seawater), the changes in the InVO4–CdMoO4 photoanode film of Comparative Example 7 and the double Z-type heterojunction photoanode film (InVO4–CdMoO4–CdS composite film) of Example 4 were tested under multiple cycles of intermittent sunlight irradiation:

[0103] The test results are as follows Figure 6 shown; from Figure 6It can be seen that the potential of the InVO4–CdMoO4 photoanode film of Comparative Example 7 shifts positively with increasing cycle number, with a significant change. This indicates that the cathodic protection effect of the InVO4–CdMoO4 photoanode film of Comparative Example 7 on steel bars gradually weakens and its stability is insufficient. In contrast, the potential of the double Z-type heterojunction photoanode film of Example 4 (InVO4–CdMoO4–CdS composite film) remains essentially unchanged with increasing cycle number, with no significant change. This indicates that the construction of the double Z-type heterojunction improves photoelectric stability and long-term cathodic protection capability, enabling long-term protection of steel bars.

[0104] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a double Z-type heterojunction photoanode film, characterized in that: The steps include: (1) Solution preparation: dissolve indium salt and cadmium salt in deionized water to form a first solution; dissolve vanadate and molybdate in warm water (60°C) to avoid hydrolysis and precipitation of vanadate to form a second solution; (2) Preparation by precipitation method: slowly add the second solution obtained in step (1) to the first solution obtained in step (1), and control the stirring speed to 300–500 rpm, add a strong alkaline solution dropwise, adjust the pH to 7.5–8.5, and form a suspension; and stir and age the suspension at 60–80°C for 1–8 hours to promote uniform growth of particles, and then alternately centrifuge and wash with deionized water and anhydrous ethanol to remove impurities; after drying the precipitate, calcinate it at high temperature (450–550°C) to obtain InVO4–CdMoO4 nanoparticles; (3) Ion layer deposition method: Immerse the InVO4–CdMoO4 nanoparticles obtained in step (2) in a cadmium salt solution and stir for 1–2 minutes to allow Cd 2+ Adsorbed on the surface of the material, and washed with deionized water to remove the adsorbed Cd 2+ ; The above particles are then transferred to a Na2S solution, stirred for 1–2 minutes, and rinsed with deionized water. This completes one deposition cycle to generate CdS. Repeat this step 1–20 times to obtain InVO4–CdMoO4–CdS.

2. The method for preparing a double Z-type heterojunction photoanode film according to claim 1, wherein: In the precipitation method, the pH is controlled at 7.5-8.5, the calcination temperature is controlled at 450-550° C., and the calcination time is 1-24 hours.

3. The method for preparing a double Z-type heterojunction photoanode film according to claim 1, wherein: The cadmium salt is an organic salt or an inorganic salt of water-soluble cadmium; The indium salt is an organic salt or an inorganic salt of water-soluble indium.

4. The method for preparing a double Z-type heterojunction photoanode film according to claim 3, wherein: The cadmium salt is at least one of cadmium nitrate, cadmium chloride, cadmium acetate and cadmium citrate; The indium salt is at least one of indium nitrate, indium chloride, indium acetate and indium citrate; the vanadate is at least one of sodium vanadate and potassium vanadate; the molybdate is at least one of sodium molybdate and potassium molybdate; and the strong base is at least one of NaOH and KOH.

5. The method for preparing a double Z-type heterojunction photoanode film according to claim 1, wherein: In step (1), the molar ratio of cadmium in the cadmium salt to indium in the indium salt is 1:8-8:1; the molar ratio of vanadate to cadmium is 1:1; and the molar ratio of molybdate to indium salt is 1:

1.

6. A double Z-type heterojunction photoanode film, characterized in that: The double Z-type heterojunction photoanode film is prepared by the method according to any one of claims 1-5.

7. The double Z-type heterojunction photoanode film according to claim 6, characterized in that: Application of the double Z-type heterojunction photoanode film in corrosion protection of metal materials in marine engineering structures.

8. The double Z-type heterojunction photoanode film according to claim 6, characterized in that: The marine engineering structure metal material protected by the double Z-type heterojunction photoanode film is located in the atmosphere, seawater or wet soil.

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