A double Z-type heterojunction photoanode film and its preparation method and application

Abstract

The present invention belongs to the technical field of corrosion inhibition of metal materials for marine engineering structures, and specifically relates to a double Z-type heterojunction photoanode film, a preparation method thereof, and an application thereof. The preparation method of the double Z-type heterojunction photoanode film of the present invention comprises the following steps: (1) placing the conductive surface of the conductive glass downward in a first solution containing a cadmium salt, an indium salt, and a sulfur source, and performing a first hydrothermal reaction to obtain a CdIn2S4 film; (2) placing the conductive surface downward in a second solution containing a zinc salt and a sulfur source, and performing a second hydrothermal reaction to obtain a CdIn2S4-ZnS composite film; (3) placing the conductive surface downward in a third solution containing a zinc salt, an indium salt, and a sulfur source, and performing a third hydrothermal reaction to obtain a CdIn2S4-ZnS-Zn3In2S6 composite film. The double Z-type heterojunction photoanode film of the present invention can achieve efficient photocathodic protection of marine engineering structures and improve 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 in particular relates to a double Z-type heterojunction photoanode film and a preparation method and application thereof. Background Art

[0002] Marine engineering structures, such as offshore oil platforms, submarine pipelines, cross-sea bridges, port terminals, and offshore wind turbine foundations, are subject to long-term service in the harsh marine environment. The high salinity, high concentration of chloride ions and dissolved oxygen, microbial activity, and wave and tidal erosion of seawater cause them to suffer extremely severe electrochemical corrosion, pitting corrosion, crevice corrosion, and microbial corrosion. This corrosion not only significantly shortens the design life of the structure but also leads to reduced structural strength, thinning of walls, leakage, and even catastrophic failure, posing a significant threat to human safety, the ecological environment, and the national economy.

[0003] Cathodic protection (CP) is currently one of the most effective and widely used technologies for preventing corrosion of metal structures in marine engineering. Traditional sacrificial anode CP relies primarily on the dissolution of metals with a more negative potential (such as Zn and Mg alloys) to provide the protective current. This method is simple in structure and does not require an external power source. However, it has significant disadvantages, including rapid anode consumption and the need for regular replacement (particularly difficult and expensive underwater), increased structural weight, uncontrollable output current (potentially leading to under- or over-protection), and poor performance in high-resistivity sediments or enclosed areas. Impressed current CP utilizes an external DC power source to drive current through auxiliary anodes to the protected structure. Its output current is adjustable and suitable for large structures. However, its core bottleneck lies in its reliance on a continuous and stable external power source. Providing stable power in deep-sea areas far from land-based power grids (such as deep-sea platforms, floating wind turbines, and submarine pipelines) is costly, technically complex, and unreliable. Reliance on fossil fuels for power generation also leads to significant carbon emissions, which is unsuitable for targeted applications. In addition, impressed current cathodic protection systems are usually complex in structure (including rectifiers, reference electrodes, and monitoring systems), have high maintenance costs, are subject to the risk of stray current interference, and the auxiliary anode itself has consumption problems.

[0004] Photocathodic protection technology is an innovative method that directly converts solar energy into electrochemical protection energy. Its basic principle is to use semiconductor photoanode materials (such as TiO2 and its modified materials, BiVO4, WO3, etc.) to generate photogenerated electron-hole pairs under light. The photogenerated electrons migrate to the protected metal structure (cathode), polarizing the cathode to the protective potential, thereby achieving corrosion protection. At the same time, the photogenerated holes can be used to oxidize substances in the environment (such as water or organic matter). Therefore, the reducing property of photoelectrons is one of the key factors determining the effectiveness of cathodic protection.

[0005] Photocathode protection photoanodes are often constructed in the form of heterojunctions, aiming to improve the efficiency of light utilization and the separation of photogenerated charges. However, most current heterojunctions are Type II, which sacrifices the redox properties of the semiconductor material, reducing the reducibility of the photogenerated electrons and making it difficult to transfer them to the metal to be protected. Consequently, they cannot provide cathodic protection for carbon steel materials used in marine engineering, or the protection effect is unsatisfactory. In contrast, while the Z-type heterojunction can maintain the strong redox ability of photogenerated carriers and theoretically achieve effective protection for carbon steel, electrons and holes at its interface are very easy to recombine, resulting in a long-term decrease in the photogenerated current and potential, poor cyclic stability, and unsatisfactory photocathode protection.

[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 double Z-type heterojunction photoanode film and its preparation method and application, so as to help solve or improve the problems of poor stability of existing photoanode materials and unsatisfactory photocathode protection effect.

[0008] In order to achieve the above-mentioned object, the present invention provides the following technical solution: a method for preparing a double Z-type heterojunction photoanode film, comprising the following steps: (1) placing the conductive surface of a conductive glass facing downward in a first solution containing a cadmium salt, an indium salt and a sulfur source, performing a first hydrothermal reaction, and obtaining a CdIn2S4 film; (2) placing the conductive surface of the conductive glass obtained by the treatment in step (1) facing downward in a second solution containing a zinc salt and a sulfur source, performing a second hydrothermal reaction, and obtaining a CdIn2S4-ZnS composite film; (3) placing the conductive surface of the conductive glass obtained by the treatment in step (2) facing downward in a third solution containing a zinc salt, an indium salt and a sulfur source, performing a third hydrothermal reaction, and obtaining a CdIn2S4-ZnS-Zn3In2S6 composite film, which is the double Z-type heterojunction photoanode film.

[0009] Preferably, the reaction temperatures of the first hydrothermal reaction, the second hydrothermal reaction and the third hydrothermal reaction are each independently selected from 90-200° C., and the reaction times are each independently selected from 8-24 h.

[0010] Preferably, the cadmium salt is an organic salt or an inorganic salt of cadmium; the indium salt is an organic salt or an inorganic salt of indium; and the zinc salt is an organic salt or an inorganic salt of zinc.

[0011] Preferably, 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 zinc salt is at least one of zinc nitrate, zinc chloride, zinc acetate and zinc citrate; and the sulfur source is thiourea.

[0012] Preferably, in step (1), the molar ratio of cadmium in the cadmium salt, indium in the indium salt, and sulfur in the sulfur source is 1:2:(1-8); in step (2), the molar ratio of zinc in the zinc salt and sulfur in the sulfur source is 1:(2-3); in step (3), the molar ratio of zinc in the zinc salt and indium in the indium salt is 3:(2-6):(7-12).

[0013] Preferably, step (1) further includes a step of pre-treating the conductive glass; the pre-treatment includes: sequentially cleaning the conductive glass with an aqueous solution containing detergent, an ethanol solution of NaOH, ethanol, and deionized water.

[0014] 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.

[0015] 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.

[0016] Preferably, the marine engineering structure metal material is located in seawater or wet soil.

[0017] Beneficial effects:

[0018] The preparation method of the double Z-type heterojunction photoanode film of the present invention forms two Z-type charge migration paths by introducing a third semiconductor material, providing multiple, directional charge separation channels, avoiding the recombination of photogenerated charges at the semiconductor interface, and improving the cyclic stability of the heterojunction.

[0019] The double Z-type heterojunction photoanode film of the present invention contains a double Z-type heterojunction structure, which can effectively solve or alleviate the problem that the photoanode materials used for photocathode protection in the prior art have poor anti-corrosion effect 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 CdIn2S4, ZnS and Zn3In2S6 have matching energy band structures. The photogenerated electrons of CdIn2S4 and Zn3In2S6 can spontaneously select and transfer to the valence band of ZnS for recombination. ZnS plays a key role as an "electron trap" and "recombination center", effectively inhibiting the recombination of photogenerated charges of CdIn2S4 and Zn3In2S6. 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 to achieve efficient separation of photogenerated charges, maximum retention of strong redox capacity and wide spectrum absorption, thereby obtaining efficient and stable photocathode protection performance.

[0020] The double Z-type heterojunction photoanode film of the present invention can shift the corrosion potential of stainless steel negatively by 0.58V 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 photoluminescence spectrum shows that the double Z-type heterojunction photoanode film of the present invention effectively improves the separation efficiency of photogenerated electron-hole pairs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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:

[0022] Figure 1 The open circuit potential (OCP) curves of the ZnS photoanode film of Comparative Example 1, the CdIn2S4-ZnS photoanode film of Comparative Example 2, and the double Z-type heterojunction photoanode film of Example 1 coupled with stainless steel under intermittent illumination conditions;

[0023] Figure 2 The open circuit potential (OCP) curves of the CdIn2S4-ZnS photoanode film of Comparative Example 2 and the double Z-type heterojunction photoanode film of Example 1 coupled with stainless steel under long-term illumination conditions;

[0024] Figure 3 The photoluminescence (PL) spectra of the ZnS photoanode film of Comparative Example 3, the CdIn2S4-ZnS photoanode film of Comparative Example 4, and the double Z-type heterojunction photoanode film of Example 2 are shown;

[0025] Figure 4 The photocurrent density-time variation (It) curves of the ZnS photoanode film of Comparative Example 3, the CdIn2S4-ZnS photoanode film of Comparative Example 4, and the double Z-type heterojunction photoanode film of Example 2;

[0026] Figure 5 The potential change curves of the CdIn2S4-ZnS photoanode film of Comparative Example 5 and the double Z-type heterojunction photoanode film of Example 3 after multiple intermittent illumination cycles;

[0027] Figure 6 The open circuit potential (OCP) curves of the ZnS photoanode film of Comparative Example 6, the CdIn2S4-ZnS photoanode film of Comparative Example 7, and the double Z-type heterojunction photoanode film of Example 4 were measured by coupling steel bars (carbon steel) in a seawater (3.5 wt% NaCl solution) environment;

[0028] Figure 7The open circuit potential (OCP) curves of the ZnS photoanode film of Comparative Example 6, the CdIn2S4-ZnS photoanode film of Comparative Example 7 and the double Z-type heterojunction photoanode film of Example 4 were respectively coupled with steel bars (carbon steel) measured in a wet soil environment. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The preparation method of the double Z-type heterojunction photoanode film of the embodiment of the present invention comprises the following steps: (1) placing the conductive surface of the conductive glass facing downward in a solution containing a cadmium salt, an indium salt and a sulfur source, performing a first hydrothermal reaction, and obtaining a CdIn2S4 film; (2) placing the conductive surface of the conductive glass obtained by the treatment in step (1) facing downward in a solution containing a zinc salt and a sulfur source, performing a second hydrothermal reaction, and obtaining a CdIn2S4-ZnS composite film; (3) placing the conductive surface of the conductive glass obtained by the treatment in step (2) facing downward in a solution containing a zinc salt, an indium salt and a sulfur source, and performing a third hydrothermal reaction, and obtaining a CdIn2S4-ZnS-Zn3In2S6 composite film, which is the double Z-type heterojunction photoanode film.

[0033] The method for preparing a double Z-shaped heterojunction photoanode film in this embodiment of the present invention combines three semiconductor materials (CdIn2S4, ZnS, and Zn3In2S6) 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.

[0034] In a preferred embodiment of the method for preparing a double Z-type heterojunction photoanode film of the present invention, the reaction temperatures of the first hydrothermal reaction, the second hydrothermal reaction and the third hydrothermal reaction are each independently selected from 90-200°C (for example, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C), and the reaction time is each independently selected from 8-24h (for example, 8h, 12h, 16h, 20h or 24h).

[0035] In a preferred embodiment of the method for preparing the double Z-type heterojunction photoanode film of the present invention, the cadmium salt is an organic salt or an inorganic salt of cadmium; the indium salt is an organic salt or an inorganic salt of indium; and the zinc salt is an organic salt or an inorganic salt of zinc.

[0036] In a preferred embodiment of the method for preparing a 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 zinc salt is at least one of zinc nitrate, zinc chloride, zinc acetate and zinc citrate; and the sulfur source is thiourea.

[0037] 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, indium in the indium salt, and sulfur in the sulfur source is 1:2:(1-8) (for example, 1:2:1, 1:2:3, 1:2:5, 1:2:6, 1:2:7 or 1:2:8); in step (2), the molar ratio of zinc in the zinc salt to sulfur in the sulfur source is 1:(2-3) (for example, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8 or 1:3); in step (3), the molar ratio of zinc in the zinc salt, indium in the indium salt and sulfur in the sulfur source is 3:(2-6):(7-12) (for example, 3:2:7, 3:2:12, 3:2:10, 3:4:7, 3:4:12, 3:4:10, 3:6:7, 3:6:12 or 3:6:9).

[0038] Preferably, in the first solution, the concentration of the cadmium 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); in the second solution, the concentration of the zinc 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); in the third solution, the concentration of the zinc 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).

[0039] In a preferred embodiment of the method for preparing a double Z-type heterojunction photoanode film of the present invention, the step of pre-treating the conductive glass is further included before step (1); the pre-treatment comprises: sequentially cleaning the conductive glass with an aqueous solution containing a detergent, an ethanol solution of NaOH, ethanol, and deionized water.

[0040] Preferably, cleaning is performed under ultrasonic conditions; the ultrasonic time is 10-30 min (eg, 10 min, 15 min, 20 min, 25 min or 30 min).

[0041] 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.

[0042] 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 effect 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 CdIn2S4, ZnS and Zn3In2S6 have matching band structures. The photogenerated electrons of CdIn2S4 and Zn3In2S6 can spontaneously select and transfer to the valence band of ZnS for recombination. ZnS plays a key role as an "electron trap" and "recombination center", effectively inhibiting the recombination of photogenerated charges of CdIn2S4 and Zn3In2S6. 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 to achieve efficient separation of photogenerated charges, maximum retention of strong redox ability and wide spectrum absorption, thereby obtaining efficient and stable photocathode protection performance.

[0043] 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.

[0044] 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 both seawater and wet soil.

[0045] The double Z-type heterojunction photoanode film of the present invention, its preparation method and application are described in detail below through specific examples.

[0046] Example 1

[0047] The method for preparing the double Z-type heterojunction photoanode film of this embodiment includes the following steps:

[0048] (1) Conductive glass pretreatment: Before the one-step hydrothermal process, the conductive glass needs to be thoroughly cleaned to improve the bonding strength between the photoanode film and the conductive glass. First, the conductive glass is placed in a beaker containing a detergent aqueous solution, an ethanol solution of NaOH, an ethanol solution, and a deionized water solution in that order. It is then ultrasonically cleaned for 10 minutes, rinsed with deionized water, and dried at 60°C for later use.

[0049] (2) Preparation of CdIn2S4 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (1) was placed downward in a reactor containing a first solution of cadmium nitrate, indium nitrate and thiourea (in the first solution, the concentration of cadmium nitrate was 1 mmol / L, the concentration of indium nitrate was 2 mmol / L, and the concentration of thiourea was 6 mmol / L; the volume of the first solution was 30 mL, and the capacity of the reactor was 50 mL). The first hydrothermal reaction was carried out at a temperature of 200°C and a reaction time of 16 h. After the reaction was completed, the reactor was cooled and washed with deionized water and dried to obtain a CdIn2S4 film.

[0050] (3) Preparation of ZnS by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (2) was placed downward in a reactor containing a second solution of zinc salt and sulfur source (the concentration of zinc nitrate in the second solution was 5 mmol / L, and the concentration of thiourea was 12 mmol / L; the volume of the second solution was 30 mL, and the capacity of the reactor was 50 mL). The hydrothermal reaction temperature was controlled to be 90°C and the reaction time was 24 h to carry out the second hydrothermal reaction. After the reaction was completed, the reactor was cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS composite film;

[0051] (4) Preparation of Zn3In2S6 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (3) is placed downward in a reactor containing a third solution of zinc salt, indium salt and sulfur source (in the third solution, the concentration of zinc nitrate is 100 mmol / L, the concentration of indium nitrate is 100 mmol / L, and the concentration of thiourea is 300 mmol / L; the volume of the third solution is 30 mL, and the capacity of the reactor is 50 mL). The hydrothermal reaction temperature is controlled to be 150°C and the reaction time is 12 h to carry out the third hydrothermal reaction. After the reaction is completed, the reactor is cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS-Zn3In2S6 composite film, which is the double Z-type heterojunction photoanode film of this embodiment.

[0052] Example 2

[0053] The method for preparing the double Z-type heterojunction photoanode film of this embodiment includes the following steps:

[0054] (1) Conductive glass pretreatment: Before the one-step hydrothermal process, the conductive glass needs to be thoroughly cleaned to improve the bonding strength between the photoanode film and the conductive glass. First, the conductive glass is placed in a beaker containing an aqueous solution of detergent, an ethanol solution of NaOH, ethanol, and deionized water in that order and ultrasonically cleaned for 30 minutes. After rinsing with deionized water, it is dried at 60°C for later use.

[0055] (2) Preparation of CdIn2S4 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (1) is placed downward in a reactor containing a first solution of cadmium salt, indium salt and thiourea (in the first solution, the concentration of cadmium chloride is 1 mol / L, the concentration of indium chloride is 2 mol / L, and the concentration of thiourea is 8 mol / L; the volume of the first solution is 30 mL, and the capacity of the reactor is 50 mL). The first hydrothermal reaction is carried out at a temperature of 90°C and a reaction time of 16 h. After the reaction is completed, the reactor is cooled, washed with deionized water, and dried to obtain a CdIn2S4 film.

[0056] (3) Preparation of ZnS by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (2) is placed downward in a reactor containing a second solution of zinc salt and sulfur source (the concentration of zinc chloride in the second solution is 1 mmol / L, and the concentration of thiourea is 3 mmol / L; the volume of the second solution is 30 mL, and the capacity of the reactor is 50 mL). The hydrothermal reaction temperature is controlled to be 200°C and the reaction time is 10 h to carry out the second hydrothermal reaction. After the reaction is completed, the reactor is cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS composite film;

[0057] (4) Preparation of Zn3In2S6 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (3) is placed face down in a reactor containing a third solution of zinc salt, indium salt and sulfur source (in the third solution, the concentration of zinc chloride is 1 mol / L, the concentration of indium nitrate is 0.8 mol / L, and the concentration of thiourea is 2.5 mol / L; the volume of the third solution is 30 mL, and the capacity of the reactor is 50 mL). The hydrothermal reaction temperature is controlled to be 90°C and the reaction time is 12 h to carry out the third hydrothermal reaction. After the reaction is completed, the reactor is cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS-Zn3In2S6 composite film, which is the double Z-type heterojunction photoanode film of this embodiment.

[0058] Example 3

[0059] The method for preparing the double Z-type heterojunction photoanode film of this embodiment includes the following steps:

[0060] (1) Conductive glass pretreatment: Before the one-step hydrothermal process, the conductive glass needs to be thoroughly cleaned to improve the bonding strength between the photoanode film and the conductive glass. First, the conductive glass is placed in a beaker containing a detergent aqueous solution, an ethanol solution of NaOH, ethanol, and deionized water in that order. It is then ultrasonically cleaned for 15 minutes, rinsed with deionized water, and dried at 60°C for later use.

[0061] (2) Preparation of CdIn2S4 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (1) is placed downward in a reactor containing a first solution of cadmium salt, indium salt and thiourea (in the first solution, the concentration of cadmium nitrate is 0.5 mol / L, the concentration of indium nitrate is 1 mol / L, and the concentration of thiourea is 0.6 mol / L; the volume of the first solution is 30 mL, and the capacity of the reactor is 50 mL). The first hydrothermal reaction is carried out at a temperature of 150°C and a reaction time of 16 h. After the reaction is completed, the reactor is cooled and washed with deionized water and dried to obtain a CdIn2S4 film.

[0062] (3) Preparation of ZnS by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (2) was placed downward in a reactor containing a second solution of zinc salt and sulfur source (the concentration of zinc nitrate in the second solution was 1 mmol / L, and the concentration of thiourea was 2 mmol / L; the volume of the second solution was 30 mL, and the capacity of the reactor was 50 mL). The hydrothermal reaction temperature was controlled to be 160°C and the reaction time was 15 h to carry out the second hydrothermal reaction. After the reaction was completed, the reactor was cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS composite film;

[0063] (4) Preparation of Zn3In2S6 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (3) is placed downward in a reactor containing a third solution of zinc salt, indium salt and sulfur source (in the third solution, the concentration of zinc nitrate is 10 mmol / L, the concentration of indium nitrate is 10 mmol / L, and the concentration of thiourea is 30 mmol / L; the volume of the third solution is 30 mL, and the capacity of the reactor is 50 mL). The hydrothermal reaction temperature is controlled to be 150°C and the reaction time is 12 h to carry out the third hydrothermal reaction. After the reaction is completed, the reactor is cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS-Zn3In2S6 composite film, which is the double Z-type heterojunction photoanode film of this embodiment.

[0064] Example 4

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

[0066] (1) Conductive glass pretreatment: Before the one-step hydrothermal process, the conductive glass needs to be thoroughly cleaned to improve the bonding strength between the photoanode film and the conductive glass. First, the conductive glass is placed in a beaker containing an aqueous solution of detergent, an ethanol solution of NaOH, ethanol, and deionized water in that order and ultrasonically cleaned for 20 minutes. After rinsing with deionized water, it is dried at 60°C for later use.

[0067] (2) Preparation of CdIn2S4 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (1) is placed downward in a reactor containing a first solution of cadmium salt, indium salt and thiourea (in the first solution, the concentration of cadmium nitrate is 10 mmol / L, the concentration of indium nitrate is 20 mmol / L, and the concentration of thiourea is 80 mmol / L; the volume of the first solution is 30 mL, and the capacity of the reactor is 50 mL). The first hydrothermal reaction is carried out at a temperature of 180°C and a reaction time of 16 h. After the reaction is completed, the reactor is cooled, washed with deionized water, and dried to obtain a CdIn2S4 film.

[0068] (3) Preparation of ZnS by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (2) is placed downward in a reactor containing a second solution of zinc salt and sulfur source (the concentration of zinc nitrate in the second solution is 50 mmol / L, and the concentration of thiourea is 100 mmol / L; the volume of the second solution is 30 mL, and the capacity of the reactor is 50 mL). The hydrothermal reaction temperature is controlled to be 150°C and the reaction time is 24 h to carry out the second hydrothermal reaction. After the reaction is completed, the reactor is cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS composite film;

[0069] (4) Preparation of Zn3In2S6 by hydrothermal method: The conductive surface of the conductive glass obtained by the treatment in step (3) is placed face down in a reactor containing a third solution of zinc salt, indium salt and sulfur source (in the third solution, the concentration of zinc nitrate is 0.5 mol / L, the concentration of indium nitrate is 0.8 mol / L, and the concentration of thiourea is 2 mol / L; the volume of the third solution is 30 mL, and the capacity of the reactor is 50 mL). The hydrothermal reaction temperature is controlled to be 150°C and the reaction time is 12 h to carry out the third hydrothermal reaction. After the reaction is completed, the reactor is cooled and washed with deionized water and dried to obtain a CdIn2S4-ZnS-Zn3In2S6 composite film, which is the double Z-type heterojunction photoanode film of this embodiment.

[0070] Comparative Example 1

[0071] The preparation method of the ZnS photoanode film in this comparative example differs from that in Example 1 only in that the conductive glass obtained by the treatment in step (1) is directly placed in the second solution for hydrothermal reaction (steps (2) and (4) are omitted); the rest are consistent with Example 1.

[0072] Comparative Example 2

[0073] The preparation method of the CdIn2S4-ZnS photoanode film in this comparative example differs from that in Example 1 only in that step (4) is omitted; the rest is consistent with Example 1.

[0074] Comparative Example 3

[0075] The only difference between the preparation method of the ZnS photoanode film in this comparative example and that in Example 2 is that the conductive glass obtained by the treatment in step (1) is directly placed in the second solution for hydrothermal reaction (steps (2) and (4) are omitted); the rest are consistent with Example 2.

[0076] Comparative Example 4

[0077] The only difference between the preparation method of the CdIn2S4-ZnS photoanode film in this comparative example and that in Example 2 is that step (4) is omitted; the rest is consistent with Example 2.

[0078] Comparative Example 5

[0079] The only difference between the preparation method of the CdIn2S4-ZnS photoanode film in this comparative example and that in Example 3 is that step (4) is omitted; the rest is consistent with Example 3.

[0080] Comparative Example 6

[0081] The preparation method of the ZnS photoanode film in this comparative example differs from that in Example 4 only in that the conductive glass obtained by the treatment in step (1) is directly placed in the second solution for hydrothermal reaction (steps (2) and (4) are omitted); the rest are consistent with Example 4.

[0082] Comparative Example 7

[0083] The only difference between the preparation method of the CdIn2S4-ZnS photoanode film in this comparative example and that in Example 4 is that step (4) is omitted; the rest is consistent with that in Example 4.

[0084] Experimental example

[0085] 1. The double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 1, the ZnS photoanode film of Comparative Example 1, and the CdIn2S4-ZnS photoanode film of Comparative Example 2 were respectively coupled to stainless steel (represented by 304SS in the figure) and open circuit potential tests were performed under intermittent lighting and lighting conditions:

[0086] Open-circuit potential measurements were performed using an electrochemical workstation (PARSTAT 4000A). A conventional three-electrode system was employed, with a photoanode-coupled metal electrode as the working electrode (WE), a saturated calomel electrode (SCE) as the reference electrode (RE), and a platinum electrode as the counter electrode (CE). During the test, a 300W xenon lamp (PLS-SXE 300) was used to simulate sunlight, and a 3.5wt% NaCl solution, designed to simulate a marine environment, was used as the electrolyte.

[0087] The open circuit potential test results under intermittent lighting conditions are as follows Figure 1 shown; from Figure 1 It can be seen that when coupled with the ZnS photoanode film of comparative example 1, the corrosion potential of stainless steel under the open-light condition dropped from -0.13V to -0.27V; when coupled with the CdIn2S4-ZnS photoanode film of comparative example 2, the corrosion potential of stainless steel dropped from -0.20V to -0.56V; and when coupled with the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 1, the corrosion potential of stainless steel dropped from -0.22V to -0.80V, and the potential of stainless steel dropped by 0.58V, which is the largest change; it shows that the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 1 can provide better photoelectric cathode protection effect for stainless steel.

[0088] The open circuit potential curve under long-term light conditions is as follows Figure 2 shown; from Figure 2It can be seen that after the light is turned on at 100 seconds, the corrosion potential of stainless steel when coupled with the CdIn2S4-ZnS photoanode film of Comparative Example 2 shifts negatively to -0.56V. As the light exposure time increases, the corrosion potential of stainless steel gradually shifts positively, reaching -0.39V at 3600 seconds. When stainless steel is coupled with the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 1, the corrosion potential of stainless steel shifts negatively to -0.80V, and there is no significant change in the corrosion potential with increasing light exposure time. This shows that the construction of the double Z-type heterojunction in Example 1 significantly improves the stability of the photoanode film and can provide better long-term and stable cathodic protection for stainless steel.

[0089] 2. The photoluminescence spectra of the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 2, the ZnS photoanode film of Comparative Example 3, and the CdIn2S4-ZnS photoanode film of Comparative Example 4 were tested:

[0090] Photoluminescence (PL) spectra were measured using a Hitachi F-7000 fluorescence spectrophotometer at room temperature, using a 300W xenon lamp as the light source, with an excitation wavelength of 370 nm and an emission wavelength range of 380 nm to 800 nm.

[0091] The test results are as follows Figure 3 shown; from Figure 3 It can be seen that the PL luminescence intensity of the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 2 is much lower than that of the ZnS photoanode film of Comparative Example 3 and the CdIn2S4-ZnS photoanode film of Comparative Example 4, indicating that the recombination efficiency of photogenerated electron-hole pairs in the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 2 is lower. This shows that the construction of the double Z-type heterojunction in the photoanode film of Example 2 further regulates the energy level structure of the CdIn2S4-ZnS heterojunction, further reducing the recombination efficiency of photogenerated electrons and holes, and achieving efficient separation of photogenerated carriers.

[0092] 3. The current density-time curves of the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 2, the ZnS photoanode film of Comparative Example 3, and the CdIn2S4-ZnS photoanode film of Comparative Example 4 were tested:

[0093] Photogenerated current density-time (Jt) measurements were performed using a Gamry Interface 5000E electrochemical workstation. The experiments were conducted in a dual-electrolytic cell system, with the working electrode connected to the photoanode material, and the counter electrode and ground wire connected to the protected metal, forming a complete test circuit. A saturated calomel electrode was used as the reference electrode.

[0094] The test results are as follows Figure 4 shown; from Figure 4 It can be seen that the photogenerated current density of ZnS photoanode film and CdIn2S4-ZnS photoanode film is 3μA / cm 2 and 30μA / cm 2 The photogenerated current density of the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 2 is 53μA / cm 2 , indicating that the separation efficiency of photogenerated electron-hole pairs of the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 2 is higher.

[0095] 4. Under multiple cycles of intermittent sunlight irradiation, the stability of the photoelectric cathode protection performance of different photoanode films was evaluated by monitoring the potential changes of the CdIn2S4-ZnS photoanode film prepared in Comparative Example 5 and the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 3:

[0096] The test results are as follows Figure 5 shown; from Figure 5 It can be seen that the potential of the CdIn2S4-ZnS photoanode film of Comparative Example 5 gradually shifts positively with increasing cycle number during multiple illumination cycles, indicating that the cathodic protection capability of the CdIn2S4-ZnS photoanode film of Comparative Example 5 gradually weakens with increasing cycle number, and its stability is limited. In contrast, the potential of the double Z-type heterojunction photoanode film of Example 3 (CdIn2S4-ZnS-Zn3In2S6 composite film) does not change significantly compared to the initial cycle potential after 40 on-off illumination cycles. This indicates that the double Z-type heterojunction structure has better photoelectric stability and long-term cathodic protection capabilities. The introduction of the double Z-type heterojunction structure significantly improves the cyclic stability of the photoanode, enabling long-term protection.

[0097] 5. In seawater (using 3.5wt% NaCl solution to simulate seawater), the open circuit potentials of the ZnS photoanode film of Comparative Example 6, the CdIn2S4-ZnS photoanode film of Comparative Example 7, and the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 4 were tested after coupling with steel bars (carbon steel; represented by Q235CS in the figure):

[0098] The test results are as follows Figure 6 shown; from Figure 6 It can be seen that when coupled with the ZnS photoanode film, the corrosion potential of the steel bar has no obvious light response, indicating that the ZnS photoanode film has no photoelectric cathode protection effect on the steel bar; when coupled with the CdIn2S4-ZnS photoanode film, the corrosion potential of the steel bar decreases from -0.56V to -0.65V, with a small decrease; when coupled with the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 4, the corrosion potential of the steel bar shifts negatively from -0.57V to -0.87V, and the potential decreases by 0.3V, with the largest change. This shows that the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 4 can provide better photoelectric cathode protection effect for carbon steel in seawater environment.

[0099] 6. In wet soil, the open circuit potentials of the ZnS photoanode film of Comparative Example 6, the CdIn2S4-ZnS photoanode film of Comparative Example 7, and the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 4 were tested after coupling with steel bars (carbon steel; represented by Q235CS in the figure):

[0100] Preparation of wet soil: The soil was air-dried and sieved. The prepared 3.5 wt% NaCl solution was added in batches to the pretreated soil, stirring until the soil moisture content reached 15%. The solution and soil were thoroughly mixed and the mixed wet soil was allowed to stand for 24 h before testing.

[0101] The test results are as follows Figure 7 shown; from Figure 7 It can be seen that the ZnS photoanode film and the CdIn2S4-ZnS photoanode film have no obvious light response in the wet soil environment, indicating that the ZnS photoanode film and the CdIn2S4-ZnS photoanode film have no significant protective effect on steel bars in wet soil. However, the potential of the steel bars coupled with the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 4 shows a significant negative shift under the light-on condition, indicating that the double Z-type heterojunction photoanode film (CdIn2S4-ZnS-Zn3In2S6 composite film) of Example 4 can provide photocathodic protection for steel bars in wet soil environments. The construction of the double Z-type heterojunction broadens the application environment of the photoanode film.

[0102] 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) placing the conductive glass with the conductive surface facing downward in a first solution containing a cadmium salt, an indium salt, and a sulfur source, and performing a first hydrothermal reaction to obtain a CdIn2S4 film; (2) placing the conductive surface of the conductive glass obtained by the treatment in step (1) downward in a second solution containing a zinc salt and a sulfur source, and performing a second hydrothermal reaction to obtain a CdIn2S4-ZnS composite film; (3) The conductive surface of the conductive glass obtained by the treatment in step (2) is placed downward in a third solution containing zinc salt, indium salt and sulfur source, and a third hydrothermal reaction is carried out to obtain a CdIn2S4-ZnS-Zn3In2S6 composite film, which is the double Z-type heterojunction photoanode film.

2. The method for preparing a double Z-type heterojunction photoanode film according to claim 1, wherein: The reaction temperatures of the first hydrothermal reaction, the second hydrothermal reaction and the third hydrothermal reaction are each independently selected from 90-200° C., and the reaction times are each independently selected from 8-24 h.

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 cadmium; The indium salt is an organic salt or an inorganic salt of indium; The zinc salt is an organic salt or an inorganic salt of zinc.

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 zinc salt is at least one of zinc nitrate, zinc chloride, zinc acetate and zinc citrate; The sulfur source is thiourea.

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, indium in the indium salt, and sulfur in the sulfur source is 1:2:(1-8); In step (2), the molar ratio of zinc in the zinc salt to sulfur in the sulfur source is 1:(2-3); In step (3), the molar ratio of zinc in the zinc salt to indium in the indium salt is 3:(2-6):(7-12).

6. The method for preparing a double Z-type heterojunction photoanode film according to claim 1, wherein: Before step (1), the method further includes the step of pre-treating the conductive glass; The pretreatment comprises: sequentially cleaning the conductive glass with an aqueous solution containing detergent, an ethanol solution of NaOH, ethanol and deionized water.

7. 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 to 6.

8. Use of the double Z-type heterojunction photoanode film as claimed in claim 7 in the corrosion protection of metal materials in marine engineering structures.

9. The use according to claim 8, characterized in that The marine engineering structural metal material is located in seawater or wet soil.

Images