A method for improving the corrosion resistance of semiconductor photoelectrochemical cathodic protection for metals with poor corrosion resistance

Abstract

A method for improving the corrosion resistance of poorly corrosion-resistant metals using semiconductor photoelectrochemical cathodic protection is disclosed, relating to the field of metal corrosion and protection. This method addresses the difficulty in transferring semiconductor photogenerated electrons to the surface of poorly corrosion-resistant metals in photoelectrochemical cathodic protection technology. The method includes the following steps: preparation of an organic coating, preparation of a semiconductor photoanode, and implementation of photoelectrochemical cathodic protection technology. This method can regulate the self-corrosion potential of the poorly corrosion-resistant metal, promoting the transfer of semiconductor photogenerated electrons to the metal, thus enabling the application of photoelectrochemical cathodic protection technology to poorly corrosion-resistant metals. This method is simple, effective, and easy to operate, and is expected to expand the application range of photoelectrochemical cathodic protection technology and improve its protection efficiency and duration for metals.

Description

Technical Field

[0001] This invention belongs to the field of metal corrosion and protection technology, specifically relating to a method for improving the photoelectrochemical cathodic protection of metals with poor corrosion resistance by semiconductor photoanodes. Background Technology

[0002] Photoelectrochemical cathodic protection technology is a green, low-carbon, and sustainable corrosion prevention strategy. However, the low efficiency of photocathode protection for metals or alloys with poor corrosion resistance, such as carbon steel, limits its application in corrosion protection engineering. Improving the photocathode protection efficiency for metals with poor corrosion resistance has become a research hotspot and challenge in this field, and is of great significance to metal corrosion engineering.

[0003] Photoelectrochemical cathodic protection technology uses sunlight as an energy source to excite photoelectrons from a semiconductor to transfer to the metal surface, causing cathodic polarization in the metal and thus slowing down or inhibiting its corrosion. Based on semiconductors, the solar energy conversion photoelectrochemical protection process mainly includes three key steps: light absorption by the semiconductor, carrier separation and migration in the semiconductor, and the transport of photoelectrons from the semiconductor surface to the protected metal. Its efficiency depends on the synergistic effect of these three steps. Therefore, the direction and efficiency of photoelectron transport between the semiconductor and the metal have a significant impact on the mechanism of action of the semiconductor in the corrosion of metals with poor corrosion resistance.

[0004] The prerequisite for photoelectron transport to a metal is that the quasi-Fermi level of the semiconductor is negative than the self-corrosion potential of the metal. The matching degree between the quasi-Fermi level of the semiconductor and the self-corrosion potential of the metal is crucial for photoelectron transport. Existing research is mostly based on the optimized design of the composition and structure of semiconductor photoanode materials, aiming to increase the photocurrent between the semiconductor and the metal by controlling the semiconductor band structure. Currently, simply controlling the semiconductor band structure is insufficient to meet the protection efficiency requirements. Furthermore, research on constructing a coupling system between the semiconductor photoanode and the physically protecting metal from the perspective of the protected metal is rarely reported, and such technology remains lacking. It is well known that the more positive the self-corrosion potential of the metal, the easier it is for semiconductor photoelectrons to transport to the metal, and the easier it is to achieve photoelectrochemical protection. Therefore, increasing the self-corrosion potential of the metal based on controlling the semiconductor band structure is expected to promote the solution of key problems in photoelectrochemical cathodic protection technology, realizing the advantages of semiconductors in metal corrosion protection to meet practical application needs. Summary of the Invention

[0005] The present invention aims to provide a method for improving the photoelectrochemical cathodic protection of poorly corrosion-resistant metals by semiconductor photoanodes. The method involves completely covering the surface of the poorly corrosion-resistant metal with an organic coating. The encapsulation effect of the organic coating shifts the self-corrosion potential of the metal positively. Under the modulating effect of the organic coating, semiconductor photoelectrons are more easily transferred to the metal, thereby improving the efficiency of semiconductor photoelectrochemical cathodic protection and achieving highly efficient protection for poorly corrosion-resistant metals.

[0006] The above-mentioned objective of this invention is achieved through the following technical solutions:

[0007] A method for improving the photoelectrochemical cathodic protection of poorly corrosion-resistant metals using semiconductor photoanodes includes the preparation of an organic coating, the preparation of a semiconductor photoanode, and the implementation of photoelectrochemical cathodic protection technology. Under the physical shielding effect of the organic coating, the self-corrosion potential of the poorly corrosion-resistant metal is effectively regulated, promoting the transfer of photogenerated electrons from the semiconductor photoanode to the metal. This method significantly improves the overall performance of the semiconductor photoelectrochemical cathodic protection for poorly corrosion-resistant metals.

[0008] The technical solution adopted in this invention is: a method for improving the photoelectrochemical cathodic protection of metals with poor corrosion resistance by semiconductor photoanodes, comprising the following steps:

[0009] (1) Preparation of organic resins:

[0010] Organic coatings are prepared on the surfaces of metals with poor corrosion resistance using processes such as brushing, spraying, dipping, electrophoretic coating, and electrostatic spraying. The organic coatings are cured at room temperature. The purpose is to form a protective organic coating film with physical shielding effect on the surface of the metals with poor corrosion resistance.

[0011] Metals with poor corrosion resistance should be mechanically polished and cleaned with organic solvents before use. The metal surface should be polished with sandpaper until no obvious scratches remain; the sample should then be ultrasonically cleaned with an organic solvent. The purpose is to remove adhering dust, oxide film, and other impurities from the metal surface.

[0012] The top of the corrosion-resistant metal surface has a reserved area not covered by an organic coating for copper wire connection;

[0013] The organic coating includes acrylic resins, epoxy resins, and silane coupling agents;

[0014] The metals with poor corrosion resistance include iron and its alloys.

[0015] (2) Fabrication of semiconductor photoanodes:

[0016] Using a conductive material as a substrate and encapsulating it with polytetrafluoroethylene tape on top, a high-efficiency semiconductor photoanode is prepared on the conductive substrate by a semiconductor thin film preparation method such as hydrothermal method, solvothermal method, oxidation method, sol-gel method, chemical vapor deposition, physical vapor deposition, or a combination of the above methods.

[0017] The conductive materials include FTO (fluorine-doped tin oxide) conductive glass, ITO (indium tin oxide) conductive glass, and titanium plates;

[0018] The top of the conductive material is encapsulated with polytetrafluoroethylene tape to prevent the semiconductor thin film from covering the conductive substrate.

[0019] The semiconductor photoanode includes elemental semiconductors, oxide semiconductors, sulfide semiconductors, nitride semiconductors, phosphide semiconductors, and their composites.

[0020] (3) Implementation of photoelectrochemical cathodic protection technology

[0021] By directly irradiating a semiconductor with sunlight or simulated sunlight, the semiconductor is induced to generate photoelectrons. A copper wire is used to connect the photoanode and the poorly resistant metal to establish an electron transport channel between the semiconductor and the poorly resistant metal, thereby realizing photoelectrochemical cathodic protection of the poorly resistant metal by the semiconductor photoanode.

[0022] The copper wire connection method is that iron alligator clips are welded to both ends of the copper wire. One alligator clip is attached to the conductive surface of the substrate where the photoanode is not covered by the semiconductor thin film, and the other alligator clip is attached to the surface of the metal where the organic coating is not covered.

[0023] Furthermore, the fabrication of the semiconductor photoanode includes the following steps:

[0024] 1) FTO conductive glass was immersed in a mixture of titanium dioxide and dopamine and heated. After drying, TiO2@PDA film was obtained on the surface of FTO conductive glass.

[0025] The mass ratio of dopamine hydrochloride, titanium dioxide, and hexamethylenetetramine in the titanium dioxide and dopamine mixture is (0.1-0.2):(2-4):1;

[0026] FTO conductive glass is inserted into a mixture of titanium dioxide and dopamine, with a reserved area on the liquid surface that is not inserted into the mixture;

[0027] 2) Pour the indium sulfide precursor solution into a high-pressure reactor, heat and react, then cool, wash with deionized water, and dry to obtain indium sulfide nanoparticles.

[0028] The indium sulfide precursor solution is an aqueous solution of indium nitrate and thioacetamide, wherein the mass ratio of indium nitrate to thiourea is (2-3):1;

[0029] 3) Indium sulfide nanoparticles were ultrasonically and uniformly dispersed in an ethanol solution to obtain an indium sulfide ethanol solution with a concentration of (1-2) g / L. The indium sulfide ethanol solution was drop-coated onto a TiO2@PDA film on the conductive surface of an FTO glass and dried. The sample was then placed in a muffle furnace with the conductive surface facing up and kept at 300-400℃ for 20-40 min to obtain an In2S3 / TiO2@PDA semiconductor photoanode.

[0030] Furthermore, a method for improving the photoelectrochemical cathodic protection of metals with poor corrosion resistance by semiconductor photoanodes includes the following steps:

[0031] (1) Preparation of silane coupling agent coating

[0032] Before using Q235 carbon steel, which has poor corrosion resistance, mechanical grinding and organic solvent cleaning are required. The metal with poor corrosion resistance is then immersed in a water bath heating solution containing a silane coupling agent mixture. The metal sheet with poor corrosion resistance is suspended in the silane coupling agent mixture, leaving a certain area on the surface of the liquid, while the rest of the metal is vertically inserted into the mixture.

[0033] Then place it in a vacuum drying oven for vacuum drying.

[0034] The silane coupling agent mixture is prepared by adding 0.30 mL of silane coupling agent (KH550) to a 50 mL mixture of ethanol and water (volume ratio 1:10) and then sonicating.

[0035] (2) Preparation of indium sulfide semiconductor photoanode:

[0036] Indium sulfide semiconductor photoanodes were prepared by a hydrothermal method. An indium sulfide precursor solution and FTO conductive glass were placed in a high-pressure reactor with a polytetrafluoroethylene substrate, heated and reacted, cooled, and rinsed with deionized water to obtain an indium sulfide semiconductor thin film on the surface of the FTO conductive glass.

[0037] The indium sulfide precursor solution is prepared by completely dissolving indium nitrate powder and thiourea powder in deionized water, wherein the mass ratio of indium nitrate powder to thiourea powder is 2:1.

[0038] Before placing the FTO conductive glass into the reactor liner, the top needs to be wrapped with PTFE tape; the purpose is to leave the conductive surface of the sample not covered on the top, which will facilitate the subsequent connection of copper wires.

[0039] (3) Photoelectrochemical cathodic protection

[0040] Indium sulfide semiconductor photoanode is directly irradiated by sunlight or simulated sunlight to induce photogenerated electrons in indium sulfide. Copper wires are used to connect the conductive surface of FTO conductive glass and the surface of Q235 carbon steel to establish an electron transport channel between the semiconductor and the carbon steel, thereby achieving photoelectrochemical cathodic protection of Q235 carbon steel by indium sulfide semiconductor photoanode.

[0041] The copper wire connection method uses copper wires with iron alligator clips at both ends. One alligator clip is attached to the part of the FTO conductive glass that is not covered with indium sulfide, and the other alligator clip is attached to the part of the Q235 carbon steel that is not covered with silane coupling agent.

[0042] Furthermore, a method for improving the photoelectrochemical cathodic protection of metals with poor corrosion resistance by semiconductor photoanodes includes the following steps:

[0043] (1) Preparation of water-based acrylic coating

[0044] Before use, the metal with poor corrosion resistance (Q345 carbon steel) is mechanically ground and cleaned with organic solvents. A water-based acrylic resin coating is prepared on the surface of the metal with poor corrosion resistance by brushing. The water-based acrylic resin is applied to the front, sides and bottom of the metal with poor corrosion resistance, but the top of the metal is not coated with water-based acrylic resin, leaving a reserved area.

[0045] (2) Preparation of indium sulfide / polydopamine / titanium dioxide composite photoanode:

[0046] FTO conductive glass was immersed in a mixture of titanium dioxide and dopamine and heated to react. After cooling and drying, a TiO2@PDA film was obtained on the surface of the FTO conductive glass.

[0047] The titanium dioxide and dopamine mixture was prepared by adding 5 mL of deionized water, 0.015 g of dopamine hydrochloride, and 0.20 g of titanium dioxide to a round-bottom flask and sonicating for 30 min. Then, 0.1 g of hexamethylenetetramine powder was added and dissolved in the solution and mixed thoroughly to obtain the titanium dioxide and dopamine mixture.

[0048] The indium sulfide precursor solution was poured into a high-pressure reactor with a polytetrafluoroethylene substrate, heated to react, cooled, washed with deionized water, and freeze-dried to obtain indium sulfide nanoparticles.

[0049] The indium sulfide precursor solution was prepared by completely dissolving indium nitrate and thioacetamide in 25 mL of deionized water, wherein the mass of indium nitrate powder and thiourea powder were 0.027 g and 0.01 g, respectively.

[0050] The prepared indium sulfide nanoparticles were uniformly dispersed in an ethanol solution and then drop-coated onto a TiO2@PDA film on the conductive surface of an FTO glass substrate. The sample was then placed in a muffle furnace and heated for a certain period of time.

[0051] The FTO conductive glass is suspended above the mixture of titanium dioxide and dopamine, with a certain area reserved on the surface of the liquid, and the rest of the FTO conductive glass is vertically inserted into the mixture.

[0052] Before use, FTO conductive glass needs to be ultrasonically cleaned three times each with acetone and ethanol until the surface is clean and free of impurities, and then dried with nitrogen before use.

[0053] (3) Photoelectrochemical cathodic protection:

[0054] The indium sulfide / polydopamine / titanium dioxide composite photoanode semiconductor photoanode is directly irradiated by sunlight or simulated sunlight, causing the indium sulfide to generate photo-generated electrons; copper wires are used to connect the conductive surface of FTO conductive glass and the surface of Q345 carbon steel to establish an electron transport channel between the semiconductor and the carbon steel, thereby realizing photoelectrochemical cathodic protection of Q345 carbon steel by the indium sulfide semiconductor photoanode.

[0055] The FTO conductive glass and Q345 carbon steel are connected by copper wires and considered as a conductive whole. The copper wires are connected by copper wires with iron alligator clips at both ends. One alligator clip is attached to the part of the FTO conductive glass that is not covered, and the other alligator clip is attached to the part of the Q345 carbon steel that is not covered by water-based acrylic resin.

[0056] The beneficial effects of this invention are:

[0057] Organic coatings can be directly applied to metal surfaces without damaging the metal structure and surface composition. Under photoexcitation, valence band electrons in the photoanode transition to the conduction band, and through conductive connections, electrons migrate from the photoanode to the metal surface, causing cathodic polarization and inhibiting electrochemical dissolution. The introduction of the organic coating on the metal surface increases the self-corrosion potential of poorly corrosion-resistant metals, making it easier for electrons in the photoanode to migrate to the metal surface under the influence of the potential difference. Therefore, the physical shielding effect of the organic coating significantly promotes the photoelectrochemical cathodic protection performance of the semiconductor photoanode for poorly corrosion-resistant metals. Furthermore, in the absence of light, the dense and firm organic coating adheres to the metal surface, preventing corrosive media from penetrating the metal and providing physical protection.

[0058] 1. In this invention, the organic coating forms a physical barrier on the surface of a poorly corrosion-resistant metal, preventing the metal from dissolving. The addition of the organic coating in photoelectrochemical cathodic protection enables the semiconductor photoanode to exhibit excellent performance. By effectively controlling the self-corrosion potential of the poorly corrosion-resistant metal through the organic coating, the electron transport channel between the semiconductor and the poorly corrosion-resistant metal is opened, promoting the transfer of photogenerated electrons from the semiconductor to the metal, and improving the photoelectrochemical cathodic protection capability of the semiconductor photoanode for the poorly corrosion-resistant metal.

[0059] 2. The preparation method involved in this invention is simple and mild, does not affect the metal surface structure, and the organic composite coating is dense and firmly adhered to the metal surface. Besides facilitating the implementation of photoelectrochemical cathodic protection technology on metals with poor corrosion resistance, the physical shielding effect of this coating on corrosive media can also inhibit metal corrosion in the absence of light, further enhancing the protective effect of this technology on metals.

[0060] 3. This invention is used to improve the photoelectrochemical cathodic protection of metals with poor corrosion resistance. This technology exhibits excellent performance in photoelectrochemical cathodic protection of metals with poor corrosion resistance. Attached Figure Description

[0061] Figure 1 The images show the photocurrent-time curves and photovoltage-time curves of the indium sulfide photoelectrochemical cathodic protection Q235 carbon steel system prepared in Example 1 and Comparative Example 1 of this invention.

[0062] Figure 2The images show the photocurrent-time curves and photovoltage-time curves of the indium sulfide / polydopamine / titanium dioxide composite layer photoelectrochemical cathodic protection Q345 carbon steel system prepared in Example 2 and Comparative Example 2 of this invention. Detailed Implementation

[0063] The following examples further illustrate specific embodiments of the present invention. It should be noted that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the present invention.

[0064] Example 1

[0065] (1) Preparation of silane coupling agent coating

[0066] Metals with poor corrosion resistance are immersed in a mixture containing silane coupling agent and heated in a water bath at 60°C for 2 hours, and then placed in a vacuum drying oven at 80°C for 12 hours.

[0067] The silane coupling agent mixture was prepared by adding 50 mL of a mixture of ethanol and water (volume ratio 1:10) to a 100 mL round-bottom flask, stirring and mixing, then adding 0.30 mL of silane coupling agent (KH550) and sonicating for 30 min.

[0068] The metal sheet is suspended above the silane coupling agent mixture, with a reserved area of ​​10 mm * 8 mm on the liquid surface, and the rest of the metal is vertically inserted into the KH550 mixture.

[0069] The metal with poor corrosion resistance is Q235 carbon steel, with dimensions of 10 mm * 25 mm * 1.5 mm.

[0070] Before use, Q235 carbon steel undergoes mechanical grinding and organic solvent cleaning. The metal surface is successively ground with 200-grit, 400-grit, and 800-grit sandpaper until no obvious scratches remain. The sample is then ultrasonically cleaned for 15 minutes each time with anhydrous ethanol and acetone. After cleaning, the sample surface is dried with nitrogen and placed in a vacuum drying oven at 50°C for 6 hours. The purpose is to remove adhering dust, oxide film, and other impurities from the metal surface.

[0071] (2) Preparation of indium sulfide semiconductor photoanode:

[0072] Indium sulfide semiconductor photoanodes were prepared using a hydrothermal method.

[0073] An indium sulfide precursor solution and FTO conductive glass were placed in a high-pressure reactor with a capacity of 50 mL polytetrafluoroethylene substrate, heated at 180°C for 8 h, cooled, and rinsed with deionized water to obtain an indium sulfide semiconductor film on the surface of the FTO conductive glass.

[0074] The indium sulfide precursor solution was prepared by completely dissolving indium nitrate powder and thiourea powder in 25 mL of deionized water, wherein the mass of indium nitrate powder and thiourea powder were 0.045 g and 0.023 g, respectively.

[0075] The FTO conductive glass measures 10 mm * 25 mm * 2 mm.

[0076] Before use, FTO conductive glass needs to be ultrasonically cleaned three times each with acetone and ethanol until the surface is clean and free of impurities, and then dried with nitrogen before use.

[0077] Before placing the FTO conductive glass into the reactor liner, the top needs to be wrapped with PTFE tape; the purpose is to leave the conductive surface of the sample not covered on the top, which will facilitate the subsequent connection of copper wires.

[0078] The FTO conductive glass is placed in the reactor liner with the conductive side facing down against the inner wall of the reactor and immersed in the mixed precursor solution.

[0079] The indium sulfide semiconductor film was rinsed with deionized water and then dried under vacuum at 50°C for 6 h.

[0080] (3) Implementation of photoelectrochemical cathodic protection technology

[0081] Indium sulfide semiconductor photoanode is directly irradiated by sunlight or simulated sunlight to induce photogenerated electrons in indium sulfide. Copper wires are used to connect the conductive surface of FTO conductive glass and the surface of Q235 carbon steel to establish an electron transport channel between the semiconductor and the carbon steel, thereby achieving photoelectrochemical cathodic protection of Q235 carbon steel by indium sulfide semiconductor photoanode.

[0082] The FTO conductive glass is connected to the Q235 carbon steel with copper wires, and the whole is considered to be conductive.

[0083] The copper wire connection method uses copper wires with iron alligator clips at both ends. One alligator clip is attached to the part of the FTO conductive glass that is not covered with indium sulfide, and the other alligator clip is attached to the part of the Q235 carbon steel that is not covered with silane coupling agent.

[0084] Example 2

[0085] (1) Preparation of water-based acrylic coating

[0086] A water-based acrylic resin coating was prepared on the surface of carbon steel using a brushing process.

[0087] Apply water-based acrylic resin to the front, sides, and bottom of the metal with poor corrosion resistance, but do not apply water-based acrylic resin to the top of the front of the metal, leaving an area of ​​10 mm * 8 mm.

[0088] The water-based acrylic resin coating on the metal front is approximately 40 μm thick, ensuring complete coverage of the four corners and bottom of the metal, and ensuring uniform resin application. It is then cured at room temperature for 7 days.

[0089] The back of the metal is coated with water-based acrylic resin, and the top of the back of the metal is not coated with water-based acrylic resin, corresponding to the front, and the area is the same as the front.

[0090] Control the thickness of the water-based acrylic resin coating on the back of the metal to be consistent with that on the front, and ensure that the resin coating is uniform. Cure at room temperature for 14 days.

[0091] The water-based acrylic resin is a (styrene-acrylic) general-purpose acrylic resin. The manufacturer and model number of the product purchased is Donglian Chemical 1065.

[0092] The metal with poor corrosion resistance is Q345 carbon steel, with dimensions of 10 mm * 25 mm * 1.5 mm.

[0093] Before use, Q345 carbon steel undergoes mechanical grinding and organic solvent cleaning. The metal surface is successively ground with 200-grit, 400-grit, and 800-grit sandpaper until no obvious scratches remain. The sample is then ultrasonically cleaned for 15 minutes each time with anhydrous ethanol and acetone. After cleaning, the sample surface is dried with nitrogen gas and placed in a vacuum drying oven at 50°C for 6 hours. The purpose is to remove adhering dust, oxide film, and other impurities from the metal surface.

[0094] (2) Fabrication of In2S3 / TiO2@PDA semiconductor photoanode:

[0095] FTO conductive glass was immersed in a mixture of titanium dioxide and dopamine and heated at 90°C for 3 h, and then placed in a vacuum drying oven at 60°C for 6 h to obtain a TiO2@PDA film on the surface of FTO conductive glass.

[0096] The titanium dioxide and dopamine mixture was prepared by adding 5 mL of deionized water, 0.015 g of dopamine hydrochloride, and 0.20 g of titanium dioxide to a 25 mL round-bottom flask and sonicating for 30 min. Then, 0.1 g of hexamethylenetetramine powder was added and dissolved in the solution, and mixed thoroughly to obtain the titanium dioxide and dopamine mixture.

[0097] The indium sulfide precursor solution was poured into a high-pressure reactor with a capacity of 50 mL polytetrafluoroethylene substrate, heated at 150 °C for 1 h, cooled, washed with deionized water, and freeze-dried.

[0098] The indium sulfide precursor solution was prepared by completely dissolving indium nitrate and thioacetamide in 25 mL of deionized water, wherein the mass of indium nitrate powder and thiourea powder were 0.027 g and 0.01 g, respectively.

[0099] 0.01 g of indium sulfide nanoparticles were ultrasonically dispersed in 10 mL of ethanol solution. 50 μL of the indium sulfide ethanol solution was drop-coated onto a TiO2@PDA film on the conductive surface of an FTO glass substrate and dried at 60 °C for 1 h. This process was repeated three times. Finally, the sample was placed with the conductive surface facing up in a muffle furnace and held at 350 °C for 30 min.

[0100] The FTO conductive glass is suspended above the mixture of titanium dioxide and dopamine, with a reserved area of ​​10 mm * 8 mm on the liquid surface, and the rest of the FTO conductive glass is vertically inserted into the mixture.

[0101] The FTO conductive glass measures 10 mm * 25 mm * 2 mm.

[0102] Before use, FTO conductive glass needs to be ultrasonically cleaned three times each with acetone and ethanol until the surface is clean and free of impurities, and then dried with nitrogen before use.

[0103] (3) Implementation of photoelectrochemical cathodic protection technology

[0104] In2S3 / TiO2@PDA semiconductor photoanode (direct irradiation with sunlight or simulated sunlight) induces indium sulfide to generate photoelectrons; copper wires are used to connect the conductive surface of FTO conductive glass and the surface of Q345 carbon steel to establish an electron transport channel between the semiconductor and the carbon steel, thereby realizing photoelectrochemical cathodic protection of Q345 carbon steel by indium sulfide semiconductor photoanode.

[0105] The FTO conductive glass is connected to the Q345 carbon steel with copper wires, and the whole is considered to be conductive.

[0106] The copper wire connection method uses copper wires with iron alligator clips at both ends. One alligator clip is attached to the part of the FTO conductive glass that is not covered, and the other alligator clip is attached to the part of the Q345 carbon steel that is not covered by water-based acrylic resin.

[0107] Comparative Example 1

[0108] Referring to steps (2) and (3) in Example 1, a system for photoelectrochemical cathodic protection of Q235 carbon steel without silane coupling agent was constructed.

[0109] (1) Preparation of indium sulfide semiconductor photoanode:

[0110] Indium sulfide semiconductor photoanodes were prepared using a hydrothermal method.

[0111] An indium sulfide precursor solution and FTO conductive glass were placed in a high-pressure reactor with a capacity of 50 mL polytetrafluoroethylene substrate, heated at 180°C for 8 h, cooled, and rinsed with deionized water to obtain an indium sulfide semiconductor film on the surface of the FTO conductive glass.

[0112] The indium sulfide precursor solution was prepared by completely dissolving indium nitrate powder and thiourea powder in 25 mL of deionized water, wherein the mass of indium nitrate powder and thiourea powder were 0.045 g and 0.023 g, respectively.

[0113] The FTO conductive glass measures 10 mm * 25 mm * 2 mm.

[0114] Before use, FTO conductive glass needs to be ultrasonically cleaned three times each with acetone and ethanol until the surface is clean and free of impurities, and then dried with nitrogen before use.

[0115] Before placing the FTO conductive glass into the reactor liner, the top needs to be wrapped with PTFE tape; the purpose is to leave the conductive surface of the sample not covered on the top, which will facilitate the subsequent connection of copper wires.

[0116] The FTO conductive glass is placed in the reactor liner with the conductive side facing down against the inner wall of the reactor and immersed in the mixed precursor solution.

[0117] The indium sulfide semiconductor film was rinsed with deionized water and then dried under vacuum at 50°C for 6 h.

[0118] (2) Implementation of photoelectrochemical cathodic protection technology

[0119] Indium sulfide semiconductor photoanode is directly irradiated by sunlight or simulated sunlight to induce photogenerated electrons in indium sulfide. Copper wires are used to connect the conductive surface of FTO conductive glass and the surface of Q235 carbon steel to establish an electron transport channel between the semiconductor and the carbon steel, thereby achieving photoelectrochemical cathodic protection of Q235 carbon steel by indium sulfide semiconductor photoanode.

[0120] The FTO conductive glass is connected to the Q235 carbon steel with copper wires, and the whole is considered to be conductive.

[0121] The copper wire connection method uses copper wires with iron alligator clips at both ends. One alligator clip is attached to the part of the FTO conductive glass that is not covered with indium sulfide, and the other alligator clip is attached to the part of the Q235 carbon steel that is not covered with silane coupling agent.

[0122] The dimensions of Q235 carbon steel are 10 mm * 25 mm * 1.5 mm.

[0123] Before use, Q235 carbon steel undergoes mechanical grinding and organic solvent cleaning. The metal surface is successively ground with 200-grit, 400-grit, and 800-grit sandpaper until no obvious scratches remain. The sample is then ultrasonically cleaned for 15 minutes each time with anhydrous ethanol and acetone. After cleaning, the sample surface is dried with nitrogen and placed in a vacuum drying oven at 50°C for 6 hours. The purpose is to remove adhering dust, oxide film, and other impurities from the metal surface.

[0124] Comparative Example 2

[0125] Referring to steps (2) and (3) in Example 2, a system for photoelectrochemical cathodic protection of Q345 carbon steel with indium sulfide without water-based acrylic resin was constructed.

[0126] (2) Fabrication of In2S3 / TiO2@PDA semiconductor photoanode:

[0127] FTO conductive glass was immersed in a mixture of titanium dioxide and dopamine and heated at 90°C for 3 h, and then placed in a vacuum drying oven at 60°C for 6 h to obtain a TiO2@PDA film on the surface of FTO conductive glass.

[0128] The titanium dioxide and dopamine mixture was prepared by adding 5 mL of deionized water, 0.015 g of dopamine hydrochloride, and 0.20 g of titanium dioxide to a 25 mL round-bottom flask and sonicating for 30 min. Then, 0.1 g of hexamethylenetetramine powder was added and dissolved in the solution, and mixed thoroughly to obtain the titanium dioxide and dopamine mixture.

[0129] The indium sulfide precursor solution was poured into a high-pressure reactor with a capacity of 50 mL polytetrafluoroethylene substrate, heated at 150 °C for 1 h, cooled, washed with deionized water, and freeze-dried.

[0130] The indium sulfide precursor solution was prepared by completely dissolving indium nitrate and thioacetamide in 25 mL of deionized water, wherein the mass of indium nitrate powder and thiourea powder were 0.027 g and 0.01 g, respectively.

[0131] 0.01 g of indium sulfide nanoparticles were ultrasonically dispersed in 10 mL of ethanol solution. 50 μL of the indium sulfide ethanol solution was drop-coated onto a TiO2@PDA film on the conductive surface of an FTO glass substrate and dried at 60 °C for 1 h. This process was repeated three times. Finally, the sample was placed with the conductive surface facing up in a muffle furnace and held at 350 °C for 30 min.

[0132] The FTO conductive glass is suspended above the mixture of titanium dioxide and dopamine, with a reserved area of ​​10 mm * 8 mm on the liquid surface, and the rest of the FTO conductive glass is vertically inserted into the mixture.

[0133] The FTO conductive glass measures 10 mm * 25 mm * 2 mm.

[0134] Before use, FTO conductive glass needs to be ultrasonically cleaned three times each with acetone and ethanol until the surface is clean and free of impurities, and then dried with nitrogen before use.

[0135] (2) Implementation of photoelectrochemical cathodic protection technology

[0136] Indium sulfide semiconductor photoanode is directly irradiated by sunlight or simulated sunlight to induce photogenerated electrons in indium sulfide. Copper wires are used to connect the conductive surface of FTO conductive glass and the surface of Q345 carbon steel to establish an electron transport channel between the semiconductor and the carbon steel, thereby achieving photoelectrochemical cathodic protection of Q345 carbon steel by indium sulfide semiconductor photoanode.

[0137] The FTO conductive glass is connected to the Q345 carbon steel with copper wires, and the whole is considered to be conductive.

[0138] The copper wire connection method uses copper wires with iron alligator clips at both ends. One alligator clip is attached to the part of the FTO conductive glass that is not covered with indium sulfide, and the other alligator clip is attached to the part of the Q345 carbon steel that is not covered with water-based acrylic resin.

[0139] The dimensions of Q345 carbon steel are 10 mm * 25 mm * 1.5 mm.

[0140] Before use, Q345 carbon steel undergoes mechanical grinding and organic solvent cleaning. The metal surface is successively ground with 200-grit, 400-grit, and 800-grit sandpaper until no obvious scratches remain. The sample is then ultrasonically cleaned for 15 minutes each time with anhydrous ethanol and acetone. After cleaning, the sample surface is dried with nitrogen gas and placed in a vacuum drying oven at 50°C for 6 hours. The purpose is to remove adhering dust, oxide film, and other impurities from the metal surface.

[0141] The photoelectrochemical cathodic protection performance of the photoelectrochemical protection systems containing organic coatings prepared in Examples 1 and 2, and the photoelectrochemical protection systems prepared in Comparative Examples 1 and 2, was tested.

[0142] The photoelectrochemical cathodic protection testing device consists of two electrolytic cells: a corrosion cell and a photocell, connected by a salt bridge. A carbon steel electrode and a photoanode, connected by wires, serve as the working electrode, silver chloride as the reference electrode, and a platinum sheet (1 cm x 1 cm) as the auxiliary electrode. The corrosion cell contains the carbon steel electrode, the silver chloride reference electrode, and the platinum sheet auxiliary electrode, with a 3.5 wt% NaCl solution as the electrolyte. The photocell contains FTO conductive glass, with a mixed solution of 0.25 mol / L Na₂S and 0.35 mol / L Na₂SO₃ as the electrolyte. A 300 W Xe lamp with an AM1.5 filter is used as the light source. The changes in photocurrent-time and photovoltage-time curves under illumination were measured using a CHI 660E electrochemical workstation, where "on" indicates illumination and "off" indicates no illumination. The performance test results of the photoelectrochemical cathodic protection coating are as follows:

[0143] Figure 1As can be seen, compared with the Q235 carbon steel surface without silane coupling agent (Comparison 1), the potential of the Q235 carbon steel surface coated with silane coupling agent under simulated sunlight irradiation (Example 1) is significantly negatively shifted. At this time, the cathodic protection potential in Example 1 drops to about -0.87 V. Figure 1 (a) This indicates that under illumination, photogenerated electrons migrate to the carbon steel surface in Example 1, providing photoelectrochemical cathodic protection for the carbon steel. Under simulated sunlight irradiation, the photocurrent density in Example 1 is greater than 0, while the photocurrent density in Comparative Example 1 is basically less than 0. Furthermore, the photocurrent density in Example 1 is significantly higher than that in Comparative Example 1. Figure 1 (b) This illustrates that in Example 1, the indium sulfide photoanode can provide cathodic protection current for carbon steel coated with silane coupling agent, while in Comparative Example 1, the photocurrent provided by the indium sulfide photoanode is insufficient to protect the carbon steel. Figure 2 It can be obtained with Figure 1 Similar results indicate that Q345 carbon steel can achieve better indium sulfide / polydopamine / titanium dioxide photoelectrochemical cathodic protection after being coated with water-based acrylic resin.

[0144] from Figure 1 and 2 It can be seen that in Examples 1 and 2, coating the carbon steel surface with silane coupling agent or water-based acrylic resin can regulate the self-corrosion potential of the carbon steel, which is beneficial for the transfer of indium sulfide photogenerated electrons to the carbon steel. In Comparative Examples 1 and 2, without coating the carbon steel surface with silane coupling agent or water-based acrylic resin, the low self-corrosion potential of the carbon steel hinders the transfer of indium sulfide photogenerated electrons to the carbon steel, and the photogenerated electrons transferred to the carbon steel surface are insufficient to resist carbon steel corrosion. Therefore, the photoanode can provide cathodic protection for the carbon steel in Examples 1 and 2, and the cathodic protection potential of Example 1 is within the cathodic protection potential criterion range; however, it is difficult to provide cathodic protection for the carbon steel in Comparative Examples 1 and 2. This method can significantly improve the photoelectrochemical cathodic protection provided by semiconductor photoanodes for metals with poor corrosion resistance.

Claims

1. A method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance, characterized in that, Includes the following steps: (1) Preparation of organic resins: An organic coating is prepared on the surface of a metal with poor corrosion resistance, and a position is reserved to be left uncovered. The organic coating is cured at room temperature, forming a protective film with physical shielding effect on the surface of the metal with poor corrosion resistance. A position is reserved at the top of the corrosion-resistant metal surface to be left uncovered for copper wire connection. (2) Fabrication of semiconductor photoanodes: A semiconductor thin film is prepared on a conductive substrate, with a reserved area at the top that is not covered by the semiconductor thin film. (3) Photoelectrochemical cathodic protection: A copper wire is used to connect the photoanode and the pre-reserved position on the poorly corrosion-resistant metal that is not covered with an organic coating, thus establishing an electron transport channel between the semiconductor and the poorly corrosion-resistant metal. The semiconductor photoanode is directly irradiated with sunlight or simulated sunlight to induce the semiconductor to generate photoelectrons; thereby realizing photoelectrochemical cathodic protection of the poorly corrosion-resistant metal by the semiconductor photoanode.

2. The method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance according to claim 1, characterized in that: The organic coating includes acrylic resins, epoxy resins, and silane coupling agents; the metal with poor corrosion resistance includes iron and its alloys.

3. The method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance according to claim 1, characterized in that: The conductive materials include FTO conductive glass, ITO conductive glass, and titanium plates; the semiconductor photoanodes include elemental semiconductors, oxide semiconductors, sulfide semiconductors, nitride semiconductors, phosphide semiconductors, and their composites.

4. The method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance according to claim 1, characterized in that: The copper wire is welded to both ends with iron alligator clips. One alligator clip is attached to the conductive surface of the substrate where the photoanode is not covered by the semiconductor thin film, and the other alligator clip is attached to the surface of the metal where the organic coating is not covered.

5. The method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance according to claim 1, characterized in that: Before use, the metal with poor corrosion resistance is mechanically polished and cleaned with organic solvents. The metal surface is polished with sandpaper until there are no obvious scratches on the surface; the sample is then ultrasonically cleaned with organic solvents.

6. The method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance according to claim 1, characterized in that: Organic coatings are prepared on metal surfaces with poor corrosion resistance using brushing, spraying, dipping, and electrophoretic coating processes.

7. The method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance according to claim 1, characterized in that: Semiconductor thin films are prepared on conductive substrates using methods such as hydrothermal, solvothermal, oxidation, sol-gel, chemical vapor deposition, physical vapor deposition, or combinations thereof.

8. The method for semiconductor photoelectrochemical cathodic protection of metals with poor corrosion resistance according to claim 1, characterized in that: The preparation of the semiconductor photoanode includes the following steps: 1) FTO conductive glass was immersed in a mixture of titanium dioxide and dopamine and heated. After drying, TiO2@PDA film was obtained on the surface of FTO conductive glass. The mass ratio of dopamine hydrochloride, titanium dioxide, and hexamethylenetetramine in the titanium dioxide and dopamine mixture is (0.1-0.2):(2-4):1; FTO conductive glass is inserted into a mixture of titanium dioxide and dopamine, with a reserved area on the liquid surface that is not inserted into the mixture. 2) Pour the indium sulfide precursor solution into a high-pressure reactor, heat and react, then cool, wash with deionized water, and dry to obtain indium sulfide nanoparticles. The indium sulfide precursor solution is an aqueous solution of indium nitrate and thioacetamide, wherein the mass ratio of indium nitrate to thiourea is (2-3):1; 3) Indium sulfide nanoparticles were ultrasonically and uniformly dispersed in an ethanol solution to obtain an indium sulfide ethanol solution with a concentration of (1-2) g / L. The indium sulfide ethanol solution was drop-coated onto a TiO2@PDA film on the conductive surface of an FTO glass and dried. The sample was then placed in a muffle furnace with the conductive surface facing up and kept at 300-400℃ for 20-40 min to obtain an In2S3 / TiO2@PDA semiconductor photoanode.

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