A cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material, its preparation method and application

Abstract

This invention relates to the field of corrosion and fouling prevention of nanomaterials, and particularly to a cascaded double-Z type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material, its preparation method, and its application. The preparation method includes the following steps: growing TiO2 nanorods on a conductive substrate to obtain a TiO2 photoelectrode; placing the TiO2 photoelectrode in a mixed solution containing Mn, Ni, In, and sulfur sources for a hydrothermal reaction to obtain the cascaded double-Z type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material. This invention solves the problems of low photoelectric conversion efficiency and slow electron migration rate inherent in TiO2, providing 310 mV of complete cathodic protection for 304 SS, achieving 100% inactivation efficiency of Pseudomonas aeruginosa within 60 min, and maintaining 100% inhibition rate in 5 photocatalytic inactivation experiments, demonstrating excellent photocatalytic sterilization stability.

Description

Technical Field

[0001] This invention relates to the field of corrosion and fouling prevention of nanomaterials, and in particular to a cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material, its preparation method and application. Background Technology

[0002] Metallic materials play an irreplaceable role in marine engineering and coastal infrastructure due to their excellent mechanical properties and machinability. However, the harsh marine environment poses a dual challenge to metallic structures: electrochemical corrosion and biofouling. Traditional protection strategies, such as organic coatings, sacrificial anodes, or impressed current cathodic protection, have limitations in terms of long-term effectiveness, environmental friendliness, and continuous energy consumption. Therefore, developing a novel protection technology that can proactively, continuously, and environmentally compatiblely address these two threats is urgently needed. Photoelectrochemical cathodic protection (PECCP) technology utilizes the property of semiconductor materials to generate photoelectrons under illumination. When coupled with 304 stainless steel (304 SS), it can provide a cathodic polarization current, thereby inhibiting the anodic dissolution reaction at its source and achieving "green" corrosion protection for PECCP. Simultaneously, photocatalytic sterilization technology utilizes photogenerated holes and reactive oxygen species (ROS) generated by semiconductors to effectively inactivate microorganisms and prevent biofilm formation. In theory, a cleverly designed photoelectrode material can synergistically utilize photogenerated electrons and holes to simultaneously achieve the dual functions of corrosion prevention and fouling prevention, providing a highly promising solution for the long-term protection of metallic materials in marine environments.

[0003] Although existing studies have reported on the application of TiO2-based composite photoelectrodes in single areas such as corrosion prevention or antifouling, the following shortcomings exist: (1) Single function: Most studies only focus on the single function of corrosion prevention or antifouling, and lack a systematic design for the synergistic effect of the two; (2) Limited charge separation efficiency: There is still room for improvement in the charge separation and transport efficiency of traditional type II or simple Z-type heterojunctions, which is difficult to meet the requirements of high-efficiency PECCP for electron injection. (3) Insufficient structural stability: Some composite structures are prone to photocorrosion or material collapse failure during long-term use, which affects the actual application life; (4) Complex manufacturing process: The preparation of some high-performance photoelectrodes requires expensive equipment or harsh conditions, which is not conducive to large-scale production.

[0004] Therefore, developing a novel TiO2-based photoelectrode material with a cascaded double-Z-type heterostructure that can synergistically achieve efficient photoelectrochemical cathodic protection and photocatalytic sterilization, and which is easy to prepare and has good stability, is of great scientific significance and application value for promoting the advancement of marine environmental metal protection technology. Summary of the Invention

[0005] Based on the above, this invention provides a cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a method for preparing a cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material, comprising the following steps: Step 1: TiO2 nanorods are grown on the surface of a conductive substrate to obtain a TiO2 photoelectrode; Step 2: The TiO2 photoelectrode is placed in a mixed solution for hydrothermal reaction to obtain a cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material; The mixed solution includes Mn source, Ni source, In source and sulfur source.

[0007] This invention enables the simultaneous in-situ growth of Ni3In2S2 / MnIn2S4 on the surface of TiO2 nanorods using a hydrothermal method on a mixed solution containing Mn, Ni, In, and S sources, thereby constructing a cascaded double-Z type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material.

[0008] In a preferred embodiment of the present invention, in step 1, a TiO2 photoelectrode is obtained by placing a conductive substrate in an aqueous hydrochloric acid solution containing Ti and K sources for a hydrothermal reaction, followed by washing and annealing.

[0009] In some embodiments of the present invention, the conductive substrate is an FTO conductive substrate; before placing the conductive substrate in an aqueous hydrochloric acid solution containing Ti source and K source for hydrothermal reaction, the present invention further includes a step of cleaning the conductive substrate with anhydrous ethanol and deionized water, the cleaning time being set to 20~40 min / time, the present invention does not make a special limitation on the number of cleaning times, and adopts the cleaning times commonly used by those skilled in the art.

[0010] In a preferred embodiment of the present invention, the hydrochloric acid aqueous solution containing Ti source and K source is prepared by adding Ti source and K source to hydrochloric acid aqueous solution and mixing; the concentration of the hydrochloric acid aqueous solution is 6~12 mol / L; the Ti source is tetraisopropyl titanate (C 12 H 28 O4Ti); the K source is potassium chloride (KCl); the ratio of the Ti source to the K source and the hydrochloric acid aqueous solution is (0.36~0.72) mL : (0.15~0.3) g : (30~60) mL.

[0011] Within the above ratio range, C12 H 28 O4Ti exhibits a moderate hydrolysis rate and a stable sol system. KCl can effectively regulate the nucleation and crystallization behavior of TiO2, thereby forming a continuous, dense, and moderately thick TiO2 substrate film on the FTO surface. When the amounts of each component are below or above the above-mentioned proportions, problems such as insufficient TiO2 loading, excessively thin or thick film layers, particle agglomeration, and film layer detachment may occur, making it impossible to obtain a suitable TiO2 substrate structure.

[0012] In a preferred embodiment of the present invention, the hydrothermal reaction is carried out at a temperature of 160-180 °C for 4-6 h; the annealing is specifically carried out at 300-500 °C for 1-3 h in an air atmosphere. The product is washed 2-5 times alternately with a 95% (v / v) ethanol aqueous solution and deionized water.

[0013] By controlling the hydrothermal temperature and time, annealing temperature and time, and other conditions within the aforementioned ranges, the crystallization behavior, microstructure, and interfacial bonding of TiO2 can be precisely controlled, thereby preparing TiO2 substrates with appropriate crystallinity, dense structure, continuous film, strong adhesion, and high purity. Conditions that are too high or too low can easily lead to problems such as poor crystallization, loose film, cracking and detachment, or impurity residue, failing to obtain the optimal TiO2 substrate structure that meets the requirements of subsequent applications.

[0014] In a preferred embodiment of the present invention, in step 2, the Mn source is MnCl2·4H2O; the Ni source is NiCl2·6H2O; the In source is InCl3·4H2O; and the sulfur source is thioacetamide (CH3CSNH2, abbreviated as TAA).

[0015] In a preferred embodiment of the present invention, in step 2, the mixed solution is prepared by dissolving a Mn source, a Ni source, an In source, and a sulfur source in water; the ratio of the amount of Mn source, Ni source, In source, and sulfur source to water is (0~0.2) mmol: (0~0.2) mmol: (0.4~0.8) mmol: (0.9~1.8) mmol: (30~60) mL.

[0016] Different composite materials were obtained by adding different amounts of Mn source and different amounts of Ni source, namely TiO2, TiO2 / Ni3In2S2 (T / NIS), TiO2 / Ni3In2S2 / MnIn2S4 (abbreviated as T / NIS / MIS) and TiO2 / MnIn2S4 (T / MIS) photoelectrode materials. When the molar ratio of Ni3In2S2 to MnIn2S4 is 4, the obtained photoelectrode is denoted as T / NIS / MIS-1. When the molar ratio of Ni3In2S2 to MnIn2S4 is 0.25, the obtained photoelectrode is denoted as T / NIS / MIS-2.

[0017] In a preferred embodiment of the present invention, in step 2, the temperature of the hydrothermal reaction is 175~195 ℃ and the time is 1~12 h.

[0018] This invention achieves controllable and robust loading of Ni3In2S2 and MnIn2S4 and their composite components onto a TiO2 substrate by strictly controlling the molar ratios of Mn, Ni, In, and S sources and the amount of solvent, and matching appropriate hydrothermal temperatures and times. This results in a composite photoelectrode with good crystallinity, a well-defined heterojunction interface, high carrier separation efficiency, excellent photoelectric response, and a stable structure. When the amounts of raw materials or reaction conditions are below the aforementioned range, the active components (Ni3In2S2 and MnIn2S4) are insufficient, leading to inadequate photoelectric response and preventing the acquisition of the optimal photoelectrode material to meet high-performance requirements. When the amounts of raw materials or reaction conditions exceed the aforementioned range, excessive aggregation of the active components occurs, obscuring the active sites of TiO2 and easily becoming secondary recombination centers for carriers, increasing the difficulty of electron-hole separation.

[0019] Step 2, after the hydrothermal reaction is completed, also includes a washing step, which specifically involves rinsing with ethanol and deionized water alternately.

[0020] The second technical solution of the present invention is a cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material (hereinafter referred to as cascaded double Z-type T / NIS / MIS photoelectrode material) prepared by the above preparation method.

[0021] The third technical solution of this invention is the application of the above-mentioned cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material in the protection of metallic materials in marine environments.

[0022] In a preferred embodiment of the present invention, the protection of marine environmental metal materials includes photoelectrochemical cathodic protection and / or photocatalytic antifouling. Specifically, it can be applied to single anticorrosive (NaCl solution) / single antifouling (a mixed solution of PBS and bacterial solution) / coupled systems (a mixed solution of NaCl and bacterial solution).

[0023] Compared with the prior art, the present invention has the following beneficial effects: This invention constructs a TiO2 / Ni3In2S2 / MnIn2S4 photoelectrode material with interwoven nanosheet-particle clusters, characterized by a cascaded double-Z heterostructure. This invention is used to systematically evaluate its synergistic efficacy in PECCP and photocatalytic inactivation of marine bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli). This synergistic strategy addresses the challenges of low photoelectric conversion efficiency and slow electron migration rate inherent in TiO2-based materials, providing 310 mV of complete cathodic protection for 304 SS. It achieves 100% inactivation efficiency of Pseudomonas aeruginosa within 60 min, and maintains 100% inhibition rate in five photocatalytic inactivation experiments, demonstrating excellent photocatalytic sterilization stability.

[0024] This invention utilizes MnIn2S4 and Ni3In2S2 to co-sensitize TiO2, forming a cascaded double Z-type heterojunction, achieving complementary advantages between the materials. On one hand, the more negative conduction band of MnIn2S4 can act as a "trap" for photogenerated electrons, allowing them to react with dissolved oxygen to generate O2. - On the other hand, Ni3In2S2 acts as an "intermediate bridge," optimizing the charge migration path while retaining the valence band of TiO2, which possesses strong oxidizing capabilities. In short, this double Z-shaped structure cleverly achieves efficient separation of photogenerated electrons and holes through the Ni3In2S2 intermediate layer, thereby synergistically improving the generation efficiency and yield of ROS.

[0025] This invention successfully fabricates a TiO2 / Ni3In2S2 / MnIn2S4 photoelectrode by co-modifying TiO2 nanorods with MnIn2S4 and Ni3In2S2 using a simple two-step hydrothermal method. The process is simple, the raw materials are readily available, and it is easy to scale up for industrial production.

[0026] This invention not only verifies the superior performance of cascaded double Z-type heterojunctions in dual applications of corrosion and fouling prevention, but also aims to elucidate the migration path of internal charge carriers and the intrinsic relationship between corrosion and fouling prevention synergy through in-depth mechanism research, thereby providing a new approach for developing next-generation bifunctional photoelectrodes for complex marine environments. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1The images are scanning electron microscope (SEM) images of the photoelectrodes prepared in Examples 1 and 2; wherein, A is the SEM image of the TiO2 photoelectrode prepared in step 1 of Example 1, B is the SEM image of the T / MIS prepared in Example 1, C is the SEM image of the T / NIS / MIS-2 prepared in Example 2, and D is the SEM image of the T / NIS prepared in Example 1.

[0029] Figure 2 The XRD patterns are of the photoelectrode materials (TiO2, T / NIS, T / NIS / MIS-1, T / NIS / MIS-2 and T / MIS photoelectrodes) prepared in Examples 1 and 2.

[0030] Figure 3 The high-resolution spectra (HRTEM) of T / NIS / MIS-2 are shown in Figures A and B1, which are the (101) and (110) crystal planes of TiO2, Figures B2 and C are the (200) and (111) crystal planes of MIS, and Figures D and E are the (104) and (110) crystal planes of NIS.

[0031] Figure 4 The OCP(a) and of the photoelectrode materials (TiO2, T / NIS, T / NIS / MIS-1, T / NIS / MIS-2 and T / MIS photoelectrode) prepared in Examples 1 and 2 are shown. i (b) Curve showing how it changes over time.

[0032] Figure 5 The LSV curve (a), PL spectrum (b), EIS spectrum (c), and Bode plot (d) of the photoelectrode materials prepared in Examples 1 and 2 are shown.

[0033] Figure 6 The images show the UV-Vis diffuse reflectance spectra (a), Tauc diagrams (b, c), and Mott-Schottky diagrams (d) of the photoelectrode materials prepared in Examples 1 and 2.

[0034] Figure 7 The graphs show the efficiency of the photoelectrode materials prepared in Examples 1 and 2 in inactivating Pseudomonas aeruginosa at different times (A), the inactivation rate of T / NIS / MIS-2 against Escherichia coli and Staphylococcus aureus (B), the OCP change curves of T / NIS / MIS-2 in a single system (anti-corrosion) and a coupled system (anti-corrosion + anti-fouling) (C), and the bar graphs comparing the single system (anti-fouling) and the coupled system (anti-corrosion + anti-fouling) (D).

[0035] Figure 8 The bar graph shows the cyclic stability of the T / NIS / MIS-2 photoelectrode prepared in Example 2 after six photocatalytic inactivations of Pseudomonas aeruginosa.

[0036] Figure 9 This is a schematic diagram illustrating the synergistic effect of corrosion and contamination prevention on the cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode of the present invention. Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] This invention relates to a dual-Z type T / NIS / MIS heterojunction photoelectrode material suitable for PECCP and prevention of marine biofouling, aiming to address the problems commonly found in current single anti-corrosion or single antifouling systems, such as low photogenerated carrier separation efficiency, low solar energy utilization, and insufficient understanding of the intrinsic relationship between anti-corrosion and antifouling synergy. Based on the good bandgap matching between TiO2, NIS, and MIS, the constructed cascaded dual-Z type heterostructure can drive photogenerated electrons (e) and holes (h). +This directional charge transfer mechanism enables efficient separation and migration along specific paths, significantly improving photoelectric conversion efficiency and simultaneously endowing the material with excellent cathodic protection properties and remarkable marine bacteria inactivation capabilities, thus achieving a unified function of corrosion prevention and antifouling. Furthermore, by precisely designing the addition amounts of NIS and MIS, this invention achieves effective control over the microstructure of MIS and NIS crystals. The resulting unique multi-level structure of interwoven nanosheets and particle clusters creates more active sites for ROS generation and provides a wide contact surface for microbial attachment, effectively increasing the likelihood of interactions between microorganisms and reactive oxygen species. This configuration design synergistically enhances light capture and carrier separation, providing an innovative approach and material platform for efficiently coupling corrosion and antifouling properties at the same electrode interface.

[0043] The cultivation methods for marine bacteria (Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus) involved in the experiments of this invention are not the focus of this invention's patent protection. This invention does not impose any particular limitations on these cultivation methods and employs techniques commonly used by those skilled in the art. In some specific experimental processes of this invention, the methods for culturing marine bacteria (Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus) are as follows: LB medium was used to culture *Pseudomonas aeruginosa*. The specific preparation method was as follows: 1.0 g sodium chloride, 1.0 g tryptone, and 0.5 g yeast extract were thoroughly dissolved in an appropriate amount of deionized water, and then the volume was adjusted to 100 mL. The prepared liquid medium was placed in an Erlenmeyer flask and sterilized at 121 °C for 20 min. After naturally cooling to room temperature, 1.0 mL of *Pseudomonas aeruginosa* bacterial suspension was aseptically inoculated. The inoculated medium was then placed in a shaker at a constant temperature (35 °C) and a constant speed (150 rpm / min) for 12 hours. If solid agar plates were to be prepared, agar powder was added at a concentration of 12.0 g / L before sterilizing the above liquid medium components. After sterilization and cooling to 50–60 °C, the agar was poured into petri dishes under aseptic conditions to solidify (the culture protocols and procedures for *Staphylococcus aureus* and *Escherichia coli* were the same).

[0044] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0045] The hydrochloric acid used in this embodiment of the invention is a 12 mol / L hydrochloric acid aqueous solution.

[0046] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1 In this embodiment, T / NIS and T / MIS photoelectrode materials are prepared using a two-step simplified hydrothermal method based on TiO2 photoelectrodes. The steps are as follows: (1) Under continuous magnetic stirring, 30 mL of hydrochloric acid was slowly added dropwise to an equal volume of pure water, and after stirring for 10 min, solution G was obtained; then 0.3 g of potassium chloride (KCl) and 0.72 mL of tetraisopropyl titanate (C) were added to solution G in sequence. 12 H 28 (O4Ti), continue stirring for 60 min until the system is homogeneous, denoted as solution H. Place the cleaned FTO conductive substrate and solution H together in a hydrothermal reactor and react hydrothermally at 180 ℃ for 6 h. After the reaction, wash the product three times alternately with 95% ethanol solution and deionized water. Finally, transfer the sample to a muffle furnace and anneal at 450 ℃ in air for 2.5 h to obtain the target TiO2 photoelectrode.

[0048] (2) Dissolve 0.2 mmol of MnCl2·4H2O, 0.4 mmol of InCl3·4H2O and 0.9 mmol of TAA together in 30 mL of deionized water to form solution K. Then place the TiO2 photoelectrode obtained in step (1) in solution K and grow in situ at 195 °C for 9 h. Finally, rinse with ethanol and deionized water alternately to obtain T / MIS photoelectrode material.

[0049] 0.2 mmol of NiCl2·6H2O, 0.4 mmol of InCl3·4H2O and 0.9 mmol of TAA were dissolved together in 30 mL of deionized water to form solution K. The TiO2 photoelectrode obtained in step (1) was then placed in solution K and grown in situ at 195 °C for 9 h. Finally, the T / NIS photoelectrode material was obtained by rinsing with ethanol and deionized water alternately.

[0050] Example 2 In this embodiment, cascaded dual-Z type T / NIS / MIS-1 and T / NIS / MIS-2 photoelectrode materials were prepared using a two-step simplified hydrothermal method based on TiO2 photoelectrodes. The steps are as follows: (1) Same as step (1) in Example 1.

[0051] (2) Dissolve 0.04 mmol of MnCl2·4H2O, 0.16 mmol of NiCl2·6H2O, 0.4 mmol of InCl3·4H2O and 0.9 mmol of TAA together in 30 mL of deionized water to form solution K. Then place the TiO2 photoelectrode obtained in step (1) in solution K and grow in situ at 195 °C for 9 h. Finally, rinse with ethanol and deionized water alternately to obtain T / NIS / MIS-1 photoelectrode material.

[0052] 0.16 mmol of MnCl2·4H2O, 0.04 mmol of NiCl2·6H2O, 0.4 mmol of InCl3·4H2O, and 0.9 mmol of TAA were dissolved together in 30 mL of deionized water to form solution K. The TiO2 photoelectrode obtained in step (2) was then placed in solution K and grown in situ at 195 °C for 9 h. Finally, the T / NIS / MIS-2 photoelectrode material was obtained by rinsing with ethanol and deionized water alternately.

[0053] The method for culturing marine bacteria (Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus) is as follows: LB medium was used to culture *Pseudomonas aeruginosa*. The specific preparation method was as follows: 1.0 g sodium chloride, 1.0 g tryptone, and 0.5 g yeast extract were thoroughly dissolved in an appropriate amount of deionized water, and then the volume was adjusted to 100 mL. The prepared liquid medium was placed in an Erlenmeyer flask and sterilized at 121 °C for 20 min. After naturally cooling to room temperature, 1.0 mL of *Pseudomonas aeruginosa* bacterial suspension was aseptically inoculated. The inoculated medium was then placed in a shaker at a constant temperature (35 °C) and a constant speed (150 rpm / min) for 12 hours.

[0054] The culture protocols and procedures for Staphylococcus aureus and Escherichia coli are the same as above.

[0055] Characterization and performance testing of photoelectrodes 1. Phase characterization of photoelectrodes The microstructure and structure (SEM) of the photoelectrodes prepared in Examples 1 and 2 were analyzed, and the results are as follows: Figure 1 As shown; Figure 1 In the image, A is the SEM image of the TiO2 photoelectrode prepared in step 1 of Example 1, B is the SEM image of the T / MIS prepared in Example 1, C is the SEM image of the T / NIS / MIS-2 prepared in Example 2, and D is the SEM image of the T / NIS prepared in Example 1. TiO2 ( Figure 1 A) exhibits a directionally aligned one-dimensional nanorod structure with uniform rod morphology (diameter 100-200 nm) and a relatively smooth surface. This structure provides a directional transport path for photogenerated carriers. Figure 1 As shown in Figure B, ultrathin nanosheets of MnIn2S4 cover the surface of TiO2 nanorods. The MnIn2S4 nanosheets are 5-10 nm thick and are stacked together, almost completely obscuring the TiO2 substrate. However, this structure increases the specific surface area of ​​the material and is expected to promote carrier separation by constructing a heterojunction structure. Figure 1As shown in Figure C, Ni3In2S2 is interwoven with MnIn2S4 nanosheets in the form of nanoparticles, forming a multi-level "sheet-particle" structure; at the same time, the interlayer spacing of MnIn2S4 nanosheets is slightly increased. This multi-level morphology significantly increases the number of active sites, which can enhance the PECCP effect on 304 SS. Figure 1 As shown in Figure D, Ni3In2S2 is generally loaded onto TiO2 in the form of aggregated nanoparticle clusters. Because the particles obscure the TiO2 substrate, the overall morphology uniformity is poor. SEM analysis reveals that the ratio of MnIn2S4 to Ni3In2S2 directly affects the dispersibility of the composite structure and its contact effect with the TiO2 interface. When pure MnIn2S4 or Ni3In2S2 modifies the TiO2 surface, the active sites are singular or the particles easily aggregate. Only the formed "plate-particle" hierarchical structure can improve the separation efficiency and transmission rate of the photoelectrode.

[0056] The XRD results of the photoelectrode materials prepared in Examples 1 and 2 were analyzed, and the results are as follows: Figure 2As shown. Pure SnO2 exhibits distinct diffraction peaks at 26.6°, 33.8°, 37.8°, 51.7°, 61.7°, and 65.7°, corresponding to its (110), (101), (200), (211), (310), and (301) crystal planes (JCPDS No. 46-1088). Meanwhile, the TiO2 sample displays characteristic peaks at 27.4°, 36.1°, 54.3°, 62.7°, and 69.8°, perfectly matching the (110), (101), (211), (002), and (112) crystal planes of tetragonal TiO2 (JCPDS No. 90-0090), confirming the high crystallinity of both compositions. Furthermore, the XRD results of four different Ni3In2S2 and MnIn2S4 contents of T / NIS / MIS composite materials were compared. Characteristic peaks at 23.2°, 33.3°, 51.7°, 62.3°, and 69.9° were observed in the T / NIS photoelectrode, corresponding to the (012), (110), (205), (027), and (220) crystal planes of the orthorhombic Ni3In2S2 (JCPDS No. 48-1776). Diffraction peaks at 14.3°, 27.6°, and 48.0° were observed in the T / MIS photoelectrode, corresponding to the (111), (311), and (440) crystal planes of the cubic spinel MnIn2S4 (JCPDS No. 79-1018). Meanwhile, it was observed that the peak intensity at 62.3° was stronger in the T / NIS / MIS-1 photoelectrode than in the T / NIS / MIS-2, which can be attributed to the increased proportion of Ni3In2S2. Conversely, with the increase of the MnIn2S4 content, the characteristic peak at 48.0° was visually observed to continuously strengthen. These XRD characterization results not only verify the integrity of the crystal structure but also confirm the tunability of its component ratios.

[0057] The HRTEM results of the T / NIS / MIS-2 photoelectrode material prepared in Example 2 were analyzed, and the results are as follows: Figure 3As shown (Insets A and B1 are the (101) and (110) crystal planes of TiO2, insets B2 and C are the (200) and (111) crystal planes of MIS, and insets D and E are the (104) and (110) crystal planes of NIS). Rod-like microstructures and interwoven MnIn2S4 and Ni3In2S2 nanosheets on their surfaces are clearly observed. The interfacial properties between different materials can be seen by magnifying the yellow area in the upper right inset. Regions A, B, C, D, and E are labeled according to the stacking of nanosheets and nanoparticles. HRTEM images clearly distinguish the crystal core and the amorphous surface regions. The (101) crystal plane of region A corresponds to the clear lattice fringes of TiO2 with a lattice spacing of 0.240 nm. Regions B1 and B2 revealed lattice fringes with spacings of 0.322 nm and 0.531 nm, respectively, which can be attributed to the (110) and (200) crystal planes of TiO2 and MnIn2S4. A lattice fringe with a spacing of 0.621 nm (region C) corresponds to the (111) crystal plane of MnIn2S4. Lattice fringes of 0.276 nm and 0.271 nm were observed in regions D and E, both belonging to Ni3In2S2, corresponding to its (104) and (110) crystal planes. In summary, the analysis confirms that the highly crystallinity TiO2, MnIn2S4, and Ni3In2S2 are tightly connected at interfaces, and the results, consistent with XRD, indicate that the T / NIS / MIS photoelectrode material has been successfully prepared.

[0058] 2. Corrosion resistance test of photoelectrode All photoelectrochemical performance tests of this invention were performed using a VersaSTAT 3F electrochemical workstation (Ametek Trading Co., Ltd., China). OCP-t curves were tested using a two-electrode system (potential change of the coupled working electrode (WE) relative to the reference electrode (RE): WE was determined using 304 SS and the photoelectrodes prepared in Examples 1-2, and RE was a saturated calomel electrode (SCE). During the test, OCP (200 s on / off time constituted one cycle) and... i (One cycle is 100 s of light on / off) Record for 5 complete cycles. it Curve testing was performed in ZRA mode. The specific wiring method was as follows: connect the prepared series of photoelectrodes to WE, and connect the 304 SS to both RE and ground (GND).

[0059] The OCP of the photoelectrode materials prepared in Examples 1 and 2 and i The results were analyzed, and the results are as follows: Figure 4As shown. In the PECCP system, after the photoelectrode is coupled to the 304 SS substrate, the negative shift in the OCP value under intermittent illumination is the core indicator for evaluating the PECCP performance of the photoelectrode. The increase in this negative potential shift reflects an increase in the number of photogenerated electrons migrating from the photoelectrode to the 304 SS substrate, directly corresponding to enhanced protective performance. Figure 4 The OCP-t results of the a-type model showed that all tested photoelectrodes exhibited a significant negative shift in OCP after light-triggered activation. This phenomenon confirms that photogenerated electrons generated within the photoelectrode under illumination can be directionally transported to the 304 SS surface via the heterojunction interface and external circuitry, thereby achieving cathode polarization protection. After loading MnIn2S4 and Ni3In2S2 onto oriented TiO2 nanorods, respectively, the stability of the coupling system was improved. E OCP The electron transfer efficiency reached 230 mV (T / MIS) and 190 mV (T / NIS), respectively, exhibiting a more pronounced negative offset characteristic compared to the 101 mV of TiO2 nanorods. This indicates that the introduction of plate-like and particulate ternary sulfides can synergistically improve the electron transfer efficiency of the system. For the composite photoelectrode with simultaneous addition of MIS-NIS, the steady-state values ​​of T / NIS / MIS-1 and T / NIS / MIS-2... E OCP The active sites were 255 mV and 311 mV, respectively, both superior to the T / MIS, T / NIS, and TiO2 photoelectrodes. This indicates that the interweaving of multi-level morphologies can significantly increase the number of active sites, thereby avoiding the obstruction of photogenerated carrier separation and migration due to the stacking or aggregation of single morphologies. Among them, the T / NIS / MIS-2 photoelectrode showed the largest... E OCP Furthermore, the negative shift potential remained consistent throughout the five light-avoidance cycles, indicating the high durability of the photoelectrode and its continuous and stable cathodic protection capability and application potential. Figure 4 Figure b shows the photoelectrode under intermittent simulated illumination conditions. it Response curve. i The value directly reflects the quality of the photoelectrochemical protection performance of the photoelectrode, which is in good consistency with the trend shown in the OCP test. Analysis and comparison of the results revealed that, compared to TiO2 (1.2 μA·cm⁻¹), -2 Of the other four photoelectrode materials, T / NIS / MIS-2 exhibits the most sensitive forward photocurrent characteristics, while T / NIS / MIS-2 demonstrates the best photocurrent response performance. i The peak value can reach 11.6 μA·cm. -2 It is approximately 9.6 times that of TiO2. It is worth noting that T / NIS / MIS-1 (10.3 μA·cm⁻¹) -2 ) and T / NIS / MIS-2i Both are higher than T / MIS (8.7 μA·cm). -2 ) and T / NIS (6.8 μA·cm -2 Photoelectrode. This indicates that, on the one hand, the construction of cascaded double Z-type heterojunctions can effectively improve photoelectric conversion efficiency, and on the other hand, the in-situ growth of MnIn2S4 and Ni3In2S2 on nanorods increases the activity of TiO2 crystal planes, greatly promoting the separation and transport of photogenerated carriers in T / NIS / MIS.

[0060] 3. Testing of photoelectric conversion efficiency, light absorption performance, and electrochemical performance of the photoelectrode. All photoelectrochemical performance tests of this invention were performed using a VersaSTAT 3F electrochemical workstation (Ametek Trading Co., Ltd., China), with a uniform solution of 3.5 wt% NaCl. Electrochemical tests included photovoltaic characteristic curves (LSV), photoluminescence spectroscopy (PL), and electrochemical impedance spectroscopy (EIS), all measured using a standard three-electrode system. The photoelectrode material served as the working electrode (WE), the platinum electrode as the counter electrode (CE), and the saturated calomel electrode (SCE) as the reference electrode (RE). LSV was measured in the range of -0.6 V to 0.8 V, and PL was measured in the range of 300–700 nm. EIS was measured at 10 nm. 5 ~10 -2 The frequency range is Hz, and the amplitude of the AC voltage is 10 mV.

[0061] LSV curve ( Figure 5 a) and PL results ( Figure 5 (b) Further investigation into electron-hole separation is possible. Throughout the entire LSV curve analysis range, T / NIS / MIS-2 exhibits the highest positive current density, reaching 870 μA·cm⁻¹ at a bias voltage of 0.8 V. -2 Approximately TiO2 (450 μA·cm) -2The electron-hole separation efficiency is 1.93 times that of the standard electron-hole photoelectrode. This is mainly attributed to the fact that adding appropriate proportions of MnIn2S4 and Ni3In2S2 can maximize the electron-hole separation efficiency. The positive current density of the above photoelectrode materials is much greater than that of the negative current density, indicating that they exhibit n-type semiconductor characteristics. In the PECCP system, the semiconductor material is the core of the PEC process, and the enhancement of its n-type semiconductor characteristics has a positive effect on improving PECCP performance. Therefore, having better n-type semiconductor properties helps to optimize the PECCP effect of the material. Compared with T, the fluorescence intensity of T / NIS / MIS-2 is reduced. The lower the illumination intensity of the PL spectrum, the more enhanced the carrier excitation and transfer process. Thanks to the construction of the cascaded double Z-type heterojunction, less electron-hole recombination occurs in the T / NIS / MIS-2 photoelectrode, thereby promoting carrier separation and further accelerating its migration. TiO2 has a similar shape to T / NIS / MIS-2, indicating that while MnIn2S4 and Ni3In2S2 enhance light absorption, they fail to introduce significant changes in emission centers during photoluminescence (PL) behavior. Furthermore, a slight blue shift was observed at the emission peaks at 550 nm and 420 nm in T / NIS / MIS-2, further revealing that the introduction of numerous MnIn2S4 and Ni3In2S2 active sites enables electron-hole spatial separation, improving light utilization efficiency and thus positively promoting PECCP.

[0062] Analyzing EIS results allows for in-depth study of carrier migration behavior at semiconductor interfaces. The equivalent circuit diagram fitted based on EIS data is shown in the inset. The radius of the arc in the Nquist plot is related to the charge transfer resistance (…). R ct Closely related to the radius of the arc, the smaller the radius, the more... R ct The smaller. For example... Figure 5 As shown in Figure c, the T / NIS / MIS-2 material exhibits the smallest arc radius. According to the fitting results, the solution resistance of each photoelectrode material (…) R s The pore resistance remains basically the same. R p The discovery of TiO2 R p The lowest value was found in T / NIS / MIS-2, indicating that the number of pores in TiO2 was reduced after the nanosheets or nanoparticles were modified, resulting in fewer electron transport paths and thus increasing the difficulty of electron migration. R ct This is a key parameter for evaluating the ease of carrier migration at the photoelectrode interface. Pure T R ct The maximum is approximately 1.3 × 10⁻⁶. 5 Ω·cm -2And T / NIS / MIS-2 R ct Significantly reduced to 4.0×10 4 Ω·cm -2 This confirms that the construction of the T / NIS / MIS-2 cascaded double Z-type heterojunction material can greatly promote the effective separation and transfer of electrons and holes, thereby improving the photoelectrochemical performance of the material. To examine the impedance values ​​of the series of photoelectrodes, their Bode plots in the dark state were analyzed. Figure 5 (d). Compared to TiO2, the series of T / NIS / MIS photoelectrodes (T / NIS / MIS-1, T / NIS / MIS-2) exhibited lower impedance values ​​in the low-frequency region of 0.01 Hz, indicating that sensitization with MnIn2S4 and Ni3In2S2 increases the conductivity of TiO2. This increased conductivity suggests a higher number of photogenerated electrons, revealing that T / NIS / MIS-2 possesses higher separation efficiency for photogenerated carriers.

[0063] Figure 6 The UV-Vis DRS of the a-type photoelectrode shows that the light absorption edges of TiO2, MIS, NIS, and T / NIS / MIS-2 photoelectrodes are located at 406 nm, 553 nm, 557 nm, and 560 nm, respectively. The T / NIS / MIS-2 photoelectrode exhibits a significant redshift in its light absorption threshold, which significantly enhances the material's ability to capture visible light. This enhanced and broadened light absorption effect is fundamental to improving the photogenerated carrier flux and directly determines the upper limit of the PECCP potential. The band widths of MIS and NIS semiconductors were calculated using the Tauc plot method. Figure 6 b and Figure 6 (c). This method involves plotting (αhν). 2 The relationship diagram relative to hν is then extrapolated to the horizontal axis (αhν). 2 The intercept obtained at the zero point is the band gap. E g The band gaps of TiO2 and MnIn2S4 were ultimately determined to be 3.04 eV and 2.12 eV, respectively, while the band gap of Ni3In2S2 was 2.07 eV. The wider band gap of TiO2 is consistent with its characteristic of responding only to ultraviolet-visible light, while the narrower band gaps of MnIn2S4 and Ni3In2S2 explain their excellent visible light trapping ability. Figure 6 The conduction band potentials of TiO2, MIS, and NIS photoelectrodes can be obtained by drawing tangents in the middle d. E CB The values ​​are -0.18 V, -0.53 V, and -0.44 V, respectively. According to the equation... E g = E VB -E CB A simple calculation can yield the corresponding valence band potential ( E VB The values ​​are 2.86 V, 1.59 V and 1.63 V, respectively.

[0064] 4. Testing of the single antifouling and anticorrosion performance of photoelectrodes Single antifouling performance test: A concentration of 2.5 × 10⁻⁶ was used. 7 cells mL -1 Pseudomonas aeruginosa (99 mL PBS + 1 mL bacterial suspension) was subjected to photocatalytic inactivation under a 300 W xenon lamp irradiation experiment. The T / NIS / MIS-2 photoelectrode (10 mm × 10 mm × 1.6 mm) was then placed on the sample holder within the photocatalytic reaction cell. Before turning on the light source, a sample was taken as a 0 min control. The experiment used a xenon lamp light source equipped with an AM 1.5G filter to simulate the solar spectrum. Throughout the reaction, the reactor temperature was maintained at 20 ℃ using an external circulating water system. Samples were taken every 20 min after the light was turned on. The obtained bacterial suspension was serially diluted and evenly spread on the surface of solid agar plates. The plates were then incubated in a constant temperature and rate incubator for 24 hours. Finally, the colonies grown on the plates were counted and statistically analyzed, as shown in formula (1).

[0065]

[0066] in, E To improve photocatalytic sterilization efficiency, C 0 and C t The numbers represent the number of colonies before and after different light exposure times.

[0067] Corrosion and fouling resistance testing: In the coupled corrosion and fouling resistance system, OCP-t testing was also conducted using a VersaSTAT 3F electrochemical workstation. *Pseudomonas aeruginosa* was transferred to a 3.5 wt% NaCl solution to prepare a solution with a concentration of approximately 2.5 × 10⁻⁶. 7 A mixed bacterial culture A was prepared at a concentration of 100 cells / mL. 304 SS was then immersed in A to form a coupled system. While continuously recording the OCP-t curve, samples were taken periodically at 20-minute intervals and plated. After 24 hours of shaking incubation, the culture was used for colony-forming unit counting analysis.

[0068] Figure 7Figure A shows a bar chart of the photocatalytic sterilization efficiency of four photoelectrode materials against *Pseudomonas aeruginosa* at different time points (in the figure, anti-corrosion represents a single anti-corrosion system, anti-corrosion+anti-biofouling represents a coupled anti-corrosion and anti-fouling system, and anti-biofouling represents a single anti-fouling system). The results show that the sterilization effect of TiO2 is very limited, with a sterilization rate of only 24.28% at 60 min, while the sterilization rates of T / MIS, T / NIS / MIS-2, and T / NIS photoelectrodes reached 94.51%, 100%, and 64.16%, respectively. Therefore, T / NIS / MIS-2 has the best sterilization effect. Figure 7 The T / NIS / MIS-2 photoelectrode prepared by the B-model exhibits activity against Staphylococcus aureus (Staphylococcus aureus). Staphylococcus aureus ) and Escherichia coli ( Escherichia coli The significant bactericidal properties indicate that the photoelectrode has broad-spectrum sterilization applicability. MIS and NIS, through the formation of a cascaded double-Z heterojunction structure with TiO2, effectively promote the spatial separation of photogenerated electron-hole pairs, enhancing the generation capacity of a large amount of ROS. Figure 7 C represents the OCP-t test results in both the single anti-corrosion and coupled systems. The potential drops when coupled with 304 SS are approximately 310 mV and 264 mV, respectively. Compared to the PECCP performance achievable in the single system (anti-corrosion), the coupled system exhibits a direct loss of 14.84%, indicating that not all photogenerated electrons separated by light excitation in the coupled system are transferred to the 304 SS surface to provide cathodic protection. Therefore, there is competition for photogenerated electrons between the anti-corrosion and anti-fouling processes. In the initial stage of light exposure, because the rate of photogenerated electron transfer to 304 SS is significantly higher than the rate of transfer to the semiconductor surface and subsequent reaction with dissolved oxygen, the sterilization rate in the coupled system is only 62.85% (compared to 86.06% for the single anti-fouling system). The overall sterilization results (…) Figure 7 The comparison between the two systems (D and H) revealed that the survival rate of *Pseudomonas aeruginosa* in the coupled system increased slightly within 60 minutes, indicating that the inactivation of microorganisms in the coupled system relies on the h-axis of the T / NIS / MIS-2 heterojunction material. + And the ·OH generated by its redox reaction, on the other hand, relies on the ·O2 generated by the reaction of the photogenerated electrons obtained from the redox reaction with dissolved oxygen. − Because the number of photoelectrons excited during illumination is limited, a "supply-demand imbalance" will occur after long-term operation, thus weakening both the anti-corrosion and anti-fouling functions. To evaluate the long-term antibacterial performance of the T / NIS / MIS-2 photoelectrode, six photocatalytic inactivation cycles were conducted against Pseudomonas aeruginosa. Figure 8The procedure followed the same steps as the single antifouling performance test described above, with a fresh PBS + Pseudomonas aeruginosa mixed solution before each photocatalytic sterilization, without changing the photoelectrode material. In the first five cycles, the inhibition rate of Pseudomonas aeruginosa was 100%. Although the colony count slightly increased in the sixth cycle, the final inhibition rate remained above 98%.

[0069] 5. Analysis of the intrinsic mechanism of corrosion and fouling prevention of cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrodes Figure 9 This diagram illustrates the underlying mechanism by which photogenerated electrons and holes simultaneously act on the cascaded double-Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode of this invention, contributing to both corrosion and fouling prevention. Due to the high energy level matching of TiO2, Ni3In2S2, and MnIn2S4, a cascaded double-Z-type heterojunction structure, facilitating efficient spatial separation of photogenerated carriers, was successfully constructed. The TiO2 / Ni3In2S2 / MnIn2S4 composite material generates electron-hole pairs under photoexcitation. Photogenerated electrons can be directly injected into 304 SS, causing cathodic polarization and thus achieving effective metal protection (Process I: Corrosion Prevention), a relatively rapid process. Simultaneously, some electrons... − It can react with O2 in the solution to produce ·O2. − (Process II: Antifouling), this process is relatively slow. On the other hand, photogenerated holes can oxidize water, producing highly reactive hydroxyl radicals ·OH (Process III). The above-mentioned photogenerated electrons, holes, and their derived ·O2... − Both TiO2 and reactive oxygen species (ROS) such as ·OH can effectively attack the cell membrane and internal components of microorganisms, leading to structural damage and death, thus contributing to antifouling efficiency. In-situ recombination of TiO2, MIS, and NIS forms an interfacial electric field, and the two built-in electric fields (IEF) synergistically direct charge flow, significantly inhibiting carrier recombination and improving charge migration efficiency. The above mechanism analysis indicates that process 3 (partial consumption of holes to generate ·OH) indirectly promotes process I (transfer of photogenerated electrons to the metal) by reducing electron-hole pair recombination; while process II and process 1 have a competitive consumption relationship for the limited photogenerated electrons, but process I has a higher priority than process II. This invention successfully achieves the dual functions of photoelectrochemical cathodic protection and highly efficient antibacterial and antifouling by constructing a cascaded double-Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode.

[0070] The present invention also experimented with adjusting the amounts of MnCl2·4H2O and NiCl2·6H2O in step (2) to 0.1 mmol each, based on Example 2, while keeping the other steps and parameters the same as in Example 2. As a result, the active components (Ni3In2S2 and MnIn2S4) of the prepared composite photoelectrode decreased, resulting in an imbalance in the ratio and thus the synergistic effect could not be exerted. The insufficient electron hybridization orbitals led to a decrease in photoelectric conversion efficiency, which in turn resulted in a weakening of photocurrent and insufficient driving force for cathodic protection. The number of surface active sites was greatly reduced, which on the one hand prevented effective adsorption and degradation of pollutants and inhibition of microorganisms, resulting in a decrease in photocatalytic antifouling ability; on the other hand, it could not provide sufficient photogenerated electrons for the metal substrate, resulting in insufficient driving force for cathodic protection and inability to effectively inhibit metal corrosion. Ultimately, the dual functions of the composite photoelectrode could not meet the application requirements.

[0071] Comparative Example 1 The only difference from Example 2 is that NiCl2·6H2O in step (2) is replaced with an equal amount of Zn source (the zinc source is zinc chloride (ZnCl2)).

[0072] The photoelectrode material prepared in Comparative Example 1 was subjected to the same effect verification as the photoelectrode material prepared in Example 2. The results showed that, compared with Example 2, the photoelectrode material prepared in Comparative Example 1 had a significantly lower photocurrent density, a weaker photoelectric response intensity, a decreased interface charge separation and transport efficiency, insufficient cathodic protection driving ability for 304 SS, and a decreased anti-corrosion performance. The ROS yield was reduced, and the photocatalytic degradation and antifouling effects on marine microorganisms were worse.

[0073] In summary, replacing the Ni source with an equimolar amount of Zn source significantly reduced both the PECCP performance and photocatalytic antifouling performance of the photoelectrode. This is because the band matching between Zn-based indium sulfide compounds and TiO2 and MnIn2S4 is poor, hindering efficient photogenerated charge separation and transport, thus resulting in a lack of excellent anti-corrosion and antifouling properties. Mn, Ni, and Zn differ fundamentally in their periodic table positions, valence electron configurations, and 3d orbital filling states. 2+ with Ni 2+ With unfilled 3d orbitals, it can undergo strong hybridization with In and S orbitals to form indium sulfide compounds that are well-matched to the band structure of TiO2, resulting in significant dd transition absorption and improved visible light response and carrier separation efficiency. Simultaneously, its high ligand field stabilization energy is beneficial for forming pure-phase, highly crystalline, and low-defect Ni3In2S2 and MnIn2S4 crystals. Meanwhile, Zn... 2+ With full-fill 3D 10 With its electronic configuration lacking crystal field stabilization energy and d orbitals not participating in conduction band construction, the Ni-Mn based indium sulfide composite system exhibits weak light absorption and readily recombines charge carriers. Therefore, its PECCP performance and photocatalytic antifouling properties are significantly superior to those of the Zn-Mn based system.

[0074] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material, characterized in that, Includes the following steps: Step 1: TiO2 nanorods are grown on the surface of a conductive substrate to obtain a TiO2 photoelectrode; Step 2: The TiO2 photoelectrode is placed in a mixed solution for hydrothermal reaction to obtain a cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material; The mixed solution includes Mn source, Ni source, In source and sulfur source.

2. The preparation method according to claim 1, characterized in that, In step 1, a TiO2 photoelectrode is obtained by placing a conductive substrate in an aqueous hydrochloric acid solution containing Ti and K sources for a hydrothermal reaction, followed by washing and annealing.

3. The preparation method according to claim 2, characterized in that, The hydrochloric acid aqueous solution containing Ti source and K source is prepared by adding Ti source and K source to hydrochloric acid aqueous solution and mixing. The concentration of the hydrochloric acid aqueous solution is 6~12 mol / L. The Ti source is tetraisopropyl titanate. The K source is KCl. The ratio of the amount of Ti source to the amount of K source and hydrochloric acid aqueous solution is (0.36~0.72) mL : (0.15~0.3) g : (30~60) mL.

4. The preparation method according to claim 2, characterized in that, The hydrothermal reaction is carried out at a temperature of 160~180 ℃ for 4~6 h; the annealing is specifically carried out at 300~500 ℃ for 1~3 h in an air atmosphere.

5. The preparation method according to claim 1, characterized in that, In step 2, the Mn source is MnCl2·4H2O; the Ni source is NiCl2·6H2O; the In source is InCl3·4H2O; and the sulfur source is thioacetamide.

6. The preparation method according to claim 1, characterized in that, In step 2, the mixed solution is prepared by dissolving Mn source, Ni source, In source and sulfur source in water; the ratio of the amount of Mn source, Ni source, In source and sulfur source to water is (0~0.2) mmol: (0~0.2) mmol: (0.4~0.8) mmol: (0.9~1.8) mmol: (30~60) mL.

7. The preparation method according to claim 1, characterized in that, In step 2, the hydrothermal reaction is carried out at a temperature of 175~195 ℃ for 1~12 h.

8. A cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the cascaded double Z-type TiO2 / Ni3In2S2 / MnIn2S4 heterojunction photoelectrode material as described in claim 8 in the protection of metallic materials in marine environments.

10. The application according to claim 9, characterized in that, Marine environmental protection using metallic materials includes photoelectrochemical cathodic protection and / or photocatalytic antifouling.

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