Chitosan / NiFe2O4 / TiO2 ternary heterojunction materials, preparation methods and applications

Abstract

This invention relates to ternary heterojunction materials for photogenerated cathodic protection, specifically to a chitosan / NiFe2O4 / TiO2 ternary heterojunction material, its preparation method, and its applications. A ternary heterojunction is formed by loading chitosan nanosheets and NiFe2O4 nanoparticles onto a TiO2 nanoarray as a substrate. Compared to pure TiO2, the chitosan / NiFe2O4 / TiO2 ternary heterojunction material of this invention improves visible light capture efficiency, hinders photogenerated carrier recombination, retains more photogenerated electrons, and thus provides excellent photogenerated cathodic protection.

Description

Technical Field

[0001] This invention relates to ternary heterojunction materials for photogenerated cathode protection, specifically to a chitosan / NiFe2O4 / TiO2 ternary heterojunction material, its preparation method, and its applications. Background Technology

[0002] Metal corrosion is a spontaneous process that always exists in nature. Especially in the harsh corrosive environment of the ocean, metallic materials often experience severe corrosion within a short period during their service life. As a major maritime power, the gradual development of its marine industry has placed new demands on the corrosion protection of metallic materials in marine engineering. Particularly in an era facing the depletion of resources and energy, the development and application of new corrosion protection technologies are a crucial guarantee for the vigorous development of the marine industry.

[0003] Currently, coating protection, corrosion inhibitor protection, anodic protection, and cathodic protection are the main methods for marine corrosion protection. Among them, cathodic protection is a commonly used and effective corrosion protection method in marine engineering. Cathodic protection mainly includes impressed current cathodic protection and sacrificial anode cathodic protection.

[0004] Sacrificial anode protection is a traditional method for corrosion protection of steel materials in marine environments, with wide applications. It is primarily used in environments with stable electrolyte solutions, such as seawater. The main principle is to connect the metal to be protected to a sacrificial anode (such as zinc, magnesium, aluminum, and their alloys) with a more negative potential, forming a large battery system in seawater. This causes cathodic polarization of the protected metal, thereby slowing down corrosion. While this method has relatively low equipment requirements and does not require external power, its limited protective potential difference, limited current supply, inability to adjust the current, and high anode consumption significantly limit its application.

[0005] Furthermore, impressed current cathodic protection technology is even more important in cathodic protection. The impressed current method provides a large number of electrons to the metal through an external DC power supply and an auxiliary anode, placing the protected metal in a state of electron surplus. This causes all points on the metal surface to reach the same negative potential, lower than the surrounding environment. This method is mainly used to protect large metal structures or those in soils with high resistivity, such as long-distance buried pipelines and large tank complexes. However, this protection method requires long-term maintenance and management, external power supply equipment, and consumes a huge amount of electricity, a drawback that is particularly prominent given the current depletion of energy and resources. This method is also widely used in corrosion protection for marine engineering, but the scarcity of electricity in marine environments severely limits its wider application and further development. In particular, the application of impressed current cathodic protection technology in open ocean environments is entirely dependent on power facilities. Therefore, developing and utilizing cathodic protection technologies suitable for open ocean environments is of paramount importance.

[0006] Capturing and utilizing solar energy is considered the most effective way to solve the current energy and environmental crisis. It is also the most promising method for solving the energy source problem for cathodic protection. Marine environments receive prolonged and continuous sunlight, offering limitless possibilities for energy development. In recent years, photogenerated cathodic protection technology, as a novel technology that can utilize solar energy, has shown great potential for powering cathodic protection in open ocean environments.

[0007] The key to photogenerated cathodic protection lies in the excellent light capture and conversion efficiency of the semiconductor. This mainly depends on the semiconductor's band structure and carrier separation efficiency. Currently, it is difficult for a single semiconductor to achieve good light capture and conversion efficiency. Therefore, seeking semiconductors with excellent light conversion efficiency and improvement strategies is an essential path for the development of photogenerated cathodic protection technology. To this end, corrosion protection researchers have conducted extensive research to explore materials with excellent conversion efficiency. Semiconductor composite heterojunction construction is currently the most competitive approach to achieve high-efficiency photoelectric conversion. The purpose of semiconductor composite heterojunction construction is to improve the capture and utilization of solar energy, while simultaneously improving the separation efficiency of photogenerated carriers, thereby providing more electrons to the external circuit (cathode protection system) to form excellent photogenerated cathodic protection performance.

[0008] Magnetic semiconductor photocatalysts, such as MFe₂O₄ (M = Fe, Ni, Cu, Co, Zn), possess high chemical and structural stability, good magnetic properties, narrow band gaps, and visible-light activity with potential electrical properties. The well-known magnetic semiconductor NiFe₂O₄ (Eg = ~1.7 eV) is unique and in high demand due to its broad visible-light absorption characteristics, good resistance to photocorrosion, and chemical stability. NiFe₂O₄, with the chemical formula AB₂O₄, is an inverse spinel structure and exhibits excellent electrical conductivity. Unfortunately, pure NiFe₂O₄ exhibits poor photocatalytic response due to the rapid recombination of photoelectron-hole pairs. Therefore, the development of NiFe₂O₄-based photocatalysts is one of the hot topics and emerging issues in the field of photocatalysis. Researchers have employed various effective and successful techniques, such as combining with other semiconductors or co-doping with non-metals, noble metals, or polymers, to improve the photocatalytic performance of NiFe₂O₄-based photocatalysts. However, there are still no reports on photogenerated cathode protection, thus requiring urgent development and utilization. Summary of the Invention

[0009] The purpose of this invention is to provide a chitosan / NiFe2O4 / TiO2 heterojunction material, its preparation and application.

[0010] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] A chitosan / NiFe2O4 / TiO2 ternary heterojunction material is formed by loading chitosan nanosheets and NiFe2O4 nanoparticles onto the surface of a TiO2 nanoarray as a substrate to form a ternary heterojunction.

[0012] A method for preparing the chitosan / NiFe2O4 / TiO2 ternary heterojunction material:

[0013] Obtain TiO2 nanotube arrays;

[0014] Chitosan nanosheets and NiFe2O4 nanoparticles were loaded onto the TiO2 nanotube array via a hydrothermal method to form a chitosan / NiFe2O4 / TiO2 ternary heterojunction material.

[0015] To elaborate further:

[0016] (a) Fe2(NO3)3·9H2O, Ni(NO3)2·6H2O, and chitosan were selected as raw materials, and ultrapure water was used as the solvent. Magnetic stirring was used to ensure uniform dissolution of all substances in the water. Simultaneously, a 10–24 mmol / L NaOH solution was used to adjust the pH to 12–13 to form a homogeneous precursor solution for later use. The precursor solution contained Fe2(NO3)3·9H2O, Ni(NO3)2·6H2O, and chitosan as raw materials. 2+ The final concentration is 2–10 mmol / L;

[0017] (b) The precursor liquid is transferred to a hydrothermal reactor, and the TiO2 nanotube array is placed at an angle in the hydrothermal reactor.

[0018] (c) The reaction vessel is placed in a forced-air drying oven and reacted at 160-200℃ for 18-24h. After natural cooling, it is washed several times with deionized water and anhydrous ethanol alternately. Finally, it is vacuum dried at 60-80℃ for 12-15h to obtain the chitosan / NiFe2O4 / TiO2 ternary heterojunction material.

[0019] In step (a), the mass ratio of Fe2(NO3)3·9H2O, Ni(NO3)2·6H2O and chitosan is (0.8079~4.3099):(0.2907~1.4535):(0.25~1.25).

[0020] The TiO2 nanotube array is obtained by anodic oxidation using a platinum sheet as the cathode, a titanium plate as the anode, and ethylene glycol containing ammonium fluoride as the electrolyte; wherein the mass ratio of ammonium fluoride to ethylene glycol is 1:150-1:200.

[0021] The anodizing method involves providing a DC voltage of 40–80V from a DC power supply, anodizing time of 0.5–2 hours, calcination at 450–600℃ in a muffle furnace for 120–200 minutes, and natural cooling to obtain a TiO2 nanotube array.

[0022] An application of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material, specifically its application in photogenerated cathodic protection.

[0023] Application of the material in metal corrosion protection.

[0024] The basic principle of this invention is as follows: a heterojunction is constructed by combining chitosan nanosheets, NiFe2O4 nanoparticles, and TiO2 nanotube arrays. The chitosan / NiFe2O4 / TiO2 ternary heterojunction material facilitates light capture and improves light utilization efficiency. Simultaneously, the chitosan / NiFe2O4 / TiO2 ternary heterojunction material hinders photogenerated carrier recombination and accelerates photogenerated carrier transfer, providing more electrons to the protected metal. This results in a negative potential shift in the protected metal, placing it in a cathodic protection state and thus mitigating corrosion. Therefore, the chitosan / NiFe2O4 / TiO2 ternary heterojunction material can effectively enhance the photogenerated cathodic protection effect of semiconductors on metals.

[0025] Advantages of this invention:

[0026] This invention obtains a chitosan / NiFe2O4 / TiO2 ternary heterojunction material with high light absorption and low carrier recombination rate by matching the semiconductor band structure and rationally optimizing the structure of the heterojunction material. This effectively improves the photoelectric performance of the photoanode material and solves the problem of poor protection performance of the photogenerated cathode. Specifically:

[0027] 1. The chitosan / NiFe2O4 / TiO2 ternary heterojunction material obtained in this invention is constructed from chitosan nanosheets, NiFe2O4 nanoparticles, and TiO2, thereby achieving excellent photoelectric separation performance to ensure the electron supply for photogenerated cathodic protection. Compared with pure TiO2, the chitosan / NiFe2O4 / TiO2 ternary heterojunction material improves light utilization efficiency, hinders photogenerated carrier recombination, accelerates photogenerated carrier transfer, provides more electrons for the protected metal, and causes a negative potential shift in the protected metal, thus placing it in a cathodic protection state and achieving the purpose of slowing down corrosion.

[0028] 2. The material obtained by this invention has strong light absorption and energy absorption, which significantly improves the light absorption range.

[0029] 3. The material obtained by this invention reduces carrier recombination efficiency and retains more electrons that are beneficial to cathodic protection.

[0030] 4. The material obtained by this invention can effectively improve the photocathode protection effect of semiconductors on metals. Attached Figure Description

[0031] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the chitosan / NiFe2O4 / TiO2 (CSNFOTs) ternary heterojunction material provided in Example 1 of this invention.

[0032] Figure 2 Scanning electron microscope (SEM) images of (a) pure TiO2 and (b) CSNFOTs ternary heterojunction materials provided in Example 1 of the present invention.

[0033] Figure 3 The graph shows the change of electrode potential over time before and after illumination, for example, of 304 stainless steel coupled with pure TiO2 and CSNFOTs ternary heterojunction material in 3.5% NaCl solution provided in Example 1 of this invention. The horizontal axis represents time (s), and the vertical axis represents electrode potential (V vs. SCE). "on" indicates illumination, and "off" indicates the light source is off.

[0034] Figure 4 The curves showing the change of photocurrent over time before and after illumination for the pure TiO2 and CSNFOTs ternary heterojunction material provided in Example 1 of this invention are shown, where the horizontal axis represents time (s) and the vertical axis represents current density (μA / cm). 2 ).

[0035] Figure 5 The curves a and b are the UV-Vis absorption spectra (UV-DRS) of the CSNFOTs ternary heterojunction material provided in Example 1 of this invention.

[0036] Figure 6 Scanning electron microscope (SEM) images of (a) NiFe2O4 / TiO2 (NFOTs) and (b) CSNFOTs ternary heterojunction materials provided in Example 2 of the present invention.

[0037] Figure 7 Example 2 of this invention shows the electrode potential changes over time before and after illumination of 304 stainless steel coupled with NiFe2O4 / TiO2 (NFOTs) and CSNFOTs ternary heterojunction materials in a 3.5% NaCl solution. The horizontal axis represents time (s), and the vertical axis represents electrode potential (V vs. SCE). "on" indicates illumination, and "off" indicates the light source is off.

[0038] Figure 8The curves showing the change of photocurrent over time before and after illumination for the NiFe2O4 / TiO2 (NFOTs) and CSNFOTs ternary heterojunction materials provided in Example 2 of this invention are shown, where the horizontal axis represents time (s) and the vertical axis represents current density (μA / cm²). 2 ).

[0039] Figure 9 The curves provided in Example 2 of this invention are the UV-Vis absorption spectra (UV-DRS) of the NiFe2O4 / TiO2 (NFOTs) and CSNFOTs ternary heterojunction materials. Detailed Implementation

[0040] The following examples further illustrate specific embodiments of the present invention. It should be noted that the specific embodiments described herein are merely for illustration and explanation and are not intended to limit the scope of the present invention.

[0041] The chitosan / NiFe2O4 / TiO2 ternary heterojunction material of this invention is composed of chitosan nanosheets and NiFe2O4 nanoparticles supported on a TiO2 nanotube array. This material facilitates light capture and improves light utilization efficiency. Simultaneously, it hinders photogenerated carrier recombination and accelerates photogenerated carrier transfer, providing more electrons to the protected metal. This results in a negative potential shift in the protected metal, placing it in a cathodic protection state and mitigating corrosion. Therefore, the chitosan / NiFe2O4 / TiO2 ternary heterojunction material effectively enhances the photogenerated cathodic protection effect of semiconductors on metals.

[0042] The photocathode protection effect of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material prepared below was tested using a dual-electrolysis cell system consisting of a photoelectrolysis cell and a corrosion electrolysis cell. In the photoelectrolysis cell, pure TiO2, NiFe2O4 / TiO2, or the chitosan / NiFe2O4 / TiO2 ternary heterojunction material was used as the anode, and the electrolyte was a solution of 0.1M Na2S and 0.2M NaOH. The corrosion electrolysis cell was a three-electrode system: the working electrode was the protected metal (304 stainless steel), the counter electrode was a Pt electrode, the reference electrode was a saturated calomel electrode (SCE), and the corrosion medium was a 3.5% NaCl solution. The photoanode was connected to the protected metal electrode via a wire, serving as the working electrode. The photoelectrolysis cell and the corrosion electrolysis cell were connected by a salt bridge (agar containing saturated KCl). A 300W high-pressure xenon lamp with a wavelength ≥400nm was used as the visible light source to directly irradiate the surface of the nanotube composite film in the photoelectrolysis cell. The potential change of the stainless steel electrode before and after irradiation was tested using an electrochemical workstation.

[0043] The photocurrent of the prepared pure TiO2, NiFe2O4 / TiO2, or chitosan / NiFe2O4 / TiO2 ternary heterojunction materials was measured using a dual-electrolysis cell system consisting of a photoelectrolysis cell and a corrosion electrolysis cell. In the photoelectrolysis cell, the pure TiO2, NiFe2O4 / TiO2, or chitosan / NiFe2O4 / TiO2 ternary heterojunction material was used as the anode, and the electrolyte was a solution of 0.1M Na2S and 0.2M NaOH. To avoid the influence of polarization on the photocurrent measurement, the 304SS electrode was connected to the ground interface (GNE) of the chemical workstation, and the reference electrode (RE) interface and the counter electrode (CE) interface of the chemical workstation were shorted.

[0044] The light absorption properties of the pure TiO2, NiFe2O4 / TiO2 or chitosan / NiFe2O4 / TiO2 ternary heterojunction materials prepared below were tested. The wavelength range of the test was 200-800 nm, with barium sulfate as the reference.

[0045] Example 1

[0046] 1) Cut commercially available titanium plates (purity 99.9%) into samples of 0.3mm×10mm×20mm, and clean them repeatedly with pure water and acetone by ultrasonication for 20 minutes each time to remove inorganic or organic impurities from the sample surface. Let them air dry at room temperature for later use.

[0047] 2) First, dissolve 0.9g of ammonium fluoride (NH4F) in 5mL of pure water. Then, add 12mL of hydrogen peroxide (H2O2) and 12mL of nitric acid (65% HNO3) sequentially and stir evenly with a magnetic stirrer to obtain a polishing solution. Immerse the treated titanium plate sample in the polishing solution and chemically polish until the sample surface is uniform, smooth, and free of impurities. Then, remove the sample and ultrasonically clean it twice, alternating between pure water and anhydrous ethanol, for 10 minutes each time, to obtain a clean titanium plate sample. Finally, store it in anhydrous ethanol for later use.

[0048] 3) The method for preparing TiO2 nanotube arrays on the surface of the titanium plate sample after the above polishing treatment is as follows:

[0049] (1) Dissolve 0.44g NH4F in 8mL of pure water, then add 80mL of ethylene glycol and stir evenly with a magnetic stirrer to obtain an electrolyte for preparing TiO2 nanotube arrays.

[0050] (2) 80 mL of the above electrolyte was placed into a 200 mL beaker. The polished and cleaned titanium plate sample was connected to the positive terminal of a DC power supply, and a platinum foil (20 mm × 20 mm) was connected to the negative terminal of the DC power supply to build a two-electrode system. The voltage was set to +20 V and the time to 1 h. After the reaction was completed, the sample was rinsed several times with pure water and anhydrous ethanol alternately. After drying at room temperature, the sample was placed in a muffle furnace, and the heating rate was set to 5 °C / min. It was calcined at 450 °C for 120 minutes, and after natural cooling, a TiO2 nanotube array was obtained. The surface morphology of the TiO2 nanotube array is as follows. Figure 2 As shown in (a), it can be seen that the nanotubes in the nanotube array are relatively uniform, with a diameter between 60 and 80 nanometers.

[0051] 4) Preparation of chitosan / NiFe2O4 / TiO2 ternary heterojunction materials

[0052] (a) Weigh 1.6159g Fe2(NO3)3·9H2O, 0.5814g Ni(NO3)2·6H2O and 0.5g chitosan, place them in a beaker containing 60mL of ultrapure water, adjust the pH to 13 with 24mmol / L NaOH solution, and stir magnetically for 1.0h to fully form a homogeneous precursor solution.

[0053] (b) The precursor liquid is transferred to a hydrothermal reactor, and the TiO2 nanotube array is placed at an angle in the hydrothermal reactor.

[0054] (c) The reaction vessel is placed in a forced-air drying oven and reacted at 180°C for 20 hours. After natural cooling, it is washed several times with deionized water and anhydrous ethanol alternately. Finally, it is vacuum dried at 60°C for 12 hours to obtain the chitosan / NiFe2O4 / TiO2 ternary heterojunction material.

[0055] Crystal structure analysis was performed on the chitosan / NiFe2O4 / TiO2 ternary heterojunction material obtained in Example 1. Figure 1The XRD patterns of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material are shown in comparison with those of the standard PDF card. The diffraction peaks of Ti in the Ti substrate at 2θ = 35.0°, 38.4°, 40.1°, 53.0°, 70.6°, and 76.2° are (JCPDS No. 44–1294). The peaks at 2θ = 25.3°, 48.1°, and 82.6° are attributed to the (101), (200), and (224) crystal planes of anatase TiO2 (JCPDS No. 21–1272). This indicates that anatase TiO2 can be successfully formed on the Ti substrate after anodizing and high-temperature calcination annealing at 450°C. Furthermore, 2θ = 18.3°, 35.6°, 62.9°, and 82.5° correspond to the NiFe2O4 (111), (311), (440), and (551) crystal planes, respectively (JCPDS No. 10-0325). 2θ = 8.8° belongs to chitosan. This indicates that the chitosan / NiFe2O4 / TiO2 ternary heterojunction material was successfully obtained using the above preparation method.

[0056] Scanning electron microscopy analysis was performed on the pure TiO2 and chitosan / NiFe2O4 / TiO2 ternary heterojunction materials obtained in Example 1. The results are shown in the figure. Figure 2 .pass Figure 2 (a) It can be seen that the nanotube array in the TiO2 nanotube array is uniformly distributed. Figure 2 (b) It can be seen that there are sheet-like chitosan nanosheets and blocky NiFe2O4 nanoparticles at the opening of the TiO2 nanotube, indicating that the chitosan nanosheets and NiFe2O4 nanoparticles jointly construct a chitosan / NiFe2O4 / TiO2 ternary heterojunction material on the surface of the TiO2 nanotube.

[0057] The pure TiO2 nanotube array and the chitosan / NiFe2O4 / TiO2 ternary heterojunction material obtained in Example 1 were coupled to 304 stainless steel, and the electrode potential of 304 stainless steel in simulated seawater was tested over time.

[0058] Depend on Figure 3 It can be seen that under intermittent illumination, the electrode potential of the 304 stainless steel coupled to the TiO2 nanotube array drops to approximately -520 mV, demonstrating a certain degree of photocathode protection. When coupled with a chitosan / NiFe2O4 / TiO2 ternary heterojunction material, the potential of the 304 stainless steel drops to around -919 mV, significantly lower than its self-corrosion potential. When the light source is cut off, the electrode potential of the stainless steel begins to rise, but it remains far below its self-corrosion potential. Upon re-illumination, the electrode potential of the stainless steel connected to the composite film drops rapidly again, indicating that the composite film exhibits good photocathode protection and stability.

[0059] To characterize the photogenerated carrier separation capability and recombination rate of the pure TiO2 nanotube array and the chitosan / NiFe2O4 / TiO2 ternary heterojunction material obtained in Example 1, the transient photocurrent spectra of the samples were tested. Figure 4 It can be seen that when the sample is pure TiO2, the maximum transient photocurrent density under switched-on conditions is 11.4 μA / cm². 2 The steady-state current is approximately 15.3 μA / cm. 2 When the sample is a chitosan / NiFe2O4 / TiO2 ternary heterojunction material, the maximum transient photocurrent under switched-on conditions is 266.7 μA / cm. 2 The transient photocurrent of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material under switched-on light is approximately 23.3 times that of a pure TiO2 nanotube array, and eventually stabilizes at 20.3 μA / cm. 2 The photocurrent intensity is approximately 1.7 times that of pure TiO2 nanotubes, far exceeding that of pure TiO2 nanotube arrays. This result indicates a significant enhancement in photocurrent intensity of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material. This is mainly because the chitosan / NiFe2O4 / TiO2 ternary heterojunction material can reduce the recombination of photogenerated electron-hole pairs, effectively improving the utilization rate of light.

[0060] The UV-Vis absorption spectra of pure TiO2 and chitosan / NiFe2O4 / TiO2 ternary heterojunction materials in Example 1 are shown in the figure. Figure 5 The test results show that the light absorption range of the pure TiO2 nanotube array is mainly in the ultraviolet region, with a spectral absorption edge of approximately 380 nm. In contrast, the chitosan / NiFe2O4 / TiO2 ternary heterojunction material exhibits significantly increased absorption intensity in both the ultraviolet and visible light regions, indicating that the chitosan / NiFe2O4 / TiO2 ternary heterojunction material effectively improves the absorption capacity of the TiO2 nanotube array for both ultraviolet and visible light.

[0061] Example 2

[0062] 1) Cut commercially available titanium plates (purity 99.9%) into samples of 0.3mm×10mm×20mm, and clean them repeatedly with pure water and acetone by ultrasonication for 20 minutes each time to remove inorganic or organic impurities from the sample surface. Let them air dry at room temperature for later use.

[0063] 2) First, dissolve 0.9g of ammonium fluoride (NH4F) in 5mL of pure water. Then, add 12mL of hydrogen peroxide (H2O2) and 12mL of nitric acid (65% HNO3) sequentially, and stir evenly with a magnetic stirrer to obtain a polishing solution. Immerse the titanium plate sample in the polishing solution and chemically polish until the sample surface is uniform, smooth, and free of impurities. After removal, ultrasonically clean the sample twice, alternating between pure water and anhydrous ethanol, for 10 minutes each time, to obtain a clean titanium plate sample. Finally, store it in anhydrous ethanol for later use.

[0064] 3) The method for preparing TiO2 nanotube arrays on the surface of titanium plate samples is as follows:

[0065] (1) Dissolve 0.44g NH4F in 8mL of pure water, then add 80mL of ethylene glycol and stir evenly with a magnetic stirrer to obtain an electrolyte for preparing TiO2 nanotube arrays.

[0066] (2) 80 mL of the above electrolyte was placed into a 200 mL beaker. The clean titanium plate sample was connected to the positive terminal of the DC power supply, and the platinum foil (20 mm × 20 mm) was connected to the negative terminal of the DC power supply to build a two-electrode system. The voltage was set to +20 V and the time was 1 h. After the reaction was completed, the sample was rinsed several times with pure water and anhydrous ethanol alternately. After drying at room temperature, the sample was placed in a muffle furnace. The heating rate was set to 5 °C / min, and the sample was calcined at 450 °C for 120 minutes. After natural cooling, TiO2 nanotube arrays were obtained.

[0067] 4) Preparation of NiFe2O4 / TiO2 materials

[0068] (a) Weigh 1.6159g Fe2(NO3)3·9H2O and 0.5814g Ni(NO3)2·6H2O, place them in a beaker containing 60mL of ultrapure water, adjust the pH to 13 with 24mmol / L NaOH solution, and stir magnetically for 1.0h to fully form a homogeneous precursor solution.

[0069] (b) The precursor liquid is transferred to a hydrothermal reactor, and the TiO2 nanotube array is placed at an angle in the hydrothermal reactor.

[0070] (c) The reaction vessel is placed in a forced-air drying oven and reacted at 180°C for 20 hours. After natural cooling, it is washed several times with deionized water and anhydrous ethanol alternately. Finally, it is vacuum dried at 60°C for 12 hours to obtain NiFe2O4 / TiO2 material.

[0071] The NiFe2O4 / TiO2 material and the chitosan / NiFe2O4 / TiO2 ternary heterojunction material obtained in Example 2 were coupled to 304 stainless steel, and the electrode potential of the 304 stainless steel in simulated seawater was tested over time. Figure 7It can be seen that under intermittent illumination, the electrode potential of the 304 stainless steel coupled to the NiFe2O4 / TiO2 material drops to approximately -776mV, demonstrating a certain degree of photocathode protection. When coupled to a chitosan / NiFe2O4 / TiO2 ternary heterojunction material, the potential of the 304 stainless steel drops to around -919mV, significantly lower than its self-corrosion potential. When the light source is cut off, the electrode potential of the stainless steel begins to rise, but it remains far below its self-corrosion potential. Upon re-illumination, the electrode potential of the stainless steel connected to the composite film drops rapidly again, indicating that the composite film has a good photocathode protection effect and good stability.

[0072] To characterize the photogenerated carrier separation capability and recombination rate of the NiFe2O4 / TiO2 material and the chitosan / NiFe2O4 / TiO2 ternary heterojunction material obtained in Example 2, the transient photocurrent spectra of the samples were tested. Figure 8 It can be seen that when the sample is NiFe2O4 / TiO2 material, the maximum transient photocurrent density under switched-on conditions is 24.5 μA / cm. 2 The steady-state current is approximately 13.3 μA / cm. 2 When the sample is a chitosan / NiFe2O4 / TiO2 ternary heterojunction material, the maximum transient photocurrent under switched-on conditions is 266.7 μA / cm. 2 The transient photocurrent of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material under switched-on light is approximately 10.8 times that of the NiFe2O4 / TiO2 material, and eventually stabilizes at 23.3 μA / cm². 2 The current intensity is approximately 1.7 times that of the NiFe2O4 / TiO2 material, significantly exceeding the transient photocurrent of the NiFe2O4 / TiO2 material. This result indicates a significant enhancement in the current intensity of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material. This is mainly because the chitosan / NiFe2O4 / TiO2 ternary heterojunction material can reduce the recombination of photogenerated electron-hole pairs, effectively improving the utilization rate of light.

[0073] The UV-Vis absorption spectra of the NiFe2O4 / TiO2 material and the chitosan / NiFe2O4 / TiO2 ternary heterojunction material in Example 2 are shown in the figure. Figure 9 The test results show that the light absorption range of the NiFe2O4 / TiO2 material is mainly in the ultraviolet light region. However, the chitosan / NiFe2O4 / TiO2 ternary heterojunction material exhibits significantly increased absorption intensity in both the ultraviolet and visible light regions, indicating that the chitosan / NiFe2O4 / TiO2 ternary heterojunction material effectively improves the absorption capacity of the TiO2 nanotube array for ultraviolet and visible light.

[0074] The chitosan / NiFe2O4 / TiO2 ternary heterojunction material described in this invention can inhibit metal corrosion, has excellent photoelectric conversion effect, and can play a good photocathode protection effect on 304 stainless steel as a photoanode.

[0075] Other preparation methods not listed above can be easily implemented under the guidance of the two preparation methods mentioned above, and will not be elaborated here.

[0076] It should be understood that those skilled in the art, under the guidance of this invention, can make various modifications, substitutions, combinations, and other variations without departing from the scope of protection of the claims of this invention. The scope of protection of this invention shall be determined by the claims.

Claims

1. A chitosan / NiFe2O4 / TiO2 ternary heterojunction material, characterized in that: Using TiO2 nanotube arrays as a substrate, chitosan nanosheets and NiFe2O4 nanoparticles are loaded onto their surface to form a ternary heterostructure.

2. A method for preparing the chitosan / NiFe2O4 / TiO2 ternary heterojunction material according to claim 1, characterized in that: (a) Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, and chitosan were selected as raw materials, and ultrapure water was used as the solvent. Magnetic stirring was used to ensure uniform dissolution of all substances in the water. Simultaneously, a 10–24 mmol / L NaOH solution was used to adjust the pH to 12–13 to form a homogeneous precursor solution for later use. The precursor solution contained Fe... 3+ The concentration is 2–10 mmol / L; (b) The precursor liquid is transferred to a hydrothermal reactor, and the TiO2 nanotube array is placed at an angle in the hydrothermal reactor; (c) The reaction vessel is placed in a forced-air drying oven and reacted at 160-200℃ for 18-24 h. After natural cooling, it is washed several times with deionized water and anhydrous ethanol alternately. Finally, it is vacuum dried at 60-80℃ for 12-15 h to obtain the chitosan / NiFe2O4 / TiO2 ternary heterojunction material.

3. The method for preparing the chitosan / NiFe2O4 / TiO2 ternary heterojunction material according to claim 2, characterized in that: In step (a), the mass ratio of Fe(NO3)3·9H2O, Ni(NO3)2·6H2O and chitosan is (0.8079~4.3099):(0.2907~1.4535):(0.25~1.25).

4. The method for preparing the chitosan / NiFe2O4 / TiO2 ternary heterojunction material according to claim 2, characterized in that: The TiO2 nanotube array is obtained by anodic oxidation using a platinum sheet as the cathode, a titanium plate as the anode, and ethylene glycol containing ammonium fluoride as the electrolyte; wherein the mass ratio of ammonium fluoride to ethylene glycol is 1:150-1:

200.

5. The preparation method of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material according to claim 4, characterized in that: The anodizing method is as follows: anodizing is performed by providing a DC voltage of 40-80V from a DC power supply for 0.5-2 hours, followed by calcination in a muffle furnace at 450-600℃ for 120-200 minutes, and then natural cooling to obtain TiO2 nanotube arrays.

6. The application of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material according to claim 1, characterized in that: Application of the chitosan / NiFe2O4 / TiO2 ternary heterojunction material in photogenerated cathodic protection.

Images