Nanosheet-modified Bi2MoO6 / TiO2 composite photo-anode material as well as preparation and application thereof

Abstract

The invention relates to a composite photo-anode material, in particular to a nanosheet modified Bi2MoO6 / TiO2 composite photo-anode material as well as preparation and application thereof. The preparation method specifically comprises the following steps: uniformly forming the nanosheet-modified Bi2MoO6 / TiO2 composite material on the surface of a TiO2 nanotube substrate by using an aqueous solution containing a Bi source and a Mo source through a hydrothermal method. According to the material disclosed by the invention, effective response to visible light can be realized by utilizing Bi2MoO6 with a relatively narrow band gap, and the Bi2MoO6 is compounded with TiO2 to form a heterojunction structure, so that spatial separation of photo-generated electrons and holes is facilitated, and the carrier recombination rate is remarkably reduced, thereby improving photo-generated current output. Through energy band matching design, the Bi2MoO6 / TiO2 material not only widens the light absorption range and improves the visible light utilization rate, but also enhances the electrochemical stability of the system, so that the Bi2MoO6 / TiO2 material still keeps excellent protection performance in complex environments such as high salinity, high humidity and intertidal zones.

Description

TECHNICAL FIELD

[0001] The application relates to a composite photo-anode material, in particular to a nanosheet modified Bi2MoO6 / TiO2 composite photo-anode material and preparation and application thereof. BACKGROUND

[0002] The existing metal corrosion prevention technologies mainly include coating protection, cathodic protection and inhibitor addition. However, these traditional methods have obvious defects. The coating material is easily affected by the environment and is aged, cracked and peeled off, especially under the conditions of ultraviolet light, salt mist and high humidity, the protection performance rapidly decreases, and once damaged, the corrosion rapidly spreads on the metal substrate. Although the cathodic protection is effective, the sacrificial anode is consumed fast, the maintenance cost is high, the impressed current system is complex, depends on continuous power, has large energy consumption, and the protection effect is uneven in the complex structure or local shielding area. The use of the inhibitor is limited by the cost and environmental regulations, and the effect is also easily affected by the external environment fluctuation, and the stability is poor.

[0003] In order to overcome the above defects, the photo-induced cathodic protection technology as a new protection means uses the semiconductor material to generate electron-hole pairs under light to realize the cathodic polarization of the metal substrate, so as to inhibit the corrosion reaction. The technology has the advantages of green energy saving, no external power supply and environmental friendliness, and is especially suitable for harsh environments such as high salt and high humidity. The photo-induced cathodic protection technology can continuously provide electrons by using light energy, which not only avoids the problems of damage of the traditional coating, consumption of the sacrificial anode and complexity of the impressed current maintenance, but also can further improve the performance through material control. For example, Cu doping can enhance the visible light absorption of TiO2, Mo doping can improve the electrical conductivity, and AgInSe2 / TiO2 heterojunction can effectively promote the charge separation, so that it still maintains stable protection under weak light conditions. However, the current photo-induced cathodic protection technology attempts to improve the light response and charge separation performance of TiO2 by means of non-metallic doping such as N, C and S or metallic doping such as Fe, Cu, Mo and rare earth elements, but the doping strategy still has limitations such as unstable impurity energy level, easy formation of recombination center, narrow optimal doping range and insufficient long-term service stability. SUMMARY

[0004] The application aims to provide a nanosheet modified Bi2MoO6 / TiO2 composite photo-anode material and preparation and application thereof.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows: A preparation method of a nanosheet modified Bi2MoO6 / TiO2 composite photo-anode material, wherein a water solution containing a Bi source and a Mo source is uniformly formed on the surface of a TiO2 nanotube substrate to form a nanosheet modified Bi2MoO6 / TiO2 composite material by a hydrothermal method.

[0006] Specifically, Bi(NO3)3·9H2O and Na2MoO4·2H2O were dissolved in deionized water and mixed to form a reaction solution. The reaction solution was then injected into a hydrothermal reactor. TiO2 nanotubes were then placed in the reactor and immersed in the reaction solution. The reaction was carried out at 180 °C for 6 to 20 hours. After the reaction, the mixture was cooled to room temperature. The TiO2 nanotube substrate was then washed repeatedly with deionized water and anhydrous ethanol, and dried. This resulted in the uniform formation of a nanosheet-modified Bi2MoO6 / TiO2 composite material on the surface of the TiO2 nanotubes.

[0007] The final concentration of Bi in the reaction solution is 0.8~1.2 mmol, and the final concentration of Mo is 0.3~0.7 mmol.

[0008] The TiO2 nanotube substrate is prepared by anodic oxidation using a platinum sheet electrode as the cathode, a pretreated titanium substrate sample as the anode, and a mixture of ammonium fluoride, deionized water, and ethylene glycol as the electrolyte.

[0009] The TiO2 nanotube array film uses a platinum sheet electrode as the cathode and a pretreated titanium substrate sample as the anode. A DC voltage of 15~30 V is provided by a DC power supply, and the anodizing time is 0.5~2 h. After treatment, the titanium substrate sample is heated to 450 ℃ in a muffle furnace at a heating rate of 5 ℃ / min and calcined at this temperature for 120 min. After natural cooling, the TiO2 nanotube array film can be obtained.

[0010] A nanosheet-modified Bi2MoO6 / TiO2 composite photoanode material is prepared by means of the method described above.

[0011] An application of the nanosheet-modified Bi2MoO6 / TiO2 composite photoanode material, specifically its application in protecting metals from corrosion using photocathodes.

[0012] Advantages and beneficial effects of this patented solution: This invention relates to a photogenerated cathodic protection composite material based on a Bi₂MoO₆ / TiO₂ heterojunction structure. By loading Bi₂MoO₆ semiconductors with visible light responsiveness onto the surface of an ordered TiO₂ nanotube array, a Z-shaped heterojunction structure is constructed, achieving highly efficient separation and transfer of photogenerated carriers. Compared to traditional BiVO₄ / TiO₂ or Bi₂Se₃ / TiO₂ nanoflower-like loading methods, loading Bi₂MoO₆ onto the TiO₂ surface in the form of nanosheets offers significant advantages.

[0013] First, Bi₂MoO₆ nanosheets have a larger specific surface area, providing more reactive sites and promoting the separation and transfer of photogenerated electrons. Second, the porous structure formed by particle stacking facilitates electrolyte permeation and carrier diffusion, resulting in a lower potential drop and longer-lasting protection during long-term open-circuit potential testing. Furthermore, Bi₂MoO₆ nanosheets more easily form tight, multi-point interfacial contacts on the TiO₂ surface, contributing to the construction of efficient and stable Z-shaped heterojunctions, enhancing interfacial electron transport capabilities, and reducing the recombination probability of photogenerated electron-hole pairs.

[0014] Furthermore, in terms of elemental synergy, the Bi₂MoO₆ / TiO₂ composite photoelectrode material achieves excellent photoelectric conversion performance and photogenerated cathodic protection capabilities through the synergistic effect of Bi, Mo, and Ti elements. Specifically, Bi₂MoO₆, composed of Bi and Mo, exhibits strong visible light response and good band structure matching, effectively absorbing sunlight and generating photogenerated carriers. The TiO₂ nanotube array formed by Ti provides highly ordered electron migration channels, significantly improving electron transport efficiency. The high oxidation state of Mo enhances the interfacial electron trapping ability, facilitating the directional migration of electrons from Bi₂MoO₆ to TiO₂; while Bi is beneficial for the separation and transfer of valence band holes, thereby reducing the recombination probability.

[0015] Meanwhile, this invention employs a low-temperature hydrothermal method combined with anodic oxidation technology, resulting in a simple and safe preparation process that avoids the requirements of high-temperature calcination and reducing atmospheres. It is suitable for large-area controlled growth and possesses significant process advantages and industrialization potential. Furthermore, Bi₂MoO₆ exhibits excellent chemical stability, remaining resistant to degradation even in neutral and weakly acidic / alkaline environments over long periods, ensuring the material's applicability in complex corrosive environments such as marine and industrial settings. Attached Figure Description

[0016] Figure 1 The flowchart shows the preparation process of pure TiO2 and Bi2MoO6 / TiO2 composite materials provided in Example 1 of this invention.

[0017] Figure 2 The images show a comparison of scanning electron microscopy (SEM) images of pure TiO2 and Bi2MoO6 / TiO2 composite materials provided in Example 1 of this invention with traditional nanosheet-loaded SEM images. The left image is the SEM image of TiO2, and the right image is the SEM image of the Bi2MoO6 / TiO2 composite material.

[0018] Figure 3The X-ray diffraction (XRD) evaluation pattern and X-ray photoelectron spectroscopy (XPS) evaluation pattern of TiO2, Bi2MoO6 and Bi2MoO6 / TiO2 composite material provided in Example 1 of the present invention are shown below. Among them, a is the XRD evaluation pattern, b is the XPS total spectrum, c is the high-resolution energy spectrum of Ti, d is the high-resolution energy spectrum of Mo, e is the high-resolution energy spectrum of Bi, and f is the high-resolution energy spectrum of O.

[0019] Figure 4 The 304 stainless steel provided in Embodiment 1 of this invention is coupled with TiO2, Bi2MoO6 and Bi2MoO6 / TiO2 composite materials. The electrode potential (OCP) and photocurrent density before and after illumination are... i-t The curves show the change of OCP over time, with the left graph showing the OCP change curve and the right graph showing the OCP change curve. i-t Change curve.

[0020] Figure 5 The images show the UV-Vis absorption spectra (UV-DRS) and Tauc spectra of TiO2, Bi2MoO6, and Bi2MoO6 / TiO2 composite materials provided in Example 1 of this invention, with the left image being the UV spectrum and the right image being the Tauc spectrum.

[0021] Figure 6 The images shown are SEM images of the BiVO4 / TiO2 composite material provided in Comparative Example 1 of the present invention. The left image is the SEM image of the Bi2MoO6 / TiO2 composite material, and the right image is the SEM image of the BiVO4 / TiO2 composite material.

[0022] Figure 7 The constant voltage test (CV) graphs of TiO2, Bi2MoO6 and Bi2MoO6 / TiO2 composite materials provided in Example 1 of the present invention are shown, where (ac) is the CV curve of TiO2, Bi2MoO6 and Bi2MoO6 / TiO2 composite materials and (d) is the ESCA fitting graph of the three.

[0023] Figure 8 The graph shows a comparison of the long-term open circuit potential (OCP) test results of the Bi2MoO6 / TiO2 composite material provided in Example 1 of this invention and the BiVO4 / TiO2 composite material provided in the comparative example. The left graph is the OCP curve of the Bi2MoO6 / TiO2 composite material, and the right graph is the OCP curve of the BiVO4 / TiO2 composite material.

[0024] Figure 9 The test results are for TiO2 and Bi2MoO6 obtained in Example 1 of this invention, which are Mott-Schottky. Figure 10This is a schematic diagram illustrating the mechanism of photogenerated cathodic protection of 304 SS by the Bi2MoO6 / TiO2 composite material provided in Example 1 of the present invention. Detailed Implementation

[0025] 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.

[0026] This invention introduces Bi₂MoO₆ nanosheets onto the surface of a TiO₂ nanotube array, forming a heterojunction structure. This structure, through band matching, enables the migration of photogenerated electrons from TiO₂ to Bi₂MoO₆ and the reverse migration of photogenerated holes, significantly suppressing electron-hole recombination and effectively improving carrier separation efficiency. Specifically, the introduction of Bi₂MoO₆ broadens the photoresponse range of TiO₂, achieving visible light absorption extension from 368 nm to 400 nm; the band gap of the composite material is reduced from 3.2 eV to 2.9 eV, improving light energy utilization efficiency; and the photocurrent density is increased to 50 µA / cm². 2 The results show that the open-circuit potential cathodic amplitude reaches -10¹⁰ mV, enhancing the photocathode protection effect. The cyclic voltammetric response curve area increases, improving the charge transport rate and reversible charge storage capacity, forming a stable anti-corrosion protective layer. Consequently, the resulting material exhibits high charge separation efficiency, a wide photoresponse range, excellent photocathode protection performance, and strong electrochemical stability, while significantly improving the photoelectrochemical protection effect of metallic materials in corrosive environments.

[0027] Example 1 1) Commercially available titanium plates with a purity of 99.9% were cut into samples with dimensions of 0.3 mm × 10 mm × 20 mm. The titanium plate samples were ultrasonically cleaned sequentially in anhydrous ethanol and deionized water for 10 min each time to remove surface oil and impurities.

[0028] 2) After cleaning, the titanium plate is immersed in a polishing solution for chemical polishing. The polishing solution is formulated as follows: 0.45 g ammonium fluoride (NH4F), 2.5 mL deionized water, 6 mL hydrogen peroxide (H2O2), and 6 mL nitric acid (HNO3). The polishing process lasts for 20 seconds at room temperature. After polishing, the sample is rinsed multiple times (3 times in this example) with anhydrous ethanol and deionized water, and then ultrasonically cleaned again for 10 min each in anhydrous ethanol and deionized water. The titanium plate sample treated as described above is stored in anhydrous ethanol for later use.

[0029] 3) Dissolve 5.57 g of ammonium fluoride (NH4F) in a mixed solution of 100 mL of deionized water and 1000 mL of ethylene glycol, and stir thoroughly with a magnetic stirrer to obtain the electrolyte for electrochemical anodizing. Using a platinum sheet electrode as the cathode and the pretreated titanium substrate sample as the anode, an electrochemical anodizing process was used to prepare a TiO2 nanotube array film (see [link to relevant documentation]). Figures 1-6 ).

[0030] Specifically, a platinum sheet was used as the cathode and a pretreated titanium sheet as the anode to construct a two-electrode system. Before use, the cleaned titanium substrate was ultrasonically cleaned for 10 min each in anhydrous ethanol and deionized water to remove surface organic matter and oxide impurities, and then air-dried. 100 mL of electrolyte was placed in a 100 mL beaker, and the two-electrode system was assembled. The pretreated titanium plate sample was connected to the positive electrode of a DC power supply, and the platinum foil (20 mm × 20 mm) was connected to the negative electrode. The voltage was set to 20 V, and the reaction time was 1 hour. After the reaction, the sample was removed and rinsed repeatedly with pure water and anhydrous ethanol alternately, and then air-dried at room temperature. The dried sample was placed in a muffle furnace and heated to 450 °C at a heating rate of 5 °C / min, and calcined at this temperature for 120 min. After calcination, it was naturally cooled to room temperature to obtain a titanium substrate with a TiO2 nanotube array structure on its surface.

[0031] 4) Weigh 0.0194 g of Bi(NO3)3·9H2O and 0.0048 g of Na2MoO4·2H2O, dissolve them in 40 mL of deionized water, and stir evenly to prepare a reaction solution. Carefully pour the prepared reaction solution into a hydrothermal reactor, avoiding the generation of bubbles to ensure the homogeneity of the reaction solution. Then, place the TiO2 nanotubes at an angle in the reactor to ensure that they are fully immersed in the precursor solution, thereby achieving a good contact effect. Place the reactor in an oven and react at 180 °C for 12 h. After the reaction, allow the reactor to cool naturally to room temperature. Subsequently, wash the product with deionized water and anhydrous ethanol alternately several times (three times in this example) to remove unreacted precursors and impurities. Finally, vacuum dry the washed product at 60 °C for 24 h to obtain the desired Bi2MoO6 / TiO2 composite material (see Figure 1 ).

[0032] Comparative Example 1) Weigh an appropriate amount of Bi(NO3)3·H2O and dissolve it in 20 mL of 4.8 M nitric acid solution to obtain the Bi precursor solution; simultaneously, dissolve NH4VO3 in 20 mL of 2.0 M NaOH solution to obtain the V precursor solution. Both solutions must be stirred thoroughly to ensure complete dissolution of the reagents.

[0033] 2) Slowly mix the two precursor solutions and stir until homogeneous. Then add P25 TiO2 powder and 0.08 mL of hexadecyltrimethylammonium bromide (CTAB) at a concentration of 10 g / L, and continue stirring to ensure uniform dispersion of the system, providing favorable conditions for the formation of the xBiVO4 / TiO2 composite structure.

[0034] 3) Transfer the well-mixed precursor solution to a hydrothermal reactor and carry out the hydrothermal reaction at 140 °C for 6 hours. After the reaction is complete, allow the reactor to cool naturally to room temperature to avoid damage to the product structure due to sudden cooling.

[0035] 4) After the system cools, collect the precipitate in the reactor and wash it repeatedly with distilled water several times to remove unreacted precursors and impurities. Finally, dry the washed product at 70 °C to obtain xBiVO4 / TiO2 (x = 66.4–100 wt%) photocatalytic material.

[0036] The pure TiO2 and Bi2MoO6 / TiO2 composite materials obtained in Example 1 were analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown. By Figure 2 (a) Analysis shows that the TiO2 nanotubes (NAs) prepared by one-step anodic oxidation are uniformly distributed on the surface of the titanium substrate, with a diameter of approximately 45-65 nm and a wall thickness of approximately 12 nm. The inset further shows that the TiO2 nanotubes are vertically aligned on the substrate surface and have a length of approximately 1 µm, which is beneficial for the directional transport of photogenerated electrons. Figure 2 (b) shows that nanosheets are uniformly grown on the surface of TiO2 nanotubes, indicating that Bi2MoO6 is loaded on the surface of TiO2 nanotubes in the form of nanosheets, forming a Bi2MoO6 / TiO2 composite structure.

[0037] The crystal structures of TiO2, Bi2MoO6, and Bi2MoO6 / TiO2 composite materials obtained in Example 1 were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) (see [link to X-ray diffraction]). Figure 3 ).like Figure 3(a) The pure TiO2 sample exhibits diffraction peaks at 25.36°, 48.15°, 53.97°, and 55.19°, corresponding to the (011), (020), (015), and (121) crystal planes of the anatase phase TiO2 (JCPDS card number 98-007-6173). The Bi2MoO6 diffraction peaks at 28.25°, 32.53°, 33.09°, and 46.66° correspond to the (131), (002), (060), and (202) crystal planes of (JCPDS card number 98-020-1865). No other impurity phases were detected, confirming the successful synthesis of the composite material. Furthermore, the weakening intensity of the TiO2 diffraction peaks indicates that the introduction of Bi2MoO6 reduced crystallinity or provided good dispersion. Figure 3 (b) The XPS full spectrum confirmed that the material contains Ti, O, Bi and Mo elements. Figure 3 (c) The Ti 2p absorption peaks are shown at 459.35 eV and 465.15 eV; Figure 3 In (d), the Mo 3d peaks are located at 232.94 eV and 236.2 eV; Figure 3 In (e), the Bi 4f peaks are located at 165 eV and 159.71 eV, indicating the presence of Bi2MoO6. Figure 3 The O 1s spectrum in (f) shows that lattice oxygen is present at 530.64 eV and adsorbed oxygen is present at 532.25 eV. The latter is attributed to oxygen vacancies, which helps to improve the photoelectric conversion performance of the composite material.

[0038] In Example 1 above, TiO2, Bi2MoO6, and Bi2MoO6 / TiO2 composite materials were coupled with 304 stainless steel, and the changes in electrode potential and photocurrent density over time in simulated seawater were tested (see Example 1). Figure 4 ). Figure 4 (a) The results show that the maximum induced potential of the pure TiO2 photoanode is -520 mV, while the OCP of the Bi2MoO6 / TiO2 composite material decreases to -1010 mV, significantly improving the cathodic protection effect. Under illumination, photogenerated electrons are transferred from TiO2 to Bi2MoO6 to 304 SS, achieving electron enrichment and cathodic protection. Simultaneously, photogenerated holes migrate from Bi2MoO6 to TiO2, extending the electron-hole pair lifetime and improving protection efficiency. After illumination stops, stored electrons can continue to be transferred, achieving long-lasting protection. Figure 4 (b) shows that the Bi2MoO6 / TiO2 composite material (reacted over 12 hours) exhibits the highest stable photocurrent density (50 µA / cm). 2 The value is much higher than that of pure TiO2 (12 µA / cm). 2 This indicates that it has excellent carrier separation and photoelectric conversion performance, and good stability under multiple cycles.

[0039] The TiO2, Bi2MoO6, and Bi2MoO6 / TiO2 composite materials obtained in Example 1 were subjected to UV-Vis absorption spectroscopy analysis (e.g., Figure 5 (As shown). The test results show that the absorption threshold of the TiO2 nanostructure is located at approximately 368 nm, indicating its weak absorption capacity for visible light with wavelengths greater than 390 nm. Therefore, it is necessary to construct a heterojunction by introducing other materials to expand the photoresponse range. Experimental results show that after loading Bi2MoO6 nanomaterials, the absorption edge of the TiO2 nanostructure redshifts to 400 nm, achieving an effective expansion of the photoresponse range. This phenomenon is attributed to the slight redshift caused by the minor structural changes of TiO2 during the composite process. Furthermore, by analyzing the Tauc plot of the above materials, the band gap width was calculated using the Kubelka-Munk method. The results show that the band gap of pure TiO2 is 3.25 eV, while the band gap of the Bi2MoO6 / TiO2 composite material decreases to 2.7 eV, indicating that the introduction of Bi2MoO6 effectively reduces the material band gap. This change is consistent with the UV-Vis diffuse reflectance spectroscopy test results, further verifying the excellent performance of the Bi2MoO6 / TiO2 composite material in expanding the photoresponse range.

[0040] Furthermore, the materials obtained in Example 1 and the comparative example were compared, see [reference]. Figure 6 Compared with flower-like BiVO4, the plate-like Bi2MoO6 structure has a more open two-dimensional morphology and a higher specific surface area. TiO2 can be more uniformly loaded on its surface to form a denser heterojunction interface, thereby reducing agglomeration, shortening the electron migration path, and significantly improving the separation and transport efficiency of photogenerated electrons.

[0041] Cyclic voltammetry (CV) tests were performed on the TiO2, Bi2MoO6, and Bi2MoO6 / TiO2 composite materials obtained in Example 1 (e.g. Figure 7 (As shown); specifically, the experiment was conducted in a standard three-electrode system, using a Bi₂MoO₆ / TiO₂ composite photoanode as the working electrode (WE), a platinum wire as the counter electrode (CE), and a SCE as the reference electrode (RE). The electrolyte was the same NaOH / Na₂S mixed solution. The CV test scan rate was set to 10–50 mV / s, and the scan potential range was selected according to the system characteristics to examine the photoresponse and electrochemical active sites of the electrodes.

[0042] The results showed that with increasing scan rate (10-50 mV / s), the current response of all three components increased, and the area under the CV curves increased, indicating improved electrochemical activity. Specifically, the TiO2 curve was narrow and asymmetrical, indicating poor charge transport performance; the Bi2MoO6 curve showed enhanced current response, indicating an increase in active sites; while the Bi2MoO6 / TiO2 composite material exhibited the largest curve area and best symmetry, maintaining excellent response even at high scan rates, reflecting superior charge transport and capacitance characteristics. Further analysis showed that the current density difference (ΔCurrent density) of Bi2MoO6 / TiO2 increased linearly with scan rate, consistently exceeding that of TiO2 and Bi2MoO6, indicating that its surface possesses higher electrochemical reactivity, faster ion / electron transport capabilities, and a larger reversible charge storage capacity. These results validate that the Bi2MoO6 / TiO2 composite material can significantly improve the corrosion resistance of TiO2, forming a stable protective layer and providing an excellent electrochemical basis for photogenerated cathodic protection.

[0043] Further, the long-term open-circuit potential (OCP) test results of Example 1 and the comparative example were compared (see Example 1). Figure 8 Specifically, in the OCP test, the 304 SS electrode was electrically connected to the working electrode (WE), and a saturated calomel electrode (SCE) was used as the reference electrode (RE). The illumination time was set to 15 h to evaluate the potential change characteristics under light-induced conditions over a longer period.

[0044] Depend on Figure 8 As can be seen, the Bi₂MoO₆ / TiO₂-12 h composite photoelectrode was first immersed in the electrolyte for 0.5 h in the dark to stabilize its open-circuit potential (OCP). Upon initial illumination, the potential of the photoelectrode rapidly decreased to approximately -950 mV, significantly lower than the self-corrosion potential of 304 stainless steel, indicating that it can effectively provide photocathode protection for the coupled 304 stainless steel. Furthermore, during continuous illumination for up to 15 h, the potential of the Bi₂MoO₆ / TiO₂-12 h photoelectrode remained unchanged, further demonstrating its excellent chemical stability. After illumination ceased, the potential of the composite photoelectrode gradually increased but did not return to its initial value, indicating that the Bi₂MoO₆ / TiO₂-12 h composite photoelectrode possesses good stability.

[0045] Tests were performed on the TiO2 and Bi2MoO6 obtained in Example 1 using the Mott-Schottky method (see [link]). Figure 9All samples exhibit positive slopes, demonstrating their n-type semiconductor characteristics. Since the flat band potential of an n-type semiconductor is typically close to its conduction band (CB) position, the conduction band potentials of TiO2 and Bi2MoO6 are -0.20 V and -0.70 V (relative to NHE), respectively. Combining the band gap energies calculated by UV-Vis DRS (3.30 eV for TiO2 and 2.51 eV for Bi2MoO6), the valence band (VB) positions of TiO2 and Bi2MoO6 can be further estimated to be 3.10 eV and 1.81 eV (relative to NHE), respectively.

[0046] The Tauc analysis and Mott-Schottky test results of the composite material obtained above demonstrate the mechanism of photogenerated cathodic protection of 304 SS by the Bi2MoO6 / TiO2 composite material obtained in Example 1 (see [link to example]). Figure 10 By constructing a Z-type heterojunction structure, photogenerated electrons and holes in Bi₂MoO₆ and TiO₂ are spatially separated at the heterojunction interface, thus overcoming the limitation of insufficient electron energy in traditional type II heterojunctions. Specifically, Bi₂MoO₆ has a more negative conduction band potential, which can provide high-energy electrons and inject them into the coupled metal substrate, causing a significant negative shift in the open-circuit potential, thereby effectively suppressing the anodic dissolution process and slowing down metal corrosion.

[0047] In summary, the Bi2MoO6 / TiO2 composite structure of the present invention can achieve controllable bandgap coupling and efficient carrier separation by constructing a stable heterojunction, avoiding the deep-level defect problem caused by doping. At the same time, it has both a wide spectral response and excellent chemical stability, thus having more significant advantages in improving photoelectrochemical performance and photogenerated cathode protection efficiency.

Claims

1. A method for preparing a nanosheet-modified Bi₂MoO₆ / TiO₂ composite photoanode material, characterized in that: A hydrothermal method was used to uniformly form a nanosheet-modified Bi2MoO6 / TiO2 composite material on the surface of a TiO2 nanotube substrate using an aqueous solution containing Bi and Mo sources.

2. The method for preparing the nanosheet-modified Bi₂MoO₆ / TiO₂ composite photoanode material according to claim 1, characterized in that: Bi(NO3)3·9H2O and Na2MoO4·2H2O were dissolved in deionized water and mixed to form a reaction solution. The reaction solution was then injected into a hydrothermal reactor. TiO2 nanotubes were then placed in the reactor and immersed in the reaction solution. The reaction was carried out at 180 °C for 6 to 20 hours. After the reaction, the mixture was cooled to room temperature. The TiO2 nanotube substrate was then washed repeatedly with deionized water and anhydrous ethanol, and dried. This resulted in the formation of a uniform nanosheet-modified Bi2MoO6 / TiO2 composite material on the surface of the TiO2 nanotubes.

3. The method for preparing the nanosheet-modified Bi₂MoO₆ / TiO₂ composite photoanode material according to claim 2, characterized in that: The final concentration of Bi in the reaction solution is 0.8~1.2 mmol, and the final concentration of Mo is 0.3~0.7 mmol.

4. The method for preparing the nanosheet-modified Bi₂MoO₆ / TiO₂ composite photoanode material according to claim 1 or 2, characterized in that: The TiO2 nanotube substrate is prepared by anodic oxidation using a platinum sheet electrode as the cathode, a pretreated titanium substrate sample as the anode, and a mixture of ammonium fluoride, deionized water, and ethylene glycol as the electrolyte.

5. The method for preparing the nanosheet-modified Bi₂MoO₆ / TiO₂ composite photoanode material according to claim 4, characterized in that: The TiO2 nanotube array film uses a platinum sheet electrode as the cathode and a pretreated titanium substrate sample as the anode. A DC voltage of 15~30 V is provided by a DC power supply, and the anodizing time is 0.5~2 h. After treatment, the titanium substrate sample is heated to 450 ℃ in a muffle furnace at a heating rate of 5 ℃ / min and calcined at this temperature for 120 min. After natural cooling, the TiO2 nanotube array film can be obtained.

6. A method for preparing nanosheet-modified Bi₂MoO₆ / TiO₂ composite photoanode material according to claim 1, characterized in that: Bi2MoO6 / TiO2 composite photoanode material modified with irregularly shaped nanosheets was prepared according to the method described in claim 1.

7. The application of the nanosheet-modified Bi₂MoO₆ / TiO₂ composite photoanode material according to claim 6, characterized in that: Application of the nanosheet-modified Bi2MoO6 / TiO2 composite photoanode material in the protection of metals from corrosion using photocathodes.

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