Hematite thin film with surface loaded titania passivation layer of ligand-free nanocrystals, method of preparation and use thereof

Abstract

The present application relates to the technical field of photocatalytic and photoelectrocatalytic material preparation, in particular to a hematite film with a surface-loaded ligand-free nanocrystal inlaid titania passivation layer and a preparation method and application thereof. The hematite film with a nanorod structure and a surface-loaded titania passivation layer, and the ligand-free nanocrystal inlaid in the titania passivation layer, and the mass fraction of the ligand-free nanocrystal in the titania passivation layer is 0.085-0.43%, the ligand-free nanocrystal is inlaid on the titania passivation layer to improve the carrier bulk transport problem of the titania passivation layer, and then the hematite / electrolyte interface is activated to obtain a high-performance hematite photoanode material.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis and photoelectrocatalysis material preparation technology, and relates to hematite thin films with ligand-free nanocrystal embedded titanium dioxide passivation layers on their surfaces, their preparation methods and applications. Background Technology

[0002] Photoelectrochemical water splitting (PEC) for hydrogen production enables large-scale, efficient utilization of solar energy. A key aspect of this technology is finding inexpensive and stable semiconductor photoelectrode materials. Hematite (α-Fe₂O₃) is considered one of the most promising photoanode materials due to its non-toxicity, low cost, good stability, suitable band structure, and excellent visible light absorption characteristics. However, the surface of hematite typically contains many unwanted surface states, primarily Fe₂O₃ in oxygen-deficient regions. 3+ / Fe 2+ Redox pairs trap holes or electrons during charging and discharging, leading to severe recombination on the hematite photoanode surface. This restricts charge transport at the semiconductor / electrolyte interface (SCLJ), resulting in an experimental photocurrent density at AM 1.5G that is significantly lower than its theoretical photocurrent density (12.6 mA cm⁻¹). -2 ).

[0003] Depositing a metal oxide passivation layer on the surface of hematite is a widely used method for passivating surface defects and activating the SCLJ interface. Among them, the titanium dioxide (TiO2) passivation layer can passivate the surface defects of hematite photoanodes, increase light absorption, and accelerate charge transfer. However, the low carrier mobility of TiO2 can hinder the transfer of photogenerated holes from α-Fe2O3 to the SCLJ, thereby limiting the oxidation reaction of water on the surface of the hematite photoanode. Therefore, how to improve the bulk carrier transport of the titanium dioxide passivation layer, and thus activate the hematite / electrolyte interface to obtain high-performance hematite photoanode materials, is a technical challenge that needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a hematite thin film with a surface-loaded ligandless nanocrystal embedded in a titanium dioxide passivation layer, its preparation method, and its application. The film comprises a hematite thin film with a nanorod structure and a surface-loaded titanium dioxide passivation layer, and ligandless nanocrystals embedded in the titanium dioxide passivation layer. The mass fraction of the ligandless nanocrystals in the surface-loaded titanium dioxide passivation layer is 0.085-0.43%. By embedding ligandless nanocrystals on the titanium dioxide passivation layer, the problem of carrier bulk phase transport in the titanium dioxide passivation layer is improved, thereby activating the hematite / electrolyte interface and obtaining a high-performance hematite photoanode material.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing a hematite thin film with a ligand-free nanocrystal-embedded titanium dioxide passivation layer on its surface includes the following steps:

[0007] (1) Preparation of α-Fe2O3 thin films;

[0008] Iron hydroxyl oxide was prepared on transparent conductive glass by hydrothermal synthesis and then sintered at high temperature to obtain α-Fe2O3 thin film;

[0009] (2) Preparation of ligand-free nanocrystalline colloidal solutions;

[0010] The original semiconductor particles were uniformly dispersed in a liquid medium to obtain a semiconductor solution. The semiconductor solution was then subjected to liquid-phase pulsed laser irradiation under ultrasonic assistance to obtain a ligand-free nanocrystalline colloidal solution.

[0011] (3) Preparation of TiO2 passivation layer precursor solution:

[0012] (4) Preparation of hematite films with ligand-free nanocrystal-embedded titanium dioxide passivation layers on the surface:

[0013] S41. Mix the ligandless nanocrystalline colloidal solution from step (2) with the TiO2 passivation layer precursor solution from step (3) to obtain a mixture.

[0014] S42. The α-Fe2O3 film from step (1) is placed in the mixture from step S41 and subjected to a solvothermal reaction. Then, it is rinsed and heat-treated in sequence to obtain a hematite film with a titanium dioxide passivation layer supported on the surface without ligand nanocrystals.

[0015] Preferably, the transparent conductive glass in step (1) is selected from fluorine-doped tin dioxide or indium tin oxide.

[0016] Preferably, the α-Fe2O3 film of step (1) is prepared according to the following steps:

[0017] S11. The transparent conductive glass is ultrasonically cleaned and dried to obtain treated conductive glass;

[0018] S12. Disperse the iron source and sodium nitrate together in ultrapure water, and then adjust the pH to 0.75-1.50 to obtain the precursor solution;

[0019] The iron source is selected from anhydrous ferric chloride or ferric chloride hexahydrate, and the molar ratio of the iron source to sodium nitrate is 6-10:1.

[0020] S13. The conductive glass processed in step S11 is immersed in the precursor solution of step S12, and then hydrothermal synthesis is carried out at 95°C for 6-12 hours to obtain an iron hydroxyl oxide film.

[0021] S14. After drying the iron hydroxyl oxide film, it is first treated at 550℃ for 2-3 hours, and then sintered at 750-800℃ for 10-20 minutes to obtain an α-Fe2O3 film with a thickness of 200-500 nm.

[0022] Preferably, in step (2), the original semiconductor particles are selected from one of CdTe, WO3, and Pt, the liquid medium is ultrapure water, and the concentration of the ligand-free nanocrystalline colloidal solution is 0.05-0.25 mg / mL.

[0023] Preferably, the ligand-free nanocrystalline colloidal solution of step (2) is prepared according to the following steps:

[0024] Under ultrasonic assistance, the semiconductor solution was irradiated with a pulsed unfocused laser beam. The output wavelength of the unfocused laser beam was 1064 nm, the pulse frequency was 30 Hz, the output spot diameter was 6-10 mm, and the laser irradiation energy density was 1000-1500 mJ / cm². 2 The irradiation time is 10-30 minutes;

[0025] The frequency of ultrasound is 20-40kHz.

[0026] Preferably, the TiO2 passivation layer precursor solution in step (3) is prepared according to the following steps: ultrapure water is frozen to 0-10℃, and then TiCl4 is added dropwise to it. After natural thawing at room temperature, the TiO2 passivation layer precursor solution is obtained.

[0027] The concentration of the TiCl4 solution was 2.5-5.5 mg / mL.

[0028] Preferably, in step S41, the volume ratio of the ligand-free nanocrystalline colloidal solution to the precursor solution of the titanium dioxide passivation layer is 1:20-80.

[0029] Preferably, in step S42, the solvothermal reaction is carried out at 60-80°C for 50-70 min, and the heat treatment is carried out at 100-120°C for 40-70 min, to obtain a hematite film with a titanium dioxide passivation layer supported on the surface without ligand nanocrystals.

[0030] The hematite film with a surface-loaded titanium dioxide passivation layer without ligands can be further annealed to obtain a hematite film with a surface-loaded titanium dioxide passivation layer without ligands and with good crystallinity. The annealing conditions are annealing at 700-800℃ for 10-20 min.

[0031] This invention also protects the hematite film with a surface-loaded, ligand-free nanocrystal-embedded titanium dioxide passivation layer prepared by the aforementioned method.

[0032] This invention also protects the application of hematite films with surface-loaded ligand-free nanocrystal-embedded titanium dioxide passivation layers in the preparation of photocatalytic and photoelectrocatalytic materials.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The preparation method of the present invention includes: preparing iron hydroxyl oxide on transparent conductive glass by hydrothermal synthesis, and forming a hematite film after high-temperature sintering; then preparing a ligand-free nanocrystalline colloidal solution by liquid-phase pulsed laser irradiation under ultrasonic assistance; finally, mixing the ligand-free nanocrystalline colloidal solution with a titanium dioxide passivation layer precursor solution to obtain a mixed solution, and placing the hematite film in the above mixed solution for solvothermal reaction, and forming a hematite photoanode film with a titanium dioxide passivation layer embedded on the surface after heat treatment.

[0035] 2. This invention introduces well-dispersed ligand-free nanocrystals into a titanium dioxide passivation layer precursor solution using selective laser irradiation technology in a liquid medium, thereby preparing a ligand-free titanium dioxide passivation layer.

[0036] 3. The ligand-free nanocrystal-embedded titanium dioxide passivation layer prepared in this invention improves the carrier transport characteristics of the titanium dioxide passivation layer. This invention composites the ligand-free nanocrystal-embedded titanium dioxide passivation layer onto the surface of a hematite photoanode film. The introduction of ligand-free nanocrystals improves the carrier transport characteristics of the titanium dioxide passivation layer, promotes carrier separation and transport at the photoanode / electrolyte interface, and thus significantly improves the photoelectric performance of the hematite photoanode. The photocurrent density of the hematite photoanode film increases from 0.52 mA cm⁻¹. -2 Increased to 2.28 mA cm -2 The improvement was approximately 338%, and this modification strategy has strong universality, providing a general alternative for adjusting the semiconductor / electrolyte interface defects and physicochemical properties of metal oxides. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the hematite film (α-Fe2O3 / TiO2-CdTe) with a titanium dioxide passivation layer supported on the surface of the present invention;

[0038] Figure 2 Figure 1 shows the SEM and XRD images of the original (before laser irradiation) CdTe particles in Embodiment 1 of the present invention, where Figure 1a is the SEM image of the original CdTe particles and Figure 2b is the XRD image of the original CdTe particles.

[0039] Figure 3 Figure 1 shows the TEM and XRD images of ligand-free CdTe nanocrystals after laser irradiation in Example 1 of the present invention, wherein Figure a is the TEM image of ligand-free CdTe nanocrystals and Figure b is the XRD image of ligand-free CdTe nanocrystals.

[0040] Figure 4 These are surface and cross-sectional SEM images of the α-Fe2O3 / TiO2-CdTe thin film in Example 1 of the present invention, wherein Figure a is a surface SEM image and Figure b is a cross-sectional SEM image;

[0041] Figure 5 Figure 1 shows surface and cross-sectional SEM images of the α-Fe2O3 thin film in Comparative Example 1 of the present invention, where Figure 1a is a surface SEM image and Figure 1b is a cross-sectional SEM image.

[0042] Figure 6 Figure 1 shows surface and cross-sectional SEM images of the α-Fe2O3 / TiO2 thin film in Comparative Example 2 of the present invention, where Figure 2a is a surface SEM image and Figure 2b is a cross-sectional SEM image.

[0043] Figure 7 These are TEM images of the α-Fe2O3 / TiO2-CdTe thin film in Example 1 of this invention at different magnifications;

[0044] Figure 8 These are TEM images of the α-Fe2O3 thin film in Comparative Example 1 of this invention at different magnifications;

[0045] Figure 9 These are TEM images of the α-Fe2O3 / TiO2 thin film in Comparative Example 2 of this invention at different magnifications;

[0046] Figure 10 The figures show the linear current-voltage curves and photoelectric conversion efficiency curves of the α-Fe2O3 thin film in Comparative Example 1, the α-Fe2O3 / TiO2 thin film in Comparative Example 2, and the α-Fe2O3 / TiO2-CdTe thin film in Example 1 of this invention, wherein Figure a is the linear current-voltage curve and Figure b is the photoelectric conversion efficiency curve.

[0047] Figure 11 Figure a shows the impedance curves and Mott-Schottky (MS) curves of the α-Fe₂O₃ thin film in Comparative Example 1, the α-Fe₂O₃ / TiO₂ thin film in Comparative Example 2, and the α-Fe₂O₃ / TiO₂-CdTe thin film in Example 1 of the present invention, wherein Figure a is the impedance curve and Figure b is the Mott-Schottky (MS) curve.

[0048] Figure 12The figures show the surface charge separation efficiency and open-circuit photovoltage of the α-Fe2O3 thin film in Comparative Example 1, the α-Fe2O3 / TiO2 thin film in Comparative Example 2, and the α-Fe2O3 / TiO2-CdTe thin film in Example 1 of this invention. Figure a shows the surface charge separation efficiency, and Figure b shows the open-circuit photovoltage.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1. Transparent glass; 2. Fluorine-doped tin dioxide layer; 3. Ligand-free CdTe nanocrystals; 4. Hematite thin film (α-Fe2O3) layer; 5. Titanium dioxide (TiO2) passivation layer. Detailed Implementation

[0051] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0052] Example 1

[0053] A method for preparing a hematite thin film with a ligand-free nanocrystal embedded titanium dioxide passivation layer on its surface includes the following steps:

[0054] (1) Preparation of α-Fe2O3 thin films;

[0055] S1. Select fluorine-doped tin dioxide transparent conductive glass (FTO) with a sheet resistance of 15Ω, a thickness of 2.2mm, a size of 20mm×25mm, and a transmittance of 85% as the substrate material. Before use, ultrasonically clean it with water, ethanol, and acetone for 30 minutes each, and then dry it with a nitrogen gun to obtain the treated conductive glass (FTO substrate).

[0056] S2. Add ferric chloride hexahydrate (FeCl3·6H2O, 2.7g, 0.01mol) and sodium nitrate (NaNO3, 8.5g, 0.1mol) to a beaker containing 100mL of ultrapure water. Stir magnetically at room temperature for 30min. Then adjust the pH of the above solution to 1.3 with concentrated hydrochloric acid (HCl) to obtain the precursor solution.

[0057] S3. Transfer the 60 mL precursor solution obtained in S2 to a 100 mL polytetrafluoroethylene (PTFE) reactor. Place the four FTO substrates from step S1 with their conductive surfaces facing down on a PTFE rack. Then place the PTFE rack containing the FTO substrates into the PTFE reactor containing the 60 mL precursor solution. Place the reactor in a 95 °C electric heating drying oven and keep it at that temperature for 10 h to carry out the hydrothermal reaction. A yellow iron hydroxyl oxide (FeOOH) film sample will grow on the FTO substrate. After naturally cooling to room temperature, remove the FeOOH, rinse it with ultrapure water, and dry it with a nitrogen gun.

[0058] S4. The FeOOH film obtained in S3 was placed in a muffle furnace and sintered in air at 550℃ for 2h to obtain an α-Fe2O3 film. The heating rate was 3℃ / min. Then, it was sintered at 800℃ for 10min. After sintering, the sample was naturally cooled to room temperature and removed to obtain the α-Fe2O3 film.

[0059] (2) Preparation of ligand-free nanocrystalline colloidal solutions;

[0060] S5. Disperse 0.5 mg of raw CdTe particles in 10 mL of ultrapure water and sonicate for 20 min to obtain a mixture;

[0061] S6. Under ultrasonic assistance at a frequency of 30 kHz, the mixture obtained in S5 is subjected to irradiation under a non-focused laser beam; wherein the pulse frequency of the non-focused laser is 30 Hz, the output wavelength is 1064 nm, the output spot diameter is 10 mm, and the laser irradiation energy density is 1200 mJ / cm². 2 After irradiation for 20 minutes, a transparent brownish-yellow colloidal solution was obtained, which is the ligand-free CdTe nanocrystal colloidal solution. The obtained ligand-free CdTe nanocrystals have a size of less than 10 nm. Figure 3 As shown in a;

[0062] (3) Preparation of TiO2 passivation layer precursor solution:

[0063] S7. After sealing the beaker containing 40 mL of ultrapure water with sealing film, freeze it in the freezer to 5°C before use. Use a pipette to slowly add 80 μL of TiCl4 solution to the above 40 mL of frozen ultrapure water. After it thaws naturally at room temperature, the TiO2 passivation layer precursor solution is obtained.

[0064] (4) Preparation of hematite films with ligand-free nanocrystal-embedded titanium dioxide passivation layers on the surface:

[0065] S8. Mix 1 mL of the ligandless CdTe nanocrystal colloidal solution obtained in S6 and the TiO2 passivation layer precursor solution obtained in S7 until homogeneous to obtain a mixed solution.

[0066] S9. Place the α-Fe2O3 film obtained in S4 into the mixed solution obtained in S8, and carry out a solvothermal reaction in a 70℃ electric heating drying oven for 60 min. Then rinse it with ultrapure water and place it in a 110℃ electric heating drying oven for 60 min of heat treatment to obtain a hematite film (α-Fe2O3 / TiO2-CdTe) with a titanium dioxide passivation layer supported on the surface.

[0067] S10. The α-Fe₂O₃ / TiO₂-CdTe film obtained in S9 is placed in a tube furnace and annealed in air at 800°C for 10 min to obtain an α-Fe₂O₃ / TiO₂-CdTe film with better crystallinity. Figure 4 The surface SEM image of α shows that an α-Fe₂O₃ / TiO₂-CdTe film with a thickness of 450 nm was prepared. Figure 4 The cross-sectional SEM image of b is shown.

[0068] Example 2

[0069] A method for preparing a hematite thin film with a ligand-free nanocrystal embedded titanium dioxide passivation layer on its surface includes the following steps:

[0070] (1) Preparation of α-Fe2O3 thin films;

[0071] S1. Select fluorine-doped tin dioxide transparent conductive glass (FTO) with a sheet resistance of 15Ω, a thickness of 2.2mm, a size of 20mm×25mm, and a transmittance of 85% as the substrate material. Before use, ultrasonically clean it with water, ethanol, and acetone for 30 minutes each, and then dry it with a nitrogen gun to obtain the treated conductive glass (FTO substrate).

[0072] S2. Add ferric chloride hexahydrate (FeCl3·6H2O, 2.16 g, 0.008 mol) and sodium nitrate (NaNO3, 8.5 g, 0.1 mol) to a beaker containing 100 mL of ultrapure water. Stir magnetically at room temperature for 30 min, then adjust the pH of the solution to 0.75 with concentrated hydrochloric acid (HCl) to obtain the precursor solution.

[0073] S3. Transfer the 60 mL precursor solution obtained in S2 to a 100 mL polytetrafluoroethylene (PTFE) reactor. Place the four FTO substrates from step S1 with their conductive surfaces facing down on a PTFE rack. Then place the PTFE rack containing the FTO substrates into the PTFE reactor containing the 60 mL precursor solution. Place the reactor in a 95 °C electric heating drying oven and keep it at that temperature for 12 h to carry out the hydrothermal reaction. A yellow iron hydroxyl oxide (FeOOH) film sample will grow on the FTO substrate. After naturally cooling to room temperature, remove the FeOOH, rinse it with ultrapure water, and dry it with a nitrogen gun.

[0074] S4. The FeOOH film obtained in S3 was placed in a muffle furnace and sintered in air at 550℃ for 2.5h to obtain an α-Fe2O3 film. The heating rate was 3℃ / min. Then, it was sintered at 780℃ for 15min. After sintering, the sample was naturally cooled to room temperature and removed to obtain the α-Fe2O3 film.

[0075] (2) Preparation of ligand-free nanocrystalline colloidal solutions;

[0076] S5. Disperse 1.5 mg of raw CdTe particles in 10 mL of ultrapure water and sonicate for 20 min to obtain a mixture;

[0077] S6. Under ultrasonic assistance at a frequency of 20 kHz, the mixture obtained in S5 is subjected to irradiation under a non-focused laser beam; wherein the pulse frequency of the non-focused laser is 30 Hz, the output wavelength is 1064 nm, the output spot diameter is 6 mm, and the laser irradiation energy density is 1500 mJ / cm². 2 After irradiation for 10 minutes, a transparent brownish-yellow colloidal solution was obtained, which is the ligand-free CdTe nanocrystal colloidal solution.

[0078] (3) Preparation of TiO2 passivation layer precursor solution:

[0079] S7. After sealing the beaker containing 40 mL of ultrapure water with sealing film, freeze it in the freezer to 10°C before use. Use a pipette to slowly add 120 μL of TiCl4 solution to the above 40 mL of frozen ultrapure water. After it thaws naturally at room temperature, the TiO2 passivation layer precursor solution is obtained.

[0080] (4) Preparation of hematite films with ligand-free nanocrystal-embedded titanium dioxide passivation layers on the surface:

[0081] S8. Mix 0.5 mL of the ligandless CdTe nanocrystal colloidal solution obtained in S6 and the TiO2 passivation layer precursor solution obtained in S7 until homogeneous to obtain a mixed solution.

[0082] S9. Place the α-Fe2O3 film obtained in S4 into the mixed solution obtained in S8, and carry out a solvothermal reaction in an 80℃ electric heating drying oven for 50 min. Then rinse it with ultrapure water and place it in a 120℃ electric heating drying oven for 40 min of heat treatment to obtain a hematite film (α-Fe2O3 / TiO2-CdTe) with a titanium dioxide passivation layer supported on the surface.

[0083] S10. Place the α-Fe2O3 / TiO2-CdTe film obtained in S9 in a tube furnace and anneal it in air at 750℃ for 15 min to obtain an α-Fe2O3 / TiO2-CdTe film with better crystallinity.

[0084] Example 3

[0085] A method for preparing a hematite thin film with a ligand-free nanocrystal embedded titanium dioxide passivation layer on its surface includes the following steps:

[0086] (1) Preparation of α-Fe2O3 thin films;

[0087] S1. Select fluorine-doped tin dioxide transparent conductive glass (FTO) with a sheet resistance of 15Ω, a thickness of 2.2mm, a size of 20mm×25mm, and a transmittance of 85% as the substrate material. Before use, ultrasonically clean it with water, ethanol, and acetone for 30 minutes each, and then dry it with a nitrogen gun to obtain the treated conductive glass (FTO substrate).

[0088] S2. Add ferric chloride hexahydrate (FeCl3·6H2O, 1.62 g, 0.006 mol) and sodium nitrate (NaNO3, 8.5 g, 0.1 mol) to a beaker containing 100 mL of ultrapure water. Stir magnetically at room temperature for 30 min, then adjust the pH of the above solution to 1.5 with concentrated hydrochloric acid (HCl) to obtain the precursor solution.

[0089] S3. Transfer the 60 mL precursor solution obtained in S2 to a 100 mL polytetrafluoroethylene (PTFE) reactor. Place the four FTO substrates from step S1 with their conductive surfaces facing down on a PTFE rack. Then place the PTFE rack containing the FTO substrates into the PTFE reactor containing the 60 mL precursor solution. Place the reactor in a 95 °C electric heating drying oven and keep it at that temperature for 10 h to carry out the hydrothermal reaction. A yellow iron hydroxyl oxide (FeOOH) film sample will grow on the FTO substrate. After naturally cooling to room temperature, remove the FeOOH, rinse it with ultrapure water, and dry it with a nitrogen gun.

[0090] S4. The FeOOH film obtained in S3 was placed in a muffle furnace and sintered in air at 550℃ for 3h to obtain an α-Fe2O3 film. The heating rate was 3℃ / min. The film was sintered at 750℃ for 20min. After sintering, the film was naturally cooled to room temperature and the sample was taken out to obtain the α-Fe2O3 film.

[0091] (2) Preparation of ligand-free nanocrystalline colloidal solutions;

[0092] S5. Disperse 2.5 mg of raw CdTe particles in 10 mL of ultrapure water and sonicate for 20 min to obtain a mixture;

[0093] S6. Under ultrasonic assistance at a frequency of 40 kHz, the mixture obtained in S5 is subjected to irradiation under a non-focused laser beam; wherein the pulse frequency of the non-focused laser is 30 Hz, the output wavelength is 1064 nm, the output spot diameter is 8 mm, and the laser irradiation energy density is 1000 mJ / cm². 2 After irradiation for 30 minutes, a transparent brownish-yellow colloidal solution was obtained, which is the ligand-free CdTe nanocrystal colloidal solution.

[0094] (3) Preparation of TiO2 passivation layer precursor solution:

[0095] S7. After sealing the beaker containing 40 mL of ultrapure water with sealing film, freeze it in the freezer to 5°C before use. Use a pipette to slowly add 40 μL of TiCl4 solution to the above 40 mL of frozen ultrapure water. After it thaws naturally at room temperature, the TiO2 passivation layer precursor solution is obtained.

[0096] (4) Preparation of hematite films with ligand-free nanocrystal-embedded titanium dioxide passivation layers on the surface:

[0097] S8. Mix 2 mL of the ligandless CdTe nanocrystal colloidal solution obtained in S6 and the TiO2 passivation layer precursor solution obtained in S7 until homogeneous to obtain a mixed solution.

[0098] S9. Place the α-Fe2O3 film obtained in S4 into the mixed solution obtained in S8, and carry out a solvothermal reaction in a 60℃ electric heating drying oven for 70 min. Then rinse it with ultrapure water and place it in a 100℃ electric heating drying oven for 70 min of heat treatment to obtain a hematite film (α-Fe2O3 / TiO2-CdTe) with a titanium dioxide passivation layer supported on the surface.

[0099] S10. Place the α-Fe2O3 / TiO2-CdTe film obtained in S9 in a tube furnace and anneal it in air at 700℃ for 20 min to obtain an α-Fe2O3 / TiO2-CdTe film with better crystallinity.

[0100] Comparative Example 1

[0101] A method for preparing a hematite photoanode thin film includes the following steps:

[0102] S1. Select fluorine-doped tin dioxide transparent conductive glass (FTO) with a sheet resistance of 15Ω, a thickness of 2.2mm, a size of 20mm×25mm, and a transmittance of 85% as the substrate material. Before use, ultrasonically clean it with water, ethanol, and acetone for 30 minutes each, and then dry it with a nitrogen gun to obtain the treated conductive glass (FTO substrate).

[0103] S2. Add ferric chloride hexahydrate (FeCl3·6H2O, 2.7g, 0.01mol) and sodium nitrate (NaNO3, 8.5g, 0.1mol) to a beaker containing 100mL of ultrapure water. Stir magnetically at room temperature for 30min. Then adjust the pH of the above solution to 1.3 with concentrated hydrochloric acid (HCl) to obtain the precursor solution.

[0104] S3. Transfer the 60 mL precursor solution obtained in S2 to a 100 mL polytetrafluoroethylene (PTFE) reactor. Place the four FTO substrates from step S1 with their conductive surfaces facing down on a PTFE rack. Then place the PTFE rack containing the FTO substrates into the PTFE reactor containing the 60 mL precursor solution. Place the reactor in a 95 °C electric heating drying oven and keep it at that temperature for 10 h to carry out the hydrothermal reaction. A yellow iron hydroxyl oxide (FeOOH) film sample will grow on the FTO substrate. After naturally cooling to room temperature, remove the FeOOH, rinse it with ultrapure water, and dry it with a nitrogen gun.

[0105] S4. The FeOOH film obtained in S3 was placed in a muffle furnace and sintered in air at 550℃ for 2h to obtain an α-Fe2O3 film. The heating rate was 3℃ / min. Then, it was sintered at 800℃ for 10min. After sintering, the sample was naturally cooled to room temperature and the α-Fe2O3 film was obtained.

[0106] S5. The α-Fe2O3 film obtained in S4 is placed in a tube furnace and annealed in air at 800°C for 10 min to obtain an α-Fe2O3 film with better crystallinity, such as... Figure 5 The surface SEM image of α shows that an α-Fe₂O₃ film with a thickness of 450 nm was prepared. Figure 5 The cross-sectional SEM image of b is shown.

[0107] Comparative Example 2

[0108] A method for preparing a hematite photoanode thin film with a surface-loaded titanium dioxide passivation layer includes the following steps:

[0109] S1. Select fluorine-doped tin dioxide transparent conductive glass (FTO) with a sheet resistance of 15Ω, a thickness of 2.2mm, a size of 20mm×25mm, and a transmittance of 85% as the substrate material. Before use, ultrasonically clean it with water, ethanol, and acetone for 30 minutes each, and then dry it with a nitrogen gun to obtain the treated conductive glass (FTO substrate).

[0110] S2. Add ferric chloride hexahydrate (FeCl3·6H2O, 2.7g, 0.01mol) and sodium nitrate (NaNO3, 8.5g, 0.1mol) to a beaker containing 100mL of ultrapure water. Stir magnetically at room temperature for 30min. Then adjust the pH of the above solution to 1.3 with concentrated hydrochloric acid (HCl) to obtain the precursor solution.

[0111] S3. Transfer the 60 mL precursor solution obtained in S2 to a 100 mL polytetrafluoroethylene (PTFE) reactor. Place the four FTO substrates from step S1 with their conductive surfaces facing down on a PTFE rack. Then place the PTFE rack containing the FTO substrates into the PTFE reactor containing the 60 mL precursor solution. Place the reactor in a 95 °C electric heating drying oven and keep it at that temperature for 10 h to carry out the hydrothermal reaction. A yellow iron hydroxyl oxide (FeOOH) film sample will grow on the FTO substrate. After naturally cooling to room temperature, remove the FeOOH, rinse it with ultrapure water, and dry it with a nitrogen gun.

[0112] S4. The FeOOH film obtained in S3 was placed in a muffle furnace and sintered in air at 550℃ for 2 hours to obtain an α-Fe2O3 film. The heating rate was 3℃ / min. -1 Then, the sample was sintered at 800℃ for 10 min. After sintering, it was naturally cooled to room temperature and the sample was removed to obtain an α-Fe2O3 film.

[0113] S5. After sealing the beaker containing 40 mL of ultrapure water with sealing film, freeze it in the freezer to 10°C before use. Use a pipette to slowly add 80 μL of TiCl4 solution to the above 40 mL of frozen ultrapure water. After it thaws naturally at room temperature, the TiO2 passivation layer precursor solution is obtained.

[0114] S6. Place the α-Fe2O3 film obtained in S4 into the TiO2 passivation layer precursor solution obtained in S5, and carry out a solvothermal reaction in a 70℃ electric heating drying oven for 60 min. Then rinse it with ultrapure water and place it in a 110℃ electric heating drying oven for 60 min of heat treatment to obtain a hematite photoanode film (α-Fe2O3 / TiO2) with a titanium dioxide passivation layer on the surface.

[0115] S7. Place the α-Fe₂O₃ / TiO₂ film obtained in S5 in a tube furnace and anneal it in air at 800°C for 10 min to obtain an α-Fe₂O₃ / TiO₂ film with better crystallinity, such as... Figure 6 The surface SEM image of a shows that an α-Fe₂O₃ / TiO₂ film with a thickness of 450 nm was prepared. Figure 6 The cross-sectional SEM image of b is shown.

[0116] The above-disclosed embodiments are merely specific examples of the present invention, but the embodiments of the present invention are not limited thereto. Any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

[0117] The hematite films with ligand-free nanocrystal inlaid titanium dioxide passivation layers prepared in Examples 1-3 have basically the same effect. The photocurrent density of the hematite photoanode films prepared in Examples 1, 1, and 2 is tested using the sample of Example 1 as an example. The specific results are shown in Table 1.

[0118] Table 1 Photocurrent Density

[0119]

[0120]

[0121] As shown in Table 1, the photocurrent densities of the α-Fe₂O₃ / TiO₂-CdTe film prepared in Example 1 and the α-Fe₂O₃ / TiO₂ film prepared in Comparative Example 2 are both higher than those of the α-Fe₂O₃ film prepared in Comparative Example 1. Furthermore, the photocurrent density of the α-Fe₂O₃ / TiO₂-CdTe film prepared in Example 1 is also higher than that of the α-Fe₂O₃ film prepared in Comparative Example 2. The photocurrent density of the α-Fe₂O₃ / TiO₂-CdTe film in Example 1 is increased by 338% and 84% compared to the α-Fe₂O₃ film in Comparative Example 1 and the α-Fe₂O₃ / TiO₂ film in Comparative Example 2, respectively.

[0122] To illustrate the effects of the present invention, the performance of the raw materials and the prepared products in Example 1, Comparative Example 1, and Comparative Example 2 were also tested. Specific results are shown in [the table below]. Figure 2-12 .

[0123] Figure 2 Figures a and b show the SEM and XRD patterns of the original CdTe particles in Example 1. Figure a is the SEM image of the original CdTe particles, and Figure b is the XRD pattern of the original CdTe particles. As can be seen from Figures a and b, the original CdTe particles are cubic phase cadmium telluride with a particle size of about 2 to 3 μm.

[0124] Figure 3 The images show the TEM and XRD patterns of ligand-free CdTe nanocrystals after laser irradiation in Example 1. Figure a shows the TEM image of the ligand-free CdTe nanocrystals, and Figure b shows the XRD pattern of the ligand-free CdTe nanocrystals. As can be seen from Figures a and b, the ligand-free CdTe nanocrystals are still cubic cadmium telluride with a size of about 3 nm, which is less than 10 nm.

[0125] Figure 4 The images show surface and cross-sectional SEM images of the α-Fe2O3 / TiO2-CdTe film in Example 1, where Figure a is the surface SEM image and Figure b is the cross-sectional SEM image. Figure 5 The images shown are surface and cross-sectional SEM images of the α-Fe2O3 thin film in Comparative Example 1, where Figure a is the surface SEM image and Figure b is the cross-sectional SEM image. Figure 6 The images show surface and cross-sectional SEM images of the α-Fe₂O₃ / TiO₂ thin film in Comparative Example 2, where Figure a is the surface SEM image and Figure b is the cross-sectional SEM image. Figure 4-6 It can be seen that after loading a TiO2 passivation layer on the surface of the α-Fe2O3 film, the particle size of the α-Fe2O3 film is significantly reduced, but the film thickness remains unchanged; after introducing ligandless CdTe nanocrystals into the TiO2 passivation layer loaded on the surface of the α-Fe2O3 film, the particle size and thickness of the film do not change significantly.

[0126] Figure 7 The images are TEM images of the α-Fe2O3 / TiO2-CdTe thin film in Example 1 at different magnifications. Figure 8 This is a TEM image of the α-Fe2O3 thin film in Comparative Example 1. Figure 9 The images show TEM images of the α-Fe₂O₃ / TiO₂ thin film in Comparative Example 2 at different magnifications. Figure 7-9 It can be seen that all three α-Fe2O3 films have good crystallinity. Compared with the α-Fe2O3 film in Comparative Example 1, the α-Fe2O3 / TiO2 film in Comparative Example 2 and the α-Fe2O3 / TiO2-CdTe film in Example 1 are uniformly coated with a TiO2 passivation layer with a thickness of about 6 nm. However, small ligand-free CdTe nanocrystals are clearly present in the TiO2 passivation layer on the surface of the α-Fe2O3 / TiO2-CdTe film in Example 1.

[0127] Figure 10The figures show the linear current-voltage (V / V) curves and photoelectric conversion efficiency (PCO) curves of the α-Fe₂O₃ thin film in Comparative Example 1, the α-Fe₂O₃ / TiO₂ thin film in Comparative Example 2, and the α-Fe₂O₃ / TiO₂-CdTe thin film in Example 1. Figure a shows the linear V / V curve, and Figure b shows the PCO curve. As can be seen from the figures, compared with the α-Fe₂O₃ thin film in Comparative Example 1 and the α-Fe₂O₃ / TiO₂ thin film in Comparative Example 2, the photocurrent density of the α-Fe₂O₃ / TiO₂-CdTe thin film in Example 1 is significantly improved, reaching 1.23 V at AM 1.5 G. RHE The photocurrent density at each location was 0.52 mA / cm². -2 and 1.24mA cm -2 Increased to 2.28 mA cm -2 The efficiency was increased by approximately 338% and 84%, respectively; the photoelectric conversion efficiency at 360 nm increased from 8.7% and 22.0% to 76.2%, respectively, representing increases of approximately 776% and 246%.

[0128] Figure 11 The impedance curves and Mott-Schottky (MS) curves of the α-Fe₂O₃ thin film in Comparative Example 1, the α-Fe₂O₃ / TiO₂ thin film in Comparative Example 2, and the α-Fe₂O₃ / TiO₂-CdTe thin film in Example 1 are shown in Figure a and Figure b, respectively. As can be seen from the figures, compared with the α-Fe₂O₃ thin film in Comparative Example 1 and the α-Fe₂O₃ / TiO₂ thin film in Comparative Example 2, the impedance of the α-Fe₂O₃ / TiO₂-CdTe thin film in Example 1 is significantly reduced, and the carrier concentration is significantly increased.

[0129] Figure 12The figures show the surface charge separation efficiency and open-circuit photovoltage of the α-Fe2O3 film in Comparative Example 1, the α-Fe2O3 / TiO2 film in Comparative Example 2, and the α-Fe2O3 / TiO2-CdTe film in Example 1. Figure a shows the surface charge separation efficiency, and Figure b shows the open-circuit photovoltage. As shown in Figure a, compared with the α-Fe2O3 film in Comparative Example 1 and the α-Fe2O3 / TiO2 film in Comparative Example 2, the surface charge separation efficiency of the α-Fe2O3 / TiO2-CdTe film in Example 1 is significantly improved. As shown in Figure b, before and after illumination, the change in band bending of the α-Fe2O3 / TiO2-CdTe film in Example 1 (200mV) is 20mV greater than that of the α-Fe2O3 / TiO2 film in Comparative Example 2 (180mV) and 70mV greater than that of the α-Fe2O3 film in Comparative Example 1 (130mV). This indicates that the α-Fe2O3 / TiO2-CdTe film has a larger built-in photovoltage and a larger reaction driving force, which can effectively promote the separation and transport of charge carriers in the film.

[0130] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a hematite thin film with a ligand-free nanocrystal-embedded titanium dioxide passivation layer on its surface, characterized in that, Includes the following steps: (1) Preparation of α-Fe2O3 thin films; Iron hydroxyl oxide was prepared on transparent conductive glass by hydrothermal synthesis and then sintered at high temperature to obtain α-Fe2O3 thin film; (2) Preparation of ligand-free nanocrystalline colloidal solutions; The original semiconductor particles were uniformly dispersed in a liquid medium to obtain a semiconductor solution. The semiconductor solution was then subjected to liquid-phase pulsed laser irradiation under ultrasonic assistance to obtain a ligand-free nanocrystalline colloidal solution. In step (2), the original semiconductor particles are selected from one of CdTe, WO3, and Pt; (3) Preparation of TiO2 passivation layer precursor solution: (4) Preparation of hematite films with ligand-free nanocrystal-embedded titanium dioxide passivation layers on the surface: S41. Mix the ligandless nanocrystalline colloidal solution from step (2) with the TiO2 passivation layer precursor solution from step (3) to obtain a mixed solution; In step S41, the volume ratio of the ligand-free nanocrystalline colloidal solution to the precursor solution of the titanium dioxide passivation layer is 1:20-80. S42. The α-Fe2O3 film from step (1) is placed in the mixture from step S41 and subjected to a solvothermal reaction. Then, it is rinsed and heat-treated in sequence to obtain a hematite film with a titanium dioxide passivation layer supported on the surface without ligand nanocrystals.

2. The method for preparing a hematite thin film with a surface-loaded, ligand-free nanocrystal-embedded titanium dioxide passivation layer according to claim 1, characterized in that, The transparent conductive glass in step (1) is selected from fluorine-doped tin dioxide or indium tin oxide.

3. The method for preparing a hematite thin film with a surface-loaded ligand-free nanocrystal-embedded titanium dioxide passivation layer according to claim 1, characterized in that, The α-Fe2O3 thin film of step (1) is prepared according to the following steps: S11. The transparent conductive glass is ultrasonically cleaned and dried to obtain treated conductive glass; S12. Disperse the iron source and sodium nitrate together in ultrapure water, and then adjust the pH to 0.75-1.50 to obtain the precursor solution; The iron source is selected from anhydrous ferric chloride or ferric chloride hexahydrate, and the molar ratio of the iron source to sodium nitrate is 6-10:

1. S13. The conductive glass processed in step S11 is immersed in the precursor solution of step S12, and then hydrothermal synthesis is carried out at 95°C for 6-12 hours to obtain an iron hydroxyl oxide film. S14. After drying the iron hydroxyl oxide film, it is first treated at 550℃ for 2-3 hours, and then sintered at 750-800℃ for 10-20 minutes to obtain an α-Fe2O3 film with a thickness of 200-500 nm.

4. The method for preparing a hematite thin film with a surface-loaded ligand-free nanocrystal-embedded titanium dioxide passivation layer according to claim 1, characterized in that, In step (2), the liquid medium is ultrapure water, and the concentration of the ligand-free nanocrystalline colloidal solution is 0.05-0.25 mg / mL.

5. The method for preparing a hematite thin film with a surface-loaded ligand-free nanocrystal-embedded titanium dioxide passivation layer according to claim 1, characterized in that, The ligand-free nanocrystalline colloidal solution of step (2) is prepared according to the following steps: Under ultrasonic assistance, the semiconductor solution was irradiated with a pulsed unfocused laser beam. The output wavelength of the unfocused laser beam was 1064 nm, the pulse frequency was 30 Hz, the output spot diameter was 6-10 mm, and the laser irradiation energy density was 1000-1500 mJ / cm². 2 The irradiation time is 10-30 minutes; The frequency of ultrasound is 20-40 kHz.

6. The method for preparing a hematite thin film with a surface-loaded ligand-free nanocrystal-embedded titanium dioxide passivation layer according to claim 1, characterized in that, The TiO2 passivation layer precursor solution in step (3) is prepared according to the following steps: ultrapure water is frozen to 0-10℃, and then TiCl4 is added dropwise to it. After natural thawing at room temperature, the TiO2 passivation layer precursor solution is obtained. The concentration of the TiCl4 solution was 2.5-5.5 mg / mL.

7. The method for preparing a hematite thin film with a surface-loaded ligand-free nanocrystal-embedded titanium dioxide passivation layer according to claim 1, characterized in that, In step S42, the solvothermal reaction is carried out at 60-80℃ for 50-70 min, and the heat treatment is carried out at 100-120℃ for 40-70 min, to obtain a hematite film with a titanium dioxide passivation layer supported on the surface without ligand nanocrystals. An annealing treatment was performed on a hematite film with a surface-loaded titanium dioxide passivation layer without ligands to obtain a hematite film with good crystallinity. The annealing conditions were annealing at 700-800℃ for 10-20 min.

8. A hematite film with a surface-loaded, ligand-free nanocrystal-embedded titanium dioxide passivation layer prepared by the preparation method according to any one of claims 1-7.

9. The application of a hematite thin film with a surface-loaded ligand-free nanocrystal embedded titanium dioxide passivation layer as described in claim 8 in the preparation of photocatalytic and photoelectrocatalytic materials.

Images