A mil-68 metal organic framework / iii-nitride nanopillar array photoanode, and a preparation method and application thereof

Abstract

The application discloses a MIL-68 metal organic framework / III-nitride nanopillar array photoanode and a preparation method and application thereof. The photoanode comprises a Si substrate, an InN or / and GaN nanopillar array grown on the Si substrate, and a MIL-68(In / Ga) metal organic framework layer in-situ grown on the surface of the nanopillar array, wherein the MIL-68(In / Ga) layer is in a three-dimensional columnar structure. By introducing the MIL-68(In / Ga) metal organic framework on the surface of the III-nitride nanopillar array, self-driven assembly of the interface is realized, and the interface bonding strength and charge transfer efficiency of the photoelectrode are significantly enhanced. The photoanode has excellent stability and high efficiency in the process of photoelectrochemical water splitting and organic pollutant degradation, and has wide application prospects in new energy conversion and environmental governance.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrode technology, specifically relating to a MIL-68 metal-organic framework / III-nitride nanopillar array photoanode, its preparation method, and its application. Background Technology

[0002] Photoelectrochemical (PEC) technology can directly convert solar energy into renewable hydrogen energy, which is an important pathway to achieving sustainable energy. However, most semiconductor materials are susceptible to photocorrosion, making it difficult to simultaneously achieve high efficiency and stability, and thus failing to meet the requirements of high-performance PEC systems. Among group III nitride materials, InN is considered an ideal photoanode material for PEC water splitting due to its suitable band structure and excellent photochemical stability, while GaN shows potential in applications such as photocatalytic degradation of dyes due to its high chemical stability and good optical properties. However, InN nanopillars still have shortcomings in carrier transport efficiency, while the wide bandgap of GaN nanopillars limits their light absorption efficiency. Therefore, developing catalysts for surface modification of InN and GaN nanopillar photoelectrodes is of great research significance for achieving high-performance PEC.

[0003] Existing literature discloses application examples of heterostructure photoelectrode materials formed by Ni(OH)2 and InN in PEC water splitting (Mengzhou Wu et al., InN nanorod / Ni(OH)2 heterojunction photoelectrode for efficient photoelectrochemical water splitting, CrystEngComm, 2023, 25, 6650-6659), and application examples of heterostructure photoelectrode materials formed by ZnO@α-Ga2O3 and GaN in PEC dye degradation (Yan-Ling Hu et al., Highly oxidative GaN:ZnO@α-Ga2O3 heterostructure as avisible-light-driven, round-the-clock photocatalyst for dye degradation and disinfection, J. Mater. Chem. A, 2025, 13, 7739-7757). These works load Ni(OH)2 or ZnO@α-Ga2O3 onto epitaxial InN or GaN nanopillars on Si(111) substrates. Although efficient PEC performance can be achieved without external bias voltage, the heterostructure interface impedance is still relatively large, making it difficult to maintain efficient, continuous, and stable hydrogen production and dye degradation processes. Summary of the Invention

[0004] To address the issue of high interfacial resistance in InN and GaN nanopillars, the primary objective of this invention is to provide a method for fabricating a photoanode based on a self-driven interface assembly of a MIL-68 metal-organic framework / III-nitride nanopillar array. The self-driven interface assembly of the MIL-68 metal-organic framework not only reduces the interfacial resistance of the photoelectrode material but also effectively promotes the separation and transport of photogenerated carriers, thereby significantly improving the photoelectric performance of the nanopillars and achieving efficient photoelectrochemical water splitting for hydrogen production and pollutant degradation. This invention provides an effective technical solution to address the efficiency loss caused by the heterofacial impedance of InN and GaN nanopillars.

[0005] Another objective of this invention is to provide a MIL-68 metal-organic framework / III-nitride nanopillar array photoanode prepared by the above method. This photoanode, as a low-cost, high-efficiency, and stable water-splitting material, exhibits a more promising strategy. Furthermore, it can effectively improve the PEC performance of InN and GaN nanopillar photoelectrodes, effectively reduce heterojunction impedance, promote the separation and transport of photogenerated carriers, and enhance the oxidation reaction kinetics at the electrode / electrolyte interface, thereby significantly improving photoelectric conversion efficiency. This provides an effective strategy for achieving efficient PEC water splitting for hydrogen production and pollutant degradation.

[0006] Another object of the present invention is to provide the application of the above-mentioned MIL-68 metal-organic framework / III-nitride nanopillar array photoanode.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for assembling a MIL-68 metal-organic framework / III-nitride nanopillar array photoanode based on a self-driven interface includes the following steps:

[0009] (1) InN and / or GaN nanopillars were grown on a Si substrate using molecular beam epitaxy.

[0010] (2) The nanopillar array obtained in step (1) is immersed in the precursor solution and a MIL-68 (In / Ga) metal-organic framework is self-assembled on its surface by a solvothermal reaction.

[0011] (3) The MIL-68 / III-nitride nanopillar array photoanode is obtained after washing and drying.

[0012] Preferably, the precursor solution in step (2) comprises terephthalic acid, acetic acid and solvent; the ratio of the three is 0.02~0.025 mmol: 0.2~0.25 mmol: 2~4 mL.

[0013] More preferably, the solvent is N,N-dimethylformamide.

[0014] Preferably, the solvothermal reaction conditions in step (2) are: temperature 120~150 ℃, time 20~36 hours.

[0015] Preferably, after growing the nanopillars in step (1), a Ti-Au electrode is first deposited on the back side of the Si substrate on which the nanopillars are grown, and then the operation in step (2) is performed; after step (3), the wire is connected to the Ti-Au electrode.

[0016] Preferably, in step (3), the washing is: soaking in N,N-dimethylformamide and methanol for 3-4 hours each time, and repeating 2-3 times; the drying temperature is 120-150 ℃ and the time is 12-15 hours.

[0017] Preferably, step (1) is specifically operated as follows: molecular beam epitaxy is used, the Si substrate temperature is controlled at 550~970 ℃, and the rotation speed is 5~10 r / min; the beam equivalent pressure of In or Ga is 3.0×10 -7 ~4.5×10 -7 Torr; nitrogen flow rate 1~3 sccm; plasma source power 200~400 W; growth time 2~4 h.

[0018] Preferably, the Si substrate in step (1) is selected from the Si (111) crystal plane (conductivity <0.005 Ω).

[0019] Preferably, the Si substrate in step (1) is ultra-low resistivity silicon with a resistivity of less than 1 Ω·cm.

[0020] More preferably, the Si substrate undergoes cleaning and annealing before the growth of nanopillars.

[0021] More preferably, the cleaning process is as follows: first, organic contaminants on the surface of the Si substrate are removed with an organic solvent, then the Si substrate is treated with HF solution to treat the surface oxide layer, and finally, it is dried with high-purity dry nitrogen gas; the annealing process is as follows: the cleaned Si substrate is placed in a reaction chamber and annealed at 900~980 °C for 10~30 min to obtain the reconstructed surface.

[0022] More preferably, the organic contaminants on the Si substrate surface are removed by sequentially cleaning in acetone and anhydrous ethanol, followed by rinsing with water; the HF solution has a mass concentration of 5-20%.

[0023] The present invention also provides a MIL-68 metal-organic framework / III-nitride nanopillar array photoanode based on self-driven interface assembly, comprising a Si substrate, wherein InN and / or GaN nanopillars are grown on the Si substrate, and a MIL-68 (In / Ga) metal-organic framework is self-driven interface assembled on the surface of the InN and / or GaN nanopillars; the MIL-68 (In / Ga) metal-organic framework is a three-dimensional columnar material.

[0024] Preferably, the height of the nanopillars is 100-500 nm, the diameter is 30-100 nm, and the density is 100-300 nanopillars / μm. 2 .

[0025] More preferably, the height of the nanopillars is 300-500 nm, the diameter is 50-80 nm, and the density is 120-250 nanopillars / μm. 2 .

[0026] MIL-68 metal-organic frameworks are materials with a regular three-dimensional porous structure and a wide absorption spectrum, enabling them to perform photocatalysis under ordinary visible light without the need for ultraviolet irradiation. Furthermore, MIL-68 possesses suitable semiconductor band positions, meeting the thermodynamic requirements for photocatalytic water splitting to produce hydrogen and oxygen. Due to the excellent electron conduction channels within its framework structure, it can effectively collect photogenerated electrons from the photoelectrode and rapidly transfer them to the counter electrode.

[0027] The MIL-68-modified InN and GaN nanopillar photoelectrode materials of the present invention have surface groups that can provide anchoring points for clusters on the surface of nanopillars, thereby avoiding or reducing the use of precious metals and reducing costs. At the same time, the presence of MIL-68 can also improve the heterostructure properties of nanopillars, reduce interfacial resistance, and enhance the separation and transport efficiency of photogenerated carriers, thereby further improving photoelectric conversion performance and realizing efficient photoelectrochemical water splitting for hydrogen production and pollutant degradation.

[0028] The MIL-68 metal-organic framework / III-nitride nanopillar array photoanode described in this invention can be used to prepare photoelectrodes.

[0029] The photoelectrode includes a photoanode and a photocathode, and the photocathode is a Pt electrode.

[0030] The MIL-68 metal-organic framework / III-nitride nanopillar array photoanode and the aforementioned photoelectrode described in this invention can both be applied to photoelectrochemical water splitting hydrogen production systems.

[0031] The system includes a MIL-68 metal-organic framework / III-nitride nanopillar array photoanode, photocathode, electrolyte, light source, and electrolytic cell; the photoanode and photocathode are respectively placed in the electrolyte, and under sunlight irradiation, the photoelectrode performs hydrogen production and / or dye degradation.

[0032] The electrolyte has a pH of 6-10, preferably 7-9; the sunlight irradiation method for the photoelectrode is parallel light irradiation.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] (1) This invention modifies InN and GaN nanopillars with MIL-68, which broadens the absorption spectrum range of photoelectrode materials, effectively passivates the surface states of nanopillars, thereby increasing photocurrent density, significantly improving photoelectric conversion efficiency, and significantly improving the performance of InN nanopillars in PEC water splitting for hydrogen production and the performance of GaN nanopillars in pollutant / dye degradation.

[0035] (2) The present invention utilizes MIL-68 to form a heterostructure that is conducive to electron transfer with InN and GaN nanopillars, effectively transferring electrons in the conduction band of the nanopillars to the appropriate energy level of MIL-68, promoting the oxidation / reduction reaction at the electrode / electrolyte interface, and enhancing the separation efficiency of photogenerated carriers.

[0036] (3) The present invention can prevent InN and GaN nanopillars from photoelectrochemical corrosion in electrolyte by modifying with MIL-68. At the same time, MIL-68 is a metal-free electrocatalyst suitable for sustainable PEC system, further enhancing the stability of photoelectrode and improving the overall photoelectric performance of device. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the MIL-68 metal-organic framework / III-nitride nanopillar array photoanode prepared in Examples 1 and 2;

[0038] Figure 2 SEM images of the photoanodes prepared in Examples 1, 2, 1, and 2 are shown below; (a) is an SEM image of the InN photoanode prepared in Comparative Example 1, (b) is an SEM image of the MIL-68(In) / InN nanopillar array photoanode prepared in Example 1, (c) is an SEM image of MIL-68(In), (d) is an SEM image of the GaN photoanode prepared in Comparative Example 2, (e) is an SEM image of the MIL-68(Ga) / GaN nanopillar array photoanode prepared in Example 2, and (f) is an SEM image of MIL-68(Ga).

[0039] Figure 3Transient fluorescence spectra of the MIL-68 (In) / InN nanopillar array photoanode material prepared in Example 1 and the InN nanopillar photoelectrode material prepared in Comparative Example 1;

[0040] Figure 4 Transient fluorescence spectra of the MIL-68 (Ga) / GaN nanopillar array photoanode material prepared in Example 2 and the GaN nanopillar photoelectrode material prepared in Comparative Example 2;

[0041] Figure 5 The graph shows the relationship between the hydrogen production of the MIL-68 (In) / InN nanopillar array photoanode material prepared in Example 1 and the InN nanopillar photoelectrode material prepared in Comparative Example 1 and the hydrogen production of the photoelectrochemical hydrogen production system under a certain bias voltage as a function of time.

[0042] Figure 6 The graph shows the relationship between the degradation efficiency of the MIL-68 (Ga) / GaN nanopillar array photoanode material prepared in Example 2 and the GaN nanopillar photoelectrode material prepared in Comparative Example 2 and the degradation efficiency of the photoelectrochemical degradation system under a certain bias voltage as a function of time.

[0043] Figure 7 This is a theoretical and computational model for the in-situ growth of the MIL-68(In) / InN nanopillar array photoanode prepared in Example 1;

[0044] Figure 8 This is a theoretical and computational model for the in-situ growth of the MIL-68(Ga) / GaN nanopillar array photoanode prepared in Example 2. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0046] Example 1

[0047] A self-driven interface-assembled MIL-68(In) / InN nanopillar array photoanode, its preparation method, and its application, comprising the following steps:

[0048] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005 Ω). First, the organic contaminants on the surface of the Si substrate were cleaned with acetone and anhydrous ethanol. Then, the Si substrate was treated with 15% HF solution to treat the surface oxide layer. Finally, it was dried with high-purity dry nitrogen. The cleaned Si substrate was then placed in the reaction chamber and annealed at 950 °C for 30 min to obtain the reconstructed surface.

[0049] (2) Photoanode fabrication: InN nanopillars were grown on a Si substrate using molecular beam epitaxy (MBE). The control conditions were as follows: Si substrate temperature 950 ℃, rotation speed 10 r / min, and In beam equivalent pressure 4.5 × 10⁻⁶. -7 The growth parameters were: Torr, nitrogen flow rate 2 sccm, plasma source power 400 W, and growth time 2 h. The InN nanopillars had a height of 300–500 nm, a diameter of 50–80 nm, and a density of 120–250 nanopillars / μm. 2 .

[0050] Ti-Au electrodes are deposited on the back side of a Si substrate by vapor deposition;

[0051] (3) The InN nanopillars were immersed in the precursor solution and transferred to a hydrothermal reactor for self-driven assembly of MIL-68(In). The precursor solution consisted of 0.025 mmol terephthalic acid, 0.25 mmol acetic acid, and 3 mL N,N-dimethylformamide. The reaction temperature was 150 °C and the reaction time was 24 h. After the reaction, the photoelectrode was washed and dried. The washing conditions were soaking in N,N-dimethylformamide and methanol for 4 hours each time, for 3 cycles. The drying conditions were 120 °C for 12 hours.

[0052] Finally, the wires are connected to the Ti-Au electrode on the back side of the Si substrate to form a photoanode.

[0053] (4) Construction of photoelectrochemical cell: The prepared photoanode was connected in series with the Pt electrode, the light source was parallel light, and the electrolyte was 0.1 mol / L Na2SO4 solution (pH=7).

[0054] The structural schematic diagram of the MIL-68(In) / InN nanopillar array photoanode in this embodiment is shown below. Figure 1 As shown.

[0055] The surface SEM image of the self-driven interface-assembled MIL-68(In) / InN nanopillar array photoanode in this embodiment is shown below. Figure 2 As shown in (b) of the diagram.

[0056] like Figure 3 As shown, in this embodiment, the photogenerated carrier lifetime of the MIL-68(In) / InN nanopillar array photoanode under sunlight irradiation is 5.20 ns.

[0057] like Figure 5 As shown, in this embodiment, the MIL-68(In) / InN nanopillar array photoanode is used in a photoelectrochemical hydrogen production system under a certain bias voltage, and the maximum efficiency of solar hydrogen production is 300.46 μmol / h. -1 .

[0058] like Figure 7 As shown in the figure, the theoretical calculation mechanism of in-situ growth of MIL-68(In) / InN nanopillar array photoanode in this embodiment shows that the original In-N bond energy is 0.798 eV, which decreases to 0.360 eV after MIL-68(In) growth. At the same time, the In-O bond energy formed is as high as 3.289 eV, indicating that the O-In-N interaction preferentially replaces the In-N bond, which verifies the feasibility of interfacial coordination and thermodynamics.

[0059] Example 2

[0060] A self-driven interface-assembled MIL-68(Ga) / GaN nanopillar array photoanode, its preparation method, and its application, comprising the following steps:

[0061] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005 Ω). First, the organic contaminants on the surface of the Si substrate were cleaned with acetone and anhydrous ethanol. Then, the Si substrate was treated with 15% HF solution to treat the surface oxide layer. Finally, it was dried with high-purity dry nitrogen. The cleaned Si substrate was then placed in the reaction chamber and annealed at 950 °C for 30 min to obtain the reconstructed surface.

[0062] (2) Photoanode fabrication: GaN nanopillars were grown on a Si substrate using molecular beam epitaxy (MBE). The control conditions were as follows: Si substrate temperature 950 ℃, rotation speed 10 r / min, and Ga beam equivalent pressure 3.4 × 10⁻⁶. -7 The growth parameters were: Torr, nitrogen flow rate 2 sccm, plasma source power 400 W, and growth time 2 h. The GaN nanopillars had a height of 300–500 nm, a diameter of 50–80 nm, and a density of 120–250 nanopillars / μm. 2 .

[0063] Ti-Au electrodes are deposited on the back side of a Si substrate by vapor deposition;

[0064] (3) GaN nanopillars were immersed in a precursor solution and transferred to a hydrothermal reactor for self-driven assembly of MIL-68 (Ga). The precursor solution consisted of 0.025 mmol terephthalic acid, 0.25 mmol acetic acid, and 3 mL N,N-dimethylformamide. The reaction temperature was 150 °C, and the reaction time was 24 h. After the reaction, the photoelectrode was washed and dried. The washing conditions were soaking in N,N-dimethylformamide and methanol for 4 hours each time, for 3 cycles. The drying conditions were 120 °C for 12 hours.

[0065] Finally, the wires are connected to the Ti-Au electrode on the back side of the Si substrate to form a photoanode.

[0066] (4) Construction of photoelectrochemical cell: The prepared photoanode was connected in series with the Pt electrode, and parallel light was used as the light source. The electrolyte was a 0.1 mol / L Na2SO4 solution (pH=7) with a Rhodamine B concentration of 30 mg·L⁻¹. -1 .

[0067] The structural schematic diagram of the MIL-68(Ga) / GaN nanopillar array photoanode in this embodiment is shown below. Figure 1 As shown.

[0068] The surface SEM image of the self-driven interface-assembled MIL-68(Ga) / GaN nanopillar array photoanode in this embodiment is shown below. Figure 2 As shown in (e) in the diagram.

[0069] like Figure 4 As shown, in this embodiment, the photogenerated carrier lifetime of the MIL-68(Ga) / GaN nanopillar array photoanode under sunlight irradiation is 6.86 ns.

[0070] like Figure 6 As shown, in this embodiment, the MIL-68 (Ga) / GaN nanopillar array photoanode is used in a photoelectrochemical dye degradation system under a certain bias voltage, and the maximum degradation efficiency of Rhodamine B is 94%.

[0071] like Figure 8 As shown in the figure, the theoretical calculation mechanism of in-situ growth of MIL-68(Ga) / GaN nanopillar array photoanode in this embodiment shows that the original Ga-N bond energy is 1.208 eV for MIL-68(In), which decreases to 0.126 eV after growing MIL-68(Ga). At the same time, the Ga-O bond energy formed is as high as 5.282 eV, indicating that the O-Ga-N interaction preferentially replaces the Ga-N bond, verifying the feasibility of interfacial coordination and thermodynamics.

[0072] Comparative Example 1

[0073] The application of InN nanopillar photoelectrode materials in the photoelectrochemical hydrogen production system includes the following steps:

[0074] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005 Ω). First, the organic contaminants on the surface of the Si substrate were cleaned with acetone and anhydrous ethanol. Then, the Si substrate was treated with 15% HF solution to treat the surface oxide layer. Finally, it was dried with high-purity dry nitrogen. The cleaned Si substrate was then placed in the reaction chamber and annealed at 950 °C for 30 min to obtain the reconstructed surface.

[0075] (2) Photocathode fabrication: Molecular beam epitaxy was used, with the Si substrate temperature controlled at 900 ℃, the Si substrate rotation speed at 10 r / min, and the In beam equivalent pressure at 1.4 × 10⁻⁶. -7 InN nanopillars were grown on Si substrates using a nitrogen flow rate of 2 sccm, a plasma source power of 400 W, and a growth time of 2 h. The InN nanopillars had a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rod / μm. -2 .

[0076] A Ti-Au electrode is deposited on the back side of a Si substrate; finally, a wire is connected to the Ti-Au electrode on the back side of the Si substrate to form a photoanode.

[0077] (3) Construction of photoelectrochemical cell: The prepared photoanode was connected in series with the Pt electrode, the light source was parallel light irradiation, and the electrolyte was 0.1 mol / L Na2SO4 solution (pH=7).

[0078] The surface SEM image of the self-driven interface InN nanopillar array photoanode in this comparative example is shown below. Figure 2 As shown in (a) of the diagram.

[0079] like Figure 3 As shown, the photogenerated carrier lifetime of the InN nanopillar array photoanode in this comparative example is 0.53 ns under sunlight irradiation.

[0080] like Figure 5 As shown, in this comparative example, the InN nanopillar array photoanode, used in a photoelectrochemical hydrogen production system under a certain bias voltage, achieves a maximum solar hydrogen production efficiency of 7.24 μmol / h. -1 .

[0081] Comparative Example 2

[0082] The application of GaN nanopillar photoelectrode materials in the photoelectrochemical hydrogen production system includes the following steps:

[0083] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005 Ω). First, the organic contaminants on the surface of the Si substrate were cleaned with acetone and anhydrous ethanol. Then, the Si substrate was treated with 15% HF solution to treat the surface oxide layer. Finally, it was dried with high-purity dry nitrogen. The cleaned Si substrate was then placed in the reaction chamber and annealed at 950 °C for 30 min to obtain the reconstructed surface.

[0084] (2) Photoanode fabrication: GaN nanopillars were grown on a Si substrate using molecular beam epitaxy (MBE). The control conditions were as follows: Si substrate temperature 950 ℃, rotation speed 10 r / min, and Ga beam equivalent pressure 3.4 × 10⁻⁶. -7 The growth parameters were: Torr, nitrogen flow rate 2 sccm, plasma source power 400 W, and growth time 2 h. The GaN nanopillars had a height of 300–500 nm, a diameter of 50–80 nm, and a density of 120–250 nanopillars / μm. 2 .

[0085] A Ti-Au electrode is deposited on the back side of a Si substrate by vapor deposition; finally, a wire is connected to the Ti-Au electrode on the back side of the Si substrate to obtain a photoanode.

[0086] (3) Construction of photoelectrochemical cell: The prepared photoanode was connected in series with the Pt electrode, and parallel light was used as the light source. The electrolyte was a 0.1 mol / L Na2SO4 solution (pH=7) with a Rhodamine B concentration of 30 mg·L⁻¹. -1 .

[0087] The surface SEM image of the GaN nanopillar array photoanode in this comparative example is shown below. Figure 2 As shown in (d) in the figure.

[0088] like Figure 4 As shown, the photogenerated carrier lifetime of the GaN nanopillar array photoanode in this comparative example is 4.87 ns under sunlight irradiation.

[0089] like Figure 6 As shown, in this comparative example, the GaN nanopillar array photoanode was used in a photoelectrochemical dye degradation system under a certain bias voltage, and the maximum degradation efficiency of Rhodamine B was 15%.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a MIL-68 metal-organic framework / III-nitride nanopillar array photoanode based on self-driven interface assembly, characterized in that, Includes the following steps: (1) InN and / or GaN nanopillars were grown on a Si substrate using molecular beam epitaxy. (2) The nanopillar array obtained in step (1) is immersed in the precursor solution and a MIL-68 (In) metal-organic framework or / and MIL-68 (Ga) metal-organic framework is self-driven assembled on its surface by a solvothermal reaction. (3) The MIL-68 metal-organic framework / III-nitride nanopillar array photoanode is obtained after washing and drying.

2. The preparation method according to claim 1, characterized in that, The precursor solution in step (2) contains terephthalic acid, acetic acid and solvent; the ratio of the three is 0.02~0.025 mmol: 0.2~0.25 mmol: 2~4 mL.

3. The preparation method according to claim 1, characterized in that, The solvothermal reaction conditions in step (2) are: temperature 120~150 ℃, time 20~36 hours.

4. The preparation method according to claim 1, characterized in that, After growing the nanopillars in step (1), Ti-Au electrodes are first deposited on the back side of the Si substrate on which the nanopillars are grown, and then the operation in step (2) is performed; after step (3), the wires are connected to the Ti-Au electrodes.

5. The preparation method according to claim 1, characterized in that, Step (1) is operated as follows: Molecular beam epitaxy is used, with the Si substrate temperature controlled at 550~970 ℃ and the rotation speed at 5~10 r / min; the beam equivalent pressure of In or Ga is 3.0×10 -7 ~4.5×10 -7 Torr; nitrogen flow rate 1~3 sccm; plasma source power 200~400 W; growth time 2~4 h.

6. The preparation method according to claim 1, characterized in that, In step (1), the Si substrate is selected with a Si (111) crystal plane.

7. A MIL-68 metal-organic framework / III-nitride nanopillar array photoanode prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The invention includes a Si substrate on which InN and / or GaN nanopillars are grown, and on the surface of the InN and / or GaN nanopillars, a self-driven interface assembles a MIL-68(In) metal-organic framework and / or a MIL-68(Ga) metal-organic framework; wherein the MIL-68(In) metal-organic framework and / or the MIL-68(Ga) metal-organic framework is a three-dimensional columnar material.

8. The MIL-68 metal-organic framework / III-nitride nanopillar array photoanode according to claim 7, characterized in that, The nanopillars have a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 nanopillars / μm. 2 .

9. The application of the MIL-68 metal-organic framework / III-nitride nanopillar array photoanode of claim 8 in the preparation of photoelectrodes or in a photoelectrochemical water splitting hydrogen production system.

10. The application according to claim 9, characterized in that, The photoelectrochemical water splitting hydrogen production system includes a MIL-68 metal-organic framework / III-nitride nanopillar array photoanode, photocathode, electrolyte, light source, and electrolytic cell; the photoanode and photocathode are respectively placed in the electrolyte, and under sunlight irradiation, the photoelectrode performs hydrogen production and / or dye degradation; The electrolyte has a pH of 6 to 10; the sunlight irradiation method for the photoelectrode is parallel light irradiation.

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