A multi-level pore structure copper modified titanium dioxide photocatalyst and a preparation method thereof

Abstract

The application discloses a kind of multi-level pore structure copper modified titanium dioxide photocatalyst and preparation method thereof, belong to photocatalytic hydrogen production material technical field.Copper-doped titanium-based MOF material is synthesized by diaminoterephthalic acid, tetrabutyl titanate and copper nitrate trihydrate through hydrothermal method, copper-doped titanium-based MOF is calcined by air and ammonia gas in two steps, and titanium dioxide composite material Cu-TiO2 / Cu with copper ion doping and copper element loading is obtained.The method is prepared by the method of calcining after synthesizing precursor, and the Cu-TiO2 / Cu with multi-level pore structure is prepared, which shows excellent water decomposition hydrogen production performance under ultraviolet light.The method is a scalable preparation method, which can be applied to the doping modification of other transition metal ions, and can fully expose noble metal sites to improve the catalytic performance and increase the atomic utilization rate.The method is simple, the reaction condition is mild, the cost is low, and has wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic water splitting for hydrogen production materials, specifically relating to a multi-level porous copper-modified titanium dioxide photocatalyst and its preparation method. Background Technology

[0002] Converting solar energy into usable hydrogen energy through photocatalysis is a potential way to solve the energy crisis. TiO2 is considered a photocatalytic material with great potential due to its strong chemical stability, redox ability, non-toxicity, and low cost. However, TiO2 also has disadvantages such as (1) a wide band gap (3.2 eV), which can only absorb ultraviolet light, which accounts for about 5% of sunlight; and (2) the photogenerated electron-hole pairs are very easy to recombine, which limits its photocatalytic performance and practical application.

[0003] To overcome these obstacles, researchers have explored a range of modification techniques. Among these, the incorporation of transition metals is widely considered an effective method for tuning the optical properties of semiconductor photocatalysts, while also providing active sites for various reactions. However, although metal dopants in nanocluster form possess tunable surface energies, they also exhibit a high tendency to aggregate, preventing the added transition metal from being sufficiently exposed to serve as active sites. Therefore, supporting metal clusters on porous micro / nanostructured materials with abundant porosity and easily accessible surfaces appears to be a viable solution, enabling the catalyst to possess highly exposed metal active sites suitable for various reactions. Thus, it is necessary to develop a simple and efficient preparation method that combines micro / nanostructured semiconductor materials with uniformly dispersed metal modifiers, thereby simultaneously achieving large interfacial contact and fully exposing active sites. Summary of the Invention

[0004] To address the aforementioned issues, this invention develops a method for preparing a photocatalyst capable of forming a hierarchical porous structure, thereby fully exposing metal ions and nanoclusters within the semiconductor, and improving the hydrogen production performance of the photocatalyst. Specifically, it utilizes a TiO2 porous framework structure formed by calcining a Ti-based MOF material in air, allowing pre-doped metal ions to be extensively exposed within the formed TiO2 framework. Further reduction and calcination provides sufficient space for the reduced metal clusters to adsorb water molecules or hydrogen ions from water and initiate hydrogen evolution reactions. Under illumination, the presence of Cu ions and nanoclusters accelerates the charge transport rate of TiO2, suppressing electron-hole recombination and resulting in excellent hydrogen production performance of the catalyst.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a multi-level porous copper-modified titanium dioxide photocatalyst includes the following steps:

[0007] (1) Diaminoterephthalic acid, tetrabutyl titanate and copper nitrate trihydrate were uniformly mixed in a mixed solvent of N,N-dimethylformamide and methanol and then transferred to a hydrothermal reactor for reaction.

[0008] (2) The product obtained in step (1) is washed multiple times, centrifuged, vacuum dried and then ground into a uniform powder using a mortar and pestle.

[0009] (3) Calcine the powder obtained in step (2) in a muffle furnace and let it cool naturally to room temperature.

[0010] (4) Calcine the powder obtained in step (3) in a tube furnace and let it cool naturally to room temperature.

[0011] Furthermore, in the mixed solution of step (1), the masses of diaminoterephthalic acid, tetrabutyl titanate, and copper nitrate trihydrate are 2.172 g, 1.04 g, and 20-60 mg, respectively. The solvent is a mixture of 40 mL of N,N-dimethylformamide and methanol, wherein the volume ratio of N,N-dimethylformamide to methanol is 1:1.

[0012] Furthermore, the hydrothermal reaction temperature in step (1) is 150℃, and the reaction time is 20 h. In the reaction, the diaminoterephthalic acid ligand, with its high coordination ability, uniformly induces the substitution doping of copper at some titanium sites, while promoting the high interaction between Cu-Ti in the generated framework.

[0013] Furthermore, the solvents used for washing in step (2) are N,N-dimethylformamide and methanol, respectively; the washing method is to disperse the precipitate obtained in step (1) in 40 mL of the solvent and wash it three times for 12, 6 and 6 h, respectively.

[0014] Furthermore, in step (3), the calcination temperature is 400℃, the calcination time is 4 h, and the heating rate is 5℃ / min. During the calcination process described in step (3), the organic ligands of the MOF material break down and are oxidized into CO2 and NO2. The Ti metal clusters are oxidized to form TiO2. Due to the inheritance of the framework structure of the MOF material, the generated TiO2 is composed of a large number of microspheres stacked together, thus possessing a porous structure.

[0015] Furthermore, in step (4), the calcination atmosphere is ammonia, the calcination temperature is 400-600℃, the calcination time is 3 h, and the heating rate is 5℃ / min. During the calcination process in step (4), due to the reducing property of NH3, the doped Cu ions are reduced to Cu nanoclusters. And due to the porous structure of the material, the Cu ions inside can also be reduced.

[0016] A hierarchical porous copper-modified titanium dioxide photocatalyst was prepared by the above method.

[0017] The application of the above-mentioned hierarchical porous copper-modified titanium dioxide photocatalyst in water splitting for hydrogen production.

[0018] The advantages of this invention are:

[0019] (1) The target catalyst is prepared by a simple hydrothermal reaction and calcination method. The process is simple, the equipment requirements are not high, and the operation is convenient, making it easy to prepare industrially.

[0020] (2) The prepared catalyst has a porous micro-nano structure, which allows the doped ions and reduced metal clusters to be fully exposed and act as active sites for hydrogen production.

[0021] (3) An scalable preparation method is provided, which can be applied to the doping and modification of other transition metals or noble metals. When applied to noble metals as hydrogen production co-catalysts, the noble metal sites can be fully exposed, thereby improving the catalytic performance and increasing its atomic utilization.

[0022] (4) The material has excellent hydrogen production stability and still exhibits a very stable hydrogen production rate after 20 h of reaction cycle. Attached Figure Description

[0023] Figure 1 A flowchart illustrating the preparation process of the Cu-TiO2 / Cu catalyst of this invention is shown.

[0024] Figure 2 The image shows a TEM image of the Cu-TiO2 / Cu catalyst of the present invention.

[0025] Figure 3 The image shows an HRTEM image of the Cu-TiO2 / Cu catalyst of the present invention.

[0026] Figure 4 The adsorption-desorption curves of the Cu-TiO2 / Cu catalyst of the present invention are shown.

[0027] Figure 5 The pore size distribution diagram of the Cu-TiO2 / Cu catalyst of the present invention is shown.

[0028] Figure 6 The current-time curve of the Cu-TiO2 / Cu catalyst of the present invention is shown.

[0029] Figure 7 The electrochemical impedance spectroscopy of the Cu-TiO2 / Cu catalyst of the present invention is shown.

[0030] Figure 8The steady-state fluorescence spectrum of the Cu-TiO2 / Cu catalyst of the present invention is shown.

[0031] Figure 9 The transient fluorescence spectrum of the Cu-TiO2 / Cu catalyst of the present invention is shown.

[0032] Figure 10 The graph shows the photocatalytic water splitting performance of the Cu-TiO2 / Cu catalyst of the present invention.

[0033] Figure 11 The graph shows the stability test results of the Cu-TiO2 / Cu catalyst for photocatalytic water splitting to produce hydrogen according to the present invention. Detailed Implementation

[0034] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0035] Example 1

[0036] This embodiment prepares porous TiO2 catalyst material according to the following steps:

[0037] 2.172 g of diaminoterephthalic acid and 1.04 g of tetrabutyl titanate were dissolved in 40 mL of a 1:1 mixture of N,N-dimethylformamide and methanol. After stirring thoroughly for 30 min, the mixture was transferred to a hydrothermal reactor and reacted at 150 °C for 20 h. The resulting precipitate was washed, dried, ground, and then calcined in a muffle furnace at 400 °C for 4 h to obtain a white powder.

[0038] Example 2

[0039] This embodiment prepares porous Cu-TiO2 catalyst material according to the following steps:

[0040] 2.172 g of diaminoterephthalic acid, 1.04 g of tetrabutyl titanate, and 10 mg of copper nitrate trihydrate were dissolved in 40 mL of a 1:1 mixture of N,N-dimethylformamide and methanol. After stirring thoroughly for 30 min, the mixture was transferred to a hydrothermal reactor and reacted at 150 °C for 20 h. The resulting precipitate was washed three times, successively with 40 mL of N,N-dimethylformamide and methanol, for 12 h, 6 h, and 6 h, respectively. After drying and grinding, the precipitate was calcined in a muffle furnace at 400 °C for 4 h to obtain a light green powder.

[0041] Example 3

[0042] This embodiment prepares porous TiO2 catalyst material according to the following steps:

[0043] 2.172 g of diaminoterephthalic acid and 1.04 g of tetrabutyl titanate were dissolved in 40 mL of a 1:1 mixture of N,N-dimethylformamide and methanol. After stirring thoroughly for 30 min, the mixture was transferred to a hydrothermal reactor and reacted at 150 °C for 20 h. The resulting precipitate was washed three times, successively with 40 mL of N,N-dimethylformamide and methanol, for 12 h, 6 h, and 6 h, respectively. After drying and grinding, the precipitate was calcined in a muffle furnace at 400 °C for 4 h to obtain a white powder. The white powder was then placed in a tube furnace and calcined at 500 °C for 3 h under an NH3 atmosphere to obtain a light gray powder.

[0044] Example 4

[0045] This embodiment prepares a porous Cu-TiO2 / Cu catalyst material according to the following steps:

[0046] 2.172 g of diaminoterephthalic acid, 1.04 g of tetrabutyl titanate, and 10 mg of copper nitrate trihydrate were dissolved in 40 mL of a 1:1 mixture of N,N-dimethylformamide and methanol. After stirring thoroughly for 30 min, the mixture was transferred to a hydrothermal reactor and reacted at 150 °C for 20 h. The resulting precipitate was washed three times, successively with 40 mL of N,N-dimethylformamide and methanol, for 12 h, 6 h, and 6 h, respectively. After drying and grinding, the precipitate was calcined in a muffle furnace at 400 °C for 4 h to obtain a light green powder. The light green powder was then calcined at 500 °C for 3 h under an NH3 atmosphere to obtain a light gray powder. The preparation process is as follows: Figure 1 As shown.

[0047] Comparative Example 1

[0048] This comparative example uses commercial photocatalyst P25 material.

[0049] Comparative Example 2

[0050] 2.172 g of diaminoterephthalic acid, 1.04 g of tetrabutyl titanate, and 20 mg of nickel chloride hexahydrate were dissolved in 40 mL of a 1:1 mixture of N,N-dimethylformamide and methanol. After stirring thoroughly for 30 min, the mixture was transferred to a hydrothermal reactor and reacted at 150 °C for 20 h. The resulting precipitate was washed, dried, ground, and calcined in a muffle furnace at 400 °C for 4 h to obtain a powder. The powder was then calcined at 500 °C for 3 h under an NH3 atmosphere to obtain Ni-TiO2 / Ni material.

[0051] Comparative Example 3

[0052] 2.172 g of diaminoterephthalic acid, 1.04 g of tetrabutyl titanate, and 20 mg of cobalt nitrate hexahydrate were dissolved in 40 mL of a 1:1 mixture of N,N-dimethylformamide and methanol. After stirring thoroughly for 30 min, the mixture was transferred to a hydrothermal reactor and reacted at 150 °C for 20 h. The resulting precipitate was washed, dried, ground, and calcined in a muffle furnace at 400 °C for 4 h to obtain a light brown powder. The resulting light green powder was calcined at 500 °C for 3 h under an NH3 atmosphere to obtain Co-TiO2 / Co.

[0053] Comparative Example 4

[0054] 2.172 g of diaminoterephthalic acid, 1.04 g of tetrabutyl titanate, and 20 mg of zinc nitrate hexahydrate were dissolved in 40 mL of a 1:1 mixture of N,N-dimethylformamide and methanol. After stirring thoroughly for 30 min, the mixture was transferred to a hydrothermal reactor and reacted at 150 °C for 20 h. The resulting precipitate was washed, dried, ground, and calcined in a muffle furnace at 400 °C for 4 h to obtain a pale yellow powder. The resulting light green powder was calcined at 500 °C for 3 h under an NH3 atmosphere to obtain Zn-TiO2 / Zn.

[0055] The following are the test results for the catalyst materials in each embodiment and comparative example:

[0056] Test 1: TEM testing of photocatalysts

[0057] The TEM image of the Cu-TiO2 / Cu catalyst material prepared in Example 4 is shown below. Figure 2 As shown, the catalyst particles are actually composed of a large number of particles with a diameter of about 10 nm stacked together, giving the catalyst particles a large number of porous structures, which can provide a large number of active surfaces for catalysis.

[0058] Test 2: HRTEM test of photocatalyst

[0059] The HRTEM image of the Cu-TiO2 / Cu catalyst material prepared in Example 4 is shown below. Figure 3 As shown, HRTEM captured clear lattice fringes, with the lattices belonging to the (101), (004), (103), and (200) crystal planes of TiO2, respectively. Furthermore, Cu (111) lattice fringes deeply embedded within the TiO2 framework were also measured in the figure, indicating that NH3 can enter the deep pores of Cu-TiO2 and reduce Cu ions to elemental Cu.

[0060] Test 3: N2 adsorption-desorption test of photocatalyst

[0061] The N2 adsorption-desorption curves of the porous TiO2 and Cu-TiO2 / Cu catalyst materials prepared in Examples 1 and 4 are shown below. Figure 4 As shown, TiO2 and Cu-TiO2 / Cu exhibit curves similar to type IV isotherms, with almost no hysteresis at high relative pressures. This is due to the highly interconnected ordered channels exhibited by MOF-derived TiO2. Figure 5 The pore size distribution diagram of the catalyst shows that the catalyst has a large number of pores with a diameter of about 2-20 nm, which further confirms the porous structure of the catalyst.

[0062] Test 4: Photocurrent Test of Photocatalyst

[0063] The current-time curves of the materials prepared in Examples 1, 2, and 4 under 30 s intermittent illumination are shown below. Figure 6 As shown in the figure. The test results show that the current density generated by Cu-TiO2 / Cu material under the same light intensity is significantly higher than that of Cu-TiO2 and TiO2, indicating that Cu-TiO2 / Cu material has the highest photoelectric conversion efficiency.

[0064] Test 5: Electrochemical Impedance Testing of Photocatalysts

[0065] The electrochemical impedance spectroscopy diagrams of the materials prepared in Examples 1, 2, and 4 are as follows: Figure 7 As shown, Cu-TiO2 / Cu has the smallest radius of curvature corresponding to the photocurrent. This indicates that the Cu-TiO2 / Cu sample has lower resistance and less charge migration resistance at the electrode-electrolyte interface, allowing electrons and holes to migrate more quickly.

[0066] Test 6: Steady-state fluorescence spectrum of photocatalyst

[0067] The steady-state fluorescence spectra of the materials prepared in Examples 1, 2, and 4 are as follows: Figure 8 As shown, after photoexcitation, all three samples reached the strongest emission signal at 380 nm, with the TiO2 sample exhibiting the highest PL signal. Pure TiO2 readily recombines photogenerated electrons and holes. The Cu-TiO2 / Cu sample showed a lower fluorescence intensity because Cu doping and the formation of nanoclusters suppressed electron-hole recombination in TiO2 and accelerated electron transfer.

[0068] Test 7: Transient fluorescence spectrum of photocatalyst

[0069] The transient time-resolved spectra of the materials prepared in Examples 1, 2, and 4 are as follows: Figure 9As shown, the fluorescence lifetime curves of the three samples conform to a third-order exponential function equation. Calculations revealed that the average fluorescence lifetime of TiO2 was 0.528 ns. After two-step calcination, the average lifetimes of the Cu-TiO2 and Cu-TiO2 / Cu photocatalysts increased to 0.728 ns and 0.819 ns, respectively. This further indicates that Cu ion doping and the formation of elemental Cu can effectively promote charge separation and transfer.

[0070] Test 8: Performance of photocatalyst in water splitting for hydrogen production (graph)

[0071] The photocatalytic water splitting performance of all embodiments and comparative examples was tested under the same conditions, and the results are as follows: Figure 10 As shown, after 5 hours of continuous irradiation with a 300 W xenon lamp, P25 did not produce hydrogen, while MOF-derived TiO2 exhibited hydrogen production performance under the same conditions. Compared to other transition metals, the Cu-modified catalyst showed significantly stronger hydrogen production performance, with the Cu-TiO2 / Cu sample achieving a hydrogen production rate of 5682 μmol g / L. -1 h -1 .

[0072] Test 9: Stability Test of Photocatalyst for Water Splitting to Hydrogen

[0073] The stability test results of the photocatalytic hydrogen production of the material prepared in Example 4 within 20 h and four cycles are as follows: Figure 11 As shown, with the addition of 5 mL of methanol in each cycle, the hydrogen production performance of the catalyst did not decrease at all within 20 h, indicating that the catalyst has excellent hydrogen production stability.

[0074] In summary, the Cu-TiO2 / Cu prepared in this invention exhibits excellent hydrogen production performance and long-term stability through water splitting. This unique structure, resulting from MOF collapse, possesses an exceptionally large specific surface area, effectively exposing copper ions and elemental particles, thereby increasing the active sites for photocatalytic water splitting. More importantly, this method may be an scalable catalyst preparation approach; by changing the type of metal ions added, titanium dioxide photocatalysts modified with different metal ions and particles can be obtained.

[0075] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that several improvements and modifications can be made without departing from the principles described in the present invention, and all of them should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a multi-level porous copper-modified titanium dioxide photocatalyst, characterized in that: The method comprises the following steps: (1) uniformly mixing diamino terephthalic acid, tetrabutyl titanate and copper nitrate with N,N-dimethylformamide and methanol, and then transferring the mixture to an autoclave for reaction; (2) washing the product obtained in step (1) repeatedly, centrifuging, vacuum drying and then grinding into a uniform powder with a mortar; (3) calcining the powder obtained in step (2) in a muffle furnace, and naturally cooling to room temperature; (4) calcining the powder obtained in step (3) in a tube furnace, and naturally cooling to room temperature; The calcination atmosphere in step (4) is ammonia, the calcination temperature is 400-600 ℃, the calcination time is 3 h, and the heating rate is 5 ℃ / min.

2. The method of claim 1, wherein: The total volume of N,N-dimethylformamide and methanol in step (1) is 40 mL, and the volume ratio is 1:

1.

3. The method of claim 1, wherein: The contents of diamino terephthalic acid, tetrabutyl titanate and copper nitrate in step (1) are 2.172 g, 1.04 mL and 20-80 mg, respectively.

4. The method of claim 1, wherein: The reaction temperature in step (1) is 150 ℃, and the reaction time is 20 h.

5. The method of claim 1, wherein, The solvents used for washing in step (2) are N,N-dimethylformamide and methanol.

6. The method of claim 5, wherein, The washing method is to disperse the precipitate obtained in step (1) in 40 mL of the solvent, and wash three times, respectively, for 12 h, 6 h and 6 h.

7. The method of claim 1, wherein, The calcination temperature in step (3) is 400 ℃, the calcination time is 4 h, and the heating rate is 5 ℃ / min.

8. The hierarchical porous copper-modified titanium dioxide photocatalyst prepared by the method of any one of claims 1-7.

9. The use of the catalyst of claim 8 in the decomposition of water to produce hydrogen.

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