Titanium-cobalt bimetal organic framework material and preparation and photocatalytic application thereof

Abstract

The invention discloses a titanium-cobalt bimetal organic framework material as well as a preparation method and photocatalytic application thereof. According to the material, a Ti4Co2 cluster formed by titanium and cobalt ions is taken as a center, 2-aminoterephthalic acid and 2-hydroxyterephthalic acid respectively form mixed organic ligands with 2, 4, 6-tri (4-pyridyl) 1, 3, 5-triazine, and the titanium-cobalt bimetal organic framework material is synthesized through a one-step solvothermal method. On the basis of a proton engineering strategy, separation and transmission of photo-generated charges are promoted by utilizing a synergistic effect of ligand functionalization, so that the activity of photocatalytic synthesis of hydrogen peroxide under the condition of no sacrificial agent is remarkably improved. The material is simple and convenient in preparation process and high in structural stability, and has huge application potential in the field of synthesis of green chemicals driven by solar energy.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a titanium-cobalt bimetallic organic framework material and its preparation and photocatalytic application. Background Technology

[0002] Hydrogen peroxide, as a green energy source, has wide applications in medical disinfection, forensic investigation, and inorganic / organic synthesis. Currently, the main industrial method for producing hydrogen peroxide is the anthraquinone process. Although this method is technically mature and has a large production scale, it has inherent drawbacks such as high energy consumption, the need for product purification, expensive equipment, and safety hazards associated with high-concentration storage. Therefore, exploring an environmentally friendly and economically friendly method for producing hydrogen peroxide is imperative for implementing the sustainable development strategy.

[0003] Photocatalysis utilizes light energy to excite catalysts to generate electrons and holes, thereby driving chemical reactions. It is an ideal technology with low operating costs, low energy consumption, and is safe and environmentally friendly. The photocatalytic preparation of hydrogen peroxide typically involves the two-electron reduction reaction of oxygen (O₂ + 2H⁺ + 2e⁻ → H₂O₂). To achieve efficient catalysis, current research largely relies on adding organic sacrificial agents (such as alcohols and oxalates) to the reaction system as hole traps or electron donors to improve charge separation efficiency. However, the consumption of sacrificial agents not only increases operating costs but also introduces secondary pollution, contradicting the principles of green chemistry. Therefore, a photocatalytic system that does not rely on sacrificial agents and uses water and air (oxygen) directly as raw materials is an ideal route for the green synthesis of hydrogen peroxide. However, this system faces a key scientific bottleneck: water, as a proton source, has a stable molecular structure and slow oxidation kinetics. The slow reaction of water oxidation (2H2O → O2 + 4H⁺ + 4e⁻) means that the entire reaction system cannot provide sufficient protons (H⁺) for the efficient reduction of oxygen, which severely restricts the generation rate and yield of hydrogen peroxide.

[0004] Metal-organic frameworks (MOFs) have shown great potential in photocatalysis due to their tunable structure, large specific surface area, and abundant active sites. However, most MOF materials suffer from insufficient chemical and thermal stability, and there is a lack of effective structural design strategies to address the critical issue of insufficient proton supply. Therefore, developing a novel MOF material with high stability that can effectively promote water oxidation and provide protons, thereby achieving efficient, sacrificial agent-free photocatalytic hydrogen peroxide production, has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a titanium-cobalt-based metal-organic framework material based on proton engineering, its preparation, and its photocatalytic application. By employing a proton engineering strategy, functional groups (-NH2, -OH) with different proton donor capabilities are selected to precisely modify the organic ligands, thereby controlling the electronic structure of the material and improving its performance in photocatalytic synthesis of hydrogen peroxide under sacrificial agent-free conditions.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a titanium-cobalt bimetallic organic framework material includes the following steps: (1) Synthesis of Ti4Co2 cluster: Benzoic acid, cobalt acetate tetrahydrate and tetraisopropyl titanate were ultrasonically mixed in an organic solvent and heated in a closed environment. After the reaction was completed, the mixture was washed and dried to obtain Ti4Co2 cluster crystals. (2) Synthesis of framework material: The Ti4Co2 cluster crystal, the first ligand and the second ligand obtained in step (1) are first dissolved in an organic solvent, and then an inorganic acid is added and ultrasonically mixed. The mixture is then placed in a closed environment for heating reaction. After the reaction is completed, the mixture is washed and dried to obtain the titanium-cobalt bimetallic organic framework material. The first ligand is selected from 2-aminoterephthalic acid and 2-hydroxyterephthalic acid; the second ligand is 2,4,6-tris(4-pyridyl)-1,3,5-triazine.

[0007] Furthermore, the molar ratio of benzoic acid, cobalt acetate tetrahydrate and tetraisopropyl titanate in step (1) is 10:0.7:1.68.

[0008] Furthermore, the heating reaction in step (1) is carried out at a temperature of 70~90℃ for 72 h.

[0009] Furthermore, in step (1), the total amount of benzoic acid, cobalt acetate tetrahydrate and tetraisopropyl titanate is in the ratio of 12.38 mmol : 10 ml to the amount of organic solvent, and the organic solvent is acetonitrile.

[0010] Furthermore, in step (2), the molar ratio of the Ti4Co2 cluster crystal, the first ligand, and the second ligand is 0.25 : (3~4.4) : 1.

[0011] Furthermore, the solvent in step (2) is a mixed solvent of N,N-dimethylacetamide and 1,3-dimethyltetrahydropyrimidine-2(1H)-one, the inorganic acid is tetrafluoroboric acid, and the volume ratio of the three is 4:2:1; the total amount of Ti4Co2 cluster crystal, the first ligand, and the second ligand is in the ratio of the amount of solvent and tetrafluoroboric acid used to 4.25~5.65 mmol:7 mL.

[0012] Furthermore, the heating reaction in step (2) is carried out at a temperature of 110 ~ 130 °C for 72 h.

[0013] The titanium-cobalt bimetallic organic framework material prepared by the above method can be applied to the photocatalytic water splitting reaction to produce hydrogen peroxide.

[0014] The beneficial effects of this invention are as follows: (1) This invention introduces different functional groups (-NH2, -OH) into the ligand through proton engineering strategy. The introduction of amino and hydroxyl groups not only broadens the absorption of visible light by the material, but also their lone pair electrons can act as electron donors to promote the reduction reaction of oxygen, thereby synergistically improving photocatalytic activity.

[0015] (2) The titanium-cobalt bimetallic organic framework catalyst prepared in this invention has a large specific surface area and abundant active sites, which is beneficial to the adsorption and mass transfer of reactants (water and oxygen). Under visible light irradiation, it achieved a hydrogen peroxide production rate of 20113 μmol / g / h. This yield is much higher than most MOF-based photocatalysts currently reported, and even better than many inorganic semiconductor catalysts (such as TiO2-based materials) and carbonitrides (C3N4). This fully demonstrates that through the synergistic design of functional ligands, a qualitative leap in catalytic performance has been achieved, significantly improving photocatalytic efficiency.

[0016] (3) The method for preparing titanium-cobalt bimetallic organic framework crystals in this invention is a one-step solvothermal method. The process is mature, has good repeatability, high stability, and is easy to realize the controllable synthesis and large-scale preparation of materials. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the TiCo2-2-NH2-H2BDC organic framework prepared in Example 1, where gray represents carbon atoms, blue represents nitrogen atoms, red represents oxygen atoms, cyan represents titanium atoms, and orange represents cobalt atoms.

[0018] Figure 2 This is a schematic diagram of the TiCo2-2-OH-H2BDC organic framework prepared in Example 2, where gray represents carbon atoms, blue represents nitrogen atoms, red represents oxygen atoms, cyan represents titanium atoms, and orange represents cobalt atoms.

[0019] Figure 3 The UV-Vis absorption spectra and Tauc diagrams of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC are shown.

[0020] Figure 4Mott-Schottky test diagrams for the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC.

[0021] Figure 5 Schematic diagram of the electronic band structure of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC.

[0022] Figure 6 Nyquist plots of the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks under temperature changes at 90% humidity.

[0023] Figure 7 The graph shows the relationship between temperature and conductivity for the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks at 90% humidity.

[0024] Figure 8 The figure shows the Arrhenius-type curves of ln(σT) versus 1000 / T for the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC at 90% humidity.

[0025] Figure 9 XRD patterns of solvent stability of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC.

[0026] Figure 10 XRD patterns of acid-base and thermal stability of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC.

[0027] Figure 11 The yield of photocatalytic hydrogen peroxide production using the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks is shown in the figure.

[0028] Figure 12 The cyclic catalytic performance of photocatalytic hydrogen peroxide production using the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC is shown in the figure. Detailed Implementation

[0029] 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.

[0030] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0031] Example 1 (1) The synthesis of Ti4Co2 metal clusters includes the following steps: Cobalt acetate tetrahydrate (0.7 mmol) and benzoic acid (1220 mg, 10 mmol) were weighed and placed in a 20 mL glass bottle. Then, 10 mL of acetonitrile and 0.5 mL of tetraisopropyl titanate were added sequentially. The mixture was sonicated (60 kHz) for 5 min to obtain a solution. The glass bottle was sealed and placed in an oven at 80 °C for 3 days. After cooling to room temperature, the solution was washed 3-4 times with acetonitrile to obtain red blocky crystals of Ti₄Co₂ clusters. The parameters were determined using a single-crystal diffractometer as follows: P-1 space group, a=13.3641(5) Å, b=15.6677(8) Å, c=23.1140(8) Å, α=86.869(3)°, β=85.507(3)° γ=77.942(4)°, V=4714.8(3)Å 3 .

[0032] (2) The synthesis of the metal-organic framework TiCo2-2-NH2-H2BDC includes the following steps: Ti4Co2 crystals (0.025 mmol), 2,4,6-tris(4-pyridyl)1,3,5-triazine (tpt) (0.1 mmol), and 2-aminoterephthalic acid (2-NH2-H2BDC) (0.3 mmol) were dissolved in N,N-dimethylformamide (DMA) / 1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone (DMPU) (4:2 mL). 1 mL of HBF4 was then added. The mixture was sonicated (60 kHz) for 5 min, sealed in a glass bottle, and heated in a 120 °C oven for 3 days. After cooling to room temperature, the solution was washed 3-4 times with DMA to obtain orange hexagonal crystals, which are the metal-organic framework TiCo2-2-NH2-H2BDC.

[0033] The parameters of the orange hexagonal crystal, as determined by a single-crystal diffractometer, are as follows: P63 / mmc space group, a=16.8485(4) Å, b=16.8485(4) Å, c=15.0161(4) Å, α=90°, β=90°, γ=120°, V=3691.6(2) Å 3 .

[0034] Example 2 The synthesis of Ti4Co2 crystals is the same as in Example 1; The synthesis of the metal-organic framework TiCo2-2-OH-H2BDC includes the following steps: Ti4Co2 crystals (0.025 mmol), 2,4,6-tris(4-pyridyl)1,3,5-triazine (tpt) (0.1 mmol), and 2-hydroxyterephthalic acid (2-OH-H2BDC) (0.44 mmol) were dissolved in DMA / DMPU (4:2 mL), followed by the addition of 1 mL of HBF4. The mixture was sonicated (60 kHz) for 5 min, then sealed in a glass bottle and heated in a 120 °C oven for 3 days. After cooling to room temperature, the mixture was washed 3-4 times with DMA to obtain orange rod-shaped crystals, which are the metal-organic framework TiCo2-2-OH-H2BDC.

[0035] The parameters of the orange rod-shaped crystal, as determined by a single-crystal diffractometer, are as follows: TiCo2-2-OH-H2BDC: Space group P63 / mmc, a=16.8842(4) Å, b=16.8842(4) Å, c=15.2252(3) Å, α=90°, β=90°, γ=120°, V=3758.85(15) Å 3 .

[0036] Figure 1 and Figure 2 These are schematic diagrams of the organic framework structures of TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC, respectively.

[0037] The calculated value of elemental analysis for TiCo2-2-NH2-H2BDC is C. 42 H 24 TiCo2N 12 O 13 , Calcd (%): C, 47.13; H, 2.26; N, 15.70. Found: C, 47.76; H, 2.23; N, 15.89.

[0038] The calculated value of elemental analysis for TiCo2-2-OH-H2BDC is C. 42 H 18 TiCo2N6O 19 , Calcd (%): C, 46.87; H, 1.69; N, 7.81. Found: C, 46.33; H, 1.82; N, 7.69.

[0039] Figure 3The UV-Vis absorption spectra and Tauc plots of the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks are shown. As shown, both organic frameworks exhibit broad absorption in the 400-800 nm visible light region, especially with a strong absorption band in the 400-500 nm band, indicating that they are both visible light-driven catalysts. The absorption intensity of the TiCo2-2-OH-H2BDC organic framework is generally higher than that of the TiCo2-2-NH2-H2BDC organic framework across the entire measurement wavelength range, meaning that the hydroxyl-modified material can capture more photons. Based on the Tauc plots, the optical band gap of the TiCo2-2-NH2-H2BDC organic framework is 1.93 eV; the optical band gap of the TiCo2-2-OH-H2BDC organic framework is 1.94 eV.

[0040] Figure 4 This is the Mott-Schottky curve of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC. As shown in the figure, the slopes of both curves are positive within the test potential range. When the slope is greater than 0, it indicates that the material is an n-type semiconductor. In n-type semiconductors, the majority carriers are free electrons. Furthermore, the intercept of the Mott-Schottky curve on the horizontal axis is the conduction band potential. The conduction band potential of TiCo2-2-NH2-H2BDC is -1.06 V; the conduction band potential of TiCo2-2-OH-H2BDC is -1.08 V.

[0041] Figure 5 This is a schematic diagram of the electronic band structure of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC.

[0042] Figure 6 This is the Nyquist plot of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC under temperature changes at 90% humidity. A smaller diameter of the semicircle in the Nyquist plot indicates a lower charge transfer resistance, less resistance to charge transfer at the material interface, and higher proton conductivity. As the temperature increases from 303 K to 363 K, the semicircle diameter of both materials decreases significantly, indicating that the temperature rise lowers the energy barrier for charge transfer and promotes charge migration, consistent with typical characteristics of semiconductor materials. More significantly, at 303 K, the semicircle diameter of TiCo2-2-OH-H2BDC is nearly 40 times smaller than that of TiCo2-2-NH2-H2BDC, indicating a substantial reduction in charge transfer resistance, meaning that the introduction of hydroxyl groups greatly improves the conductivity of the material.

[0043] Figure 7This is a graph showing the relationship between temperature and conductivity of the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks at 90% humidity. The results show that, under high humidity (90%), the conductivity of TiCo2-2-OH-H2BDC increases significantly with increasing temperature, and the value is much higher than that of TiCo2-2-NH2-H2BDC. This indicates that the introduction of the -OH group greatly enhances the proton conductivity of the material, providing an important charge transport guarantee for its excellent photocatalytic performance.

[0044] Figure 8 This is an Arrhenius-type curve of ln(σT) versus 1000 / T for the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks at 90% humidity. The results show that modifying the ligand from amino to hydroxyl lowers the activation energy of the material. This means that in TiCo2-2-OH-H2BDC, the energy barrier for proton transport is lower, and migration becomes easier, thus significantly enhancing the material's conductivity kinetically.

[0045] Figure 9 The images show the solvent stability XRD patterns of the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks. The two materials were immersed in various organic solvents (24 h), and the results show that the two materials exhibit excellent chemical stability in various organic solvents.

[0046] Figure 10 The XRD patterns show the acid-base and thermal stability of the organic frameworks TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC. Furthermore, the two materials were immersed in solutions of different acidity and alkalinity for 24 h, and the results showed that both materials remained stable in the crystal range of pH 3-11. The XRD patterns after heating the two materials showed that the crystals remained stable at 250 °C, demonstrating that both materials possess good thermal stability.

[0047] Application Example 1 Take 2 mg of each of the catalysts prepared in Examples 1 and 2, disperse them in 10 mL of pure water, continuously purge oxygen (5 mL / min), and magnetically stir under irradiation with a 300 W xenon lamp (equipped with a 420 nm cutoff filter). Take samples at regular intervals to detect the hydrogen peroxide concentration.

[0048] The results are as follows Figure 11As shown, using the TiCo2-2-NH2-H2BDC organic framework as a catalyst, the corresponding product yielded 5176 μmol / g of hydrogen peroxide after 1 hour of reaction. Using the TiCo2-2-OH-H2BDC organic framework as a catalyst, the yield was 20113 μmol / g, approximately four times that of the TiCo2-2-NH2-H2BDC organic framework, demonstrating the unique advantage of hydroxyl groups in promoting photocatalytic reactions.

[0049] The reaction solution and catalyst were centrifuged to separate water and catalyst. The upper aqueous phase was taken out, and the remaining catalyst was dried and recovered in a 65°C oven overnight. The recovered catalyst was then subjected to photocatalytic testing again. Figure 12 This is a cyclic catalytic performance diagram of the photocatalytic production of hydrogen peroxide using the TiCo2-2-NH2-H2BDC and TiCo2-2-OH-H2BDC organic frameworks. The results show that after five repeated photocatalytic test cycles, the hydrogen peroxide production rate of both materials did not decrease significantly, and their performance remained stable.

[0050] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a titanium-cobalt bimetallic organic framework material, characterized in that: Comprising the following steps: (1) Synthesis of Ti4Co2 cluster: benzoic acid, cobalt acetate tetrahydrate and titanium acid tetraisopropyl ester are mixed in an organic solvent under ultrasonic, heated in a closed environment, washed and dried after reaction to obtain Ti4Co2 cluster crystals; (2) Synthesis of framework material: Ti4Co2 cluster crystals, first ligand and second ligand obtained in step (1) are dissolved in an organic solvent, then inorganic acid is added and mixed under ultrasonic, heated in a closed environment, washed and dried after reaction to obtain the titanium-cobalt bimetallic organic framework material; The first ligand is selected from one of 2-amino terephthalic acid and 2-hydroxy terephthalic acid; and the second ligand is 2,4,6-tris (4-pyridyl) -1,3,5-triazine.

2. The method of claim 1, wherein: The molar ratio of benzoic acid, cobalt acetate tetrahydrate and titanium acid tetraisopropyl ester in step (1) is 10:0.7:1.

68.

3. The method of claim 1, wherein: The temperature of the heating reaction in step (1) is 70-90℃, and the time is 72-96h.

4. The method of claim 1, wherein: The total amount of benzoic acid, cobalt acetate tetrahydrate and titanium acid tetraisopropyl ester and the amount of organic solvent in step (1) are 12.38 mmol:10 ml, and the organic solvent is acetonitrile.

5. The method of claim 1, wherein: The molar ratio of Ti4Co2 cluster crystals, first ligand and second ligand in step (2) is 0.25:(3-4.4):

1.

6. The method of claim 1, wherein: The organic solvent in step (2) is a mixed solvent of N,N-dimethylacetamide and 1,3-dimethyltetrahydro-2 (1H) -pyrimidinone, and the inorganic acid is tetrafluoroboric acid, and the volume ratio of the three is 4:2:1; the total amount of Ti4Co2 cluster crystals, first ligand and second ligand and the amount of organic solvent and inorganic acid are 4.25-5.65 mmol:7 mL.

7. The method of claim 1, wherein: The temperature of the heating reaction in step (2) is 110-130℃, and the time is 72-96h.

8. A titanium-cobalt bimetallic organic framework material prepared by the preparation method of any one of claims 1-7.

9. The titanium-cobalt bimetallic organic framework material of claim 8 is applied in the reaction of photocatalytic decomposition of water to produce hydrogen peroxide.

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