Defective NH2-Ni-MOF, preparation method and application

Abstract

The invention discloses defective NH2-Ni-MOF as well as a preparation method and application thereof, and belongs to the field of piezoelectric electro-catalytic hydrogen production. The method comprises the following steps: firstly, synthesizing a precursor NH2-Ni-MOF through a solvothermal method, putting the NH2-Ni-MOF material and a grinding ball into a ball mill together by a seller, and grinding to obtain defective NH2-Ni-MOF; and the grinding ball is a mixture of five large balls with the diameter of 10 mm and fifteen small balls with the diameter of 5 mm. The D3-NH2-Ni-MOF prepared by mixing and grinding the grinding balls in a specific proportion realizes the synergistic effect of high-energy impact and high-frequency grinding, and successfully introduces lattice defects with the maximum concentration. The defect structure can effectively promote separation and migration of photon-generated carriers and enhance the piezoelectric polarization effect of the material under the ultrasonic action, so that the piezoelectric synergistic photocatalytic performance is remarkably improved. Under the combined action of sun illumination and ultrasonic vibration, the D3-NH2-Ni-MOF catalyst is dispersed in a methanol aqueous solution, and efficient and stable water decomposition hydrogen production activity can be achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of piezoelectric photocatalytic hydrogen production, and particularly relates to a defect NH2-Ni-MOF, a preparation method and application. BACKGROUND

[0002] Photocatalytic technology can efficiently convert solar energy into chemical energy due to its green and environmentally friendly characteristics, and is a key approach to solving the problems of energy crisis and environmental pollution. Among numerous photocatalysts, metal-organic frameworks (MOFs) have become potential materials for photocatalytic hydrogen production due to their adjustable porous structure. However, the serious recombination of photo-generated electron-hole pairs greatly limits the photocatalytic efficiency of MOFs. To overcome this problem, researchers have developed strategies such as ligand functionalization, metal doping, and construction of heterojunctions, but these strategies have not achieved satisfactory results. Under mechanical stretching or strain, piezoelectric materials deform along the asymmetric direction, causing the internal positive and negative charge centers to shift, resulting in spontaneous polarization. At this time, the two opposite surfaces of the material gather positive and negative charges, respectively, forming an internal electric field. This electric field can effectively separate the photo-generated carriers and further enhance the catalytic activity of the material, providing a new direction for the development of photocatalytic technology. Therefore, it is necessary to study the polarity regulation of MOFs. Mechanical grinding is an efficient, green and simple method. The high-energy collision and shearing force generated by mechanical ball milling directly transfers mechanical energy to MOF crystals, inducing ligand loss and generating coordination unsaturated metal sites by breaking the metal-ligand coordination bond, and increasing surface defects by reducing particle size, thereby creating a high-activity material rich in defects and even partially amorphous. In addition, the grinding process can cause partial collapse of the pores to form a hierarchical micro-mesoporous structure, or irregular distortion of the cage-like cavities, increasing the defect density. Such pore defects not only increase the specific surface area, but also optimize the diffusion path of reactants through the confinement effect. In addition, the formation of defects can increase the asymmetry of the material to some extent, thereby enhancing the polarization ability of the material. In summary, MOFs materials have attracted much attention in the field of energy catalysis due to their unique structural characteristics. Introducing light and mechanical stress into the MOF system to study piezoelectric photocatalytic reactions has become a research hotspot. This multi-field synergy can effectively promote the separation of photo-generated carriers and improve the catalytic efficiency. At the same time, the modification of MOF-based catalysts through defect regulation strategies can effectively regulate the electronic structure and surface active sites of the material. The combination of the two not only overcomes the problem of carrier recombination in traditional photocatalysis, but also significantly enhances the catalytic activity of the material. Therefore, MOF-based piezoelectric photocatalysts based on defect regulation have great potential in the field of clean energy production such as hydrogen production, and are expected to provide a new technical path for solving the energy crisis. SUMMARY

[0003] The present application aims to provide a defective NH2-Ni-MOF (D-NH2-Ni-MOF), a preparation method and an application, the material of the present application introduces defects of different concentrations by regulating the mechanical ball milling process, thereby significantly improving the piezophotocatalytic performance, and the material can be applied to piezophotocatalytic water decomposition to produce hydrogen.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is: The present application first provides a preparation method of defective NH2-Ni-MOF, comprising: The NH2-Ni-MOF material is placed in a ball mill together with grinding balls for grinding to obtain defective NH2-Ni-MOF, and the grinding balls are 5 large balls with a diameter of 10 mm and 15 small balls with a diameter of 5 mm.

[0005] Preferably, the rotation speed of the ball mill is set to 450 rpm, and the grinding time is 90 minutes.

[0006] Preferably, the mass ratio of the grinding balls to NH2-Ni-MOF is 50:1.

[0007] Preferably, the preparation method of the NH2-Ni-MOF material comprises: Step one: dissolve nickel nitrate hexahydrate in a solvent and ultrasonically dissolve it, then add 2-amino terephthalic acid solution to form a mixed solution; Step two: place the mixed solution obtained in step one into a reaction container to enter a dissolution heat reaction to obtain the NH2-Ni-MOF material.

[0008] Preferably, the mass ratio of nickel nitrate hexahydrate to 2-amino terephthalic acid in step one is 0.9:1.

[0009] Preferably, the reaction temperature in step two is 110 DEG C, and the reaction time is 24 h.

[0010] The present application also provides defective NH2-Ni-MOF obtained by the above preparation method.

[0011] The present application also provides the application of the above defective NH2-Ni-MOF as a catalyst in piezophotocatalytic water decomposition to produce hydrogen.

[0012] Preferably, the application method comprises: The above defective NH2-Ni-MOF is ultrasonically dispersed in a methanol aqueous solution, nitrogen is introduced into the solution, then the reactor is placed in a sweep frequency ultrasonic cleaning instrument with a power of 300 W and a frequency of 50 kHz, and at the same time, a 300 W xenon lamp is used to simulate sunlight for irradiation, and piezophotocatalytic hydrogen production reaction is carried out.

[0013] Preferably, the catalytic reaction is carried out at a constant temperature of 25℃.

[0014] Advantages of the present application The application provides a defective NH2-Ni-MOF (D-NH2-Ni-MOF), a preparation method and application. The application first uses a solvothermal method to prepare a NH2-Ni-MOF with a complete structure, and then uses a mechanical ball milling method to perform defect engineering regulation on the NH2-Ni-MOF, and successfully constructs a catalytic material with different defect concentrations by precisely controlling the size ratio of the milling balls. The milling balls are mixed with five large balls with a diameter of 10 mm and 15 small balls with a diameter of 5 mm. The defect structure can effectively promote the separation and migration of photo-generated carriers, and enhance the piezoelectric polarization effect of the material under the action of ultrasound, thereby significantly improving the piezoelectric synergistic photocatalytic performance. Under the combined action of sunlight and ultrasonic vibration, the D3-NH2-Ni-MOF catalyst is dispersed in a methanol aqueous solution, and high-efficiency and stable water splitting for hydrogen production can be realized. The method is simple in process and strong in regulation, and provides a new idea for designing high-performance piezoelectric photocatalytic materials. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 FIG. 1 is a scanning electron microscope image of NH2-Ni-MOF, D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF.

[0016] Figure 2 FIG. 5 is a photocurrent response test diagram of NH2-Ni-MOF, D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF.

[0017] Figure 3 FIG. 7 is a fluorescence spectrum diagram of NH2-Ni-MOF, D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF.

[0018] Figure 4 FIG. 9 is an electrochemical impedance diagram of NH2-Ni-MOF, D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF.

[0019] Figure 5 FIG. 11 is a schematic diagram of piezoelectric photocatalytic water splitting for hydrogen production of D-NH2-Ni-MOF under sunlight (λ > 380 nm).

[0020] Figure 6is a piezophotocatalytic hydrogen evolution contrast chart of NH2-Ni-MOF, D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF under sunlight (λ>380 nm). DETAILED DESCRIPTION

[0021] The present application first provides a preparation method of defective NH2-Ni-MOF, comprising: The NH2-Ni-MOF material is placed in a ball mill together with grinding balls, and grinding is performed, the rotation speed of the ball mill is preferably 450 rpm, and the grinding time is preferably 90 minutes, to obtain defective NH2-Ni-MOF; the grinding balls are a mixture of 5 large balls with a diameter of 10 mm and 15 small balls with a diameter of 5 mm. The optimized ratio of the high impact energy provided by the large balls and the high frequency grinding provided by the small balls synergistically can effectively introduce the maximum concentration of defects into the crystal structure of NH2-Ni-MOF, and obtain the target product with the highest defect concentration. The mass ratio of the grinding balls to NH2-Ni-MOF is preferably 50:1. The filling rate of the ball mill jar is calculated to be 20%-30%.

[0022] According to the present application, the preparation method of the NH2-Ni-MOF material comprises: Step one: dissolve nickel nitrate hexahydrate in a solvent and ultrasonically dissolve, the solvent is preferably N,N-dimethylformamide (DMF), and the ultrasonic dissolution time is preferably 30 min, then add a DMF solution of 2-amino terephthalic acid to form a mixed solution; the mass ratio of nickel nitrate hexahydrate to 2-amino terephthalic acid is preferably 0.9:1; Step two: place the mixed solution obtained in step one into a reaction container to enter a dissolution heat reaction, the reaction temperature is preferably 110℃, and the reaction time is preferably 24h, after the reaction is completed, naturally cool to room temperature, centrifuge the obtained green precipitate, wash with DMF and anhydrous ethanol three times in turn, and finally dry in a 60℃ vacuum drying box for 12 hours, to obtain the NH2-Ni-MOF material.

[0023] The present application also provides defective NH2-Ni-MOF obtained by the above preparation method.

[0024] The present application also provides the application of the above defective NH2-Ni-MOF as a catalyst in piezophotocatalytic water decomposition for hydrogen production.

[0025] According to the present application, the application method comprises: The defect NH2-Ni-MOF is ultrasonically dispersed in a 10 vol% methanol sacrificial agent aqueous solution, nitrogen is introduced into the solution, then the reactor is placed in a sweep frequency ultrasonic cleaning instrument with a power of 300 W and a frequency of 50 kHz, and irradiation is performed with a 300 W xenon lamp to simulate sunlight, and a piezoelectric photocatalytic hydrogen production reaction is performed. The catalytic reaction is preferably carried out at a constant temperature of 25°C.

[0026] The application will be further described in detail below with reference to specific examples. The raw materials involved in the examples are commercially available.

[0027] Example 1 (I) Preparation of NH2-Ni-MOF: 0.18 g of Ni(NO3)2·6H2O was weighed and placed in 15 mL of N,N-dimethylformamide (DMF), and ultrasonic treatment was performed for 30 min to fully dissolve it. Under continuous stirring, 10 mL of a DMF solution containing 0.2 g of 2-amino terephthalic acid (NH2-BDC) was slowly added to form a mixed solution. Then the mixed solution was transferred to a 50 mL three-necked flask and reacted at 110°C for 24 h. After the reaction was completed, the product was separated by centrifugation and washed with DMF and anhydrous ethanol three times in turn, and finally dried at 60°C under vacuum for 12 h to obtain NH2-Ni-MOF.

[0028] (II) Preparation method of defect NH2-Ni-MOF (D-NH2-Ni-MOF) is as follows: 200 mg of NH2-Ni-MOF material synthesized by a solvothermal method was weighed as a precursor, and was loaded into a ball mill jar with a volume of 100 mL together with a specific ratio of grinding balls. The rotation speed of the ball mill was set to 450 rpm, and the grinding time was 90 minutes to prepare the target product defect NH2-Ni-MOF (D3-NH2-Ni-MOF), wherein the grinding balls are 5 zirconium oxide grinding balls with a diameter of 10 mm and 15 zirconium oxide grinding balls with a diameter of 5 mm mixedly used.

[0029] Comparative Example 1 The preparation method and conditions are the same as those of Example 1, except that the grinding balls are 10 zirconium oxide grinding balls with a diameter of 10 mm, and D1-NH2-Ni-MOF is prepared. Under this condition, the defect concentration of the obtained material is low due to the large gap between the large balls and the insufficient grinding effect.

[0030] Comparative Example 2 The preparation method and conditions are the same as Example 1, except that the grinding balls are 30 zirconium oxide grinding balls with a diameter of 5 mm, to obtain D2-NH2-Ni-MOF. Under this condition, although the grinding frequency is high, the impact kinetic energy of the small balls is insufficient, and the defect concentration of the obtained material is limited.

[0031] The defective NH2-Ni-MOF prepared in Example 1 and Comparative Examples 1-2 is detected, Figure 1 are scanning electron microscope images of NH2-Ni-MOF, D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF. Among them Figure 1 (a) is a scanning electron microscope image of NH2-Ni-MOF; Figure 1 (b) is a scanning electron microscope image of D1-NH2-Ni-MOF; Figure 1 (c) is a scanning electron microscope image of D 2- NH2-Ni-MOF; Figure 1 (d) is a scanning electron microscope image of D 3- NH2-Ni-MOF. From Figure 1 (a) can be seen, NH2-Ni-MOF presents a nanosheet structure; as Figure 1 (b-d) shows that the defective NH2-Ni-MOF (D1-NH2-Ni-MOF, D2-Ni-MOF and D3-Ni-MOF) also shows a nanosheet structure, which indicates that the grinding process has little effect on the morphology of NH2-Ni-MOF.

[0032] Figure 2 are the photocurrent response test images of NH2-Ni-MOF and D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF. As Figure 2 shown, the photocurrent intensity of the defective NH2-Ni-MOF (D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF) is significantly higher than that of NH2-Ni-MOF, which indicates that the generation of defects makes the separation efficiency of photo-generated electron-hole pairs higher, and the photocurrent intensity of D3-NH2-Ni-MOF is the largest, because D3-NH2-Ni-MOF has more defects, and a stronger internal built-in electric field is generated under the action of ultrasonic waves, which significantly improves the separation efficiency of carriers.

[0033] Figure 3 are the fluorescence spectra of NH2-Ni-MOF and D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF. From Figure 3It can be seen that the fluorescence intensity of D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF is significantly reduced compared with NH2-Ni-MOF, which further indicates that the introduction of defects reduces the recombination rate of photo-generated carriers of NH2-Ni-MOF.

[0034] Figure 4 are the electrochemical impedance diagrams of NH2-Ni-MOF and D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF. From the diagrams, it can be seen that the charge transfer resistance of the defect NH2-Ni-MOF (D1-NH2-Ni-MOF, D2-NH2-Ni-MOF and D3-NH2-Ni-MOF) is reduced, and D3-NH2-Ni-MOF has the lowest charge transfer resistance, which indicates that the introduction of defects is conducive to the transfer and separation of carriers in the material. While D3-NH2-Ni-MOF has more defects, it is more polar and more prone to deformation under the action of ultrasound, and the internal built-in electric field generated effectively inhibits the recombination of photo-generated carriers. Figure 4

[0035] Example 2 Piezophotocatalytic hydrogen evolution from water by NH2-Ni-MOF and defect NH2-Ni-MOF The reaction was carried out in a quartz glass reactor, a xenon lamp was used as a light source to simulate sunlight, and a sweep frequency ultrasonic cleaner with a power of 300 W was used to provide ultrasonic waves, and the frequency was set to 50 kHz. 10 mg of catalyst (NH2-Ni-MOF and D1-NH2-Ni-MOF, D2-NH2-Ni-MOF or D3-NH2-Ni-MOF) was ultrasonically dispersed in a mixed solvent composed of 20 mL of methanol and 180 mL of deionized water, and high-purity nitrogen was introduced into the reaction system for 10 minutes to remove oxygen. The quartz glass reactor was placed in the sweep frequency ultrasonic cleaner, and the xenon lamp and sweep frequency ultrasonic cleaner were turned on to start the piezophotocatalytic reaction. After two hours of reaction, the amount of hydrogen gas generated was detected offline by gas chromatography.

[0036] Figure 5 The piezophotocatalytic hydrogen evolution from water by D-NH2-Ni-MOF catalyst under the synergistic action of sunlight and ultrasonic waves is shown in the schematic diagram. The core of the process lies in the deep regulation of the intrinsic physical properties of the material by defect engineering. Under the action of the mechanical vibration provided by the external ultrasonic wave, the crystal lattice of the catalyst is micro-deformed, causing the relative displacement of the positive and negative charge centers, thereby polarizing and generating an internal built-in electric field (i.e. piezoelectric electric field). This internal built-in electric field provides a strong driving force for the directional migration of photo-generated carriers, which can effectively overcome the Coulomb attraction between electrons and holes, greatly improving the separation efficiency, which is the key to the fundamental improvement of the catalytic performance.​

[0037] Experimental results Figure 6 ) to verify the above mechanism with detailed data, and clearly reveal the structure-activity relationship between defect concentration and catalytic performance. The original NH2-Ni-MOF has a weak piezoelectric response due to its highly regular crystal structure and good symmetry, and the generated internal electric field strength is limited, so its piezoelectric photocatalytic hydrogen production rate is low, only 89.3 μmol / g / h. After introducing defects by ball milling, the activity of all modified materials shows a significant increase, but the increase varies due to the difference in defect concentration. Among them, the hydrogen production rate of D1-NH2-Ni-MOF prepared with large-size grinding balls increased to 253.2 μmol / g / h, which indicates that the mechanical impact of large balls can cause partial lattice distortion, but due to insufficient grinding, the defect introduction efficiency is limited. The hydrogen production rate of D2-NH2-Ni-MOF prepared with small-size grinding balls reached 352.8 μmol / g / h, which benefited from the high-frequency grinding of small balls to achieve a more uniform defect distribution, but due to the insufficient impact, it is difficult to create deeper defect sites.

[0038] It is worth noting that D3-NH2-Ni-MOF prepared by using a mixed strategy of large and small balls showed a overwhelming performance advantage, with a hydrogen production rate of 491.1 μmol / g / h, which was 5.5 times, 1.9 times and 1.4 times that of the original sample, D1 sample and D2 sample, respectively. This outstanding performance is attributed to the optimization of defect concentration and type achieved by this scheme. The high-speed ball milling process, under the synergistic effect of high-energy impact provided by large balls and high-frequency grinding provided by small balls, effectively causes serious lattice distortion and breaks a large number of metal-ligand coordination bonds in NH2-Ni-MOF, thereby creating a large number of coordination unsaturated metal sites (defect sites) and ligand vacancies.

[0039] These dense defects, which essentially destroy the overall symmetry of the MOFs framework, greatly enhance the macroscopic polarity of the material. Therefore, under the action of ultrasound, D3-NH2-Ni-MOF can generate a much stronger built-in electric field than other samples. This strong electric field acts as an efficient "sorting machine", greatly accelerating the separation of photo-generated electron-hole pairs and inhibiting their recombination. In addition, these defect sites themselves also become efficient electron capture and transport centers, effectively reducing the electron transport resistance of the material, thereby significantly increasing the interface electron transfer rate, enabling it to participate more quickly in water reduction reactions. This study successfully applies the mechanical ball milling method, a simple and easy-to-expand physical method, to the precise defect engineering of MOFs materials. By creatively regulating the size ratio of the grinding balls (mixing large and small balls), we achieve controllable construction of the defect concentration and type of the material, abandoning the use of complex synthesis procedures, harsh conditions or expensive reagents in traditional chemical methods. Secondly, this method not only demonstrates that the creation of defects enables the catalytic performance of NH2-Ni-MOF to be improved, but also reveals the internal relationship between "defect structure-piezoelectric effect-carrier behavior-catalytic performance" through systematic comparative experiments (D1, D2, D3), providing clear theoretical guidance and design principles for designing high-performance piezoelectric photocatalytic materials. Finally, the method of this invention has broad application prospects: the preparation process is simple, low-cost and easy to scale up, greatly reducing the technical threshold and cost of future industrial production. Given the above advantages, D3-NH2-Ni-MOF catalyst, as an efficient, stable and cost-effective catalytic material, has great application potential and broad commercial prospects in the future large-scale solar-driven water splitting hydrogen production industrialization process, providing a novel and feasible technical path for the development of clean energy technology and the realization of the "carbon neutral" goal.

Claims

1. A method for preparing a defective NH2-Ni-MOF, characterized in that, The application relates to a preparation method of a defective NH2-Ni-MOF and application of the defective NH2-Ni-MOF. The NH2-Ni-MOF material is placed in a ball mill together with grinding balls to perform grinding, so as to obtain the defective NH2-Ni-MOF; the grinding balls are 5 large balls with a diameter of 10 mm and 15 small balls with a diameter of 5 mm.

2. The method for preparing a defective NH2-Ni-MOF according to claim 1, characterized in that, The rotation speed of the ball mill is set to 450 rpm, and the grinding time is 90 minutes.

3. The method for preparing defective NH2-Ni-MOF according to claim 1, characterized in that, The mass ratio of the grinding balls to the NH2-Ni-MOF is 50:

1.

4. The method for preparing defective NH2-Ni-MOF according to claim 1, characterized in that, The preparation method of the NH2-Ni-MOF material comprises the following steps: Step one: ultrasonic dissolution of nickel nitrate hexahydrate in a solvent, then adding 2-amino terephthalic acid solution to form a mixed solution; Step two: placing the mixed solution obtained in step one into a reaction container to perform a dissolution heat reaction, so as to obtain the NH2-Ni-MOF material.

5. The method for preparing defective NH2-Ni-MOF according to claim 4, characterized in that, The mass ratio of nickel nitrate hexahydrate to 2-amino terephthalic acid in step one is 0.9:

1.

6. The method of claim 4, wherein the defect-free NH2-Ni-MOF is prepared by the steps of: The reaction temperature in step two is 110 DEG C, and the reaction time is 24 hours.

7. The defective NH2-Ni-MOF obtained by the preparation method in claim 1.

8. Application of the defective NH2-Ni-MOF in claim 1 as a catalyst in piezophotocatalytic water decomposition for hydrogen production.

9. Use according to claim 8, characterized in that, The application method comprises the following steps: The defective NH2-Ni-MOF is ultrasonically dispersed in a methanol aqueous solution, nitrogen is introduced into the solution, then, the reactor is placed in a sweep-frequency ultrasonic cleaning instrument with a power of 300 W and a frequency of 50 kHz, and a 300 W xenon lamp is used to simulate sunlight to perform piezophotocatalytic hydrogen production reaction.

10. Use according to claim 9, characterized in that, The catalytic reaction is performed at a constant temperature of 25 DEG C.

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