SrTiO3 / NH2-MIL-125(Ti) Piezoelectric-Composite Photocatalyst and Its Preparation Method

Abstract

The present invention discloses a SrTiO3 / NH2-MIL-125(Ti) piezoelectric composite photocatalyst and a preparation method thereof. The preparation method includes: in the first step, tetrabutyl titanate and strontium nitrate are added to a mixed solution of ethanolamine and sodium hydroxide, and hydrothermal crystallization reaction is carried out to obtain SrTiO3; in the second step: the SrTiO3 synthesized above is dispersed in a mixed solution of N,N-dimethylformamide and anhydrous methanol under stirring, and then a certain amount of 2-aminoterephthalic acid and tetrabutyl titanate are added in sequence, and hydrothermal crystallization reaction is carried out to obtain the SrTiO3 / NH2-MIL-125(Ti) composite material. The process of the present invention is simple, environmentally friendly and has low production cost. Due to the piezoelectric effect of SrTiO3 in the prepared composite photocatalyst, photo-generated carriers can be effectively separated under the action of the built-in electric field, thus having excellent piezoelectric photocatalytic hydrogen production performance.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric-photocatalytic materials, and specifically refers to a SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst and a preparation method thereof. Background Art

[0002] In today's world, rapid urbanization and the sharp growth of economy and population have led to a huge demand for energy, and most of the demand is met by fossil fuel combustion, which will bring serious environmental consequences. And the non-renewability of fossil fuels also increases people's concerns about energy utilization. Therefore, people have long been pursuing the development of a sustainable, economical and environmentally friendly alternative energy source to meet the growing energy demand. Among various non-renewable energy sources, hydrogen fuel has become an ideal clean and environmentally friendly energy source due to its high energy density per unit mass and the fact that its combustion by-products are clean water.

[0003] Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials formed by the self-assembly of metal ions or their clusters and organic ligands. Their structural functions can be adjusted, and they have a large specific surface area, high porosity and abundant active sites. Among them, the Ti-based MOF NH2-MIL-125(Ti) is a photocatalyst with good hydrothermal stability, which can be prepared from 2-aminoterephthalic acid and tetrabutyl titanate. It has a suitable band gap, and the conduction band position is more negative than the hydrogen potential, and it can realize the application of hydrogen production by water splitting under visible light. However, in the process of photocatalytic electron transition, due to the influence of Coulomb attraction, there is still a problem of easy recombination of photo-generated electrons and holes. Therefore, the photocatalytic hydrogen production performance of NH2-MIL-125(Ti) still needs to be further improved.

[0004] Generally speaking, the built-in electric field generated by piezoelectric materials under external forces can be utilized to alleviate the problem of photogenerated carrier recombination during the photocatalytic process. Piezoelectric materials applied in photocatalysis can be divided into two categories. One category is single-component piezoelectric materials that can absorb photon energy, known as photo-piezoelectric semiconductors; the other category is heterostructures formed by the combination of piezoelectric materials and photo-semiconductors. By combining piezoelectric materials with photo-semiconductors, through the synergistic effect of the two materials, the separation of photo-generated electrons and holes in the composite can be effectively promoted, thereby enhancing the piezo-photocatalytic hydrogen production efficiency. Currently, some heterostructures obtained by combining piezoelectric materials with photo-semiconductors, such as TiO2@ZnO (Wang Z, Hu T, He H, et al. Enhanced H2 production of TiO2 / ZnO nanowires Co-using solar and mechanical energy through piezo-photocatalytic effect [J]. ACS Sustainable Chemistry & Engineering, 2018, 6(8): 10162-10172), MoSe2@TiO2 (Han Q, Du S, Wang Y, et al. Direct Z-scheme MoSe2 / TiO2 heterostructure with improved piezoelectric and piezo-photocatalytic performance [J]. Journal of Colloid and Interface Science, 2022, 622: 637-651), and PbTiO3@CdS (Huang X, Lei R, Yuan J, et al. Insight into the piezo-photo coupling effect of PbTiO3 / CdS composites for piezo-photocatalytic hydrogen production [J]. Applied Catalysis B: Environmental, 2021, 282: 119586), etc., show that with the assistance of the piezoelectric effect, the composite materials have higher photocatalytic performance compared to the corresponding monomers. However, so far, there are relatively few research reports on the use of heterostructures obtained by combining piezoelectric materials with MOF-based materials for piezo-photocatalytic hydrogen production. Summary of the Invention

[0005] The object of the present invention is to solve the deficiencies of the above-mentioned background technology, and to provide a SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst and its preparation method, so as to alleviate the problem of easy recombination of photogenerated carriers in single-component catalysts.

[0006] The technical solution of the present invention is as follows: A preparation method of a SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst, characterized by comprising the following steps:

[0007] A. Under a water bath environment of 40-60°C, tetrabutyl titanate and ethanolamine are mixed, then sodium hydroxide solution is dropped in, and then strontium nitrate solution is added under vigorous stirring. The obtained liquid is transferred to a polytetrafluoroethylene stainless steel hydrothermal autoclave, and hydrothermal reaction is carried out at 180-200°C for 20-24 h. After the reaction is completed, the solid product is washed and dried to obtain SrTiO3 powder;

[0008] B. Weigh the SrTiO3 powder synthesized in step A according to 12.5-37.5% of the mass of the designed NH2-MIL-125(Ti). The SrTiO3 powder is uniformly dispersed in a solvent formed by mixing N,N-dimethylformamide and anhydrous methanol. Take the corresponding amounts of 2-aminoterephthalic acid and tetrabutyl titanate according to the mass of the designed NH2-MIL-125(Ti), add them in sequence and stir evenly. The obtained liquid is transferred to a polytetrafluoroethylene stainless steel hydrothermal autoclave, and hydrothermal reaction is carried out at 150-180°C for 20-24 h. After the reaction is completed, the solid product is washed and dried to obtain the SrTiO3 / NH2-MIL-125(Ti) composite piezoelectric-photocatalyst.

[0009] Preferably, in step A, the dosage of ethanolamine is 2-6 mL of ethanolamine corresponding to each 1 mmol of tetrabutyl titanate, the concentration of the sodium hydroxide solution is 2-4 mol / L, and the concentration of the strontium nitrate solution is 2-4 mol / L, wherein the molar ratio of tetrabutyl titanate, sodium hydroxide, and strontium nitrate is 1:(7-14):(1-2).

[0010] Further, in step A, the dosage of ethanolamine is 4 mL of ethanolamine corresponding to each 1 mmol of tetrabutyl titanate, the concentration of the sodium hydroxide solution is 3 mol / L, the concentration of the strontium nitrate solution is 2 mol / L, and the molar ratio of tetrabutyl titanate, sodium hydroxide, and strontium nitrate is 1:10.5:1.

[0011] Further, in step A, hydrothermal reaction is carried out at 180°C for 24 h; in step B, hydrothermal reaction is carried out at 150°C for 24 h.

[0012] Preferably, in step A, the process of washing and drying the solid product is to wash it 2 times with anhydrous ethanol and deionized water respectively, and then dry it in a vacuum drying oven at 60°C for 12 h.

[0013] Preferably, in step B, -N,N-dimethylformamide and anhydrous methanol are mixed in a volume ratio of 9:1 to form a solvent, and the solvent dosage corresponding to every 0.05 - 0.15 g of SrTiO3 is 40 - 50 mL.

[0014] Preferably, in step B, the dosages of 2-aminoterephthalic acid and tetrabutyl titanate are as follows: for every 0.4 g of NH2-MIL-125(Ti) designed to be generated, 0.56 g of 2-aminoterephthalic acid and 0.6 mL of tetrabutyl titanate are used.

[0015] Preferably, in step B, 2-aminoterephthalic acid is added and stirred for 5 - 10 min, and then tetrabutyl titanate is added and stirred for 20 - 30 min.

[0016] Preferably, in step B, the process of washing and drying the solid product is to wash it 3 times with -N,N-dimethylformamide and anhydrous methanol respectively, and then dry it in a vacuum drying oven at 60 °C for 12 h.

[0017] The present invention also provides a SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst, which is prepared by any of the above preparation methods.

[0018] The present invention also provides an application of the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst, and the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst is applied to the piezoelectric-photocatalytic water splitting for hydrogen production reaction.

[0019] Preferably, the piezoelectric-photocatalytic water splitting for hydrogen production reaction includes the following steps:

[0020] Disperse the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst in water containing Na2S / Na2SO3 as a sacrificial reagent. For every 1 L of water, 0.4 - 0.6 g of the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst is used, and carry out hydrolysis for hydrogen production under the conditions of a 300 W xenon lamp as the light source and a ultrasonic generator with a power set to 80 - 100 W as the external force source.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. In the existing single-component catalysts, photo-generated carriers are prone to recombination. In the present invention, SrTiO3 and NH2-MIL-125(Ti) are compounded to obtain a heterostructure, and the piezoelectric effect of SrTiO3 is utilized to enable the composite catalyst to generate more effective photo-generated electrons and holes to participate in the water splitting hydrogen production reaction.

[0023] 2. The catalytic principle of preparing the composite catalyst in the present invention is that under light illumination, when the photon energy absorbed by SrTiO3 and NH2-MIL-125(Ti) is greater than their band gaps, the electrons in the valence band will be excited to the conduction band, forming photo-generated electrons, while holes are left in the valence band. Under the combined action of ultrasonic waves, the polar displacement will occur between the anions and cations of SrTiO3, resulting in internal polarization, thus forming a built-in electric field. Driven by the built-in electric field, electrons and holes can be effectively separated. Since SrTiO3 and NH2-MIL-125(Ti) form a type-II heterojunction, the electrons in the conduction band of SrTiO3 will be transferred to the conduction band of NH2-MIL-125(Ti) to carry out the hydrogen production reaction by reducing water, while the holes in the valence band of NH2-MIL-125(Ti) will be transferred to the valence band of SrTiO3 to carry out the corresponding oxidation reaction.

[0024] 3. The advantages of the preparation method of the present invention are simple process, environmental friendliness and low production cost. Brief Description of the Drawings

[0025] Figure 1 XRD patterns of Examples 1-3 and Comparative Examples;

[0026] Figure 2 SEM images of Comparative Examples;

[0027] Figure 3 SEM images of Example 2;

[0028] Figure 4 XPS spectra of Example 2;

[0029] Figure 5 PFM images of Example 2;

[0030] Figure 6 Piezo-photocatalytic water splitting hydrogen production performance diagrams of Examples 1-3 and Comparative Examples. Detailed Description of the Invention

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following examples are used to further elaborate on the present invention in detail. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention. The following specific examples further illustrate the present invention in detail. The reagents used in the examples are all commercially available products without special description, and the methods used are all conventional methods in the art without special description.

[0032] Example 1

[0033] This example provides a preparation method of a SrTiO3 / NH2-MIL-125(Ti) piezo-composite photocatalyst, including the following steps:

[0034] Preparation of A. SrTiO3

[0035] (a) Under a water bath environment at 60 °C, 10 mmol of tetrabutyl titanate was mixed with 40 mL of ethanolamine to obtain solution A;

[0036] (b) 35 mL of sodium hydroxide solution (3 mol / L) was added dropwise to solution A to obtain suspension B;

[0037] (c) Under vigorous stirring, 5 mL of an aqueous solution containing 10 mmol of strontium nitrate was added to suspension B to obtain suspension C;

[0038] (d) Suspension C was transferred to a polytetrafluoroethylene stainless steel hydrothermal autoclave and kept at 180 °C for 24 h;

[0039] (e) The obtained solid product was washed twice with anhydrous ethanol and deionized water respectively, and then dried in a vacuum drying oven at 60 °C for 12 h to obtain SrTiO3.

[0040] Preparation of B. SrTiO3 / 12.5% NH2-MIL-125(Ti) Composite Piezoelectric-Photocatalyst

[0041] (a) It was designed to generate 0.4 g of NH2-MIL-125(Ti). Under stirring conditions, 0.05 g of the above-synthesized SrTiO3 was dispersed in a solvent formed by mixing 36 mL of N,N-dimethylformamide and 4 mL of anhydrous methanol;

[0042] (b) 0.56 g of 2-aminoterephthalic acid was added to the above mixture, and stirring was maintained for 5 min. Then, 0.6 mL of tetrabutyl titanate was added dropwise, and stirring was maintained for 30 min;

[0043] (c) The obtained mixture was transferred to a polytetrafluoroethylene stainless steel hydrothermal autoclave and kept at 150 °C for 24 h;

[0044] (d) The obtained solid product was washed three times with N,N-dimethylformamide and anhydrous methanol respectively, and then dried in a vacuum drying oven at 60 °C for 12 h to prepare SrTiO3 / 12.5% NH2-MIL-125(Ti) composite piezoelectric-photocatalyst.

[0045] Example 2

[0046] This example provides a preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst, including the following steps:

[0047] A. Preparation of SrTiO3

[0048] The operation process is the same as that in Example 1

[0049] Preparation of B.SrTiO3 / 25% NH2-MIL-125(Ti) Composite Piezoelectric-Photocatalyst

[0050] The operation process is the same as that of Example 1 except for the following differences

[0051] Disperse 0.1 g of the synthesized SrTiO3 above in a mixed solution of 36 mL of N,N-dimethylformamide and 4 mL of anhydrous methanol under stirring

[0052] Example 3

[0053] A. Preparation of SrTiO3

[0054] The operation process is the same as that of Example 1

[0055] The operation process for the preparation of B.SrTiO3 / 37.5% NH2-MIL-125(Ti) composite piezoelectric-photocatalyst is the same as that of Example 1 except for the following differences

[0056] Disperse 0.15 g of the synthesized SrTiO3 above in a mixed solution of 36 mL of N,N-dimethylformamide and 4 mL of anhydrous methanol under stirring

[0057] Comparative Example

[0058] This comparative example provides a preparation method of NH2-MIL-125(Ti), and the steps are as follows

[0059] (a) Add 0.56 g of 2-aminoterephthalic acid to a mixed solution of 36 mL of N,N-dimethylformamide and 4 mL of anhydrous methanol, and stir for 5 min

[0060] (b) Drop 0.6 mL of tetrabutyl titanate into the above mixed solution and stir for 30 min

[0061] (c) Transfer the obtained mixture to a polytetrafluoroethylene stainless steel hydrothermal autoclave and keep it at 150 °C for 24 h

[0062] (d) Wash the obtained solid product 3 times with N,N-dimethylformamide and anhydrous methanol respectively, and then dry it in a vacuum drying oven at 60 °C for 12 h to obtain NH2-MIL-125(Ti).

[0063] Performance Test

[0064] XRD Pattern: See Appendix Figure 1 , Figure 1 is the XRD pattern of the SrTiO3 / NH2-MIL-125(Ti) composite piezoelectric-photocatalyst obtained in Examples 1-3 of the present invention and the comparative example. FromFigure 1 It can be seen that the diffraction peaks of SrTiO3 appear significantly at 2θ of 32°, 39.6°, 46°, 51.8°, 57.2° and 67.2°, which coincide with the (110), (111), (200), (210), (211) and (220) crystal planes of cubic SrTiO3 with card number 00-040-1500. The diffraction peaks of NH2-MIL-125 can also be well matched with the previously reported and simulated diffraction peaks, indicating the successful synthesis of the comparative example. In the XRD patterns of the samples synthesized in Examples 1-3, the diffraction peaks of SrTiO3 and NH2-MIL-125(Ti) appear simultaneously, indicating the successful preparation of the SrTiO3 / NH2-MIL-125(Ti) composite piezoelectric-photocatalyst.

[0065] SEM images: See Appendix Figure 2 and 3 , Figure 2 Figure Figure 3 is the SEM image of pure NH2-MIL-125(Ti). It can be seen that the synthesized NH2-MIL-125(Ti) has a disk-like morphology.

[0066] XPS spectra: See Appendix Figure 4 , Figure 4 Figure

[0067] is the XPS spectrum of Example 2 of the present invention, which shows that the SrTiO3 / 25% NH2-MIL-125(Ti) composite piezoelectric-photocatalyst is composed of elements C, O, N, Ti and Sr.

[0067] PFM images: See Appendix Figure 5 , Figure 5 Figure Figure 5 is the PFM image of Example 2 of the present invention. As shown in Figure 5 (a), it shows granular SrTiO3 and disk-like NH2-MIL-125(Ti). Figure 5 (b) shows a complete amplitude butterfly curve, which confirms a distinct piezoelectric response. Its loop is asymmetric, with a voltage offset of about 9V, indicating the presence of significant self-polarization. Figure 5 (c) is the phase hysteresis loop. The non-coincident closed loop indicates that as the applied electric field changes, the sample undergoes a phase conversion from -40° to 110°, and has a non-zero remanent polarization, which means the sample has good piezoelectric properties.

[0068] The catalysts obtained in Examples 1-3 of the present invention, the comparative examples, and SrTiO3 powder were subjected to piezoelectric-photocatalytic water splitting for hydrogen production. The reaction was carried out in a top-irradiation type photoreactor (Pyrex glass), which was connected to a closed gas circulation system. An ultrasonic generator model JC-QX-10L was placed directly below the photoreactor.

[0069] The specific steps are as follows:

[0070] Disperse the photocatalyst powder (25 mg) in 50 mL of water containing 0.018 mol of Na2S and 0.013 mol of Na2SO3 as sacrificial agents. Use a vacuum pump to evacuate the air in the sealed gas circulation system, and the temperature of the system is controlled at 25 °C by circulating water. A 300 W xenon lamp equipped with a 350 nm - 780 nm filter is used as the light source, and an ultrasonic generator with a power set to 100 W is used as the external force source. In the experiment, the ultrasound is turned on every 30 min for 30 min. Automatic sampling is performed every 1 h. The automatic sampling system connects the integrated circulation system to a gas chromatograph. The gas chromatograph (GC) is equipped with a thermal conductivity detector (TCD molecular sieve column 3 m in length) uses nitrogen as the carrier gas. The inlet, chromatographic column, and detector temperatures are 160, 100, and 160 °C, respectively. Finally, the hydrogen production performance is obtained based on the peak area.

[0071] The test results of the piezoelectric-photocatalytic water splitting for hydrogen production are shown in the appendix Figure 6 , Figure 6 which is a comparative diagram of the piezoelectric-photocatalytic performance of the catalysts obtained in Examples 1-3 of the present invention, the comparative examples, and SrTiO3 powder. It can be seen from the figure that the SrTiO3 / NH2-MIL-125(Ti) composite material has higher piezoelectric-photocatalytic activity than single SrTiO3 and the comparative example NH2-MIL-125(Ti). And when the mass percentage of SrTiO3 is 25%, the piezoelectric-photocatalytic performance of the composite piezoelectric-photocatalyst is the best, and the hydrogen production rate on the best catalyst reaches 1562.27 μmol g -1 h -1 .

Claims

1. A preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst, characterized in that, It includes the following steps: A. Under a water bath environment of 40 - 60 °C, mix tetrabutyl titanate with ethanolamine, then dropwise add sodium hydroxide solution, and then add strontium nitrate solution under vigorous stirring. Transfer the obtained liquid to a polytetrafluoroethylene stainless steel hydrothermal autoclave, and carry out hydrothermal reaction at 180 - 200 °C for 20 - 24 h. After the reaction ends, wash and dry the solid product to obtain SrTiO3 powder; B. Weigh the SrTiO3 powder synthesized in step A according to 12.5 - 37.5% of the mass of NH2-MIL-125(Ti) designed to be generated. Uniformly disperse the SrTiO3 powder in a solvent formed by mixing N,N-dimethylformamide and anhydrous methanol. Take the corresponding amounts of 2-aminoterephthalic acid and tetrabutyl titanate according to the mass of NH2-MIL-125(Ti) designed to be generated, add them in sequence and stir evenly. Transfer the obtained liquid to a polytetrafluoroethylene stainless steel hydrothermal autoclave, and carry out hydrothermal reaction at 150 - 180 °C for 20 - 24 h. After the reaction ends, wash and dry the solid product to obtain SrTiO3 / NH2-MIL-125(Ti) composite piezoelectric-photocatalyst.

2. The preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 1, characterized in that, In step A, the dosage of ethanolamine is 2 - 6 mL of ethanolamine corresponding to every 1 mmol of tetrabutyl titanate, the concentration of sodium hydroxide solution is 2 - 4 mol / L, and the concentration of strontium nitrate solution is 2 - 4 mol / L. The molar ratio of tetrabutyl titanate, sodium hydroxide, and strontium nitrate is 1:(7 - 14):(1 - 2).

3. The preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 1, characterized in that, In step A, carry out hydrothermal reaction at 180 °C for 24 h; in step B, carry out hydrothermal reaction at 150 °C for 24 h.

4. The preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 1, characterized in that, In step A, the process of washing and drying the solid product is to wash it 2 times with anhydrous ethanol and deionized water respectively, and then dry it in a vacuum drying oven at 60 °C for 12 h.

5. The preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 1, characterized in that, In step B, N,N-dimethylformamide and anhydrous methanol are mixed in a volume ratio of 9:1 to form a solvent, and the solvent dosage corresponding to every 0.05 - 0.15 g of SrTiO3 is 40 - 50 mL.

6. The preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 1, characterized in that, In step B, add 2-aminoterephthalic acid and stir for 5 - 10 min, and then add tetrabutyl titanate and stir for 20 - 30 min.

7. The preparation method of SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 1, characterized in that, In step B, the process of washing and drying the solid product is to wash it 3 times with N,N-dimethylformamide and anhydrous methanol respectively, and then dry it in a vacuum drying oven at 60 °C for 12 h.

8. A SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst, characterized in that, Prepared by any one of the preparation methods in the above claims 1 - 7.

9. An application of the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 8, characterized in that, The SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst is applied to the piezoelectric-photocatalytic water splitting for hydrogen production reaction.

10. The application of the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst according to claim 9, characterized in that, The piezoelectric-photocatalytic water splitting for hydrogen production reaction includes the following steps: Disperse the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst in water containing Na2S / Na2SO3 as a sacrificial reagent. For every 1 L of water, use 0.4 - 0.6 g of the SrTiO3 / NH2-MIL-125(Ti) piezoelectric-composite photocatalyst, and carry out hydrolysis for hydrogen production under the conditions of a 300 W xenon lamp as the light source and a ultrasonic generator with a power set to 80 - 100 W as the external force source.

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