Bi-Ti dual-base metal organic framework photocatalytic material, preparation method and application

Abstract

The present invention discloses a metal organic framework photocatalytic material Bi x Ti y ‑BTC and its preparation method and application. The method disclosed in the present invention uses a hydrothermal method to synthesize Ti-doped Bi‑BTC, where Ti replaces the metal nodes in the MOF structure to obtain the metal organic framework material Bi x Ti y ‑BTC, wherein x:y is 1:1‑1:3. The photocatalytic material disclosed in the present invention, the introduction of Ti is beneficial to increase the photocatalytic active sites, and the ability to degrade unsymmetrical dimethylhydrazine is enhanced, especially further in Bi x Ti y The magnetic nano-Fe3O4 is loaded on BTC, which increases the specific surface area and improves the overall valence band position of the material, making it more efficient in utilizing visible light, thereby further promoting the improvement of photocatalytic activity. At the same time, it realizes the convenient separation and recovery of the material, which is conducive to recycling.

Description

Technical Field

[0001] The present invention relates to a metal organic framework material, in particular to a metal organic framework material Bi x Ti y -BTC and its preparation method, as well as the application of the material. Background Art

[0002] Unsymmetrical dimethylhydrazine (UDMH) is a primary fuel for missiles, satellites, spacecraft, and launch vehicles. It boasts high specific impulse and excellent thermal stability. However, UDMH is highly toxic and poses carcinogenic and mutagenic risks to humans. The wastewater generated during its production, transportation, and use also causes severe ecological pollution and poses a serious threat to human health.

[0003] Existing treatment methods for UDMH wastewater primarily include adsorption, ion exchange, membrane permeation, biodegradation, and chemical treatment. Physical treatment methods, such as adsorption and ion exchange, require no chemical agents and offer advantages such as simplicity and practicality. However, the regeneration of adsorbent and ion exchange materials can easily lead to secondary pollution. Biodegradation is environmentally friendly, but microbial survival and reproduction are sensitive to factors such as temperature and pH, placing strict restrictions on its use. High-temperature UDMH wastewater generated during engine testing and rocket ignition requires cooling before it can be used.

[0004] In response to the problems with the above methods, chemical oxidation methods are gaining increasing attention and playing an important role in the treatment of UDMH wastewater. These methods include the Fenton process, photocatalytic oxidation, and supercritical (near) water oxidation. The key to photocatalytic oxidation is the preparation and selection of photocatalytically active substances.

[0005] In recent years, metal-organic framework materials (MOFs) have attracted widespread attention from researchers. These materials are based on the self-assembly of transition metal ions and organic ligands to form periodic network structures, forming different framework structures, which in turn exhibit different optical properties, adsorption properties, electromagnetic properties, etc. They have advantages such as rich topological structures, high specific surface area, low density, high porosity, and structural tailorability. They are widely used in various fields of production and life, such as gas storage, chemical separation, light harvesting, chemical sensing, and photocatalysis. Therefore, the application of MOF materials in the photocatalytic treatment of UDMH wastewater may become a new opportunity to promote the treatment of UDMH wastewater.

[0006] On the other hand, due to the unique 6s 2The partial overlap of electrons with the O 2p orbital is beneficial to reducing the band gap of the semiconductor material and responding to visible light, while the MOF structure can provide more active sites, which helps to improve the photocatalytic activity. Therefore, the bismuth-based MOF photocatalytic material formed by combining Bi elements with MOF materials has great potential for development.

[0007] For example, Chinese patent application CN114835233A uses soluble bismuth salts and non-toxic organic acids to form a porous bismuth-based metal-organic framework material as a chlorine removal agent. The bismuth-based MOF material is added to chlorine-containing wastewater, the pH value and stirring time of the wastewater are adjusted, and the molar ratio of bismuth ions to chloride ions is controlled. After filtration, a qualified filtrate with a low chlorine concentration and a bismuth oxychloride product are obtained.

[0008] For example, prior art discloses Bi-BTC materials made with trimesic acid (H3BTC) as a ligand, which exhibits excellent photocatalytic oxygen production activity. Kong et al. also disclosed the synthesis of a Bi-based MOF material, Bi-TBAPy, using pentafluorobenzoic acid and 2,2-bipyridine as organic ligands, which exhibits excellent photocatalytic degradation activity for the organic dye Congo red. On the other hand, some researchers have used Ti to construct MOFs for the degradation of organic pollutants. The most common material is MIL-125 (Ti), but its wide band gap of 3.69 eV limits its use of visible light.

[0009] However, neither the aforementioned patent application nor research on materials such as Bi-BTC, Bi-TBAPy, and MIL-125(Ti) has demonstrated that MOF materials have good degradation capabilities for UDMH wastewater. Therefore, how to fully utilize the properties of MOFs to develop a metal-organic framework material with good degradation capabilities for UDMH wastewater is an urgent problem to be solved. Summary of the Invention

[0010] In order to solve the above problems, the inventors proposed a method to use a hydrothermal method to dope Ti into Bi-BTC to replace the metal nodes of the MOF structure, and obtain the metal organic framework material Bi x Ti y -BTC method, wherein x:y is 1:1-1:3, the introduction of Ti is beneficial to increase the photocatalytic active sites and enhance the ability to degrade unsymmetrical dimethylhydrazine; further, by x Ti y -BTC is loaded with magnetic Fe3O4, which increases the specific surface area and improves the overall valence band position of the material, making it more efficient in utilizing visible light and further enhancing its photocatalytic activity. At the same time, it enables convenient separation and recovery of the material, making it easier to recycle.

[0011] In a first aspect, the present invention provides a Bi-Ti dual-base metal organic framework photocatalytic material.

[0012] In a second aspect, the present invention provides a method for preparing the above-mentioned Bi-Ti dual-base metal organic framework photocatalytic material.

[0013] In a third aspect, the present invention provides an application of the above-mentioned Bi-Ti double-base metal organic framework photocatalytic material in the photocatalytic degradation of unsymmetrical dimethylhydrazine wastewater.

[0014] Regarding the first aspect, the present invention discloses a Bi-Ti double-base metal organic framework photocatalytic material, whose molecular formula is BixTiy-BTC, wherein the range of x:y is 1:1-1:3, and the material has a lamellar structure and a specific surface area of not less than 16.7m 2 / g. BTC represents the BTC series of MOF materials.

[0015] Furthermore, the material is also compounded with magnetic nano-Fe3O4, namely Bi x Ti y -BTC / Fe3O4.

[0016] Regarding the second aspect, the preparation method of the material is as follows,

[0017] S1, preparing a mixed solution of N,N-dimethylformamide and methanol, adding Bi(NO3)3·5H2O, and stirring to obtain a mixed solution A;

[0018] S2, adding trimesic acid to the mixed solution A, and continuing to stir and mix uniformly to obtain a mixed solution B;

[0019] S3, adding butyl titanate dropwise to the mixed solution B at a molar ratio of Bi to Ti of x:y, and continuing stirring to obtain a mixed solution C;

[0020] S4, transferring the mixed solution C into a polytetrafluoroethylene-lined hydrothermal reactor, heating it to a certain temperature at a certain heating rate, keeping it at that temperature for a period of time, and then slowly cooling it to room temperature;

[0021] S5, filtering the product obtained in step S4, washing it multiple times, and drying it to obtain a powdered solid sample, namely Bi x Ti y -BTC, where x:y is 1:1-1:3 and the material has a lamellar structure.

[0022] Furthermore, in S1, the volume ratio of N,N-dimethylformamide and methanol is 1:1-1:5, and the volume mass ratio of the mixed solution of N,N-dimethylformamide and methanol to Bi(NO3)3·5H2O is 20-50 mL:1-4 g.

[0023] Furthermore, in S1, electromagnetic stirring is used for 10 min to 5 h.

[0024] Furthermore, in S2, the mass ratio of Bi(NO3)3·5H2O to trimesic acid is 1:0.7-1.

[0025] Furthermore, in S4, the conditions for the hydrothermal reaction are to raise the temperature to 120-200°C at a rate of 1-5°C / min, keep the temperature for 40-50 hours, and then slowly cool the furnace to room temperature.

[0026] Furthermore, in S5, the product is washed alternately with N,N-dimethylformamide and methanol three times, and dried at 70-100° C. for 5-20 h in a vacuum drying manner.

[0027] Furthermore, in the above preparation method, magnetic nano-Fe3O4 is also added, wherein the mass ratio of the amount of magnetic nano-Fe3O4 to Bi(NO3)3·5H2O is 1:20-50. Specifically, the magnetic nano-Fe3O4 can be added by any of the following methods:

[0028] (1) In S1, before adding the Bi(NO3)3·5H2O, the magnetic nano-Fe3O4 is added to the mixed solution of N,N-dimethylformamide and methanol;

[0029] (2) In S3, before adding the butyl titanate, the magnetic nano-Fe3O4 is added to the mixed solution B.

[0030] Further preferably, after adding the magnetic nano-Fe3O4, a uniform and stable suspension is obtained by ultrasonic dispersion, thereby providing favorable conditions for subsequent reactions and uniform loading of Fe3O4.

[0031] Regarding the third aspect, the present invention provides an application of the above-mentioned material, that is, applying the Bi-Ti double-base metal organic framework photocatalytic material to the photocatalytic degradation treatment of unsymmetrical dimethylhydrazine wastewater.

[0032] The technical solution of the present invention successfully synthesized Ti-doped Bi-BTC by hydrothermal method, wherein Ti replaced the metal nodes of MOF structure to form a MOF material, namely metal organic framework material Bi x Ti y -BTC, where x:y is 1:1-1:3. In the present invention, the Ti 3d orbital and the O 2p orbital hybridize to form a new valence band top, thereby regulating the material band gap structure; at the same time, a small amount of Ti 3+ Defects can serve as capture traps for photogenerated electrons, which is beneficial to improving the separation efficiency of photogenerated electron-hole pairs.

[0033] According to the technical solution of the present invention, as the amount of Ti doping increases, the specific surface area of the material gradually increases, the spatial structure of the material becomes richer, and the introduction of Ti is conducive to increasing the photocatalytic active sites. After research, it was found that when the Bi / Ti molar ratio is 1:1-1:3, that is, when the composition of the metal organic framework material is between Bi1Ti1-BTC and Bi1Ti3-BTC, its performance is optimal and the photoresponse current density is high. A Bi / Ti molar ratio that is too high or too low will lead to a decrease in photocatalytic activity. The materials with the above ratios were tested and the degradation rates of UDMH wastewater in 240 minutes were 97.02% and 99.47%, which are much higher than the degradation rates of Bi-BTC, Bi3Ti1-BTC and Ti-BTC in 240 minutes for UDMH wastewater. And from the perspective of particle size, the incorporation of Ti plays a role in dispersing particles and preventing accumulation.

[0034] The preferred technical solution of the present invention is to further x Ti y -BTC loaded with magnetic nano-Fe3O4, nano-Fe3O4 can also prevent Bi x Ti y -BTC accumulation and agglomeration, thereby increasing the specific surface area; since the valence band of Fe3O4 is higher than that of Bi x Ti y -BTC helps improve the overall valence band position of the material, enabling greater utilization of visible light and thus enhancing photocatalytic activity. Test results show that Bi1Ti3-BTC / Fe3O4 achieves a 99.63% degradation rate of UDMH wastewater in 240 minutes, significantly higher than Bi1Ti1-BTC and Bi1Ti3-BTC. Furthermore, the loading of magnetic Fe3O4 facilitates the separation and recovery of the material, facilitating recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The SEM images of the samples prepared in Examples 1-2 and Comparative Examples 1-3 are shown; Figure 1 (a) is the SEM image of the sample prepared in Comparative Example 1, Figure 1 (b) is the SEM image of the sample prepared in Comparative Example 2, Figure 1 (c) is the SEM image of the sample prepared in Example 1. Figure 1 (d) is the SEM image of the sample prepared in Example 2. Figure 1 (e) is the SEM image of the sample prepared in Comparative Example 3;

[0036] Figure 2 This is the SEM image of the sample prepared in Example 3;

[0037] Figure 3The XRD patterns of the samples prepared in Examples 1-2 and Comparative Examples 1-3 are shown;

[0038] Figure 4 This is the XRD pattern of the sample prepared in Example 3;

[0039] Figure 5 The adsorption-desorption isotherm curves and pore size distribution diagrams of the samples prepared in Examples 1-2 and Comparative Examples 1-3;

[0040] Figure 6 UV-vis absorption spectra of the materials obtained in Examples 1-2 and Comparative Examples 1-3;

[0041] Figure 7 This is a graph showing the degradation effects of the samples prepared in Examples 1-3 and Comparative Examples 1-3 on UDMH wastewater. DETAILED DESCRIPTION

[0042] In order to better explain the present invention, the present invention is explained and illustrated through the following specific embodiments.

[0043] Example 1

[0044] A method for preparing a Bi-Ti bimetallic metal organic framework photocatalytic material Bi1Ti1-BTC comprises the following steps:

[0045] S1. Prepare 27 mL of a mixed solution of N,N-dimethylformamide (DMF) and methanol (MeOH) in a volume ratio of 1:3, add 1.940 g of Bi(NO3)3·5H2O, and stir under electromagnetic stirring for 30 min to obtain a mixed solution A;

[0046] S2, adding 1.576 g of trimesic acid (H3BTC) to the mixed solution A, and continuing to stir and mix uniformly to obtain a mixed solution B;

[0047] S3, adding butyl titanate (TBOT) dropwise to the mixed solution B at a molar ratio of Bi to Ti of 1:1, and continuing stirring for 30 min to obtain a mixed solution C;

[0048] S4, transfer the mixed solution C into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, heat it to 150°C at a rate of 2°C / min, keep it at that temperature for 48 h, and then slowly cool it to room temperature in the furnace;

[0049] S5. Filter the product obtained in step S4, wash it three times with N,N-dimethylformamide (DMF) and methanol (MeOH) respectively, and dry it in vacuum at 80° C. for 12 h to obtain a powdered solid sample, which is the Bi-Ti bimetallic metal organic framework photocatalytic material Bi1Ti1-BTC.

[0050] Example 2

[0051] A method for preparing a Bi-Ti bimetallic organic framework photocatalytic material Bi1Ti3-BTC comprises the following steps:

[0052] S1. Prepare 50 mL of a mixed solution of N,N-dimethylformamide (DMF) and methanol (MeOH) in a volume ratio of 1:4, add 2.100 g of Bi(NO3)3·5H2O, and stir under electromagnetic stirring for 1 h to obtain a mixed solution A;

[0053] S2, adding 2.100 g of trimesic acid (H3BTC) to the mixed solution A, and continuing to stir and mix uniformly to obtain a mixed solution B;

[0054] S3, adding butyl titanate (TBOT) dropwise to the mixed solution B at a molar ratio of Bi to Ti of 1:3, and continuing stirring for 30 min to obtain a mixed solution C;

[0055] S4, transfer the mixed solution C into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, heat it to 200°C at a rate of 5°C / min, keep it warm for 40 hours, and then slowly cool it to room temperature in the furnace;

[0056] S5. Filter the product obtained in step S4, wash it three times with N,N-dimethylformamide (DMF) and methanol (MeOH), and dry it in vacuo at 70° C. for 18 h to obtain a powdered solid sample, which is recorded as Bi1Ti3-BTC.

[0057] Example 3

[0058] A method for preparing a Bi-Ti dual-base metal organic framework photocatalytic material Bi1Ti3-BTC / Fe3O4 comprises the following steps:

[0059] S1. Prepare 40 mL of a mixed solution of N,N-dimethylformamide (DMF) and methanol (MeOH) in a volume ratio of 1:1. Add 50 mg of magnetic nano-Fe3O4 powder to the mixed solution and disperse it by ultrasonication to obtain a stable and uniform suspension. Then, add 1.940 g of Bi(NO3)3·5H2O and stir the mixture by electromagnetic stirring for 30 min to obtain a mixed solution A.

[0060] S2, adding 1.576 g of trimesic acid (H3BTC) to the mixed solution A, and continuing to stir and mix uniformly to obtain a mixed solution B;

[0061] S3, adding butyl titanate (TBOT) dropwise to the mixed solution B at a molar ratio of Bi to Ti of 1:3, and continuing stirring for 30 min to obtain a mixed solution C;

[0062] S4, transfer the mixed solution C into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, heat it to 120°C at a rate of 2°C / min, keep it at that temperature for 50 h, and then slowly cool it to room temperature;

[0063] S5. Filter the product obtained in step S4, wash it three times with N,N-dimethylformamide (DMF) and methanol (MeOH), and dry it in vacuo at 80°C for 12 h to obtain a powdered solid sample, which is recorded as Bi1Ti3-BTC / Fe3O4.

[0064] Comparative Example 1

[0065] A method for preparing a metal-organic framework material Bi-BTC comprises the following steps:

[0066] S1. Prepare 27 mL of a mixed solution of N,N-dimethylformamide (DMF) and methanol (MeOH) in a volume ratio of 1:3, add 1.940 g of Bi(NO3)3·5H2O, and stir under electromagnetic stirring for 30 min to obtain a mixed solution A;

[0067] S2, adding 1.576 g of trimesic acid (H3BTC) to the mixed solution A, and continuing to stir and mix uniformly to obtain a mixed solution B;

[0068] S3, transfer the mixed solution B into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, heat it to 150°C at a rate of 2°C / min, keep it at that temperature for 48 h, and then slowly cool it to room temperature;

[0069] S4, filtering the product obtained in step S3, washing it three times with N,N-dimethylformamide (DMF) and methanol (MeOH), respectively, and vacuum drying it at 80° C. for 12 h to obtain a powdered solid sample, which is recorded as a metal-organic framework material Bi-BTC.

[0070] Comparative Example 2

[0071] A method for preparing a metal-organic framework material Bi3Ti1-BTC comprises the following steps:

[0072] S1. Prepare 27 mL of a mixed solution of N,N-dimethylformamide (DMF) and methanol (MeOH) in a volume ratio of 1:3, add 1.940 g of Bi(NO3)3·5H2O, and stir under electromagnetic stirring for 30 min to obtain a mixed solution A;

[0073] S2, adding 1.576 g of trimesic acid (H3BTC) to the mixed solution A, and continuing to stir and mix uniformly to obtain a mixed solution B;

[0074] S3, adding butyl titanate dropwise to the mixed solution B at a molar ratio of Bi to Ti of 3:1, and continuing stirring for 30 minutes to obtain a mixed solution C;

[0075] S4, transfer the mixed solution C into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, heat it to 150°C at a rate of 2°C / min, keep it at that temperature for 48 h, and then slowly cool it to room temperature;

[0076] S5. Filter the product obtained in step S4, wash it three times with N,N-dimethylformamide (DMF) and methanol (MeOH), and dry it in vacuo at 80° C. for 12 h to obtain a powdered solid sample, which is recorded as a metal-organic framework material Bi3Ti1-BTC.

[0077] Comparative Example 3

[0078] A method for preparing a metal-organic framework material Ti-BTC comprises the following steps:

[0079] S1. Prepare 27 mL of a mixed solution of N,N-dimethylformamide (DMF) and methanol (MeOH) in a volume ratio of 1:3, add 1.3612 g of butyl titanate, and stir under electromagnetic stirring for 30 min to obtain a mixed solution A;

[0080] S2, adding 1.576 g of trimesic acid (H3BTC) to the mixed solution A, and continuing to stir and mix uniformly to obtain a mixed solution B;

[0081] S3, transfer the mixed solution B into a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, heat it to 150°C at a rate of 2°C / min, keep it at that temperature for 48 h, and then slowly cool it to room temperature;

[0082] S4, filtering the product obtained in step S3, washing it three times with N,N-dimethylformamide (DMF) and methanol (MeOH), respectively, and vacuum drying it at 80° C. for 12 h to obtain a powdered solid sample, which is recorded as the metal-organic framework material Ti-BTC.

[0083] Figure 1 The SEM images of the photocatalytic materials obtained in Examples 1-2 and Comparative Examples 1-3 are shown. Figure 1 (c) It can be seen that the metal organic framework material Bi1Ti1-BTC obtained in Example 1 is a lamellar structure, specifically a lamellar structure formed by the accumulation of primary particles. Figure 1 (d) It can be seen that the metal organic framework material Bi1Ti1-BTC obtained in Example 2 also has a lamellar structure, which is also formed by the accumulation of primary particles. The width of the lamellar structure is about 10 μm. Figure 1(a) shows that the Bi-BTC obtained in Comparative Example 1 is composed of tetrahedral units arranged one by one into a layered structure, and then randomly stacked to form particles; Figure 1 (b) shows that the combination of the tetrahedral units of Bi3Ti1-BTC obtained in Comparative Example 2 becomes more orderly, forming a uniform "X"-shaped structure (about 200 μm × 450 μm); Figure 1 (e) It can be seen that the Ti-BTC in Comparative Example 3 has a flower-like structure.

[0084] In addition, from Figure 1 The particle size shown can be found Figure 1 (a) to Figure 1 (e) The particle size decreases from >100 μm of Bi-BTC to about 10 μm, indicating that the incorporation of Ti plays a role in dispersing particles and preventing accumulation.

[0085] Figure 2 This is the SEM image of Bi1Ti3-BTC / Fe3O4 obtained in Example 3. It can be seen that after Bi1Ti3-BTC in Example 3 is loaded with magnetic nano-Fe3O4, the morphology is basically unchanged and it still has a lamellar stacking structure, but the particle size becomes smaller, about 5 to 10 μm.

[0086] Figure 3 The XRD patterns of the photocatalytic materials obtained in Examples 1-2 and Comparative Examples 1-3 are shown in FIG. x Ti y -BTC, the main characteristic diffraction peaks of Bi-BTC are 9.78°, 10.65°, 11.89°, 12.49°, 14.26°, 17.43°, and 23.87°, which are consistent with the (011), (110), (020), (101), (021), (121), and (221) crystal planes reported in the literature. In addition, the diffraction peaks at 29.32° and 33.86° are also relatively obvious, indicating that Bi-BTC has been successfully synthesized. With the introduction of Ti, the diffraction peaks at 9.78°, 10.65°, 14.26°, and 23.87° gradually weaken, and new diffraction peaks appear at 8.10°, 9.45°, 10.31°, 17.43°, 19.62°, and 21.89°, and they are enhanced with the increase of Ti content. At the same time, it can be found that the diffraction peaks of Bi-BTC at 11.89° and 12.49° are still retained in Ti-BTC, indicating that the original metal node Bi has been successfully replaced by Ti. SEM element mapping and EDS testing also show that in Bi1Ti1-BTC, Ti has successfully replaced Bi and entered the metal node of the MOF material.

[0087] Figure 4 The XRD pattern of the material obtained in Example 3 shows that the diffraction peaks of the product Bi1Ti3-BTC / Fe3O4 prepared in Example 3 at 8.10°, 9.45°, 10.32°, 11.68°, 12.49°, 13.64°, 15.42°, 17.88°, 19.5°, 21.89° and 27.24° are characteristic peaks of Bi1Ti3-BTC; and the characteristic diffraction peaks at 30.06°, 35.46°, 43.04° and 62.50° belong to the (220), (311), (511) and (440) crystal planes of Fe3O4 (PDF#72-2303), respectively, which proves the successful loading of Fe3O4 by Bi1Ti3-BTC.

[0088] like Figure 5 As shown, the specific surface area and pore size data of the materials obtained by BET analysis of Examples 1-2 and Comparative Examples 1-3 are shown. Figure 5 As shown in Figures 5(a) and 5(b), the isotherms of Bi-BTC and Bi3Ti1-BTC show that the amount of gas adsorption is very small in the low-pressure region, while the adsorption increases rapidly in the high-pressure region, which can be attributed to type II and III isotherms. These are mainly surface (non-porous) or macropore adsorption and gas-solid interaction adsorption, with less mesoporous structure. The isotherm of Bi1Ti1-BTC transitions to type IV, with a subtle monolayer adsorption inflection point B, indicating a small amount of microporous adsorption. Figure 5 (d) and 5(e) are the isothermal curves of Bi1Ti3-BTC and Ti-BTC, respectively, which are type IV. There is an obvious B point in the low-pressure area, indicating that the microporous structure has increased significantly; and the adsorption amount of the medium increases with the increase of pressure, indicating that the mesoporous structure has increased significantly. In addition, all BixTiy-BTC hysteresis loops belong to the H3 type, with no adsorption limitation in the high-pressure area, which is given by sheet materials or slit-type pores, which is consistent with the SEM conclusion. Further analysis of the pore size distribution, such as Figure 5 As shown in (f), Bi-BTC and Bi3Ti1-BTC have almost uniform pore sizes, but the amount of medium adsorption is very small, indicating that there are few micropores and mesoporous structures; however, the pore volume of Bi1Ti1-BTC, Bi1Ti3-BTC, and Ti-BTC gradually increases, mainly mesopores, with a small amount of micropores. The main pore size range is 2-50nm, which belongs to mesoporous materials, and the pore volume of Ti-BTC increases significantly. Through testing, the BET specific surface areas of Bi-BTC, Bi3Ti1-BTC, Bi1Ti1-BTC, Bi1Ti3-BTC, and Ti-BTC are 7.74m 2 / g, 8.56m 2 / g, 16.79m 2 / g, 62.42m 2 / g、126m 2 / g, which proves that the introduction of Ti can enrich the pore structure of the material and is positively correlated with the amount of Ti incorporated; the increase in specific surface area may be due to the 4+ Bi 3+ This is caused by an extra bonding site, which in turn increases the supporting organic framework structure.

[0089] Figure 6 The UV-vis absorption spectra of the materials obtained in Examples 1-2 and Comparative Examples 1-3 are shown. As the amount of Ti added increases, Bi x Ti y The response intensity of the -BTC materials to visible light gradually increases, among which Bi1Ti3-BTC has the strongest response to visible light, but the visible light response of Ti-TBC decreases sharply. This is because Ti 4+ The introduction of Ti 3d orbital and O 2p orbital to form a new valence band top, which improves the valence band of the material; at the same time, the Fermi levels of Bi-BTC and Ti-BTC are in different positions, causing their Fermi levels to move towards each other, forming a new Fermi level, thereby reducing the band gap of the material and causing the material's response range to redshift. 4+ When it exists as a single metal node, there is only a single Ti-BTC. At this time, Ti 4s is the main contributor to the conduction band, while the valence band is formed by the hybridization of O 2p and a small amount of N 2p orbitals, which lowers the valence band and thus increases the overall band gap.

[0090] Band gap fitting calculations revealed that the band gap energies of Bi-BTC, Bi3Ti1-BTC, Bi1Ti1-BTC, Bi1Ti3-BTC, and Ti-BTC are 2.57 eV, 2.45 eV, 2.13 eV, 2.07 eV, and 2.60 eV, respectively. This indicates that when the molar ratio of Bi to Ti is 1:3, the band gap is lowest and the utilization rate of visible light is highest. Furthermore, XPS valence band spectra of Bi1Ti3-BTC reveal a VB of 1.98 eV, which in turn infers a corresponding conduction band (CB) of -0.09 eV.

[0091] Wastewater treatment experiments were conducted on the photocatalytic materials obtained in the above examples and comparative examples, as follows.

[0092] Unsymmetrical dimethylhydrazine (UDMH) photocatalytic degradation experiment: The UDMH photocatalytic degradation device is based on the CEL-LAB500E photocatalytic device. A 350W xenon lamp with circulating cooling water is used as the light source. A filter (AM 1.5) is installed around the light source to simulate sunlight. Six 50ml quartz tubes (with covers) are set around the light source. The bottom of each quartz tube is a micro electromagnetic stirring platform. The rotation speed is set to about 60r / min. The light intensity at the quartz light position is adjusted to 100mW / cm2 A screen was placed 2 cm from the bottom of the quartz tube, on which the products (photocatalysts) prepared in Examples 1-3 and Comparative Examples 1-3 were placed. 40 ml of 100 mg / L UDMH wastewater was then added to the test tube, and the photocatalyst concentration was set to 0.5 g / L. Adsorption equilibrium was performed for 30 min under dark conditions, and then a photocatalytic degradation experiment was performed. Samples were taken every 30 min for testing. The results are shown in Figure 2. Figure 7 shown.

[0093] Depend on Figure 7 It can be seen that Bi x Ti y -BTC's photocatalytic degradation effect on UDMH wastewater improves with increasing Ti doping levels. The best degradation effect is achieved when the molar ratio of Ti to Bi is 3:1, followed by a molar ratio of Ti to Bi of 1:1. In addition, Bi1Ti3-BTC loaded with Fe3O4 not only achieves magnetic recovery but also enhances photocatalytic activity. This can be attributed to the following: on the one hand, the loading of Fe3O4 reduces the band gap of the material and enhances the utilization of visible light; on the other hand, nanoparticles of Fe3O4 infiltrate it as a supporting structure during the hydrothermal process, effectively preventing the accumulation of Bi1Ti3-BTC materials and forming a larger specific surface area, which in turn provides more catalytic active sites. The degradation rates of the products prepared in Examples 1-3 for UDMH wastewater within 180 min were 88.86%, 94.95% and 97.58%, which were significantly higher than the degradation rates of 46.45%, 71.56% and 87.53% of the products prepared in Comparative Examples 1-3 for UDMH wastewater within 180 min. The degradation effects of the products prepared in Examples 1-3 (Examples 1-3 correspond to 97.02%, 99.47% and 99.63%, respectively) were significantly higher than the degradation rates of the products prepared in Comparative Examples 1-3 for UDMH wastewater within 240 min (Comparative Examples 1-3 correspond to 58.73%, 79.83% and 95.41%, respectively).

[0094] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. Application of a Bi-Ti double-base metal organic framework photocatalytic material in the photocatalytic degradation of unsymmetrical dimethylhydrazine wastewater, characterized in that: The material is also compounded with magnetic nano-Fe3O4, and the molecular formula of the material is Bi x Ti y -BTC / Fe3O4, wherein the range of x:y is 1:1-1:3, the material has a lamellar structure, and the specific surface area is not less than 16.7m 2 / g.

2. The use according to claim 1, characterized in that The preparation method of the Bi-Ti dual-base metal organic framework photocatalytic material comprises the following steps: S1, preparing a mixed solution of N,N-dimethylformamide and methanol, adding Bi(NO3)3·5H2O, and stirring to obtain a mixed solution A; S2, adding trimesic acid to the mixed solution A, stirring to obtain a mixed solution B; S3, adding butyl titanate dropwise to the mixed solution B at a molar ratio of Bi to Ti of x:y, and stirring to obtain a mixed solution C; S4, subjecting the mixed solution C to a hydrothermal reaction, and then cooling it to room temperature; S5, filtering, washing, and drying the product obtained in step S4 to obtain a powdered sample, namely the Bi-Ti dual-base metal-organic framework photocatalytic material; The mass ratio of the Bi(NO3)3·5H2O to the trimesic acid is 1:0.7-1; Magnetic nano-Fe3O4 is also added in the preparation method, and the mass ratio of the magnetic nano-Fe3O4 to Bi(NO3)3·5H2O is 1:20-50. The magnetic nano-Fe3O4 is added according to any of the following methods: (1) in S1, before adding the Bi(NO3)3·5H2O, the magnetic nano-Fe3O4 is added to the mixed solution of N,N-dimethylformamide and methanol; (2) in S3, before adding the butyl titanate, the magnetic nano-Fe3O4 is added to the mixed solution B.

3. The use according to claim 2, characterized in that In S1, the volume ratio of N,N-dimethylformamide and methanol is 1:1-1:5, and the volume mass ratio of the mixed solution of N,N-dimethylformamide and methanol to Bi(NO3)3·5H2O is 20-50 mL:1-4 g.

4. The use according to claim 2, characterized in that In S4, the conditions for the hydrothermal reaction are to raise the temperature to 120-200°C at a rate of 1-5°C / min, keep the temperature for 40-50 hours, and then slowly cool the furnace to room temperature.

5. The use according to claim 2, characterized in that In S5, the washing is performed by washing with N,N-dimethylformamide and methanol alternately for 3 times, and the drying is performed by vacuum drying at 70-100° C. for 5-20 h.

6. The use according to claim 2, characterized in that After adding the magnetic nano-Fe3O4, a uniform and stable suspension is obtained by ultrasonic dispersion.

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