Nano composite material with photocatalytic memory effect as well as preparation method and application of nano composite material

Abstract

The invention provides a nano composite material with a photocatalytic memory effect and a preparation method of the nano composite material. The invention also provides an application of the nano composite material with the photocatalytic memory effect in photocatalytic degradation of glyphosate. According to the nano composite material with the photocatalytic memory effect, through the synergistic effect of the NaBiO3 / BiO2-x heterojunction and the UiO-66, the nano composite material has the photocatalytic memory effect and efficient adsorption capacity, and the dark-state glyphosate degradation rate is remarkably improved compared with that of a traditional material; zr6O4 (OH) 4 clusters in a UiO-66 skeleton provide a high specific surface area and strong enrichment sites, so that dual-function coupling of selective adsorption and catalytic degradation of glyphosate is realized; the prepared nano composite material can realize continuous catalytic degradation under a non-illumination condition through released and stored photo-induced electrons and specific adsorption of a Zr-O site of UiO-66 and a glyphosate phosphonic acid group in a dark environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic nanomaterials, and particularly relates to a nanocomposite with a photocatalytic memory effect, a preparation method thereof, and an application thereof. Background Art

[0002] With the intensive development of modern agriculture, the problem of residues of organophosphorus herbicides represented by glyphosate in soil and water bodies has become increasingly serious. Due to its high chemical stability and strong water solubility, glyphosate can enter rivers and lakes through surface runoff, not only threatening the balance of the aquatic ecosystem, but its metabolite aminomethylphosphonic acid has also been proven to have neurotoxicity and carcinogenic risks. The traditional physical adsorption method has the defects of low treatment efficiency and easy generation of secondary pollution, while the photocatalytic technology has become a research hotspot for water purification due to its advantages of being green and pollution-free and being able to mineralize organic substances.

[0003] Although wide-bandgap semiconductors represented by TiO2 have the advantages of low cost and non-toxicity, their inherent defects such as narrow light response range and high recombination rate of photo-generated carriers severely restrict the catalytic efficiency. In addition, conventional photocatalytic materials highly rely on continuous light illumination for energy supply, and their activity rapidly decays under the condition of no light source, resulting in bottlenecks such as nighttime catalytic interruption and poor adaptability to complex water environments in practical applications. Summary of the Invention

[0004] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide a nanocomposite with a photocatalytic memory effect, a preparation method thereof, and an application thereof. The prepared photocatalytic nanocomposite can not only efficiently adsorb glyphosate in water, but also has an obvious photocatalytic memory effect, and its performance of degrading glyphosate in the dark after illumination is better than that of the nanocomposite of TiO2 loaded on UiO-66.

[0005] To achieve the above purpose, the solutions adopted by the present invention are as follows:

[0006] In the first aspect, the present invention provides a nanocomposite with a photocatalytic memory effect, which is a nanocomposite in which NaBiO3 / BiO 2-x heterostructure nanoparticles are loaded on a zirconium-based metal-organic framework UiO-66; the UiO-66 uses a Zr6O4(OH)4 cluster as a structural node, and the NaBiO3 / BiO 2-x mass ratio of the heterostructure nanoparticles to the zirconium-based metal-organic framework UiO-66 is (1-3):(0.5-2).

[0007] Preferably, the NaBiO3 / BiO 2-xHeterostructured nanoparticles are in-situ grown on the surface of the zirconium-based metal-organic framework UiO-66 by a hydrothermal method to form a three-dimensional porous composite structure. The specific surface area of the obtained nanocomposite is 500 - 800 m 2 / g, and the pore size distribution is 1 - 5 nm.

[0008] Preferably, the surface of the nanocomposite is further modified with trisodium citrate.

[0009] In a second aspect, the present invention also provides a method for preparing the above-mentioned nanocomposite with a photocatalytic memory effect, including the following steps:

[0010] Step S1, dissolve NaBiO3 powder in an NaOH solution, carry out a hydrothermal reaction at a temperature of 160 - 200 °C for 4 - 8 hours, wash and dry to obtain NaBiO3 / BiO 2-x heterostructured nanoparticles;

[0011] Step S2, dissolve ZrCl4 and terephthalic acid in a mixed solvent of N,N-dimethylformamide and glacial acetic acid, carry out a solvothermal reaction at a temperature of 100 - 130 °C for 12 - 24 hours, wash and dry to obtain the zirconium-based metal-organic framework UiO-66;

[0012] Step S3, disperse the NaBiO3 / BiO 2-x heterostructured nanoparticles obtained in Step S1, the zirconium-based metal-organic framework UiO-66 obtained in Step S2, and trisodium citrate in deionized water, carry out a secondary hydrothermal reaction at a temperature of 100 - 150 °C for 2 - 4 hours, wash and dry to obtain the said nanocomposite.

[0013] Preferably, in Step S1, the mass concentration of the NaOH solution is 2.0 - 3.0 M, the solid-liquid ratio of the NaBiO3 powder to the NaOH solution is (0.5 - 2.0) g : (50 - 100) mL, ultrasonically stir for 30 - 90 minutes. After the hydrothermal reaction, centrifuge and wash, and then carry out vacuum drying at 60 - 100 °C for 6 - 12 hours.

[0014] Preferably, in Step S2, the molar ratio of ZrCl4 to terephthalic acid is (0.8 - 1.2) : 1. After the solvothermal reaction, wash 3 - 5 times with N,N-dimethylformamide and methanol in sequence.

[0015] Preferably, in Step S3, the mass ratio of the NaBiO3 / BiO 2-x heterostructured nanoparticles, the zirconium-based metal-organic framework UiO-66, and trisodium citrate is (1 - 3) : (0.5 - 2) : (0.1 - 0.5). After the secondary hydrothermal reaction, the drying temperature is 40 - 60 °C, and the drying time is 6 - 14 hours.

[0016] In the third aspect, the present invention also provides an application of the above-mentioned nanocomposite with photocatalytic memory effect in photocatalytic degradation of glyphosate.

[0017] Preferably, it includes the following steps:

[0018] Step (1), adding the above-mentioned nanocomposite into the water body containing glyphosate;

[0019] Step (2), pre-treating under visible light;

[0020] Step (3), after turning off the light source, continuously reacting for 30 - 180 minutes in a dark environment at 25 - 35 °C;

[0021] Step (4), detecting the residual concentration of glyphosate after centrifugal separation, and the degradation rate of glyphosate ≥ 90%.

[0022] Preferably, in step (1), the dosage of the above-mentioned nanocomposite is 0.5 - 2.0 g / L, and the concentration of glyphosate in the water body is 10 - 50 mg / L; in step (2), a xenon lamp light source with a 420 nm cut-off filter is used, and the light intensity is 200 - 500 W / m 2 , the pre-treatment time is 30 - 60 minutes; in step (3), the continuous reaction time is 90 - 150 minutes; in step (4), the degradation rate of glyphosate ≥ 95%, and the detection method for the residual concentration of glyphosate is: after the residual glyphosate is subjected to nitrosation treatment, the concentration of glyphosate is quantitatively detected by a spectrophotometer at a wavelength of 242 nm.

[0023] Preferably, in the dark environment, the above-mentioned nanocomposite realizes continuous catalytic degradation under the condition of no light by releasing the stored photo-generated electrons and specifically adsorbing the phosphonic acid group of glyphosate through the Zr - O sites of UiO - 66.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The prepared nanocomposite with photocatalytic memory effect of the present invention, through the synergistic effect of the NaBiO3 / BiO2 - x heterojunction and UiO - 66, has both photocatalytic memory effect and high adsorption capacity, and the dark-state glyphosate degradation rate is significantly improved compared with traditional materials; the Zr6O4(OH)4 cluster in the UiO - 66 framework provides a high specific surface area and strong enrichment sites, realizing the dual-functional coupling of selective adsorption and catalytic degradation of glyphosate; the prepared nanocomposite can realize continuous catalytic degradation under the condition of no light by releasing the stored photo-generated electrons and specifically adsorbing the phosphonic acid group of glyphosate through the Zr - O sites of UiO - 66. Description of the Drawings

[0026] Figure 1 TEM image of the nanocomposite with photocatalytic memory effect prepared in Example 1 of the present invention.

[0027] Figure 2 XPS image of the nanocomposite with photocatalytic memory effect prepared in Example 1 of the present invention.

[0028] Figure 3 Comparison of the degradation performance of glyphosate wastewater (concentration 50 mg / L) after the nanocomposite with photocatalytic memory effect prepared in Example 1 of the present invention was pre-irradiated with visible light for 60 minutes and stored in a dark environment for 0, 1, 2, and 5 hours respectively. Detailed implementation manners

[0029] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific implementation manners.

[0030] The present invention provides a nanocomposite with photocatalytic memory effect, which is a nanocomposite in which NaBiO3 / BiO 2-x heterostructured nanoparticles are loaded on zirconium-based metal-organic framework UiO-66.

[0031] In the nanocomposite with photocatalytic memory effect provided by the present invention, the zirconium-based metal-organic framework UiO-66 (UiO = University of Oslo) adopted in the present invention is a rigid metal-organic framework (MOFs) material with a three-dimensional ordered pore structure self-assembled with zirconium (Zr) as the metal center and terephthalic acid (H2BDC) as the organic ligand. It has high hydrothermal, chemical, and mechanical stability, and is formed by connecting each Zr6O4(OH)4 cluster with 12 terephthalic acid (H2BDC) ligands. It has the highest coordination number of organic ligands to metal clusters in MOFs materials. Compared with traditional porous materials such as zeolite molecular sieves and activated carbon, it has an ultra-high specific surface area (can exceed 7000 m 2 / g) and a permanent porosity (up to 0.9 cm 3 / g). Its unique octahedral structure and Zr6O4(OH)4 clusters can provide sites for the loading of nanoparticles as a carrier. The rich ligand structure and large specific surface area can also enhance the adsorption and ion exchange performance of pollutants, and form strong chemical adsorption with the glyphosate phosphate group in water.

[0032] In the nano-composite material with photocatalytic memory effect provided by the present invention, the zirconium-based metal-organic framework UiO-66 used in the present invention is usually prepared by a solvothermal method. The present invention provides a preparation method of the zirconium-based metal-organic framework UiO-66, which includes the following steps: dissolving zirconium source ZrCl4 and ligand terephthalic acid (H2BDC) in a mixed solvent of N,N-dimethylformamide and glacial acetic acid, carrying out a solvothermal reaction at a temperature of 100-130 °C for 12-24 hours, and obtaining the product after washing and drying.

[0033] In the preparation process of the above-mentioned zirconium-based metal-organic framework UiO-66 provided by the present invention, glacial acetic acid is used as a regulator to synthesize UiO-66, and UiO-66 with ligand defects is obtained. That is, in the obtained UiO-66, each Zr6O4(OH)4 cluster is connected to less than 12 terephthalic acid (H2BDC) ligands, and the regulator molecules occupy the remaining ligand sites. The increase in defects improves its specific surface area and pore volume, and forms a capping effect, thereby improving the loading rate of metal nanoparticles as carriers and enhancing the adsorption capacity for pollutants.

[0034] In the preparation process of the above-mentioned zirconium-based metal-organic framework UiO-66 provided by the present invention, the molar ratio of ZrCl4 to terephthalic acid is controlled to be (0.8-1.2):1. Within this molar ratio range, UiO-66 with appropriate ligand defects can be obtained. After the solvothermal reaction, it is washed with N,N-dimethylformamide and methanol 3-5 times in sequence.

[0035] In the nano-composite material with photocatalytic memory effect provided by the present invention, the NaBiO3 / BiO 2-x heterostructure nanoparticles are composed of two different bismuth-containing semiconductor materials, NaBiO3 and BiO 2-x The bismuth-containing compounds have excellent visible light absorption ability and high organic matter degradation ability due to their unique electronic structures, that is, they have a photocatalytic effect capable of decomposing pollutants under light illumination. BiO 2-x has been proven to be able to directly mineralize organic pollutants into small molecule substances such as CO2 and H2O without the generation of intermediate products. Moreover, the relatively high photocatalytic activity of BiO 2-x is mainly attributed to its relatively narrow bandgap, which greatly increases the absorption of visible light. At the same time, the two different bismuth-containing compounds with heterostructure have characteristics different from single bismuth-containing compounds, and can effectively promote the separation of photo-generated carriers through the built-in electric field, improving the photocatalytic effect. Moreover, in the NaBiO3 / BiO 2-x heterojunction material, due to the valence state change of bismuth ions, light energy storage can be realized, endowing the material with a "photocatalytic memory effect" of continuously releasing electrons to drive the degradation of organic pollutants such as glyphosate under dark conditions.

[0036] In the nanocomposite material with photocatalytic memory effect provided by the present invention, the NaBiO3 / BiO 2-x The heterogeneous structure nanoparticles are prepared by the following method: dissolving NaBiO3 powder in NaOH solution, hydrothermally reacting at 160-200°C for 4-8 hours, washing and drying. In the preparation method, the mass concentration of the NaOH solution is 2.0-3.0M, the solid-liquid ratio of NaBiO3 powder to the NaOH solution is (0.5-2.0)g: (50-100)mL, ultrasonic stirring is performed for 30-90 minutes, and after the hydrothermal reaction, centrifugal washing is performed and vacuum drying is performed at 60-100°C for 6-12 hours. Within this ratio range, well-crystallized NaBiO3 / BiO with a nanosheet structure can be generated. 2-x Heterostructured nanoparticles.

[0037] In the nanocomposite material with photocatalytic memory effect provided by the present invention, NaBiO3 / BiO 2-x The heterogeneous structure nanoparticles are loaded on the zirconium-based metal organic framework UiO-66, which not only utilizes the excellent visible light absorption ability and high organic degradation ability of the NaBiO3 / BiO2-x heterojunction, but also realizes light energy storage through the change of bismuth ion valence state, giving the material a "photocatalytic memory effect" of continuous release of electrons to drive glyphosate degradation under dark conditions. At the same time, the Zr6O4(OH)4 clusters in the UiO-66 framework provide high specific surface area and specific adsorption sites, forming strong chemical adsorption with glyphosate phosphonic acid groups. 2-x The nanocomposite material obtained by loading heterostructured nanoparticles on the zirconium-based metal organic framework UiO-66 not only has the photocatalytic memory effect and high-efficiency adsorption capacity through the synergistic effect of NaBiO3 / BiO2-x heterojunction and UiO-66, but also significantly improves the dark-state glyphosate degradation rate compared with traditional materials.

[0038] In the nanocomposite material with photocatalytic memory effect provided by the present invention, NaBiO3 / BiO 2-x The heterogeneous structure nanoparticles are loaded on the zirconium-based metal organic framework UiO-66, and the loading method is a conventional hydrothermal preparation method. 2-x The heterogeneous structure nanoparticles are in situ grown on the surface of the zirconium-based metal organic framework UiO-66 by a hydrothermal method, and the surface of the formed three-dimensional porous composite material is modified by trisodium citrate, which specifically comprises the following steps: the NaBiO3 / BiO 2-xHeterostructured nanoparticles, zirconium-based metal-organic framework UiO-66 obtained by the above method, and trisodium citrate (C6H5Na3O7·2H2O) are dispersed in deionized water, and a secondary hydrothermal reaction is carried out at a temperature of 100-150 °C for 2-4 hours. After washing and drying, the nanocomposite material of the present invention is obtained. The three-dimensional porous composite material modified by trisodium citrate has enhanced stability, increased active sites for reaction, smaller particle size and uniform morphology, and a small and dense pore structure, which can increase the specific surface area of the three-dimensional porous composite material. The specific surface area of the finally obtained nanocomposite material is 500-800 m 2 / g, and the pore size distribution is 1-5 nm.

[0039] According to the method of the present invention, the nanocomposite material with a photocatalytic memory effect as described above is applied to the photocatalytic degradation of glyphosate. It is confirmed by the examples of the present invention that the nanocomposite material prepared by the present invention not only has a photocatalytic effect capable of decomposing pollutants under light irradiation, but also can specifically adsorb glyphosate phosphonic acid groups by releasing stored photogenerated electrons and Zr-O sites of UiO-66 in the dark environment, realizing continuous catalytic degradation under dark conditions. The mechanism may be as follows: The NaBiO3 / BiO2-x heterojunction in the nanocomposite material stores light energy through the valence state change of bismuth ions, endowing the composite material with a "photocatalytic memory effect" of continuously releasing electrons to drive the degradation of glyphosate under dark conditions. At the same time, the Zr6O4(OH)4 cluster in the UiO-66 framework provides a high specific surface area and specific adsorption sites, forming a strong chemical adsorption with the glyphosate phosphonic acid group. The present invention solves the technical bottleneck of the interruption of the activity of traditional photocatalytic materials at night through a photocatalysis-adsorption bifunctional coupling mechanism, and has significant application value in complex water environments.

[0040] The following examples are used to further illustrate the present invention. The purpose is to better understand the content of the present invention and reflect the substantial characteristics of the present invention. Therefore, the examples given should not be regarded as limiting the protection scope of the present invention. It is also specifically pointed out that the specific experimental methods and equipment involved in the examples are conventional methods or implemented according to the conditions recommended by the manufacturer's instructions without special instructions, and the reagents involved are commercially available without special instructions.

[0041] Example 1:

[0042] This example provides a nanocomposite material with a photocatalytic memory effect, and its preparation method includes the following steps:

[0043] S1. Add 0.8 g of NaBiO3 powder to 50 mL of NaOH solution with a concentration of 2.0 M, and ultrasonically stir for 90 minutes to form a uniform suspension;

[0044] S2. Transfer the suspension to a polytetrafluoroethylene-lined autoclave and react at 160 °C for 8 hours, then cool naturally to obtain black reactant one.

[0045] S3. Centrifuge and separate reactant one, then wash it with deionized water until neutral, and dry it in vacuum at 60 °C for 12 hours to obtain the NaBiO3 / BiO2-x composite material.

[0046] S4. Dissolve 0.8 mmol of ZrCl4 and 1.0 mmol of terephthalic acid in a mixed solvent of 20 mL of DMF and 1 mL of glacial acetic acid, and ultrasonically treat for 40 minutes to obtain a precursor solution.

[0047] S5. React the precursor solution at 100 °C for 24 hours, wash it 3 times with DMF and methanol in sequence, and dry it in vacuum at 40 °C for 10 hours to prepare the UiO-66 white powder.

[0048] S6. Weigh NaBiO3 / BiO2-x, UiO-66 and trisodium citrate according to the mass ratio of 1:0.5:0.1, disperse them in 50 mL of deionized water, and ultrasonically stir for 60 minutes.

[0049] S7. React the mixed solution at 100 °C for 4 hours, centrifuge it, wash it 5 times with methanol and deionized water, and dry it in vacuum at 60 °C for 8 hours to obtain the final nanocomposite material.

[0050] Pollutant removal application:

[0051] Take 100 mL of simulated wastewater containing glyphosate (50 mg / L), add 0.1 g of the nanocomposite material prepared in Example 1, transfer it to a xenon lamp photocatalytic reactor equipped with a 420 nm cut-off filter (light source power 300 W, light intensity 400 W / m 2 ), adjust the solution temperature to 30 °C, and turn on the magnetic stirrer (rotation speed 200 r / min). Turn on the light source for visible light irradiation treatment for 60 minutes, then turn off the light source and continue to react for 120 minutes under dark conditions. After the reaction solution is centrifuged (8000 rpm, 15 minutes), take the supernatant, add 1.0 mmol / L nitrosation reagent, vortex and mix for 5 minutes, filter through a 0.22 μm organic filter membrane. After the residual glyphosate is treated with the nitrosation reagent, the absorbance is measured at a wavelength of 242 nm using a UV-2600 type spectrophotometer, and the glyphosate degradation rate is measured to be 96.7%.

[0052] Figure 1 Figure 27 is the transmission electron microscope (TEM) image of the zirconium-based metal-organic framework supported NaBiO3 / BiO2-x nanocomposite material prepared in Example 1. As Figure 1 can be seen, the surface of the nanocomposite material is rough, indicating that numerous NaBiO3 / BiO2-x nanoparticles are loaded on UiO-66.

[0053] Figure 2 For XPS analysis of the elements on its surface, the characteristic peaks corresponding to Bi 4f, Bi 4d, Fe 2p, Zr 3d and O 1s can be clearly found, indicating that the material synthesized in Example 1 contains the main elements composed of NaBiO3 / BiO2-x and UiO-66.

[0054] Figure 3 The comparison of the degradation and removal rates of glyphosate (50 mg / L) wastewater after the material prepared in Example 1 was irradiated with visible light for 60 minutes and stored in the dark for 0, 1, 2, and 5 hours respectively. As can be seen from the figure, even if the composite material is stored in the dark for 5 hours after pre-illumination, 69.1% of glyphosate can still be degraded in the dark, indicating that the material has a significant "photocatalytic memory effect" after illumination.

[0055] Example 2:

[0056] This example provides a nanocomposite material with a photocatalytic memory effect, and its preparation method includes the following steps:

[0057] S1. Add 1.5 g of NaBiO3 powder to 80 mL of NaOH solution with a concentration of 2.8 M, and ultrasonically stir for 45 minutes to form a uniform suspension;

[0058] S2. Transfer the suspension to a polytetrafluoroethylene-lined autoclave, react at 190 °C for 5 hours, and naturally cool to obtain a dark brown reactant one;

[0059] S3. Centrifuge and separate reactant one, wash it with deionized water until neutral, and vacuum dry at 90 °C for 8 hours to obtain the NaBiO3 / BiO 2-x composite material;

[0060] S4. Dissolve 1.0 mmol of ZrCl4 and 1.0 mmol of terephthalic acid in a mixed solvent of 35 mL of DMF and 2 mL of glacial acetic acid, and ultrasonically treat for 25 minutes to obtain a precursor solution;

[0061] S5. React the precursor solution at 120 °C for 18 hours, wash it 5 times with DMF and methanol in turn, and vacuum dry at 50 °C for 9 hours to obtain the UiO-66 white powder;

[0062] S6. Weigh NaBiO3 / BiO 2-x 、UiO-66 and trisodium citrate according to the mass ratio of 2:1:0.3, disperse them in 80 mL of deionized water, and ultrasonically stir for 40 minutes;

[0063] S7. The mixed solution is reacted at 130 °C for 3 hours, washed 5 times with methanol and deionized water after centrifugation, and vacuum dried at 50 °C for 10 hours to obtain the final nanocomposite.

[0064] Pollutant removal application:

[0065] Take 100 mL of simulated wastewater containing glyphosate (50 mg / L), add 0.1 g of the nanocomposite prepared in Example 2, and transfer it to a xenon lamp photocatalytic reactor equipped with a 420 nm cut-off filter (light source power 350 W, light intensity 450 W / m 2 ), adjust the solution temperature to 30 °C, and turn on the magnetic stirrer (rotation speed 200 r / min). Turn on the light source for visible light irradiation treatment for 60 minutes, then turn off the light source and continue to react for 120 minutes under dark conditions. After the reaction solution is centrifuged (8000 rpm, 15 minutes), take the supernatant, add 1.0 mmol / L nitrosation reagent, vortex mix for 5 minutes, filter through a 0.22 μm organic filter membrane. After the residual glyphosate is treated with the nitrosation reagent, the absorbance is measured at a wavelength of 242 nm using a UV-2600 type spectrophotometer, and the glyphosate degradation rate is measured to be 98.1%.

[0066] Example 3:

[0067] This example provides a nanocomposite with a photocatalytic memory effect, and its preparation method includes the following steps:

[0068] S1. Add 2.0 g of NaBiO3 powder to 100 mL of NaOH solution with a concentration of 3.0 M, and ultrasonically stir for 30 minutes to form a homogeneous suspension;

[0069] S2. Transfer the suspension to a polytetrafluoroethylene-lined autoclave, react at 200 °C for 4 hours, and naturally cool to obtain the first brown-black reactant;

[0070] S3. Centrifuge and separate the first reactant, wash it with deionized water until neutral, and vacuum dry at 100 °C for 6 hours to obtain the NaBiO3 / BiO2-x composite;

[0071] S4. Dissolve 1.2 mmol of ZrCl4 and 1.0 mmol of terephthalic acid in a mixed solvent of 50 mL of DMF and 3 mL of glacial acetic acid, and ultrasonically treat for 20 minutes to obtain a precursor solution;

[0072] S5. The precursor solution is reacted at 130 °C for 12 hours, washed 4 times with DMF and methanol in sequence, and vacuum dried at 60 °C for 8 hours to obtain the UiO-66 white powder;

[0073] S6. Weigh NaBiO3 / BiO2-x, UiO-66 and trisodium citrate according to the mass ratio of 3:2:0.5, disperse them in 100 mL of deionized water, and ultrasonically stir for 30 minutes;

[0074] S7. React the mixed solution at 150 °C for 2 hours, wash it 5 times with methanol and deionized water after centrifugation, and vacuum dry it at 40 °C for 12 hours to obtain the final nanocomposite.

[0075] Pollutant removal application:

[0076] Take 200 mL of simulated wastewater containing glyphosate (60 mg / L), add 0.2 g of the nanocomposite prepared in Example 3, transfer it to a xenon lamp photocatalytic reactor equipped with a 420 nm cut-off filter (light source power 400 W, light intensity 500 W / m 2 ), adjust the solution temperature to 32 °C, and turn on the magnetic stirrer (rotation speed 300 r / min). Turn on the light source for visible light irradiation treatment for 90 minutes, then turn off the light source and continue to react for 180 minutes under dark conditions. After centrifugal separation of the reaction solution (10,000 rpm, 25 minutes), take the supernatant, add 1.5 mmol / L nitrosation reagent, vortex mix for 10 minutes, filter through a 0.22 μm organic filter membrane. After the residual glyphosate is treated with the nitrosation reagent, the absorbance is measured at a wavelength of 242 nm using a UV-2600 type spectrophotometer, and the glyphosate degradation rate is measured to be 95.3%.

[0077] Comparative Example 1:

[0078] S1. Add 1.0 g of commercial TiO2 nanopowder to 75 mL of 2.5 M NaOH solution, and ultrasonically stir for 60 minutes to form a homogeneous suspension;

[0079] S2. Transfer the suspension to a polytetrafluoroethylene-lined autoclave, react at 180 °C for 6 hours, and naturally cool to obtain Reactant 1 (Note: The hydrothermal conditions are the same as those in Example 1, but no Bi-based heterojunction is formed);

[0080] S3. Centrifuge and separate Reactant 1, wash it with deionized water until neutral, and vacuum dry it at 80 °C for 9 hours to obtain TiO2 powder;

[0081] S4 - S7. The subsequent steps are exactly the same as those in Example 1. Compound TiO2, UiO-66 and trisodium citrate according to the mass ratio of 2:1:0.3, and finally prepare TiO2 / UiO-66 nanocomposite.

[0082] Pollutant removal application:

[0083] Take 100 mL of simulated wastewater containing glyphosate (50 mg / L), add 0.1 g of the nanocomposite prepared in Comparative Example 1, transfer it to a xenon lamp photocatalytic reactor equipped with a 420 nm cut-off filter (light source power 300 W, light intensity 400 W / m2), adjust the solution temperature to 30 °C, and turn on the magnetic stirrer (rotation speed 200 r / min). Turn on the light source for visible light irradiation treatment for 60 minutes, then turn off the light source and continue the reaction for 120 minutes under dark conditions. After the reaction solution is centrifuged (8000 rpm, 15 minutes), take the supernatant, add 1.0 mmol / L nitrosation reagent, vortex mix for 5 minutes, filter through a 0.22 μm organic filter membrane. After the residual glyphosate is treated with the nitrosation reagent, the absorbance is measured at a wavelength of 242 nm using a UV-2600 type spectrophotometer, and the glyphosate degradation rate is measured to be 52.8%.

[0084] Comparative Example 2:

[0085] S1. Add 0.8 g of NaBiO3 powder to 50 mL of 2.0 M NaOH solution, and ultrasonically stir for 90 minutes to form a uniform suspension;

[0086] S2. Transfer the suspension to a polytetrafluoroethylene-lined autoclave, react at 160 °C for 8 hours, and naturally cool to obtain black reactant I;

[0087] S3. Centrifuge and separate reactant I, wash it with deionized water until neutral, and vacuum dry at 60 °C for 12 hours to obtain the NaBiO3 / BiO 2-x composite material;

[0088] Pollutant removal application:

[0089] Take 100 mL of simulated wastewater containing glyphosate (50 mg / L), add 0.1 g of the composite material prepared in Comparative Example 2, transfer it to a xenon lamp photocatalytic reactor equipped with a 420 nm cut-off filter (light source power 350 W, light intensity 450 W / m2), adjust the solution temperature to 30 °C, and turn on the magnetic stirrer (rotation speed 200 r / min). Turn on the light source for visible light irradiation treatment for 60 minutes, then turn off the light source and continue the reaction for 120 minutes under dark conditions. After the reaction solution is centrifuged (8000 rpm, 15 minutes), take the supernatant, add 1.0 mmol / L nitrosation reagent, vortex mix for 5 minutes, filter through a 0.22 μm organic filter membrane. After the residual glyphosate is treated with the nitrosation reagent, the absorbance is measured at a wavelength of 242 nm using a UV-2600 type spectrophotometer, and the glyphosate degradation rate is measured to be 76.5%.

[0090] The removal rates of glyphosate by the nanocomposites prepared in Examples 1, 2, and 3 and the products obtained in Comparative Examples 1 and 2 are summarized in Table 1 below.

[0091] Table 1

[0092]

[0093] From the glyphosate removal rates of Example 1 and Comparative Example 1 in Table 1, it can be seen that the photocatalytic nanocomposite of zirconium-based metal-organic framework loaded with NaBiO3 / BiO2-x of the present invention can have a photocatalytic memory effect of releasing electrons in the dark, significantly enhancing its catalytic activity after the end of illumination. At the same time, combined with Figure 3 It also shows that the material synthesized in Example 1 has a significant "photocatalytic memory effect" after illumination.

[0094] From the removal rates of Example 1 and Comparative Example 2 in Table 1, it can be seen that on the basis of Comparative Example 2, the photocatalytic nanocomposite of the present invention uses a NaBiO3 / BiO2-x heterojunction material loaded on a zirconium-based metal-organic framework, which can significantly enhance the adsorption effect of the composite on glyphosate, and the dark-state glyphosate degradation rate is significantly improved, thereby enhancing the efficiency of subsequent photocatalytic oxidation of glyphosate.

[0095] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A nanocomposite material having a photocatalytic memory effect, characterized in that: NaBiO3 / BiO 2-x A nanocomposite material in which heterogeneous structured nanoparticles are loaded on a zirconium-based metal organic framework UiO-66; the UiO-66 has Zr6O4(OH)4 clusters as structural nodes, the NaBiO3 / BiO 2-x The mass ratio of the heterogeneous structure nanoparticles to the zirconium-based metal organic framework UiO-66 is (1-3): (0.5-2).

2. The nanocomposite material with photocatalytic memory effect according to claim 1, characterized in that: The NaBiO3 / BiO 2-x The heterogeneous structure nanoparticles are in situ grown on the surface of the zirconium-based metal organic framework UiO-66 by a hydrothermal method to form a three-dimensional porous composite structure. The specific surface area of ​​the obtained nanocomposite material is 500-800m 2 / g, and the pore size distribution is 1-5nm.

3. The nanocomposite material with photocatalytic memory effect according to claim 1, characterized in that: The surface of the nanocomposite material is also modified by trisodium citrate.

4. A method for preparing a nanocomposite material having a photocatalytic memory effect according to any one of claims 1 to 3, characterized in that: The steps include: Step S1, dissolving NaBiO3 powder in NaOH solution, hydrothermally reacting at 160-200°C for 4-8 hours, washing and drying to obtain NaBiO3 / BiO 2-x Heterostructured nanoparticles; Step S2, dissolving ZrCl4 and terephthalic acid in a mixed solvent of N,N-dimethylformamide and glacial acetic acid, performing a solvothermal reaction at a temperature of 100-130° C. for 12-24 hours, and washing and drying to obtain a zirconium-based metal organic framework UiO-66; Step S3, the NaBiO3 / BiO obtained in step S1 2-x The heterogeneous structure nanoparticles, the zirconium-based metal organic framework UiO-66 obtained in step S2 and trisodium citrate are dispersed in deionized water, and a secondary hydrothermal reaction is carried out at a temperature of 100-150° C. for 2-4 hours. After washing and drying, the nanocomposite material is obtained.

5. The preparation method according to claim 4, characterized in that: In step S1, the mass concentration of the NaOH solution is 2.0-3.0M, and the solid-liquid ratio of NaBiO3 powder to the NaOH solution is (0.5-2.0) g: (50-100) mL, ultrasonically stirred for 30-90 minutes, hydrothermally reacted, centrifuged and washed, and then vacuum dried at 60-100°C for 6-12 hours.

6. The preparation method according to claim 4, characterized in that: In step S2, the molar ratio of ZrCl4 to terephthalic acid is (0.8-1.2):

1. After the solvent thermal reaction, the mixture is washed with dimethylformamide and methanol for 3-5 times in sequence.

7. The preparation method according to claim 4, characterized in that: In step S3, NaBiO3 / BiO 2-x The mass ratio of heterostructured nanoparticles, zirconium-based metal organic framework UiO-66 and trisodium citrate is (1-3): (0.5-2): (0.1-0.5). After the secondary hydrothermal reaction, the drying temperature is 40-60° C. and the drying time is 6-14 hours.

8. Use of the nanocomposite material with photocatalytic memory effect as claimed in any one of claims 1 to 3 in photocatalytic degradation of glyphosate, characterized in that: The nanocomposite material can achieve continuous catalytic degradation in the absence of light by releasing stored photogenerated electrons and specific adsorption of the Zr-O sites of UiO-66 and the glyphosate phosphonic acid groups in a dark environment.

9. The use according to claim 8, characterized in that: The steps include: Step (1), adding the nanocomposite material into water containing glyphosate; Step (2), pretreatment under visible light; Step (3), after turning off the light source, continue the reaction in a dark environment at 25-35°C for 30-180 minutes; Step (4), detecting the residual concentration of glyphosate after centrifugal separation, and the degradation rate of glyphosate is ≥ 90%.

10. The use according to claim 9, characterized in that: In step (1), the dosage of the nanocomposite material is 0.5-2.0 g / L, and the concentration of glyphosate in the water is 10-50 mg / L; in step (2), a xenon lamp light source with a 420 nm cutoff filter is used, and the light intensity is 200-500 W / m 2 , the pretreatment time is 30-60 minutes; in step (3), the continuous reaction time is 90-150 minutes; in step (4), the degradation rate of glyphosate is ≧95%, and the method for detecting the residual concentration of glyphosate is as follows: after the residual glyphosate is treated by nitrosation, the glyphosate concentration is quantitatively detected by a spectrophotometer at a wavelength of 242nm.

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