Preparation method, product and application of monatomic catalytic material

Abstract

The invention relates to the technical field of radioactive wastewater treatment, in particular to a preparation method, a product and application of a monatomic catalytic material. The monatomic catalytic material is prepared by replacing a metal center Zn < 2 + > of ZIF-8 with Pt < 4 + >. The monatomic catalytic material provided by the invention can quickly and effectively remove uranium (VI) under optical excitation. The monatomic catalytic material has the characteristic of high photocatalytic rate, the raw materials required for preparing the monatomic catalytic material are cheap and easy to obtain, the preparation process is simple and convenient, and the synthesis efficiency is high. In a simulation experiment of high-concentration uranium (VI), the photocatalytic uranium removal effect is excellent, and the method has excellent practical applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of radioactive wastewater treatment, and in particular to a preparation method, product and application of a single-atom catalytic material. Background Art

[0002] With the expansion of nuclear energy applications and the continued mining of uranium, the generation of radioactive uranium-containing wastewater is inevitable. The environmental pollution caused by uranium wastewater can be long-lasting and irreversible, especially without effective treatment. Once contamination spreads, it can take decades or even longer to restore ecological balance. Therefore, the treatment and management of uranium wastewater is crucial.

[0003] Traditional wastewater treatment methods include physical, chemical, and biological methods. Physical methods primarily include evaporation, centrifugation, and ion exchange; chemical methods involve precipitation, redox reactions, and solvent extraction; and biological methods utilize the metabolic activities of microorganisms to remove radioactive substances. However, each of these methods has its own advantages and disadvantages, including high treatment costs, complex operations, and the risk of secondary contamination.

[0004] Photocatalysis is the process of light exciting electrons on photocatalytic materials to cause them to jump from the valence band to the conduction band, thereby forming free electrons and holes. These free electrons and holes can be used to react with pollutants, thereby achieving the purpose of pollutant degradation.

[0005] Photocatalytic materials have broad application prospects, with innovative applications in environmental governance, energy conversion, and organic synthesis. For example, in the energy conversion field, photocatalytic water splitting can produce high-purity hydrogen fuel, enabling the direct conversion and storage of solar energy. With the development of renewable energy and the demand for energy transformation, photocatalytic materials will become a key technology for achieving sustainable energy conversion and storage.

[0006] However, today's photocatalysts have problems such as complex preparation methods, low photocatalytic performance, insufficient activity in the visible light range, and poor stability, which make it impossible to put photocatalytic materials into industrial production, limiting the industrial development and industrial application of photocatalysis. Therefore, it is of great significance to prepare a photocatalyst with a simple synthesis method that can be industrialized, stable performance that can be industrialized, good photocatalytic performance that can be applied in a wide range, and for photocatalytic reduction of uranium treatment wastewater in the field of radioactive wastewater treatment. Summary of the Invention

[0007] In view of this, the present invention provides a single-atom catalytic material with a simple preparation method, excellent photocatalytic performance and good stability, as well as a preparation method and application thereof.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] One of the technical solutions of the present invention is a single-atom catalytic material, based on Pt 4+ Replace the metal center Zn of ZIF-8 2+ Prepared.

[0010] The second technical solution of the present invention is a method for preparing the above-mentioned single-atom catalytic material, which comprises adding a chloroplatinic acid solution to a ZIF-8 solution to react and obtain the single-atom catalytic material.

[0011] The third technical solution of the present invention is the use of the above-mentioned single-atom catalytic material in the photocatalytic reduction of hexavalent uranium to tetravalent uranium.

[0012] A fourth technical solution of the present invention is a method for photocatalytically reducing hexavalent uranium to tetravalent uranium, wherein the hexavalent uranium in the uranium-containing wastewater is reduced to tetravalent uranium by adding the above-mentioned single-atom catalytic material to uranium-containing wastewater and irradiating it with ultraviolet light or 300-700nm simulated sunlight.

[0013] The present invention discloses the following technical effects:

[0014] The single-atom catalytic material of the present invention can quickly and effectively remove uranium (VI) under light excitation. It features a high photocatalytic rate, is prepared from readily available, inexpensive raw materials, and has a simple preparation process and high synthesis efficiency. In simulated experiments with high-concentration uranium (VI), it demonstrated excellent photocatalytic uranium removal performance, demonstrating excellent practical applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is the X-ray diffraction pattern (XRD) of the single-atom catalytic material prepared in Example 1 of the present invention.

[0017] Figure 2 This is the ultraviolet absorption spectrum of the single-atom catalytic material prepared in Example 1 of the present invention.

[0018] Figure 3 The removal rate of uranyl in wastewater by the single-atom catalytic material prepared in Example 1 of the present invention at pH = 5.

[0019] Figure 4 This is the X-ray photoelectron spectrum (XPS) of the single-atom catalytic material prepared in Example 1 of the present invention.

[0020] Figure 5 This is a diagram showing the effect of five consecutive cycle experiments on the single-atom catalytic material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0023] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0024] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0025] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0026] The "room temperature" in the present invention, unless otherwise specified, refers to 20-35°C.

[0027] In order to overcome the problems of existing photocatalysts such as complex preparation methods, poor photocatalytic performance, insufficient activity in the visible light range, and poor stability, the present invention modifies metal organic frameworks (MOFs). MOFs are widely used in the preparation and modification of adsorption materials because of their porous structure and large specific surface area. Among them, ZIF-8 has extremely strong structural stability and a larger specific surface area, and can perform adsorption stably and efficiently. Therefore, the present invention modifies the metal center of ZIF-8. By constructing an efficient electron transfer path between the metal center and the structure, the material can release a large number of electron-hole pairs under light excitation, so that ZIF-8 has the effect of reduction, that is, photocatalytic performance. By selecting a metal with a higher electron-pushing ability, the photocatalytic activity of the material is made stronger. Finally, the present invention determines to use platinum as the metal center to construct a photocatalytic active center to prepare Pt / ZIF-8 photocatalytic material.

[0028] By replacing the metal center of ZIF-8 (Zn with Pt), this method can impart photocatalytic activity to the material for use in the photocatalytic field. Furthermore, the ZIF-8 structure itself possesses multiple ionic defects. This method utilizes chloride ion vacancies within the ZIF-8 structure to introduce metal atoms into the ZIF-8 structure, creating a new metal center. This method is simple to operate and can be modified without harsh conditions. This method can facilitate the subsequent industrialization and large-scale synthesis of photocatalytic materials. It has extremely high practical value and is of great significance for promoting the development of nuclear wastewater treatment technology.

[0029] The first aspect of the present invention provides a single-atom catalytic material, Pt 4+ Replace the metal center Zn of ZIF-8 2+ Prepared.

[0030] A second aspect of the present invention provides a method for preparing the above-mentioned single-atom catalytic material, comprising adding a chloroplatinic acid solution to a ZIF-8 solution for reaction to obtain the single-atom catalytic material.

[0031] In a preferred embodiment of the present invention, the solvent of the ZIF-8 solution is acetone.

[0032] In a preferred embodiment of the present invention, the solvent of the chloroplatinic acid solution is acetone.

[0033] In a preferred embodiment of the present invention, the mass ratio of ZIF-8 in the ZIF-8 solution to chloroplatinic acid in the chloroplatinic acid solution is (3-7):1.

[0034] The present invention does not impose any particular limitation on the concentrations of the ZIF-8 solution and the chloroplatinic acid solution. The amounts of the solvents in the ZIF-8 solution and the chloroplatinic acid solution can ensure the smooth reaction of ZIF-8 and chloroplatinic acid.

[0035] The raw materials used in the present invention can all be obtained through commercial channels and are of analytically pure grade, and do not require secondary treatment when used.

[0036] In a preferred embodiment of the present invention, the reaction temperature is room temperature and the reaction time is 9-12 hours.

[0037] In a preferred embodiment of the present invention, stirring is further performed during the reaction process, and the stirring speed is 500-550 r / min.

[0038] In a preferred embodiment of the present invention, after the reaction is completed, the steps of suction filtration, collecting the solid product, and sequentially washing and drying the solid product are further included.

[0039] The drying temperature is 25-60° C., and the drying time is 8-12 hours.

[0040] In some embodiments of the present invention, the method for preparing ZIF-8 comprises the following steps:

[0041] Zn(NO₃)₂·6H₂O, 2-methylimidazole, and a solvent are mixed and reacted at room temperature for 6 hours, followed by filtration, washing, and drying to obtain ZIF-8. The molar ratio of Zn(NO₃)₂·6H₂O to 2-methylimidazole is 1:7.9-10; the solvent is methanol. The amount of methanol used is not particularly limited, and the amount of methanol used is sufficient to fully dissolve the Zn(NO₃)₂·6H₂O and 2-methylimidazole and allow for sufficient reaction.

[0042] ZIF-8 obtained by other routes, such as commercial routes, is also suitable for the present invention.

[0043] The present invention utilizes a vacancy introduction method to successfully introduce metal ions into a zeolite imidazole framework-8 (ZIF-8) carrier using chloride ions by utilizing chloride vacancies present in ZIF-8. Zeolite imidazole framework-8 (ZIF-8) is an excellent carrier for embedding metal nanoparticles due to its robust structure and porosity. Therefore, the present invention focuses on producing single-atom platinum sites with catalytic activity through a ligand exchange strategy, fixing them on zeolite imidazole framework-8 (ZIF-8), and introducing catalytically active single-atom platinum sites on ZIF-8 to exhibit catalytic activity.

[0044] The synthetic route of the present invention simply involves the reaction of H2PtCl6·6H2O with ZIF-8 in an organic solvent. The Cl ligand of H2PtCl6·6H2O exchanges with the 2-methylimidazole (2-MeIm) of the framework, resulting in Pt anchoring on the framework. In the method of the present invention, Pt ions selectively replace zinc in ZIF-8 through partial ligand exchange triggered by chloride ions, which results in single Pt atoms anchored on the framework and zinc dissociated into the solvent. The reaction proceeds at normal temperature and does not require subsequent treatment under harsh conditions, which allows the structural integrity and porosity of ZIF-8 to be well preserved.

[0045] A third aspect of the present invention provides the use of the above-mentioned single-atom catalytic material in the photocatalytic reduction of hexavalent uranium to tetravalent uranium.

[0046] A fourth aspect of the present invention provides a method for photocatalytically reducing hexavalent uranium to tetravalent uranium. The hexavalent uranium in the uranium-containing wastewater can be reduced to tetravalent uranium by adding the above-mentioned single-atom catalytic material to uranium-containing wastewater and irradiating it with ultraviolet light or 300-700nm simulated sunlight.

[0047] In a preferred embodiment of the present invention, the pH value of the uranium-containing wastewater is 2-8, and more preferably, the pH value is 5.

[0048] In a preferred embodiment of the present invention, when the single-atom photocatalytic material is mixed with uranium-containing wastewater to carry out photocatalytic reduction of uranium (VI), the temperature of the reaction system is 20-40°C.

[0049] In a preferred embodiment of the present invention, the concentration of uranium in the uranium-containing wastewater is 10 ppm-150 ppm.

[0050] UO2 in the present invention 2+ The test method for the removal rate is as follows:

[0051] A 350W xenon lamp equipped with a 420nm filter was used as a visible light source. 10-25mg of single-atom catalytic material solid powder was placed in 20-50mL of 10ppm-150ppm UO2 2+ Solution (UO2 was prepared by dissolving uranyl nitrate in deionized water 2+ solution); dilute nitric acid and sodium carbonate were used to adjust the solution pH to 2-8. Then, the sample was irradiated under simulated sunlight for 1.5 hours and analyzed for UO2 at a wavelength of 650nm. 2+ The absorbance of different irradiation times is converted into UO2 2+ removal rate.

[0052] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0053] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] This embodiment provides a method for preparing a single-atom catalytic material (Pt / ZIF-8), and the synthesis route is as follows:

[0056]

[0057] Step 1: Dissolve 300 mg (1.01 mmol) of Zn(NO3)2·6H2O in 30 ml of methanol and stir at room temperature to fully disperse it. Add 660 mg (8.04 mmol) of 2-methylimidazole to the above solution and stir at room temperature for 6 hours. Filter and wash the product with methanol four times, and then ultrasonically wash the product on the filter paper to allow the unreacted reactants to be fully dissolved in the solvent (methanol). Repeat this operation three times and dry in vacuo at 75°C overnight to obtain ZIF-8.

[0058] Step 2: Disperse 100 mg of the synthesized ZIF-8 in 5 ml of acetone and stir at room temperature for 5 min to obtain a ZIF-8 solution; then dissolve 17.6 mg (0.034 mmol) of H2PtCl6·6H2O in 5 ml of acetone to obtain a chloroplatinic acid solution, slowly add the chloroplatinic acid solution to the ZIF-8 solution at room temperature, and react at 550 r / min for 10 h (9-12 h). Filter the product with acetonitrile, and ultrasonically wash the product on the filter paper to allow the unreacted reactants to be fully dissolved in the solvent (acetonitrile). Repeat this operation three times, and vacuum dry overnight at 25°C to obtain a single-atom catalytic material (Pt / ZIF-8).

[0059] Figure 1 This is the X-ray diffraction pattern (XRD) of the single-atom catalytic material obtained in Example 1 of the present invention. After comparing the results shown in the pattern with the ZIF-8 pattern, it is proved that the structure of ZIF-8 has not changed before and after modification, which proves that the synthesis according to the shown principle is successful.

[0060] Figure 2 This is the ultraviolet absorption spectrum of the single-atom catalytic material obtained in Example 1 of the present invention. The ultraviolet absorption spectrum shows that the single-atom catalytic material absorbs sunlight in the range of 260nm-600nm.

[0061] Figure 3The figure shows the removal rate of uranyl in wastewater by the single-atom catalytic material obtained in Example 1 of the present invention under pH=5 (test method: using a xenon lamp as a visible light source, 15 mg of the single-atom catalytic material solid powder prepared in Example 1 as a photocatalyst was placed in 40 mL of 10 ppm UO2 2+ The solution was prepared by adjusting the pH of the solution to 5 using dilute nitric acid and sodium carbonate. The solution was then irradiated under simulated sunlight for 1.5 hours and the sample was analyzed for UO2 at a wavelength of 650 nm. 2+ The absorbance of different irradiation times is converted into UO2 2+ The removal rate of Figure 3 It can be seen that the uranium removal rate of the single-atom catalytic material reaches a maximum of 91.45% at 75 minutes and 90.4% at 90 minutes, which proves that the material reaches the maximum photocatalytic limit of about 91% at around 75 minutes.

[0062] Figure 4 This is the XPS graph of the single-atom catalytic material prepared in Example 1. Figure 4 It can be seen that Pt element appears in the material, and Pt element partially replaces the Zn site to form Pt / ZIF-8 material.

[0063] Figure 5 This is the effect diagram of the single-atom catalytic material prepared in Example 1 after 5 consecutive cycles of experiments; sodium bicarbonate was selected as the eluent to elute uranium; Figure 5 It can be seen that after the single-atom catalytic material prepared in Example 1 repeated 5 cycles of uranium adsorption, reduction and desorption, it still maintained a uranium removal rate of more than 85% under 75 minutes of light irradiation.

[0064] Comparative Example 1

[0065] The only difference from Example 1 is that step 1 is omitted and ZIF-8 in step 2 is replaced by 8.04 mmol of ZIF-67. The obtained catalytic material is recorded as Pt / ZIF-67.

[0066] The catalytic material prepared in Comparative Example 1 was subjected to the same effect verification as in Example 1. The results showed that the activity and performance of the photocatalytic material prepared in Comparative Example 1 were very low, with a uranium removal rate of only 70.8% in 75 minutes, and poor structural stability of the material as determined by thermogravimetric analysis.

[0067] Comparative Example 2

[0068] The only difference from Example 1 is that 0.034 mmol of H2PtCl6·6H2O in step 2 is replaced by 0.034 mmol of ferrous chloride. The resulting catalytic material is designated as Fe / ZIF-8.

[0069] The catalytic material prepared in Comparative Example 2 was subjected to the same effect verification as in Example 1. The results showed that the performance of Fe / ZIF-8 was far inferior to that of Pt / ZIF-8 obtained in Example 1. The uranium removal rate was only about 50% after 75 minutes of reaction, which was much lower than that of Pt / ZIF-8 in Example 1.

[0070] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A single-atom catalytic material, characterized in that: Pt 4+ Replace the metal center Zn of ZIF-8 2+ Prepared.

2. A method for preparing the single-atom catalytic material according to claim 1, characterized in that: A chloroplatinic acid solution is added to the ZIF-8 solution to react and obtain the single-atom catalytic material.

3. The preparation method according to claim 2, characterized in that The solvent of the ZIF-8 solution is acetone.

4. The preparation method according to claim 2, characterized in that The solvent of the chloroplatinic acid solution is acetone.

5. The preparation method according to claim 2, characterized in that The mass ratio of ZIF-8 in the ZIF-8 solution to chloroplatinic acid in the chloroplatinic acid solution is (3-7):

1.

6. The preparation method according to claim 2, characterized in that The reaction temperature is room temperature, and the reaction time is 9-12 hours.

7. The preparation method according to claim 6, characterized in that Stirring is also performed during the reaction process, and the stirring speed is 500-550 r / min.

8. The preparation method according to claim 2, characterized in that After the reaction is completed, the steps of suction filtration, collecting the solid product, and sequentially washing and drying the solid product are further included.

9. Use of the single-atom catalytic material according to claim 1 in the photocatalytic reduction of hexavalent uranium to tetravalent uranium.

10. A method for photocatalytic reduction of hexavalent uranium to tetravalent uranium, characterized in that: The hexavalent uranium in the uranium-containing wastewater can be reduced to tetravalent uranium by adding the single-atom catalytic material described in claim 1 to uranium-containing wastewater and irradiating the wastewater with ultraviolet light or 300-700nm simulated sunlight.

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