Preparation method of monatomic catalytic material, product and application

Abstract

This invention relates to the field of radioactive wastewater treatment technology, and in particular to a method for preparing a single-atom catalytic material, its product, and its application. The single-atom catalytic material of this invention uses Pt... 4+ Replace the Zn metal center of ZIF-8 2+ The single-atom catalytic material of this invention can rapidly and effectively remove uranium (VI) under photoexcitation. This single-atom catalytic material features a fast photocatalytic rate, and the raw materials required for its preparation are inexpensive and readily available, with a simple preparation process and high synthesis efficiency. In simulated experiments with high-concentration uranium (VI), the photocatalytic removal of uranium exhibits excellent results, demonstrating excellent practical applicability.

Description

Technical Field

[0001] This invention relates to the field of radioactive wastewater treatment technology, and in particular to a method for preparing a single-atom catalytic material, its product, and its application. Background Technology

[0002] With the expansion of nuclear energy applications and the continuous mining of uranium, the treatment and management of uranium wastewater has become crucial.

[0003] Traditional wastewater treatment methods include physical, chemical, and biological methods. Physical methods mainly 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, such as high treatment costs, complex operation, and the risk of secondary pollution.

[0004] Photocatalysis involves the photoexcitation of electrons on a photocatalytic material, causing them to transition from the valence band to the conduction band, thus creating free electrons and holes. These free electrons and holes can then react with pollutants, thereby achieving the goal of pollutant degradation.

[0005] Photocatalytic materials have a wide range of applications, with innovative applications in environmental governance, energy conversion, and organic synthesis. For example, in energy conversion, high-purity hydrogen fuel can be produced through the photocatalytic water splitting reaction, enabling the direct conversion and storage of solar energy. With the development of renewable energy and the demand for energy transition, photocatalytic materials will become a crucial technology for achieving sustainable energy conversion and storage.

[0006] However, current photocatalysts suffer from problems such as complex preparation methods, low photocatalytic performance, insufficient activity in the visible light range, and poor stability. These issues prevent photocatalytic materials from being put into industrial production, thus limiting the industrial development and application of photocatalysis. Therefore, it is of great significance to prepare a photocatalyst with a simple synthesis method that can be industrially produced, stable performance that can be industrially applied, and good photocatalytic performance that can be applied in a wide range of applications for the photocatalytic reduction of uranium to treat 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 simple preparation method, excellent photocatalytic performance and good stability, as well as its preparation method and application.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] One of the technical solutions of this invention is a single-atom catalytic material, using Pt. 4+ Replace the Zn metal center of ZIF-8 2+ It was obtained.

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

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

[0012] The fourth technical solution of the present invention is a method for photocatalytically reducing hexavalent uranium to tetravalent uranium. The above-mentioned single-atom catalytic material is added to uranium-containing wastewater and irradiated with ultraviolet light or 300-700nm simulated sunlight to reduce hexavalent uranium in uranium-containing wastewater to tetravalent uranium.

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

[0014] The single-atom catalytic material of this invention can rapidly and effectively remove uranium (VI) under photoexcitation. This single-atom catalytic material features a fast photocatalytic rate, and the raw materials required for its preparation are inexpensive and readily available, with a simple preparation process and high synthesis efficiency. In simulated experiments with high-concentration uranium (VI), the photocatalytic removal of uranium exhibits excellent results, demonstrating excellent practical applicability. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[0017] Figure 2 The image shows the ultraviolet absorption spectrum of the single-atom catalytic material prepared in Example 1 of this invention.

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

[0019] Figure 4 The image shows the X-ray photoelectron spectrum (XPS) of the single-atom catalytic material prepared in Example 1 of this invention.

[0020] Figure 5 The image shows the effect of five consecutive cycles of the single-atom catalytic material prepared in Example 1 of this invention. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of 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 terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

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

[0026] Unless otherwise specified, "room temperature" in this invention refers to 20-35°C.

[0027] To overcome the problems of complex preparation methods, low photocatalytic performance, insufficient activity in the visible light range, and poor stability of existing photocatalysts, this invention modifies metal-organic frameworks (MOFs). MOFs are widely used in the preparation and modification of adsorption materials due to their porous structure and large specific surface area. Among them, ZIF-8 has extremely strong structural stability and a larger specific surface area, enabling stable and efficient adsorption. Therefore, this invention modifies the metal center of ZIF-8. By constructing an efficient electron transfer pathway for the metal center and structure, the material can release a large number of electron-hole pairs under photoexcitation, giving ZIF-8 a reduction function, i.e., photocatalytic performance. By selecting a metal with higher electron-donating ability, the photocatalytic activity of the material is further enhanced. Finally, this invention determines that platinum is used as the metal center to construct the photocatalytic active center to prepare Pt / ZIF-8 photocatalytic materials.

[0028] This invention enables photocatalytic activity in ZIF-8 materials by replacing the metal center (Zn with Pt). Furthermore, the ZIF-8 structure itself possesses various ionic defects; this invention utilizes chloride ion vacancies in ZIF-8 to introduce metal atoms and construct novel metal centers. This method is simple to operate and requires no stringent conditions for modification. It facilitates the subsequent industrialization and large-scale synthesis of photocatalytic materials, possessing high practical value and significant implications for advancing nuclear wastewater treatment technology.

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

[0030] A second aspect of the present invention provides a method for preparing the above-mentioned single-atom catalytic material, wherein a chloroplatinic acid solution is added to a ZIF-8 solution and reacted 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 for 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] This invention does not impose any particular limitation on the concentration of ZIF-8 solution and chloroplatinic acid solution. The amount of solvent used in ZIF-8 solution and chloroplatinic acid solution is sufficient to ensure the smooth reaction between ZIF-8 and chloroplatinic acid.

[0035] All raw materials used in this invention are commercially available and are of analytical purity, requiring no secondary processing before use.

[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, the reaction process is further characterized by stirring at a speed of 500-550 r / min.

[0038] In a preferred embodiment of the present invention, after the reaction is completed, the process further includes filtration, collection of solid products, and sequential washing and drying of the solid products.

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

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

[0041] Zn(NO3)2·6H2O, 2-methylimidazole, and solvent were mixed and reacted at room temperature for 6 hours. The mixture was then filtered, washed, and dried to obtain ZIF-8. The molar ratio of Zn(NO3)2·6H2O to 2-methylimidazole was 1:7.9-10; the solvent was methanol. The amount of methanol used is not particularly limited in this invention; it is sufficient to ensure that Zn(NO3)2·6H2O and 2-methylimidazole are fully dissolved and reacted.

[0042] ZIF-8 obtained through other means, such as commercially available sources, is also applicable to this invention.

[0043] This invention utilizes a vacancy introduction method, employing chloride ions to successfully introduce metal ions into a zeolite imidazole framework-8 (ZIF-8) support using chloride ions at chloride vacancies present in ZIF-8. Due to its robust structure and porosity, the zeolite imidazole framework-8 (ZIF-8) is an excellent support for embedding metal nanoparticles. Therefore, this invention focuses on creating catalytically active single-atom platinum sites through a ligand exchange strategy, fixing them onto the zeolite imidazole framework-8 (ZIF-8), and introducing catalytically active single platinum sites onto ZIF-8 to enable it to exhibit catalytic activity.

[0044] The synthetic route of this 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 to the framework. In the method of this invention, through partial ligand exchange triggered by chloride ions, Pt ions selectively replace zinc in ZIF-8, which results in individual Pt atoms anchoring to the framework, while zinc dissociates into the solvent. This reaction is carried out under normal temperature conditions and does not require subsequent processing under harsh conditions, which allows the structural integrity and porosity of ZIF-8 to be well preserved.

[0045] The third aspect of this invention provides the application of the above-described single-atom catalytic material in the photocatalytic reduction of hexavalent uranium to tetravalent uranium.

[0046] The fourth aspect of this invention provides a method for photocatalytically reducing hexavalent uranium to tetravalent uranium. The method involves adding the aforementioned single-atom catalytic material to uranium-containing wastewater and subjecting it to ultraviolet or 300-700nm simulated sunlight irradiation, thereby reducing hexavalent uranium in the uranium-containing wastewater to tetravalent uranium.

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

[0048] In a preferred embodiment of the present invention, when the single-atom photocatalytic material is mixed with uranium-containing wastewater for the 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 10ppm-150ppm.

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

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

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

[0053] The technical solutions provided by the present invention will be 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 synthetic route is shown below:

[0056]

[0057] Step 1: Dissolve 300 mg (1.01 mmol) Zn(NO3)2·6H2O in 30 ml of methanol and stir at room temperature to ensure complete dispersion. Add 660 mg (8.04 mmol) 2-methylimidazole to the above solution and stir at room temperature for 6 h. Wash the product four times with methanol by vacuum filtration, and then wash the product on the filter paper with ultrasonication to ensure that the unreacted reactants are completely dissolved in the solvent (methanol). Repeat this operation three times. Dry under vacuum 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 is also acceptable). Filter the product with acetonitrile and ultrasonically wash the product on the filter paper to fully dissolve the unreacted reactants into the solvent (acetonitrile). Repeat this operation three times. Dry under vacuum at 25 °C overnight to obtain the single-atom catalytic material (Pt / ZIF-8).

[0059] Figure 1 The X-ray diffraction (XRD) pattern of the single-atom catalytic material obtained in Example 1 of this invention is shown. The comparison between the XRD pattern and the ZIF-8 pattern proves that the structure of ZIF-8 did not change before and after modification, proving that the synthesis was successful according to the principle shown.

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

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

[0062] Figure 4 The XPS image of the single-atom catalytic material prepared in Example 1 is shown below. Figure 4 It can be seen that Pt elements are present in the material, and Pt elements partially replace the Zn sites, forming Pt / ZIF-8 material.

[0063] Figure 5 The image shows the effect of five consecutive cycles of experiments on the single-atom catalytic material prepared in Example 1; sodium bicarbonate was selected as the eluent to elute uranium; from Figure 5 As can be seen from the example, the single-atom catalytic material prepared in Example 1 still maintains a uranium removal rate of over 85% after five cycles of uranium adsorption-reduction and desorption under 75 min 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 with 8.04 mmol of ZIF-67. The resulting catalyst is denoted 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 photocatalytic material prepared in Comparative Example 1 had very low activity and performance, with a uranium removal rate of only 70.8% after 75 minutes. Furthermore, thermogravimetric analysis revealed that the material had poor structural stability.

[0067] Comparative Example 2

[0068] The only difference from Example 1 is that the 0.034 mmol H2PtCl6·6H2O in step 2 is replaced with 0.034 mmol ferrous chloride. The resulting catalyst is designated Fe / ZIF-8.

[0069] The catalytic material prepared in Comparative Example 2 was subjected to the same performance 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. After 75 min of reaction, the uranium removal rate was only about 50%, which was much lower than that of Pt / ZIF-8 in Example 1.

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

Claims

1. The application of a single-atom catalytic material in the photocatalytic reduction of hexavalent uranium to tetravalent uranium, characterized in that, To the ZIF-8 solution, a chloroplatinic acid solution was added to react with Pt 4+ replacing the metal center Zn of ZIF-8 2+ to obtain the single-atom catalytic material; The mass ratio of ZIF-8 in the ZIF-8 solution to chloroplatinic acid in the chloroplatinic acid solution is (3-7):

1.

2. The application according to claim 1, characterized in that, The solvent for the ZIF-8 solution is acetone.

3. The application according to claim 1, characterized in that, The solvent for the chloroplatinic acid solution is acetone.

4. The application according to claim 1, characterized in that, The reaction was carried out at room temperature for 9-12 hours.

5. The application according to claim 4, characterized in that, The reaction process also involves stirring at a speed of 500-550 r / min.

6. The application according to claim 1, characterized in that, After the reaction is completed, the process also includes filtration, collection of solid products, and sequential washing and drying of the solid products.

7. The application according to claim 1, characterized in that, By adding the single-atom catalytic material to uranium-containing wastewater and subjecting it to ultraviolet or 300-700nm simulated sunlight irradiation, hexavalent uranium in the wastewater can be reduced to tetravalent uranium.

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