Preparation and application of titanium dioxide catalyst for uranium separation

Abstract

The invention discloses the preparation and application of a titanium dioxide catalyst for uranium separation, comprising: synthesizing SiO2@TiO2 nanospheres using a silicon source and a titanium source, dispersing to obtain a SiO2@TiO2 nanosphere dispersion; adding a manganese salt to the SiO2@TiO2 nanosphere dispersion to react to obtain SiO2@Mn-SAs / TiO2@SiO2; calcining the SiO2@Mn-SAs / TiO2@SiO2, dispersing, stirring and centrifuging, washing and drying to obtain Mn-SAs / TiO2; and dispersing the uranium into a hydroxyethylidene diphosphonic acid or H3PO4 solution, stirring, washing, and drying to prepare a titanium dioxide catalyst. The titanium dioxide catalyst for uranium separation prepared by the present invention is used for catalytic reduction of U(VI) in high-fluorine uranium-containing wastewater, promotes effective electron-hole separation and transfer of the Mn-SAs / TiO2@HEDP catalyst and the Mn-SAs / TiO2@PO4 catalyst, and simultaneously improves the removal rate of U(VI) in the high-fluorine uranium-containing wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of radioactive wastewater treatment and catalytic material preparation, and more specifically, relates to the preparation and application of a titanium dioxide catalyst for uranium separation. Background Art

[0002] With the rapid development of the nuclear energy industry, uranium-containing wastewater is inevitably produced. Concentrating and recovering uranium from radioactive wastewater is particularly important for environmental protection and the healthy and sustainable development of nuclear energy. In particular, nuclear industry production processes such as uranium enrichment, uranium conversion, and fuel element manufacturing will produce a large amount of high-fluorine uranium-containing wastewater. Since fluoride ions and uranium ions easily form UO2F in the water environment system, the uranium-containing wastewater will be generated. - , UO2F2(aq) and UO2F3 - The extraction of uranium from high-fluorine uranium wastewater becomes more difficult due to the formation of complexes such as uranium nitrate and uranium nitrate. More importantly, the enriched uranium in the wastewater alleviates the growing demand for nuclear fuel. Based on the large difference in solubility between uranium oxidation states, the reduction of soluble hexavalent uranium (U(VI)) to slightly soluble tetravalent uranium (V(IV)) is an effective enrichment method. Among the existing reduction methods, U(VI) reduction based on semiconductor photocatalysis has attracted much attention due to its simplicity, greenness, high efficiency and environmental friendliness.

[0003] However, due to the narrow visible light absorption range and lack of surface restriction sites of traditional photocatalysts, the rationally designed Mn-TiO2@PO4 photocatalytic materials have a poor performance in treating F - The actual wastewater system with higher ion concentration still has the problem of insufficient competition for uranyl ions. Based on the progress made in the previous research on basic band regulation coupled with surface functional modification strategy, it has been proved that it has excellent durability and anti-interference ability in complex systems. Therefore, there is an urgent need to explore photocatalysts with more catalytic active sites on the surface to achieve efficient uranium extraction from high-fluorine uranium-containing radioactive wastewater. Multi-site catalysts have gradually become the design criteria for conventional semiconductor light-assisted treatment of U(VI) in radioactive wastewater. However, F - Easy with UO2 2+ The complexation of ligands in high-fluoride uranium radioactive wastewater increases the challenge of uranium separation in this system. Unfortunately, current multi-site photocatalysts do not mention practical treatment methods for fluoride-containing uranium radioactive wastewater. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0005] In order to achieve these objects and other advantages according to the present invention, a method for preparing a titanium dioxide catalyst is provided, comprising the following steps:

[0006] Step 1: adding manganese salt to the SiO2@TiO2 nanosphere dispersion to react and obtain SiO2@Mn-SAs / TiO2@SiO2;

[0007] Step 2, calcining SiO2@Mn-SAs / TiO2@SiO2, dispersing, stirring, centrifuging, washing and drying to obtain Mn-SAs / TiO2;

[0008] Step 3: Disperse into hydroxyethylidene diphosphonic acid or H3PO4 solution, stir, wash, and dry to prepare a titanium dioxide catalyst.

[0009] Preferably, in the step 1, the SiO2@TiO2 nanospheres use a silicon source and a titanium source, and the specific method includes:

[0010] S11. Seal and stir ethanol, H2O, and ammonia water at room temperature for ten minutes, add tetraethyl orthosilicate, and stir vigorously for 2 to 12 hours; centrifuge the product, wash twice with water and ethanol, and then disperse in ethanol to form an ethanol dispersion of SiO2 nanospheres;

[0011] S12. Acetonitrile and aqueous ammonia are then added to the SiO2 nanosphere ethanol dispersion solution and ultrasonically treated until the SiO2 nanoparticles are dispersed to obtain solution A; at the same time, anhydrous ethanol and acetonitrile are mixed with tetrabutyl titanate to obtain a transparent solution B; solution A and solution B are mixed and stirred for 2 to 6 hours, centrifuged, washed several times with ethanol, and then washed twice with pure water to obtain SiO2@TiO2 nanospheres; the SiO2@TiO2 nanospheres are dispersed in 40 mL of pure water to obtain a SiO2@TiO2 nanosphere dispersion.

[0012] Preferably, in said S11, the volume ratio of ethanol, H2O, ammonia water, tetraethoxysilane and ethanol used for dispersion is 10-30mL:1-10mL:0.1-2mL:0.1-2mL:10-100mL;

[0013] In S12, the volume ratio of acetonitrile and ammonia water used to prepare solution A is 5-30 mL:0.1-0.8 mL; the volume ratio of anhydrous ethanol, acetonitrile and tetrabutyl titanate used to prepare solution B is 1-20 mL:1-20 mL:0.1-2 mL.

[0014] Preferably, in the step 1, the specific method of adding manganese salt to the SiO2@TiO2 nanosphere dispersion to obtain SiO2@Mn-SAs / TiO2@SiO2 by reaction includes:

[0015] MnCl2·4H2O is added to the SiO2@TiO2 nanosphere dispersion and vigorously stirred for 2 to 5 hours; the product is centrifuged, washed twice with pure water, and dispersed in a polyvinyl pyrrolidone aqueous solution and stirred for 2 to 12 hours;

[0016] Secondly, the product was centrifuged and redispersed in a mixture of ethanol and pure water, and sonicated to obtain a well-dispersed solution;

[0017] Finally, ammonia water and tetraethyl orthosilicate are added and stirred for 2 to 8 hours; the product is centrifuged, washed with ethanol and pure water respectively, and dried under vacuum for 2 to 8 hours to obtain SiO2@Mn-SAs / TiO2@SiO2.

[0018] Preferably, the volume mass ratio of the obtained SiO2@TiO2 nanosphere dispersion, MnCl2·4H2O and polyvinyl pyrrolidone aqueous solution is 10-80 mL: 2-10 mg: 10-80 mL; the concentration of polyvinyl pyrrolidone in the polyvinyl pyrrolidone aqueous solution is 0.005-0.06 g / mL; the volume ratio of ethanol and pure water is 10-60 mL: 1-15 mL; and the volume ratio of ammonia water and tetraethyl orthosilicate is 0.5-5 mL: 0.2-5 mL.

[0019] Preferably, in step 2, the method for synthesizing Mn-SAs / TiO2 comprises:

[0020] SiO2@Mn-SAs / TiO2@SiO2 is calcined in air and dispersed in NaOH solution. The product is stirred at 60-90°C for 2-8 hours, centrifuged, washed with pure water and ethanol, and dried under vacuum at 60-80°C to obtain Mn-SAs / TiO2.

[0021] Preferably, the calcination temperature of SiO2@Mn-SAs / TiO2@SiO2 is 500-800°C, the calcination time is 2-8 hours, the concentration of the NaOH solution is 0.1-0.8M, and the amount of the NaOH solution is 400-800 mL.

[0022] Preferably, the specific method of step three includes:

[0023] Mn-SAs / TiO2 is dispersed in a hydroxyethylidene diphosphonic acid solution or a H3PO4 solution and stirred at 60-80°C for 2-14 hours; after washing with ethanol and deionized water several times, respectively, the mixture is dried at 60-80°C for 2-24 hours to obtain a Mn-SAs / TiO2@HEDP catalyst or a Mn-SAs / TiO2@PO4 catalyst, respectively.

[0024] Preferably, the concentration of the hydroxyethylidene diphosphonic acid solution is 0.010 to 0.0180 M, and the volume of the hydroxyethylidene diphosphonic acid solution or H3PO4 solution is 10 to 60 mL.

[0025] The invention discloses an application of a titanium dioxide catalyst for uranium separation. The method for applying the titanium dioxide catalyst to the photocatalytic reduction of uranium comprises: adding the titanium dioxide catalyst to wastewater containing U(VI), wherein the mass volume ratio of the titanium dioxide catalyst to the wastewater containing U(VI) is 0.5-100g:1-200mL; and under light conditions, the titanium dioxide catalyst performs photocatalytic reduction on U(VI).

[0026] The present invention includes at least the following beneficial effects: The present invention provides a titanium dioxide (Mn-SAs / TiO2@HEDP) catalyst for uranium separation, which has surface-rich Mn single atom sites and functionally modified organic phosphate sites, and is used to catalytically reduce U(VI) in high-fluorine uranium-containing wastewater. The catalyst with dual active sites promotes the effective electron-hole separation and transfer of Mn-SAs / TiO2@HEDP, while improving the visible light response and electron lifetime. It is worth noting that Mn single atoms and organic phosphates not only provide more uranyl capture sites, but also optimize the electronic structure and electron transfer pathway of TiO2. Therefore, the U(VI) removal rate of Mn-SAs / TiO2@HEDP in fluorine-containing uranium wastewater is 94%, and the F - The U(VI) removal efficiency in a uranium solution with a concentration of 5 g / L was still as high as 88%. This study provides a precedent for the design of multi-site catalysts and provides theoretical guidance for the treatment of fluorine-containing uranium wastewater in the nuclear industry.

[0027] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 HRTEM image of the Mn-SAs / TiO2@HEDP catalyst prepared in Example 1 of the present invention at a scale of 50 nm;

[0029] Figure 2 HRTEM image of the Mn-SAs / TiO2@HEDP catalyst prepared in Example 1 of the present invention at a scale of 5 nm;

[0030] Figure 3 TEM-EDX elemental mapping image of the Mn-SAs / TiO2@HEDP catalyst prepared in Example 1 of the present invention;

[0031] Figure 4The distribution state image of Ti element in the TEM-EDX element mapping image of Mn-SAs / TiO2@HEDP catalyst;

[0032] Figure 5 The distribution state image of O element in the TEM-EDX element mapping image of Mn-SAs / TiO2@HEDP catalyst;

[0033] Figure 6 The distribution state image of P element in TEM-EDX element mapping image of Mn-SAs / TiO2@HEDP catalyst;

[0034] Figure 7 The distribution state image of Mn element in the TEM-EDX element mapping image of Mn-SAs / TiO2@HEDP catalyst;

[0035] Figure 8 This is the HAADF image of the Mn-SAs / TiO2@HEDP catalyst prepared in Example 1 of the present invention;

[0036] Figure 9 This is a STEM image of the Mn-SAs / TiO2@HEDP catalyst prepared in Example 1 of the present invention;

[0037] Figure 10 XRD spectra of TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP;

[0038] Figure 11 FTIR spectra of TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP;

[0039] Figure 12 UV-visible spectra of TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP;

[0040] Figure 13 Tauc / Davis-Mott plots of TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP;

[0041] Figure 14 The adsorption and catalytic time curves of U(VI) by TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP under simulated sunlight and darkness;

[0042] Figure 15 The results of Mn-SAs / TiO2@HEDP under different F - The removal rate of U(VI) at the concentration;

[0043] Figure 16 The reusability of Mn-SAs / TiO2@HEDP in multiple cycles;

[0044] Figure 17 The effect of photocatalytic reduction of U(VI) by Mn-SAs / TiO2@HEDP at different pH values;

[0045] Figure 18 The effect of Mn-SAs / TiO2@HEDP on U(VI) removal under different ion interferences;

[0046] Figure 19 The effect of original U(VI) concentration on the removal of U(VI) by Mn-SAs / TiO2@HEDP and the maximum extraction equilibrium;

[0047] Figure 20 is the XRD spectrum of the product after photocatalytic reduction of Mn-SAs / TiO2@HEDP;

[0048] Figure 21 ESR signals of TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP to DMPO-·OH;

[0049] Figure 22 ESR signals of TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP to DMPO-·O2-;

[0050] Figure 23 LSV curves of U(VI) reduction by TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4Mn-SAs / TiO2@HEDP. DETAILED DESCRIPTION

[0051] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0052] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0053] Example 1

[0054] This embodiment provides a method for preparing a Mn-SAs / TiO2@HEDP catalyst for uranium separation, comprising the following steps:

[0055] Step 1: Synthesize SiO2@TiO2 nanospheres using a silicon source and a titanium source, and disperse to obtain a SiO2@TiO2 nanosphere dispersion. The specific method includes:

[0056] S11. Seal 23 mL of ethanol, 4.3 mL of H₂O, and 0.6 mL of aqueous ammonia and stir for 10 minutes at room temperature. Add 0.86 mL of tetraethyl orthosilicate (TEOS) to the mixture and stir vigorously for 6 hours. Centrifuge the product, wash twice with water and ethanol, and then disperse in 40 mL of ethanol to obtain an ethanol dispersion of SiO₂ nanospheres.

[0057] S12. Then, 14 mL of acetonitrile and 0.4 mL of ammonia water were added to the SiO2 nanosphere ethanol dispersion solution and ultrasonicated until the SiO2 nanoparticles were dispersed (solution A). At the same time, 6 mL of anhydrous ethanol and 2 mL of acetonitrile were mixed with 0.8 mL of tetrabutyl titanate to obtain a transparent solution (solution B). Solution A and solution B were mixed and stirred for 3 h, the product was centrifuged, washed several times with ethanol, and then washed twice with pure water. The SiO2@TiO2 nanospheres were dispersed in 40 mL of pure water to obtain a SiO2@TiO2 dispersion;

[0058] Step 2: Add manganese salt to the SiO2@TiO2 nanosphere dispersion to react and obtain SiO2@Mn-SAs / TiO2@SiO2. The specific method includes: first, add 6.3mg MnCl2·4H2O to the SiO2@TiO2 dispersion and stir vigorously for 3 hours. After centrifugation, wash the product twice with pure water and disperse it in 40mL water containing 0.4g PVP and stir for 8 hours; secondly, centrifuge the product and disperse it again in a mixture of 46mL ethanol and 8.6mL pure water, and ultrasonically treat it to obtain a fully dispersed solution; finally, add 1.2mL ammonia water and 1.6mL TEOS and stir for 4 hours. Centrifuge the product, wash it several times with ethanol and pure water respectively, and dry it under vacuum for 4 hours;

[0059] Step 3: calcining SiO2@Mn-SAs / TiO2@SiO2, dispersing, stirring, centrifuging, washing and drying to obtain Mn-SAs / TiO2. The specific method includes: calcining SiO2@Mn-SAs / TiO2@SiO2 in air at 600°C for 4 hours, and dispersing it in 500 mL of 0.5M NaOH solution, stirring the product at 80°C for 6 hours, centrifuging, washing with pure water and ethanol several times, and drying it under vacuum at 80°C to obtain Mn-SAs / TiO2.

[0060] Step 4: Disperse the Mn-SAs / TiO2 in a hydroxyethylidene diphosphonic acid (HEDP) solution, stir, wash, and dry to prepare a Mn-SAs / TiO2@HEDP catalyst. The specific method includes dispersing 100 mg of Mn-SAs / TiO2 in 20 mL of a 0.0125 M HEDP solution and stirring at 80°C for 4 hours. After washing several times with ethanol and deionized water, the mixture was dried at 80°C for 12 hours to obtain the Mn-SAs / TiO2@HEDP catalyst.

[0061] The Mn-SAs / TiO2@HEDP catalyst prepared in this example is applied to the photocatalytic reduction of U(VI) in U(VI)-containing wastewater. The Mn-SAs / TiO2@HEDP catalyst is added to the U(VI)-containing wastewater and catalytically reduces U(VI) under light conditions.

[0062] Example 2

[0063] This embodiment provides a method for preparing a Mn-SAs / TiO2@PO4 catalyst for uranium separation, wherein the hydroxyethylidene diphosphonic acid (HEDP) solution in step 4 is replaced with an H3PO4 solution, and the rest of the preparation method is the same as that in Example 1.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing hollow TiO2 nanospheres, comprising the following steps:

[0066] Step 1: Synthesize SiO2@TiO2 nanospheres using a silicon source and a titanium source, and disperse to obtain a SiO2@TiO2 nanosphere dispersion. The specific method includes:

[0067] S11. Seal 23 mL of ethanol, 4.3 mL of H₂O, and 0.6 mL of aqueous ammonia and stir for 10 minutes at room temperature. Add 0.86 mL of tetraethyl orthosilicate (TEOS) to the mixture and stir vigorously for 6 hours. Centrifuge the product, wash twice with water and ethanol, then disperse in 40 mL of ethanol.

[0068] S12. Then, 14 mL of acetonitrile and 0.4 mL of ammonia water were added to the above-mentioned SiO2 nanosphere solution and ultrasonicated until the SiO2 nanoparticles were dispersed (solution A). At the same time, 6 mL of anhydrous ethanol and 2 mL of acetonitrile were mixed with 0.8 mL of tetrabutyl titanate to obtain a transparent solution (solution B). Solutions A and B were mixed and stirred for 3 h, the product was centrifuged, washed several times with ethanol, and then washed twice with pure water. The amorphous SiO2@TiO2 nanospheres were dispersed in 40 mL of pure water to obtain a SiO2@TiO2 dispersion;

[0069] Step 2: calcining SiO2@TiO2 nanospheres, dispersing, stirring, centrifuging, washing and drying to obtain hollow TiO2 nanospheres. The specific method includes: calcining SiO2@TiO2 nanospheres in air at 600°C for 4 hours, and dispersing them in 500 mL of 0.5M NaOH solution, stirring the product at 80°C for 6 hours, centrifuging, washing with pure water and ethanol several times, and drying under vacuum at 80°C to obtain hollow TiO2 nanospheres.

[0070] Electrochemical characterization was performed using a three-electrode electrochemical workstation (CHI-660E, Shanghai, China). An Ag / AgCl (3.5 M KCl electrolyte) reference electrode was used. A platinum wire electrode served as the reaction electrode, and the catalyst-coated carbon paper served as the working electrode. The working electrode was prepared by mixing 3 mg of the Mn-SAs / TiO2@HEDP catalyst prepared in Example 1, 30 μL of a 0.5 wt% Nafion solution, and 2 mL of ethanol, followed by sonication to achieve a thorough dispersion. The resulting mixture was then evenly coated onto a 1 cm × 2 cm piece of carbon paper. Linear voltammetry (LSV) curves of the Ag / AgCl catalyst were measured using a 0.5 M NaCl solution containing 80 μg / LU(VI), a sampling rate of 5 mV / s, and a potential gradient between 0.2 V and -1.6 V. The photocurrent density was recorded in a 0.5 M NaCl solution by switching a xenon lamp on and off every 30 seconds. The catalyst impedance was measured in a 1 M KHCO3 solution.

[0071] All photocatalytic experiments used 10 mg Mn-SAs / TiO2@HEDP catalyst and 20 mL U(VI) solution [C U(VI) =8mg / L, 20mg / L, 50mg / L, 100mg / L]. The solid-liquid ratio in the circulation test was 1:2, and C U(VI) =8mg / LC F - =1g / L solution. The reaction system consists of a wavelength of full spectrum and an intensity of 200mW / cm 2 The samples were irradiated with a xenon lamp. The samples were placed in the dark for 120 minutes to reach the adsorption-desorption dynamic equilibrium before photocatalysis. The pH value of the uranium solution was adjusted with HNO3 and NaOH to determine the acid resistance in the pH study. Ion interference (C U(VI) :C M =1:10, M=K + , Na + , Mg 2+ , Sr 2+ , Zn 2+ , CO3 2- , SO4 2- ,HCO3 -After photocatalysis, the U(VI) concentration was analyzed by UV spectrophotometry at a wavelength of 651.8 nm. The U(VI) removal rate (%) and the mass of U(VI) extracted (mg / g) were calculated as [(C0-C0) / C0]×100% and (C0-C0)×V / m, respectively, where C is the final concentration of U(VI) (mg / L), C0 is the initial concentration of U(VI) (mg / L), V is the volume of the solution (L), and m is the mass of the sample (g).

[0072] In order to further analyze the morphology, crystal type and element distribution of Mn-SAs / TiO2@HEDP, high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray (EDX) were used. HRTEM images showed that the thickness of the hollow nanosphere structure composed of 5nm TiO2 nanocrystals was about 20nm before and after surface functional modification, as shown in Figure 2. Figure 1 As shown. Figure 2 As shown in Figure 2, the clear lattice fringe spacing (0.35 nm) corresponds to the (101) crystal plane of anatase TiO2 (PDF-#73-1764), further confirming that the crystal type of the prepared hollow TiO2 nanospheres is anatase. In addition, the EDS elemental spectrum of Mn-SAs / TiO2@HEDP nanospheres, Figure 3 Shows the TEM-EDX elemental mapping image of the Mn-SAs / TiO2@HEDP catalyst. Figure 4-Figure 7 The distribution states of Ti, O, P, and Mn elements are shown respectively. It is worth noting that the unique hollow structure of Mn-SAs / TiO2@HEDP enables the local accumulation of Ti and O elements to form obvious hollow spheres, while P and Mn are only evenly distributed on the surface of the nanospheres without obvious aggregation.

[0073] In addition, high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was used to determine the atomic resolution position of Mn atoms in the TiO2 nanospheres. Considering the Mn atom loading on the TiO2 surface, the bright spots on the TiO2 nanospheres were attributed to single Mn atoms, such as Figure 8 and Figure 9 In addition, the ordered atomic arrangement indicates that the introduction of Mn element does not distort the TiO2 lattice.

[0074] In addition, in order to further clarify the crystal type of Mn-SAs / TiO2@HEDP prepared in Example 1 and to further study its chemical composition and surface structure, we used X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Figure 10 As shown, the X-ray diffraction spectra of Mn-SAs / TiO2 (prepared by step 3 in Example 1), Mn-SAs / TiO2@PO4 (prepared by Example 2) and Mn-SAs / TiO2@HEDP (prepared by Example 1) did not show diffraction peaks similar to those of manganese oxide, while the diffraction peaks of surface acid modification were similar to those of TiO2. Comparison with the standard PDF-#73-1764 card confirmed that the crystal type of the prepared hollow TiO2 (prepared by Comparative Example 1) nanospheres was anatase, and the prepared Mn single atoms were atomically dispersed. At the same time, as Figure 11 As shown, the phosphate groups are connected to the Ti atoms on the TiO2 surface through PO bonds, thereby constructing uranium ion coordination sites.

[0075] like Figure 12 As shown in Figure 2, compared with pristine TiO2, the Mn single atom site improves the utilization of near-infrared light and extends the light absorption wavelength of TiO2. Figure 13 As shown, the calculated band gaps of Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP are 2.91 eV, which is lower than the 3.14 eV band gap of pristine TiO2.

[0076] There are a lot of F-containing - The presence of radioactive wastewater significantly affects the catalyst's ability to catalyze the reduction of uranium. Therefore, we evaluated the catalyst's ability to extract uranium from radioactive wastewater under simulated sunlight. Figure 14 The graph shows the uranium extraction and reaction time curves of TiO2 (prepared by Comparative Example 1), Mn-SAs / TiO2 (prepared by step 3 in Example 1), Mn-SAs / TiO2@PO4 (prepared by Example 2) and Mn-SAs / TiO2@HEDP (prepared by Example 1) in simulated radioactive wastewater. Figure 14 The vertical dashed line in the figure represents the boundary between sunlight and darkness, where the F -The concentration was 1 g / L. Compared with pristine TiO2, the adsorption performance of Mn-SAs / TiO2 for uranium was significantly enhanced. This is because the Mn single atoms provide abundant active sites, bringing uranium ions closer to the Mn single-atom sites. The adsorption performance of Mn-SAs / TiO2@PO4 was slightly improved by surface phosphoric acid modification, but it was not significant compared to Mn-SAs / TiO2@HEDP. This suggests that the Mn single-atom sites and organophosphate modification can provide more uranyl capture sites, enhancing TiO2's competitiveness for uranyl in fluorine-containing radioactive wastewater. Subsequently, the reaction system was exposed to simulated sunlight, and TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4, and Mn-SAs / TiO2@HEDP each showed significant improvements in photocatalytic performance. After 120 minutes of illumination, Mn-SAs / TiO2 demonstrated a 69% U(VI) removal rate, which is significantly better than the 20% removal rate achieved by TiO2. In addition, compared with Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP further showed 6% and 25% photocatalytic enhancement, respectively, indicating that the modification of Mn single atom sites and surface organic phosphate groups can effectively improve the extraction rate of U(VI). In particular, Mn-SAs / TiO2@HEDP showed an excellent removal rate of 94%. However, in this system, inorganic phosphoric acid did not provide sufficient uranyl capture capacity. Figure 15 As shown, the Mn-SAs / TiO2@HEDP was further evaluated at different F - The extraction efficiency of uranium under the conditions of concentration. - With the increase of concentration, although the ability of Mn-SAs / TiO2@HEDP to compete with uranium ions decreased, - When the concentration is 5 g / L, Mn-SAs / TiO2@HEDP can maintain an 88% U(VI) removal rate. Figure 16 As shown, we also selected a simulated radioactive wastewater system with a fluorine concentration of 5 g / L and conducted catalyst cycling experiments to further evaluate the cyclic stability of Mn-SAs / TiO2@HEDP. After five photocatalytic cycles, Mn-SAs / TiO2@HEDP was able to maintain 85% of the U(VI) catalytic efficiency.

[0077] In order to be closer to the real fluorine-containing radioactive wastewater system, the stability of the Mn-SAs / TiO2@HEDP photocatalytic material was further evaluated through catalytic experiments with a wide range of pH values. Figure 17As shown in Figure 2, although the extraction efficiency of Mn-SAs / TiO2@HEDP for U(VI) was not ideal at pH 3, the catalytic performance of Mn-SAs / TiO2@HEDP maintained a significant removal rate of 88% within the pH range of 4 to 10. + , K + 、Sr 2+ etc.) and anions (CO3 2- 、HCO3 - etc.) were added into the photocatalytic system to study the effect of Mn-SAs / TiO2@HEDP on the photocatalytic extraction performance of U(VI). Figure 18 As shown in Figure 2, Mn-SAs / TiO2@HEDP can maintain more than 90% of its catalytic reduction performance under cation interference. It is worth noting that the selected anions (CO3 2- 、HCO3 - ) can coordinate with uranium ions in the photocatalytic system, reducing the ability of Mn-SAs / TiO2@HEDP to compete with uranium ions, but Mn-SAs / TiO2@HEDP still maintains a significant catalytic reduction performance of more than 87%. In addition, Figure 19 As shown in the figure, Mn-SAs / TiO2@HEDP still has significant U(VI) catalytic performance for U(VI) solutions with initial concentrations ranging from 8ppm to 100ppm. When the initial U(VI) concentration is 100mg / L, the U(VI) extraction capacity of Mn-SAs / TiO2@HEDP is calculated to be 288mg / g. According to the above analysis, the single atomic sites of Mn-SAs / TiO2@HEDP participate in the competitive coordination of uranium ions with organophosphorus groups, and the dual competitive sites contribute to the catalytic activity of Mn-SAs / TiO2@HEDP in F-containing solutions. - Excellent U(VI) removal performance in radioactive wastewater. In addition, single-atom sites can also adjust the band structure of TiO2 and expand its photoreaction range.

[0078] like Figure 20 As shown, the XRD patterns of Mn-SAs / TiO2@PO4 after photocatalysis exhibit unique characteristic diffraction peaks corresponding to the standard calcined uranium hydrate (UO2)O2·2H2O. Furthermore, it can be inferred that the uranium species in Mn-SAs / TiO2@HEDP are amorphous and difficult to form diffraction peaks. Notably, the XRD diffraction peaks of Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP remain well-defined before and after photocatalysis, indicating their structural stability.

[0079] In addition, electron paramagnetic resonance (EPR) was used to detect the active species of Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP during the photocatalytic reduction process. Figure 21 、 Figure 22 As shown, no ·OH and ·O2 - Under light conditions, the characteristic peaks of ·OH and ·O2 were clearly observed on TiO2, Mn-SAs / TiO2 and Mn-SAs / TiO2@PO4. - The characteristic peak signal of Mn-SAs / TiO2@HEDP is significant. Importantly, no ESR signal is observed on Mn-SAs / TiO2@HEDP. Compared with the original TiO2, the ESR signal of Mn-SAs / TiO2 is significantly enhanced. This is because Mn-SAs / TiO2 responds more widely to visible light and can provide more electrons and holes under light to further generate O2 with water and dissolved oxygen. - Although the ESR signal of Mn-SAs / TiO2@PO4 is stronger than that of pristine TiO2, it is significantly lower than that of Mn-SAs / TiO2. This is because the surface phosphate groups act as electron transfer bridges, reducing the direct reaction of surface electrons with dissolved oxygen to form ·O2. - , and also blocked the further reaction of holes with water to form ·OH. More importantly, the organic phosphate group directly acts as a directional bridge for the transfer of electrons, completely blocking the reaction of electrons with dissolved oxygen to form ·O2 - , and also blocked the further reaction of holes with water to generate ·OH. In addition, the linear sweep voltammetry (LSV) curves of U(VI) reduction were used to analyze the reduction activation energy and overpotential of TiO2, Mn-SAs / TiO2, Mn-SAs / TiO2@PO4 and Mn-SAs / TiO2@HEDP. Figure 23 As shown in Figure 3, Mn-SAs / TiO2@HEDP highlights the most positive reduction potential. This result suggests that the abundant organophosphate groups serve as powerful trapping sites for uranium ions and bridges for directional electron transfer, contributing to the excellent reduction activation energy and overpotential of TiO2.

[0080] In summary, the present invention regulates the electronic structure of TiO2 hollow nanospheres by constructing single atomic sites on the TiO2 surface and modifying organic phosphate groups, thereby effectively enhancing the photocatalytic activity and selective reduction of uranium. The dual active sites of Mn-SAs / TiO2@HEDP show obvious competition for uranyl ions in fluorine-containing uranium wastewater. After photocatalysis, the U(VI) removal rate is as high as 94%, and the U(VI) reduction efficiency is as high as 88%. The catalyst with dual active sites promotes the effective electron-hole separation and transfer of Mn-SAs / TiO2@HEDP, while improving the visible light response and electron lifetime. When Mn-SAs / TiO2@HEDP is placed under light, the photogenerated electrons are guided from the semiconductor conduction band to the uranyl ions coordinated by the phosphate group. Unlike traditional semiconductors, the photogenerated electrons directly reduce U(VI) without producing ·O2 - , thereby stabilizing the existence of reduced U(IV). In addition, the unique coordination structure of Mn-SAs / TiO2@HEDP and uranyl ions ensures the effective capture of uranyl by phosphate groups. - The removal efficiency of U(VI) in 5g / L uranium solution was still as high as 88%. This study not only opened up a new field for the photocatalytic reduction of uranium using a dual-site catalyst, but also provided a theoretical basis for the treatment of fluorine-containing uranium wastewater in the nuclear industry.

[0081] The number of devices and processing scales described herein are intended to simplify the description of the present invention. Applications, modifications, and variations of the present invention will be readily apparent to those skilled in the art.

[0082] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a titanium dioxide catalyst for uranium separation, characterized in that: The following steps are involved: Step 1: Preparation of SiO2@Mn-SAs / TiO2@SiO2, specifically comprising: S11. Seal and stir ethanol, H2O, and ammonia water at room temperature for 10 minutes, add tetraethyl orthosilicate, and stir vigorously for 2 to 12 hours; centrifuge the product, wash twice with water and ethanol, and then disperse in ethanol to obtain an ethanol dispersion of SiO2 nanospheres; S12. Add acetonitrile and ammonia water to the ethanol dispersion solution of SiO2 nanospheres and ultrasonicate until the SiO2 nanoparticles are dispersed to obtain solution A; at the same time, mix anhydrous ethanol and acetonitrile with tetrabutyl titanate to obtain a transparent solution B; mix solution A and solution B and stir for 2 to 6 hours, centrifuge, wash several times with ethanol, and then wash twice with pure water to obtain SiO2@TiO2 nanospheres; disperse the SiO2@TiO2 nanospheres in 40 mL of pure water to obtain a SiO2@TiO2 nanosphere dispersion; S13, adding MnCl2·4H2O to the SiO2@TiO2 nanosphere dispersion and vigorously stirring for 2-5 hours; centrifuging the product, washing it twice with pure water, and dispersing it in a polyvinyl pyrrolidone aqueous solution and stirring it for 2-12 hours; S14, centrifuging the product and redispersing it in a mixture of ethanol and pure water, and sonicating it to obtain a fully dispersed solution; S15. Add ammonia water and tetraethyl orthosilicate to the solution in S14 and stir for 2-8 hours; centrifuge the product, wash with ethanol and pure water, respectively, and dry under vacuum for 2-8 hours to obtain SiO2@Mn-SAs / TiO2@SiO2; Step 2: calcining SiO2@Mn-SAs / TiO2@SiO2 in air and dispersing it in a NaOH solution. The product was stirred at 60-90°C for 2-8 hours, centrifuged, washed with pure water and ethanol, and dried under vacuum at 60-80°C to obtain Mn-SAs / TiO2. Step 3: Disperse Mn-SAs / TiO2 into hydroxyethylidene diphosphonic acid or H3PO4 solution, stir, wash, and dry to prepare a titanium dioxide catalyst for uranium separation.

2. The method for preparing a titanium dioxide catalyst for uranium separation according to claim 1, wherein: In the S11, the volume ratio of ethanol, H2O, ammonia water, tetraethyl orthosilicate and ethanol used for dispersion is 10-30 mL: 1-10 mL: 0.1-2 mL: 0.1-2 mL: 10-100 mL; In S12, the volume ratio of acetonitrile and ammonia water used to prepare solution A is 5-30 mL:0.1-0.8 mL; the volume ratio of anhydrous ethanol, acetonitrile and tetrabutyl titanate used to prepare solution B is 1-20 mL:1-20 mL:0.1-2 mL.

3. The method for preparing a titanium dioxide catalyst for uranium separation according to claim 1, wherein: In the S13, the volume mass ratio of the SiO2@TiO2 nanosphere dispersion, MnCl2·4H2O and polyvinyl pyrrolidone aqueous solution is 10~80mL:2~10mg:10~80mL; the concentration of polyvinyl pyrrolidone in the polyvinyl pyrrolidone aqueous solution is 0.005~0.06 g / mL; In the S14, the volume ratio of ethanol to pure water is 10-60 mL:1-15 mL; In the S15, the volume ratio of ammonia water to tetraethyl orthosilicate is 0.5-5 mL:0.2-5 mL.

4. The method for preparing a titanium dioxide catalyst for uranium separation according to claim 1, wherein: The calcination temperature of SiO2@Mn-SAs / TiO2@SiO2 is 500~800℃, the calcination time is 2~8 hours, the concentration of NaOH solution is 0.1~0.8M, and the amount of NaOH solution used is 400~800mL.

5. The method for preparing a titanium dioxide catalyst for uranium separation according to claim 1, wherein: The specific method of step three includes: Mn-SAs / TiO2 was dispersed in hydroxyethylidene diphosphonic acid solution or H3PO4 solution and stirred at 60-80°C for 2-14 hours; after washing with ethanol and deionized water several times, respectively, the mixture was dried at 60-80°C for 2-24 hours to obtain Mn-SAs / TiO2@HEDP catalyst and Mn-SAs / TiO2@PO4 catalyst, respectively.

6. The method for preparing a titanium dioxide catalyst for uranium separation according to claim 5, characterized in that: The concentration of the hydroxyethylidene diphosphonic acid solution is 0.010-0.0180 M, and the volume of the hydroxyethylidene diphosphonic acid solution or H3PO4 solution is 10-60 mL.

7. Use of a titanium dioxide catalyst for uranium separation, wherein the titanium dioxide catalyst for uranium separation is prepared by the method for preparing the titanium dioxide catalyst for uranium separation according to any one of claims 1 to 6, characterized in that: The method of applying the titanium dioxide catalyst separated from uranium to the photocatalytic reduction of uranium includes: adding the titanium dioxide catalyst separated from uranium into wastewater containing U(VI), wherein the mass volume ratio of the titanium dioxide catalyst to the wastewater containing U(VI) is 0.5-100 mg:1-200 mL; and under light conditions, the titanium dioxide catalyst performs photocatalytic reduction on U(VI).

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