Photocatalytic material for immobilizing technetium as well as preparation method and application of photocatalytic material

Abstract

The invention discloses a photocatalytic material for immobilizing technetium and a preparation method and application thereof.The preparation method comprises the steps that sodium sulfide with the concentration being 1-10 mol L <-1 > and oxysalt of sulfur with the same concentration are prepared and then mixed, and a first mixed solution is obtained; and vigorously stirring the first mixed solution, dropwise adding a cadmium salt aqueous solution with the concentration of 1-6 mol L <-1 >, continuously stirring, standing and precipitating, washing the obtained precipitate with water for 2-3 times, filtering and drying to obtain the photocatalytic material for immobilizing technetium. The prepared photocatalytic material for immobilizing technetium has the advantages that the adsorption surface rich in sulfur is used for driving migration of photon-generated carriers, the carrier recombination rate is reduced, the number of reaction sites is large, and the like. Meanwhile, the photocatalytic material can effectively fix technetium in a solution in a neutral solution with the pH value of 7 by utilizing visible light, an antioxidant stable technetium sulfide phase is formed in situ, no heavy metal cadmium is dissolved out basically, and the photocatalytic material has environmental friendliness of waste discharge treatment.

Description

Technical Field

[0001] The present invention relates to the fields of photocatalysis and the fixation or purification of radionuclides in the environment, and relates to a photocatalytic material, a preparation method thereof, and an application thereof, and particularly relates to a photocatalytic material capable of rapidly fixing technetium, a preparation method thereof, and an application thereof. Background Art

[0002] Technetium-99 ( 99 Tc) is a β-radionuclide (E 5 = 297.5 keV) with a long half-life (2.13×10 βmax a), and mainly comes from the fission processes of uranium-235 ( 235 U), uranium-238 ( 238 U), and plutonium-239 ( 239 Pu). It is worth noting that 99 Tc usually exists in the form of a high-salt anion (TcO4 - ), and it is not easy to form complexes with minerals or organic substances in an aerobic environment. Once the annual intake of Tc reaches 0.04 mSv, the risk of developing cancer or other radiation-related health problems will increase significantly. Conventional TcO4 - remediation methods include physicochemical adsorption / ion exchange methods, chemical reduction / sequestration methods, etc. Tc(VII)O4 - can be reduced to poorly soluble Tc(IV)O2·nH2O (log Ksp = -8.4), and then can be fixed by simple filtration. However, chemical reduction is often accompanied by a long reaction time and a cumbersome process flow, and adsorption / ion exchange also faces challenges such as secondary pollution.

[0003] In view of the clean, environmentally friendly and low-cost strategy, photocatalysis is more suitable for environmental remediation. Although titanium dioxide (TiO2) has been used for photocatalytic reduction of Tc(VII) / Re(VII) (a chemical analogue of Tc(VII)), the stability of its reduction product is poor under neutral or alkaline conditions. On the one hand, the increase in pH value will reduce the valence band potential of TiO2, resulting in a decrease in the reduction rate. On the other hand, this is because when the pH value exceeds 5, Tc(IV)O2·nH2O can be converted into a soluble substance [Tc(IV)O(OH)3] - , thus inhibiting the reduction and removal of Re(VII). It is worth noting that reduced technetium sulfide phases (such as Tc2S7 and TcS2) exhibit enhanced antioxidant properties, and this property becomes more significant with the increase in pH value. Although it is possible to directly add H2S or HS -To establish a sulfide environment, but these methods are not ideal for the reduction and fixation of Tc in the groundwater environment. Promoting the formation of Tc-S through in-situ sulfide generation can be used as a promising sequestration strategy.

[0004] In the currently reported studies, photocatalytic materials that can be used to reduce and separate TcO4 - / ReO4 - (ReO4 - is a non-radioactive analogue of TcO4 - basically have poor applicability in a neutral / weakly alkaline aqueous solution environment. Especially in the complex environment of natural water systems, it is impossible to achieve efficient and selective fixation of TcO4 - / ReO4 - . Therefore, it limits the application of photocatalysis in the environmental purification treatment of technetium. Therefore, it is very necessary to design a photocatalytic material with high photocatalytic efficiency, excellent chemical stability, environmental friendliness, and low cost. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problem that existing photocatalysts (such as P25 or anatase) cannot efficiently separate technetium or rhenium (rhenium is a non-radioactive analogue of technetium) in neutral aqueous solutions, and to provide a photocatalytic material for quickly fixing technetium, its preparation method and application. This photocatalytic material can utilize visible light and has a separation efficiency of more than 70% for ReO4 - in a neutral solution with pH = 7 within 2 hours.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] The present invention first discloses a photocatalytic material for fixing technetium. This photocatalytic material is a cubic phase cadmium sulfide material with a sulfur-rich modification on its surface, presenting as a powder, with a band gap of 2.0 - 2.5 eV, an average particle size of 300 - 500 nm, and a specific surface area of 50 - 60 m 2 g -1 .

[0008] The present invention also discloses a preparation method of a photocatalytic material for fixing technetium, including the following steps:

[0009] S1. Prepare a sodium sulfide solution with a concentration of 1 - 10 mol / L -1 and an oxygen-containing salt of sulfur with a concentration of 1 - 10 mol / L -1 , and then mix them to obtain a first mixed solution for standby;

[0010] S2. Vigorously stir the first mixed solution and gradually add a solution with a concentration of 1 - 6 mol / L -1A cadmium salt aqueous solution is continuously stirred, allowed to stand for precipitation, and the obtained precipitate is washed 2 to 3 times with water, filtered, and dried to obtain a photocatalytic material.

[0011] Further, the sulfur-containing oxygenate salt described in step S1 is selected from any one of sodium sulfate, sodium thiosulfate, sodium sulfite, and dithionate sodium.

[0012] Further, the cadmium salt aqueous solution described in step S2 is selected from any one of cadmium nitrate aqueous solution, cadmium acetate aqueous solution, cadmium oxalate aqueous solution, and cadmium chloride aqueous solution.

[0013] Further, the continuous stirring time described in step S2 is 15 - 120 minutes.

[0014] Further, the drying conditions described in step S2 are: drying at 60 - 180 °C for 24 hours.

[0015] The present invention also discloses a photocatalytic material for fixing technetium prepared by any one of the above preparation methods.

[0016] The present invention also discloses an application of the above-mentioned photocatalytic material for fixing technetium in environmental treatment.

[0017] Further, the application includes:

[0018] Placing the photocatalytic material for fixing technetium in a neutral aqueous solution containing a certain concentration of technetium and irradiating it with simulated sunlight for 2 h can effectively reduce and fix technetium in the solution.

[0019] The beneficial effects of the present invention:

[0020] The present invention prepares a photocatalytic material for fixing technetium. This photocatalytic material has an adsorption surface rich in sulfur to drive the migration of photo-generated carriers, with advantages such as a reduced carrier recombination rate and a large number of reaction sites. At the same time, this photocatalytic material can utilize visible light to efficiently fix technetium in a solution at pH = 7, in-situ form a stable sulfurized technetium phase with antioxidant properties, and there is basically no dissolution of heavy metal cadmium, showing environmental friendliness for waste treatment. Description of the Drawings

[0021] Figure 1 SEM image of the photocatalytic material prepared in Example 1.

[0022] Figure 2 XRD pattern of the photocatalytic material prepared in Example 1.

[0023] Figure 3 TEM image of the photocatalytic material prepared in Example 1.

[0024] Figure 4UU-Vis diagram of the photocatalytic material prepared in Example 1.

[0025] Figure 5 Nitrogen adsorption and desorption diagram of the photocatalytic material prepared in Example 1.

[0026] Figure 6 Performance of the product of the present invention in fixing rhenium (VII) under visible light.

[0027] Figure 7 Product analysis of the product of the present invention in fixing rhenium (VII) under visible light

[0028] Figure 8 Cd during the fixation of rhenium by the product of the present invention under visible light 2+ Dissolution situation.

[0029] Figure 9 Performance comparison of the product of the present invention in fixing rhenium and technetium under visible light. Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] (1) Prepare sodium sulfide with a concentration of 4 mol / L -1 and cadmium nitrate with a concentration of 4 mol / L -1 , and then mix them to obtain a first mixed solution;

[0033] (2) Slowly add dropwise an aqueous solution of cadmium nitrate with a concentration of 1 mol / L -1 to the first mixed solution, and then continue stirring for 60 minutes to obtain a second mixed solution;

[0034] (3) Let the precipitate obtained in the second mixed solution stand, wash it 3 times with water, filter, and dry it at 80 °C for 24 hours to obtain a cubic phase cadmium sulfide photocatalytic material. The SEM diagram of the cubic phase cadmium sulfide photocatalytic material prepared in this example is as shown in the appendix Figure 1 shown, and the morphological characteristics of the material can be determined; the XRD diagram is as shown in the appendix Figure 2 shown, and it can be determined that the material is synthesized correctly and effectively; the TEM diagram is as shown in the appendix Figure 3 shown, showing a clear material morphology; the UV-Vis diagram is as shown in the appendix Figure 4 shown, showing excellent visible light absorption ability; the nitrogen adsorption and desorption diagram is as shown in the appendix Figure 5 shown, with a specific surface area as high as 52.2 m 2 / g.

[0035] Example 2

[0036] (1) Prepare with a concentration of 7 mol / L-1 of sodium sulfide with a concentration of 7 mol / L -1 and cadmium sulfate with a concentration of 7 mol / L, and then mix them to obtain a first mixed solution;

[0037] (2) Slowly add dropwise an aqueous solution of cadmium oxalate with a concentration of 1 mol / L -1 to the first mixed solution, and then continue to stir for 30 minutes to obtain a second mixed solution;

[0038] (3) Let the precipitate obtained in the second mixed solution stand, wash it 3 times with water, filter, and dry it at 120 °C for 24 hours to obtain a cubic-phase cadmium sulfide photocatalytic material.

[0039] Example 3

[0040] (1) Prepare sodium sulfide with a concentration of 5 mol / L -1 and sodium thiosulfate with a concentration of 5 mol / L, and then mix them to obtain a first mixed solution; -1 (2) Slowly add dropwise an aqueous solution of cadmium chloride with a concentration of 4 mol / L

[0041] to the first mixed solution, and then continue to stir for 15 minutes to obtain a second mixed solution; -1 (3) Let the precipitate obtained in the second mixed solution stand, wash it 3 times with water, filter, and dry it at 180 °C for 24 hours to obtain a cubic-phase cadmium sulfide photocatalytic material.

[0042] (3) Let the precipitate obtained in the second mixed solution stand, wash it 3 times with water, filter, and dry it at 180 °C for 24 hours to obtain a cubic-phase cadmium sulfide photocatalytic material.

[0043] Application Example 1

[0044] Photocatalytic reduction and fixation experiment of rhenium (rhenium is a non-radioactive analogue of technetium) in the laboratory:

[0045] The experimental conditions are to adjust the pH of the solution to 6 - 8 with H2SO4 and NaOH, and irradiate with visible light for 2 h. The remaining amount A of rhenium is detected by inductively coupled plasma emission spectroscopy. A = C t / C0 × 100%, where C t and C0 represent the concentration of rhenium at a certain moment and the initial moment, respectively. As Figure 6 shown, for a 10 mg / L -1 rhenium solution, 50% of rhenium can be effectively fixed after 120 min of light irradiation. Combining X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy and synchrotron radiation X-ray absorption spectroscopy analysis (as Figure 7 shown), the in-situ formation of rhenium sulfide phase is confirmed, and the dissolution of Cd 2+ during the reaction process is lower than 3 μg / L (as Figure 8 shown), with basically no dissolution, proving the environmental friendliness of this method for waste treatment.

[0046] Application Example 2

[0047] Photocatalytic Reduction and Fixation of Rhenium in Lake Water

[0048] Perform the following photocatalytic experiment on the cubic cadmium sulfide photocatalytic material prepared in Example 1.

[0049] Catalyst-lake water system test: Use lake water as the reaction water for the experiment under the experimental conditions, and then irradiate with visible light for 2 h. Detect the remaining amount A of rhenium by inductively coupled plasma emission spectrometry. A = C t / C0 × 100%, where C t and C0 represent the concentrations of rhenium at a certain moment and the initial moment, respectively. The results are as Figure 6 shown. For a 10 mg / L rhenium solution, 50% of rhenium can be effectively fixed after 120 min of light irradiation, which is consistent with the test results using laboratory water.

[0050] Application Example 3

[0051] Photocatalytic Reduction and Fixation of Rhenium in Groundwater

[0052] Perform the following photocatalytic experiment on the cubic cadmium sulfide photocatalytic material prepared in Example 2.

[0053] Catalyst-groundwater system test: Use lake water as the reaction water for the experiment under the experimental conditions, and then irradiate with visible light for 2 h. Detect the remaining amount A of rhenium by inductively coupled plasma emission spectrometry. A = C t / C0 × 100%, where C t and C0 represent the concentrations of rhenium at a certain moment and the initial moment, respectively. The results are as Figure 6 shown. For a 10 mg / L rhenium solution, 50% of rhenium can be effectively fixed after 120 min of light irradiation, which is consistent with the test results using laboratory water.

[0054] Application Example 4

[0055] Comparison of the Reduction and Fixation of Rhenium and Technetium by a Photocatalytic Material for Fixing Technetium

[0056] Perform the following photocatalytic test on the cubic cadmium sulfide photocatalytic material prepared in Example 3: The experimental conditions are to adjust the solution pH = 7 with H2SO4 and NaOH and irradiate with visible light for 2 h. Detect the remaining amounts A of technetium / rhenium by a liquid scintillation counter and inductively coupled plasma emission spectrometry respectively. A = C t / C0 × 100%, where C t and C0 represent the concentrations of rhenium / technetium at a certain moment and the initial moment, respectively. The results are as Figure 9 shown. Under the same reaction conditions, the photocatalytic material has a better reduction and fixation efficiency for technetium than the simulated element rhenium, attributed to its higher redox potential.

[0057] In summary, the cubic-phase cadmium sulfide photocatalytic material prepared by the present invention has excellent photocatalytic performance and can effectively photocatalytically reduce and immobilize technetium in natural waters.

[0058] The description and drawings of the present invention are considered to be illustrative rather than restrictive. Based on the present invention, those skilled in the art can make some substitutions and deformations of some technical features without creative labor according to the disclosed technical content, and all are within the protection scope of the present invention.

Claims

1. A photocatalytic material for fixing technetium, wherein: The photocatalytic material is a cubic cadmium sulfide material with a sulfur-rich modification on its surface, showing a powdery form, a band gap of 2.0 - 2.5 eV, an average particle size of 300 - 500 nm, and a specific surface area of 50 - 60 m 2 g -1 .

2. A preparation method of the photocatalytic material for fixing technetium according to claim 1, comprising: S1. Prepare sodium sulfide with a concentration of 1 - 10 mol / L -1 and an oxygen-containing salt of sulfur with a concentration of 1 - 10 mol / L -1 , then mix them to obtain a first mixed solution for standby; S2. Vigorously stir the first mixed solution and dropwise add an aqueous cadmium salt solution with a concentration of 1 - 6 mol / L -1 , continuously stir, let it stand for precipitation, wash the obtained precipitate 2 - 3 times with water, filter and dry to obtain a photocatalytic material for fixing technetium.

3. According to the preparation method described in claim 2, wherein: The oxygen-containing salt of sulfur described in step S1 is selected from any one of sodium sulfate, sodium thiosulfate, sodium sulfite, and sodium dithionate.

4. According to the preparation method described in claim 2, wherein: The cadmium salt aqueous solution described in step S2 is selected from any one of cadmium nitrate aqueous solution, cadmium acetate aqueous solution, cadmium oxalate aqueous solution, or cadmium chloride aqueous solution.

5. According to the preparation method described in claim 2, wherein: The continuous stirring time in step S2 is 15 - 120 minutes.

6. According to the preparation method described in claim 2, wherein: The drying conditions in step S2 are: drying at 60 - 180 °C for 24 hours.

7. A photocatalytic material for fixing technetium prepared by the preparation method according to any one of claims 2 to 6.

8. An application of the photocatalytic material for fixing technetium according to claim 1 or 7 in environmental treatment.

9. According to the application described in claim 8, comprising: Placing the photocatalytic material for fixing technetium in a neutral aqueous solution containing technetium and irradiating it with simulated sunlight for 2 h can achieve the reduction and fixation of technetium in the solution.

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