Visible light catalytic material for efficiently reducing hexavalent uranyl ions as well as preparation method and application of visible light catalytic material

Abstract

The invention relates to the technical field of uranium-containing wastewater treatment, in particular to a visible light catalytic material for efficiently reducing hexavalent uranyl ions as well as a preparation method and application of the visible light catalytic material. When hexavalent uranyl ions in wastewater are reduced by a conventional photocatalysis method, organic matters such as methanol, ethanol and the like need to be additionally added as sacrificial agents, so that the treatment cost is increased, and new pollutants are easily introduced. In order to solve the problems, the invention provides the visible light catalytic material for efficiently reducing the hexavalent uranyl ions, Fe < 2 + > is adsorbed on the surface of BiOBr in a solution through electrostatic interaction, then Fe < 2 + > and S < 2-> are subjected to a co-precipitation reaction on the surface of BiOBr, and finally, a target product BiOBr / FeS can be obtained after room-temperature aging. According to the visible light catalytic material, no sacrificial agent needs to be added in the process of reducing the hexavalent uranyl ions, compounding of electron-hole pairs can be effectively inhibited by means of the unique structure and performance of the visible light catalytic material, and the treatment cost is remarkably reduced while efficient reduction of the hexavalent uranyl ions is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of uranium-containing wastewater treatment technology, specifically to a visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions, its preparation method, and its application. Background Technology

[0002] With the booming development of the nuclear energy industry, uranium mining and beneficiation processes inevitably generate large amounts of radioactive waste. This waste contains uranium, especially uranium in the form of hexavalent uranyl ions (U(VI)), which poses a potential and serious threat to the environment and human health. When the U(VI) concentration in wastewater exceeds 5 mg / L, it exceeds the emission standards set by the World Health Organization. If this uranium-containing wastewater is discharged directly without effective treatment, uranium will continuously migrate and accumulate in the environment, not only polluting soil and water bodies and disrupting the ecological balance, but also potentially entering the human body through the food chain, causing various radiation-related diseases such as cancer and gene mutations. Therefore, the efficient treatment of uranium-containing wastewater and the reuse of uranium resources have become critical environmental issues that urgently need to be addressed.

[0003] Extracting uranium from uranium-containing wastewater presents numerous challenges. On one hand, the concentration of uranium in the wastewater is typically low, making effective separation and enrichment difficult. On the other hand, various ions often coexist in the wastewater, and these ions may interact with uranium ions, interfering with the extraction process and further increasing the difficulty of treatment. Therefore, developing a technology capable of effectively extracting uranium from wastewater with low concentrations and complex ion coexistence is of significant practical importance.

[0004] In the field of uranium-containing wastewater treatment, a variety of treatment technologies have been developed, including electrocoagulation, adsorption, membrane separation, biological reduction, and photocatalysis. However, these methods all have certain limitations.

[0005] Electrocoagulation: As an advanced coagulation-flocculation method, electrocoagulation generates a coagulant through the charge interaction between the cathode and anode, inducing metal cations to dissolve in water and generating hydroxyl ions at the cathode. This method is effective in removing uranium; however, its electrocoagulation equipment consumes a large amount of energy during operation, which not only increases treatment costs but also contradicts the current trend of energy conservation and emission reduction.

[0006] Adsorption method: The adsorption method mainly utilizes adsorbents such as mesoporous carbon and activated carbon to transfer uranium pollutants from the aqueous phase to the solid phase. However, this method has significant shortcomings. The adsorbent has a limited number of active sites, resulting in low adsorption efficiency. Moreover, the adsorbent is difficult to regenerate, and the regeneration process may cause secondary pollution. In addition, the regeneration cost is high, which limits its large-scale application.

[0007] Membrane separation: Membrane separation can selectively separate U(VI) from the aqueous phase, mainly including technologies such as ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). The advantages of this method are its excellent removal efficiency and potential for uranium recovery. However, the application of membrane separation technology requires professional operation, and the membrane recovery rate is relatively low. The membrane's lifespan is limited, and the cost of replacing the membrane is high. These factors restrict the widespread application of membrane separation.

[0008] Biological reduction: This method utilizes a biological system to reduce the U(VI) content in wastewater. Microorganisms convert U(VI) into insoluble U(IV) through metabolic activity, thereby removing uranium. This method is green and efficient, but it is costly and requires strict control of reaction conditions, such as temperature, pH, and nutrients; otherwise, the activity of the microorganisms and the treatment effect will be affected. Furthermore, biological methods are prone to secondary pollution; for example, microbial metabolic products may have adverse environmental impacts.

[0009] Photocatalysis: The photocatalytic treatment of uranium involves reducing U(VI) to U(IV), with the resulting U(IV) then adsorbed onto the surface of a photocatalyst. This method is simple to operate, has a high removal rate, is environmentally friendly, and has the potential for large-scale application, making it a promising candidate technology. However, existing photocatalytic materials still face some challenges in terms of synthesis processes, efficiency, and secondary pollution. For example, the synthesis processes of some photocatalytic materials are complex and costly; some materials may require the addition of sacrificial agents during photocatalysis to achieve better removal results (e.g., titanium dioxide is a common photocatalytic material; under illumination, electrons in its valence band transition to the conduction band, forming conduction band electrons (e0). - ) and valence band holes (h + However, some electrons and holes recombine rapidly, reducing photocatalytic efficiency. In the degradation of organic pollutants, to suppress electron-hole recombination, organic compounds such as methanol and ethanol are often added as sacrificial agents. These sacrificial agents have strong reducing properties and preferentially react with holes. For example, methanol (CH3OH) is oxidized by holes and decomposes itself into small molecules such as carbon dioxide and water, thus consuming holes and allowing more electrons to participate in the reduction reaction, reducing dissolved oxygen in the water to superoxide radicals (·O2). - Reactive oxygen species (ROS) can further oxidize and decompose organic pollutants, improving degradation efficiency. However, this not only increases treatment costs but may also introduce new pollutants. Summary of the Invention

[0010] The problem with existing technologies is that conventional photocatalytic methods for reducing hexavalent uranyl ions in wastewater require the addition of organic compounds such as methanol and ethanol as sacrificial agents, which not only increases treatment costs but also easily introduces new pollutants. To address these issues, this invention provides a visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions, the preparation method of which includes the following steps: Fe in aqueous solution under room temperature, gas protection, and sealed conditions 2+ Fe adsorbs onto the BiOBr surface via electrostatic interaction. 2 + On the surface of BiOBr and S 2- A coprecipitation reaction occurs, followed by aging at room temperature to obtain a visible light catalytic material, denoted as BiOBr / FeS.

[0011] Preferably, Fe in the coprecipitation reaction process 2+ The source is water-soluble ferrous salts.

[0012] Preferably, the water-soluble divalent iron salt is FeSO4·7H2O.

[0013] Preferably, S in the coprecipitation reaction process 2- The source is water-soluble metal sulfides.

[0014] Preferably, the water-soluble metal sulfide is sodium hydrate sulfide.

[0015] Preferably, the hydrated sodium sulfide is Na2S·9H2O.

[0016] Preferably, the protective gas is nitrogen or an inert gas.

[0017] Preferably, the aging time at room temperature is at least 0.5 hours and no more than 24 hours.

[0018] Preferably, during the coprecipitation reaction, S in the aqueous solution 2- with Fe 2+ The molar ratio of BiOBr to all S in the reaction system is 1:1. 2- With all Fe 2+ The mass ratio of the total mass is 1:1.

[0019] The BiOBr (CAS:144701-48-4) of this invention can be purchased externally or manufactured in-house. The preparation method of BiOBr is as follows: 0.485 g Bi(NO3)3·5H2O and 0.119 g KBr were dissolved in 20 mL of ethylene glycol (EG), stirred evenly, and then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was hydrothermally reacted at 160 °C for 12 h. The solid product was collected, washed successively with deionized water and anhydrous ethanol, and then dried to obtain BiOBr.

[0020] Beneficial effects: (1) In the conventional photocatalytic reduction of hexavalent uranyl ions in wastewater, it is usually necessary to add organic substances such as methanol and ethanol as sacrificial agents. The role of these sacrificial agents is to consume the holes generated during the photocatalytic process, reduce the recombination of electron-hole pairs, and thus improve the photocatalytic reduction efficiency. However, adding sacrificial agents not only increases the purchase cost of chemical reagents for wastewater treatment, but also requires precise control of the amount added, which increases the complexity and cost of operation. Moreover, the sacrificial agent may not be able to react completely during the reaction, and the residual sacrificial agent and its reaction intermediates can easily become new pollutants, causing secondary pollution to the environment. However, the BiOBr / FeS visible light photocatalytic material prepared in this invention does not require the addition of any sacrificial agent in the process of reducing hexavalent uranyl ions. With its unique structure and performance, this material can effectively suppress the recombination of electron-hole pairs, allowing more electrons to participate in the reduction reaction of hexavalent uranyl ions. While ensuring efficient reduction of hexavalent uranyl ions, it significantly reduces the treatment cost and avoids the problem of introducing new pollutants due to the addition of sacrificial agents, making it more environmentally friendly.

[0021] (2) The visible light catalytic material preparation method of the present invention is simple to operate and can be carried out at room temperature, under gas protection, and in a sealed state. During the co-precipitation process, Fe in the aqueous solution 2+ Adsorbed onto the BiOBr surface via electrostatic interaction, followed by Fe 2+ On the surface of BiOBr and S 2- A co-precipitation reaction occurs, followed by aging at room temperature to obtain the target product, BiOBr / FeS. The entire preparation process does not require complex equipment or harsh reaction conditions, such as high temperature and high pressure, and the technical requirements for operators are relatively low. This simple synthesis process makes it easy to achieve large-scale industrial production of this material, which can meet the large demand for photocatalytic materials in practical uranium-containing wastewater treatment projects.

[0022] (3) In the coprecipitation reaction process of the present invention, S in the aqueous solution 2- with Fe 2+ The molar ratio is 1:1, and S 2- with Fe 2+The amount of BiOBr added is based on a 1:1 mass ratio of BiOBr to FeS. Precise raw material proportioning ensures the reaction proceeds in the intended direction, generating photocatalytic materials with ideal structure and composition. This precise proportioning helps optimize the electronic structure and surface properties of the material, improving its light absorption capacity and electron-hole pair separation efficiency, thereby significantly enhancing its reduction capacity for hexavalent uranyl ions and enabling the material to exhibit superior performance in practical uranium-containing wastewater treatment. Attached Figure Description

[0023] Figure 1 The target products obtained in Example 1 and Comparative Examples 1-4 were added as reducing agents to 100 mL of uranium-containing wastewater. The amount of reducing agent added was 5 mg. After adsorption for 20 min under light-protected conditions, photocatalytic reaction was carried out for 40 min under fluorescent light. The reduction and removal results of hexavalent uranyl ions were then tested.

[0024] Figure 2 Example 1: The target product obtained was added as a reducing agent to 100 mL of uranium-containing wastewater with different pH values. The amount of reducing agent added was 5 mg. After adsorption for 20 min under light-protected conditions, a photocatalytic reaction was carried out for 40 min under fluorescent light. The results of the reduction and removal of hexavalent uranyl ions were obtained.

[0025] Figure 3 XRD pattern of BiOBr / FeS obtained in Example 1. Detailed Implementation

[0026] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0027] Example 1

[0028] A method for preparing a visible light photocatalyst material that efficiently reduces hexavalent uranyl ions is as follows: (1) Under the conditions of room temperature, nitrogen protection and sealing, deionized water was added to a four-necked flask, and 0.2g BiOBr was added while stirring. After the addition was completed, the mixture was stirred for 20 min. Then FeSO4·7H2O was added while stirring. After the addition was completed, the mixture was stirred for 60 min to obtain a mixed solution. (2) Dissolve Na2S·9H2O in 15 mL of deionized water and slowly add it dropwise to the above mixture. After the addition is complete, stir the reaction for 60 min. After the reaction is complete, let it stand for 24 h to age. After aging, vacuum filter the reaction solution and freeze-dry it (freeze-dry for 12 h at -60℃) to obtain the visible light photocatalyst BiOBr / FeS (its XRD is as shown in the attached instruction manual). Figure 3As shown), the amounts of FeSO4·7H2O and Na2S·9H2O added during the co-precipitation process were determined based on a 1:1 mass ratio of BiOBr to FeS. The mass of FeS was calculated based on the mass of BiOBr, and the mass of S in FeS was determined based on the mass of BiOBr. 2- with Fe 2+ The amount of FeSO4·7H2O and Na2S·9H2O added was calculated from the molar amounts.

[0029] Comparative Example 1 is the same as Example 1, except that the amount of FeSO4·7H2O and Na2S·9H2O added during the co-precipitation process in Comparative Example 1 is based on a BiOBr to FeS mass ratio of 1:2. The mass of FeS is calculated based on the mass of BiOBr, and the mass of S in FeS is calculated based on the mass of BiOBr. 2- with Fe 2+ The amount of FeSO4·7H2O and Na2S·9H2O added was calculated from the molar amounts.

[0030] Comparative Example 2 is the same as Example 1, except that the amounts of FeSO4·7H2O and Na2S·9H2O added during the co-precipitation process in Comparative Example 2 are based on a BiOBr to FeS mass ratio of 2:1. The mass of FeS is calculated based on the mass of BiOBr, and the mass of S in FeS is calculated based on the mass of BiOBr. 2- with Fe 2+ The amount of FeSO4·7H2O and Na2S·9H2O added was calculated from the molar amounts.

[0031] Comparative Example 3 is BiOBr.

[0032] Comparative Example 4 is FeS, with CAS number 1317-37-9.

[0033] Performance testing

[0034] Preparation of uranium-containing wastewater: Add 0.059 g of sodium chloride and 1.0675 g of MES buffer (also known as 2-(N-morpholine)ethanesulfonic acid monohydrate, purchased externally, CAS number 145224-94-8) to 100 mL of an aqueous solution of hexavalent uranyl ions with a mass concentration of 20 mg / L. Adjust the pH of the solution to 6 with NaOH.

[0035] Test (1): The materials obtained in Example 1 and Comparative Examples 1-4 were added to 100 mL of uranium-containing wastewater as reducing agents. The amount of reducing agent added was 5 mg. After adsorption for 20 min under light-protected conditions, photocatalytic reaction was carried out for 40 min under fluorescent light. The reduction and removal test results of hexavalent uranyl ions are shown in the appendix of the instruction manual. Figure 1(BiOBr / FeS (1:1) represents Example 1, BiOBr / FeS (1:2) represents Comparative Example 1, and BiOBr / FeS (2:1) represents Comparative Example 2) as shown.

[0036] Test (2): The pH of the uranium-containing wastewater was adjusted to 4, 5, 7, and 8 respectively. The remaining steps were carried out according to Test (1). The reducing agent obtained in Example 1 was added to the aqueous solution of hexavalent uranyl ions for testing. The reduction and removal test results of hexavalent uranyl ions are shown in the appendix of the instruction manual. Figure 2 As shown.

[0037] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions, characterized in that, The preparation method includes the following steps: Fe in aqueous solution under room temperature, gas protection, and sealed conditions 2+ Fe is adsorbed onto the BiOBr surface through electrostatic interaction. 2+ On the surface of BiOBr and S 2- A coprecipitation reaction occurs, followed by aging at room temperature to obtain a visible light catalytic material, denoted as BiOBr / FeS.

2. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 1, characterized in that, Fe during the coprecipitation reaction 2+ The source is water-soluble divalent iron salt.

3. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 2, characterized in that, The water-soluble divalent ferric salt is FeSO4·7H2O.

4. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 1, characterized in that, S during the coprecipitation reaction 2- The source is water-soluble metal sulfides.

5. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 4, characterized in that, The water-soluble metal sulfide is sodium hydrate sulfide.

6. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 5, characterized in that, Sodium sulfide hydrate is Na2S·9H2O.

7. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 1, characterized in that, The protective gas is nitrogen or an inert gas.

8. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 1, characterized in that, The aging time at room temperature should be at least 0.5 hours and no more than 24 hours.

9. The visible light photocatalytic material for the efficient reduction of hexavalent uranyl ions according to claim 1, characterized in that, During the coprecipitation reaction, S in the aqueous solution 2- with Fe 2+ The molar ratio of BiOBr to all S in the reaction system is 1:

1. 2- With all Fe 2+ The mass ratio of the total mass is 1:

1.

10. A method for treating wastewater containing hexavalent uranyl ions, characterized in that, The visible light catalytic material described in any one of claims 1-9 is added to the wastewater as a reducing agent.

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