A heterojunction photocatalytic reduction U(VI) material and preparation method thereof

Abstract

The present invention discloses a heterojunction photocatalytic reduction U(VI) material and a preparation method thereof. The Z-type heterostructure of the self-assembled photocatalytic reduction material Cs2AgBiBr6 and La2AlFeO6 of the present invention can perform photocatalysis under visible light conditions, thus solving the problem that existing photocatalytic materials can only absorb ultraviolet light. The separation efficiency of photogenerated electrons and holes is effectively improved, the recombination rate is suppressed, and charge separation is promoted. The material of the present invention has high cyclic stability and good catalytic efficiency, and can be effectively used for the catalytic reduction of U(VI), reducing U(VI) with strong solubility and migration ability in radioactive wastewater into U(IV) in a stable precipitated form.

Description

Technical Field

[0001] The invention belongs to the technical field of radioactive wastewater treatment, and particularly relates to a heterojunction photocatalytic reduction U(VI) material and a preparation method thereof. Background Art

[0002] The main methods for treating uranium-containing wastewater generated during the nuclear fuel cycle include physical, chemical, and biological methods. Physical methods include adsorption, membrane separation, and evaporation concentration; chemical methods include chemical precipitation and ion exchange; and biological methods include microbial treatment and plant treatment technologies. Adsorption is the most commonly used method for treating radioactive uranium-containing wastewater. It has the advantages of a wide range of raw materials, low price, simple preparation method, and good stability, but the adsorbent is limited by its adsorption capacity. Membrane separation has the advantages of high purification coefficient, low energy consumption, and simple operating equipment and process, but the compatibility of the membrane is easily affected by environmental factors and its stability is poor. Evaporation has high efficiency, produces less wastewater, and has a high decontamination multiple, but has disadvantages such as high cost, high energy consumption, and high safety risks. Chemical precipitation has the advantages of low price, simple treatment equipment, and the ability to reduce most radioactive nuclides, but is easily affected by factors such as solution pH, ionic strength, reaction temperature and time, has harsh operating conditions, and the large amount of sediment generated can easily cause secondary pollution. Ion exchange can achieve good purification effects, but ion exchange resins are easily interfered by coexisting ions and have disadvantages such as high cost. Phytotreatment technology and microbial treatment have the advantages of low cost, environmental friendliness, and simple process, but have disadvantages such as long treatment cycle and the inability to recover uranium resources after treatment. Therefore, traditional uranium-containing wastewater treatment methods are limited by factors such as low diffusion kinetics, complex reaction conditions, low selectivity, and interference from coexisting ions. They have disadvantages such as high cost, poor treatment effect, and easy secondary pollution. In related technologies, economical and efficient, highly selective, non-secondary-pollution, reusable, green and sustainable semiconductor photocatalytic reduction is adopted. However, the band gap of semiconductor photocatalytic reduction is too wide and can only absorb ultraviolet light. Ultraviolet light accounts for less than 5% of the entire solar spectrum (below 400nm), while visible light energy with a wavelength of 400-750nm accounts for about 43% of the solar energy; and the recombination rate of photogenerated electrons and holes is high, resulting in very low quantum efficiency; the stability of semiconductor catalyst materials is poor. Summary of the Invention

[0003] In view of the above technical problems existing in the prior art, the purpose of the present invention is to provide a new type of heterojunction photocatalytic reduction U(VI) material that can not only absorb ultraviolet light, but also has strong stability and can achieve high electron-hole separation efficiency, and a preparation method thereof.

[0004] To achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is as follows: a heterojunction photocatalytic reduction U(VI) material, which is a photocatalyst of a Z-type heterojunction self-assembled by an inorganic halogen perovskite and an oxide perovskite.

[0005] Furthermore, the inorganic halogen perovskite and oxide perovskite are Cs2AgBiBr6 and La2AlFeO6 respectively.

[0006] The present invention also provides a method for preparing a heterojunction photocatalytic reduction U(VI) material, comprising the following steps:

[0007] (1) grinding and mixing appropriate amounts of inorganic halogen perovskite and oxide perovskite in an isopropanol environment to obtain a mixture solution;

[0008] (2) stirring and centrifuging the mixture solution to collect the precipitate;

[0009] (3) The precipitate was washed with isopropyl alcohol and dried in a vacuum drying oven to obtain a heterogeneous photocatalyst.

[0010] Furthermore, in step (1), the inorganic halogen perovskite and oxide perovskite are Cs2AgBiBr6 and La2AlFeO6, respectively.

[0011] Furthermore, the preparation method of the inorganic halogen perovskite Cs2AgBiBr6 comprises the following steps:

[0012] (1) Add stoichiometric CsBr, AgBr, and BiBr to HBr acid (48%) and stir;

[0013] (2) The stirred mixture is heated in an oil bath and then cooled naturally;

[0014] (3) centrifuging the cooled mixture, collecting the precipitate and vacuum drying;

[0015] (4) dissolving the dried solid in dimethyl sulfoxide to obtain a clear solution;

[0016] (5) The transparent solution was added to dichloromethane, and the solid was collected by centrifugation and vacuum dried to obtain Cs2AgBiBr6.

[0017] Furthermore, in step (5), Cs2AgBiBr6 is a nanocrystal.

[0018] Furthermore, the preparation method of the oxide perovskite La2AlFeO6 comprises the following steps:

[0019] (1) La(NO3)3·6H2O, Al(NO3)3·9H2O, and Fe(NO3)3·9H2O were dissolved in citric acid according to the molar ratio to obtain a solution;

[0020] (2) adding aqueous ammonia to the above solution and heating it in a constant temperature water bath until the solution becomes a viscous wet gel;

[0021] (3) The wet gel is dried at a constant temperature, calcined at a high temperature, and ground to obtain La2AlFeO6.

[0022] The present invention also provides an application of a heterojunction photocatalytic reduction U(VI) material, wherein the material is used for catalytic reduction of U(VI) in radioactive wastewater.

[0023] The present invention also provides an application of a heterojunction photocatalytic reduction U(VI) material, wherein the material is used for catalytic reduction of U(VI) in radioactive wastewater to U(IV) in a stable precipitated form under visible light conditions.

[0024] The beneficial effects brought about by the technical solution of the present invention are that the heterojunction photocatalytic reduction U(VI) material of the present invention is a Z-type heterostructure self-assembled by Cs2AgBiBr6 and La2AlFeO6, which can perform photocatalysis under visible light conditions, solving the problem that existing photocatalytic materials can only absorb ultraviolet light; effectively improving the separation efficiency of photogenerated electrons and holes and suppressing the recombination rate; and the material of the present invention has high cyclic stability and good catalytic efficiency, and can be effectively used for catalytic reduction of U(VI), reducing U(VI) with strong solubility and migration ability in radioactive wastewater to U(IV) in a stable precipitated form, thereby improving the recovery and utilization rate of uranium resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation process of the heterojunction photocatalytic reduction U(VI) material according to Example 1 of the present invention;

[0026] Figure 2 This is an SEM image of the heterojunction photocatalytic reduction U(VI) material prepared by the method of Example 1 of the present invention;

[0027] Figure 3 Schematic diagram of the preparation process of Cs2AgBiBr6 according to Example 2 of the present invention;

[0028] Figure 4 This is a SEM image of Cs2AgBiBr6 prepared by the method of Example 2 of the present invention;

[0029] Figure 5 Schematic diagram of the preparation process of La2AlFeO6 according to Example 2 of the present invention;

[0030] Figure 6This is a SEM image of La2AlFeO6 prepared by the method of Example 2 of the present invention;

[0031] Figure 7 This is a diagram showing the effect of cyclic photocatalytic reduction of U(VI) by the heterojunction photocatalytic reduction U(VI) material prepared by the method of Example 2 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0033] Example 1

[0034] The present invention provides a heterojunction photocatalytic reduction material for U(VI). The material is a Z-type heterojunction photocatalyst composed of a self-assembled inorganic halogen perovskite and an oxide perovskite. Current photocatalytic materials have a wide bandgap and can only absorb ultraviolet light. The high recombination rate of photogenerated electrons and holes results in very low quantum efficiency. The material of the present invention can achieve photocatalysis under visible light conditions, promote charge separation, and improve catalytic reduction efficiency.

[0035] Preferably, the inorganic halogen perovskite and oxide perovskite are Cs2AgBiBr6 and La2AlFeO6 respectively.

[0036] Refer to the attached Figure 1 The present invention also provides a method for preparing a heterojunction photocatalytic reduction U(VI) material, comprising the following steps:

[0037] (1) grinding and mixing appropriate amounts of inorganic halogen perovskite and oxide perovskite in an isopropanol environment to obtain a mixture solution;

[0038] (2) stirring and centrifuging the mixture solution to collect the precipitate;

[0039] (3) The precipitate is washed with isopropyl alcohol and dried in a vacuum drying oven to obtain a heterogeneous photocatalytic reduction material.

[0040] Preferably, in step (1), the inorganic halogen perovskite and oxide perovskite are Cs2AgBiBr6 and La2AlFeO6, respectively.

[0041] Refer to the attached Figure 2 The heterojunction photocatalytic reduction U(VI) material prepared in the embodiment of the present invention has a crystalline structure, good particle dispersion, and uniform particle size.

[0042] Preferably, the preparation method of the inorganic halogen perovskite Cs2AgBiBr6 comprises the following steps:

[0043] (1) Add stoichiometric CsBr, AgBr, and BiBr to HBr acid (48%) and stir;

[0044] (2) The stirred mixture is heated in an oil bath and then cooled naturally;

[0045] (3) centrifuging the cooled mixture, collecting the precipitate and vacuum drying;

[0046] (4) dissolving the dried solid in dimethyl sulfoxide to obtain a clear solution;

[0047] (5) The transparent solution was added to dichloromethane, and the solid was collected by centrifugation and vacuum dried to obtain Cs2AgBiBr6.

[0048] Preferably, in step (5), Cs2AgBiBr6 is nanocrystal.

[0049] Preferably, the preparation method of the oxide perovskite La2AlFeO6 comprises the following steps:

[0050] (1) La(NO3)3·6H2O, Al(NO3)3·9H2O, and Fe(NO3)3·9H2O were dissolved in citric acid according to the molar ratio to obtain a solution;

[0051] (2) adding aqueous ammonia to the above solution and heating it in a constant temperature water bath until the solution becomes a viscous wet gel;

[0052] (3) The wet gel is dried at a constant temperature, calcined at a high temperature, and ground to obtain La2AlFeO6.

[0053] An embodiment of the present invention further provides an application of a heterojunction photocatalytic reduction U(VI) material, wherein the material is used for catalytic reduction of uranium in radioactive wastewater.

[0054] An embodiment of the present invention also provides an application of a heterojunction photocatalytic reduction U(VI) material, wherein the material is used to catalytically reduce U(VI) in radioactive wastewater to a stable form of U(IV) under visible light conditions; the stable form of U(IV) is UO2.

[0055] Example 2

[0056] The method of Example 1 of the present invention is used to prepare a heterojunction photocatalytic reduction U(VI) material, comprising the following steps:

[0057] (1) Grind 100 mg of Cs2AgBiBr6 and 100 mg of La2AlFeO6 in equal proportions in an agate mortar under isopropanol to obtain a solution suspended in isopropanol (20 mL).

[0058] (2) The mixture was vigorously stirred for 5 h and the solid was collected by centrifugation at 6000 rpm for 5 min;

[0059] (3) The solid was washed with isopropanol and dried in a vacuum drying oven at 60°C to obtain a heterojunction photocatalytic reduction material.

[0060] Refer to the attached Figure 3 The preparation method of Cs2AgBiBr6 comprises the following steps:

[0061] (1) Add stoichiometric amounts of CsBr, AgBr, and BiBr to 10 mL of HBr (48%) and stir for 30 min. The amount of CsBr used is 0.426 g, 2.0 mmol; the amount of AgBr used is 0.188 g, 1.0 mmol; and the amount of BiBr used is 0.449 g, 1.0 mmol.

[0062] (2) The stirred mixture was heated in an oil bath at 110°C for 2 h and then cooled naturally to room temperature;

[0063] (3) Centrifuging the cooled orange Cs2AgBiBr6 HBr solution, collecting the precipitate and drying it in a vacuum at 60°C for 24 h;

[0064] (4) The dried solid was dissolved in 50 mM dimethyl sulfoxide to obtain a clear solution;

[0065] (5) 1 mL of the transparent solution was added to 10 mL of dichloromethane, and the solid was collected by centrifugation and dried in vacuum at 60°C to obtain Cs2AgBiBr6 nanocrystals.

[0066] Refer to the attached Figure 4 The Cs2AgBiBr6 prepared in the embodiment of the present invention has a small particle size and is easy to react with La2AlFeO6.

[0067] Refer to the attached Figure 5 The preparation method of the oxide perovskite La2AlFeO6 comprises the following steps:

[0068] (1) La(NO3)3·6H2O, Al(NO3)3·9H2O, and Fe(NO3)3·9H2O were dissolved in 1.5 times the molar amount of the metal ions in citric acid at a molar ratio of 2:1:1 to obtain a solution;

[0069] (2) adding aqueous ammonia to the above solution and heating it in a constant temperature water bath at 70°C until the solution becomes a viscous wet gel;

[0070] (3) The wet gel was dried at a constant temperature of 100°C, calcined at a high temperature of 700°C, and ground to obtain La2AlFeO6.

[0071] Refer to the attached Figure 6 , the pure phase La2AlFeO6 is in irregular blocks of varying sizes and has varying degrees of sintering.

[0072] Heterojunction photocatalytic reduction U(VI) materials with Cs2AgBiBr6 and La2AlFeO6 in ratios of 1:1, 1:2 and 1:3 were prepared respectively by the methods of the embodiments of the present invention; and the materials were used to photocatalytically reduce U(VI).

[0073] A 300-W Xe lamp (Solar edge 700, set to 100 mW cm -2 ) is used as a light source. 20 mg of the photocatalytic reduction material prepared in the embodiment of the present invention is dispersed in 50 mL of uranyl solution with a concentration of 50 mg / L, the photocatalytic reactor is connected to a constant temperature cooling water device, and the air valve is opened to pass nitrogen to exclude dissolved oxygen in the solution. First, the magnetic stirrer speed is set to 500 r / min. After mixing for 1 hour under light-proof conditions, 1 mL of the mixed solution is taken using a microporous filter membrane, and the U concentration in the mixed solution is measured to exclude the influence of adsorption on the system. Subsequently, the Xe lamp is turned on to carry out a photocatalytic reduction experiment. 1 mL of the mixed solution is taken at regular intervals to measure the U concentration in the mixed solution at different time periods. The photocatalytic reduction U (VI) experiment is carried out for a total of 3 hours, and the U concentration in the final mixed solution is measured after 3 hours. The results show that when the La2AlFeO6 / Cs2AgBiBr6 ratio is 1:1, 2:1 and 3:1, the ratios of photocatalytic reduction U (VI) within 3 hours are 85.6%, 90.2% and 80.4% respectively, so the La2AlFeO6 / Cs2AgBiBr6 ratio of 2:1 is determined to be the optimal mixing ratio.

[0074] The embodiment of the present invention was used to prepare a Cs2AgBiBr6@La2AlFeO6 heterojunction photocatalytic reduction U(VI) material with a Cs2AgBiBr6:La2AlFeO6 ratio of 1:2, and four cycles of photocatalytic reduction of U(VI) were performed.

[0075] Refer to the attached Figure 7 , indicating that the heterojunction photocatalytic reduction U(VI) material prepared in the embodiment of the present invention has good cyclic catalytic effect and high stability.

[0076] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A heterojunction photocatalytic reduction U(VI) material, characterized in that: The material is a photocatalyst of a Z-type heterojunction self-assembled by an inorganic halogen perovskite and an oxide perovskite; The inorganic halogen perovskite and oxide perovskite are Cs2AgBiBr6 and La2AlFeO6 respectively.

2. The method for preparing a heterojunction photocatalytic reduction U(VI) material according to claim 1, characterized in that: The following steps are involved: (1) grinding and mixing appropriate amounts of inorganic halogen perovskite and oxide perovskite in an isopropanol environment to obtain a mixture solution; (2) stirring and centrifuging the mixture solution to collect the precipitate; (3) The precipitate was washed with isopropyl alcohol and dried in a vacuum drying oven to obtain a heterogeneous photocatalyst.

3. The method for preparing a heterojunction photocatalytic reduction U(VI) material according to claim 2, wherein: The preparation method of the inorganic halogen perovskite Cs2AgBiBr6 comprises the following steps: (1) Add stoichiometric CsBr, AgBr, and BiBr to HBr acid (48%) and stir; (2) The stirred mixture is heated in an oil bath and then cooled naturally; (3) centrifuging the cooled mixture, collecting the precipitate and vacuum drying; (4) dissolving the dried solid in dimethyl sulfoxide to obtain a clear solution; (5) The transparent solution was added to dichloromethane, and the solid was collected by centrifugation and vacuum dried to obtain Cs2AgBiBr6.

4. The method for preparing a heterojunction photocatalytic reduction U(VI) material according to claim 3, wherein: In the step (5), Cs2AgBiBr6 is a nanocrystal.

5. The method for preparing a heterojunction photocatalytic reduction U(VI) material according to claim 2, wherein: The preparation method of the oxide perovskite La2AlFeO6 comprises the following steps: (1) La(NO3)3·6H2O, Al(NO3)3·9H2O, and Fe(NO3)3·9H2O were dissolved in citric acid according to the molar ratio to obtain a solution; (2) adding aqueous ammonia to the above solution and heating it in a constant temperature water bath until the solution becomes a viscous wet gel; (3) The wet gel is dried at a constant temperature, calcined at a high temperature, and ground to obtain La2AlFeO6.

6. The use of the heterojunction photocatalytic reduction U(VI) material according to claim 1, characterized in that: The material is used for catalytic reduction of uranium in radioactive wastewater.

7. The use of the heterojunction photocatalytic reduction U(VI) material according to claim 1, characterized in that: The material is used for catalytic reduction of U(VI) in radioactive wastewater to U(IV) in a stable precipitated form under visible light conditions.

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