CN112919545B - Preparation method of tungsten oxide nanosheet rich in oxygen vacancies for treating radioactive wastewater - Google Patents

Preparation method of tungsten oxide nanosheet rich in oxygen vacancies for treating radioactive wastewater Download PDF

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CN112919545B
CN112919545B CN202110098970.XA CN202110098970A CN112919545B CN 112919545 B CN112919545 B CN 112919545B CN 202110098970 A CN202110098970 A CN 202110098970A CN 112919545 B CN112919545 B CN 112919545B
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tungsten oxide
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starch
oxygen vacancies
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CN112919545A (en
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何嵘
雷佳
竹文坤
刘欢欢
温逢春
江新颖
董云
李宸
任俨
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Southwest University of Science and Technology
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Abstract

The invention disclosesA preparation method of tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater comprises the following steps: adding sodium tungstate into water, stirring for dissolving, then adding a reducing agent, stirring, adding a hydrochloric acid solution, stirring again to obtain a mixed solution, transferring the mixed solution into a high-pressure reaction kettle, reacting at 115-135 ℃ for 20-30 hours, cooling to room temperature, performing centrifugal separation on precipitates, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at the temperature of 60-70 ℃; the dried solid is placed in N2Calcining for 2-6 hours at 400-550 ℃ in the atmosphere, and cooling to room temperature to obtain tungsten oxide nanosheets rich in oxygen vacancies; WO due to the strong scattering of gamma rays by the W atom3The crystal structure is still maintained in radioactive environment, which makes WO3Becomes a promising photocatalyst for treating radioactive wastewater. The introduction of oxygen vacancy widens the response range to visible light, and enhances WO3The nano sheets adsorb U (VI), so that the photocatalytic activity is improved.

Description

Preparation method of tungsten oxide nanosheet rich in oxygen vacancy for treating radioactive wastewater
Technical Field
The invention relates to a preparation method of defect-rich nanosheets, in particular to a preparation method of oxygen vacancy-rich tungsten oxide nanosheets for treating radioactive wastewater.
Background
Due to uranium mining, nuclear power plant operation, nuclear accidents/wars and the like, a large amount of radioactive wastewater containing uranium is discharged into the environment. Uranium has the characteristics of strong radioactivity, long half-life, high toxicity, easy migration and the like. The long-term explosion of uranium can pose a considerable hazard to human health and the ecological environment. Therefore, it is an urgent and significant problem to separate and extract uranium from radioactive uranium-containing wastewater efficiently, safely and at low cost. The traditional uranium-bearing waste water treatment technology mainly comprises an adsorption method, an evaporation concentration method, a membrane separation technology and a chemical precipitation method.
Generally, uranium-containing radioactive wastewater systems contain a variety of soluble organic substances (tannic acid (TA), citric acid, oxalic acid, sulfamates, ethylenediaminetetraacetic acid, etc.), which chelate uranium and increase the difficulty of uranium treatment. The photocatalysis technology can degrade organic matters and reduce uranium into low-price products. In this case, the semiconductor photocatalyst is excited by light to generate electron-hole pairs. The photo-generated holes decompose water adsorbed on the surface of the photocatalyst to generate hydroxyl radicals. The photo-generated electrons reduce oxygen to active ionic oxygen, which in turn degrades organic matter to carbon dioxide and water. Therefore, the photoproduction electrons reduce hexavalent uranium (U (VI)) into pentavalent uranium (U (V)) or tetravalent uranium (U (IV)), so that the reduction and immobilization of uranium are realized. However, as a key factor, the uranium reduction product readily occupies limited active sites on the semiconductor material, thereby limiting continuous photocatalytic reduction. Therefore, the development of a semiconductor photocatalyst with a higher active center to realize the treatment of the uranium-containing organic wastewater is a concern.
In recent years, various semiconductor materials (e.g., TiO)2、g-C3N4And WO3) A photocatalyst studied to extract toxic metal ions. WO due to the strong scattering of gamma rays by the W atom3The crystal structure is still maintained in radioactive environment, which makes WO3Becomes a promising photocatalyst for treating radioactive wastewater. However, WO3The forbidden band width is large, the responsivity to visible light is poor, the photo-generated charges are easy to compound, the electron utilization rate is low, and the WO is limited3Practical application in the field of U (VI) extraction. Recently, it has been reported that oxygen defect engineering in semiconductors enhances light collection by narrowing the band gap, and that oxygen vacancies also serve as active centers to enhance charge carriersThereby finally obtaining better photocatalytic performance. Thus, WO3The oxygen defect engineering in the method is a potential way for realizing the separation and recovery of uranium in the uranium-containing organic wastewater.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
To achieve these objects and other advantages in accordance with the present invention, there is provided a method for preparing oxygen vacancy rich tungsten oxide nanoplates for treating radioactive wastewater, comprising the steps of:
adding sodium tungstate into water, stirring for dissolving, then adding a reducing agent, stirring for 10-20 min, adding a hydrochloric acid solution A, stirring for 25-45 min again to obtain a mixed solution, transferring the mixed solution into a high-pressure reaction kettle, then reacting for 20-30 hours at 115-135 ℃, cooling to room temperature, performing centrifugal separation on precipitates, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at the temperature of 60-70 ℃;
step two, putting the solid dried in the step one in N2Calcining for 2-6 hours at 400-550 ℃ in the atmosphere, and cooling to room temperature to obtain the tungsten oxide nanosheet rich in oxygen vacancies.
Preferably, in the first step, the mass ratio of sodium tungstate to water is 1: 800-1000; the mass ratio of the sodium tungstate to the reducing agent is 1: 3-5; the concentration of the hydrochloric acid solution A is 5-7 mol/L; the mass volume ratio of the sodium tungstate to the hydrochloric acid solution A is 1 g: 85-95 mL.
Preferably, the reducing agent is one or a mixture of more of citric acid, glucose, ascorbic acid, starch, chitosan and inulin.
Preferably, the reducing agent is citric acid and glucose with the mass ratio of 1: 2.5-3.5.
Preferably, the reducing agent is acidolysis starch, and the preparation method of the acidolysis starch comprises the following steps: adding 20-25 parts of starch into a supercritical carbon dioxide reactor according to parts by weight, introducing carbon dioxide, swelling the starch for 60-90 min by using the supercritical carbon dioxide at the temperature of 40-60 ℃ and the pressure of 15-20 MPa, then decompressing at the speed of 1-2 MPa/min, after decompressing, adding 1-2 parts of hydrochloric acid solution B, introducing the carbon dioxide again, reacting for 30-60 min at the temperature of 40-50 ℃ and the pressure of 15-20 MPa, then decompressing at the speed of 1-2 MPa/min, precipitating, filtering, washing and drying to obtain the acidolysis starch.
Preferably, the concentration of the hydrochloric acid solution B is 0.05-0.15 mol/L; the starch is cassava starch or corn starch.
Preferably, in the first step, before the mixed solution is transferred into the high-pressure reaction kettle, an Nd: YAG pulse laser is used for carrying out ultraviolet pulse laser irradiation on the mixed solution.
Preferably, the irradiation time of the ultraviolet pulse laser is 15-25 min; the wavelength of the ultraviolet pulse laser irradiation is 355nm, the pulse width is 10-20 ns, and the pulse frequency is 10-30 Hz; the single pulse energy is 35-125 mJ.
Preferably, in the first step, before drying in a vacuum oven, the washed precipitate is placed in a supercritical device and soaked in a supercritical acetone-water system at 360-370 ℃ and 10-18 MPa for 10-15 min; the volume ratio of acetone to water in the supercritical acetone-water system is 1:2.
The invention at least comprises the following beneficial effects:
(1) WO due to the strong scattering of gamma rays by the W atom3The crystal structure is still maintained in radioactive environment, which makes WO3Becomes a promising photocatalyst for treating radioactive wastewater.
(2) The introduction of oxygen vacancy widens the response range to visible light, and enhances WO3The nano sheets adsorb U (VI), so that the photocatalytic activity is improved.
(3) The tungsten oxide nano-sheet rich in oxygen vacancies can simultaneously realize the photocatalytic reduction of uranium and the photooxidation of organic matters.
(4) By utilizing an oxygen defect engineering strategy, a potentially efficient semiconductor photocatalyst can be designed, and the uranium (VI) removal/reduction efficiency and the degradation of organic matters in the uranium-containing radioactive wastewater are improved.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Description of the drawings:
fig. 1 is an SEM image of tungsten oxide nanoplates prepared by comparative example 1, example 2 of the present invention;
fig. 2 is a TEM image and an HRTEM image of tungsten oxide nanoplates prepared by comparative example 1 of the present invention;
fig. 3 is a TEM image and HRTEM of tungsten oxide nanoplates prepared in example 1 of the present invention;
fig. 4 is a TEM image and HRTEM of tungsten oxide nanoplates prepared in example 2 of the present invention;
fig. 5 is an Electron Paramagnetic Resonance (EPR) spectrum of tungsten oxide nanoplates prepared in comparative example 1, example 1 and example 2 of the present invention;
fig. 6 shows the results of adsorption-catalytic reduction experiments on u (vi) by the tungsten oxide nanosheets prepared in comparative example 1, example 1 and example 2 of the present invention;
fig. 7 shows the results of adsorption-catalytic reduction experiments of TA by the tungsten oxide nanosheets prepared in comparative example 1, example 1 and example 2 of the present invention;
fig. 8 shows the results of adsorption-catalytic reduction experiments (different pH) on u (vi) by the tungsten oxide nanosheets prepared in comparative example 1, and example 2 of the present invention;
fig. 9 shows the results of adsorption-catalytic reduction experiments on u (vi) (different u (vi) initial concentrations) by tungsten oxide nanosheets prepared in example 2 of the present invention;
fig. 10 shows the experimental results of adsorption-catalytic reduction of u (vi) by tungsten oxide nanosheets prepared in example 2 of the present invention (different amounts of added tungsten oxide nanosheets);
fig. 11 is the result of the adsorption-catalytic reduction experiment of the tungsten oxide nanosheets prepared in examples 1, 3, 4 and 5 of the present invention on u (vi);
fig. 12 shows the results of adsorption-catalytic reduction experiments on TA by the tungsten oxide nanosheets prepared in examples 1, 3, 4 and 5 of the present invention.
The specific implementation mode is as follows:
the present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.
It will be understood that terms such as "having," "including," and "comprising," as used herein, do not preclude the presence or addition of one or more other elements or groups thereof.
Example 1:
a preparation method of tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater comprises the following steps:
step one, adding 0.033g of sodium tungstate into 30mL of water, stirring for dissolving, then adding 0.0315g of citric acid and 0.099g of glucose, stirring for 15min, adding 3mL of hydrochloric acid solution of 6mol/L, stirring again for 30min to obtain a mixed solution, transferring the mixed solution into a 50mL polytetrafluoroethylene high-pressure reaction kettle, reacting for 24 hours at 120 ℃, cooling to room temperature, performing centrifugal separation on a precipitate, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at 60 ℃;
step two, putting the solid dried in the step one in N2Calcining for 2 hours at 500 ℃ in the atmosphere, and cooling to room temperature to obtain the tungsten oxide nanosheet rich in oxygen vacancies.
Comparative example 1:
a preparation method of tungsten oxide nanosheets comprises the following steps:
step one, adding 0.033g of sodium tungstate into 30mL of water, stirring for dissolving, then adding 0.0315g of citric acid and 0.099g of glucose, stirring for 15min, adding 3mL of hydrochloric acid solution A of 6mol/L, stirring again for 30min to obtain a mixed solution, transferring the mixed solution into a 50mL polytetrafluoroethylene high-pressure reaction kettle, then reacting for 24 hours at 120 ℃, cooling to room temperature, carrying out centrifugal separation on precipitates, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at 60 ℃;
and step two, calcining the solid dried in the step one for 2 hours at 500 ℃ in an air atmosphere, and cooling to room temperature to obtain the tungsten oxide nanosheet.
Example 2:
a preparation method of tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater comprises the following steps:
step one, adding 0.033g of sodium tungstate into 30mL of water, stirring for dissolving, then adding 0.0315g of citric acid and 0.099g of glucose, stirring for 15min, adding 3mL of hydrochloric acid solution A of 6mol/L, stirring again for 30min to obtain a mixed solution, transferring the mixed solution into a 50mL polytetrafluoroethylene high-pressure reaction kettle, then reacting for 24 hours at 120 ℃, cooling to room temperature, carrying out centrifugal separation on precipitates, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at 60 ℃;
step two, putting the solid dried in the step one in N2Calcining for 4 hours at 500 ℃ in the atmosphere, and cooling to room temperature to obtain the tungsten oxide nanosheet rich in oxygen vacancies.
Example 3:
a preparation method of tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater comprises the following steps:
step one, adding 0.033g of sodium tungstate into 30mL of water, stirring for dissolving, then adding 0.1305g of acidolyzed starch, stirring for 15min, adding 3mL of hydrochloric acid solution A with the concentration of 6mol/L, stirring for 30min again to obtain a mixed solution, transferring the mixed solution into a 50mL polytetrafluoroethylene high-pressure reaction kettle, reacting at 120 ℃ for 24 hours, cooling to room temperature, performing centrifugal separation on precipitates, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at 60 ℃;
step two, putting the solid dried in the step one in N2Calcining for 2 hours at 500 ℃ in the atmosphere, and cooling to room temperature to obtain tungsten oxide nanosheets rich in oxygen vacancies;
the preparation method of the acidolysis starch comprises the following steps: adding 20g of starch into a supercritical carbon dioxide reactor, introducing carbon dioxide, swelling the starch for 90min by using the supercritical carbon dioxide at the temperature of 45 ℃ and the pressure of 18MPa, then decompressing at the speed of 1MPa/min, adding 1g of hydrochloric acid solution B after decompression, introducing the carbon dioxide again, reacting for 60min at the temperature of 40 ℃ and the pressure of 15MPa, then decompressing at the speed of 1MPa/min, precipitating, filtering, washing and drying to obtain acidolysis starch; the concentration of the hydrochloric acid solution B is 0.1 mol/L;
example 4:
a preparation method of tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater comprises the following steps:
step one, adding 0.033g of sodium tungstate into 30mL of water, stirring and dissolving, then adding 0.1305g of acid hydrolyzed starch, stirring for 15min, adding 3mL of hydrochloric acid solution A at 6mol/L, stirring again for 30min to obtain a mixed solution, and performing ultraviolet pulse laser irradiation on the mixed solution by using an Nd-YAG pulse laser; then transferring the irradiated mixed solution into a 50mL polytetrafluoroethylene high-pressure reaction kettle, reacting for 24 hours at 120 ℃, cooling to room temperature, performing centrifugal separation on the precipitate, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at 60 ℃; the irradiation time of the ultraviolet pulse laser is 25 min; the wavelength of the ultraviolet pulse laser irradiation is 355nm, the pulse width is 20ns, and the pulse frequency is 25 Hz; the single pulse energy is 60 mJ; ultraviolet pulse laser is adopted for irradiation, and the mixed solution is subjected to pretreatment irradiation, so that the reduction reaction is more complete, and the prepared tungsten oxide nanosheet has more excellent performance;
step two, putting the solid dried in the step one in N2Calcining for 2 hours at 500 ℃ in the atmosphere, and cooling to room temperature to obtain tungsten oxide nanosheets rich in oxygen vacancies;
the preparation method of the acidolysis starch comprises the following steps: adding 20g of starch into a supercritical carbon dioxide reactor, introducing carbon dioxide, swelling the starch for 90min by using the supercritical carbon dioxide at the temperature of 45 ℃ and the pressure of 18MPa, then decompressing at the speed of 1MPa/min, adding 1g of hydrochloric acid solution B after decompression, introducing the carbon dioxide again, reacting for 60min at the temperature of 40 ℃ and the pressure of 15MPa, then decompressing at the speed of 1MPa/min, precipitating, filtering, washing and drying to obtain acidolysis starch; the concentration of the hydrochloric acid solution B is 0.1 mol/L; the starch is cassava starch;
example 5:
a preparation method of tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater comprises the following steps:
step one, adding 0.033g of sodium tungstate into 30mL of water, stirring and dissolving, then adding 0.1305g of acid hydrolyzed starch, stirring for 15min, adding 3mL of hydrochloric acid solution A at 6mol/L, stirring again for 30min to obtain a mixed solution, and performing ultraviolet pulse laser irradiation on the mixed solution by using an Nd-YAG pulse laser; then transferring the irradiated mixed solution into a 50mL polytetrafluoroethylene high-pressure reaction kettle, reacting at 120 ℃ for 24 hours, cooling to room temperature, centrifugally separating precipitates, and washing with distilled water and absolute ethyl alcohol for a plurality of times; soaking the washed precipitate in supercritical device at 365 deg.C and 18MPa for 15 min; then drying the mixture for 24 hours in a vacuum oven at 60 ℃; the volume ratio of acetone to water in the supercritical acetone-water system is 1: 2; the irradiation time of the ultraviolet pulse laser is 25 min; the wavelength of the ultraviolet pulse laser irradiation is 355nm, the pulse width is 20ns, and the pulse frequency is 25 Hz; the single pulse energy is 60 mJ; by soaking in a supercritical acetone-water system, organic matters after reaction can be completely removed, so that the performance of the prepared tungsten oxide nanosheet is more excellent;
step two, putting the solid dried in the step one in N2Calcining for 2 hours at 500 ℃ in the atmosphere, and cooling to room temperature to obtain tungsten oxide nanosheets rich in oxygen vacancies;
the preparation method of the acidolysis starch comprises the following steps: adding 20g of starch into a supercritical carbon dioxide reactor, introducing carbon dioxide, swelling the starch for 90min by using the supercritical carbon dioxide at the temperature of 45 ℃ and the pressure of 18MPa, then decompressing at the speed of 1MPa/min, adding 1g of hydrochloric acid solution B after decompression, introducing the carbon dioxide again, reacting for 60min at the temperature of 40 ℃ and the pressure of 15MPa, then decompressing at the speed of 1MPa/min, precipitating, filtering, washing and drying to obtain acidolysis starch; the concentration of the hydrochloric acid solution B is 0.1 mol/L; the starch is cassava starch;
fig. 1a is an SEM image of tungsten oxide nanoplates prepared in comparative example 1; FIG. 1b is a schematic representation of the preparation of example 1SEM image of oxygen vacancy rich tungsten oxide nanoplatelets of (a); fig. 1c is an SEM image of oxygen vacancy rich tungsten oxide nanoplates prepared in example 2; fig. 2a is a TEM image of tungsten oxide nanoplates prepared in comparative example 1; figure 2b is HRTEM of tungsten oxide nanoplates prepared in comparative example 1; fig. 3a is a TEM image of tungsten oxide nanoplates prepared in example 1; figure 3b is HRTEM of tungsten oxide nanoplates prepared in example 1; fig. 4c is a TEM image of tungsten oxide nanoplates prepared in example 2; figure 4b is HRTEM of tungsten oxide nanoplates prepared in example 2; WO prepared in comparative example 1 containing no oxygen vacancy as shown in TEM image3Exhibit the morphology of the nanoplatelets. WO prepared in comparative example 13In the HRTEM image of the nanosheet, two single crystals WO3Due to two different lattice fringes with a interplanar spacing of 3.6 and 3.8, respectively. Thus, WO prepared in comparative example 13The nanoplatelets are oriented to have a surface of (010); as the oxygen vacancy content increased, the defective tungsten oxide nanoplate products (prepared in examples 1 and 2) are shown by TEM images to be comparable to WO prepared in comparative example 13Similar nanosheet morphology was maintained. The nanoplatelets prepared in example 1 showed ordered lattices even at the edges of the sample, indicating insufficient oxygen vacancies. As revealed by TEM and HRTEM images of the tungsten oxide nanosheets prepared in example 2, small pits appear on the surface, increasing the contact area and providing more adsorption sites for catalytic reactions; with the pits, slight lattice disorder and dislocation were observed in the nanosheets, demonstrating the presence of a large number of defects.
Fig. 5 is an Electron Paramagnetic Resonance (EPR) spectrum of tungsten oxide nanoplates prepared in comparative example 1, example 1 and example 2; as shown in fig. 5, the tungsten oxide nanosheet prepared in comparative example 1 was relatively weak in signal, indicating a lack of oxygen vacancies; in the case of defective tungsten oxide nanoplates (prepared in examples 1 and 2), symmetric ESR signals were observed for the tungsten oxide nanoplates prepared in example 2 and the tungsten oxide nanoplates prepared in example 1 at g ═ 2.003, indicating that electrons were trapped at oxygen vacancies. In addition, the tungsten oxide nanoplatelets prepared in example 2 showed a clearer signal than the tungsten oxide nanoplatelets prepared in example 1, indicating that the tungsten oxide nanoplatelets prepared in example 2 are rich in oxygen vacancies.
Carrying out adsorption-catalytic reduction experiments of U (VI) on the tungsten oxide nanosheets prepared in comparative example 1, example 1 and example 2; in 20mL of tannic acid-containing U (VI) solution (C)U(Ⅵ)＝8mg/L,CTA (tannic acid)1mg/L, 0.25G/L m/V, 293K T293K, pH 4.8)), 5mg of the sample (tungsten oxide nanoplates prepared in example 1, example 2, comparative example 1) was added, stirred at a speed of 600r/min for 60min under dark conditions, then subjected to simulated solar irradiation (300-W Xe lamp BL-GHX-V with AM1.5G filter), stirred at a speed of 600r/min, and the material properties were characterized by testing the u (vi) concentration in the solution for different reaction times; u (VI) solution is prepared by uranyl nitrate; measuring the concentration of U (VI) in the solution before and after adsorption by using a double ultraviolet-visible spectrophotometer; all experiments were performed in triplicate and the mean values were taken; FIG. 6 shows the results of the experiment; fig. 6 shows that in the dark, the removal rate of u (vi) by the tungsten oxide nanoplates prepared in example 2 was 39% in an equilibrium state, which is better than the tungsten oxide nanoplates prepared in comparative example 1 (18%) and example 1 (25%); this is primarily due to the introduction of oxygen vacancies which enhance the adsorption of u (vi) onto the photocatalyst surface. After simulated sunlight is introduced into a reaction system, the removal rate of the tungsten oxide nanosheets prepared in comparative example 1 to U (VI) is not weakened, while the removal rate of the tungsten oxide nanosheets prepared in example 1 to U (VI) is as high as 73.4% (90min), and the defect introduction is proved to effectively improve the removal rate of U (VI). In particular, the tungsten oxide nanoplates prepared in example 2 showed significant U (VI) extraction capacity, as well as a 94.2% removal rate (90 min). The above results show that the introduction of oxygen vacancies effectively improves the u (vi) removal efficiency. The treatment ability of the tungsten oxide nanosheet photocatalyst prepared in comparative example 1, and example 2 to TA (20 mL of U (VI) solution C containing tannic acid, respectively) was further evaluated in consideration of the coexistence of organic matters in the industrial uranium-containing wastewaterU(Ⅵ)＝8mg/L,CTA (tannic acid)5mg of a sample (tungsten oxide nanosheets prepared in example 1, example 2 and comparative example 1) was added to 1mg/L, 0.25g/L, 293K and 4.8 pH, stirred at a speed of 600r/min in the dark for 60min, and then simulated sunlight was appliedShooting (300-W Xe lamp BL-GHX-V equipped with AM1.5G filter), stirring at 600r/min, and measuring TA concentration in the solution at different reaction times); as shown in fig. 7, the introduction of oxygen vacancies enhanced the adsorption of TA, and the tungsten oxide nanoplatelets prepared in example 2 decomposed 97.4% of TA upon 90 minutes of light irradiation.
Carrying out adsorption-catalytic reduction experiments of u (vi) on the tungsten oxide nanosheets prepared in comparative example 1, and example 2; in 20mL of a solution of tannic acid in U (VI) (C)U(Ⅵ)＝8mg/L,CTA (tannic acid)Adding 5mg of sample (tungsten oxide nanosheets prepared in example 1, example 2 and comparative example 1) into 1mg/L, 0.25G/L and 293K, wherein the pH value is 2.8, 3.8, 4.8, 5.8, 7.8 and 9.8, applying simulated sunlight irradiation (300-W Xe lamp BL-GHX-V provided with AM1.5G filter), stirring at the speed of 600r/min for 120min, testing the concentration of U (VI) in the solution before and after adsorption, and calculating the removal rate which is equal to (C)0-Ct)/C0×100％，C0As initial concentration, CtIs the post-adsorption concentration; u (VI) solution is prepared by uranyl nitrate; measuring the concentration of U (VI) in the solution before and after adsorption by using a double ultraviolet-visible spectrophotometer; all experiments were performed in triplicate and the mean values were taken; the results are shown in FIG. 8; the removal rate of U (VI) increases sharply as the pH increases from 2.8 to 4.8, and then remains high at pH 4.8; at a pH of>At 4.8, a tendency was observed that the removal rate was decreased. Moreover, the tungsten oxide nanoplates prepared in example 2 exhibited higher uranium removal rates than the tungsten oxide nanoplates prepared in example 1 and comparative example 1 under various pH conditions.
Subjecting the tungsten oxide nanoplates prepared in example 2 to adsorption-catalytic reduction experiments of u (vi) (different u (vi) initial concentrations); in 20mL of tannic acid-containing U (VI) solution (C)U(Ⅵ)＝8mg/L,50mg/L,100mg/L,150mg/L,and 200mg/L,CTA (tannin)5mg of a sample (tungsten oxide nanosheets prepared in example 2) was added to 1mg/L, m/V0.25G/L, T293K, pH 4.8, simulated sunlight irradiation (300-W Xe lamp BL-GHX-V with AM1.5G filter) was applied, stirring was carried out at a speed of 600r/min for 120min, the u (vi) concentration in the solution before and after adsorption was measured, the removal rate was calculated, and the removal rate was (C) was0-Ct)/C0×100％，C0As initial concentration, CtIs the post-adsorption concentration; u (VI) solution is prepared by uranyl nitrate; measuring the concentration of U (VI) in the solution before and after adsorption by using a double ultraviolet-visible spectrophotometer; all experiments were performed in triplicate and the mean values were taken; the results are shown in FIG. 9; during the photocatalytic reduction process, a high U (VI) removal rate is maintained in a wide U (VI) concentration range. The tungsten oxide nanoplates prepared in example 2 showed a high removal rate of 63.4% for u (vi) even when the initial concentration of uranium was 200 mg/L.
Subjecting the tungsten oxide nanoplates prepared in example 2 to an adsorption-catalytic reduction experiment of u (vi) (different amounts of tungsten oxide nanoplates were added); in 20mL of tannic acid-containing U (VI) solution (C)U(Ⅵ)＝8mg/L,CTA (tannin)1mg/L, 0.1g/L, 0.15g/L, 0.2g/L, 0.25g/L, 0.3g/L, 0.35g/L, 0.4 g/L; samples of different masses (tungsten oxide nanosheets prepared in example 2) were added to a solution of T293K and pH 4.8, simulated solar radiation (300-W Xe lamp BL-GHX-V with AM1.5G filter) was applied, stirring was carried out at a speed of 600r/min for 120min, the concentration of u (vi) in the solution before and after adsorption was measured, and the removal rate was calculated as (C)0-Ct)/C0×100％，C0As initial concentration, CtIs the post-adsorption concentration; u (VI) solution is prepared by uranyl nitrate; measuring the concentration of U (VI) in the solution before and after adsorption by using a double ultraviolet-visible spectrophotometer; all experiments were performed in triplicate and the mean values were taken; the results are shown in FIG. 10; when the solid-liquid ratio is more than 0.25, the removal rate is maintained>The high level of 95% indicates an optimum solid-to-liquid ratio of 0.25 g/L.
Subjecting the tungsten oxide nanoplates prepared in example 1, example 3, example 4 and example 5 to an adsorption-catalytic reduction experiment of u (vi); in 20mL of tannic acid-containing U (VI) solution (C)U(Ⅵ)＝8mg/L,CTA (tannic acid)1mg/L, m/V0.25 g/L, T293K, pH 4.8) to 5mg of sample (tungsten oxide nanoplates prepared in example 1, example 3, example 4 and example 5) was added, stirred at a speed of 600r/min for 60min under dark conditions, then simulated daylight illumination (300-W Xe lamp BL-GHX-V with am1.5g filter) was applied, stirred at a speed of 600r/min, and passed the testThe U (VI) concentration in the solution at different reaction time characterizes the material performance; u (VI) solution is prepared by uranyl nitrate; measuring the concentration of U (VI) in the solution before and after adsorption by using a double ultraviolet-visible spectrophotometer; all experiments were performed in triplicate and the average was taken; FIG. 11 shows the results of the experiment; fig. 11 shows that in the dark, the removal rate of u (vi) by the tungsten oxide nanosheets prepared in examples 3, 4 and 5 is superior to that of the tungsten oxide nanosheets prepared in example 1 in an equilibrium state. After simulated sunlight is introduced into a reaction system, the removal rate of the tungsten oxide nanosheets prepared in examples 3, 4 and 5 to U (VI) is also superior to that of the tungsten oxide nanosheets prepared in example 1. The treatment ability of the tungsten oxide nanoplatelets photocatalyst prepared in example 1, example 3, example 4 and example 5 to TA (in 20mL of U (VI) solution C containing tannic acid, respectively) was further evaluated in consideration of coexistence of organic matters in industrial uranium-containing wastewaterU(Ⅵ)＝8mg/L,CTA (tannin)5mg of sample (tungsten oxide nanoplates prepared in example 1, example 3, example 4 and example 5) was added to 1mg/L, m/V0.25 g/L, T293K, pH 4.8, stirred at a speed of 600r/min under dark conditions for 60min, then simulated daylight illumination (300-W Xe lamp BL-GHX-V with am1.5g filter) was applied, stirred at a speed of 600r/min, and the TA concentration in the solution was measured by testing for different reaction times); as shown in fig. 12, the removal rate of TA by the tungsten oxide nanoplatelets prepared in examples 3, 4 and 5 was also superior to that of the tungsten oxide nanoplatelets prepared in example 1, regardless of dark or light conditions.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable in various fields of endeavor to which the invention pertains, and further modifications may readily be made by those skilled in the art, it being understood that the invention is not limited to the details shown and described herein without departing from the general concept defined by the appended claims and their equivalents.

Claims (4)

1. A preparation method of tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater is characterized by comprising the following steps:
adding sodium tungstate into water, stirring for dissolving, then adding a reducing agent, stirring for 10-20 min, adding a hydrochloric acid solution A, stirring for 25-45 min again to obtain a mixed solution, transferring the mixed solution into a high-pressure reaction kettle, then reacting for 20-30 hours at 115-135 ℃, cooling to room temperature, performing centrifugal separation on precipitates, and washing with distilled water and absolute ethyl alcohol for several times; then drying the mixture for 24 hours in a vacuum oven at the temperature of 60-70 ℃;
step two, putting the solid dried in the step one in N2Calcining for 2-6 hours at 400-550 ℃ in the atmosphere, and cooling to room temperature to obtain tungsten oxide nanosheets rich in oxygen vacancies;
the reducing agent is acidolysis starch, and the preparation method of the acidolysis starch comprises the following steps: adding 20-25 parts of starch into a supercritical carbon dioxide reactor according to parts by weight, introducing carbon dioxide, swelling the starch for 60-90 min by using the supercritical carbon dioxide at the temperature of 40-60 ℃ and the pressure of 15-20 MPa, then decompressing at the speed of 1-2 MPa/min, after decompressing, adding 1-2 parts of hydrochloric acid solution B, introducing the carbon dioxide again, reacting for 30-60 min at the temperature of 40-50 ℃ and the pressure of 15-20 MPa, then decompressing at the speed of 1-2 MPa/min, precipitating, filtering, washing and drying to obtain acidolysis starch;
in the first step, before the mixed solution is transferred into a high-pressure reaction kettle, performing ultraviolet pulse laser irradiation on the mixed solution by using an Nd-YAG pulse laser; the irradiation time of the ultraviolet pulse laser is 15-25 min; the wavelength of the ultraviolet pulse laser irradiation is 355nm, the pulse width is 10-20 ns, and the pulse frequency is 10-30 Hz; the single pulse energy is 35-125 mJ.
2. The method for preparing tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater according to claim 1, wherein in the first step, the mass ratio of sodium tungstate to water is 1: 800-1000; the mass ratio of the sodium tungstate to the reducing agent is 1: 3-5; the concentration of the hydrochloric acid solution A is 5-7 mol/L; the mass volume ratio of the sodium tungstate to the hydrochloric acid solution A is 1 g: 85-95 mL.
3. The method for preparing tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater according to claim 1, wherein the concentration of the hydrochloric acid solution B is 0.05 to 0.15 mol/L; the starch is cassava starch or corn starch.
4. The method for preparing tungsten oxide nanosheets rich in oxygen vacancies for treating radioactive wastewater as set forth in claim 1, wherein in the first step, the washed precipitate is placed in a supercritical apparatus and immersed for 10-15 min in a supercritical acetone-water system at a temperature of 360-370 ℃ and a pressure of 10-18 MPa before being dried in a vacuum oven; the volume ratio of acetone to water in the supercritical acetone-water system is 1:2.
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