An oxygen-vacancy-containing bi@bi4ti3o 12 Method for selective photocatalytic degradation of pollutants by nanosheets

Abstract

An oxygen-containing vacancy Bi@Bi4Ti3O 12 The application relates to a method for selective photocatalytic degradation of pollutants by nanosheets, belonging to the field of photocatalytic degradation of organic pollutants. The method is used for degrading cationic dyes such as rhodamine B, methylene blue and basic orange II as pollutants in the presence of oxygen-containing vacancy Bi@Bi4Ti3O 12 nanosheets under visible light irradiation. Research shows that the catalyst has selective degradation activity on the above pollutants, and the degradation rate of cationic pollutants such as rhodamine B, methylene blue and basic orange II reaches 95.47-99.31%, which is much higher than the degradation rate (13.36%) of most anionic pollutants. The method has the advantages of simple operation, low cost, high efficiency and the like, can selectively remove cationic dyes in textile industrial wastewater, and has a good practical prospect in environmental protection such as sewage purification.

Description

TECHNICAL FIELD

[0001] The present application relates to an oxygen-vacancy-containing Bi@Bi4Ti3O 12 The method for selective visible light photocatalytic degradation of low-concentration, high-toxicity and difficult-to-degrade pollutants by nanosheets. BACKGROUND

[0002] Dye wastewater, as an environmental pollutant that exhibits toxicity and carcinogenicity to humans and other organisms, is usually from the textile and printing industries. The pollutant composition in dye wastewater is complex and can exist in the water environment for a long time, so it is necessary to develop suitable and reliable methods for treating dye wastewater. Currently, the methods for treating dye wastewater usually include biodegradation, physical adsorption and chemical removal, etc. However, the biodegradation method has low efficiency, and the physical adsorption method only transfers the dye molecules from the wastewater to the surface of the adsorbent, and the new pollutants generated still need subsequent treatment. In contrast, photocatalytic removal of dye molecules in dye wastewater has the advantages of complete and reliable degradation, good economy, etc.

[0003] Bi4Ti3O 12 As a bismuth-based Aurivillius-type composite oxide, the layered structure with alternating positive and negative charge layers enables it to have a strong interlayer electric field, which is conducive to carrier separation and migration from the bulk to the surface. The presence of oxygen vacancies can expand its light absorption range, promote electron transfer and provide reactive sites. The deposition of Bi as an electron acceptor further enhances electron transfer and promotes carrier separation.

[0004] Photocatalytic selective degradation of cationic dyes in wastewater can remove specific dye molecules without affecting other dye molecules, which has certain practicability. At present, although there are some reports on the removal of organic dyes by Bi4Ti3O 12 as a photocatalyst, but there is no application of oxygen-vacancy-containing Bi@Bi4Ti3O 12 nanosheets in selective degradation of ionic dyes under visible light irradiation. SUMMARY

[0005] The purpose of the present application is to provide an oxygen-vacancy-containing Bi@Bi4Ti3O 12 nanosheet method for selective degradation of dyes under photocatalytic action, which takes rhodamine B, methylene blue, basic orange II and other cationic dyes as pollutants, and the oxygen-vacancy-containing Bi@Bi4Ti3O 12The nanosheet is degraded under xenon lamp irradiation in the presence of the nanosheet. Research shows that the catalyst has selective degradation activity on the pollutants, and the degradation rate of cationic pollutants such as rhodamine B, methylene blue and basic orange II is as high as 95.47-99.31%, which is much higher than the degradation rate (13.36%) of most anionic pollutants. The method has the advantages of simple operation, low cost, high efficiency, and can selectively remove cationic dyes in textile industrial wastewater, and has good practical prospect in environmental protection such as sewage purification.

[0006] The Bi@Bi4Ti3O 12 The method for selective photocatalytic degradation of low-concentration, high-toxicity and difficult-to-degrade pollutants by nanosheet is characterized by the following steps:

[0007] a. The Bi@Bi4Ti3O 12 The nanosheet is added to a cationic or / and anionic dye solution with a concentration of 1*10 -5 mol / L, ultrasonic dispersion is performed for 5 min to make it uniform and stable, then it is magnetically stirred in the dark for 30 min to ensure that the pollutants and the catalyst reach adsorption-desorption equilibrium; 20-30 (preferably 25) mg of the Bi@Bi4Ti3O 12 nanosheet corresponds to 100 mL of the dye solution;

[0008] b. The reaction system is irradiated under visible light to further remove 5 mL of the solution in step a in a centrifuge tube, then the beaker containing the remaining solution system is placed under a xenon lamp for light irradiation, and the magnetic stirring is kept at 350 r / min during the irradiation, then 5 mL of sample is taken every fixed time interval;

[0009] c. After centrifugation of the removed sample, the supernatant is taken to test the ultraviolet-visible absorption spectrum, and the degradation efficiency of the pollutants is analyzed.

[0010] The cationic dye in step a is rhodamine B, methylene blue, basic orange II or other dyes in cationic state dissolved in water; the anionic dye is methyl orange, acid red 18 or other dyes in anionic state dissolved in water; the cationic dye solution can be acidic, neutral or alkaline;

[0011] In step b, the xenon lamp is provided with a 420 nm filter, and the light absorption range is expanded to the visible light region.

[0012] The fixed time interval for sampling in step b can be 2, 20 and 30 min.

[0013] The photocatalytic degradation of dyes by the catalyst is generally applicable to cationic dyes, because the catalyst surface is negatively charged and is easy to electrostatically attract cationic dyes, but is not applicable to all anionic dyes, for example, Congo red can be adsorbed on the catalyst surface by hydrogen bonds and other ways.

[0014] The selective photocatalytic degradation of cationic dyes by the catalyst shows selective photocatalytic degradation of cationic dyes under the condition that the solution pH is near 7 or greater than 7; the catalyst still shows good visible light photocatalytic effect when the acid-base range is widened to strong acidic or strong basic conditions; the catalyst has obvious degradation activity on Basic Orange II and still shows high catalytic activity under acidic conditions with pH of 4, and achieves 99.03% effective degradation within 60 min; further selection of alkaline conditions, degradation is carried out at pH of 10, and 97.23% degradation is achieved within 120 min.

[0015] The Bi@Bi4Ti3O 12 The method for selective photocatalytic degradation of cationic dyes by the Bi@Bi4Ti3O

[0016] The Bi@Bi4Ti3O 12 nanosheet in the presence of oxygen vacancies under visible light irradiation. Research shows that the catalyst has selective degradation activity on the above pollutants, and the degradation rate of cationic pollutants such as Rhodamine B, methylene blue and Basic Orange II is as high as 95.47-99.31%, which is much higher than the degradation rate of most anionic pollutants (13.36%). The method has the advantages of simple operation, low cost and high efficiency, and can selectively remove cationic dyes in textile industrial wastewater, and has good practical prospect in environmental protection such as sewage purification. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The SEM image of the Bi@Bi4Ti3O 12 nanosheet with oxygen vacancies of the present application, and it can be seen from the figure that the catalyst is in the form of nanosheet, and the length and thickness are about 200 nm and 30 nm, respectively;

[0018] Figure 2 The SEM image of the Bi@Bi4Ti3O 12XRD pattern of the nanosheet, curve a is the catalyst, short vertical line b is the standard PDF card, and the catalyst is a pure phase Bi4Ti3O 12 There is no other impurity phase;

[0019] Figure 3 Bi@Bi4Ti3O 12 XPS pattern of the nanosheet, and the existence of Bi element and oxygen vacancy OVs can be seen from the figure;

[0020] Figure 4 Degradation effect diagram of cationic dyes in examples 1-3 and anionic dyes in examples 4-5, and it can be seen from the figure that the Bi@Bi4Ti3O 12 The nanosheet has strong adsorption and photocatalytic degradation effect on cationic dyes basic orange II, methylene blue and rhodamine B, and has weak adsorption and photocatalytic degradation effect on anionic dyes methyl orange and acid red 18;

[0021] Figure 5 Degradation effect diagram of example 6, and it can be seen from the figure that in the mixed solution system of cationic and anionic dyes, the Bi@Bi4Ti3O 12 The nanosheet preferentially degrades cationic dyes;

[0022] Figure 6 Degradation effect diagram of replacing the Bi@Bi4Ti3O 12 Nanosheet in examples 1-5 with oxygen vacancy with OVs-Bi4Ti3O 12 .

[0023] Figure 7 Degradation effect diagram of the Bi@Bi4Ti3O 12 Nanosheet in example 1 with oxygen vacancy on cationic dye basic orange II under a wide range of pH. DETAILED DESCRIPTION

[0024] The application will be described in detail below in combination with the drawings and examples, but the application is not limited to the following examples.

[0025] Bi@Bi4Ti3O 12The nanosheet catalyst is mixed and ground for 30 min with 62.5 mmol of sodium chloride and potassium chloride as molten salt, then 5 mmol of Bi2O3 and 7.5 mmol of TiO2 are added and ground for another 30 min to obtain a uniformly mixed powder; then a reducing agent, urea (1.5 g), is added to further increase the oxygen vacancies, and the grinding is continued for 30-60 min to obtain a uniform and fine powder; finally, the powder is moved to a crucible and placed in a muffle furnace, and heated at a rate of 2°C / min to 700°C and calcined for 2 h. After the reaction is completed, the temperature is lowered to room temperature at a rate of 2°C / min, and the sample is washed with a mixture of deionized water and anhydrous ethanol, dried at 60°C, ground, and the target product is obtained.

[0026] The reducing agent selected in the synthesis of the catalyst is urea, and other reducing agents such as glyoxal, ascorbic acid, sodium borohydride, glucose, lactic acid, tartaric acid, citric acid, etc. can also be selected, with urea being the preferred choice; the amount of urea can be 0.0-3.5 g (1.5 g is preferred in the following examples).

[0027] Example 1:

[0028] a. Dissolve 1.24 mg of cationic dye Basic Orange II in 100 mL of deionized water, then place it in an ultrasonic bath to make it a uniform and stable solution, and then use a glass rod to drain the uniform and stable solution into a 500 mL volumetric flask and make up to volume.

[0029] b. Take 100 mL of the solution obtained in step a into a beaker, and then take 5 mL into a centrifuge tube;

[0030] c. Add 25 mg of oxygen vacancy-containing Bi@Bi4Ti3O 12 Nanosheet to the remaining solution in step b, ultrasonically treat for 5 min to make it uniform and stable, then avoid light and magnetically stir for 30 min to ensure complete adsorption of the dye molecules.

[0031] d. Take 5 mL of the solution in step c into a centrifuge tube, then place the beaker containing the remaining solution system under a xenon lamp with a 420 nm filter, and keep the magnetic stirring at 350 r / min during the irradiation, take 5 mL of sample every 20 min, a total of 7 times;

[0032] e. After centrifugation of the removed sample, test the supernatant for UV-Vis absorption spectrum to analyze the degradation efficiency of the pollutants.

[0033] Example 2:

[0034] a. Dissolve 1.87 mg of cationic dye methylene blue in 100 mL of deionized water, then place it in an ultrasonic bath to make it a uniform and stable solution, and then use a glass rod to drain the uniform and stable solution into a 500 mL volumetric flask and make up to volume.

[0035] b. Take 100 mL of the solution obtained in step a into a beaker, and take 5 mL into a centrifuge tube;

[0036] c. Add 25 mg of Bi@Bi4Ti3O 12 nanoplatelets containing oxygen vacancies into the remaining solution in step b, and ultrasonically treat for 5 min to make it uniformly stable, then magnetically stir in the dark for 30 min to ensure complete adsorption of the dye molecules.

[0037] d. Take 5 mL of the solution in step c into a centrifuge tube, and then place the beaker containing the remaining solution system under irradiation of a xenon lamp with a 420 nm filter, while keeping the magnetic stirring at 350 r / min, take 5 mL of sample every 20 min, for a total of 7 times;

[0038] e. After centrifugation of the removed sample, test the supernatant for ultraviolet-visible absorption spectrum to analyze the degradation efficiency of the pollutants.

[0039] Example 3:

[0040] a. Dissolve 2.40 mg of cationic dye rhodamine B in 100 mL of deionized water, and then ultrasonically treat to make it a uniformly stable solution, and then use a glass rod to introduce the uniformly stable solution into a 500 mL volumetric flask and make up to volume.

[0041] b. Take 100 mL of the solution obtained in step a into a beaker, and take 5 mL into a centrifuge tube;

[0042] c. Add 25 mg of Bi@Bi4Ti3O 12 nanoplatelets containing oxygen vacancies into the remaining solution in step b, and ultrasonically treat for 5 min to make it uniformly stable, then magnetically stir in the dark for 30 min to ensure complete adsorption of the dye molecules.

[0043] d. Take 5 mL of the solution in step c into a centrifuge tube, and then place the beaker containing the remaining solution system under irradiation of a xenon lamp with a 420 nm filter, while keeping the magnetic stirring at 350 r / min, take 5 mL of sample every 2 min, for a total of 5 times;

[0044] e. After centrifugation of the removed sample, test the supernatant for ultraviolet-visible absorption spectrum to analyze the degradation efficiency of the pollutants.

[0045] Example 4:

[0046] a. Dissolve 1.64 mg of anionic dye methyl orange in 100 mL of deionized water, and then ultrasonically treat to make it a uniformly stable solution, and then use a glass rod to introduce the uniformly stable solution into a 500 mL volumetric flask and make up to volume.

[0047] b. Take 100 mL of the solution obtained in step a in a beaker and transfer 5 mL to a centrifuge tube;

[0048] c. Add 25 mg of oxygen vacancy containing Bi@Bi4Ti3O 12 nanoplatelets to the remaining solution in step b, sonicate for 5 min to make it homogeneously stable, then magnetically stir in the dark for 30 min to ensure complete adsorption of dye molecules.

[0049] d. Transfer 5 mL of the solution in step c to a centrifuge tube, then place the beaker containing the remaining solution system under a xenon lamp with a 420 nm filter, keep magnetic stirring at 350 r / min during the irradiation, take 5 mL sample every 20 min, a total of 7 times;

[0050] e. After centrifugation of the removed sample, test the supernatant for UV-Vis absorption spectrum to analyze the degradation efficiency of pollutants.

[0051] Example 5:

[0052] a. Dissolve 3.02 mg of anionic dye acid red 18 in 100 mL of deionized water, then treat it in an ultrasonic wave to make it a homogeneously stable solution, use a glass rod to drain the homogeneously stable solution into a 500 mL volumetric flask and make up to volume.

[0053] b. Take 100 mL of the solution obtained in step a in a beaker and transfer 5 mL to a centrifuge tube;

[0054] c. Add 25 mg of oxygen vacancy containing Bi@Bi4Ti3O 12 nanoplatelets to the remaining solution in step b, sonicate for 5 min to make it homogeneously stable, then magnetically stir in the dark for 30 min to ensure complete adsorption of dye molecules.

[0055] d. Transfer 5 mL of the solution in step c to a centrifuge tube, then place the beaker containing the remaining solution system under a xenon lamp with a 420 nm filter, keep magnetic stirring at 350 r / min during the irradiation, take 5 mL sample every 30 min, a total of 5 times;

[0056] e. After centrifugation of the removed sample, test the supernatant for UV-Vis absorption spectrum to analyze the degradation efficiency of pollutants.

[0057] Example 6:

[0058] a. Mix 50 mL of anionic dye acid red 18 and 50 mL of cationic dye methylene blue with a concentration of 1 x 10 -5 mol / L in a beaker, sonicate.

[0059] b. Take 5 mL of the solution in step a and place it in a centrifuge tube;

[0060] c. Add 25 mg of the Bi@Bi4Ti3O 12 nanoplatelets with oxygen vacancies to the remaining solution in step b, and ultrasonically treat for 5 min to make it uniform and stable, then magnetically stir in the dark for 30 min to ensure complete adsorption of the dye molecules.

[0061] d. Take 5 mL of the solution in step c and place it in a centrifuge tube, then place the beaker containing the remaining solution system under a xenon lamp with a 420 nm filter, and maintain magnetic stirring at 350 r / min during the irradiation, take 5 mL of the sample every 20 min, a total of 7 times;

[0062] e. After centrifugation of the removed sample, test the supernatant for UV-visible absorption spectrum to analyze the degradation efficiency of the pollutants.

[0063] Table 1

[0064]

[0065] Table 1 is the final degradation rate of five dyes by Bi@Bi4Ti3O 12 nanoplatelets with oxygen vacancies and the control catalyst. From the table and Figure 4 、 5 it can be seen that the control catalyst Bi4Ti3O 12 has no selective degradation effect on cationic dyes, and Bi@Bi4Ti3O 12 nanoplatelets with oxygen vacancies have higher degradation rates and selectivity than the control catalyst Bi4Ti3O 12 and OVs-Bi4Ti3O 12 , which is due to the increase in oxygen vacancy concentration and the generation of Bi element.

[0066] Bi4Ti3O 12 catalysts without oxygen vacancies and Bi element have no selective degradation activity on the above pollutants, while the catalysts described in the present application show high selective degradation activity compared with the control group. The catalysts described in the present application not only achieve efficient and selective degradation of pollutants in a neutral environment, but also still show high catalytic activity in a wide range of acid-base environments with pH of 4-10.

[0067] The above examples and the accompanying drawings illustrate the basic principles, main features and advantages of the present application. The present application is not limited to the above examples, and the above examples and the specification are only illustrative of the principles of the present application. Within the scope of the principles of the present application, the present application can have various changes and improvements, and these changes and improvements are protected by the present application.

Claims

1. An oxygen-vacancy-containing Bi@Bi4Ti3O 12 The application of nanosheets in the selective photocatalytic degradation of cationic dye pollutants is characterized by, Bi@Bi4Ti3O containing oxygen vacancies 12 The nanosheet catalyst was prepared by mixing and grinding 62.5 mmol of sodium chloride and potassium chloride as molten salts for 30 min, followed by the addition of 5 mmol of Bi₂O₃ and 7.5 mmol of TiO₂, and grinding for another 30 min to obtain a uniformly mixed powder. Then, 1.5 g of urea was added as a reducing agent to further increase oxygen vacancies, and grinding continued for 30-60 min to obtain a uniform, fine powder. Finally, the powder was transferred to a crucible and placed in a muffle furnace at 2... o Heating at a rate of C / min to 700 o Calcination at C for 2 h; after the reaction is complete, 2 o Cool to room temperature at a rate of C / min, wash the sample with a mixture of deionized water and anhydrous ethanol, and 60 o C is dried and ground to obtain the target product.

2. The application according to claim 1, characterized in that, Includes the following steps: a) Incorporating oxygen-containing vacancy Bi@Bi4Ti3O 12 Nanosheets were added to a concentration of 1×10 -5 In a mol / L cationic and / or anionic dye solution, the mixture was ultrasonically dispersed for 5 min to ensure homogeneity and stability, followed by magnetic stirring in the dark for 30 min to ensure that the pollutants and catalyst reached adsorption-desorption equilibrium; each 20-30 mg of Bi@Bi4Ti3O4 containing oxygen vacancies... 12 The nanosheets correspond to 100 mL of dye solution; b. The reaction system is carried out under visible light irradiation while being stirred. c. After centrifuging the extracted sample, take the supernatant to test the ultraviolet-visible absorption spectrum and analyze the degradation efficiency of pollutants.

3. The application according to claim 2, characterized in that, Bi@Bi4Ti3O with oxygen vacancies per 25mg 12 The nanosheets correspond to 100 mL of dye solution.

4. The application according to claim 2, characterized in that, The cationic dye in step a is Rhodamine B, methylene blue, basic orange II, or other dyes that are soluble in water and exist in a cationic state. The anionic dye in step a is methyl orange, acid red 18, or other dyes that are soluble in water and exist in an anionic state.

5. The application according to claim 2, characterized in that, Cationic dye solutions can be acidic, neutral, or alkaline.

6. The application according to claim 2, characterized in that, In step b, the xenon lamp is equipped with a 420nm filter, which expands the light absorption range into the visible light region.

7. The application according to claim 2, characterized in that, The fixed time intervals for sampling in step b include 2, 20, and 30 minutes.

8. The application according to claim 2, characterized in that, The catalyst exhibits selective photocatalytic degradation of cationic dyes at solution pH around 7 or above 7. When the acid-base range is further broadened to strongly acidic or strongly alkaline conditions, the catalyst still shows good visible light photocatalytic performance. It demonstrates significant degradation activity for Basic Orange II, exhibiting high catalytic activity even at an acidic pH of 4, achieving 99.03% effective degradation within 60 minutes. Further alkaline conditions, specifically at pH 10, resulted in 97.23% degradation within 120 minutes.

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