Use of a two-dimensional polyoxometalate nanomaterial

Abstract

The application discloses application of a two-dimensional polyoxometalate nanomaterial, and the two-dimensional polyoxometalate nanomaterial is applied to photocatalytic degradation of organic dyes; the two-dimensional polyoxometalate nanomaterial has a sheet layer structure; and the sheet layer structure is formed by polyoxometalate clusters arranged in a hexagonal shape. Through the application, the degradation of dyes can be realized quickly and efficiently, the two-dimensional polyoxometalate nanomaterial used has excellent cycle stability, and the production cost of dye degradation is greatly saved.

Description

TECHNICAL FIELD

[0001] The application relates to an application of a two-dimensional polyoxometalate nanomaterial, in particular to an application of a two-dimensional polyoxometalate nanomaterial in photocatalytic degradation of dyes, and belongs to the technical field of dye treatment. BACKGROUND

[0002] Nowadays, with the rapid development of social economy, environmental pollution is increasingly serious. A series of refractory pollutants, such as halogenated phenols, antibiotics, dyes and heavy metals, are detected in various environmental matrices such as wastewater, soil, air and even biological matrix. Under this background, many technologies have been developed to eliminate environmental pollutants, which are divided into physical methods, chemical methods, biological methods and the like. The physical method includes adsorption and flocculation, which is simple to operate but low in efficiency. The chemical method includes the use of chlorine-containing compounds or oxides to completely purify pollutants, but secondary pollutants and toxic by-products are inevitably generated when chemical reagents are used. Biological catalysis needs higher cost to improve the purity, stability and activity of enzymes.

[0003] In recent years, solar-driven photocatalytic technology is considered as an advanced oxidation process and an environmental protection strategy, which can effectively and continuously remove various environmental pollutants. However, most of the photocatalysts reported at present far cannot meet the requirements of practical application. These photocatalysts still have some problems, such as being suitable for effectively removing only a single pollutant under specific conditions, rapid recombination of photo-generated carriers and poor stability, serious internal photo-generated electron / hole recombination and low catalytic performance. Therefore, it is imperative to design a photocatalyst with low cost, high efficiency and stable photochemical performance and enable it to efficiently degrade organic dyes. SUMMARY

[0004] In view of the deficiencies in the prior art, the application aims to provide an application of a two-dimensional polyoxometalate nanomaterial in photocatalytic degradation of organic dyes, realize rapid and efficient degradation of organic dyes, and has the characteristics of simple operation and mild reaction conditions. Meanwhile, the two-dimensional polyoxometalate nanomaterial used in the application is rich in metal ions, has good electron storage capacity, is stable in structure and not easy to be oxidized, has excellent cycle stability and catalytic activity, and greatly saves the production cost of dye degradation.

[0005] In order to achieve the above technical purpose, the application provides an application of a two-dimensional polyoxometalate nanomaterial, which is applied to photocatalytic degradation of organic dyes; the two-dimensional polyoxometalate nanomaterial has a sheet structure; and the sheet structure is composed of polyoxometalate clusters arranged in a hexagonal shape.

[0006] The present application makes full use of the fact that the two-dimensional polyoxometalate nanomaterial contains a large number of polyoxometalate clusters, which are rich in metal ions, have good electron storage capacity, and have high chemical affinity. In the polyoxometalate of the present application, there are neodymium atoms and tungsten atoms, in which the neodymium atoms replace the tungsten atoms of the keggin-type phosphotungstic acid and form four coordination bonds with the surface oxygen atoms, and are connected with two adjacent polyoxometalate clusters to form a zigzag linear arrangement, having a hexagonal layered structure. The highly ordered structure enables the electron sharing of the two-dimensional polyoxometalate nanomaterial to occur between multiple clusters, forming a "supramolecule" with interlayer electron delocalization, and producing a corresponding synergistic effect. The two-dimensional polyoxometalate used in the present application can be used for photocatalysis, and the mechanism is that the two-dimensional polyoxometalate nanomaterial has a suitable band gap (2.88 eV), and when the material is irradiated with visible light, the photo-generated electrons on the valence band will jump to the conduction band, leaving corresponding holes on the valence band to form electron-hole pairs. Due to the special hexagonal arrangement of the material, the sharing effect of the electron-hole pairs is greatly enhanced, and in addition, the material is dispersed in an organic dye solution, a large number of hydroxyl radicals and superoxide ion radicals are generated in the process, which have strong oxidizing properties and can quickly and efficiently oxidize organic dyes to promote the degradation of organic dyes. In addition, the two-dimensional polyoxometalate cluster has the property of high specific surface area, which also promotes the stability of the Keggin unit and provides more active sites, thereby further improving the catalytic performance of the polyoxometalate cluster.

[0007] As a preferred scheme, the thickness of the sheet structure is 1.5-5 nm.

[0008] As a preferred scheme, the two-dimensional polyoxometalate nanomaterial is used for photocatalytic degradation of organic dyes by mixing the two-dimensional polyoxometalate nanomaterial with a solution containing organic dyes, adjusting the pH of the solution to weakly acidic to neutral, and performing a photocatalytic degradation reaction.

[0009] As a preferred scheme, the organic dye is at least one of methylene blue, crystal violet and rhodamine B.

[0010] As a preferred scheme, the solid-liquid ratio of the two-dimensional polyoxometalate nanomaterial to the organic dye is 10-15 mg:100 mL. Under light conditions, if the amount of two-dimensional polyoxometalate nanomaterial is too low, the catalytic rate is too low and the dye cannot be completely degraded; and as the amount of two-dimensional polyoxometalate nanomaterial increases, the number of active sites decreases due to the agglomeration of the catalyst powder and the light scattering effect, resulting in a decrease in the degradation efficiency of the dye, so that the activity of the catalytic degradation of the dye increases first and then decreases.

[0011] As a preferred solution, the concentration of the dye is 10-50 mg / L. The concentration of the dye also affects the rate of catalytic degradation, because too high initial concentration makes the path of photons into the dye solution shorter, light penetration decreases, and the number of dye molecules adsorbed on the surface of the catalyst increases, hindering effective contact with active oxygen. The two-dimensional polyoxometalate nanomaterial prepared by the present application has good degradation capacity in the range of 10-50 mg / L, and further preferably the concentration of the dye is 10-30 mg / L.

[0012] As a preferred solution, the pH of the solution is controlled to be 4.5-7.5. The present application uses NaOH and HCl to adjust the acidity and alkalinity of the solution. When the solution system is in a weakly acidic environment, the catalytic activity of the two-dimensional polyoxometalate nanomaterial is higher, but an excessively acidic environment can destroy the structure of the organic dye, and therefore, further preferably the pH of the solution is controlled to be 4.5-5.5.

[0013] As a preferred solution, the condition of the photocatalytic degradation reaction is that a xenon lamp light source is used, and the temperature is 20-30°C.

[0014] As a preferred solution, the mixing time is 40-60 min.

[0015] As a preferred solution, the preparation method of the two-dimensional polyoxometalate nanomaterial is that a solution containing ammonium cations is added dropwise to a mixed solution containing tungstophosphoric acid and neodymium salt, and then ultrasonic and centrifugal are performed in sequence to obtain the two-dimensional polyoxometalate nanomaterial.

[0016] As a preferred solution, the neodymium salt is neodymium nitrate and a hydrate of neodymium nitrate.

[0017] As a preferred solution, the molar ratio of the tungstophosphoric acid and the neodymium salt is 1:1-5. When the proportion of the neodymium salt is too low, the two-dimensional polyoxometalate nanomaterial prepared is excessively stacked, and when the proportion of the neodymium salt is too high, the holes in the two-dimensional polyoxometalate nanomaterial prepared are broken, forming a nanobelt structure.

[0018] As a preferred solution, the ammonium cations are provided by hexadecyl trimethyl ammonium bromide and / or tetrabutyl ammonium bromide. If the ammonium cations with shorter alkyl chains are not sufficient to support the two-dimensional porous structure, the pores will partially collapse, and the preferred ammonium cations with longer alkyl chains in the present application can support the holes, forming a sheet structure.

[0019] As a preferred solution, the molar ratio of the ammonium cations to the tungstophosphoric acid is 2-3:1.

[0020] As a preferred scheme, the concentration of the solution containing ammonium cations is 0.2-0.5 μmol / L, and the solvent used is chloroform. The use of chloroform in the present application can make the ammonium cations fully dissolved and stabilize the material morphology.

[0021] As a preferred scheme, the ultrasonic time is 5-20 min. The ultrasonic treatment can promote the mixing and reaction of the solution.

[0022] Compared with the prior art, the technical scheme of the present application has the following beneficial technical effects:

[0023] 1) The catalyst structure of the two-dimensional polyoxometalate nanomaterial provided by the present application is easy to control, has good electron transport capacity and excellent thermal / chemical stability, has a hexagonal hole-shaped sheet structure, and thus has a large specific surface area, is stable in structure and not easy to be oxidized, has excellent cycle stability and catalytic activity, and greatly saves the production cost of dye degradation.

[0024] 2) The method for degrading dyes by the two-dimensional polyoxometalate nanomaterial provided by the present application can quickly and efficiently realize the degradation of dyes, and has the characteristics of simple operation and mild reaction conditions. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The transmission electron microscope images of the two-dimensional polyoxometalate nanomaterial prepared in Example 1 at different positions. As can be seen from the images, the two-dimensional polyoxometalate nanomaterial of the present application has a uniform structure, and is composed of a plurality of two-dimensional polyoxometalate clusters arranged in a hexagonal hole-shaped structure.

[0026] Figure 2 The high-angle annular dark field scanning transmission electron microscope image of the two-dimensional polyoxometalate nanomaterial prepared in Example 1. From the image, the hole structure of the two-dimensional polyoxometalate nanomaterial can be more clearly seen. Figure 2 Figure 3 The element distribution map of the two-dimensional polyoxometalate nanomaterial prepared in Example 1, wherein Figure 3 (d) is the distribution map of W element; Figure 3 (a) is the distribution map of Nd element; Figure 3 (c) is the distribution map of P element; Figure 3 (b) is the distribution map of O element.

[0027] Figure 4 The catalytic degradation activity of rhodamine B of the two-dimensional polyoxometalate nanomaterial under dark conditions with a dosage of 15 mg and under xenon lamp light source irradiation with a dosage of 5-25 mg (the concentration of the dye is 30 mg / L) Figure 4 (a) and the degradation rate Figure 4 (b).​

[0028] Figure 5 Catalytic degradation activity of two-dimensional polyoxometalate nanomaterials on Rhodamine B solution under light irradiation at different pH values (the amount of two-dimensional polyoxometalate nanomaterials is 15 mg) Figure 5 (a) and degradation rate Figure 5 (b).

[0029] Figure 6 Catalytic degradation activity of two-dimensional polyoxometalate nanomaterials on Rhodamine B solution under light irradiation at different concentrations Figure 6 (a) and degradation rate Figure 6 (b) comparison chart.

[0030] Figure 7 Catalytic degradation activity of two-dimensional polyoxometalate nanomaterials on Rhodamine B solution under light irradiation with different active species trapping agents Figure 7 (a) and degradation rate Figure 7 (b) comparison chart.

[0031] Figure 8 Comparison chart of the effect of two-dimensional polyoxometalate nanomaterials prepared in Example 1 on different dyes. Among them Figure 8 (a) ~ Figure 8 (b) comparison chart of the catalytic activity and degradation rate of two-dimensional polyoxometalate nanomaterials prepared in Example 1 on Rhodamine B, methylene blue and crystal violet.

[0032] Figure 9 Chart of the cycle stability of two-dimensional polyoxometalate nanomaterials prepared in Example 1 in the process of catalytic degradation of Rhodamine B.

[0033] Figure 10 Process chart of two-dimensional polyoxometalate nanomaterials prepared in Example 1.

[0034] Figure 11 Performance chart of two-dimensional polyoxometalate nanomaterials prepared in Example 1. Among them Figure 11 (a) is: UV-Vis spectrum chart; Figure 11 (b) is a band gap chart; Figure 11 (c) is a Mott-Schottky curve chart. DETAILED DESCRIPTION

[0035] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a variety of ways beyond those specifically described herein without departing from the scope of the present application, and it is understood that it can be employed in other different embodiments or carried out in a different way by those skilled in the art without departing from the spirit and scope of the present application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0037] In the embodiments of the present application, unless otherwise specified, the chemical reagents used can be obtained by purchase or existing preparation methods, and the instruments and equipment used are conventional devices in the prior art.

[0038] Example 1

[0039] Preparation of two-dimensional polyoxometalate nanomaterials:

[0040] 1) 29 mg of phosphotungstic acid (H3PW12O40) and 14 mg of neodymium nitrate hexahydrate (NdN3O9·6H2O) were dissolved in 10 mL of deionized water at a molar ratio of 1:3, and stirred for 30 minutes. 12 O 40

[0041] 2) 4.5 mg of cetyltrimethylammonium bromide (CTAB) and 4 mg of tetrabutylammonium bromide (TBAB) were fully dissolved in 50 mL of chloroform.

[0042] 3) The organic solution obtained in step 2 was slowly added (the addition rate was 1 mL / s) to the solution obtained in step 1, and the mixed solution was stirred for 10 hours.

[0043] 4) The stirred mixed solution was ultrasonically treated for 5 minutes.

[0044] 5) The ultrasonically treated solution was centrifuged at 8000 rpm for 5 minutes. The supernatant was carefully removed, and finally the precipitate was dried in a vacuum oven at 40°C overnight to obtain two-dimensional graphene-like structure polyoxometalate nanomaterials.

[0045] Application of two-dimensional polyoxometalate nanomaterials in photocatalytic degradation of dye decomposition:

[0046] 1) 15 mg of two-dimensional graphene-like structure polyoxometalate nanomaterials were added to 100 mL of rhodamine B solution with a concentration of 30 mg / L and stirred uniformly, then transferred to a photocatalytic reaction kettle, the magnetic stirrer was turned on, and the mixture was stirred in the dark for 60 min, and the pH value of the solution system was adjusted to 4.5, 5.5, 6.5 and 7.5 using NaOH and HCl respectively.

[0047] 2) The xenon lamp light source was vertically hit on the liquid surface of the glass container, the xenon lamp light source was 10 cm away from the liquid surface of the glass container, and the photocatalytic degradation reaction was carried out at a system temperature of 20°C.

[0048] ​3) every 10 minutes, take three milliliters of solution, filter with filter membrane, and then determine the concentration of rhodamine B in the solution by UV-visible spectroscopy.

[0049] The catalytic degradation activity and degradation rate of rhodamine B are shown in Table 1. Figure 5 As shown in the figure, when the pH value of the solution system is 4.5-7.5, the two-dimensional polyoxometalate nanomaterials exhibit good catalytic activity, and the catalytic efficiency is the fastest and the catalytic activity is the highest when the pH value is 4.5, and the smaller the concentration of residual rhodamine B in the solution is.

[0050] Example 2

[0051] The difference between this example and Example 1 is only that the mass of the two-dimensional polyoxometalate nanomaterials is replaced by 5 mg, 10 mg, 20 mg, 25 mg under light conditions and 15 mg under dark conditions, the pH value of the solution system is 4.5, and the other conditions are consistent.

[0052] The catalytic degradation activity and degradation rate of rhodamine B are shown in Table 1. Figure 4 As shown in Table 1, when in the dark condition, even if the amount of the two-dimensional polyoxometalate nanomaterials is 15 mg, there is almost no catalytic activity. Under light conditions, as the amount of the catalyst increases, the catalytic degradation activity of the two-dimensional polyoxometalate nanomaterials on rhodamine B increases, and when the amount of the two-dimensional polyoxometalate nanomaterials is 15 mg, the two-dimensional polyoxometalate nanomaterials have the strongest degradation capacity on rhodamine B. When the amount of the two-dimensional polyoxometalate nanomaterials continues to increase, the degradation rate of the two-dimensional polyoxometalate nanomaterials on rhodamine B decreases. This is mainly due to the agglomeration and light scattering effect of the catalyst powder, the decrease of the number of active sites, and the decrease of the degradation efficiency of the dye.

[0053] Example 3

[0054] The difference between this example and Example 1 is only that the concentration of the rhodamine B solution is replaced by 10 mg / L, 20 mg / L, 40 mg / L and 50 mg / L, the pH value of the solution system is 4.5, and the other conditions are consistent.

[0055] The catalytic degradation activity and degradation rate of rhodamine B are shown in Table 1. Figure 6 As shown in Table 1, the two-dimensional polyoxometalate nanomaterials prepared by the present application have good degradation capacity in the range of 10-50 mg / L, and when the concentration of rhodamine B is 10 mg / L, the two-dimensional polyoxometalate nanomaterials have the strongest degradation capacity on rhodamine B. When the initial concentration of the dye is low, there is sufficient catalyst to react with it, so the degradation effect under the low-concentration solution is the strongest.

[0056] Example 4

[0057] The embodiment is only different from example 1 in that methanol (MeOH), p-BQ and IPA are added respectively as capturing agents, the pH value of the solution system is 4.5, and the rest conditions are consistent.

[0058] The catalytic degradation activity and degradation rate of rhodamine B are shown in Figure 7 It can be obviously seen that different capturing agents have certain influence on the degradation rate of two-dimensional polyoxometalate nanomaterials on rhodamine B. The degradation rate is obviously decreased after adding methanol, which indicates that the hole of two-dimensional polyoxometalate nanomaterials plays a certain role in the catalytic process.

[0059] Example 5

[0060] The embodiment is only different from example 1 in that rhodamine B is replaced by methylene blue and crystal violet with the same concentration respectively, the pH value of the solution system is controlled to be 4.5, and the rest conditions are consistent.

[0061] The effect comparison chart of two-dimensional polyoxometalate nanomaterials on different dyes is shown in Figure 8 It can be seen from the chart that the two-dimensional polyoxometalate nanomaterials prepared by the application have certain degradation activity on rhodamine B (RhB), methylene blue (MB) and crystal violet (CV).

[0062] Example 6

[0063] The two-dimensional polyoxometalate nanomaterials prepared in example 1 are subjected to the rhodamine B catalytic degradation cycle stability determination according to the conditions of example 1, and the pH value of the solution is controlled to be 4.5. The results are shown in Figure 9 The results show that the catalytic degradation rate has no change compared with the initial value after the three cycle stability tests of the two-dimensional polyoxometalate nanomaterials, which indicates that the two-dimensional polyoxometalate nanomaterials have excellent cycle stability.

[0064] The above is only a specific embodiment of the application, but the protection scope of the application is not limited to this. Any changes or replacements within the technical range disclosed by the application can be easily thought by those skilled in the art, which should be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. An application of a two-dimensional polyoxometalate nanomaterial, characterized in that: The two-dimensional polyoxometalate nanomaterials are used for photocatalytic degradation of organic dyes; the two-dimensional polyoxometalate nanomaterials have a layered structure; the layered structure is composed of polyoxometalate clusters arranged in hexagons; The preparation method of the two-dimensional polyoxometalate nanomaterial is as follows: a solution containing ammonium cations is added dropwise to a mixed solution containing phosphotungstic acid and neodymium salt, and then ultrasonic and centrifuged sequentially to obtain the nanomaterial. The molar ratio of phosphotungstic acid to neodymium salt is 1:1 to 5; The application process is as follows: after mixing two-dimensional polyoxometalate nanomaterials with a solution containing organic dyes, the pH of the solution is adjusted to weakly acidic to neutral, and then a photocatalytic degradation reaction is carried out.

2. The application of the two-dimensional polyoxometalate nanomaterial according to claim 1, characterized in that: The thickness of the sheet structure is 1.5–5 nm.

3. The application of the two-dimensional polyoxometalate nanomaterial according to claim 2, characterized in that: The organic dye is at least one of methylene blue, crystal violet, and rhodamine B.

4. The application of the two-dimensional polyoxometalate nanomaterial according to claim 3, characterized in that: The solid-liquid ratio of the two-dimensional polyoxometalate nanomaterial to the organic dye is 10-15 mg: 100 mL; the concentration of the organic dye is 10-50 mg / L.

5. The application of the two-dimensional polyoxometalate nanomaterial according to claim 1, characterized in that: The pH of the solution is controlled to be between 4.5 and 7.

5.

6. The application of the two-dimensional polyoxometalate nanomaterial according to claim 1, characterized in that: The conditions for the photocatalytic degradation reaction are: a xenon lamp light source is used, and the temperature is 20-30℃.

7. The application of the two-dimensional polyoxometalate nanomaterial according to claim 1, characterized in that: The mixing time is 40–60 minutes.

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