A water-soluble BiO 2-x nanomaterial and its preparation method and application

Abstract

The present invention relates to a water-soluble BiO 2‑x nanomaterial, its preparation method and application, belonging to the technical field of nanomaterials, and solves the problem of poor water solubility of BiO 2‑x nanomaterials in the prior art. The method comprises the following steps: dissolving hydroxides of alkali metals and bismuthates, stirring to obtain a suspension, heating the suspension for hydrothermal reaction to obtain BiO 2‑x powder; adding an aqueous solution of sodium hexametaphosphate to the BiO 2‑x powder for the first ball milling, then adding an aqueous solution of polyvinylpyrrolidone for the second ball milling, washing, and freeze-drying to obtain the water-soluble BiO 2‑x nanomaterial. The method of the present invention forms a composite material by wet ball milling the synthesized BiO 2‑x powder with a sodium hexametaphosphate solution and a polyvinylpyrrolidone solution, improving the water solubility of the BiO 2‑x nanomaterial and further enhancing its catalytic ability.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a water-soluble BiO 2-x Nanomaterials and their preparation methods and applications. Background Art

[0002] The structure and morphology of nanomaterials have a great influence on the performance and application of nanomaterials. The preparation of nanomaterials with specific structures has important academic significance and application value for developing new areas of nanomaterial performance. Photocatalysis is based on the application of semiconductors, which undergo the following steps during the excitation process under appropriate conditions: light absorption, charge separation, and conversion of surface reactants. TiO2 is a photocatalyst with a wide band gap that has been studied in detail, along with titanates and tantalates. These semiconductors with negative conduction band (CB) potentials are stable. They have shown the best photocatalytic activity to date in pollutant degradation and H2 production. However, due to its wide band gap, it can only be excited by ultraviolet light, which accounts for only 5% of the solar spectrum. In order to improve the utilization of solar energy, semiconductors with narrow band gaps must be developed.

[0003] Nano BiO 2-x It is a special morphology BiO 2-x Powder material, layered BiO 2-x As a potential catalyst, it has attracted widespread attention. The material has a narrow band gap of 1.5 to 1.8 eV and has good catalytic activity in H2 production, pollutant degradation and O2 activation. 2-x The photocatalysts are bismuth-based oxides rich in oxygen vacancies, which exhibit satisfactory light absorption in the ultraviolet-visible-near-infrared (UV-Vis-NIR) light range. 2-x The smaller the particle size, the more oxygen vacancy defects are exposed on the surface, and the stronger the photocatalytic performance is. Therefore, it is possible to directly prepare nano-BiO 2-x Worth studying.

[0004] Currently, BiO 2-x Nanosheets are mainly synthesized by hydrothermal method. The nanosheets are tightly bound together and present block shape, which greatly reduces the active sites on the surface of the nanosheets, inhibits their photocatalytic effect, and has poor dispersibility. At present, the main methods for breaking layered materials into sheet materials are: concentrated acid intercalation, inorganic metal intercalation (Li, Na, K), ultrasonic crushing and other methods. Concentrated acid intercalation can easily break BiO with oxygen vacancy defects. 2-x Oxidized to Bi2O3; Inorganic metal ions are usually active metal ions that break up layered BiO in aqueous solution 2-x It is easy to be dangerous when ultrasonically breaking the layered BiO 2-xIt takes a long time, usually more than 8 hours, the crushing efficiency is still low, the yield is low, and the energy consumption is large. Summary of the Invention

[0005] In view of the above analysis, embodiments of the present invention aim to provide a water-soluble BiO 2-x nanomaterials and their preparation methods and applications, which are used to solve the problem of poor water solubility of BiO 2-x nanomaterials prepared by existing methods.

[0006] On the one hand, the present invention provides a method for preparing a water-soluble BiO 2-x nanomaterial, which includes the following steps:

[0007] (1) Dissolve the hydroxide of an alkali metal and bismuthate, stir to obtain a suspension, heat the suspension for hydrothermal reaction to obtain BiO 2-x powder;

[0008] (2) Add an aqueous solution of sodium hexametaphosphate to the BiO 2-x powder for the first ball milling, then add an aqueous solution of polyvinylpyrrolidone for the second ball milling, wash, and freeze-dry to obtain the water-soluble BiO 2-x nanomaterial;

[0009] wherein, x is 0.2 - 0.55.

[0010] Further, in step (1), the mass ratio of the hydroxide of an alkali metal to bismuthate is 0.5 - 1.5:1.

[0011] Further, in step (1), the purity of bismuthate ≥ 85%, the temperature of the hydrothermal reaction is 130 - 160 °C, and the reaction time is 4 - 8 h.

[0012] Further, in step (1), the BiO 2-x powder is spherical, and the particle size is 10 - 50 nm.

[0013] Further, in step (2), the mass ratio of BiO 2-x powder to sodium hexametaphosphate is 0.1 - 10:1, and the mass ratio of polyvinylpyrrolidone to BiO 2-x powder is 0.5 - 10:1.

[0014] Further, in step (2), before adding sodium hexametaphosphate, the BiO 2-x powder is subjected to plasma ball milling treatment.

[0015] Further, the plasma ball milling treatment is carried out by dielectric barrier discharge, with a rotation speed of 900 - 1100 rpm, a plasma discharge frequency of 8 - 9 KHz, and a ball milling time of 2 - 4 h.

[0016] Further, in step (2), the rotation speed of the first ball milling is 450 - 600 rpm, the ball milling time is 1 - 3 h, the rotation speed of the second ball milling is 450 - 600 rpm, and the ball milling time is 2 - 3 h.

[0017] Second, the present invention provides a water-soluble BiO 2-x nanomaterials prepared by the method described above.

[0018] Third, the present invention provides an application of the water-soluble BiO 2-x nanomaterials prepared by the method in photocatalysts.

[0019] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0020] (1) In the method of the present invention, the synthesized BiO 2-x powder is ball milled with a sodium hexametaphosphate solution and a polyvinylpyrrolidone solution to form a composite material. Sodium hexametaphosphate is wrapped on the surface of the BiO 2-x powder, improving its water solubility. The BiO 2-x powder will be dispersed after ball milling, and continuous ball milling will oxidize it into bismuth oxide. Adding polyvinylpyrrolidone can further improve the water solubility of the BiO 2-x nanomaterials and prevent the oxidation reaction from proceeding, further improving its catalytic ability;

[0021] (2) In the present invention, high-purity bismuthate is selected as the raw material, and BiO 2-x nanomaterials with smaller particle sizes can be synthesized, making it have better modifiability, improving its surface modification ability, and providing new possibilities for improving its application;

[0022] (3) The method of the present invention uses plasma ball milling technology to break the agglomerated BiO 2-x into small spherical shapes. Since plasma ball milling is carried out in a sealed tank, the problem that the agglomerated BiO 2-x is easily oxidized is avoided. The contact between the plasma and BiO 2-x further increases the number of oxygen defects in BiO 2-x , further improving the catalytic performance of BiO 2-x ; The BiO 2-x nanomaterials prepared by plasma ball milling in the method of the present invention have good water solubility, and BiO 2-xThe solubility of the nanomaterials in water reaches over 5000 ppm. When dissolved in water, the catalytic active sites can be fully exposed, so they have high catalytic ability and catalytic efficiency.

[0023] (4) The preparation method of the present invention is simple and easy to implement, with mild conditions and easy to control. There is no need to additionally add organic stabilizers or dispersants, which is convenient for large-scale production, popularization and application.

[0024] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combined solutions. Other features and advantages of the present invention will be described in the subsequent specification. Moreover, some advantages can be made obvious from the specification or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained through the content specifically pointed out in the specification and the drawings. Description of the Drawings

[0025] The drawings are only for the purpose of showing specific embodiments and are not considered as a limitation to the present invention. Throughout the drawings, the same reference signs denote the same components.

[0026] Figure 1 SEM morphology diagram of the BiO 2-x powder prepared in Example 1;

[0027] Figure 2 XRD diagram of the BiO 2-x powder prepared in Example 1;

[0028] Figure 3 XPS diagram of the BiO 2-x powder prepared in Example 1;

[0029] Figure 4 EPS diagram of the BiO 2-x powder prepared in Example 1;

[0030] Figure 5 TEM diagram of the water-soluble BiO 2-x nanomaterials prepared in Example 1;

[0031] Figure 6 UV spectrum diagram of the water-soluble BiO 2-x nanomaterials after redissolution prepared in Example 1;

[0032] Figure 7 SEM diagram of the ultrafine BiO 2-x powder prepared in Example 4;

[0033] Figure 8 XRD diagram of the ultrafine BiO 2-x powder prepared in Example 4;

[0034] Figure 9 The UV-visible spectra of the BiO 2-x nanomaterials solutions prepared in Examples 1-4 and Comparative Examples 1-3. Detailed implementation manners

[0035] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. The accompanying drawings form a part of the present invention and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0036] A specific embodiment of the present invention discloses a method for preparing a water-soluble BiO 2-x nanomaterial, comprising the following steps:

[0037] (1) Dissolve the hydroxide of an alkali metal and bismuthate, stir to obtain a suspension, and heat the suspension for hydrothermal reaction to obtain BiO 2-x powder;

[0038] (2) Add an aqueous solution of sodium hexametaphosphate to the BiO 2-x powder for the first ball milling, then add an aqueous solution of polyvinylpyrrolidone for the second ball milling, wash, and freeze-dry to obtain the water-soluble BiO 2-x nanomaterial;

[0039] where x is 0.2 - 0.55.

[0040] Compared with the prior art, the method of the present invention forms a composite material by wet ball milling the synthesized BiO 2-x powder with a sodium hexametaphosphate solution and a polyvinylpyrrolidone solution, improving the water solubility of the BiO 2-x nanomaterial and further enhancing its catalytic ability.

[0041] It should be noted that after the hydrothermal reaction, cooling, centrifugation, washing, and drying treatments are carried out in sequence.

[0042] It should be noted that both ball millings of the present invention modify BiO 2-x in a wet method so that it can be dispersed in water. Adding PVP using the wet method can avoid oxidation to Bi2O3 and maintain the BiO 2-x stability and ensure its photocatalytic activity.

[0043] It should be noted that the hydroxide of the alkali metal is sodium hydroxide or potassium hydroxide, and the bismuthate is sodium bismuthate or potassium bismuthate.

[0044] Exemplarily, the hydroxide of the alkali metal is NaOH, and the bismuthate is NaBiO3.

[0045] Specifically, in step (1), the purity of the bismuthate is ≥85%.

[0046] It should be noted that through a large number of experiments, the inventor found that when the purity of the bismuthate is ≥85%, the prepared BiO 2-x powder is spherical under the SEM electron microscope, with a diameter of 1-50 nm. Moreover, from the data of X-ray photoelectron spectroscopy and electron paramagnetic resonance spectrometer, it can be known that the BiO 2-x powder prepared in the present invention contains a large number of defects.

[0047] Specifically, the mass ratio of the alkali metal hydroxide to the bismuthate is 0.5-1.5:1, such as 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1.

[0048] Specifically, in step (1), the purity of the bismuthate is ≥85%, the temperature of the hydrothermal reaction is 130-160 °C, such as 130 °C, 140 °C, 150 °C, 160 °C, and the reaction time is 4-8 h, such as 4 h, 5 h, 6 h, 7 h, 8 h.

[0049] It should be noted that when the temperature is lower than 130 °C, the bismuthate decomposes incompletely, and the produced BiO 2-x powder is impure. Through a large number of experiments, the inventor found that with the bismuthate of the present invention's purity, the reaction can be fully completed below 160 °C.

[0050] Specifically, in step (1), the described BiO 2-x powder is spherical, with a particle size of 10-50 nm.

[0051] Specifically, in step (2), the mass ratio of the BiO 2-x powder to sodium hexametaphosphate is 0.1-10:1, such as 0.1:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0052] It should be noted that if the amount of sodium hexametaphosphate used is too small, the modification will be incomplete, reducing the yield of water-soluble bismuth oxide. If the amount used is too high, it will cause waste, and the impurities in sodium hexametaphosphate will contaminate bismuth oxide. Considering comprehensively, the mass ratio of the BiO 2-x powder to sodium hexametaphosphate is 0.1-10:1.

[0053] Specifically, in step (2), the mass ratio of polyvinylpyrrolidone to the BiO 2-x powder is 0.5-10:1, such as 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0054] It should be noted that if the amount of polyvinylpyrrolidone (PVP) is too small, it cannot protect bismuth oxide, resulting in the oxidation of bismuth oxide during ball milling. The PVP solution has viscosity. If the amount is too large, it will re-aggregate during the subsequent centrifugal washing process, reducing its water solubility.

[0055] Specifically, in step (2), before adding sodium hexametaphosphate, the BiO 2-x powder is subjected to plasma ball milling treatment.

[0056] Specifically, the concentration of the aqueous solution of sodium hexametaphosphate is 0.5 - 5 g / mL, such as 0.5 g / mL, 1 g / mL, 2 g / mL, 3 g / mL, 4 g / mL, 5 g / mL, and the concentration of the aqueous solution of polyvinylpyrrolidone is 0.1 - 0.5 g / mL, such as 0.1 g / mL, 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, 0.5 g / mL.

[0057] It should be noted that the method of the present invention also includes plasma ball milling treatment. The plasma ball milling treatment breaks the agglomerated BiO 2-x into small spherical shapes. Since the plasma ball milling is carried out in a sealed tank, the problem that the agglomerated BiO 2-x is easily oxidized is avoided. The highly active particles of the plasma adsorb on BiO 2-x to increase the surface activity of the material. At the same time, mechanical ball milling introduces fresh surfaces and increases the number of oxygen defects in BiO 2-x , further improving the activity of BiO 2-x . In addition, plasma ball milling uses high-energy electrons generated by the plasma to cause grain boundary slip and even dislocation of the crystal through impact, forming an ultrafine flaky structure.

[0058] Specifically, the plasma ball milling treatment adopts a dielectric barrier discharge method, with a rotation speed of 900 - 1100 rpm, such as 900 rpm, 950 rpm, 1000 rpm, 1050 rpm, 1100 rpm, a plasma discharge frequency of 8 - 9 KHz, such as 8 KHz, 8.2 KHz, 8.4 KHz, 8.6 KHz, 8.8 KHz, 9.0 KHz, and ball milling for 2 - 4 h, such as 2 h, 2.5 h, 3 h, 3.5 h, 4 h.

[0059] Specifically, in step (2), the rotational speed of the first ball milling is 450 - 600 rpm, for example, 450 rpm, 500 rpm, 550 rpm, 600 rpm, and the ball milling time is 1 - 3 h, for example, 1 h, 1.5 h, 2 h, 2.5 h, 3 h. The rotational speed of the second ball milling is 450 - 600 rpm, for example, 450 rpm, 500 rpm, 550 rpm, 600 rpm, and the ball milling time is 2 - 3 h, for example, 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3.0 h.

[0060] It should be noted that in the present invention, the water-soluble BiO 2-x nanomaterials are subjected to freeze-drying preservation treatment and can be redissolved after freeze-drying.

[0061] Specifically, the freeze-drying temperature is -18°C to -12°C, for example, -18°C, -17°C, -16°C, -15°C, -14°C, -13°C, -12°C, and the freeze-drying time is 10 - 14 h, 10 h, 11 h, 12 h, 13 h, 14 h.

[0062] Another specific embodiment discloses a water-soluble BiO prepared by the method described above 2-x nanomaterials.

[0063] It should be noted that the BiO 2-x nanomaterials in this embodiment have good water solubility. The BiO 2-x nanomaterials prepared by plasma ball milling treatment have a solubility in water of more than 5000 ppm, and only through two ball milling treatments, the BiO 2-x nanomaterials have a solubility in water of 1200 ppm. This is because the BiO 2-x powder is ball milled with sodium hexametaphosphate and polyvinylpyrrolidone to form a composite material, improving the water solubility of the BiO 2-x nanomaterials and further enhancing its catalytic ability.

[0064] It should be noted that in the present invention, x in BiO 2-x is 0.2 - 0.55.

[0065] Another specific embodiment discloses the application of the water-soluble BiO prepared by the method described above 2-x nanomaterials in photocatalysts.

[0066] The water-soluble BiO 2-x nanomaterials described in the present invention have high solubility in water, which can fully expose the catalytic active sites. Therefore, the catalytic ability and catalytic efficiency are improved.

[0067] Example 1

[0068] Preparation method of a water-soluble BiO 2-x nanomaterials, comprising the following steps:

[0069] (1) Add 20 g of NaOH powder with a purity of 96% to 250 mL of water to prepare a sodium hydroxide solution. Add 30 g of NaBiO3 powder with a purity of 85% to 250 mL of water, stir evenly, add it to the sodium hydroxide solution, adjust the pH to about 12, and continue stirring for 30 min to form a stable suspension;

[0070] Transfer the suspension to a 2 L polytetrafluoroethylene reactor for hydrothermal reaction. The reaction temperature is 130 °C and the time is 5 h. Cool to room temperature, pour off the supernatant, take the precipitate for centrifugation, wash it 5 times with deionized water, and dry it at 80 °C to obtain dark brown BiO 2-x powder with a particle size of 10 - 50 nm;

[0071] (2) Dissolve 0.25 g of sodium hexametaphosphate in 2 mL of water, add 0.5 g of the above-mentioned BiO 2-x powder, and perform the first ball milling for 3 h using an agate pot at a rotation speed of 450 rpm. Centrifuge and wash it three times with deionized water, and the centrifugation and washing parameters are 8000 rpm and 5 min;

[0072] Then add 3 mL of a polyvinylpyrrolidone solution with a concentration of 0.1 g / mL for the second ball milling for 3 h at a rotation speed of 450 rpm. Centrifuge and wash it three times with deionized water, and the centrifugation and washing parameters are 8000 rpm and 5 min, and freeze-dry to obtain the water-soluble BiO 2-x nanomaterials, where x is 0.2 - 0.55;

[0073] In step (1) of this example, the SEM morphology diagram of the obtained BiO 2-x powder is as shown in Figure 1 . It can be seen from Figure 1 that the BiO 2-x powder prepared in this example is spherical, with a diameter of 10 - 50 nm.

[0074] The XRD diagram of BiO 2-x powder is as shown in Figure 2 . The XPS spectrum is as shown in Figure 3 . The EPS spectrum is as shown in Figure 4 . It can be analyzed from the XPS spectrum in Figure 3 that bismuth oxide contains 532.61 eV, which proves the existence of oxygen defects in the bismuth oxide material. The g value of common oxygen vacancy defects in Figure 4 is about 2.003. Therefore, it is proved that the BiO 2-x powder contains a large number of defects.

[0075] The water-soluble BiO prepared in this example 2-x The TEM image of the Figure 5 nanomaterials is shown as 2-x follows. After ball milling, the originally agglomerated BiO 2-x is processed into dispersed spherical BiO

[0076] The water-soluble BiO 2-x nanomaterials prepared in this example are redissolved to obtain a BiO 2-x aqueous solution. The spectrum of the BiO 2-x aqueous solution is measured using a UV spectrophotometer, and the results are shown as Figure 6 follows. The water-soluble BiO 2-x can be dispersed in water, and after dilution, its UV absorbance is negatively correlated with the dilution factor.

[0077] The specific method is as follows:

[0078] (a) Measure 30 ml of the water-soluble BiO 2-x nanomaterials and place them in a freeze dryer for freeze drying. The freeze drying time at -15°C is 12 h to obtain BiO 2-x lyophilized powder;

[0079] (b) Weigh the BiO 2-x lyophilized powder and prepare a BiO 2-x solution with concentrations of 33 ppm, 100 ppm, 200 ppm, and 250 ppm. Measure its concentration using a UV spectrophotometer and prepare a standard curve.

[0080] Example 2

[0081] A preparation method of a water-soluble BiO 2-x nanomaterial in this example includes the following steps:

[0082] (1) Add 20 g of KOH powder with a purity of 96% to 250 mL of water to prepare a sodium hydroxide solution. Add 20 g of KBiO3 powder with a purity of 85% to 250 mL of water, stir evenly, add it to the sodium hydroxide solution, adjust the pH to about 12, and continue stirring for 30 min to form a stable suspension;

[0083] Transfer the suspension to a 2 L polytetrafluoroethylene reaction kettle for hydrothermal reaction. The reaction temperature is 145°C and the time is 8 h. Cool to room temperature, pour off the supernatant, take the precipitate for centrifugation, and then wash it 5 times with deionized water and dry it at 80°C to obtain dark brown BiO 2-x powder with a particle size of 10 - 50 nm;

[0084] (2) Dissolve 0.25 g of sodium hexametaphosphate in 2 mL of water, add 1.25 g of the BiO 2-x powder, and perform the first ball milling for 2 h using an agate pot at a rotation speed of 550 rpm. Centrifuge and wash three times with deionized water, with the centrifugation and washing parameters being 8000 rpm and 5 min;

[0085] Then add 5 mL of a polyvinylpyrrolidone solution with a concentration of 0.125 g / mL and perform the second ball milling for 2.5 h at a rotation speed of 550 rpm. Centrifuge and wash three times with deionized water, with the centrifugation and washing parameters being 8000 rpm and 5 min, and then freeze-dry to obtain the water-soluble BiO 2-x nanomaterial, where x is 0.2 - 0.55.

[0086] Example 3

[0087] A preparation method of the water-soluble BiO 2-x nanomaterial in this example includes the following steps:

[0088] (1) Add 30 g of NaOH powder with a purity of 96% to 250 mL of water to prepare a sodium hydroxide solution. Add 20 g of NaBiO3 powder with a purity of 85% to 250 mL of water, stir evenly, add it to the sodium hydroxide solution, adjust the pH to about 12, and continue stirring for 30 min to form a stable suspension;

[0089] Transfer the suspension to a 2 L polytetrafluoroethylene reaction kettle for hydrothermal reaction. The reaction temperature is 160 °C and the time is 4 h. Cool to room temperature, pour off the supernatant, take the precipitate for centrifugation, and then wash 5 times with deionized water and dry at 80 °C to obtain dark brown BiO 2-x powder with a particle size of 10 - 50 nm;

[0090] (2) Dissolve 1 g of sodium hexametaphosphate in 0.2 mL of water, add 10 g of the BiO 2-x powder, and perform the first ball milling for 6 h using an agate pot at a rotation speed of 600 rpm. Centrifuge and wash three times with deionized water, with the centrifugation and washing parameters being 8000 rpm and 5 min;

[0091] Then add 1 mL of a polyvinylpyrrolidone solution with a concentration of 5 g / mL and perform the second ball milling for 2 h at a rotation speed of 600 rpm. Centrifuge and wash three times with deionized water, with the centrifugation and washing parameters being 8000 rpm and 5 min, and then freeze-dry to obtain the water-soluble BiO 2-x nanomaterial, where x is 0.2 - 0.55.

[0092] Example 4

[0093] The water-soluble BiO in this example 2-xThe preparation method of the nanomaterial is the same as that of Example 1, except that before adding sodium hexametaphosphate in step (2), the BiO 2-x powder is subjected to plasma ball milling treatment using a PBMS plasma ball mill, adopting a dielectric barrier discharge method, with a rotation speed of 1000 rpm, a plasma discharge frequency of 8.5 KHZ, and ball milling for 3 h to obtain ultrafine BiO 2-x powder.

[0094] The SEM morphology of the ultrafine BiO 2-x powder in this example is as shown in Figure 7 and the XRD is as shown in Figure 8 . Figure 8 Compared with the XRD in Figure 2 , the spectral width of the XRD in this example is larger, indicating that the particle size of the ultrafine BiO 2-x powder is smaller, and the particle diameter is 10 - 20 nm.

[0095] Comparative Example 1

[0096] The preparation method of the BiO 2-x nanomaterial in this comparative example is different from that of Example 1 in that the second ball milling treatment with polyvinylpyrrolidone solution is removed in step (2).

[0097] Comparative Example 2

[0098] The preparation method of the BiO 2-x nanomaterial in this comparative example is different from that of Example 1 in that the first ball milling treatment with sodium hexametaphosphate solution is removed in step (2).

[0099] Comparative Example 3

[0100] The preparation method of the BiO 2-x nanomaterial in this comparative example is different from that of Example 1 in that the purity of the NaBiO3 powder in step (1) is 80%.

[0101] Test Example 1

[0102] The water solubility of the BiO 2-x nanomaterials prepared in Examples 1 - 4 and Comparative Examples 1 - 3 was tested respectively, and the results are shown in Table 1.

[0103] Experimental method: Weigh 0.2 g of the BiO 2-x nanomaterials in Examples 1 - 4 and Comparative Examples 1 - 3 respectively, dissolve them in 20 ml of water to prepare a solution, stir ultrasonically to dissolve them fully, after standing for 10 min, measure their ultraviolet absorption values with an ultraviolet spectrophotometer, prepare a standard curve according to the method of Example 1, and calculate the concentration of the BiO 2-x aqueous solution. The ultraviolet absorption curve is as shown inFigure 9 as shown

[0104] Table 1

[0105]

[0106] As can be seen from Table 1, compared with Examples 1-3, the concentration of BiO 2-x nanomaterials is higher, indicating that after the plasma ball milling treatment, the agglomerated bismuth oxide spheres will be dispersed and coated with sodium hexametaphosphate (SHMP), improving the water solubility of bismuth oxide.

[0107] Compared with Example 1, the concentration in Comparative Example 1 decreased significantly. This is because after adding PVP, PVP will modify the surface of bismuth oxide to prevent it from agglomerating, further improving its water solubility and preventing it from being oxidized during the ball milling process.

[0108] Compared with Example 1, the concentration in Comparative Example 2 decreased significantly. This is because sodium hexametaphosphate is coated on the surface of the BiO 2-x powder, improving the water solubility.

[0109] Compared with Example 1, the concentration in Comparative Example 3 decreased significantly. This is because using high-purity bismuthate as the raw material can synthesize BiO with a smaller particle size 2-x nanomaterials, making it have better modifiability and improving the water solubility.

[0110] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of a water-soluble spherical BiO 2-x nanomaterials, characterized in that It includes the following steps: (1) Dissolve the hydroxide of an alkali metal and bismuthate, with the purity of the bismuthate ≥ 85%, where the bismuthate is sodium bismuthate or potassium bismuthate, stir to obtain a suspension, heat the suspension for hydrothermal reaction, with the temperature of the hydrothermal reaction being 130 - 140 °C and the reaction time being 4 - 8 h, to obtain BiO 2-x powder, and the BiO 2-x powder is spherical with a particle size of 10 - 50 nm; (2) Add an aqueous solution of sodium hexametaphosphate to the BiO 2-x powder for the first ball milling. The first ball milling time is 1 - 3 h. Then add an aqueous solution of polyvinylpyrrolidone for the second ball milling. The rotation speed of the second ball milling is 450 - 600 rpm, and the second ball milling time is 2 - 3 h. The mass ratio of the BiO 2-x powder to sodium hexametaphosphate is 0.1 - 10:1, and the mass ratio of polyvinylpyrrolidone to the BiO 2-x powder is 0.5 - 10:

1. Wash and freeze-dry to obtain the water-soluble spherical BiO 2-x nanomaterial; wherein, x is 0.2 - 0.55; In step (2), before adding sodium hexametaphosphate, it further includes subjecting the BiO 2-x powder to plasma ball milling treatment; The described BiO 2-x nanomaterials have a solubility in water of more than 5000 ppm.

2. A preparation method of a water-soluble spherical BiO 2-x nanomaterials, characterized in that In step (1), the mass ratio of the alkali metal hydroxide to the bismuthate is 0.5 - 1.5:

1.

3. A preparation method of a water-soluble spherical BiO 2-x nanomaterials, characterized in that The plasma ball milling treatment adopts a dielectric barrier discharge method, with a rotation speed of 900 - 1100 rpm, a plasma discharge frequency of 8 - 9 KHz, and a ball milling time of 2 - 4 h.

4. A preparation method of a water-soluble spherical BiO 2-x nanomaterials, characterized in that, In step (2), the rotation speed for the first ball milling is 450 - 600 rpm, and the rotation speed for the second ball milling is 450 - 600 rpm.

5. A water-soluble spherical BiO prepared by the method according to any one of claims 1-4 2-x nanomaterials.

6. Application of the water-soluble spherical BiO 2-x nanomaterials prepared by the method of any one of claims 1-4 in a photocatalyst.

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