Purification method of boron nitride nanotube

Abstract

The invention is suitable for the technical field of boron nitride nanotube purification, and provides a boron nitride nanotube purification method, which comprises: placing a boron nitride nanotube in a dispersant, carrying out ultrasonic dispersion treatment, and filtering; heating the dispersed and filtered boron nitride nanotube in an air atmosphere, carrying out high-temperature impurity oxidation to obtain a product containing oxide impurities, and cooling; washing the product containing the oxide impurities with water, and then putting the washed product into an aqua regia solution for pickling; and repeatedly washing and centrifuging a product obtained after acid pickling for several times, then washing and centrifuging by using ethanol, taking a sinking solute, and drying to obtain the purified boron nitride nanotube. Through a series of physical and chemical treatment steps, metal oxide impurities in the BNNT can be effectively removed, the purity of the BNNT is improved, and the boron nitride nanotube obtained after purification is high in purity, uniform in morphology, good in crystallinity and good in stability.

Description

Technical Field

[0001] The invention belongs to the technical field of boron nitride nanotube purification, and in particular relates to a method for purifying boron nitride nanotubes. Background Art

[0002] Boron nitride nanotubes (BNNTs) are widely used due to their unique physical and chemical properties. However, the preparation process often introduces small amounts of impurities that are difficult to remove, such as oxidized metal catalysts, amorphous boron, nanocages, and irregular BN materials. These impurities severely impact the performance and applications of BNNTs. Therefore, purification of BNNTs is a key step in producing high-quality BNNTs.

[0003] Recent studies have shown that the intercalation properties of phosphoric acid can be used to wet-heat etch BN materials, effectively removing impurities such as nanocages and less ordered BN materials. This method can achieve a mass yield of purified materials as high as 29%. However, the method is relatively cumbersome, the use of organic solvents increases costs, and some BNNTs are lost during the purification process, resulting in a need for improved yield. In addition, foreign researchers have also used ultrasonic dispersion technology combined with organic solvent washing to further improve the purity and dispersibility of BNNTs. This method has improved the purity of BNNTs to a certain extent, but there are still some technical difficulties, such as the complex purification process, high cost, and environmental unfriendliness. Domestic researchers have also achieved a series of important results in the field of boron nitride nanotube purification. For example, in high-temperature oxidation and acid washing, by optimizing the oxidation temperature and acid washing conditions, they have successfully removed metal impurities and amorphous boron from BNNTs, and the purity of the purified BNNTs can reach over 80%. However, this method still needs to be further optimized in terms of purification efficiency and cost control, otherwise it will not meet the needs of large-scale production.

[0004] In summary, although current BNNT purification technology can remove impurities to a certain extent, it still needs further optimization to improve efficiency and purity. Therefore, the development of an efficient and low-cost BNNT purification method is crucial for its industrial application. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a method for purifying boron nitride nanotubes, aiming to solve the problems raised in the above background technology.

[0006] The embodiment of the present invention is implemented as follows: a method for purifying boron nitride nanotubes comprises the following steps:

[0007] The boron nitride nanotubes are placed in a dispersant, subjected to ultrasonic dispersion treatment, and then filtered;

[0008] The dispersed and filtered boron nitride nanotubes are heated in an air atmosphere to oxidize the impurities at high temperature to obtain a product containing oxide impurities, and then cooled;

[0009] The product containing oxide impurities is washed with water, and the product obtained after washing is then placed in aqua regia solution for acid washing;

[0010] The product obtained after acid washing is repeatedly washed with water and centrifuged several times, then washed with ethanol and centrifuged, and the precipitated solute is removed and dried to obtain purified boron nitride nanotubes.

[0011] Preferably, in the step of placing the boron nitride nanotubes in a dispersant, the dispersant is ethanol or deionized water.

[0012] Preferably, the ultrasonic dispersion treatment step is performed for 5-30 minutes.

[0013] Preferably, the dispersed and filtered boron nitride nanotubes are heated in an air atmosphere to oxidize high-temperature impurities to obtain a product containing oxide impurities. In the cooling step, the heating rate is 3-5°C / min, the cooling rate is 3-5°C / min, the temperature for oxidizing high-temperature impurities is 600-800°C, and the oxidation time is 0.5-6 hours.

[0014] Preferably, the water washing time is 1-5 hours, and the water washing temperature is 40-100°C.

[0015] Preferably, the aqua regia is obtained by mixing hydrochloric acid and nitric acid in a volume ratio of 3:1, the concentration of hydrochloric acid is 12 mol / L, and the concentration of nitric acid is 8-16 mol / L.

[0016] Preferably, the pickling temperature is 40-65° C., and the time is 1-85 hours.

[0017] Preferably, in the step of repeatedly washing and centrifuging the product obtained after acid washing for several times, and then washing with ethanol and centrifuging, the centrifugal speed is 5000-8000 r / min, and the single centrifugation time is 5-10 min.

[0018] Preferably, in the step of removing the precipitated solute and drying it, the drying temperature is 80-90° C. and the drying time is 12-24 hours.

[0019] A method for purifying boron nitride nanotubes provided in an embodiment of the present invention can effectively remove metal oxide impurities in BNNTs and improve the purity of BNNTs through a series of physical and chemical treatment steps. The mass percentage of BNNTs after purification can reach more than 93%. The boron nitride nanotubes obtained after purification have high purity, uniform morphology, good crystallinity, and good stability. The purification process is simple and easy to perform and can be easily industrialized. Common chemical reagents and equipment are used to reduce production costs. The reagents and solvents used in the purification process are easy to handle and recycle, and are environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure shows a comparison of XRD patterns of the purified boron nitride nanotubes and the unpurified boron nitride nanotubes according to Example 1 of the present invention;

[0021] Figure 2 Comparison of Fourier transform infrared spectra of the purified boron nitride nanotubes and the unpurified boron nitride nanotubes according to Example 1 of the present invention;

[0022] Figure 3 This is a Raman spectrum of the purified boron nitride nanotubes according to Example 1 of the present invention;

[0023] Figure 4 This is a SEM image of the purified boron nitride nanotubes according to Example 1 of the present invention;

[0024] Figure 5 TEM image of the purified boron nitride nanotubes according to Example 1 of the present invention;

[0025] Figure 6 This is the XPS graph of the purified boron nitride nanotubes in Example 1 of the present invention;

[0026] Figure 7 This is a SEM image of the purified boron nitride nanotubes according to Example 2 of the present invention.

[0027] Figure 8 This is the SEM image of the sample prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0030] Example 1: A method for purifying boron nitride nanotubes, comprising the following steps:

[0031] (1) 145 mg of boron nitride nanotubes were placed in 30 mL of deionized water, ultrasonically dispersed for 10 min, and filtered.

[0032] (2) placing the treated boron nitride nanotubes in a box furnace, heating the temperature to 800°C at a heating rate of 5°C / min in an air atmosphere, and keeping the temperature for 3 hours to oxidize the impurities at high temperature to obtain a product containing oxide impurities;

[0033] (3) The obtained product containing impure oxides was washed in 30 mL of deionized water and soaked for 10 min to remove the water-soluble oxide impurities;

[0034] (4) measuring 10 mL of a 16 mol / L nitric acid solution and 30 mL of a 12 mol / L hydrochloric acid solution, slowly adding the nitric acid solution to the hydrochloric acid solution and stirring uniformly to obtain an aqueous regia solution; placing the product obtained in step (3) in the prepared aqueous regia solution, setting the temperature to 40° C. in an electric furnace, and acid washing for 24 hours to remove metal oxide impurities;

[0035] (5) The product after treatment in step (4) is washed with water (5 mL of deionized water, wherein the deionized water temperature is 40°C, and the time is 1 hour), the centrifugal speed is set to 8000 r / min, the centrifugal time is 5 minutes, after centrifugation, the supernatant is removed, the precipitated solute is taken out, and then repeatedly washed with water and centrifuged 3 to 5 times; then washed twice with 5 mL of ethanol, the centrifugal speed is set to 8000 r / min, the centrifugal time is 5 minutes, and the precipitated solute is taken out; covered with plastic wrap, placed in a 90°C oven and dried at high temperature for 12 hours, and the purified boron nitride nanotubes are obtained.

[0036] The purified boron nitride nanotubes of Example 1 were analyzed and compared with the unpurified boron nitride nanotubes to obtain the XRD pattern shown in FIG. Figure 1 As shown, it can be seen that the characteristic peaks of boron nitride exist at 2θ = 26.6°, 41.6°, 55.1°, and 75.8°, respectively. The crystal quality is good, and no obvious impurity peaks appear.

[0037] Infrared images such as Figure 2 As shown, it can be seen that no obvious impurities appear after purification;

[0038] Raman spectrum Figure 3 As shown, it is the characteristic peak of boron nitride, without obvious impurity peak;

[0039] SEM pictures Figure 4 As shown, it can be seen that the purified boron nitride nanotubes are pure boron nitride nanotubes without obvious impurities;

[0040] TEM images Figure 5As shown, it can be seen that the purified boron nitride nanotubes are hollow multi-walled boron nitride nanotubes, and no impurity diffraction fringes appear;

[0041] XPS pictures Figure 6 As shown, it can be seen that there is almost no Fe and Mg metal elements in the purified boron nitride nanotubes; in the B1s diagram, there is an obvious BN bond peak near 190-191eV, and the B atom content is calculated to be 46.55% according to the sensitivity factor method; in the N1s diagram, there is an obvious BN bond peak near 398.04eV, and the B atom content is calculated to be 46.49% according to the sensitivity factor method; the element content is shown in Table 1:

[0042] Table 1

[0043]

[0044] After calculation, the purity of pure BNNT is 93.1%.

[0045] Example 2: Compared with Example 1, the only difference is that the deionized water in step (1) is adjusted to anhydrous ethanol. The other steps are the same as Example 1 to obtain purified boron nitride nanotubes.

[0046] The boron nitride nanotubes purified in Example 2 were analyzed and the SEM images were obtained as shown in FIG. Figure 7 As shown, it can be seen that the purified boron nitride nanotubes are pure boron nitride nanotubes without obvious impurities.

[0047] Example 3: Compared with Example 1, the only difference is that the pickling time in step (4) is adjusted to 60 hours. The other steps are the same as Example 1 to obtain purified boron nitride nanotubes.

[0048] Example 4: Compared with Example 1, the only difference is that the pickling time in step (4) is adjusted to 48 hours. The other steps are the same as Example 1 to obtain purified boron nitride nanotubes.

[0049] Comparative Example 1: Compared with Example 1, the only difference is that the pickling time in step (4) is adjusted to 150 h, and the other steps are the same as Example 1.

[0050] The sample prepared in Comparative Example 1 was analyzed and the SEM images were obtained as shown in FIG. Figure 8 As shown, it can be seen that the acid reagent etches the boron nitride nanotubes, and the morphology of the purified boron nitride nanotubes is destroyed, and the hollow tube shape is transformed into an etched shape with uneven morphology.

[0051] Comparative Example 2, compared with Example 1, the only difference is that the pickling temperature in step (4) is changed to 23 ° C. The other steps are the same as Example 1;

[0052] The obtained material still contains unreacted metal oxide impurities, and purified boron nitride nanotubes cannot be obtained.

[0053] Comparative Example 3, compared with Example 1, the only difference is that the holding time in the box furnace in step (2) is adjusted to 1 h, and the other steps are the same as Example 1;

[0054] The obtained material still contains a small amount of unreacted amorphous boron powder, and the above-mentioned purified boron nitride nanotubes cannot be obtained.

[0055] Comparative Example 4, compared with Example 1, the only difference is that the temperature in the box furnace in step (2) is raised to 1000° C., and the other steps are the same as Example 1;

[0056] A layer of glassy product, boron oxide, forms on the surface of the obtained sample, and purified boron nitride nanotubes cannot be obtained.

[0057] Comparative Example 5: Compared with Example 1, the only difference is that the temperature in the box furnace in step (2) is raised to 400°C;

[0058] The obtained sample still contains some boron powder that has not been removed by oxidation, and it is impossible to obtain purified boron nitride nanotubes.

[0059] Comparative Example 6, compared with Example 1, the only difference is that the aqueous regia solution is replaced by a mixed acid of a hydrochloric acid solution and a sulfuric acid solution with concentrations of 12 mol / L and 18.4 mol / L, respectively, and the volume ratio of the hydrochloric acid solution to the sulfuric acid solution is 3:1. The other steps are the same as in Example 1;

[0060] The obtained sample still contains some metal oxides that have not reacted completely with the acid, and contains some insoluble sulfuric acid impurities, and it is impossible to obtain purified boron nitride nanotubes.

[0061] Comparative Example 7, compared with Example 1, the only difference is that the aqueous regia solution is replaced by a hydrochloric acid solution with a concentration of 12 mol / L, and the other steps are the same as those in Example 1;

[0062] The obtained sample still contains some metal oxides that have not reacted completely with the acid, and it is impossible to obtain purified boron nitride nanotubes.

[0063] Comparative Example 8, compared with Example 1, the only difference is that the aqueous regia solution is replaced by a nitric acid solution with a concentration of 16 mol / L, and the other steps are the same as those in Example 1;

[0064] After adding nitric acid dropwise, a large amount of reddish-brown toxic gas is generated, which is nitrogen dioxide. The reaction is violent and highly dangerous. In addition, the reaction product still contains a certain amount of metal oxides, and it is impossible to obtain purified boron nitride nanotubes.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for purifying boron nitride nanotubes, characterized in that: The following steps are involved: The boron nitride nanotubes are placed in a dispersant, subjected to ultrasonic dispersion treatment, and then filtered; The dispersed and filtered boron nitride nanotubes are heated in an air atmosphere to oxidize the impurities at high temperature to obtain a product containing oxide impurities, and then cooled; The product containing oxide impurities is washed with water, and the product obtained after washing is then placed in aqua regia solution for acid washing; The product obtained after acid washing is repeatedly washed with water and centrifuged several times, then washed with ethanol and centrifuged, and the precipitated solute is removed and dried to obtain purified boron nitride nanotubes.

2. The method for purifying boron nitride nanotubes according to claim 1, characterized in that: In the step of placing the boron nitride nanotubes in a dispersant, the dispersant is ethanol or deionized water.

3. The method for purifying boron nitride nanotubes according to claim 1, characterized in that: The ultrasonic dispersion treatment step lasts for 5-30 minutes.

4. The method for purifying boron nitride nanotubes according to claim 1, wherein: The dispersed and filtered boron nitride nanotubes are heated in an air atmosphere to oxidize high-temperature impurities to obtain a product containing oxide impurities. In the cooling step, the heating rate is 3-5°C / min, the cooling rate is 3-5°C / min, the temperature for oxidizing the high-temperature impurities is 600-800°C, and the oxidation time is 0.5-6 hours.

5. The method for purifying boron nitride nanotubes according to claim 1, characterized in that: The water washing time is 1-5 hours, and the water washing temperature is 40-100°C.

6. The method for purifying boron nitride nanotubes according to claim 1, characterized in that: The aqua regia is obtained by mixing hydrochloric acid and nitric acid in a volume ratio of 3:1, the concentration of hydrochloric acid is 12 mol / L, and the concentration of nitric acid is 8-16 mol / L.

7. The method for purifying boron nitride nanotubes according to claim 1, characterized in that: The pickling temperature is 40-65° C. and the pickling time is 1-85 hours.

8. The method for purifying boron nitride nanotubes according to claim 1, characterized in that: In the step of repeatedly washing the product obtained after acid washing with water and centrifuging it several times, and then washing it with ethanol and centrifuging it, the centrifugal speed is 5000-8000 r / min, and the single centrifugation time is 5-10 minutes.

9. The method for purifying boron nitride nanotubes according to claim 1, characterized in that: In the step of removing the precipitated solute and drying it, the drying temperature is 80-90° C. and the drying time is 12-24 hours.

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