A boron nitride nanosheet and a preparation method thereof

Abstract

The application provides a boron nitride nanosheet and a preparation method thereof. A eutectic solvent prepared from lidocaine and thymol is used to replace a traditional organic solvent to strip h-BN (hexagonal boron nitride), and ball milling and liquid-phase ultrasonic are combined to efficiently prepare BNNS (boron nitride nanosheet). Meanwhile, the non-covalent functionalization of BNNS is realized by using the pi-pi interaction. The method is green, environmentally friendly, simple to operate and low in cost, and can meet the demand of efficiently preparing functionalized BNNS.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material preparation technology, specifically relating to a boron nitride nanosheet and its preparation method, and in particular to a method for preparing functionalized BNNS using a eutectic solvent. Background Technology

[0002] Boron nitride nanosheets (BNNS) possess numerous excellent properties, including good mechanical properties, corrosion resistance, high temperature resistance, and insulation. In particular, their thermal conductivity is significantly higher than that of pure boron nitride, with few-layer BNNS exhibiting thermal conductivity as high as 400-2000 W / (m·K). Therefore, BNNS can serve as an ideal thermal conductive material for high-tech fields such as 5G communications, aerospace, and microelectronics. BNNS is commonly prepared using a liquid-phase ultrasonic method. While traditional organic solvents such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP) have good exfoliation effects on h-BN, they suffer from high volatility, toxicity, and environmental pollution. Therefore, using green solvents to replace these traditional organic solvents to achieve green, low-cost, and efficient preparation of BNNS has significant application value.

[0003] Eutectic solvents (DES) are a novel type of green solvent composed of hydrogen bond acceptors and hydrogen bond donors. Compared with traditional organic solvents, DES has the advantages of simple preparation, wide availability, low cost, low toxicity, tunable composition and properties, good solubility, and low volatility. However, there are few reports on the use of eutectic solvents to exfoliate two-dimensional layered materials. Yang et al. (Yang B, Zhang SH, Lv J, et al. Large-scale and green production of multi-layer graphene in deep eutectic solvents[J]. Journal of Materials Science, 2021, 56(7):4615-4623.) used expanded graphite as raw material and DES prepared by choline chloride-urea as exfoliation medium to prepare graphene with a thickness of 11-12 layers and a lateral size of 2-5 μm by wet ball milling exfoliation technology. The Zahra team (Mohammadpour Z, Abdollahi SH, Safavi A. Sugar-based natural deep eutectic mixtures as green intercalating solvents for high-yield preparation of stable MoS2 nanosheets: Application to electrocatalysis of hydrogen evolution reaction[J]. ACS Applied Energy Materials, 2018, 1(11): 5896-5906.) used a 5 mL glass syringe as the exfoliation device and prepared natural eutectic solvents using natural sugar-based materials (glucose, fructose, and sucrose) and water as exfoliation aids. MoS2 was exfoliated using shear force generated by plunger rotation, resulting in nanosheets with an average thickness of approximately 4 nm and a length of approximately 150 nm, with a yield of up to 44%.Shan et al. (Shan Q, Ding QH, Wang XY, et al. Electrochemical preparation of hydroxylated boron nitride nanosheets for solid-state flexible supercapacitors using deep eutectic solvent and water mixture as electrolytes[J]. Langmuir, 2022, 38(26): 8169-8178.) prepared DES with choline chloride-urea and mixed it with water to form an electrolyte. They then used an electrochemical method to exfoliate h-BN, obtaining OH-BNNS with an average lateral dimension of 625 nm and a thickness of 6 layers. Although hexagonal boron nitride has a layered structure similar to graphite, the "lip-lip" interaction between layers and the alternating presence of BN atoms within the layers make the exfoliation and functionalization of h-BN more difficult.

[0004] Based on this, the present invention provides a method for preparing functionalized BNNS using a eutectic solvent. By using a eutectic solvent instead of traditional organic solvents to exfoliate h-BN, BNNS is efficiently prepared through a combination of ball milling and liquid-phase ultrasonication. Simultaneously, non-covalent functionalization of BNNS is achieved by utilizing the π-π interactions between lidocaine and the benzene ring on thymol. This method is environmentally friendly, simple to operate, and low-cost, meeting the demand for efficient preparation of functionalized BNNS. Summary of the Invention

[0005] The first objective of this invention is to provide a method for preparing BNNS using a green solvent, thereby solving the problems of high volatility, toxicity, and environmental pollution associated with traditional organic solvents such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP).

[0006] The second objective of this invention is to provide a method for efficiently preparing BNNS by combining ball milling and ultrasound. This method utilizes the solid state of HBA and HBD to pre-exfoliate h-BN. During the ball milling process, HBA and HBD gradually form DES that wet h-BN, weakening the interlayer forces. Combined with subsequent ultrasound treatment, BNNS is prepared efficiently.

[0007] The third objective of this invention is to provide a method for preparing functionalized BNNS, which utilizes lidocaine and the benzene ring on thymol to non-covalently functionalize the BNNS surface through π-π interactions.

[0008] To achieve the objectives of this invention, the technical solution is as follows:

[0009] On one hand, the present invention proposes a method for preparing functionalized BNNS using a eutectic solvent, comprising the following steps: mixing and ball milling hydrogen bond acceptor HBA, hydrogen bond donor HBD and hexagonal boron nitride h-BN, dispersing the resulting mixture in a eutectic solvent and sonicating it, centrifuging at low speed and taking the supernatant to obtain a stable dispersed BNNS suspension; wherein, the eutectic solvent is prepared by mixing hydrogen bond acceptor HBA and hydrogen bond donor HBD.

[0010] Optionally, in one embodiment, the hydrogen bond acceptor HBA is N-diethylaminoacetyl-2,6-dimethylaniline (lidocaine), and the hydrogen bond donor HBA is 5-methyl-2-isopropylphenol (thymol).

[0011] Optionally, in one embodiment, the molar ratio of HBA to HBA in the eutectic solvent is 2:8-6:4, such as 3:7, 4:6, 5:5, etc.

[0012] Optionally, in one embodiment, the temperature is 60-80°C during the mixing process of the eutectic solvent.

[0013] Furthermore, the temperature during the mixing and preparation of DES is set to 60°C.

[0014] Optionally, in one embodiment, during the ball milling process, the molar ratio of HBA to HBD is 2:8-6:4, which is the same as the molar ratio of HBA to HBD in the eutectic solvent, such as 3:7, 4:6, 5:5, etc.

[0015] Optionally, in one implementation, the total mass ratio of HBA and HBD to h-BN is 35:1-30:1.

[0016] Furthermore, during the ball milling process, the total mass ratio of HBA and HBD to h-BN is 100:3.

[0017] Optionally, in one embodiment, during the ball milling process, the grinding balls used are 8mm zirconia balls, in quantity 5-10, the ball milling speed is 1500-2500rpm, and the ball milling time is 7-15min.

[0018] Optionally, in one embodiment, during the ultrasonication process, the ball-milled mixture is dispersed in a eutectic solvent, wherein the h-BN concentration is 4-8 mg / g.

[0019] Furthermore, during the ultrasound process, additional DES is added to bring the h-BN concentration to 4 mg / g.

[0020] Optionally, in one embodiment, during the ultrasound process, the ultrasound power is set to 100-400W, the processing time is 4-10 hours, the working time is 5 seconds, and the pause is 1 second.

[0021] Optionally, in one embodiment, during low-speed centrifugation, the centrifugation speed is set to 2000-6000 rpm and the centrifugation time is 8-15 min.

[0022] Optionally, in one embodiment, the yield of the functionalized BNNS prepared by the method of the present invention is greater than 45%, and further, the yield is 45% to 65%.

[0023] On the other hand, the present invention proposes a functionalized BNNS, which is prepared according to any of the methods described above.

[0024] Optionally, in one embodiment, the thickness of the BNNS prepared by the present invention is about 4 nm, specifically 3 to 5 nm.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] First, this invention uses a novel green solvent—deuterated eutectic solvent (DES)—as a stripping agent, which has advantages such as low vapor pressure, low toxicity, low cost and availability, and customizable composition. This effectively solves the problems of high volatility, toxicity, and environmental pollution associated with traditional organic solvents such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP).

[0027] Secondly, both lidocaine and thymol used in this invention are solids at room temperature, and they can form DES during high-speed stirring. Ball milling them with h-BN can not only pre-exfoliate h-BN, but also wet h-BN with the formed DES to weaken the interlayer forces, thus efficiently preparing few-layer BNNS in the subsequent ultrasonic process.

[0028] Finally, during the preparation of BNNS, lidocaine and the benzene ring of thymol can be used to perform non-covalent functionalization on the surface of BNNS through π-π interactions.

[0029] In summary, the technical method of this invention has the characteristics of low cost, simple process and green environmental protection, which enables it to meet the needs of efficient preparation of functionalized BNNS, and the yield of the obtained BNNS is greater than 45%, with a maximum of 63.3%. Attached Figure Description

[0030] Figure 1 SEM images of h-BN and the prepared BNNS used in Example 1.

[0031] Figure 2This is a TEM image of the BNNS prepared in Example 1.

[0032] Figure 3 The image shows the AFM image and thickness diagram of the BNNS prepared in Example 1.

[0033] Figure 4 The XPS spectra of h-BN and the prepared BNNS used in Example 1 are shown in (a) as the full XPS spectrum and (b) as the B1s spectrum.

[0034] Figure 5 The yield of BNNS prepared in Examples 1-5 is given. Detailed Implementation

[0035] This invention proposes a method for preparing functionalized BNNS using a eutectic solvent, specifically including the following steps:

[0036] S1. Prepare a eutectic solvent (DES) by stirring and mixing a suitable hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) for later use.

[0037] S2. Directly mix and ball-mill HBA, HBD and h-BN;

[0038] S3. The obtained ball-milled mixture is dispersed in the DES prepared in step S1 and subjected to ultrasonic treatment. After low-speed centrifugation, the supernatant is taken to obtain a stable BNNS suspension.

[0039] Furthermore, the hydrogen bond acceptor is lidocaine, and the hydrogen bond donor is thymol.

[0040] Furthermore, the molar ratio of HBA to HBD is 2:8-6:4, such as 3:7, 4:6, 5:5, etc.

[0041] Furthermore, the temperature during the mixing and preparation of DES is set to 60-80℃.

[0042] Furthermore, during the ball milling process, the molar ratio of HBA to HBD is the same as that used in the preparation of DES described above.

[0043] Furthermore, during the ball milling process, the total mass ratio of HBA and HBD to h-BN is 35:1-30:1.

[0044] Furthermore, during the ball milling process, the grinding balls used are 8mm zirconia balls, numbering 5-10 balls, with a milling speed of 1500-2500 rpm and a milling time of 7-15 minutes.

[0045] Furthermore, during the ultrasound process, additional DES is added to bring the h-BN concentration to 4-8 mg / g.

[0046] Furthermore, during the ultrasound process, the ultrasound power is set to 100-400W, the processing time is 4-10 hours, the working time is 5 seconds, and the pause is 1 second.

[0047] Furthermore, during high-speed centrifugation, the centrifugation speed is set to 2000-6000 rpm and the centrifugation time is 8-15 min.

[0048] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0049] Example 1:

[0050] Lidocaine and thymol were mixed in a beaker at a molar ratio of 5:5 and heated and stirred at 60°C until a homogeneous, transparent, and stable eutectic solvent (DES) was formed.

[0051] Take 5g of lidocaine and thymol with a molar ratio of 5:5 and pour them into a ball mill jar. Add 150mg of h-BN powder, then put in 7 8mm zirconia balls for ball milling. Set the ball milling speed to 2000rpm and the ball milling time to 10min.

[0052] After ball milling, take 3g of dispersion, add 17g of prepared DES, and perform ultrasonic exfoliation. Set the ultrasonic power to 200W, the processing time to 6h, the working time to 5s, and the pause time to 1s.

[0053] After sonication, the suspension was poured into centrifuge tubes and centrifuged at 2000 rpm for 10 min in a high-speed centrifuge. The supernatant was collected to obtain the BNNS dispersion. The remaining unpeeled h-BN was washed with ethanol and deionized water to remove residual solvent and then dried for use in BNNS yield calculation.

[0054] BNNS yield is calculated using the differential weight method, as shown in the following formula:

[0055]

[0056] Where m0 is the mass of h-BN, m1 is the mass of the centrifuge tube, and m2 is the total mass of the unstripped h-BN and the centrifuge tube after centrifugation.

[0057] The mass of h-BN is (150 / 5)*3=90mg.

[0058] Examples 2-5:

[0059] Examples 2-5 differ from Example 1 in that the molar ratio of lidocaine to thymol is 2:8, 3:7, 4:6, and 6:4, while the other steps are the same. Details are as follows:

[0060] Example 2:

[0061] Lidocaine and thymol were mixed in a beaker at a molar ratio of 2:8 and heated and stirred at 60°C until a homogeneous, transparent, and stable eutectic solvent (DES) was formed.

[0062] Take 5g of lidocaine and thymol with a molar ratio of 2:8 and pour them into a ball mill jar. Add 150mg of h-BN powder, then put in 7 8mm zirconia balls for ball milling. Set the ball milling speed to 2000rpm and the ball milling time to 10min.

[0063] After ball milling, take 3g of dispersion, add 17g of prepared DES, and perform ultrasonic exfoliation. Set the ultrasonic power to 200W, the processing time to 6h, the working time to 5s, and the pause time to 1s.

[0064] After sonication, the suspension was poured into centrifuge tubes and centrifuged at 2000 rpm for 10 minutes in a high-speed centrifuge to remove unpeeled h-BN and obtain BNNS dispersion.

[0065] The BNNS yield calculation is the same as in Example 1.

[0066] Example 3:

[0067] Lidocaine and thymol were mixed in a beaker at a molar ratio of 3:7 and heated and stirred at 60°C until a homogeneous, transparent, and stable eutectic solvent (DES) was formed.

[0068] Take 5g of lidocaine and thymol with a molar ratio of 3:7 and pour them into a ball mill jar. Add 150mg of h-BN powder, then put in 7 8mm zirconia balls for ball milling. Set the ball milling speed to 2000rpm and the ball milling time to 10min.

[0069] After ball milling, take 3g of dispersion, add 17g of prepared DES, and perform ultrasonic exfoliation. Set the ultrasonic power to 200W, the processing time to 6h, the working time to 5s, and the pause time to 1s.

[0070] After sonication, the suspension was poured into centrifuge tubes and centrifuged at 2000 rpm for 10 minutes in a high-speed centrifuge to remove unpeeled h-BN and obtain BNNS dispersion.

[0071] The BNNS yield calculation is the same as in Example 1.

[0072] Example 4:

[0073] Lidocaine and thymol were mixed in a beaker at a molar ratio of 4:6 and heated and stirred at 60°C until a homogeneous, transparent, and stable eutectic solvent (DES) was formed.

[0074] Take 5g of lidocaine and thymol with a molar ratio of 4:6 and pour them into a ball mill jar. Add 150mg of h-BN powder, then put in 7 8mm zirconia balls for ball milling. Set the ball milling speed to 2000rpm and the ball milling time to 10min.

[0075] After ball milling, take 3g of dispersion, add 17g of prepared DES, and perform ultrasonic exfoliation. Set the ultrasonic power to 200W, the processing time to 6h, the working time to 5s, and the pause time to 1s.

[0076] After sonication, the suspension was poured into centrifuge tubes and centrifuged at 2000 rpm for 10 minutes in a high-speed centrifuge to remove unpeeled h-BN and obtain BNNS dispersion.

[0077] The BNNS yield calculation is the same as in Example 1.

[0078] Example 5:

[0079] Lidocaine and thymol were mixed in a beaker at a molar ratio of 6:4 and heated and stirred at 60°C until a homogeneous, transparent, and stable eutectic solvent (DES) was formed.

[0080] Take 5g of lidocaine and thymol with a molar ratio of 6:4 and pour them into a ball mill jar. Add 150mg of h-BN powder, then put in 7 8mm zirconia balls for ball milling. Set the ball milling speed to 2000rpm and the ball milling time to 10min.

[0081] After ball milling, take 3g of dispersion, add 17g of prepared DES, and perform ultrasonic exfoliation. Set the ultrasonic power to 200W, the processing time to 6h, the working time to 5s, and the pause time to 1s.

[0082] After sonication, the suspension was poured into centrifuge tubes and centrifuged at 2000 rpm for 10 minutes in a high-speed centrifuge to remove unpeeled h-BN and obtain BNNS dispersion.

[0083] The BNNS yield calculation is the same as in Example 1.

[0084] Figure 1 The images show SEM images of h-BN and the prepared BNNS used in Example 1. Figure 1 The original bulk h-BN has a lateral size between 20-30 μm and a thickness ranging from several hundred nanometers to 2 μm, exhibiting various irregular morphologies. After exfoliation, the lateral size of the obtained BNNS is reduced to 1-5 μm, and the thickness is also significantly thinner, with the edges curling up, indicating successful exfoliation.

[0085] Figure 2 This is a TEM image of the BNNS prepared in Example 1. Figure 2The BNNS in the middle is similar in color to the base lining, and the surface BNNS is thinner.

[0086] Figure 3 AFM image of BNNS prepared in Example 1 ( Figure 3 a) and BNNS thickness diagram ( Figure 3 b), Figure 3 The AFM plot shows that the thickness of BNNS is around 4nm, indicating that the present invention can prepare BNNS with a large aspect ratio in a green and efficient manner.

[0087] Figure 4 The XPS spectra of h-BN and the prepared BNNS used in Example 1 are shown. During the industrial preparation process, the original h-BN contained some C and O elements due to incomplete edge structures. Fitting the B1s peak, both h-BN and BNNS showed a characteristic peak of a BN bond at 190.5 eV and a characteristic peak of BO at 191.5 eV. The ratio of the characteristic peak areas of BO to BN did not change significantly before and after exfoliation, indicating that the solvent and BNNS did not form covalent bonds. However, Table 1 shows that the C content in BNNS increased significantly after exfoliation, suggesting that the BNNS surface may have undergone non-covalent interactions with the solvent system. Given that the solvent contains a benzene ring structure, this is presumably a π-π interaction.

[0088] Table 1. XPS elemental content analysis of h-BN and BNNS

[0089]

[0090]

[0091] Figure 5 The figures show the yields of BNNS prepared by exfoliation in Examples 1-5. It can be seen from the figures that the yields obtained in Examples 1-4 are all relatively high. It can also be seen that the ratio of lidocaine to thymol has a significant impact on the yield of BNNS prepared by exfoliation. When the ratio of lidocaine to thymol is 5:5, the prepared DES has the highest yield of h-BN, which is 63.3%.

[0092] In summary, this invention provides a green and efficient method for preparing functionalized BNNS. Compared with traditional technologies, it not only uses a green and environmentally friendly eutectic solvent as the exfoliation agent, but also achieves non-covalent functionalization during the exfoliation process, which is simple and efficient.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing functionalized BNNS using a eutectic solvent, characterized in that, The process includes the following steps: mixing and ball-milling hydrogen bond acceptor HBA, hydrogen bond donor HBD, and hexagonal boron nitride h-BN; dispersing the resulting ball-milled mixture in a eutectic solvent and sonicating it; centrifuging at low speed and taking the supernatant to obtain a stable dispersed BNNS suspension; wherein, the eutectic solvent is prepared by mixing hydrogen bond acceptor HBA and hydrogen bond donor HBD. The hydrogen bond acceptor HBA is N-diethylaminoacetyl-2,6-dimethylaniline, and the hydrogen bond donor HBD is 5-methyl-2-isopropylphenol.

2. The method according to claim 1, characterized in that, In the eutectic solvent, the molar ratio of HBA to HBD is 2:8-6:

4.

3. The method according to claim 1, characterized in that, During the mixing process of the eutectic solvent, the temperature is 60-80℃.

4. The method according to claim 1, characterized in that, During the ball milling process, the molar ratio of HBA to HBD is 2:8-6:4, and the total mass ratio of HBA and HBD to the mass ratio of h-BN is 35:1-30:

1.

5. The method according to claim 1, characterized in that, During the ball milling process, 5-10 8 mm zirconia balls are used, the milling speed is 1500-2500 rpm, and the milling time is 7-15 min.

6. The method according to claim 1, characterized in that, During the ultrasonic process, the ball-milled mixture is dispersed in a eutectic solvent, wherein the h-BN concentration is 4-8 mg / g.

7. The method according to claim 1, characterized in that, During the ultrasound process, the ultrasound power is set to 100-400 W, the processing time is 4-10 h, the operation time is 5 s, and the pause time is 1 s.

8. The method according to claim 1, characterized in that, During low-speed centrifugation, set the centrifugation speed to 2000-6000 rpm and the centrifugation time to 8-15 min.

9. A functionalized BNNS, prepared according to the method of any one of claims 1-8.

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