阅读说明：本技术 一种高产率、大尺寸氮化硼纳米片的制备方法 (Preparation method of high-yield large-size boron nitride nanosheet ) 是由 袁凤 秦余杨 陈功宇 左晓兵 曹振兴 包健 郑玉斌 于 2019-11-08 设计创作，主要内容包括：本发明公开了一种高产率、大尺寸氮化硼纳米片的制备方法。该方法基于增加层状材料的层间距可显著降低其层间作用力的原理,利用羟基基团与氢气间剧烈的反应热,实现六方氮化硼的低温热膨胀,随后借助水结冰时的体积膨胀即可将膨胀氮化硼有效剥离成氮化硼纳米片。所得氮化硼纳米片的平均横向尺寸可达1.62～1.78μm,产率可达39.3～43.7%,有效解决了现有方法制备的氮化硼纳米片产率低、尺寸小的难题。本发明所制得的氮化硼纳米片可广泛应用于电子封装材料、半导体器件、高温导热复合材料及高温、氧化环境中工作的器件等方面。(The invention discloses a preparation method of a high-yield and large-size boron nitride nanosheet. The method is based on the principle that the interlayer spacing of the layered material is increased to obviously reduce the interlayer acting force of the layered material, utilizes the violent reaction heat between hydroxyl groups and hydrogen to realize the low-temperature thermal expansion of hexagonal boron nitride, and then can effectively strip the expanded boron nitride into the boron nitride nanosheets by virtue of the volume expansion during the icing of water. The average transverse size of the obtained boron nitride nanosheet can reach 1.62-1.78 microns, the yield can reach 39.3-43.7%, and the problems of low yield and small size of the boron nitride nanosheet prepared by the conventional method are effectively solved. The boron nitride nanosheet prepared by the method can be widely applied to the aspects of electronic packaging materials, semiconductor devices, high-temperature heat-conducting composite materials, devices working in high-temperature and oxidation environments and the like.)

1. A preparation method of high-yield large-size boron nitride nanosheets is characterized by comprising the following steps:

(1) carrying out heat treatment on hydroxyl functionalized boron nitride in a hydrogen atmosphere to obtain expanded boron nitride;

(2) dispersing expanded boron nitride in water, and performing ultrasonic dispersion for 30-60 min to obtain an expanded boron nitride dispersion liquid;

(3) preserving the temperature of the dispersion liquid for 10-30 h in an environment with the temperature of 2-10 ℃, then reducing the temperature to-10 to-30 ℃, and continuing preserving the temperature for 10-30 h;

(4) repeating the step (3) for more than 1 time;

(5) and (3) centrifuging the dispersion liquid obtained in the step (4) for 10-45 min at a centrifugal speed of 3000-5000 rpm, collecting supernatant after centrifugation, and placing the supernatant at 60-120 ℃ for vacuum drying for 6-12 h to obtain the boron nitride nanosheet.

2. The method of claim 1, wherein the hexagonal boron nitride powder is dispersed in a sodium hydroxide solution with a concentration of 40-50 wt% for oxidation treatment for 45-70 h, the reaction temperature is 60-90 ℃, and the reaction product is subjected to suction filtration, washing and vacuum drying to obtain the hydroxyl-functionalized boron nitride.

3. The method of claim 2, wherein the ratio of hexagonal boron nitride powder to sodium hydroxide solution is 1-5 mg: 1 ml.

4. The method of claim 2, wherein the drying is performed at 60 to 120 ℃ for 6 to 12 hours under vacuum.

5. The method of claim 1, wherein the hydroxyl functionalized boron nitride is heat treated in a tube furnace with continuous hydrogen gas introduction to obtain expanded boron nitride.

6. The method according to claim 1 or 5, wherein the heat treatment temperature is 200 to 300 ℃ and the holding time is 10 to 30 s.

7. The method of claim 1, wherein the volume of solvent water in the expanded boron nitride dispersion is 20 to 50 times the volume of expanded boron nitride.

8. The method of claim 1, wherein step (3) is repeated 3 to 5 times.

9. The method of claim 1, wherein the supernatant is collected and dried under vacuum at 60-120 ℃ for 6-12 hours.

10. The method of claim 1, wherein the average lateral dimension of the prepared boron nitride nanosheets is 1.62-1.78 μm, and the yield is 39.3-43.7%.

Technical Field

The invention belongs to the field of two-dimensional nano materials, and relates to a preparation method of a high-yield and large-size boron nitride nanosheet.

Background

Graphene is a novel two-dimensional nanomaterial, and due to excellent thermal, mechanical and electrical properties, the research hot tide of graphene is rapidly raised worldwide since the graphene is successfully prepared. While researches on graphene and its family derivatives are being carried out, boron nitride nanosheets, which are two-dimensional layered materials with a graphene-like lamellar structure, are also attracting the interests of scientific researchers. Boron nitride nanosheets are isoelectronic bodies of graphene, each layer is of a hexagonal structure formed by alternating arrangement of N and B atoms, and are often referred to as "white graphene" or "boron nitride" because they are white. Compared with graphene, boron nitride nanosheets have many unique properties, such as wide energy band gaps, excellent electrical insulating properties, high thermal conductivity, extremely high oxidation resistance, thermal stability, and the like. The excellent performances enable the boron nitride nanosheets to be more practical than graphene in the aspects of electronic packaging materials, semiconductor devices, high-temperature heat-conducting composite materials, devices working in high-temperature and oxidation environments and the like.

In order to support the application exploration of the boron nitride nanosheet, in recent years, researchers continuously explore a simple, energy-saving and effective method for preparing the boron nitride nanosheet. At present, the reported preparation techniques can be mainly divided into two categories: one is a "bottom-up" route and the other is a "top-down" route. The method from bottom to top is to synthesize the boron nitride nanosheet by growth and self-assembly from small molecules or precursors, and mainly comprises a chemical vapor deposition method, a solid-phase reaction method and the like. Although large-size and high-yield boron nitride nanosheets can be prepared by such methods, problems of complex processes, harsh reaction conditions, low-purity products, and the like severely limit the large-scale application of such methods. The top-down method which is simple in operation is the most commonly adopted technology, and mainly comprises a mechanical stripping method, a chemical stripping method, an ultrasonic stripping method and the like. The main basis of all stripping methods is to create a large enough external force to destroy the interlayer force of the hexagonal boron nitride, so as to strip the boron nitride nanosheet from the three-dimensional structure thereof. However, boron nitride has not only van der waals forces but also partial ionic bonding characteristics between sheets, which results in much stronger interlayer forces of boron nitride than that of graphite. Therefore, boron nitride nanosheets are difficult to obtain by conventional exfoliation methods like graphene. In addition, due to strong acting force between the layers, in the stripping process, large-piece boron nitride often breaks at the defect part to form small fragments which are easy to strip, and then stripping occurs, so that the size of the obtained boron nitride nanosheet can be obviously reduced. In summary, the difficulty in peeling and the small size are one of the main problems faced by the widespread use of boron nitride nanosheets.

Disclosure of Invention

In order to solve the problems of low yield and small size of the boron nitride nanosheet prepared by the existing method, the invention aims to provide a preparation method of the boron nitride nanosheet with high yield and large size.

The technical scheme for realizing the invention is as follows:

a method for preparing high-yield large-size boron nitride nanosheets is based on the principle that interlayer spacing of a layered material is increased to remarkably reduce interlayer acting force of the layered material, low-temperature thermal expansion of hexagonal boron nitride is achieved by means of intense reaction heat between hydroxyl groups and hydrogen, and then the expanded boron nitride can be effectively stripped into the boron nitride nanosheets by means of volume expansion during water freezing.

The preparation method of the high-yield large-size boron nitride nanosheet comprises the following steps:

(1) dispersing hexagonal boron nitride powder in a sodium hydroxide aqueous solution with the concentration of 40-50 wt% for oxidation treatment for 45-70 h, wherein the reaction temperature is 60-90 ℃, and performing suction filtration, washing and vacuum drying on a reaction product to obtain hydroxyl functionalized boron nitride;

(2) carrying out heat treatment on the hydroxyl functionalized boron nitride obtained in the step (1) in a hydrogen atmosphere to obtain expanded boron nitride;

(3) dispersing the expanded boron nitride obtained in the step (2) in distilled water, and performing ultrasonic dispersion for 30-60 min to obtain an expanded boron nitride dispersion liquid;

(4) preserving the temperature of the dispersion liquid obtained in the step (3) for 10-30 h in an environment with the temperature of 2-10 ℃, then reducing the temperature to-10 to-30 ℃, and continuing preserving the temperature for 10-30 h;

(5) repeating the step (4) for more than 1 time;

(6) and (3) centrifuging the dispersion liquid obtained in the step (5) for 10-45 min at a centrifugal speed of 3000-5000 rpm, collecting supernatant after centrifugation, and placing the supernatant at 60-120 ℃ for vacuum drying for 6-12 h to obtain the boron nitride nanosheet.

Preferably, in the step (1), the dosage ratio of the hexagonal boron nitride powder to the sodium hydroxide aqueous solution is 1-5 mg: 1 ml.

Preferably, in the step (1), vacuum drying is carried out at 60-120 ℃ for 6-12 h.

Preferably, in the step (2), the hydroxyl functionalized boron nitride is placed in a tubular furnace into which hydrogen is continuously introduced for heat treatment to obtain the expanded boron nitride, the heat treatment temperature is 200-300 ℃, and the heat preservation time is 10-30 s.

Preferably, in step (3), the volume of the distilled water is 20 to 50 times the volume of the expanded boron nitride.

Preferably, in the step (5), the step (4) is repeated for 3 to 5 times.

Preferably, in the step (6), the supernatant is collected and placed at 60-120 ℃ for vacuum drying for 6-12 hours.

The average transverse size of the boron nitride nanosheet prepared by the method can reach 1.62-1.78 microns, and the yield can reach 39.3-43.7%.

Compared with the prior art, the invention has the advantages that:

(1) the preparation method has the advantages of simple preparation process, mild conditions, no environmental pollution, high production efficiency, low cost and good controllability.

(2) The average transverse size of the prepared boron nitride nanosheet can reach 1.62-1.78 microns, the yield can reach 39.3-43.7%, the yield is far higher than that obtained by a stripping method reported in the current literature, and the problems of low yield and small size of the current boron nitride nanosheet are solved.

(3) The crystal structure of the boron nitride nanosheet is not damaged in the preparation process, and any impurity is not introduced.

Drawings

Fig. 1 is a schematic diagram of a preparation process of boron nitride nanosheets.

Fig. 2 is a transmission electron microscope image of the boron nitride nanosheets produced in example 1.

Detailed Description

For a better understanding of the technical content of the invention, reference should be made to the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.

It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.

With reference to fig. 1, boron nitride nanoplates according to the present invention are prepared by the steps given in the following examples.