Method for directly synthesizing boron nitride by nitrogen
By employing sodium borohydride and halide salts under nitrogen atmosphere, the synthesis of hexagonal boron nitride is achieved at lower temperatures, producing high-purity h-BN suitable for industrial applications with enhanced catalytic activity.
Patent Information
- Application Number
- CN202410043894.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-12
- Publication Date
- 2025-07-15
AI Technical Summary
The existing hexagonal boron nitride synthesis technology has problems such as high energy consumption, complex processing, low purity, and expensive raw materials, making it difficult to achieve a green and efficient synthesis route.
Hexagonal borohydride and halide additives are heat treated under a nitrogen atmosphere, followed by washing with water regia to prepare hexagonal boron nitride to avoid the introduction of carbon/oxygen elements and achieve low temperature synthesis.
The preparation process is simple, the hexagonal boron nitride has high purity, and it has better catalytic activity in oxygen-propane oxidation and dehydrogenation reaction.
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Figure CN120308923A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of synthesis and preparation of hexagonal boron nitride, and particularly relates to a method for directly synthesizing boron nitride from nitrogen gas. Background Art
[0002] Hexagonal boron nitride (h-BN), known as "white graphene", has a structure similar to that of graphene while having different properties. Due to its excellent properties such as an atomically ultra-flat surface, free hanging bonds, and charged impurities, it has long attracted people's attention. In h-BN, alternating B and N atoms are bonded by sp2 in the plane to form a hexagonal crystal lattice, and such layers are stacked to form bulk h-BN. The sp2 bond of B-N is a strong in-plane σ bond, resulting in high in-plane thermal conductivity, chemical stability, and strength within the layer; the empty π orbitals make h-BN have good electrical conductivity. Due to its excellent electrical, mechanical, optical, thermal, and physicochemical properties, h-BN has broad application prospects in the fields of catalysis, optoelectronics, sensors, electronics, and biomedical research. In recent years, the demand for hexagonal boron nitride has been increasing day by day, but there are still problems in the synthesis technology of h-BN such as high energy consumption, complex processing, low purity, and expensive raw materials, which prompts the search for a green, efficient, and simple synthesis route for hexagonal boron nitride synthesis technology.
[0003] h-BN was first synthesized by Balmain in 1842 [Balmain W H. Bemerkungen über die Bildung von Verbindungen des Bors und Siliciums mit Stickstoff und gewissen Metallen [J]. Journal für Praktische Chemie, 1842, 27(1): 422-430.], and its structural arrangement was first proposed by Pease in 1952. The lattice parameters he reported were 2.504 Å (a) and 6.661 Å (c). With the development of science and technology, there are more and more synthesis routes for h-BN. At present, the methods for synthesizing hexagonal boron nitride mainly include solid-phase synthesis method, chemical vapor deposition method, high-temperature and high-pressure synthesis method, microwave molten salt method, etc. Among them, the single crystal synthesized and grown by the high-pressure and high-temperature (HPHT) method is the most commonly used device in physical research. In this method, C and O are easily incorporated into the single crystal, and at the same time, the high temperature and high pressure also bring higher energy consumption, which promotes the increase in the cost of synthesizing hexagonal boron nitride. The chemical vapor deposition method (CVD: The chemical vapor deposition method) in chemical vapor deposition generally uses gaseous raw materials to deposit h-BN on the surface of a certain catalytic substrate in a high-temperature reaction furnace. Commonly used substrates are Al2O3 and other inert substrates, such as: Cu, Ni, Pt, Fe and their alloys. The gaseous raw materials used in the CVD reaction process are usually organic or inorganic gases containing B and N. For example: Using boron trichloride (BCl3) and ammonia (NH3) as the boron source and nitrogen source, and nitrogen as the carrier gas, hexagonal boron nitride films are grown on a silicon substrate at a deposition temperature range of 900-1300 °C and a total pressure of 100 Pa by low-pressure chemical vapor deposition. The physical vapor deposition method (PVD: The physical vapor deposition methods) can regulate the formation of few-layer h-BN thin films. High-quality few-layer h-BN thin films can be controllably synthesized with B by reactive magnetron sputtering in an N2 / Ar atmosphere. Only benign and non-toxic reagents are used in this process. The controllability of the chemical vapor deposition method is poor and it is not suitable for industrial production. The solid-state reaction method (SSR: solid-state synthesis) refers to uniformly mixing boron-containing compounds and nitrogen-containing compounds (the nitrogen source generally selects a precursor that can produce NH3), carrying out solid-state reactions under continuous high-temperature conditions, and obtaining boron nitride powders with high crystallinity and uniform particle size after subsequent impurity removal treatment of the calcined products. It usually prepares h-BN under an N2 atmosphere.
[0004] Other synthesis methods such as microwave molten salt method, solvothermal synthesis method, self-propagating technology, carbothermal synthesis technology, ion beam sputtering technology, laser-induced reduction method, etc. are all relatively complex chemical engineering processes, and most of them require precise control to ensure the purity and specific properties of the target product for application, with high energy consumption (high temperature and high pressure) and expensive raw materials (such as boron elemental powder). Summary of the Invention
[0005] In order to solve the problems existing in the prior art, the present invention aims to provide a method for directly synthesizing boron nitride from nitrogen. Using sodium borohydride and nitrogen as raw materials and adding a halide auxiliary agent, it realizes the direct synthesis of h-BN using nitrogen as the nitrogen source at a lower temperature, and is used in the oxygen-propane oxidative dehydrogenation reaction, having better catalytic activity than commercial boron nitride.
[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:
[0007] A method for directly synthesizing hexagonal boron nitride from nitrogen. Under a nitrogen atmosphere, a mixture of sodium borohydride and halide salt is used as the reaction raw material. After heat treatment and then washing with aqua regia, hexagonal boron nitride is obtained.
[0008] The halide salt is selected from one or more of LiCl, LiBr, LiI, NaCl, NaBr, Nal, KCl, KBr, KI, MnCl2, FeCl3, ZnCl2, and NiCl2.
[0009] Further, the mass ratio of sodium borohydride to halide salt is 1:1 to 2; preferably 1:1.5.
[0010] Further, the halide salt is selected from one or more of LiCl, LiBr, LiI, NaBr, Nal, MnCl2, and FeCl3; preferably one or more of LiCl, LiBr, LiI, and MnCl2.
[0011] Further, the temperature of the heat treatment is 600 - 800 °C; preferably 700 °C.
[0012] Further, the aqua regia washing process is: soaking the sample obtained after heat treatment in aqua regia at 60 - 100 °C for 8 - 12 h.
[0013] The beneficial effects of the present invention are reflected in:
[0014] The present invention selects sodium borohydride and nitrogen as raw materials, adds a halide auxiliary agent, and realizes the synthesis of h-BN directly using nitrogen as the nitrogen source at a relatively low temperature. This method is based on using inorganic materials as raw materials, avoiding the introduction of carbon / oxygen elements, and realizing the preparation of hexagonal boron nitride from inorganic salts. Its preparation process is simple, the purity of hexagonal boron nitride is high, and when it is used in the oxidative dehydrogenation reaction of oxygen-propane, it has better catalytic activity than commercial boron nitride. Description of the Drawings
[0015] Figure 1 TEM images of h-BN in Examples 1-5;
[0016] Figure 2 XRD patterns of h-BN in Examples 1-5;
[0017] Figure 3 FITR spectra of h-BN in Examples 1-5;
[0018] Figure 4 XRD patterns of h-BN in Examples 6 and 7;
[0019] Figure 5 XRD patterns of h-BN in Examples 8 and 9;
[0020] Figure 6 Activity test diagram of the oxidative dehydrogenation reaction of oxygen-propane of h-BN in Example 1;
[0021] Figure 7 Activity test diagram of the oxidative dehydrogenation reaction of oxygen-propane of h-BN in Example 2;
[0022] Figure 8 Activity test diagram of the oxidative dehydrogenation reaction of oxygen-propane of h-BN in Example 3;
[0023] Figure 9 Activity test diagram of the oxidative dehydrogenation reaction of oxygen-propane of h-BN in Example 4;
[0024] Figure 10 Activity test diagram of the oxidative dehydrogenation reaction of oxygen-propane of h-BN in Example 5;
[0025] Figure 11 XRD pattern of Comparative Example 2;
[0026] Figure 12 XRD pattern of Comparative Example 4;
[0027] Figure 13 Activity test diagram of the oxidative dehydrogenation reaction of oxygen-propane of commercial h-BN in Comparative Example 5. Detailed Description of the Invention
[0028] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the exemplified embodiments are not intended to limit the present invention.
[0029] Example 1
[0030] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of lithium bromide powder (LiBr) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid treatment is carried out on the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-LiBr. Its yield is 47.04%.
[0031] Perform TEM, XRD, and FITR analyses on BN-LiBr, and the results are as Figures 1-3 shown. The lattice spacing measured in the TEM image is 0.34 nm; the XRD pattern shows that its main diffraction peak positions are at 26.3° and 42.3°; the FITR spectrum shows that it has vibrations at 1344 cm -1 and 772 cm -1 .
[0032] Evaluate the catalytic performance of the BN-LiBr catalyst in the oxidative dehydrogenation of oxygen-propane in a fixed-bed reactor under atmospheric pressure. Take 200 mg of the BN-LiBr sample and fix the catalyst bed with quartz wool in a quartz reaction tube (i.d. = 10 mm). The reaction feed gas composition is as follows: 99.9 vol.% propane (C3H8), 99.9 vol.% oxygen (O2), and nitrogen (N2) as the balance gas (propane / oxygen / nitrogen = 1 / 1.5 / 3.5). The space velocity is controlled at 7200 mL·g -1 ·h -1 , the reaction pressure is 0.1 MPa, and the reaction temperature is controlled at 440 - 520 °C. The gas products are separated and detected online by a gas chromatograph (Agilent 8860), which is equipped with an alumina-packed column and a flame ionization detector (FID). Analysis and calculation show that when the reaction temperature reaches 500 °C, the propane conversion rate is 33.42%, the propylene yield is 23.33%, and the olefin yield is 27.42%. See Figure 6 , and this catalyst is used for the activity test of the oxidative dehydrogenation of oxygen-propane.
[0033] Example 2
[0034] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of sodium chloride powder (NaCl) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, perform acid treatment on the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-NaCl. Its yield is 3.24%.
[0035] Perform TEM, XRD, and FITR analyses on BN-NaCl, and the results are as Figures 1-3 shown. The lattice spacing measured in the TEM image is 0.35 nm; the XRD pattern shows that its main diffraction peak positions are at 26.3° and 42.3°; the FITR spectrum shows that vibrations occur at 1377 cm -1 and 807 cm -1 .
[0036] Evaluate the catalytic performance of the BN-NaCl catalyst in the oxidative dehydrogenation of propane with oxygen in a fixed-bed reactor under atmospheric pressure. Take 200 mg of the BN-NaCl sample and fix the catalyst bed with quartz wool in a quartz reaction tube (i.d. = 10 mm). The reaction feed gas composition is: 99.9 vol.% propane (C3H8), 99.9 vol.% oxygen (O2), and nitrogen (N2) as the balance gas (propane / oxygen / nitrogen = 1 / 1.5 / 3.5), and the space velocity is controlled at 7200 mL·g -1 ·h -1 , the reaction pressure is 0.1 MPa, and the reaction temperature is controlled at 440 - 520 °C. The gas products are separated and detected online by a gas chromatograph (Agilent 8860), which is equipped with an alumina-packed column and a flame ionization detector (FID). Analysis and calculation show that when the reaction temperature reaches 500 °C, the propane conversion rate is 23.35%, the propylene yield is 17.62%, and the olefin yield is 20.06%. See Figure 7 , this catalyst is used for the activity test of the oxidative dehydrogenation of propane with oxygen.
[0037] Example 3
[0038] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of potassium bromide powder (KBr) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Then place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-KBr. Its yield is 6.75%.
[0039] Perform TEM, XRD, and FITR analyses on BN-KBr, and the results are as Figures 1-3 shown. The lattice spacing measured in the TEM image is 0.345 nm; the XRD pattern shows that its main diffraction peak positions are at 26.3° and 42.3°; the FITR spectrum shows that vibrations occur at 1372 cm -1 and 812 cm -1 .
[0040] Evaluate the catalytic performance of the BN-KBr catalyst in the oxidative dehydrogenation of propane with oxygen in a fixed-bed reactor under atmospheric pressure. Take 200 mg of the BN-KBr sample and fix the catalyst bed with quartz wool in a quartz reaction tube (i.d. = 10 mm). The reaction feed gas composition is as follows: 99.9 vol.% propane (C3H8), 99.9 vol.% oxygen (O2), and nitrogen (N2) as the balance gas (propane / oxygen / nitrogen = 1 / 1.5 / 3.5). The space velocity is controlled at 7200 mL·g -1 ·h -1 , the reaction pressure is 0.1 MPa, and the reaction temperature is controlled at 440 - 520 °C. The gas products are separated and detected online by a gas chromatograph (Agilent 8860), which is equipped with an alumina-packed column and a flame ionization detector (FID). Analysis and calculation show that when the reaction temperature reaches 500 °C, the propane conversion rate is 21.50%, the propylene yield is 16.27%, and the olefin yield is 18.53%. See Figure 8 , and this catalyst is used for the activity test of the oxidative dehydrogenation of propane with oxygen.
[0041] Example 4
[0042] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of manganese chloride powder (MnCl2) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Then place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-MnCl2. Its yield is 34.45%.
[0043] Perform TEM, XRD, and FITR analyses on BN-MnCl2, and the results are as Figures 1-3 shown. The lattice spacing measured in the TEM image is 0.35 nm; the XRD pattern shows that its main diffraction peak positions are at 26.3° and 42.3°; the FITR spectrum shows that vibrations occur at 1383 cm -1 and 810 cm -1 .
[0044] Evaluate the catalytic performance of the BN-MnCl2 catalyst in the oxidative dehydrogenation of oxygen-propane in a fixed-bed reactor under atmospheric pressure. Take 200 mg of the BN-MnCl2 sample and fix the catalyst bed with quartz wool in a quartz reaction tube (i.d. = 10 mm). The reaction feed gas composition is as follows: 99.9 vol.% propane (C3H8), 99.9 vol.% oxygen (O2), and nitrogen (N2) as the balance gas (propane / oxygen / nitrogen = 1 / 1.5 / 3.5). The space velocity is controlled at 7200 mL·g -1 ·h -1 , the reaction pressure is 0.1 MPa, and the reaction temperature is controlled at 440 - 520 °C. The gas products are separated and detected online by a gas chromatograph (Agilent 8860), which is equipped with an alumina-packed column and a flame ionization detector (FID). Analysis and calculation show that when the reaction temperature reaches 500 °C, the propane conversion rate is 18.23%, the propylene yield is 9.42%, and the olefin yield is 10.55%. See Figure 9 . This catalyst is used for the activity test of the oxidative dehydrogenation of oxygen-propane.
[0045] Example 5
[0046] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of ferric chloride powder (FeCl3) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Then place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-FeCl3. Its yield is 17.28%.
[0047] Perform TEM, XRD, and FITR analyses on BN-FeCl3, and the results are as Figures 1-3 shown. The lattice spacing measured in the TEM image is 0.34 nm; the XRD pattern shows that its main diffraction peak positions are at 26.3° and 42.3°; the FITR spectrum shows vibrations at 1341 cm -1 and 778 cm -1 .
[0048] Evaluate the catalytic performance of the BN-FeCl3 catalyst in the oxidative dehydrogenation of oxygen-propane in a fixed-bed reactor under atmospheric pressure. Take 200 mg of the BN-FeCl3 sample and fix the catalyst bed with quartz wool in a quartz reaction tube (i.d. = 10 mm). The reaction feed gas composition is as follows: 99.9 vol.% propane (C3H8), 99.9 vol.% oxygen (O2), and nitrogen (N2) as the balance gas (propane / oxygen / nitrogen = 1 / 1.5 / 3.5), and the space velocity is controlled at 7200 mL·g -1 ·h -1 . The reaction pressure is 0.1 MPa, and the reaction temperature is controlled at 440 - 520 °C. The gas products are separated and detected online by a gas chromatograph (Agilent 8860), which is equipped with an alumina-packed column and a flame ionization detector (FID). Analysis and calculation show that when the reaction temperature reaches 500 °C, the propane conversion rate is 28.02%, the propylene yield is 20.00%, and the olefin yield is 23.66%. See Figure 10 for the activity test of this catalyst in the oxidative dehydrogenation of oxygen-propane.
[0049] Example 6
[0050] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of zinc chloride powder (ZnCl2) in a nickel mortar in the glove box. Grind the above raw materials thoroughly until uniform, and then store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-ZnCl2. Its yield is 2.88%.
[0051] Perform XRD analysis on BN-ZnCl2, and the results are as Figure 4 shown. The XRD pattern shows that the positions of its main diffraction peaks are at 26.3° and 42.3°.
[0052] Example 7
[0053] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of nickel chloride powder (NiCl2) in a nickel mortar in the glove box. Grind the above raw materials thoroughly until uniform, and then store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-NiCl2. Its yield is 2.95%.
[0054] Perform XRD analysis on BN-NiCl2, and the results are as Figure 4 shown. The XRD pattern shows that the positions of its main diffraction peaks are at 26.3° and 42.3°.
[0055] Example 8
[0056] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of lithium bromide powder (LiBr) in a nickel mortar in a glove box. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 4 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. Wait until there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-LiBr-4h. Its yield is 16.94%. Its XRD pattern is shown in Figure 5 .
[0057] Example 9
[0058] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of lithium bromide powder (LiBr) in a nickel mortar in a glove box. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 16 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. Wait until there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-LiBr-16h. Its yield is 48.22%. Its XRD pattern is shown in Figure 5 .
[0059] Example 10
[0060] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of lithium chloride powder (LiCl) in a nickel mortar in a glove box. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. Wait until there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, and then dry and collect the sample to obtain BN powder. This sample is labeled BN-LiCl. Its yield is 28.22%.
[0061] Example 11
[0062] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of lithium iodide powder (LiI) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C with an oil bath to allow it to react fully at this temperature to remove impurities. Wait until there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, then dry and collect the sample to obtain BN powder. This sample is labeled BN-LiI. Its yield is 30.28%.
[0063] Example 12
[0064] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of sodium bromide powder (NaBr) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C with an oil bath to allow it to react fully at this temperature to remove impurities. Wait until there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, then dry and collect the sample to obtain BN powder. This sample is labeled BN-NaBr. Its yield is 18.58%.
[0065] Example 13
[0066] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of sodium iodide powder (NaI) in a glove box in a nickel mortar. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C with an oil bath to allow it to react fully at this temperature to remove impurities. Wait until there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, then dry and collect the sample to obtain BN powder. This sample is labeled BN-NaI. Its yield is 15.46%.
[0067] Example 14
[0068] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of potassium chloride powder (KCl) in a nickel mortar in a glove box. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C with an oil bath to make it react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, then dry and collect the sample to obtain BN powder. This sample is labeled BN-KCl. Its yield is 8.44%.
[0069] Example 15
[0070] Weigh 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of potassium iodide powder (KI) in a nickel mortar in a glove box. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C with an oil bath to make it react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, then dry and collect the sample to obtain BN powder. This sample is labeled BN-KI. Its yield is 5.67%.
[0071] Comparative Example 1
[0072] Weigh 3.0 g of sodium borohydride powder (NaBH4) in a glove box and store it in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place it in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, it is found that there is no sample residue in the alumina crucible.
[0073] Comparative Example 2
[0074] Weigh 3.0 g of sodium tetrafluoroborate powder (NaBF4) and 4.5 g of lithium bromide powder (LiBr) in a nickel mortar in a glove box. Grind the above raw materials thoroughly until uniform, and store them in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, place them in a tube furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure is as follows: heat up to 700 °C and maintain for 24 h. After the heat treatment, acid-treat the sample: soak the sample in aqua regia overnight, and heat it to 80 °C with an oil bath to make it react fully at this temperature to remove impurities. When there are no bubbles in the sample soaked in aqua regia, centrifuge and wash it with deionized water until neutral, then dry and collect the sample. By Figure 11XRD analysis found that no BN peak appeared.
[0075] Comparative Example 3
[0076] In the glove box, 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of magnesium chloride powder (MgCl2) were weighed into a nickel mortar. The above raw materials were fully ground until uniform and then stored in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, it was placed in a tubular furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure was as follows: heated to 700 °C and maintained for 24 h. After the heat treatment, it was found that no sample remained, indicating that boron nitride could not be formed under the action of magnesium chloride halide.
[0077] Comparative Example 4
[0078] In the glove box, 3.0 g of sodium borohydride powder (NaBH4) and 4.5 g of aluminum chloride powder (AlCl3) were weighed into a nickel mortar. The above raw materials were fully ground until uniform and then stored in a reagent bottle filled with a nitrogen atmosphere for later use. Subsequently, it was placed in a tubular furnace filled with a nitrogen atmosphere for heat treatment. The specific heat treatment procedure was as follows: heated to 700 °C and maintained for 24 h. After the heat treatment, the sample was subjected to acid treatment: the sample was soaked in aqua regia overnight and heated to 80 °C in an oil bath to allow it to react fully at this temperature to remove impurities. When there were no more bubbles in the sample soaked in aqua regia, it was centrifugally washed with deionized water and then dried in an oven. And XRD analysis was performed on this sample, as Figure 12 , and it was found that there was no obvious BN peak.
[0079] Comparative Example 5
[0080] The catalytic performance of a commercial boron nitride catalyst in the oxidative dehydrogenation of oxygen - propane was evaluated in an atmospheric pressure fixed - bed reactor. 200 mg of a commercial boron nitride sample (purchased from Shanghai Merck Technology Co., Ltd., 97%) was taken, and the catalyst bed was fixed with quartz wool in a quartz reaction tube (i.d. = 10 mm). The reaction feed gas composition was: 99.9 vol.% propane (C3H8), 99.9 vol.% oxygen (O2), and nitrogen (N2) as the balance gas (propane / oxygen / nitrogen = 1 / 1.5 / 3.5), and the space velocity was controlled at 7200 mL·g -1 ·h -1 , the reaction pressure was 0.1 MPa, and the reaction temperature was controlled at 440 - 520 °C. The gas products were separated and detected online by a gas chromatograph (Agilent 8860), which was equipped with an alumina packed column and a flame ionization detector (FID). Analysis and calculation showed that when the reaction temperature reached 500 °C, the propane conversion rate was 13.15%, the propylene yield was 10.40%, and the olefin yield was 11.44%. See Figure 13 , and this catalyst was used for the activity test of the oxidative dehydrogenation of oxygen - propane.
Claims
1. A method for directly synthesizing hexagonal boron nitride from nitrogen, characterized in that: Under a nitrogen atmosphere, a mixture of sodium borohydride and a halide salt is used as a reaction raw material. After heat treatment and then washing with aqua regia, hexagonal boron nitride is obtained. The halide salt is selected from one or more of LiCl, LiBr, LiI, NaCl, NaBr, NaI, KCl, KBr, KI, MnCl₂, FeCl₃, ZnCl₂, and NiCl₂.
2. The method for directly synthesizing hexagonal boron nitride from nitrogen according to claim 1, characterized in that: The mass ratio of sodium borohydride to the halide salt is 1:1 to 2.
3. The method for directly synthesizing hexagonal boron nitride from nitrogen according to claim 2, characterized in that: The mass ratio of sodium borohydride to the halide salt is 1:1.
5.
4. The method for directly synthesizing hexagonal boron nitride from nitrogen gas according to claim 1, characterized in that: The halide salt is selected from one or more of LiCl, LiBr, LiI, NaBr, NaI, MnCl₂, and FeCl₃.
5. The method for directly synthesizing hexagonal boron nitride from nitrogen according to claim 4, characterized in that: The halide salt is selected from one or more of LiCl, LiBr, LiI, and MnCl₂.
6. The method for directly synthesizing hexagonal boron nitride from nitrogen gas according to claim 5, characterized in that: The halide salt is LiBr.
7. The method for directly synthesizing hexagonal boron nitride from nitrogen according to claim 1, characterized in that: The temperature of the heat treatment is 600 to 800 °C.
8. The method for directly synthesizing hexagonal boron nitride from nitrogen according to claim 7, characterized in that: The temperature of the heat treatment is 700 °C.
9. The method for directly synthesizing hexagonal boron nitride from nitrogen according to claim 1, characterized in that: The aqua regia washing process is as follows: The sample obtained after heat treatment is immersed in aqua regia at 60 to 100 °C for 8 to 12 h.