Porous carbon / single-layer porous hexagonal boron nitride composite film, preparation method and application thereof

Abstract

The application discloses a kind of porous carbon / single-layer porous hexagonal boron nitride composite film.By controlling the precursor amount and hydrogen carrier gas flow of low-pressure gas phase chemical reaction, and reaction temperature, pressure and time, single-layer porous hexagonal boron nitride film is formed on the surface of single crystal copper foil (111).The film has high-density triangular nanopores, which are formed by defects formed during film growth, and the size is determined by the number of atoms missing from the pores, and the film has a narrow pore size distribution;Spin coating, pyrolysis is carried out on the surface of the film to form a porous carbon layer that acts as a protective support, to realize the construction of porous carbon / single-layer porous hexagonal boron nitride composite film.The composite film is used for CO2 / N2, H2 / CH4 system high-temperature separation, has high permeation rate and high selectivity for CO2, H2 at different temperatures, and the film has good high-temperature stability and long-term stability.In the field of carbon capture and hydrogen separation, it shows good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a gas separation membrane, in particular to a single-layer porous hexagonal boron nitride film and a preparation method thereof. BACKGROUND

[0002] Single-layer crystal thin film is an ideal membrane separation material. Its atomic-level film thickness can be converted into the smallest mass transfer resistance, and the mass transfer flux of molecules is improved as much as possible. In recent years, single-layer graphene is considered as a very potential atomic thin film candidate material. For this purpose, nanometer holes are introduced into the water-impermeable graphite lattice by post-synthesis etching and bottom-up synthesis methods. However, both methods cannot accurately control the structure of the nanometer hole, and irregular and poor selective holes are usually generated, thereby affecting the mass transfer. Single-layer hexagonal boron nitride is similar in structure to graphene and is often used in the field of devices, but has many unique advantages as a separation membrane. First, compared with graphene, the pore shape of the hBN thin film is more regular, which is a triangular hole, and the chemical group of nitrogen end-capping can also significantly improve the chemical stability of the pore. At the same time, molecular simulation studies show that the mass transfer speed of molecules through the hBN nanometer hole is faster than that through the graphene nanometer hole. In addition, the insulating properties of hBN exhibit lower noise advantage than graphene or other conductive 2D materials when measuring the transmembrane current. Finally, hBN has higher chemical and thermal stability, and can operate under more severe conditions, meeting the requirements of many real-world applications.

[0003] The preparation method of the hBN thin film is similar to that of graphene, which is usually prepared by mechanical exfoliation or vapor deposition. Among them, the mechanical exfoliation method has high cost and low efficiency, and the thickness of the obtained sheet is uneven, and the size is often limited to microns. However, continuous high-quality defect-free hBN thin films can be obtained by chemical vapor deposition method, which has the potential to prepare large-area thin films in the future. However, it is still a great challenge to precisely construct high-density sub-nanometer holes on the hBN thin film to realize molecular transmission. SUMMARY

[0004] In view of the above prior art, the present application provides a preparation method of a single-layer porous hexagonal boron nitride film, which is simple and controllable. The prepared film can be used for CO2 / N2 and H2 / CH4 system separation, and has ultra-high CO2 / N2 and H2 / CH4 separation performance and stability.

[0005] To solve the above problems, the application provides a porous carbon / single-layer porous hexagonal boron nitride composite film, which is prepared by taking a single-crystal copper foil (111) as a substrate and placing the substrate in a chemical vapor deposition chamber with a pressure of 0.1-0.5 Torr, keeping the temperature of the substrate at 900-1050 DEG C, introducing cyclo-borazane or ammonia borane with a volume flow rate of 0.2 sccm as a precursor, introducing hydrogen with a volume flow rate of 10-50 sccm as a protective gas, and reacting for 1 hour, so that a single-layer porous hexagonal boron nitride film is formed on the surface of the single-crystal copper foil (111) substrate; the film has triangular nanopores with a density of 1.4x10 12 ~2x10 12 2 cm-2; the size of the triangular nanopores is determined by the number of missing nitrogen and boron atoms at the position during the reaction, wherein 95%-98% of the triangular nanopores are missing 2-5 atoms; a porous carbon layer with a thickness of 100 nm±25 nm and a pore size of 20-40 nm is formed on the surface of the film by spin coating and pyrolysis, and the copper foil is removed to obtain the porous carbon / single-layer porous hexagonal boron nitride composite film.

[0006] The preparation method of the porous carbon / single-layer porous hexagonal boron nitride composite film comprises the following steps:

[0007] 1) annealing a copper foil in an argon-hydrogen mixed gas to obtain a single-crystal copper foil (111);

[0008] 2) treating the single-crystal copper foil (111) obtained in step 1) in hydrogen at 900-1050 DEG C for 10 min, then introducing cyclo-borazane or ammonia borane with a volume flow rate of 0.2 sccm to grow a hexagonal boron nitride film on the surface of the single-crystal copper foil (111), thereby obtaining a hexagonal boron nitride / copper composite film, which is denoted as hBN / Cu film;

[0009] 3) spin coating and pyrolyzing the hBN / Cu film to form a porous carbon layer with a thickness of 100 nm±25 nm as a protective layer, thereby obtaining a porous carbon / hexagonal boron nitride / copper composite film, which is denoted as NPC / hBN / Cu film;

[0010] 4) removing the copper foil from the NPC / hBN / Cu film obtained in step 3), rinsing the film, and transferring the film to a porous tungsten substrate to obtain a suspended porous carbon / hexagonal boron nitride composite film, which is denoted as NPC / hBN film.

[0011] Further, in the preparation method, the single-crystal copper foil (111) is annealed in an argon-hydrogen mixed gas at a temperature of 900-1050 DEG C for 10-30 min.

[0012] ​The specific content of the step 2) includes: placing a quartz boat in a tube furnace of a CVD reactor, keeping at 1000℃ for 6h by using hydrogen and argon mixed gas, and cooling to room temperature; cleaning the single crystal copper foil (111) prepared in the step 1) with isopropanol, and loading into the quartz boat after drying; under the hydrogen carrier gas with a volume flow rate of 10-50sccm, heating the tube furnace to 900-1050℃, after 10min, introducing the azaborine or ammonia borane with a volume flow rate of 0.2sccm into the CVD reactor, controlling the total pressure to be 0.1-0.5Torr, and the reaction time is 1h, during the reaction, porous hexagonal boron nitride films are grown on both sides of the single crystal copper foil (111), after the reaction, the azaborine or ammonia borane gas flow is closed, and the tube furnace program is terminated, and the product is cooled to room temperature with the furnace, and the hBN / Cu film is obtained.

[0013] In the step 2), the process of cleaning and drying the single crystal copper foil (111) is as follows: placing the single crystal copper foil (111) into an isopropanol solution, cleaning by using an ultrasonic cleaning machine for 5-10min, and the ultrasonic power is 40W, and then blowing the cleaned single crystal copper foil (111) by using a nitrogen gun.

[0014] The specific content of the step 3) includes: taking polystyrene-poly-4-vinylpyridine and furanose according to the mass ratio of 1:2, taking N,N-dimethylformamide as a solvent, preparing a solution with a polystyrene-poly-4-vinylpyridine mass fraction of 4.35%, heating the solution to 180℃ in an autoclave to prepare a spin coating solution; pasting the hBN / Cu film prepared in the step 2) on a glass sheet with the front side upward, placing the above spin coating solution on the front side of the hBN / Cu film, and sequentially performing twice spin coating treatment, and each spin coating is as follows: the amount of the spin coating solution is 100μL / cm 2 , in the spin coating process, first spin coating at 1000rpm for 30s, and then spin coating at 1500rpm for 30s; pyrolyzing the spin coated sample in argon and hydrogen mixed gas at 500℃ for 1h to generate the porous carbon layer with a thickness of 100nm±25nm, and the NPC / hBN / Cu film is obtained.

[0015] Meanwhile, the porous carbon / single-layer porous hexagonal boron nitride composite film prepared by the preparation method is used for separating CO2 in a CO2 / N2 mixed gas system, or is used for separating H2 in a H2 / CH4 mixed gas system; under the conditions of 30-250℃ and raw gas pressure of 1-3bar, the permeation flux of CO2 is 1×10 -6 -3.8×10 -6 mol·m -2 ·s -1 ·Pa -1, CO2 / N2 selectivity of 14.4; average permeation rate of H2 of 2.2*10 -5 ~ 6.8*10 -6 mol·m -2 ·s -1 ·Pa -1 , average selectivity of H2 / CH4 of 7~21.9.

[0016] Compared with the prior art, the present application has the advantages of:

[0017] (1) The present application provides a preparation method of porous carbon / single-layer porous hexagonal boron nitride composite film, which realizes efficient separation of CO2 / N2 and H2 / CH4 by using the composite film. In the preparation method, hydrogen is introduced as a protective gas by low-pressure chemical vapor deposition, and borazine or ammonia borane is used as a precursor. The growth temperature, growth time and precursor flow rate are adjusted to realize the regulation of the size and defect pores of the single crystal of hexagonal boron nitride, and finally a single-layer porous hexagonal boron nitride film is formed on the surface of a single crystal copper foil (111).

[0018] (2) The single-layer porous hexagonal boron nitride film synthesized by low-pressure chemical vapor deposition has an ultra-high density of sub-nanometer pores (2*10 12 cm -2 ), and at the same time, the ultra-thin film thickness helps to reduce the mass transfer resistance and improve the gas transmission rate. The regular triangular pores help to precisely construct the mass transfer channels and realize more efficient molecular sieving. The prepared single-layer porous hexagonal boron nitride film has higher chemical and thermal stability, and can separate CO2 in a high-temperature CO2 / N2 mixed gas system and separate H2 in a high-temperature H2 / CH4 mixed gas system. Under the conditions of 150℃ and raw gas pressure of 2bar, the average permeation flux of CO2 of the hBN-1050 film is 2.55*10 -6 mol·m -2 ·s -1 ·Pa -1 , and the CO2 / N2 selectivity is 4.1. Under the conditions of 150℃ and raw gas pressure of 2bar, the average permeation flux of H2 of the hBN-900 film is 4.4*10 -6 mol·m -2 ·s -1 ·Pa -1 , and the average selectivity of H2 / CH4 is 13.8.

[0019] (3) The method is simple and controllable in preparation process, and the prepared single-layer porous hexagonal boron nitride film has molecular sieve pore channels, and realizes high-throughput gas separation. The prior art can currently prepare a continuous and defect-free large-area boron nitride film, or can prepare a boron nitride film with micron-sized pores, but the pore size is too large and the pore size is uneven, and gas separation cannot be realized. The single-layer porous hexagonal boron nitride film with a centimeter specification can be directly prepared by the chemical deposition method, the film has a high density of sub-nanometer pores (2x10 12 cm -2 )(1050), the pore size distribution is uniform, the pore size meets the molecular sieving of H2 and CO2, and the universality is strong, and can be expanded to other gas separation systems by adjusting the pore size, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1(a) is a scanning electron microscope image of the formed porous carbon film.

[0021] Figure 1(b) is an atomic force microscope image of the formed porous carbon film.

[0022] Figure 2 Figure 1(c) is a scanning electron microscope image of the single-layer film obtained when the single-crystal copper foil (111) is kept at 1050°C for 60 min during the preparation process of Example 1, that is, the scanning electron microscope image of hBN-1050.

[0023] Figure 3(a) is an atomic force microscope image of hBN transferred to a SiO2 / Si substrate from the hexagonal boron nitride / copper composite film obtained in step 2) of Example 1.

[0024] Figure 3(b) is an atomic force microscope image of hBN transferred to a SiO2 / Si substrate from the hexagonal boron nitride / copper composite film obtained in step 2) of Example 2.

[0025] Figure 3(c) is an atomic force microscope image of hBN transferred to a SiO2 / Si substrate from the hexagonal boron nitride / copper composite film obtained in step 2) of Example 3.

[0026] Figure 4(a) is an AC-HRTEM image of hBN in the hexagonal boron nitride / copper composite film obtained in step 2) of Example 1.

[0027] Figure 4(b) is a pore size distribution graph of hBN in the hexagonal boron nitride / copper composite film obtained in step 2) of Example 1.

[0028] Figure 5(a) is a function relationship between the gas permeability and the molecular kinetic diameter of the Example 1 sample NPC / hBN-1050 at 250°C.

[0029] Figure 5(b) is the gas permeability and separation selectivity of the sample NPC / hBN-1050 of Example 1 for H2 / CO2, H2 / CH4 system at 250℃.

[0030] Figure 5(c) is the gas permeability and separation selectivity of the samples of Examples 1-4 for H2 / CH4, CO2 / N2 at 150℃, respectively.

[0031] Figure 6(a) is a scanning electron microscope image of a monolayer film obtained by keeping the single crystal copper foil (111) at 800℃ for 60min during the preparation of the sample of Comparative Example 1.

[0032] Figure 6(b) is a scanning electron microscope image of a monolayer film obtained by keeping the single crystal copper foil (111) at 1000℃ for 60min during the preparation of the sample of Example 4.

[0033] Figure 6(c) is a scanning electron microscope image of a monolayer film obtained by keeping the single crystal copper foil (111) at 1070℃ for 60min during the preparation of the sample of Comparative Example 2.

[0034] Figure 7(a) is a scanning electron microscope image of a monolayer film obtained by keeping the single crystal copper foil (111) at 1050℃ for 60min during the preparation of the sample of Comparative Example 3 at a precursor flow rate of 0.1sccm.

[0035] Figure 7(b) is a scanning electron microscope image of a monolayer film obtained by keeping the single crystal copper foil (111) at 1050℃ for 60min during the preparation of the sample of Comparative Example 4 at a precursor flow rate of 2sccm.

[0036] Figure 8 Figure 5(c) is the gas permeability and separation selectivity of the samples of Examples 1-4 for H2 / CH4, CO2 / N2 at 150℃, respectively. DETAILED DESCRIPTION

[0037] The design idea of the porous carbon / monolayer porous hexagonal boron nitride composite film proposed by the present application is that by controlling the reaction temperature, reaction pressure, reaction time and precursor amount of low-pressure gas phase chemical reaction, a monolayer porous hexagonal boron nitride film can be formed on the surface of a single crystal copper foil (111). The film has a high density of triangular nanoholes, and the density of the triangular nanoholes is 1.4×10 12 ~2×10 12 cm-2. 2; the triangular nanopore is a defect formed in the process of thin film growth, and the pore size is determined by the number of atoms missing in the pore, and the pore size distribution of the film is relatively narrow, wherein 95% to 98% of the triangular nanopores are missing 2 to 5 atoms. The porous carbon film having a supporting effect on the single-layer porous hexagonal boron nitride layer can be formed by spin coating and pyrolysis on the surface of the thin film. The composite film is used for high-temperature separation in a CO2 / N2, H2 / CH4 separation system, and has a high permeation rate and high selectivity for CO2 and H2 at different temperatures, and the film has good high-temperature stability and long-term stability. It has good application prospect in the fields of carbon capture and hydrogen separation. The preparation process of the above porous carbon / single-layer porous hexagonal boron nitride composite film mainly comprises: preparing a single crystal copper foil (111) as a substrate, placing the substrate in a chemical vapor deposition chamber at 0.1-0.5 Torr, keeping the temperature of the substrate at 900-1050℃, and introducing 0.2sccm of cyclo-borazane or ammonia borane as a precursor, and 10-50sccm of hydrogen as a protective gas to grow for 1 hour or more, so as to prepare and form a single-layer porous hexagonal boron nitride thin film on the surface of the single crystal copper foil (111) substrate. A porous carbon layer with a thickness of 100nm±25nm and a pore size of 20-40nm can be formed on the surface of the thin film by spin coating and pyrolysis, so as to realize the preparation of the porous carbon / single-layer porous hexagonal boron nitride composite film.

[0038] The technical solutions of the present application will be further described in detail below in combination with specific examples and tables. The specific examples described are only used to explain and illustrate the present application, and do not limit the present application. The single-layer porous hBN thin film prepared in the examples is denoted as

[0039] Example 1:

[0040] A porous carbon / single-layer porous hexagonal boron nitride composite film (NPC / hBN-1050 film) is prepared, and the steps are as follows:

[0041] Step 1) Single crystal copper foil (111): 2x3cm 2 The copper foil is placed on a quartz boat and put into a 1-inch quartz tube matched with the tube furnace, and the quartz boat is located in the center of the tube furnace. The tube furnace is heated to 1075℃ in an Ar / H2 mixed gas with a flow rate of 100sccm, and maintained at 1075℃ for 3h at a pressure of 700Torr, and a single crystal copper foil (111) is obtained by annealing.

[0042] Step 2) Preparation of hBN / Cu film: the single crystal copper foil (111) prepared in step 1) is placed in an isopropanol solution and cleaned by ultrasonic wave for 10 min with an ultrasonic power of 40 W, and then the cleaned single crystal copper foil (111) is dried by nitrogen gun and loaded into a CVD reactor. The quartz boat as a carrier is pretreated by being placed in a tube furnace and treated at 1000℃ for 6 h by using hydrogen and argon mixed gas; under the hydrogen carrier gas with a volume flow rate of 10 sccm, the tube furnace is heated to 1050℃, after 10 min, the CVD reactor is introduced with a volume flow rate of 0.2 sccm of borazine, the total pressure is controlled to be 0.1 Torr, and the reaction time is 1 h. During the reaction, porous hexagonal boron nitride (hBN) thin films are grown on both sides of the single crystal copper foil (111). After the reaction, the borazine gas flow is turned off, and the tube furnace program is terminated. The product is cooled to room temperature with the furnace, and a hexagonal boron nitride / copper composite film, i.e. the hBN / Cu film, is prepared.

[0043] Figure 2 The surface structure of the hBN thin film is shown. It can be observed from the image that the formed hBN thin film surface has a small amount of wrinkles and particles, and the overall film is continuous and defect-free. Figure 3(a) shows an atomic force microscope image of the hBN transferred from the obtained hBN / Cu film to a SiO2 / Si substrate. The hBN layer thickness of the film is 0.7 nm. Figures 4(a) and 4(b) show the pore structure and distribution of the hBN thin film, wherein the pore size shows a logarithmic distribution.

[0044] In the process of growing the hexagonal boron nitride thin film on the surface of the single crystal copper foil (111) in step 2) of the present application, the volume flow rate of hydrogen is 10-50 sccm, and the reaction pressure is 0.1-0.5 Torr. The reaction pressure is positively correlated with the hydrogen flow rate. When the hydrogen flow rate is 10 sccm, the reaction pressure is 0.1 Torr; when the hydrogen flow rate is 20 sccm, the reaction pressure is 0.2 Torr; when the hydrogen flow rate is 30 sccm, the reaction pressure is 0.3 Torr; when the hydrogen flow rate is 40 sccm, the reaction pressure is 0.4 Torr; when the hydrogen flow rate is 50 sccm, the reaction pressure is 0.5 Torr. The reaction time is 1 h.

[0045] Step 3) Preparation of NPC / hBN / Cu film: polystyrene-poly-4-vinylpyridine and furanose were weighed according to the mass ratio of 1:2, a solution with a polystyrene-poly-4-vinylpyridine mass fraction of 4.35% was prepared in N,N-dimethylformamide, and the solution was heated to 180°C in an autoclave to prepare a spin coating solution; the hBN / Cu film prepared in step 2) was attached to a glass sheet with the front side facing up, and the spin coating solution was placed on the front side of the hBN / Cu film, and two spin coating processes were performed in turn, with the spin coating solution used in each process being 100 μL / cm 2 . During each spin coating process, the solution was first spin coated at 1000 rpm for 30 s, and then at 1500 rpm for 30 s; the spin-coated sample was pyrolyzed in an argon-hydrogen mixed gas at 500°C for 1 h to form a porous carbon layer as a protective layer, thereby obtaining the NPC / hBN / Cu film; the surface structure of the porous carbon layer is shown in FIGS. 1(a) and 1(b), and the pore size is 20-40 nm; the thickness of the porous carbon layer is 100 nm ± 25 nm.

[0046] Step 4) Removal of copper foil to prepare NPC / hBN film: the NPC / hBN / Cu prepared in step 3) was floated in a 10% mass fraction Na2S2O8 aqueous solution for 5 min to remove the hBN film on the back side, and then transferred to a 10% mass fraction Na2S2O8 aqueous solution to etch the copper foil. After removing the copper foil, the NPC / hBN film was rinsed in deionized water three times to remove residues. The washed NPC / hBN film was transferred to a porous tungsten substrate to obtain a suspended NPC / hBN film; the porous tungsten substrate was polished to a bright finish with an aqueous diamond polishing paste (specification W0.5) before use, and treated in an O2 plasma with a flow rate of 60 sccm at a power of 30 W for 20 s. The NPC / hBN film obtained in this example is denoted as NPC / hBN-1050 film.

[0047] The NPC / hBN-1050 film was used for CO2 / N2, H2 / CH4 system separation, as shown in FIG. 5(c), under the conditions of 150°C and raw gas pressure of 2 bar, the average permeation rate of H2 was 6.78 × 10 -6 mol·m -2 ·s -1 ·Pa -1 , and the average selectivity of H2 / CH4 was 10.7; under the conditions of 150°C and raw gas pressure of 2 bar, the average permeation flux of CO2 of the NPC / hBN-1050 film was 2.55 × 10 - 6 mol·m -2 ·s -1 ·Pa -1with a CO2 / N2 selectivity of 4.1. The H2 permeance of the membrane was 3.2 x 10 -5 mol m -2 s -1 Pa -1 with a H2 / CH4 selectivity of 7.0. The average permeance of CO2 was 7.0 x 10 -6 mol m -2 s -1 Pa -1 with a CO2 / N2 selectivity of 2.47. Figure 5(a) is a plot of the gas permeability of the NPC / hBN-1050 membrane as a function of the molecular kinetic diameter at 250°C, and Figure 5(b) is a plot of the gas selectivity of the NPC / hBN-1050 membrane for different gases at 250°C, H 2 / The CO2 selectivity was 4.93, the H2 / CH4 selectivity was 8.52, the H2 / SF6 selectivity was 72.53, and the CO2 / N2 selectivity was 3.1. It can be determined from this that the molecular sieving ability of the NPC / hBN-1050 membrane is that, although the kinetic diameter of nitrogen is smaller than that of methane, the permeability of nitrogen is slightly lower than that of methane, because the adsorption of methane on hBN is stronger than that of nitrogen, which means that there is more gas transmission of methane by the surface diffusion mechanism.

[0048] Example 2:

[0049] An NPC / hBN-900 membrane was prepared in the same manner as in Example 1, except that in step 2), the temperature for growing a monolayer of porous hBN film on both sides of the single-crystal copper foil (111) by CVD reaction was changed from 1050°C to 900°C. The resulting porous carbon / monolayer of porous hexagonal boron nitride composite membrane was denoted as NPC / hBN-900, and Figure 3(b) shows an atomic force microscope image of the hBN transferred from the hBN / Cu membrane obtained in step 2) of this example to a SiO2 / Si substrate. The thickness of the hBN layer of this membrane was 0.7 nm.

[0050] The NPC / hBN-900 membrane was used for CO2 / N2 and H2 / CH4 separation, as shown in Figure 5(c). The H2 permeance of the NPC / hBN-900 membrane was 4.4 x 10 -6 mol m -2 s -1 Pa -1 with a H2 / CH4 selectivity of 13.8; and the CO2 permeance was 2.01 x 10 -6 mol m -2 s -1· Pa -1 with a CO2 / N2 selectivity of 2.9.

[0051] Example 3:

[0052] An NPC / hBN-1035s film was prepared in the same manner as in Example 1, except that in step 2), the volume flow rate of the precursor introduced into the CVD reactor was changed from 0.2 sccm of borazine to 0.2 sccm of ammonia borane, and the temperature for CVD reaction to grow a single-layer porous hBN film was changed from 1050 °C to 1035 °C. The resulting porous carbon / single-layer porous hexagonal boron nitride composite film was denoted as NPC / hBN-1035s film. Figure 3(c) shows an atomic force microscope image of the hBN transferred from the hBN / Cu film obtained in step 2) of this example 3 to a SiO2 / Si substrate, and the hBN layer thickness of this film was 2.3 nm.

[0053] The NPC / hBN-1035s film was used for CO2 / N2 and H2 / CH4 system separation. As shown in Figure 5(c), the permeation flux of CO2 of the NPC / hBN-1035s film was 1.04 x 10 -6 mol m -2 s -1 · Pa -1 with a CO2 / N2 selectivity of 2.5; and the permeation flux of H2 of the NPC / hBN-1035s film was 2.199 x 10 -5 mol m -2 s -1 · Pa -1 with a H2 / CH4 selectivity of 7.

[0054] Example 4:

[0055] An NPC / hBN-1000 film was prepared in the same manner as in Example 1, except that in step 2), the temperature for CVD reaction to grow a single-layer porous hBN film was changed from 1050 °C to 1000 °C. The resulting porous carbon / single-layer porous hexagonal boron nitride composite film was denoted as NPC / hBN-1000 film, and the surface structure of this film is shown in Figure 6(b). It can be observed from the image that there are a small amount of wrinkles and particles on the surface of the formed hBN film, and the overall film is continuous and defect-free.

[0056] The NPC / hBN-1000 film was used for H2 / CH4 system separation. As shown in Figure 5(c), the average permeation rate of H2 was 5.33 x 10 -6mol·m -2 ·s -1 ·Pa -1 The average selectivity of H2 / CH4 was 11.5; the average permeation flux of CO2 was 2.53 × 10⁻⁶. -6 mol·m -2 ·s -1 ·Pa -1 Its CO2 / N2 selectivity is 3.8.

[0057] Comparative Example 1:

[0058] The preparation process of an NPC / hBN-800 membrane is basically the same as that in Example 1, except that the temperature of the CVD reaction to grow the monolayer porous hBN film in step 2) is changed from 1050℃ to 800℃. The resulting porous carbon / monolayer porous hexagonal boron nitride composite membrane is denoted as NPC / hBN-800 membrane. The surface structure of this membrane is shown in Figure 6(a). The image shows that the surface of the formed hBN film has micron-sized irregular defects, indicating discontinuous growth. This is because the CVD reaction temperature is too low, resulting in slow growth and a large number of defects, making it difficult to grow a continuous film.

[0059] The NPC / hBN-800 membrane was used for separation in an H2 / CH4 system, such as... Figure 8 As shown, under the conditions of 150℃ and feed gas pressure of 2 bar, the average permeability of H2 is 4.87 × 10⁻⁶. -5 mol·m -2 ·s -1 ·Pa -1 The average selectivity of H2 / CH4 was 3.62; the average permeation flux of CO2 was 1.68 × 10⁻⁶. -5 mol·m -2 ·s -1 ·Pa -1 Its CO2 / N2 selectivity is 2.5.

[0060] Comparative Example 2:

[0061] The preparation process of an NPC / hBN-1070 membrane is basically the same as that in Example 1, except that the temperature of the CVD reaction for growing the monolayer porous hBN film in step 2) is changed from 1050℃ to 1070℃. The resulting porous carbon / monolayer porous hexagonal boron nitride composite membrane is denoted as NPC / hBN-1070 membrane. The surface structure of this membrane is shown in Figure 6(c). The image shows that the surface of the formed hBN film has micron-sized irregular defects, indicating discontinuous growth. Due to the excessively high growth temperature, the amount of precursor adsorption is reduced, making it impossible to form a continuous boron nitride film.

[0062] The NPC / hBN-1070 membrane was subjected to H2 / CH4 system separation, as shown in Figure 8 the average permeation rate of H2 was 3.98 x 10 -5 mol m -2 s -1 Pa -1 , the average selectivity of H2 / CH4 was 1.42; the average permeation flux of CO2 was 1.95 x 10 -5 mol m -2 s -1 Pa -1 , and the CO2 / N2 selectivity was 2.7.

[0063] Comparative Example 3:

[0064] An NPC / hBN-1050b membrane was prepared in the same manner as in Example 1, except that in step 2), the flow rate of the precursor for CVD reaction and growth of the single-layer porous hBN film was changed from 0.2 sccm of the cyclo-borazane introduced to 0.1 sccm of the cyclo-borazane introduced. The resulting porous carbon / single-layer porous hexagonal boron nitride composite film was denoted as NPC / hBN-1050b membrane, and the surface structure of the membrane is shown in Fig. 7(a). It can be observed from the image that the surface of the hBN film formed has micron-sized random defects and discontinuous growth. This is because the insufficient supply of the precursor results in the failure to form a continuous film.

[0065] The NPC / hBN-1050b membrane was subjected to H2 / CH4 system separation, as shown in Figure 8 the average permeation rate of H2 was 3.22 x 10 -5 mol m -2 s -1 Pa -1 , the average selectivity of H2 / CH4 was 1.51; the average permeation flux of CO2 was 2.21 x 10 -5 mol m -2 s -1 Pa -1 , and the CO2 / N2 selectivity was 1.05.

[0066] Comparative Example 4:

[0067] A NPC / hBN-1050c film was prepared in the same manner as in Example 1, except that the flow rate of the precursor for CVD reaction growth of the single-layer porous hBN film in Step 2) was changed from 0.2 sccm to 2.0 sccm, and the resulting porous carbon / single-layer porous hexagonal boron nitride composite film was denoted as NPC / hBN-1050c film. The surface structure of the film is shown in Fig. 7(b), and it can be observed from the image that the formed hBN film is continuously grown, but irregular clusters are formed on the surface. This is due to the too high flow rate of the precursor, which causes the nucleation rate of the molecules to be too high.

[0068] The NPC / hBN-1050c film was separated in a H2 / CH4 system, and the results are shown in Table 1. Figure 8 At 150℃ and a raw gas pressure of 2 bar, the average permeation rate of H2 was 5.37 x 10 -5 mol m -2 s -1 Pa -1 , the average selectivity of H2 / CH4 was 2.31, the average permeation flux of CO2 was 4.22 x 10 -5 mol m -2 s -1 Pa -1 , and the CO2 / N2 selectivity was 1.93.

[0069] From the above Examples 1-4 and Comparative Examples 1-4, it can be concluded that according to the preparation method of the present application, by adjusting the growth temperature of the single-layer porous hexagonal boron nitride film and the flow rate of the precursor used for growth, the reaction kinetics in the CVD reaction process is adjusted, thereby affecting the growth and pore structure of the single-layer porous hexagonal boron nitride film. When the CVD reaction temperature is too low, such as the reaction temperature of 800℃ in Comparative Example 1, the hBN film formed has micron-sized irregular defects on the surface, and the growth is discontinuous, as shown in Fig. 6(a). This is because the CVD reaction temperature is too low, which causes the growth of porous hexagonal boron nitride to be slow, affecting the crystallinity of the boron nitride film growth, thereby generating a large number of defects, making it difficult to grow a continuous film, and thus affecting the molecular sieving ability of the gas, as shown in Table 1. Figure 8 When the temperature is too high, such as the reaction temperature of 1070℃ in Comparative Example 2, the hBN film formed has micron-sized irregular defects on the surface, and the growth is discontinuous, as shown in Fig. 6(c). Because the growth temperature is too high, the amount of precursor adsorption is reduced, and a continuous boron nitride film cannot be formed, thereby affecting the molecular sieving ability of the gas, as shown in Table 1. Figure 8As shown in Fig. 7(b). In the CVD reaction process, when the flow rate of the introduced precursor cycloborazane or ammonia borane is too high, such as the volume flow rate of the cycloborazane introduced in Comparative Example 4 is 2.0 sccm, the excessive raw material flow rate will form amorphous clusters during the growth process, as shown in Fig. 7(b). Although the formed hBN film is continuously grown, due to the excessive flow rate of the precursor, the nucleation rate of the molecules is too fast, resulting in the formation of irregular clusters on the surface. These clusters do not have molecular sieving properties, such as Figure 8 As shown in Fig. 7(a). In the CVD reaction process, when the flow rate of the introduced precursor cycloborazane or ammonia borane is too low, such as the volume flow rate of the cycloborazane introduced in Comparative Example 3 is 0.1 sccm, as shown in Fig. 7(a), due to the insufficient supply of the precursor, the formed surface has micron-sized irregular defects, the growth is discontinuous, and a continuous boron nitride film cannot be formed.

[0070] In the development process of the preparation method of the present application, through a large number of experiments and researches on adjusting the growth temperature, growth time and flow rate of the precursor, it is finally determined that the growth temperature is 900-1050℃, the growth time is 1h, and the volume flow rate of the introduced precursor is 0.2 sccm, so as to realize the regulation of the growth size and defect pores of the hexagonal boron nitride single crystal, and finally form a single-layer porous hexagonal boron nitride film on the surface of the single-crystal copper foil (111).

[0071] Although the present application has been described above with reference to the drawings, the present application is not limited to the specific embodiments described above, and the specific embodiments described above are only illustrative but not limiting. Those skilled in the art can make many modifications under the inspiration of the present application without departing from the spirit of the present application, can predict the penetration and selectivity of other gases in the boron nitride film, and can be used in the field of gas separation or other molecular separation. These all belong to the protection scope of the present application.

Claims

1. A porous carbon / single-layered porous hexagonal boron nitride composite film, characterized by, Single crystal copper foil (111) is used as substrate and placed in a chemical vapor deposition chamber with a pressure of 0.1-0.5 Torr, the temperature of the substrate is kept at 900-1050℃, cyclo-borazane or ammonia borane is used as precursor with a volume flow of 0.2 sccm, hydrogen is used as protective gas with a volume flow of 10-50 sccm, the reaction time is 1 hour, and a single-layer porous hexagonal boron nitride film is formed on the surface of the single crystal copper foil (111) substrate after the reaction; the film has a density of 1.4×10 12 -2×10 12 pores / cm 2 , and the triangular nanopores have a pore size determined by the number of missing nitrogen and boron atoms at the position during the reaction, wherein 95%-98% of the triangular nanopores have 2-5 missing atoms; a porous carbon layer with a thickness of 100 nm±25 nm and a pore size of 20-40 nm is formed on the surface of the film by spin coating and pyrolysis, and the copper foil is removed to obtain the product.

2. The method for producing a porous carbon / single-layered porous hexagonal boron nitride composite film according to claim 1, characterized by, The method comprises the following steps: 1) annealing a copper foil in argon-hydrogen mixed gas to obtain a single crystal copper foil (111); 2) treating the single crystal copper foil (111) obtained in step 1) in hydrogen gas at 900-1050 ℃ for 10 min, then introducing cyclo-borazane or ammonia borane with a volume flow rate of 0.2 sccm to grow a hexagonal boron nitride film on the surface of the single crystal copper foil (111), thereby obtaining a hexagonal boron nitride / copper composite film, denoted as hBN / Cu film; 3) spin-coating and pyrolyzing the hBN / Cu film to form a porous carbon layer with a thickness of 100 nm±25 nm as a protective layer, thereby obtaining a porous carbon / hexagonal boron nitride / copper composite film, denoted as NPC / hBN / Cu film; 4) removing the copper foil from the NPC / hBN / Cu film obtained in step 3) and rinsing it clean, and then transferring it to a porous tungsten substrate to obtain a suspended porous carbon / hexagonal boron nitride composite film, denoted as NPC / hBN film.

3. The production method according to claim 2, wherein In step 2), the following steps are included: 2-1) placing a quartz boat in a tube furnace of a CVD reactor, and using hydrogen-argon mixed gas to keep the temperature at 1000 ℃ for 6 h and then cool to room temperature; cleaning the single crystal copper foil (111) obtained in step 1) with isopropanol, and then drying and loading it into the quartz boat; 2-2) under the hydrogen carrier gas with a volume flow rate of 10-50 sccm, heating the tube furnace to 900-1050 ℃, and after 10 min, introducing cyclo-borazane or ammonia borane with a volume flow rate of 0.2 sccm into the CVD reactor, controlling the total pressure to be 0.1-0.5 Torr, and the reaction time to be 1 h; during the reaction, porous hexagonal boron nitride films are grown on both sides of the single crystal copper foil (111); after the reaction, the cyclo-borazane or ammonia borane gas flow is turned off, and the tube furnace program is terminated; the product is cooled to room temperature with the furnace, thereby obtaining the hBN / Cu film.

4. The production method according to claim 3, wherein The process of cleaning and drying the single crystal copper foil (111) is as follows: placing the single crystal copper foil (111) into an isopropanol solution, cleaning it with an ultrasonic cleaning machine for 5-10 min at an ultrasonic power of 40 W, and then blowing the cleaned single crystal copper foil (111) with a nitrogen gun.

5. The production method according to claim 2, wherein The step 3) comprises the following steps: 3-1) weighing polystyrene-poly-4-vinylpyridine and furanose according to a mass ratio of 1:2, using N,N-dimethylformamide as a solvent to prepare a solution with a polystyrene-poly-4-vinylpyridine mass fraction of 4.35%, and heating the solution to 180 ℃ in an autoclave to obtain a spin-coating solution; 3-2) The hBN / Cu film prepared in step 2) was attached to a glass sheet with the front side facing upward, and the spin coating solution prepared in step 3-1) was placed on the front side of the hBN / Cu film, and spin coating was performed twice, each time with an amount of 100 μL / cm 2 of the spin coating solution, and in the spin coating process, first spin coating was performed at 1000 rpm for 30 s, and then spin coating was performed at 1500 rpm for 30 s; 3-3) pyrolyzing the sample after spin-coating in step 3-2) in argon-hydrogen mixed gas at 500 ℃ for 1 h to form the porous carbon layer with a thickness of 100 nm±25 nm, thereby obtaining the NPC / hBN / Cu film.

6. Use of the porous carbon / single-layered porous hexagonal boron nitride composite film prepared according to the production method of any one of claims 2 to 5, characterized by, The composite membrane is used for separating CO2 in a CO2 / N2 mixed gas system, and the average permeation flux of CO2 is 1×10 -6 ~3.8×10 -6 mol·m -2 ·s -1 ·Pa -1 at 30-250℃ and under a raw gas pressure of 1-3bar, and the average selectivity of CO2 / N2 is 14.

4.

7. Use of the porous carbon / single-layered porous hexagonal boron nitride composite film prepared according to the production method of any one of claims 2 to 5, characterized in that, The composite membrane is used for separating H2 in H2 / CH4 mixed gas system, and the average permeation rate of H2 is 2.2×10 -5 ~ 6.8×10 -6 mol·m -2 ·s -1 ·Pa -1 at 30~250℃ and under the conditions of 1~3bar of raw gas pressure, and the average selectivity of H2 / CH4 is 7~21.9.

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