CN114225717B - Boron nitride film and preparation method and application thereof - Google Patents

Boron nitride film and preparation method and application thereof Download PDF

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CN114225717B
CN114225717B CN202111560755.3A CN202111560755A CN114225717B CN 114225717 B CN114225717 B CN 114225717B CN 202111560755 A CN202111560755 A CN 202111560755A CN 114225717 B CN114225717 B CN 114225717B
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boron nitride
water
porous
filter membrane
temperature
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CN114225717A (en
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殷红
高金铃
陈乐�
高伟
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Jilin University
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0079—Manufacture of membranes comprising organic and inorganic components
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
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    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
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    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
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    • C04B35/62227—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products obtaining fibres
    • C04B35/62272—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products obtaining fibres based on non-oxide ceramics
    • C04B35/62286—Fibres based on nitrides
    • C04B35/6229—Fibres based on nitrides based on boron nitride
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    • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

Abstract

The invention provides a boron nitride film and a preparation method and application thereof, relating to the technical field of filter membranes. The preparation method comprises the following steps: 1) Dissolving boric acid and melamine in water, stirring, and heating until the water is completely evaporated to obtain a precursor; 2) Drying the precursor, heating under the action of ammonia-containing mixed atmosphere in combination with a program, carrying out sintering reaction, and naturally cooling to room temperature to obtain porous boron nitride fibers; 3) And mixing the porous boron nitride fiber with water to obtain a suspension, and dispersing the suspension on a filter membrane substrate to obtain the boron nitride film. The porous boron nitride film obtained by the invention is mainly used in the treatment of separation, filtration and the like, and the porous boron nitride nanofiber prepared in the process is super-hydrophilic and provides a large number of adsorption active sites, so that the filter film has the rapid and efficient molecular separation capability under the condition of no additional pressure drive. In addition, the obtained boron nitride 3D film has thermal and chemical stability, can work under extreme conditions and can realize simple regeneration.

Description

Boron nitride film and preparation method and application thereof
Technical Field
The invention belongs to the technical field of filter membranes, and particularly relates to a boron nitride film and a preparation method and application thereof.
Background
With the continuous development of human society, the ecological environment in the global scope is increasingly worsened. Wherein the problem of water pollution becomes an important restriction factor for the sustainable development of human economy. The water resource crisis has become a common problem for all people, and all countries in the world are focusing on the rational utilization of water resources and the research of water pollution treatment technology. Unlike traditional water purifying methods, such as distillation, extraction, evaporation, adsorption, etc., membrane separation technology has become an important technology for solving the problem of sewage treatment due to its advantages of simple operation, economy, environmental friendliness, high safety, etc.
In recent years, a series of filter membrane preparation materials have been developed successively. Such as graphite and graphene oxide, transition metal dichalcogenides, zeolites, microporous silica, nitrides, and the like. For example, yang et al prepared an ultrathin graphene membrane with randomly distributed pinholes, interconnected by short channels, improved the permeability of the membrane to organic solvents, and the removal rate of small molecular weight organic dyes in methanol reached 99.9% [ Nat Mater,2017,16,1198-1202]. Li et al found that a few-layer molybdenum disulfide filtration membrane has a high-efficiency seawater desalination function due to a small diffusion length in molecular transport [ Nano Lett,2019,19,5194-5204]. Although the prior filter membrane achieves better separation performance, the prior filter membrane also has the following problems such as poor penetration to partial solvent; most films are degraded, have material failure and pollution under severe environments such as high temperature, acid and alkaline media, and are not beneficial to long-term use.
The boron nitride nanosheet, as one of the representatives of two-dimensional materials, has excellent performances of wide band gap (about 6 ev), high mechanical strength, good thermal stability (1500 ℃ in air), corrosion resistance and the like, and is an ideal separation membrane material. However, the inherent super-hydrophobic property of boron nitride makes the boron nitride not easy to disperse in aqueous solution, the filter membrane is not easy to prepare, and the existing boron nitride ultrafiltration membrane needs pressure driving, has energy loss and has poor effect of molecular separation in organic solvent. Therefore, how to design a boron nitride filter membrane which is stable in dispersion in aqueous solution, easy to prepare, and has high permeability and high selectivity is the key of practical application.
Disclosure of Invention
The invention provides a boron nitride film, a preparation method thereof and a filter membrane obtained by applying the boron nitride film, which does not need to be driven by extra energy, is environment-friendly, stable and efficient, is easy to prepare and regenerate, and can be used under extreme conditions.
The invention provides a preparation method of a boron nitride film, which comprises the following steps:
1) Dissolving boric acid and melamine in water, stirring, and heating until the water is completely evaporated to obtain a precursor;
2) Drying the precursor, combining with temperature programming under the action of ammonia-containing mixed atmosphere, carrying out sintering reaction, and naturally cooling to room temperature to obtain porous boron nitride fibers;
3) And mixing the porous boron nitride fiber with water to obtain a suspension, and dispersing the suspension on a filter membrane substrate to obtain the boron nitride film.
Further, in the step 1), the molar ratio of the boric acid to the melamine is 1; the total concentration of the boric acid and the melamine in the water is 30-50 g/L.
Further, in the step 1), the temperature of the water is 60-70 ℃; the temperature rise is specifically to 90-95 ℃.
Further, in the step 2), the drying temperature is 80-100 ℃; the drying time is 12 to 18 hours.
Further, in the step 2), under the action of the mixed atmosphere containing ammonia gas, the sintering reaction is carried out by combining with temperature programming, specifically: only introducing inert gas, heating to 800-1200 ℃ at 3-10 ℃/min, maintaining the constant temperature, introducing ammonia gas, stopping introducing ammonia gas after sintering reaction for 4-6 hours, only introducing inert gas, cooling to 200 ℃ at 3-10 ℃/min, and stopping introducing gas.
Further, in the step 2), introducing inert gas at a flow rate of 100-200sccm; the flow rate of the introduced ammonia gas was 50sccm.
Further, in the step 2), the length of the porous boron nitride fiber is 0.6-16 μm.
Further, in the step 3), the concentration of the porous boron nitride fiber in water is 40-200 mg/L;
in the step 3), the filter membrane substrate is a polytetrafluoroethylene filter membrane, polyether sulfone, mixed fiber resin, organic nylon or polyvinylidene fluoride.
The invention also provides the boron nitride film prepared by any one of the preparation methods.
The invention also provides the application of the boron nitride film in filtration and separation.
The invention has the following advantages:
according to the invention, boric acid and melamine are used as precursors, and sintering reaction is carried out under the mixed atmosphere containing ammonia gas and inert gas by combining with the programmed temperature rise condition to obtain the porous boron nitride fiber modified by hydroxyl and amino, so that the porous boron nitride fiber has hydrophilicity, and then the porous boron nitride fiber is mixed with aqueous solution to obtain stable suspension which is dispersed on the base of a filter membrane to obtain the boron nitride 3D film. The porous boron nitride fiber prepared by the invention is different from a nanosheet in appearance, the porous boron nitride fiber modified by hydroxyl and amino can be stacked to form a 3D structure, a molecular transmission path is increased, and the porous characteristic of the porous boron nitride fiber can provide an extra open edge for functional groups to form bonds, so that the boron nitride has super-hydrophilicity and provides a large number of adsorption active sites, and the filter membrane has quick and efficient molecular separation capability under the condition of no extra pressure drive, thereby saving energy and protecting the environment. In addition, the obtained boron nitride 3D film has thermal and chemical stability, can work under extreme conditions and can realize simple regeneration.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1-1 is a scanning electron micrograph of a boron nitride fiber obtained in example 1 of the present invention;
FIGS. 1-2 are TEM photographs of boron nitride fibers obtained in example 1 of the present invention;
FIG. 2-1 is a scanning electron micrograph of a boron nitride fiber obtained in example 2 of the present invention;
FIG. 2-2 is a fiber length distribution diagram of boron nitride fibers produced in example 2 of the present invention;
FIG. 3 is a photograph showing the Tyndall effect test of a boron nitride fiber suspension prepared in example 1 of the present invention;
FIG. 4 is a structural diagram of a home-made simple filtration apparatus in example 2 of the present invention;
FIG. 5 is a photograph of a boron nitride fiber filter membrane prepared in example 2 of the present invention;
FIG. 6 is a comparative graph of the solution before and after filtration in example 2 of the present invention;
FIG. 7 is a photograph showing the comparison between the filtration membrane of example 4 of the present invention and 0.2M sulfuric acid and sodium hydroxide solution before and after soaking for one month.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The embodiments and features of the embodiments of the invention may be combined with each other without conflict.
An embodiment of the invention provides a preparation method of a boron nitride film, which comprises the following steps:
1) Dissolving boric acid and melamine in water, stirring, and heating until the water is completely evaporated to obtain a precursor;
2) Drying the precursor, combining with temperature programming under the action of ammonia-containing mixed atmosphere, carrying out sintering reaction, and naturally cooling to room temperature to obtain porous boron nitride fibers;
3) And mixing the porous boron nitride fibers with water to obtain a suspension, and dispersing the suspension on a filter membrane substrate to obtain the boron nitride film.
According to the preparation method of the boron nitride 3D film provided by the embodiment of the invention, boric acid and melamine are adopted to prepare a precursor, and after drying, sintering reaction is carried out under the mixed atmosphere containing ammonia gas and inert gas in combination with a programmed temperature rise condition, so that the porous boron nitride fiber modified by hydroxyl and amino is obtained. The gas participates in the sintering reaction, so that the obtained porous boron nitride fiber has large specific surface area and uniform pore size distribution, and meanwhile, the porous boron nitride fiber has super-hydrophilicity due to the modification of hydroxyl and amino. Then mixing with water to obtain stable suspension, dispersing the suspension in the filter membrane substrate, and then stacking to obtain the boron nitride film with the 3D structure.
The method is simple to operate, and the obtained membrane has outstanding filtering and separating effects. The porous boron nitride fiber obtained in the preparation process is different from a nanosheet in shape, has nanofiber channels, can be stacked to form a 3D structure by dispersing the porous boron nitride fiber into a film, increases a molecular transmission path, and can realize that small molecules are allowed to pass through and large molecules are intercepted for size screening. Meanwhile, due to the porous characteristic of the porous boron nitride fiber, an extra open edge can be provided for functional group bonding (hydroxyl, amino and the like), so that the boron nitride is super-hydrophilic, a large number of adsorption active sites are provided, and the filter membrane can have the rapid and efficient molecular separation capacity under the condition of no extra pressure drive, and is energy-saving and environment-friendly.
In addition, the obtained boron nitride 3D film has thermal and chemical stability, can work under extreme conditions (strong acid and strong alkali), can realize cyclic regeneration, and can still maintain high filtering performance after being recycled for more than 5 times.
In the step 1) of the embodiment of the invention, boric acid and melamine are used as raw materials, the boric acid and the melamine are dissolved in water, and then the water is evaporated to prepare the precursor.
Specifically, in step 1), the molar ratio of boric acid to melamine is 1.
In one embodiment of the invention, the total concentration of the boric acid and the melamine in the water is 30-50 g/L. Preferably, the total concentration of boric acid and melamine in water is 40g/L. It is to be noted that the total concentration of boric acid and melamine in water is the concentration of the sum of the masses of boric acid and melamine in water.
In one embodiment of the invention, the temperature of water is 60-70 ℃; preferably, the temperature of the water is 65 ℃. The water is deionized water.
In an embodiment of the invention, in the step 1), the temperature is maintained at the water temperature during stirring.
In an embodiment of the present invention, in the step 1), the temperature is specifically raised to 90 to 95 ℃.
In the step 2) of the embodiment of the invention, after the precursor is dried, high-temperature sintering is carried out under the condition of mixed atmosphere containing ammonia gas, the escaped gas is convenient to form a porous structure, and under the action of mixed atmosphere of ammonia gas and inert gas such as argon gas, the porous boron nitride fiber is modified with hydroxyl and amino, so that the inherent super-hydrophobic property of boron nitride is effectively improved, the boron nitride fiber has super-hydrophilicity, the solution can pass through the boron nitride fiber, and organic molecules can be effectively separated without driving force.
In an embodiment of the invention, in the step 2), the drying temperature is 80-100 ℃. Preferably, the temperature of the drying is 90 ℃. The drying time is 12 to 18 hours.
In an embodiment of the invention, in step 2), the drying is performed in a forced air drying oven.
In an embodiment of the present invention, in step 2), under the action of a mixed atmosphere containing ammonia gas, the sintering reaction is performed by combining with temperature programming, specifically: only introducing inert gas, heating to 800 ℃ at a speed of 3-10 ℃/min, maintaining the constant temperature, introducing ammonia gas, stopping introducing ammonia gas after sintering reaction for 4-6 hours, only introducing inert gas, cooling to 200 ℃ at a speed of 3-10 ℃/min, and stopping introducing gas.
Specifically, in the temperature programming process, the temperature raising rate may be 3 to 10 ℃/min, specifically 3 ℃/min, 4 ℃/min, 5 ℃/min, 6 ℃/min, 7 ℃/min, 8 ℃/min, 9 ℃/min, 10 ℃/min, and the like. The cooling rate can be 3-10 deg.C/min, specifically 3 deg.C/min, 4 deg.C/min, 5 deg.C/min, 6 deg.C/min, 7 deg.C/min, 8 deg.C/min, 9 deg.C/min, 10 deg.C/min, etc.
Specifically, after the temperature is programmed to 800-1200 ℃, the constant temperature is maintained, and the sintering reaction is carried out under the condition of introducing ammonia gas and argon gas. Specifically, the temperature programming may be performed to 800 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, or the like.
Specifically, after the sintering reaction is carried out for 4 to 6 hours, the reaction is almost completed, the introduction of ammonia gas is stopped, and the temperature is lowered only in the presence of an inert gas.
In an embodiment of the present invention, in the step 2), the flow rate of the inert gas is 100-200sccm. The flow rate of the introduced ammonia gas was 50sccm.
In an embodiment of the present invention, in the step 2), the porous boron nitride fiber is a white powdery porous boron nitride fiber. Wherein the length of the porous boron nitride fiber is 0.6-16 μm.
In an embodiment of the present invention, in the step 2), the inert gas includes at least one of argon and nitrogen.
It is noted that the room temperature is 0 to 30 ℃.
In the step 3) of the embodiment of the invention, the porous boron nitride fiber modified by hydroxyl and amino has super-hydrophilicity, can be mixed with water to obtain stable suspension, and lays a good foundation for subsequent film formation by suction filtration. In one embodiment of the invention, in the step 3), the concentration of the porous boron nitride fiber in water is 40-200 mg/L.
In an embodiment of the present invention, in the step 3), the dispersing is specifically performed by using a vacuum filtration method. The vacuum filtration method is a conventional membrane preparation method and can be referred to as the following references: chen, J.Wang, D.Liu, C.Yang, Y.Liu, R.S.Ruoff, W.Lei, functional born nitride membranes with an ultra solvent transport protocol for molecular separation, nat Commun,9 (2018) 1902 ]
In an embodiment of the present invention, in step 3), the filter membrane substrate is a polytetrafluoroethylene filter membrane, polyethersulfone, mixed fiber resin, organic nylon or polyvinylidene fluoride. The filter membrane substrate is a commercial filter membrane.
The embodiment of the invention also provides the boron nitride film prepared by any one of the preparation methods. The boron nitride film prepared by the embodiment of the invention is a filtering film with a 3D structure formed by tightly stacking porous boron nitride fibers, and has a high-efficiency filtering effect. In addition, the obtained boron nitride 3D film has extremely strong thermal and chemical stability, can work under extreme conditions and can realize simple regeneration. The boron nitride films with different thickness and size can be prepared by adjusting the content of the boron nitride fibers in the turbid liquid and controlling the film forming thickness. Specifically, the thickness of the boron nitride film is 20 to 50 μm; specifically, 20 μm, 30 μm, 40 μm and 50 μm can be mentioned.
An embodiment of the invention also provides any one of the boron nitride films and application thereof in filtration and separation. The boron nitride film obtained by the invention is used for filtering, separating and removing organic pollutants, and the filter film has the rapid and efficient molecular separation capability under the condition of no additional pressure drive, and is energy-saving and environment-friendly.
The present invention will be described in detail with reference to examples.
Example 1A preparation method of a boron nitride 3D film comprises the following steps:
(1) Boric acid and melamine are used as a boron source and a nitrogen source to prepare a precursor, 0.05mol of boric acid and 0.025mol of melamine are dissolved in 150ml of 65 ℃ deionized water by using a constant-temperature magnetic stirrer, and the temperature is raised to 90 ℃ until the water is completely evaporated (the whole process is stirred).
(2) Transferring the obtained precursor into an air-blast drying oven, drying for 12 hours at 90 ℃, then transferring into a tubular furnace, and carrying out sintering reaction under the action of mixed atmosphere containing ammonia gas by combining temperature programming, wherein the method specifically comprises the following steps: introducing argon only, heating to 800 ℃ at the speed of 5 ℃/min, maintaining the constant temperature, introducing ammonia gas simultaneously (namely introducing the argon gas and the ammonia gas simultaneously after heating to 800 ℃), stopping introducing the ammonia gas after sintering reaction for 4-6 hours, introducing the argon gas only at the speed of 5 ℃/min, cooling to 200 ℃, and stopping introducing the argon gas, wherein the flow of introducing the inert gas is 100-200sccm; introducing ammonia gas with the flow rate of 50sccm, and naturally cooling to room temperature to obtain the white powdery porous boron nitride fiber.
(3) Dispersing porous boron nitride fibers in deionized water to enable the concentration of the porous boron nitride fibers in the water to be 40-200 mg/L, stirring to form stable suspension, and performing suction filtration on the boron nitride to form boron nitride 3D films with the thicknesses of 20 micrometers, 30 micrometers, 40 micrometers and 50 micrometers on a commercial polytetrafluoroethylene filter membrane substrate by adopting vacuum filtration equipment.
Example 2Preparation method of boron nitride 3D film
The difference from example 1 is that in step (2), the sintering reaction was carried out by programming the temperature to 900 ℃.
Example 3Preparation method of boron nitride 3D film
The difference from example 1 is that in step (2), the rate of temperature rise and temperature decrease is 3 ℃/min.
Comparative example 1Preparation method of boron nitride 3D film
The difference from example 1 is that in step (2), only argon gas was introduced during temperature programming, and no ammonia gas was introduced. Because ammonia gas is not introduced in the sintering reaction process, and the existence of hydrophilic amino groups in the porous boron nitride fibers is not detected by adopting infrared spectroscopy, the porous boron nitride fibers cannot be mixed with water to form stable turbid liquid, and the preparation of the filter membrane cannot be carried out.
Test example 1Example 1 testing of the Properties of porous boron nitride fibers
FIG. 1-1 is a scanning electron micrograph of the porous boron nitride fiber obtained in example 1, showing that the average length of the porous boron nitride fiber is 1.7. + -. 1.1. Mu.m.
Fig. 1-2 are transmission electron micrographs of the porous boron nitride fiber obtained in example 1, which show that the uniform distribution of the porous structure in the boron nitride fiber increases the specific surface area of the material and provides more nanochannels for the molecules to pass through, so that the molecules can rapidly pass through without being driven by an external force.
The obtained porous boron nitride was stirred and dispersed in deionized water to form a stable suspension, and the degree of uniform dispersion was measured by the tyndall effect, and the result is shown in fig. 3. FIG. 3 is a photograph of a suspension of boron nitride fibers irradiated with laser light, from which a clear light path can be seen, i.e., the porous boron nitride fibers can be stably dispersed in deionized water without agglomeration and precipitation.
Test example 2 Example 2 Performance testing of porous boron nitride fibers
The test method was the same as in test example 1. The SEM image of the resulting material is shown in FIG. 2-1. The length size distribution of the corresponding porous boron nitride fibers is shown in fig. 2-2. The porous boron nitride fibers had an average length of 2.7 μm and a major length of less than 6.3. Mu.m.
Test example 3Performance testing of porous boron nitride fibers prepared in examples 1 and 3
The specific surface area and the average pore size distribution of examples 1 and 3 are shown in table 1.
TABLE 1
Specific surface area Pore volume Average pore diameter
Example 1 1437m 2 /g 1.083cm 3 /g 3.014nm
Example 3 1403m 2 /g 1.181cm 3 /g 3.366nm
From table 1, it can be seen that by comparing the specific surface area and the pore size distribution of the boron nitride fibers obtained in example 1 and example 3, the specific surface area of the obtained material is slightly smaller but the average pore size is relatively larger with a lower temperature increase rate.
Test example 1The boron nitride 3D film obtained in example 1 was examined for the effect of filtering rhodamine B organic dye and methylene blue organic dye, respectively
The boron nitride 3D film from example 1, after the filter membrane was stabilized, was carefully transferred to a filtration apparatus to test it against a home-made organic solution (containing rhodamine B (12 mg L) -1 ) An organic dye of (4); containing methylene blue (8 mg L) -1 ) Organic dyes of (ii) filtration performance. FIG. 4 is a self-made simple filtration apparatus, which is composed of three parts, the upper filter cup is a feed inlet, the lower filter cup with the same size is a filtered solution collection chamber, and the filter membrane is placed inPlacing the filter cups at the joint position and fixing the filter cups by using a duck bill clip.
And (3) under the atmospheric pressure at room temperature, the organic solution spontaneously flows to carry out molecular screening, and the collected filtered solution is subjected to ultraviolet-visible light absorption spectrum analysis on the content of organic molecules to determine the filtering effect.
FIG. 5 is a photograph of the filter to be tested, the working diameter of the filter used in this experiment being 4 cm. The inlet was filled with 40ml of the solution to be tested and the outlet collected the filtered solution.
FIG. 6 is a comparison graph of the solution before and after filtration, and the filtering effect of the boron nitride filter membrane with the thickness of 20 μm and 40 μm on the solution is as high as more than 99% through ultraviolet spectrum analysis. Namely, the filter membrane can effectively filter organic molecules with different types and sizes.
Test example 2Examination of the penetration Properties of the boron nitride 3D film obtained in example 1 into various organic solvents
The boron nitride 3D film prepared in example 1 and having a thickness of 20 μm was carefully transferred to a filtration apparatus after the membrane was stabilized to test its permeability to various solvents.
The experimental environment was room temperature and atmospheric pressure, the filtration equipment used was the same as the home-made simple filtration equipment in test example 1, and the solvents used in the home-made solution included methanol, ethanol, acetone, deionized water, rhodamine B solution, and methylene blue solution. After the solution is stably permeated, the solvent which passes through the filter membrane within 10 minutes is collected, the flux of the filter membrane to different solvents is obtained by calculation after the volume is measured, and the result is shown in table 2.
From table 2, it can be seen that the porous boron nitride fiber filter membrane showed good flux for all solutions. In particular acetone, the flux of the filter membrane to acetone reaches 868L m without additional pressure drive -2 h -1 . Due to the difference of the solvent viscosity, the corresponding flux of the high-viscosity solvent is reduced, and the flux of the filter membrane to water can reach 326L m on the premise of ensuring the interception effect to be more than 99 percent -2 h -1 . Namely, the filter membrane can realize high flux under normal pressure and efficiently filter different molecules.
TABLE 2 flux of 20 μm boron nitride filters for different solutions
Kind of solution Methanol Ethanol Acetone (II) Water (I) Methylene blue Rhodamine B
Flux (L m) -2 h -1 ) 745 223 868 326 400 362
Test example 3Examination of the filtration Performance of the boron nitride 3D film obtained in example 1 under extreme conditions
0.2M sulfuric acid and sodium hydroxide solutions were prepared, and the boron nitride 3D thin film prepared in example 1 and having a thickness of 20 μ M was immersed for one month. The soaked filter membrane was taken out, washed to neutral with deionized water, dried in a drying oven, and transferred to a filter apparatus for filtration performance test, and the results are shown in fig. 7.
FIG. 7 shows the signal level at 0.2MThe photos of the filter membrane before and after the filter membrane is soaked in the sulfuric acid and sodium hydroxide solution for one month are compared, and the photos show that the surface structure of the filter membrane has no obvious change. It was used in methylene blue (8 mg L) -1 ) The organic dye is subjected to filtration test to obtain a colorless transparent solution, and ultraviolet visible light absorption spectrum test shows that the retention and filtration of methylene blue molecules still reach more than 99%. I.e. the filter membrane can be stably present under extreme conditions (in strong acid and strong base environments) without losing its filtering performance on molecules.
Test example 4Examination of the reproducibility of the boron nitride 3D film obtained in example 1
The boron nitride filter membrane prepared in example 1 and having a thickness of 20 μm and a thickness of 50 μm was subjected to a regeneration performance test. Dissolving methylene blue dye in deionized water and ethanol solvent respectively, and testing the filtering performance and regeneration performance of 20-micron and 50-micron filter membranes respectively. 40ml of the solution was taken for each experiment and filtered. And repeatedly washing the filtered filter membrane with deionized water and alcohol for 4-5 times (by adopting vacuum filtration equipment), and filtering the washed filter membrane again for the solution to test the regeneration performance of the filter membrane. The results are shown in Table 3.
As can be seen from table 3, the molecular filtration efficiency was tested on methylene blue aqueous solution and methylene blue ethanol solution after 5 regenerations of the two thickness filters. The separation performance of the 20-micron filter membrane on methylene blue aqueous solution is still up to 82%, and the separation performance of the 50-micron filter membrane on methylene blue ethanol solution is up to 76%. Namely, the boron nitride filter membrane can be regenerated and recycled by a simple method.
TABLE 3 molecular separation efficiency of filter membranes after 5 regenerations on methylene blue aqueous solution and methylene blue ethanol solution
Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5
20μm 99％ 95％ 92％ 87％ 82％
50μm 96％ 84％ 87％ 83％ 76％
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A preparation method of a boron nitride film is characterized by comprising the following steps:
1) Dissolving boric acid and melamine in water, stirring, and heating until the water is completely evaporated to obtain a precursor;
2) Drying the precursor, combining with temperature programming under the action of ammonia-containing mixed atmosphere, carrying out sintering reaction, and naturally cooling to room temperature to obtain porous boron nitride fibers;
in the step 2), under the action of the mixed atmosphere containing ammonia gas, the sintering reaction is carried out by combining with temperature programming, specifically: only introducing inert gas, heating to 800-1200 ℃ at a speed of 3-10 ℃/min, maintaining the constant temperature, simultaneously introducing ammonia gas, after sintering reaction for 4-6 hours, stopping introducing ammonia gas, only introducing inert gas at a speed of 3-10 ℃/min, cooling to 200 ℃, and stopping introducing air;
3) And mixing the porous boron nitride fiber with water to obtain a suspension, and dispersing the suspension on a filter membrane substrate to obtain the boron nitride film.
2. The production method according to claim 1,
in the step 1), the molar ratio of the boric acid to the melamine is 1 to 2 to 1; the total concentration of the boric acid and the melamine in water is 30 to 50g/L.
3. The method according to claim 1,
in the step 1), the temperature of the water is 60 to 70 ℃; the temperature rise is specifically to 90-95 ℃.
4. The production method according to claim 1,
in the step 2), the drying temperature is 80-100 ℃; the drying time is 12 to 18 hours.
5. The production method according to claim 1,
in the step 2), introducing inert gas with the flow rate of 100-200sccm; the flow rate of ammonia gas was 50sccm.
6. The method according to claim 1,
in the step 2), the length of the porous boron nitride fiber is 0.6 to 16 mu m.
7. The production method according to claim 1,
in the step 3), the concentration of the porous boron nitride fiber in water is 40-200 mg/L;
in the step 3), the filter membrane substrate is a polytetrafluoroethylene filter membrane, polyether sulfone, mixed fiber resin, organic nylon or polyvinylidene fluoride.
8. A boron nitride film produced by the production method according to any one of claims 1 to 7.
9. Use of the boron nitride film of claim 8 in filtration and separation.
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