阅读说明：本技术 垂直取向石墨烯/纳米纤维复合膜材料及其制备方法和应用 (Vertical orientation graphene/nano-fiber composite membrane material and preparation method and application thereof ) 是由 曲良体 张盼盼 程虎虎 于 2019-11-11 设计创作，主要内容包括：本发明提供了垂直取向石墨烯/纳米纤维复合膜材料及其制备方法和应用。所述垂直取向石墨烯/纳米纤维复合膜材料包括：石墨烯,石墨烯具有垂直取向且阵列排布的通道；纳米纤维,纳米纤维穿梭于石墨烯和通道中。由此,该复合膜材料作为蒸馏介质时,可以有效的提高蒸馏效率,降低蒸馏能耗,缩短蒸馏时长；而且,纳米纤维的引入,可使得复合膜材料具有优异的机械性能,进而使其可被压缩、弯曲和拉伸,且保持其结构不被破坏,进而长期保持较高的蒸馏效率。(The invention provides a vertically-oriented graphene/nanofiber composite membrane material as well as a preparation method and application thereof. The vertically-oriented graphene/nanofiber composite membrane material comprises: the graphene is provided with vertically-oriented channels arranged in an array; and the nano fibers shuttle in the graphene and the channels. Therefore, when the composite membrane material is used as a distillation medium, the distillation efficiency can be effectively improved, the distillation energy consumption is reduced, and the distillation time is shortened; moreover, the introduction of the nano-fiber can enable the composite membrane material to have excellent mechanical properties, so that the composite membrane material can be compressed, bent and stretched, the structure of the composite membrane material is kept not to be damaged, and the high distillation efficiency is kept for a long time.)

1. A vertically-oriented graphene/nanofiber composite film material, comprising:

graphene having vertically oriented and arrayed channels;

a nanofiber shuttled between the graphene and the channel.

2. The composite film material of claim 1, wherein the channels have a width of 25 to 300 microns.

3. A method of preparing the vertically aligned graphene/nanofiber composite membrane material of claim 1 or 2, comprising:

mixing the graphene oxide dispersion liquid and the nanofiber dispersion liquid to obtain a mixed liquid;

placing the mixed solution into a preset container, and contacting the bottom of the preset container with a cold source to perform directional freezing in the direction from bottom to top to obtain a vertically-oriented graphene oxide/nanofiber composite membrane material;

freeze-drying the vertically oriented graphene oxide/nanofiber composite membrane material;

and carrying out reduction treatment on the vertically-oriented graphene oxide/nanofiber composite membrane material after freeze drying so as to obtain the vertically-oriented graphene/nanofiber composite membrane material.

4. The method according to claim 3, wherein the concentration of the graphene oxide dispersion is 1 to 10mgmL ^-1The concentration of the nanofiber dispersion liquid is 3-15 mg mL ^-1，

Optionally, the diameter of the nanofiber in the nanofiber dispersion liquid is 50-1000 nm;

optionally, the material of the nanofiber is selected from at least one of polyimide, polyacrylonitrile, cellulose acetate, chitosan, polyvinyl alcohol, polylactic acid, silicon dioxide, aluminum oxide, titanium dioxide, cuprous oxide, manganese oxide, cobaltosic oxide, vanadium pentoxide and zirconium oxide.

5. The method according to claim 4, wherein the mixed solution contains the graphene oxide dispersion liquid and the nanofiber dispersion liquid in a mass ratio of 1: (0.1-10).

6. The method of claim 3, wherein the temperature of the directional freezing is-196 ℃ to-50 ℃, and the time of the directional freezing is 10 to 30 minutes.

7. The method according to claim 3, wherein the temperature of the freeze drying is-54 ℃ to-48 ℃, and the time of the freeze drying is 36 to 72 hours.

8. The method according to claim 3, wherein the reduction treatment is selected from laser reduction, chemical reduction or thermal annealing reduction,

optionally, the conditions of the laser reduction are: the laser intensity is 0.5-15W, and the reduction time is 0.2-20 s;

optionally, the conditions of the chemical reduction are: the reducing agent is hydrazine hydrate, and the reducing time is 5-24 hours;

optionally, the conditions of the thermal annealing reduction are: the reduction is carried out in a protective atmosphere, the reduction temperature is 300-1000 ℃, and the reduction time is 2-6 hours.

9. A distillation medium, characterized in that at least a part is composed of the vertically aligned graphene/nanofiber composite membrane material according to claim 1 or 2.

10. A distillation apparatus comprising a distillation medium according to claim 9, said distillation medium being disposed on the surface of the liquid to be distilled.

Technical Field

The invention relates to the technical field of materials, in particular to a vertically-oriented graphene/nanofiber composite membrane material and a preparation method and application thereof.

Background

Distillation is a key technology for purifying and separating liquid from a mixture with different component boiling points in the chemical industry, and is widely applied to industries such as petroleum, chemical industry, light industry, food processing and the like. The conventional distillation process is a process in which a liquid is heated to boiling by a conventional heat source, and the resulting vapor escapes from the liquid/vapor interface and is directed to a condensing unit where it is cooled and re-condensed into a liquid for purification and separation. However, the traditional distillation is an energy-intensive and low-efficiency (energy conversion efficiency is only 5% -20%) chemical industrial liquid separation and purification process.

Therefore, the distillation process for effectively improving the distillation efficiency and reducing the energy consumption needs to be deeply researched.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, an object of the present invention is to provide a vertically aligned graphene/nanofiber composite membrane material, which can effectively improve distillation efficiency or reduce distillation energy consumption.

In one aspect of the present invention, the present invention provides a vertically aligned graphene/nanofiber composite film material (hereinafter may be referred to as a composite film material). According to an embodiment of the present invention, the vertically aligned graphene/nanofiber composite film material includes: graphene having vertically oriented and arrayed channels; a nanofiber shuttled between the graphene and the channel. From this, when this composite film material was as distillation medium, can effectual improvement distillation efficiency, reduce the distillation energy consumption, it is long, specific to shorten the distillation: the composite membrane material can be arranged on the surface of a liquid to be distilled to serve as a distillation medium, on one hand, the composite membrane material has a vertically-oriented channel structure, liquid is transmitted along the inner wall of the channel in the composite membrane material during distillation, and the channel cannot be filled with the liquid, so that the distillation area of the solution is increased (namely the contact area of the liquid and the composite membrane material is larger), and the distillation rate of the solution is increased; on the other hand, the acting force of the solution molecules on the surface of the composite membrane material is weakened, the evaporation enthalpy of the solution molecules is reduced, the evaporation of the solution on the surface of the composite membrane material can be accelerated, and the energy required by distillation is reduced, so that the effect of interface enhanced distillation is realized, the distillation efficiency is effectively improved, the distillation energy consumption is reduced, and the distillation time is shortened. In addition, the introduction of the nano-fiber can enable the composite membrane material to have excellent mechanical properties, so that the composite membrane material can be compressed, bent and stretched, the structure of the composite membrane material is kept not to be damaged, and the high distillation efficiency is kept for a long time.

According to the embodiment of the invention, the width of the channel is 25-300 microns.

In another aspect of the present invention, the present invention provides a method of preparing a vertically aligned graphene/nanofiber composite membrane material. According to an embodiment of the invention, the method comprises: mixing the graphene oxide dispersion liquid and the nanofiber dispersion liquid to obtain a mixed liquid; placing the mixed solution into a preset container, and contacting the bottom of the preset container with a cold source to perform directional freezing in the direction from bottom to top to obtain a vertically oriented graphene oxide/nano-fiber composite membrane material; freeze-drying the vertically oriented graphene oxide/nanofiber composite membrane material; and carrying out reduction treatment on the vertically-oriented graphene oxide/nanofiber composite membrane material after freeze drying so as to obtain a vertically-oriented graphene/nanofiber composite membrane material. Therefore, the graphene structure with vertical orientation can be obtained through the directional freezing treatment, so that when the composite membrane material is used as a distillation medium, the distillation efficiency can be effectively improved, the distillation energy consumption is reduced, and the distillation time is shortened; in addition, the preparation method is simple and easy to operate, has mature process and is easy for industrial production.

According to the embodiment of the invention, the concentration of the graphene oxide dispersion liquid is 1-10 mg mL ^-1The concentration of the nanofiber dispersion liquid is 3-15 mg mL ^-1Optionally, the diameter of the nanofiber in the nanofiber dispersion liquid is 50-1000 nm; optionally, the material of the nanofiber is selected from at least one of polyimide, polyacrylonitrile, cellulose acetate, chitosan, polyvinyl alcohol, polylactic acid, silicon dioxide, aluminum oxide, titanium dioxide, cuprous oxide, manganese oxide, cobaltosic oxide, vanadium pentoxide and zirconium oxide.

According to an embodiment of the present invention, in the mixed solution, a mass ratio of the graphene oxide dispersion liquid to the nanofiber dispersion liquid is 1: (0.1-10).

According to the embodiment of the invention, the temperature of the directional freezing is-196 ℃ to-50 ℃, and the time of the directional freezing is 10-30 minutes.

According to the embodiment of the invention, the temperature of the freeze drying is-54 ℃ to-48 ℃, and the time of the freeze drying is 36-72 hours.

According to an embodiment of the invention, the reduction treatment is selected from laser reduction, chemical reduction or thermal annealing reduction, optionally under the conditions of: the laser intensity is 0.5-15W, and the reduction time is 0.2-20 s; optionally, the conditions of the chemical reduction are: the reducing agent is hydrazine hydrate, and the reducing time is 5-24 hours; optionally, the conditions of the thermal annealing reduction are: the reduction is carried out in a protective atmosphere, the reduction temperature is 300-1000 ℃, and the reduction time is 2-6 hours.

In yet another aspect of the invention, the invention provides a distillation medium. According to an embodiment of the present invention, at least a portion of the distillation medium is composed of the vertically aligned graphene/nanofiber composite membrane material as described above. Therefore, the distillation medium can effectively improve the distillation efficiency, reduce the distillation energy consumption, shorten the distillation time and realize the effect of interface enhanced distillation. It will be understood by those skilled in the art that the distillation medium has all the features and advantages of the vertically oriented graphene/nanofiber composite membrane material and the preparation method thereof, and will not be described in detail herein.

In yet another aspect of the present invention, a distillation apparatus is provided. According to an embodiment of the invention, the distillation apparatus comprises a distillation medium as described above, which is arranged on the surface of the liquid to be distilled. Therefore, the distillation device can effectively improve the distillation efficiency, reduce the distillation energy consumption and shorten the distillation time. It will be understood by those skilled in the art that the distillation apparatus has all the features and advantages of the distillation medium described above and will not be described in any greater detail herein.

Drawings

Fig. 1 is a scanning electron microscope image of a vertically aligned graphene/nanofiber composite film material in one embodiment of the present invention.

Fig. 2 is a flow chart for preparing a vertically oriented graphene/nanofiber composite membrane material in another embodiment of the present invention.

FIG. 3 is a schematic view showing the structure of a distillation apparatus according to still another embodiment of the present invention.

FIG. 4 is a schematic view showing a partial structure of a distillation apparatus according to still another embodiment of the present invention.

Fig. 5 is an SEM image of silica nanofibers in example 1.

Fig. 6 is a graph of the compression performance of the vertically oriented graphene/nanofiber composite membrane material of example 1 at different degrees of compression.

Fig. 7 is a contact angle test chart of water on the surface of the vertically aligned graphene/nanofiber composite membrane material in example 1.

Fig. 8 is a photograph showing a mirror image of the state of water transport in the vertically oriented channels inside the vertically oriented graphene/nanofiber composite membrane material in example 1.

FIG. 9 is a graph of the thermal differential analysis of water in the conventional distillation and interface enhanced distillation process of example 1.

FIG. 10 is a graph showing the rectification rate of water from room temperature to boiling point in the conventional distillation and interface enhanced distillation processes in example 1.

Fig. 11 is a contact angle test chart of the surface of the ethanol vertically aligned graphene/nanofiber composite membrane material in example 2.

Fig. 12 is a photograph showing a mirror image of the transport state of ethanol in the vertically oriented channels inside the vertically oriented graphene/nanofiber composite membrane material in example 2.

FIG. 13 is a graph of thermal differential analysis of ethanol in the conventional distillation and interface enhanced distillation processes of example 2.

FIG. 14 is a graph of the rectification rate of ethanol from room temperature to boiling point in conventional distillation and interface enhanced distillation processes in example 2.

FIG. 15 is a graph showing the fractional distillation yields of water from water/N, N-dimethylformamide mixed solutions having different polarities using conventional distillation and interfacial enhanced distillation in example 3.

FIG. 16 is a graph showing the fractional distillation yield of N, N-dimethylformamide from a mixed solution of N, N-dimethylformamide/dimethylsulfoxide in example 4 using conventional distillation and interfacial enhanced distillation.

FIG. 17 is a graph of the yield of aniline purification from aniline solution with easy deterioration using conventional distillation and interfacial enhanced distillation in example 5.

Fig. 18 is an SEM image of the graphene/nanofiber composite membrane material having a honeycomb-shaped microstructure in comparative example 1.

Fig. 19 is a microphotograph of a state of water transport within a graphene/nanofiber composite membrane material having a honeycomb-shaped microstructure in comparative example 1.

Fig. 20 is a graph of compression cycle performance of the vertically oriented graphene film material of comparative example 2 at a 50% degree of compression.

Detailed Description

The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

In one aspect of the present invention, the present invention provides a vertically aligned graphene/nanofiber composite film material (hereinafter may be referred to as a composite film material). According to an embodiment of the present invention, referring to fig. 1, a vertically aligned graphene/nanofiber composite film material includes: graphene 10, the graphene 10 having vertically oriented and arrayed channels 30; nanofibers 20, the nanofibers 20 shuttling in the graphene 10 and channels 30. From this, when this composite film material was as distillation medium, can effectual improvement distillation efficiency, reduce the distillation energy consumption, it is long, specific to shorten the distillation: the composite membrane material can be arranged on the surface of a liquid to be distilled to serve as a distillation medium, on one hand, the composite membrane material has a vertically-oriented channel structure, liquid is transmitted along the inner wall of the channel in the composite membrane material during distillation, and the channel cannot be filled with the liquid, so that the distillation area of the solution is increased (namely the contact area of the liquid and the composite membrane material is larger), and the distillation rate of the solution is increased; on the other hand, liquid, solid and gaseous three phases coexist in the composite membrane material, the acting force of solution molecules is weakened, the evaporation enthalpy of the solution molecules is reduced, the evaporation of the solution on the surface of the composite membrane material can be accelerated, and the energy required by distillation is reduced, so that the effect of interface enhanced distillation is realized, the distillation efficiency is effectively improved (namely the evaporation rate of the distillate is improved), the distillation energy consumption is reduced, and the distillation time is shortened. In addition, the introduction and shuttling dispersion of the nano fibers in the graphene can enable the composite membrane material to have excellent mechanical properties, so that the composite membrane material can be compressed, bent and stretched, the structure of the composite membrane material is kept from being damaged, and higher distillation efficiency is kept for a long time.

The graphene has vertically oriented and arrayed channels, which means that graphene sheets in the graphene are vertically oriented and arranged, and vertically ordered channels with a certain distance are formed between the graphene sheets, that is, the channels are also vertically oriented; the "channel inner wall" refers to a graphene sheet.

According to an embodiment of the invention, the width of the channels (i.e. the channel pitch in fig. 1) is 25-300 micrometers, such as 25 micrometers, 30 micrometers, 50 micrometers, 80 micrometers, 100 micrometers, 120 micrometers, 125 micrometers, 140 micrometers, 150 micrometers, 180 micrometers, 195 micrometers, 200 micrometers, 220 micrometers, 240 micrometers, 260 micrometers, 280 micrometers or 300 micrometers. Therefore, the width of the channel is in the range, the distillation efficiency of the composite membrane material as a distillation medium is high, the speed is high, and the structural stability of the composite membrane material is good; if the width of the channel is less than 25 micrometers, the channel is relatively easily filled when liquid is transmitted in the composite membrane material, so that the distillation efficiency is reduced; if the width of the channel is greater than 300 μm, the distillation rate is relatively reduced.

The widths of the channels in the vertically-oriented graphene/nanofiber composite membrane material may be uniform or different, as long as the widths of the channels are distributed in a range of 25 to 300 micrometers.

According to the embodiment of the invention, the sheet diameter, the thickness and the like of the graphene have no special requirements, and a person skilled in the art can flexibly select the graphene according to the actual situation, and the requirements are not limited herein.

According to the embodiment of the invention, the specific material of the nanofiber can be at least one selected from polyimide, polyacrylonitrile, cellulose acetate, chitosan, polyvinyl alcohol, polylactic acid, silicon dioxide, aluminum oxide, titanium dioxide, cuprous oxide, manganese oxide, cobaltosic oxide, vanadium pentoxide and zirconium oxide, the material has excellent mechanical properties, the mechanical properties of the composite membrane material can be effectively improved, and the preparation process of the nanofiber of the material is simple and mature.

According to an embodiment of the present invention, the diameter of the nanofibers is 50-1000 nm, such as 50nm, 100 nm, 150 nm, 200nm, 250 nm, 300 nm, 350nm, 400 nm, 450nm, 500 nm, 550 nm, 600nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm. Therefore, the nanofiber with the diameter is good in mechanical property, and the mechanical property of the composite membrane material can be effectively improved.

According to the embodiment of the invention, when the composite membrane material is used as a distillation medium, the composite membrane material is arranged on the surface of a liquid to be distilled, and compared with the traditional distillation process without the distillation medium, the distillation rate of the distillation process using the composite membrane material as the distillation medium is 180-300% higher than that of the traditional distillation process within the temperature range from room temperature to the boiling point of the solution; fractions with the same quality are collected, the energy required by the distillation process is reduced, and the energy conversion efficiency is improved; in the distillation process, for different liquid feeding, the energy-saving efficiency is about 4-60%, and the time is saved by about 45-70%; the evaporation enthalpy of different liquids can be reduced by 107-129%.

According to the embodiment of the present invention, when the composite membrane material is used as a distillation medium for distillation, there is no particular limitation on the solvent to be distilled, and examples of the solvent to be distilled include common solvents such as alkanes, alcohols, lipids, ketones, amines, phenols, and benzenes: in some embodiments, it may be useful to distill liquid mixtures of different polarity (which may be liquid mixtures of different boiling points), such as ethanol/water, water/N, N-dimethylformamide, 1, 4-dioxane/chlorobenzene; in other embodiments, it may be used to distill high boiling point mixtures such as N, N-dimethylformamide/dimethylsulfoxide, dimethylsulfoxide/N-methylpyrrolidone, ethylene glycol/N-methylpyrrolidone, and the like; in still other embodiments, it may be used for distillative purification of high temperature perishable solutions such as aniline, ethyl acetoacetate, ethyl benzoate, and the like.

In some embodiments, when the composite membrane material is used as a distillation medium to distill mixed solutions with different polarities and different boiling points, compared with the traditional distillation, the distillation rate is improved by 187-284%, the purity of the collected fraction is 93.0-99.5%, the energy-saving efficiency is about 40.6-51.6%, the time-saving efficiency is about 45.9-59.8%, and the emission of greenhouse gases and pollution gases is reduced.

In other embodiments, when the composite membrane material is used as a distillation medium to distill a high-boiling-point mixed solution, a fraction with higher purity can be collected at a temperature lower than the boiling point, compared with the conventional distillation, the distillation temperature can be reduced by 11 ℃ to 39 ℃, compared with the conventional distillation (the fraction collection temperature of the conventional distillation process is the boiling point of the fraction), the fraction can be collected at the temperature lower than the boiling point by the distillation process using the composite membrane material as the distillation medium within the same time, the purity of the collected fraction is 98.0% to 99.8%, and the energy-saving efficiency is 10.9% to 30.8%.

In still other embodiments, when the composite film material is used as a distillation medium to purify a high-temperature perishable solution, a fraction with higher purity can be collected at a temperature lower than the boiling point, compared with the conventional distillation, the distillation temperature of the distillation process using the composite film material as the distillation medium can be reduced by 5 ℃ to 47 ℃, compared with the conventional distillation (the fraction collection temperature is at the boiling point), the distillation process can collect the fraction at a temperature lower than the boiling point, the collected fraction purity is 98.0% to 99.8%, and the energy-saving efficiency is 4.8% to 42.5%.

In another aspect of the present invention, the present invention provides a method of preparing a vertically aligned graphene/nanofiber composite membrane material. According to an embodiment of the present invention, referring to fig. 2, a method of preparing a vertically-aligned graphene/nanofiber composite membrane material includes:

s100: and mixing the graphene oxide dispersion liquid and the nanofiber dispersion liquid to obtain a mixed liquid.

According to the embodiment of the invention, the mass ratio of the graphene oxide dispersion liquid to the nanofiber dispersion liquid in the mixed liquid is 1 (0.1-10), such as 1:0.1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, and 1: 10. Therefore, the distillation membrane material of the vertically-oriented graphene/nanofiber composite membrane material can be effectively prepared, the good vertically-oriented structure of graphene can be guaranteed, the mechanical property of the membrane material can be compounded by adding the nanofibers in the proportion into the graphene oxide solution, the composite membrane material can be bent, stretched and compressed, the composite membrane material is not easily damaged in the distillation process, and the stability of the structure and the performance can be kept in various solutions (such as common solvents of alkanes, alcohols, lipids, ketones, amines, phenols, benzenes and the like).

According to the embodiment of the invention, the concentration of the graphene oxide dispersion liquid (namely the concentration of the graphene oxide in the graphene oxide dispersion liquid) is 1-10 mg mL ^-1E.g. 1mg mL ^-1、2mg mL ^-1、3mg mL ^-1、4mg mL ^-1、5mg mL ^-1、6mgmL ^-1、7mg mL ^-1、8mg mL ^-1、9mg mL ^-1、10mg mL ^-1. Therefore, the dispersion effect of the graphene oxide is good, and the accumulation of the graphene oxide can be effectively avoided; if the concentration of the graphene oxide dispersion liquid is more than 10mg mL ^-1Partial graphene oxide accumulation may be caused, and the performance of the finally obtained vertically-oriented graphene/nanofiber composite membrane material is affected.

Wherein, the specific method for preparing the graphene oxide dispersion liquid has no special requirements, and the skilled person canSo as to be flexibly selected according to actual conditions. In some embodiments, the graphene oxide dispersion is prepared using a Hummers method, comprising the steps of: putting 240mL of concentrated sulfuric acid (98 wt%) in a 2000mL beaker in an ice-water bath, respectively adding 9g of graphite powder and 9g of sodium nitrate during stirring, continuing stirring for 2 hours, then adding 24g of potassium permanganate, then placing the beaker in a water bath kettle at 36 ℃ and stirring for 1.5h to form viscous slurry, then adding 400mL of deionized water into the beaker, stirring for 20min, then raising the temperature to 85 ℃ and continuing stirring for 30min, finally adding 1000mL of deionized water, cooling to room temperature and slowly adding 60mL of hydrogen peroxide (30 wt%), wherein the solution is changed from dark brown to golden yellow, carrying out suction filtration on the solution, firstly washing by using a mixed solution of 200mL of hydrochloric acid (37 wt%) and 200mL of water, then washing by using a mixed solution of 100mL of hydrochloric acid and 900mL of water, and finally washing by using deionized water until the color of a precipitate on the filter paper is changed into black; the black product was then redispersed in 600mL of deionized water and incubated at 4000rpm min ^-1Maintaining the rotation speed of the reactor for 30min, removing visible impurities at the lower layer, and then maintaining the upper layer product at 10000rpm min ^-1Maintaining the rotating speed for 30min, and removing supernatant; finally, putting the obtained graphene oxide solution into a dialysis bag for dialysis for about four weeks until the pH value of the solution is 7 to obtain the high-concentration 15-20 mgmL ^-1The graphene oxide dispersion liquid of (a); finally, diluting with water and performing ultrasonic dispersion to obtain the product with the concentration of 1-10 mgmL ^-1The graphene oxide dispersion liquid of (1).

According to the embodiment of the present invention, the concentration of the nanofiber dispersion (i.e., the concentration of the nanofibers in the nanofiber dispersion) is 3 to 15mg mL ^-1E.g. 3mg mL ^-1、4mg mL ^-1、5mg mL ^-1、6mg mL ^-1、7mg mL ^-1、8mg mL ^-1、9mg mL ^-1、10mg mL ^-1、11mg mL ^-1、12mg mL ^-1、13mg mL ^-1、14mg mL ^-1、15mg mL ^-1. Therefore, the mechanical property of the prepared vertically-oriented graphene/nanofiber composite membrane material can be effectively improved; if the concentration of the nanofiber dispersion is more than 15mg mL ^-1Then nanofibers may appearThe phenomena of dispersion unevenness and accumulation further affect the mechanical properties of the vertically oriented graphene/nanofiber composite membrane material.

According to an embodiment of the present invention, the diameter of the nanofibers in the nanofiber dispersion is 50-1000 nm, such as 50nm, 100 nm, 200nm, 300 nm, 400 nm, 500 nm, 600nm, 700 nm, 800 nm, 900 nm, 1000 nm. The nano-fiber with the diameter is convenient to prepare, and the mechanical property of the composite membrane material can be better improved.

According to an embodiment of the present invention, the material of the nanofibers is selected from at least one of polyimide, polyacrylonitrile, cellulose acetate, chitosan, polyvinyl alcohol, polylactic acid, silica, alumina, titania, cuprous oxide, manganous oxide, cobaltous oxide, vanadium pentoxide, and zirconia. Therefore, the material has excellent mechanical properties, the mechanical properties of the composite membrane material can be effectively improved, and the preparation process of the nano-fibers of the material is simple and mature.

According to the embodiment of the invention, the preparation method of the nano-fiber has no special requirements, and the skilled person can flexibly select the nano-fiber according to the actual situation. In some embodiments, the nanofibers can be produced by electrospinning, specifically, the production steps include: preparing electrostatic spinning precursor solution with certain viscosity and fluidity, wherein the mass concentration of the solution can be 16-25%. 5mL of solution is absorbed by using a needle tube and fixed in a clamping groove of an electrostatic spinning device, a roller covered by aluminum foil is used as a receiving device, the receiving distance between a needle head and the receiving device is adjusted, and electrostatic spinning is carried out by setting positive voltage at the needle head, negative voltage at the receiving device and feeding speed. Wherein, the inner diameter of the needle can be 0.16-3.0 mm, the positive voltage of the needle can be 10-25 kV, and the negative voltage of the receiver can be 2-5 kV, and the feeding speed can be 0.5-1.2 mm min ^-1The receiving distance can be 10-30 cm, and the electrostatic spinning film forming time can be 1-12 h. After spinning is finished, collecting the nano-fibers on the aluminum foil, storing at room temperature to volatilize the residual solvent to obtain a nano-fiber precursor, and oxidizing or annealing and sintering the nano-fiber precursorAnd processing to obtain the nano-fiber.

And then, shearing the solid nanofiber membrane by using a refiner, and dispersing the solid nanofiber membrane in a solvent to prepare a nanofiber dispersion liquid, wherein the output power of the refiner is 130W, the no-load rotating speed is 8000-30000, the dispersion head is 1-250 mL, and the shearing dispersion time can be 20-80 min, so that the concentration of the nanofiber membrane is 3-15 mg mL ^-1A nanofiber dispersion.

S200: and placing the mixed solution into a preset container, and contacting the bottom of the preset container with a cold source to perform directional freezing from bottom to top in the direction to obtain the vertically oriented graphene oxide/nano-fiber composite membrane material with a large surface area. In the directional freezing process, the bottom of a preset container is in contact with a cold source, and cold air of the cold source gradually freezes the mixed solution from bottom to top, so that graphene oxide sheets in graphene oxide are vertically arranged in an oriented manner, and highly ordered channels are formed among the graphene oxide sheets; meanwhile, the nano fibers are shuttled and dispersed in the graphene and the channel, so that the strength of the composite membrane material can be improved, the surface area of the vertical orientation structure can be further increased, the evaporation area of the to-be-distilled liquid is increased, and the transmission and distillation speed of the to-be-distilled liquid is accelerated.

According to the embodiment of the invention, the temperature of the directional freezing is-196 ℃ to-50 ℃ (such as-196 ℃, 195 ℃, 190 ℃, 180 ℃, 170 ℃, 160 ℃, 150 ℃, 140 ℃, 130 ℃, 120 ℃, 110 ℃, 100 ℃, 90 ℃, 80 ℃, 70 ℃, 60 ℃ and 50 ℃), and the time of the directional freezing is 10 to 30 minutes (such as 10 minutes, 15 minutes, 20 minutes, 25 minutes and 30 minutes). Therefore, in the temperature range, the vertically-oriented graphene oxide/nanofiber composite membrane material can be quickly and effectively formed, and graphene oxide and nanofibers cannot be damaged; if the freezing temperature is lower than-195 ℃, the cost of a cold source is high, and the nanofiber and the graphene oxide can be damaged by freezing, so that the performance of the prepared composite membrane material is influenced; if the temperature is greater than-50 ℃, it is difficult to obtain a highly ordered vertically oriented structure.

According to the temperature requirement of the cold source, a person skilled in the art can flexibly select an appropriate cold source, in some embodiments, the cold source can be liquid nitrogen, and the bottom of a preset container filled with mixed liquid is contacted with the surface of the liquid nitrogen during directional freezing, so that the directional freezing from bottom to top is carried out.

According to the embodiment of the present invention, the specific material of the predetermined container is not particularly required, as long as the structure and performance can be maintained stable under the orientation condition, and the mixed solution does not undergo side reaction, for example, a polytetrafluoroethylene container, a glass container, and a container made of plastic such as polyethylene or polypropylene can be selected. The shape of the predetermined container is not particularly limited as long as it can satisfy the directional freezing of the mixed solution from the bottom up, and the predetermined container may be, for example, a container such as a test tube, a flask, a petri dish, or a conical flask.

S300: and (3) freeze-drying the vertically oriented graphene oxide/nanofiber composite membrane material. And removing the solvent in the vertically-oriented graphene oxide/nano-fiber composite membrane material by freeze drying.

According to the embodiment of the invention, the temperature of freeze drying is-54 ℃ to-48 ℃ (-54 ℃, 53 ℃, 52 ℃, 51 ℃, 50 ℃, 49 ℃ and 48 ℃), and the time of freeze drying is 36 to 72 hours (such as 36 hours, 40 hours, 45 hours, 50 hours, 55 hours, 60 hours, 65 hours and 70 hours). Under the conditions, the solvent in the vertically-oriented graphene oxide/nanofiber composite membrane material can be effectively and completely removed.

S400: and (3) carrying out reduction treatment on the vertically-oriented graphene oxide/nanofiber composite membrane material after freeze drying so as to obtain the vertically-oriented graphene/nanofiber composite membrane material. Through reduction treatment, graphene oxide can be reduced into graphene, and the vertically oriented graphene/nanofiber composite membrane material is obtained.

According to an embodiment of the invention, the reduction treatment is selected from laser reduction, chemical reduction or thermal annealing reduction. Wherein, the laser reduction conditions are as follows: the laser intensity is 0.5-15W (such as 0.5W, 1W, 3W, 5W, 7W, 9W, 11W, 13W and 15W), and the reduction time is 0.2-20 s; the conditions for the chemical reduction are: the reducing agent is hydrazine hydrate, and the reducing time is 5-24 hours; the conditions of the thermal annealing reduction are as follows: the reduction is carried out in a protective atmosphere (such as nitrogen, helium and/or argon), the reduction temperature is 300-1000 ℃ (such as 300 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃ and 1000), and the reduction time is 2-6 hours. Therefore, the reduction conditions can quickly and efficiently reduce the graphene oxide into the graphene, and the reduction rate is high.

According to the embodiment of the invention, the graphene structure with vertical orientation can be obtained through the directional freezing treatment, so that when the composite membrane material is used as a distillation medium, the distillation efficiency can be effectively improved, the distillation energy consumption is reduced, and the distillation time is shortened, specifically: the composite membrane material can be arranged on the surface of a liquid to be distilled to serve as a distillation medium, on one hand, the composite membrane material has a vertically-oriented channel structure, liquid is transmitted along the inner wall of the channel in the composite membrane material during distillation, and the channel cannot be filled with the liquid, so that the distillation area of the solution is increased (namely the contact area of the liquid and the composite membrane material is larger), and the distillation rate of the solution is increased; on the other hand, the acting force of the solution molecules on the surface of the composite membrane material is weakened, the evaporation enthalpy of the solution molecules is reduced, the evaporation of the solution on the surface of the composite membrane material can be accelerated, and the energy required by distillation is reduced, so that the distillation efficiency is effectively improved, the distillation energy consumption is reduced, and the distillation time is shortened. In addition, the introduction of the nano-fiber can enable the composite membrane material to have excellent mechanical properties, so that the composite membrane material can be compressed, bent and stretched, and the structure of the composite membrane material is kept from being damaged; in addition, the preparation method is simple and easy to operate, has mature process and is easy for industrial production.

In yet another aspect of the invention, the invention provides a distillation medium. According to an embodiment of the present invention, at least a portion of the distillation medium is composed of the vertically aligned graphene/nanofiber composite membrane material as described above. Therefore, the distillation medium can effectively improve the distillation efficiency, reduce the distillation energy consumption, shorten the distillation time and realize the effect of interface enhanced distillation. It will be understood by those skilled in the art that the distillation medium has all the features and advantages of the vertically oriented graphene/nanofiber composite membrane material and the preparation method thereof, and will not be described in detail herein.

According to the embodiment of the invention, when the distillation is carried out by using the distillation medium, the distillation medium is arranged on the surface of the liquid to be distilled, and compared with the traditional distillation process without the distillation medium, the distillation speed of the distillation process by using the distillation medium is 180-300% higher than that of the traditional distillation process within the temperature range from room temperature to the boiling point of the solution; fractions with the same quality are collected, the energy required by the distillation process is reduced, and the energy conversion efficiency is improved; in the distillation process, for different liquid feeding, the energy-saving efficiency is about 4-60%, and the time is saved by about 45-70%; the evaporation enthalpy of different liquids can be reduced by 107-129%.

According to the embodiment of the present invention, when the distillation is performed by using the distillation medium, there is no particular limitation on the solvent to be distilled, and examples of the solvent to be distilled include common solvents such as alkanes, alcohols, lipids, ketones, amines, phenols, and benzenes: in some embodiments, it may be useful to distill liquid mixtures of different polarity (which may be liquid mixtures of different boiling points), such as ethanol/water, water/N, N-dimethylformamide, 1, 4-dioxane/chlorobenzene; in other embodiments, it may be used to distill high boiling point mixtures such as N, N-dimethylformamide/dimethylsulfoxide, dimethylsulfoxide/N-methylpyrrolidone, ethylene glycol/N-methylpyrrolidone, and the like; in still other embodiments, it may be used for distillative purification of high temperature perishable solutions such as aniline, ethyl acetoacetate, ethyl benzoate, and the like.

In some embodiments, when the composite membrane material is used as a distillation medium to distill mixed solutions with different polarities and different boiling points, compared with the traditional distillation, the distillation rate is improved by 187-284%, the purity of the collected fraction is 93.0-99.5%, the energy-saving efficiency is about 40.6-51.6%, the time-saving efficiency is about 45.9-59.8%, and the emission of greenhouse gases and pollution gases is reduced.

In other embodiments, when the composite membrane material is used as a distillation medium to distill a high-boiling-point mixed solution, a fraction with higher purity can be collected at a temperature lower than the boiling point, compared with the conventional distillation, the distillation temperature can be reduced by 11 ℃ to 39 ℃, compared with the conventional distillation (the fraction collection temperature of the conventional distillation process is the boiling point of the fraction), the fraction can be collected at the temperature lower than the boiling point by the distillation process using the composite membrane material as the distillation medium within the same time, the purity of the collected fraction is 98.0% to 99.8%, and the energy-saving efficiency is 10.9% to 30.8%.

In still other embodiments, when the composite film material is used as a distillation medium to purify a high-temperature perishable solution, a fraction with higher purity can be collected at a temperature lower than the boiling point, compared with the conventional distillation, the distillation temperature of the distillation process using the composite film material as the distillation medium can be reduced by 5 ℃ to 47 ℃, compared with the conventional distillation (the fraction collection temperature is at the boiling point), the distillation process can collect the fraction at a temperature lower than the boiling point, the collected fraction purity is 98.0% to 99.8%, and the energy-saving efficiency is 4.8% to 42.5%.

In yet another aspect of the present invention, a distillation apparatus is provided. According to an embodiment of the present invention, referring to fig. 3 and 4, the distillation apparatus comprises the distillation medium 100 described above, the distillation medium 100 being disposed on the surface of the liquid 40 to be distilled. Therefore, the distillation device can effectively improve the distillation efficiency, reduce the distillation energy consumption and shorten the distillation time. It will be understood by those skilled in the art that the distillation apparatus has all the features and advantages of the distillation medium described above and will not be described in any greater detail herein.

It will be understood by those skilled in the art that the distillation apparatus of the present invention includes the necessary structures or components of a conventional distillation apparatus in addition to the distillation medium 100, such as shown in fig. 3 (taking a laboratory distillation apparatus as an example), and the distillation apparatus further includes a heating source 200, a distillation flask 300, a hob table 400, a thermometer 500, a distillation head 600, a condenser tube 700, a bull horn 800 and a receiving flask 900 in addition to the distillation medium 100, wherein the connection manner and requirements of the above structures are consistent with those of a conventional distillation apparatus, and will not be described herein in detail.