CN106984194A - A kind of modifying super hydrophobicity nano fibrous membrane and its preparation method and application - Google Patents

Abstract

The invention discloses a preparation method of a superhydrophobic modified nanofiber membrane. The steps are: mixing a hydrophobic high polymer, an electrolyte and a solvent A to obtain a high polymer spinning solution, and obtaining a nanofiber membrane after electrospinning; Disperse carbon nanofibers and nanocarbon particles in solvent B to obtain a carbon nanofiber dispersion and a nanocarbon particle dispersion, which are sequentially coated on the nanofiber membrane and dried to obtain a precursor; finally, hot pressing is performed to obtain Superhydrophobic modified nanofibrous membrane. The invention discloses a method for preparing a superhydrophobic modified nanofiber membrane, which avoids the generation of a large number of nodes caused by directly doping nanoparticles into an electrospinning solution. The method is simple and convenient, and the prepared modified nanofiber membrane The fiber membrane has good hydrophobic performance, large porosity, large flux, and extremely high rejection rate, which meets the needs of membranes used in the membrane distillation process.

Description

A kind of superhydrophobic modified nanofiber membrane and its preparation method and application

technical field

The invention relates to the field of membrane distillation separation, in particular to a superhydrophobic modified nanofiber membrane and its preparation method and application.

Background technique

Membrane distillation is a relatively potential desalination membrane technology, which has received more and more attention in recent years. Because it can be operated at a relatively low temperature, it is considered an energy-saving membrane separation method, and it is also widely used in areas that are sensitive to temperature, such as fruit juice concentration and sugar concentration. Although it has the advantage of low energy consumption, membrane distillation separation technology has not been applied on a large scale. The main reason is that it mainly uses hydrophobic porous membranes, which are easily hydrophilized. Membrane distillation uses a membrane as a physical gas-liquid barrier that only allows gas molecules to pass through. Because of this, membrane distillation has high requirements for the membrane. Once the hydrophobicity is not strong, the membrane is easily wetted. In order to expand the application range of membrane distillation, the development of more hydrophobic membranes has become the main research point of membrane distillation technology.

The preparation of membranes for membrane distillation mainly includes the phase inversion method and the electrospinning method that has appeared in recent years. Among them, the nanofibrous membrane has been rapidly applied due to its high porosity, highly hydrophobic membrane surface, and interconnected pores. The patent document with the publication number CN103263856 A discloses a preparation method of electrospinning hydrophobic nanofiber porous membrane for membrane distillation. The hydrophobic functional polymer material is dissolved in a solvent to obtain a polymer spinning solution for electrospinning. The hydrophobic nanofiber porous membrane is obtained by silk, and then heat-treated to obtain the electrospun hydrophobic nanofiber porous membrane for membrane distillation, which has been well applied in membrane distillation. However, due to the high porosity, the water contact angle of the nanofiber porous membrane is only 120-135°, which still has the disadvantage that the surface of the membrane is easily wetted. Therefore, the relevant research hotspots in recent years are mainly on improving the hydrophobicity of the surface of nanofiber membranes. The main methods include vapor deposition on the surface of nanofiber membranes, nanofiber membranes with special-shaped structures, and mixed-matrix nanofiber membranes doped with nanoparticles. For example, the Chinese patent document with the publication number CN 105696197 A discloses a method for preparing a C-type core-shell nanofiber membrane and an eccentric shaft nanofiber membrane, in which a hydrophobic polymer is dissolved in a solvent to form a shell solution; The hydrophilic polymer is dissolved in a solvent to form a core layer solution, which is electrospun separately to obtain a C-type core-shell nanofiber membrane. This specific structure improves the defects of low membrane porosity, low heat conversion efficiency, low water vapor flux and easy wetting of membrane pores, and has been successfully applied in membrane distillation. In the process of modifying electrospinning membranes, mixed matrix membranes have become an important membrane fabrication method. In the process of fabricating mixed matrix membranes, doping nanoparticles in the membrane is the main modification method. Due to the wide selectivity of doping nanoparticles and the simplicity of the doping process, the fabrication of mixed matrix membranes has become the mainstream of electrospinning membrane modification. Commonly used doping materials include hydrophobic clay, TiO ₂ , SiO ₂ , carbon nanotubes, polytetrafluoroethylene particles, graphene and other materials. For example, the Chinese patent document with the publication number CN 105413488 A discloses a method for preparing a superhydrophobic membrane. The hydrophobic organic polymer material and nanoparticles are dissolved in an organic solvent to prepare an electrospinning liquid, and the electrostatic spinning The nanofiber membrane is obtained by film making, and the nanofiber membrane is heat-treated; then titanium dioxide is prepared, and it is covered on the surface of the nanofiber membrane and treated; a silane solution is prepared, and it is covered on the surface of the nanofiber membrane covered with titanium dioxide. After post-treatment, a superhydrophobic film was obtained. In this application, the characteristics of hydrophobicity of these nanoparticles are used, and they are doped in the nanofiber membrane, which can improve the hydrophobicity of the membrane surface. However, due to the easy agglomeration of nanoparticles, the nanofiber membranes prepared by the doping method all have different degrees of nanofiber nodes. Especially in the electrospinning process, the nanoparticles that have been dispersed may reunite during the spinning process. For example Y.Liao (Y.Liao, R.Wang, AGFane, Fabrication of Bioinspired Composite Nanofiber Membranes with Robust Superhydrophobicity for Direct Contact Membrane Distillation, Environ.Sci.Technol., 48 (2014) 6335-6341.) adopts SiO ₂ mixed matrix nanofiber Fibrous membranes, resulting in more knots. Australian scientist Tijing, LD once used carbon nanotubes doped in electrospinning solution to make nanofibrous membrane (Tijing, LD; Woo, YC; Shim, W.-G.; He, T.; Choi, J.- S.; Kim, S.-H.; Shon, HK, Superhydrophobic nanofiber membrane containingcarbon nanotubes for high-performance direct contact membranedistillation. J. Membrane Sci. 2016, 502, 158-170.). However, from the surface of the membrane, the membrane contains a large number of nodes, and the existence of nodes in the nanofiber membrane will destroy the structure of the nanofiber membrane, reduce the porosity, and deteriorate the separation performance of the nanofiber membrane. Although many studies have adopted the method of better dispersing nanoparticles, it is difficult to fundamentally change the defects of hybrid electrospinning.

Carbon nanofiber (CNF) is a carbon material with a large aspect ratio, a small number of defects, and a dense structure. The surface of carbon nanofibers is formed by carbon atoms. Due to the non-polar characteristics of carbon atoms, it is extremely difficult to form hydrogen bonds with water molecules, so it is extremely hydrophobic. Similar to carbon nanofibers, the surface of nano-carbon powder is also composed of carbon atoms, which is extremely hydrophobic, and due to its nano-scale size, the surface energy of nano-carbon powder is lower. After covering the surface of the film, nano-carbon powder not only passes through itself The hydrophobic characteristics of the film increase the hydrophobicity of the membrane surface, and further increase the hydrophobicity of the membrane by forming a rough membrane surface, that is, a micro-nano structure. Although carbon nanofibers have a high modulus, their toughness is poor, and currently they cannot be made into membranes and used in membrane distillation.

Contents of the invention

The invention discloses a method for preparing a superhydrophobic modified nanofiber membrane, which avoids the generation of a large number of nodes caused by directly doping nanoparticles into an electrospinning solution. The method is simple and convenient, and the prepared modified nanofiber membrane The fiber membrane has good hydrophobic performance, large porosity, large flux, and extremely high rejection rate, which meets the needs of membranes used in the membrane distillation process.

The specific technical scheme is as follows:

A method for preparing a superhydrophobic modified nanofiber membrane, comprising the steps of:

(1) mixing a hydrophobic polymer, an electrolyte and a solvent A to obtain a polymer spinning solution, and obtaining a nanofiber membrane after electrospinning;

(2) Disperse carbon nanofibers and nanocarbon particles in solvent B to obtain carbon nanofiber dispersion and nanocarbon particle dispersion respectively, and apply them successively on the nanofiber membrane described in step (1), after drying get the precursor;

(3) Hot pressing the precursor obtained in step (2) to obtain the superhydrophobic modified nanofiber membrane.

The invention adopts a brand-new method for covering the surface of carbon nanofiber network and nanocarbon particles, and the carbon nanofiber is made into a film for application in membrane distillation. In the invention, the nanofiber membrane made of hydrophobic polymer is used as the substrate, and the superhydrophobic carbon nanofiber network and nanocarbon particles are sequentially covered on the surface of the substrate under the premise of ensuring the strength of the membrane, which greatly improves the hydrophobicity of the nanofiber membrane. sex.

As a preference, in step (1), the hydrophobic high polymer is selected from polyvinylidene fluoride (PVDF), polystyrene (PS), polyhexafluoropropylene-vinylidene fluoride copolymer (PVDF-HFP ), polysulfone (PSF) or polyethersulfone (PES);

The solvent A is selected from a true solvent, or a mixture of a true solvent and a diluent;

The true solvent is selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), dimethyl At least one of sulfoxide (DMSO), dimethyl carbonate (DMC); the diluent is selected from at least one of methyl ethyl ketone, acetone, hexane, butanone ethyl acetate;

Among them, the true solvent can dissolve the polymer, and the function of the diluent is to reduce the viscosity of the polymer solution to make the electrospinning process easier, and it is an unnecessary solvent.

Preferably, the solvent A is selected from a mixture of a true solvent and a diluent, and the weight ratio of the true solvent to the diluent is 3-5:1. Further preferably, the true solvent is selected from DMF, DMAc or NMP, and the diluent is selected from acetone.

In step (1), the mass percent concentration of the high polymer spinning solution is the mass percent concentration of the high polymer in the high polymer spinning solution; preferably, the mass percent concentration of the high polymer spinning solution 4 to 30%.

The pore size of the nanofiber membrane is mainly affected by the diameter of the nanofiber, and the diameter of the nanofiber is mainly related to the molecular weight of the polymer, the concentration of the polymer and the type of the polymer. For a particular kind of polymer, its molecular weight and concentration have the most important influence on the diameter of the nanofibrous membrane. At the same polymer concentration, the greater the molecular weight of the polymer in the electrospinning solution, the higher the viscosity of the formed electrospinning solution. In the electrospinning process, the higher the viscosity of the electrospinning solution, the more difficult it is to eject from the electrospinning solution, the greater the degree of fiber adhesion, and the thicker the nanofibers formed, the thicker fibers lead to the formation of membrane pores. get bigger. Similarly, the higher the concentration of polymers with the same molecular weight, the greater the viscosity, and the thicker the nanofibers formed, the thicker fibers also lead to larger membrane pores. Therefore, the electrospinning process mainly depends on the combination of the concentration and molecular weight of the polymer to obtain a suitable nanofiber diameter. In addition, the viscosity of different polymers is not the same, and the spinning conditions should be determined according to the characteristics of different polymers during the electrospinning process. In membrane distillation, the membrane pores are mainly between 0.1 and 0.8 μm. Therefore, through proper wire diameter control, membrane pores suitable for membrane distillation can be obtained. Further preferably, the mass percent concentration of the polymer spinning solution is 4-15%.

Because there is almost no charge in the polymer solution, the conductivity of the pure polymer solution is not good, and it is not easy to eject during the electrospinning process. In order to improve the conductivity of the electrospinning solution, an appropriate amount of electrolyte was added to the electrospinning solution to improve the conductivity of the solution. Preferably, the electrolyte is selected from lithium chloride, sodium chloride or potassium chloride. During the electrospinning process, too much charge can affect the whipping of the fibers and also have an adverse effect on the formation of the fibers. Therefore, the amount of electrolyte added is generally small, and preferably, the mass percent concentration of the electrolyte in the polymer spinning solution is 0.001-0.01%.

Preferably, in step (1), the prepared polymer spinning solution is left to stand overnight to remove air bubbles, and then electrospinning is performed.

Preferably, the electrospinning process is as follows: the voltage is 8-40kV, the advancing speed of the spinning solution is 0.2-4mL/min, the distance from the needle point to the receiving drum is 8-25cm, and the inner diameter of the electrospinning needle is 0.1-4mL/min. 1.0mm, the relative humidity of the air during spinning is 45±10%, the ambient temperature is 20±15°C, the speed of the receiving drum is 4-50r/min, and the electrospinning time is 4-20 hours

Preferably, in step (2), the carbon nanofibers have a diameter of 50-200 nm and a length of 10-100 μm;

The diameter of the nano-carbon particles is 10-80nm.

The surface of carbon nanofibers and nano-carbon powders is formed by carbon atoms, and has strong non-polarity. At the same time, because of the strong interaction between carbon nanofibers and carbon nanofibers, it is very easy to Difficult to disperse in a large amount of solvents (S.Parveen, S.Rana, R.Fangueiro, A Review on Nanomaterial Dispersion, Microstructure, and Mechanical Properties of Carbon Nanotube and NanofiberReinforced Cementitious Composites, Journal of Nanomaterials, (2013).). On the surface of the nanofiber membrane, due to the use of hydrophobic polymer spinning, the surface has strong non-polarity and high hydrophobicity. After some solvents are sprayed on the surface, the droplets will shrink during the solvent volatilization process. The carbon nanofibers in the solvent are agglomerated during droplet shrinkage.

Based on the above specific application occasions, the solvent is required to have high volatility to reduce the instability of droplets on the membrane surface; at the same time, it must meet the requirements of less polarity, better compatibility with the membrane surface, and proper interaction. .

Preferably, in step (2), the solvent B is at least one selected from ethanol, methanol, acetone, ether, benzene, toluene, hexane, cyclohexane, petroleum ether, and ethyl acetate. More preferably, it is methanol, acetone or ethyl acetate.

The solvent B used in the carbon nanofiber dispersion and the carbon nanoparticle dispersion can be the same or different.

Further, in order to avoid the problem of poor dispersibility of carbon nanofibers, the present invention uses a dispersion liquid with dilute concentrations of carbon nanofibers and nano-carbon powders to avoid their agglomeration in solvent B. Preferably, the concentrations of the carbon nanofiber dispersion and the carbon nanoparticle dispersion are independently selected from 0.05 g/L to 10 g/L. More preferably, it is 0.1 to 1 g/L.

The coating method specifically adopted in the present invention is spray gun spraying. In the spraying process, the carbon nanofiber dispersion is sprayed first, and after the solvent is volatilized, the nanocarbon particle dispersion is sprayed. Using this spraying sequence can increase the roughness of the film surface , further increasing the hydrophobicity of the membrane. In addition, it is necessary to pay attention to each spraying. After the carbon nanofiber dispersion or nanocarbon particle dispersion is sprayed, if the solvent is not volatilized, stop spraying, and continue spraying after it dries.

Preferably, in step (2), the deposition density of carbon nanofibers on the nanofiber film is 5-100 g/m ² ; the deposition density of carbon nano-particles is 5-50 g/m ² . Further preferably, the deposition density of the carbon nanofibers is 15-30 g/m ² , and the deposition density of the carbon nano-particles is 5-20 g/m ² .

After dispersing the carbon nanofiber and nanocarbon powder, use a spray gun to spray for many times. When spraying the carbon nanofiber or nanocarbon powder dispersion, spray the dispersion on the surface of the film, and continue spraying after the solvent evaporates to prevent solvent Accumulate on the membrane surface, which in turn causes agglomeration of the nanoparticles in the solvent. This spraying method can avoid the disadvantage of easy agglomeration in conventional spraying.

In order to combine the carbon nanofibers on the surface with the superhydrophobic layer of nanocarbon particles and the free state nanofibers formed by electrospinning into a film, the invention adopts hot pressing treatment. The temperature of hot pressing should be selected according to the properties of the polymer, generally slightly lower than the melting point of the polymer. Preferably, in step (3), the hot pressing is carried out in vacuum, the hot pressing time is 1-3 hours, the hot pressing temperature is 80-300° C., and the hot-pressing pressure is 0.2-5 MPa. A further preferred hot pressing temperature is 160-240° C., and the pressure is 5 MPa.

The invention also discloses the superhydrophobic modified nanofiber membrane prepared according to the above method, which is composed of a composite carbon structure superhydrophobic layer composed of carbon nanofiber superhydrophobic network and nanocarbon particles on the surface and a nanofiber membrane base layer. The water contact angle of the superhydrophobic modified nanofiber membrane is 150°-170°.

The invention also discloses the application of the superhydrophobic modified nanofiber membrane in membrane distillation. The average pore diameter of the superhydrophobic modified nanofiber membrane is 0.1-0.85 μm, the porosity is 60-90%, and the film thickness is 60 μm. ~200 μm; preferably, the average pore diameter is 0.15-0.35 μm, the porosity is 75-85%, the film thickness is 80-130 μm, and the water contact angle is 150°-170°.

Compared with prior art, the present invention has following advantage:

(1) The present invention uses hydrophobic high polymers as raw materials, prepares nanofiber membranes through electrospinning technology, and then uses it as a substrate, and deposits carbon nanofiber networks and nanocarbon particles on the surface of the substrate sequentially through spraying technology Composite superhydrophobic layer, so as to obtain the superhydrophobic modified nanofiber membrane, the preparation process is simple and easy, and it is easy to realize industrialized large-scale production;

(2) The superhydrophobic modified nanofiber membrane prepared by the present invention has a water contact angle of up to 170° due to the presence of carbon nanofiber network and nanocarbon particles on the surface. When applied to the membrane distillation process, it can effectively prevent membrane Membrane wetting during distillation can effectively improve membrane flux.

detailed description

Example 1

In this example, a polyethersulfone nanofiber membrane modified by a carbon nanofiber network and nanocarbon particles with a pore size of 0.20 μm for membrane distillation is prepared, which can be used for seawater desalination. The specific preparation method includes the following steps:

(1) Dissolve 15 parts of polyethersulfone (molecular weight: 450,000) and 0.01 part of potassium chloride in 68 parts of N,N-dimethylformamide and 17 parts of acetone mixed solvent, and dissolve in a water bath at 55°C for 5 hours, Obtain a polyethersulfone electrospinning solution, and leave the solution overnight to remove air bubbles;

The above parts are parts by mass, unless otherwise specified, the same below.

(2) Electrospinning the polyethersulfone spinning solution for 12 hours to prepare a polyethersulfone nanofiber membrane. Wherein the needle of the syringe is a flat needle, and the needle is connected to the positive pole of the high voltage power supply. The process parameters of electrospinning are: needle inner diameter 0.49mm, high-voltage power supply voltage 20kV, electrospinning extrusion speed 1.0mL/h, distance from needle tip to receiving drum 16cm, ambient temperature 28°C, ambient relative humidity 40-50% , the thickness of the polyethersulfone nanofiber membrane prepared by this process is 90 μm, the average flow pore size is 0.20 μm, the pore size distribution range is 0.15-0.32 μm, and the porosity is 82%;

(3) Dissolve carbon nanofibers (diameter 80-100nm, length 5-15μm) and nano-carbon powder (diameter 30-50nm) in methanol, stir mechanically for 2 hours, and disperse in ultrasonic for 4 hours to obtain concentrations 0.1g/L methanol dispersion of carbon nanofibers and nanocarbon powder. The carbon nanofiber dispersion is sprayed onto the nanofiber film prepared in step (2) with a spray gun to obtain a carbon nanofiber network with a surface deposition density of 18g/m ² , and then spray one layer of nano carbon powder on the surface, nano carbon powder The deposition density is 10g/m ² . Pay attention when spraying. After the dispersion is sprayed, if the solvent is not volatilized, stop spraying. After it dries, continue spraying. After spraying, carbon nanofibers and nanocarbon particles are modified. Polyethersulfone nanofiber membrane, which is fully dried in an oven;

(4) Dry the polyethersulfone nanofiber membrane prepared in step (3) at 80°C for 12 hours, and after the solvent in it is completely volatilized, place the modified polyethersulfone nanofiber membrane on two smooth stainless steel surfaces. In the middle of the plate, pressurize to 5Mpa, take it out by hot pressing at 238°C for 2 hours, and obtain the polyethersulfone nanofiber membrane modified by the carbon nanofiber network and nanocarbon particles for membrane distillation, so the amount of carbon material deposited on the surface of the process is very small After testing, the thickness and porosity of the polyethersulfone nanofiber membrane prepared by this process did not change significantly, the average flow pore size was 0.18 μm, and the pore size distribution range was 0.13-0.30 μm.

Adding the carbon nanofiber network for membrane distillation prepared in Example 1 and the polyethersulfone nanofiber membrane A modified by nanocarbon particles and the unmodified polyethersulfone nanofiber membrane B were used for vacuum membrane distillation performance comparison test, The feed is 3.5% NaCl solution, and the electrical conductivity of the membrane distillation output liquid of A and B membrane materials is 11 μS/cm, and the rejection rate calculated based on this is greater than 99.98%. Under the same operating conditions, compared with membrane B, the flux of membrane A is 29kg/m ² h, which is 55% larger than that of membrane B, and the wetting time of membrane A is 45h, which is 200% longer than that of membrane B;

The carbon nanofiber network for membrane distillation prepared in Example 1 and the polyethersulfone nanofiber membrane modified by nanocarbon particles were tested for water contact angle. The water contact angle was 169.0°, and the minimum osmotic pressure test was 210kPa.

Example 2

In this example, a vinylidene fluoride hexafluoropropylene copolymer nanofiber membrane modified with a carbon nanofiber network and nanocarbon particles for membrane distillation with a membrane pore diameter of 0.35 μm was prepared. The specific preparation method includes the following steps:

(1) Dissolve 12 parts of vinylidene fluoride hexafluoropropylene copolymer (molecular weight: 600,000) and 0.01 part of sodium chloride in a mixed solvent of 70 parts of N-methylpyrrolidone and 18 parts of acetone, and stir at a constant temperature in a water bath at 60°C Dissolved for 6 hours to obtain a uniform and stable vinylidene fluoride hexafluoropropylene copolymer spinning solution, which was allowed to stand overnight to remove air bubbles;

(2) Electrospinning the vinylidene fluoride hexafluoropropylene copolymer spinning solution for 15 hours to prepare a vinylidene fluoride hexafluoropropylene copolymer nanofiber membrane. Wherein the needle of the syringe is a flat needle, and the needle is connected to the positive pole of the high voltage power supply. The process parameters of electrospinning are: electrospinning extrusion speed 0.8mL/h, high voltage power supply voltage 22kV, needle inner diameter 0.49mm, distance from needle tip to receiving drum 18cm, ambient temperature 27°C, ambient relative humidity 40-50% , the vinylidene fluoride hexafluoropropylene copolymer nanofiber membrane obtained by this process has a thickness of 90 μm, an average flow pore size of 0.35 μm, a porosity of 78%, and a pore size distribution range of 0.21 to 0.42 μm;

(3) Dissolve carbon nanofibers (diameter 100-150nm, length 10-35μm) and nano-carbon particles (diameter 50-70nm) in a certain amount of acetone, mechanically stir for 2 hours, disperse in ultrasonic for 4 hours, respectively An acetone dispersion of carbon nanofibers and nanocarbon particles with a concentration of 0.1 g/L was obtained. First, the carbon nanofiber dispersion is sprayed onto the nanofiber film prepared in step ( ² ) with a spray gun to obtain a carbon nanofiber network layer with a surface deposition density of 30g/m2, and then spray a layer of carbon nanoparticle on it , the deposition density is 10g/m ² , pay attention when spraying, stop spraying if the solvent is not volatilized after the dispersion is sprayed, and continue spraying after it dries, after two sprays, a modified nanofiber film is obtained;

(4) Dry the modified polyvinylidene fluoride hexafluoropropylene copolymer nanofiber membrane prepared in step (3) at 80° C. for 12 hours, and after the solvent therein is completely volatilized, the modified The polyvinylidene fluoride hexafluoropropylene copolymer nanofiber membrane is placed between two smooth stainless steel plates, pressurized to 5Mpa, and hot pressed at 170°C for 2 hours to take it out, and then the carbon nanofiber network and nanocarbon particle modification for membrane distillation are obtained. The permanent vinylidene fluoride hexafluoropropylene copolymer nanofiber membrane has an average flow pore size of 0.31 μm and a pore size distribution range of 0.17 to 0.38 μm.

The vinylidene fluoride hexafluoropropylene copolymer nanofiber film A and the surface unmodified vinylidene fluoride hexafluoropropylene copolymer added with the carbon nanofiber network and nanocarbon particle modified carbon nanofiber network prepared in Example 2 Nanofiber membrane B was used for vacuum membrane distillation performance comparison test. The feed was 3.5% NaCl solution. The electrical conductivity of the membrane distillation output liquid of the two membrane materials A and B was 15 μS/cm, and the calculated rejection rate was greater than 99.97%. Under the same operating conditions, compared with membrane B, the flux of membrane A is 50% larger than that of membrane B, and the wetting time of membrane A is 80% longer than that of membrane B;

The carbon nanofiber network for membrane distillation prepared in Example 2 and the nanofiber membrane modified by nanocarbon particles were tested for water contact angle, and the water contact angle was 161.0°, and the minimum osmotic pressure test was 178kPa.

Example 3

In this example, a polyvinylidene fluoride nanofiber membrane modified by a carbon nanofiber network and nanocarbon particles with a pore size of 0.29 μm for membrane distillation was prepared. The specific preparation method includes the following steps:

(1) Dissolve 6 parts of polyvinylidene fluoride (molecular weight: 800,000) and 0.004 part of lithium chloride in 94 parts of dimethylacetamide solvent, and stir at 55°C for 4 hours to obtain a uniform and stable polyvinylidene difluoride Vinyl fluoride spinning solution, which was allowed to stand overnight to remove air bubbles;

(2) Electrospinning the solution prepared in (1) for 17 hours to prepare a polyvinylidene fluoride nanofiber membrane. The needle in the electrospinning process is a flat needle, and the needle is connected to the positive pole of the high voltage power supply. The process parameters of electrospinning are: high-voltage power supply voltage 18kV, inner diameter of needle head 0.59mm, distance from needle tip to receiving drum is 16cm, extrusion speed of electrospinning is 1mL/h, rotating speed of receiving drum is 20r/min, spinning process temperature is 20°C , the relative humidity of the environment is 45±5%, the thickness of the polyvinylidene fluoride nanofiber membrane prepared by this process is 100 μm, the average flow pore size is 0.29 μm, the pore size distribution range is 0.20-0.38 μm, and the porosity is 85%;

(3) Dissolve a certain amount of carbon nanofibers (diameter 150-200nm, length 50-100μm) and nano-carbon particles (diameter 60-80nm) in an appropriate amount of ethyl acetate, mechanically stir for 2 hours, and disperse in ultrasonic for 4 hours , make concentration respectively carbon nanofiber and carbon nanoparticle ethyl acetate dispersion liquid that concentration is 1g/L.First carbon nanofiber ethyl acetate dispersion liquid is sprayed on the nanofiber membrane that makes in the step (2) with spray gun, Obtain a carbon nanofiber network film with a surface deposition density of 20g/m ² , then spray nano-carbon particle ethyl acetate solution on the film surface, and the deposition density of nano-carbon particles is 10g/m ^2. Pay attention when spraying, after the dispersion liquid is sprayed If the solvent is not volatilized, stop spraying, and continue spraying after drying to obtain a nanofiber film modified by carbon nanofiber network and nanocarbon particles on the surface;

(4) Dry the nanofiber network obtained in step (3) and the nanofiber membrane modified by nanocarbon particles for 12 hours at 80°C, and after the solvent in it is completely evaporated, the modified polyylidene fluoride The ethylene nanofiber membrane is placed between two smooth stainless steel plates, pressurized to 5Mpa, and taken out by hot pressing at 164°C for 2 hours, and the carbon nanofiber network and nanocarbon particle modified polyvinylidene fluoride nanofibers for membrane distillation are obtained. The membrane has an average flow pore size of 0.27 μm and a pore size distribution range of 0.16 to 0.35 μm.

The polyvinylidene fluoride nanofiber membrane A and the unmodified polyvinylidene fluoride nanofiber membrane B which are modified with the carbon nanofiber network and nanocarbon particles prepared in Example 3 are used as direct contact membranes Distillation performance comparison test. The feed is 3.5% NaCl solution, and the electrical conductivity of the membrane distillation output liquid of the two membrane materials A and B is 10 μS/cm, and the rejection rate calculated based on this is greater than 99.98%. Under the same operating conditions, compared with membrane B, the flux of membrane A is 32kg/m ² h, which is 64% larger than that of membrane B, and the wetting time of membrane A is 41h, which is 78% longer than that of membrane B;

The carbon nanofiber network for membrane distillation prepared in Example 3 and the nanofiber membrane modified by nanocarbon particles were tested for water contact angle, and the water contact angle was 165.0°, and the minimum osmotic pressure test was 210kPa.

Claims (10)

1. a preparation method of superhydrophobic modified nanofiber membrane, is characterized in that, comprises the steps: (1) mixing a hydrophobic polymer, an electrolyte and a solvent A to obtain a polymer spinning solution, and obtaining a nanofiber membrane after electrospinning; (2) Disperse carbon nanofibers and nanocarbon particles in solvent B to obtain carbon nanofiber dispersion and nanocarbon particle dispersion respectively, and apply them successively on the nanofiber membrane described in step (1), after drying get the precursor; (3) Hot pressing the precursor obtained in step (2) to obtain the superhydrophobic modified nanofiber membrane. 2. the preparation method of superhydrophobic modified nanofiber membrane according to claim 1 is characterized in that, in step (1), described hydrophobic high polymer is selected from polyvinylidene fluoride, polystyrene, Polyhexafluoropropylene-vinylidene fluoride copolymer, polysulfone or polyethersulfone; Described electrolyte is selected from lithium chloride, sodium chloride or potassium chloride; The solvent A is selected from a true solvent, or a mixture of a true solvent and a diluent; The true solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, dimethyl sulfoxide, and dimethyl carbonate ; The diluent is selected from at least one of methyl ethyl ketone, acetone, hexane, butanone, and ethyl acetate; The mass percentage concentration of the high polymer spinning solution is 4-30%. 3 . The method for preparing a superhydrophobic modified nanofiber membrane according to claim 2 , characterized in that, the mass percent concentration of the electrolyte in the polymer spinning solution is 0.001-0.01%. 4 . 4. The preparation method of the superhydrophobic modified nanofiber membrane according to claim 1, 2 or 3, characterized in that, in step (1), the electrospinning process is: the voltage is 8 ~ 40kV, the spinning The advancing speed of the silk solution is 0.2-4mL/min, the distance from the needle tip to the receiving drum is 8-25cm, the inner diameter of the electrospinning needle is 0.1-1.0mm, the relative humidity of the air during the spinning process is 45±10%, and the ambient temperature is 20±15°C, the rotational speed of the receiving drum is 4-50r/min, and the electrospinning time is 4-20 hours. 5. The preparation method of superhydrophobic modified nanofiber membrane according to claim 1, characterized in that, in step (2), the diameter of the carbon nanofiber is 50-200nm, and the length is 10-100 μm; The diameter of the nano-carbon particles is 10-80nm. 6. the preparation method of superhydrophobic modified nanofiber membrane according to claim 5 is characterized in that, described solvent B is selected from ethanol, methyl alcohol, acetone, ether, benzene, toluene, hexane, hexanaphthene, petroleum At least one of ether and ethyl acetate; The concentrations of the carbon nanofiber dispersion and the carbon nanoparticle dispersion are independently selected from 0.05 g/L to 10 g/L. 7. the preparation method of superhydrophobic modified nanofiber membrane according to claim 1, is characterized in that, in step (2), the carbon nanofiber deposition density on the nanofiber membrane is 5～100g/m ² ; The deposition density of nano-carbon particles is 5-50 g/m ² . 8. The preparation method of the superhydrophobic modified nanofiber membrane according to claim 1, characterized in that, in step (3), the hot pressing is carried out in vacuum, the hot pressing time is 1～3h, and the hot pressing The temperature is 80-300°C, and the hot pressing pressure is 0.2-5 MPa. 9. A superhydrophobic modified nanofiber membrane prepared according to the method according to any one of claims 1 to 8, characterized in that it comprises a nanofiber membrane and a composite superhydrophobic membrane deposited on at least one surface of the nanofiber membrane. hydrophobic layer; The composite superhydrophobic layer is composed of carbon nanofiber network and carbon nanoparticle; The water contact angle of the superhydrophobic modified nanofiber membrane is 150°-170°. 10. An application of the superhydrophobic modified nanofiber membrane according to claim 9 in membrane distillation, wherein the average pore diameter of the superhydrophobic modified nanofiber membrane is 0.1 to 0.85 μm, and the porosity is 60-90%, the film thickness is 60-200 μm, and the water contact angle is 150°-170°.