CN110559859A - electrostatic spinning nanofiber-based double-skin forward osmosis membrane and preparation method thereof - Google Patents
electrostatic spinning nanofiber-based double-skin forward osmosis membrane and preparation method thereof Download PDFInfo
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- B01D61/002—Forward osmosis or direct osmosis
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- B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
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- B01D65/10—Testing of membranes or membrane apparatus; Detecting or repairing leaks
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- B01D71/06—Organic material
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Abstract
The invention discloses an electrostatic spinning nanofiber-based double-skin forward osmosis membrane and a preparation method thereof. The preparation method comprises the following steps: dissolving the high polymer in a solvent to prepare a spinning solution; carrying out electrostatic spinning on the spinning solution to obtain an electrostatic spinning nanofiber base film; and (3) carrying out interfacial polymerization reaction on the upper surface and the lower surface of the electrostatic spinning nanofiber base film to finally obtain the electrostatic spinning nanofiber-based double-skin forward osmosis membrane with the electrostatic spinning nanofiber as the base film and a double-skin structure. The invention has the advantages that the high porosity and the three-dimensional through hole structure of the electrostatic spinning nanofiber can effectively relieve the internal concentration polarization phenomenon in the base membrane and improve the water flux of the forward osmosis membrane; the double-skin structure can effectively prevent solute in raw material liquid from entering the base membrane layer, and endows the membrane surface with excellent anti-pollution performance, thereby preparing the forward osmosis membrane with high flux and strong anti-pollution.
Description
Technical Field
the invention belongs to the technical field of forward osmosis membranes, and particularly relates to an electrostatic spinning nanofiber-based double-skin forward osmosis membrane and a preparation method thereof.
Background
Forward Osmosis (FO) is an osmotically driven membrane separation process that has received attention from many researchers due to its unique advantages of no need for applied pressure, relatively low membrane fouling, etc. The forward osmosis technology is praised as a new technology with the most potential for desalination and water purification, and has wide application prospects in the field of water treatment, such as seawater desalination, drinking water purification, domestic sewage recycling, industrial wastewater treatment, garbage leachate treatment, medicine and food concentration and the like. Despite the rapid development of forward osmosis technology in recent years, the forward osmosis technology is not perfect in practical application, a series of technical barriers still exist to prevent the industrial development of the forward osmosis technology, and the forward osmosis technology is not likely to replace Reverse Osmosis (RO) technology at present. One of the main challenges of applying forward osmosis technology from laboratory to industrial process is that no forward osmosis membrane with high performance is available, so many problems to be solved in practical application are faced, such as: the flux of the forward osmosis membrane produced at present cannot be compared with the high water flux of reverse osmosis; the severe internal concentration polarization phenomenon (ICP) causes a significant reduction in filtration efficiency; in addition, although the forward osmosis process is not as serious as the membrane fouling problem in the pressure-driven membrane process, the membrane fouling phenomenon is still unavoidable, and the problems of membrane cleaning and membrane life shortening caused by the membrane fouling phenomenon are still not negligible. Therefore, research and development of high-performance forward osmosis membranes are carried out, and preparation of the forward osmosis membrane with high flux and strong pollution resistance is still the focus of current research.
Disclosure of Invention
Aiming at the problems, the invention provides an electrostatic spinning nanofiber-based double-skin forward osmosis membrane and a preparation method thereof, and the electrostatic spinning nanofiber-based double-skin forward osmosis membrane with high flux and strong stain resistance is prepared through a special structural design.
The electrostatic spinning nanofiber-based double-skin forward osmosis membrane comprises a base membrane layer consisting of electrostatic spinning nanofibers and polyamide skin layers positioned on the upper side and the lower side of the base membrane layer (namely, the two polyamide skin layers are combined to form a double-skin structure), wherein the polyamide skin layers comprise a first compact skin layer facing a liquid drawing side and a second loose skin layer facing a raw material liquid side in the application process.
The polyamide skins on both sides of the base film have different degrees of densification, wherein: the first skin layer is denser than the second skin layer and can be used as a selective separation functional layer to intercept solute ions in the draw solution; the second cortex is looser than the first cortex, and solute in the raw material liquid can be effectively prevented from entering and depositing in the base membrane on the premise of not obviously increasing the mass transfer resistance.
Further, the base film layer is an electrostatic spinning nanofiber base film layer; the polyamide skin layer is prepared by carrying out interfacial polymerization reaction on the upper surface and the lower surface of the base film layer by using an aqueous phase solution of a polyamine compound and an organic phase solution of a polybasic acyl chloride compound.
As a general technical concept, the present invention also provides a method for preparing the above electrospun nanofiber-based double-skin forward osmosis membrane, comprising the steps of:
Preparation of electrostatic spinning solution: adding a high polymer into a solvent, stirring at a specified temperature to dissolve the high polymer in the solvent, and standing for defoaming to prepare a spinning solution;
Preparing an electrostatic spinning nanofiber base film: filling the spinning solution obtained in the step I into an injector, performing electrostatic spinning on the spinning solution by using electrostatic spinning equipment, covering a layer of aluminum foil on a collector to receive the nano-fibers prepared by electrostatic spinning, and finally removing the aluminum foil to obtain an electrostatic spinning nano-fiber base film;
Preparing interfacial polymerization reaction solution: respectively dissolving two parts of polyamine compound in two parts of deionized water, uniformly stirring, and respectively preparing a first aqueous phase solution and a second aqueous phase solution, wherein the mass concentration of the polyamine compound in the first aqueous phase solution is greater than that of the polyamine compound in the second aqueous phase solution; respectively dissolving two parts of polyacyl chloride compounds in two parts of organic solvents, uniformly stirring, and respectively preparing a first organic phase solution and a second organic phase solution, wherein the mass concentration of the polyacyl chloride compounds in the first organic phase solution is greater than that of the polyacyl chloride compounds in the second organic phase solution;
Preparing a double-skin forward osmosis membrane: fixing the electrostatic spinning nanofiber basement membrane prepared in the second step in a plate frame, pouring a first aqueous phase solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring the first aqueous phase solution after a first designated time, removing redundant solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring a first organic phase solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring the first organic phase solution after a second designated time, naturally drying in the air, then placing the electrostatic spinning nanofiber basement membrane in an oven for heat treatment, and forming a first skin layer on the upper surface of the electrostatic spinning nanofiber basement membrane; and then pouring a second aqueous phase solution on the lower surface of the electrostatic spinning nanofiber base film, pouring the second aqueous phase solution after a third designated time and removing redundant solution on the lower surface of the electrostatic spinning nanofiber base film, then pouring a second organic phase solution on the lower surface of the electrostatic spinning nanofiber base film, pouring the second organic phase solution after a fourth designated time, naturally drying in the air, then placing the film in an oven for heat treatment, forming a second skin layer on the lower surface of the electrostatic spinning nanofiber base film, and finally obtaining the electrostatic spinning nanofiber base double-skin layer forward osmosis film with the electrostatic spinning nanofiber as the base film and a double-skin layer structure.
preferably, the high polymer is one or more of polysulfone (PSf), Polyethersulfone (PES), Polyacrylonitrile (PAN), Polystyrene (PS), polyvinylidene fluoride (PVDF), Polyethylene (PE), polypropylene (PP), Cellulose Acetate (CA), Cellulose Triacetate (CTA), polyethylene terephthalate (PET), Polyimide (PI), Nylon (Nylon), polyvinyl alcohol (PVA), and polyvinyl pyrrolidone (PVP), and the mass concentration of the high polymer is 12-25%; the solvent is a solvent capable of dissolving the high polymer and comprises one or more of N, N-Dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), 1, 4-dioxane, dichloromethane, trichloromethane, tetrahydrofuran, toluene, acetone, methanol, ethanol, formic acid, acetic acid and water; the designated temperature in the first step is 25-95 ℃, and the stirring time in the first step is 6-24 hours; the temperature of the standing defoaming in the step I is 25-95 ℃, and the time of the standing defoaming in the step I is 12-48 hours.
Preferably, the collector is a cylindrical collecting roller, and the process conditions of the electrostatic spinning in the step (II) are as follows: the rotating speed of a roller of the collector is 100-500 rpm; the electrostatic spinning method comprises the following steps that a plain needle head is used during electrostatic spinning, the inner diameter of the plain needle head is 0.6-1.0mm, the plain needle head horizontally reciprocates in a direction perpendicular to a rolling shaft of a collector in the electrostatic spinning process, and the moving speed is 0.5-2.0 cm/s; the spinning voltage is 15-25 kV; the receiving distance between the flat-mouth needle head and the collector is 8-20 cm; the extrusion rate of the spinning solution is 0.5-2 ml/h; the spinning temperature is 23-28 ℃, and the spinning humidity is 15-25% RH.
Preferably, the polyamine compound contains at least two reactive amino groups, and comprises any one or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, sym-phenylenediamine, ethylene diamine, propylene diamine, hexamethylene diamine, 1, 4-hexamethylene diamine, 1, 3-hexamethylene diamine and piperazine;
The polybasic acyl chloride compound at least contains two reactive acyl chloride groups, including one or more of trimesoyl chloride, paraphthaloyl chloride, isophthaloyl chloride and phthaloyl chloride;
The organic solvent is an organic solvent which can dissolve acyl chloride monomers but not polyamide in aliphatic hydrocarbons, cycloaliphatic hydrocarbons and aromatic hydrocarbons of which the monomers contain 4-12 carbon atoms, and comprises n-hexane, cyclohexane, n-heptane, xylene and Isopar-G.
Preferably, the mass concentration of the polyamine compound in the first aqueous phase solution is 3.0-5.0%, and the mass concentration of the polyamine compound in the second aqueous phase solution is 1.0-3.0%; the mass concentration of the polybasic acyl chloride compound in the first organic phase solution is 0.1-0.5%, and the mass concentration of the polybasic acyl chloride compound in the second organic phase solution is 0.05-0.3%.
Preferably, the first designated time is 2-5 min; the second designated time is 1-3 min; the third designated time is 1-3 min; the fourth designated time is 0.5-2 min; naturally airing in the air for 2-5 min; the temperature of the oven is 40-80 ℃; the heat treatment time is 5-15 min.
Compared with the prior art, the invention has the advantages that: according to the method, the electrostatic spinning nanofiber-based double-skin forward osmosis membrane is prepared by performing interfacial polymerization on the upper surface and the lower surface of the electrostatic spinning nanofiber base membrane, so that the phenomenon of internal concentration polarization in the base membrane can be relieved, the flux of the membrane is improved, solute in a raw material solution can be effectively prevented from entering the porous base membrane layer, and the surface of the membrane is endowed with excellent anti-pollution performance. The equal interfacial polymerization one deck polyamide cortex in electrostatic spinning nanofiber basement rete both sides has effectively improved the antipollution performance on membrane surface, and regard as the base film of two cortex forward osmosis membranes with electrostatic spinning nanofiber, can slow down the interior concentration polarization phenomenon in the basement membrane, compensate the not enough in the aspect of two cortex structures additionally increase the mass transfer resistance to a certain extent for the forward osmosis membrane of preparation can have the excellent performance of high flux and strong anti-soil concurrently. In addition, the double-skin forward osmosis membrane can flexibly adjust the compactness of the second skin layer according to different conditions of feed liquid treatment.
Testing the membrane performance:
indicators for evaluating forward osmosis membrane performance include water flux and reverse salt flux. Deionized water is used as a raw material solution, 1M NaCl solution is used as a drawing solution, and the temperature of a test solution is kept at 25 +/-1 ℃. The method comprises the steps of loading a tested forward osmosis membrane into a testing membrane module, sealing the peripheral edge of the membrane by a silica gel pad, driving a raw material liquid and a drawing liquid to respectively flow in pipelines at two sides of the membrane in a cross flow mode under the drive of a peristaltic pump, and keeping the flow rates of the liquid at two sides of the membrane consistent by adjusting the rotating speeds of the peristaltic pumps at two sides of the raw material liquid and the drawing liquid. The change of the side conductivity of the raw material liquid and the change of the side mass of the drawing liquid are collected on line by a conductivity meter and a precision balance, and the water flux (J) of the membrane in unit time and unit area is calculated according to the following formulaw) And reverse salt flux (J)s)。
In the formula, Jwwater flux of the membrane, L/m2H or LMH; Δ m is the mass change, g, of the side of the draw solution within Δ t time; rho is the density of water, g/cm3；Amis the effective area of the forward osmosis membrane, m2(ii) a Δ t is the operating time, h; j. the design is a squaresFor reverse salt flux, g/m2H or gMH; v0And C0the volume (L) and the salt concentration (g/L) of the liquid side of the raw material at the beginning; vtAnd CtThe volume (L) and the salt concentration (g/L) on the feed liquid side at time t are shown.
The anti-pollution performance of the forward osmosis membrane is also an important index for evaluating the membrane performance, and three typical representative organic pollutants, namely polysaccharide pollutant Sodium Alginate (SA), protein pollutant Bovine Serum Albumin (BSA) and humus pollutant (HA), are selected for organic pollution in the forward osmosis process to carry out a membrane pollution experiment. Utilize forward osmosis unit, in the pollutant solution that will dispose pours into the raw materials fluid reservoir into, use 1M's NaCl solution to carry out the membrane pollution experiment as drawing the liquid, the experiment operation is 2h, the flux decay condition of real-time detection forward osmosis process. After the pollution experiment is finished, cleaning the polluted membrane, wherein the specific cleaning conditions are as follows: and (3) performing circulating flushing by using 2L of deionized water for 30min in a cross flow mode, then flushing by using the deionized water for 5min, and testing the water flux after cleaning to obtain the flux recovery rate.
Drawings
FIG. 1 is a sectional structure SEM image of an electrospun nanofiber-based double-skin forward osmosis membrane of the invention.
Fig. 2 is a first skin SEM image of an electrospun nanofiber-based double skin forward osmosis membrane of the present invention.
fig. 3 is a second skin SEM image of an electrospun nanofiber-based double skin forward osmosis membrane of the present invention.
illustration of the drawings: 1. a first skin layer; 2. electrostatic spinning of nanofiber-based membranes; 3. a second skin layer.
Detailed Description
The present invention will be described in further detail with reference to the following examples.
Example 1
(1) Adding 20g of PVDF into a mixed solvent of 64g of DMF and 16g of acetone, stirring and dissolving for 24h at 25 ℃, standing for 48h at 25 ℃ to completely defoam, and finally preparing a spinning solution with the mass concentration of 20%;
(2) And (2) putting the spinning solution into an injector, and carrying out electrostatic spinning by using a 0.8mm plain end needle, wherein the extrusion rate of the spinning solution is 1.0ml/h, the spinning voltage is 15kV, the receiving distance from the top end of the needle to the collector is 15cm, the rotating speed of the collector is 300rpm, the horizontal reciprocating movement rate of the plain end needle along the direction of a roller of the collector is 1.0cm/s, the spinning temperature is 25 ℃, and the relative humidity is 25% RH.
(3) dissolving m-phenylenediamine and ethylenediamine in deionized water with the mass concentration of 3.0% and 0.5% respectively to serve as a first aqueous phase solution, and dissolving trimesoyl chloride in n-hexane with the mass concentration of 0.20% to serve as a first organic phase solution; dissolving piperazine in water with the mass concentration of 3.0%, fully stirring and dissolving to obtain a second aqueous phase solution, and dissolving trimesoyl chloride in n-hexane with the mass concentration of 0.30% to obtain a second organic phase solution;
(4) Fixing the PVDF nanofiber basement membrane in a plate frame, pouring a first aqueous phase solution into the upper surface of the PVDF nanofiber basement membrane, pouring off the first aqueous phase solution after 5min, removing redundant solution on the surface of the PVDF nanofiber basement membrane by using filter paper, pouring a first organic phase solution into the upper surface of the PVDF nanofiber basement membrane, pouring off the PVDF nanofiber basement membrane after 2min, naturally airing the PVDF nanofiber basement membrane in the air for 2min, and then placing the PVDF nanofiber basement membrane in an 80 ℃ drying oven for heat treatment for 10min to form a first skin layer on the upper surface; and then pouring a second aqueous phase solution on the lower surface of the PVDF nanofiber base film, pouring the second aqueous phase solution after 3min, removing the redundant solution on the lower surface by using filter paper, pouring a second organic phase solution on the lower surface, taking out after 2min, airing in the air for 2min, and then placing in a 60 ℃ drying oven for heat treatment for 5min to form a second skin layer on the lower surface of the PVDF nanofiber base film.
(5) the PVDF electrostatic spinning nanofiber-based double-skin forward osmosis membrane prepared by the method takes deionized water as a raw material solution and 1M NaCl solution as an extraction solution, the water flux measured at 25 ℃ is 24.7LMH, and the salt reverse flux is 3.4 gMH. A pollution experiment is carried out by using 1g/L of simulated pollutants (namely the concentrations of SA, BSA and HA are all 1g/L), the flux is attenuated by 17% in 2 hours, and the flux recovery rate after cleaning is 96%.
Comparative example 1
This comparative example was prepared in a substantially similar manner to example 1, except that the base film in the step (2) was prepared by a phase inversion method, comprising the steps of: and (3) casting the spinning solution onto a clean glass plate by using a scraper, standing in the air for 30s, and quickly and horizontally placing into deionized water for solidification to obtain the base film prepared by the phase inversion method.
The prepared phase inversion method based double-skin forward osmosis membrane takes deionized water as raw material liquid and 1M NaCl solution as drawing liquid, and the water flux measured at 25 ℃ is 18.4LMH, and the salt reverse flux is 3.1 gMH. A pollution experiment is carried out by using 1g/L of simulated pollutants (namely the concentrations of SA, BSA and HA are all 1g/L), the flux is attenuated by 15% in 2 hours, and the flux recovery rate after cleaning is 97%.
Example 1 compared with comparative example 1, the preparation and test conditions were the same except for the preparation method of the base film, example 1 is a nanofiber base film prepared by an electrospinning method, and comparative example 1 is a base film prepared by a phase inversion method. The test results show that the water flux of example 1 is higher than that of comparative example 1, which shows that the internal concentration polarization phenomenon in the basement membrane layer can be reduced by using the electrospun nano-fiber as the basement membrane, and the prepared forward osmosis membrane has higher water flux.
Example 2
(1) Adding 12g of Nylon into 70.4g of formic acid and 17.6g of dichloromethane, heating, stirring and dissolving for 12h at 50 ℃, standing for 12h at 50 ℃ to completely defoam, and finally preparing a spinning solution with the mass concentration of 12%;
(2) the spinning solution is filled into an injector, electrostatic spinning is carried out by adopting a 0.6mm plain end needle, the extrusion speed of the spinning solution is 0.5ml/h, the spinning voltage is 25kV, the receiving distance from the top end of the needle to a collector is 8cm, the rotating speed of the collector is 100rpm, the horizontal reciprocating movement speed of the plain end needle along the direction of a rolling shaft of the collector is 0.5cm/s, the spinning temperature is 23 ℃, and the relative humidity is 15% RH.
(3) Dissolving m-phenylenediamine in water with the mass concentration of 3.0%, fully stirring the solution to be used as a first aqueous phase solution, and dissolving trimesoyl chloride in n-heptane with the mass concentration of 0.10% to be used as a first organic phase solution; dissolving m-phenylenediamine and piperazine in water with the mass concentration of 1.5% and 0.5% respectively to obtain a second aqueous phase solution, and dissolving isophthaloyl dichloride in n-heptane with the mass concentration of 0.10% to obtain a second organic phase solution;
(4) fixing the Nylon electrostatic spinning nanofiber basement membrane in a plate frame, pouring a first aqueous phase solution into the upper surface of the Nylon electrostatic spinning nanofiber basement membrane, pouring off the first aqueous phase solution after 3min, removing redundant solution on the surface of the Nylon electrostatic spinning nanofiber basement membrane by using filter paper, pouring a first organic phase solution into the upper surface of the Nylon electrostatic spinning nanofiber basement membrane, pouring off the Nylon electrostatic spinning nanofiber basement membrane after 2min, naturally airing the Nylon electrostatic spinning nanofiber basement membrane for 5min in the air, and then placing the Nylon electrostatic spinning nanofiber basement membrane in an oven at 80 ℃ for heat treatment for 5min to form a first; and then pouring a second aqueous phase solution on the lower surface of the Nylon electrostatic spinning nanofiber base film 2, pouring the second aqueous phase solution after 2min, removing the redundant solution on the lower surface by using filter paper, then continuously pouring a second organic phase solution on the lower surface of the Nylon electrostatic spinning nanofiber base film, taking out after 1min, airing in the air for 5min, and then placing the Nylon electrostatic spinning nanofiber base film in a 70 ℃ drying oven for heat treatment for 8min to enable the lower surface of the Nylon electrostatic spinning nanofiber base film 3 to form a second skin layer.
(5) the Nylon electrostatic spinning nanofiber-based double-skin forward osmosis membrane prepared by the method takes deionized water as a raw material solution and 1M NaCl solution as an extraction solution, and the water flux measured at 25 ℃ is 35.2LMH and the salt reverse flux is 2.8 gMH. A pollution experiment is carried out by using simulated pollutants of 5g/L (namely the concentrations of SA, BSA and HA are all 5g/L), the flux is attenuated by 36% in 2 hours, and the flux recovery rate after cleaning is 93%.
Comparative example 2
This comparative example was prepared in a substantially similar manner to example 2, except that interfacial polymerization was not performed on the lower surface of the base film in the step (4), to obtain a Nylon electrospun nanofiber-based single-skin forward osmosis membrane.
The prepared Nylon electrostatic spinning nanofiber-based single-skin forward osmosis membrane takes deionized water as a raw material solution and 1M NaCl solution as an extraction solution, the water flux measured at 25 ℃ is 30.5LMH, and the salt reverse flux is 6.1 gMH. A pollution experiment is carried out by using simulated pollutants of 5g/L (namely the concentrations of SA, BSA and HA are all 5g/L), the flux is attenuated by 55% in 2h, and the flux recovery rate after cleaning is 78%.
Example 2 the same conditions were used for the test and preparation, except that the structure of the lower surface of the base film was different from that of comparative example 2, in which example 2 a second skin layer was interfacially polymerized on the lower surface of the base film, and the interfacial polymerization was not performed on the lower surface of the base film of comparative example 2. The test results show that the flux attenuation ratio of example 2 is low and the flux recovery rate is high in a pollution experiment, which indicates that the second skin layer facing the raw material liquid side can improve the anti-pollution performance of the membrane surface, and the double-skin forward osmosis membrane has more excellent anti-pollution performance than the single-skin forward osmosis membrane.
Example 3
(1) Adding 15g of PVDF and 10g of PAN into 75g of DMAc, heating, stirring and dissolving for 6h at 80 ℃, standing for 12h at 80 ℃ to completely defoam the solution, and finally preparing a spinning solution with the mass concentration of 25%;
(2) the spinning solution is filled into an injector, electrostatic spinning is carried out by adopting a 1.0mm plain end needle, the extrusion speed of the spinning solution is 2.0ml/h, the spinning voltage is 20kV, the receiving distance from the top end of the needle to a collector is 20cm, the rotating speed of the collector is 500rpm, the horizontal reciprocating movement speed of the plain end needle along the direction of a roller of the collector is 2.0cm/s, the spinning temperature is 28 ℃, and the relative humidity is 20% RH.
(3) Dissolving m-phenylenediamine and hexamethylenediamine in water, wherein the mass concentration of the m-phenylenediamine and the hexamethylenediamine is 4.0% and 1.0% respectively, taking the m-phenylenediamine and the hexamethylenediamine as first aqueous phase solutions, and dissolving trimesoyl chloride in n-hexane, wherein the mass concentration of the trimesoyl chloride is 0.50%, and taking the solution as a first organic phase solution; dissolving m-phenylenediamine in water with the mass concentration of 1.0 percent to serve as a second aqueous phase solution, and dissolving trimesoyl chloride in n-hexane with the mass concentration of 0.05 percent to serve as a second organic phase solution;
(4) Fixing the PVDF/PAN electrostatic spinning nanofiber base membrane in a plate frame, pouring a first aqueous phase solution into the upper surface of the PVDF/PAN electrostatic spinning nanofiber base membrane, pouring out the first aqueous phase solution after 2min, removing the redundant solution on the surface of the PVDF/PAN electrostatic spinning nanofiber base membrane by using filter paper, pouring a first organic phase solution into the upper surface of the PVDF/PAN electrostatic spinning nanofiber base membrane, pouring out the first organic phase solution after 1min, naturally airing the PVDF/PAN electrostatic spinning nanofiber base membrane for 3min in the air, and then placing the PVDF/PAN electrostatic spinning nanofiber base membrane in a 60-DEG C; and then pouring a second aqueous phase solution on the lower surface of the PVDF/PAN electrostatic spinning nanofiber base membrane, pouring the second aqueous phase solution after 1min, removing the redundant solution on the lower surface by using filter paper, then continuously pouring a second organic phase solution on the lower surface of the PVDF/PAN electrostatic spinning nanofiber base membrane, taking out after 0.5min, airing in the air for 3min, and then placing the PVDF/PAN electrostatic spinning nanofiber base membrane in a 40 ℃ drying oven for heat treatment for 15min to form a second skin layer on the lower surface of the PVDF/PAN electrostatic spinning nanofiber base membrane.
(5) The PVDF/PAN electrostatic spinning nanofiber-based double-skin forward osmosis membrane prepared by the method takes deionized water as a raw material solution, 1M NaCl solution as an extraction solution, the water flux measured at 25 ℃ is 28.1LMH, and the salt reverse flux is 2.6 gMH. A pollution experiment is carried out by using 10g/L of simulated pollutants (namely the concentration of SA, BSA and HA is 10g/L), the flux is attenuated by 64% in 2 hours, and the flux recovery rate after cleaning is 93%.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (8)
1. An electrostatic spinning nanofiber-based double-skin forward osmosis membrane is characterized by comprising a base membrane layer consisting of electrostatic spinning nanofibers and polyamide skin layers respectively positioned on the upper side and the lower side of the base membrane layer; the polyamide skin layer comprises a dense first skin layer facing the draw solution side and a loose second skin layer facing the feed solution side during application.
2. The electrospun nanofiber-based double-skin forward osmosis membrane according to claim 1, wherein the base membrane layer is an electrospun nanofiber-based membrane layer; the polyamide skin layer is prepared by respectively carrying out interfacial polymerization reaction on the upper surface and the lower surface of the base film layer by using an aqueous phase solution of a polyamine compound and an organic phase solution of a polybasic acyl chloride compound.
3. A method of preparing the electrospun nanofiber-based double-skin forward osmosis membrane of claim 1 or 2, comprising the steps of:
Preparation of electrostatic spinning solution: adding a high polymer into a solvent, stirring at a specified temperature to dissolve the high polymer in the solvent, and standing for defoaming to prepare a spinning solution;
preparing an electrostatic spinning nanofiber base film: filling the spinning solution obtained in the step I into an injector, performing electrostatic spinning on the spinning solution by using electrostatic spinning equipment, covering a layer of aluminum foil on a collector to receive the nano-fibers prepared by electrostatic spinning, and finally removing the aluminum foil to obtain an electrostatic spinning nano-fiber base film;
Preparing interfacial polymerization reaction solution: respectively dissolving two parts of polyamine compound in two parts of deionized water, uniformly stirring, and respectively preparing a first aqueous phase solution and a second aqueous phase solution, wherein the mass concentration of the polyamine compound in the first aqueous phase solution is greater than that of the polyamine compound in the second aqueous phase solution; respectively dissolving two parts of polyacyl chloride compounds in two parts of organic solvents, uniformly stirring, and respectively preparing a first organic phase solution and a second organic phase solution, wherein the mass concentration of the polyacyl chloride compounds in the first organic phase solution is greater than that of the polyacyl chloride compounds in the second organic phase solution;
Preparing a double-skin forward osmosis membrane: fixing the electrostatic spinning nanofiber basement membrane prepared in the second step in a plate frame, pouring a first aqueous phase solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring the first aqueous phase solution after a first designated time, removing redundant solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring a first organic phase solution on the upper surface of the electrostatic spinning nanofiber basement membrane, pouring the first organic phase solution after a second designated time, naturally drying in the air, then placing the electrostatic spinning nanofiber basement membrane in an oven for heat treatment, and forming a first skin layer on the upper surface of the electrostatic spinning nanofiber basement membrane; and then pouring a second aqueous phase solution on the lower surface of the electrostatic spinning nanofiber base film, pouring the second aqueous phase solution after a third designated time and removing redundant solution on the lower surface of the electrostatic spinning nanofiber base film, then pouring a second organic phase solution on the lower surface of the electrostatic spinning nanofiber base film, pouring the second organic phase solution after a fourth designated time, naturally drying in the air, then placing the film in an oven for heat treatment, forming a second skin layer on the lower surface of the electrostatic spinning nanofiber base film, and finally obtaining the electrostatic spinning nanofiber base double-skin layer forward osmosis film with the electrostatic spinning nanofiber as the base film and a double-skin layer structure.
4. The method for preparing the electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, wherein the high polymer is one or more of polysulfone (PSf), Polyethersulfone (PES), Polyacrylonitrile (PAN), Polystyrene (PS), polyvinylidene fluoride (PVDF), Polyethylene (PE), polypropylene (PP), Cellulose Acetate (CA), Cellulose Triacetate (CTA), polyethylene terephthalate (PET), Polyimide (PI), Nylon (Nylon), polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP), and the mass concentration of the high polymer is 12-25%; the solvent is a solvent capable of dissolving the high polymer and comprises one or more of N, N-Dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), 1, 4-dioxane, dichloromethane, trichloromethane, tetrahydrofuran, toluene, acetone, methanol, ethanol, formic acid, acetic acid and water; the designated temperature in the first step is 25-95 ℃, and the stirring time in the first step is 6-24 hours; the temperature of the standing defoaming in the step I is 25-95 ℃, and the time of the standing defoaming in the step I is 12-48 hours.
5. The method for preparing the electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, wherein the collector is a cylindrical collecting roller, and the process conditions of the electrospinning in the step (II) are as follows: the rotating speed of a roller of the collector is 100-500 rpm; the electrostatic spinning method comprises the following steps that a plain needle head is used during electrostatic spinning, the inner diameter of the plain needle head is 0.6-1.0mm, the plain needle head horizontally reciprocates in a direction perpendicular to a rolling shaft of a collector in the electrostatic spinning process, and the moving speed is 0.5-2.0 cm/s; the spinning voltage is 15-25 kV; the receiving distance between the flat-mouth needle head and the collector is 8-20 cm; the extrusion rate of the spinning solution is 0.5-2 ml/h; the spinning temperature is 23-28 ℃, and the spinning humidity is 15-25% RH.
6. The method for preparing an electrospun nanofiber-based double skin forward osmosis membrane according to claim 3, characterized in that said polyamine compound contains at least two reactive amino groups, comprising any one or more of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, s-phenylenediamine, ethylenediamine, propylenediamine, hexamethylenediamine, 1, 4-cyclohexanediamine, 1, 3-cyclohexanediamine, piperazine;
The polybasic acyl chloride compound at least contains two reactive acyl chloride groups, including one or more of trimesoyl chloride, paraphthaloyl chloride, isophthaloyl chloride and phthaloyl chloride;
The organic solvent is an organic solvent which can dissolve acyl chloride monomers but not polyamide in aliphatic hydrocarbons, cycloaliphatic hydrocarbons and aromatic hydrocarbons of which the monomers contain 4-12 carbon atoms, and comprises n-hexane, cyclohexane, n-heptane, xylene and Isopar-G.
7. The method for preparing an electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, characterized in that the mass concentration of the polyamine compound in the first aqueous phase solution is 3.0% to 5.0%, and the mass concentration of the polyamine compound in the second aqueous phase solution is 1.0% to 3.0%; the mass concentration of the polybasic acyl chloride compound in the first organic phase solution is 0.1-0.5%, and the mass concentration of the polybasic acyl chloride compound in the second organic phase solution is 0.05-0.3%.
8. The method for preparing an electrospun nanofiber-based double-skin forward osmosis membrane according to claim 3, wherein the first specified time is 2-5 min; the second designated time is 1-3 min; the third designated time is 1-3 min; the fourth designated time is 0.5-2 min; naturally airing in the air for 2-5 min; the temperature of the oven is 40-80 ℃; the heat treatment time is 5-15 min.
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