CN113385044A - Nanofiltration membrane prepared based on electrostatic enhanced reaction surface segregation method and application thereof - Google Patents
Nanofiltration membrane prepared based on electrostatic enhanced reaction surface segregation method and application thereof Download PDFInfo
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Abstract
The invention discloses a method for preparing a nanofiltration membrane based on electrostatic enhanced reaction surface segregation. The method mainly comprises the following steps: preparing a quaternary ammonium salt modifier with positive charges by adopting an emulsion polymerization method initiated by a redox cerium salt system; then dissolving the modifier and the film forming polymer in a solvent, stirring and heating to prepare a film building liquid; and finally, adding a polysulfonic acid solution with negative charges into the coagulating bath to prepare the anti-pollution dye separation membrane by a non-solvent induced phase inversion method. The advantages of the invention mainly include: the preparation method can adjust the surface property of the selective separation layer by adjusting the number of quaternary ammonium salt monomers in the modifier and the concentration of the polysulfonic acid in the coagulating bath; the separation membrane prepared by the method has ultra-oleophobic property under water and ultra-strong anti-pollution property; the membrane prepared by the method has good dye separation performance; the dye separation active layer can be constructed and the anti-pollution performance of the membrane surface can be realized simultaneously in the phase inversion process.
Description
Technical Field
The invention relates to a method for preparing an anti-pollution dye separation membrane by carrying out electrostatic enhanced reaction surface segregation, and belongs to the technical field of preparation of anti-pollution nanofiltration membranes.
Background
Water resource shortage and water quality deterioration are common challenges for mankind in the 21 st century. It is estimated that 80% of the wastewater worldwide is discharged directly without treatment, causing great damage to the environment and ecology, and also causing serious waste of resources. Wherein, the dye wastewater contains benzene series, naphthalene series, anthraquinone, aniline, benzidine, metal, salt and other compounds, has the characteristics of high chemical oxygen demand, high chroma and high toxicity, has carcinogenic, teratogenic and mutagenic three-cause threats to organisms, and is one of industrial wastewater which is difficult to treat. China becomes the first major country of the production quantity, trade quantity and consumption quantity of dyes in the world, however, the produced dye wastewater not only causes great waste of resources, but also generates huge burden on the environment, and becomes one of important factors threatening the water environmental safety in China. Therefore, the advanced treatment and the reuse of the dye wastewater meet the great national requirements.
New, efficient, green membrane technology is one of the most competitive water treatment technologies in the 21 st century. The core of membrane technology is to prepare selective separation membranes for device integration and application. Compared with the traditional water treatment technologies such as precipitation, distillation, flocculation, adsorption and the like, the membrane technology has the following advantages: the energy consumption is low. The membrane technology mainly realizes separation based on physical properties, is mostly carried out at normal temperature, and has the theoretical energy efficiency higher than that of rectification by 90 percent. And secondly, the operation is simple. The membrane separation device is compact and small in size, equipment can be flexibly configured according to the treatment capacity, and centralized operation is facilitated. And thirdly, the application is wide. The membrane technology has almost no requirements on the type and the pollution degree of sewage, can realize liquid separation without adding an auxiliary agent, and does not cause secondary pollution.
Membrane fouling is a bottleneck problem in the development of membrane technology. The pollutants in the wastewater can block the membrane pores, and a filter cake layer is formed on the surface of the membrane, so that serious membrane pollution is caused, and serious problems of sharp flux reduction, energy consumption increase, frequent cleaning, short service life and the like are caused. Among them, organic contaminants inevitably undergo hydrogen bonding interaction, van der waals force or hydrophobic interaction at the membrane surface and are difficult to remove from the water purification system. For a dye separation membrane system with smaller membrane pores, the blockage is easier, so that the problem of organic pollutants in the dye separation system is particularly urgent to solve.
Disclosure of Invention
Aiming at the prior art, the construction of an ultra-strong hydration layer on the surface of the membrane is an effective anti-pollution strategy, the invention provides a method for preparing a nanofiltration membrane based on an electrostatic enhanced reaction surface segregation method, and the preparation method is to construct a dye separation membrane with a selective separation layer with underwater super-oleophylic and anti-pollution performances by an electrostatic enhanced surface segregation phase separation method. Under the action of strong electrostatic force, the poly sulfonic acid with negative charge in the coagulating bath enhances the segregation of hydrophilic quaternary ammonium groups with positive charge in the membrane building liquid, and a selective separation layer is directly assembled in situ in the non-solvent induced phase separation process, so that the method has the characteristics of simplicity, easiness in operation and excellent membrane performance.
In order to solve the technical problems, the invention provides a method for preparing a nanofiltration membrane based on electrostatic enhanced reaction surface segregation, which comprises the following steps:
the method comprises the following steps: preparation of the quaternary ammonium salt modifier with positive charge: dissolving pluronic F127 and methacryloyloxyethyl trimethyl ammonium chloride into a certain amount of deionized water according to a molar ratio of 16-64, wherein the mass ratio of the deionized water to the pluronic F127 is 15: 1; adding a cerium ammonium nitrate initiator, stirring at a high speed in a nitrogen atmosphere, carrying out a polymerization reaction for 8 hours at 60 ℃, dialyzing to obtain a quaternary ammonium salt modified polymer with positive charges, and marking as F127-Qn, wherein n is the molar ratio of pluronic F127 to methacryloyloxyethyl trimethyl ammonium chloride;
step two: preparing a membrane building liquid: mixing the F127-Qn prepared in the step one and a solvent according to a mass ratio of 2: 1: 8, adding the mixture into a container, heating and stirring the mixture for 8 hours at the temperature of 60 ℃, and then standing and defoaming the mixture for 2 hours at the temperature of 60 ℃ until no obvious bubbles exist for later use;
step three: preparation of negatively charged polysulfonic acid coagulation bath: adding 1-5% of a negatively charged polysulfonic acid aqueous solution in percentage by mass into a container, and carrying out ultrasonic treatment until the solution is fully dissolved for later use;
step four: in-situ synthesis of a nanofiltration membrane: cooling the casting solution prepared in the second step to room temperature, pouring the casting solution on a glass plate, scraping the casting solution into a liquid film with the thickness of 240 microns, keeping the temperature at 25 ℃, putting the liquid film into the polysulfonic acid coagulating bath with negative charges prepared in the third step for 5 minutes, curing, forming the film and taking out the film; and taking the solid film off the glass plate, and soaking the solid film in deionized water for 24 hours to obtain the nanofiltration membrane.
In the method for preparing a nanofiltration membrane, in the first step, the molar ratio of pluronic F127 to methacryloyloxyethyl trimethyl ammonium chloride is preferably 64.
In the second step, the film-forming polymer is FR921-2 type polyvinylidene fluoride, and the solvent is dimethyl sulfoxide.
In the third step, the mass percent of the polysulfonic acid aqueous solution is 4%.
Compared with the prior art, the invention has the beneficial effects that:
the preparation method can adjust the properties of the thickness, chemical composition, surface Zeta potential and the like of the selective separation layer generated in situ by changing the feed ratio of the polysulfonic acid in the coagulating bath, further regulate and control the composition structure and performance of the nanofiltration membrane, and realize dye separation, underwater superoleophobic property and strong anti-fouling property.
The nanofiltration membrane prepared by the invention is used for separating the anti-pollution dye; the separation performance was: the pure water flux is 45-124 Lm-2h-1bar-1A, AThe ERXIN blue rejection rate is 99.7-100%, the Congo red rejection rate is 95.7-99.7%, and the methyl blue rejection rate is 95.9-97.9%; the oil-water emulsion of the pump oil of 0.9g/L is used as a filter, and the underwater super oleophobic and anti-pollution performance is as follows: the Zeta potential on the surface is-15.6-13.7 mV, the underwater oil contact angle is 151-167.3 mV, the permeability recovery rate (FRR) is 93.4-99.9%, the total permeability reduction rate (DRt) is 1.3-15.6%, the reversible permeability reduction rate (DRr) is 1.2-16.4%, and the irreversible permeability reduction rate (DRir) is 0.1-6.6%.
Drawings
FIG. 1 shows the underwater super-oleophobic property of the nanofiltration membrane prepared in comparative examples 1-3 and example 4.
Fig. 2 is an anti-contamination index of the nanofiltration membrane prepared in comparative examples 1 and 3 and example 4, which comprises: permeability recovery (FRR), irreversible permeability reduction (DRir), total permeability reduction (DRt), and reversible permeability reduction (DRr); wherein the filtrate is 0.9g/L pump oil water emulsion.
Detailed Description
The invention provides a method for preparing a nanofiltration membrane based on electrostatic enhanced reaction surface segregation, which has the design concept that: it is known that, the improvement of the hydrophilicity of the membrane surface is an effective measure for improving the anti-fouling property of the membrane surface, and water molecules can form a hydration layer on the hydrophilic membrane surface to prevent the interaction between the membrane surface and organic pollutants. The electrostatically induced hydration is 7 times higher water absorption than the hydrogen bond induced hydration. Thus, the ionized groups on the membrane surface can provide strong hydration to form a hydrated layer, inhibiting contaminants from reaching the membrane surface. Surface segregation is a simple in-situ modification method, and charged hydrophilic groups can be enriched on the surface of the membrane in the phase separation process. The enrichment effect of charged hydrophilic groups can be further enhanced by adding reactants that undergo strong electrostatic interactions with the segregating agent in the coagulation bath. In the method for preparing the nanofiltration membrane, the anti-pollution modifier is added into the membrane casting solution in advance in an in-situ blending mode to form a homogeneous system, and then the homogeneous system is coupled with a phase conversion process, so that the in-situ construction of the surface of the membrane can be realized. The preparation method has the advantages that the membrane modification process and the phase inversion process are synchronously carried out, the method does not depend on the membrane main body structure, and complex post-treatment steps are not needed.
The invention provides a method for preparing an anti-pollution dye separation membrane by static enhanced reaction surface segregation, which mainly adopts an emulsion polymerization method initiated by a redox cerium salt system to prepare a quaternary ammonium salt modifier with positive charges; then dissolving the modifier and the film forming polymer in a solvent, stirring and heating to prepare a film building liquid; and finally, adding a polysulfonic acid solution with negative charges into the coagulating bath, and finally synthesizing the nanofiltration membrane in situ by a non-solvent induced phase inversion method. The membrane modification process and the phase transformation process are carried out synchronously, the membrane is independent of a membrane main body structure, complex post-treatment steps are not needed, and a dye separation active layer is constructed and the anti-pollution performance of the membrane surface is realized simultaneously in the phase transformation process. In the preparation process, the surface property of the selective separation layer is adjusted by adjusting the number of quaternary ammonium salt monomers in the modifier and the concentration of the polysulfonic acid in the coagulating bath; the nanofiltration membrane prepared by the method has good dye separation performance, and has good dye separation performance, underwater super-oleophobic property and super-strong anti-pollution performance when being used for anti-pollution dye separation.
The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.
Comparative example 1, a comparative separation membrane 1 was prepared by the following process:
adding 800mg of FR921-2 type polyvinylidene fluoride, 400mg of pluronic F127 and 3200mg of dimethyl sulfoxide into a round-bottom flask, heating and stirring in a water bath at 60 ℃ for 8 hours, and standing and defoaming for 2 hours to prepare the casting solution. And pouring the casting solution on a glass plate, scraping the casting solution into a liquid film with the thickness of about 240 mu m, putting the liquid film into a constant-temperature 25 ℃ deionized water coagulating bath, curing for 5min to form a film, taking the film from the glass plate, and soaking the film in deionized water for 24h to prepare the comparative separation membrane 1.
Fig. 1 shows the underwater oil contact angle of the comparative example separation membrane 1, and fig. 2 shows the anti-contamination index of the comparative example separation membrane 1 for a pump oil-water emulsion having a filtrate of 0.9 g/L.
Comparative example separation Membrane 1 was used as a dye separation Membrane with a pure water specific flux of 501Lm-2h-1bar-1(ii) a AThe retention rates of the Erxin blue, the Congo red and the methyl blue are respectively 96.1%, 81.6% and 82.4%; zeta potential-12.1 mV; the underwater oil contact angle is 129.2 degrees; the anti-pollution indices FRR, DRt, DRr and DRir are 64.0%, 36.6%, 0.64% and 36.0%, respectively.
In the test data of the invention, Zeta potential is measured by a Zeta potential analyzer, the underwater oil contact angle is obtained by measuring a contact angle meter, and flux, rejection rate, FRR, DRir, DRt and DRr are calculated by the following formulas:
flux-volume/membrane area/time/pressure
Retention rate is dye absorbance after filtration/crude dye absorbance 100%
FRR ═ recovery water flux/water flux 100%
DRir ═ water flux-recovery water flux)/water flux 100%
DRt ═ 100% of (water flux-oil flux)/water flux
DRir ═ recovery water flux-oil flux)/water flux 100%
Wherein, the anti-pollution test process test solution is firstly water and is recorded as water flux, then the test solution is changed into oil and is recorded as oil flux, finally the test solution is changed into water and is recorded as recovery water flux, and the absorbance is measured by an ultraviolet visible spectrophotometer.
Comparative example 2, a comparative separation membrane 2 was prepared by the following process:
step one, adding 800mg of FR921-2 type polyvinylidene fluoride, 400mg of pluronic F127 and 3200mg of dimethyl sulfoxide into a round-bottom flask, heating and stirring for 8 hours in a water bath at 60 ℃, and standing and defoaming for 2 hours to prepare a casting solution.
And step two, pouring the casting solution prepared in the step one onto a glass plate, scraping the casting solution into a liquid film with the thickness of about 240 microns, putting the liquid film into a coagulating bath of a 4% polysulfonic acid aqueous solution at the constant temperature of 25 ℃, curing for 5min to form a film, taking the film off the glass plate, and soaking the film in deionized water for 24h to prepare the separation membrane 2 for the comparative example.
Fig. 1 shows the underwater oil contact angle of the comparative example separation membrane 2. The pure water specific flux of the separation membrane 2 of this comparative example was 388Lm-2h-1bar-1(ii) a Alxin blue and steelThe fruit red and methyl blue retention rates are 96.6%, 77.2% and 24.6% respectively; zeta potential-30.3 mV; underwater oil contact angle 147 °; the anti-pollution indices FRR, DRt, DRr and DRir were 67.8%, 34.8%, 33.8% and 32.2%, respectively.
Comparative example 3, comparative example separation membrane 3 was prepared by the following steps:
step one, preparing a quaternary ammonium salt modifier with positive charges: 5.33g of pluronic F127 and 4.812mL of methacryloyloxyethyl trimethyl ammonium chloride (molar ratio 64) were dissolved in 80mL of deionized water (mass ratio of deionized water to pluronic F127 was 15: 1); adding cerium ion initiator, stirring at high speed under nitrogen atmosphere, performing polymerization reaction at 60 deg.C for 8 hr, dialyzing to obtain quaternary ammonium salt modified polymer with positive charge, labeled as F127-Q64。
Step two, 800mg of FR921-2 type polyvinylidene fluoride and 400mg of F127-Q prepared in the step one64Adding 3200mg of dimethyl sulfoxide into a round-bottom flask, heating and stirring in a water bath at 60 ℃ for 8 hours, and standing and defoaming for 2 hours to obtain the membrane casting solution.
And step three, pouring the casting solution prepared in the step two onto a glass plate, scraping the casting solution into a liquid film with the thickness of about 240 microns, putting the liquid film into a deionized water coagulating bath with the constant temperature of 25 ℃, curing for 5min to form a film, taking the film from the glass plate, and soaking the film in deionized water for 24h to obtain the comparative example separation membrane 3.
FIG. 1 shows the underwater oil contact angle of the proportional separation membrane 3, FIG. 2 shows the anti-fouling index of the proportional separation membrane 3, wherein the filtrate is 0.9g/L pump oil water emulsion, and the pure water specific flux of the proportional separation membrane 3 is 467Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are 97.1%, 79.7% and 75.3% respectively; zeta potential 20.3 mV; the underwater oil contact angle is 129 degrees; the anti-pollution indices FRR, DRt, DRr and DRir were 73.7%, 42.1%, 15.8% and 26.3%, respectively.
Comparative example 4, comparative example separation membrane 4 was prepared by the following steps:
step one, preparing a quaternary ammonium salt modifier with positive charges: 5.33g of Pluronic F127 and 0.3mL of methacryloyloxyethyltrimethyl ammonium chloride (molar ratio 4)Dissolving in 80mL of deionized water; adding cerium ion initiator, stirring at high speed under nitrogen atmosphere, performing polymerization reaction at 60 deg.C for 8 hr, dialyzing to obtain quaternary ammonium salt modified polymer with positive charge, labeled as F127-Q4。
Step two, 800mg of FR921-2 type polyvinylidene fluoride and 400mg of F127-Q prepared in the step one4Adding 3200mg of dimethyl sulfoxide into a round-bottom flask, heating and stirring in a water bath at 60 ℃ for 8 hours, and standing and defoaming for 2 hours to obtain the membrane casting solution.
And step three, pouring the casting solution prepared in the step two onto a glass plate, scraping the casting solution into a liquid film with the thickness of about 240 microns, putting the liquid film into a deionized water coagulating bath with the constant temperature of 25 ℃, curing for 5min to form a film, taking the film from the glass plate, and soaking the film in deionized water for 24h to obtain the comparative example separation membrane 4.
Comparative example separation Membrane 4 pure Water specific flux 418Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are 96.6%, 88.7% and 52.9% respectively; zeta potential-41.8 mV; the underwater pump oil contact angle is 149 degrees; the anti-pollution indices FRR, DRt, DRr and DRir were 75.6%, 40.3%, 18.6% and 24.4%, respectively.
Comparative example 5, a comparative example separation membrane 5 was prepared by the following steps:
step one, preparing a quaternary ammonium salt modifier with positive charges: 5.33g of pluronic F127 and 9.624mL of methacryloyloxyethyltrimethyl ammonium chloride (molar ratio 128) were dissolved in 80mL of deionized water; adding cerium ion initiator, stirring at high speed under nitrogen atmosphere, performing polymerization reaction at 60 deg.C for 8 hr, dialyzing to obtain quaternary ammonium salt modified polymer with positive charge, labeled as F127-Q128。
Step two, 800mg of FR921-2 type polyvinylidene fluoride and 400mg of F127-Q prepared in the step one128Adding 3200mg of dimethyl sulfoxide into a round-bottom flask, heating and stirring in a water bath at 60 ℃ for 8 hours, and standing and defoaming for 2 hours to obtain the membrane casting solution.
And step three, pouring the casting solution prepared in the step two onto a glass plate, scraping the casting solution into a liquid film with the thickness of about 240 microns, putting the liquid film into a deionized water coagulating bath with the constant temperature of 25 ℃, curing for 5min to form a film, taking the film from the glass plate, and soaking the film in deionized water for 24h to obtain the comparative example separation membrane 5.
Comparative example separation Membrane 5 pure Water specific flux 418Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are 96.6%, 88.7% and 52.9% respectively; zeta potential-41.8 mV; the underwater pump oil contact angle is 149 degrees; the anti-pollution indices FRR, DRt, DRr and DRir were 75.6%, 40.3%, 18.6% and 24.4%, respectively.
Comparative example separation Membrane 5 had a pure water specific flux of 330Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are 96.6%, 73.7% and 59.0% respectively; zeta potential 37.4 mV; the underwater pump oil contact angle is 161 degrees; the anti-pollution indices FRR, DRt, DRr and DRir were 86.2%, 32.6%, 23.5% and 13.8%, respectively.
Example 1, preparation of example separation membrane 1, the preparation procedure was as follows:
step one, dissolving 5.33g of pluronic F127 and 4.812mL of methacryloyloxyethyl trimethyl ammonium chloride (the molar ratio is 64) in 80mL of deionized water; adding cerium ion initiator, stirring at high speed under nitrogen atmosphere, performing polymerization reaction at 60 deg.C for 8 hr, dialyzing to obtain quaternary ammonium salt modified polymer with positive charge, labeled as F127-Q64。
Step two, 800mg of FR921-2 type polyvinylidene fluoride and 400mg of F127-Q prepared in the step one64Adding 3200mg of dimethyl sulfoxide into a round-bottom flask, heating and stirring in a water bath at 60 ℃ for 8 hours, and standing and defoaming for 2 hours to obtain the membrane casting solution.
Step three: adding 1% by mass of a negatively charged polysulfonic acid aqueous solution into a container, and carrying out ultrasonic treatment for 0.5h until the solution is fully dissolved to prepare a negatively charged coagulation bath for later use;
step four, cooling the casting solution prepared in the step two to room temperature, pouring the casting solution onto a glass plate, scraping the casting solution into a liquid film with the thickness of about 240 microns, keeping the temperature at 25 ℃, putting the glass plate into the poly sulfonic acid coagulation bath with negative charges prepared in the step three, curing for 5min to form a film, taking the glass plate down, and soaking the glass plate in deionized water for 24h to obtain the nanofiltration membrane marked as the separation membrane 1 in the embodiment.
Practice ofExample separation Membrane 1 had a pure water specific flux of 45Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are 100%, 98.4% and 95.9% respectively; the Zeta potential is 6.5 mV; underwater oil contact angle 159.8 °; the anti-pollution indices FRR, DRt, DRr and DRir were 94.5%, 5.6%, 101% and 4.5%, respectively.
Example 2, preparation of example separation membrane 2, the preparation process was substantially the same as in example 1 except that: in the third step, the mass percent of the water solution of the polysulfonic acid with negative charges is changed from 1 percent to 2 percent, and finally the nanofiltration membrane is marked as an anti-pollution separation membrane 2.
Example the separation membrane 2 had a pure water specific flux of 121Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are respectively 99.9%, 99.7% and 97.6%; zeta potential 13.7 mV; the underwater oil contact angle is 167.3 degrees; the anti-pollution indices FRR, DRt, DRr and DRir were 98.2%, 2.2%, 0.33% and 1.8%, respectively.
Example 3, an anti-contamination dye separation membrane 3 was prepared by substantially the same procedure as in example 1 except that: in the third step, the mass percent of the negatively charged polysulfonic acid aqueous solution is changed from 1% to 3%, and finally the prepared nanofiltration membrane is marked as an example separation membrane 3.
Example the pure water specific flux of the separation membrane 3 was 119Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are respectively 100%, 97.3% and 97.4%; zeta potential 10.5 mV; the underwater oil contact angle is 161.3 degrees; the anti-pollution indices FRR, DRt, DRr and DRir were 97.3%, 10.2%, 12.4% and 2.7%, respectively.
Example 4, preparation of example separation membrane 4, the preparation process was substantially the same as in example 1 except that: in the third step, the mass percent of the negatively charged polysulfonic acid aqueous solution is changed from 1% to 4%, and finally the prepared nanofiltration membrane is marked as an example separation membrane 4.
FIG. 1 shows the underwater oil contact angle of the separation membrane 4 of the example, and FIG. 2 shows the anti-fouling index of the separation membrane 4 of the example with a 0.9g/L filtrate of oil-water emulsion of pump oil. EXAMPLES separation membranes4 pure water specific flux of 124Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are respectively 100%, 98.3% and 97.9%; zeta potential-6.5 mV; underwater oil contact angle 166.9 °; the anti-pollution indices FRR, DRt, DRr and DRir are 99.9%, 1.3%, 1.2% and 0.1%, respectively.
Example 5, preparation of example separation membrane 5, the preparation process was substantially the same as in example 1 except that: in the third step, the mass percent of the negatively charged polysulfonic acid aqueous solution is changed from 1% to 5%, and finally the prepared nanofiltration membrane is marked as an example separation membrane 5.
Example the separation membrane 5 had a pure water specific flux of 124Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are respectively 100%, 98.3% and 97.9%; zeta potential-15.6 mV; underwater oil contact angle 166.4 °; the anti-pollution indices FRR, DRt, DRr and DRir are 99.0%, 1.7%, 2.7% and 1.0%, respectively.
Example 6, preparation example separation membrane 6, the preparation process was substantially the same as in example 1 except that: in the first step, the amount of methacryloyloxyethyltrimethyl ammonium chloride was changed from 4.812mL to 1.203mL (i.e., the molar ratio of methacryloyloxyethyltrimethyl ammonium chloride was changed from 64 to 16), and in the second step, the mass percent of the negatively charged polysulfonic acid aqueous solution was changed from 1% to 4%, and finally the nanofiltration membrane prepared was recorded as the separation membrane 6 of example.
Example the separation membrane 6 had a pure water specific flux of 96.8Lm-2h-1bar-1(ii) a The retention rates of the alcian blue, the congo red and the methyl blue are respectively 99.7%, 95.7% and 96.2%; zeta potential-3.8 mV; an underwater pump oil contact angle is 151 degrees; the anti-pollution indices FRR, DRt, DRr and DRir were 93.4%, 15.6%, 16.4% and 6.6%, respectively.
The flux and separation performance of the anti-contamination dye separation membranes prepared in examples 1 to 6 of the present invention are compared with those of the separation membranes prepared in comparative examples 1 to 5 as shown in table 1:
TABLE 1 analysis of separation Membrane flux and separation Performance
The underwater superoleophobic and anti-pollution performances of the anti-pollution dye separation membranes prepared in examples 1 to 6 of the invention and the separation membranes prepared in comparative examples 1 to 5 are compared as shown in Table 2:
TABLE 2 analysis of the underwater superoleophobic and anti-contamination Properties of separation Membrane
In conclusion, the preparation method provided by the invention can form the membrane by a one-step method, the structure of the anti-pollution layer on the surface of the membrane can be regulated and controlled by the concentration of the polysulfonic acid in the coagulating bath, the retention rate of the dye is increased by adding the polysulfonic acid in the coagulating bath, the surface of the membrane becomes super oleophobic underwater, and the anti-pollution performance is enhanced. With the increase of the concentration of the polysulfonic acid, the flux of the separation membrane is reduced firstly and then tends to be unchanged, and the Zeta potential is positive and then negative. When the mass percent of the polysulfonic acid in the coagulating bath is 4%, the prepared dye separation membrane has better comprehensive performance. The separation performance of the dye separation membrane is influenced by the different molar ratios of F127 and methacryloyloxyethyltrimethyl ammonium chloride, the separation performance of the dye is firstly increased and then decreased along with the increase of the molar ratio n, and when n is 64, the prepared nanofiltration membrane has better dye separation performance.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.
Claims (5)
1. A method for preparing a nanofiltration membrane based on electrostatic enhanced reaction surface segregation is characterized by comprising the following steps:
the method comprises the following steps: preparation of the quaternary ammonium salt modifier with positive charge: dissolving pluronic F127 and methacryloyloxyethyl trimethyl ammonium chloride into a certain amount of deionized water according to a molar ratio of 16-64, wherein the mass ratio of the deionized water to the pluronic F127 is 15: 1; adding a cerium ammonium nitrate initiator, stirring at a high speed in a nitrogen atmosphere, carrying out a polymerization reaction for 8 hours at 60 ℃, dialyzing to obtain a quaternary ammonium salt modified polymer with positive charges, and marking as F127-Qn, wherein n is the molar ratio of pluronic F127 to methacryloyloxyethyl trimethyl ammonium chloride;
step two: preparing a membrane building liquid: mixing the F127-Qn prepared in the step one and a solvent according to a mass ratio of 2: 1: 8, adding the mixture into a container, heating and stirring the mixture for 8 hours at the temperature of 60 ℃, and then standing and defoaming the mixture for 2 hours at the temperature of 60 ℃ until no obvious bubbles exist for later use;
step three: preparation of negatively charged polysulfonic acid coagulation bath: adding 1-5% of a negatively charged polysulfonic acid aqueous solution in percentage by mass into a container, and carrying out ultrasonic treatment until the solution is fully dissolved for later use;
step four: in-situ synthesis of a nanofiltration membrane: cooling the casting solution prepared in the second step to room temperature, pouring the casting solution on a glass plate, scraping the casting solution into a liquid film with the thickness of 240 microns, keeping the temperature at 25 ℃, putting the liquid film into the polysulfonic acid coagulating bath with negative charges prepared in the third step for 5 minutes, curing, forming the film and taking out the film; and taking the solid film off the glass plate, and soaking the solid film in deionized water for 24 hours to obtain the nanofiltration membrane.
2. The method for preparing nanofiltration membrane according to claim 1, wherein in the first step, the pluronic F127 and the methacryloyloxyethyltrimethyl ammonium chloride are mixed in a molar ratio of 64.
3. The method for preparing nanofiltration membrane according to claim 1 or 2, wherein in the second step, the film-forming polymer is FR921-2 type polyvinylidene fluoride, and the solvent is dimethyl sulfoxide.
4. The method for preparing nanofiltration membrane according to claim 1 or 2, wherein in the third step, the mass percent of the aqueous solution of polysulfonic acid is 4%.
5. The application of the nanofiltration membrane prepared based on the surface segregation through the electrostatic enhanced reaction is characterized in that the nanofiltration membrane prepared by the method for preparing the nanofiltration membrane is used for separating the anti-pollution dye;
the separation performance was: the pure water flux is 45-124 Lm-2h-1bar-1The Alsinoblue rejection rate is 99.7-100%, the Congo red rejection rate is 95.7-99.7%, and the methyl blue rejection rate is 95.9-97.9%;
the oil-water emulsion of the pump oil of 0.9g/L is used as a filter, and the underwater super oleophobic and anti-pollution performance is as follows: the Zeta potential on the surface is-15.6-13.7 mV, the underwater oil contact angle is 151-167.3 mV, the permeability recovery rate (FRR) is 93.4-99.9%, the total permeability reduction rate (DRt) is 1.3-15.6%, the reversible permeability reduction rate (DRr) is 1.2-16.4%, and the irreversible permeability reduction rate (DRir) is 0.1-6.6%.
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