CN110917891B - Preparation method of modified polyacrylonitrile forward osmosis membrane - Google Patents
Preparation method of modified polyacrylonitrile forward osmosis membrane Download PDFInfo
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Abstract
The invention belongs to the field of new materials, and relates to a preparation method of a modified polyacrylonitrile forward osmosis membrane, wherein the forward osmosis membrane is obtained by chemically modifying PAN, a PAN membrane is modified by NaOH, HCl and the like, then an MOFs material-Cu-BTC with a porous structure is introduced, and a continuous and compact Cu-BTC membrane layer is obtained on the surface of the membrane by a layer-by-layer self-assembly method, so that the performance of the membrane is better improved, the salt rejection rate and the organic pollutant separation efficiency of the membrane are improved, the water flux of the membrane is not influenced, the double improvement of the salt rejection rate and the water flux is realized, and meanwhile, the modified polyacrylonitrile forward osmosis membrane has good tolerance of organic solvents, acids and alkalis, and the application range of the modified separation membrane is widened; meanwhile, the smooth surface of the material is not beneficial to the breeding of bacteria, and the pollution resistance of the modified separation membrane can be improved.
Description
Technical Field
The invention relates to the technical field of new materials, and particularly provides a preparation method of a modified polyacrylonitrile forward osmosis membrane.
Background
Along with the increasing of population density year by year, the scale and the range of production and living are continuously enlarged, the demand of human beings on fresh water resources is larger and larger, and the water resources which can be utilized at the present stage are very deficient. Most of the area of the earth is covered by oceans. At present, a plurality of water treatment modes such as seawater desalination, wastewater recycling and the like are generally adopted to obtain sufficient fresh water supply, but the modes are at the cost of consuming a large amount of energy. The membrane separation technology is a new technology for water treatment application, has the characteristics of high output efficiency, environmental friendliness, low energy consumption, strong adaptability, small occupied area and the like, and is practically applied to the fields of wastewater treatment, sewage recycling, seawater desalination and the like.
Forward Osmosis (FO) technology uses the osmotic pressure difference across a membrane to drive water across a permselective membrane to produce net transport and obtain pure water. The forward osmosis membrane technology has the unique advantages over other technologies of no or only low applied pressure and strong anti-fouling properties. In recent years, FO membranes have made great progress and have also expanded the field in which they can be used. Nevertheless, the drawbacks of low water flux, low salt rejection and insufficient mechanical strength of the membrane have inhibited the further development of FO technology. It is imperative to produce FO membranes that can meet the requirements of high water flux and high salt rejection.
Polyacrylonitrile (PAN) is a very important membrane material, has good solvent resistance, thermal stability, chemical stability and mechanical properties, and is suitable for preparing a basement membrane of a water treatment membrane. Therefore, polyacrylonitrile membranes have been used as membrane materials in the fields of water treatment, hemodialysis, chemical industry, agriculture, food and the like. However, PNA membranes are less hydrophilic and can be chemically modified to increase their hydrophilic properties. The commonly used modification methods mainly include physical modification and chemical modification. The physical modification is to physically dope substances with the functions of pollution resistance, hydrophilicity and the like into a separation layer of the PNA membrane or coat the PNA membrane on the surface of the PNA membrane so as to improve the performance of the PNA membrane; the chemical modification means that a modifying agent is utilized to treat a membrane material, and various functional groups are introduced to the surface of the membrane to improve the surface performance of the membrane. Metal organic framework Materials (MOFs) are a class of inorganic-organic hybrid materials formed by coordination of metal ions and organic ligands. By virtue of the advantages of controllable aperture, stable performance and the like, the method has attracted extensive attention in modification aspects of gas separation membranes, organic macromolecular separation membranes and the like. The modification methods of the existing polyacrylonitrile membrane are physical blending modification and chemical grafting modification. The MOFs is introduced into the preparation process of the membrane by a physical modification method, the common method is that the MOFs and a small molecular pore-forming agent are used as mixed additives and mixed and dissolved with PAN by a blending method to prepare a membrane casting solution, and the prepared membrane has defects on the surface due to the uneven dispersion of the additives, so that a water channel is formed on the surface of the membrane, salt ions permeate the membrane along the channel, the flux of the membrane is increased when the membrane is used for water treatment, and the salt rejection rate is reduced; in the conventional chemical grafting modification, for example, a polyamide membrane layer is modified on the surface of polyacrylonitrile by an interfacial polymerization method, and according to literature reports, the modified composite membrane has the characteristics of large contact angle, poor hydrophilicity, lower retention rate than that of a base membrane and no practical significance for water treatment.
However, the prior art does not have the related art of better applying metal organic framework Materials (MOFs) to the forward osmosis membrane, and the corresponding technical teaching is lacking to help those skilled in the art to overcome the above-mentioned drawbacks of the prior art and obtain a better forward osmosis membrane.
Disclosure of Invention
Aiming at the blank existing in the prior art, the invention provides a preparation method of a modified polyacrylonitrile forward osmosis membrane, the forward osmosis membrane is obtained by chemically modifying PAN, the PAN membrane is modified by NaOH, HCl and the like, then an MOFs material with a porous structure, namely Cu-BTC, is introduced, and a continuous and compact Cu-BTC membrane layer is obtained on the surface of the membrane by a layer-by-layer self-assembly method, so that the performance of the membrane is better improved, the salt rejection rate and the organic pollutant separation efficiency of the membrane are improved, the water flux of the membrane is not influenced, the double improvement of the salt rejection rate and the water flux is realized, and meanwhile, the modified polyacrylonitrile forward osmosis membrane has good tolerance of organic solvents, acids and alkalis, and the application range of the modified separation membrane is widened; meanwhile, the smooth surface of the material is not beneficial to the breeding of bacteria, and the pollution resistance of the modified separation membrane can be improved.
The main ideas of the invention are as follows:
the inventors have discovered that the incorporation of MOFs into PAN substrate membranes greatly improves the overall performance of the composite membrane. The Cu-BTC crystal is a porous material with a three-dimensional network structure, which is formed by main pore channels with the diameter of 0.9nm and side pore channels with the diameter of 0.35 nm; in theory, richer water channels and higher salt rejection rate can be constructed for the water treatment process.
The performance of the polyacrylonitrile base membrane can be optimized by hydrolyzing the polyacrylonitrile membrane in an alkaline environment, so that the charged treatment of the polyacrylonitrile base membrane is realized, a large amount of carboxylate (-COO-) can be formed on the surface of the polyacrylonitrile membrane after the polyacrylonitrile membrane is hydrolyzed under the alkaline condition, the carboxylate serving as polyanion can be combined with polycation to be combined through the electrostatic adsorption principle to form a cross-linked structure, the structure can prevent the peeling phenomenon between the modified layer and the base membrane, the operation stability and the service life of the composite membrane can be improved, and the mechanical strength and the biocompatibility of the composite membrane can be enhanced.
Based on the method, the polyacrylonitrile-based membrane is alkalized and acidified, and MOFs materials are self-assembled layer by layer on the modified polyacrylonitrile-based membrane: Cu-BTC crystal, and then testing and characterizing the MOFs modified polyacrylonitrile forward osmosis membrane.
The specific technical scheme of the invention is as follows:
a preparation method of a modified polyacrylonitrile forward osmosis membrane comprises the following specific steps:
(1) pretreatment of polyacrylonitrile-based film
Cutting a polyacrylonitrile ultrafiltration membrane to be modified into sheets with corresponding specifications, soaking the sheets in an ultrapure water solution for 24 hours at room temperature, taking out the soaked membrane, washing the membrane with ultrapure water after taking out, and drying the membrane in an electrothermal blowing drying oven at 40 ℃ for later use after washing;
through the pretreatment, the pollution on the surface of the base film can be prevented, and the influence on the next modification can be prevented;
(2) hydrolysis modification of polyacrylonitrile base membrane:
preparing 2.0mol/L NaOH solution for later use; placing the polyacrylonitrile ultrafiltration membrane to be modified in a culture dish, adding a prepared NaOH solution into the culture dish, standing the polyacrylonitrile ultrafiltration membrane in a constant-temperature water bath at 50-60 ℃ for 0.5-0.8h for hydrolysis, taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane, and repeatedly washing the polyacrylonitrile ultrafiltration membrane with ultrapure water for multiple times until the washing liquid is neutral; after washing, drying in an electrothermal blowing dry box at 40 ℃, and after drying, sealing and storing in a sealing bag, wherein the process is an alkalization process of the film;
(3) hydrolysis modification of polyacrylonitrile base membrane:
0.5mol/L HCl solution was prepared and stirred continuously with a glass rod. After fully and uniformly stirring, putting the alkalized polyacrylonitrile ultrafiltration membrane into a culture dish, adding a prepared HCl solution, taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane after 0.5-0.8h for hydrolysis based on the amount of the HCl solution, repeatedly washing the hydrolyzed polyacrylonitrile ultrafiltration membrane with ultrapure water for many times, drying the washed polyacrylonitrile ultrafiltration membrane in an electrothermal blowing dry box at 40 ℃, putting the polyacrylonitrile ultrafiltration membrane into a sealing bag for sealing and storing after drying, wherein the process is an acidification process of the membrane;
(4) layer-by-layer self-assembly of Cu-BTC
Respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 4.0g of trimesic acid and 10mL of triethanolamine to prepare solution A;
respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 6.4g of copper nitrate hexahydrate into the beaker to prepare solution B;
soaking the alkalized and acidified polyacrylonitrile ultrafiltration membrane in the solution A for 5-10h, taking out, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, soaking in the solution B for 5-10h, taking out the membrane, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, and drying in an electrothermal blowing dry box at 40 ℃; the process is a cyclic test process of Cu-BTC in-situ growth;
repeating 4-6 circulation processes according to the flow, and drying the composite membrane after the growth of the circulation soaking in an electrothermal blowing drying oven at 40 ℃ to complete the layer-by-layer self-assembly of Cu-BTC and obtain the target modified polyacrylonitrile composite membrane;
the polyacrylonitrile ultrafiltration membrane is a commercial membrane purchased in the market, and besides, the scheme provided by the application can also be suitable for modification of cellulose acetate membranes and polyether sulfone membranes;
in the prior art, single alkaline modification or acidic modification is generally adopted for modification of a polyacrylonitrile ultrafiltration membrane, the invention simultaneously applies acidification and alkalization for the first time, and the modification effect is better after alkalization and acidification are verified; and the modified polyacrylonitrile ultrafiltration membrane is self-assembled with MOFs materials layer by layer: the Cu-BTC crystal greatly improves the tolerance of the polyacrylonitrile ultrafiltration membrane, and the Cu-BTC membrane layer is a crystal membrane layer, has good chemical stability, does not react with acid, alkali and salt under general conditions, and is insoluble in organic solvent, so that the integral tolerance is improved, the use range of the polyacrylonitrile ultrafiltration membrane is improved, the requirement on the use environment is reduced, and the polyacrylonitrile ultrafiltration membrane has wider popularization and application values.
The inventor carries out related performance detection on the modified polyacrylonitrile composite membrane, and the result shows that the water flux of the modified composite membrane to NaCl solution is 12.97L/(m)2H), the salt rejection for the NaCl solution was 95.80%. Compared with most PAN modified forward osmosis membranes reported in the prior literature (the flux is higher and is 6L/(m)2H) about, the salt rejection is higher by about 80%) compared with the flux and salt rejection performance; meanwhile, the modified forward osmosis composite membrane is subjected to an antibacterial test, gram-negative escherichia coli is used as a tested strain for testing the antibacterial performance of the membrane, the antibacterial rate of the composite membrane is calculated by using a flat plate counting method, the antibacterial rate is 99.9%, the antibacterial effect is excellent, the anti-pollution capacity of the membrane is outstanding, and the forward osmosis composite membrane is obviously improved compared with the existing membrane.
Furthermore, the inventor provides the best implementation scheme, which comprises the following specific steps:
(1) pretreatment of polyacrylonitrile-based film
Cutting a polyacrylonitrile ultrafiltration membrane to be modified into sheets with corresponding specifications, soaking the sheets in an ultrapure water solution for 24 hours at room temperature, taking out the soaked membrane, repeatedly washing the membrane for 5 times by using ultrapure water after taking out, and drying the membrane in an electrothermal blowing drying oven at 40 ℃ for later use after washing;
(2) hydrolysis modification of polyacrylonitrile base membrane:
preparing 2.0mol/L NaOH solution for later use; placing a polyacrylonitrile ultrafiltration membrane to be modified in a culture dish, adding a prepared NaOH solution into the culture dish, standing the polyacrylonitrile ultrafiltration membrane in a constant-temperature water bath at 60 ℃ for 0.8h for hydrolysis, taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane, and repeatedly washing the polyacrylonitrile ultrafiltration membrane with ultrapure water for multiple times until the washing liquid is neutral; after washing, drying in an electrothermal blowing dry box at 40 ℃, and after drying, sealing and storing in a sealing bag, wherein the process is an alkalization process of the film;
(3) hydrolysis modification of polyacrylonitrile base membrane:
0.5mol/L HCl solution was prepared and stirred continuously with a glass rod. After fully and uniformly stirring, putting the alkalized polyacrylonitrile ultrafiltration membrane into a culture dish, adding a prepared HCl solution, wherein the use amount of the HCl solution is based on the fact that the polyacrylonitrile ultrafiltration membrane can be soaked, placing the polyacrylonitrile ultrafiltration membrane at normal temperature for 0.8h for hydrolysis, then taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane, repeatedly washing the polyacrylonitrile ultrafiltration membrane with ultrapure water for many times, drying the polyacrylonitrile ultrafiltration membrane in an electrothermal blowing dry box at 40 ℃, and putting the polyacrylonitrile ultrafiltration membrane into a sealing bag for sealing and storing after drying, wherein the process is an acidification process of the membrane;
(4) layer-by-layer self-assembly of Cu-BTC
Respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 4.0g of trimesic acid and 10mL of triethanolamine to prepare solution A;
respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 6.4g of copper nitrate hexahydrate into the beaker to prepare solution B;
soaking the alkalized and acidified polyacrylonitrile ultrafiltration membrane in the solution A for 10h, taking out after 10h, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, then soaking in the solution B for 10h, taking out the membrane, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, and then drying in an electrothermal blowing drying oven at 40 ℃; the process is a cyclic test process of Cu-BTC in-situ growth;
repeating 4-6 circulation processes according to the flow, and drying the composite membrane after the growth of the circulation soaking in an electrothermal blowing drying oven at 40 ℃ to complete the layer-by-layer self-assembly of Cu-BTC and obtain the target modified polyacrylonitrile composite membrane;
the polyacrylonitrile composite membrane obtained by adopting the preferred scheme has the best effect.
In conclusion, the technical scheme of the invention obtains the continuous and compact Cu-BTC film layer by assembling on the surface of the polyacrylonitrile ultrafiltration membrane, so that the performance of the membrane is better improved, the salt rejection rate and the organic pollutant separation efficiency of the membrane are improved, the water flux of the membrane is not influenced, the double improvement of the salt rejection rate and the water flux is realized, and the polyacrylonitrile ultrafiltration membrane has good tolerance to organic solvents, acids and alkalis and widens the application range of the modified separation membrane; meanwhile, the smooth surface of the material is not beneficial to the breeding of bacteria, and the pollution resistance of the modified separation membrane can be improved.
Drawings
FIG. 1 is a bacteriostatic effect diagram of a modified polyacrylonitrile forward osmosis membrane obtained by the invention,
in the figure, 0 is a bacterial colony map of a blank group; 0' is a bacterial colony map of the PAN basement membrane added; 1 is a bacterial colony graph of a PAN composite membrane added with Cu-BTC;
FIG. 2 is an XRD spectrum of Cu-BTC;
FIG. 3 is an XRD spectrum of a modacrylic film after Cu-BTC assembly;
FIG. 4 is an FTIR spectrum of a modacrylic film after Cu-BTC assembly.
Detailed Description
The present invention will be described in further detail with reference to the following examples, but it should not be construed that the scope of the above subject matter is limited to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention, and the following embodiments are all completed by adopting the conventional prior art except for the specific description. The polyacrylonitrile ultrafiltration membranes in the following examples are all commercial membranes, and are specifically selected from: a product of Zhongkoreiyang film technology, Inc.
Example 1
A preparation method of a modified polyacrylonitrile forward osmosis membrane comprises the following specific steps:
(1) pretreatment of polyacrylonitrile-based film
Cutting the polyacrylonitrile ultrafiltration membrane to be modified into square pieces of 8cm multiplied by 8cm, soaking in an ultrapure water solution for 24h at room temperature, taking out the soaked membrane after 24h, repeatedly washing for 5 times by using ultrapure water after being taken out, and drying in an electrothermal blowing drying oven at 40 ℃ after washing for later use.
(2) Hydrolysis modification of polyacrylonitrile base membrane: alkalization process
40.0g of NaOH was weighed on an electronic balance and placed in a 500mL beaker, and 500mL of ultrapure water was added to the beaker and stirred with a glass rod to prepare a 2.0mol/L NaOH solution for use. And (2) placing the polyacrylonitrile ultrafiltration membrane to be modified in a culture dish, adding the prepared NaOH solution into the culture dish, standing for 0.5h in a constant-temperature water bath at 50 ℃ for hydrolysis, taking out the hydrolyzed polyacrylonitrile membrane after 0.5h, and repeatedly washing with ultrapure water for multiple times until the washing liquid is neutral. And after washing, drying in an electrothermal blowing dry box at 40 ℃, and after drying, putting the film into a sealing bag for sealing and storing, wherein the process is an alkalization process of the film.
(3) Hydrolysis modification of polyacrylonitrile base membrane: acidification process
479mL of ultrapure water was measured with a 500mL measuring cylinder and placed in a 500mL beaker, then 21mL of HCl solution (analytical grade) was measured with a 50mL measuring cylinder in a fume hood and poured into the beaker containing the ultrapure water to prepare a 0.5mol/L HCl solution, and stirring was continued with a glass rod. After the materials are fully and uniformly stirred, the alkalized polyacrylonitrile membrane is placed into a culture dish, a prepared HCl solution is added into the culture dish, the culture dish is placed at normal temperature for 0.5 hour for hydrolysis, the hydrolyzed polyacrylonitrile membrane is taken out after 0.5 hour, the polyacrylonitrile membrane is repeatedly washed by ultrapure water for many times, after washing, drying treatment is carried out in an electrothermal blowing dry box at 40 ℃, after drying, the polyacrylonitrile membrane is placed into a sealing bag for sealed storage, and the process is an acidification process of the membrane.
(4) Layer-by-layer self-assembly of Cu-BTC
Respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 4.0g of trimesic acid and 10mL of triethanolamine to prepare solution A;
n, N-dimethylformamide, ultrapure water and absolute ethyl alcohol were measured out and placed in 1000mL beakers each having 300mL of each, and then 6.4g of copper nitrate hexahydrate was added thereto to prepare a solution B. And (2) placing the polyacrylonitrile membrane for later use in the solution A for soaking for 5h, taking out the polyacrylonitrile membrane after 5h, repeatedly washing the polyacrylonitrile membrane with ethanol and ultrapure water for multiple times, then placing the polyacrylonitrile membrane in the solution B for soaking for 5h, taking out the polyacrylonitrile membrane after 5h, repeatedly washing the polyacrylonitrile membrane with ethanol and ultrapure water for multiple times, and then placing the polyacrylonitrile membrane in an electrothermal blowing drying oven at 40 ℃ for drying treatment, wherein the process is a cyclic test process of Cu-BTC in-situ growth. And after drying, placing the membrane in the solution A for soaking for 5h, taking out the membrane after 5h, repeatedly washing the membrane with ethanol and ultrapure water for many times, placing the membrane in the solution B for soaking for 5h, taking out the membrane, repeatedly washing the membrane with ethanol and ultrapure water for many times, placing the membrane in an electrothermal blowing drying box at 40 ℃ for drying treatment, repeating the steps in such a way, totally repeating 4 circulation processes, and placing the composite membrane after the growth of the circular soaking in the electrothermal blowing drying box at 40 ℃ for drying treatment for later use.
And (3) performance testing: after the modified forward osmosis composite membrane is made into a membrane component, the membrane component is loaded into equipment, and performance test is started. The size of our membrane area was measured to be 7.5cm2(7.5×10-4m2) The experimental time is 1 min. The water flux and the flux of the returned salt (converted salt cut-off) were measured for NaCl solutions each having a concentration of 1 mol/L. The result shows that the water flux of the modified composite membrane to NaCl solution is 12.87L/(m)2H) the salt rejection for the NaCl solution was 95.15%. Compared with most reports in the prior literaturePAN modified forward osmosis membrane (higher flux at 6L/(m)2H) and the salt rejection rate is higher by about 80 percent).
The modified forward osmosis composite membrane is subjected to an antibacterial test, gram-negative escherichia coli is taken as a tested strain for testing the antibacterial performance of the membrane, and the antibacterial rate of the composite membrane is calculated by a plate counting method, so that the antibacterial rate is 98.8%. The bacteriostatic effect was excellent, and it was found that the membrane had excellent anti-fouling ability.
Example 2
A preparation method of a modified polyacrylonitrile forward osmosis membrane comprises the following specific steps:
(1) pretreatment of polyacrylonitrile-based film
Cutting the polyacrylonitrile ultrafiltration membrane to be modified into square pieces of 8cm multiplied by 8cm, soaking in an ultrapure water solution for 24h at room temperature, taking out the soaked membrane after 24h, repeatedly washing for 5 times by using ultrapure water after being taken out, and drying in an electrothermal blowing drying oven at 40 ℃ after washing for later use.
(2) Hydrolysis modification of polyacrylonitrile base membrane: alkalization process
40.0g of NaOH was weighed on an electronic balance and placed in a 500mL beaker, and 500mL of ultrapure water was added to the beaker and stirred with a glass rod to prepare a 2.0mol/L NaOH solution for use. And (2) placing the polyacrylonitrile ultrafiltration membrane to be modified in a culture dish, adding the prepared NaOH solution into the culture dish, standing for 0.6h in a constant-temperature water bath at 55 ℃ for hydrolysis, taking out the hydrolyzed polyacrylonitrile membrane after 0.6h, and repeatedly washing with ultrapure water for multiple times until the washing liquid is neutral. And after washing, drying in an electrothermal blowing dry box at 40 ℃, and after drying, putting the film into a sealing bag for sealing and storing, wherein the process is an alkalization process of the film.
(3) Hydrolysis modification of polyacrylonitrile base membrane: acidification process
479mL of ultrapure water was measured with a 500mL measuring cylinder and placed in a 500mL beaker, then 21mL of HCl solution (analytical grade) was measured with a 50mL measuring cylinder in a fume hood and poured into the beaker containing the ultrapure water to prepare a 0.5mol/L HCl solution, and stirring was continued with a glass rod. After the materials are fully and uniformly stirred, the alkalized polyacrylonitrile membrane is placed into a culture dish, a prepared HCl solution is added into the culture dish, the culture dish is placed at normal temperature for 0.6 hour for hydrolysis, the hydrolyzed polyacrylonitrile membrane is taken out after 0.6 hour, the polyacrylonitrile membrane is repeatedly washed by ultrapure water for many times, after washing, the polyacrylonitrile membrane is dried in an electrothermal blowing dry box at the temperature of 40 ℃, and after drying, the polyacrylonitrile membrane is placed into a sealing bag for sealed storage, wherein the process is an acidification process of the membrane.
(4) Layer-by-layer self-assembly of Cu-BTC
Respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 4.0g of trimesic acid and 10mL of triethanolamine to prepare solution A;
n, N-dimethylformamide, ultrapure water and absolute ethyl alcohol were measured out and placed in 1000mL beakers each having 300mL of each, and then 6.4g of copper nitrate hexahydrate was added thereto to prepare a solution B. And (2) placing the polyacrylonitrile membrane for later use in the solution A for soaking for 8h, taking out after 8h, repeatedly washing the polyacrylonitrile membrane with ethanol and ultrapure water for many times, then placing the polyacrylonitrile membrane in the solution B for soaking for 8h, taking out the polyacrylonitrile membrane after 8h, repeatedly washing the polyacrylonitrile membrane with ethanol and ultrapure water for many times, and then placing the polyacrylonitrile membrane in an electrothermal blowing drying oven at 40 ℃ for drying treatment, wherein the process is a cycle test process of Cu-BTC in-situ growth. And after drying, placing the membrane in the solution A for soaking for 8h, taking out the membrane after 8h, repeatedly washing the membrane with ethanol and ultrapure water for many times, placing the membrane in the solution B for soaking for 8h, taking out the membrane, repeatedly washing the membrane with ethanol and ultrapure water for many times, placing the membrane in an electrothermal blowing drying box at 40 ℃ for drying treatment, repeating the steps in such a way, totally repeating 5 circulation processes, and placing the composite membrane after the growth of the circular soaking in the electrothermal blowing drying box at 40 ℃ for drying treatment for later use.
And (3) performance testing: after the modified forward osmosis composite membrane is made into a membrane component, the membrane component is loaded into equipment, and performance test is started. The size of our membrane area was measured to be 7.5cm2(7.5×10-4m2) The experimental time is 1 min. The water flux and the flux of the returned salt (converted salt cut-off) were measured for NaCl solutions each having a concentration of 1 mol/L. The result shows that the water flux of the modified composite membrane to NaCl solution is 12.94L/(m)2H), the salt rejection for the NaCl solution was 95.50%. Compared with most PAN modified forward osmosis membranes reported in the prior literature (the flux is higher and is 6L/(m)2H) and the salt rejection rate is higher by about 80 percent).
The modified forward osmosis composite membrane is subjected to an antibacterial test, gram-negative escherichia coli is taken as a tested strain for testing the antibacterial performance of the membrane, and the antibacterial rate of the composite membrane is calculated by a flat plate counting method, so that the antibacterial rate is 99.0%. The bacteriostatic effect was excellent, and it was found that the membrane had excellent anti-fouling ability.
Example 3
A preparation method of a modified polyacrylonitrile forward osmosis membrane comprises the following specific steps:
(1) pretreatment of polyacrylonitrile-based film
Cutting a polyacrylonitrile ultrafiltration membrane (commercial membrane) to be modified into square pieces of 8cm multiplied by 8cm, soaking in an ultrapure water solution for 24 hours at room temperature, taking out the soaked membrane after 24 hours, repeatedly washing for 5 times by using the ultrapure water after taking out, and drying in an electrothermal blowing drying oven at 40 ℃ after washing for later use.
(2) Hydrolysis modification of polyacrylonitrile base membrane: alkalization process
40.0g of NaOH was weighed on an electronic balance and placed in a 500mL beaker, and 500mL of ultrapure water was added to the beaker and stirred with a glass rod to prepare a 2.0mol/L NaOH solution for use. And (2) placing the polyacrylonitrile ultrafiltration membrane to be modified in a culture dish, adding the prepared NaOH solution into the culture dish, standing for 0.8h in a constant-temperature water bath at 60 ℃ for hydrolysis, taking out the hydrolyzed polyacrylonitrile membrane after 0.8h, and repeatedly washing with ultrapure water for multiple times until the washing liquid is neutral. And after washing, drying in an electrothermal blowing dry box at 40 ℃, and after drying, putting the film into a sealing bag for sealing and storing, wherein the process is an alkalization process of the film.
(3) Hydrolysis modification of polyacrylonitrile base membrane: acidification process
479mL of ultrapure water was measured with a 500mL measuring cylinder and placed in a 500mL beaker, then 21mL of HCl solution (analytical grade) was measured with a 50mL measuring cylinder in a fume hood and poured into the beaker containing the ultrapure water to prepare a 0.5mol/L HCl solution, and stirring was continued with a glass rod. After the materials are fully and uniformly stirred, the alkalized polyacrylonitrile membrane is placed into a culture dish, a prepared HCl solution is added into the culture dish, the culture dish is placed at normal temperature for 0.8 hour for hydrolysis, the hydrolyzed polyacrylonitrile membrane is taken out after 0.8 hour, the polyacrylonitrile membrane is repeatedly washed by ultrapure water for many times, after washing, drying treatment is carried out in an electrothermal blowing dry box at 40 ℃, after drying, the polyacrylonitrile membrane is placed into a sealing bag for sealed storage, and the process is an acidification process of the membrane.
(4) Layer-by-layer self-assembly of Cu-BTC
Respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 4.0g of trimesic acid and 10mL of triethanolamine to prepare solution A;
n, N-dimethylformamide, ultrapure water and absolute ethyl alcohol were measured out and placed in 1000mL beakers each having 300mL of each, and then 6.4g of copper nitrate hexahydrate was added thereto to prepare a solution B. And (2) placing the polyacrylonitrile membrane for later use in the solution A for soaking for 10h, taking out the polyacrylonitrile membrane after 10h, repeatedly washing the polyacrylonitrile membrane with ethanol and ultrapure water for multiple times, then placing the polyacrylonitrile membrane in the solution B for soaking for 10h, taking out the polyacrylonitrile membrane after 10h, repeatedly washing the polyacrylonitrile membrane with ethanol and ultrapure water for multiple times, and then placing the polyacrylonitrile membrane in an electrothermal blowing drying oven at 40 ℃ for drying treatment, wherein the process is a cyclic test process of Cu-BTC in-situ growth. And after drying, placing the membrane in the solution A for soaking for 10 hours, taking out the membrane after 10 hours, repeatedly washing the membrane with ethanol and ultrapure water for many times, placing the membrane in the solution B for soaking for 10 hours, taking out the membrane, repeatedly washing the membrane with ethanol and ultrapure water for many times, placing the membrane in an electrothermal blowing drying box at 40 ℃ for drying treatment, repeating the steps in this way, totally repeating 6 circulation processes, and placing the composite membrane after the growth of the circular soaking in the electrothermal blowing drying box at 40 ℃ for drying treatment for later use.
And (3) performance testing: after the modified forward osmosis composite membrane is made into a membrane component, the membrane component is loaded into equipment, and performance test is started. The size of our membrane area was measured to be 7.5cm2(7.5×10-4m2) The experimental time is 1 min. Water flux and Return salt flux (converted) were measured with respect to NaCl solutions each having a concentration of 1mol/LSalt cut-off rate). The result shows that the water flux of the modified composite membrane to NaCl solution is 12.97L/(m)2H), the salt rejection for the NaCl solution was 95.80%. Compared with most PAN modified forward osmosis membranes reported in the prior literature (the flux is higher and is 6L/(m)2H) and the salt rejection rate is higher by about 80 percent).
The modified forward osmosis composite membrane is subjected to an antibacterial test, gram-negative escherichia coli is used as a tested strain for testing the antibacterial performance of the membrane, and the antibacterial rate of the composite membrane is calculated by a flat plate counting method, so that the antibacterial rate is 99.9%. The bacteriostatic effect was excellent, and it was found that the membrane had excellent anti-fouling ability.
In addition, the inventors performed relevant tests on the modacrylic forward osmosis membrane obtained in this example, and the results are shown in fig. 2 to 4:
FIGS. 2 and 3 are XRD spectra of Cu-BTC and XRD spectra of polyacrylonitrile membrane in example 3 modified by Cu-BTC metal organic framework material layer by layer self-assembly, respectively, comparing XRD spectra of acidified polyacrylonitrile membrane modified by Cu-BTC and Cu-BTC, according to XRD spectra, the acidified polyacrylonitrile membrane modified by Cu-BTC shows characteristic diffraction peaks at 2 theta of 6.70 degrees, 9.48 degrees, 11.62 degrees, 13.44 degrees and 14.66 degrees, and by comparison, the positions of the peaks can correspond to the diffraction peaks of XRD spectra of Cu-BTC, which shows that the experiment succeeds in growing Cu-BTC metal organic framework material on the surface of acidified polyacrylonitrile membrane;
FIG. 4 is an FTIR spectrum of a polyacrylonitrile film obtained after Cu-BTC material growth, as can be seen at 1625cm-1An asymmetric stretching vibration peak of carboxylic acid group (-COO-) appears at 1465cm-1And 1383cm-1A symmetric stretching vibration peak of carboxylic acid group (-COO-); the characteristic absorption peak of Cu-BTC is 767cm-1And 720cm-1Here, the two absorption peaks are due to the substitution of the group on the benzene ring by Cu. Comparing the infrared spectrum with the corresponding literature, it can be seen that the peak position is basically consistent with the infrared spectrum in the literature. Further illustrates the success of the experiment in acidificationCu-BTC which is a metal organic framework material is grown on the surface of the polyacrylonitrile membrane.
Claims (2)
1. A preparation method of a modified polyacrylonitrile forward osmosis membrane is characterized by comprising the following steps: the method comprises the following specific steps:
(1) pretreatment of polyacrylonitrile-based film
Cutting a polyacrylonitrile ultrafiltration membrane to be modified into sheets with corresponding specifications, soaking the sheets in an ultrapure water solution for 24 hours at room temperature, taking out the soaked membrane, washing the membrane with ultrapure water after taking out, and drying the membrane in an electrothermal blowing drying oven at 40 ℃ for later use after washing;
(2) hydrolysis modification of polyacrylonitrile base membrane:
preparing 2.0mol/L NaOH solution for later use; placing the polyacrylonitrile ultrafiltration membrane to be modified in a culture dish, adding a prepared NaOH solution into the culture dish, standing the polyacrylonitrile ultrafiltration membrane in a constant-temperature water bath at 50-60 ℃ for 0.5-0.8h for hydrolysis, taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane, and repeatedly washing the polyacrylonitrile ultrafiltration membrane with ultrapure water for multiple times until the washing liquid is neutral; after washing, drying in an electrothermal blowing dry box at 40 ℃, and after drying, sealing and storing in a sealing bag, wherein the process is an alkalization process of the film;
(3) hydrolysis modification of polyacrylonitrile base membrane:
preparing 0.5mol/L HCl solution, continuously stirring with a glass rod, fully and uniformly stirring, putting the alkalized polyacrylonitrile ultrafiltration membrane into a culture dish, adding the prepared HCl solution into the culture dish, placing the culture dish at normal temperature for 0.5-0.8h for hydrolysis, taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane after 0.5-0.8h, repeatedly washing with ultrapure water for many times, drying in an electrothermal blowing dry box at 40 ℃ after washing, and putting the dried polyacrylonitrile ultrafiltration membrane into a sealing bag for sealing and storing, wherein the process is an acidification process of the membrane;
(4) layer-by-layer self-assembly of Cu-BTC
Respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 4.0g of trimesic acid and 10mL of triethanolamine to prepare solution A;
respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 6.4g of copper nitrate hexahydrate into the beaker to prepare solution B;
soaking the alkalized and acidified polyacrylonitrile ultrafiltration membrane in the solution A for 5-10h, taking out, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, soaking in the solution B for 5-10h, taking out the membrane, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, and drying in an electrothermal blowing dry box at 40 ℃; the process is a cyclic test process of Cu-BTC in-situ growth;
repeating 4-6 circulation processes according to the flow, and drying the composite membrane after the growth of the circulation soaking in an electrothermal blowing drying oven at 40 ℃ to complete the layer-by-layer self-assembly of Cu-BTC, thereby obtaining the target modified polyacrylonitrile composite membrane.
2. The method for preparing a modacrylic forward osmosis membrane according to claim 1, characterized in that:
the method comprises the following specific steps:
(1) pretreatment of polyacrylonitrile-based film
Cutting a polyacrylonitrile ultrafiltration membrane to be modified into sheets with corresponding specifications, soaking the sheets in an ultrapure water solution for 24 hours at room temperature, taking out the soaked membrane, repeatedly washing the membrane for 5 times by using ultrapure water after taking out, and drying the membrane in an electrothermal blowing drying oven at 40 ℃ for later use after washing;
(2) hydrolysis modification of polyacrylonitrile base membrane:
preparing 2.0mol/L NaOH solution for later use; placing a polyacrylonitrile ultrafiltration membrane to be modified in a culture dish, adding a prepared NaOH solution into the culture dish, standing the polyacrylonitrile ultrafiltration membrane in a constant-temperature water bath at 60 ℃ for 0.8h for hydrolysis, taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane, and repeatedly washing the polyacrylonitrile ultrafiltration membrane with ultrapure water for multiple times until the washing liquid is neutral; after washing, drying in an electrothermal blowing dry box at 40 ℃, and after drying, sealing and storing in a sealing bag, wherein the process is an alkalization process of the film;
(3) hydrolysis modification of polyacrylonitrile base membrane:
preparing 0.5mol/L HCl solution, continuously stirring with a glass rod, fully and uniformly stirring, putting the alkalized polyacrylonitrile ultrafiltration membrane into a culture dish, adding the prepared HCl solution into the culture dish, placing the culture dish at normal temperature for 0.8h for hydrolysis, taking out the hydrolyzed polyacrylonitrile ultrafiltration membrane, repeatedly washing the polyacrylonitrile ultrafiltration membrane with ultrapure water for many times, drying the polyacrylonitrile ultrafiltration membrane in an electrothermal blowing dry box at 40 ℃, placing the polyacrylonitrile ultrafiltration membrane into a sealing bag for sealing and storing after the polyacrylonitrile ultrafiltration membrane is washed, wherein the process is an acidification process of the membrane;
(4) layer-by-layer self-assembly of Cu-BTC
Respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 4.0g of trimesic acid and 10mL of triethanolamine to prepare solution A;
respectively measuring 300mL of N, N-dimethylformamide, ultrapure water and absolute ethyl alcohol, placing the measured solution in a 1000mL beaker, and adding 6.4g of copper nitrate hexahydrate into the beaker to prepare solution B;
soaking the alkalized and acidified polyacrylonitrile ultrafiltration membrane in the solution A for 10h, taking out after 10h, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, then soaking in the solution B for 10h, taking out the membrane, repeatedly washing with ethanol and ultrapure water until no residual reagent is on the surface, and then drying in an electrothermal blowing drying oven at 40 ℃; the process is a cyclic test process of Cu-BTC in-situ growth;
repeating 4-6 circulation processes according to the flow, and drying the composite membrane after the growth of the circulation soaking in an electrothermal blowing drying oven at 40 ℃ to complete the layer-by-layer self-assembly of Cu-BTC, thereby obtaining the target modified polyacrylonitrile composite membrane.
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