CN111589308A - Composite nanofiltration membrane with heavy metal interception capacity - Google Patents
Composite nanofiltration membrane with heavy metal interception capacity Download PDFInfo
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Abstract
The invention discloses a composite nanofiltration membrane with heavy metal interception capability, which is obtained by depositing aminocucurbituril intercalated graphene on a porous base membrane, wherein a base membrane layer is a nanofiber membrane prepared from graphene oxide, tyrosine, carboxymethyl hydroxypropyl guar gum and polyacrylamide serving as raw materials by adopting an electrostatic spinning method; the composite nanofiltration membrane has good stability and high water flux, and has good interception capability on divalent/high-valent anions, heavy metal ions and anionic dyes; is expected to be applied to the treatment of wastewater polluted by heavy metals and organic dyes.
Description
Technical Field
The invention belongs to the field of nanofiltration membrane preparation, and particularly relates to a composite nanofiltration membrane with heavy metal interception capability.
Background
In recent years, with the development of economy and the promotion of global industrialization, the industrial wastewater contains various pollutants which are difficult to decompose, such as heavy metals, organic dyes and the like, and threatens the health of human bodies; the treatment of industrial wastewater becomes one of the environmental problems which are urgently needed to be solved at present; with the development of membrane separation technology, the adoption of the membrane separation technology to treat wastewater pollution is welcomed due to low cost and environmental friendliness;
the nanofiltration membrane is widely applied to wastewater treatment because of low energy consumption, high flux and good interception capability of ions and organic matters, and the existing single-layer nanofiltration membrane cannot meet the requirements of good interception performance and high flux; in order to solve the problem, a composite method is usually adopted to obtain the composite membrane, wherein the composite method is to adopt a separation layer with micro-nano pore size on an ultrafiltration or microfiltration base membrane, different materials can be adopted as the base membrane and the separation layer, but the base membrane and the separation layer have larger difference in swelling degree and weaker bonding force, so that the separation layer and the base membrane are separated in the later use and cleaning process, and the usability of the membrane is reduced; meanwhile, the separation layer can obviously influence the interception performance and flux of the composite membrane, so that the separation layer with good selective screening capacity is prepared and has an important function; the traditional composite method comprises an interface polymerization method or a surface coating method, the flux of the nanofiltration membrane can be reduced due to the thicker structural compact functional layer, and the operating pressure needs to be increased to obtain higher flux, so that the operating cost can be increased; in addition, the interfacial polymerization method needs to consume a large amount of organic solvent, and the residue of the organic solvent can cause environmental pollution; meanwhile, the traditional nanofiltration membrane liquid has low rejection rate of heavy metal ions and even cannot realize rejection; therefore, research and development of a composite nanofiltration membrane with heavy metal interception capability are urgently needed.
The electrostatic spinning method is to make charged high molecular solution or melt flow and deform in the electrostatic field, when the electric field force is large enough, the polymer liquid drop can overcome the surface tension to form jet trickle, then the fibre matter is obtained by the solidification of solvent evaporation or melt cooling, the preparation of nanofiber membrane by the electrostatic spinning method becomes a main method of the present nanofiber membrane, the nanofiber membrane has good adsorption filtration ability because of its porous structure and large specific surface area, but the problem of low mechanical strength and poor separation performance exists when the pure nanofiber membrane is used as the filtration membrane; therefore, the electrostatic spinning membrane is used as a base membrane, and the functional layer is compounded on the surface of the base membrane, so that the mechanical strength and the separation performance of the composite membrane can be obviously improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a composite nanofiltration membrane with heavy metal interception capability, the composite nanofiltration membrane is obtained by depositing aminocucurbituril intercalated graphene on a porous base membrane, and the base membrane layer is a nanofiber membrane prepared from graphene oxide, tyrosine, carboxymethyl hydroxypropyl guar gum and polyacrylamide serving as raw materials by adopting an electrostatic spinning method; the composite nanofiltration membrane has good stability and high water flux, and has good interception capability on divalent/high-valent anions, anionic dyes and heavy metal ions; is expected to be applied to the treatment of wastewater polluted by heavy metals and organic dyes;
the technical scheme for solving the technical problem of the invention is as follows:
a composite nanofiltration membrane with heavy metal interception capability is obtained by depositing aminocucurbituril intercalated graphene on a porous base membrane, wherein the porous base membrane is prepared by taking graphene oxide, tyrosine, carboxymethyl hydroxypropyl guar gum and polyacrylamide as raw materials and adopting an electrostatic spinning method; the preparation method specifically comprises the following steps:
(1) preparation of aminocucurbituril intercalated graphene
1-1) preparing graphene oxide powder by using a Hummers method;
1-2) preparation of aminocucurbituril intercalated graphene: dispersing graphene oxide powder in a hydrochloric acid solution of tyrosine, and performing ultrasonic dispersion at 40-50 ℃ for 20-24 h; obtaining graphene dispersion liquid; adding aminocucurbituril into the mixture, and continuing to perform ultrasonic dispersion for 5-6 hours to obtain a cucurbituril intercalated graphene dispersion solution;
(2) preparation of a base film:
dispersing graphene oxide powder in a hydrochloric acid solution of tyrosine, and performing ultrasonic dispersion at 40-50 ℃ for 20-24 h; obtaining graphene dispersion, and sequentially adding carboxymethyl hydroxypropyl guar gum and polyacrylamide into the graphene dispersion; adding deionized water into the solution, and fully and uniformly stirring to obtain a spinning solution; injecting the spinning solution into an injection pump of a spinning device, obtaining a nanofiber membrane through electrostatic spinning, taking the nanofiber membrane down from a metal substrate, soaking the nanofiber membrane in a cross-linking agent solution, and taking the nanofiber membrane out to obtain a base membrane for later use;
(3) preparation of composite nanofiltration membrane
Depositing different amounts of the aminocucurbituril intercalated graphene dispersion liquid obtained in the step (1) on the base film obtained in the step (2) by adopting a vacuum filtration method, and drying to obtain a composite nanofiltration membrane;
preferably, the amino cucurbituril in the step (1) is amino cucurbit [7] urea;
preferably, the hydrochloric acid solution of tyrosine in step (1) is obtained by dispersing tyrosine in hydrochloric acid solution;
preferably, the concentration of the hydrochloric acid solution is 1mol/L, and the concentration of the hydrochloric acid solution of tyrosine is 25-30 g/L;
preferably, the weight ratio of the aminocucurbituril to the tyrosine to the graphene oxide in the step (1) is 0.5-1:6: 2;
preferably, the mass concentration of the spinning solution in the step (2) is 20-30%;
preferably, the addition amount of the graphene oxide in the step (2) is 0.5-1.0% of the weight of the spinning solution; the adding amount of the tyrosine accounts for 1-3% of the weight of the spinning solution; the addition amount of the carboxymethyl hydroxypropyl guar gum accounts for 5-10% of the weight of the spinning solution; the weight ratio of the polyacrylamide to the carboxymethyl hydroxypropyl guar gum is 2: 1;
preferably, the electrospinning conditions are as follows: electrostatic spinning voltage is 14-15kV, and the diameter of a needle head of the injection pump is 1-1.5 mm; the flow rate of the injection pump is 0.1-0.4mL/h, the spinning distance is 16-18cm, the spinning temperature is 20-30 ℃, and the relative humidity is 40-50%;
preferably, the cross-linking agent in the step (2) is a mixed solution of boric acid and glutaraldehyde;
preferably, the weight ratio of the boric acid to the glutaraldehyde in the mixed solution of the boric acid and the glutaraldehyde is 2: 1;
the graphene oxide has a two-dimensional structure and adjustable physicochemical properties, and graphene oxide films with different film fluxes can be obtained by adjusting the number of superposed graphene oxide layers and the distance between graphene oxide layers or changing functional groups on the surface of the graphene oxide; simple graphene oxide lamellae tend to stack and do not separate efficiently to provide sufficient surface area and porosity, and tend to collapse and fracture without good mechanical strength;
in the presence of tyrosine, supramolecular aminocucurbituril is inserted between graphene oxide lamella layers, and the existence of tyrosine reduces graphene oxide into graphene on one hand and reacts with aminocucurbituril on the other hand to increase the dispersion amount of the aminocucurbituril in graphene dispersion liquid so as to be beneficial to intercalation reaction of cucurbituril; the intercalation of cucurbituril not only increases the interlayer spacing of graphene oxide; the hydrophobic cavity of the porous membrane also has the functions of adsorbing organic molecules and complexing heavy metal ions;
the method is characterized in that the nanofiber base membrane with good mechanical property is prepared by controlling the proper proportion of graphene oxide, tyrosine, carboxymethyl hydroxypropyl guar gum and polyacrylamide in the spinning solution; the polyacrylamide is an anionic linear high polymer material and has good water solubility and heavy metal ion flocculation; the polyacrylamide shows higher viscosity at lower concentration, and spinning at lower concentration causes low spinning rate and even spinning can not be carried out, even though the mechanical strength of the nanofiber membrane obtained by successful spinning is weaker, the mechanical strength of the polyacrylamide nanofiber is improved by taking the tyrosine reduced graphene oxide as a reinforcing agent and a rheology modifier;
according to the invention, the aminocucurbituril intercalated graphene oxide is used as a separation layer and deposited on a base membrane formed by graphene oxide composite carboxymethyl hydroxypropyl guar gum and polyacrylamide to obtain the nanofiltration membrane, the base membrane layer has good hydrophilicity, the surface of the base membrane layer is rich in carboxyl, amino and other groups, and the base membrane layer is connected with the separation layer through hydrogen bonds and chemical bonding, so that the swelling separation of the nanofiltration membrane separation layer and the base membrane layer is effectively avoided, and the stability of the nanofiltration membrane is improved;
the invention adopts a one-step method to prepare the aminocucurbituril intercalated graphene oxide: tyrosine is used as a reducing agent and an intercalation solvent is distributed between layers of graphene oxide, and on one hand, graphene oxide is oxidized to obtain graphene with a lamellar structure; on the other hand, an alpha, beta-unsaturated carbonyl compound formed by oxidizing tyrosine reacts with amino on the surface of the aminocucurbituril to enable the aminocucurbituril to be intercalated between graphene oxide layers, so that the dissolving dispersibility of the aminocucurbituril is improved; meanwhile, the supermolecular structure of the aminocucurbituril improves the interlayer structure of graphene, and avoids the agglomeration of graphene; the graphene is hydrophilic, the amino cucurbituril intercalated between layers is hydrophilic in end groups, and the inner cavity is hydrophobic, so that a hydrophilic-hydrophobic alternate structure layer is formed, the water flux of the nanofiltration membrane is improved, and the interception amount of the nanofiltration membrane on organic matters is also improved;
the invention adopts an electrostatic spinning method to prepare and obtain the tyrosine reduced graphene oxide composite carboxymethyl hydroxypropyl guar gum/polyacrylamide nano-fiber membrane; the nanofiber membrane has a micro-nano pore structure, a large specific surface area and reaction active sites, and provides a rich space structure for deposition of graphene; on one hand, the graphene obtained by reducing graphene oxide with tyrosine improves the conductivity of the spinning solution; on the other hand, the rheological property of the spinning solution is obviously improved, the viscosity of the carboxymethyl hydroxypropyl guar gum/polyacrylamide spinning solution is effectively reduced, the solid content of the spinning solution is improved, the spinning efficiency is improved, the energy consumption is reduced, and the cost is reduced; in addition, tyrosine contains benzene rings and forms pi-pi action with graphene sheet layers, so that the dispersity of graphene in spinning solution is increased, and binding sites of the graphene and polymers are increased; the reduced tyrosine, carboxymethyl hydroxypropyl guar gum and polyacrylamide react with hydrogen bond and chemical bonding to form fiber with a poly-network structure; the mechanical property of the spinning fiber is effectively improved; the carboxymethyl hydroxypropyl guar gum and the polyacrylamide belong to anionic polymers, the surfaces of the polymers are rich in functional groups such as carboxyl, amino and the like, the polymers have good interception performance on negative ions, and the polymers can complex heavy metals through organic groups on the surfaces and have a complexing adsorption effect on the heavy metal ions;
advantageous effects
According to the invention, the nanofiber membrane prepared by an electrostatic spinning method is used as a base membrane, the thickness of the base membrane is effectively reduced, and the nanofiltration membrane with a loose porous structure is obtained by depositing aminocucurbituril intercalated graphene oxide with different thicknesses on the surface of the base membrane as a separation layer; the stability of the nanofiltration membrane is effectively improved by combining chemical bonding and electrostatic action between the base membrane and the separation layer;
according to the invention, the nanofiltration membrane obtained by depositing a deposition layer obtained by controlling the appropriate proportion of the aminocucurbituril, the graphene oxide and the tyrosine on the surface of the nanofiber base membrane has good separation capacity;
the surface of the composite nanofiltration membrane with heavy metal interception capability has heavy metal complexing groups, so that the composite nanofiltration membrane not only has good interception capability on bivalent/high-valence negative ions, but also has strong adsorption effect on heavy metals; the nanofiltration membrane is expected to be applied to treatment of heavy metal/organic dye polluted wastewater;
the composite nanofiltration membrane has high flux and good interception capability, and the water flux reaches 83.8L/m under lower operation pressure (0.2MPa)2H.bar or more; for steelFruit red, MgSO4And heavy metal Cr3+The retention rate of the composite material reaches more than 90 percent, and the composite material shows higher water flux and good organic matter and heavy metal retention capacity;
Detailed Description
Example 1
Preparing graphene oxide powder: the preparation method of the graphene oxide by using the Hummers method specifically comprises the following steps: adding 50g of sodium nitrate and 300g of potassium permanganate into 100g of flake graphite, uniformly stirring, adding 2000ml of 98% concentrated sulfuric acid into the flake graphite, reacting for 2 hours under the ice-water bath condition, reacting for 2 hours at 30 ℃, adding 4L of deionized water into the reaction system, keeping the temperature at 80 ℃ for 30 minutes, cooling, and adding 1L of 30% H2O2A solution; performing centrifugal separation, pickling the product, and drying to obtain graphene oxide powder for later use;
preparation of amino cucurbit [7] urils:
(1) dissolving 1.4g cucurbituril [7] in 40ml of toluene solvent, adding acyl chloride solution, wherein the molar ratio of CB [7] to acyl chloride solution is 1: 14, placing the solution in an inert gas protected environment, heating and refluxing for 12-36 h at 60-80 ℃, and evaporating toluene to obtain imidazolium salt;
(2) adding 14ml of an organic solution (7mol/L) of ammonia into imidazole salt, heating and refluxing for 12-36 h at 60-80 ℃ under the protection of inert gas, evaporating to remove a solvent, adding a proper amount of deionized water, washing, and drying to obtain the guanidine cucurbituril. Dispersing guanidine cucurbituril in a methanol medium, adding a reducing agent (sodium borohydride or borane) at a molar ratio of guanidine cucurbituril [7] urea to the reducing agent of 1: 14, stirring until the reaction is complete, and removing methanol to obtain a crude product of the amino cucurbituril;
(3) adding a proper amount of dichloromethane and water into the crude product of the aminocucurbituril, stirring, standing the solution at room temperature, removing a water layer, vacuum-drying the remaining solution, and repeating for 3 times to obtain pure aminocucurbituril [7] urea; and (5) standby.
Preparation of aminocucurbituril intercalated graphene dispersion liquid 3:
dispersing 5g of graphene oxide powder obtained by the preparation in 500mL of 30g/L tyrosine hydrochloric acid solution, and performing ultrasonic dispersion at 40 ℃ for 24 hours; obtaining graphene dispersion liquid; adding 1.25g of aminocucurbit [7] urea into the system, continuing to perform ultrasonic dispersion for 5 hours to obtain an aminocucurbit urea intercalated graphene dispersion liquid 3 for later use;
preparation of aminocucurbituril intercalated graphene dispersion liquid 4
Dispersing 5g of graphene oxide powder obtained by the preparation in 500mL of 30g/L tyrosine hydrochloric acid solution, and performing ultrasonic dispersion at 50 ℃ for 20 hours; obtaining graphene dispersion liquid; adding 1.88g of aminocucurbituril [7] into the system, continuing to perform ultrasonic dispersion for 5 hours to obtain an aminocucurbituril intercalated graphene dispersion solution 4 for later use;
preparation of aminocucurbituril intercalated graphene dispersion liquid 5
Dispersing 5g of graphene oxide powder obtained by the preparation in 500mL of 30g/L tyrosine hydrochloric acid solution, and performing ultrasonic dispersion at 50 ℃ for 20 hours; obtaining graphene dispersion liquid; adding 2.5g of aminocucurbit [7] urea into the system, continuing to perform ultrasonic dispersion for 5 hours to obtain an aminocucurbit urea intercalated graphene dispersion solution 5 for later use;
the method is adopted to obtain different aminocucurbituril intercalated graphene dispersions by adjusting the addition amounts of aminocucurbituril [7] urea and tyrosine, and the dispersions are shown in table 1.
TABLE 1
When the addition amount of the aminocucurbituril is increased, the aminocucurbituril in the dispersion liquid cannot be completely dispersed, so that the dispersion liquid is not uniform;
| numbering | Graphene oxide/g | Tyrosine/g | Amino gourd [7]]Urea/g | Remarks for note |
| Dispersion 1 | 5g | 15 | / | |
| Dispersion 2 | 5g | 15 | 0.5 | |
| Dispersion 3 | 5g | 15 | 1.25 | |
| Dispersion 4 | 5g | 15 | 1.88 | |
| Dispersion 5 | 5g | 15 | 2.5 | |
| Dispersion 6 | 5g | 15 | 3 | |
| Dispersion 7 | 5g | 15 | 3.5 | Non-uniformity of the dispersion |
| Dispersion 8 | 5g | / | 1.25 | Non-uniformity of the dispersion |
| Dispersion 9 | 5g | / | / |
When tyrosine is not added into the dispersion liquid, the dispersibility of the aminocucurbituril in the dispersion liquid is reduced, and the content of the aminocucurbituril between graphene lamella layers is reduced;
example 2
Preparation of nanofiber-based membranes
Preparation of base film 1
5g of graphene oxide powder prepared in example 1 is dispersed in 1L of hydrochloric acid solution of 30g/L of tyrosine (the concentration of the hydrochloric acid solution is 1mol/L), and ultrasonic treatment is carried out at 60 ℃ for 10 h; obtaining graphene dispersion, and adding 50g of carboxymethyl hydroxypropyl guar gum and 100g of polyacrylamide into the graphene dispersion; fully and uniformly stirring to obtain spinning solution; injecting the spinning solution into an injection pump of a spinning device, obtaining a nanofiber membrane through electrostatic spinning, taking the nanofiber membrane down from a metal substrate, soaking the nanofiber membrane in a mixed solution of boric acid and glutaraldehyde, and taking out the nanofiber membrane to obtain a base membrane 1 for later use; wherein the electrostatic spinning voltage is 14kV, and the diameter of a needle head of the injection pump is 1 mm; the flow rate of an injection pump is 0.1mL/h, the spinning distance is 16cm, the spinning temperature is 30 ℃, and the relative humidity is 40%; wherein the diameter of the nano-fiber in the nano-fiber membrane is 800nm, the thickness of the fiber membrane is 110 μm, and the porosity is 83%; the breaking strength is 39.63cN, and the breaking elongation is 37.56%;
preparation of base film 2
Taking 7.5g of graphene oxide powder prepared in example 1, dispersing in 1L of hydrochloric acid solution of 30g/L tyrosine (the concentration of hydrochloric acid is 1mol/L), and carrying out ultrasonic treatment at 60 ℃ for 10 h; obtaining graphene dispersion liquid, and sequentially adding 75g of carboxymethyl chitosan and 150g of polyacrylamide into the graphene dispersion liquid; adding deionized water and stirring uniformly to obtain a spinning solution; injecting the spinning solution into an injection pump of a spinning device, obtaining a nanofiber membrane through electrostatic spinning, taking the nanofiber membrane down from a metal substrate, soaking the nanofiber membrane in a mixed solution of boric acid and glutaraldehyde, and taking out the nanofiber membrane to obtain a base membrane 3 for later use; wherein the electrostatic spinning voltage is 15kV, and the diameter of the needle head of the injection pump is 1.5 mm; the flow rate of the injection pump is 0.4mL/h, the spinning distance is 18cm, the spinning temperature is 25 ℃, and the relative humidity is 45%; wherein the diameter of the nano-fiber in the nano-fiber membrane is 700nm, the thickness of the fiber membrane is 120 μm, and the porosity is 85%; the breaking strength is 41.78cN, the breaking elongation is 45.23%;
preparation of base film 3
Taking 15g of graphene oxide powder prepared in example 1, dispersing the graphene oxide powder in 1L of hydrochloric acid solution (the concentration of hydrochloric acid is 1mol/L) of 30g/L tyrosine, and carrying out ultrasonic treatment at 60 ℃ for 10 h; obtaining graphene dispersion liquid, and sequentially adding 100g of carboxymethyl chitosan and 200g of polyacrylamide into the graphene dispersion liquid; adding deionized water into the solution and stirring the solution uniformly to obtain spinning solution; injecting the spinning solution into an injection pump of a spinning device, obtaining a nanofiber membrane through electrostatic spinning, taking the nanofiber membrane down from a metal substrate, soaking the nanofiber membrane in a mixed solution of boric acid and glutaraldehyde, and taking out the nanofiber membrane to obtain a base membrane for later use; wherein the electrostatic spinning voltage is 15kV, and the diameter of the needle head of the injection pump is 1.5 mm; the flow rate of the injection pump is 0.4mL/h, the spinning distance is 18cm, the spinning temperature is 20 ℃, and the relative humidity is 50%; wherein the diameter of the nano-fiber in the nano-fiber membrane is 600nm, the thickness of the fiber membrane is 110 μm, and the porosity is 80%; the breaking strength is 48.67cN, and the breaking elongation is 46.56%;
changing the concentration of the graphene oxide, and obtaining base films 4-6 by the same preparation method of the base film 3 in other steps; the mechanical properties of the film were tested, and the results were as follows:
preparation of base film 7
The preparation method of the basement membrane 7 is the same as that of the basement membrane 3, except that tyrosine is not added in the spinning solution in the preparation process of the basement membrane 7; the diameter of the nano-fiber in the obtained nano-fiber basement membrane is 700nm, the thickness of the fiber membrane is 100 mu m, and the porosity is 75 percent; the breaking strength is 27.83cN, and the breaking elongation is 28.78%;
preparation of base film 8
The preparation method of the base film 8 is the same as that of the base film 3, except that the carboxymethyl guar gum in the spinning solution is replaced by polyacrylamide with the same quantity in the preparation process of the base film 8; the diameter of the nano-fiber in the obtained nano-fiber basement membrane is 600nm, the thickness of the fiber membrane is 98 mu m, and the porosity is 83%; the breaking strength is 34.63cN, and the breaking elongation is 35.65%;
preparation of base film 9
The preparation method of the base film 9 is the same as that of the base film 3, except that polyacrylamide in the spinning solution is replaced by equivalent carboxymethyl guar gum in the preparation process of the base film 9; the diameter of the nano-fiber in the obtained nano-fiber basement membrane is 900nm, the thickness of the fiber membrane is 120 mu m, and the porosity is 90 percent; the breaking strength is 24.83cN, and the breaking elongation is 25.76%;
example 3
Preparation of composite nanofiltration membrane with heavy metal interception capability
(1) Preparation of aminocucurbituril intercalated graphene oxide dispersion (same as example 1)
(2) Preparation of the base film (same as example 2)
(3) Depositing the amino cucurbituril intercalated graphene dispersion liquid 1-9 obtained in the embodiment on the base film obtained in the step (2) by adopting a vacuum filtration method to obtain a composite nanofiltration membrane with heavy metal interception capability, which is sequentially marked as LNF-1, LNF-2, LNF-3, LNF-4, LNF-5, LNF-6, LNF-7, LNF-8 and LNF-9;
example 4
Preparation of composite nanofiltration membrane with heavy metal interception capability
(1) Preparing an aminocucurbituril intercalated graphene oxide dispersion liquid: example 1 preparation of the obtained cucurbituril intercalated graphene dispersion 5;
(2) preparation of a base film: example 2 preparation of the obtained base film 3;
(3) depositing the aminocucurbituril intercalated graphene dispersion liquid 5 prepared in the embodiment 1 on the base membrane 5-9 prepared in the embodiment 2 respectively by adopting a vacuum filtration method to obtain a composite nanofiltration membrane with heavy metal interception capability, which is sequentially marked as LNF-10, LNF-11, LNF-12, LNF-13 and LNF-14;
separation performance test experiment of composite nanofiltration membrane with heavy metal interception capacity
The water flux and the separation performance of the composite nanofiltration membrane (LNF-1-14) prepared by the method are tested; the separation performance of all membranes was tested by controlling the operating pressure at 0.2MPa with a concentration of 100ppm Congo Red (anionic dye) and 1g/L MgSO4、1g/LCr3+The separation performance of the composite nanofiltration membrane is characterized as the sample liquid to be treated, and the test results are shown in table 2.
TABLE 2
The separation performance of the LNF-10, the LNF-11, the LNF-12 and the LNF-14 cannot be tested due to the weak mechanical property;
the method is characterized in that the nanofiber base membrane with good mechanical property is prepared by controlling the proper proportion of graphene oxide, tyrosine, carboxymethyl hydroxypropyl guar gum and polyacrylamide in the spinning solution;
as can be seen from Table 2, the composite nanofiltration membranes (LNF-3, LNF-4 and LNF-5) with heavy metal rejection capability prepared by the method have the water flux reaching 83.8L/m under the lower operation pressure (0.2MPa)2H.bar or more; for anionic dyes Congo red, MgSO4And heavy metal Cr3+The retention rate of the composite material reaches more than 90 percent, and the composite material shows higher water flux and good organic matter and heavy metal retention capacity;
the separation performance of the composite nanofiltration membrane prepared by taking the aminocucurbituril intercalated graphene as a separation layer is superior to that of the composite nanofiltration membrane taking pure graphene oxide as the separation layer; with the increase of the proportion of the aminocucurbituril to the graphene oxide, the water flux of the composite membrane, Congo red and MgSO4And heavy metal Cr3+The retention rate of the water-soluble polymer shows a trend of increasing firstly and then reducing, and the water flux is obviously reduced; when the ratio of the aminocucurbituril to the tyrosine to the graphene oxide is 1:6:2, the composite nanofiltration membrane is used for congo red and MgSO4And heavy metal Cr3+The interception rate of the water reaches the maximum, the water is basically and completely intercepted, and the water flux reaches the maximum;
in conclusion, the composite nanofiltration membrane obtained by depositing a membrane with a micro-nano pore structure on the surface of a nanofiber membrane by using the cavity structure of the aminocucurbituril and the lamellar structure of the graphene has high water flux, heavy metal and organic dye retention rate, and all raw materials and the proportion thereof play an important role in ensuring the separation performance of the nanofiltration membrane; the composite nanofiltration membrane prepared by the invention is expected to be applied to treatment of heavy metal and organic dye wastewater.
In summary, the composite nanofiltration membrane prepared by the present invention with high flux and good organic dye retention capability is described in the above embodiments, which are only used for illustrating the technical solution of the present invention and not for limiting, and other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention shall be covered by the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.
Claims (10)
1. A composite nanofiltration membrane with heavy metal interception capability is characterized in that the composite nanofiltration membrane is obtained by depositing aminocucurbituril intercalated graphene on a porous base membrane, wherein the porous base membrane is prepared by taking graphene oxide, tyrosine, carboxymethyl hydroxypropyl guar gum and polyacrylamide as raw materials and adopting an electrostatic spinning method; the preparation method specifically comprises the following steps:
(1) preparation of aminocucurbituril intercalated graphene
1-1) preparing graphene oxide powder by using a Hummers method;
1-2) preparation of aminocucurbituril intercalated graphene: dispersing graphene oxide powder in a hydrochloric acid solution of tyrosine, and performing ultrasonic dispersion at 40-50 ℃ for 20-24 h; obtaining graphene dispersion liquid; adding the aminocucurbituril into the solution, and continuing to perform ultrasonic dispersion for 5-6h to obtain an aminocucurbituril intercalated graphene dispersion solution;
(2) preparation of a base film:
dispersing graphene oxide powder in a hydrochloric acid solution of tyrosine, and performing ultrasonic dispersion at 40-50 ℃ for 20-24 h; obtaining graphene dispersion, and sequentially adding carboxymethyl hydroxypropyl guar gum and polyacrylamide into the graphene dispersion; adding deionized water into the solution, and fully and uniformly stirring to obtain a spinning solution; injecting the spinning solution into an injection pump of a spinning device, obtaining a nanofiber membrane through electrostatic spinning, taking the nanofiber membrane off a metal substrate, soaking the nanofiber membrane in a cross-linking agent solution, and taking out the nanofiber membrane to obtain a base membrane for later use;
(3) preparation of composite nanofiltration membrane
And (3) depositing the amino cucurbituril intercalated graphene dispersion liquid with different amount in the step (1) onto the base film in the step (2) by adopting a vacuum filtration method, and drying to obtain the composite nanofiltration membrane.
2. The composite nanofiltration membrane with heavy metal rejection capacity of claim 1, wherein the amino cucurbituril in the step (1) is amino cucurbit [7] urea.
3. The composite nanofiltration membrane with heavy metal rejection capacity of claim 1, wherein the hydrochloric acid solution of tyrosine obtained in step (1) is obtained by dispersing tyrosine in hydrochloric acid solution.
4. The composite nanofiltration membrane with heavy metal rejection capacity of claim 3, wherein the concentration of the hydrochloric acid solution is 1mol/L, and the concentration of the hydrochloric acid solution of tyrosine is 25-30 g/L.
5. The composite nanofiltration membrane with heavy metal rejection capacity of claim 1, wherein the weight ratio of the aminocucurbituril to the tyrosine to the graphene oxide in the step (1) is 0.5-1:6: 2.
6. The composite nanofiltration membrane with heavy metal rejection capability of claim 1, wherein the mass concentration of the spinning solution in the step (2) is 20-30%.
7. The composite nanofiltration membrane with heavy metal rejection capability of claim 1, wherein the graphene oxide is added in an amount of 0.5-1.0% by weight of the spinning solution in the step (2); the adding amount of the tyrosine accounts for 1-3% of the weight of the spinning solution; the addition amount of the carboxymethyl hydroxypropyl guar gum accounts for 5-10% of the weight of the spinning solution; the weight ratio of the polyacrylamide to the carboxymethyl hydroxypropyl guar gum is 2: 1.
8. The composite nanofiltration membrane with heavy metal rejection capability according to claim 1, wherein the electrospinning conditions are as follows: electrostatic spinning voltage is 14-15kV, and the diameter of a needle head of the injection pump is 1-1.5 mm; the flow rate of the injection pump is 0.1-0.4mL/h, the spinning distance is 16-18cm, the spinning temperature is 20-30 ℃, and the relative humidity is 40-50%.
9. The composite nanofiltration membrane with heavy metal rejection capability of claim 1, wherein the cross-linking agent in the step (2) is a mixed solution of boric acid and glutaraldehyde.
10. The composite nanofiltration membrane with heavy metal rejection capability of claim 9, wherein the weight ratio of the boric acid to the glutaraldehyde in the mixed solution of the boric acid and the glutaraldehyde is 1: 2.
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