CN114225716A - Graphene oxide modified composite nanofiltration membrane as well as preparation method and application thereof - Google Patents
Graphene oxide modified composite nanofiltration membrane as well as preparation method and application thereof Download PDFInfo
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- CN114225716A CN114225716A CN202111531246.8A CN202111531246A CN114225716A CN 114225716 A CN114225716 A CN 114225716A CN 202111531246 A CN202111531246 A CN 202111531246A CN 114225716 A CN114225716 A CN 114225716A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/02—Inorganic material
- B01D71/021—Carbon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/027—Nanofiltration
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/08—Apparatus therefor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0079—Manufacture of membranes comprising organic and inorganic components
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/02—Inorganic material
- B01D71/024—Oxides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
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- B01D71/024—Oxides
- B01D71/027—Silicium oxide
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/56—Polyamides, e.g. polyester-amides
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
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Abstract
The invention provides a graphene oxide modified composite nanofiltration membrane as well as a preparation method and application thereof. The graphene oxide modified composite nanofiltration membrane has good stability and uniformity, good hydrophilicity, water flux, salt rejection rate and heavy metal rejection rate, and can be better applied to treatment of heavy metal wastewater.
Description
Technical Field
The invention belongs to the technical field of preparation and improvement of nanofiltration membranes, and particularly relates to a graphene oxide modified composite nanofiltration membrane as well as a preparation method and application thereof.
Background
In recent years, the problems of water resource shortage, water pollution and the like are aggravated, and the membrane technology occupies more and more important position in the field of water treatment due to the characteristics of high efficiency, energy conservation and the like. At present, the traditional water treatment membrane faces the bottleneck of performance improvement, and research and development of a separation membrane with stronger permeation and separation performance is urgent. By using novel nano materials, such as graphene, carbon nano tubes and the like, nano water channels of the nano materials can be introduced into a membrane structure, and a new opportunity is provided for the development of a new generation of separation membranes. However, the design and control of the existing nano material are not deep yet, so that the membrane structure is unstable or uneven, and the function of the nano material is difficult to be exerted. In addition, the further development of the nano-material composite membrane is limited by the complicated preparation process and long time consumption. The design innovation of the membrane material and the structure thereof plays a key role in improving the permeation separation capability and the chemical and mechanical stability of the membrane, and the inorganic carbon nano material, particularly the graphene and the derivatives thereof, is considered to be one of the most promising materials.
Graphene is composed of a single layer of carbon atoms and has a two-dimensional honeycomb lattice structure. These structural features make this class of materials exhibit unique ultra-thin layer (monoatomic thickness) morphology and excellent physicochemical stability, which is considered to be one of the ideal separation membrane materials. However, the full carbon element composition of graphene makes it chemically inert, and is difficult to be used for practical preparation and application of separation membranes. And graphene oxide (a two-dimensional nanosheet prepared by oxidative exfoliation of graphite) may be used as a separation membrane material. The graphene oxide has the advantage of excellent water dispersibility while keeping the characteristics of the graphene, so that the graphene oxide can be induced and loaded on a substrate and plays roles in permeation and separation depending on pore channels among graphene oxide sheets. In addition, the graphene oxide is rich in oxygen-containing functional groups (hydroxyl groups, epoxy groups and the like), and provides active reaction sites for regulating and controlling the chemical properties of the graphene oxide.
Graphene oxide generally has a high oxidation degree, and although oxygen-containing functional groups on the graphene oxide have hydrophilicity and modifiability, chemical chelation or intermolecular interaction formed between the oxygen-containing functional groups and a large number of solute molecules and ions uncontrollably enlarges the interlayer spacing of the graphene oxide, i.e., pores for trapping, sieving ions or molecules become large, and the functionality and stability of a graphene oxide separation layer are weakened, so that the membrane rejection rate is reduced. The pore channels on the graphene oxide membrane are regulated and controlled by physical and chemical means, so that the compactness of the graphene oxide membrane can be effectively improved. The physical method mainly etches a small hole with the diameter less than 1nm on a non-oxidized graphene sheet through ion bombardment, electron bombardment or an oxidant to be used as a water permeation channel, but is difficult to apply due to high precision, complex operation process and the like. The chemical method mainly solves the problem of the reduction of the membrane stability caused by the existence of the oxidizing group through the cross-linking/reducing reaction between the modifying agent/reducing agent and the functional group on the graphene oxide.
CN 112717719a discloses a method for preparing a graphene oxide composite nanofiltration membrane by a spray coating method, which comprises the following steps: 1) preparing graphene oxide nanosheets with different oxidation degrees, and ultrasonically dispersing the graphene oxide nanosheets in a good solvent according to a proportion; 2) selecting an ultrafiltration membrane such as polysulfone as a basement membrane, and soaking the ultrafiltration membrane in a hydrophilization solvent to perform surface hydrophilization treatment; 3) preparing a dispersion liquid of a graphene oxide modifier; 4) and respectively pouring the graphene oxide solution and the modifier aqueous solution into two spray gun material liquid tanks, and alternately spraying the two material liquids on the soaked base membrane for multiple times to finally obtain the graphene oxide composite nanofiltration membrane which can be continuously prepared, can realize a spraying membrane-making process on the base membrane with any area, and has low operating pressure and high desalting stability. The patent adopts a pressure spraying method to prepare the nanofiltration membrane, so that the time consumption is long, and the further development of the nanofiltration membrane is limited.
CN 109847599A discloses a preparation method and application of a dopamine intercalation copolymerization graphene oxide nanofiltration membrane, wherein the preparation method comprises the following steps: (1) dispersing graphene oxide in water, and performing ultrasonic treatment to uniformly disperse the graphene oxide to obtain a graphene oxide aqueous dispersion; (2) taking a certain amount of graphene oxide aqueous dispersion, carrying out vacuum filtration on the graphene oxide aqueous dispersion to the surface of a polysulfone ultrafiltration membrane, wherein the molecular weight cut-off of the polysulfone ultrafiltration membrane is 5kD-100kD, the vacuum filtration vacuum degree of the vacuum filtration is 0.05-0.08MPa, and then stabilizing at room temperature for 1-2 hours to obtain a GO membrane; the dosage of the graphene oxide aqueous dispersion is 7-100mg/m in terms of the mass of graphene oxide2Polysulfone ultrafiltration membranes; (3) then carrying out vacuum filtration on a certain amount of dopamine solution to the inner layer of the GO membrane, wherein the vacuum degree of the vacuum filtration is 0.05-0.08MPa, so as to obtain dGO membrane; the dosage of the dopamine solution is 0.08-0.4g/m in terms of the mass of dopamine in the solution2A polysulfone membrane; (4) then, pumping and filtering a certain amount of initiator to dGO membranes, wherein the vacuum degree of the vacuum filtration is 0.04-0.06MPa, and initiating dopamine polymerization in situ; (5) and (4) carrying out vacuum drying on the membrane obtained in the step (4) at the temperature of 40-70 ℃ to promote further polymerization of dopamine, so as to obtain the dopamine intercalation copolymerization graphene nanofiltration membrane. The patent adopts a vacuum filtration method to prepare the nanofiltration membrane, and although the method solves the problem of long time consumption, the dispersion of dispersed substances in a dispersion liquid on the surface of the membrane is uneven, so that the application of the nanofiltration membrane is restricted.
Therefore, it is one of the problems to be solved in the art to provide a preparation method for nanofiltration membrane, which can uniformly disperse substances and is time-consuming.
Disclosure of Invention
The invention aims to provide a graphene oxide modified composite nanofiltration membrane as well as a preparation method and application thereof. The graphene oxide modified composite nanofiltration membrane prepared by adopting a mode of combining vacuum filtration and pressure spraying and utilizing intermolecular van der Waals force to stack the graphene oxide nanosheets of the intercalated nanoparticles on the nanofiltration membrane base membrane layer by layer has better stability and uniformity.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a preparation method of a graphene oxide modified composite nanofiltration membrane, which comprises the following steps:
(1) mixing the graphene oxide dispersion liquid and the nano particle dispersion liquid, and then sequentially carrying out ultrasonic treatment and magnetic stirring to obtain a uniformly mixed dispersion liquid;
(2) immersing a nanofiltration membrane in a dopamine solution, and then carrying out water bath oscillation to obtain a treated nanofiltration membrane;
(3) carrying out vacuum filtration on the treated nanofiltration membrane obtained in the step (2), and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated nanofiltration membrane to obtain a precursor of the modified composite nanofiltration membrane;
(4) sequentially cleaning and drying the precursor of the modified composite nanofiltration membrane obtained in the step (3) to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
According to the invention, a mode of combining vacuum filtration and pressure spraying is adopted, and the graphene oxide nanosheets of the intercalated nanoparticles are stacked on the nanofiltration membrane base film layer by utilizing intermolecular van der Waals force, so that the prepared graphene oxide modified composite nanofiltration membrane has good stability and uniformity.
After the graphene oxide dispersion liquid and the nanoparticle dispersion liquid are mixed in the step (1), if the total solution amount of the graphene oxide dispersion liquid and the nanoparticle dispersion liquid is too small, in order to ensure uniform mixing in the subsequent ultrasonic treatment and magnetic stirring processes, a proper amount of deionized water needs to be added into the mixed solution. According to the invention, the addition amount of deionized water is not limited, and the loading amounts of graphene oxide and nano particles on the graphene oxide modified composite nanofiltration membrane are not influenced.
The graphene oxide and the nano particles in the graphene oxide modified composite nanofiltration membrane prepared by the invention are uniformly loaded on the nanofiltration membrane, the loading of the graphene oxide increases a large number of hydrophilic functional groups on the surface of the original membrane, and the resistance of a water flow channel formed by stacking graphene oxide sheets is small, so that water molecules can rapidly pass through the channel with the sheet structure at low friction resistance. Meanwhile, under the action of electrostatic resistance and molecular exclusion, substances such as salt solution ions, heavy metal ions and the like are trapped on the feeding side. Due to the adjustability of the interlayer spacing of the graphene oxide, the interlayer spacing of the graphene oxide can be adjusted by doping nanoparticles between the graphene oxide interlayers. The graphene oxide doped with the nano particles is loaded on the surface of an original polyamide nanofiltration membrane, due to the doping of the nano particles, the interlayer spacing of the graphene oxide is increased, water molecules can pass through a nano channel with lower friction resistance, and meanwhile, due to the existence of functional groups (hydroxyl, carboxyl and the like) which are easy to ionize on the edge of the surface of the graphene oxide, the surface of the membrane still presents electronegativity and is subjected to the combined action of electrostatic repulsion and molecular exclusion, so that other ions, macromolecular substances and the like outside the water molecules are intercepted.
Preferably, the nanoparticle dispersion of step (1) comprises a titania nanoparticle dispersion and/or a silica nanoparticle dispersion.
Preferably, the concentration of the titanium dioxide nanoparticle dispersion is 0.01 to 0.05mg/mL, and may be, for example, 0.01mg/mL, 0.02mg/mL, 0.03mg/mL, 0.04mg/mL, or 0.05mg/mL, but is not limited to the recited values, and other values within the range are equally applicable.
Preferably, the silica nanoparticle dispersion has a concentration of 0.01 to 0.05mg/mL, but is not limited to the recited values, and other values within the numerical range not recited are equally applicable.
The concentration of the nanoparticle dispersion liquid is 0.01-0.05mg/mL, and more preferably 0.02mg/mL, when the concentration of the nanoparticle dispersion liquid is too high, a membrane channel is blocked, so that the water flux is reduced, and when the concentration of the nanoparticle dispersion liquid is too low, the intercalation regulation effect is not obvious, so that the water flux of the graphene oxide membrane cannot be effectively improved.
Preferably, the concentration of the graphene oxide dispersion in step (1) is 0.3-0.8mg/mL, and may be, for example, 0.3mg/mL, 0.35mg/mL, 0.4mg/mL, 0.45mg/mL, 0.5mg/mL, 0.55mg/mL, 0.6mg/mL, 0.65mg/mL, 0.7mg/mL, 0.75mg/mL, or 0.8mg/mL, but is not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the mass ratio of the graphene oxide dispersion liquid to the nanoparticle dispersion liquid in the step (1) is (1-5):1, and for example, the mass ratio may be 1:1, 2:1, 3:1, 4:1 or 5:1, but the invention is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the time of the ultrasonic treatment in the step (1) is 1.5 to 3 hours, for example, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, but is not limited to the enumerated values, and other unrecited values in the numerical range are also applicable.
Preferably, the magnetic stirring time in step (1) is 6-10h, such as 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, but not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the magnetic stirring speed in step (1) is 1800-2500rpm, such as 1800rpm, 1900rpm, 2000rpm, 2100rpm, 2200rpm, 2300rpm, 2400rpm or 2500rpm, but not limited to the values listed, and other values not listed in the numerical range are also applicable.
Preferably, the nanofiltration membrane of step (2) comprises any one of a polyamide nanofiltration membrane, a hydrophilic PVDF nanofiltration membrane or a mixed cellulose nanofiltration membrane.
Preferably, the concentration of the dopamine solution in step (2) is 1-2.5mg/mL, and may be, for example, 1mg/mL, 1.3mg/mL, 1.6mg/mL, 1.9mg/mL, 2.2mg/mL, or 2.5mg/mL, but is not limited to the recited values, and other values within the range are equally applicable.
Preferably, the water bath oscillation time in the step (2) is 4-7h, for example, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h or 7h, but not limited to the enumerated values, and other unrecited values in the numerical range are also applicable; further preferably 6 hours.
Preferably, the vacuum degree of vacuum filtration in step (3) is 0.06-0.1MPa, such as 0.1MPa, 0.09MPa, 0.08MPa, 0.07MPa or 0.06MPa, but not limited to the values listed, and other values not listed in the numerical range are also applicable; more preferably 0.08 MPa.
Preferably, the pressure spraying in step (3) is performed at a spraying speed of 1-2mL/min, such as 1mL/min, 1.2mL/min, 1.4mL/min, 1.6mL/min, 1.8mL/min, or 2mL/min, but not limited to the values recited, and other values not recited in the range of values are also applicable; further preferably 1.3 mL/min.
Preferably, the pressure spraying in step (3) is performed at a spraying pressure of 20-30psi, such as 20psi, 21psi, 22psi, 23psi, 24psi, 25psi, 26psi, 27psi, 28psi, 29psi, or 30psi, but not limited to the values recited, and other values not recited in the range are equally applicable; and more preferably 25 psi.
Preferably, the drying temperature in step (4) is 40-80 ℃, for example, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃, but not limited to the recited values, and other values not recited in the numerical range are also applicable; further preferably 60 ℃.
Preferably, the drying time in step (4) is 2-5min, such as 2min, 2.5min, 3min, 3.5min, 4min, 4.5min or 5min, but not limited to the recited values, and other values not recited in the range of values are also applicable; more preferably 3 min.
As a preferable embodiment of the production method of the first aspect of the present invention, the production method comprises the steps of;
(1) the method comprises the following steps of (1-5):1, adding a proper amount of deionized water, performing ultrasonic treatment for 1.5-3h, and magnetically stirring at the rotation speed of 1800 plus 2500rpm for 6-10h to obtain uniformly mixed dispersion liquid; the concentration of the nanoparticle dispersion liquid is 0.01-0.05 mg/mL; the concentration of the graphene oxide dispersion liquid is 0.3-0.8 mg/mL;
(2) immersing the nanofiltration membrane in a dopamine solution with the concentration of 1-2.5mg/mL, and then carrying out water bath oscillation for 4-7h to obtain a treated nanofiltration membrane;
(3) carrying out vacuum filtration on the treated nanofiltration membrane obtained in the step (2) under the vacuum degree of 0.06-0.1MPa, and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated nanofiltration membrane at the injection speed of 1-2mL/min under the pressure of 20-30psi to obtain a precursor of the modified composite nanofiltration membrane;
(4) cleaning the precursor of the modified composite nanofiltration membrane obtained in the step (3), and drying at the temperature of 40-80 ℃ for 2-5min to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
In a second aspect, the invention provides a graphene oxide modified composite nanofiltration membrane, which is prepared by the preparation method in the first aspect.
The load capacity of the nano particles on the graphene oxide modified composite nanofiltration membrane is 0.5-15mg/m2For example, it may be 0.5mg/m2、2mg/m2、5mg/m2、7.0mg/m2、9.0mg/m2、11.0mg/m2、13.0mg/m2Or 15.0mg/m2But not limited to the recited values, other values not recited within the numerical range are equally applicable.
In a third aspect, the invention provides an application of the graphene oxide modified composite nanofiltration membrane prepared in the first aspect, and the graphene oxide modified composite nanofiltration membrane is used for treating heavy metal wastewater.
The recitation of numerical ranges herein includes not only the above-recited numerical values, but also any numerical values between non-recited numerical ranges, and is not intended to be exhaustive or to limit the invention to the precise numerical values encompassed within the range for brevity and clarity.
Compared with the prior art, the invention has the following beneficial effects:
(1) the graphene oxide modified composite nanofiltration membrane prepared by combining the suction filtration preparation method and the pressure spraying preparation method has good stability and uniformity;
(2) according to the graphene oxide modified composite nanofiltration membrane provided by the invention, by adjusting the proper proportion of graphene oxide and nano particles, the water flux of the composite nanofiltration membrane can be improved, and meanwhile, the composite nanofiltration membrane can keep a higher interception rate, and the water purification efficiency is improved;
(3) the graphene oxide modified composite nanofiltration membrane provided by the invention can improve the interception effect of heavy metal ions by adjusting the proper ratio of graphene oxide to nano particles, and the interception effect is about 90%.
Drawings
Fig. 1 is a surface SEM image and an EDS image of a graphene oxide-modified composite nanofiltration membrane provided in example 1 of the present invention;
fig. 2 is a surface SEM image and an EDS image of the graphene oxide-modified composite nanofiltration membrane provided in example 5 of the present invention;
figure 3 is a surface SEM image and EDS image of an untreated polyamide nanofiltration membrane provided by the blank of the present invention;
FIG. 4 is a water flux test result of the composite membranes provided in examples 1-4 of the present invention and a blank control;
FIG. 5 is a water flux test result of composite membranes provided in examples 5-8 of the present invention and a blank control;
FIG. 6 is a water flux test result of composite membranes provided in comparative examples 1-3 and a blank according to the present invention;
FIG. 7 is a graph of the salt rejection test results for composite membranes provided in examples 1-4 of the present invention and a blank control;
FIG. 8 is a graph of the salt rejection test results for composite membranes provided in examples 5-8 of the present invention and a blank control;
FIG. 9 is a graph of the salt rejection test results for composite membranes provided in comparative examples 1-3 and a blank according to the present invention;
FIG. 10 shows the results of hydrophilicity tests of composite membranes provided in examples 1 to 4 of the present invention;
FIG. 11 shows the results of hydrophilicity tests of composite membranes provided in examples 5 to 8 of the present invention;
FIG. 12 shows the results of Zeta potential tests conducted on inventive example 2, example 6 and a blank control group;
FIG. 13 shows the results of heavy metal ion rejection tests for the composite membranes provided in examples 5-8 and the blank control;
fig. 14 is a schematic view of a preparation method of the graphene oxide modified composite nanofiltration membrane provided by the invention.
Detailed Description
The technical solution of the present invention will be further described with reference to the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is shown in fig. 14 and comprises the following steps:
(1) mixing the graphene oxide dispersion liquid and the titanium dioxide nano particle dispersion liquid according to the mass ratio of 1:1, adding a proper amount of deionized water, carrying out ultrasonic treatment for 2 hours, and magnetically stirring at the rotating speed of 2000rpm for 8 hours to obtain uniformly mixed dispersion liquid; the concentration of the titanium dioxide nano particle dispersion liquid is 0.02 mg/mL; the concentration of the graphene oxide dispersion liquid is 0.5 mg/mL;
(2) immersing the polyamide nanofiltration membrane in a dopamine solution with the concentration of 2mg/mL, and then carrying out water bath oscillation for 6 hours to obtain a treated polyamide nanofiltration membrane;
(3) carrying out vacuum filtration on the treated polyamide nanofiltration membrane obtained in the step (2) under the vacuum degree of 0.08MPa, and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated polyamide nanofiltration membrane at the spraying speed of 1.5mL/min under the pressure of 25psi to obtain a precursor of the modified composite nanofiltration membrane;
(4) cleaning the precursor of the modified composite nanofiltration membrane obtained in the step (3), and drying at the temperature of 60 ℃ for 3min to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOT 1.
The surface SEM image and EDS image of the graphene oxide-modified composite nanofiltration membrane prepared in this example are shown in fig. 1.
Example 2
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is the same as that of embodiment 1 except that the mass ratio of the graphene oxide dispersion liquid and the titanium dioxide nanoparticle dispersion liquid in the step (1) is changed to 2: 1.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOT 2.
Example 3
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is the same as that of embodiment 1 except that the mass ratio of the graphene oxide dispersion liquid and the titanium dioxide nanoparticle dispersion liquid in the step (1) is changed to 3: 1.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOT 3.
Example 4
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is the same as that of embodiment 1 except that the mass ratio of the graphene oxide dispersion liquid and the titanium dioxide nanoparticle dispersion liquid in the step (1) is changed to 4: 1.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOT 4.
Example 5
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is shown in fig. 14 and comprises the following steps:
(1) mixing the graphene oxide dispersion liquid and the silicon dioxide nano particle dispersion liquid according to the mass ratio of 1:1, adding a proper amount of deionized water, carrying out ultrasonic treatment for 2 hours, and magnetically stirring at the rotating speed of 2000rpm for 8 hours to obtain uniformly mixed dispersion liquid; the concentration of the silicon dioxide nanoparticle dispersion liquid is 0.02 mg/mL; the concentration of the graphene oxide dispersion liquid is 0.5 mg/mL;
(2) immersing the polyamide nanofiltration membrane in a dopamine solution with the concentration of 2mg/mL, and then carrying out water bath oscillation for 5 hours to obtain a treated polyamide nanofiltration membrane;
(3) carrying out vacuum filtration on the treated polyamide nanofiltration membrane obtained in the step (2) under the vacuum degree of 0.08MPa, and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated polyamide nanofiltration membrane at the spraying speed of 1.5mL/min under the pressure of 30psi to obtain a precursor of the modified composite nanofiltration membrane;
(4) cleaning the precursor of the modified composite nanofiltration membrane obtained in the step (3), and drying at the temperature of 60 ℃ for 3min to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOS 1.
The surface SEM image and EDS image of the graphene oxide-modified composite nanofiltration membrane prepared in this example are shown in fig. 2.
Example 6
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is the same as that in embodiment 5 except that the mass ratio of the graphene oxide dispersion liquid and the silicon dioxide nanoparticle dispersion liquid in the step (1) is changed to 2: 1.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOS 2.
Example 7
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is the same as that in embodiment 5 except that the mass ratio of the graphene oxide dispersion liquid and the silicon dioxide nanoparticle dispersion liquid in the step (1) is changed to 3: 1.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOS 3.
Example 8
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and the preparation method of the graphene oxide modified composite nanofiltration membrane is the same as that in embodiment 5 except that the mass ratio of the graphene oxide dispersion liquid and the silicon dioxide nanoparticle dispersion liquid in the step (1) is changed to 4: 1.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOS 4.
Example 9
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and a preparation method of the graphene oxide modified composite nanofiltration membrane comprises the following steps:
(1) mixing the graphene oxide dispersion liquid and the titanium dioxide nano particle dispersion liquid according to the mass ratio of 5:1, adding a proper amount of deionized water, performing ultrasonic treatment for 3 hours, and magnetically stirring at the rotating speed of 2500rpm for 6 hours to obtain uniformly mixed dispersion liquid; the concentration of the titanium dioxide nanoparticle dispersion liquid is 0.05 mg/mL; the concentration of the graphene oxide dispersion liquid is 0.3 mg/mL;
(2) immersing the hydrophilic pvdf nanofiltration membrane in a dopamine solution with the concentration of 1mg/mL, and then carrying out water bath oscillation for 7 hours to obtain a treated hydrophilic pvdf nanofiltration membrane;
(3) carrying out vacuum filtration on the treated nanofiltration membrane obtained in the step (2) under the vacuum degree of 0.1MPa, and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated hydrophilic pvdf nanofiltration membrane at the spraying speed of 1mL/min under the pressure of 20psi to obtain a precursor of the modified composite nanofiltration membrane;
(4) cleaning the precursor of the modified composite nanofiltration membrane obtained in the step (3), and drying at the temperature of 40 ℃ for 5min to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOT 5.
Example 10
The embodiment provides a graphene oxide modified composite nanofiltration membrane, and a preparation method of the graphene oxide modified composite nanofiltration membrane comprises the following steps:
(1) mixing the graphene oxide dispersion liquid and the titanium dioxide nano particle dispersion liquid according to the mass ratio of 3:1, adding a proper amount of deionized water, performing ultrasonic treatment for 1.5h, and magnetically stirring at the rotating speed of 1800rpm for 10h to obtain uniformly mixed dispersion liquid; the concentration of the titanium dioxide nanoparticle dispersion liquid is 0.05 mg/mL; the concentration of the graphene oxide dispersion liquid is 0.8 mg/mL;
(2) immersing the hydrophilic pvdf nanofiltration membrane in a dopamine solution with the concentration of 2.5mg/mL, and then carrying out water bath oscillation for 4 hours to obtain a treated mixed cellulose nanofiltration membrane;
(3) carrying out vacuum filtration on the treated mixed cellulose nanofiltration membrane obtained in the step (2) under the vacuum degree of 0.06MPa, and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated mixed cellulose nanofiltration membrane at the spraying speed of 2mL/min under the pressure of 30psi to obtain a precursor of the modified composite nanofiltration membrane;
(4) cleaning the precursor of the modified composite nanofiltration membrane obtained in the step (3), and drying at the temperature of 80 ℃ for 2min to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
The graphene oxide modified composite nanofiltration membrane prepared in the embodiment is marked as GOT 6.
Comparative example 1
The comparative example provides a composite nanofiltration membrane, and the preparation method of the composite nanofiltration membrane comprises the following steps:
(1) immersing the polyamide nanofiltration membrane in a dopamine solution with the concentration of 2mg/mL, and then carrying out water bath oscillation for 5 hours to obtain a treated polyamide nanofiltration membrane;
(2) carrying out vacuum filtration on the treated polyamide nanofiltration membrane obtained in the step (1) under the vacuum degree of 0.08MPa, and spraying the graphene oxide dispersion liquid with the concentration of 0.5mg/mL onto the treated polyamide nanofiltration membrane at the spraying speed of 1.5mL/min under the pressure of 30psi to obtain a precursor of the composite nanofiltration membrane;
(3) and (3) cleaning the precursor of the modified composite nanofiltration membrane obtained in the step (2), and drying at the temperature of 60 ℃ for 3min to obtain the composite nanofiltration membrane.
The composite nanofiltration membrane prepared by the comparative example is marked as NF-GO.
Comparative example 2
The comparative example provides a composite nanofiltration membrane, and the preparation method of the composite nanofiltration membrane is the same as that of the comparative example 1 except that the graphene oxide dispersion liquid with the concentration of 0.5mg/mL in the step (2) is replaced by the titanium dioxide dispersion liquid with the concentration of 0.02 mg/mL.
The composite nanofiltration membrane prepared by the comparative example is marked as NF-TiO2。
Comparative example 3
The comparative example provides a composite nanofiltration membrane, and the preparation method of the composite nanofiltration membrane is the same as that of the comparative example 1 except that the graphene oxide dispersion liquid with the concentration of 0.5mg/mL in the step (2) is replaced by the silicon dioxide dispersion liquid with the concentration of 0.02 mg/mL.
The composite nanofiltration membrane prepared by the comparative example is marked as NF-SiO2。
Blank control
The untreated polyamide nanofiltration membranes used in examples 1 to 8 of the invention were used as a blank control and labeled NF.
The surface SEM image and the EDS image of the untreated polyamide nanofiltration membrane are shown in figure 1.
Application example 1
The composite membranes provided in examples 1-10, comparative examples 1-3, and the blank were subjected to water flux testing.
In this application the unit of water flux is in LMH and the filtration mode is dead-end filtration.
The nitrogen steel cylinder is a pressurizing device, is connected to the upper part of the membrane testing device through a pneumatic soft copper pipe after passing through a pressure reducing valve, can provide stable testing pressure for the inside of the testing device after the pressure reducing valve screw rod is adjusted to the specified pressure, and the liquid can flow out from the bottom of the testing device when the water has transmembrane pressure difference on the surface of the membrane to be tested. In the stage of testing the water flux of the membrane, firstly, prepressing the membrane to be tested at 2.0MPa for 2h, adjusting the pressure to be tested, calculating the mass difference of the last 15min liquid receiving beaker after the device stably operates, and calculating the water flux of the membrane under the pressure.
The water flux test results for the composite membranes provided in examples 1-4 and the blank are shown in fig. 4.
The water flux test results for the composite membranes provided in examples 5-8 and the blank are shown in fig. 5.
The results of the water flux tests for the composite membranes provided in comparative examples 1-3 and the blank are shown in fig. 6.
Application example 2
The composite membranes provided in examples 1-10, comparative examples 1-3, and the blank were subjected to salt rejection tests.
The test conditions were: the concentration of magnesium sulfate is 2000ppm, the test pressure is 0.6MPa, 0.8MPa, 1.0MPa, 1.2MPa and 1.4MPa respectively, and the filtration mode is cross flow pressurization and dead end filtration.
The method for testing the salt rejection rate comprises the following steps: the conductivity K of the initial salt solutionfAs an index of the original concentration, the conductivity K of the filtered liquid obtained after filtrationpAs the concentration index after interception, the following formula is adopted for calculation, and the concentration index is used as the test result of the membrane salt interception rate.
In the formula, KpConductivity (S/m), K, of the solution at the permeate sidefAs the conductivity (S/m) of the solution on the raw material side, R is the rejection.
Examples 1-4 and the blank provide composite membranes with salt rejection test results as shown in figure 7.
Examples 5-8 and the blank provide composite membranes with salt rejection test results as shown in figure 8.
The salt rejection test results for the composite membranes provided by comparative examples 1-3 and the blank are shown in fig. 9.
Application example 3
The composite membranes provided in examples 1-10 were subjected to a hydrophilicity test.
The results of the hydrophilicity tests of the composite membranes provided in examples 1-4 are shown in FIG. 10; the results of the hydrophilicity tests of the composite membranes provided in examples 5-8 are shown in FIG. 11.
Application example 4
The composite membranes provided in example 2, example 6 and the blank control were subjected to a Zeta potential test, the results of which are shown in fig. 12.
Application example 5
The composite membranes provided in examples 5-8 and the blank were tested for heavy metal ion rejection, the results of which are shown in fig. 13.
The heavy metal ion interception test standard is as follows: the operation pressure is 0.75MPa, and the heavy metal ions are copper ions.
As can be seen from analyzing fig. 4 and fig. 5, the water flux test results show that the composite membranes provided in examples 1 to 4 and the composite membranes provided in examples 5 to 8 have almost the same change rule in the whole, that is, the water flux increases with the increase of the proportion of the graphene oxide, which is because the water flux of the composite membranes increases due to the presence of the hydrophilic functional groups on the surface of the graphene oxide. The increase of the load substance can lead to the reduction of the water flow channel and influence the water flux.
As can be seen from the analysis of FIG. 6, in the figure, NF is an original nanofiltration membrane, NF-GO is a composite membrane only loaded with Graphene Oxide (GO), and NF-TiO2Is a composite film of singly loaded titanium dioxide, NF-SiO2Is a composite film singly supporting silicon dioxide. Compared with the original nanofiltration membrane (NF), the water flux of the composite membrane (NF-GO) loaded with the graphene oxide is obviously improvedComposite membrane (NF-TiO) for respectively and independently loading two kinds of nano particles2And NF-SiO2) The water flux is not increased compared with the original composite membrane, and is slightly reduced compared with the water flux of the original nanofiltration membrane (NF), probably because the nano particles are independently loaded on the surface of the base membrane, the pore diameter on the surface of the base membrane is blocked, and the water flux of the composite membrane is reduced. The test result shows that the single-loaded nano particles have no obvious effect on improving the water flux of the nanofiltration membrane.
From the analysis of fig. 7-8, it can be seen that the rejection of the composite membrane is increased compared to the original nanofiltration membrane (NF) for the appropriate doping quality ratio.
Analysis of figure 9 shows that retention rate test results show that the retention rates of composite membranes respectively and independently loaded with nanoparticles are better than those of original nanofiltration membranes (NF), the hydrophilic nanoparticles are mainly loaded on the surfaces of the membranes, water permeable pore diameters and paths of the membranes are influenced, and the reduction of the pore diameters of the membranes improves the retention performance of the membranes on ions. The rejection rate of the composite membrane loaded with the graphene oxide is slightly reduced compared with that of an original nanofiltration membrane (NF), the reason may be that GO is too high in concentration and cannot be sufficiently dispersed, so that the number of functional layer holes of the NF membrane is increased to a certain extent, and the rejection performance of the composite membrane to inorganic salts is reduced to a certain extent according to the size screening principle. The test result shows that the load of the nano particles can effectively improve the interception performance of the nanofiltration membrane.
Analysis of FIGS. 10 and 11 shows that GO/TiO2When the contact angles of the four groups of composite films are respectively 1:1, 2:1, 3:1 and 4:1, the contact angles of the four groups of composite films are respectively 53.25 degrees, 53.98 degrees, 61.43 degrees and 63.38 degrees; GO/SiO2The contact angles of the composite films under different mass ratios are respectively tested to be 48.5 degrees, 50.36 degrees, 57.47 degrees and 59.83 degrees. The contact angle of the composite membrane is increased and the hydrophilicity is reduced along with the increase of the mass ratio of the Graphene Oxide (GO), because the graphene oxide presents the property of a surfactant, the edge of the graphene oxide is provided with ionizable carboxyl (-COOH), hydroxyl (-OH) and other hydrophilic groups to enable the graphene oxide to have hydrophilicity, the central basal plane area of the graphene oxide is provided with unoxidized graphene nano-domains, and the existence of hydrophobic pi conjugated areas enables the contact angle of the composite membrane to present gradual increase along with the increase of the mass ratio of the Graphene Oxide (GO)Plus trend.
Analysis of fig. 12 shows that the Zeta potential of the membrane surface generally decreases with increasing pH for both the original base membrane and the prepared composite membrane at the tested pH of 5-9. In the test range, the Zeta potentials of the surfaces of the three membrane samples are all negative, namely the membrane surfaces of the three membranes are all electronegative, and the Zeta potentials are ranked from high to low as follows: NF, GOT2, GOS 2. Compared with the original base membrane, the Zeta potential of the prepared composite membrane is obviously reduced and changed within the test pH range, because the graphene oxide is loaded on the surface of the original membrane, and a large number of oxygen-containing functional groups (-COOH, -OH and other oxygen-containing charged groups and the like) carried by the graphene oxide enable the electronegativity of the surface of the membrane to be more obvious, and the Zeta potential is obviously reduced compared with the original nanofiltration membrane.
As can be seen from the analysis of FIG. 13, the rejection rate of the prepared composite membrane is increased compared with that of the original nanofiltration membrane when the concentration of the composite membrane prepared by the method is tested, and the GOS4 composite membrane is used for Cu2+The interception performance is improved most obviously, and the four groups of composite membranes have good performance in the aspect of treatment of heavy metal copper ions by observing and analyzing test results. The composite membrane has the advantages that the heavy metal retention performance is improved mainly based on the following two reasons, one is due to a molecular exclusion mechanism of graphene oxide purified water, and the other reason is that the composite membrane has improved heavy metal processing performance due to the fact that the prepared composite membrane has electronegativity on the surface and is subjected to electrostatic action.
In conclusion, the graphene oxide modified composite nanofiltration membrane prepared by the method disclosed by the invention has better stability and uniformity by stacking the graphene oxide nanosheets of the intercalated nanoparticles on the nanofiltration membrane base membrane layer by utilizing the intermolecular van der waals force in a mode of combining vacuum filtration and pressure spraying. The graphene oxide modified composite nanofiltration membrane provided by the invention has good hydrophilicity, water flux and salt rejection rate, and can be better applied to treatment of heavy metal wastewater.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. A preparation method of a graphene oxide modified composite nanofiltration membrane is characterized by comprising the following steps:
(1) mixing the graphene oxide dispersion liquid and the nano particle dispersion liquid, and then sequentially carrying out ultrasonic treatment and magnetic stirring to obtain a uniformly mixed dispersion liquid;
(2) immersing a nanofiltration membrane in a dopamine solution, and then carrying out water bath oscillation to obtain a treated nanofiltration membrane;
(3) carrying out vacuum filtration on the treated nanofiltration membrane obtained in the step (2), and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated nanofiltration membrane to obtain a precursor of the modified composite nanofiltration membrane;
(4) sequentially cleaning and drying the precursor of the modified composite nanofiltration membrane obtained in the step (3) to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
2. The production method according to claim 1, wherein the nanoparticle dispersion liquid of step (1) comprises a titanium dioxide nanoparticle dispersion liquid and/or a silicon dioxide nanoparticle dispersion liquid;
preferably, the concentration of the titanium dioxide nanoparticle dispersion is 0.01-0.05 mg/mL;
preferably, the concentration of the silica nanoparticle dispersion is 0.01-0.05 mg/mL;
preferably, the concentration of the graphene oxide dispersion liquid in the step (1) is 0.3-0.8 mg/mL.
3. The preparation method according to claim 1 or 2, wherein the mass ratio of the graphene oxide dispersion liquid to the nanoparticle dispersion liquid in the step (1) is (1-5: 1;
preferably, the time of the ultrasonic treatment in the step (1) is 1.5-3 h;
preferably, the magnetic stirring time in the step (1) is 6-10 h;
preferably, the rotation speed of the magnetic stirring in step (1) is 1800-.
4. The preparation method according to any one of claims 1 to 3, wherein the nanofiltration membrane of step (2) comprises a polyamide nanofiltration membrane, a hydrophilic PVDF nanofiltration membrane or a mixed cellulose nanofiltration membrane;
preferably, the concentration of the dopamine solution is 1-2.5 mg/mL;
preferably, the water bath oscillation time of the step (2) is 4-7h, preferably 6 h.
5. The production method according to any one of claims 1 to 4, wherein the degree of vacuum in the vacuum filtration in step (3) is 0.06 to 0.1MPa, preferably 0.08 MPa.
6. The production method according to any one of claims 1 to 5, wherein the pressure spraying in step (3) is carried out at a spraying rate of 1 to 2mL/min, preferably 1.3 mL/min;
preferably, the pressure spraying in step (3) has a spraying pressure of 20-30psi, preferably 25 psi.
7. The method according to any one of claims 1 to 6, wherein the drying temperature in step (4) is 40 to 80 ℃, preferably 60 ℃;
preferably, the drying time in step (4) is 2-5min, preferably 3 min.
8. The production method according to any one of claims 1 to 7, characterized by comprising the steps of:
(1) the method comprises the following steps of (1-5):1, carrying out ultrasonic treatment for 1.5-3h, and magnetically stirring at the rotation speed of 1800 plus 2500rpm for 6-10h to obtain uniformly mixed dispersion liquid; the concentration of the nanoparticle dispersion liquid is 0.01-0.05 mg/mL; the concentration of the graphene oxide dispersion liquid is 0.3-0.8 mg/mL;
(2) immersing the nanofiltration membrane in a dopamine solution with the concentration of 1-2.5mg/mL, and then carrying out water bath oscillation for 4-7h to obtain a treated nanofiltration membrane;
(3) carrying out vacuum filtration on the treated nanofiltration membrane obtained in the step (2) under the vacuum degree of 0.06-0.1MPa, and spraying the uniformly mixed dispersion liquid obtained in the step (1) onto the treated nanofiltration membrane at the injection speed of 1-2mL/min under the pressure of 20-30psi to obtain a precursor of the modified composite nanofiltration membrane;
(4) cleaning the precursor of the modified composite nanofiltration membrane obtained in the step (3), and drying at the temperature of 40-80 ℃ for 2-5min to obtain the graphene oxide modified composite nanofiltration membrane;
the step (1) and the step (2) are not in sequence.
9. A graphene oxide modified composite nanofiltration membrane, wherein the graphene oxide modified composite nanofiltration membrane is obtained by the preparation method of any one of claims 1 to 8;
the load capacity of the nano particles on the graphene oxide modified composite nanofiltration membrane is 0.5-15mg/m2。
10. The application of the graphene oxide modified composite nanofiltration membrane of claim 9, wherein the graphene oxide modified composite nanofiltration membrane is used for treating heavy metal wastewater.
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