CN114733370B - Layer-by-layer self-assembly preparation method of sulfonated graphene nanofiltration membrane - Google Patents

Layer-by-layer self-assembly preparation method of sulfonated graphene nanofiltration membrane Download PDF

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CN114733370B
CN114733370B CN202210564505.5A CN202210564505A CN114733370B CN 114733370 B CN114733370 B CN 114733370B CN 202210564505 A CN202210564505 A CN 202210564505A CN 114733370 B CN114733370 B CN 114733370B
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CN114733370A (en
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邵文尧
王蕊
陈玉清
彭雅娟
罗世翊
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Xiamen University
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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
    • 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
    • B01D67/0002—Organic membrane manufacture
    • 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
    • B01D67/0086—Mechanical after-treatment
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    • 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
    • B01D67/0095—Drying
    • 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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    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
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    • B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
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    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
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    • B01D71/06—Organic material
    • B01D71/44—Polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds, not provided for in a single one of groups B01D71/26-B01D71/42
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    • B01D71/06—Organic material
    • B01D71/66—Polymers having sulfur in the main chain, with or without nitrogen, oxygen or carbon only
    • B01D71/68—Polysulfones; Polyethersulfones
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    • B01D2323/00—Details relating to membrane preparation
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    • B01D—SEPARATION
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
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    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

Abstract

A layer-by-layer self-assembly preparation method of sulfonated graphene nanofiltration membranes belongs to the field of nanofiltration membrane preparation. The steps are as follows: fully mixing SG solution and PEI aqueous solution, and performing ultrasonic treatment to obtain a mixed solution; PES film in the ultrafiltration cup is pre-pressed stably; and pouring the ultrasonic mixed solution into an ultrafiltration cup containing the PES membrane for pressure filtration, and drying the membrane to obtain the sulfonated graphene nanofiltration membrane. The self-assembled nanofiltration membrane is prepared by taking SG and PEI as common stacking materials, the SG has better dispersibility than common graphene, PEI can provide amino groups, the combination of the SG and the PEI is favorable for stacking the membrane, and can strengthen the positive electric property of the membrane surface, the PES membrane and SG/PEI are well combined, the concentration of SG is 0.2mg/mL, the membrane performance is optimal when the concentration of PEI is 0.05%, and the water flux is 8.5LMH. The Evansi blue rejection was 99.15%. Compared with a self-assembled film simply stacked with PEI, the self-assembled film has a certain water flux improvement.

Description

Layer-by-layer self-assembly preparation method of sulfonated graphene nanofiltration membrane
Technical Field
The invention belongs to the field of nanofiltration membrane preparation, and particularly relates to a layer-by-layer self-assembly preparation method of a sulfonated graphene nanofiltration membrane, wherein a Polyethersulfone (PES) ultrafiltration membrane is used as a bottom membrane, polyethylenimine (PEI) is used as a cationic additive, and the sulfonated graphene nanofiltration membrane is mixed with Sulfonated Graphene (SG) to be stacked.
Background
The nanofiltration membrane has high removal rate for specific particles due to the unique surface charge characteristic and smaller pore diameter, and belongs to a pressure driven membrane, so that the nanofiltration technology has the advantages of low operation pressure, low energy consumption, high running efficiency-cost ratio, high automation, high flux and the like in the membrane separation process, and has wide application prospect in the aspect of water purification treatment. Although nanofiltration membranes have a high rejection rate for high-valence salts and low-relative molecular-mass organic substances, the rejection rate for monovalent inorganic salts decreases rapidly with increasing solution concentration.
In terms of the preparation method of the nanofiltration membrane, the interfacial polymerization method, the L-S phase conversion method, the chemical modification method, the Layer-by-Layer self-assembly method and the like are included at present, wherein the Layer-by-Layer self-assembly (LBL) technology is taken as a new technology which is rapidly developed, and the stacking of assembly materials can be easily realized. Layer-by-layer self-assembly plays an increasingly important role in the fields of chemistry, physics, biology, materials, nano science, medicine and the like, and advances in technology and economic development are continuously promoted.
The high-performance membrane material can better realize the aperture of nano-scale (0.5-2 nm) of the nanofiltration membrane. The graphene composite material has a plurality of excellent performances, and the unique structure is favorable for surface functionalization to obtain modified graphene with better performances, for example, the graphene oxide obtained through oxidation improves the hydrophilicity of graphene due to the introduced hydroxyl and carboxyl, and the sulfonated graphene obtained through sulfonation also has good dispersibility, so that the graphene composite material is a promising film preparation material.
Disclosure of Invention
The invention aims to provide a layer-by-layer self-assembly preparation method of a sulfonated graphene nanofiltration membrane. The PES ultrafiltration membrane is used as a bottom membrane, polyethyleneimine (PEI) and Sulfonated Graphene (SG) are used as stacking materials, and a layer-by-layer self-assembly technology is utilized, so that the nanofiltration membrane with high rejection rate of monovalent inorganic salt, wide application range and better membrane performance is prepared.
The invention comprises the following steps:
1) Preparing 80mL of SG solution and performing ultrasonic treatment;
2) Preparing 80mL of PEI aqueous solution, and magnetically stirring for 1h;
3) Thoroughly mixing 80mL of SG solution and 80mL of PEI aqueous solution, and performing ultrasonic treatment;
4) Fixing a bottom film in a ultrafilter cup, and performing pressure filtration on 100mL of ultrapure water under 1bar for prepressing stabilization;
5) And pouring the mixed solution obtained by fully mixing the ultrasonic SG and PEI into an ultrafiltration cup with a bottom membrane for pressurized filtration, and placing the membrane after PEI and SG are transferred to the PES ultrafiltration bottom membrane into a 60 ℃ oven for forced air drying for 1h to obtain the sulfonated graphene nanofiltration membrane.
In step 1), the concentration of the SG solution may be 0.01-0.4 mg/mL, preferably 0.2mg/mL; the ultrasonic time can be 1h, and the ultrasonic frequency is 60Hz;
in step 2), the mass percentage concentration of the PEI aqueous solution may be 0.01 to 0.4wt%, preferably 0.05wt%; the magnetic stirring time can be more than 1 h.
In the step 3), the volumes of the SG solution and the polyethyleneimine aqueous solution are 1:1; the time of the ultrasonic treatment can be 20min, and the ultrasonic treatment is carried out after the SG solution and the PEI solution are fully mixed so as to further enhance the dispersibility of SG in the solution.
In the step 4), the base membrane adopts a PES ultrafiltration base membrane, and before the PES ultrafiltration base membrane is used, the PES ultrafiltration base membrane can be soaked in ultrapure water for more than 1h, and 100mL of ultrapure water is pre-pressed at 1 bar.
In step 5), the pressure filtration is stopped when the permeate volume is 125mL, the pressure not exceeding 1.6bar. The water flux of the prepared sulfonated graphene nanofiltration membrane is 8.5LMH, and the rejection rate of Evan blue is 99.15%.
The invention determines the volume of the filtered solution to design the loading capacity of the membrane surface stacking material; the uniform dispersion of the SG in water is realized, PEI is used as an additive to jointly stack in the pressure filtration process, so that the aggregation of the SG is avoided, and the surface integrity of the prepared self-assembled film is ensured.
Compared with the prior art, the invention has the outstanding advantages that: according to the invention, the self-assembled nanofiltration membrane is prepared by taking SG and PEI as common stacking materials, the SG has better dispersibility than common graphene, PEI can provide amino groups, and the combination of the SG and the PEI is favorable for stacking the membrane, and can strengthen the positive electricity property of the membrane surface, which is not possessed by common graphene oxide. The optimal membrane preparation condition for screening the sulfonated graphene nanofiltration membrane is that the SG concentration is 0.2mg/mL, the PEI concentration is 0.05wt%, the water flux of the prepared sulfonated graphene nanofiltration membrane is 8.5LMH, the retention rate of Evan blue is 99.15%, and the water flux of the sulfonated graphene nanofiltration membrane is superior to the retention rate of the basement membrane 68.41%, so that the sulfonated graphene nanofiltration membrane has excellent dye retention performance. Compared with a self-assembled film simply stacked with PEI, the self-assembled film has a certain water flux improvement.
Drawings
FIG. 1 is a schematic diagram of an apparatus for preparing self-assembled films and testing film properties.
Fig. 2 is an evans blue concentration standard curve. The standard curve is plotted from absorbance measured by an ultraviolet spectrophotometer.
FIG. 3 is a graph of the effect of stack PEI concentration alone (in wt%) on self-assembled nanofiltration membrane performance.
FIG. 4 is a graph showing the effect of SG concentration (expressed in mg/mL) on the performance of self-assembled nanofiltration membranes at a fixed PEI concentration of 0.05 wt%.
FIG. 5 is a SEM image of the surface of self-assembled nanofiltration membranes at different SG concentrations at a fixed PEI concentration of 0.05 wt%. Wherein a: c (SG) ＝0.1mg/mL，b：c (SG) ＝0.2mg/mL，c：c (SG) ＝0.3mg/mL，d：c (SG) ＝0.4mg/mL。
FIG. 6 is a SEM image of a cross section of a self-assembled nanofiltration membrane at different SG concentrations at a fixed PEI concentration of 0.05 wt%. Wherein a is 1 ：c (SG) ＝0.1mg/mL，b 1 ：c (SG) ＝0.2mg/mL，c 1 ：c (SG) ＝0.3mg/mL，d 1 ：c (SG) ＝0.4mg/mL。
FIG. 7 is an infrared spectrum of PES substrate film, self-assembled film with PEI material only stacked and SG/PEI composite stacked.
FIG. 8 is a graph showing the effect of water contact angle on the surface of SG/PEI self-assembled nanofiltration membranes at different SG concentrations.
FIG. 9 shows the morphology of SG/PEI self-assembled nanofiltration membranes at different SG concentrations at a fixed PEI concentration of 0.05 wt%. Wherein (I) c (SG) ＝0.1mg/mL，(II)c (SG) ＝0.2mg/mL，(III)c (SG) ＝0.3mg/mL，(IV)c (SG) ＝0.4mg/mL。
Detailed Description
In order to facilitate a better understanding of the technology of the present invention, some non-limiting examples are now further disclosed to illustrate the present invention in further detail. The reagents used in the present invention are all commercially available either directly or can be prepared by the methods described in the present invention.
According to the invention, polyethyleneimine (PEI) and Sulfonated Graphene (SG) are used as self-assembly stacking materials, a novel nanofiltration membrane with better membrane performance is prepared by a layer-by-layer self-assembly technology on the basis of PES ultrafiltration membrane as a bottom membrane, and characterization analysis is performed on the nanofiltration membrane. The following is a specific implementation step in the film preparation process.
1. Preparing a layer-by-layer self-assembled film:
example 1:
80mL of a 0.05wt% aqueous solution of polyethylenimine was prepared, and the mixture was magnetically stirred for 1 hour to determine the pH. Thoroughly mixed with 80mL of ultrapure water, and the pH was measured after 20 minutes of sonication. A PES ultrafiltration bottom membrane (soaked in ultrapure water for more than 1h before use) is arranged in an ultrafiltration cup (figure 1), and 100mL of ultrapure water is pressed and filtered under 1bar for prepressing; pouring the polyethyleneimine water solution into a ultrafilter cup, pressurizing and filtering 125mL of filtrate at 1.6bar, pouring out the residual mixed solution and taking out a membrane; the membrane is placed in a 60 ℃ oven for forced air drying for 1 hour for standby.
Example 2:
80mL of the aqueous polyethyleneimine solution prepared in the first step of example 1 was concentrated to 0.1wt%, and the rest was treated in the same manner as in example 1.
Example 3:
80mL of the aqueous polyethyleneimine solution prepared in the first step of example 1 was concentrated to 0.2wt%, and the rest was treated in the same manner as in example 1.
Example 4:
80mL of the aqueous polyethyleneimine solution prepared in the first step of example 1 was concentrated to 0.3wt%, and the rest was treated in the same manner as in example 1.
Example 5:
80mL of the aqueous polyethyleneimine solution prepared in the first step of example 1 was concentrated to 0.4wt%, and the rest was treated in the same manner as in example 1.
Example 6:
preparing 80mL of 0.1mg/mL sulfonated graphene aqueous solution, performing ultrasonic treatment at 60Hz for 1h, and measuring the pH; then, 80mL of a 0.05wt% aqueous solution of polyethyleneimine was prepared, and the mixture was magnetically stirred for 1 hour to determine the pH. 80mL of the sulfonated graphene solution and 80mL of the polyethyleneimine aqueous solution are fully mixed, and the pH of the mixed solution is measured after ultrasonic treatment for 20 min. A PES ultrafiltration bottom membrane (soaked in ultrapure water for more than 1h before use) is arranged in an ultrafiltration cup (figure 1), and 100mL of ultrapure water is preloaded at 1bar for prepressing; pouring the mixed solution into a ultrafilter cup, pressurizing and filtering out 125mL of filtrate at 1.6bar, pouring out the rest mixed solution and taking out the membrane; the membrane was air dried in an oven at 60℃for 1h for use (FIG. 9 (I)).
Example 7:
the membrane surface morphology was as shown in FIG. 9 (II) except that the concentration of 80mL of the aqueous polyethyleneimine solution prepared in the first step in example 6 was changed to 0.2mg/mL, and the same procedure as in example 1 was repeated.
Example 8:
the membrane surface morphology was as shown in FIG. 9 (III) except that the concentration of 80mL of the aqueous polyethyleneimine solution prepared in the first step in example 6 was changed to 0.3mg/mL, and the same procedure as in example 1 was repeated.
Example 9:
the membrane surface morphology was as shown in FIG. 9 (IV) except that the concentration of 80mL of the aqueous polyethyleneimine solution prepared in the first step in example 6 was changed to 0.4mg/mL, and the same procedure as in example 1 was repeated.
2. Film morphology characterization:
the surface morphology and the cross-section structure of the membrane were observed and characterized by means of a SIGMA scanning electron microscope from ZEISS, germany: the main surface morphology observation step is to cut and spray metal on the dried sample film to improve the conductivity of the sample, then to adhere the scanning electron microscope sample to the conductive adhesive tape of the sample holder,the sample holder is placed in a sample chamber, and the sample chamber is evacuated and pressurized to observe the sample. The samples of this example were surface morphology characterized at 20KV acceleration voltage and 20000 times magnification (results of examples 6-9 are shown in FIG. 5, panels a-d); the observation of the cross-section structure is to put the dried sample into liquid nitrogen for brittleness treatment, then take out and break instantly, vertically adhere the cross-section upwards to the conductive adhesive tape of the sample holder, and the subsequent steps are the same as above, the sample of the embodiment performs the cross-section structure characterization under the acceleration voltage of 20KV and the amplification factor of 10000 times (the results of the embodiments 6-9 are shown as the graph a in FIG. 6) 1 ～d 1 Shown), the film thickness of each membrane is marked in the figure.
3. Film surface group analysis:
the film surface chemistry was analyzed using a VERTXE 70 fourier transform infrared spectrometer manufactured by Bruker spectroscopy, germany. The main principle is that the Michelson interferometer is used to make the two beams of optical path difference change according to a certain speed to form interference light, then the interference light acts on the sample, and the computer is used to make Fourier transform of the interference signal detected by the detector to obtain the spectrogram. The results of the infrared spectra of examples 6 to 9 are shown in FIG. 7, 3307cm -1 The characteristic peak at the position can be-OH brought by a dehydrating agent added in a commodity film, which is compared with a PES (polyether sulfone) bottom film standard infrared spectrum by 3307cm -1 The place should be smoother; 1680cm -1 The characteristic peak at is the stretching vibration of-c=c-; 648cm -1 The characteristic peak at the position is the characteristic peak of the sulfonic acid group; PES basement membrane + PEI membrane-c=c-at 1680cm -1 Band shifts occur at this point, indicating interactions between vinyl and polyethersulfone; 648cm in PES substrate film+PEI+SG film -1 Characteristic peaks at the sites indicate that sulfonic acid groups were successfully introduced into the membrane surface; the intensity of each peak in PES bottom film + PEI + SG film is insufficient due to the excessive thickness of the film layer caused by adding SG and PEI at the same time.
4. Membrane hydrophilic performance measurement:
the contact angle of the film surface is measured by adopting an SPCAX3 type contact angle measuring instrument produced by Beijing Hake test instrument factory: the sample was cut into 1X 1cm pieces 2 Size was measured on glass slides with double sided tape, and each sample was averaged after 5 determinations. Each of which is provided withThe water contact angle results of the examples are shown in fig. 8. When the concentration of SG is 0.2mg/mL, the contact angle is minimum, and the membrane hydrophilicity is best, so that water molecules are promoted to move to the surface of the membrane due to the fact that the content of hydrophilic groups on the surface of the membrane is higher at the moment, and the water flux is increased. And as the SG concentration increases, the film surface stacking degree increases, resulting in an increase in film surface roughness, so that the contact angle increases.
5. Membrane separation performance test:
the nanofiltration membrane separation performance evaluation parameters mainly comprise two aspects of water flux and retention rate, and the membrane separation performance test is carried out by using a Stirred Cell 400mL ultrafiltration cup manufactured by Amicon company in Germany. The testing device mainly comprises an ultrafiltration cup which is connected with a nitrogen steel bottle and can be operated at high pressure, and the tail end of the testing device is connected with a measuring cylinder for measuring the volume of the permeate liquid and calculating the water flux. The effective test area of the membrane in the ultrafiltration cup is about 40cm 2 。
5.1 Water flux test:
the flux of a membrane, also called the transmission rate, refers to the volume of liquid passing through a unit membrane area in a unit time under a certain pressure, and the calculation formula is as follows:
j-membrane flux, LMH; q-volume of permeate in a certain time, unit: l is; s-effective area of membrane, m 2 The method comprises the steps of carrying out a first treatment on the surface of the t-test time, unit: h.
pouring 300mL of ultrapure water into a device, and prepressing 50mL under the condition of 4 bar; after the prepressing is finished, the condition is kept unchanged, and the volume Q of the permeation liquid in the t time is measured; finally, the water flux is calculated from equation 1.
5.2 retention test:
the rejection rate of a membrane represents the rejection capability of the membrane to a certain solute, is another important index of the membrane separation process, and is calculated by the following formula:
wherein, the retention rate of R-film,%; c (C) 1 Permeate concentration, unit: g/L; c (C) 2 -initial concentration of feed liquid, unit: g/L.
Test for Evan blue rejection:
300mL of 50mg/L Evan's blue aqueous solution is prepared, and 10mL of the solution is pre-pressed under the condition of 4bar after the solution is poured into a device; after the pre-pressing is completed, the condition is kept unchanged, the volume Q of the permeation liquid in the t time is measured, and the water flux is calculated by a formula 1. Measuring the absorbance of the concentrated solution and the permeate by using an ultraviolet spectrophotometer; plotted evans blue ABS-concentration standard curve (see fig. 2): abs=0.07613c+0.00633 (r 2 = 0.99975), the corresponding concentration of evans blue was calculated, and the rejection of evans blue by the membrane was calculated from equation 2.
FIG. 1 is a schematic diagram of an apparatus for preparing self-assembled films and testing film properties. Mainly comprises an ultrafiltration cup which is connected with a nitrogen steel bottle and can be operated at high pressure, and a lifting table is used for adjusting the height.
FIG. 3 shows the membrane flux and rejection for examples 1-5, with PEI concentration of 0.05wt% being the preferred value.
FIG. 4 shows membrane flux and rejection for examples 6-9, with SG concentration of 0.2mg/mL being the preferred value.
Analysis of the above characterization and film performance results led to the following conclusions:
when the PEI concentration is 0.05wt%, the flux of the nanofiltration membrane is increased and then decreased with the increase of the SG concentration, the interception rate is decreased and then increased, but the total retention rate is maintained above 99%. The rejection rate of Evans blue is 68.41% when no SG is added, and compared with the rejection rate of Evans blue, the rejection rate of Evans blue is greatly improved after SG is added, probably because sulfonic acid groups on SG are combined with amino groups on PEI, and the membranes are more densely deposited on the surfaces of the membranes in a layer-by-layer assembled manner. And when the concentration of SG is 0.2mg/mL, the flux of the membrane is highest, the rejection rate is relatively low, but still the rejection rate is kept above 99%, which is probably because the surface of the membrane contains abundant hydrophilic groups at the moment, and the mass transfer process resistance of water is reduced. From the SEM results, it was also demonstrated that as the SG concentration further increased, the thickness of the dense layer on the membrane surface further increased, the fluid resistance continued to increase, resulting in a decrease in water flux.
Experiments prove that: SG has better dispersibility than ordinary graphene, PEI can provide amino groups, and the PEI and PEI are combined to facilitate stacking to form a film, and can strengthen the positive electric property of the surface of the film, which cannot be achieved by ordinary graphene oxide. PEI ensures the stability and integrity of the membrane structure, prevents the aggregation of SG, and ensures that the concentration of SG can be formed within the range of 0-0.4 mg/mL. The optimal membrane preparation condition for screening the sulfonated graphene nanofiltration membrane is that the SG concentration is 0.2mg/mL, the PEI concentration is 0.05wt%, the water flux of the prepared sulfonated graphene nanofiltration membrane is 8.5LMH, the retention rate of Evan blue is 99.15%, and the water flux of the sulfonated graphene nanofiltration membrane is superior to the retention rate of the basement membrane 68.41%, so that the sulfonated graphene nanofiltration membrane has excellent dye retention performance. Compared with a self-assembled film simply stacked with PEI, the self-assembled film has a certain water flux improvement.
The invention discloses a method for preparing a sulfonated graphene nanofiltration membrane by a layer-by-layer self-assembly technology. Sulfonated Graphene (SG) and Polyethyleneimine (PEI) are selected as self-assembled stacking materials, and the influence of the assembly concentration and the loading capacity of the sulfonated graphene and the polyethyleneimine on the separation performance of the nanofiltration membrane is examined. By characterizing the film by scanning electron microscopy, infrared spectroscopy, contact angle, etc., it is found that: the Polyethersulfone (PES) ultrafiltration membrane combines well with SG/PEI, and the membrane performance is optimal when the concentration of SG is 0.2mg/mL and the concentration of PEI is 0.05%. The water flux was 8.5LMH at this time. The Evansi blue rejection was 99.15%. This is due to the large amount of hydrophilic groups brought about by the addition of SG with PEI and the dense film layer formed by adding them which together affect the film properties.
The foregoing is merely a preferred embodiment of the present invention, and it will be apparent to those skilled in the art that modifications and variations can be made without departing from the technical principles of the present invention, and the invention is also intended to be limited to the following claims.

Claims (4)

1. The layer-by-layer self-assembly preparation method of the sulfonated graphene nanofiltration membrane is characterized by comprising the following steps of:
1) Preparing SG solution 80 and mL, and performing ultrasonic treatment; the concentration of the SG solution is 0.01-0.4 mg/mL; the ultrasonic time is 1h, and the ultrasonic frequency is 60Hz;
2) Preparing PEI aqueous solution 80mL, and magnetically stirring for 1h; the mass percentage concentration of the PEI aqueous solution is 0.01-0.4 wt%; the magnetic stirring time is more than 1h;
3) Fully mixing 80mL of SG solution and 80mL of PEI aqueous solution, and performing ultrasonic treatment to obtain a mixed solution; the volumes of the SG solution and the polyethyleneimine aqueous solution are 1:1; the ultrasonic treatment is carried out for 20min, and the SG solution and the PEI solution are fully mixed and then are subjected to ultrasonic treatment so as to further enhance the dispersibility of SG in the solution;
4) Fixing a bottom film in a ultrafilter cup, and performing press filtration on 100mL ultrapure water under 1bar for prepressing stabilization; the basement membrane adopts a PES ultrafiltration basement membrane, and before the PES ultrafiltration basement membrane is used, the PES ultrafiltration basement membrane is soaked in ultrapure water for more than 1h, and the PES ultrafiltration basement membrane is pre-pressed into 100mL ultrapure water under 1 bar;
5) Pouring the mixed solution obtained in the step 3) into an ultrafiltration cup with a bottom membrane for pressurized filtration, and placing a membrane after PEI and SG are transferred to a PES ultrafiltration bottom membrane into an oven for forced air drying to obtain the sulfonated graphene nanofiltration membrane; the pressure filtration is stopped when the volume of the permeate is 125mL, and the pressure is not more than 1.6bar.
2. The layer-by-layer self-assembly preparation method of the sulfonated graphene nanofiltration membrane according to claim 1, wherein in the step 1), the concentration of the SG solution is 0.2 mg/mL.
3. The layer-by-layer self-assembly preparation method of the sulfonated graphene nanofiltration membrane as claimed in claim 1, wherein in the step 2), the mass percentage concentration of the PEI aqueous solution is 0.05 wt%.
4. A sulfonated graphene nanofiltration membrane prepared by the preparation method of any one of claims 1 to 3.
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