CN114887498B - Graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate - Google Patents
Graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate Download PDFInfo
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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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- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/027—Nanofiltration
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- 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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- B01D71/06—Organic material
- B01D71/74—Natural macromolecular material or derivatives thereof
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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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D2323/50—Control of the membrane preparation process
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Abstract
The invention discloses a graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate, which is formed by stacking a graphene oxide sodium alginate stable structure GO-SA prepared by modifying the surface of sodium alginate SA as a spacer of a graphene oxide GO sheet layer and the graphene oxide sheet layer by layer. The composite nanofiltration membrane has undulation and folds on the surface, the section is of a layer stacking structure, and a stable structure GO-SA is embedded between graphene oxide nano layers in the stacking structure. Experiments prove that the composite nanofiltration membrane has higher water flux than a pure graphene oxide membrane, the water flux can be increased along with the increase of the addition amount of GO-SA, the composite nanofiltration membrane also has outstanding performance in terms of separating dyes, has excellent interception performance on the tested Evan blue, and is indicated to be widely applied to preparation of water flux and filtration performance equipment and textile dye wastewater treatment equipment.
Description
Technical Field
The invention relates to a composite nanofiltration membrane and preparation and application thereof, in particular to a graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate and preparation and application thereof, and belongs to the technical field of wastewater treatment materials.
Background
Water purification and water treatment have become one of the major problems facing humans, for which many studies have been carried out to find effective solutions. Membrane separation materials require regulation of the effective entrapment of contaminants and the permeability of the membrane. The effective entrapment is closely related to pore structure and membrane thickness affects permeability. From this point of view, inorganic membranes (ceramics, silicon, zeolites, etc.) and polymeric membranes (polyimide (PI), polyamide (PA), polyacrylonitrile (PAN), polysulfone (PSF), polyvinylidene fluoride (PVDF) are not the best choice for transport 2D materials are now emerging as ideal materials for research and development of new membranes.
Common 2D separation membrane materials include graphene-based (GO) materials, covalent Organic Frameworks (COFs), and Metal Organic Frameworks (MOFs). Compared with other two-dimensional materials, the Graphene Oxide (GO) membrane has an inner surface hole, can selectively adsorb pollutants, and has great potential in improving membrane separation due to the high specific surface area and controllable pore diameter of the GO membrane. Due to the unique two-dimensional structure of GO, the membrane has high mechanical strength and good adsorptivity, and can be expected to become an ideal filter membrane material by adjusting the interlayer spacing and the aperture of GO or functionally modifying GO.
The physicochemical properties of the lamellar graphene oxide membrane structure can be regulated and controlled by different modification methods. The functionalized modified GO can have unique properties such as chemical stability and retention degradation, which makes the membrane suitable for materials of different separation systems. The unique performances enable the GO to meet different filtering requirements, and the application prospect in the field of wastewater purification is wide.
The oxygen-containing functional groups on the surface and the edge of the graphene oxide can provide reaction sites with other materials, and the interlayer spacing of the film can be regulated and controlled by intercalating small molecules or macromolecules into the graphene oxide. The intercalation mode is generally divided into two types, namely physical compounding and chemical crosslinking. Experiments prove that the graphene oxide film obtained through physical intercalation and other modes has a great promotion effect on improving the water permeability. Through retrieval, the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate (water permeability and dye selectivity) is formed by combining oxygen-containing groups on graphene oxide and oxygen-containing groups on sodium alginate through hydrogen bonds to generate a graphene oxide sodium alginate stable structure GO-SA serving as a spacer of graphene oxide sheets and stacking the graphene oxide sheets layer by layer, and the preparation and application of the graphene oxide/sodium alginate composite nanofiltration membrane are not reported yet.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate, and the preparation and application thereof.
The graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate is characterized in that: the composite nanofiltration membrane is formed by stacking graphene oxide sodium alginate stable structure GO-SA prepared by modifying the surface of sodium alginate SA as a spacer of graphene oxide GO sheets and graphene oxide sheets layer by layer; the surface of the composite nanofiltration membrane is uneven and provided with folds with different sizes; the film section presents a layered stacked structure, and the interlayer spacing is 0.93+/-0.02 nm; the stacked structure is provided with a graphene oxide sodium alginate stable structure GO-SA which is used as a spacer and is prepared by modifying the surface of sodium alginate SA, and the graphene oxide sodium alginate stable structure GO-SA is embedded between graphene oxide nanometer layers; the mixing volume ratio of graphene oxide to GO-SA in the composite nanofiltration membrane is 1-9:1-3, the control of the membrane on water flux or retention rate is determined by the mixing volume ratio of graphene oxide to GO-SA, if the mixing addition amount of GO-SA is increased, the interlayer spacing of graphene oxide sheets is increased, the membrane water flux is increased, the membrane retention rate is reduced, and meanwhile, the contact angle of the composite nanofiltration membrane is also increased, but the angle of the contact angle is still the same<90 °, the membrane is still hydrophilic; if the mixed addition amount of the GO-SA is reduced, the result is opposite; the graphene oxide sodium alginate stable structure GO-SA is formed by combining an oxygen-containing group on graphene oxide and an oxygen-containing group on sodium alginate through hydrogen bonds, and is prepared by the following method: mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and then performing freeze drying to obtain GO-SA with a stable structure; scanningThe electron microscope image shows that the GO-SA sample has uneven surface, different sizes of hole structures which are communicated with each other, smooth surface of the hole wall structure, and different sizes and numbers of folds and ravines; infrared spectrum shows GO-SA at 1027cm -1 The characteristic peak of C-O-C is stronger than GO, at 3255cm -1 The characteristic peak of the stretching vibration representing-OH is stronger than SA at 1597 and 1408cm -1 The characteristic peaks representing the stretching vibration of the symmetrical and asymmetrical COO-groups are stronger than SA.
Wherein: the mixing volume ratio of graphene oxide to graphene oxide sodium alginate stable structure GO-SA in the composite nanofiltration membrane is preferably 4:1.
In the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate: the interlayer spacing of the composite nanofiltration membrane is preferably 0.93nm; the composite nanofiltration membrane comprises the following components in percentage by mass: graphene oxide accounts for 70+/-5, and sodium alginate with the viscosity of 1.05-1.15 Pa.s accounts for 30+/-5; the contact angle of the composite nanofiltration membrane and water is preferably 65.76 °.
The preparation method of the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate comprises the following steps:
(1) Preparing graphene oxide sodium alginate stable structure GO-SA by modifying the surface of sodium alginate SA:
sodium alginate SA with the viscosity of 1.05-1.15 Pa.s is dissolved in deionized water to prepare sodium alginate aqueous solution with the concentration of 20 mg/mL; then mixing the mixture with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, carrying out ultrasonic oscillation for 30+/-5 minutes, stirring for 2 hours, and freeze-drying to obtain GO-SA with a stable structure;
(2) Preparation of graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate:
dispersing graphene oxide GO and GO-SA in distilled water through ultrasonic treatment respectively to prepare aqueous solutions with the concentration of 0.20-1 mg/mL, and mixing the GO aqueous solution with the same concentration with the GO-SA aqueous solution according to the volume ratio of 1-9:1-3 to prepare a graphene oxide/sodium alginate compound; then, adding graphene oxide/sodium alginate composite into a cellulose acetate membrane with the aperture of 0.22um as a substrate membrane, carrying out suction filtration to form a membrane by a vacuum suction filtration method under the pressure of 1bar, and naturally drying the membrane to obtain the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate; the mixing volume ratio of the GO aqueous solution to the GO-SA aqueous solution is different, the suction filtration amount of the graphene oxide/sodium alginate composite is different, and the prepared graphene oxide/sodium alginate composite nanofiltration membrane is different.
Wherein: the concentration of the prepared aqueous solution in the step (2) is preferably 0.25mg/mL; preferably, the GO aqueous solution with the same concentration and the GO-SA aqueous solution are mixed according to the volume ratio of 4:1 to prepare the graphene oxide/sodium alginate compound.
The preparation method comprises the following steps: in the step (2), a cellulose acetate membrane with the aperture of 0.22um is used as a substrate membrane, preferably 10+/-2 ml of graphene oxide/sodium alginate composite is added, and the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate is prepared by vacuum filtration under the pressure of 1 bar.
The graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate is applied to preparation of water flux or nanofiltration performance equipment.
The invention relates to application of a graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate in preparation of textile dye wastewater treatment equipment.
According to the invention, the oxygen-containing groups on GO and SA can be combined together through hydrogen bonds, the sodium alginate is modified through graphene oxide to obtain a GO-SA sample, then the GO and GO-SA solutions with the same concentration are prepared, the mixed solution is prepared according to a specific proportion, and then the quantitative solution is prepared into the composite nanofiltration membrane through vacuum filtration. Experiments prove that: the contact angle of the pure graphene oxide filter membrane and water is 43.02 degrees, the contact angle of the composite nanofiltration membrane and water is 65.76 degrees, and the hydrophilicity of the graphene oxide/sodium alginate composite nanofiltration membrane is higher than that of the pure graphene oxide membrane. According to XRD test analysis, the interlayer spacing of the graphene oxide filter membrane is about 0.83nm, and the interlayer spacing of the graphene oxide/sodium alginate composite filter membrane is 0.93nm, because the addition of GO-SA increases the interlayer spacing of the membrane. Through scanning tests, the surface of the composite membrane has more undulation and more folds, and a transmission channel can be provided for quick passing of water molecules; the cross section can see a distinct and good layered stack.
The prepared film was subjected to a water flux and an Evans Blue (EB) retention performance test.
The water flux test results of different composite nanofiltration membrane samples show that the water flux of the graphene oxide/sodium alginate composite filtration membrane is far greater than that of a pure graphene oxide membrane under the same sample volume, which indicates that sodium alginate plays a certain role between graphene oxide sheets. The result of controlling the water flux can be achieved by controlling the amount of the added GO-SA, and the water flux of the membrane is increased along with the increase of the added GO-SA, which also proves that the controllable composite nanofiltration membrane is successfully prepared.
The test results of the entrapment rate of different composite nanofiltration membrane samples on the Evan blue show that the entrapment rate of pure graphene oxide on the Evan blue is 79.58%, the entrapment capacity of the graphene oxide/sodium alginate composite nanofiltration membrane on the Evan blue is reduced along with the increase of the addition amount of GO-SA, but compared with the pure graphene oxide membrane, the entrapment rate of the composite nanofiltration membrane on the Evan blue is firstly enhanced and then weakened, and the effect of controlling the entrapment rate can be achieved by controlling the addition amount of GO-SA. The interlayer spacing of the graphene oxide filtering membrane is changed through the addition of sodium alginate, different water fluxes and the retention rate of Evan's blue are shown, and the application prospect in preparing water fluxes or filtering performance equipment is shown to be wide.
The invention also provides a graphene oxide sodium alginate stable structure GO-SA for preparing the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate, which is characterized in that: the graphene oxide sodium alginate stable structure GO-SA is generated by combining oxygen-containing groups on graphene oxide and oxygen-containing groups on sodium alginate through hydrogen bonds, and a scanning electron microscope image shows that the GO-SA sample has uneven surface, has different hole structures which are communicated with each other, has smooth hole wall structure surface and folds and ravines with different sizes and numbers; infrared spectrum shows GO-SA at 1027cm -1 The characteristic peak of C-O-C is stronger than GO, at 3255cm -1 The characteristic peak of the stretching vibration representing-OH is stronger than SA at 1597 and 1408cm -1 The characteristic peaks representing the stretching vibration of the symmetrical and asymmetrical COO-groups are stronger than SA; the method comprises the following steps: mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and then performing freeze drying to obtain the GO-SA with a stable structure.
The invention discloses a graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate, and preparation and application thereof. Firstly, preparing graphene oxide sodium alginate stable structure GO-SA by modifying the surface of sodium alginate SA, wherein nano-sized sodium alginate is provided with hydroxyl and carboxyl, and the hydroxyl and carboxyl can be reacted with oxygen-containing groups of graphene oxide to uniformly disperse the sodium alginate on graphene oxide nano sheets through hydrogen bonding, so that the stable structure GO-SA is successfully synthesized; the modified graphene oxide sodium alginate stable structure GO-SA is used as a spacer of graphene oxide sheets, a GO-SA sample is prepared into an aqueous solution with the same concentration as graphene oxide, a mixed solution is prepared by the set volume ratio of the GO-SA sample and the graphene oxide, and then a quantitative graphene oxide/sodium alginate composite solution is prepared into a graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate through vacuum filtration. According to the invention, the modified sodium alginate is added as a graphene oxide lamellar spacer to increase lamellar spacing, so that water permeability and dye molecule separation performance are improved, and selective filtration of some substances is realized. The control of the membrane on the water flux or the rejection rate is determined by the mixed volume ratio of the graphene oxide and the GO-SA, if the mixed addition amount of the GO-SA is increased, the interlayer spacing of graphene oxide sheets is increased, the membrane water flux is increased, the membrane rejection rate is reduced, and meanwhile, the contact angle of the composite nanofiltration membrane is also increased; if the mixed addition amount of the GO-SA is reduced, the result is opposite; through adjusting the mixing volume ratio of the GO aqueous solution and the GO-SA aqueous solution, the amount of the graphene oxide/sodium alginate composite is filtered, and finally the optimal graphene oxide/sodium alginate composite nanofiltration membrane is obtained, and through testing, the membrane has controllable water flux and filtering performance.
The preparation method has the outstanding advantages that after the graphene oxide/sodium alginate composite solution is obtained, the graphene oxide/sodium alginate composite nanofiltration membrane is directly obtained by vacuum suction filtration, the whole preparation process is green and pollution-free, and the membrane has excellent filtration performance, and particularly has higher rejection rate for Evan's blue. The graphene oxide/sodium alginate composite nanofiltration membrane disclosed by the invention is expected to be widely applied to preparation of water flux or filtration performance equipment.
Drawings
Fig. 1: scanning Electron Microscope (SEM) image of GO-SA.
Fig. 2: infrared plot of GO-SA.
Fig. 3: scanning Electron Microscope (SEM) images of graphene oxide/sodium alginate composite nanofiltration membranes.
Wherein (a) is a surface scanning image of the composite nanofiltration membrane, and (b) is a cross-sectional image of the composite nanofiltration membrane. The figure shows that the surface of the composite nanofiltration membrane is uneven and has folds with different sizes, thereby providing a transmission channel for quick passing of water molecules; the cross section can see a distinct and good layered stack.
Fig. 4: water contact angle test patterns of the composite nanofiltration membrane of samples with different proportions.
As seen from the figure, as the addition amount of GO-SA increases, the contact angle of the composite nanofiltration membrane also increases, but the angle of the contact angle is still <90 °, which also proves that the composite nanofiltration membrane in the invention is also a hydrophilic membrane.
Fig. 5: x-ray diffraction (XRD) patterns of the composite nanofiltration membranes of samples of different proportions.
According to the XRD pattern, the interlayer spacing of GO is calculated to be 0.83nm, but the interlayer spacing of the graphene oxide/sodium alginate composite nanofiltration membrane is calculated to be 0.93nm, and the interlayer spacing of GO is increased by adding SA.
Fig. 6: and (3) a water flux test result graph of different composite nanofiltration membrane samples.
As can be seen from the figure, the water flux of the composite nanofiltration membrane also increased with increasing SA addition. This is determined by the interlayer spacing of the filtration membrane, and the addition of SA increases the interlayer spacing of the membrane, and the water flux of the composite nanofiltration membrane also increases.
Fig. 7: retention ratio of different sample composite nanofiltration membranes to evans blue.
As can be seen from the graph, the retention rate is related to the amount of SA added. The larger the added amount of SA, the worse the membrane retention is, because the addition of SA increases the interlayer spacing of the membrane, the increase of the interlayer spacing influences the size effect of the membrane, the larger the interlayer spacing makes the dye easier to pass through the membrane, the size effect of the membrane becomes worse, more dye molecules penetrate the membrane, and the retention becomes worse.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are only preferred embodiments of the present invention, and it should be noted that the following descriptions are merely for explaining the present invention, and are not limiting in any way, and any simple modification, equivalent variation and modification of the embodiments according to the technical principles of the present invention are within the scope of the technical solutions of the present invention.
In the following examples, materials, reagents and the like used, unless otherwise specified, were obtained commercially.
Example 1 preparation of graphene oxide sodium alginate stable Structure GO-SA
Mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and then performing freeze drying to obtain the GO-SA with a stable structure.
FIG. 1 is a Scanning Electron Microscope (SEM) image of GO-SA, showing that the GO-SA sample has rough surface, different sizes of cross-linked hole structures, smooth surface of the hole wall structure, and different sizes and numbers of folds and ravines.
FIG. 2 is an infrared image of GO-SA, from which the infrared spectral characteristic band 1038cm of GO can be seen -1 Representing the tensile vibration of C-O-C. GO-like material as compared with GOSA at 1027cm -1 The characteristic peak at which C-O-C is represented is significantly stronger. 3233, 1594 and 1406cm for pure SA samples -1 Representing the sum of the stretching vibration of-OH, the stretching vibration of symmetrical and asymmetrical COO-, respectively. GO-SA at 3255cm -1 The peak intensity at (2) is higher than at SA because the addition of GO increases the hydrogen bonding effect at 1597 and 1408cm -1 The two peaks seen correspond to the stretching vibrations of the symmetrical and asymmetrical COO-groups in the alginate, which are significantly stronger than the SA sample, because of the carboxylic acid formed by the hydrogen bond between GO and sodium alginate. Due to the strong interactions of GO with SA. In conclusion, the data prove that the GO-SA sample with the stable structure is successfully prepared, and the structure is generated by combining oxygen-containing groups on graphene oxide and oxygen-containing groups on sodium alginate through hydrogen bonds.
Example 2 preparation of graphene oxide/sodium alginate composite nanofiltration membrane with controllable Water flux or retention rate
(1) Preparation of surface modified sodium alginate (GO-SA): mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and then performing freeze drying to obtain the GO-SA with a stable structure.
(2) Dispersing graphene oxide GO and GO-SA in distilled water through ultrasonic treatment respectively to prepare aqueous solutions with the concentration of 0.25mg/mL, and mixing the GO aqueous solution with the same concentration with the GO-SA aqueous solution according to the volume ratio of 4:1 to prepare a graphene oxide/sodium alginate compound; then, 10ml of graphene oxide/sodium alginate composite is added by taking a cellulose acetate membrane with the aperture of 0.22um as a substrate membrane, the membrane is filtered by vacuum filtration under the pressure of 1bar, and the membrane is naturally dried, so that the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate is obtained.
And testing the prepared composite nanofiltration membrane by a scanning electron microscope so as to observe the morphology of the membrane.
Fig. 3 is a Scanning Electron Microscope (SEM) image of a graphene oxide/sodium alginate composite nanofiltration membrane. The figure shows that the surface of the composite nanofiltration membrane is uneven and has folds with different sizes, thereby providing a transmission channel for quick passing of water molecules; the cross section can see a distinct and good layered stack. The stacked structure is provided with a graphene oxide sodium alginate stable structure GO-SA serving as a spacer, and the graphene oxide sodium alginate stable structure GO-SA is embedded between graphene oxide nanometer layers.
Example 3
(1) Preparation of surface modified sodium alginate (GO-SA): mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and then performing freeze drying to obtain the GO-SA with a stable structure.
(2) Dispersing graphene oxide GO and GO-SA in distilled water through ultrasonic treatment respectively to prepare aqueous solutions with the concentration of 0.25mg/mL, and mixing the GO aqueous solutions with the same concentration with the GO-SA aqueous solutions according to the volume ratio of 9:1, 4:1, 7:3, 3:2 and 1:1 respectively to prepare a series of graphene oxide/sodium alginate complexes; then, taking a cellulose acetate membrane with the aperture of 0.22um as a substrate membrane, respectively adding 10ml of graphene oxide/sodium alginate composite, carrying out suction filtration to form a membrane by a vacuum suction filtration method under the pressure of 1bar, and naturally drying the membrane to obtain a series of graphene oxide/sodium alginate composite nanofiltration membranes with controllable water flux or retention rate. The mixing volume ratio of the GO aqueous solution to the GO-SA aqueous solution is different, the suction filtration amount of the graphene oxide/sodium alginate composite is different, and the prepared graphene oxide/sodium alginate composite nanofiltration membrane is different.
For comparison, pure graphene oxide membranes were obtained by vacuum filtration of 10mL of pure GO aqueous dispersion; finally, all films were completely dried at room temperature. The hydrophilicity of the membrane is an important reference basis for membrane characterization, and the dried membrane is subjected to water contact angle test to test the hydrophilicity of the membrane. The inter-layer spacing can affect the water flux and dye retention of the membrane, and XRD testing is performed on the membrane to determine the size of the inter-layer spacing of the membrane, which can help to estimate the retention performance of the membrane.
Fig. 4 is a graph showing the contact angle of the different filters prepared in example 3, and it can be seen from the graph that the water contact angle of each prepared film increases with the increase of the GO-SA content, the surface hydrophilicity is weakened, but the angle of the contact angle is still <90 °, and the film is still a hydrophilic film.
FIG. 5 is a graph of X-ray diffraction (XRD) patterns of filter films of samples of different proportions. From XRD patterns, it can be calculated that the interlayer spacing of GO is 0.83nm, while that of the composite nanofiltration membrane is 0.93nm, and the addition of SA increases the interlayer spacing of GO.
Example 4
(1) Preparation of surface modified sodium alginate (GO-SA): mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and then performing freeze drying to obtain the GO-SA with a stable structure.
(2) Dispersing graphene oxide GO and GO-SA in distilled water through ultrasonic treatment respectively to prepare aqueous solutions with the concentration of 0.25mg/mL, and mixing the GO aqueous solutions with the same concentration with the GO-SA aqueous solutions according to the volume ratio of 9:1, 4:1, 7:3, 3:2 and 1:1 respectively to prepare a series of graphene oxide/sodium alginate complexes; then, taking a cellulose acetate membrane with the aperture of 0.22um as a substrate membrane, respectively adding 10ml of graphene oxide/sodium alginate composite, carrying out suction filtration to form a membrane by a vacuum suction filtration method under the pressure of 1bar, and naturally drying the membrane to obtain a series of graphene oxide/sodium alginate composite nanofiltration membranes with controllable water flux or retention rate. The mixing volume ratio of the GO aqueous solution to the GO-SA aqueous solution is different, the suction filtration amount of the graphene oxide/sodium alginate composite is different, and the prepared graphene oxide/sodium alginate composite nanofiltration membrane is different.
For comparison, pure graphene oxide membranes were obtained by vacuum filtration of 10mL of pure GO aqueous dispersion; finally, all films were completely dried at room temperature. The prepared film was subjected to a water flux and an evans blue retention performance test.
FIG. 6 is a graph of the results of the filtration membrane water flux test for different samples, wherein the water flux of the composite membrane increases with increasing SA addition. This is determined by the interlayer spacing of the filtration membrane, and the addition of SA increases the interlayer spacing of the membrane, and the water flux of the composite membrane increases.
FIG. 7 is a graph showing the results of the test of the rejection rate of Evan's blue by the filter membrane of different samples, and it can be seen from the graph that the rejection rate is related to the addition amount of SA. The larger the added amount of SA, the worse the membrane retention is, because the addition of SA increases the interlayer spacing of the membrane, the increase of the interlayer spacing influences the size effect of the membrane, the larger the interlayer spacing makes the dye easier to pass through the membrane, the size effect of the membrane becomes worse, more dye molecules penetrate the membrane, and the retention becomes worse.
Claims (9)
1. The graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate is characterized in that: the composite nanofiltration membrane is formed by stacking graphene oxide sodium alginate stable structure GO-SA prepared by modifying the surface of sodium alginate SA as a spacer of graphene oxide GO sheets and graphene oxide sheets layer by layer; the surface of the composite nanofiltration membrane is uneven and provided with folds with different sizes; the film section presents a layered stacked structure, and the interlayer spacing is 0.93+/-0.02 nm; the stacked structure is provided with a graphene oxide sodium alginate stable structure GO-SA which is used as a spacer and is prepared by modifying the surface of sodium alginate SA, and the graphene oxide sodium alginate stable structure GO-SA is embedded between graphene oxide nanometer layers; the mixing volume ratio of graphene oxide to GO-SA in the composite nanofiltration membrane is 1-9:1-3, the control of the membrane on water flux or retention rate is determined by the mixing volume ratio of graphene oxide to GO-SA, if the mixing addition amount of GO-SA is increased, the interlayer spacing of graphene oxide sheets is increased, the membrane water flux is increased, the membrane retention rate is reduced, and meanwhile, the contact angle of the composite nanofiltration membrane is also increased, but the angle of the contact angle is still the same<90 °, the membrane is still hydrophilic; if the mixed addition amount of the GO-SA is reduced, the result is opposite; the graphene oxide sodium alginate stable structure GO-SA is formed by combining an oxygen-containing group on graphene oxide and an oxygen-containing group on sodium alginate through hydrogen bonds, and is prepared by the following method: mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and performing freeze drying to obtain GO-SA with a stable structure; scanning electron microscope image shows GO-SA sample surfaceThe corrugated structure has different sizes of mutually communicated hole structures, the surface of the hole wall structure is smooth, and folds and ravines with different sizes and numbers are arranged; infrared spectrum shows GO-SA at 1027cm -1 The characteristic peak at which C-O-C is represented is stronger than GO at 3255cm -1 The characteristic peak of the stretching vibration representing-OH is stronger than SA at 1597 and 1408cm -1 The characteristic peaks representing the stretching vibration of the symmetrical and asymmetrical COO-groups are stronger than SA.
2. The graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate according to claim 1, wherein the graphene oxide/sodium alginate composite nanofiltration membrane is characterized in that: the mixing volume ratio of graphene oxide to graphene oxide sodium alginate stable structure GO-SA in the composite nanofiltration membrane is 4:1.
3. The graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate according to claim 1, wherein the graphene oxide/sodium alginate composite nanofiltration membrane is characterized in that: the interlayer spacing of the composite nanofiltration membrane is 0.93nm; the composite nanofiltration membrane comprises the following components in percentage by mass: graphene oxide accounts for 70+/-5%, and sodium alginate with the viscosity of 1.05-1.15 Pa.s accounts for 30+/-5%; the contact angle of the composite nanofiltration membrane and water is 65.76 degrees.
4. The preparation method of the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate, disclosed in claim 1, comprises the following steps:
(1) Preparing graphene oxide sodium alginate stable structure GO-SA by modifying the surface of sodium alginate SA:
dissolving sodium alginate SA with the viscosity of 1.05-1.15 Pa.s in deionized water to prepare sodium alginate aqueous solution with the concentration of 20 mg/mL; then mixing the mixture with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, carrying out ultrasonic oscillation for 30+/-5 minutes, stirring for 2 hours, and then freeze-drying to obtain GO-SA with a stable structure;
(2) Preparation of graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate:
dispersing graphene oxide GO and GO-SA in distilled water through ultrasonic treatment respectively to prepare aqueous solutions with the concentration of 0.20-1 mg/mL, and mixing the GO aqueous solution with the same concentration with the GO-SA aqueous solution according to the volume ratio of 1-9:1-3 to prepare a graphene oxide/sodium alginate compound; then, adding graphene oxide/sodium alginate composite into a cellulose acetate membrane with the aperture of 0.22um as a substrate membrane, carrying out suction filtration to form a membrane by a vacuum suction filtration method under the pressure of 1bar, and naturally drying the membrane to obtain the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate; the mixing volume ratio of the GO aqueous solution to the GO-SA aqueous solution is different, the suction filtration amount of the graphene oxide/sodium alginate composite is different, and the prepared graphene oxide/sodium alginate composite nanofiltration membrane is different.
5. The method of manufacturing according to claim 4, wherein: the concentration of the prepared aqueous solution in the step (2) is 0.25mg/mL; and mixing the GO aqueous solution with the same concentration with the GO-SA aqueous solution according to the volume ratio of 4:1 to prepare the graphene oxide/sodium alginate compound.
6. The method of manufacturing according to claim 4, wherein: in the step (2), a cellulose acetate membrane with the aperture of 0.22um is used as a substrate membrane, a graphene oxide/sodium alginate composite with the aperture of 10+/-2 ml is added, and the graphene oxide/sodium alginate composite nanofiltration membrane with the controllable water flux or retention rate is prepared by vacuum filtration under the pressure of 1 bar.
7. The application of the graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate in preparation of nanofiltration performance equipment according to one of claims 1-3.
8. The use of a graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate according to one of claims 1-3 in the preparation of textile dye wastewater treatment equipment.
9. Graphite oxide for preparing graphene oxide/sodium alginate composite nanofiltration membrane with controllable water flux or retention rate according to one of claims 1-3Alkene sodium alginate stable structure GO-SA, its characterized in that: the graphene oxide sodium alginate stable structure GO-SA is generated by combining oxygen-containing groups on graphene oxide and oxygen-containing groups on sodium alginate through hydrogen bonds, and a scanning electron microscope image shows that the GO-SA sample has uneven surface, has different hole structures which are communicated with each other, has smooth hole wall structure surface and folds and ravines with different sizes and numbers; infrared spectrum shows GO-SA at 1027cm -1 The characteristic peak at which C-O-C is represented is stronger than GO at 3255cm -1 The characteristic peak of the stretching vibration representing-OH is stronger than SA at 1597 and 1408cm -1 The characteristic peaks representing the stretching vibration of the symmetrical and asymmetrical COO-groups are stronger than SA; the method comprises the following steps: mixing sodium alginate SA aqueous solution with the concentration of 20mg/mL and the viscosity of 1.05-1.15 Pa.s with graphene oxide GO aqueous solution with the concentration of 4mg/mL according to the volume ratio of 10:1.5, performing ultrasonic vibration for 30+/-5 minutes, stirring for 2 hours, and performing freeze drying to obtain the GO-SA with a stable structure.
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