CN117160246A - Method for stabilizing graphene oxide cortex and ultrafiltration base membrane - Google Patents

Abstract

The invention discloses a method for stabilizing graphene oxide cortex and ultrafiltration base membrane, and belongs to the technical field of membrane separation. The method for stabilizing the graphene oxide cortex and the ultrafiltration base membrane includes the following steps: functionalizing the PAN membrane to obtain a functionalized PAN membrane, then coating the graphene oxide on the functionalized PAN membrane, and heat-treating to obtain Graphene oxide composite membrane. By optimizing membrane production parameters (EDA adsorption time, post-adsorption heat treatment temperature, GO thickness, etc.), the present invention obtains a graphene oxide composite membrane (GO composite membrane) with improved screening performance and more stable pore structure.

Description

A method for stabilizing graphene oxide cortex and ultrafiltration base membrane

Technical field

The present invention relates to the field of membrane separation technology, and in particular to a method for stabilizing graphene oxide cortex and ultrafiltration base membrane.

Background technique

Graphene oxide (GO), as a new two-dimensional material, not only has the advantages of strong mechanical properties, good dispersion properties and can be prepared in large quantities, but also has the characteristics of hydrophilicity, antibacterial properties and excellent chlorine resistance. It is a kind of Excellent water treatment surface materials are expected to be used in separation processes such as ultrafiltration, nanofiltration, reverse osmosis, and pervaporation.

There are many methods to build a graphene oxide separation layer, mainly through the self-assembly process to form a two-dimensional stacked structure. The specific assembly drive types include pressure drive and dispersion volatilization drive. Among them, pressure drive is a pressure-assisted self-assembly method. This method can be divided into two types: "pressure filtration" and "negative pressure filtration". Its characteristic is that a certain concentration of GO dispersion is selected, and the pressure assists Under this condition, the GO cortex in the dispersion is deposited on the base film to obtain a GO composite film. The advantages of this method are convenience, speed, controllable separation layer thickness, adjustable film formation speed and GO layer microstructure.

Establishing a stable interaction between the functional layer and the cortex of the GO composite membrane can avoid the problem of separation layer shedding caused by fluid convection and other operations during the actual use of the membrane. When building this stable interaction, the surface of the base film is often functionalized to have functional groups that can form strong interactions with the GO sheets. In the construction of GO composite membranes, most of the base membrane modification methods used are polydopamine surface modifications that have broad compatibility with the material surface. However, this method itself has certain limitations. The polydopamine surface modification method achieves surface functionalization in the form of depositing small polydopamine particles onto the modified surface. In the face of some pores that have high requirements on surface morphology, especially ultrafiltration base membranes whose surface is only 10nm horizontal, During the modification process, pore blocking may occur, reducing the flux of membrane separation. For base films whose surfaces are prone to clogging, how to effectively functionalize the surface while maintaining the surface pore structure is a direction that requires efforts.

Contents of the invention

The purpose of the present invention is to provide a method for stabilizing the graphene oxide cortex and the ultrafiltration base membrane to solve the problems existing in the above-mentioned prior art. The PAN membrane used in the present invention is a common microfiltration membrane construction material. PAN on the membrane surface controls hydrolysis, which can realize carboxylation of the surface structure, and then form a covalent bond with the oxygen-containing groups on the GO surface, or it can be secondary functionalized with the diamine cross-linking agent first, and then interact with the GO separation layer. The interception performance can be improved while effectively maintaining the microstructure of the small pores (as evidenced by surface electron microscopy (SEM) photos, specifically: the surface morphology of the PAN membrane after hydrolysis and carboxylation and amino secondary functionalization Similar to PAN, significant surface voids are still maintained).

In order to achieve the above objects, the present invention provides the following solutions:

One of the technical solutions of the present invention: a method for stabilizing the graphene oxide cortex and the ultrafiltration base membrane, including the following steps:

Functionalize the PAN film (PAN base film) to obtain a functionalized PAN film, then coat graphene oxide on the functionalized PAN film, and obtain a graphene oxide composite film after heat treatment.

Further, the functionalized PAN film includes a carboxyl functionalized PAN film or an amino functionalized PAN film; the temperature of the heat treatment is 25-100°C, and the time is 0.5h.

Furthermore, the heat treatment method is air blast drying oven heating treatment, vacuum drying oven heating treatment, electrothermal treatment, microwave heating treatment, light radiation heating treatment or wind heat treatment.

Furthermore, the temperature of the heat treatment is 80°C and the time is 0.5h.

Furthermore, the graphene oxide is coated in the form of a dispersion; the concentration of the dispersion is 0.4 mg/mL, and the volume is 20-40 μL.

Further, the preparation method of the carboxyl functionalized PAN membrane (functionalized and hydrolyzed at the molecular level) includes the following steps:

The PAN membrane is placed in an alkaline solution, shaken in a water bath, and then soaked in an acidic solution to obtain the carboxyl functionalized PAN membrane.

PAN membrane is a must choice, which provides a material basis for hydrolysis.

Further, the alkaline solution is a NaOH solution with a concentration of 1.5 mol/L; the water bath oscillation temperature is 50°C and the time is 1 hour; the acidic solution is a hydrochloric acid solution with a concentration of 1 mol/L; the soaking The time is 24h.

Further, the preparation method of the amino-functionalized PAN membrane (functionalized at the molecular level, hydrolyzed and EDA functionalized) includes the following steps:

The carboxyl functionalized PAN membrane is placed in an ethylenediamine solution (EDA solution), shaken in a water bath and then dried to obtain an amino functionalized PAN membrane.

Further, the concentration of the ethylenediamine solution is 10 mg/mL; the water bath shaking temperature is 25°C, and the time is 1 to 30 min; the drying temperature is 80°C, and the time is 0.5h.

The PAN membrane is functionalized at the molecular level to ensure the maintenance of the micropore structure (there are often about 10nm gaps on the surface of the microfiltration membrane).

Further, the preparation method of graphene oxide specifically includes: mixing acid solution, graphene and potassium permanganate and heating the reaction, then pouring the reacted solution on ice and mixing evenly, and adding hydrogen peroxide dropwise. After completion, centrifuge and the precipitate is the graphene oxide.

Further, the acid solution is a mixed solution of concentrated sulfuric acid (18.4 mol/L) and concentrated phosphoric acid (14.6 mol/L) with a volume ratio of 5:1; the temperature of the heating reaction is 40°C and the time is 6 hours.

Furthermore, the coating method includes vacuum filtration method, spin coating method, pressure assembly method or gas-liquid interface assembly method.

The second technical solution of the present invention: a graphene oxide composite membrane prepared by the above method.

The third technical solution of the present invention: the application of the above-mentioned graphene oxide composite membrane in nanofiltration interception, reverse osmosis, forward osmosis, ultrafiltration, pervaporation or oil-water separation.

Furthermore, the objects intercepted by the nanofiltration include inorganic divalent anions, inorganic trivalent anions, negatively charged organic small molecules or neutral small molecules with a molecular weight of 200 or more.

The invention discloses the following technical effects:

(1) The method of the present invention solves the problem of unstable interaction between the functional layer and the cortex of the GO composite membrane. At the same time, it can tightly connect the graphene oxide composite membrane to the substrate, avoid the peeling off of the cortex, and improve the interception performance.

(2) The graphene oxide composite membrane prepared by the method of the present invention has excellent nanofiltration performance.

(3) By optimizing membrane production parameters (EDA adsorption time, post-adsorption heat treatment temperature, GO thickness, etc.), the present invention obtains a graphene oxide composite membrane (GO composite membrane) with improved screening performance and more stable pore structure.

(4) In the present invention, the PAN membrane is subjected to hydrolysis carboxylation and ethylenediamine functionalization twice, and the prepared GO composite membrane has better interception performance (during the base membrane treatment process, the second ethylenediamine functionalization Parameters, composite membrane heat treatment parameters, etc. are very critical in the preparation process of composite membrane performance).

(5) The present invention uses the common PAN microfiltration membrane as the base, and separately studies the effects of single carboxyl functionalized base membrane and secondary functionalized base membrane on the performance of the composite membrane, specifically: (1) on the surface of the PAN base membrane Carry out hydrolysis to achieve carboxyl functionalization, and then directly connect the GO cortex to obtain a stable GO composite membrane (PAN-COOH-GO composite membrane); (2) Hydrolyze the surface of the PAN-based membrane to achieve carboxyl functionalization, and then functionalize the carboxyl groups. The chemical-based membrane is secondary functionalized with ethylenediamine to obtain an ultrafiltration membrane that is amino-functionalized at the molecular level. Using this secondary functionalized ultrafiltration membrane as the base, the GO separation layer is stabilized through covalent bonding. On the upper surface of the base film, a GO composite film (PAN-COOH-EDA-GO composite film) with a stabilizing effect between the cortex and the base film was prepared. The ion interception performance of the composite membrane was tested with a laboratory cross-flow membrane performance evaluator. The results showed that the GO composite membrane (PAN-COOH-EDA-GO) prepared by the present invention based on the secondary functionalized PAN ultrafiltration membrane was compared with Both the base carboxyl-bonded GO composite membrane (PAN-COOH-GO) and the base-free strong interaction GO composite membrane (PAN-GO) have improved retention properties.

(6) The usual surface deposition method is to deposit particles with a diameter of several nanometers to tens of nanometers on the surface of the microporous membrane, which can easily block the pores. The present invention uses functionalization at the molecular level, with a size within 1 nm and will not block pores. When the method of the present invention is used to treat an ultrafiltration membrane, its pores and PAN will not change much (it will hardly affect the pore morphology of the membrane surface and will not block the pores of the ultrafiltration base membrane), which can be proved from the comparison of SEM photos. If a GO separation layer is added, the pores will be converted from ultrafiltration to nanofiltration, and the pores will be converted from 10nm level to 1nm level (GO dense layer).

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the drawings of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without exerting creative efforts.

Figure 1 shows the SEM images of PAN, PAN-COOH, and PAN-COOH-EDA membranes;

Figure 2 shows the surface infrared spectra of PAN, PAN-COOH, and PAN-COOH-EDA films;

Figure 3 is a graph showing the nanofiltration performance results of the PAN-COOH-EDA-GO membrane prepared under different adsorption times in Examples 5 to 6 of the present invention;

Figure 4 is a graph showing the nanofiltration performance results of PAN-COOH-EDA-GO composite membranes prepared using different heat treatment temperatures in Examples 5 and 7 of the present invention;

Figure 5 is a graph showing the nanofiltration performance results of PAN-COOH-EDA-GO composite membranes prepared using different volumes of graphene oxide standard dispersions in Examples 5 and 8 of the present invention;

Figure 6 is a graph showing the pure water flux test results of the PAN-GO composite membrane prepared in Comparative Example 2 of the present invention;

Figure 7 is a graph showing the pure water flux test results of the PAN-COOH-EDA-GO composite membrane prepared in Example 5 of the present invention;

Figure 8 is a graph showing the nanofiltration performance results of the PAN-COOH-EDA-GO composite membrane prepared in Example 5 of the present invention under different interception objects;

Figure 9 is a graph showing the nanofiltration performance results of the PAN-COOH-EDA-GO composite membrane prepared in Example 5 of the present invention and the PAN-COOH-diamine-GO composite membrane prepared in Comparative Example 1 of the present invention under different diamines;

Figure 10 is a diagram showing the nanofiltration performance results of the PAN-GO composite membrane prepared in Comparative Example 2 of the present invention under different water soaking times;

Figure 11 is a graph showing the nanofiltration performance results of the PAN-COOH-EDA-GO composite membrane prepared in Example 5 of the present invention under different water soaking times.

Detailed ways

Various exemplary embodiments of the invention will now be described in detail. This detailed description should not be construed as limitations of the invention, but rather as a more detailed description of certain aspects, features and embodiments of the invention.

It should be understood that the terms used in the present invention are only used to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges in the present invention, it should be understood that every intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or value intermediate within a stated range and any other stated value or value intermediate within a stated range is also included within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded from the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only the preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and/or materials in connection with which the documents relate. In the event of conflict with any incorporated document, the contents of this specification shall prevail.

It will be apparent to those skilled in the art that various modifications and changes can be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to the skilled person from the description of the invention. The specification and examples are intended to be illustrative only.

The words "includes", "includes", "has", "contains", etc. used in this article are all open terms, which mean including but not limited to.

Example 1

The preparation of graphene oxide (GO) refers to the classic hummers method. The specific steps are as follows:

(1) Add 240mL of a mixture of concentrated sulfuric acid (18.4mol/L) and concentrated phosphoric acid (14.6mol/L) with a volume ratio of 5:1, 5.0g graphene solid, and 25.0g potassium permanganate solid into a 500mL round In the bottom flask, after reacting for 6 hours at 40°C, stop heating. After cooling to room temperature, pour the solution on about 400g of ice and mix evenly. Then slowly add 20mL of hydrogen peroxide dropwise. After the dropwise addition is completed, the solution is heated at 4000r/min. After separation with a centrifuge for 4 hours, the supernatant was discarded, and the solid was the crude GO product.

(2) Wash the crude GO product with 1 mol/L HCl solution 8 times, collect the solid, and then wash it 5 times with RO water (reverse osmosis water) (the conductivity of the last supernatant is measured, if it is 0ms/cm, Indicates that the ions attached to its surface have been washed away) and the resulting solid is collected. Disperse the washed solid in 200 mL of RO water, perform suction filtration using a PVDF membrane with a pore size of 0.45 μm as the base, and vacuum dry the obtained filter cake at room temperature to obtain graphene oxide paper.

(3) Disperse a certain mass of graphene oxide paper into deionized water, ultrasonicate at room temperature for 5 minutes to promote uniform dispersion, and obtain a graphene oxide standard dispersion (GO-ss) with a concentration of 0.4 mg/mL.

Example 2

Preparation of PAN-COOH membrane (carboxyl functionalized PAN membrane), the specific steps are as follows:

Add 200mL ethanol to a 500mL beaker, then place the PAN membrane in the ethanol, and place the beaker in a water bath oscillator to shake for 1 hour (temperature is 25°C). Replace with 300mL of new ethanol, leave to soak for 12 hours, and use RO water. Please wash it twice, take out the membrane and place it in 300mL RO water, soak it for 24 hours, and fully replace the remaining ethanol. After cleaning, remove the RO water on the surface of the membrane and place it in a beaker containing 400mL NaOH solution (concentration: 1.5mol/L) , place the beaker in a 50°C constant-temperature water bath oscillator to react for 1 hour (temperature is 50°C), take out the diaphragm, wash it 3 times with RO water, immerse it in 200 mL of HCl solution with a concentration of 1 mol/L, and soak it at room temperature for 24 hours. Protonate, take out the membrane and wash it with RO water for 30 minutes with shaking (temperature is 25°C). Repeat washing three times and then immerse it in 300mL of RO water. Shake for 24 hours. Take it out to get the PAN-COOH membrane. Immerse the PAN-COOH membrane in RO water and refrigerate it. Save for later use.

Example 3

The specific steps for the preparation of PAN-COOH-EDA membrane under different adsorption times are as follows:

Move 20 mL of ethylenediamine solution with a concentration of 10 mg/mL into 5 clean weighing bottles respectively, take out 5 PAN-COOH films prepared in Example 2, dry the surface moisture, and place them in the weighing bottles. Adsorb for 1 min, 3 min, 5 min, 15 min, and 30 min respectively in a water bath oscillator (temperature is 25°C). After the adsorption is completed, take out the membrane, dry the ethylenediamine solution on the surface, and then place it in an 80°C oven for 0.5h and take it out. Cool the diaphragm to room temperature, soak it in ethanol and place it in a water bath oscillator for cleaning for 0.5h (temperature is 25°C). Repeat 4 times. Take the diaphragm out to dry, immerse it in RO water, and place it in a water bath oscillator for cleaning ( The temperature is 25°C), and the PAN-COOH-EDA membrane is prepared and stored in RO water for later use.

Example 4

Preparation of PAN-COOH-GO composite membrane, the specific steps are as follows:

(1) In a beaker, mix 30 μL of the graphene oxide standard dispersion (GO standard dispersion) prepared in Example 1 with 15 mL of deionized water to obtain a film-making liquid; cover the mouth of the beaker with plastic wrap and tie it with a rubber band Seal and place the film-forming liquid in an ultrasonic cleaner for 5 minutes to obtain film-forming liquid G.

(2) Take out the glass sand core filter device, and clean the device three times with tap water and RO water respectively. After cleaning the glass sand core with RO water, place the PAN-COOH membrane prepared in Example 2 on the glass sand core, and use Use paper to absorb the air bubbles between the diaphragm and the sand core and assemble the device; take out the film-making liquid G and pour it into the glass sand core filter device. After the liquid level is stable and motionless, connect the vacuum circulating water pump; use vacuum auxiliary Coat GO onto the PAN-COOH membrane using the suction filtration assembly method. After drying at room temperature, heat-treat in an oven at 80°C for 1 hour to obtain a PAN-COOH-GO membrane with carboxyl-linked skin layers (PAN-COOH-GO composite membrane or oxidized membrane). Graphene composite membrane), take it out and keep it for later use.

Example 5

Preparation of PAN-COOH-EDA-GO composite membrane, the specific steps are as follows:

(1) In a beaker, mix 30 μL of the graphene oxide standard dispersion (GO standard dispersion) prepared in Example 1 with 15 mL of deionized water to obtain a film-making liquid; cover the mouth of the beaker with plastic wrap and tie it with a rubber band Seal and place the film-forming liquid in an ultrasonic cleaner for 5 minutes to obtain film-forming liquid G.

(2) Take out the glass sand core filter device and clean the device three times with tap water and RO water respectively. After cleaning the glass sand core with RO water, place the PAN-COOH-EDA membrane with an adsorption time of 3 minutes in Example 3. On the glass sand core, use paper to absorb the air bubbles between the diaphragm and the sand core and assemble the device; take out the film-making liquid G and pour it into the glass sand core filter device. After the liquid level is stable and motionless, connect the vacuum Circulating water pump; use vacuum-assisted filtration assembly method (vacuum filtration method) to coat GO on the PAN-COOH-EDA membrane, dry at room temperature, and then heat-treat in an 80°C oven (blast drying oven) for 1 hour to prepare PAN-COOH-EDA-GO membrane (PAN-COOH-EDA-GO composite membrane or graphene oxide composite membrane) with amino-linked skin layer, take out and keep it for later use.

Example 6

Same as Example 5, the only difference is that the PAN-COOH-EDA membrane in step (1) is replaced with the PAN-COOH-EDA membrane with adsorption times of 1 min, 5 min, 15 min, and 30 min in Example 3 to obtain 4 types. Different PAN-COOH-EDA-GO composite membranes (graphene oxide composite membranes).

Example 7

Same as Example 5, the only difference is that the heat treatment temperatures in step (2) were replaced with 25°C, 60°C and 100°C respectively to obtain 3 different PAN-COOH-EDA-GO composite membranes (graphene oxide composite membranes). membrane).

Example 8

Same as Example 5, except that the volume of the graphene oxide standard dispersion in step (1) was replaced with 20 μL, 25 μL, 35 μL and 40 μL respectively, and four different PAN-COOH-EDA-GO composite membranes were prepared. (graphene oxide composite membrane).

Comparative example 1

Prepare GO composite membranes under different diamine cross-linking. The preparation of each composite membrane is the same as in Example 5. The only difference is that the ethylenediamine cross-linking agent of the PAN-COOH-EDA-GO composite membrane in step (2) is replaced by Other diamines are: tris(2-aminoethyl)amine and diethylenetriamine, and two different PAN-COOH-diamine-GO composite membranes (graphene oxide composite membranes) were prepared.

Comparative example 2

Same as Example 4, the only difference is that the PAN-COOH based membrane in step (2) is changed to a PAN ultrafiltration membrane to prepare a PAN-GO composite membrane.

Effect example 1

Field emission scanning electron microscopy (SEM) was used to characterize the surface morphology of PAN film, PAN-COOH film, and PAN-COOH-EDA film. The results are shown in Figure 1.

As can be seen from Figure 1, the pore structure on the upper surface of the diaphragm made by hydrolysis (PAN-COOH membrane) and subsequent hydrolysis and EDA functionalization (PAN-COOH-EDA membrane) is clear, and there is no obvious blockage. Phenomenon.

Effect example 2

The surface chemical structure of PAN membrane, PAN-COOH membrane, and PAN-COOH-EDA membrane (adsorption time is 3 minutes) was characterized (surface ATR-IR). The results are shown in Figure 2.

As can be seen from Figure 2, compared with the PAN film, the PAN-COOH film has a new peak at 1696cm ^-1 , which corresponds to the peak of the carbonyl group in the carboxylate group, verifying the hydrolysis results on the surface of the PAN film; PAN- In the COOH-EDA film, new peaks appeared at 1682cm ^-1 and 1566, which corresponded to the carboxyl group and the carbonyl group in the amide bond respectively, indicating that part of the carboxyl group was converted into an amide group, confirming that EDA was functionalized to PAN-COOH in a covalent bond. surface.

Membrane separation performance characterization (nanofiltration performance)

A laboratory cross-flow filtration device was used to test the nanofiltration performance of the composite membrane. Each membrane was controlled to be prepressed at 0.7MPa for 2 hours, and the membrane data were obtained under parallel testing of three membranes. The test solution is 1g/L 1800mL Na ₂ SO ₄ solution. Use a weighed plastic centrifuge tube to collect the liquid (record its mass as m ₁ ), and start recording the time when the first drop of liquid falls. Stop timing when it reaches about 3 mL, and record the time as t ₂ . Finally, use a plastic centrifuge tube to collect the liquid. Take 3 mL of the original solution into the tube, and place these plastic centrifuge tubes on the centrifuge tube rack for testing. Weigh the total mass m ₂ of the plastic centrifuge tube and the connected liquid. Measure the conductivity of the solution in each plastic centrifuge tube.

Permeate flux and solute rejection are calculated from Equation 1 and Equation 2:

Flux (flux) = 84.87 × (m ₂ -m ₁ )/Δt (L·m ^-2 ·h ^-1 ) Formula 1

Rej (rejection rate) = (1-C _p /C _f ) × 100% Formula 2

C _p : osmotic solubility; C _f : feed liquid solubility.

Compare the nanofiltration performance of PAN-COOH-EDA-GO composite membranes prepared under different membrane-making parameters. The specific membrane-making parameters include: EDA adsorption time, EDA processing temperature, and the volume of graphene oxide standard dispersion.

Effect example 3

The nanofiltration performance of the PAN-COOH-EDA-GO composite membrane prepared by using the PAN-COOH-EDA membrane prepared under different adsorption times in Examples 5 to 6 was measured. The results are shown in Figure 3.

Test conditions: Na ₂ SO ₄ , salt concentration: 1g/L, 0.7MPa, cross-flow flow: 30LPH.

As can be seen from Figure 3, the PAN-COOH-GO composite membrane without EDA adsorption (adsorption time is 0 min) maintains a good rejection rate, but the flux is very small, and there is almost no possibility of practical application. After adsorbing EDA, the flux increased significantly. In the PAN-COOH-EDA-GO composite membrane prepared with a PAN-COOH-EDA membrane with an adsorption time of 3 minutes, the flux increased to 14L·m ^2- ·h ^-1 . Sodium sulfate rejection also improved slightly (to 91%). Compared with PAN-COOH-GO membrane, the flux increased significantly, and the rejection rate increased by 3%.

Effect Example 4

The nanofiltration performance of the PAN-COOH-EDA-GO composite membrane prepared at different heat treatment temperatures in Examples 5 and 7 was measured. The results are shown in Figure 4.

Test conditions: Na ₂ SO ₄ , salt concentration: 1g/L, 0.7MPa, cross-flow flow: 30LPH.

As can be seen from Figure 4, the heat treatment effect is best at 80°C, indicating that the carboxyl group and the amino group are dehydrated and condensed, and the effect is obvious after the temperature reaches 80°C.

Effect Example 5

The nanofiltration performance of the PAN-COOH-EDA-GO composite membrane prepared by using different volumes of graphene oxide standard dispersions in Examples 5 and 8 was measured. The results are shown in Figure 5.

Test conditions: Na ₂ SO ₄ , salt concentration: 1g/L, 0.7MPa, cross-flow flow: 30LPH.

As can be seen from Figure 5, as the loading of graphene oxide (GO) increases, the retention of sodium sulfate by the PAN-COOH-EDA-GO composite membrane gradually increases, and the dosage of the graphene oxide standard dispersion is 30 μL. When (GO loading is 0.96 μg·cm ^-2 ), the retention rate reaches the maximum value. As the amount of graphene oxide standard dispersion increases, the water flux gradually decreases. Taking into account the two indicators of rejection rate and flux, 30 μL was selected as the optimal membrane volume of the GO standard dispersion (GO loading capacity was 0.96 μg·cm ^-2 ).

Membrane pure water flux-pressure relationship test

Use a laboratory cross-flow filtration device to test the nanofiltration performance of the composite membrane, and control each membrane to gradually change the operating pressure at 0.1→0.7→0.1MPa, once every 10 minutes. Membrane data are obtained through parallel testing of three membranes, and the test liquid is pure water. Use a weighed plastic centrifuge tube to receive the liquid (record its mass as m ₁ ), and record the time from when the first drop of liquid falls. After 10 minutes, stop receiving the liquid, and record the total mass of the liquid in the centrifuge tube, m ₂ . Adjust the operating pressure and start the next liquid contact cycle immediately after stabilization.

The permeate flux is calculated from Equation 3:

Flux=84.87×6×(m ₂ -m ₁ )(L·m- ² ·h ^-1 ·bar ^-1 ) Formula 3

Effect Example 5

(1) Measure the pure water flux of the PAN-GO composite membrane prepared in Comparative Example 2. The results are shown in Figure 6.

Test conditions: RO water, 0.1→0.7→0.1MPa, cross-flow flow 30LPH.

(2) Measure the pure water flux of the PAN-COOH-EDA-GO composite membrane prepared in Example 5. The results are shown in Figure 7.

Test conditions: RO water, 0.1→0.7→0.1MPa, cross-flow flow 30LPH.

It can be seen from Figures 6 and 7 that the flux-pressure curves of the two composite membranes change in a similar pattern, and both have two stages: (1) In the early stage of pressurization, the water flux decreases significantly as the operating pressure increases. , indicating that the interlayer channel structure of GO significantly decreases as the pressure increases; (2) when the pressure reaches 0.7MPa and then decreases, the water flux no longer changes with the operating pressure, indicating that after high-pressure compaction, the membrane The structure can be stabilized. There are also certain differences between PAN-GO membrane and PAN-COOH-EDA-GO membrane. The PAN-COOH-EDA-GO membrane is lower than the PAN-GO membrane in the initial stage of pressurization, and when the flux enters the stable period after depressurization, The water flux is higher than that of the PAN-GO membrane, indicating that the addition of -COOH-EDA-, on the one hand, has a stabilizing effect on the channels of the GO cortex, without obvious super-large pores; on the other hand, it is beneficial to the maintenance of the pores of the GO cortex. Since the flux of the PAN-COOH-GO membrane was too low and the change effect could not be measured under the existing conditions, this test was not performed.

Effect example 6

The nanofiltration performance of the PAN-COOH-EDA-GO composite membrane in Example 5 for different interception objects was measured. The results are shown in Figure 8.

Test conditions: interception object concentration: 1g/L, 0.7MPa, cross-flow flow: 30LPH, interception objects are: sodium sulfate, C ₆ H ₁₂ O ₆ (glucose), magnesium sulfate, magnesium chloride, sodium chloride.

It can be seen from Figure 8 that the composite membrane has the best interception effect on sodium sulfate, and the interception rates of sodium sulfate, C ₆ H ₁₂ O ₆ , magnesium sulfate, magnesium chloride, and sodium chloride decrease in order, which is similar to the pattern of the GO separation layer. , indicating that the cross-linked ultrafiltration base membrane and separation layer are treated here mainly to stabilize the separation layer and base membrane, and have no impact on the structure and surface properties of the separation layer itself.

Effect example 7

Determination of the nanofiltration performance of the PAN-COOH-EDA-GO composite membrane prepared in Example 5 of the present invention (adsorption for 3 minutes) and the PAN-COOH-diamine-GO composite membrane prepared using different diamine cross-linking agents in Comparative Example 1 , the results are shown in Figure 9.

Test conditions: sodium sulfate concentration: 1g/L, 0.7MPa, cross-flow flow: 30LPH.

It can be seen from Figure 9 that among different diamine cross-linking agents, the ethylene diamine cross-linked composite membrane has the best interception effect on sodium sulfate. The effect of the other two longer chain diamines is significantly reduced, and the degree of reduction increases with the chain. The length increases and intensifies, indicating that short-chain diamines are more suitable for linking the PAN-COOH-based membrane and the GO separation layer.

Effect example 8

Stability experiment of ultrafiltration base membrane and separation layer with or without cross-linking. Soak the PAN-COOH-EDA-GO composite membrane (adsorbed for 3 minutes in Example 5) and the PAN-GO composite membrane (prepared in Comparative Example 2) in RO water for a certain period of time, respectively, for subsequent sodium sulfate retention experiments. Soaking time They are: 0h, 0.5h, 1h, 24h. Among them, 0h represents the composite membrane without soaking. The nanofiltration performance of the PAN-GO composite membrane and PAN-COOH-EDA-GO composite membrane in Comparative Example 2 after soaking in water was measured. The results are shown in Figures 10 to 11.

Test conditions: sodium sulfate concentration: 1g/L, 0.7MPa, cross-flow flow: 30LPH.

As can be seen from Figure 10, the sodium sulfate interception effect of the PAN-GO composite membrane decreased significantly after soaking in water, while the PAN-COOH-EDA-GO composite membrane remained almost unchanged (Figure 11 The interception rate dropped within 2% ), indicating that after the PAN-COOH-based membrane and the GO separation layer are cross-linked by -COO-EDA- chains, the underwater structure of the membrane is stable, and it is expected to be used in complex actual nanofiltration separations.

The present invention designed a way to covalently link the PAN ultrafiltration base membrane and the GO separation layer. By optimizing parameters such as EDA adsorption time, post-adsorption heat treatment temperature, GO cortex thickness (the amount of graphene oxide standard dispersion), etc. PAN-COOH-EDA-GO composite membrane with improved retention performance. From the sodium sulfate retention experiment of the composite membrane, the pure water flux-operating pressure experiment, and the membrane performance experiment after soaking in water, it can be seen that the PAN-COOH-EDA-GO composite membrane has a more stable membrane structure than the PAN-GO composite membrane, and is more stable than the PAN-GO composite membrane. The PAN-COOH-GO composite membrane maintains abundant water passages (avoiding a sharp drop in flux). The present invention carries out a new treatment process for PAN membrane, and obtains a composite membrane with stable structure and improved screening performance, which is expected to be a GO composite membrane for practical application.

The above-described embodiments only describe the preferred modes of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, those of ordinary skill in the art can make various modifications to the technical solutions of the present invention. Deformations and improvements shall fall within the protection scope determined by the claims of the present invention.

Claims (10)

1. The method for stabilizing the graphene oxide skin layer and the ultrafiltration base membrane is characterized by comprising the following steps of:

and carrying out functionalization treatment on the PAN film to obtain a functionalized PAN film, then coating graphene oxide on the functionalized PAN film, and carrying out heat treatment to obtain the graphene oxide composite film.

2. The method of stabilizing a graphene oxide skin layer and ultrafiltration membrane of claim 1, wherein the functionalized PAN membrane comprises a carboxyl-functionalized PAN membrane or an amino-functionalized PAN membrane; the temperature of the heat treatment is 25-100 ℃ and the time is 0.5h.

3. The method for stabilizing a graphene oxide skin layer and an ultrafiltration membrane according to claim 2, wherein the preparation method of the carboxyl-functionalized PAN membrane comprises the following steps:

and placing the PAN film in an alkaline solution, oscillating in a water bath, and then placing the PAN film in an acidic solution for soaking to obtain the carboxyl functional PAN film.

4. The method for stabilizing a graphene oxide skin layer and an ultrafiltration membrane according to claim 3, wherein the alkaline solution is a NaOH solution with a concentration of 1.5mol/L; the temperature of the water bath oscillation is 50 ℃ and the time is 1h; the acid solution is hydrochloric acid solution, and the concentration is 1mol/L; the soaking time is 24 hours.

5. The method for stabilizing graphene oxide skin and ultrafiltration membrane according to claim 2, wherein the preparation method of the amino-functionalized PAN membrane comprises the following steps:

and placing the carboxyl functional PAN film in an ethylenediamine solution, oscillating in a water bath, and drying to obtain the amino functional PAN film.

6. The method of stabilizing a graphene oxide skin layer and ultrafiltration membrane according to claim 5, wherein the concentration of the ethylenediamine solution is 10mg/mL; the temperature of the water bath oscillation is 25 ℃ and the time is 1-30 min; the temperature of the drying is 80 ℃ and the time is 0.5h.

7. The method for stabilizing a graphene oxide skin layer and an ultrafiltration membrane according to claim 1, wherein the preparation method of graphene oxide specifically comprises: and mixing the acid liquor, the graphene and the potassium permanganate, heating for reaction, pouring the reacted solution into ice, uniformly mixing, dropwise adding hydrogen peroxide, centrifuging after the dropwise adding is finished, and precipitating to obtain the graphene oxide.

8. The method for stabilizing a graphene oxide skin layer and an ultrafiltration membrane according to claim 7, wherein the acid solution is a mixed solution of 18.4mol/L concentrated sulfuric acid and 14.6mol/L concentrated phosphoric acid in a volume ratio of 5:1; the temperature of the heating reaction is 40 ℃ and the time is 6 hours.

9. A graphene oxide composite membrane prepared by the method of any one of claims 1 to 8.

10. Use of the graphene oxide composite membrane of claim 9 in nanofiltration rejection, reverse osmosis, forward osmosis, ultrafiltration, pervaporation or oil-water separation.