Amino-modified graphene oxide hydrophilic film as well as preparation method and application thereof

Abstract

The invention discloses an amino-modified graphene oxide hydrophilic membrane as well as a preparation method and application thereof, and belongs to the technical field of membrane material preparation. The preparation method comprises the following steps: carrying out hydrophilic modification on graphene oxide by using an amino group modified substance through a blending method to obtain a membrane casting solution, and defoaming to prepare the hydrophilic membrane. The preparation method of the hydrophilic film is simple, amino groups and groups such as hydroxyl groups on the surface of the graphene oxide are strongly adsorbed through hydrogen bonds, and the hydrophilic film is relatively stable in property. According to the preparation method, the graphene oxide is directly subjected to surface hydrophilic modification, the graphene oxide hydrophilic film is prepared by adopting a blending method, a base film does not need to be used, and the production cost of the hydrophilic film is reduced; compared with an existing common commodity microfiltration membrane, the hydrophilic performance of the hydrophilic membrane is greatly improved, meanwhile, compared with a microfiltration membrane which is subjected to amino modified graphene oxide graft modification by taking a commercial microfiltration membrane as a base membrane, the hydrophilic performance of the hydrophilic membrane is equivalent to that of the commercial microfiltration membrane, and the hydrophilic membrane has higher cost performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane material preparation, and particularly relates to an amino-modified graphene oxide hydrophilic membrane and a preparation method and application thereof. BACKGROUND

[0002] Membrane separation technology uses the selective permeability of a membrane to each component of a mixed fluid substance to achieve separation, purification and concentration. It has become one of the common supporting technologies for solving global major problems such as energy, environment and water resources, because it does not require chemical additives, saves energy, is environmentally friendly and renewable. However, the hydrophilicity and anti-fouling performance of most commercial microfiltration membranes / nanofiltration membranes still need to be improved, and more and more researches on the hydrophilic modification of membrane materials are being carried out.

[0003] Graphene oxide (GO) is an important derivative of graphene, which is rich in polar oxygen-containing functional groups such as hydroxyl, oxygen-containing groups and edge carboxyl groups, and has good dispersibility and hydrophilicity in water. In recent years, graphene oxide has achieved good development as a membrane material, but there are not many studies on the hydrophilic modification of GO membranes. A preparation method of an amino-modified graphene oxide grafted modified ultrafiltration / microfiltration membrane is disclosed in Chinese patent CN104001436A. A commercial ultrafiltration / microfiltration membrane coated with polydopamine is used as a base membrane, and the base membrane is grafted and modified with amino-modified graphene oxide. The final hydrophilic membrane has high mechanical strength, good chemical stability, high pure water permeation capacity, and can effectively slow down membrane fouling and concentration polarization. However, the preparation method of the hydrophilic membrane before and after the amino modification and grafting modification is relatively complicated. The hydrophilic modification of the base membrane based on polyvinylidene fluoride (PVDF) finally realizes a pure water contact angle of 53.2° for the microfiltration membrane. The cost performance of this hydrophilic modification method is not high, and the amino-modified graphene oxide cannot be used without the commercial base membrane.

[0004] In summary, it is still necessary to develop a hydrophilic membrane based on graphene oxide derivatives, which has a simple preparation method, good hydrophilicity, strong stability and excellent anti-fouling performance. SUMMARY

[0005] 1. Problem to be solved In order to improve the hydrophilicity and anti-fouling ability of the membrane, the application provides a preparation method of an amino-modified graphene oxide hydrophilic membrane, which has a simple preparation method, good hydrophilicity, strong stability and excellent anti-fouling performance. The prepared hydrophilic membrane does not need to rely on the use of a commercial base membrane, which saves production cost, and the hydrophilic performance (pure water contact angle 58°) of the hydrophilic membrane is comparable to that of the hydrophilic membrane prepared by hydrophilic modification of a commercial PVDF microfiltration membrane (53.2°), which has high cost performance.

[0006] 2. Technical scheme In order to solve the above problems, the technical scheme adopted by the application is as follows: The application provides a preparation method of an amino-modified graphene oxide hydrophilic membrane, which comprises the following steps: The graphene oxide is added into a dispersant, and is subjected to cell crushing and ultrasonic treatment to obtain a graphene oxide dispersion solution; lithium chloride and an amino-modifying substance are added into the graphene oxide dispersion solution, and are subjected to dissolution and stirring to obtain a casting solution; and the casting solution is subjected to defoaming and casting to obtain the amino-modified graphene oxide hydrophilic membrane.

[0007] Further, the graphene oxide is added into the dispersant in a mass fraction of 0.1% to 1%.

[0008] Further, the graphene oxide is added into the dispersant in a mass fraction of 0.1%.

[0009] Further, the graphene oxide is added into the dispersant in a mass fraction of 0.5%.

[0010] Further, the graphene oxide is added into the dispersant in a mass fraction of 1%.

[0011] Further, the dispersant comprises an N, N-dimethylacetamide solvent.

[0012] Further, the cell crushing comprises: adopting a cell crusher with a power of 200 to 1200 W to perform treatment for 25 to 35 min.

[0013] Further, the cell crushing comprises: adopting a cell crusher with a power of 460 W to perform treatment for 30 min.

[0014] Further, the ultrasonic treatment comprises: adopting an ultrasonic cleaner with a power of 3 KW and a frequency of 20 KHz to perform treatment for 5 to 15 min.

[0015] Further, the lithium chloride is added into the dispersion solution in a mass fraction of 0.1% to 0.3%; in the application, the lithium chloride is used for assisting film formation, increasing porosity and improving certain hydrophilicity.

[0016] Further, the amino-modifying substance is added into the graphene oxide dispersion solution in a mass fraction of 0.1% to 0.5%.

[0017] Further, the amino-modifying substance comprises an ethylenediamine solution and / or a propylenediamine solution, and the mass fraction of the ethylenediamine solution and / or the propylenediamine solution is 0.2% to 0.3%; in the application, the amino groups of the ethylenediamine and the propylenediamine can form hydrogen bonds with groups such as surface hydroxyl groups of the graphene oxide, so that the amino groups and the graphene oxide are strongly adsorbed, the film is finally stable, the amino-modifying substance is not easy to fall off, and the hydrophilicity of the film is greatly improved.

[0018] Further, the amino-modified substance includes an ethylenediamine solution and a propylenediamine solution.

[0019] Further, the dissolving is performed in an oven at a temperature of 80-90°C.

[0020] Further, the dissolving is performed in an oven at a temperature of 80°C.

[0021] Further, the defoaming is performed in a vacuum drying oven.

[0022] Further, the film casting includes: pouring the defoamed casting solution on a glass plate with non-woven fabric attached, using a doctor blade to cast a film, immediately immersing in a coagulation bath to solidify into a film, then performing heat treatment on the solidified film, and then immersing in deionized water, drying to obtain an amino-modified graphene oxide film.

[0023] Further, the film casting temperature is 20-30°C.

[0024] Further, the film casting humidity is < 60%; it is to be noted that too dry environment will affect the film coagulation.

[0025] Further, the doctor blade is used to cast on the glass plate at a speed of 100-120 mm / min.

[0026] Further, the doctor blade is used to cast on the glass plate at a speed of 100 mm / min; the speed is to ensure that the formed film is flat and has no voids.

[0027] Further, the coagulation bath is a polyvinyl alcohol with a mass fraction of 10-15%.

[0028] Further, the heat treatment is performed in an oven at 60-80°C for 4-5 h.

[0029] Further, the heat treatment is performed in an oven at 70°C for 4 h; it is to be noted that the heat treatment in the present application helps to slightly reduce the graphene oxide, which can increase the hydrophilicity.

[0030] Further, the immersion time is 2-4 d; the purpose is to remove the excess solvent in the hydrophilic film.

[0031] The present application also provides an amino-modified graphene oxide hydrophilic film prepared by the above method.

[0032] Further, the above-mentioned graphene oxide hydrophilic membrane has a pure water contact angle of 58-62° on the membrane surface; it should be noted that the present application prepares graphene oxide hydrophilic membranes with different concentrations by changing the amount of graphene oxide added, uses the pure water contact angle on the membrane surface as an index to determine the hydrophilic or hydrophobic performance of the membrane surface, and finally obtains a graphene oxide hydrophilic membrane with a pure water contact angle of 58-62°.

[0033] The present application also provides the application of the above-mentioned amino-modified graphene oxide hydrophilic membrane in water treatment.

[0034] Further, the above-mentioned water treatment includes organic matter separation and recovery, oil-water separation, desalination, etc.

[0035] 3. Beneficial effects Compared with the prior art, the present application has the following beneficial effects: (1) The present application provides an amino-modified graphene oxide hydrophilic membrane and its preparation method and application, which uses a blending method to modify the hydrophilicity of graphene oxide with ethylenediamine and propylenediamine amino groups, forms hydrogen bonds between the amino groups and the surface hydroxyl groups of graphene oxide, and the two are strongly adsorbed, so that the amino-modified substance is not easy to fall off, and the final film-forming property is stable.

[0036] (2) The present application provides an amino-modified graphene oxide hydrophilic membrane and its preparation method and application, which directly modifies the surface hydrophilicity of graphene oxide, and uses a blending method to prepare a graphene oxide hydrophilic membrane, which does not need to rely on a base film for use, thereby reducing the production cost of the hydrophilic membrane; at the same time, compared with the existing hydrophilic modification of commercial PVDF microfiltration membranes (pure water contact angle 53.2°), the hydrophilic performance of the modified graphene oxide hydrophilic membrane of the present application (pure water contact angle 58°) is comparable, has good anti-pollution performance, and has higher cost performance. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a comparison chart of the pure water contact angle and pure water flux of the commercial PVDF microfiltration membrane and the amino-modified graphene oxide hydrophilic membrane. DETAILED DESCRIPTION

[0038] The present application will be further described below in conjunction with specific embodiments.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the term "and / or" used herein includes any and all combinations of one or more related listed items.

[0040] When specific conditions are not specified in the examples, they are carried out under conventional conditions or according to the manufacturer's recommendations. When the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained commercially.

[0041] As used herein, the term "about" is used to provide flexibility to a given term, measurement, or value. The degree of flexibility of a particular variable will be readily determined by one of skill in the art. As used herein, the term "at least one of" is intended to mean one or more of the listed items. For example, "at least one of A, B, and C" includes A alone, B alone, C alone, as well as combinations such as AB, AC, BC, and ABC. Concentrations, amounts, and other numerical data can be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be construed as having been followed to following the principle of including and disclosing all the individual values reasonably encompassed within that range. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited values of 1 to about 4.5, but also individual values and sub-ranges within the indicated range, such as 2 to 4, 3, and 3.5. The same principle applies to ranges reciting only one numerical value, such as "less than about 4.5," which should be interpreted to include all values less than 4.5, up to and including the value of about 4.5. Such an interpretation applies regardless of the breadth of the range or the characteristics being described.

[0042] Example 1 The present embodiment provides a method for preparing an amino-modified graphene oxide hydrophilic membrane and a prepared hydrophilic membrane.

[0043] The specific steps are as follows: 1) Preparation of graphene oxide dispersion The graphene oxide was added to the organic solvent N,N-dimethylacetamide (DMAC) at a mass fraction of 0.1%, then placed in a cell crusher (power 460 W) for 30 min, and then treated with an ultrasonic cleaner (power 3 KW, frequency 20 KHz) for 10 min to obtain a uniformly dispersed graphene oxide dispersion; 2) Preparation of casting solution Lithium chloride was added to the above graphene oxide dispersion at a mass fraction of 0.1%, and after stirring to disperse uniformly, a mass fraction of 0.2% ethylenediamine solution and a mass fraction of 0.2% propylenediamine solution were added, and the mixture was dissolved in an oven at 80°C, and a uniform casting solution was obtained by mechanical stirring; 3) Deaeration and membrane preparation The casting solution is placed in a vacuum drying oven for degassing, and the completely degassed uniform casting solution is cast on a glass plate with non-woven fabric attached under the conditions of a temperature of 30°C and a humidity of 50%, and a doctor blade is used to scrape the film at a speed of 100 mm / min, and then the film is immediately immersed in a coagulation bath (10% polyvinyl alcohol by mass fraction) to solidify and form a film, and then the solidified film is placed in an oven for heat treatment at 70°C for 4 h, and then the film is immersed in deionized water for 3 d to remove excess solvent, and after drying, an amino-modified graphene oxide hydrophilic film is obtained.

[0044] Example 2 The present embodiment provides a method for preparing an amino-modified graphene oxide hydrophilic film and a prepared hydrophilic film.

[0045] The specific steps are as follows: 1) The graphene oxide is added to the organic solvent N,N-dimethylacetamide (DMAC) at a mass fraction of 0.5%, and then placed in a cell crusher (same as in Example 1) for 30 min, and then ultrasonic (same as in Example 1) dispersion treatment is performed for 10 min to obtain a uniformly dispersed graphene oxide dispersion liquid; 2) Preparation of casting solution The lithium chloride is added to the above graphene oxide dispersion liquid at a mass fraction of 0.1%, and after stirring to disperse uniformly, a 0.2% ethylenediamine solution and a 0.2% propylenediamine solution are added, and the mixture is dissolved in an oven at 80°C with mechanical stirring to obtain a uniform casting solution; 3) Preparation of hydrophilic film The casting solution is placed in a vacuum drying oven for degassing, and the completely degassed uniform casting solution is cast on a glass plate with non-woven fabric attached under the conditions of a temperature of 30°C and a humidity of 50%, and a doctor blade is used to scrape the film at a speed of 100 mm / min, and then the film is immediately immersed in a coagulation bath (10% polyvinyl alcohol by mass fraction) to solidify and form a film, and then the solidified film is placed in an oven for heat treatment at 70°C for 4 h, and then the film is immersed in deionized water for 3 d to remove excess solvent, and after drying, an amino-modified graphene oxide hydrophilic film is obtained.

[0046] Example 3 The present embodiment provides a method for preparing an amino-modified graphene oxide hydrophilic film and a prepared hydrophilic film.

[0047] The specific steps are as follows: 1) The graphene oxide dispersion liquid is prepared as in Example 1.

[0048] The graphene oxide is added to the solvent N,N-dimethylacetamide (DMAC) at a mass fraction of 1%, and then placed in a cell crusher (same as in Example 1) for 30 min, and then ultrasonic (same as in Example 1) dispersion treatment is performed for 10 min to obtain a uniformly dispersed graphene oxide dispersion liquid; 2) Preparation of casting solution Lithium chloride was added to the above graphene oxide dispersion solution at a mass fraction of 0.1%, and after stirring to disperse uniformly, 0.2% ethylenediamine solution and 0.2% propylenediamine solution were added, and the mixture was dissolved in an oven at 80°C with mechanical stirring to obtain a uniform casting solution; 3) Preparation of hydrophilic membrane The above casting solution was degassed in a vacuum drying oven, and the uniformly degassed casting solution was poured onto a glass plate with non-woven fabric attached at a temperature of 20°C and a humidity of 60%. The casting solution was then scraped into a film with a doctor blade at a speed of 50 mm / min, and immediately immersed in a coagulation bath (10% polyvinyl alcohol by mass) to solidify and form a film. The solidified film was then heat treated in an oven at 70°C for 4 h, and then immersed in deionized water for 3 d to remove excess solvent. After drying, an amino-modified graphene oxide hydrophilic membrane was obtained.

[0049] Example 4 In this example, the hydrophilic properties of the amino-modified graphene oxide hydrophilic membranes prepared in Examples 1-3 were investigated.

[0050] Specifically, a contact angle measuring instrument (Ningbo Haishu Maishi Detection Technology Co., Ltd., A-200) was used to measure the contact angle of pure water on the surface of a commercial PVDF microfiltration membrane (Tianjin Teng Experimental Equipment Co., Ltd., average pore size 0.45 μm) and the different concentrations of graphene oxide hydrophilic membranes (GO-0.1, GO-0.5, GO-1) prepared in Examples 1-3, respectively, as an index to determine the hydrophilic or hydrophobic properties of the membrane surface. The smaller the contact angle of pure water on the membrane surface, the better the hydrophilicity.

[0051] At the same time, the pure water flux of the PVDF microfiltration membrane and the graphene oxide hydrophilic membrane was determined according to the GB / T 43300-2023 Ceramic Flat Membrane Pure Water Flux Test Method. Before the experiment, the PVDF microfiltration membrane and the graphene oxide hydrophilic membrane of different concentrations were pre-filtered with pure water at a pressure of 0.05 Mpa for 3 h to remove excess ethanol and other solvents, and the membranes were compacted. During the test, each membrane was filtered with pure water at a pressure of 0.1 Mpa for 30 min, and the pure water flux of the membrane was calculated after the flux was stable. J w1 [L·(m 2 ·h) -1 ]. The calculation formula is J w1 = V / At , where: V is the filtered water volume (L); A is the effective membrane area (m 2 ); t is the filtration time (h).

[0052] The contact angle and pure water flux test results are as follows: Figure 1 As shown in the figure, the contact angle of pure water in the graphene oxide hydrophilic membrane at different concentrations is lower than that of the PVDF microfiltration membrane, indicating that the hydrophilicity of the hydrophilic membrane in this application is superior to that of the commercial PVDF microfiltration membrane. With increasing GO concentration, the contact angle of pure water decreases from 62° to 58°, indicating that the hydrophilicity of the membrane gradually increases with increasing GO concentration, which is attributed to the effect of the hydrophilic groups in GO. Simultaneously, with increasing GO concentration, the pure water flux gradually increases to a maximum value. When the GO concentration continues to increase to 1, excessively high hydrophilicity may interrupt the connection of the internal pores of the composite membrane, thereby reducing the number of pores through which pure water flows rapidly, resulting in a certain decrease in pure water flux.

[0053] Example 5 This embodiment investigates the antifouling properties of the amino-modified graphene oxide hydrophilic membranes prepared in Examples 1-3.

[0054] Specifically, a commercial PVDF microfiltration membrane (same as in Example 4) and hydrophilic membranes of different concentrations from Examples 1-3 were used to filter 500 mL of humic acid (HA) solution (100 mg / L) at a pressure of 0.05 MPa. After the flux stabilized, the membranes were backwashed with pure water at a pressure of 0.02 MPa for 1 min, followed by a pure water filtration test at a pressure of 0.1 MPa. The specific test was the same as in Example 4, and the membrane flux was recorded. J w2 Based on the pure water flux of the membrane before and after backwashing. J w1 (Initial pure water flux measured in Example 4) and J w2 (Pure water flux after backwashing of contaminated water), calculate flux decay rate. R The specific calculation formula is as follows: R =[( J w1 - J w2 ) / J w1 ×100%. The antifouling performance of the membrane is inversely proportional to the flux decay rate; that is, the stronger the antifouling performance, the lower the flux decay rate.

[0055] Table 1. Comparison of antifouling performance of different membranes

[0056] The anti-fouling performance results are shown in Table 1, it can be seen that the anti-fouling performance of different concentrations of graphene oxide hydrophilic membrane is stronger than that of PVDF microfiltration membrane, which is due to the hydrophobicity of PVDF itself, which makes the membrane easy to be contaminated. By comparing the flux decay rate with the pure water contact angle, it can be seen that the stronger the hydrophilicity of the membrane, the stronger the anti-fouling ability, among which the hydrophilicity and anti-fouling ability of GO-1 hydrophilic membrane are the strongest. On the one hand, the stronger the hydrophilicity of the membrane, the easier it is to form a layer of hydration, reducing the contact between the membrane and the pollutants, thereby enhancing the anti-fouling ability of the membrane; on the other hand, the increase of negative charge on the membrane surface increases the electrostatic repulsion of the pollutants, reducing the aggregation of the pollutants on the surface.

Claims

1. A method for preparing an amino-modified graphene oxide hydrophilic film, characterized by, The method comprises: The graphene oxide is added into a dispersant, and is subjected to cell pulverization and ultrasonic treatment to obtain a graphene oxide dispersion solution; lithium chloride and an amino-modified substance are added into the graphene oxide dispersion solution, and are subjected to dissolution and stirring to obtain a casting solution; the casting solution is subjected to defoaming and casting to obtain an amino-modified graphene oxide hydrophilic film.

2. The method of claim 1, wherein, The graphene oxide is added into the dispersant at a mass fraction of 0.1% to 1%.

3. The method according to claim 1 or 2, characterized in that, The dispersant comprises an N,N-dimethylacetamide solvent.

4. The method of claim 3, wherein, The lithium chloride is added into the graphene oxide dispersion solution at a mass fraction of 0.1% to 0.3%; and / or The amino-modified substance is added into the graphene oxide dispersion solution at a mass fraction of 0.1% to 0.5%.

5. The method of claim 4, wherein, The amino-modified substance comprises an ethylenediamine solution and / or a propylenediamine solution.

6. The method of claim 5, wherein, The casting comprises: pouring the defoamed casting solution on a glass plate with non-woven fabric attached, scraping the casting solution into a film with a scraper at a certain temperature and humidity, immediately immersing the film into a coagulation bath for solidification, then performing heat treatment on the solidified film, and then immersing the heat-treated film into deionized water for soaking, drying to obtain the amino-modified graphene oxide hydrophilic film.

7. The method of claim 6, wherein, The casting temperature is 20 to 30℃; and / or The casting humidity is less than 60%; and / or The scraper is scraped on the glass plate at a speed of 100 to 120 mm / min.

8. The method of claim 7, wherein, The heat treatment is performed at 60 to 80℃ for 4 to 5 h; and / or the soaking time is 2 to 4 d.

9. An amino-modified graphene oxide hydrophilic film prepared by the method of any one of claims 1 to 8.

10. Application of the amino-modified graphene oxide hydrophilic film of claim 9 in water treatment.

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