Preparation method of super-hydrophilic metal-doped graphene oxide oil-water separation membrane

Abstract

The invention discloses a preparation method of a super-hydrophilic metal-doped graphene oxide oil-water separation membrane, which mainly comprises the following steps: (1) preparation of graphene oxide: graphene is used as a raw material, and a modified Hummers method is utilized to prepare the graphene oxide; and (2) preparation of metal-loaded monatomic graphene oxide: mixing graphene oxide prepared by using a modified Hummers method with 1mol / L ferric trichloride in an acidic aqueous solution, stirring, washing with water, re-dispersing ferric iron-doped graphene oxide sheets formed after washing in water for storage, and drying to obtain the metal-loaded monatomic graphene oxide. A ferric iron graphene oxide dispersion liquid with a stable form is obtained; and (3) adding ionized water into the ferric iron-containing graphene oxide dispersion liquid for dilution, and carrying out suction filtration on the diluted dispersion liquid on a PES film by using a terminal suction filtration device to form a film. The oil-in-water separation membrane disclosed by the invention can be used for separating an oil-in-water emulsion by utilizing the super-hydrophilic property of the oil-in-water separation membrane, and can be used for activating hydrogen peroxide to degrade a surfactant in the emulsion at the same time, so that the flow rate of oil-water separation is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of materials, and particularly to a method for preparing a superhydrophilic metal-doped graphene oxide oil-water separation membrane. Background Art

[0002] The current global water resource crisis is intensifying. Insoluble oils and soluble organic pollutants are common water pollutants in domestic sewage with high production and emission. In most of the methods developed so far, the separation or decomposition of pollutants is highly difficult, and common industrial methods consume energy, time, and resources. In contrast, membrane filtration technology is a water remediation method with high throughput and low energy consumption. However, when using this method for pollutant separation, factors such as surface properties, pore size, and membrane thickness need to be considered. Due to the advantages of superwetting membranes such as high selectivity and simple preparation process, filter membranes with extreme wetting properties have been developed for treating oily wastewater.

[0003] Graphene oxide (GO) is an important graphene derivative. Due to the presence of abundant oxygen-containing functional groups, it is well-dispersed in water and has been used in new membrane technologies. Inspired by the layered structure and high hydrophilicity of clam shells and fish scales, atomically thin graphene oxide nanosheets can be used as the substrate for constructing underwater superoleophobic membranes for oil-water separation. For example, an underwater superoleophobic membrane formed by dip-coating graphene oxide on the surface of a stainless steel mesh can be used to separate layered oil-water mixtures using its superoleophobic property, but it is not suitable for emulsions due to its large pore size. Graphene oxide flakes have self-assembled into two-dimensional membranes on commercial and modified microfiltration membranes. The presence of smaller interlayer spacing and a stable hydration layer enables these 2D membranes to effectively prevent the penetration of oil droplets in emulsions. However, water-soluble organic pollutants still exist in the graphene oxide interlayer, greatly hindering water flow and reducing the flux. To solve the membrane fouling problem, doping catalysts on the GO membrane can effectively remove organic pollutants in the GO interlayer. For example, patent CN109126851A prepares a visible light-responsive Ag 3 PO 4 / GO / g-C 3 N 4 ternary composite photocatalyst. Photocatalytic performance experiments show that the ternary composite photocatalyst provided by the invention has better photocatalytic performance compared to g-C 3 N 4 、Ag 3 PO 4 and Ag 3 PO 4Both / GO have high photocatalytic degradation performance for rhodamine B. However, there is currently no combination of photocatalytic degradation of organic pollutants and water treatment. Therefore, combining the catalytic oxidation technology of the membrane with the emulsion separation of the superwetting membrane can prevent one of the phase solutions while using the catalytic oxidation technology to remove the remaining organic matter in the emulsion separation, greatly improving the separation efficiency and separation rate.

[0004] In summary, the preparation of an oil-water separation membrane with catalytic activity and anti-oil pollution is helpful for wastewater treatment in industrial production. Ordinary superhydrophilic membranes will be oil-polluted and lose their hydrophilic ability when treating a large amount of oil-polluted aqueous solutions. Therefore, developing a superhydrophilic membrane with self-cleaning ability can efficiently degrade the organic matter passing through the membrane and the membrane surface. Combining the oxidation degradation technology with extreme wetting to separate oil-water mixtures and treat actual polluted water is a very promising future technology for industrial wastewater treatment. Summary of the Invention

[0005] In order to solve the above deficiencies of the prior art, the present invention proposes a preparation method of a superhydrophilic metal-doped graphene oxide oil-water separation membrane.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A preparation method of a superhydrophilic metal-doped graphene oxide oil-water separation membrane, the main steps are:

[0007] (1) Preparation of graphene oxide: Using graphene as the raw material, graphene oxide is prepared by the modified Hummers method;

[0008] (2) Preparation of metal single-atom doped graphene oxide: The graphene oxide prepared by the modified Hummers method obtained in step (1) is mixed with 1 mol / L ferric chloride in an acidic aqueous solution and stirred, and then washed with water. After washing, the graphene oxide flakes doped with trivalent iron are redispersed in water for storage to obtain a stable form of trivalent iron graphene oxide dispersion;

[0009] (3) Add deionized water to dilute the trivalent iron graphene oxide dispersion, and the diluted dispersion is filtered into a membrane on a PES membrane using a terminal filtration device. The obtained Fe-GO membrane is dried at 60 °C for 2 hours, and the mass ratio of the trivalent iron graphene oxide dispersion to deionized water is 1:95 - 105.

[0010] Furthermore, the preparation method of the modified Hummers method includes:

[0011] Add graphite powder to concentrated acid and stir evenly, then add potassium permanganate and stir for 2 - 6 h. Add water and hydrogen peroxide solution to the resulting solution. When the reaction stops bubbling, disperse the resulting reaction solution in water and centrifuge. Take the lower-layer solid and disperse it in hydrochloric acid solution. The rewashed and centrifuged solid product is graphene oxide. Among them, the concentration of concentrated sulfuric acid is 99%, and the concentration of perchloric acid is 65% - 80%.

[0012] Further, in step (3),

[0013] Ultrasonically disperse 30% of the total amount of the ferric ion graphene oxide dispersion in a solvent to form a seed suspension, and then obtain a crystallized support through a vacuum and coating process;

[0014] Pour the remaining 70% of the ferric ion graphene oxide dispersion into a reaction kettle and add the crystallized support. Through high-temperature decomposition, a thermal crystallization reaction is carried out. After the reaction is completed, add ionized water for dilution. The diluted dispersion is filtered and formed on a PES membrane using a terminal suction filtration device.

[0015] Further, in step (3), the temperature of the thermal crystallization reaction is 200 - 220 °C, and the reaction time is 4 - 9 h.

[0016] Further, in step (3), the mass ratio of the ferric ion graphene oxide dispersion to the solvent is 1:3. The solvent is a mixed solution of sodium hydroxide and potassium hydroxide, and the mass ratio of the sodium hydroxide and potassium hydroxide solutions is 1:0.2 - 0.4.

[0017] Further, in step (2), the ferric ion graphene oxide sheets are also doped with metals, and the types of metals are one or more of iron, cobalt, and ruthenium.

[0018] Further, in the modified Hummers method preparation, the ratio of graphite powder to potassium permanganate is 1:1 - 1:6, and the volume ratio of hydrogen peroxide to concentrated acid is 1:3 - 1:10.

[0019] Further, in step (2), the volume of water added is equal to the volume of the acidic aqueous solution.

[0020] Further, in step (2), the pH value of the acidic aqueous solution can be 1 - 6.

[0021] Further, the base film required in step (3) is selected from one of polyethersulfone film, polypropylene film, and nylon 66 film.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] First, the oil-in-water separation membrane of the present invention can utilize its superhydrophilic property to separate oil-in-water emulsions, and can simultaneously activate hydrogen peroxide to degrade surfactants in the emulsion, increasing the flow rate of oil-water separation;

[0024] Second, the GO membrane prepared in the present invention has a self-cleaning function. After being contaminated with oleic acid, the activation of hydrogen peroxide by the Fe-GO membrane can effectively remove the oleic acid on the surface and restore the underwater superoleophobic and air superhydrophilic wetting properties;

[0025] Third, the trivalent iron prepared in the present invention has a very strong activation effect on hydrogen peroxide. Only 50 μL of hydrogen peroxide can continuously degrade 1 L of malachite green dye solution.

[0026] Fourth, as a mineralizing agent for molecular sieve crystallization, controlling the pH value is beneficial to the rearrangement to form the primary structural unit of the molecular sieve. By adding a crystallization support, the growth of graphene can be guided, and at the same time, it also promotes the crystallization rate of the molecular sieve membrane crystals, reduces energy consumption, accelerates the adsorption rate of carbon source molecules, and makes the crystal grains evenly distributed and of appropriate size. Description of the Drawings

[0027] Figure 1 is the spreading process of water droplets in air. The water droplets can spread rapidly on the prepared membrane within one second;

[0028] Figure 2 is a photo of the contact angle of the prepared membrane in oil. The contact angle of oil in water is greater than 150°;

[0029] Figure 3 (1), (2), (3), (4), and (5) in are optical photos before and after separating oil-in-water (lubricating oil, n-hexane, toluene, lubricating oil, diesel) emulsions.

[0030] Figure 4 is a schematic diagram of the separation rate.

[0031] Figure 5 is the process of Fe-GO and GO degrading malachite green staining solution;

[0032] Figure 6 a and b are the self-cleaning processes of the prepared membrane. Photos of the contact angles of water in air and oil in water before and after the membrane surface contaminated with oleic acid is treated with hydrogen peroxide are shown. Detailed Embodiments

[0033] The invention will be described in detail below with reference to the drawings and embodiments.

[0034] In the following embodiments, the purity of ethanol ≥ 99.97%.

[0035] In the following examples, the method for preparing the oil-in-water emulsion is as follows: Distilled water and a non-polar solvent (petroleum ether, toluene, dodecane) are mixed at a volume ratio of 100:1, and Tween 20 (0.1 g / L) is added. After shaking well, the oil-in-water emulsion is obtained (when using lubricating oil or diesel, an oil-in-water lubricating oil emulsion or an oil-in-water diesel emulsion is obtained respectively). The separation efficiency is obtained by measuring the COD by comparing the oil content in the filtrate after separation with distilled water.

[0036] In the following examples, the method for preparing the oleic acid solution is to dissolve 1 mL of the oleic acid solution in 10 mL of ethanol.

[0037] In the following examples, the method for preparing the malachite green solution is to completely dissolve 0.0025 g of malachite green dye in 250 mL of deionized water to prepare a 10 mM / L malachite green solution.

[0038] The following examples will further illustrate the present invention, but the content of the present invention is not limited thereto at all.

[0039] Example 1

[0040] A preparation method of a super-hydrophilic metal-doped graphene oxide oil-water separation membrane includes the following steps:

[0041] (1) Graphite powder is added to concentrated sulfuric acid and stirred evenly, then potassium permanganate is added and stirred for 3 h; water and hydrogen peroxide solution are added to the obtained solution. When the reaction stops bubbling, the obtained reaction solution is dispersed with water and centrifuged. The lower-layer solid is dispersed in hydrochloric acid solution, and the centrifuged solid product is washed and centrifuged again to obtain graphene oxide. Among them, the concentration of concentrated sulfuric acid is 99%. The mass ratio of graphite to potassium permanganate is 1:2; the addition amount of concentrated acid is 40 mL, the dosage of graphite powder is 1 g, the addition amount of water is 40 mL, and the addition amount of 30% hydrogen peroxide is 10 mL.

[0042] (2) Centrifuge three times with water first at 9000 r / min, then three times with hydrochloric acid, and finally wash with water by centrifugation until neutral, each time for 10 min. The concentration of the hydrochloric acid solution is 1 mol / L.

[0043] (3) The obtained graphene oxide is prepared by modifying the modified Hummers method. It is mixed with ferric chloride at 1 mol / L in an acidic aqueous solution (pH = 3), and the obtained mixture is stirred for 4 h. After washing with water, the formed iron-doped graphene oxide sheets are redispersed in water for storage.

[0044] (4) Take 1 mL of a stable iron-doped graphene oxide dispersion, ultrasonically disperse 30% of the total amount of the iron(III)-doped graphene oxide dispersion in a solvent to form a seed suspension, and then obtain a crystallized support through a vacuum and coating process; pour the remaining 70% of the iron(III)-doped graphene oxide dispersion into a reaction kettle and add the crystallized support, and carry out a thermal crystallization reaction through high-temperature decomposition. The temperature of the thermal crystallization reaction is 210 °C, and the reaction time is 8 h. The mass ratio of the iron(III)-doped graphene oxide dispersion to the solvent is 1:3, and the solvent is a mixed solution of sodium hydroxide and potassium hydroxide. The mass ratio of the sodium hydroxide and potassium hydroxide solutions is 1:0.3. Add 100 mL of deionized water for dilution, and filter the diluted dispersion into a film on a PES membrane using a terminal filtration device. Dry the obtained iron-doped graphene oxide film at 60 °C for 2 hours.

[0045] Mix distilled water and petroleum ether at a volume ratio of 100:1, add Tween 20 (0.1 g / L), and shake well to obtain an oil-in-water emulsion. Using a filtration device, separate the oil-in-water petroleum ether emulsion in a filter cup under a negative pressure of 40 kPa, record the required time, collect the filtrate, use distilled water as a control sample, measure the COD of the obtained filtrate, and obtain a separation efficiency of 99.97%.

[0046] As Figure 2 shown in

[0047] Example 2

[0048] A preparation method of a superhydrophilic metal-doped graphene oxide oil-water separation membrane, comprising the following steps:

[0049] (1) Add graphite powder to perchloric acid and stir evenly, then add potassium permanganate and stir for 2 h; add water and hydrogen peroxide solution to the obtained solution. When the reaction stops bubbling, disperse the obtained reaction solution in water by centrifugation, and take the lower-layer solid and disperse it in hydrochloric acid solution. The solid product obtained by re-washing and centrifuging is graphene oxide. Among them, the concentration of perchloric acid is 70%, the mass ratio of graphite to potassium permanganate is 1:3; when the addition amount of concentrated acid is 40 mL, the dosage of graphite powder is 1 g, the addition amount of water is 40 mL, and the addition amount of 30% hydrogen peroxide is 10 mL.

[0050] (2) Centrifuge three times with water first at 9000 r / min, then centrifuge three times with hydrochloric acid, and finally wash with water by centrifugation until neutral, with each centrifugation for 10 min. The concentration of the hydrochloric acid solution is 1 mol / L.

[0051] (3) The graphene oxide prepared by modifying the modified Hummers method is obtained. It is mixed with ferric chloride at 1 mole per liter in an acidic aqueous solution (pH = 3), and the resulting mixture is stirred for 4 hours. After washing with water, the formed ferric-doped graphene oxide sheets are redispersed in water for storage.

[0052] (4) Take 1 mL of the stable ferric-doped graphene oxide dispersion, add 100 mL of deionized water for dilution, and the diluted dispersion is filtered and formed into a membrane on a PES membrane using a terminal suction filtration device. The obtained Fe-GO membrane is dried at 60 °C for 2 hours.

[0053] Distilled water and n-hexane are mixed at a volume ratio of 100:1, and Tween 20 (0.1 g / L) is added. After shaking well, an oil-in-water emulsion is obtained. Using a filtration device, the n-hexane-in-water emulsion is separated in a filter cup under a negative pressure of 40 kPa, the required time is recorded, the filtrate is collected, and distilled water is used as a control sample to measure the COD of the obtained filtrate, and the separation efficiency is 99.98%.

[0054] As Figure 3 (2) shows the optical comparison diagram before and after the separation of the n-hexane-in-water emulsion prepared by membrane separation in this example. It can be seen that the filtrate becomes clear and transparent.

[0055] Example 3

[0056] A preparation method of a superhydrophilic metal-doped graphene oxide oil-water separation membrane, comprising the following steps:

[0057] (1) Graphite powder is added to perchloric acid and stirred evenly, then potassium permanganate is added and stirred for 4 h; water and hydrogen peroxide solution are added to the obtained solution. When the reaction stops bubbling, the obtained reaction solution is dispersed with water and centrifuged. The solid in the lower layer is dispersed in hydrochloric acid solution, and the centrifuged solid product is washed again, and the obtained product is graphene oxide. The concentration of perchloric acid is 80%. The mass ratio of graphite to potassium permanganate is 1:3; the addition amount of concentrated sulfuric acid is 40 mL, the amount of graphite powder used is 0.1 g, the addition amount of water is 35 mL, and the addition amount of 30% hydrogen peroxide is 10 mL.

[0058] (2) Centrifuge three times with water first at 9000 r / min, then three times with hydrochloric acid, and finally wash with water by centrifugation until neutral, each centrifugation for 10 min. The concentration of the hydrochloric acid solution is 1 mol / L.

[0059] (3) The graphene oxide prepared by modifying the modified Hummers method is obtained. It is mixed with ferric chloride at 1 mole per liter in an acidic aqueous solution (pH = 3), and the resulting mixture is stirred for 4 hours. After washing with water, the formed ferric-doped graphene oxide sheets are redispersed in water for storage.

[0060] (4) Take 1 mL of the stable iron(III)-doped graphene oxide dispersion, add 100 mL of deionized water for dilution, and filter the diluted dispersion into a film on a PES membrane using a terminal filtration device. Dry the obtained Fe-GO film at 60 °C for 2 hours.

[0061] Mix distilled water and toluene at a volume ratio of 100:1, add Tween 20 (0.1 g / L), and shake well to obtain an oil-in-water emulsion. Using a filtration device, separate the toluene-in-water emulsion in a filter cup under a negative pressure of 40 kPa, record the required time, collect the filtrate, use distilled water as a control sample, measure the COD of the obtained filtrate, and obtain a separation efficiency of 99.98%.

[0062] As Figure 3 shown in

[0063] Example 4

[0064] A preparation method of a superhydrophilic metal-doped graphene oxide oil-water separation membrane, comprising the following steps:

[0065] (1) Add graphite powder to concentrated sulfuric acid and stir evenly, then add potassium permanganate and stir for 6 h. Add water and hydrogen peroxide solution to the obtained solution. When the reaction stops bubbling, disperse the obtained reaction solution with water and centrifuge. Take the lower-layer solid and disperse it in hydrochloric acid solution. Wash and centrifuge the obtained solid product again, and the obtained product is graphene oxide. Among them, the concentration of concentrated sulfuric acid is 99%. The mass ratio of graphite to potassium permanganate is 1:3; the addition amount of concentrated sulfuric acid is 40 mL, the amount of graphite powder used is 1 g, the addition amount of water is 40 mL, and the addition amount of 30% hydrogen peroxide is 10 mL.

[0066] (2) Centrifuge three times with water first at 9000 r / min, then three times with hydrochloric acid, and finally wash and centrifuge with water until neutral, each time for 10 min. The concentration of the hydrochloric acid solution is 1 mol / L.

[0067] (3) The obtained graphene oxide is prepared by modifying the improved Hummers method. Mix it with ferric chloride at 1 mol / L in an acidic aqueous solution (pH = 3), and stir the obtained mixture for 4 hours. After washing with water, redisperse the formed iron(III)-doped graphene oxide sheets in water for storage.

[0068] (4) Take 1 mL of the stable iron(III)-doped graphene oxide dispersion, add 100 mL of deionized water for dilution, and filter the diluted dispersion into a film on a PES membrane using a terminal filtration device. Dry the obtained GO film at 60 °C for 2 hours.

[0069] Mix distilled water and lubricating oil at a volume ratio of 100:1, add Tween 20 (0.1 g / L), and shake well to obtain an oil-in-water emulsion. Using a filtration device, separate the oil-in-water lubricating oil emulsion in a filter cup under a negative pressure of 40 kPa, record the required time, collect the filtrate, use distilled water as a control sample, measure the COD of the obtained filtrate, and obtain a separation efficiency of 99.97%.

[0070] As Figure 3 (4) shown, the optical comparison diagram before and after the separation of the oil-in-water lubricating oil emulsion prepared by membrane separation in this example can be seen that the filtrate becomes clear and transparent.

[0071] Example 5

[0072] A preparation method of a superhydrophilic metal-doped graphene oxide oil-water separation membrane, comprising the following steps:

[0073] (1) Add graphite powder to concentrated sulfuric acid and stir evenly, then add potassium permanganate and stir for 6 h. Add water and hydrogen peroxide solution to the obtained solution. When the reaction stops bubbling, disperse the obtained reaction solution with water and centrifuge. Take the lower-layer solid and disperse it in hydrochloric acid solution. Wash and centrifuge the solid product again to obtain graphene oxide. Among them, the concentration of concentrated sulfuric acid is 99%. The mass ratio of graphite to potassium permanganate is 1:3; the addition amount of concentrated sulfuric acid is 40 mL, the amount of graphite powder used is 1 g, the addition amount of water is 40 mL, and the addition amount of 30% hydrogen peroxide is 10 mL.

[0074] (2) Centrifuge three times with water at 9000 r / min first, then centrifuge three times with hydrochloric acid, and finally wash and centrifuge with water until neutral. Centrifuge for 10 min each time, and the concentration of hydrochloric acid solution is 1 mol / L.

[0075] (3) The obtained graphene oxide is prepared by modifying the modified Hummers method. Mix it with ferric chloride at 1 mole per liter in an acidic aqueous solution (pH = 3), and stir the obtained mixture for 4 hours. After washing with water, the formed ferric-ion-doped graphene oxide sheets are redispersed in water for storage.

[0076] (4) Take 1 mL of the stable ferric-ion-doped graphene oxide dispersion, add 100 mL of deionized water for dilution, and filter the diluted dispersion onto a PES membrane using a terminal filtration device to form a membrane. Dry the obtained GO membrane at 60 °C for 2 hours.

[0077] Mix distilled water and diesel at a volume ratio of 100:1, add Tween 20 (0.1 g / L), and shake well to obtain an oil-in-water emulsion. Using a filtration device, separate the diesel-in-water emulsion in a filter cup under a negative pressure of 40 kPa, record the required time, collect the filtrate, use distilled water as a control sample, measure the COD of the obtained filtrate, and obtain a separation efficiency of 99.97%.

[0078] As Figure 3 (5) shown, the optical contrast diagram before and after the separation of the diesel-in-water emulsion prepared by membrane separation in this example can be seen that the filtrate becomes clear and transparent.

[0079] Example 6

[0080] Preparation and separation of an iron-doped graphene oxide membrane capable of degrading malachite green solution.

[0081] (1) Add graphite powder to concentrated sulfuric acid and stir evenly, then add potassium permanganate and stir for 4 h; add water and hydrogen peroxide solution to the obtained solution, and when the reaction stops bubbling, disperse the obtained reaction solution with water and centrifuge. Take the lower-layer solid and disperse it in hydrochloric acid solution, and re-wash and centrifuge the obtained solid product to obtain graphene oxide. Among them, the concentration of concentrated sulfuric acid is 99%. The mass ratio of graphite to potassium permanganate is 1:3; the addition amount of concentrated sulfuric acid is 40 mL, the amount of graphite powder used is 1 g, the addition amount of water is 40 mL, and the addition amount of 30% hydrogen peroxide is 10 mL.

[0082] (2) Centrifuge three times with water at 9000 r / min first, then centrifuge three times with hydrochloric acid, and finally centrifuge and wash with water until neutral, each centrifugation for 10 min, and the concentration of hydrochloric acid solution is 1 mol / L.

[0083] (3) The obtained graphene oxide was prepared by modifying the modified Hummers method. Mix with ferric chloride at 1 mole per liter in an acidic aqueous solution (pH = 3), and stir the obtained mixture for 4 hours. After washing with water, the formed iron-doped graphene oxide sheets are redispersed in water for storage.

[0084] (4) Take 1 mL of the stable iron-doped graphene oxide dispersion, add 100 mL of deionized water for dilution, and filter the diluted dispersion onto a PES membrane using a terminal filtration device to form a membrane. Dry the obtained GO membrane at 60 degrees Celsius for 2 hours.

[0085] As Figure 6 a shown, using a terminal filtration device, place 250 mL of solution in a filter tube and separate it under a negative pressure of 80 kPa, record the required time, observe the color change of the filtered solution, and collect the green leaves to judge the content of malachite green in the filtrate using ultraviolet spectroscopy.

[0086] Example 7

[0087] An iron-doped graphene surface that can be self-cleaned.

[0088] (1) Add graphite powder to concentrated sulfuric acid and stir evenly, then add potassium permanganate and stir for 3 h. Add water and hydrogen peroxide solution to the obtained solution. When the reaction stops bubbling, disperse the obtained reaction solution with water and centrifuge. Take the lower-layer solid and disperse it in hydrochloric acid solution. Wash and centrifuge the solid product again, and the obtained product is graphene oxide. Among them, the concentration of concentrated sulfuric acid is 99%. The mass ratio of graphite to potassium permanganate is 1:3; the addition amount of concentrated sulfuric acid is 40 mL, the amount of graphite powder used is 1 g, the addition amount of water is 40 mL, and the addition amount of 30% hydrogen peroxide is 10 mL.

[0089] (2) Centrifuge three times with water at 9000 r / min first, then centrifuge three times with hydrochloric acid, and finally centrifuge and wash with water until neutral. Centrifuge for 10 min each time, and the concentration of hydrochloric acid solution is 1 mol / L.

[0090] (3) The obtained graphene oxide is prepared by modifying the modified Hummers method. Mix it with ferric chloride at 1 mol / L in an acidic aqueous solution (pH = 3), and stir the obtained mixture for 4 h. After washing with water, the formed iron-doped graphene oxide sheets are redispersed in water for storage.

[0091] (4) Take 1 mL of the stable iron(III)-doped graphene oxide dispersion, add 100 mL of deionized water for dilution, and filter the diluted dispersion into a film on a PES membrane using a terminal suction filtration device. Dry the obtained GO film at 60 °C for 2 h.

[0092] As Figure 6 shown in a, use oleic acid to contaminate the surface of the prepared film, observe the contact angles of water in air and oil in water on the surface of the contaminated prepared film, utilize the activation of the prepared film to hydrogen peroxide, treat the surface of the prepared film with 10 mM / L hydrogen peroxide, and observe the contact angles of water in air and oil in water on the prepared film after treatment. It is found that the film can restore the lubricating properties of superhydrophilic in air and superoleophobic underwater before oleic acid contamination.

[0093] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the scope of the patent and protection of the present invention should be subject to the appended claims.

Claims

1. A method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane, characterized in that: The main steps are: (1) Preparation of graphene oxide: Graphene is used as raw material and graphene oxide is prepared by a modified Hummers method; (2) Preparation of metal-loaded single-atom graphene oxide: The graphene oxide prepared by the modified Hummers method obtained in step (1) is mixed with 1 mol / L ferric chloride in an acidic aqueous solution and stirred, and then washed with water. After washing, the formed trivalent iron-doped graphene oxide sheets are redispersed in water for storage to obtain a trivalent iron graphene oxide dispersion in a stable form; (3) Add ionized water to the ferric graphene oxide dispersion to dilute it, and use a terminal filtration device to filter the diluted dispersion on a PES membrane to form a membrane. The obtained Fe-GO membrane is dried at 60 degrees Celsius for 2 hours, and the mass ratio of the ferric graphene oxide dispersion to the ionized water is 1:95-105.

2. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 1, characterized in that: The modified Hummers method preparation method includes: Add graphite powder to concentrated acid and stir evenly, then add potassium permanganate and stir for 2-6 hours, add water and hydrogen peroxide solution to the resulting solution, and when the reaction stops bubbling, disperse the resulting reaction solution with water and centrifuge, take the lower layer of solid and disperse it in hydrochloric acid solution, re-wash the centrifuged solid product, which is graphene oxide. The concentration of concentrated sulfuric acid is 99%, and the concentration of perchloric acid is 65%-80%.

3. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 1, characterized in that: In step (3), Ultrasonic dispersion of graphene oxide containing 30% trivalent iron in a solvent to form a seed suspension, and then obtain a crystallized support through vacuum and coating processes; Pour the graphene oxide dispersion with a remaining amount of 70% of trivalent iron into the reactor and add a crystallization support. Perform thermal crystallization reaction through high-temperature decomposition. After the reaction is completed, add ionized water for dilution. The diluted dispersion is filtered on the PES membrane using a terminal filtration device to form a membrane.

4. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 3, characterized in that: In step (3), the temperature of the thermal crystallization reaction is 200-220° C., and the reaction time is 4-9 hours.

5. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 4, characterized in that: In step (3), the mass ratio of the ferric graphene oxide dispersion to the solvent is 1:3, the solvent is a mixed solution of sodium hydroxide and potassium hydroxide, and the mass ratio of the sodium hydroxide and potassium hydroxide solutions is 1:0.2-0.

4.

6. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 1, characterized in that: In step (2), the trivalent iron graphene oxide sheet is also doped with a metal, and the metal type is one or more of iron, cobalt, and ruthenium.

7. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 2, characterized in that: In the modified Hummers method, the ratio of graphite powder to potassium permanganate is 1:1-1:6, and the volume ratio of hydrogen peroxide to concentrated acid is 1:3-1:

10.

8. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 6, characterized in that: In step (2), the volume of water added is equal to the volume of the acidic aqueous solution.

9. The method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to claim 6, characterized in that: The pH value of the acidic aqueous solution in step (2) is 1-6.

10. A method for preparing a super hydrophilic metal-doped graphene oxide oil-water separation membrane according to any one of claims 1 to 9, characterized in that: The base membrane required in step (3) is selected from one of polyethersulfone membrane, polypropylene membrane and nylon 66 membrane.

Images