Three-dimensional porous super-hydrophilic / oleophobic charged melamine foam and its preparation method and application

Abstract

The present invention discloses a three-dimensional porous super-hydrophilic / oleophobic charged melamine foam and its preparation method and application. The foam is obtained by immersing dedoped melamine foam in an anhydrous ethanol solution of perfluorooctanoic acid for secondary doping, followed by cleaning and drying; the dedoped melamine foam is obtained by immersing polyaniline-modified melamine foam in an anhydrous ethanol solution of polyethyleneimine and di(3-methoxysilylpropyl)amine, reacting in a water bath, and then drying and solidifying. The obtained three-dimensional porous super-hydrophilic / oleophobic charged melamine foam can be used for efficient demulsification and separation of anionic surfactant-stabilized oil-in-water emulsions, with an average permeation flux of the emulsion during the separation process of 35,000 L·m ‑2 ·h ‑1 Above, the separation efficiency is greater than 97%.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-water separation, and in particular to a three-dimensional porous super-hydrophilic / oleophobic charged melamine foam, and a preparation method and application thereof. Background Art

[0002] The rapid demulsification and separation of surfactant-stabilized oil-in-water emulsions in the petroleum industry is a challenge. The key to separating emulsified oil and water lies in demulsification. Traditional ultrafiltration methods utilize the fact that the pore size of ultrafiltration membranes is smaller than the emulsified oil droplets, intercepting oil droplets larger than the membrane pore size and allowing only water to pass through, thereby achieving emulsified oil and water separation. However, this size screening method requires a very small membrane pore size and low porosity, resulting in high filtration resistance and low separation flux. Increasing the operating pressure is necessary to increase the tangential flow velocity on the membrane surface and improve the separation flux. However, increasing the operating pressure also increases the radial pressure on the membrane surface, which may destroy the hydration layer on the membrane surface and cause irreversible contamination.

[0003] In response to the above problems, researchers have dotted low surface energy substances on the membrane surface to form a dual antifouling mechanism with the hydration layer, which has the function of resisting oil pollution and releasing oil pollution, and can effectively prolong the emulsion separation time. Technical literature 1 (Xueting Zhao et al., Fabrication of antifouling polymer-inorganic hybridmembranes through the synergy of biomimetic mineralization and nonsolventinduced phase separation, Journal of Materials Chemistry A, 2015, 3, 7287-7295) reported a hybrid membrane with inorganic hydrophilic microdomains and organic low surface energy microdomains prepared by in situ biomimetic mineralization and nonsolventinduced phase separation. The synergistic effect of the antifouling and defouling mechanisms makes the membrane have a separation flux of 90L·m in the process of separating water-in-oil emulsions. -2 ·h -1 ) decreases to zero, and the separation time is effectively extended (60 min). Technical document 2 (Mingrui He et al., Oil / water separation membranes with a fluorine island structure forstable high flux, Journal of Materials Chemistry A, 2021, 9, 6905-6912) reported a membrane with a discrete fluorine island structure distributed on a continuous hydrophilic area. The membrane achieved a stable separation flux of 770 L·m when separating oil-in-water emulsions.-2 ·h -1 bar -1 , the separation time is as long as 40 minutes. Although the introduction of fluorine-containing low surface energy on the separation membrane surface can effectively resist and release oil contamination, maintain a stable separation flux, and prolong the separation time, the separation flux of the membrane is too low to separate a large amount of emulsion in a short period of time. In addition, the pressure applied during the separation process also increases additional energy consumption.

[0004] Charged demulsification refers to the electrostatic interaction between the ionic surfactant and the surface charge of the material on the emulsified oil droplets. The surfactant migrates and rearranges on the oil droplets, the stability of the oil droplets is reduced, and the parts with smaller repulsion between the oil droplets are easily aggregated and demulsified. Usually, the demulsification effect of electrostatic attraction is better than that of electrostatic repulsion. Technical document 3 (Lidong Feng et al., Phytic acid and graphene oxide functionalized sponge with special-wettabilityand electronegativity for oil-in-water emulsion separation in single-step, Journal of Hazardous Materials, 2022, 435, 129003) reports a phytic acid graphene oxide functionalized sponge with special wettability and electronegativity. The sponge is placed in the emulsion and shaken simply to separate the water-in-oil emulsion stabilized by the cationic surfactant. However, it is limited by the surface charge. The sponge can only purify 25mL of emulsion in 20min minutes, and the separation efficiency is only 94.14%. Chinese invention patent application CN114733499A discloses a Janus positively and negatively charged superhydrophilic / underwater superoleophobic copper foam assembled from amino- and carboxylated carbon nanotubes. This foam, which utilizes long separation channels and electrostatic demulsification, can rapidly and efficiently separate oil-in-water emulsions stabilized by ionic surfactants. Under gravity alone, the permeation flux reaches 16,222.3 to 31,063.9 L·m. -2 ·h - 1. However, after separating about 100 mL of emulsion, the separation efficiency decreases and needs to be cleaned and restored.

[0005] Existing research suggests that electrostatic attraction offers a fast, efficient, and low-cost demulsification effect. However, after partially separating the emulsified oil and water, the majority of the surface charge on the material is taken up by the surfactant, significantly reducing the surface charge and even causing a shift in the wettability of the material surface. This prevents newly introduced emulsified oil droplets encapsulated by the surfactant from continuing to demulsify through interaction with the material surface. The shift in wettability can also cause accumulated oil droplets after demulsification to adhere to the material surface, leading to irreversible contamination. Therefore, how to slow down the adsorption of surfactants on the material surface and improve demulsification capabilities without affecting the separation effect is crucial for its practical application. Summary of the Invention

[0006] The purpose of the present invention is to provide a separation process in which the average permeation flux of the emulsion is 35000 L·m -2 ·h -1 The above is a three-dimensional porous superhydrophilic / underwater superoleophobic charged melamine foam with a stable oil-in-water emulsion having a separation efficiency greater than 97% and a preparation method thereof.

[0007] Another object of the present invention is to provide a method for applying the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam in separating anionic surfactant-stabilized oil-in-water emulsions.

[0008] The object of the present invention is achieved through the following technical solutions:

[0009] A three-dimensional porous super-hydrophilic / oleophobic charged melamine foam is obtained by immersing dedoped melamine foam in an anhydrous ethanol solution of perfluorooctanoic acid, performing secondary doping, and then cleaning and drying. The dedoped melamine foam is obtained by immersing polyaniline-modified melamine foam in an anhydrous ethanol solution of polyethyleneimine and di(3-methoxysilylpropyl)amine, reacting in a water bath at 50-70°C for 1-2 hours, and then drying and solidifying. The polyaniline-modified melamine foam is obtained by immersing melamine foam in a precooled mixed solution of aniline and hydrochloric acid, adding a precooled mixed aqueous solution of ammonium persulfate and hydrochloric acid, reacting in an ice-water bath for 3-6 hours, and then removing, cleaning, and drying.

[0010] To further achieve the purpose of the present invention, preferably, the secondary doping is achieved by horizontal-rotational oscillation on a shaker for 3-8 hours; the rotation speed of the shaker during the horizontal-rotational oscillation is 150-200 rpm; and the concentration of the perfluorooctanoic acid in anhydrous ethanol is 6-12 g / L.

[0011] Preferably, the molecular weight of the polyethyleneimine is 600-1800; the concentration of the polyethyleneimine in anhydrous ethanol is 3.5-6 g / L; and 3.5-5.5 mL of di(3-methoxysilylpropyl)amine is added to each liter of anhydrous ethanol.

[0012] Preferably, the concentration of aniline in the ice-water bath reaction solution is 0.05-0.15 mol / L, the concentration ratio of ammonium persulfate to aniline is 1:1.8-1:2.2, and the concentration of hydrochloric acid in the aniline and hydrochloric acid and in the ammonium persulfate and hydrochloric acid is 0.8-1.2 mol / L; and the precooling is carried out in an ice-water bath at 0-5°C.

[0013] Preferably, the ice-water bath temperature is 0-5° C., and the magnetic stirring speed is 20-40 rpm; the drying and curing is carried out in an oven, the drying and curing temperature is 70-90° C., and the drying and curing time is 1.5-3 h.

[0014] Preferably, the cleaning and drying after the secondary doping is to rinse the foam with deionized water 3 to 5 times, and the drying is carried out in an oven at a drying temperature of 50-80° C. and a drying time of 1-3 hours;

[0015] The cleaning after the reaction in the ice water bath is to repeatedly wash with deionized water while squeezing the sponge until the cleaning liquid is neutral; the cleaning and drying after the reaction in the ice water bath is to dry in an oven after cleaning, the drying temperature is 40-50°C, and the drying time is 8-12h.

[0016] Preferably, the melamine foam is ultrasonically cleaned with anhydrous ethanol and deionized water for 10-15 minutes respectively before use and then dried.

[0017] The preparation method of the three-dimensional porous super hydrophilic / oleophobic charged melamine foam comprises the following steps:

[0018] 1) Clean and dry the melamine foam;

[0019] 2) preparing a mixed solution of aniline and hydrochloric acid and a mixed solution of ammonium persulfate and hydrochloric acid respectively, precooling them in an ice-water bath, immersing the melamine foam obtained in step 1) in the precooled mixed solution of aniline and hydrochloric acid, and then adding the precooled mixed aqueous solution of ammonium persulfate and hydrochloric acid. After reacting in an ice-water bath for 3-6 hours, the mixture is removed, washed, and dried to obtain a polyaniline-modified melamine foam;

[0020] 3) immersing the polyaniline-modified melamine foam obtained in step 2) in an anhydrous ethanol solution of polyethyleneimine and di(3-methoxysilylpropyl)amine, reacting in a water bath at 50-70° C. for 1-2 hours, removing the foam and drying and curing it to obtain a dedoped melamine foam;

[0021] 4) Immersing the dedoped melamine foam obtained in step 3) in an ethanol solution of perfluorooctanoic acid, and then horizontally-rotatingly oscillating on a shaker for 3-8 hours for secondary doping, removing it, cleaning it, and drying it to obtain a three-dimensional porous super hydrophilic / oleophobic charged melamine foam.

[0022] The method for applying the three-dimensional porous superhydrophilic / oleophobic charged melamine foam in separating anionic surfactant-stabilized oil-in-water emulsions is as follows: multiple sheets of superhydrophilic / oleophobic charged melamine foam are stacked and loaded into a separation tube, and anionic surfactant-stabilized oil-in-water emulsion is poured from the top. The emulsion relies on its own gravity to penetrate the melamine foam separation layer, and simultaneously demulsifies and separates the oil and water.

[0023] Preferably, the number of sheets of the super hydrophilic / oleophobic charged melamine foam is 10 to 15 sheets, which are cut into discs with the same diameter as the separation tube, with a diameter of 1.4 to 1.7 cm and a thickness of 0.4 to 0.5 cm; the oil phase in the oil-in-water emulsion is selected from one or more of toluene and peanut oil; the anionic surfactant is sodium dodecyl sulfate or sodium dodecylbenzene sulfonate; the average permeation flux of the emulsion during the separation process is 35,000 L·m -2 ·h -1 The separation efficiency is greater than 97%, and 300 mL can be separated continuously within 3 minutes (effective separation area 1.77 cm -2 ) above lotion.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1) The super-hydrophilic / oleophobic charged melamine foam obtained in the present invention has super-hydrophilicity in air, with a water contact angle of 0°, a certain oleophobicity, with an oil contact angle of 125.5-128.4°, and has a high repellency to oil underwater, with an underwater oil contact angle of 158.9-162.1°, and has excellent anti-oil performance.

[0026] 2) The super-hydrophilic / oleophobic charged melamine foam with large submillimeter pores (0.1-0.2 mm) obtained by the present invention forms a long separation channel by stacking. Combined with the electrostatic attraction mechanism and the introduced fluorine-containing low surface energy, it can quickly and efficiently separate a large amount of anionic surfactant-stabilized oil-in-water emulsion in a short time. The average permeation flux of the emulsion during the separation process is 35000 L·m -2 ·h -1 Above, the separation efficiency is greater than 97%.

[0027] 3) The raw materials for preparing the super hydrophilic / oleophobic charged melamine foam obtained by the present invention are cheap and readily available, the preparation cost is low, the preparation process is simple and mild, it is harmless to the environment, and can be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a diagram of the emulsion separation mechanism of the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam obtained in the present invention;

[0029] Figure 2 This is a scanning electron microscope (SEM) image of the melamine foam that has only been cleaned in Example 1;

[0030] Figure 3 This is a scanning electron microscope (SEM) image of the three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared in Example 1;

[0031] Figure 4 This is a partially enlarged scanning electron microscope (SEM) image of the three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared in Example 1;

[0032] Figure 5 This is a photograph of the contact angle of the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam prepared in Example 1 to deionized water;

[0033] Figure 6 This is a photograph of the contact angle of the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam prepared in Example 1 to toluene;

[0034] Figure 7 This is a photograph of the contact angle of peanut oil on the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam prepared in Example 1;

[0035] Figure 8 This is a photograph of the contact angle of the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam prepared in Example 1 to 1,2-dichloroethane underwater;

[0036] Figure 9 is the X-ray photoelectron spectrum of the three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared in Example 1;

[0037] Figure 10 Zeta potential diagram of the three-dimensional porous superhydrophilic / oleophobic charged melamine foam prepared in Example 1 at different pH values;

[0038] Figure 11 This is a scanning electron microscope (SEM) image of the control group melamine foam prepared in Comparative Example 1;

[0039] Figure 12 This is a scanning electron microscope (SEM) image of the melamine foam of the control group prepared in Comparative Example 2;

[0040] Figure 13 Zeta potential diagrams of the products obtained in Comparative Example 1 and Comparative Example 2;

[0041] Figure 14 The separation flux of the three melamine foams prepared in Example 1, Comparative Example 1 and Comparative Example 2 in the process of separating emulsified oil and water;

[0042] Figure 15The total organic carbon content (TOC) of the filtrate during the process of separating emulsified oil and water using three types of melamine foam prepared in Example 1, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0043] For a better understanding of the present invention, the present invention is further described below with reference to embodiments and drawings. However, the scope of protection claimed by the present invention is not limited to the scope represented by the embodiments.

[0044] Due to the low separation flux of general membrane materials, the easy adsorption saturation of charges in the electrostatic attraction demulsification mechanism, and the limited anti-fouling ability of ordinary superhydrophilic / superoleophilic / underwater superoleophobic materials, special wettability materials cannot simultaneously guarantee: 1) high separation flux; 2) high separation efficiency; 3) high continuous separation volume when separating emulsified oil and water.

[0045] After the polyaniline layer grows on the melamine foam skeleton of the present invention, the originally smooth surface of the foam skeleton becomes rough; after being modified with polyethyleneimine containing rich amino groups, the hydrophilicity and charge of the material are enhanced; the secondary doping of perfluorooctanoic acid makes the foam oleophobic, but does not affect its hydrophilicity. The water contact angle of the material in the air is 0°, and the oil contact angle is 124.2-126.5°. Therefore, the present invention introduces fluorine-containing low surface energy into the prepared superhydrophilic / superoleophilic charged melamine foam to prepare a three-dimensional porous superhydrophilic / oleophobic charged melamine foam, which can achieve rapid separation of a large amount of anionic surfactant-stabilized water-in-oil emulsion in a short time under the drive of the emulsion's own gravity. The emulsion demulsification and separation mechanism is as follows Figure 1As shown in the figure: 1) Super hydrophilicity, which allows water to spread quickly on the surface of the material to form a hydration layer. At the same time, the flow of water in the hydration layer allows the filtrate to pass through the material quickly and promotes the contact between the material surface and the emulsion; 2) Positive charge, the positive charge on the surface of the material produces electrostatic attraction with the anionic surfactant, the surfactant migrates and rearranges on the oil droplets, the oil stability is reduced, and the areas with smaller repulsion between the oil droplets coalesce and break the emulsion; 3) Long separation channel, multiple foams are stacked to form a long separation bed, which prolongs the separation channel and the residence time of the emulsion in the foam. At the same time, the foam is not compressed during the stacking process, maintaining the original large pore size to ensure high separation flux; 4) Introduction of fluorine-containing low surface energy: ① Electrostatic attraction During the demulsification process, the direct contact between some surfactant-coated oil droplets and the material surface is prevented to slow down the adsorption saturation of the surfactant on the material surface. Compared with the super-hydrophilic / super-lipophilic charged melamine foam without the introduction of fluorine-containing low surface energy, its demulsification ability is improved, and the emulsion separation amount is three times that of the super-hydrophilic / super-lipophilic charged melamine foam; ② When a certain amount of surfactant is adsorbed on the material surface, the wettability of the material surface may change. In addition, when the radial intrusion pressure of the emulsion on the material surface is too large, the hydration layer may be destroyed, which will lead to irreversible pollution problems. The dual anti-fouling mechanism formed by the fluorine-containing low surface energy and the hydration layer can enhance the ability to resist oil pollution.

[0046] Example 1

[0047] (1) Melamine foam (size 2 cm × 2 cm × 0.5 cm) was ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min respectively to remove dust and impurities on the surface, and then placed in a forced air drying oven to dry before use.

[0048] (2) Prepare 1 mol / L hydrochloric acid solution, add 0.2 mol / L aniline to the prepared hydrochloric acid solution to form a homogeneous solution A, then immerse the melamine foam obtained in step (1) in the solution, repeatedly squeeze to completely soak the sponge, and then place it in an ice-water bath for precooling; add 0.1 mol / L ammonium persulfate to the prepared hydrochloric acid solution to form a homogeneous solution B, and place it in an ice-water bath for precooling; after precooling, quickly add solution B to solution A (solution A and solution B are equal in amount), place it in a 0°C ice-water bath, and react for 3 hours under 30 rpm magnetic stirring; after the reaction is completed, remove the foam, repeatedly wash it with deionized water, and squeeze the sponge at the same time until the washing solution is neutral, and then place it in a 40°C forced air drying oven for drying for 12 hours before taking it out for use.

[0049] (3) Weigh 0.1 g of polyethyleneimine with a molecular weight of 1800 and 0.1 mL of di(3-methoxysilylpropyl)amine and dissolve them in 25 mL of anhydrous ethanol solution. Immerse a piece of melamine foam obtained in step (2) in the solution, react in a 60°C water bath for 1 hour, then remove the foam, place it in an 80°C oven for drying and curing for 2 hours, and then remove it.

[0050] (4) Weigh 0.25 g of perfluorooctanoic acid and dissolve it in 25 mL of anhydrous ethanol solution, and dissolve it by ultrasonication; immerse the melamine foam obtained in step (3) in the solution, and then oscillate horizontally and rotary on a shaker with a rotation speed of 150 rpm for 5 hours to perform secondary doping; after the end, take it out, rinse it with deionized water 3 to 5 times, and then place it in a 60°C oven to dry for 2 hours to obtain a three-dimensional porous super hydrophilic / oleophobic charged melamine foam.

[0051] Figure 2 This is a scanning electron microscope (SEM) image of the original melamine foam. Figure 2 It can be seen that the unmodified melamine foam skeleton has a smooth surface and a large foam pore size, ranging from about 100 to 200 μm.

[0052] Figure 3 This is a scanning electron microscope (SEM) image of a three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared in Example 1. Figure 3 It can be seen that the modification process did not change the pore size of melamine foam.

[0053] Figure 4 This is a locally enlarged scanning electron microscope (SEM) image of the three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared in Example 1. Figure 4 It can be seen that the surface of the prepared foam skeleton is covered with a layer of papillary polyaniline, which effectively increases the roughness of the foam skeleton surface and also greatly improves the superhydrophilic wetting properties and oleophobic properties.

[0054] Figure 5-8 The following are photos of the contact angles of a three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared in Example 1 to deionized water, toluene, peanut oil in the air, and 1,2-dichloroethane underwater. The contact angle of deionized water on the melamine foam surface in the air is 0°, the contact angle of toluene on the melamine foam surface is 126°, the contact angle of peanut oil on the melamine foam surface is 128°, and the contact angle of 1,2-dichloroethane on the melamine foam surface underwater is 160°, indicating the super hydrophilic / oleophobic / underwater super oleophobic properties of the melamine foam.

[0055] Figure 9 This is the XPS surface elemental analysis diagram of a three-dimensional porous superhydrophilic / oleophobic charged melamine foam prepared in Example 1. The analysis contains a large amount of N elements, which mainly come from the amino groups in polyaniline, polyethyleneimine, di(3-methoxysilylpropyl)amine and the melamine foam itself. The analysis also contains F elements, which come from -CF3 and -CF2 in perfluorooctanoic acid, indicating the successful introduction of fluorine-containing low surface energy.

[0056] Figure 10 This is a Zeta potential diagram of a three-dimensional porous superhydrophilic / oleophobic charged melamine foam prepared in Example 1 at different pH values. The analysis shows that the surface of the melamine foam is positively charged, and as the pH increases, the positive charge decreases slightly but still maintains a strong positive charge, indicating that positive charges can exist in large quantities in the melamine foam.

[0057] Example 2

[0058] (1) Melamine foam (size 2 cm × 2 cm × 0.5 cm) was ultrasonically cleaned with anhydrous ethanol and deionized water for 10 min respectively to remove dust and impurities on the surface, and then placed in a forced air drying oven to dry before use.

[0059] (2) Prepare 1 mol / L hydrochloric acid solution, add 0.3 mol / L aniline to the prepared hydrochloric acid solution to form a homogeneous solution A, then immerse the melamine foam obtained in step (1) in the solution, repeatedly squeeze to completely soak the sponge, and then put it into an ice-water bath for precooling; add 0.15 mol / L ammonium persulfate to the prepared hydrochloric acid solution to form a homogeneous solution B, and put it into an ice-water bath for precooling; after precooling, quickly add solution B to solution A (solution A and solution B are equal in amount), place it in a 3°C ice-water bath, and react for 3 hours under magnetic stirring at 40 rpm; after the reaction is completed, remove the foam, repeatedly wash it with deionized water, and squeeze the sponge at the same time until the washing solution is neutral, and then place it in a 45°C forced air drying oven for drying for 10 hours before taking it out for use.

[0060] (3) Weigh 0.1 g of polyethyleneimine with a molecular weight of 1800 and 0.1 mL of di(3-methoxysilylpropyl)amine and dissolve them in 25 mL of anhydrous ethanol solution. Immerse a piece of melamine foam obtained in step (2) in the solution, react in a 60°C water bath for 1 hour, then remove the foam, place it in an 80°C oven for drying and curing for 2 hours, and then remove it.

[0061] (4) Weigh 0.25 g of perfluorooctanoic acid and dissolve it in 25 mL of anhydrous ethanol solution, and dissolve it by ultrasonication; immerse the melamine foam obtained in step (3) in the solution, and then oscillate horizontally and rotary on a shaker with a rotation speed of 150 rpm for 5 hours to perform secondary doping; after the end, take it out, rinse it with deionized water 3 to 5 times, and then dry it in a 60°C oven for 2 hours to obtain a super hydrophilic / oleophobic charged melamine foam.

[0062] Example 3

[0063] (1) Melamine foam (size 2 cm × 2 cm × 0.5 cm) was ultrasonically cleaned with anhydrous ethanol and deionized water for 10 min respectively to remove dust and impurities on the surface, and then placed in a forced air drying oven to dry before use.

[0064] (2) Prepare 1 mol / L hydrochloric acid solution, add 0.2 mol / L aniline to the prepared hydrochloric acid solution to form a homogeneous solution A, then immerse the melamine foam obtained in step (1) in the solution, repeatedly squeeze to completely soak the sponge, and then put it into an ice-water bath for precooling; add 0.1 mol / L ammonium persulfate to the prepared hydrochloric acid solution to form a homogeneous solution B, and put it into an ice-water bath for precooling; after precooling, quickly add solution B to solution A (solution A and solution B are equal in amount), place it in a 5°C ice-water bath, and react for 4 hours under 30 rpm magnetic stirring; after the reaction is completed, remove the foam, repeatedly wash it with deionized water, and squeeze the sponge at the same time until the washing solution is neutral, and then place it in a 40°C forced air drying oven for drying for 12 hours before taking it out for use.

[0065] (3) Weigh 0.15 g of polyethyleneimine with a molecular weight of 600 and 0.13 mL of di(3-methoxysilylpropyl)amine and dissolve them in 25 mL of anhydrous ethanol solution. Immerse a piece of melamine foam obtained in step (2) in the solution, react in a 60°C water bath for 1 hour, then remove the foam, place it in an 80°C oven for drying and curing for 2 hours, and then remove it.

[0066] (4) Weigh 0.25 g of perfluorooctanoic acid and dissolve it in 25 mL of anhydrous ethanol solution, and dissolve it by ultrasonication; immerse the melamine foam obtained in step (3) in the solution, and then oscillate horizontally and rotary on a shaker with a rotation speed of 150 rpm for 5 hours to perform secondary doping; after the end, take it out, rinse it with deionized water 3 to 5 times, and then dry it in a 60°C oven for 2 hours to obtain a super hydrophilic / oleophobic charged melamine foam.

[0067] Example 4

[0068] (1) Melamine foam (size 2 cm × 2 cm × 0.5 cm) was ultrasonically cleaned with anhydrous ethanol and deionized water for 10 min respectively to remove dust and impurities on the surface, and then placed in a forced air drying oven to dry before use.

[0069] (2) Prepare 1 mol / L hydrochloric acid solution, add 0.2 mol / L aniline to the prepared hydrochloric acid solution to form a homogeneous solution A, then immerse the melamine foam obtained in step (1) in the solution, repeatedly squeeze to completely soak the sponge, and then place it in an ice-water bath for precooling; add 0.1 mol / L ammonium persulfate to the prepared hydrochloric acid solution to form a homogeneous solution B, and place it in an ice-water bath for precooling; after precooling, quickly add solution B to solution A (solution A and solution B are equal in amount), place it in a 0°C ice-water bath, and react for 3 hours under 30 rpm magnetic stirring; after the reaction is completed, remove the foam, repeatedly wash it with deionized water, and squeeze the sponge at the same time until the washing solution is neutral, and then place it in a 40°C forced air drying oven for drying for 12 hours before taking it out for use.

[0070] (3) Weigh 0.1 g of polyethyleneimine with a molecular weight of 1800 and 0.1 mL of di(3-methoxysilylpropyl)amine and dissolve them in 25 mL of anhydrous ethanol solution. Immerse a piece of melamine foam obtained in step (2) in the solution, react in a 55°C water bath for 1.5 hours, then remove the foam, place it in a 70°C oven for drying and curing for 2.5 hours, and then remove it.

[0071] (4) Weigh 0.2 g of perfluorooctanoic acid and dissolve it in 25 mL of anhydrous ethanol solution, and dissolve it by ultrasonication; immerse the melamine foam obtained in step (3) in the solution, and then oscillate horizontally and rotary on a shaker with a rotation speed of 120 rpm for 6 hours to perform secondary doping; after the end, take it out, rinse it with deionized water 3 to 5 times, and then place it in a 60°C oven to dry for 2 hours to obtain a super hydrophilic / oleophobic charged melamine foam.

[0072] Example 5

[0073] (1) Melamine foam (size 2 cm × 2 cm × 0.5 cm) was ultrasonically cleaned with anhydrous ethanol and deionized water for 10 min respectively to remove dust and impurities on the surface, and then placed in a forced air drying oven to dry before use.

[0074] (2) Prepare 1 mol / L hydrochloric acid solution, add 0.3 mol / L aniline to the prepared hydrochloric acid solution to form a homogeneous solution A, then immerse the melamine foam obtained in step (1) in the solution, repeatedly squeeze to completely soak the sponge, and then put it into an ice-water bath for precooling; add 0.15 mol / L ammonium persulfate to the prepared hydrochloric acid solution to form a homogeneous solution B, and put it into an ice-water bath for precooling; after precooling, quickly add solution B to solution A (solution A and solution B are equal in amount), place it in a 0°C ice-water bath, and react for 3 hours under 30 rpm magnetic stirring; after the reaction is completed, remove the foam, repeatedly wash it with deionized water, and squeeze the sponge at the same time until the washing solution is neutral, and then place it in a 45°C forced air drying oven for drying for 12 hours before taking it out for use.

[0075] (3) Weigh 0.12 g of polyethyleneimine with a molecular weight of 1800 and 0.1 mL of di(3-methoxysilylpropyl)amine and dissolve them in 25 mL of anhydrous ethanol solution. Immerse a piece of melamine foam obtained in step (2) in the solution, react in a 60°C water bath for 1 hour, then remove the foam, place it in a 70°C oven for drying and curing for 2.5 hours, and then remove it.

[0076] (4) Weigh 0.2 g of perfluorooctanoic acid and dissolve it in 25 mL of anhydrous ethanol solution, and dissolve it by ultrasonication; immerse the melamine foam obtained in step (3) in the solution, and then oscillate horizontally and rotary on a shaker with a rotation speed of 150 rpm for 5 hours to perform secondary doping; after the end, take it out, rinse it with deionized water 3 to 5 times, and then place it in a 60°C oven to dry for 1.5 hours to obtain a super hydrophilic / oleophobic charged melamine foam.

[0077] Example 6

[0078] The contact angle of a super hydrophilic / oleophobic charged melamine foam prepared in Examples 1 to 5 was measured at room temperature using the JC2000C1 contact angle meter of Shanghai Zhongchen Digital Technology Equipment Co., Ltd., including contact angle experiments of water and oil in the air and contact angle experiments of oil underwater. The specific results are shown in Table 1. The test process adopts a general test method. When testing the water contact angle of the foam, the material is placed on the test platform, and a micro syringe is used to inject 5 μL of water droplets onto the surface of the material. When testing the underwater contact angle of the foam, the foam is placed in a transparent quartz glass tank filled with water, and a micro syringe is used to inject 5 μL of oil droplets onto the surface of the material. All images (or videos) during the contact angle test are captured by the high-speed camera provided in the contact angle meter. During the test, 5 different points are selected for the same material and the average value is taken.

[0079] Table 1

[0080]

[0081] As can be seen from Table 1, the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam prepared by the method of the present invention has a contact angle of 0° for water in air, a contact angle of 125.5-128.4° for oil (toluene and peanut oil) in air, and a contact angle of 1,2-dichloroethane underwater between 158.9-162.1°, indicating that it has super-hydrophilic / oleophobic / underwater super-oleophobic properties. This is because polyaniline increases the roughness of the melamine foam, and the surface is compositely modified with high-surface-energy amino groups and low-surface-energy fluorine-containing groups, which enables the melamine foam to exhibit both super-hydrophilicity and oleophobicity in air.

[0082] The present invention was compared with super hydrophilic / underwater super oleophobic and hydrophobic / oleophobic melamine foam as a control group.

[0083] Comparative Example 1

[0084] (1) Melamine foam (size 2 cm × 2 cm × 0.5 cm) was ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min respectively to remove dust and impurities on the surface, and then placed in a forced air drying oven to dry before use.

[0085] (2) Prepare 1 mol / L hydrochloric acid solution, add 0.2 mol / L aniline to the prepared hydrochloric acid solution to form a homogeneous solution A, then immerse the melamine foam obtained in step (1) in the solution, repeatedly squeeze to completely soak the sponge, and then place it in an ice-water bath for precooling; add 0.1 mol / L ammonium persulfate to the prepared hydrochloric acid solution to form a homogeneous solution B, and place it in an ice-water bath for precooling; after precooling, quickly add solution B to solution A (solution A and solution B are equal in amount), place it in a 0°C ice-water bath, and react for 3 hours under 30 rpm magnetic stirring; after the reaction is completed, remove the foam, repeatedly wash it with deionized water, and squeeze the sponge at the same time until the washing solution is neutral, and then place it in a 40°C forced air drying oven for drying for 12 hours before taking it out for use.

[0086] (3) Weigh 0.1 g of polyethyleneimine with a molecular weight of 1800 and 0.1 mL of di(3-methoxysilylpropyl)amine and dissolve them in 25 mL of anhydrous ethanol solution. Immerse a piece of melamine foam obtained in step (2) in the solution, react in a 60°C water bath for 1 hour, then take out the foam, place it in an 80°C oven for drying and curing for 2 hours, and then take it out to obtain a superhydrophilic / superoleophilic / underwater superoleophobic charged melamine foam as a control group.

[0087] Figure 11 This is a scanning electron microscope (SEM) image of the super hydrophilic / super oleophilic / underwater super oleophobic charged melamine foam prepared in Comparative Example 1. Figure 11 It can be seen that the surface roughness and pore size of the melamine foam prepared in Comparative Example 1 are not significantly different from those of the melamine foam prepared in Example 1.

[0088] Comparative Example 2

[0089] (1) Melamine foam (size 2 cm × 2 cm × 0.5 cm) was ultrasonically cleaned with anhydrous ethanol and deionized water for 15 min respectively to remove dust and impurities on the surface, and then placed in a forced air drying oven to dry before use.

[0090] (2) Prepare 1 mol / L hydrochloric acid solution, add 0.2 mol / L aniline to the prepared hydrochloric acid solution to form a homogeneous solution A, then immerse the melamine foam obtained in step (1) in the solution, repeatedly squeeze to completely soak the sponge, and then place it in an ice-water bath for precooling; add 0.1 mol / L ammonium persulfate to the prepared hydrochloric acid solution to form a homogeneous solution B, and place it in an ice-water bath for precooling; after precooling, quickly add solution B to solution A (solution A and solution B are equal in amount), place it in a 0°C ice-water bath, and react for 3 hours under 30 rpm magnetic stirring; after the reaction is completed, remove the foam, repeatedly wash it with deionized water, and squeeze the sponge at the same time until the washing solution is neutral, and then place it in a 40°C forced air drying oven for drying for 12 hours before taking it out for use.

[0091] (3) Using ammonia water as a dedoping agent, a piece of melamine foam obtained in step (2) was immersed in the ammonia solution, and horizontally-rotationally shaken on a shaker with a rotation speed of 150 rpm for 1 hour, then taken out, rinsed with deionized water 3 to 5 times, and placed in a 60°C oven to dry for 2 hours before being taken out.

[0092] (4) Weigh 0.25 g of perfluorooctanoic acid and dissolve it in 25 mL of anhydrous ethanol solution, and dissolve it by ultrasonication; immerse the melamine foam obtained in step (3) in the solution, and then oscillate horizontally and rotary on a shaker with a rotation speed of 150 rpm for 10 hours to perform secondary doping; after the end, take it out, rinse it with deionized water 3 to 5 times, and then dry it in a 60°C oven for 2 hours to obtain a hydrophobic / oleophobic melamine foam as a control group.

[0093] Figure 12 This is a scanning electron microscope (SEM) image of the hydrophobic / oleophobic melamine foam prepared in Comparative Example 2. Figure 12 It can be seen that the surface roughness and pore size of the melamine foam prepared in Comparative Example 2 are not significantly different from those of the melamine foam prepared in Example 1, because the roughness of the prepared foam surface is provided by the growing papillary polyaniline.

[0094] Figure 13 The Zeta potential diagrams of the melamine foams prepared in Comparative Example 1 and Comparative Example 2 at pH 7 show that the Zeta potential of the super-hydrophilic / underwater super-oleophobic charged melamine foam prepared in Comparative Example 1 is similar to that of the super-hydrophilic / oleophobic charged melamine foam prepared in Example 1. Both are provided by a large number of amino groups on polyethyleneimine and a small number of imino groups on polyaniline. However, the hydrophobic / oleophobic melamine foam prepared in Comparative Example 2 is only provided by the -NH- on polyaniline and the H + The binding provides a small amount of charge, so the zeta potential is not high.

[0095] Application Examples

[0096] Separation test of oil-in-water emulsion

[0097] The following oil-water separation test was performed on a three-dimensional porous superhydrophilic / oleophobic charged melamine foam prepared in Examples 1 to 5: the prepared three-dimensional porous superhydrophilic / oleophobic charged melamine foam was cut into a cylindrical shape with a diameter of 1.5 cm. 11 cut foam pieces were stacked in sequence and loaded into the bottom of a glass separation tube (without compression). Then, a piece of uncut foam was placed at the very bottom of the separation tube. The sand core filter device (the sand core had been removed) and the separation tube filled with foam were clamped and sealed with a clamp. An anionic surfactant-stabilized oil-in-water emulsion was poured from the top, maintaining the height of the emulsion column above the separation column at approximately 2 cm. The emulsion, under its own gravity, permeated the melamine foam separation layer. During this period, the emulsified oil droplets and the charged foam surface were demulsified and coalesced by electrostatic attraction. Due to the dual anti-fouling effect of the hydration layer and low surface energy on the foam surface, some oil droplets were discharged along with the water phase, while the remaining portion could be mostly discharged by pressurization, thereby reducing the problem of severe reduction in separation flux caused by oil clogging. Separation flux (J, L·m -2 ·h -1 ) and separation efficiency (R, %) were calculated using the following formulas (1) and (2), respectively. The specific results of separation efficiency and permeate flux during the continuous separation of 300 mL of anionic surfactant-stabilized toluene-in-water emulsion are shown in Table 2.

[0098]

[0099] Where V(L) is the filtration volume, A(m 2 ) is the effective filtration area, and t(h) is the filtration time. feed and C filtration (ppm) are the TOC contents in the original emulsion and the filtrate, respectively.

[0100] Table 2

[0101]

[0102]

[0103] The results show that the separation flux of Examples 1 to 5 is all above 40,000 L·m -2 ·h -1 After separating 500 mL of emulsified oil and water, the separation flux remains at 20,000 L·m -2 ·h -1The above results demonstrate high emulsified oil-water permeability. The separation efficiencies of Examples 1-5, measured before separation of 300 mL of emulsified oil-water, all remained above 97%, demonstrating high emulsified oil-water separation performance. The separation efficiency is calculated based on the organic carbon content. Due to the repulsive effect of the introduced fluorinated low surface energy on some surfactants, the filtrate contains some surfactants, which are used as part of the organic carbon content in the filtrate for separation efficiency calculation. Therefore, the actual separation efficiency for oil in the emulsion is higher.

[0104] After cutting the super-hydrophilic / super-oleophilic / underwater super-oleophobic melamine foam prepared in Comparative Example 1 and the hydrophobic / oleophobic melamine foam prepared in Comparative Example 2, they were loaded into two glass tubes respectively. The number of loading sheets (12 sheets) and the process were consistent with those described above. To ensure that the immersion pressure of the emulsified oil-water separation process is consistent, the emulsion liquid column height above the separation column is maintained at about 2 cm. The melamine foam prepared in Comparative Example 2 was first infiltrated with anhydrous ethanol before separating the emulsion.

[0105] Figure 14 、 Figure 15 The separation flux of three melamine foams with different wettability prepared in Example 1, Comparative Example 1 and Comparative Example 2 when separating toluene-in-water emulsion stabilized by anionic surfactant and the TOC content in the filtrate. Figure 14 As can be seen, during the initial separation process, the melamine foams prepared in Example 1 and Comparative Example 1 exhibited superhydrophilic properties, resulting in rapid water penetration and a high separation flux. As the amount of emulsion separated increased, the separation fluxes of both the melamine foams of Example 1 and Comparative Example 1 decreased, but the rate of decrease was faster in Comparative Example 1. This may be because the fluorine-containing low surface energy introduced into the melamine foam prepared in Example 1 possessed certain oil-repellent properties. During the separation process, under the dual antifouling effects of the hydration layer and the fluorine-containing low surface energy, some oil droplets were discharged with the flowing aqueous phase. Therefore, the problem of oil clogging in the foam was less severe than that of the melamine foam prepared in Comparative Example 1. Due to its hydrophobic nature, the melamine foam prepared in Comparative Example 2 exhibited a very low separation flux throughout the entire separation process. Furthermore, due to its oleophobic nature, the separation flux remained very stable and decreased slowly during the separation process. Figure 15It can be seen that the melamine foam prepared in Comparative Example 1 has a low TOC content in the filtrate during the first 100 mL of emulsion separation, and has a good emulsion separation effect; the melamine foam prepared in Example 1 has a low TOC content in the filtrate during the first 300 mL of emulsion separation, and has an excellent emulsion separation effect; the melamine foam prepared in Comparative Example 2 has an excellent separation effect during the first 400 mL of emulsion separation. This shows that the separation abilities of the three different foams are different. Since the Zeta potentials of the melamine foam surfaces prepared in Example 1 and Comparative Example 1 are similar, the Zeta potential of the melamine foam surface prepared in Comparative Example 2 is lower than that of the first two sponges. Therefore, the difference in the emulsion separation amount is not caused by the size of the material surface charge, but because the introduction of the fluorine-containing low surface energy slows down the adsorption of the surfactant on the material surface, improves the demulsification ability, and thus improves the emulsion separation amount.

[0106] The three-dimensional porous super-hydrophilic / oleophobic charged melamine foam of the present invention can be used for rapid demulsification and separation of oil-in-water emulsions stabilized by anionic surfactants: multiple sheets of super-hydrophilic / oleophobic charged melamine foam are stacked and loaded into a separation tube, and the oil-in-water emulsion stabilized by anionic surfactants is poured from the top. The emulsion relies on its own gravity to permeate through the melamine foam separation layer, and demulsification and oil-water separation are carried out simultaneously. The average permeation flux of the emulsion during the separation process is 35000 L·m -2 ·h -1 Above, the separation efficiency is greater than 97%, on the existing separation device (effective separation area 1.77cm -2 ) can continuously separate more than 300mL of emulsion within 3 minutes. Compared with the existing technology, it has obvious advantages:

[0107] Table 3 shows the comparison between the three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared by the present invention and the prior art materials in terms of one-time continuous separation of surfactant-stabilized emulsified oil and water.

[0108] Table 3

[0109]

[0110]

[0111] In the table, prior art 1 (J.Hazard.Mater.2021,415,125677), prior art 2 (ACSAppl.Mater.Interfaces.2020,12,19130-19139) and prior art 3 (J.Hazard.Mater.2021,420126681) use membrane materials as base materials, modify them to obtain superhydrophilic / underwater superoleophobic membranes, which can be used for the separation of surfactant-stabilized oil-in-water emulsions. It can be seen from Table 3 that the separation flux and one-time emulsion separation amount are not high when separating oil-in-water emulsions.

[0112] Prior Art 4 (Sep. Purif. Technol. 234, 2020, 116082) introduced a low-surface-energy substance on the membrane surface to enhance the membrane's antifouling capabilities, extending the emulsion separation time to 60 minutes. However, the separation flux was extremely low, and the total emulsion separation volume remained low. In particular, prior Art 1 to 4, which utilize membranes as substrates, require pressurized separation of oil-in-water emulsions, which undoubtedly increases energy consumption.

[0113] Prior art 5 (Sep. Purif. Technol. 2022, 289, 120779) uses stainless steel mesh as the base material. The modified stainless steel mesh obtained by superhydrophilic / underwater superoleophobic stainless steel mesh can be used for surfactant-stabilized water-in-oil emulsion separation under the gravity of the emulsion itself, but because its separation flux is not high, the one-time continuous emulsion separation amount is very low.

[0114] Prior art 6 (J.Mater.Chem.A.2021,9,13170) uses the modified superhydrophilic / underwater superoleophobic copper foam to separate surfactant-stabilized oil-in-water emulsions. Similar to the present invention, it utilizes the electrostatic attraction mechanism and long separation channel effect to give it an ultra-high separation flux. However, during the demulsification separation process, due to electrostatic attraction, a large amount of surfactant is directly adsorbed on the surface of the material, resulting in the rapid neutralization of the positive charge on the surface of the material, a decrease in positive charge, insufficient demulsification ability, and a low total separation amount.

[0115] Prior art 7 (Green Chem., 2015, 17, 3093), prior art 8 (ACS Appl. Mater. Interfaces. 2019, 11, 36638-36648) and prior art 9 (J. Hazard. Mater. 2021, 408, 124408) use foam as the base. Their own or modified superhydrophilic / underwater superoleophobic properties enable them to be used for the separation of surfactant-stabilized oil-in-water emulsions after compression. However, due to the "size screening" effect, the separation flux is too low, the emulsion separation time is very long, and the total separation amount is not high.

[0116] Existing technology 10 (J.Hazard.Mater.2022,435,129003) also uses sponge as the base material, and utilizes the superhydrophilicity, negative charge and porous properties of the modified foam to separate surfactant-stabilized water-in-oil emulsions by adsorption. However, due to its limited surface charge, its one-time emulsion separation amount is also very low.

[0117] Compared with the above existing technologies, the three-dimensional porous super hydrophilic / oleophobic charged melamine foam prepared by the present invention has obvious advantages in separation flux, total separation amount and separation time.

[0118] The implementation methods of the present invention are not limited to the above-mentioned embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A three-dimensional porous super-hydrophilic / oleophobic charged melamine foam, characterized by: The dedoped melamine foam is obtained by immersing the dedoped melamine foam in an anhydrous ethanol solution of perfluorooctanoic acid, followed by secondary doping, and then washing and drying. The dedoped melamine foam is obtained by immersing polyaniline-modified melamine foam in an anhydrous ethanol solution of polyethyleneimine and di(3-trimethoxysilylpropyl)amine, reacting in a water bath at 50-70°C for 1-2 hours, and then drying and solidifying. The polyaniline-modified melamine foam is obtained by immersing the melamine foam in a pre-cooled mixed solution of aniline and hydrochloric acid, then adding a pre-cooled mixed aqueous solution of ammonium persulfate and hydrochloric acid, reacting in an ice-water bath for 3-6 hours, and then taking out, washing, and drying.

2. The three-dimensional porous super hydrophilic / oleophobic charged melamine foam according to claim 1, characterized in that: The secondary doping is achieved by horizontal-rotational oscillation on a shaker for 3-8 hours; the rotation speed of the shaker during the horizontal-rotational oscillation is 150-200 rpm; the concentration of the perfluorooctanoic acid in anhydrous ethanol is 6-12 g / L.

3. The three-dimensional porous super hydrophilic / oleophobic charged melamine foam according to claim 1, characterized in that: The molecular weight of the polyethyleneimine is 600-1800; the concentration of the polyethyleneimine in anhydrous ethanol is 3.5-6 g / L; and 3.5-5.5 mL of di(3-trimethoxysilylpropyl)amine is added to each liter of anhydrous ethanol.

4. The three-dimensional porous super hydrophilic / oleophobic charged melamine foam according to claim 1, characterized in that: The concentration of aniline in the ice-water bath reaction solution is 0.05-0.15 mol / L, the concentration ratio of ammonium persulfate to aniline is 1:1.8-1:2.2, and the concentration of hydrochloric acid in the aniline and hydrochloric acid as well as in the ammonium persulfate and hydrochloric acid is 0.8-1.2 mol / L; and the precooling is carried out in an ice-water bath at 0-5°C.

5. The three-dimensional porous super hydrophilic / oleophobic charged melamine foam according to claim 1, characterized in that: The ice water bath temperature is 0-5°C, and the magnetic stirring speed is 20-40 rpm; the drying and curing is carried out in an oven, the drying and curing temperature is 70-90°C, and the drying and curing time is 1.5-3 hours.

6. The three-dimensional porous super hydrophilic / oleophobic charged melamine foam according to claim 1, characterized in that: The cleaning and drying after the secondary doping are to rinse the foam with deionized water 3 to 5 times, and to dry it in an oven at a temperature of 50 to 80° C. and a drying time of 1 to 3 hours; The cleaning after the reaction in the ice water bath is to repeatedly wash with deionized water while squeezing the sponge until the cleaning liquid is neutral; the cleaning and drying after the reaction in the ice water bath is to dry in an oven after cleaning, the drying temperature is 40-50°C, and the drying time is 8-12h.

7. The three-dimensional porous super hydrophilic / oleophobic charged melamine foam according to claim 1, characterized in that: The melamine foam is ultrasonically cleaned with anhydrous ethanol and deionized water for 10-15 minutes respectively before use, and then dried.

8. The method for preparing the three-dimensional porous super hydrophilic / oleophobic charged melamine foam according to any one of claims 1 to 7, characterized in that The steps include: 1) Clean and dry the melamine foam; 2) preparing a mixed solution of aniline and hydrochloric acid and a mixed solution of ammonium persulfate and hydrochloric acid respectively, precooling them in an ice-water bath, immersing the melamine foam obtained in step 1) in the precooled mixed solution of aniline and hydrochloric acid, and then adding the precooled mixed aqueous solution of ammonium persulfate and hydrochloric acid. After reacting in an ice-water bath for 3-6 hours, the mixture is removed, washed, and dried to obtain a polyaniline-modified melamine foam; 3) immersing the polyaniline-modified melamine foam obtained in step 2) in an anhydrous ethanol solution of polyethyleneimine and di(3-trimethoxysilylpropyl)amine, reacting in a water bath at 50-70° C. for 1-2 hours, removing the foam and drying and curing it to obtain a dedoped melamine foam; 4) Immersing the dedoped melamine foam obtained in step 3) in an ethanol solution of perfluorooctanoic acid, and then horizontally-rotatingly oscillating on a shaker for 3-8 hours for secondary doping, removing it, cleaning it, and drying it to obtain a three-dimensional porous super hydrophilic / oleophobic charged melamine foam.

9. A method for using the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam according to any one of claims 1 to 7 in separating an anionic surfactant-stabilized oil-in-water emulsion, characterized in that: Multiple sheets of superhydrophilic / oleophobic charged melamine foam are stacked and loaded into a separation tube, and an anionic surfactant-stabilized water-in-oil emulsion is poured in from the top. The emulsion relies on its own gravity to penetrate the melamine foam separation layer, simultaneously breaking the emulsion and separating the oil and water.

10. The method for using the three-dimensional porous super-hydrophilic / oleophobic charged melamine foam according to claim 9 in separating anionic surfactant-stabilized oil-in-water emulsions, characterized in that: The number of sheets of the super-hydrophilic / oleophobic charged melamine foam is 10 to 15, which are cut into discs with the same diameter as the separation tube, with a diameter of 1.4 to 1.7 cm and a thickness of 0.4 to 0.5 cm; the oil phase in the oil-in-water emulsion is selected from one or more of toluene and peanut oil; the anionic surfactant is sodium dodecyl sulfate or sodium dodecylbenzene sulfonate; the average permeation flux of the emulsion during the separation process is 35,000 L·m -2 ·h -1 Above, the separation efficiency is greater than 97%.

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