阅读说明：本技术 一种超双疏膜及其制备方法和应用 (Super-amphiphobic membrane and preparation method and application thereof ) 是由 黄满红 孟李君 郑盛阳 吕嫣 孔壮 于 2021-07-20 设计创作，主要内容包括：本发明涉及一种超双疏膜及其制备方法和应用,该超双疏膜包括基体膜以及先后在基体膜上形成的PDA/PEI沉积层和二氧化硅粒子矿化层,且该超双疏膜具有高含氟表面；制备方法包括：将多巴胺和PEI溶解于Tris缓冲溶液,配制沉积溶液；将润湿后的基体膜置于其中沉积；通过原硅酸四甲酯、盐酸和PBS缓冲液配制矿化溶液；将沉积膜置于其中进行表面矿化；最后对膜表面进行低表面能改性。与现有技术相比,本发明超双疏膜的粗糙表面结构以及超低表面能赋予膜超双疏特性,使得其水接触角大于167°,矿物油接触角大于135°,该膜用于DCMD工艺时,能够抵御含有0.5mM SDS的高盐水的润湿,获得稳定的MD性能。(The invention relates to a super-amphiphobic membrane and a preparation method and application thereof, wherein the super-amphiphobic membrane comprises a substrate membrane and a PDA/PEI (personal digital assistant/polyetherimide) deposition layer and a silica particle mineralization layer which are sequentially formed on the substrate membrane, and the super-amphiphobic membrane has a high fluorine-containing surface; the preparation method comprises the following steps: dissolving dopamine and PEI in a Tris buffer solution to prepare a deposition solution; depositing the wetted substrate film; preparing a mineralized solution by using tetramethyl orthosilicate, hydrochloric acid and a PBS (phosphate buffer solution); placing the deposited film therein for surface mineralization; and finally, modifying the surface of the membrane with low surface energy. Compared with the prior art, the rough surface structure and the ultralow surface energy of the super-amphiphobic membrane endow the membrane with super-amphiphobic characteristics, so that the water contact angle of the membrane is more than 167 degrees, the mineral oil contact angle of the membrane is more than 135 degrees, and when the membrane is used for a DCMD (chemical vapor deposition) process, the membrane can resist the wetting of high-salt water containing 0.5mM SDS (sodium dodecyl sulfate), and stable MD performance is obtained.)

1. A super-amphiphobic membrane is characterized by comprising a substrate membrane, and a PDA/PEI deposition layer and a silica particle mineralization layer which are sequentially formed on the substrate membrane, wherein the super-amphiphobic membrane has a high fluorine-containing surface.

2. The super-amphiphobic membrane of claim 1, wherein the matrix membrane is a microporous hydrophobic membrane comprising a PP membrane, a PVDF membrane, or other microporous membrane material with low surface energy.

3. The super-amphiphobic membrane of claim 1, wherein the high fluorine-containing surface is formed by de-ethanolic reaction of at least one of PDTS or 9-FAS with a mineralized layer of silica particles to graft fluorine-containing branches to the membrane surface.

4. The preparation method of the super amphiphobic membrane according to any one of claims 1 to 3, characterized by comprising the following steps:

s1: dissolving dopamine and polyethyleneimine in Tris buffer solution to prepare deposition solution, placing the wetted substrate film in the deposition solution for deposition, and forming a PDA/PEI codeposition layer on the substrate film as a medium layer of organic and inorganic interfaces;

s2: dissolving tetramethyl orthosilicate in hydrochloric acid solution and PBS buffer solution which are equal in amount to prepare mineralized solution, soaking the membrane prepared in the step S1 in the mineralized solution, and carrying out surface mineralization to enable silicon dioxide particles to uniformly grow on the membrane wall to form a silicon dioxide particle mineralized layer;

s3: and (2) carrying out de-ethanol reaction on at least one of PDTS or 9-FAS and a silicon dioxide particle mineralized layer, grafting a fluorine-containing branched chain on the surface of the membrane, and carrying out low surface energy modification on the surface of the membrane to obtain the super-amphiphobic membrane.

5. The method for preparing the super-amphiphobic membrane according to the claim 4, wherein the step S1 comprises any one or more of the following conditions:

(i) the quality of dopamine and polyethyleneimine is the same;

(ii) the concentration of the dopamine and the polyethyleneimine is 1-4 g/L;

(iii) the concentration of the Tris buffer solution is 0.1-0.5mol/L, and the pH value is 8-9;

(iv) the matrix membrane is a microporous hydrophobic membrane with the aperture of 0.22-0.45 mu m;

(v) soaking the substrate membrane in an organic solvent for sufficient wetting, and absorbing excess solvent on the surface of the membrane by using filter paper to obtain the wetted substrate membrane, wherein the organic solvent is ethanol or isopropanol, and the soaking time is 20-50 seconds;

(vi) the deposition time is 1-6 hours;

(vii) the method also comprises the steps of rinsing with ultrapure water after deposition, and drying in an oven, wherein the drying time is 6-24 hours.

6. The method for preparing the super-amphiphobic membrane according to the claim 4, wherein the step S2 comprises any one or more of the following conditions:

(i) the PBS buffer solution is prepared by adopting monopotassium phosphate and dipotassium phosphate and is obtained by adjusting the pH value of the solution by using dilute hydrochloric acid;

(ii) the dosage ratio of the tetramethyl orthosilicate to the PBS buffer solution and the hydrochloric acid solution is 0.1-0.2 mL:10mL:10 mL;

(iii) the solubility of the hydrochloric acid solution is 0.1 mM;

(iv) the soaking time is 2-10 hours;

(v) also comprises a drying process after the surface mineralization, wherein the drying temperature is 65 ℃, and the drying time is at least 24 hours.

7. The method for preparing the super-amphiphobic membrane according to the claim 4, wherein the step S3 comprises any one or more of the following conditions:

(i) mixing absolute ethyl alcohol and at least one of PDTS or 9-FAS to prepare a low surface energy modification solution, and soaking the membrane obtained in the step S2 in the low surface energy modification solution to modify the surface of the membrane with low surface energy;

(ii) the dosage ratio of the absolute ethyl alcohol to the PDTS or 9-FAS is 22.55mL to 0.45 mL;

(iii) and step S3, the whole process is carried out under the protection of argon.

8. The method for preparing the super-amphiphobic membrane according to claim 4, further comprising the step S4: placing the super-amphiphobic membrane prepared in the step S3 in a vacuum drying oven to enable the super-amphiphobic membrane to react fully; the temperature of the vacuum oven is 80-90 ℃ and the time is 2-3 hours.

9. Use of a super-amphiphobic membrane according to any of claims 1 to 3, wherein said super-amphiphobic membrane is used in a direct contact membrane distillation process for desalting a high salt water containing SDS.

10. Use of a super-amphiphobic membrane according to claim 9, wherein the salt component in the high salt water is sodium chloride or other inorganic salt, at a concentration of 10-100g/L, and the concentration of SDS is 0-0.5mM, (and not 0).

Technical Field

The invention belongs to the technical field of membranes for membrane distillation, and particularly relates to a super-amphiphobic membrane and a preparation method and application thereof.

Background

The Membrane Distillation (MD) technology is a new Membrane separation technology in recent years, has the advantages of low energy consumption, low Membrane pollution, high rejection rate, simple operation and the like, and has wide application prospect in the aspect of desalting high salt water. Traditional microporous hydrophobic membranes such as PP membranes and PVDF membranes have low permeation flux when used in the MD process, have the defects of easy scaling and easy wetting after long-time running, and greatly limit the practical industrial application of MD, so that the exploration and preparation of super-amphiphobic MD membranes which have excellent performance and can resist the wetting of low-surface tension substances are urgently needed, on one hand, the MD performance can be effectively improved, and the stability of long-time running is improved. On the other hand, the application field of the MD technology can be further widened.

The construction of the super-amphiphobic membrane has two necessary conditions, namely that the membrane surface has high roughness and can form a concave-convex structure, and the membrane material has ultralow surface energy. Following these two conditions, most of the current super-amphiphobic film preparation methods add nanoparticles such as silicon dioxide, titanium dioxide and the like on the film to construct a rough concave-convex structure, form an organic-inorganic composite film, and then reduce the surface energy of the film through surface fluorination. When the composite membrane prepared by the method is used in the MD process, inorganic particles are easy to fall off after long-time running, and the defect that the inorganic particles are not uniformly coated on the membrane easily exists.

Disclosure of Invention

The invention aims to solve the defects that an MD (membrane distillation) membrane is easy to wet by low surface energy liquid, has poor stability in long-time operation and the like in the prior art, and provides a super-amphiphobic membrane and a preparation method and application thereof.

The purpose of the invention can be realized by the following technical scheme:

the invention provides a super-amphiphobic membrane, which comprises a substrate membrane and a PDA/PEI (poly dopamine/polyethyleneimine) deposition layer and a silica particle mineralization layer which are sequentially formed on the substrate membrane, wherein the super-amphiphobic membrane has a high fluorine-containing surface.

The super-amphiphobic membrane has a rough concave-convex structure and ultra-low surface energy, and can resist wetting of various liquids with different surface energies. When the high-surface-energy-content water-based oil-based emulsion is applied to the MD technology, the wetting of low-surface-energy substances in high-salt water can be effectively prevented, and the stable MD performance is maintained.

Preferably, the matrix membrane is a microporous hydrophobic membrane, and comprises a PP membrane, a PVDF membrane or other microporous membrane materials with low surface energy.

Preferably, the high fluorine-containing surface is formed by grafting fluorine-containing branches (carbon-fluorine branches) onto the membrane surface by de-ethanolic reaction of at least one of PDTS (1H, 2H-perfluorodecyltriethoxysilane) or 9-FAS (triethoxy (1H, 2H-nonafluorohexyl) silane) with the silica particle mineralized layer.

The second aspect of the present invention provides a method for preparing the super-amphiphobic membrane, which is characterized by comprising the following steps:

s1: dissolving dopamine and polyethyleneimine in Tris buffer solution to prepare deposition solution, placing the wetted substrate film in the deposition solution for deposition, and forming a PDA/PEI codeposition layer on the substrate film as a medium layer of organic and inorganic interfaces;

s2: dissolving tetramethyl orthosilicate in hydrochloric acid solution and PBS buffer solution which are equal in amount to prepare mineralized solution, soaking the membrane prepared in the step S1 in the mineralized solution, and carrying out surface mineralization to enable silicon dioxide particles to uniformly grow on the membrane wall to form a silicon dioxide particle mineralized layer;

s3: and (2) carrying out de-ethanol reaction on at least one of PDTS or 9-FAS and a silicon dioxide particle mineralized layer, grafting a fluorine-containing branched chain on the surface of the membrane, and carrying out low surface energy modification on the surface of the membrane to obtain the super-amphiphobic membrane.

The inorganic particles are grown on the surface of the membrane by adopting a chemical bond grafting or electrostatic attraction method, so that the inorganic particles can be uniformly distributed on the membrane, and the firmness can be ensured, so that the inorganic particles are not easy to fall off from the surface of the membrane. The bionic co-deposition technology of polydopamine/polyethyleneimine (PDA/PEI) can regulate and control the interface compatibility of the organic-inorganic composite membrane, and is favorable for preparing a defect-free high-performance composite membrane. PDA/PEI is deposited on a microporous PVDF membrane, then the membrane is soaked in a precursor tetramethyl orthosilicate solution, and silicon dioxide particles which are uniformly coated can be generated on the membrane wall through hydrolysis under the weak acid condition, so that the concave-convex structure is obtained. Finally, the super-amphiphobic membrane can be obtained through low surface energy modification. The film has high water contact angle and high contact angle for low surface energy liquid. The method is used for the MD process and can be used for treating high-salt wastewater with low surface energy.

Preferably, in step S1, the dopamine and polyethyleneimine are of the same mass.

Preferably, in the step S1, the concentration of both dopamine and polyethyleneimine is 1-4 g/L; further preferably, the concentration of dopamine and polyethyleneimine are both 2 g/L.

Preferably, in step S1, the concentration of the Tris buffer solution is 0.1-0.5mol/L and the pH value is 8-9.

Preferably, in step S1, the substrate membrane is a microporous hydrophobic membrane with a pore size of 0.22-0.45 μm.

Preferably, in step S1, the substrate film is soaked in an organic solvent to be sufficiently wetted, and excess solvent on the surface of the film is absorbed by using filter paper, so as to obtain the wetted substrate film, wherein the organic solvent is ethanol or isopropanol, and the soaking time is 20-50 seconds.

Preferably, in step S1, the deposition time is 1-6 hours.

Preferably, step S1 further includes rinsing with ultrapure water after deposition, and drying in an oven, wherein the drying time is 6-24 hours.

Preferably, in step S2, the PBS buffer is prepared by using potassium dihydrogen phosphate and dimethyl hydrogen phosphate, and adjusting the pH of the solution using dilute hydrochloric acid.

Preferably, in step S2, the ratio of the amount of the tetramethyl orthosilicate to the amount of the PBS buffer solution and the hydrochloric acid solution is 0.1-0.2 mL:10mL:10 mL; further preferably, the ratio of the amount of tetramethylorthosilicate to the amount of PBS buffer and hydrochloric acid solution is 0.15mL:10mL:10 mL.

Preferably, in step S2, the hydrochloric acid solution has a solubility of 0.1 mM.

Preferably, in step S2, the soaking time is 2-10 hours.

Preferably, step S2 further includes a drying process after the surface mineralization, wherein the drying temperature is 65 ℃, and the drying time is at least 24 hours.

Preferably, in step S3, the low surface energy modification solution is prepared by mixing absolute ethanol with at least one of PDTS or 9-FAS, and the membrane obtained in step (2) is immersed in the low surface energy modification solution to achieve low surface energy modification of the membrane surface.

Preferably, in step S3, the ratio of the amount of the absolute ethanol to the amount of PDTS or 9-FAS is 22.55mL to 0.45 mL.

Preferably, in step S3, the whole process of step S3 is performed under an argon protective atmosphere.

Preferably, the method further comprises step S4: placing the super-amphiphobic membrane prepared in the step S3 in a vacuum drying oven to enable the super-amphiphobic membrane to react fully; the temperature of the vacuum oven is 80-90 ℃ and the time is 2-3 hours.

In a third aspect, the invention provides the use of the super-amphiphobic membrane in a Direct Contact Membrane Distillation (DCMD) process for desalting a high brine containing SDS.

Preferably, the salt component in the high-salt water is sodium chloride or other inorganic salt at a concentration of 10-100g/L and the concentration of SDS is 0-0.5mM (and not 0).

Preferably, in desalting the high-salt water containing SDS, the temperature of the raw material liquid is controlled to 50-90 ℃ and the temperature of the penetrating liquid is controlled to 10-25 ℃.

Compared with the prior art, the super-amphiphobic membrane prepared by the PDA/PEI deposition technology, the mineralization technology and the low surface energy modification technology has ultra-low surface energy and a concave-convex structure. Compared with a common hydrophobic membrane, the hydrophobic membrane not only has a water contact angle of more than 160 degrees, but also can resist wetting of low surface energy liquid (such as SDS). In addition, the mechanical property and the liquid inlet pressure are also obviously improved, so that the high anti-wettability, the salt retention rate and the operation stability of the composite material are always kept in the MD operation process. Because dopamine has strong adhesion, the silicon dioxide growing on the surface of the membrane is very firm and is not easy to fall off in long-time operation, and the service performance of the membrane is greatly enhanced.

Drawings

FIG. 1 is a surface topography of a PDA/PEI modified membrane prepared in comparative example 1.

Fig. 2 is a surface topography of the mineralized film prepared in comparative example 2.

FIG. 3 is a surface topography of the super-amphiphobic membrane prepared in comparative example 3.

Fig. 4 is a contact angle graph of the super amphiphobic film prepared in example 1.

Fig. 5 is a direct contact MD process layout.

FIG. 6 is a comparison of MD performance of unmodified PVDF membrane and super amphiphobic membrane when high saline containing 0.5mM SDS was applied to MD.

Fig. 7 is a schematic structural view of the super-amphiphobic membrane prepared in example 1.

Detailed Description

A super-amphiphobic membrane comprises a substrate membrane, and a PDA/PEI (polyethylene terephthalate/polyetherimide) deposition layer and a silica particle mineralization layer which are sequentially formed on the substrate membrane, wherein the super-amphiphobic membrane has a high fluorine-containing surface.

The matrix membrane is a microporous hydrophobic membrane, and comprises a PP membrane, a PVDF membrane or other microporous membranes with low surface energy; preferably, the matrix membrane is a PVDF membrane. The high fluorine containing surface is preferably formed by grafting fluorine containing branches (carbon-fluorine branches) onto the membrane surface by de-ethanolic reaction of at least one of PDTS or 9-FAS with the silica particle mineralized layer.

The preparation method of the super-amphiphobic membrane comprises the following steps:

s1: dissolving dopamine and polyethyleneimine in a Tris buffer solution to prepare a deposition solution, and placing the wetted substrate film in the deposition solution for deposition to form a PDA/PEI deposition layer;

s2: dissolving tetramethyl orthosilicate in hydrochloric acid solution and PBS buffer solution which are equal in amount to prepare mineralized solution, soaking the membrane prepared in the step (1) in the mineralized solution, and carrying out surface mineralization to enable silicon dioxide particles to uniformly grow on the membrane wall to form a silicon dioxide particle mineralized layer;

s3: and (2) carrying out de-ethanol reaction on at least one of PDTS or 9-FAS and a silicon dioxide particle mineralized layer, grafting a fluorine-containing branched chain on the surface of the membrane, and carrying out low surface energy modification on the surface of the membrane to obtain the super-amphiphobic membrane.

In step S1: preferably, the dopamine and polyethyleneimine are the same in mass; preferably, the concentration of the dopamine and the polyethyleneimine is 1-4 g/L, and further preferably, the concentration of the dopamine and the polyethyleneimine is 2 g/L; preferably, the concentration of the Tris buffer solution is 0.1-0.5mol/L, and the pH value is 8-9; the matrix membrane is preferably a microporous hydrophobic membrane with the pore diameter of 0.22-0.45 mu m; preferably, the substrate membrane is fully wetted by soaking the substrate membrane in an organic solvent, and the excess solvent on the surface of the membrane is absorbed by using filter paper to obtain the wetted substrate membrane, wherein the organic solvent is ethanol or isopropanol, and the soaking time is 20-50 seconds; the deposition time is preferably 1 to 6 hours; the step preferably further comprises the steps of rinsing with ultrapure water after deposition, and drying in an oven, wherein the drying time is 6-24 hours.

In step S2: the PBS buffer is preferably prepared by using potassium dihydrogen phosphate and dimethyl hydrogen phosphate, and adjusting the pH of the solution using dilute hydrochloric acid; the dosage ratio of the tetramethyl orthosilicate to the PBS buffer solution and the hydrochloric acid solution is preferably 0.1-0.2 mL to 10mL, and the dosage ratio of the tetramethyl orthosilicate to the PBS buffer solution and the hydrochloric acid solution is further preferably 0.15mL to 10 mL; the solubility of the hydrochloric acid solution is preferably 0.1 mM; the soaking time is preferably 2-10 hours; the step preferably further comprises a drying process after the surface mineralization, wherein the drying temperature is 65 ℃ and the drying time is at least 24 hours.

In step S3: preferably, absolute ethyl alcohol and at least one of PDTS or 9-FAS are mixed to prepare a low surface energy modification solution, and the membrane obtained in the step (2) is soaked in the low surface energy modification solution to realize low surface energy modification of the membrane surface; the ratio of the absolute ethyl alcohol to the PDTS or 9-FAS is preferably 22.55mL to 0.45 mL; the whole process of the step is preferably carried out under the protection of argon.

The method preferably further comprises step S4: placing the super-amphiphobic membrane prepared in the step S3 in a vacuum drying oven to enable the super-amphiphobic membrane to react fully; the temperature of the vacuum oven is 80-90 ℃ and the time is 2-3 hours.

The super-amphiphobic membrane is applied to a membrane, and is used in a direct contact type membrane distillation process to desalt high-salt water containing SDS. Preferably, the salt component in the high-salt water is sodium chloride or other inorganic salt at a concentration of 10-100g/L and the concentration of SDS is 0-0.5mM (and not 0). Preferably, in desalting the high-salt water containing SDS, the temperature of the raw material liquid is controlled to 50-90 ℃ and the temperature of the penetrating liquid is controlled to 10-25 ℃.

The invention is described in detail below with reference to the figures and specific embodiments.

Comparative example 1:

6.057g of Tris powder was weighed into 1L of ultrapure water to prepare 0.5mM Tris buffer, and the pH was adjusted to 8.5 using 0.1mM diluted hydrochloric acid solution. And respectively weighing dopamine and PEI with the concentration of 2g/L and dissolving the dopamine and PEI in the Tris buffer solution to prepare the PDA/PEI sediment solution. Soaking the PVDF microporous membrane with the aperture of 0.22 mu m in absolute ethyl alcohol for 20-50 seconds, taking out the PVDF microporous membrane, and then sucking the excessive ethyl alcohol on the surface of the PVDF microporous membrane by using filter paper. The membrane was then carefully placed in the PDA/PEI deposition solution described above and allowed to double-side deposit for 2 hours. The deposition solution was kept shaking on a shaker at a shaking speed of 60rpm to ensure uniform deposition of the PDA/PEI layer on the membrane. The resulting membrane is hydrophilic and non-hydrophobic.

Comparative example 2:

6.057g of Tris powder was weighed into 1L of ultrapure water to prepare 0.5mM Tris buffer, and the pH was adjusted to 8.5 using 0.1mM diluted hydrochloric acid solution. And respectively weighing dopamine and PEI with the concentration of 2g/L and dissolving the dopamine and PEI in the Tris buffer solution to prepare the PDA/PEI sediment solution. Soaking the PVDF microporous membrane with the aperture of 0.22 mu m in absolute ethyl alcohol for 20-50 seconds, taking out the PVDF microporous membrane, and then sucking the excessive ethyl alcohol on the surface of the PVDF microporous membrane by using filter paper. The membrane was then carefully placed in the PDA/PEI deposition solution described above and allowed to double-side deposit for 2 hours. The deposition solution was kept shaking on a shaker at a shaking speed of 60rpm to ensure uniform deposition of the PDA/PEI layer on the membrane. The resulting membrane is hydrophilic and non-hydrophobic.

0.2M PBS buffer was prepared using 0.2M potassium dihydrogen phosphate and 0.2M dimethyl hydrogen phosphate and adjusted to pH 6 using dilute hydrochloric acid. 10mL of PBS buffer, 10mL of 0.1mM hydrochloric acid solution and 0.15mL of tetramethyl orthosilicate solution were mixed and stirred for 15 minutes to obtain a mineralized solution. The PDA/PEI deposited films described above were soaked in the mineralization solution for 6 hours. The solution is placed in a shaking table in the mineralization process and is always kept stirred. The surface of the membrane is tightly coated with silica particles, and the hydrophilicity of the obtained membrane is further enhanced.

Example 1:

6.057g of Tris powder was weighed into 1L of ultrapure water to prepare 0.5mM Tris buffer, and the pH was adjusted to 8.5 using 0.1mM diluted hydrochloric acid solution. And respectively weighing dopamine and PEI with the concentration of 2g/L and dissolving the dopamine and PEI in the Tris buffer solution to prepare the PDA/PEI sediment solution. Soaking the PVDF microporous membrane with the aperture of 0.22 mu m in absolute ethyl alcohol for 20-50 seconds, taking out the PVDF microporous membrane, and then sucking the excessive ethyl alcohol on the surface of the PVDF microporous membrane by using filter paper. The membrane was then carefully placed in the PDA/PEI deposition solution described above and allowed to double-side deposit for 2 hours. The deposition solution was kept shaking on a shaker at a shaking speed of 60rpm to ensure uniform deposition of the PDA/PEI layer on the membrane. The resulting membrane is hydrophilic and non-hydrophobic.

0.2M PBS buffer was prepared using 0.2M potassium dihydrogen phosphate and 0.2M dimethyl hydrogen phosphate and adjusted to pH 6 using dilute hydrochloric acid. 10mL of PBS buffer, 10mL of 0.1mM hydrochloric acid solution and 0.15mL of tetramethyl orthosilicate solution were mixed and stirred for 15 minutes to obtain a mineralized solution. The PDA/PEI deposited films described above were soaked in the mineralization solution for 6 hours. The solution is placed in a shaking table in the mineralization process and is always kept stirred. The membrane wall is tightly coated by the silicon dioxide particles, and the hydrophilicity of the obtained membrane is further enhanced.

The mineralized membrane is soaked in a vacuum glove box after 22.55mL of absolute ethanol and 0.45mL of PDTS solution are mixed, and the mineralized membrane is soaked in the solution for 24 hours, so that the PDTS can generate a de-ethanol reaction with silicon dioxide, and a fluorine-containing branched chain is firmly grafted on the surface of the membrane. Thereby greatly reducing the surface energy of the film. After the reaction was completed, the membrane was placed in a vacuum oven at 90 ℃ for two hours. The film obtained at the moment has ultralow surface energy, the contact angle to water is 167.4 degrees, the film has super-hydrophobic property, and meanwhile, the contact angle to mineral oil of the film reaches 136 degrees, and the film has super-amphiphobic property. As shown in fig. 4.

The film performance was tested using a direct contact MD device. The effective membrane area is 14.6cm². The flow rate on the permeate side during operation was 0.15m/s, the pressure 5kPa and the temperature 25 ℃. The flow rate of the feed liquid was 0.2m/s, the pressure was 5kPa, and the temperature was 60 ℃. The temperature of the raw material liquid and the penetrating liquid are respectively regulated and controlled by a constant-temperature water bath and a cooling tank. The starting material solution and the permeate had initial volumes of 2L and 150mL, respectively, and were circulated by two gear pumps. During MD operation, the permeate was placed on an electronic balance and the conductivity was measured by a conductivity meter. The balance and conductivity were connected to a computer via software and data was recorded every 30 seconds. After the MD operation was carried out for 1 hour, 0.1mM SDS was added to the raw material solution and the operation was continued for 2 hours. Then, the concentration of SDS in the raw material solution was increased by 0.1mM every 2 hours until the total concentration of SDS reached 0.3mM, and then 0.2mM SDS was added for the last 2 hours of operation. As described above, the MD running time was 9 hours in total, and the SDS concentration finally added to the raw material solution was 0.5 mM. The direct contact MD process is shown in figure 5.

FIG. 1 shows that the film surface morphology does not change much after the PDA/PEI codeposition modification.

FIG. 2 shows that after the mineralization modification of tetramethyl orthosilicate, silica particles appear on the membrane wall, and the surface of the membrane is rougher.

FIG. 3 shows that more silica particles are generated on the wall of the super-amphiphobic membrane prepared after PDTS modification, the surface is rougher, and the membrane pores are not blocked.

Figure 4 shows that the membrane has a high contact angle for both water and mineral oil and is resistant to wetting by low surface energy substances.

Fig. 5 is a process flow diagram of a direct contact MD device.

FIG. 6 shows that the MD performance of a conventional hydrophobic PVDF membrane continues to decrease when 0.1mM SDS is added to the stock solution. And the super-amphiphobic membrane can resist the wetting of high saline with the concentration of 0.5mMSDS, and the stable MD performance is kept.

Fig. 7 shows that the surface of the super-amphiphobic membrane prepared in example 1 has a rough concave-convex structure, and can resist wetting of liquids with various surface tensions by combining with fluorosilane modification, thereby being beneficial to improvement of long-term operation stability in the MD process.

The embodiments described above are intended to facilitate the understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.