A biomimetic super-hydrophobic and oleophobic composite film and a preparation method thereof

Abstract

The application discloses a kind of biomimetic super-hydrophobic oleophobic composite membrane and preparation method thereof, belong to membrane distillation technical field.The preparation method of biomimetic super-hydrophobic oleophobic composite membrane of the application includes the following steps: step 1, preparation polydopamine modified base film;Step 2, polydopamine modified base film is placed in titanate solution and carries out hydrothermal reaction;The temperature of the hydrothermal reaction is 80~150 DEG C, and the time is 12~48h;Step 3, low surface energy processing.The biomimetic super-hydrophobic oleophobic composite membrane prepared in the application has excellent super-hydrophobic and oleophobic characteristics, significant chemical and thermal stability.

Description

Technical Field

[0001] This invention belongs to the field of membrane distillation technology, specifically relating to a biomimetic superhydrophobic and oleophobic composite membrane and its preparation method. Background Technology

[0002] Rapid industrialization and urbanization, along with a surge in population, not only necessitate a greater supply of freshwater but also consume more energy, exacerbating the energy crisis and triggering a global problem—freshwater scarcity. Simultaneously, the overexploitation and utilization of non-renewable resources has caused devastating damage to the ecological environment, resulting in severe water pollution. The rational use of water resources, such as seawater desalination or the recycling of industrial wastewater to obtain freshwater for reuse, is crucial to meeting production and domestic needs. Membrane distillation technology, with its unique advantages including the ability to handle high-salinity solutions, high separation efficiency, and effective utilization of low-grade renewable energy, holds great promise for desalination. However, the membrane, as the core component of the membrane distillation process, determines its operational stability. Various factors, including membrane fouling, membrane wetting, and the lack of suitable membranes, have hindered the development and large-scale industrial application of membrane distillation technology.

[0003] Superhydrophobic membranes can prevent membrane wetting and ensure normal membrane operation. However, with environmental degradation, various pollutants such as surfactants accumulate in wastewater. These pollutants are easily adsorbed and aggregated on hydrophobic or superhydrophobic surfaces, thereby deteriorating membrane performance. Superhydrophobic membranes are not advantageous in the treatment of brine containing surfactants and other organic matter.

[0004] Amphiphilic surfaces repel both water and low-surface-tension liquids such as surfactants, and have significant potential for improving antifouling properties. However, the properties of existing amphiphilic surfaces require further improvement. Summary of the Invention

[0005] Therefore, the present invention provides a biomimetic superhydrophobic and oleophobic composite film and its preparation method. The biomimetic superhydrophobic and oleophobic composite film prepared by the present invention has excellent superhydrophobic and oleophobic properties and significant chemical and thermal stability.

[0006] To this end, the present invention provides the following technical solution.

[0007] In a first aspect, the present invention provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, comprising the following steps:

[0008] Step 1: Prepare a polydopamine-modified base film;

[0009] Step 2: Place the polydopamine-modified base film in a titanate solution for a hydrothermal reaction;

[0010] The hydrothermal reaction is carried out at a temperature of 80–150°C for a time of 12–48 hours.

[0011] Step 3: Low surface energy treatment.

[0012] Furthermore, in step 2, the hydrothermal reaction temperature is ≥100℃ and the reaction time is ≥12h;

[0013] Preferably, the reaction temperature is 120–150°C and the reaction time is 12–48 h.

[0014] Furthermore, the titanate solution raw materials include a titanium source and an acid solution, wherein the mass of the titanium source is 2.5% to 7.5% of the mass of the acid solution;

[0015] Optionally, the titanium source includes at least one of tetrabutyl titanate, Na2Ti3O7, or Na2Ti2O5;

[0016] Optionally, the pH of the acid solution is 1 to 5;

[0017] Optionally, the acid solution is dilute hydrochloric acid.

[0018] Furthermore, step 3 includes immersing the product of step 2 in a mixed solution of low surface energy material and alcohol solvent for 12 to 48 hours.

[0019] Furthermore, step 3 satisfies at least one of the following conditions:

[0020] (1) The low surface energy material is fluorosilane;

[0021] (2) The low surface energy material includes at least one of perfluorooctyltrichlorosilane, perfluorododecyltrichlorosilane, perfluorooctyltriethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, and perfluorodecyltrimethoxysilane.

[0022] (3) The alcohol solvent is one of methanol, ethanol, isopropanol, and butanol;

[0023] (4) The concentration of the low surface energy material in the mixed solution is 0.5-2.0 vol%.

[0024] (5) Heat-treat the soaked membrane at 90-135℃ for 1-4 hours.

[0025] Furthermore, step 1 includes: placing the base membrane in dopamine buffer and shaking at 15–50°C for 6–24 hours at a shaking rate of 100–500 rpm;

[0026] Optionally, the oscillation can be either a reciprocating oscillation or a cyclotron oscillation.

[0027] Furthermore, the base film material is an organic polymer material or an inorganic ceramic material.

[0028] Furthermore, the base film material is polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethylene, polyacrylonitrile, aluminum oxide, titanium dioxide, or zirconium dioxide.

[0029] Furthermore, the concentration of dopamine hydrochloride in the dopamine buffer solution is 0.2–2.0 g / L.

[0030] Furthermore, the base membrane is a porous membrane.

[0031] Furthermore, step 3 also includes: cooling the heat-treated film and then cleaning and drying it;

[0032] Preferably, the cleaning includes rinsing multiple times with isopropanol and deionized water, respectively;

[0033] Preferably, the drying temperature is 20–60°C.

[0034] Furthermore, in step 1, the base membrane is first pretreated and then added to a dopamine buffer solution. The pretreatment method is to wet and rinse the base membrane in an organic solvent; optionally, the organic solvent is one or more of methanol, ethanol, isopropanol, and n-hexane.

[0035] Furthermore, in step 1, after the base membrane is kept at a constant temperature of 15-50°C and shaken in dopamine buffer for 6-24 hours, it also includes rinsing with deionized water and drying.

[0036] Furthermore, the preparation method of the dopamine buffer includes: adding dopamine hydrochloride to the buffer solution and stirring at room temperature to form the buffer solution.

[0037] Furthermore, the buffer solution is one of Tris-HCl buffer, NaAc-HAc buffer, or phosphate buffer.

[0038] Furthermore, the concentration of the Tris buffer is 10–100 mM.

[0039] Furthermore, the drying temperature in steps 1 to 3 is 20–60°C.

[0040] In one possible design, the specific process of step 1 is as follows: first, add dopamine hydrochloride to the buffer solution, and continuously stir in a magnetic stirrer at room temperature to form a uniform dopamine buffer solution. Then, immerse the pretreated base film in the dopamine buffer solution and oscillate it repeatedly in a constant temperature shaker. After the reaction is complete, take it out, wash and dry it to obtain the polydopamine modified base film.

[0041] Step 2 involves the following steps: First, hydrochloric acid and deionized water are mixed. Then, tetrabutyl titanate is added dropwise to the dilute hydrochloric acid and stirred thoroughly. Finally, the polydopamine-modified base membrane is immersed in a reaction vessel containing a tetrabutyl titanate solution. After hydrothermal reaction, the membrane is removed, repeatedly rinsed with deionized water, and dried to obtain a porous membrane with a micro / nano multi-layered rough structure. Tetrabutyl titanate hydrolyzes under acidic conditions to generate titanium hydroxide, which then reacts hydrothermally to generate titanium dioxide.

[0042] Step 3, the fluorination process, is as follows: First, the fluorosilane is hydrolyzed. Then, the porous membrane with in-situ grown nanoparticles is immersed in the hydrolyzed fluorosilane for treatment. After that, it is transferred to a vacuum drying oven for heat treatment. After naturally cooling to room temperature, it is rinsed and dried to obtain a biomimetic superhydrophobic and oleophobic composite membrane based on in-situ growth.

[0043] Fluorosilanes hydrolyze in alcohols to form highly polarized -Si(OH)3 groups. The -OH groups in the hydrolyzed fluorosilane -Si(OH)3 groups form hydrogen bonds with the hydroxyl groups on the surface of titanium dioxide and undergo a dehydration condensation reaction, forming stable covalent bonds at the interface.

[0044] The biomimetic superhydrophobic and oleophobic composite membrane prepared by this invention has good wettability and antifouling ability in membrane distillation testing applications.

[0045] Secondly, the present invention provides a biomimetic superhydrophobic and oleophobic composite membrane prepared according to the preparation method described above.

[0046] The technical solution of this invention has the following advantages:

[0047] 1. The preparation method of the biomimetic superhydrophobic and oleophobic composite film provided by the present invention includes the following steps: Step 1, preparing a polydopamine modified base film; Step 2, placing the polydopamine modified base film in a titanate solution for hydrothermal reaction, wherein the hydrothermal reaction temperature is 80-150℃ and the time is 12-48h; Step 3, low surface energy treatment.

[0048] Titanium dioxide is generated through a hydrothermal reaction of titanate solution. The introduction of hydroxyl groups through polydopamine modification enhances the adhesion between titanium dioxide and the membrane surface. As the hydrothermal reaction time increases, titanium dioxide crystals are loaded onto the membrane surface and within the membrane pores, gradually growing to construct a micro / nano-rough surface morphology. This invention employs an in-situ growth method to modify the base membrane, which is simple to operate and effectively improves the stability issues associated with modifying nanoparticles using chemical binders or electrostatic attraction.

[0049] The biomimetic superhydrophobic and oleophobic composite membrane prepared by the method of this invention has good hydrophobic and oleophobic properties and stability.

[0050] 2. In the preparation method of the biomimetic superhydrophobic and oleophobic composite film provided by the present invention, in step 2, the hydrothermal reaction temperature is ≥100℃ and the reaction time is ≥12h. By controlling the hydrothermal conditions within this range, nano-titanium dioxide with different morphologies and sizes is formed, thereby controlling the morphology and size of the nano-titanium dioxide to a state in which nanoparticle aggregates and nanopillars grow in situ simultaneously and are synergistically and uniformly distributed. By controlling reaction conditions, nanomaterials with different morphologies and sizes are obtained, and micro / nano-level multi-layered rough structures are constructed on the membrane surface. Compared to the surface of nanoparticles without layers, the surface roughness of the composite membrane is increased (when a droplet is stationary on a rough solid surface and the size of the droplet is larger than the scale of the rough structure of the solid surface, the droplet cannot penetrate into the grooves of the solid surface because air is trapped between the droplet and the solid surface, forming a gas film. The droplet and the solid surface form a composite contact, that is, the apparent liquid-solid contact surface is actually composed of both liquid-solid and gas-liquid contact surfaces. For low surface energy solid surfaces, the solid surface presents particles of varying sizes, and its surface roughness increases, filling more air between the particles, which helps to reduce the contact between solid and liquid. In addition, the surface tension of water is greater than that of low surface energy solids. Due to the surface tension, water droplets on low surface energy rough solid surfaces are spherical. From a microscopic perspective, water droplets are "suspended" on the rough structure of the solid surface, making it difficult for pollutants to adhere to the solid surface). This reduces the contact area between pollutants and the membrane surface, weakening the adhesion of pollutants to the membrane surface.

[0051] 3. The preparation method of the biomimetic superhydrophobic and oleophobic composite film provided by the present invention includes step 3: soaking the product of step 2 in a mixed solution of low surface energy material and alcohol solvent for 12 to 48 hours.

[0052] The low surface energy material is first hydrolyzed in alcohol to generate -OH functional groups. The -OH functional groups form hydrogen bonds with the hydroxyl groups on the surface of titanium dioxide and undergo dehydration condensation reaction to form stable covalent bonds at the interface. That is, the low surface energy fluorosilane coupling agent is grafted onto the membrane surface and membrane pores to reduce the solid surface energy of the composite membrane.

[0053] This invention grafts low surface energy materials onto nano-titanium dioxide via chemical bonds, which exhibits long-term chemical stability compared to physical coating modification.

[0054] 4. The preparation method of the biomimetic superhydrophobic and oleophobic composite membrane provided by the present invention, wherein step 1 includes: placing the base membrane in a dopamine buffer solution and shaking at 15-50°C for 6-24 hours at a shaking rate of 100-500 rpm. The present invention does not require the addition of an external oxidant; conventional air oxidation can achieve polydopamine synthesis. This avoids the formation of an excessively thick polydopamine layer that could clog the membrane pores. Attached Figure Description

[0055] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0056] Figure 1 This is a surface field emission scanning electron microscope image of the biomimetic superhydrophobic and oleophobic composite film of Example 1 at 10k magnification;

[0057] Figure 2 This is a surface field emission scanning electron microscope image of the biomimetic superhydrophobic and oleophobic composite film of Example 2 at 10k magnification;

[0058] Figure 3 This is a surface field emission scanning electron microscope image of the biomimetic superhydrophobic and oleophobic composite film of Example 3 at 30k magnification;

[0059] Figure 4 These are surface field emission scanning electron microscope (SEM) images of the biomimetic superhydrophobic and oleophobic composite film of Example 4 at magnifications of 30k and 10k. Detailed Implementation

[0060] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0061] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0062] In direct contact membrane distillation, composite membranes are applied, with permeate flux, separation performance, and resistance to wetting and fouling serving as key indicators of membrane performance. A mixture containing various contaminants such as inorganic salts, organic matter, and surfactants is used as the feed solution. The conductivity changes of both the feed solution and permeate are monitored in real-time using a conductivity meter, while the mass changes of the permeate are recorded using an electronic analytical balance. The permeate flux is calculated based on these mass changes, and the degree of wetting and fouling is analyzed through these changes. Changes in the conductivity of both the feed solution and permeate reflect changes in salt concentration, further indicating the membrane's salt rejection rate, thus characterizing the membrane's separation performance.

[0063] The permeation flux of the membrane can be calculated using the following formula:

[0064]

[0065] Where J is the membrane permeation flux, kg / m³ 2 •h; ΔW is the increase in mass of permeate, kg; A is the effective area of ​​the membrane in the membrane module, m². 2 Δt is the time interval (h) during the membrane distillation process.

[0066] The salt rejection rate of the membrane, also known as the salt cutoff rate, can be calculated using the following formula:

[0067]

[0068] Where R is the salt rejection rate; C f and C p Here, represents the mass concentrations of the feed solution and permeate, respectively, in mg / L. In both the feed solution and permeate, the mass concentration is directly proportional to the conductivity. Therefore, the conductivity of the feed solution and permeate can be used to replace their mass concentrations to calculate the membrane rejection rate, thus analyzing the membrane's separation performance.

[0069] The surface microstructure of the membrane samples was characterized and analyzed using an S-4800 field emission scanning electron microscope (HITACHI S-4800, Japan). The changes in the contact angle and roll-off angle of the liquid on the membrane surface were measured using an optical contact angle meter (DataPhysics OCA15EC, Germany) to characterize the wetting behavior of the membrane surface.

[0070] Example 1

[0071] This embodiment provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, including the following steps:

[0072] (1) Polydopamine modification: The PVDF membrane was first wetted and rinsed with anhydrous ethanol for 60 min, then removed and repeatedly washed with deionized water. It was then immersed in a 2.0 g / L dopamine buffer solution formed by adding dopamine hydrochloride to Tris-HCl buffer solution with a Tris concentration of 50 mM and a pH of 8.50. The membrane was shaken repeatedly in a water bath at 200 rpm for 12 h at room temperature. After the reaction was complete, the membrane was removed, repeatedly washed with deionized water and soaked for 12 h to remove unreacted dopamine from the surface. Finally, it was dried in a vacuum drying oven at 35 ℃ to obtain a polydopamine modified PVDF membrane.

[0073] (2) In-situ growth of nanoparticles: 1.5g of tetrabutyl titanate was added dropwise to 60ml of dilute hydrochloric acid with pH=3. The solution was prepared by magnetic stirring at 25℃ for 2h and then transferred to a 100ml reaction vessel. The polydopamine-modified PVDF membrane was then immersed in the tetrabutyl titanate solution and hydrothermally reacted at 120℃ for 24h. After removal, it was repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 35℃ to obtain a PVDF membrane with a micro-nano multi-layer rough structure.

[0074] (3) Low surface energy treatment: The PVDF membrane with micro-nano multi-layer rough structure is transferred into an isopropanol solution containing 1 vol% perfluorododecyltrichlorosilane and soaked for 48 h at 25 °C for grafting treatment. Then it is transferred to a vacuum drying oven at 120 °C for heat treatment for 2 h. After natural cooling to room temperature, it is repeatedly rinsed with isopropanol and deionized water to remove fluorosilane molecules that did not participate in the grafting reaction from the membrane surface and membrane pores. Finally, it is dried in a vacuum drying oven at 35 °C to obtain a biomimetic superhydrophobic and oleophobic composite membrane with slip effect.

[0075] Figure 1 This is a surface field emission scanning electron microscope (SEM) image at 10kx of the biomimetic superhydrophobic and oleophobic composite membrane prepared in this embodiment, based on in-situ growth. Compared to the original PVDF membrane, the biomimetic superhydrophobic and oleophobic PVDF composite membrane exhibits in-situ growth of nanoparticles, with nanoclusters and nanopillars uniformly dispersed. Because the nanoclusters and nanopillars are uniformly distributed on the membrane surface and not at the same horizontal height, they form different hierarchical structures, resulting in a multi-layered morphological structure and an uneven, rough structure. This improves the wettability of the composite membrane surface. The water contact angle of the biomimetic superhydrophobic and oleophobic PVDF composite membrane increases to 175.0±1.0°, the roll-off angle is close to 2°, and the oil contact angle increases to 136.0±1.5°, demonstrating both superhydrophobic and oleophobic effects.

[0076] The biomimetic superhydrophobic and oleophobic PVDF composite membrane was immersed in strong acid, neutral liquid and strong alkali for 48 h and in a constant temperature vacuum drying oven at 100℃ for 120 h respectively. The contact angle and roll-off angle remained basically stable, indicating that the composite membrane has good chemical stability and thermal stability.

[0077] Using a high-concentration brine containing organic humic acid, surfactants, and gasoline as the treatment solution, the biomimetic superhydrophobic and oleophobic PVDF composite membrane maintained a high permeation flux and a salt rejection rate close to 100%, exhibiting strong repulsion of pollutants and demonstrating excellent overall antifouling performance. In contrast, the permeation flux of the original PVDF membrane decreased sharply and even became completely wetted. The permeation flux of the composite membrane remained stable at approximately 37.0 kg / m³. 2 •h; However, as the membrane distillation operation time increased, the PVDF primary membrane exhibited varying degrees of fouling. After 148 hours of operation, the permeate flux of the PVDF primary membrane gradually decreased to 10.8 kg / m³.2 ·h.

[0078] Example 2

[0079] This embodiment provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, including the following steps:

[0080] (1) Polydopamine modification: The PVDF membrane was first wetted and rinsed with anhydrous ethanol for 60 min, then removed and repeatedly washed with deionized water. It was then immersed in a 2.0 g / L dopamine buffer solution formed by adding dopamine hydrochloride to Tris-HCl buffer solution with a Tris concentration of 50 mM and a pH of 8.50. The membrane was shaken repeatedly in a water bath at 200 rpm for 12 h at room temperature. After the reaction was complete, the membrane was removed, repeatedly washed with deionized water and soaked for 12 h to remove unreacted dopamine from the surface. Finally, it was dried in a vacuum drying oven at 35 ℃ to obtain a polydopamine modified PVDF membrane.

[0081] (2) In-situ growth of nanoparticles: 1.5g of tetrabutyl titanate was added dropwise to 60ml of dilute hydrochloric acid with pH=3. The solution was prepared by magnetic stirring at 25℃ for 2h and then transferred to a 100ml reaction vessel. The polydopamine-modified PVDF membrane was then immersed in the tetrabutyl titanate solution and hydrothermally reacted at 90℃ for 12h. After removal, it was repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 35℃ to obtain a PVDF membrane with a micro-nano rough structure.

[0082] (3) Low surface energy treatment: The PVDF membrane with micro-nano rough structure is transferred into an isopropanol solution containing 1 vol% perfluorododecyltrichlorosilane, and is soaked and grafted at 25°C for 24 h. Then it is heat-treated in a vacuum drying oven at 120°C for 2 h. After naturally cooling to room temperature, it is repeatedly rinsed with isopropanol and deionized water to remove fluorosilane molecules that did not participate in the grafting reaction from the membrane surface and membrane pores. Finally, it is dried in a vacuum drying oven at 35°C to obtain a biomimetic superhydrophobic and oleophobic composite membrane.

[0083] Figure 2 The image shows the surface field emission scanning electron microscope (SEM) image of the in-situ grown biomimetic superhydrophobic and oleophobic composite film prepared in this embodiment at 10k magnification. Compared with the original PVDF film, the biomimetic superhydrophobic and oleophobic PVDF composite film has nanoparticles grown in situ on the surface and the nanoparticles are uniformly distributed, forming a rough surface structure. The wettability of the composite film surface is improved. The water contact angle of the PVDF composite film surface increases to 158.0±1.0°, the roll-off angle is less than 10°, and the oil contact angle increases to 108.0±0.5°, exhibiting both superhydrophobic and oleophobic effects.

[0084] Example 3

[0085] This embodiment provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, including the following steps:

[0086] (1) Polydopamine modification: The PTFE membrane was first wetted and rinsed with anhydrous ethanol for 60 min, then removed and repeatedly washed with deionized water. It was then immersed in a 2.0 g / L dopamine buffer solution formed by adding dopamine hydrochloride to Tris-HCl buffer solution with a Tris concentration of 50 mM and a pH of 8.50. The membrane was shaken repeatedly in a water bath at 200 rpm for 24 h at room temperature. After the reaction was complete, the membrane was removed, repeatedly washed with deionized water and soaked for 12 h to remove unreacted dopamine from the surface. Finally, it was dried in a vacuum drying oven at 35 ℃ to obtain a polydopamine modified PTFE membrane.

[0087] (2) In-situ growth of nanoparticles: 1.5g of tetrabutyl titanate was added dropwise to 60ml of dilute hydrochloric acid with pH=3. The solution was prepared by magnetic stirring at 25℃ for 2h and then transferred to a 100ml reaction vessel. The polydopamine-modified PTFE membrane was then immersed in the tetrabutyl titanate solution and hydrothermally reacted at 105℃ for 24h. After removal, it was repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 35℃ to obtain a PTFE membrane with a micro-nano multi-layer rough structure.

[0088] (3) Low surface energy treatment: The PTFE membrane with micro-nano multi-layer rough structure is transferred into an isopropanol solution containing 1 vol% perfluorododecyltrichlorosilane, and is soaked and grafted at 25°C for 24 h. Then it is heat-treated in a vacuum drying oven at 120°C for 2 h. After naturally cooling to room temperature, it is repeatedly rinsed with isopropanol and deionized water to remove fluorosilane molecules that did not participate in the grafting reaction from the membrane surface and membrane pores. Finally, it is dried in a vacuum drying oven at 35°C to obtain a biomimetic superhydrophobic and oleophobic composite membrane.

[0089] Figure 3 This is a surface field emission scanning electron microscope (SEM) image at 10kx of the biomimetic superhydrophobic and oleophobic composite membrane prepared in this embodiment, based on in-situ growth. Compared to the original PTFE membrane, the biomimetic superhydrophobic and oleophobic PTFE composite membrane exhibits an uneven, rough structure due to the in-situ growth of nanoclusters and nanopillars of varying sizes on its surface. This improves the wettability of the composite membrane surface. In this embodiment, the water contact angle of the composite membrane surface reaches 168.0°, the roll-off angle is close to 8°, and the oil contact angle is 122.0°, demonstrating both superhydrophobic and oleophobic effects.

[0090] Example 4

[0091] This embodiment provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, including the following steps:

[0092] (1) Polydopamine modification: The PVDF membrane was first wetted and rinsed with anhydrous ethanol for 60 min, then removed and repeatedly washed with deionized water. It was then immersed in a 2.0 g / L dopamine buffer solution formed by adding dopamine hydrochloride to Tris-HCl buffer solution with a Tris concentration of 50 mM and a pH of 8.50. The membrane was shaken repeatedly in a water bath at 200 rpm for 12 h at room temperature. After the reaction was complete, the membrane was removed, repeatedly washed with deionized water and soaked for 12 h to remove unreacted dopamine from the surface. Finally, it was dried in a vacuum drying oven at 35 ℃ to obtain a polydopamine modified PVDF membrane.

[0093] (2) In-situ growth of nanoparticles: 1.5g of tetrabutyl titanate was added dropwise to 60ml of dilute hydrochloric acid with pH=3. The solution was prepared by magnetic stirring at 25℃ for 2h and then transferred to a 100ml reaction vessel. The polydopamine-modified PVDF membrane was then immersed in the tetrabutyl titanate solution and hydrothermally reacted at 120℃ for 48h. After removal, it was repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 35℃ to obtain a PVDF membrane with a micro-nano multi-layer rough structure.

[0094] (3) Low surface energy treatment: The PVDF membrane with micro-nano multi-layer rough structure is transferred into an isopropanol solution containing 1 vol% perfluorododecyltrichlorosilane, and is soaked and grafted at 25°C for 48 h. Then it is heat-treated in a vacuum drying oven at 120°C for 2 h. After naturally cooling to room temperature, it is repeatedly rinsed with isopropanol and deionized water to remove fluorosilane molecules that did not participate in the grafting reaction from the membrane surface and membrane pores. Finally, it is dried in a vacuum drying oven at 35°C to obtain a biomimetic superhydrophobic and oleophobic composite membrane.

[0095] Figure 4 The images show surface field emission scanning electron microscope (SEM) images of the in-situ grown biomimetic superhydrophobic and oleophobic composite film prepared in this embodiment at magnifications of 10k and 30k. Compared to the original PVDF film, the biomimetic superhydrophobic and oleophobic PVDF composite film features in-situ grown clusters and nanopillars of varying sizes, constructing a rough "cauliflower"-like morphology. This improves the wettability of the composite film surface. In this embodiment, the water contact angle of the composite film surface reaches 177.5°, the roll-off angle is close to 1.5°, and the oil contact angle is 145.0°, demonstrating both superhydrophobic and oleophobic effects.

[0096] Example 5

[0097] This embodiment provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, including the following steps:

[0098] (1) Polydopamine modification: The PVDF membrane was first wetted and rinsed with anhydrous ethanol for 60 min, then removed and repeatedly washed with deionized water. It was then immersed in a 2.0 g / L dopamine buffer solution formed by adding dopamine hydrochloride to Tris-HCl buffer solution with a Tris concentration of 50 mM and a pH of 8.50. The membrane was shaken repeatedly in a water bath at 200 rpm for 12 h at room temperature. After the reaction was complete, the membrane was removed, repeatedly washed with deionized water and soaked for 12 h to remove unreacted dopamine from the surface. Finally, it was dried in a vacuum drying oven at 35 ℃ to obtain a polydopamine modified PVDF membrane.

[0099] (2) In-situ growth of nanoparticles: First, tetrabutyl titanate was added dropwise to 60ml of dilute hydrochloric acid with pH=3 and magnetically stirred at 25℃ for 2h to obtain a tetrabutyl titanate solution. Then, the solution was transferred to a 100ml reaction vessel. Subsequently, the polydopamine-modified PVDF membrane was immersed in the tetrabutyl titanate solution and hydrothermally reacted at 130℃ for 24h. After removal, it was repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 35℃ to obtain a PVDF membrane with a micro-nano multi-layer rough structure.

[0100] (3) Low surface energy treatment: The PVDF membrane with micro-nano multi-layer rough structure is transferred into an isopropanol solution containing 1 vol% perfluorododecyltrichlorosilane, and is soaked and grafted at 25°C for 48 h. Then it is heat-treated in a vacuum drying oven at 120°C for 2 h. After naturally cooling to room temperature, it is repeatedly rinsed with isopropanol and deionized water to remove fluorosilane molecules that did not participate in the grafting reaction from the membrane surface and membrane pores. Finally, it is dried in a vacuum drying oven at 35°C to obtain a biomimetic superhydrophobic and oleophobic composite membrane.

[0101] Compared to the original PVDF membrane, the biomimetic superhydrophobic and oleophobic PVDF composite membrane features in-situ growth of nanoparticle clusters and nanopillars on its surface, with a significant increase in nanopillar diameter. This improves the wettability of the composite membrane surface. In this embodiment, the water contact angle of the composite membrane surface reaches 176.2°, the roll-off angle is close to 2°, and the oil contact angle is 141.0°, demonstrating both superhydrophobic and oleophobic effects.

[0102] Example 6

[0103] This embodiment provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, including the following steps:

[0104] (1) Polydopamine modification: The PVDF membrane was first wetted and rinsed with anhydrous ethanol for 60 min, then removed and repeatedly washed with deionized water. It was then immersed in a 1.0 g / L dopamine buffer solution formed by adding dopamine hydrochloride to Tris-HCl buffer solution with a Tris concentration of 50 mM and a pH of 8.50. The membrane was shaken repeatedly in a water bath at 200 rpm for 12 h at room temperature. After the reaction was complete, the membrane was removed, repeatedly washed with deionized water and soaked for 12 h to remove unreacted dopamine from the surface. Finally, it was dried in a vacuum drying oven at 35 ℃ to obtain a polydopamine modified PVDF membrane.

[0105] (2) In-situ growth of nanoparticles: 1.5g of tetrabutyl titanate was added dropwise to 60ml of dilute hydrochloric acid with pH=3. The solution was prepared by magnetic stirring at 25℃ for 2h and then transferred to a 100ml reaction vessel. The polydopamine-modified PVDF membrane was then immersed in the tetrabutyl titanate solution and hydrothermally reacted at 120℃ for 24h. After removal, it was repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 35℃ to obtain a PVDF membrane with a micro-nano multi-layer rough structure.

[0106] (3) Low surface energy treatment: The PVDF membrane with micro-nano multi-layer rough structure is transferred into an ethanol solution containing 2 vol% perfluorododecyltrichlorosilane and soaked at 25°C for 48 h for grafting treatment. Then it is transferred to a vacuum drying oven at 120°C for heat treatment for 4 h. After natural cooling to room temperature, it is repeatedly rinsed with isopropanol and deionized water to remove fluorosilane molecules that did not participate in the grafting reaction from the membrane surface and membrane pores. Finally, it is placed in a vacuum drying oven at 35°C to dry, and a biomimetic superhydrophobic and oleophobic composite membrane with slip effect can be obtained.

[0107] Comparative Example 1

[0108] This embodiment provides a method for preparing a biomimetic superhydrophobic and oleophobic composite film, including the following steps:

[0109] (1) Polydopamine modification: The PVDF membrane was first wetted and rinsed with anhydrous ethanol for 60 min, then removed and repeatedly washed with deionized water. It was then immersed in a 2.0 g / L dopamine buffer solution formed by adding dopamine hydrochloride to Tris-HCl buffer solution with a Tris concentration of 50 mM and a pH of 8.50. The membrane was shaken repeatedly in a water bath at 200 rpm for 12 h at room temperature. After the reaction was complete, the membrane was removed, repeatedly washed with deionized water and soaked for 12 h to remove unreacted dopamine from the surface. Finally, it was dried in a vacuum drying oven at 35 ℃ to obtain a polydopamine modified PVDF membrane.

[0110] (2) In-situ growth of nanoparticles: 1.5g of tetrabutyl titanate was added dropwise to 60ml of dilute hydrochloric acid with pH=3. The solution was prepared by magnetic stirring at 25℃ for 2h and then transferred to a 100ml reaction vessel. Polydopamine-modified PVDF membrane was then immersed in the tetrabutyl titanate solution and hydrothermally reacted at 60℃ for 6h. After removal, it was repeatedly rinsed with deionized water and finally dried in a vacuum drying oven at 35℃.

[0111] (3) Low surface energy treatment: The hydrothermally treated PVDF membrane is transferred into an isopropanol solution containing 1 vol% perfluorododecyltrichlorosilane and soaked at 25°C for 12 hours for grafting treatment. Then it is transferred to a vacuum drying oven at 120°C for heat treatment for 2 hours. After natural cooling to room temperature, it is repeatedly rinsed with isopropanol and deionized water to remove fluorosilane molecules that did not participate in the grafting reaction from the membrane surface and membrane pores. Finally, it is placed in a vacuum drying oven at 35°C to dry, and a biomimetic superhydrophobic and oleophobic composite membrane can be obtained.

[0112] Compared to the superhydrophobic and oleophobic composite membrane prepared in the example, the surface of this PVDF composite membrane basically does not exhibit titanium dioxide nanoparticles or nanopillar morphology. According to the contact angle test, the contact angle of water on the surface of the composite membrane in this example is 143.5° and the contact angle of oil is 106.0°, showing a weaker hydrophobic and oleophobic effect.

[0113] In summary, the composite membrane of the present invention exhibits a water contact angle of ≥150.0° and an oil contact angle of ≥100.0°. As demonstrated in Examples 1, 3, 4, and 5, when the hydrothermal reaction temperature is ≥100℃ and the reaction time is ≥12h, a micro-nano multi-layered rough structure can be formed, thereby improving the hydrophobic and oleophobic properties. Preferably, when the reaction temperature is 120.0~150.0℃ and the reaction time is 12~48h, the surface water contact angle is ≥175.0° and the oil contact angle is ≥136.0°, exhibiting excellent wettability and antifouling ability.

[0114] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a biomimetic superhydrophobic and oleophobic composite film, characterized in that, Includes the following steps: Step 1: Prepare a polydopamine-modified base film; Step 2: Place the polydopamine-modified base film in a titanate solution for a hydrothermal reaction; The hydrothermal reaction is carried out at a temperature of 100-150℃ for 12-48 hours. Step 3: Low surface energy treatment; The specific process of step 1 is as follows: First, add dopamine hydrochloride to the buffer solution and stir continuously in a magnetic stirrer at room temperature to form a uniform dopamine buffer solution. Then, immerse the pretreated base membrane in the dopamine buffer solution and oscillate it repeatedly in a constant temperature shaker. After the reaction is complete, take it out, wash and dry it to obtain a polydopamine modified base membrane. The specific process of step 2 is as follows: First, hydrochloric acid and deionized water are mixed. Then, tetrabutyl titanate is added dropwise to dilute hydrochloric acid and stirred thoroughly. Finally, the polydopamine-modified base film is immersed in a reaction vessel containing tetrabutyl titanate solution. After hydrothermal reaction, it is taken out, rinsed repeatedly with deionized water, and dried to obtain a porous membrane with a micro-nano multi-layered rough structure. Tetrabutyl titanate hydrolyzes under acidic conditions to generate titanium hydroxide, which is then converted into titanium dioxide through hydrothermal reaction. The specific process of step 3 is as follows: First, the fluorosilane is hydrolyzed, then the porous membrane of in-situ grown nanoparticles is immersed in the hydrolyzed fluorosilane for treatment, and then transferred to a vacuum drying oven for heat treatment. After naturally cooling to room temperature, it is rinsed and dried to obtain a biomimetic superhydrophobic and oleophobic composite membrane based on in-situ growth.

2. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 1, characterized in that, In step 2, the hydrothermal reaction temperature is 120~150℃.

3. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 1, characterized in that, The raw materials for titanate solutions include a titanium source and an acid solution, with the mass of the titanium source being 2.5 to 7.5% of the mass of the acid solution.

4. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 3, characterized in that, The titanium source includes at least one of tetrabutyl titanate, Na2Ti3O7, or Na2Ti2O5.

5. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 3, characterized in that, The pH of the acid solution is 1-5.

6. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 3, characterized in that, The acid solution is dilute hydrochloric acid.

7. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 1, characterized in that, Step 3 includes immersing the product from step 2 in a mixed solution of low surface energy material and alcohol solvent for 12-48 hours.

8. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 7, characterized in that, Step 3 satisfies at least one of the following conditions: (1) The low surface energy material is a fluorosilane; (2) The low surface energy material includes at least one of perfluorooctyltrichlorosilane, perfluorododecyltrichlorosilane, perfluorooctyltriethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, and perfluorodecyltrimethoxysilane. (3) The alcohol solvent is one of methanol, ethanol, isopropanol, and butanol; (4) The concentration of the low surface energy material in the mixed solution is 0.5~2.0 vol% (5) Heat-treat the soaked membrane at 90~135 ℃ for 1~4 h.

9. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to any one of claims 1-8, characterized in that, Step 1 includes: placing the base membrane in dopamine buffer and shaking at 15-50 °C for 6-24 h at a shaking rate of 100-500 rpm.

10. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 9, characterized in that, Oscillation is either reciprocating oscillation or cyclonic oscillation.

11. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 9, characterized in that, The base film material is an organic polymer material or an inorganic ceramic material.

12. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 9, characterized in that, The base film material is polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethylene, polyacrylonitrile, aluminum oxide, titanium dioxide, or zirconium dioxide.

13. The method for preparing the biomimetic superhydrophobic and oleophobic composite film according to claim 9, characterized in that, The concentration of dopamine hydrochloride in the dopamine buffer solution is 0.2~2.0 g / L.

14. A biomimetic superhydrophobic and oleophobic composite membrane prepared by the preparation method according to any one of claims 1-13.

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