Preparation method of super-hydrophobic film and application thereof

Abstract

The present application relates to the technical field of super-hydrophobic product, in particular to a preparation method of super-hydrophobic membrane and its application. The present application uses green solvent triethyl phosphate as the solvent of the casting solution, which is non-toxic, harmless and friendly to the environment. Combined with PVDF which has good chemical stability and simple morphology control, and high viscosity hydroxyethyl cellulose which enhances the mechanical strength, a super-hydrophobic STEP / PVDF-SHMs membrane with good mechanical strength and high membrane flux is prepared. Then, the selective adsorption capacity, anti-fouling ability and oil-water separation of dispersed oil / emulsified oil of the material are explored. Finally, the degradation performance and degradation mechanism are explored. Through the study of its application performance, it is preliminarily determined that the super-hydrophobic STEP / PVDF-SHMs membrane has strong tolerance to the surrounding harsh environment, and has certain practical application value for marine oil spill events and catering wastewater.

Description

Technical Field

[0001] This invention relates to the field of superhydrophobic product technology, specifically to a method for preparing a superhydrophobic membrane and its application. Background Technology

[0002] Currently, methods for treating oily wastewater mainly include adsorption, distillation, chemical treatment, and membrane separation technology. Membrane separation technology has a very broad application prospect due to its high efficiency, environmental friendliness (no secondary pollution), ease of membrane morphology control, and strong practical applicability. In the field of membrane separation, polyvinylidene fluoride (PVDF) polymers are widely used due to their good chemical stability, simple morphology control, and excellent film-forming properties. However, the low water vapor flux and poor mechanical properties of pure PVDF membranes severely affect their application performance. Therefore, it is crucial to prepare PVDF membranes with excellent membrane flux and strong mechanical properties. The first consideration is to add high-viscosity hydroxyethyl cellulose (HEC) to increase the mechanical properties of the membrane, making it elastic and reusable. Secondly, considering the selection of the casting solution solvent, organic solvents are commonly used in the casting solutions for preparing PVDF membranes.

[0003] Against this backdrop, green solvents have become a key issue in membrane fabrication research. TEP was selected as the green solution and used as the casting solution for PVDF membranes. Then, a simple and environmentally friendly spray-assisted solvent-induced phase separation (SANIPS) method was employed to fabricate the superhydrophobic membrane. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing superhydrophobic films and their applications, thereby resolving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a superhydrophobic film, characterized by comprising the following steps: Step 1: Preparation of casting solution The polyvinylidene fluoride (PVDF) powder was dried overnight in a vacuum drying oven at 60°C for further use. Take 15 wt% PVDF and use triethyl phosphate as a green solvent, stir at 80℃ for 6 h to make it fully dissolved; Add high-viscosity hydroxyethyl cellulose of different concentrations to the casting solution and stir the mixture at 80°C for 24 h to ensure thorough mixing. Pour the casting solution into a petri dish and degas at room temperature for 4 hours to remove air bubbles; Step 2: Cultivation of bacterial suspension The selected oleophilic bacteria were: A1: Acinetobacter rofibrinosus; BTS: Bacillus thuringiensis; A6: Pseudomonas aeruginosa; F1: Nocardia fulvidracoides; SP: Penicillium oxalate. The five activated bacteria were selected and each 100 μL was inoculated into five sterile nutrient broth media and cultured by shaking at 37°C and 120 r / min. After 48 hours, observe whether it becomes turbid, then take 50 mL of each and put them into a 250 mL Erlenmeyer flask to mix and prepare a mixed bacterial culture medium; Furthermore, the bacterial count was observed using a hemocytometer to ensure that the bacterial count reached 1×10⁻⁶. 8 CFU / mL or higher; store at 4°C until use. Step 3: Loading microorganisms onto SHMs Take 1 g of “single-pore” silica hollow spheres (SHMs) prepared by the microemulsion system, wash and dry them several times for later use; By combining autonomous growth and multiple concentrations, microorganisms cultured in step two were grown in large quantities inside and outside hollow spheres to prepare microbial-loaded silica hollow spheres. Step 4: Preparation of TEP / PVDF-SHMs membrane materials After completely defoaming the casting solution in step one, cool it to room temperature, take the SHMs loaded with microorganisms prepared in step three, and dope them into the casting solution. Then, the polyethylene glycol solution is continuously sprayed onto the casting liquid. During spraying, the spray bottle moves at a constant speed on the petri dish to ensure uniformity. Immediately pour distilled water into the petri dish and incubate in a water bath for 24 hours to allow phase separation to occur. Finally, the formed membrane is freeze-dried to obtain TEP / PVDF-SHMs membrane material; Step 5: Preparation of hydrophobic STEP / PVDF-SHMs membranes PDMS and n-hexane were stirred and mixed to prepare a hydrophobic modified solution; The modified liquid was sprayed onto the TEP / PVDF-SHMs prepared in step four in small amounts multiple times; it was then dried at room temperature, and the prepared hydrophobic membrane was named STEP / PVDF-SHMs.

[0006] Preferably, in step (2) of step one, the green solvent may also be Tamisolve® NxG (Taminco, Gent, Belgium) or polymethyl methacrylate (PMMA).

[0007] Preferably, in step (3) of step one, the concentration of the high-viscosity hydroxyethyl cellulose is 6 wt%.

[0008] Preferably, in step three (2), the methods of loading microorganisms on the "single-pore" silica hollow spheres also include adsorption, encapsulation and cross-linking.

[0009] Preferably, in step four (1), the detailed conditions for loading microorganisms into SHMs are: stirring at 100 r / min for 2 min to uniformly mix them into 10 mL of casting solution.

[0010] Preferably, in step four (2), the concentration of the polyethylene glycol solution is 20%, the spraying time of the polyethylene glycol is 3 s, and the spraying is repeated back and forth.

[0011] Preferably, in step five (1), the ratio of PDMS to n-hexane is 1:2 by mass.

[0012] Preferably, in step five (2), the amount of modified liquid sprayed is 0.5 g.

[0013] Compared with existing technologies, the beneficial effects of this invention are as follows: First, this invention uses triethyl phosphate, a green and environmentally friendly solvent, as the solvent for the casting solution, which is non-toxic, harmless, and environmentally friendly. Combined with PVDF, which has good chemical stability and is easy to control in morphology, and high-viscosity hydroxyethyl cellulose to enhance its mechanical strength, a superhydrophobic STEP / PVDF-SHMs membrane with good mechanical strength and high membrane flux is prepared. Second, the selective adsorption capacity, antifouling ability, and oil-water separation of dispersed / emulsified oils of this material are investigated. Finally, its degradation performance and degradation mechanism are investigated. Through the study of its application performance, it is preliminarily determined that the superhydrophobic STEP / PVDF-SHMs membrane exhibits strong tolerance to harsh environments and has certain practical application value for marine oil spills and catering wastewater treatment. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the preparation route of the superhydrophobic film using a green solvent according to the present invention; Figure 2 (af) represents the mechanical strength of the membranes prepared by adding different amounts of high-viscosity hydroxyethyl cellulose according to the present invention; Figure 3 (ad) shows the morphology of the superhydrophobic STEP / PVDF-SHMs membrane, proving the successful preparation of the composite membrane; Figure 3 (e) is a test of the bacterial activity of the superhydrophobic STEP / PVDF-SHMs membrane; Figure 4 (ab) are the hydrophobic angle test and selective adsorption capacity of the superhydrophobic STEP / PVDF-SHMs membrane; Figure 4(ce) is a test for the antifouling performance of superhydrophobic STEP / PVDF-SHMs; Figure 5 (ac) represents the oil-water separation capability of superhydrophobic STEP / PVDF-SHMs; Figure 5 (d) is the separation efficiency of superhydrophobic STEP / PVDF-SHMs; Figure 5 (ef) represents the separation of emulsified oil by superhydrophobic STEP / PVDF-SHMs; Figure 6 This is a comparison of the diesel removal rates of superhydrophobic STEP / PVDF-SHMs and free bacteria; Figure 7 The degradation mechanism of superhydrophobic STEP / PVDF-SHMs; Figure 8 (a) Membrane flux test of STEP / PVDF-SHMs membrane for n-hexane, chloroform and diesel; Figure 8 (b) Cyclic test of hexane and chloroform flux of STEP / PVDF-SHMs membrane. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0016] A method for preparing a superhydrophobic film, such as Figure 1 As shown, it includes the following steps: Step 1: Preparation of Casting Solution 15 wt% PVDF was dissolved in triethyl phosphate as a green solvent and stirred at 80 °C for 6 h to ensure complete dissolution. To enhance the mechanical properties of the membrane, high-viscosity hydroxyethyl cellulose (1, 3, and 6 wt%) at different concentrations was added to the casting solution, and the mixture was stirred at 80 °C for 24 h to ensure thorough mixing. Then, the casting solution was poured into a petri dish and degassed at room temperature for 4 h to remove air bubbles.

[0017] Step 2: Doping SHMs loaded with microorganisms Take 0.1g of SHMs loaded with microorganisms and stir at 100 r for 2 min to uniformly mix them into 10 mL of casting solution.

[0018] Step 3: Preparation of TEP / PVDF-SHMs membrane A 20% polyethylene glycol solution was then continuously sprayed onto the casting solution for 3 seconds. During spraying, the spray bottle was moved at a uniform speed over the petri dish to ensure uniformity. Distilled water was then immediately poured into the petri dish, and the mixture was in a water bath for 24 hours to allow phase separation. The resulting membrane was then freeze-dried.

[0019] Step 4: Superhydrophobic STEP / PVDF-SHMs membrane A hydrophobic modification solution was prepared by mixing PDMS and n-hexane at a mass ratio of 1:2. The modification solution was sprayed onto TEP / PVDF-SHMs in small, multiple applications. After drying at room temperature, the prepared hydrophobic membrane was named STEP / PVDF-SHMs and used for characterization and testing. The preparation flow chart is shown below. Figure 1 .

[0020] like Figure 2 (af) shows the mechanical strength of the membrane after adding different amounts of HEC. (ad) By adding 1wt%, 3wt%, 5wt%, and 6wt%, the compression cycle tests show that the mechanical strength increases with increasing HEC content, with the best mechanical strength observed at 6wt% HEC content. (ef) With an HEC content of 6wt%, the compression cycle tests were conducted with the addition of 0.3g and 0.1g of SHMs, revealing that the mechanical strength was better with the addition of 0.1g of SHMs.

[0021] like Figure 3 As shown in (ab), the formation process of the STEP / PVDF-SHMs film was observed under visual and optical microscopes. The phase separation process and the film formation process can be directly observed from the figure.

[0022] like Figure 3 As shown in (cc"), the surface morphology of the STEP / PVDF-SHMs membrane was observed under SEM. (c) shows that the membrane surface has abundant pores; (c') through internal observation of the membrane, the successful doping of SHMs inside can be seen. (c") After spraying a PDMS hydrophobic layer, it can be seen that the surface of the membrane is a dense hydrophobic layer without pores.

[0023] like Figure 3 As shown in (d-d'), EDS analysis of STEP / PVDF-SHMs membranes. (d) is the membrane without hydrophobic modification, which is rich in Si and N elements; (d') is the membrane after hydrophobic modification, and the surface of the material showed no N element after testing, proving that the hydrophobic layer is completely encapsulated.

[0024] like Figure 3(e) shows the bacterial activity test of the STEP / PVDF-SHMs membrane. After the membrane was prepared, it was cut into pieces, diluted, and then cultured for microorganisms. It can be seen that the microbial activity was very good, proving that the entire membrane preparation process does not affect the survival of microorganisms and is very microbial-friendly.

[0025] Example 2: The superhydrophobic membrane prepared using a green solvent according to the present invention exhibits superior selective adsorption and self-cleaning capabilities. Place 20 mL of distilled water in a petri dish and stain the diesel fuel with Oil Red O. The diesel fuel, being less dense, floats on the surface. Place the material in the water with tweezers; the material selectively adsorbs the diesel fuel.

[0026] If sludge, strong acid solutions with pH=1 and pH=14 are dropped onto the membrane, the membrane will self-clean and will not be contaminated by these solutions.

[0027] like Figure 4 (ab) shows the hydrophobic angle and selective adsorption capacity of the STEP / PVDF-SHMs membrane. (a) PVDF-SHMs without PDMS hydrophobic coating have no hydrophobicity and a contact angle with water of 0°. The hydrophobic angle of the membrane after PDMS hydrophobic coating can reach 153.2°. (b) Diesel fuel was stained with Oil Red O, and a small piece of the membrane was cut from it in a petri dish. The selective adsorption of diesel fuel by the membrane can be observed.

[0028] like Figure 4 As shown in (ce), the STEP / PVDF-SHMs membrane also exhibits antifouling properties. In Figure (c), muddy water is dropped onto the membrane, and it can be seen that the muddy water flows directly down and does not remain on the membrane surface, thus not fouling the membrane. In Figure (de), strong acid and strong base solutions with pH=1 and pH=14 are dropped onto the membrane surface, and it can be seen that they do not corrode the membrane.

[0029] Example 3: Application of the present invention in preparing superhydrophobic membranes using green solvents in oil-water separation.

[0030] like Figure 5 (ab) The STEP / PVDF-SHMs membrane of the present invention has significant separation capability for oil-water separation of diesel and chloroform.

[0031] like Figure 5 (c) The STEP / PVDF-SHMs membrane of the present invention also has the ability to demulsify emulsified oil, and can separate emulsified oil.

[0032] Example 4: Application of the present invention in the preparation of superhydrophobic films using green solvents in biodegradation.

[0033] Diesel adsorption degradation experiments were conducted, and the adsorption concentration of diesel at a wavelength of 257 nm was determined using a UV spectrophotometer to evaluate the adsorption performance of diesel. Diesel concentrations of 1, 2, 3, 4, 5, 6, 7, and 8 g / L were prepared using the external standard method. The diesel was analyzed by UV spectrophotometry, and a diesel standard curve was plotted. All adsorption experiments were performed three times, and the average absorbance was used for UV measurement. The residual concentration was determined by fitting the absorbance value to the standard curve.

[0034] At room temperature, 0.1 g of the optimally sized microspheres were placed in saturated diesel fuel and allowed to stand for 24 h, 72 h, 120 h, 168 h, 216 h, and 240 h to degrade the diesel fuel with maximum adsorption capacity. The degradation efficiency was investigated as time increased at the maximum adsorption capacity. The adsorption of diesel fuel was compared with that of free bacteria without fixed material.

[0035] Diesel adsorption degradation experiments were conducted, and the adsorption concentration of diesel at a wavelength of 257 nm was measured using a UV spectrophotometer to evaluate the adsorption performance of diesel. Quantitative analysis was performed using GC-MS (Thermo Scientific TSQ 9610, Thermo Fisher Scientific (China) Co., Ltd.), and the degradation rate was calculated using a standard curve.

[0036] like Figure 6 It can be seen that the STEP / PVDF-SHMs membrane can remove diesel fuel at a rate of over 90%, which is more than 40% higher than the degradation capacity of free bacteria.

[0037] like Figure 7 The degradation mechanism of long-chain alkanes was explained in detail. Metabolites from the degradation of diesel fuel by mixed bacteria were detected by GC-MS. Further analysis of the diesel fuel degradation revealed the following mechanism: microorganisms directly oxidize the terminal methyl groups of straight-chain alkanes, catalyzing the formation of alcohols under the action of a mixture of oxygenases, dehydrogenases, and hydratases in magnesium oxide. These alcohols are then further oxidized to aldehydes and fatty acids. The fatty acids enter the β-oxidation and TCA cycles, ultimately producing CO2 and H2O.

[0038] like Figure 8 (a) Membrane flux tests of STEP / PVDF-SHMs membranes for n-hexane, chloroform, and diesel fuel. The membrane flux of STEP / PVDF-SHMs for n-hexane was tested to be 1441 L / m. -2 h -1 The membrane flux for diesel fuel was 1926 L / m. -2 h -1 The membrane flux for chloroform is 658 L / m³. -2 h -1 ; like Figure 8(b) The STEP / PVDF-SHMs membrane achieves a chloroform resistance of 658 L / m after 10 cycles of use. -2 h -1 The value for n-hexane reached 1441 L m. -2 h -1 The membrane flux of STEP / PVDF-SHMs was tested by cycling. After 10 cycles, the membrane flux of hexane and chloroform decreased, but the membrane flux remained relatively stable.

[0039] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a superhydrophobic film, characterized in that, Includes the following steps: Step 1: Preparation of casting solution The polyvinylidene fluoride (PVDF) powder was dried in a vacuum drying oven at 60°C for further use. PVDF was dissolved in triethyl phosphate (TEP) at a ratio of 15 wt% and stirred at 80°C for 6 h to obtain a casting solution. Add hydroxyethyl cellulose to the casting solution and stir the mixture at 80°C for 24 h to ensure thorough mixing, thus obtaining the casting solution with added hydroxyethyl cellulose. The casting solution with added hydroxyethyl cellulose was poured into a petri dish and degassed at room temperature for 4 h to remove air bubbles, resulting in a degassed casting solution. Step 2: Cultivation of Microorganisms The selected oleophilic bacteria were: A1: Acinetobacter lophii; BTS: Bacillus thuringiensis; A6: Pseudomonas aeruginosa; F1: Nocardia fulva; SP: Penicillium oxalate. After activation, 100 μL of each of the five bacteria were inoculated into five sterile nutrient broth media and cultured by shaking at 37°C and 120 r / min. After 48 hours, 50 ml of each sample was taken and mixed in a 250 ml Erlenmeyer flask to prepare a microbial culture medium. Ensure the number of bacteria reaches 1×10 8 CFU / mL or higher; store at 4°C until use. Step 3: Loading microorganisms onto "single-pore" silica hollow spheres (SHMs) Take the SHMs prepared from the microemulsion system, wash and dry them for later use; By combining autonomous growth and concentration, microorganisms in the microbial culture medium prepared in step two are grown inside and outside hollow spheres to prepare microbial-loaded SHMs. Step 4: Preparation of TEP / PVDF-SHMs membrane Cool the defoamed casting solution obtained in step one to room temperature, take the microbial-loaded SHMs prepared in step three and dope them into the defoamed casting solution; then spray the polyethylene glycol solution onto the casting solution. When spraying, the spray bottle moves at a constant speed on the culture dish to ensure uniformity. Then pour distilled water into a petri dish and incubate in a water bath for 24 hours to allow phase separation and membrane formation. Finally, the formed membrane is freeze-dried to obtain a TEP / PVDF-SHMs membrane; Step 5: Preparation of superhydrophobic membranes STEP / PVDF-SHMs Polydimethylsiloxane (PDMS) was mixed with n-hexane to prepare a hydrophobic modified solution. The hydrophobic modification liquid was sprayed onto the TEP / PVDF-SHMs membrane prepared in step four; it was then dried at room temperature to obtain the superhydrophobic membrane STEP / PVDF-SHMs.

2. The method for preparing a superhydrophobic film according to claim 1, characterized in that: In step one, the concentration of the hydroxyethyl cellulose is 6 wt%.

3. The method for preparing a superhydrophobic membrane according to claim 1, characterized in that: In step three, the SHMs are loaded with microorganisms by at least one of the following methods: adsorption, encapsulation, and cross-linking.

4. The method for preparing a superhydrophobic membrane according to claim 1, characterized in that: In step five, the ratio of PDMS to n-hexane is 1:2 by mass.

5. The method for preparing a superhydrophobic film according to claim 1, characterized in that: In step five, the amount of the hydrophobic modified liquid sprayed is 0.5 g.

6. A superhydrophobic membrane prepared by any one of the superhydrophobic membranes according to claims 1-5.

7. The application of the superhydrophobic membrane according to claim 6 in oil-water separation.

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