CN113774655A

CN113774655A - Full-water-based super-hydrophobic coating with reversible wettability as well as preparation method and application thereof

Info

Publication number: CN113774655A
Application number: CN202111088266.2A
Authority: CN
Inventors: 陶芙蓉; 刘学亚; 刘利彬; 崔月芝
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2021-09-16
Filing date: 2021-09-16
Publication date: 2021-12-10
Anticipated expiration: 2041-09-16
Also published as: CN113774655B

Abstract

The invention discloses a full water-based super-hydrophobic coating with reversible wettability and a preparation method and application thereof,the preparation method comprises the following steps: mixing FS-3100 aqueous solution and nano TiO₂Mixing and stirring the mixture and cellulose in proportion to form suspension; adding AS and KH-570 into the suspension drop by drop, and stirring uniformly; finally, adding FAS into the mixture, and continuously stirring to obtain a coating; coating the coating on the surface of a substrate to obtain the fully water-based super-hydrophobic coating with reversible wettability. The surface with full water-based reversible wettability prepared by the invention has photocatalytic performance, the original wettability is super-hydrophobic/super-oleophilic, the wettability is converted into super-hydrophilic/underwater super-oleophobic after UV irradiation, and the wettability can be recovered after heating.

Description

Full-water-based super-hydrophobic coating with reversible wettability as well as preparation method and application thereof

Technical Field

The invention belongs to the technical field of paint preparation, and particularly relates to a full water-based super-hydrophobic coating with reversible wettability, and a preparation method and application thereof.

Background

The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.

The development of industry has led to an increasing pollution of water resources by various pollutants. Research has shown that materials with extreme wettability have great potential in oil-water separation. Therefore, super-hydrophobic/super-oleophilic, super-hydrophilic/underwater super-oleophobic and responsive wettability materials are produced. As is well known, a superhydrophobic surface consists of a micro-nano structure and a low surface energy substance. In recent years, production techniques such as photolithography, sol-gel method, chemical vapor deposition method, electrostatic spinning method, and the like have been improved. The most common wet chemical method in these technologies is to use organic solvent to disperse micro-nano particles or dissolve low-surface-energy substances when preparing super-hydrophobic materials, but the organic solvent is usually toxic or volatile. The use of organic solvents not only increases the production cost and the environmental risk but also is not conducive to large-scale production. The use of toxic and volatile organic solvents should be reduced.

In fact, water is a desirable solvent. However, the development of all-water-based superhydrophobic coatings has been slow, since the low surface energy materials required to prepare superhydrophobic surfaces are essentially insoluble in water, and organic binders for improving the mechanical strength of superhydrophobic surfaces are not suitable for use in aqueous systems. The existing preparation methods for the full water-based super-hydrophobic are as follows: "paint + glue" and "one-piece". The 'paint + glue' method separately uses water and adhesive, and solves the problem that organic adhesive is insoluble in water. But the operation is complex compared with the integral type, and the method is not suitable for large-scale production. Some preparation methods utilize water-soluble inorganic Adhesives (AP) to replace traditional organic adhesives (epoxy resin and the like) to prepare the super-hydrophobic material, so that the mechanical strength of the super-hydrophobic system is enhanced. Although the above-mentioned preparation method is "one-piece", coatings prepared using inorganic binders often require very high temperatures during curing, and are obviously not suitable for some substrates that are not resistant to high temperatures.

In addition, the wettability of the existing all-water-based super-hydrophobic coating is single, and most of the coating used in the preparation process is non-renewable resources.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a full water-based super-hydrophobic coating with reversible wettability, and a preparation method and application thereof.

In order to achieve the purpose, the invention is realized by the following technical scheme:

in a first aspect, the invention provides a preparation method of a full water-based super-hydrophobic coating with reversible wettability, which comprises the following steps:

mixing FS-3100 aqueous solution and nano TiO₂Mixing and stirring the mixture and cellulose in proportion to form suspension;

adding AS and KH-570 into the suspension, and then uniformly stirring;

finally, adding FAS into the mixture, and continuously stirring to obtain a coating;

coating the coating on the surface of a substrate to obtain the fully water-based super-hydrophobic coating with reversible wettability.

In some embodiments, AS and KH-570 are added dropwise to the suspension. The reaction can be more fully carried out when the solution is gradually added dropwise.

In some embodiments, the concentration of the FS-3100 aqueous solution is 0.1-0.5. mu.l/ml, preferably 0.2. mu.l/ml.

Further, nano TiO₂And cellulose at a mass ratio of 2 to 5:1, preferably 3 to 5:1, and more preferably 4: 1.

In some embodiments, FS-3100 aqueous, nano-scaleTiO₂Mixing with cellulose, and stirring at 50-70 deg.C for a set time to form suspension.

Further, FS-3100 aqueous solution and nano TiO₂Mixing with cellulose, and stirring at 55-65 deg.C for 1-2 hr to obtain suspension. Further preferably, the suspension is formed by stirring at 60 ℃ for 1.5 h.

In some embodiments, the volume ratio of suspension, AS and KH-570 is 15-25: 2-3:1.

Further, AS and KH-570 are added dropwise to the suspension, followed by stirring at 55-65 ℃ for 0.5-1.5h, preferably at 60 ℃ for 1 h. Too high temperature AS, KH-570 and FAS react too quickly, which accelerates the agglomeration between particles, leading to particle cross-linking; the temperature is too low, the reaction is insufficient, and the modification of the silane coupling agent on the particles is influenced.

In some embodiments, FAS is added to the suspension at a concentration of 0.01-0.03g/ml, preferably 0.0232 g/ml.

Further, after FAS is added to the suspension, stirring is continued for 2-4h, preferably 3 h.

In some embodiments, the coating is prepared by a dipping method for the flexible substrate; for the hard substrate, the spraying mode is adopted for preparation.

In a second aspect, the invention provides a full water-based super-hydrophobic coating with reversible wettability, which is prepared by the preparation method.

In a third aspect, the invention provides application of the all-water-based super-hydrophobic coating with reversible wettability in oil-water separation and photocatalytic degradation of soluble pollutants in water.

In a fourth aspect, the invention provides a preparation method of a filter cloth for oil-water separation and wastewater purification, which comprises the steps of preparing a coating and preparing the filter cloth by soaking cotton cloth; wherein the content of the first and second substances,

the preparation of the coating comprises the following steps: mixing FS-3100 aqueous solution and nano TiO₂Mixing and stirring the mixture and cellulose to form a suspension;

dropwise adding AS and KH-570 into the suspension, uniformly mixing, adding FAS into the suspension, and stirring for a set time to obtain a coating;

and soaking the cotton fabric into the coating for a set time, and taking out and drying to obtain the coating.

In a fifth aspect, the invention provides a filter cloth for oil-water separation and wastewater purification, which is prepared by the preparation method.

The above one or more embodiments of the present invention have the following beneficial effects:

the surface with full water-based reversible wettability prepared by the invention has photocatalytic performance, the original wettability is super-hydrophobic/super-oleophilic, the wettability is converted into super-hydrophilic/underwater super-oleophobic after UV irradiation, and the wettability can be recovered after heating.

The coating utilizes TiO₂The (25nm) and cellulose (25 μm) structure micro-nano roughness, and silane coupling agent AS and KH-570 which can react with water are used for connecting the particles, so that the adhesive force between the particles can be enhanced. FAS is used to reduce the surface tension of the system, thereby obtaining a superhydrophobic surface.

The surface has good super-hydrophobicity, and also has good mechanical stability and chemical stability. The cotton cloth modified by the coating can separate insoluble oil (light oil and heavy oil) in water, can separate stable emulsion, and can even degrade water-soluble organic pollutants (MB, MO and the like). This can satisfy the need for providing an idea for the purification of more complex water pollution systems.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a mechanism and flow diagram for the preparation of coatings according to one or more embodiments of the present invention;

fig. 2 is SEM images of original cotton fabric (a) and modified cotton fabric (b). The modified cotton fabric is mapped to elements of C (C), F (d), N (e), Ti (F), Si (g) and O (h). TGA curves (i) for original and modified superhydrophobic cotton fabrics. Change (j) of the same position of the water drop on the modified glass with time WCA;

fig. 3 shows the change of the image of the water drop on the surface of the coated glass under UV irradiation and heating (a), and the wettability conversion cycle (b). Underwater oil contact angles (c) of the UV treated modified cotton to different organic liquids. HR-XPS spectra of F1s (e), O1s (F) and C1s (g) on the surface of the modified cotton cloth before (upper) UV irradiation, after (middle) UV irradiation and after (lower) heating. Modified cotton wettability transformation mechanism diagram (h);

figure 4 is the change in WCA after rubbing 480 times (inset is the picture of water drops after rubbing cotton) (a) for the modified superhydrophobic cotton. Abrasion test the weight of the sandpaper coated glass is 100g, and the inset is the picture (b) of the experimental set-up. The WCA of the modified glass changes after soaking in different organic solvents (c). The WCA of the modified glass changed within 10min in acid-base solutions of different pH (d). Maintaining the modified glass in different acid-base solutions for super-hydrophobic soaking time and WCA (e);

FIG. 5 is a diagram showing the separation of an oil-water mixture by using a modified cotton cloth;

FIG. 6 is a digital image of the separation of water (a) in diesel, water (b) in octane, water (c) in tetrachloromethane and water (d) in dichloromethane with a modified superhydrophobic cotton fabric, respectively. DLS results of droplet sizes before and after filtration of four water-in-oil emulsions (insets) are (e-h), respectively; flux and separation efficiency (i) of different water-in-oil emulsions;

FIG. 7 is a digital image of an emulsion of diesel oil (a), octane (b), tetrachloromethane (c) and dichloromethane (d) in water separated from each other by a super hydrophilic cotton cloth. The DLS results for droplet sizes before and after filtration of the four oil-in-water emulsions (insets) are (e-h), respectively. Flux and separation efficiency (i) of different oil-in-water emulsions;

FIG. 8 is a mechanism diagram (a) of the modified cotton cloth degrading the dye in water. Degradation of 10. mu.g/mL, 30. mu.g/mL, 50. mu.g/mL MB solution, the UV-visible absorption spectrum of MB solution (b-d) with increasing UV irradiation time. Change in degradation rate the same cotton cloth 6 was multiplied by 10 μ g/mL MB of degradation (f) solution. The solution for the sixth degradation of the UV-visible absorption spectrum of the modified cotton cloth by 10 μ g/mL MB (g). Comparison of degradation rates with or without modification of cotton (h). Comparison of kinetically-explained degradation rates with or without modified cotton (i);

fig. 9 is a diagram showing in situ separation and degradation of a mixture of MB contaminated water and dichloromethane;

FIG. 10 is the change in WCA after oleic acid staining, UV irradiation and heating of the coated cotton fabric (a). Sudan III (b) and MB (c) digital photographs of the degradation of stained cotton fabric. Digital photograph (d) of hexagonal glass mask dyed with MB solution in air after uv irradiation. Photograph of glass in water with hexagonal superhydrophobic regions (e).

In fig. 11, SEM image (a) of cotton surface coating, elemental analysis image (b) of cotton surface coating, water contact angle (d) in air of cotton, wood, glass after coating modification, and rolling angle image (e) of water drop on modified glass surface;

FIG. 12 is EDS and XPS plots of modified cotton cloth surfaces;

FIG. 13 shows the WCA variation of the modified glass treated at high temperature 150 ℃ to 300 ℃ (a) and low temperature-10 ℃ to-50 ℃ (b) for 2 h.

FIG. 14 comparison of the first and sixth degradation rates of MB by the same piece of cotton cloth (a). Color change of different concentrations of MB solutions with UV irradiation (b). Absorption spectrum (c) of MO. Congo red photographs, color comparison before and after degradation of MB + MO mixed solution with Sudan B (d).

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Experimental part

1) Material

Titanium dioxide (TiO)₂) (anatase, hydrophilic, particle size 10-25nm), alpha-cellulose (25 μm) gamma-methacryloxypropyl (KH-570, C)₁₀H₂₀O₅Si), N-aminoethyl-gamma-aminopropyltrimethoxysilane (AS, C)₈H₂₂N₂O₃Si), n-octane, oleic acid, Sudan III, Congo Red by the Aladdin company;

FS-3100 is supplied by DuPont;

1H,1H,2H, 2H-perfluorodecyl trimethoxysilane (FAS) is supplied by Fuji chemical industries, Inc. of Thai, Ji nan Gum;

methylene chloride, carbon tetrachloride, diesel oil, gasoline, ethanol, N-dimethylformamide, sodium chloride (NaCl), sodium hydroxide (NaOH), hydrochloric acid (HCl), petroleum ether, 1, 2-dichloroethane, toluene, ammonia water, acetic acid, Tween-80, and span-80 and Sudan Ming B are provided by national pharmaceutical Agents Co., Ltd;

methylene Blue (MB) and Methyl Orange (MO) were provided by tianjinda mao chemicals, ltd.

All reagents were analytically pure and no special handling. The cotton fabric was a commercial cotton cloth, washed ultrasonically with distilled water and ethanol for 30min, and then completely dried in an oven at 60 ℃.

2) The preparation method of the all-water-based super-hydrophobic coating with reversible wettability comprises the following steps:

FS-3100 (4. mu.l) was added to 20ml of deionized water and sonicated for 20min to form a homogeneous solution. Adding appropriate amount of TiO into the aqueous solution₂And cellulose (mass ratio 4:1), stirred at 60 ℃ for 1.5h to form a suspension, and 2.5ml of AS and 1ml of KH-570 were added dropwise to the suspension, stirred at 60 ℃ for 1 h. Finally, 0.5g of FAS was added thereto, and stirring was continued for 3 hours. The washed cotton cloth was then immersed in the emulsion for approximately 30min and placed in an oven at 100 ℃ to dry. For the preparation of substrates of hard material (glass, wood, aluminium sheets), the suspension is sprayed onto the surface by means of a spray gun (ET4000, STAT, Germany) at a distance of 10cm from the surface. Curing for 8h in a forced air drying oven at 100 ℃ to obtain the super-hydrophobic coating.

3) Testing of Superhydrophobic coating Properties

1. Coating to substrate adhesion test

In order to test the adhesion of the coatings to different substrates, the coatings adhered to the different substrates were adhered to spindles with AB glue, the spindles were loaded with 200g weights, and then dried at room temperature for 3 days. The adhesion between the coating and the substrate was tested by means of pulling with an adhesion tester.

2. Wettability conversion

The modified cotton cloth and glass sheet are super-hydrophobic/super-oleophilic in air environment, and pass through UV-LED lamp (0.45W/cm)^-2λ 365nm) for 90min, the wettability is changed into super-hydrophilic/underwater super-oleophobic. Soaking the irradiated cotton cloth and glass sheet in water, drying in a 150 deg.C forced air drying oven for 12 hr, and recovering to super-hydrophobic/super-oleophylic state. And continuing to research the frequency problem of the modified cotton cloth wettability conversion according to the steps.

3. Preparation of surfactant-containing emulsion

Water-in-oil emulsion: 0.35g of span 80 is weighed and added into a single-neck round-bottom flask, then 57ml of dichloromethane, n-octane, diesel oil and carbon tetrachloride are respectively added, stirred at room temperature until the dichloromethane, the n-octane, the diesel oil and the carbon tetrachloride are completely dissolved, then 1ml of deionized water is added, and stirring is continued at room temperature for 2 hours, thus forming the water-in-oil emulsion with 4 kinds of surfactants.

Oil-in-water emulsion: weighing 0.3g of Tween 80, adding into a single-neck round-bottom flask, adding 60ml of deionized water, stirring at room temperature until the Tween is completely dissolved, adding 2ml of dichloromethane, n-octane, diesel oil and carbon tetrachloride, and continuously stirring at room temperature for 2 hours to form 4 surfactant-stabilized oil-in-water emulsions.

4. Separation of immiscible oil-water mixture and emulsion

Separation of immiscible oil and water mixtures

Separating heavy oil and water with super-hydrophobic/super-oleophilic cotton cloth, irradiating with UV, and converting into super-hydrophilic/underwater super-oleophilic cotton cloth to separate light oil and water. Methylene chloride, 1, 2-dichloroethane, and carbon tetrachloride were used as heavy oils and petroleum ether, toluene, n-octane, and gasoline were used as light oils. The oil (stained with Sudan III) and water (stained with methylene blue) were poured into a separation apparatus at a volume ratio of 1:1 and the oil and water were separated under gravity alone. Note that the cotton cloth was wetted before separating the light oil and water from the ultra hydrophilic/underwater ultra oleophobic cotton cloth. Calculating the flux in the separation process:

wherein V (L) is the volume of the mobile phase before separation, S (m)²) Effective area of cotton cloth separation, and t (h) time of oil-water separation.

5. Separation of oil-in-water and water-in-oil emulsions

And separating the water-in-oil emulsion and the oil-in-water emulsion by using a separation device. 30ml of the emulsion was poured into a separate device and the throughput was calculated by recording the time 20ml of emulsion was collected.

6. UV degradation Property

First, 30ml of prepared 10. mu.g/ml, 30. mu.g/ml, 50. mu.g/ml Methylene Blue (MB) aqueous solution and prepared superhydrophobic cotton cloth (3 m. times.3 cm) were put into a 50ml centrifuge tube, respectively. The centrifuge tube was placed at a distance of about 10cm from the UV-LED lamp and irradiated for a certain time until the solution became colorless. During the degradation process, 3ml of the solution was taken out every 30min and the absorbance of MB was measured with an ultraviolet spectrophotometer. After each degradation, heating the cotton cloth in the air at 120 ℃ for 1h, and performing next degradation after the cotton cloth is dried. The degradation rate (η,%) is given by the formula:

wherein A is₀And A_tThe absorbance at 665nm of the original solution and the solution after t-time irradiation, respectively. (Note: 665nm is a characteristic peak of the MB solution in visible light.)

7. Testing and characterization

The surface morphology of the coatings was measured using a thermal field emission scanning electron microscope (SEM, Germany) with supressatm 55 in Germany at 5 kV. Energy dispersive x-ray (EDX) spectroscopy was observed with a scanning electron microscope (SEM, germany). Thermogravimetric analysis (TGA) was performed using a thermogravimetric analyzer (mettle-toledo). The static contact angle and sliding angle of the surface were measured by a contact angle meter (SL250 USA KINO Industry co., Ltd). The underwater contact angle was measured using the KR ü SS DSA25S (Germany) contact angle system. The composition of the cotton surface was tested using x-ray photoelectron spectroscopy (XPS, Thermo, America, ESCALABXi +). 365nm ultraviolet lamp (SJMAEA-SJUV4M, Shanghai, China) was used for the light irradiation treatment of cotton fabric. The absorbance of the colored solution was measured with an ultraviolet-visible spectrophotometer (UV-2600, Japan). The droplet size was characterized by Dynamic Light Scattering (DLS), Zetasizer Nano ZS 90. The adhesion of the prepared coatings to different substrates was tested using a pull-off adhesion tester (XH-M, Beijing, China).

4) Results and discussion

1. Surface topography and chemical characterization

As described above, the superhydrophobic/superoleophilic all-water-based paint was prepared using a simple method, as shown in FIG. 1. Adding TiO into the mixture₂Dispersing the nano particles and cellulose into an aqueous solution containing a fluorine-containing surfactant (DuPont, FS-3100), adding three silanes of AS, KH-570 and FAS, simply blending, and modifying different substrates by spraying or dip coating. Two silane coupling agents, AS and KH-570, on the one hand aggregate the nanoparticles, building up the roughness required for superhydrophobic coatings, and on the other hand can link the particles to the substrate. FAS, in turn, can lower the surface energy of the coating and complete the hydrophobic modification of the particles. It is known that water has a surface tension of 72.8N/m, and that fluorosurfactants can reduce the surface tension of solvent water and enhance the water solubility of the modified hydrophobic particles.

The surface topography and the chemical composition of the surface of the modified cotton cloth were studied, as shown in fig. 2. In fig. 2a, it can be observed that the cotton surface before modification is smooth and flat. In FIG. 2b, the cotton cloth after modification is rough in surface and TiO₂The nano particles are aggregated into clusters with different sizes under the action of the coupling agent, and the clusters and the micron-sized cellulose particles jointly form the micro-nano roughness required by the super-hydrophobicity. In FIG. 11a, clustered TiO can be seen₂And the cellulose is tightly combined with the flaky cellulose, and the compact structure is more favorable for stabilizing the super-hydrophobicity of the surface.

FIGS. 2C-h, FIG. 12 are EDS and XPS graphs of the modified cotton cloth surface, which shows that C, O, N, F, Si, Ti are uniformly distributed on the cotton cloth surface, and this also shows that the cotton cloth can be successfully modified by a simple dip coating method. The specific content of these elements on the surface of the cotton is presented in FIG. s1 b. In addition, the TGA test showed that the mass ratio of the modified cotton cloth was 27.86%. The above data indicate that water-based superhydrophobic/superoleophilic coatings have been successfully prepared and cotton cloth has been successfully modified.

2. Original wettability

The water contact angle of cotton cloth, wood and glass modified by the coating in the air can reach 160.2 degrees (+ -2 degrees), 156.3 degrees (+ -2 degrees and 163 degrees (+ -2 degrees) (FIG. 11 c), the rolling angles are respectively 9.7 degrees, 5.6 degrees and 3.0 degrees (FIG. 11d), and FIG. 11e is a picture of the rolling angle of water drops on the surface of the modified glass. In FIG. 11c, NaCl, NaOH (1M), HCl (1M) and strongly oxidizing potassium permanganate droplets were spherical on modified wood, cotton, glass. In addition, the coating also has super-hydrophobic properties under oil, and it can be seen from fig. 11e that water (stained by MB) is spherical on the modified glass surface in n-octane. Fig. 2j illustrates the change in water contact angle for a water drop over 9min, and it can be seen that the contact angle ranges from 164 ° (± 2 °) to 158 ° (± 2 °).

3. Wettability transformation and transformation mechanism

The wettability of the original modified cotton cloth is super-hydrophobic/super-oleophilic in air, after UV irradiation for 90min, the wettability is changed into super-hydrophilic/super-oleophobic under water, the wettability can be restored to a super-hydrophobic/super-oleophilic state by heating for 12h at 120 ℃, and the contact angle change in the process is shown as figure 3 a. In fig. 3b it is shown that the modified cotton cloth can be repeatedly switched 3 times between superhydrophobic/superoleophilic and superhydrophilic/underwater superoleophobic. To test the underwater superoleophobicity of cotton cloth after UV irradiation, the contact angles of various light and heavy oils in water were tested. In fig. 3c it is shown that the underwater contact angles for the different oils are all over 150 deg., demonstrating that the cotton fabric has a very good oil repellency.

To investigate the mechanism of the wettability transition, XPS of cotton before and after UV irradiation was analyzed. In FIG. 3d, the change of F, O, C elements before and after UV irradiation is large in the XPS full spectrum. FIG. 3f shows a high resolution spectrum of O1 s. The modified cotton cloth has 4 obvious fitting values of 532.7eV, 532.5eV, 531.1eV and 529.6eV, which represent Si-O-Si, Ti-O-H, Si-O-Ti and Ti-O-Ti. By contrast passing throughThe different treated cotton cloths, O1s, were found to have a significant increase in the Ti-O-H peak area fraction after light irradiation, whereas the Ti-O-H peak area fraction after heating decreased again. Similarly, in FIG. 3g, the high resolution spectrum of C1s shows-CF at 293.8eV and 291.7eV₃、-CF₂The peak area also decreased after the UV irradiation treatment, but recovered after the heating treatment. With respect to-CF₃and-CF₂The change in F1s in FIG. 3e is also evidenced by the change in the pattern of the changes before and after UV irradiation.

From the results of XPS analysis, the mechanism of the modified cotton wettability transition was presumed as shown in fig. 3 h. In TiO₂Has O on the surface₂And H₂Adsorption equilibrium of O. After UV irradiation, TiO on the one hand₂The surface generates a large number of hydrophilic hydroxyl groups. Table S1 shows that the Ti-O-H peak area fraction increased from 34.02% to 51.19% after UV irradiation. On the other hand, TiO₂There is a partial degradation of the low surface energy substances (FAS) on the surface. The two reasons are that the wettability of the modified cotton cloth is changed. But after heating, the TiO₂Oxygen vacancies on the surface will adsorb air O₂So as to replace hydrophilic hydroxyl and restore the super-hydrophobicity of the cotton cloth. In addition, FAS has the property of migrating to the surface at high temperature, which also helps the cotton cloth to recover superhydrophobicity.

4. Stability of the preparation of coatings

To test the durability of the coatings, the WCA was tested under different environments, as shown in fig. 4.

Cotton cloth rubbing test:

the modified cotton cloth was repeatedly rubbed with hands for 3s for 480 times. The change in contact angle during rubbing is shown in fig. 4 a. After the kneading is finished, the water contact angle of the cotton cloth can still reach 152.8 degrees.

Abrasive paper abrasion test:

the coated glass sheet was placed upside down on sandpaper (1000 mesh), and then loaded with a 100g weight, and the cycle was repeated at 20cm, and 10 cycles were allowed. The change in water contact angle during this process is shown in figure 4 b. The results show that the superhydrophobicity remains after abrasion. And the adhesion strength was measured with an adhesion tester. The adhesion strength of the coating on different substrates can reach megapascals levels (e.g., 6.5MPa on ceramic).

Organic liquid and salt solution soaking resistance test:

the modified glass sheet still can keep super-hydrophobicity after being soaked in absolute ethyl alcohol, n-octane, dichloromethane, DMF, tetrahydrofuran, water and sodium chloride (0.1M) solution for 7 days. The WCA after soaking is shown in fig. 4 c.

Acid and alkali resistance test:

soaking the modified glass sheet in NaOH (0.1M), NH₃H₂O(25％)，CH₃COOH, HCl (0.1M,1.0M), aqua regia, and test the WCA of the glass over 10 min. In fig. 4d it can be seen that the WCA of the treated glass sheets did not change much, but the WCA of the glass sheets soaked with aqua regia became 145.9 ° at 10min, still maintaining superhydrophobicity. In fig. 4e, the longest soaking time to maintain superhydrophobicity in the above environment is explored and the coating is found to be more suitable in an acidic environment than a strongly basic environment. Wherein the soak time in HCl (0.1M) was up to 103h and the WCA was 150.1 deg..

And (3) temperature testing: the modified glass was placed at various temperatures (-50 ℃ C. -300 ℃ C.) for 2h and tested for WCA. The variation in WCA is shown in fig. 13, demonstrating that coatings treated at different temperatures can still remain superhydrophobic.

5. Purified water

Oil/water mixture separation

Cotton is the most commonly used 2D material for oil and water separation. The modified cotton cloth is clamped between two glass containers to form an oil-water mixture separating device. Because the modified cotton cloth can be subjected to wettability conversion, different types of oil-water mixture can be separated according to requirements. For the mixture of heavy oil (dichloromethane, 1, 2-dichloroethane, carbon trichloride) and water, modified cotton cloth was used directly. The modified cotton cloth has super-hydrophobicity/super-lipophilicity, heavy oil flows down rapidly under the action of gravity, and water is isolated above the cotton cloth, so that the heavy oil and the water are separated. In fig. 5a, methylene chloride and water were separated by modified cotton. For the mixture of light oil and water, we only need to irradiate the modified cotton cloth with UV to be hydrophilic. In fig. 5b, the superhydrophilic cotton cloth was first wetted with water, and then a mixture of light oil (petroleum ether) and water was poured into the apparatus, and it was found that water passed through the cotton cloth, while petroleum ether was blocked above the cotton cloth by the underwater superoleophobic properties of the cotton cloth. In fig. 5c, several other model oil and water separation efficiencies and throughputs were also tested, with separation efficiencies > 90%. In addition, methylene chloride and petroleum ether were selected as representatives of heavy oil and light oil, respectively, and the separation efficiency of cotton cloth separation was tested 20 times. As can be seen in fig. 5d, the separation efficiency after 20 times and the initial separation efficiency did not change much. This also proves that the oil-water separation efficiency of the cotton cloth is stable.

Water-in-oil and oil-in-water emulsion separation

Water-in-oil or oil-in-water emulsions are the most common oil-water mixtures. Compared with the heterogeneous mixture of oil and water, the emulsion is more stable and is more difficult to separate. The separation of different water-in-oil and oil-in-water emulsions was successfully carried out with modified cotton cloth.

Separation of water-in-oil emulsion: in FIGS. 6a-d, four emulsions were prepared, a-d corresponding to water-in-diesel, water-in-n-octane, water-in-carbon tetrachloride, and water-in-methylene chloride, respectively. Before separation, the emulsion was milk-like in color, turbid. The emulsion after separation became clear and transparent. To further demonstrate the ability of cotton to separate the above emulsion. Dynamic light scattering (DLC) experiments were performed on the emulsions before and after separation, and DLS results for droplet sizes before and after filtration of the four oil-in-water emulsions (insets) are shown in FIGS. 6e-h, respectively (FIG. 6e is a DLS result chart for water-in-diesel, FIG. 6f is a DLS result chart for water-in-n-octane, FIG. 6g is a DLS result chart for water-in-carbon tetrachloride, and FIG. 6h is a DLS result chart for water-in-methylene chloride). The particle size of the emulsion before separation is 100nm-1000nm, and the particle size after separation is below 100 nm. The separation efficiency and flow of the cotton cloth to the four emulsions were also calculated. Figure 6i shows the flux and separation efficiency of different oil-in-water emulsions, from which it can be seen that the separation efficiency of all four emulsions is > 95%.

The wettability can be converted to superhydrophilicity by UV irradiation, and therefore, the separation of oil-in-water emulsions is also possible: modified cotton cloth is used for separating emulsions of diesel oil in water, n-octane oil in water, carbon tetrachloride in water and dichloromethane in water. In FIGS. 7a-b, a photographic comparison of four oil-in-water emulsions before and after separation is shown. The oil-in-water emulsion was milky white before separation. The emulsion after separation is colorless and transparent. FIGS. 7e-h are graphs of the particle size change before and after separation of the four emulsions. Before and after separation, the particle size was changed from 1000-2000nm to 6-15 nm. In fig. 7i, the separation efficiency and throughput of the hydrophilic cotton cloth separated oil-in-water emulsion is shown, and separation efficiency > 99% can be seen.

Photocatalytic degradation of soluble pollutants in water

The actual contaminated water contains not only insoluble oils but also soluble organic chemicals. The modified cotton cloth can degrade soluble pollutants in water through photocatalysis. The mechanism for photocatalytic degradation of soluble contaminants in water is shown in fig. 8 a. TiO 2₂The (anatase) nano particles have strong photoresponse, and can generate high-activity photo-generated electron-hole pairs under the irradiation of ultraviolet rays. A portion of the photogenerated electrons and holes migrate to the TiO₂Surface and H of surface₂O and O₂Reaction to generate high-activity O₂·^-And OH radicals, which are capable of undergoing redox reactions in the presence of water-soluble contaminants to decompose organic species into H₂O and CO₂Etc. to clean water. In order to test the degradation capability of the modified cotton cloth, three methylene blue aqueous solutions of 10. mu.g/mL, 30. mu.g/mL and 50. mu.g/mL are prepared. Under the conditions of the same volume (35mL), the same cotton cloth size (3cm multiplied by 3cm), the same illumination intensity and the same illumination distance (10cm), the degradation of the solutions with the three concentrations respectively needs 150min, 180min and 210 min.

In the process, the solution becomes lighter and lighter until clear, as shown in FIG. 14 b. In order to accurately measure the concentration change of MB, the absorbance of the solution was measured every 30 min. In FIGS. 8b-d, it can be seen that the characteristic MB peak (665nm) is decreasing with increasing irradiation time, indicating that methylene blue is gradually being degraded. In addition, to test the degradation of methylene blue solution by cottonThe liquid circulation performance is that the same piece of modified cotton cloth is used for degrading 10 mu g/mL methylene blue solution for multiple times, and the cotton cloth needs to be dried in an oven at 90 ℃ for 30min between two degradations. The results show that cotton cloth can continuously degrade 6 times of methylene blue solution, and the degradation efficiency of 6 times is stable, as shown in fig. 8 f. In FIG. 8g, the absorbance change over time was measured for the 6 th time, and it can be seen that the absorbance change for the sixth time was slightly faster than the absorbance change for the first time in FIG. 8 c. Presumably, the reason is that TiO increased with the UV irradiation time₂At the same time as MB in the water is degraded, some of the compounds grafted on the cotton cloth are also degraded. This results in TiO₂The exposed sites increase and the degradation rate increases. A graph comparing the first and sixth degradation rates is shown in fig. 14 a. The methylene blue solution is subject to self-degradation under UV irradiation. To explore the effect of self-degradation of the MB solution, the degradation rates of the MB solutions with and without modified cotton were compared, as shown in fig. 8 h. The results show that the modified cotton cloth degrades at a much faster rate than the rate of self-degradation during the overall degradation process. FIG. 8i shows the first order reaction rate constant (k) of the degradation process. Compared with the modified cotton cloth, the degradation rate of the modified cotton cloth is 21-71 times of the self-degradation rate. In addition to using the modified cotton cloth to degrade the MB solution, other common pollutant dyes such as Congo red, Methyl Orange (MO), rhodamine B and mixed solution of MB and MO are explored, and the modified cotton cloth can be finally changed into transparent through degradation, as shown in FIG. 14 d. And FIG. 14c shows the change in absorbance of MO during degradation.

In situ separation and degradation of wastewater

Besides the coating cotton fabric can be degraded and separated independently, the coating cotton fabric is expected to realize the purification of wastewater through an in-situ separation-degradation process. As shown in FIG. 9, a mixture of dichloromethane (30mL, Sudan III staining) and MB-contaminated water (30mL, 10. mu.g/mL) was selected as the target wastewater. The coated cotton fabric was first able to immediately separate the dichloromethane from the aqueous MB solution before uv irradiation due to the superhydrophobicity of the coated cotton fabric. Upon UV irradiation for 100min, MB, which is soluble in water, is degraded. Meanwhile, under the irradiation of ultraviolet rays, the super-hydrophobicity of the coated cotton fabric is gradually changed into super-hydrophilicity. And finally, the purified water permeates into the cotton fabric for collection. The in-situ separation-degradation system can simultaneously separate oil and soluble pollutants and meet higher purification requirements of the industry.

Photocatalytic extension applications

Superhydrophobic surfaces are susceptible to contamination by non-volatile oils. The coated cotton fabric is subjected to photocatalytic removal by using a mixture of oleic acid and absolute ethyl alcohol (volume ratio is 1:1), and the super-hydrophobic property of the coating is detected by ultraviolet irradiation and heating treatment. As shown in fig. 10a, the WCA dropped to around 40 ° after the coated cotton fabric was contaminated with oleic acid. After ultraviolet irradiation and heating, the fabric recovers the super-hydrophobicity, and the WCA is larger than 150 degrees. This process can be reused several times without losing the superhydrophobicity of the coating. The photocatalytic performance of the cotton fabric under ultraviolet irradiation is proved through the degradation of oleic acid. Furthermore, contamination of cotton fabrics with different dyes (e.g. sudan III and MB) can be cleaned by degradation of these dyes under uv irradiation (fig. 10b,10 c).

In addition, different shaped masks may be used to design the imprint in the water. As shown in fig. 10d, a hexagonal mask was used to cover the coated glass. After UV irradiation, the coated glass becomes superhydrophilic except for the hexagonal portion. The superhydrophilic portion was easily stained by MB solution, while the covered portion was not stained due to superhydrophobicity (fig. 10 d). When placed in water, the hexagonal superhydrophobic portions will reflect light due to the large number of bubbles, as shown in fig. 10 e.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a full water-based super-hydrophobic coating with reversible wettability is characterized by comprising the following steps: the method comprises the following steps:

adding AS and KH-570 into the suspension, and stirring uniformly;

2. The method for preparing the all-water-based superhydrophobic coating with reversible wettability according to claim 1, characterized in that: adding AS and KH-570 dropwise to the suspension;

further, the concentration of the FS-3100 aqueous solution is 0.1 to 0.5. mu.l/ml, preferably 0.2. mu.l/ml.

3. The method for preparing the all-water-based superhydrophobic coating with reversible wettability according to claim 1, characterized in that: nano TiO 2₂And cellulose at a mass ratio of 2 to 5:1, preferably 3 to 5:1, and more preferably 4: 1.

4. The method for preparing the all-water-based superhydrophobic coating with reversible wettability according to claim 1, characterized in that: the volume ratio of the suspension, AS and KH-570 is 15-25: 2-3: 1;

further, AS and KH-570 are added dropwise to the suspension, followed by stirring at 55-65 ℃ for 0.5-1.5h, preferably at 60 ℃ for 1 h.

5. The method for preparing the all-water-based superhydrophobic coating with reversible wettability according to claim 1, characterized in that: FAS is added to the suspension at a concentration of 0.01-0.03g/ml, preferably 0.0232 g/ml;

6. The method for preparing the all-water-based superhydrophobic coating with reversible wettability according to claim 1, characterized in that: when the coating is prepared, the flexible substrate is prepared by adopting a dipping method; for the hard substrate, the spraying mode is adopted for preparation.

7. An all-water-based super-hydrophobic coating with reversible wettability, which is characterized in that: prepared by the preparation method of any one of claims 1 to 6.

8. The use of the all water-based superhydrophobic coating with reversible wettability according to claim 7 for oil-water separation and photocatalytic degradation of soluble pollutants in water.

9. A preparation method of filter cloth for oil-water separation and wastewater purification is characterized by comprising the following steps: the method comprises the steps of preparing a coating and preparing filter cloth by dipping cotton cloth; wherein the content of the first and second substances,

10. A filter cloth for oil-water separation and wastewater purification is characterized in that: the preparation method of the compound is as claimed in claim 9.