A method for preparing a cotton fabric with underwater superoleophobic and oil-water superhydrophobic properties and its application in oil-water separation.

Abstract

This invention belongs to the field of functional textile materials and interface wettability control technology, and discloses a method for preparing cotton fabric with underwater superoleophobic and oil-water superhydrophobic properties and its application in oil-water separation. The method first dissolves nano-titanium dioxide and n-octanol in ethanol to obtain an alcohol phase mixture; then dissolves dopamine hydrochloride and Tris-HCl in deionized water to obtain an aqueous phase mixture; the two phases are mixed and the pH is adjusted to 8.0–8.5, allowing dopamine to oxidize and self-polymerize, forming a composite coating system synergistically with n-octanol, nano-titanium dioxide, and polydopamine; the cotton fabric is then impregnated and dried at 75–85°C for 2–4 h to obtain a cotton fabric with a surface polydopamine / n-octanol / nano-titanium dioxide composite coating. This fabric exhibits superhydrophilicity and oleophilicity in air, with underwater oil contact angles and oil-water contact angles both greater than 155°. Washing with ethanol, drying, and re-pre-wetting allow for reversible switching between the two superwetting properties. It can be used for the efficient separation of oil-water mixtures and oil-in-water and water-in-oil emulsions under gravity.

Description

Technical Field

[0001] This invention belongs to the field of functional textile materials and interface wettability control technology, specifically relating to a method for preparing cotton fabrics with underwater superoleophobic and oil-water superhydrophobic properties and their application in the separation of oil-water mixtures and oil-water emulsions. More specifically, this invention relates to utilizing the biomimetic adhesion properties of polydopamine, combined with n-octanol and nano-titanium dioxide, to construct a stable micro-nano composite rough structure on the surface of cotton fabrics, thereby obtaining a separation material with underwater superhydrophobic and reversible wetting switching capabilities. Background Technology

[0002] With the continuous increase in activities such as oil extraction, oil refining, chemical production, machinery processing, food processing, and domestic wastewater discharge, the discharge of oily wastewater and oil-water mixed pollutants is constantly increasing. Oil pollutants in water bodies usually exist in the form of floating oil, dispersed oil, emulsified oil, and dissolved oil. Among them, emulsified oil is the most difficult to treat due to its small droplet size and high interfacial stability. If discharged directly without effective treatment, it will not only disrupt the ecological balance of aquatic bodies and reduce dissolved oxygen and light transmittance, but may also accumulate through the food chain, posing potential hazards to human health.

[0003] Existing methods for treating oily wastewater mainly include gravity sedimentation, flotation, adsorption, membrane separation, chemical demulsification, and biological treatment. However, these methods generally suffer from problems such as complex processes, high energy consumption, high costs, susceptibility to secondary pollution, or insufficient adaptability to complex oil-water systems. In recent years, separation materials based on special interfacial wettability have received widespread attention in the field of oil-water separation due to their advantages such as high efficiency, low energy consumption, and ease of operation.

[0004] Among them, underwater superwetting materials can achieve efficient and selective separation of oil or water phases by utilizing interfacial selective repulsion under pre-wetting conditions. Generally, underwater superoleophobic materials are suitable for separation systems where the water phase preferentially permeates, while underwater superhydrophobic materials are suitable for separation systems where the oil phase preferentially permeates. If the same material possesses both underwater superoleophobic and underwater superhydrophobic properties, it can achieve switching of wetting states and bidirectional separation according to different operating conditions, thus having higher application value in the field of complex oil-water system treatment.

[0005] However, existing underwater superoleophobic and hydrophobic separation materials still have the following shortcomings: First, the preparation process often relies on fluorine-containing compounds or complex surface processing technology, resulting in high preparation costs and insufficient environmental friendliness; Second, the adhesion between the coating and the substrate is weak, and performance degradation is prone to occur under conditions such as friction, acid and alkali corrosion, and ultraviolet irradiation; Third, most materials only have a single underwater wetting property, making it difficult to achieve reversible switching between underwater superoleophobic and oil-based superhydrophobic properties.

[0006] Therefore, developing a cotton fabric material with a simple preparation process, environmental friendliness, strong adhesion between the coating and the substrate, superoleophobic properties underwater and superhydrophobic properties underwater, and the ability to efficiently separate oil-water mixtures and oil-water emulsions is of great research significance and application prospects. Summary of the Invention

[0007] One objective of this invention is to provide a method for preparing cotton fabrics with superoleophobic properties underwater and superhydrophobic properties in oil. This method utilizes the biomimetic adhesion of polydopamine, combined with the synergistic effect of n-octanol and nano-titanium dioxide, to construct a stable micro-nano composite rough structure on the surface of the cotton fabric. This results in a cotton fabric that exhibits superhydrophilic and oleophilic properties in air, superoleophobic properties underwater, and superhydrophobic properties in oil, while also possessing reversible switching capability for wettability, excellent durability, and good oil-water separation performance.

[0008] The second objective of this invention is to provide the application of the above-mentioned cotton fabric in the separation of oil-water mixtures, the separation of water-in-oil emulsions, and the separation of oil-in-water emulsions.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a cotton fabric with underwater superoleophobic and oil-water superhydrophobic properties includes the following steps: (1) Nano-titanium dioxide and n-octanol were added to ethanol and dispersed by shearing to obtain a uniformly dispersed alcohol phase mixture; (2) Add dopamine hydrochloride and Tris-HCl to deionized water and mix well to obtain an aqueous mixture; (3) Mix the alcohol phase mixture from step (1) with the aqueous phase mixture from step (2), stir evenly, and adjust the pH to weak alkalinity so that dopamine undergoes oxidative self-polymerization and n-octanol, nano-titanium dioxide and polydopamine work together to form a composite coating system. (4) Immerse the original cotton fabric in the reaction solution obtained in step (3), take it out and heat and dry it to form a stable polydopamine / n-octanol / nano titanium dioxide composite coating on the surface of the cotton fabric, and obtain a cotton fabric with underwater superoleophobic and oil-water superhydrophobic properties.

[0010] Preferably, in step (1), the amount of nano-titanium dioxide added is 1~1.5 g, the amount of n-octanol added is 0.5~1 mL, and the volume of ethanol is 50 mL.

[0011] Preferably, in step (1), the amount of dopamine hydrochloride added is 0.4~0.6 g, the amount of Tris-HCl added is 0.24~0.30 g, and the volume of deionized water is 50 mL.

[0012] Preferably, in step (3), the pH of the mixture is adjusted to 8.0~8.5 and reacted under stirring conditions for 18~24 h.

[0013] Preferably, in step (4), the drying temperature is 75~85℃ and the drying time is 2~4 h.

[0014] Preferably, the cotton fabric prepared according to the above preparation method has a micro-nano composite rough structure on its surface, which is composed of a polydopamine adhesion layer and n-octanol-modified nano-titanium dioxide; the cotton fabric can be rapidly wetted by water and oil in air, and has a contact angle of more than 155° with oil droplets underwater and a contact angle of more than 155° with water droplets underwater.

[0015] The present invention also provides a method for reversibly switching the wettability of the above-mentioned cotton fabric, characterized in that: when the cotton fabric is pre-wetted with water, it exhibits superoleophobic properties underwater; when the cotton fabric is pre-wetted with oil, it exhibits superhydrophobic properties underwater; and the reversible switching between the two states is achieved by washing with ethanol, drying, and re-pre-wetting.

[0016] The present invention also provides an application of the above-mentioned cotton fabric in oil-water separation, characterized in that: the cotton fabric is clamped in a separation device and pre-wetted with a target continuous phase, and efficient separation of oil-water mixture or oil-water emulsion is achieved under gravity drive.

[0017] According to the above applications, the oil-water mixture includes one or more of the following systems: dichloromethane / water, toluene / water, chloroform / water, xylene / water, and n-hexane / water.

[0018] According to the above applications, the emulsion includes oil-in-water emulsions and water-in-oil emulsions.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The preparation process is simple and the conditions are mild. This invention uses a combination of solution mixing, impregnation and heating drying to complete the surface functionalization of cotton fabrics. It does not require complex equipment and harsh reaction conditions, and is suitable for large-scale preparation. (2) The coating is firmly bonded to the substrate. Polydopamine has excellent biomimetic adhesion ability and can form a stable adhesion layer on the surface of cotton fabric, so that n-octanol and nano titanium dioxide can be firmly loaded on the fiber surface, thereby improving the stability and durability of the coating; (3) It possesses both underwater superoleophobic and oil-water superhydrophobic properties. The resulting cotton fabric exhibits superhydrophilicity and oleophilicity in air, and its contact angle with various oil droplets can reach more than 155° underwater, and its contact angle with water droplets can also reach more than 155° in oil, demonstrating excellent underwater superhydrophobic and superhydrophobic properties; (4) Possesses reversible switching capability for wettability. Cotton fabrics can be used for underwater superoleophobic separation after being pre-wetted with water; and can be used for underwater superhydrophobic separation after being pre-wetted with oil. After washing with ethanol and re-pre-wetting, it can switch between the above two states multiple times to meet the requirements of separation on demand; (5) Excellent durability. The obtained cotton fabric can still maintain a high contact angle under strong acid, strong alkali and ultraviolet irradiation conditions; the contact angle changes little after 100 times of sandpaper rubbing, indicating that it has good mechanical stability and environmental adaptability. Attached Figure Description

[0020] Figure 1 Scanning electron microscope (SEM) images of the surface morphology of cotton fabrics after treatment with different components. (a) and (b) are SEM images of Comparative Example 2 and their corresponding magnifications; (c) and (d) are SEM images of Comparative Example 3 and their corresponding magnifications; (e) and (f) are SEM images of Example 1 and their corresponding magnifications. Figure 2 The figures show the test results of the acid resistance, alkali resistance, UV resistance, and abrasion resistance of the cotton fabric obtained by this invention. (a) pH=1, (b) pH=14, (c) UV light, (d) friction; Figure 3 The images show the macroscopic appearance and microscopic observation results of the cotton fabric obtained in this invention before and after separation of water-in-oil emulsion and oil-in-water emulsion. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. For those skilled in the art, equivalent substitutions, simple modifications, or combination optimizations made to the present invention without departing from the spirit and substance of the present invention should all fall within the scope of protection of the present invention.

[0022] Example 1: A method for preparing a polydopamine / n-octanol / titanium dioxide cotton fabric includes the following steps: (1) Weigh 1 g of nano titanium dioxide and 0.5 mL of n-octanol, add them to 50 mL of ethanol, and disperse them evenly using a high-speed shearing method to obtain an alcohol phase dispersion; (2) Weigh 0.4 g of dopamine hydrochloride and 0.24 g of Tris-HCl, add them to 50 mL of deionized water, mix well, and obtain an aqueous mixture; (3) The above alcohol phase dispersion and aqueous phase mixture were mixed and stirred evenly under high shear. The pH of the system was adjusted to 8.5 and reacted for 24 h under stirring conditions. During this process, dopamine underwent oxidative self-polymerization to form polydopamine, while n-octanol and nano-titanium dioxide synergistically participated in the construction of the surface composite structure; (4) Immerse the original cotton fabric in the above reaction solution to ensure that the coating system is in full contact with the cotton fabric fibers. After removal, place it in an 80°C oven to dry for 2 hours. A stable polydopamine / n-octanol / nano titanium dioxide composite coating can be formed on the surface of the cotton fabric, resulting in a cotton fabric with underwater superoleophobic and oil-based superhydrophobic properties.

[0023] Example 2: This embodiment is basically the same as that of embodiment 1, except that in step (1), 1.5 g of nano titanium dioxide and 1 mL of n-octanol are weighed, and the other conditions are the same as those in embodiment 1.

[0024] Comparative Example 1: Untreated commercial cotton fabric was used as a sample of raw cotton fabric.

[0025] Comparative Example 2: A method for preparing n-octanol / titanium dioxide cotton fabric includes the following steps: (1) Weigh 1 g of nano titanium dioxide and 0.5 mL of n-octanol, add them to 50 mL of ethanol, and disperse them evenly by high-speed shearing to obtain an alcohol phase dispersion; (2) The original cotton fabric was immersed in the above alcohol phase dispersion to ensure that the coating system was in full contact with the cotton fabric fibers. After removal, it was placed in an oven at 80°C for 2 h to dry, thus obtaining n-octanol / titanium dioxide cotton fabric.

[0026] Comparative Example 3: A method for preparing a polydopamine / n-octanol cotton fabric includes the following steps: (1) Take 0.5 mL of n-octanol and add it to 50 mL of ethanol. Disperse it evenly using a high-speed shearing method to obtain an alcohol phase dispersion; (2) Take 0.4 g of dopamine hydrochloride and 0.24 g of Tris-HCl, add them to 50 mL of deionized water, mix well, and obtain an aqueous mixture; (3) The above alcohol phase dispersion and aqueous phase mixture were mixed and stirred evenly under high shear. The pH of the system was adjusted to 8.5 and reacted for 24 h under stirring conditions. During this process, dopamine undergoes oxidative self-polymerization to form polydopamine, while n-octanol synergistically participates in the construction of the surface composite structure; (4) Immerse the original cotton fabric in the above reaction solution to ensure that the coating system is in full contact with the cotton fabric fibers. After removal, place it in an oven at 80°C for 2 hours to dry, and obtain polydopamine / n-octanol cotton fabric.

[0027] Performance Testing and Results Analysis To verify the surface morphology, wettability, stability, and oil-water separation performance of the underwater superoleophobic and oil-water superhydrophobic fabrics obtained in this invention, the samples obtained in the examples and comparative examples were tested as follows.

[0028] Surface wettability test The surface wettability of each sample was tested in air, underwater, and in oil, using chloroform as a simulated oil. The results are shown in Table 1. In Comparative Example 1, the water contact angle in air was (112.0 ± 1.5)°, and the oil contact angle in air was approximately 0°. In Examples 1 and 2, the water and oil contact angles in air were close to 0°, while the oil contact angle underwater and the water contact angle underwater both exceeded 150°. These results indicate that the polydopamine / n-octanol / titanium dioxide cotton fabric exhibits superhydrophilic and oleophilic properties in air, superoleophobic underwater, and superhydrophobic in oil, demonstrating that the modified cotton fabric possesses superhydrophobic and superhydrophobic properties underwater.

[0029] Table 1 Surface wettability of different cotton fabrics

[0030] Surface morphology analysis The formation of underwater superaphtholytic surfaces is closely related to the rough structure of the material surface. The morphology of the sample coating was characterized by scanning electron microscopy, and the results are shown in [Figure number missing]. Figure 1 Different component combinations significantly affect the surface structure and stability. In Comparative Example 2, which contains only n-octanol and nano-titanium dioxide, although solid particles adhere to the surface of the cotton fibers, the particles are not firmly attached and easily fall off after friction. In Comparative Example 3, which contains only n-octanol and polydopamine, a black coating forms on the fiber surface, but no obvious rough micro / nano structure is formed. In Example 1, which contains n-octanol, polydopamine, and nano-titanium dioxide simultaneously, a large number of densely distributed protrusions form on the fiber surface, constructing a stable micro / nano composite rough structure, thereby endowing the cotton fabric with excellent underwater superhydrophobic properties.

[0031] Underwater superhydrophobicity and reversible switching test of wettability The cotton fabric obtained in Example 1 was completely pre-wetted with water or oil, and the contact angles of different oils or water were measured underwater or in oil. Trichloromethane, toluene, dichloromethane, xylene, and n-hexane were used as simulated oils. The results are shown in Table 2. The test results show that the underwater oil contact angle of the cotton fabric reached over 155°, indicating excellent underwater superoleophobic properties; its oil-water contact angle reached over 158°, indicating excellent oil-water superhydrophobic properties.

[0032] Table 2. Underwater oleophobicity and oil-water hydrophobicity of polydopamine / n-octanol / titanium dioxide cotton fabrics

[0033] The cotton fabric from Example 1 was first pre-wetted with water, and its underwater oil contact angle was measured. Then, the fabric was washed with anhydrous ethanol to remove the pre-wetting liquid, dried, and then pre-wetted with oil again, and the oil-water contact angle was measured. This process was repeated multiple times for switching tests, and the results are shown in Table 3. The results indicate that the cotton fabric can stably switch between an underwater superoleophobic state and an oil-superhydrophobic state, and the contact angle remains at a high level, demonstrating its good reversible response capability.

[0034] Table 3 Reversible switching of wettability of polydopamine / n-octanol / titanium dioxide cotton fabrics

[0035] Durability test The test results of the acid resistance, alkali resistance, UV resistance and abrasion resistance of the cotton fabric obtained by this invention are shown in the figure. Figure 2 .

[0036] The cotton fabric obtained in Example 1 was immersed in hydrochloric acid solution (pH=1) and sodium hydroxide solution (pH=14) for 48 hours, respectively. Samples were taken periodically, and the underwater oil contact angle and the oil-water contact angle were measured. The results showed that the contact angle of the cotton fabric changed little in acidic and alkaline environments, remaining above 155°, indicating that it has excellent acid and alkali resistance.

[0037] The cotton fabric obtained in Example 1 was irradiated under 254 nm ultraviolet light with a light intensity of 0.1 W / cm². 2 The irradiation distance was 15 cm, and the duration was 48 h. The results showed that there was no significant decrease in the underwater oil contact angle and the oil-water contact angle, indicating that it has good UV resistance.

[0038] The cotton fabric obtained in Example 1 was fixed on a substrate, and 80-grit sandpaper was used as the friction material. The cotton fabric was rubbed back and forth under a pressure of 2N, with a single rubbing distance of 10 cm. The test results showed that after 100 friction cycles, the underwater oil contact angle and the oil-water contact angle of the cotton fabric only decreased slightly, and the overall angle was still above 155°, indicating that the coating has excellent mechanical stability.

[0039] Oil-water mixture separation performance test Using the cotton fabric obtained in Example 2 as the separation medium, gravity-driven separation was performed on mixed systems of dichloromethane / water, trichloromethane / water, toluene / water, xylene / water, and petroleum ether / water, with an oil-to-water volume ratio of 1:1. The separation flux and efficiency results are shown in Table 4. Regardless of whether the oil phase density was higher or lower than that of water, the corresponding separation efficiency reached over 99%, and the water flux was greater than 2700 L·m⁻¹. -2 ·h -1 .

[0040] Table 4. Separation performance of polydopamine / n-octanol / titanium dioxide cotton fabric for different oil-water mixtures

[0041] Oil-water emulsion separation performance test 1 mL of chloroform and 0.1 wt% Tween 80 were added to 99 mL of deionized water, and the mixture was stirred at 400 rad / min for 4 h to obtain a stable oil-in-water emulsion. 1 mL of water and 0.1 wt% Tween 80 were added to 99 mL of toluene, and the mixture was stirred at 400 rad / min for 4 h to obtain a stable water-in-oil emulsion. The cotton fabric obtained in Example 1 was used as a separation membrane to separate the chloroform oil-in-water emulsion and the toluene water-in-oil emulsion under gravity.

[0042] like Figure 3 As shown, the emulsion was milky white before separation and a large number of micron-sized droplets could be observed under a microscope; after separation, the filtrate became significantly clearer, and no obvious oil or water droplets were observed under a microscope, indicating that the cotton fabric has excellent separation effect on both water-in-oil emulsions and oil-in-water emulsions.

[0043] It should be noted that the present invention is not limited to the specific embodiments described above. Equivalent substitutions, simple modifications, or combined optimizations made by those skilled in the art to the technical solutions of the present invention without departing from the spirit and essence of the invention should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a cotton fabric with underwater superoleophobic and oil-water superhydrophobic properties, characterized in that, Includes the following steps: (1) Nano-titanium dioxide and n-octanol were added to ethanol and dispersed by shearing to obtain an alcohol phase mixture; (2) Add dopamine hydrochloride and Tris-HCl to deionized water and mix well to obtain an aqueous mixture; (3) Mix the alcohol phase mixture with the aqueous phase mixture, stir evenly, and adjust the pH of the system to weak alkalinity so that dopamine undergoes oxidative self-polymerization and n-octanol, nano titanium dioxide and polydopamine synergistically form a composite coating system. (4) The pretreated cotton fabric is immersed in the reaction solution obtained in step (3), and then heated and dried to form a stable polydopamine / n-octanol / nano titanium dioxide composite coating on the surface of the cotton fabric, thereby obtaining a cotton fabric with underwater superoleophobic and oil-water superhydrophobic properties.

2. The preparation method according to claim 1, characterized in that, In step (1), the amount of nano-titanium dioxide added is 1 to 1.5 g, the amount of n-octanol added is 0.5 to 1 mL, and the volume of ethanol is 50 mL.

3. The preparation method according to claim 1, characterized in that, In step (2), the amount of dopamine hydrochloride added is 0.4-0.6 g, the amount of Tris-HCl added is 0.24-0.30 g, and the volume of deionized water is 50 mL.

4. The preparation method according to claim 1, characterized in that, In step (3), the pH of the system is adjusted to 8.0 to 8.5 and reacted for 18 to 24 h under stirring conditions.

5. The preparation method according to claim 1, characterized in that, In step (4), the heating and drying temperature is 75-85℃ and the drying time is 2-4 h.

6. The cotton fabric prepared by the method according to any one of claims 1 to 5, characterized in that, The surface of the cotton fabric has a micro-nano composite rough structure composed of a polydopamine adhesion layer and n-octanol-modified nano-titanium dioxide.

7. The cotton fabric according to claim 6, characterized in that, The cotton fabric can be rapidly wetted by both water and oil in the air, and has a contact angle of more than 155° with oil droplets underwater and a contact angle of more than 155° with water droplets underwater.

8. A method for reversibly switching the wettability of the cotton fabric as described in claim 6 or 7, characterized in that, The cotton fabric exhibits an underwater superoleophobic state after being pre-wetted with water, and an oil-based superhydrophobic state after being pre-wetted with oil; the underwater superoleophobic state and the oil-based superhydrophobic state can be reversibly switched through ethanol washing, drying and re-pre-wetting.

9. The application of the cotton fabric according to claim 6 or 7 in oil-water separation, characterized in that, The cotton fabric is clamped in the separation device and pre-wetted with a target continuous phase to achieve the separation of oil-water mixtures or oil-water emulsions under gravity drive.

10. The application according to claim 9, characterized in that, The target continuous phase is water or oil; when water is used as the pre-wetting continuous phase, the cotton fabric is used for separation where the water phase preferentially permeates; when oil is used as the pre-wetting continuous phase, the cotton fabric is used for separation where the oil phase preferentially permeates.

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