Pda / cyclodextrin modified alumina-based superhydrophilic composite membrane for oil-water separation

Abstract

The application discloses a polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane for efficiently separating oil and water as well as a preparation method and application thereof, and belongs to the technical field of environment functional material preparation, and specifically adopts a wet impregnation oxidation method to synthesize the polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane. The composite membrane has good oil-water separation performance, can efficiently and selectively intercept oil in oil-in-water emulsion, provides an effective solution for continuously polluting the environment by oily wastewater, and has great application potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of environmental functional material preparation, and particularly relates to a polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane for efficient oil-water separation and a preparation method and application thereof. BACKGROUND

[0002] Oil and related industries inevitably produce a large amount of oil-water mixture in the process of industrial production and operation. The traditional separation technology has the disadvantages of low efficiency and large energy consumption. Considering sustainability, it is urgent to develop a fast, economical and environmentally friendly oil-water separation method to realize the full recovery of oil and water in oily wastewater.

[0003] Designing the surface of the ceramic membrane into a super-hydrophilic interface can selectively intercept oil in the oil-water mixture, and can greatly reduce the fouling by avoiding direct contact between the oil and the interface. Dopamine is a relatively common catecholamine substance. The amino group contained in lysine and the catechol in 3,4-dihydroxy-L-phenylalanine (DOPA) in the molecular structure of dopamine can spontaneously oxidize and polymerize to form polydopamine (PDA) in a weak alkaline environment. The strong covalent / non-covalent interaction between catechol and the surface of the ceramic membrane base can enable dopamine to be firmly deposited on the surface of the ceramic membrane, and the rich hydrophilic groups (i.e. hydroxyl and amino functional groups) from the PDA modified layer can impart the ceramic membrane with stronger hydrophilicity, which is conducive to the efficient oil-water separation, and is a new type of composite membrane with potential development prospects. β-cyclodextrin (β-CD) is a natural cyclic oligosaccharide composed of 7 pyranose units connected by α-(1-4) bonds. The molecular structure is wide at the top and narrow at the bottom, and the hollow barrel shape. The inside of the hollow barrel is hydrophobic, and the outside is hydrophilic due to the presence of a large number of hydroxyl groups. Due to the special barrel structure and rich hydroxyl functional groups of β-cyclodextrin, it can provide a convenient channel for water molecule transmission, greatly improving the hydrophilicity and permeability of the membrane surface. SUMMARY

[0004] The purpose of the present application is to provide a polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane for efficient oil-water separation and a preparation method and application thereof. The composite membrane has good oil-water separation performance, and its preparation process is simple, the production cost is low, the requirement for equipment is not high, and it has good application prospect.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane for efficient oil-water separation is prepared by oxidizing dopamine to polydopamine by wet impregnation oxidation method, then making it cross-linking reaction with β-cyclodextrin, and uniformly dispersing on the surface of alumina ceramic membrane; the preparation method comprises the following steps:

[0007] 1) Pretreatment of alumina ceramic membrane: ultrasonic treatment of alumina ceramic membrane in deionized water and anhydrous ethanol for 20 min respectively, then the ceramic membrane surface was washed thoroughly with deionized water and dried at 60 DEG C for 12 h;

[0008] 2) Preparation of polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane: dopamine and beta-cyclodextrin were dissolved in Tris buffer solution to obtain a mixed solution containing 20 mg / mL dopamine and 20 mg / mL beta-cyclodextrin; then the pretreated alumina ceramic membrane was immersed in the obtained mixed solution, and oscillated in a shaking bed at 25 DEG C and 75 rpm for 1-4 h to make the self-polymerization reaction occur on the surface of the alumina ceramic membrane, then the reacted alumina ceramic membrane was washed with deionized water for three times, and then naturally dried to obtain the polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane.

[0009] Further, the alumina ceramic membrane is specifically a microfiltration alumina ceramic membrane with a pore size of 1 μm.

[0010] Further, the mass ratio of polydopamine in the composite membrane is 15.2%-17.8%, and the mass ratio of beta-cyclodextrin is 18.2%-19.6%.

[0011] The obtained polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane can separate oil in water emulsion, so it can be used for the treatment of oily wastewater.

[0012] The significant advantages of the present application are:

[0013] (1) The present application firstly loads dopamine and beta-cyclodextrin on the microfiltration alumina ceramic membrane by self-polymerization of dopamine into polydopamine and cross-linking reaction with beta-cyclodextrin, and develops a new type of oil-water separation material with super-hydrophilic material highly dispersed on the microfiltration ceramic membrane.

[0014] (2) The preparation method of the present application is simple and convenient, and the composite membrane can be quickly synthesized.

[0015] (3) The composite membrane prepared by the present application can realize efficient oil-water separation, and can separate oil in water emulsion, which provides a potential solution for the continuous pollution of oily wastewater to the environment, and has high practical value. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The surface macrograph and field emission scanning electron microscope graph of Al2O3 original membrane (a) and polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane (b-f) obtained in examples 1-4.

[0017] Figure 2 X-ray photoelectron spectroscopy analysis diagram of the Al2O3 original film and the polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite film obtained in Example 3.

[0018] Figure 3 Oil-water separation effect diagram of the Al2O3 original film and the polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite film obtained in Example 3. DETAILED DESCRIPTION

[0019] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0020] Preparation of Tris buffer solution: weigh 6.06 g of tris(hydroxymethyl)aminomethane in a beaker, add 15 mL of 1 mol / L hydrochloric acid, and then transfer to a 1000 mL volumetric flask after mixing uniformly, and finally dilute to 1000 mL with deionized water to prepare a Tris buffer solution.

[0021] Pretreatment of alumina ceramic membrane: a microfiltration alumina ceramic membrane with a diameter of 47 mm, a thickness of 3.0 mm, and a pore size of 1 μm was ultrasonically treated in deionized water and anhydrous ethanol for 20 min respectively, and after ultrasonic treatment, the ceramic membrane surface was thoroughly washed with deionized water, and finally dried at 60 ℃ for 12 h, marked as Al2O3 original film.

[0022] Example 1 Preparation of polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite film

[0023] Weigh 60 mg of dopamine and 60 mg of β-cyclodextrin in a culture dish, add 30 mL of Tris buffer solution to prepare a dopamine / cyclodextrin mixed solution, then immerse the pretreated alumina ceramic membrane in the culture dish and put it into a shaking bed, and oscillate at 25 ℃ and 75 rpm for 1 h, so that a self-polymerization reaction occurs on the surface of the alumina ceramic membrane, take out the reacted alumina ceramic membrane, wash it with deionized water three times, and then dry naturally to obtain a polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite film, marked as 1 h-PDA / CD-Al2O3 film.

[0024] Example 2 Preparation of polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite film

[0025] Take 60 mg dopamine and 60 mg β-cyclodextrin in a culture dish, add 30 mL Tris buffer solution to prepare a dopamine / cyclodextrin mixed solution, then immerse the pretreated alumina ceramic membrane in the culture dish and put it into a shaker, oscillate at 25 °C and 75 rpm for 2 h, so that the self-polymerization reaction occurs on the surface of the alumina ceramic membrane. Take out the reacted alumina ceramic membrane, wash it with deionized water three times, and dry it naturally to obtain a polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane, denoted as 2 h-PDA / CD-Al2O3 membrane.

[0026] Example 3 Preparation of polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane

[0027] Take 60 mg dopamine and 60 mg β-cyclodextrin in a culture dish, add 30 mL Tris buffer solution to prepare a dopamine / cyclodextrin mixed solution, then immerse the pretreated alumina ceramic membrane in the culture dish and put it into a shaker, oscillate at 25 °C and 75 rpm for 3 h, so that the self-polymerization reaction occurs on the surface of the alumina ceramic membrane; take out the reacted alumina ceramic membrane, wash it with deionized water three times, and dry it naturally to obtain a polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane, denoted as 3 h-PDA / CD-Al2O3 membrane.

[0028] Example 4 Preparation of polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane

[0029] Take 60 mg dopamine and 60 mg β-cyclodextrin in a culture dish, add 30 mL Tris buffer solution to prepare a dopamine / cyclodextrin mixed solution, then immerse the pretreated alumina ceramic membrane in the culture dish and put it into a shaker, oscillate at 25 °C and 75 rpm for 4 h, so that the self-polymerization reaction occurs on the surface of the alumina ceramic membrane; take out the reacted alumina ceramic membrane, wash it with deionized water three times, and dry it naturally to obtain a polydopamine / cyclodextrin modified alumina-based super-hydrophilic composite membrane, denoted as 4 h-PDA / CD-Al2O3 membrane.

[0030] Performance test

[0031] Figure 1Macroscopic images and field emission scanning electron microscope (FESEM) images of the original Al2O3 film and the polydopamine / cyclodextrin-modified alumina-based superhydrophilic composite films obtained in Examples 1-4 are shown. As can be seen from the images, compared to the original Al2O3 film, the surface color depth of the polydopamine / cyclodextrin-modified alumina-based superhydrophilic composite films obtained in Examples 1-4 is directly proportional to the self-polymerization reaction time. Furthermore, the original Al2O3 ceramic film surface is relatively smooth, while with increasing deposition time, larger PDA / CD aggregates gradually appear on the film surface, thus increasing the film roughness. In addition, experiments showed that the composite layer of the 3 h-PDA / CD-Al2O3 film did not detach after repeated rinsing or immersion in deionized water.

[0032] Figure 2 X-ray photoelectron spectroscopy (XPS) spectra of the original Al2O3 film and the polydopamine / cyclodextrin-modified alumina-based superhydrophilic composite film obtained in Example 3. The figures show that the Al2p peak at 73.65 eV on the original Al2O3 film can be attributed to Al-O bonds, but no Al2p peak can be identified on the 3 h-PDA / CD-Al2O3 film. This is because the PDA / CD layer formed on the surface of the original Al2O3 film completely covers the Al2O3. Simultaneously, compared to the original Al2O3 film, a new N1s peak of an NC bond can be observed at 399.48 eV, indicating the presence of a PDA / CD coating on the film surface.

[0033] Figure 3 The graph shows the oil-water separation performance of the original Al2O3 membrane and the polydopamine / cyclodextrin-modified alumina-based superhydrophilic composite membrane obtained in Example 3. As can be seen from the graph, the flux of the original Al2O3 membrane for all three oil-in-water emulsions decreased significantly within 1 h, with the maximum decrease observed in the dichloromethane emulsion flux, from 412.86 ± 24.23 L / m³. 2 h dropped sharply to 190.03 ± 20.19 L / m 2 This indicates significant membrane fouling. The flux decline of the 3 h-PDA / CD-Al2O3 membrane for all three oil-in-water emulsions was much smaller than that of the original Al2O3 membrane. Furthermore, the initial flux of the original Al2O3 membrane for all three oil-in-water emulsions was lower than that of the 3 h-PDA / CD-Al2O3 membrane, with the 3 h-PDA / CD-Al2O3 membrane exhibiting the highest flux for the dichloromethane emulsion, at 496.74 ± 25.36 L / m³. 2 Furthermore, the oil rejection rate of the 3 h-PDA / CD-Al2O3 membrane is much higher than that of the original Al2O3 membrane. Among them, the 3 h-PDA / CD-Al2O3 membrane has the highest oil rejection rate for n-hexane emulsion, reaching 99.86%, and the oil rejection rates for the other two emulsions can also reach over 99%.

[0034] The above merely describes preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A highly efficient polydopamine / cyclodextrin-modified alumina-based superhydrophilic composite membrane for oil-water separation, characterized in that: Dopamine was oxidized to polydopamine using a wet impregnation oxidation method, and then it was cross-linked with β-cyclodextrin and uniformly dispersed on the surface of an alumina ceramic membrane to obtain a polydopamine / β-cyclodextrin modified alumina-based superhydrophilic ceramic composite membrane with high oil-water separation performance.

2. The polydopamine / cyclodextrin modified alumina-based superhydrophilic composite membrane according to claim 1, characterized in that: The composite membrane contains 15.2%-17.8% polydopamine and 18.2%-19.6% β-cyclodextrin by mass.

3. A method for preparing a polydopamine / cyclodextrin modified alumina-based superhydrophilic composite membrane as described in claim 1, characterized in that: Includes the following steps: 1) Pretreatment of alumina ceramic membrane: The alumina ceramic membrane was ultrasonically treated in deionized water and anhydrous ethanol for 20 min respectively, then the surface of the ceramic membrane was thoroughly rinsed with deionized water and dried at 60 ℃ for 12 h. 2) Preparation of polydopamine / cyclodextrin modified alumina-based superhydrophilic composite membrane: Dopamine and β-cyclodextrin were dissolved in Tris buffer solution to obtain a mixed solution containing 20 mg / mL dopamine and 20 mg / mL β-cyclodextrin; the pretreated alumina ceramic membrane was then impregnated with the obtained mixed solution and shaken in a shaker for 1-4 h to allow self-polymerization reaction to occur on the surface of the alumina ceramic membrane; the reacted alumina ceramic membrane was then washed three times with deionized water and allowed to dry naturally to obtain the polydopamine / cyclodextrin modified alumina-based superhydrophilic composite membrane.

4. The method for preparing the polydopamine / cyclodextrin modified alumina-based superhydrophilic composite membrane according to claim 3, characterized in that: The alumina ceramic membrane is specifically a microfiltration alumina ceramic membrane with a pore size of 1 μm.

5. The method for preparing the polydopamine / cyclodextrin modified alumina-based superhydrophilic composite membrane according to claim 3, characterized in that: The oscillation in step (2) is performed at a temperature of 25 ℃ and a rotation speed of 75 rpm.

6. The application of the polydopamine / cyclodextrin modified alumina-based superhydrophilic composite membrane as described in claim 1 in the treatment of oily wastewater.

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