Preparation method and application of tannic acid-metal complex hydrophilic modified membrane

Abstract

The invention discloses a preparation method and application of a tannic acid-metal complex hydrophilic modified membrane, belonging to the technical field of preparation of environmental functional materials. The preparation method comprises: dissolving tannic acid and a metal ion precursor in a solvent respectively to obtain a tannic acid solution and a metal ion precursor solution; spraying the tannic acid solution onto a base membrane, and after the solvent evaporates, continuing to spray the metal ion precursor solution and volatilizing the solvent to complete a spray assembly, and repeating the spray assembly several times to obtain the tannic acid-metal complex hydrophilic modified membrane. The invention sprays TA and metal ions onto the membrane surface through a spray self-assembly method to assemble the TA-metal complex, so that the base membrane surface is converted from hydrophobic to hydrophilic, thereby realizing large-scale preparation of super-hydrophilic surfaces and effective utilization of raw materials. The prepared membrane exhibits super-hydrophilicity / underwater super-oleophobicity, can efficiently separate different oil-in-water emulsions, and has good anti-fouling properties.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of environmental functional materials, and particularly relates to a preparation method and application of a tannic acid-metal complex hydrophilic modified membrane. Background Art

[0002] The discharge of large amounts of oily wastewater poses a serious threat to human health and the ecological environment, and is an important issue that needs to be addressed urgently. At present, the main oily wastewater treatment technologies at home and abroad include physical methods, chemical methods, physical and chemical methods, biological methods, membrane separation methods, etc. Superhydrophilic / underwater superoleophobic membranes have low adhesion to oil, which can effectively prevent oil droplets from adhering to the membrane surface. They have great advantages in treating oil-in-water emulsions, and therefore have attracted widespread attention from researchers. Surface hydrophilic modification is a commonly used method for hydrophilic modification of membrane surfaces. Because this method is simple to operate, researchers usually use physical and chemical effects to deposit a layer of hydrophilic substances on the membrane surface, such as chitosan, polyvinyl alcohol, polyphenol compounds, etc. Among them, polyphenol compounds have huge advantages in membrane surface modification and have now become an important field in membrane surface modification.

[0003] Tannic acid (TA) is a natural polyphenol compound that is widely found in the roots, stems, leaves of plants and some beverages. TA molecules exhibit unique physical and chemical properties due to their special structure. TA molecules contain a large number of catechol and pyrogallol structures that can undergo complex reactions with some metal ions; in addition, TA has an adhesion force similar to that of dopamine and can adhere firmly to various surfaces; TA molecules contain a large number of phenolic hydroxyl groups, which make TA highly hydrophilic, and after being deposited on the membrane surface, it greatly improves the hydrophilicity of the membrane. Inventions CN202011168021.6, CN202010487168.5, CN202011000599.0 and CN202110060911.3 use blending, traditional solution impregnation and other methods to deposit polyphenol compounds and other substances to obtain super-hydrophilic surfaces. However, the existing technology still has problems such as large-scale preparation limitations and waste of raw materials. Therefore, finding a new, simpler and more direct preparation method is of great significance for the development of super-hydrophilic membranes. Summary of the Invention

[0004] In order to solve the above problems in the prior art, the present invention provides a preparation method and application of a tannic acid-metal complex hydrophilic modified membrane.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a tannic acid-metal complex hydrophilic modified membrane, comprising the following steps: dissolving tannic acid and a metal ion precursor in a solvent respectively to obtain a tannic acid solution and a metal ion precursor solution; spraying the tannic acid solution onto a base membrane, and after the solvent evaporates, continuing to spray the metal ion precursor solution and volatilizing the solvent to complete one spraying assembly, and repeating the spraying assembly several times to obtain the tannic acid-metal complex hydrophilic modified membrane.

[0007] Preferably, the solvent comprises water, methanol or ethanol.

[0008] Preferably, the metal ions include Fe(III) and / or Ti(IV); and the concentrations of the tannic acid solution and the metal ion precursor solution are both 0.5-4 mg / mL.

[0009] More preferably, the metal ion is Ti(IV).

[0010] Preferably, the base membrane comprises polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polypropylene (PP) or polyethersulfone (PES) filter membrane.

[0011] Preferably, the spraying volume ratio of the tannic acid solution to the metal ion precursor solution is 1:(0.5-2), and the amount of the spraying liquid can be flexibly adjusted according to the area of ​​the base film.

[0012] Preferably, during each spraying assembly process, the ratio of the spraying amount of the tannic acid solution to the diameter of the base film is 1 mL: (40-50) mm; the spraying assembly is repeated 2-6 times, and the spraying pressure and distance can be flexibly adjusted according to the spray gun model and actual conditions.

[0013] The present invention also provides a tannic acid-metal complex hydrophilic modified membrane prepared according to the above-mentioned preparation method.

[0014] The present invention also provides the application of the above-mentioned tannic acid-metal complex hydrophilic modified membrane in the treatment of oily wastewater.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention provides a preparation method of a tannic acid-metal complex hydrophilic modified membrane. TA and metal ions are sprayed onto the membrane surface by a spray self-assembly method to assemble into a TA-metal complex, thereby converting the surface of the base membrane from hydrophobic to hydrophilic, thereby achieving large-scale preparation of super-hydrophilic surfaces and effective utilization of raw materials. The prepared membrane exhibits super-hydrophilicity / underwater super-oleophobicity, can efficiently separate different oil-in-water emulsions, and has good anti-fouling properties.

[0017] Different metal ions can be used when modifying the hydrophobic base membrane using the method of the present invention. Studies have found that the spray-assembled TA-Ti(IV) complex modified membrane has excellent superhydrophilicity / underwater superoleophobicity, is applicable to a wide pH range, and has good environmental stability.

[0018] The method of the present invention can be used to modify almost all common hydrophobic membrane substrates, has strong practicality and a wide range of applications; the spray assembly method is simple to operate, can accurately control the amount of solution used, and does not waste raw materials; the spray assembly method can be used for hydrophilic modification of base membranes of any shape or area, and is easy to prepare hydrophilic modified membranes on a large scale. The spray self-assembly method solves the technical drawbacks of traditional solution-impregnated hydrophilic modified membranes, such as difficulty in scalability and waste of raw materials, and is suitable for popularization and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 The figures are actual pictures of the PVDF base membrane that has not been hydrophilically modified and the hydrophilic modified membranes obtained in Examples 1 to 4 and SEM pictures at different magnifications, wherein (a1) to (e1) are actual pictures of the PVDF base membrane and the hydrophilic modified membranes prepared in Examples 1 to 4, (a2) to (e2) are SEM pictures of the PVDF base membrane and the hydrophilic modified membranes prepared in Examples 1 to 4 magnified 1000 times; (a3) ​​to (e3) are SEM pictures of the PVDF base membrane and the hydrophilic modified membranes prepared in Examples 1 to 4 magnified 10000 times;

[0021] Figure 2 In the figure, (a) is a physical picture of the PVDF base membrane, the PVDF membrane modified with different TA-metal ion complexes prepared in Example 3 and Comparative Examples 1 to 4, and (b) is a physical picture of the TA solution and the complexes of TA with different metal ions;

[0022] Figure 3 This is a physical picture of the large-sized hydrophilic modified membrane PP@TA-Ti5 membrane obtained in Example 5;

[0023] Figure 4 The results of underwater oil contact angle test of PVDF@TA-Ti5 prepared in Example 3 after being immersed in different pH solutions for 12 hours;

[0024] Figure 5 This is a photo of oil rebounding on the surface of PVDF@TA-Ti5 membrane;

[0025] Figure 6 Microscopic and optical photographs of different emulsions before and after separation. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention are now described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0027] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in the stated range is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] The present invention provides a preparation method of a tannic acid-metal complex hydrophilic modified membrane, comprising the following steps: dissolving tannic acid and a metal ion precursor in a solvent respectively to obtain a tannic acid solution and a metal ion precursor solution; spraying the tannic acid solution onto a base membrane, and after the solvent evaporates, continuing to spray the metal ion precursor solution and volatilizing the solvent to complete one spraying assembly, and repeating the spraying assembly operation several times to obtain the tannic acid-metal complex hydrophilic modified membrane.

[0032] In some preferred embodiments, the solvent includes water, methanol or ethanol.

[0033] In some preferred embodiments, the metal ions include Fe(III) and / or Ti(IV); and the concentrations of the tannic acid solution and the metal ion precursor solution are both 0.5-4 mg / mL.

[0034] In some preferred embodiments, the metal ion is Ti(IV), the concentration of the tannic acid solution is 2 mg / mL, and the concentration of the metal ion precursor solution is 2 mg / mL.

[0035] In some preferred embodiments, the base membrane includes polyvinylidene fluoride, polytetrafluoroethylene, polypropylene or polyethersulfone filter membrane.

[0036] In some preferred embodiments, the spraying volume ratio of the tannic acid to the metal ions is 1:1, and the amount of the spraying liquid is flexibly adjusted according to the area of ​​the base film.

[0037] In some preferred embodiments, during each spray assembly process, the ratio of the spray volume of the tannic acid solution to the diameter of the base film is 1 mL: (40-50) mm; the spray assembly is repeated 2-6 times, and the spraying pressure and distance can be flexibly adjusted according to the spray gun model and actual conditions.

[0038] The present invention also provides a tannic acid-metal complex hydrophilic modified membrane prepared according to the above-mentioned preparation method.

[0039] The present invention also provides the application of the above-mentioned tannic acid-metal complex hydrophilic modified membrane in the treatment of oily wastewater.

[0040] Example 1

[0041] The preparation steps of the tannic acid-metal complex hydrophilic modified membrane are as follows:

[0042] Step 1, solution preparation: weigh 20 mg of TA and dissolve it in 10 mL of anhydrous ethanol to obtain a TA solution with a concentration of 2 mg / mL; weigh 40 mg of a 50 wt% titanium di(2-hydroxypropionic acid) diammonium dihydroxide aqueous solution and dissolve it in 10 mL of anhydrous ethanol to obtain a 2 mg / mL titanium di(2-hydroxypropionic acid) diammonium dihydroxide spray solution, hereinafter referred to as Ti(IV) solution;

[0043] Step 2: Fix the PVDF base membrane to be modified (47 mm in diameter) vertically on a substrate with double-sided tape. First, use a spray gun to spray 1 mL of TA solution onto the membrane at a pressure of 30 PSI and a distance of 10 cm, and let it stand until the solvent evaporates; then use a spray gun to spray 1 mL of Ti (IV) solution onto the membrane at a pressure of 30 PSI and a distance of 10 cm, and assemble it with TA, and let it stand until the solvent evaporates. This is a spray assembly cycle, and the obtained hydrophilic modified membrane is recorded as PVDF@TA-Ti1.

[0044] Examples 2 to 4

[0045] The same as Example 1, except that in step 2, after completing one spray assembly cycle, the same operation is repeated, and the assembly cycle is continued for 2, 4 and 6 times respectively (the total number of assembly times is 3, 5 and 7 times respectively), and the obtained hydrophilic modified membranes are respectively recorded as: PVDF@TA-Ti3, PVDF@TA-Ti5 and PVDF@TA-Ti7.

[0046] Figure 1 The figures are actual pictures of the PVDF base membrane that has not been hydrophilically modified and the hydrophilically modified membranes obtained in Examples 1 to 4 and SEM pictures at different magnifications, wherein (a1) to (e1) are actual pictures of the PVDF base membrane, PVDF@TA-Ti1, PVDF@TA-Ti3, PVDF@TA-Ti5 and PVDF@TA-Ti7 prepared in Examples 1 to 4, (a2) to (e2) are SEM pictures of the PVDF base membrane, PVDF@TA-Ti1, PVDF@TA-Ti3, PVDF@TA-Ti5 and PVDF@TA-Ti7 prepared in Examples 1 to 4 at a magnification of 1000 times; (a3) ​​to (e3) are SEM pictures of the PVDF base membrane, PVDF@TA-Ti1, PVDF@TA-Ti3, PVDF@TA-Ti5 and PVDF@TA-Ti7 prepared in Examples 1 to 4 at a magnification of 10,000 times. As can be seen from the image, the original PVDF base membrane is white. As the number of spray assembly cycles increases, the membrane surface turns yellow and gradually deepens. The SEM image shows that the PVDF membrane has a porous structure. As the number of spray assembly cycles increases, the TA-Ti complex adheres to the membrane surface, and the membrane pore size gradually decreases. A large number of agglomerated particles appear after 7 spray assembly cycles. Therefore, the number of spray assembly cycles should not be too many.

[0047] Comparative Examples 1 to 4

[0048] The same as Example 3, except that the 40 mg of di(2-hydroxypropionic acid) diammonium dihydroxide titanium aqueous solution (50 wt%) in step 1 is replaced by 20 mg of FeCl3, 20 mg of nickel chloride hexahydrate, 20 mg of cobalt chloride hexahydrate and 20 mg of AlCl3, respectively, and the obtained products are recorded as: PVDF@TA-Fe, PVDF@TA-Ni, PVDF@TA-Co and PVDF@TA-Al, respectively.

[0049] Figure 2 In the figure, (a) is a physical picture of PVDF base membrane, different TA-metal ion complex modified PVDF membranes prepared in Example 3 and Comparative Examples 1 to 4 ( Figure 2PVDF@TA-Ti in (a) refers to the PVDF@TA-Ti prepared in Example 3. (b) is a photograph of TA solution and TA complexed with different metal ions (i.e., without spraying, the same raw materials corresponding to Example 3 and Comparative Examples 1 to 4 were directly mixed). Figure 2 It shows that the complexes of Ni(II) and Al(III) with TA have no obvious color, the complex of Co(II) with TA is light blue, the complex of Fe(III) with TA is purple, and the complex of Ti(IV) with TA is yellow.

[0050] Example 5

[0051] The same as Example 1, except that the PVDF base membrane to be modified in step 2 is replaced by a PP base membrane with a size of about 25 cm*17 cm to obtain a hydrophilic modified membrane PP@TA-Ti5.

[0052] Figure 3 This is a physical picture of the large-scale hydrophilic modified membrane PP@TA-Ti5 membrane obtained in Example 5, which proves that this method is suitable for the preparation of large-scale hydrophilic membranes.

[0053] After the PVDF@TA-Ti5 prepared in Example 3 was immersed in different pH solutions for 12 h, its underwater oil contact angle was tested. Figure 4 As shown in the figure, the underwater oil contact angles of the immersed membranes are between 160-168°, which is not significantly lower than the unimmersed contact angle of 165.2°, proving that the PVDF@TA-Ti5 membrane has good stability in weak acid and weak base environments.

[0054] A stream of oil (petroleum ether dyed with oil red) was sprayed onto the surface of the PVDF@TA-Ti5 membrane using a syringe. Figure 5 This is a photo of oil rebounding on the surface of PVDF@TA-Ti5 membrane. It can be seen that the oil beam rebounds on the membrane surface and does not adhere to the membrane surface, proving that PVDF@TA-Ti5 has good anti-oil adhesion.

[0055] The oil-water emulsion separation performance was evaluated using a filtration device. Four emulsions, sunflower oil, liquid paraffin, ethylene dichloride, petroleum ether, and n-hexane, were prepared: 99 mL of water was mixed with 1 mL of the oil, 50 mg of sodium dodecyl sulfate (SDS) was added, and the mixture was sonicated for 30 minutes, followed by stirring for 24 hours. A water-pre-soaked PVDF@TA-Ti5 membrane was mounted on the filtration device. 15 mL of the emulsion was poured into the device and filtration separation was performed at a pressure of 0.01 MPa.

[0056] Figure 6These are micrographs and optical photographs of different emulsions before and after separation. It can be seen from the figure that the milky white oil-water emulsion becomes clear after membrane separation. The micrograph shows that the small oil droplets in the emulsion are effectively separated.

[0057] The PVDF base membrane in step 2 of Example 3 was replaced with a polytetrafluoroethylene (PTFE) membrane and a polyethersulfone (PES) membrane, respectively. The underwater oil contact angle, acid and alkali stability, and water-oil separation performance of the resulting hydrophilic modified membranes were tested according to the above method. The results showed that the underwater oil contact angles were all greater than 160°, and the underwater oil contact angles after immersion in solutions of different pH (3-12) for 12 hours could still be maintained above 160°.

[0058] The above description is only a preferred specific embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention within the technical scope disclosed in the present invention, and these changes should be covered by the scope of protection of the present invention.

Claims

1. A tannic acid-metal complex hydrophilic modified membrane, characterized in that: The preparation method of the tannic acid-metal complex hydrophilic modified membrane includes the following steps: dissolving tannic acid and a metal ion precursor in a solvent respectively to obtain a tannic acid solution and a metal ion precursor solution; spraying the tannic acid solution onto a base membrane, and after the solvent evaporates, continuing to spray the metal ion precursor solution and volatilizing the solvent to complete one spraying assembly, repeating the spraying assembly 5 times to obtain the tannic acid-metal complex hydrophilic modified membrane; the metal ion is Ti(IV).

2. The tannic acid-metal complex hydrophilic modified membrane according to claim 1, characterized in that: The solvent includes water, methanol or ethanol.

3. The tannic acid-metal complex hydrophilic modified membrane according to claim 1, characterized in that: The concentrations of the tannic acid solution and the metal ion precursor solution are both 0.5-4 mg / mL.

4. The tannic acid-metal complex hydrophilic modified membrane according to claim 1, characterized in that: The base membrane includes polyvinylidene fluoride, polytetrafluoroethylene, polypropylene or polyethersulfone filter membrane.

5. The tannic acid-metal complex hydrophilic modified membrane according to claim 1, characterized in that: The spraying volume ratio of the tannic acid solution to the metal ion precursor solution is 1:(0.5-2).

6. The tannic acid-metal complex hydrophilic modified membrane according to claim 1, characterized in that: During each spraying assembly process, the ratio of the spraying amount of the tannic acid solution to the diameter of the base film was 1 mL: (40-50) mm.

7. Use of the tannic acid-metal complex hydrophilic modified membrane according to claim 1 in the treatment of oily wastewater.

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