Silver nanowire-based oil-water separation membrane, preparation method and application thereof

Abstract

The application relates to the technical field of oil-water separation membranes, and discloses an oil-water separation membrane based on silver nanowires, a preparation method and application, the oil-water separation membrane comprises a modified layer and nanocellulose formed on the surface of a base film; the modified layer is a structure obtained by depositing polydopamine on the surface of silver nanowires. The silver nanowires (AgNWs) are modified by polydopamine, polydopamine particles are deposited on the surface of the silver nanowires, the composite film has micro / nano rough structures, the composite film is endowed with hydrophilic / underwater superoleophobic wetting performance, and therefore the anti-pollution performance of the PDA / AgNWs / CNF composite film is improved.

Description

Technical Field

[0001] This invention relates to oil-water separation membranes, specifically, to an oil-water separation membrane based on silver nanowires, its preparation method, and its application. Background Technology

[0002] Membrane separation technology, characterized by low cost and simple operation, is widely considered to have enormous application potential in treating oily wastewater. This technology can realize wastewater resource recovery, alleviate environmental problems, and further mitigate water scarcity. However, in oil-water separation applications, the membrane material surface is highly susceptible to adsorption of pollutants, leading to severe membrane fouling, clogging membrane pores, reducing separation efficiency, and shortening the lifespan of the oil-water separation membrane. Currently, traditional oil-water separation membranes commonly suffer from membrane fouling problems, severely limiting the practical application of membrane separation technology in this field. Improving the antifouling performance of membrane materials is an important research direction in membrane separation technology and has significant implications for its practical application in water treatment. Summary of the Invention

[0003] <Technical Problem Solved by the Invention>

[0004] This technology aims to address the problem of membrane fouling caused by the easy adsorption of contaminants by existing oil-water separation membranes.

[0005] <Technical Solution Adopted in This Invention>

[0006] To address the aforementioned technical problems, this invention utilizes the self-polymerization of dopamine under alkaline conditions to modify the surface of silver nanowires, obtaining a polydopamine-modified silver nanowire composite material (PDA / AgNWs). Next, a substrate membrane is selected, and the polydopamine-modified silver nanowires (PDA / AgNWs) are uniformly mixed with nanocellulose (CNF). The PDA / AgNWs / CNF composite membrane is then prepared by vacuum filtration.

[0007] The details are as follows:

[0008] First, the present invention provides an oil-water separation membrane based on silver nanowires, the oil-water separation membrane comprising a modification layer formed on the surface of a base membrane and nanocellulose; the modification layer is a structure obtained by depositing polydopamine on the surface of silver nanowires.

[0009] Second, the present invention provides a method for preparing an oil-water separation membrane based on silver nanowires, comprising the following steps:

[0010] The modified layer dispersion and the nanocellulose dispersion were prepared separately, and then the oil-water separation membrane was obtained by vacuum filtration together with the base membrane.

[0011] Third, this invention provides the application of silver nanowire-based oil-water separation membranes in the field of oil-water separation.

[0012] <Technical Mechanism Employed in This Invention>

[0013] This invention modifies silver nanowires (AgNWs) with polydopamine. The polydopamine particles deposited on the surface of the silver nanowires give the composite film a micro- and nano-rough structure, endowing the composite film surface with hydrophilic / underwater superoleophobic wetting properties, thereby improving the antifouling performance of the PDA / AgNWs / CNF composite film.

[0014] <Beneficial effects achieved by the present invention>

[0015] (1) The AgNWs / CNF and PDA / AgNWs / CNF composite membranes prepared in this invention both have high pure water flux, which are 5790.39 L·m⁻¹, respectively. -2 ·h -1 ·bar -1 5028.49 L·m -2 ·h -1 ·bar -1 Contact angle test results show that the PDA / AgNWs / CNF composite membrane has excellent wetting properties.

[0016] (2) Both AgNWs / CNF and PDA / AgNWs / CNF composite membranes have good separation effects on oil-water emulsions stabilized by surfactants. The results show that the separation effect of the above composite membranes on emulsions can reach more than 99.0%. Attached Figure Description

[0017] Figure 1 Infrared spectra of AgNWs / CNF powder and PDA / AgNWs / CNF composite film;

[0018] Figure 2 XPS energy dispersive spectroscopy of AgNWs / CNF and PDA / AgNWs / CNF composite films;

[0019] Figure 3 The image shows the contact angle test results of AgNWs / CNF and PDA / AgNWs / CNF composite films;

[0020] Figure 4 Figure 1 shows the underwater oil contact angle test results of the PDA / AgNWs / CNF composite membrane under different oil-water emulsion conditions.

[0021] Figure 5 SEM image of AgNWs powder and PDA / AgNWs / CNF composite film;

[0022] Figure 6 The graph shows the pure water flux test results of AgNWs / CNF and PDA / AgNWs / CNF composite membranes;

[0023] Figure 7 Figure 1 shows the separation performance of the PDA / AgNWs / CNF composite membrane for different oil-water emulsions.

[0024] Figure 8 The graph shows the cycle test results of the PDA / AgNWs / CNF composite membrane. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0026] First, the present invention provides an oil-water separation membrane based on silver nanowires, the oil-water separation membrane comprising a modification layer formed on the surface of a base membrane and nanocellulose; the modification layer is a structure obtained by depositing polydopamine on the surface of silver nanowires (AgNWs).

[0027] In this invention, the modified layer is prepared by adding silver nanowires to a Tris-HCl buffer solution under alkaline conditions, dispersing them, adding dopamine, reacting, centrifuging, collecting the lower layer, and obtaining the modified layer.

[0028] In this invention, the reaction temperature is 18–30°C and the reaction time is 20–30 h.

[0029] In this invention, the amounts of silver nanowires and dopamine added to 100 mL of Tris-HCl buffer solution are 0.3 g and 0.1 g, respectively.

[0030] Second, the present invention provides a method for preparing the aforementioned oil-water separation membrane based on silver nanowires, comprising the following steps:

[0031] The modified layer dispersion and the nanocellulose dispersion were prepared separately, and then the oil-water separation membrane was obtained by vacuum filtration together with the base membrane.

[0032] Specifically, a modified layer dispersion with a concentration of 0.2 mg / mL and a nanocellulose dispersion with a concentration of 1 mg / mL were prepared. After sonication, the modified layer dispersion, nanocellulose dispersion and deionized water were stirred and sonicated in a volume ratio of 15:1:34. Then, they were combined with the base membrane and filtered under reduced pressure to obtain an oil-water separation membrane.

[0033] Furthermore, a 0.22μm mixed acid fiber membrane was selected as the base membrane.

[0034] Third, the present invention provides an application of the aforementioned oil-water separation membrane in the field of oil-water separation.

[0035] <Example>

[0036] Example 1

[0037] A method for preparing an oil-water separation membrane based on silver nanowires includes the following steps:

[0038] (1) Preparation of AgNWs / CNF composite membrane

[0039] 100 mL of 0.2 mg / mL AgNWs dispersion and 100 mL of 1 mg / mL nanocellulose (CNF) dispersion were prepared and sonicated for 1 h. Then, 1 mL of the CNF dispersion (1 mg / mL) and 15 mL of the PDA / AgNWs solution (0.2 mg / mL) were placed in beakers, diluted with water to 50 mL, stirred with a glass rod for 2 min at room temperature, and then sonicated for 10 min. Using a 0.22 μm mixed acid cellulose (CN / CA) membrane as the substrate, the above solutions were filtered under reduced pressure to prepare the AgNWs / CNF composite membrane.

[0040] Example 2

[0041] A method for preparing an oil-water separation membrane based on silver nanowires includes the following steps:

[0042] (1) Preparation of PDA / AgNWs composite material

[0043] Prepare 100 mL of 0.1 mol / L triaminomethane hydrochloride (Tris-HCl) buffer solution. Adjust the pH of the buffer solution to 8.5 using 0.1 mol / L sodium hydroxide solution. Add 10 mL of sonicated and uniformly dispersed silver nanowires (AgNWs) dispersion to the buffer solution. After sonicating until uniformly dispersed, add 0.1 g of dopamine to the solution and stir at 24 °C for 24 hours. After the reaction is complete, centrifuge the product at 8000 rpm for 10 min, wash off excess dopamine with deionized water, collect the lower layer product, and dry it to obtain the PDA / AgNWs composite material.

[0044] (2) Preparation of PDA / AgNWs / CNF composite membrane

[0045] 100 mL of 0.2 mg / mL PDA / AgNWs dispersion and 100 mL of 1 mg / mL CNF dispersion were prepared and sonicated for 1 h. Then, 1 mL of the CNF dispersion (1 mg / mL) and 15 mL of the PDA / AgNWs solution (0.2 mg / mL) were placed in beakers, diluted with water to 50 mL, stirred with a glass rod for 2 min at room temperature, and then sonicated for 10 min. Using a 0.22 μm mixed acid cellulose (CN / CA) membrane as the substrate, the above solutions were filtered under reduced pressure to prepare a PDA / AgNWs / CNF composite membrane.

[0046] <Experimental Example>

[0047] Using the composite membranes prepared in Examples 1 and 2 as samples, the chemical composition, microstructure and structure of the composite material and the composite membrane were characterized by FTIR, XPS and SEM. The wettability, water flux, antifouling performance and oil-water emulsion separation efficiency of AgNWs / CNF composite membrane and PDA / AgNWs / CNF composite membrane were compared and evaluated.

[0048] <atr-ftir>

[0049] Figure 1 The infrared spectrum (ATR-FTIR) of AgNWs / CNF powder and PDA / AgNWs / CNF composite film.

[0050] In the infrared spectrum of silver nanoparticles, 1630 cm⁻¹ -1 The absorption peak at 3200 cm⁻¹ corresponds to the stretching vibration of the carbonyl group in polyvinylpyrrolidone. The infrared spectrum of the composite material containing polydopamine-modified silver nanowires (PDA / AgNWs) shows a peak at 3200 cm⁻¹. -1 The absorption peak at 2982 cm⁻¹ is the -NH stretching vibration peak. -1 and 2854cm -1 The absorption peak belongs to the -CH2 antisymmetric and symmetric stretching vibration peak of PDA, 1564 cm⁻¹. -1 and 1388cm -1 The absorption peaks at 1025 cm⁻¹ are the -NH shear vibration peak and the -CH₂ bending vibration peak, respectively. Additionally, at 1025 cm⁻¹... -1 The absorption peak at that point represents the characteristic absorption peak of PDA carbon oxides.

[0051] The above infrared spectral analysis demonstrates the successful modification of silver nanowires by polydopamine (PDA).

[0052] <xrd>

[0053] Figure 2 XPS spectra of AgNWs / CNF and PDA / AgNWs / CNF composite films.

[0054] Absorption peaks corresponding to C1s, Ag 3d, and O1s were observed in all the spectra. Among them, compared with the XPS spectrum of AgNWs / CNF, a clear N1s peak can be observed in the spectrum of PDA / AgNWs / CNF composite film, which indicates that PDA has successfully modified silver nanowires.

[0055] <Hydrophilic properties>

[0056] The hydrophilicity of oil-water separation membranes is an important performance indicator. This experiment tested the contact angle of AgNWs / CNF and PDA / AgNWs / CNF composite membranes. The results of water wetting of the composite membrane surface in air are shown in [the figure]. Figure 3 (a).

[0057] from Figure 3 (a) It can be seen that when the water droplets begin to contact the membrane surface, the water contact angle (WCA) of the AgNWs / CNF membrane and the PDA / AgNWs / CNF membrane are 33.5° and 21.7°, respectively.

[0058] The above results indicate that both AgNWs / CNF and PDA / AgNWs / CNF composite membranes exhibit good hydrophilicity in air.

[0059] Based on the change in contact angle over time, it can be known that ( Figure 3 (a)):

[0060] The water contact angle (WCA) of the PDA / AgNWs / CNF composite membrane rapidly decreased to 0° within a short period, while the water contact angle of the AgNWs / CNF composite membrane only decreased slightly within a short period. This indicates that the micro- and nano-rough structure of the PDA / AgNWs / CNF composite membrane is beneficial to its adsorption of water molecules, demonstrating strong hydrophilicity.

[0061] The underwater oil contact angle (OCA) measurements showed that the OCA values ​​for AgNWs / CNF and PDA / AgNWs / CNF composite membranes were 156.3° and 160.2°, respectively (see [reference]). Figure 3 (b)).

[0062] Before and after modification, the underwater oil contact angle of the modified composite membrane was greater than 150°, exhibiting a high underwater oil contact angle and demonstrating underwater superoleophobic properties. This indicates that the prepared PDA / AgNWs / CNF composite membrane possesses a rough structure with high surface energy, which is beneficial for the composite membrane to capture water molecules and form a water film, thereby reducing the contact area between oil droplets and the membrane surface. Therefore, the composite membrane exhibits underwater superoleophobic properties.

[0063] <Wetting properties>

[0064] Figure 4 The underwater oil contact angle of the PDA / AgNWs / CNF composite membrane under different oil-water emulsion conditions.

[0065] The underwater oil contact angle of the PDA / AgNWs / CNF composite membrane was measured under different oil-water emulsion conditions. Figure 4 As shown, the underwater oil contact angles of the PDA / AgNWs / CNF composite membrane for petroleum ether, n-hexane, dichloroethane, and diesel emulsions are 161.64°, 164.74°, 160.17°, and 166.31°, respectively. Under various oil-water emulsions, the underwater oil contact angle of the PDA / AgNWs / CNF composite membrane is greater than 150°, demonstrating its underwater superoleophobic properties. This indicates that the prepared PDA / AgNWs / CNF composite membrane possesses excellent surface hydrophilic / underwater superoleophobic wetting characteristics, enabling the composite membrane to rapidly capture water molecules underwater to form a hydration layer, reducing the contact between oil droplets and the membrane surface, and thus improving the antifouling performance of the composite membrane.

[0066] <sem>

[0067] Figure 5 (ab) are scanning electron microscope (SEM) images of AgNWs powder and PDA / AgNWs / CNF composite film, respectively.

[0068] Figure 5 (a) and (a1) are microscopic morphology images of AgNWs powder, showing a linear structure with uniform and large pores on the film surface. However, the PDA / AgNWs / CNF composite film formed by modifying silver nanowires with polydopamine exhibits significantly reduced surface porosity and a rough, dense, and three-dimensional structure. Figure 5 (b)).

[0069] Figure 5 (b, b1) are SEM images of the PDA / AgNWs / CNF composite film. A large number of particulate structures can be observed in the images, and the surface roughness is significantly increased, indicating that polydopamine has successfully modified the surface of silver nanowires.

[0070] Through with Figure 5 Further comparison of (a, a1) reveals that the three-dimensional structure of the PDA / AgNWs / CNF composite film contains tiny particles, indicating that polydopamine microparticles are formed on the surface of the silver nanowires by modifying them with polydopamine.

[0071] <Membrane flux>

[0072] Membrane flux is closely related to membrane structure and hydrophilicity. Microporous membranes with high average pore size, high porosity, and loose structure have lower resistance to water flow and therefore higher pure water flux. Membranes with higher hydrophilicity have better affinity for water, facilitating the passage of water molecules, and thus also have higher water flux.

[0073] This experiment measured the pure water flux of the prepared AgNWs / CNF and PDA / AgNWs / CNF composite membranes. The results are shown in [Figure number missing]. Figure 6 .

[0074] The results showed that the pure water flux of the AgNWs / CNF and PDA / AgNWs / CNF composite membranes was 5790.39 L·m⁻¹. -2 ·h -1 ·bar -1 5028.49 L·m -2 ·h -1 ·bar -1 This indicates that both composite membranes have high pure water flux. After dopamine modification, the water flux of the composite membrane shows a slight decreasing trend. This is because the dense and tiny polydopamine particles loaded on the surface of silver nanowires slightly reduce the pore size of the composite membrane, resulting in an increase in the resistance of water molecules to passing through the membrane, and thus a slight decrease in the water flux of the membrane.

[0075] <Separation Performance>

[0076] This experiment investigated the separation performance of the PDA / AgNWs / CNF composite membrane for different oil-water emulsions. The results are shown in [Figure Number]. Figure 7 (a, b).

[0077] The results showed that the PDA / AgNWs / CNF composite membrane had a good separation effect on various emulsions stabilized by sodium dodecyl sulfate (SDS), with a separation efficiency of over 99.0%. This indicates that the PDA / AgNWs / CNF composite membrane can quickly break up various stable oil-water emulsions and achieve effective separation of the emulsions.

[0078] Depend on Figure 7 As shown, the PDA / AgNWs / CNF composite membrane effectively resists hexane (1144.21 L·m⁻¹). -2 ·h -1 ·bar -1 ), petroleum ether (2330.28 L·m -2 ·h -1 ·bar -1 ), toluene (1248.91 L·m -2 ·h -1 ·bar -1 ), cyclohexane (841.77 L·m -2 ·h -1 ·bar -1 ), diesel (64.33 L·m) -2 ·h -1 ·bar -1 Emulsions generally exhibit high separation performance. However, the processing throughput varies for different oil-water emulsions, which is related to factors such as the adhesion properties of different oils and their concentration in the emulsion.

[0079] <Anti-fouling properties>

[0080] Figure 8 Cyclic testing of PDA / AgNWs / CNF composite membrane.

[0081] This experimental example investigated the antifouling performance of the PDA / AgNWs / CNF composite membrane through cyclic testing. An SDS-stabilized n-hexane oil-water emulsion was used as the fouling model in the test. Figure 8 It can be seen that during the nine-cycle test, the PDA / AgNWs / CNF composite membrane consistently exhibited good separation performance for the n-hexane oil-water emulsion. Furthermore, the water flux and emulsion throughput of the PDA / AgNWs / CNF composite membrane did not show significant decreases during the cycling process, with the water flux remaining at 4593.33 L·m⁻¹. -2 ·h -1 ·bar -1 This is because dopamine modifies the surface of silver nanowires to form a polydopamine / silver nanowire composite material. Tiny and dense polydopamine particles are loaded on the silver nanowires, which improves the hydrophilicity of the PDA / AgNWs / CNF composite membrane surface. At the same time, a micro-nano rough structure is constructed on the membrane surface, which is conducive to the rapid formation of a hydration film by water molecules on the membrane surface and reduces the adhesion of oil to the membrane surface. Therefore, the water flux can be restored by cleaning the membrane surface with pure water.

[0082] Cyclic test results show that the PDA / AgNWs / CNF composite membrane has good antifouling ability and high reusability, which improves the repeatability and service life of the composite membrane in application.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.< / sem> < / xrd>

Claims

1. An oil-water separation membrane based on silver nanowires, characterized in that, This oil-water separation membrane includes a modification layer formed on the surface of a base membrane and nanocellulose; the modification layer is a structure obtained by depositing polydopamine on the surface of silver nanowires; The modified layer was prepared by adding silver nanowires to a Tris-HCl buffer solution under alkaline conditions, dispersing them, adding dopamine, reacting, centrifuging, collecting the lower layer, and obtaining the modified layer. In 100 mL of Tris-HCl buffer solution, the amounts of silver nanowires and dopamine added were 0.3 g and 0.1 g, respectively. The preparation method of the oil-water separation membrane includes the following steps: preparing a modified layer dispersion with a concentration of 0.2 mg / mL and a nanocellulose dispersion with a concentration of 1 mg / mL, respectively, and after sonication, mixing the modified layer dispersion, nanocellulose dispersion and deionized water in a volume ratio of 15:1:34, followed by stirring and sonication, and then filtering them together with a base membrane under reduced pressure to obtain the oil-water separation membrane.

2. The oil-water separation membrane based on silver nanowires according to claim 1, characterized in that, The reaction temperature is 18~30℃, and the reaction time is 20~30h.

3. The oil-water separation membrane based on silver nanowires according to claim 1, characterized in that, A 0.22 μm mixed acid fiber membrane was selected as the base membrane.

4. The application of the oil-water separation membrane as described in any one of claims 1 to 3 in the field of oil-water separation.

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