Composite separation membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of composite membrane materials, and discloses a composite separation membrane as well as a preparation method and application thereof. According to the invention, keratin fiber is used as a main preparation raw material, graphene oxide is used as a functional additive, and the composite separation membrane with a heterogeneous structure and a self-supporting characteristic is prepared through negative pressure suction filtration and post-treatment. The composite separation membrane not only has excellent pollutant interception capability, but also realizes biodegradation. Compared with a traditional petroleum-based separation membrane (such as an organic nylon membrane), the composite separation membrane meets the basic separation performance requirement, meanwhile, the preparation cost is lower, the process is simpler and more convenient, the composite separation membrane is environmentally friendly, the composite separation membrane can be naturally degraded by soil microorganisms after being used, and wide industrial application prospects are shown; the device is especially suitable for water treatment and separation of other pollutants.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite membrane materials, and relates to a composite separation membrane, a preparation method thereof and an application thereof. Background Art

[0002] With the continuous acceleration of the industrialization and urbanization processes, the problem of water pollution has become increasingly severe. Especially in the field of industrial wastewater treatment, higher requirements are put forward for separation membrane technology. Most traditional separation membranes use petroleum-based polymer materials, which not only have complex preparation processes and high costs, but also are often difficult to achieve complete degradation during the post-use treatment process, easily causing environmental burdens and secondary pollution. Therefore, it is particularly urgent to develop new separation membranes that can be biodegradable, low-cost, have simple processes and are environmentally friendly.

[0003] Wool waste, as a common by-product in the livestock industry, has been mostly simply treated or used with low value for a long time. Wool is rich in natural polymer substances such as keratin (about 90%), and has excellent biocompatibility and natural degradability. At present, there is extensive research on the extraction of wool keratin, and the highest extraction rate can reach 79.9±0.5%, but the complete utilization of wool waste has still not been achieved. On the other hand, in recent years, graphene oxide has received extensive attention in the field of membrane materials due to its unique two-dimensional layered structure, excellent mechanical properties and outstanding chemical stability.

[0004] The prior art CN112899792A discloses a heat-generating composite fabric and a preparation method thereof. This patent uses graphene and keratin for the preparation of textile products. On the one hand, ordinary textile products cannot meet the sewage treatment requirements. On the other hand, this patent introduces harmful substances such as viscose fiber, modified melamine formaldehyde resin, and NMMO solution (N-methylmorpholine-N-oxide solution) in the preparation method, causing environmental pollution during the preparation and post-use treatment.

[0005] In order to promote and drive the high-value utilization of wool waste, and at the same time achieve innovative improvements to existing water treatment membrane materials, the industry urgently needs a composite membrane material that is environmentally friendly, has strong filtering or adsorption ability and excellent mechanical properties. Summary of the Invention

[0006] In order to solve the problems that in the preparation of existing separation membranes, many substances that are difficult to degrade or even environmentally harmful are introduced, and there are problems such as poor stability, separation selectivity and low mechanical strength, the present invention makes full use of the advantages of keratin and natural fiber skeletons in wool waste, and combines the unique functions of graphene oxide to prepare a composite separation membrane with a heterogeneous structure and self-supporting characteristics. For this reason, the present invention provides the following technical solutions.

[0007] In a first aspect, the present invention provides a composite separation membrane, which uses keratin fibers as the main raw material for preparation, graphene oxide as an additive, and has a heterogeneous structure and self-supporting characteristics.

[0008] Furthermore, in the above composite separation membrane, the keratin used for preparing the keratin fibers includes: wool keratin.

[0009] In a second aspect, the present invention provides a method for preparing the composite separation membrane, including: preparation of a composite casting solution, preparation of the composite separation membrane, and post-treatment of the composite separation membrane.

[0010] Furthermore, in the above preparation method, the composite casting solution is prepared by mixing a graphene oxide dispersion with keratin fibers, where the concentration of the graphene oxide dispersion is 1 - 5 mg / mL, and the usage amount of the keratin fibers is 10 - 50 times the weight of the graphene oxide.

[0011] Furthermore, in the above preparation method, the method for preparing the keratin fibers includes:

[0012] Cutting wool fibers into small segments, soaking them in a NaHCO3 solution to remove lipids, followed by washing and drying to obtain degreased wool; preparing an extraction solution to extract the keratin fibers from the degreased wool; separating, washing, drying, and pulverizing the keratin fibers to obtain purified wool keratin fibers.

[0013] Furthermore, during the degreasing process, the concentration of the NaHCO3 solution is 0.2 - 0.4 M, and the degreasing reaction time is 2 - 4 h; during the process of extracting the keratin fibers, the extraction solution contains a reducing agent, a protective lubricant, and a solubilizer; the pH of the extraction solution is 11 - 11.5; the extraction temperature is 70 - 90 °C, and the extraction time is 4 - 6 h.

[0014] Furthermore, the reducing agent is L-cysteine, and the usage amount of L-cysteine is 10 - 30% of the weight of the wool; the protective lubricant is urea, and the concentration of urea in the extraction solution is 6 - 8 M; the solubilizer is sodium dodecyl sulfate, and the concentration of sodium dodecyl sulfate in the extraction solution is 0.02 - 0.04 M; the pH of the extraction solution is adjusted with NaOH.

[0015] Furthermore, in the above preparation method, the composite casting solution is deposited by a negative pressure filtration method to obtain the composite separation membrane.

[0016] Furthermore, in the above preparation method, the post-treatment of the composite separation membrane includes: hot pressing and cross-linking treatment.

[0017] Specifically, the preparation steps of the composite separation membrane are as follows:

[0018] 1) Cut the wool fibers into small pieces, soak them in a NaHCO3 solution with a concentration of 0.2 - 0.4M for 2 - 4h to remove lipids, then wash and dry them. The drying temperature is 40 - 80°C and the time is 6 - 8h to obtain degreased wool;

[0019] 2) Use L-cysteine at 10 - 30% of the wool weight as a reducing agent, urea with a concentration of 6 - 8M as a protective lubricant, and sodium dodecyl sulfate (SDS) with a concentration of 0.02 - 0.04M as a solubilizer to prepare an extraction solution, and adjust the pH of the extraction solution to 11 - 11.5 with NaOH; Immerse the degreased wool prepared in 1) in the extraction solution at 70 - 90°C for 4 - 6h to extract keratin fibers;

[0020] 3) After the extraction, separate the wool keratin fibers from the keratin solution, then wash and dry the keratin fibers. The drying temperature is 40 - 80°C and the time is 6 - 8h, and then crush them through a 200-mesh sieve to obtain purified keratin fibers;

[0021] 4) Prepare a graphene oxide dispersion with a concentration of 1 - 5mg / mL, add the purified keratin fibers, so that the mass ratio of graphene oxide to keratin fibers is 1:10 - 50, and ball mill for 30 - 90min to fully disperse to obtain a composite casting solution;

[0022] 5) Use a water-based mixed cellulose membrane as the base membrane, wet clean it, take an appropriate amount of the composite casting solution, and filter it under a negative pressure of 0.8 - 1bar for 1 - 5h to deposit the composite casting solution to obtain a composite separation membrane with a heterogeneous structure;

[0023] 6) Heat press the composite separation membrane at 90 - 140°C for 5 - 20min, with a pressure of 0.1 - 0.3kPa. After the base membrane naturally falls off, a composite separation membrane with self-supporting ability is obtained.

[0024] 7) Put the composite separation membrane into a 0.1 - 0.3M Fe 3+ metal ion solution, crosslink at 40 - 80°C for 30 - 90min to obtain a composite separation membrane with a heterogeneous structure and self-supporting ability, and store it in deionized water; The main component of the functional layer of the composite separation membrane is graphene oxide, and the main component of the support layer is wool keratin fibers; The thickness ratio of the functional layer to the support layer is 1 - 1.5:50 - 100.

[0025] Thirdly, the present invention provides the application of the composite separation membrane. Specifically, the composite separation membrane is used for water treatment.

[0026] The present invention, "A Composite Separation Membrane and Its Preparation Method and Application", has at least the following beneficial effects: The present invention proposes a biodegradable composite separation membrane that directly extracts keratin fibers from wool waste. In the preparation process, a natural keratin fiber network structure is formed by the negative pressure filtration method, combined with the embedding of graphene oxide and the post-treatment process, to prepare a composite separation membrane with a heterogeneous structure and self-supporting characteristics. The heterogeneous structure means that each functional component (keratin fiber, graphene oxide) inside the separation membrane shows characteristics of local enrichment and uneven dispersion at the microscale. This structure enables different regions to have different pore structures and surface chemical properties, thus realizing the organic combination of high permeability and high rejection rate. The self-supporting characteristic means that the separation membrane can still maintain sufficient mechanical strength and stability without relying on an additional organic or inorganic support substrate, thereby simplifying the subsequent application process and reducing the process cost. The self-supporting characteristic is of great significance for the installation and long-term operation of membrane modules in the actual water treatment process, and can effectively avoid problems such as a decrease in permeation efficiency or structural damage caused by the instability of the support layer of traditional membrane materials.

[0027] The present invention constructs a heterogeneous structure with multiple pore sizes through the synergistic effect of keratin fibers and graphene oxide, effectively improving the rejection rate of the membrane body to pollutants. Under the conditions of 25 °C and a dye concentration of 100 mg / mL, the rejection rate of Congo red dye (CR) reaches 99.39%, and the rejection rate of methyl orange dye (MO) reaches 86.92%, showing a significant improvement compared with the pure keratin fiber separation membrane.

[0028] The present invention not only realizes the efficient recycling of wool waste, but also compared with traditional petroleum-based separation membranes, the composite separation membrane prepared by the present invention uses environmentally friendly raw materials, no organic solvents are added during the preparation process, and the process is simple and the cost is low. Through the natural degradation test of the composite separation membrane prepared by the present invention, the water-based mixed cellulose membrane and the organic nylon membrane, it is known that the composite separation membrane can be completely degraded on the surface of moist soil in about 77 days, with a fast degradation rate and no harmful substances produced, meeting the requirements of green and low-carbon environmental protection development.

[0029] The present invention can simultaneously obtain wool keratin and keratin fibers by controlling the dosage of the reducing agent to achieve the complete utilization of wool waste. Description of the Drawings

[0030] Figure 1 Scanning electron microscope images of the front (left) and back (right) sides of the composite separation membrane prepared in Example 2 of the present invention.

[0031] Figure 2 Scanning electron microscope image of the cross-section of the composite separation membrane prepared in Example 2 of the present invention.

[0032] Figure 3Natural degradation process diagrams of the composite separation membrane prepared in Example 2 of the present invention (left), a commercially available aqueous mixed cellulose microfiltration membrane (middle), and a commercial nylon microfiltration membrane (right). Detailed implementation manners

[0033] The present invention will be described below in conjunction with embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0034] Example 1

[0035] This example provides the preparation of a composite separation membrane.

[0036] 1) Weigh 8.4 g of NaHCO3 and dissolve it in 500 mL of deionized water to prepare a 0.2 M NaHCO3 solution; cut 25 g of wool fibers into small segments (about 1 - 2 cm), soak them in the NaHCO3 solution for 2 h to remove the lipids on the surface of the wool fibers, then wash and dry at 60 °C for 8 h to obtain degreased wool;

[0037] 2) Dissolve 3.75 g of L-cysteine, 192 g of urea, and 2.306 g of sodium dodecyl sulfate (SDS) in 400 mL of deionized water, and adjust the pH of the solution to 11.3 with 1 M NaOH to obtain an extraction solution; weigh 25 g of the degreased wool prepared in 1), soak it in the extraction solution, and react at 90 °C under sealed conditions for 4 h to extract keratin fibers;

[0038] 3) After the extraction, separate the wool keratin fibers from the keratin solution with a 400-mesh sieve, then wash and dry. The drying temperature is 60 °C and the drying time is 8 h. Crush and pass through a 200-mesh sieve to obtain purified keratin fibers;

[0039] 4) Prepare a 10 mL graphene oxide dispersion with a concentration of 1 mg / mL, add 0.5 g of purified keratin fibers (i.e., the mass ratio of graphene oxide to keratin fibers is 1:50), and add water to a total volume of 120 mL, and ball mill for 30 min to obtain a composite casting solution.

[0040] 5) Use an aqueous mixed cellulose membrane as the substrate membrane, wet clean it, take 30 mL of the composite casting solution and filter it under negative pressure (0.98 bar) for 1 h to deposit the composite casting solution on the substrate membrane to obtain a composite separation membrane with a heterogeneous structure.

[0041] 6) Heat press the composite separation membrane at 90 °C for 10 min under a pressure of 0.2 kPa. After the substrate membrane naturally detaches, a composite separation membrane with self-supporting ability is obtained.

[0042] 7) Place the composite separation membrane in a 0.1 M Fe 3+ metal ion solution and crosslink it at 70 °C for 30 min to obtain a composite separation membrane with a heterogeneous structure and self-supporting ability, which is stored in deionized water.

[0043] Example 2

[0044] This example provides a method for preparing a composite separation membrane.

[0045] Steps 1) - 3) are the same as in Example 1.

[0046] 4) Prepare a 5.5 mL graphene oxide dispersion with a concentration of 3 mg / mL, add 0.5 g of purified keratin fibers (i.e., the mass ratio of graphene oxide to keratin fibers is 1:30), and add water to a total volume of 120 mL. Ball mill for 30 min to obtain a composite casting solution.

[0047] 5) Use a water-based mixed cellulose membrane as the substrate membrane, wet clean it, and take 30 mL of the composite casting solution and filter it under negative pressure (0.98 bar) for 2 h to deposit the composite casting solution on the substrate membrane, obtaining a composite separation membrane with a heterogeneous structure.

[0048] 6) Heat press the composite separation membrane at 90 °C for 10 min under a pressure of 0.2 kPa. After the substrate membrane naturally detaches, a composite separation membrane with self-supporting ability is obtained.

[0049] 7) Place the composite separation membrane in a 0.1 M Fe 3+ metal ion solution and crosslink it at 70 °C for 60 min to obtain a composite separation membrane with a heterogeneous structure and self-supporting ability, which is stored in deionized water.

[0050] Figure 1 This is the scanning electron microscope image of the front (left) and back (right) sides of the composite separation membrane prepared in this example. Figure 2 This is the scanning electron microscope image of the cross-section of the composite separation membrane prepared in this example.

[0051] Example 3

[0052] This example provides a method for preparing a composite separation membrane.

[0053] Steps 1) - 3) are the same as in Example 1.

[0054] 4) Prepare a 10 mL graphene oxide dispersion with a concentration of 5 mg / mL, add 0.5 g of purified keratin fibers (i.e., the mass ratio of graphene oxide to keratin fibers is 1:10), and add water to a total volume of 120 mL. Ball mill for 90 min to obtain a composite casting solution.

[0055] 5) Use a water-based mixed cellulose membrane as the substrate membrane, wet clean it, take 30 mL of the composite casting solution and filter it under negative pressure (0.98 bar) for 4 h to deposit the composite casting solution on the substrate membrane, obtaining a composite separation membrane with a heterogeneous structure.

[0056] 6) Hot press the composite separation membrane at 90 °C for 10 min under a pressure of 0.2 kPa. After the substrate membrane naturally falls off, a composite separation membrane with self-supporting ability is obtained.

[0057] 7) Place the composite separation membrane in a 0.1 M Fe 3+ metal ion solution and crosslink it at 70 °C for 90 min to obtain a composite separation membrane with a heterogeneous structure and self-supporting ability, which is stored in deionized water.

[0058] Comparative Example 1

[0059] This comparative example provides a preparation of a composite separation membrane.

[0060] The preparation method of this comparative example is the same as that of Example 1, except that graphene oxide is not added. Take 30 mL of the casting solution after ball milling, filter it under negative pressure and deposit it on the mixed cellulose substrate membrane to obtain a pure keratin fiber separation membrane, which is stored in deionized water.

[0061] Example 4

[0062] This example describes the treatment ability of the composite separation membranes prepared in Examples 1 to 3 and the keratin fiber separation membrane prepared in Comparative Example 1 for dye-containing wastewater.

[0063] Use a crossflow filtration device for filtration tests. Test method:

[0064] At 25 °C, use anionic dyes Congo Red (CR) and Methyl Orange (MO) to simulate the pollutants in the wastewater. The initial pH value of the wastewater is 7, and the pollutant concentration is 100 mg / mL; in terms of m 2 / L, the ratio of the composite separation membrane area to the volume of dye-containing wastewater is 1:250 - 1000. Install the composite separation membrane in the crossflow filtration device. After the device operates stably, collect the filtrate from below, and evaluate the treatment ability of the composite separation membrane for CR wastewater and MO wastewater by calculating the flux and rejection rate; use pure water as a control. The test results are shown in Table 1.

[0065] In the above test, the calculation formula for flux is: J = V / (S×T×P0);

[0066] In the formula:

[0067] J - flux, L / (m 2 ·h·bar);

[0068] V - water volume, L;

[0069] S - area of the filtration membrane, m 2 ;

[0070] T - time for water to pass through the separation membrane, h;

[0071] P0 - standard atmospheric pressure difference, bar.

[0072] The calculation formula for the dye rejection rate is: R = 100%×(C0 - C t ) / C0;

[0073] In the formula:

[0074] R - dye rejection rate, %;

[0075] C0 - average dye concentration before the reaction, mg / mL;

[0076] C t - average dye concentration at the reaction time t (min), mg / mL.

[0077] Table 1. Treatment capacity of the composite separation membrane for dye-containing wastewater

[0078] Index Example 1 Example 2 Example 3 Comparative Example 1 <![CDATA[Pure water flux (L / (m 2 ·h·bar))]]> 21.12 12.73 2.39 71.62 <![CDATA[CR flux (L / (m 2 ·h·bar))]]> 19.67 11.93 1.07 70.44 CR rejection rate (%) 96.45 98.01 99.39 94.64 <![CDATA[MO flux (L / (m 2 ·h·bar))]]> 20.78 10.57 1.95 68.45 MO rejection rate (%) 76.84 80.39 86.92 60.56

[0079] As can be seen from Table 1, after introducing graphene oxide into the keratin fiber separation membrane, during the negative pressure filtration process, part of the graphene oxide passes through the keratin fiber skeleton and deposits on the substrate membrane, and the other part of the graphene oxide is embedded inside the keratin fiber skeleton, resulting in an increase in the dye rejection rate of the composite separation membrane. Among them, the CR rejection rate reaches 99.39%, and the MO rejection rate reaches 86.92%, which is significantly improved compared with the pure keratin fiber separation membrane prepared in Comparative Example 1. The composite separation membrane provided by the present invention improves the rejection rate of wastewater pollutants at a certain flux.

[0080] Example 5

[0081] This example describes the natural degradation process of the composite separation membrane, aqueous mixed cellulose membrane, and organic nylon membrane prepared in Example 2.

[0082] Test method: Fill commercially available nutrient soil to the 3 / 5 position of a long strip-shaped cultivation pot, add water and let it stand to cultivate the ecological microenvironment for 7 days. Then place the prepared composite separation membrane (left), commercially available aqueous mixed cellulose microfiltration membrane (middle), and organic nylon membrane (right) evenly distributed in the cultivation pot and make marks. Add 50 mL of tap water along the inner wall of the cultivation pot every 2 days to maintain the soil humidity, and take pictures every 7 days to record the degradation process.

[0083] Test results: Figure 3 This is a natural degradation process diagram of the composite separation membrane (left), commercially available aqueous mixed cellulose microfiltration membrane (middle), and organic nylon membrane (right) prepared in Example 2 of the present invention. As Figure 3 can be seen, the composite separation membrane can achieve complete degradation after 77 days of the natural degradation test. This is because during the extraction of keratin fibers, the scale layer of wool waste is damaged and part of the keratin is dissolved. Therefore, keratinase and other enzymes secreted by microorganisms in the soil can directly decompose keratin fibers, accelerating the degradation process of the composite separation membrane, confirming that the composite separation membrane has more excellent biodegradability than other conventional composite membranes.

[0084] The above-described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the present invention claimed, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art under the premise of not making creative efforts based on the concept of the present invention fall within the scope of protection of the present invention.

Claims

1. A composite separation membrane, characterized in that, The composite separation membrane uses keratin fibers as the main raw material for preparation, graphene oxide as an additive, and has a heterogeneous structure and self-supporting characteristics.

2. The composite separation membrane according to claim 1, wherein The keratin for preparing keratin fibers includes: wool keratin.

3. The preparation method of the composite separation membrane according to claim 1, characterized in that, Including: Preparation of the composite casting solution, preparation of the composite separation membrane, and post-treatment of the composite separation membrane.

4. The preparation method according to claim 3, characterized in that, The composite casting solution is prepared by mixing a graphene oxide dispersion with keratin fibers, where the concentration of the graphene oxide dispersion is 1 - 5 mg / mL, and the usage amount of keratin fibers is 10 - 50 times the weight of graphene oxide.

5. The preparation method according to claim 4, characterized in that, The preparation method of the keratin fibers includes: Cut wool fibers into small segments, soak them in a NaHCO3 solution to remove lipids to obtain degreased wool, and then wash and dry; Prepare an extraction solution to extract the keratin fibers from the degreased wool; Separate, wash, dry, and pulverize the keratin fibers to obtain purified wool keratin fibers.

6. The preparation method according to claim 5, characterized in that, During the degreasing process, the concentration of the NaHCO3 solution is 0.2 - 0.4 M, and the degreasing reaction time is 2 - 4 h; During the process of extracting keratin fibers, the extraction solution contains a reducing agent, a protective lubricant, and a solubilizer; the pH of the extraction solution is 11 - 11.5; the extraction temperature is 70 - 90 °C, and the extraction time is 4 - 6 h.

7. According to the preparation method described in claim 6, wherein: The reducing agent is L-cysteine, and the usage amount of L-cysteine is 10 - 30% of the weight of wool; The protective lubricant is urea, and the concentration of urea in the extraction solution is 6 - 8 M; The solubilizer is sodium dodecyl sulfate, and the concentration of sodium dodecyl sulfate in the extraction solution is 0.02 - 0.04 M; Adjust the pH of the extraction solution with NaOH.

8. The preparation method according to claim 3, characterized in that, Deposit the composite casting solution by vacuum filtration to obtain the composite separation membrane.

9. The preparation method according to claim 3, characterized in that, The post-treatment of the composite separation membrane includes: hot pressing and cross-linking treatment.

10. Use of the composite separation membrane according to claim 1, characterized in that, The composite separation membrane is used for water treatment.

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