Preparation and application of carbon nanotube-polyamide composite membrane

Abstract

The invention discloses preparation and application of a carbon nanotube-polyamide composite membrane. The preparation method comprises the following steps: firstly, dispersing a carbon nanotube and a surfactant in water to obtain a carbon nanotube dispersion liquid; dissolving m-phenylenediamine or piperazine in water to obtain a water-phase solution, dissolving trimesoyl chloride in an organic solvent to obtain an oil-phase solution, sequentially pouring the water-phase solution and the oil-phase solution on the surface of the porous support layer for interfacial polymerization and drying to obtain a polyamide membrane; and finally, uniformly depositing the carbon nanotubes on the surface of the polyamide membrane through evaporation self-assembly or suction filtration to obtain the carbon nanotube-polyamide composite membrane. The carbon nanotubes can improve the surface hydrophilicity of the membrane and enhance the anti-pollution performance of the membrane; the carbon nanotubes also have conductivity, hypochlorite and chlorine free radicals in water are reduced and converted through an electrochemical reduction effect, the chlorine resistance service life of the polyamide membrane is remarkably prolonged, hydroxyl free radicals are generated at the same time, and pollutants intercepted on the surface of the membrane can be efficiently degraded.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to the preparation and application of a carbon nanotube-polyamide composite membrane. Background Technology

[0002] Membrane separation technology has been widely applied in advanced wastewater treatment, material separation and concentration, resource recycling, and household drinking water purification. As a highly efficient water treatment technology, membrane separation technology has advantages such as high separation precision, no phase change, small footprint, and environmental friendliness. Seawater desalination and water reuse technologies based on membrane separation are becoming increasingly popular. In the vast membrane industry, reverse osmosis membranes and nanofiltration membranes account for approximately 50% of the membrane market. Among them, polyamide membrane composite membranes are the most researched and widely used type of membrane in reverse osmosis and nanofiltration. A typical polyamide membrane structure includes: a nonwoven fabric that provides mechanical support, a porous support layer synthesized using a phase inversion process, and a highly cross-linked ultrathin polyamide functional layer. However, polyamide membranes still have some problems: (1) Poor chlorine resistance: Some groups in the polyamide layer have high reactivity to active chlorine, which causes changes in the polyamide cross-linking network structure or even chain breakage, resulting in weakened interaction between the polyamide layer and the base membrane layer and detachment, shortening the service life of the membrane; (2) Membrane fouling: Pollutants accumulate on the membrane surface, increasing the resistance to water molecule mass transfer, resulting in a significant decrease in membrane flux and reduced separation efficiency; (3) The trapped pollutants still need to be treated in a secondary manner. Summary of the Invention

[0003] To address the problems of poor chlorine resistance, easy fouling, and the need for secondary treatment of pollutants in existing polyamide membranes, the present invention aims to provide a method for preparing and applying a carbon nanotube-polyamide composite membrane. The carbon nanotube-polyamide composite membrane is obtained by uniformly dispersing carbon nanotubes on the surface of a polyamide membrane through filtration or evaporation self-assembly. On the one hand, carbon nanotubes can improve the hydrophilicity of the membrane surface, enhancing its antifouling performance; on the other hand, carbon nanotubes possess electrical conductivity and can reduce and convert hypochlorite and chlorine free radicals in water through electrochemical reduction, significantly enhancing the chlorine resistance life of the polyamide membrane. Furthermore, the reduction of chlorine simultaneously generates hydroxyl free radicals (…). . OH) can efficiently degrade pollutants trapped on the membrane surface, potentially achieving "zero emissions" and improving the membrane's antifouling performance.

[0004] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a carbon nanotube-polyamide composite film, comprising the following steps: (1) Preparation of carbon nanotube dispersion: Carbon nanotubes and surfactants were dispersed in water at a mass ratio of 1:5 to 5:0.1, and carbon nanotube dispersion was prepared by circulating stirring and sonication. (2) Preparation of polyamide membrane: m-phenylenediamine or piperazine is dissolved in water to prepare an aqueous solution, and pyromellitic chlorotrimethylammonium chloride is dissolved in an organic solvent to prepare an oil solution; the aqueous solution is poured evenly onto the surface of the porous support layer, soaked, and then the oil solution is poured evenly into it to carry out interfacial polymerization reaction, and dried to prepare a polyamide membrane; (3) Place the carbon nanotube dispersion from step (1) on the surface of the polyamide membrane prepared in step (2), and deposit the carbon nanotubes on the surface of the polyamide membrane by means of evaporation self-assembly or filtration to obtain a carbon nanotube-polyamide composite membrane.

[0005] Based on the above technical solution, further, the mass ratio of carbon nanotubes and surfactants in step (1) is 1:2 to 2:1.

[0006] Based on the above technical solution, further, the mass ratio of carbon nanotubes to water in step (1) is 1:100 to 1:500.

[0007] Based on the above technical solution, the surfactant in step (1) is sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or hexadecyltrimethylammonium bromide, preferably sodium dodecyl sulfate.

[0008] Based on the above technical solution, further, in step (1), the number of cycles of stirring and sonication is 2 to 10, the stirring time is 20 to 40 min, and the sonication time is 20 to 40 min.

[0009] Based on the above technical solution, further, in step (2), the mass fraction of intermediate phenylenediamine or piperazine in the aqueous phase solution is 1.0~2.0wt%, preferably 1.0~1.5wt%, and the mass fraction of trimesoyl chloride in the oil phase solution is 0.05~0.3wt%, preferably 0.1~0.2wt%; the organic solvent is n-hexane, cyclohexane, acetone or chloroform.

[0010] Based on the above technical solution, further, the porous support layer in step (2) is made of polysulfone, polyethersulfone, polystyrene, polyvinylidene fluoride, polyacrylonitrile or polyethylene, preferably polysulfone or polyethersulfone.

[0011] Based on the above technical solution, further, in step (2), the soaking time is 2~20 min, preferably 4~6 min, and the time for the interfacial polymerization reaction between m-phenylenediamine or piperazine and trimesoyl chloride is 0.5~5 min, preferably 0.2~2 min; the drying is specifically drying at 50~80℃ for 5~30 min.

[0012] Based on the above technical solution, further, the unit area mass of carbon nanotubes loaded on the surface of the polyamide film in step (3) is 0.2~2.5 mg cm⁻¹. -2 .

[0013] Secondly, the present invention provides a carbon nanotube-polyamide composite film prepared by the above-described preparation method.

[0014] Thirdly, the present invention provides the application of the above-mentioned carbon nanotube-polyamide composite membrane in wastewater purification.

[0015] Based on the above technical solution, the wastewater further contains hypochlorite or chlorine free radicals.

[0016] Based on the above technical solution, the carbon nanotube-polyamide composite membrane is further connected to the cathode, with the counter electrode being the anode, and a voltage of 0.1~3.0V is applied. The filtration mode adopts either a dead-end or cross-current mode.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The carbon nanotube-polyamide composite film of the present invention has low production cost, short cycle, simple preparation process, and does not require expensive chemical reagents and equipment. (2) The carbon nanotube-polyamide composite membrane of the present invention not only has good separation performance and antifouling performance, but also can reduce and transform hypochlorite and chlorine free radicals in situ in the carbon nanotube layer through electrochemical action, while generating free radicals with oxidizing properties. . OH) can not only degrade pollutants, but also further improve their anti-pollution performance. Attached Figure Description

[0018] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0019] Figure 1 This is a schematic diagram of the structure of the carbon nanotube-polyamide composite film prepared in Example 1.

[0020] Figure 2 The graph shows the antifouling performance test results of the carbon nanotube-polyamide composite membrane and the polyamide membrane in Example 4. Detailed Implementation

[0021] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0022] Example 1 This embodiment provides a method for preparing a carbon nanotube-polyamide composite film (CNT-PA film), comprising the following steps: (1) Preparation of carbon nanotube dispersion 1.0 g of carbon nanotubes and 1.0 g of sodium dodecyl sulfate were mixed and dispersed in 200 mL of ultrapure water. The mixture was circulated, stirred, and sonicated. Undispersed carbon nanotubes were removed by centrifugation. The stirring time for each cycle was 30 min, and the sonication time for each ultrasonic disruption cycle was 30 min.

[0023] (2) Preparation of polyamide film A 1.0 wt% aqueous solution was prepared by dissolving m-phenylenediamine in water, and a 0.1 wt% oil solution was prepared by dissolving trimesoyl chloride in n-hexane. The m-phenylenediamine solution was poured onto the surface of a polysulfone porous support layer. After 5 min, the excess m-phenylenediamine solution was removed from the membrane surface with a rubber rod. The trimesoyl chloride / n-hexane solution was then poured in, and the reaction was carried out at room temperature for 1 min. The membrane was then heated in a 60℃ oven for 10 min to promote complete reaction, thus preparing a polyamide membrane.

[0024] (3) Preparation of carbon nanotube-polyamide film The carbon nanotube dispersion from step (1) was placed on the surface of the polyamide membrane prepared in step (2), and carbon nanotubes were deposited on the polyamide membrane surface by filtration, with a deposition density of 0.28 mg / cm³. -2 .

[0025] The carbon nanotube-polyamide composite membrane prepared in this embodiment was subjected to hydrophilicity, pure water flux, and salt rejection tests. The polyamide membrane prepared according to step (2) of this embodiment was used as a control. The salt rejection test was conducted using a 500 mg / L sodium chloride aqueous solution or a sodium sulfate aqueous solution. Cross-flow filtration was used, and the test pressure was 4 bar. The test results are shown in Table 1.

[0026] Table 1. Test results of hydrophilicity, pure water flux, and salt rejection rate of carbon nanotube-polyamide composite membrane and polyamide membrane.

[0027] Example 2 The difference between this embodiment and Example 1 is that in step (2), the aqueous phase solution is m-phenylenediamine / aqueous solution with a mass fraction of 1.5 wt%, and the oil phase solution is trimesoyl chloride / n-hexane with a mass fraction of 0.2 wt%. The remaining steps are the same as in Example 1.

[0028] Example 3 The difference between this embodiment and Embodiment 1 is that the unit area mass of carbon nanotubes loaded on the surface of the polyamide film in step (3) is 1.13 mg / cm². -2 The remaining steps are the same as in Example 1.

[0029] The carbon nanotube-polyamide composite membrane prepared in this embodiment was subjected to hydrophilicity, pure water flux, and salt rejection tests. The salt rejection test used a 500 mg / L sodium chloride or sodium sulfate aqueous solution. A cross-flow filtration mode was employed, and the test pressure for both pure water flux and salt rejection was 4 bar. The test results are shown in Table 1.

[0030] Example 4 The difference between this embodiment and Embodiment 1 is that the unit area mass of carbon nanotubes loaded on the surface of the polyamide film in step (3) is 2.26 mg / cm². -2 The other steps are the same as in Example 1.

[0031] The carbon nanotube-polyamide composite membrane prepared in this embodiment was subjected to hydrophilicity, pure water flux, and salt rejection tests. The salt rejection test used a 500 mg / L sodium chloride or sodium sulfate aqueous solution. A cross-flow filtration mode was employed, and the test pressure for both pure water flux and salt rejection was 4 bar. The test results are shown in Table 1.

[0032] This embodiment also includes a sodium hypochlorite removal performance test. The specific process is as follows: The carbon nanotube-polyamide composite membrane or polyamide membrane prepared in this embodiment is placed in a membrane module. The membrane module consists of a carbon nanotube-polyamide composite membrane, a titanium electrode, and a counter electrode from top to bottom. The carbon nanotube layer of the carbon nanotube-polyamide composite membrane is in close contact with the titanium electrode (cathode), and the counter electrode is the anode. The voltage is set to 0~-1.0 V. A 4 ppm sodium hypochlorite aqueous solution is filtered using a cross-flow mode. The solution is in contact with the carbon nanotube surface of the carbon nanotube-polyamide composite membrane. The pressure is adjusted to stabilize at 4 bar. The test results are shown in Table 2.

[0033] Table 2. Effects of applying 0 to -1.0 V voltage externally to the carbon nanotube-polyamide composite film on chlorine treatment of the polyamide film.

[0034] Long-term antifouling tests were conducted on the carbon nanotube-polyamide composite membrane and the polyamide membrane prepared in this embodiment. A mixed aqueous solution of 2 ppm sodium hypochlorite and 100 ppm humic acid was used as the feed solution, and the voltage was set to 0~-1.0 V. The test results are as follows: Figure 2 As shown.

[0035] Example 5 The difference between this embodiment and embodiment 4 is that the influent is a mixed aqueous solution of 2 ppm sodium hypochlorite and 2 ppm rhodamine B, the voltage is 0 to -2.5 V, and the remaining steps are the same as in embodiment 4.

[0036] The test results of the Rhodamine B removal performance of the carbon nanotube-polyamide composite membrane in this embodiment are shown in Table 3.

[0037] Table 3. Pollutant treatment efficiency of carbon nanotube-polyamide composite membrane under externally applied voltage of 0 to -2.5 V

[0038] Example 6 The difference between this embodiment and embodiment 5 is that the influent is a mixed aqueous solution of 2 ppm sodium hypochlorite and 2 ppm methylene blue, while the remaining steps are the same as in embodiment 5.

[0039] The methylene blue removal performance of the carbon nanotube-polyamide composite membrane prepared in this embodiment was tested, and the test results are shown in Table 3.

[0040] The test results of Examples 1, 3, 4 and the control polyamide membrane show that depositing carbon nanotubes on the surface of the polyamide membrane significantly improves the hydrophilicity of the membrane surface without affecting the pure water flux and salt rejection rate. The chlorine removal effect of the carbon nanotube-polyamide composite membrane is better than that of the polyamide membrane, and the chlorine removal performance of the carbon nanotube-polyamide composite membrane is significantly improved with the increase of voltage, indicating that the carbon nanotube-polyamide composite membrane has excellent chlorine resistance under electric assistance.

[0041] From the test results of Example 4 ( Figure 2 It can be seen that the flux decay rate of the carbon nanotube-polyamide composite film is slower when 0V and -1.0V voltages are applied, indicating that the antifouling performance of the carbon nanotube-polyamide composite film is better than that of the polyamide film. Furthermore, the antifouling performance of the carbon nanotube-polyamide composite film is further improved under electrochemical assistance.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon nanotube-polyamide composite film, characterized in that, Includes the following steps: (1) Carbon nanotubes and surfactants are mixed in a mass ratio of 1:5~5: Carbon nanotubes were dispersed in water at a ratio of 0.1, and then circulated, stirred, and sonicated to prepare a carbon nanotube dispersion. (2) Dissolve m-phenylenediamine or piperazine in water to prepare an aqueous solution, and dissolve pyromellitic chloride in an organic solvent to prepare an oil solution; pour the aqueous solution evenly onto the surface of the porous support layer, soak it, and then pour the oil solution evenly into it to carry out the interfacial polymerization reaction and dry it to prepare a polyamide film. (3) Place the carbon nanotube dispersion from step (1) on the surface of the polyamide membrane prepared in step (2), and deposit the carbon nanotubes on the surface of the polyamide membrane by means of evaporation self-assembly or filtration to obtain a carbon nanotube-polyamide composite membrane.

2. The preparation method according to claim 1, characterized in that, The mass ratio of carbon nanotubes to surfactant in step (1) is 1:2 to 2:1; the surfactant is sodium dodecylbenzenesulfonate, sodium dodecyl sulfate or hexadecyltrimethylammonium bromide, preferably sodium dodecyl sulfate.

3. The preparation method according to claim 1, characterized in that, The mass ratio of carbon nanotubes to water in step (1) is 1:100 to 1:500; the number of cycles of stirring and sonication is 2 to 10, the stirring time is 20 to 40 min, and the sonication time is 20 to 40 min.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass fraction of intermediate phenylenediamine or piperazine in the aqueous phase solution is 1.0~2.0wt%, preferably 1.0~1.5wt%, and the mass fraction of trimesoyl chloride in the oil phase solution is 0.05~0.3wt%, preferably 0.1~0.2wt%; the organic solvent is n-hexane, cyclohexane, acetone or chloroform.

5. The preparation method according to claim 1, characterized in that, The porous support layer in step (2) is made of polysulfone, polyethersulfone, polystyrene, polyvinylidene fluoride, polyacrylonitrile or polyethylene, preferably polysulfone or polyethersulfone.

6. The preparation method according to claim 1, characterized in that, In step (2), the soaking time is 2~20 min, preferably 4~6 min, and the interfacial polymerization reaction time of m-phenylenediamine or piperazine with trimesoyl chloride is 0.5~5 min, preferably 0.2~2 min; the drying is specifically drying at 50~80℃ for 5~30 min.

7. The preparation method according to claim 1, characterized in that, The carbon nanotubes loaded on the surface of the polyamide film in step (3) have a unit area mass of 0.2~2.5 mg cm⁻¹. -2 .

8. The carbon nanotube-polyamide composite film prepared by the preparation method according to any one of claims 1-7.

9. The application of the carbon nanotube-polyamide composite membrane according to claim 8 in wastewater purification.

10. The application according to claim 9, characterized in that, The wastewater contains hypochlorite or chlorine free radicals.

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