Composite cross-linked pollution electrically responsive film and preparation method and application thereof

Abstract

The application discloses a composite cross-linked pollution electrical response film and a preparation method and application thereof. The composite cross-linked pollution electrical response film comprises an O-MWCNTs inlaid PVDF base film and an O-MWCNTs modified layer activated by EDC and cross-linked on the base film through MXDA. The diamine groups in MXDA and oxygen-containing groups in the activated carboxyl groups undergo ester-like reactions, and the O-MWCNTs modified layer and the base film are tightly combined through amide bonds. The composite cross-linked pollution electrical response film prepared by the application has good blocking performance, strong anti-pollution property and high durability, and has good anti-pollution property, acid and alkali resistance and electrochemical performance, can produce electrochemical signal response to organic macromolecular proteins, and can timely observe the pollution degree of the film.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology for wastewater treatment, and in particular to a composite cross-linked electro-responsive membrane for pollution, its preparation method, and its application. Background Technology

[0002] Membrane separation technology is currently the mainstay of wastewater treatment, with advantages such as high efficiency, high output, low cost, and simple operation. This ultrafiltration technology can purify, refine, separate, and concentrate wastewater, and is showing remarkable prospects in the field of wastewater purification.

[0003] Currently, membrane separation technology for wastewater treatment has undergone significant innovation, but problems remain, including poor antifouling properties, poor durability, insensitivity to acids and alkalis, high cost of membrane fouling detection, and membrane fouling itself. To investigate membrane fouling and improve membrane durability, in addition to modifying the membrane itself, membrane reactors can be used to receive reaction signals to monitor the degree of membrane fouling. This allows for further investigation of the membrane fouling process and timely cleaning and replacement of fouled membranes to extend their lifespan. Common testing methods involve monitoring the biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), pH value, and flow rate of the filtered solution. However, this indirect detection method is cumbersome, costly, time-consuming, and carries safety risks. Therefore, there is an urgent need for a rapid, sensitive, convenient, low-cost, and selective direct detection method.

[0004] Compared to other detection signals, electrical signals are the most sensitive and rapid. To introduce the corresponding electrical signals into membranes for direct detection, attention has been focused on inorganic conductive materials. Carbon nanomaterials have thus come into the research field. Carbon nanomaterials such as carbon nanotubes and graphene possess properties such as high surface area, high mechanical strength, excellent chemical inertness, and outstanding water transport. Carboxylated carbon nanotubes are among the most common one-dimensional nanotube materials, exhibiting hydrophilicity, providing transport channels, excellent electrical properties, superior adsorption and sieving performance, chemical stability, and high mechanical strength. They are one of the best modifying materials for preparing composite polymer separation membranes for direct pollution electrical signal transmission.

[0005] Combining carboxylated carbon nanotubes with polymers to form stable, efficient, and sensitive electrochemically responsive composite membranes for pollution is a common modification method. Surface modification, while maximizing its effect, suffers from insufficient adhesion, leading to wrinkling, shrinkage, and even peeling off of the base membrane. To improve the bonding strength between the modified layer and the base membrane while maintaining the carbon nanotube loading, researchers have focused on cross-linked structures, which exhibit better mechanical properties and stability in their composite membranes. Summary of the Invention

[0006] The purpose of this invention is to address the technical deficiencies of existing pollution electrochemical response composite membranes by providing a composite cross-linked pollution electrochemical response membrane.

[0007] Another object of the present invention is to provide a method for preparing the composite cross-linked contamination electrical response membrane.

[0008] Another objective of this invention is to provide the application of the composite cross-linked fouling electroresponsive membrane in wastewater purification. This composite cross-linked fouling electroresponsive membrane can improve membrane lifespan in the field of wastewater purification and detect fouling conditions to enable timely replacement and cleaning of severely fouled membranes.

[0009] The technical solution adopted to achieve the purpose of this invention is:

[0010] A composite cross-linked electrochemically responsive membrane comprises an O-MWCNTs (carboxylated carbon nanotubes) embedded PVDF (polyvinylidene fluoride) base film and an O-MWCNTs modification layer cross-linked onto the base film by MXDA (m-phenylenediamine) activated by EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride). The diamine groups in MXDA undergo an esterification-like reaction with the oxygen-containing groups in the activated carboxyl groups, tightly binding the O-MWCNTs modification layer to the base film via amide bonds. Figure 1 As shown.

[0011] Another aspect of the present invention includes a method for preparing the composite cross-linked contamination-responsive membrane, comprising the following steps:

[0012] Step 1: O-MWCNTs are uniformly dispersed in DMAc (N,N-dimethylacetamide), then PVDF powder and PVP (polyvinylpyrrolidone) are added and heated and stirred. After the polymer is completely swollen, a casting solution is obtained. The casting solution is then degassed under vacuum, and a semi-embedded PVDF base film of flat O-MWCNTs is prepared using a phase inversion method. In this step, the effective carboxyl groups are exposed for subsequent crosslinking reactions. Blending O-MWCNTs can improve the barrier properties and mechanical strength of the film.

[0013] Step 2: The O-MWCNT activated by EDC is uniformly dispersed in deionized water to obtain an activated O-MWCNT dispersion. The MXDA (m-phenylenediamine) powder is uniformly dispersed in deionized water to obtain an MXDA solution. The MXDA solution and the activated O-MWCNT dispersion are sequentially pre-coated onto the semi-embedded PVDF base membrane of the flat O-MWCNTs obtained in Step 1 through a vacuum filtration device to obtain a composite cross-linked pollution-responsive membrane intermediate.

[0014] Step 3: The composite cross-linked fouling electroresponsive membrane intermediate obtained in Step 2 is subjected to thermostatic treatment, causing the EDC-activated O-MWCNTs modification layer and the O-MWCNTs semi-embedded PVDF base membrane to be cross-linked together via MXAD, thus obtaining the composite cross-linked fouling electroresponsive membrane. The diamine groups in MXDA undergo an esterification-like reaction with the oxygen-containing groups in the carboxyl groups, which are then covalently linked together to improve the bonding strength of the modification layer.

[0015] In the above technical solution, the O-MWCNT has a purity >95 wt.%, an outer diameter of 10-20 nm, a length of 10-30 μm, and the MXDA powder is AR grade.

[0016] In the above technical solution, in step 1, O-MWCNT is dispersed in DMAc using a cell disruption sonicator at 0-4℃, with a sonication power of 100-200W and a sonication time of 1-2h.

[0017] In the above technical solution, in step 1, the amount of PVDF added to the casting solution is 10-15%, the amount of PVP added is 0.5-2.5%, the amount of DMAc added is 80-90%, and the amount of O-MWCNT added is 1-2 wt.% of the total solid content in the casting solution.

[0018] In the above technical solution, in step 1, after the casting solution is mechanically stirred at 60-80℃ for 5-10 hours, it is vacuum degassed for 1 hour. Using a 100-300μm scraper, it is scraped into a flat plate on a glass plate, and then immersed in deionized water for mass transfer. The water is changed every 6-24 hours to obtain a flat O-MWCNTs semi-embedded PVDF base film. Figure 2 As shown.

[0019] In the above technical solution, in step 2, the concentration of O-MWCNT activated by EDC in the activated O-MWCNT dispersion is 0.5-2 g / L. The activated O-MWCNT dispersion is obtained by sonicating the cell disruptor for 30-90 minutes at a temperature of 0-4℃ and a power of 100-200W.

[0020] The concentration of the MXDA solution is 0-2 g / L and not 0 g / L.

[0021] In the above technical solution, in step 2, 5-30 ml of MXDA solution is first coated onto the semi-embedded PVDF base film of flat O-MWCNTs, followed by 5-30 ml of activated O-MWCNT dispersion.

[0022] In the above technical solution, the solidification time in step 3 is 1-3 hours, and the solidification temperature is 50-100℃.

[0023] Another aspect of the present invention includes the application of the composite cross-linked fouling electrical response membrane in wastewater purification.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. The composite cross-linked fouling electroresponsive membrane prepared by this invention not only has good interception performance, strong antifouling properties, and high durability, but also exhibits good antifouling, acid and alkali resistance, and electrochemical performance. It can generate electrochemical signal responses to organic macromolecular proteins, allowing for timely monitoring of the membrane's fouling level.

[0026] 2. This invention incorporates the electrical properties of O-MWCNTs into a composite membrane, enabling the composite membrane to possess a sensitive response signal to macromolecular protein contaminants, using a dedicated membrane cell (such as...). Figure 3 As shown, tests conducted using a four-probe resistivity meter revealed that the resistance ranged from the non-conductive PVDF base film to 1.33 MΩ for the PVDF film with semi-embedded O-MWCNTs, and then decreased to 40.72 Ω for the composite cross-linked contamination electrical response film coated with an activated O-MWCNT layer, exhibiting sensitive electrical signal responsiveness.

[0027] 3. This invention utilizes an esterification-like reaction to prepare a sandwich-structured composite membrane with high bonding strength, and uses a self-made membrane pool to receive the membrane's response signal to directly detect the membrane's fouling status. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the cross-linking structure of the composite membrane.

[0029] Figure 2 (a) is the O-MWCNTs semi-embedded PVDF base film, and (b) is the surface morphology of the composite cross-linked film.

[0030] Figure 3 It is a dedicated electrical signal receiving membrane cell structure.

[0031] Figure 4 The trends of composite membrane resistance and flux with varying pollution levels are shown. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0033] In the following examples, a Keithley 2700 four-probe resistance meter and a Koster CHI604E electrochemical workstation were used to receive the electrochemical signals of the composite membrane. Scanning electron microscopy (SEM) was used to characterize the morphology of the prepared composite membrane. A laboratory-made membrane cell was used to test the flux of the composite membrane. A UV-2450 ultraviolet spectrophotometer was used to test the rejection rate of the composite membrane.

[0034] Example 1

[0035] A composite cross-linked fouling electrically responsive membrane is prepared by the following method:

[0036] Step 1: O-MWCNTs were uniformly dispersed in a DMAc solution by sonication at 180W for 1 hour using a cell disruption sonicator to obtain an O-MWCNT DMAc solution. A casting solution was then prepared. The casting solution composition was: 15% PVDF, 1% PVP, and 84% O-MWCNT DMAc solution, with O-MWCNTs accounting for 0.5 wt.% of the total solids in the casting solution. The prepared casting solution was mechanically stirred at 70℃ for 6 hours, then vacuum degassed for 1 hour. A 200μm scraper was used to scrape the solution into a flat plate on a glass plate, which was then immersed in deionized water for mass transfer. The water was changed every 12 hours to obtain a PVDF-based membrane with semi-embedded O-MWCNTs.

[0037] Step 2: Prepare the modification layer. O-MWCNTs (39 wt.% EDC) were placed in deionized water and sonicated for 1 hour at 4°C and 180W using a cell disruption sonicator to obtain an activated O-MWCNT dispersion with a concentration of 0.5 g / L. Simultaneously, an MXDA solution with a concentration of 0.5 g / L was prepared. 10 mL each of the prepared MXDA solution and the activated O-MWCNT dispersion were then sequentially loaded onto the PVDF substrate membrane containing the semi-embedded O-MWCNTs obtained in Step 1 using a vacuum filtration device to obtain the composite membrane.

[0038] Step 3: Place the composite membrane obtained in Step 2 on an 80°C heating platform for 10 minutes until the solvent is completely evaporated to obtain a composite cross-linked fouling electrical response membrane with a sheet resistance of 73.51Ω and a BSA rejection rate of 93.50%.

[0039] Example 2

[0040] A composite cross-linked fouling electrically responsive membrane is prepared by the following method:

[0041] Step 1: O-MWCNTs were uniformly dispersed in DMAc solution by sonication at 180W for 1 hour using a cell disruption sonicator to obtain an O-MWCNT DMAc solution. Then, a casting solution was prepared. The casting solution composition was: 15% PVDF, 1% PVP, and 84% O-MWCNT DMAc solution, with O-MWCNTs accounting for 0.5 wt.% of the total solids in the casting solution. The prepared casting solution was mechanically stirred at 70℃ for 6 hours, then vacuum degassed for 1 hour. A 200μm scraper was used to scrape the solution into a flat plate on a glass plate, which was then immersed in deionized water for mass transfer. The water was changed every 12 hours to obtain a PVDF-based membrane with semi-embedded O-MWCNTs.

[0042] Step 2: Prepare the modification layer. O-MWCNTs (39 wt.% EDC) were placed in deionized water and sonicated for 1 hour at 4°C and 180W using a cell disruption sonicator to obtain an activated O-MWCNT dispersion with a concentration of 0.5 g / L. Simultaneously, an MXDA solution with a concentration of 1 g / L was prepared. 10 mL each of the prepared MXDA solution and the activated O-MWCNT dispersion were then sequentially loaded onto the PVDF-based membrane containing the semi-embedded O-MWCNTs obtained in Step 1 using a vacuum filtration device to obtain the composite membrane.

[0043] Step 3: Place the composite membrane obtained in Step 2 on an 80°C heating stage for 10 minutes until the solvent is completely evaporated to obtain a composite cross-linked fouling electrically responsive membrane. Its sheet resistivity reaches 40.72 Ω, and the BSA rejection rate is 97.89%.

[0044] Example 3

[0045] A composite cross-linked fouling electrically responsive membrane is prepared by the following method:

[0046] Step 1: O-MWCNTs were uniformly dispersed in a DMAc solution using a cell disruption sonicator at 180W for 1 hour to obtain an O-MWCNT DMAc solution. A casting solution was then prepared. The casting solution composition was: 15% PVDF, 1% PVP, and 84% O-MWCNT DMAc solution, with O-MWCNTs accounting for 0.5 wt.% of the total solids in the casting solution. The prepared casting solution was mechanically stirred at 70℃ for 6 hours, then vacuum degassed for 1 hour. A 200μm scraper was used to scrape the solution into a flat plate on a glass plate, which was then immersed in deionized water for mass transfer. The water was changed every 12 hours to obtain a PVDF-based membrane with semi-embedded O-MWCNTs.

[0047] Step 2: Prepare the modification layer. O-MWCNTs (39 wt.% EDC) were placed in deionized water and sonicated for 1 hour at 4°C and 180W using a cell disruptor to obtain a 1 g / L activated O-MWCNT dispersion. Simultaneously, a 1 g / L MXDA solution was prepared. 10 mL each of the prepared MXDA solution and the activated O-MWCNT dispersion were then sequentially loaded onto the PVDF-based membrane containing the semi-embedded O-MWCNTs obtained in Step 1 using a vacuum filtration device to obtain the composite membrane.

[0048] Step 3: The composite membrane obtained in Step 2 is heated on an 80°C heating stage for 10 minutes until the solvent is completely evaporated, resulting in a composite cross-linked fouling electrically responsive membrane. Its sheet resistivity reaches 28.34 Ω, and the BSA rejection rate is 99.16%.

[0049] like Figure 1 As shown, the composite cross-linked electrochemically responsive membrane obtained in Examples 1-3 above comprises an O-MWCNTs (carboxylated carbon nanotubes) embedded PVDF (polyvinylidene fluoride) base membrane and an O-MWCNTs modification layer cross-linked onto the base membrane by MXDA (m-phenylenediamine). The diamine groups in MXDA undergo an esterification-like reaction with the oxygen-containing groups in the carboxyl groups, tightly binding the O-MWCNTs modification layer to the base membrane through amide bonds.

[0050] The morphology of the composite cross-linked fouling electrically responsive membrane obtained in Example 1 was characterized by SEM, such as... Figure 2 As shown in (a), O-MWCNTs are partially embedded in the PVDF membrane, providing active sites for the subsequent crosslinking process. (b) shows the surface morphology of the composite membrane after MXDA crosslinking of the O-MWCNTs modified layer.

[0051] pass Figure 3 The self-made electrical signal receiving membrane cell structure shown can be used to test the flux and electrical signal of the composite cross-linked contamination electrical response membrane of the present invention in real time.

[0052] Organic macromolecular protein pollutants were treated using the composite cross-linked electro-responsive membrane obtained in Example 1. Figure 3 A dedicated electrical signal receiving membrane cell structure can be used to obtain the resistance and normalized flux as a function of pollution conditions, such as... Figure 4 As shown, the composite cross-linked fouling electrical response membrane exhibits a sensitive and precise fouling electrical response signal.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 composite cross-linked fouling electrically responsive membrane, characterized in that, It includes an O-MWCNTs embedded PVDF base film and an O-MWCNTs modified layer crosslinked on the base film by MXDA and activated by EDC. The diamine group in MXDA undergoes an esterification reaction with the oxygen-containing group in the activated carboxyl group, and the O-MWCNTs modified layer is tightly bonded to the base film by amide bonds.

2. The method for preparing the composite cross-linked contamination-responsive membrane as described in claim 1, characterized in that, Includes the following steps: Step 1: O-MWCNTs are uniformly dispersed in DMAc, then PVDF powder and PVP are added and heated and stirred. After the polymer is completely swollen, a casting solution is obtained. The casting solution is then degassed under vacuum, and a semi-embedded PVDF base film of flat O-MWCNTs is prepared by phase inversion method. In this step, effective carboxyl groups are exposed for subsequent crosslinking reactions. Blending O-MWCNT can improve the membrane's barrier properties and mechanical strength. Step 2: O-MWCNTs activated by EDC are uniformly dispersed in deionized water to obtain an activated O-MWCNT dispersion. MXDA powder is uniformly dispersed in deionized water to obtain an MXDA solution. The MXDA solution and the activated O-MWCNT dispersion are sequentially pre-coated onto the semi-embedded PVDF base membrane of flat O-MWCNTs obtained in Step 1 through a vacuum filtration device to obtain a composite cross-linked pollution-responsive membrane intermediate. Step 3: Perform thermosetting on the composite cross-linked pollution electrical response membrane intermediate obtained in Step 2, so that the O-MWCNTs modified layer activated by EDC and the O-MWCNTs semi-embedded PVDF base film are cross-linked together by MXAD to obtain the composite cross-linked pollution electrical response membrane.

3. The preparation method according to claim 2, characterized in that, The O-MWCNT has a purity >95 wt.%, an outer diameter of 10-20 nm, and a length of 10-30 μm. The MXDA powder is AR grade.

4. The preparation method according to claim 2, characterized in that, In step 1, O-MWCNTs are dispersed in DMAc using a cell disruption sonicator at 0-4°C, with a sonication power of 100-200W and a sonication time of 1-2 hours.

5. The preparation method according to claim 2, characterized in that, In step 1, the amount of PVDF added to the casting solution is 10-15%, the amount of PVP added is 0.5-2.5%, the amount of DMAc added is 80-90%, and the amount of O-MWCNT added is 1-2 wt.% of the total solid content in the casting solution.

6. The preparation method according to claim 2, characterized in that, In step 1, the casting solution is mechanically stirred at 60-80℃ for 5-10 hours, then vacuum degassed for 1 hour. A 100-300μm scraper is used to scrape the solution into a flat plate on a glass plate. The plate is then immersed in deionized water for mass transfer. The water is changed every 6-24 hours to obtain a flat O-MWCNTs semi-embedded PVDF base film.

7. The preparation method according to claim 2, characterized in that, In step 2, the concentration of O-MWCNT activated by EDC in the activated O-MWCNT dispersion is 0.5-2 g / L. The activated O-MWCNT dispersion is obtained by sonicating the cell disruptor for 30-90 minutes at a temperature of 0-4℃ and a power of 100-200W. The concentration of the MXDA solution is 0-2 g / L and not 0 g / L.

8. The preparation method according to claim 2, characterized in that, In step 2, 5-30 ml of MXDA solution is first coated onto the semi-embedded PVDF substrate of flat O-MWCNTs, followed by 5-30 ml of activated O-MWCNT dispersion.

9. The preparation method according to claim 2, characterized in that, In step 3, the curing time is 1-3 hours and the curing temperature is 50-100℃.

10. The application of the composite cross-linked fouling electrical response membrane as described in claim 1 in wastewater purification.

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