Method for preparing multi-walled carbon nanotube electro-catalytic membrane based on swelling effect and application of multi-walled carbon nanotube electro-catalytic membrane

Abstract

The invention belongs to the technical field of sewage treatment, and discloses a method for preparing a multi-walled carbon nanotube electro-catalytic membrane based on a swelling effect and application of the multi-walled carbon nanotube electro-catalytic membrane based on the swelling effect. S2, swelling and filling: preparing a swelling dispersion liquid by adopting a multi-walled carbon nanotube, and carrying out first modification treatment on the pretreated PVDF base membrane to obtain a swelling membrane; s3, filtering and coating: preparing a loading solution by adopting a multi-walled carbon nanotube to carry out secondary modification treatment on the swelling membrane, so as to prepare a multi-walled carbon nanotube electro-catalysis membrane; the multi-walled carbon nanotube electro-catalysis membrane prepared by the method can be used for removing ibuprofen in a water environment in an electro-catalysis membrane filtration system. According to the prepared multi-walled carbon nanotube electro-catalytic membrane, the electrochemical performance of a CNTs-PVDF membrane can be enhanced, and the removal effect on ibuprofen can be improved through a net-shaped structure formed on the surface of a PVDF base membrane; the electrochemical removal efficiency on the ibuprofen solutions with different initial concentrations is high, and the removal rate on the low-concentration ibuprofen solution exceeds 90%.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and in particular to a method for preparing a multi-walled carbon nanotube electrocatalytic membrane based on a swelling effect and an application thereof. Background Art

[0002] In daily life, there are many kinds of drug-like organic compounds involved, and the absorption and metabolism of these compounds by the human body are incomplete. This directly leads to the unmetabolized active ingredients of drugs entering the water environment through various pathways. Ibuprofen (IBU) has antipyretic, analgesic, and anti-inflammatory effects. Its accumulation in water bodies not only affects the water environment, but also may eventually threaten human health as it is transmitted through the food chain.

[0003] Traditional sewage treatment processes cannot effectively decompose pharmaceutical organic compounds. Therefore, advanced oxidation processes (AOPs) such as photocatalysis, Fenton oxidation and electrochemical oxidation have been mostly used in recent years to remove pharmaceutical organic compounds such as IBU. The Chinese invention patent (CN201610279013.6) uses titanium dioxide as a catalytic material to remove ibuprofen. The price of the catalyst used in this method is relatively high, which increases the process cost of material preparation, and the control requirements during the reaction are strict, especially in terms of light source control; the Chinese invention patent (CN202210843995.2) uses CuFe bimetallic single atoms as catalysts to remove ibuprofen. The heating rate of roasting in this method is strictly controlled, and there are strict requirements for the weight ratio of added nitrogen-containing organic matter; the short-term removal rate of ibuprofen under different pH conditions is significantly different. The above method requires the introduction of new catalytic oxidation materials / metal particles, and the initial concentration used to remove ibuprofen is relatively high, which is not suitable for practical applications. The concentration of ibuprofen in sewage is generally low, about tens of micrograms per liter of sewage, and the concentration of ibuprofen in sewage in some areas is about 2 mg / L. Therefore, it is urgent to develop a method for removing ibuprofen with a simple preparation process, few influencing factors, and a wide range of application conditions.

[0004] Electrochemical oxidation is a process in which an electrolyte gains or loses electrons to generate OH and H 2 O 2 Strong oxidants such as chlorine and chlorine can be used to remove the difficult-to-degrade organic matter in the water. Electrochemical advanced oxidation technology includes electrochemical separation technology and electrocatalytic oxidation technology. Among them, electrochemical separation technology can organically combine membrane filtration adsorption and electrochemical degradation to remove the difficult-to-degrade organic matter, thereby reducing reaction time and energy consumption.

[0005] The electrocatalytic membrane filtration system combines electrocatalytic technology with membrane filtration technology. It uses the electrocatalytic process to carry out redox reactions on pollutants, and uses the membrane separation function to achieve efficient filtration and separation of substances. The electrodes in the electrocatalytic process can promote the degradation of pollutants, reduce the deposition of pollutants on the membrane surface, slow down membrane pollution, and improve filtration efficiency and membrane service life. The advantages of electrocatalytic membrane filtration devices include efficient degradation of organic pollutants, inhibition of biological fouling, and reduction of the use of chemical agents.

[0006] In the membrane filtration process, the membrane reactor is usually affected by the structure, and carbon nanotubes (CNTs) are widely used in membrane surface modification due to their excellent electronic, mechanical and chemical properties. These characteristics give the filter membrane based on CNTs a high specific surface area and excellent electrochemical activity, making the CNTs membrane combined with electrochemical degradation technology an effective deep treatment process that can effectively remove micropollutants such as antibiotics in the water environment. The swelling effect refers to the phenomenon that the membrane material absorbs liquid and expands in a specific solvent or solution. Through this process, the pore structure and arrangement of the molecular chains of the membrane may change, thereby improving its conductivity. Through the swelling effect, in-situ filling of CNTs in the pores of polyvinylidene fluoride (PVDF) membranes can further enhance the electrochemical properties of CNTs-PVDF membranes on the one hand, and alleviate the problem of pore clogging on the other hand.

[0007] Therefore, the present invention provides a method for preparing a multi-walled carbon nanotube electrocatalytic membrane through a swelling effect, wherein the multi-walled carbon nanotube electrocatalytic membrane not only has excellent pollutant removal capability, but also has the capability of alleviating membrane fouling effect. Summary of the invention

[0008] The present invention aims to provide a method for preparing a multi-walled carbon nanotube electrocatalytic membrane based on the swelling effect. The multi-walled carbon nanotube electrocatalytic membrane prepared by this method can be used in an aqueous environment to effectively decompose pharmaceutical organic compounds in the aqueous environment, and has excellent pollutant removal capabilities and the ability to alleviate membrane fouling effects.

[0009] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect, comprising the following steps: S1, PVDF base membrane pretreatment; S2, swelling and filling, using multi-walled carbon nanotubes to prepare a swelling dispersion to perform a first modification treatment on the PVDF base film pretreated in step S1 to obtain a swelling film; S3, filtering and coating, using a multi-walled carbon nanotube-prepared loading liquid to perform a second modification treatment on the swollen membrane in step S2 to obtain a multi-walled carbon nanotube electrocatalytic membrane.

[0010] Preferably, the method for pretreating the PVDF base membrane is to wash the PVDF base membrane with anhydrous ethanol and ultrapure water in sequence.

[0011] It should be noted here that anhydrous ethanol is used to remove dust and organic matter on the surface of the PVDF base membrane, while ultrapure water is used to remove residual ethanol on the surface of the PVDF base membrane; the treated PVDF base membrane needs to be soaked in ultrapure water and stored at low temperature for future use, and the ultrapure water should be replaced at least once every 24 hours.

[0012] Preferably, the method for the first modification treatment is to first subject the prepared swelling dispersion to water bath ultrasonic treatment, then put the PVDF base film pretreated in step S1 into the ultrasonically treated swelling dispersion, and continue the ultrasonic treatment to obtain a swelling film.

[0013] Preferably, in step S2, the swelling dispersion is prepared by adding multi-walled carbon nanotubes into xylene.

[0014] Preferably, the mass volume ratio of the multi-walled carbon nanotubes to xylene is 1-3 mg:1 ml.

[0015] Preferably, the multi-walled carbon nanotubes are any one of conventional carbon nanotubes, carboxylated carbon nanotubes or hydroxylated carbon nanotubes.

[0016] Preferably, the multi-walled carbon nanotubes have a diameter of 10-60 nm and a length of less than 5 μm.

[0017] Preferably, the temperature of the ultrasonic treatment is 60±5° C., the water bath ultrasonic treatment time of the prepared swelling dispersion is 30-45 min, the PVDF base film is put into the ultrasonically treated swelling dispersion, and the ultrasonic treatment time is continued for 60-90 min.

[0018] Preferably, in step S3, the surface of the swollen membrane is rinsed with anhydrous ethanol and ultrapure water in sequence before filtering and coating.

[0019] It should be noted here that anhydrous ethanol is used to remove xylene on the surface of the swollen membrane, while ultrapure water is used to remove residual ethanol on the surface of the swollen membrane.

[0020] Preferably, in step S3, the preparation method of the loading liquid is to place multi-walled carbon nanotubes with a diameter of 40-60 nm in an ethanol solution with a volume fraction of 45%-55%, and ultrasonically treat for 30-45 minutes, and the mass ratio of the multi-walled carbon nanotubes in the loading liquid to the multi-walled carbon nanotubes in the swelling dispersion is 5:4-12.

[0021] Preferably, in step S3, the second modification treatment method is to filter at a constant pressure of 0.09-0.11 MPa by negative pressure filtration to make the multi-walled carbon nanotubes evenly adhere to the surface of the swollen membrane to obtain a multi-walled carbon nanotube electrocatalytic membrane.

[0022] The present invention also provides a multi-walled carbon nanotube electrocatalytic membrane prepared by the method.

[0023] The present invention also provides the use of the multi-walled carbon nanotube electrocatalytic membrane in an electrocatalytic membrane filtration system to remove pharmaceutical organic compounds in a water environment, wherein the initial pH value of the water environment is 3-11, and the pharmaceutical organic compounds include but are not limited to ibuprofen.

[0024] Compared with the prior art, the present invention has the following beneficial effects: 1. The multi-walled carbon nanotube electrocatalytic membrane prepared by the present invention through the swelling effect can enhance the electrochemical performance of the CNTs-PVDF membrane due to the oxygen-containing groups on the surface of the multi-walled carbon nanotubes, thereby improving the removal effect of IBU, and the carboxylated and hydroxylated carbon nanotubes have better effects. This is because the carbon nanotubes after carboxylation and hydroxylation are not easy to agglomerate and have good dispersibility, and can maintain a large dispersion in the swelling liquid, thereby forming more network structures on the surface of the PVDF base membrane; 2. The electrochemical removal efficiency of the multi-walled carbon nanotube electrocatalytic membrane prepared by the present invention for low-concentration IBU solution is more than 90%, which indicates that the COOH@CNTs-PVDF modified membrane can efficiently remove IBU under low-concentration pollutant conditions, showing good application potential; and the electrochemical removal efficiency of the multi-walled carbon nanotube membrane prepared by the present invention for high-concentration IBU solution is greater than 70%. Compared with the original membrane, the optimal multi-walled carbon nanotube membrane can be significantly improved by 63.22%. The above results show that compared with the original membrane, the multi-walled carbon nanotube electrocatalytic membrane prepared by the present invention has a significant effect on the removal of IBU in wastewater, and its operating stability is also significantly better than that of the original membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a SEM image of the PVDF base film used in the present invention; Figure 2 The SEM images of electrocatalytic membranes AC prepared by conventional carbon nanotubes under different modification conditions in the present invention (a is electrocatalytic membrane A; b is electrocatalytic membrane B; c is electrocatalytic membrane C); Figure 3 The SEM images of the electrocatalytic membrane DF prepared by using conventional carbon nanotubes under different modification conditions in the present invention (d is the electrocatalytic membrane D; e is the electrocatalytic membrane E; f is the electrocatalytic membrane F); Figure 4The SEM images of the electrocatalytic membrane GI prepared by using conventional carbon nanotubes under different modification conditions in the present invention (g is the swollen membrane G; h is the swollen membrane H; i is the swollen membrane I); Figure 5 The surface images of the PVDF-based membrane of the present invention taken with an InLens detector after swelling with COOH-MWCNTs, OH-MWCNTs and MWCNTs (a is electrocatalytic membrane A, b is electrocatalytic membrane J, and c is electrocatalytic membrane M); Figure 6 The cross-sectional view of the PVDF-based membrane of the present invention taken with a SE2 detector after swelling with COOH-MWCNTs, OH-MWCNTs and MWCNTs (a is electrocatalytic membrane A, b is electrocatalytic membrane J, and c is electrocatalytic membrane M); Figure 7 This is a comparison chart of the operating stability of the PVDF-based membrane of the present invention after being swollen and modified by COOH-MWCNTs; Figure 8 The linear sweep voltammetry curves and cyclic voltammetry curves of the modified membranes with different functional groups of the present invention are shown; Fig. 9 : EIS spectra of the modified membranes with different functional groups of the present invention; Fig.10 This is a comparison diagram of the removal effect of IBU under different pH conditions of the present invention; Fig.11 A comparison diagram of the removal effect of IBU under different voltage conditions of the present invention; Fig.12 This is a comparison diagram of the removal effect of IBU under high concentration conditions of the present invention; Fig.13 This is a comparison chart of the removal effect of IBU under low concentration conditions of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0027] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0028] Example:

[0029] A method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect comprises the following steps: S1. PVDF base film pretreatment First, clean the PVDF base membrane with anhydrous ethanol to remove dust and organic matter on the surface of the PVDF base membrane; then wash it with ultrapure water for 3 times to remove residual ethanol on the surface of the PVDF base membrane; finally, soak the PVDF base membrane in ultrapure water and store it in a low temperature environment, and ensure that the water is replaced every 24 hours.

[0030] S2, swelling and filling, performing the first modification treatment on the PVDF base film pretreated in step S1 First, add an appropriate amount of multi-walled carbon nanotubes (the amount of multi-walled carbon nanotubes (MWCNTs) added, the specifications and size information are shown in Table 1) into 40 ml of xylene to prepare a swelling dispersion; then ultrasonically treat the swelling dispersion for 30 minutes in a 60°C water bath, then put the pretreated PVDF base membrane into the swelling solution, and continue ultrasonicating for 60 minutes, for a total of 90 minutes; after the ultrasonication, cool to room temperature, rinse the swollen membrane surface with anhydrous ethanol to remove residual xylene, and finally wash with ultrapure water 3 times to remove ethanol to obtain a swollen membrane; store the swollen membrane in a sealed bag containing a small amount of pure water for later use.

[0031] S3, filtering and coating, performing a second modification treatment on the swollen membrane in step S2 50 mg of multi-walled carbon nanotubes with a diameter of 40-60 nm were placed in a 50% volume fraction ethanol solution and ultrasonically treated for 30 minutes to prepare a loading liquid; negative pressure filtration was performed at a constant pressure of 0.1 MPa to make the multi-walled carbon nanotubes evenly adhere to the surface of the swollen membrane to obtain a multi-walled carbon nanotube electrocatalytic membrane.

[0032] Table 1 Swelling modified dispersion ratio parameters of different swelling loaded membranes

[0033] Note: E0 is the original CNTs-PVDF membrane (only loaded but not swollen). The purity of carboxyl and hydroxyl groups in the carboxylated and hydroxylated carbon nanotubes during the modification process is > 95wt%.

[0034] Test example: 1 Experimental methods 1.1 Experimental equipment The electrochemical membrane reactor of the experimental device involved in this test example adopts an acrylic shell design, and the internal components include a perforated titanium mesh, an insulating silicone gasket, a titanium ring, a support gasket, and an electrocatalytic membrane made from a modified PVDF membrane, wherein the titanium sheet and the perforated titanium mesh (purity>99%) are 2mm thick. The electrochemical membrane filtration experimental conditions are all based on an initial pH value of 7 and a Na 2 SO 4 As background electrolyte, 25 mg / L initial IBU was used and 2 V voltage was applied for the experiment.

[0035] 1.2 Characterization of the morphology and structure of multi-walled carbon nanotube electrocatalytic films - scanning electron microscopy Sample preparation method: scrape the surface of different multi-walled carbon nanotube electrocatalytic membranes prepared in the examples, fix the fallen multi-walled carbon nanotube powder on the copper sample stage, and use SIGMA HD scanning electron microscope to analyze the morphological structure changes of the multi-walled carbon nanotube electrocatalytic membranes before and after modification.

[0036] A small amount of thin film sample was directly adhered to the conductive adhesive, and gold was sprayed for 45 seconds using a Quorum SC7620 sputtering coater at a current of 10 mA. A ZEISS Sigma 300 scanning electron microscope was then used to photograph the sample morphology, EDS spectrum, and other tests. The acceleration voltage was 3 kV when photographing the morphology.

[0037] 1.3 Characterization of electrochemical performance of multi-walled carbon nanotube electrocatalytic films 1.3.1 Linear voltammetric curve scanning The LSV curve scanning adopts a three-electrode working system of working electrode, reference electrode and counter electrode, with a platinum sheet (2cm×2cm) electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and a multi-walled carbon nanotube electrocatalytic film prepared in the example as the working electrode. The scanning voltage range of Shanghai Chenhua CHI760E electrochemical workstation is 0~2.5V, the scanning speed is 0.02V / s, and the test solution is 500mL of 0.5mol / L H 2 SO 4 .

[0038] 1.3.2 Cyclic voltammetry curve scanning The CV curve scanning adopts a three-electrode working system of working electrode, reference electrode and counter electrode, with a platinum sheet (2cm×2cm) electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and a multi-walled carbon nanotube electrocatalytic film prepared in the example as the working electrode. The scanning voltage range is 0~1.5V, the scanning rate is 2.0mV / s, and the test solution is 25mg / LIBU and 0.5mol / L Na 2 SO 4 Mix the solution.

[0039] 1.3.3 Electrochemical impedance spectroscopy The EIS curve analysis adopts a three-electrode working system of working electrode, reference electrode and counter electrode. The working electrode is the multi-walled carbon nanotube electrocatalytic film prepared in the example, the platinum sheet (2cm×2cm) electrode is the counter electrode, and the Ag / AgCl electrode is the reference electrode. The test environment is Na 2 SO 4 Solution, concentration is 0.5mol / L, test voltage is 5.0-10mV AC voltage, frequency range is 105 Hz~10 -2 Hz.

[0040] 1.4 Study on the performance of multi-walled carbon nanotube electrocatalytic membranes 1.4.1 Flux comparison The determination of membrane pure water flux uses nitrogen to pressurize pure water to the membrane assembly, and the transmembrane pressure is monitored by a pressure gauge. The electronic balance is connected to a notebook to record the water output volume in real time. After the transmembrane pressure reaches a stable state, the pure water flux is calculated by the formula.

[0041] 1.4.2 Comparison of IBU removal effects The experimental device consists of four parts: water inlet and outlet system, power system, electrocatalytic membrane assembly and power supply system. The water inlet and outlet system is composed of a customized acrylic water storage device as a feed tank and a beaker as a water outlet container; a nitrogen bottle, an adjustable air valve and supporting pipes provide power for the water sample to enter the membrane assembly; a DC power supply provides a stable voltage. The simulated IBU wastewater is injected into the liquid inlet tank in advance, and flows to the water inlet at the top of the reactor through nitrogen pressure, undergoes adsorption and electrochemical oxidation reactions inside the reactor, and flows into the water outlet container through the water outlet below the reactor. The experiment explores the effects of different influencing parameters on the removal effect by changing the solution pH value, the size of the applied voltage and the initial pollutant concentration.

[0042] 1.4.3 Comparison of IBU removal effects under different pH conditions When the initial pH value of the solution was 3.0, 5.0, 7.0, 9.0 and 11.0, 0.01 mol / L Na 2 SO 4 As background electrolyte, 25 mg / L initial IBU was used and 2 V voltage was applied for the experiment.

[0043] 1.4.4 Comparison of IBU removal effects under different voltage conditions When the applied voltage of the reaction is selected to be 0V, 1V, 2V and 3V, 0.01mol / L Na 2 SO 4 As background electrolyte, the experiment was conducted with an initial IBU of 25 mg / L and an initial pH of 7.

[0044] 1.4.5 Comparison of IBU removal effects under different concentration conditions When the initial IBU concentration of the solution is selected as high concentration 10mg / L, 25mg / L, 50mg / L and low concentration 0.5mg / L, 1mg / L, 2mg / L, 0.01mol / L Na 2 SO 4 As the background electrolyte, the initial pH value was 7 and the experiment was carried out with an applied voltage of 2V.

[0045] 2 Experimental results 2.1 Study on membrane surface characteristics Figure 1 This is the SEM image of the PVDF base film (EHT=2.00kV, WD=5.2mm, Mag=10.00KX, Signal A=InLens). Figure 2 a is the SEM image of electrocatalytic membrane A (EHT=3.00kV, WD=7.6mm, Mag= 21.00 KX, Signal A=InLens), Figure 2 b is the SEM image of electrocatalytic membrane B (EHT=3.00kV, WD=5.2mm,Mag=21.00KX,Signal A=InLens), Figure 2 Figure c is the SEM image of electrocatalytic membrane C (EHT=3.00kV, WD=5.2mm, Mag=21.00KX, Signal A=InLens). Figure 3 Figure d is the SEM image of electrocatalytic membrane D (EHT=3.00kV, WD=5.2mm, Mag=21.00KX, Signal A=InLens). Figure 3 Figure e is the SEM image of electrocatalytic membrane E (EHT=3.00kV, WD=5.2mm, Mag=21.00KX, Signal A=InLens). Figure 3 f is the SEM image of electrocatalytic membrane F (EHT=3.00kV, WD=5.2mm, Mag= 21.00KX, Signal A=InLens) Figure 4 g is the SEM image of electrocatalytic membrane G (EHT=3.00kV, WD=5.2mm,Mag=21.00KX,Signal A=InLens), Figure 4 h is the SEM image of the electrocatalytic membrane IH (EHT=3.00kV, WD=5.2mm, Mag=21.00KX, Signal A=InLens), Figure 4 i is the SEM image of electrocatalytic film I (EHT=3.00kV, WD=5.2mm, Mag=21.00KX, Signal A=InLens); where EHT represents the acceleration voltage, WD represents the working distance or the focal length of the objective lens, Mag represents the magnification, and Signal A=InLens represents the use of the InLens detector.

[0046] according to Figures 1 to 4The experimental results show that with the increase of MWCNTs dosage, the number of loads on the membrane surface and in the pores increases significantly, and the number of pores on the membrane surface gradually decreases. This is because MWCNTs have good dispersibility and high specific surface area, and are easy to fill and distribute in the membrane material, increasing the load of the pores inside the membrane. With the increase of dosage, MWCNTs not only enhance the mechanical properties of the membrane, but also affect the porosity and structure of the membrane. When the size of MWCNTs increases, the swelling effect increases the density of the membrane, resulting in the closure or filling of the pores of the membrane and a decrease in porosity. It can be seen that changes in the dosage of MWCNTs and the swelling of the membrane size will significantly affect the microstructure and pore distribution of the membrane.

[0047] Figure 5 a is the SEM image of electrocatalytic membrane A (EHT=3.00kV, WD=7.6mm, Mag=21.00KX, Signal A=InLens), Figure 5 b is the SEM image of electrocatalytic membrane J (EHT=3.00kV, WD=5.2mm, Mag=21.00KX,Signal A=InLens), Figure 5 Figure c is the SEM image of the electrocatalytic membrane M (EHT=3.00kV, WD=7.6mm, Mag=21.00KX, Signal A=InLens). Figure 6 Figure a is the SEM image of electrocatalytic membrane A (EHT=3.00kV, WD=7.4mm, Mag=1.00KX, Signal A=SE2). Figure 6 Figure b is the SEM image of electrocatalytic membrane J (EHT=3.00kV, WD=7.4mm, Mag=1.00KX, Signal A=SE2). Figure 6 c is the SEM image of the electrocatalytic membrane M (EHT=3.00kV, WD=7.3mm, Mag= 1.00KX, Signal A=SE2), where EHT is the accelerating voltage, WD is the working distance or the focal length of the objective lens, Mag is the magnification, Signal A=InLens means using the InLens detector, and Signal A=SE2 means using the SE2 detector.

[0048] according to Figure 5 and Figure 6From the electron microscopy morphology of the electrocatalytic membrane surface and cross-section, it can be found that there is not much difference in the diameter and length of COOH-MWCNTs, OH-MWCNTs and MWCNTs, which indicates that the strong acidification conditions have not changed the overall structure of MWCNTs. However, the carbon nanotubes adsorbed on the surface of the carboxyl-treated membrane are more evenly distributed, and the agglomeration phenomenon is greatly reduced, which is more conducive to improving the filtration efficiency. The main reason for this is that the COOH- group will produce negative ions in the solution, thereby increasing the polarity of the MWCNTs surface and significantly reducing its agglomeration tendency, making the carbon nanotubes in the swelling dispersion more dispersed and more evenly adsorbed on the surface of the PVDF-based membrane during the swelling process.

[0049] 2.2 Flux comparison According to the results in Table 2, the pure water flux of the multi-walled carbon nanotube electrocatalytic membrane obtained by swelling conventional carbon nanotubes is greatly reduced compared with the original membrane. The main reason for this phenomenon is that after a layer of MWCNTs is loaded on the membrane surface, the pore size of the original membrane is reduced, which reduces the pure water flux of the membrane. Since the pure water flux of the membrane is not only related to the pore size of the membrane, but also to the number of pores on the membrane surface. After the loading of MWCNTs, the number of pores on the surface of the PVDF-based membrane changes, resulting in a decrease in pure water flux. The number of pores on the surface of the swollen loaded membrane made by swelling and then loading will be further reduced, resulting in a further decrease in pure water flux. However, the multi-walled carbon nanotube electrocatalytic membrane obtained after swelling of carboxylated and hydroxylated carbon nanotubes not only did not show a significant decrease but increased. This is because the carbon nanotubes after carboxylation and hydroxylation are not easy to agglomerate and have good dispersion, and can maintain a large dispersion in the swelling liquid, thereby forming more mesh structures on the surface of the PVDF-based membrane.

[0050] 2.3 Pollutant removal effect It can be found from Table 2 that the removal effect of IBU for MWCNTs of the same size gradually decreases with the increase of the dosage. This is because with the increase of the dosage of MWCNTs, the dispersibility of MWCNTs in the PVDF membrane becomes worse, and it is easy to agglomerate, resulting in uneven pore structure of the membrane, reducing the effective filtration area, and thus reducing the efficiency of pollutant removal; on the other hand, high dosage of MWCNTs may block the pores of the membrane, reduce water flux, and affect the transmission and removal effect of pollutants. However, in terms of the overall effect, the removal effect of the swollen membrane is better than that of the original membrane loaded with MWCNTs only, and the removal effect of pollutants by carboxylation and hydroxylation is more significant. This is because carbon nanotubes have better dispersion properties after carboxylation and hydroxylation, and contain more oxygen-containing groups on the surface of carbon nanotubes. At the same time, more defects and active sites are created during the acidification process, and have a higher oxygen evolution potential, so they have better electrochemical oxidation performance. The above results all show that the multi-walled carbon nanotube membrane prepared by the swelling effect has a good removal effect on drug substances, and the effect of carboxylation and hydroxylation of carbon nanotubes is better.

[0051] Table 2 Pure water flux and pollutant removal effect of different swelling load membranes No. Electrocatalytic membrane name <![CDATA[Pure water flux L / (m 2 ·h)]]> IBU removal rate (%) E0 CNTs-PVDF 1466.0 50.3 S1 <![CDATA[S 1 @CNTs-PVDF]]> 1163.2 70.4 S2 <![CDATA[S 2 @CNTs-PVDF]]> 1002.7 67.2 S3 <![CDATA[S 3 @CNTs-PVDF]]> 864.4 63.2 M1 <![CDATA[M 1 @CNTs-PVDF]]> 753.3 70.4 M2 <![CDATA[M 2 @CNTs-PVDF]]> 656.3 66.9 M3 <![CDATA[M 3 @CNTs-PVDF]]> 671.3 55.9 L1 <![CDATA[L 1 @CNTs-PVDF]]> 722.9 64.8 L2 <![CDATA[L 2 @CNTs-PVDF]]> 637.0 62.1 L3 <![CDATA[L 3 @CNTs-PVDF]]> 596.3 55.9 COOH1 <![CDATA[COOH 1 @CNTs-PVDF]]> 1621.6 82.1 COOH2 <![CDATA[COOH 2 @CNTs-PVDF]]> 1481.9 78.8 COOH3 <![CDATA[COOH 3 @CNTs-PVDF]]> 1454.6 74.9 OH1 <![CDATA[OH 1 @CNTs-PVDF]]> 1501.7 77.7 OH2 <![CDATA[OH 2 @CNTs-PVDF]]> 1541.3 76.9 OH3 <![CDATA[OH 3 @CNTs-PVDF]]> 1623.6 74.0 2.4 Operation stability The present invention uses COOH@CNTs-PVDF as the electrode material in the electrochemical reaction device to explore its stability in the process of removing IBU. The specific data are as follows Figure 7 The experiment adopted a cyclic use method. After each reaction, the membrane was washed with ethanol and pure water for multiple times and used for the next cycle. The results showed that after four cycles, the removal efficiency of IBU within 60 minutes of treatment was 82.4%, 78.2%, 74.4% and 64.9%, respectively, showing a gradually decreasing trend.

[0052] This reduction in removal efficiency may be due to the following two aspects: first, the active sites involved in the electrochemical reaction gradually decrease during the cycle; second, the pollutants accumulated on the membrane surface gradually clog the membrane pores, reducing the material transfer efficiency. It is worth noting that the removal efficiency of the first three cycles decreased relatively slowly, while the IBU removal efficiency of the fourth cycle decreased by nearly 10% compared with the third cycle. This significant decrease may be related to the shedding of some of the loaded carbon nanotubes during the cleaning process after the third cycle, resulting in a large loss of active sites.

[0053] Although the IBU removal efficiency of COOH@CNTs-PVDF membrane decreases after recycling, its stability is still significantly better than that of traditional electrode materials and has certain research significance.

[0054] 2.5 Electrochemical properties Figure 8 The multi-walled carbon nanotube electrocatalytic film S is shown in 1 Linear sweep voltammetry (LSV) curves and cyclic voltammetry (CV) curves of @CNTs-PVDF, OH@CNTs-PVDF, COOH@CNTs-PVDF and CNTs-PVDF. 1 @CNTs-PVDF shows a lower current response, and the electrochemical activity of the material is low; while COOH@CNTs-PVDF has the highest current response, indicating that the material has the best electrochemical activity under this condition. In addition, the current response of COOH@CNTs-PVDF is wider, indicating that it has better electrochemical activity and greater charge transfer ability. As the potential increases, the current density also increases, indicating that the electrode has a significant current response during the potential change. COOH@CNTs-PVDF has the highest current density, indicating that its electrochemical reaction is the strongest. The current density of COOH@CNTs-PVDF rises the fastest, and the reaction rate is the highest. 1 The reaction rates of @CNTs-PVDF and OH@CNTs-PVDF are slower. This is because carboxylated carbon nanotubes are introduced during the modification of COOH@CNTs-PVDF, which makes it have higher catalytic activity or larger specific surface area, thus affecting the electrochemical performance. It also shows that COOH@CNTs-PVDF can obtain faster current response from the electrolyte solution at the same potential, reduce energy consumption and reduce the occurrence of oxygen evolution reaction.

[0055] Fig. 9 The results show that the charge transfer resistance of different materials, COOH@CNTs-PVDF, exhibits the smallest semicircular impedance, indicating that the material has the lowest charge transfer resistance. This is attributed to the introduction of carboxyl functional groups, which enhances the interfacial interaction between the material and the electrolyte, thereby promoting the electron transfer process, so that COOH@CNTs-PVDF exhibits excellent conductivity in electrochemical performance. In the electrocatalytic membrane filtration system, interception and electrochemical oxidation are the two main ways to remove IBU, and electrochemical oxidation usually plays a leading role.

[0056] 2.6 Removal effect of IBU by electrocatalytic membrane filtration system under different pH conditions The effect of the initial pH value of the IBU solution on the removal of IBU by the swelling supported membrane electrocatalytic membrane filtration system was investigated. Based on the actual water treatment application, five different initial solution pH values ​​were set, namely 3, 5, 7, 9, and 11, and the IBU electrochemical membrane filtration experiment was carried out. The details of the degradation rate are shown in Fig.10As shown. When the initial pH value of the solution was 3.0, 5.0, 7.0, 9.0 and 11.0, the degradation efficiency of IBU by COOH@CNTs-PVDF reached 83.3%, 79.1%, 80.1%, 71.8% and 70.5% in 60 min, respectively. The degradation efficiency basically showed a trend of gradually decreasing with the increase of pH value. At pH 3, the removal rate of IBU of different swelling load membranes reached more than 70%, which shows that strong acidic solution is conducive to the degradation of IBU. Under alkaline conditions, oxygen is precipitated, which hinders the formation of ∙OH; the increase of pH value leads to the decrease of the electrode potential of hydrogen evolution and oxygen evolution, and the side reaction is aggravated, which reduces the degradation effect. It is important to note that the pKa of IBU is 5.30. When the pH value is <5.30, IBU exists mainly as a cation in the solution; when the pH value is >5.30, IBU exists mainly as an anion in the solution. When the pH value is 3, the applied voltage forms a stable electric field in the solution, and IBU in the form of cations migrates toward the cathode under the action of the electric field force, increasing the directional migration efficiency and thus improving the degradation efficiency of IBU.

[0057] 2.7 Removal effect of IBU by electrocatalytic membrane filtration system under different voltage conditions Fig.11 It can be observed that the removal effect of IBU increases with the increase of voltage, which indicates that a stronger electric field has a higher degradation efficiency for IBU. The removal rates of IBU by COOH@CNTs-PVDF reached 78.28% and 80.15%, respectively. IBU was significantly degraded. With the increase of voltage, the number of electrons generated increased, the content of hydroxyl radicals increased, and the removal rate of pollutants increased. The experimental results show that the swelling load membrane has a certain interception effect on IBU. In the first 15 minutes, the interception effect achieved a good effect, and the removal rate was close to 50%. However, with the operation of the electrocatalytic membrane filtration system, the interception effect of the membrane decreased significantly and finally stabilized at about 35%. Under the condition of power (anode voltage of 2.0V), the removal effect of IBU by swelling load membrane oxidation was significantly higher than that of the single interception effect. In the electrocatalytic membrane filtration system, interception and electrochemical oxidation are the two main ways to remove IBU, and electrochemical oxidation usually plays a leading role. 2.8 Removal effect of IBU by electrocatalytic membrane filtration system under different concentration conditions (1) Removal effect of IBU under high concentration conditions The effect of IBU solution concentration on the removal of IBU by the swelling supported membrane electrocatalytic membrane filtration system was investigated. Three different solution concentration values ​​were set in the experiment, namely 10, 25, and 50 mg / L. Fig.12As shown. When the initial concentration of IBU increased from 10 mg / L to 50 mg / L, the removal rate of IBU by COOH@CNTsPVDF decreased from 83.14% to 64.42%. This is because high concentration of IBU will wrap the active sites on the surface of carbon nanotubes layer by layer, and unreacted IBU will have difficulty in contacting the active sites, resulting in a decrease in the degradation efficiency of the electrode for pollutants. In addition, under the condition of high concentration of IBU, as the electro-Fenton degradation reaction proceeds, a large amount of intermediates produced in the solution will compete with IBU for adsorption and active sites on the membrane surface, resulting in a decrease in the degradation efficiency of IBU. In the application of advanced oxidation technology to degrade wastewater, the initial pH value of the pollutant solution has an important influence on the generation of free radicals and the removal of pollutants.

[0058] (2) IBU removal effect under low concentration conditions In order to evaluate the feasibility of COOH@CNTs-PVDF modified membrane in practical applications, the present invention also investigated its electrochemical removal efficiency in IBU solutions with different initial concentrations (2 mg / L, 1 mg / L and 0.5 mg / L). Fig.13 The experimental results in the experiment show that after the electrochemical reaction device was operated for 60 minutes, the removal rates of IBU reached 94.4%, 96.1% and 98.5%, respectively. The removal rate of IBU exceeded 90% at all tested concentrations. This result shows that under low-concentration pollutant conditions, COOH@CNTs-PVDF modified membrane can efficiently remove IBU and show good application potential.

[0059] In summary, the present invention adopts a simple preparation method, and performs two modification treatments on the PVDF base film. The multi-walled carbon nanotube membrane prepared by the present invention has a high electrochemical removal efficiency for IBU solutions of different initial concentrations, among which the electrochemical removal efficiency for low-concentration IBU solutions exceeds 90%, and the electrochemical removal efficiency for high-concentration IBU solutions is greater than 70%. Compared with the original membrane, the optimal multi-walled carbon nanotube membrane can be significantly improved by 63.22%. The above results show that the COOH@CNTs-PVDF modified membrane can efficiently remove IBU under low-concentration pollutant conditions, showing good application potential; and compared with the original membrane, it has a significant effect on the removal of IBU in sewage, and the operating stability is also significantly better than the original membrane.

[0060] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the technical solution of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect, characterized in that: The steps include: S1, PVDF base membrane pretreatment; S2, swelling and filling, using multi-walled carbon nanotubes to prepare a swelling dispersion to perform a first modification treatment on the PVDF base film pretreated in step S1 to obtain a swelling film; S3, filtering and coating, using a multi-walled carbon nanotube-prepared loading liquid to perform a second modification treatment on the swollen membrane in step S2 to obtain a multi-walled carbon nanotube electrocatalytic membrane.

2. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 1, characterized in that: The method for pretreating the PVDF base film is to wash the PVDF base film with anhydrous ethanol and ultrapure water in sequence.

3. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 1, characterized in that: The method of the first modification treatment is to firstly subject the prepared swelling dispersion to water bath ultrasonic treatment, then put the PVDF base film pretreated in step S1 into the ultrasonically treated swelling dispersion, and continue the ultrasonic treatment to obtain a swelling film.

4. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 3, characterized in that: In step S2, the swelling dispersion is prepared by adding multi-walled carbon nanotubes into xylene.

5. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 4, characterized in that: The mass volume ratio of the multi-walled carbon nanotubes to xylene is 1-3 mg:1 ml.

6. A method for preparing a multi-walled carbon nanotube electrocatalytic film based on swelling effect according to any one of claims 3 to 5, characterized in that: The multi-walled carbon nanotubes are any one of conventional carbon nanotubes, carboxylated carbon nanotubes or hydroxylated carbon nanotubes.

7. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 6, characterized in that: The carbon nanotubes have a diameter of 10-60 nm and a length of less than 5 μm.

8. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 3, characterized in that: The temperature of the ultrasonic treatment is 60±5° C., the time of the water bath ultrasonic treatment of the prepared swelling dispersion is 30-45 minutes, the PVDF base film is put into the ultrasonically treated swelling dispersion, and the ultrasonic treatment is continued for 60-90 minutes.

9. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 1, characterized in that: In step S3, the surface of the swollen membrane is rinsed with anhydrous ethanol and ultrapure water in sequence before filtering and coating.

10. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 1, characterized in that: In step S3, the preparation method of the loading liquid is to place multi-walled carbon nanotubes with a diameter of 40-60 nm in an ethanol solution with a volume fraction of 45%-55%, and ultrasonically treat for 30-45 minutes. The mass ratio of the multi-walled carbon nanotubes in the loading liquid to the multi-walled carbon nanotubes in the swelling dispersion is 5:4-12.

11. The method for preparing a multi-walled carbon nanotube electrocatalytic film based on the swelling effect according to claim 1, characterized in that: In step S3, the second modification treatment method is to filter at a constant pressure of 0.09-0.11 MPa by negative pressure filtration to make the multi-walled carbon nanotubes evenly adhere to the surface of the swollen membrane to obtain a multi-walled carbon nanotube electrocatalytic membrane.

12. A multi-walled carbon nanotube electrocatalytic film prepared by the method according to any one of claims 7 to 11.

13. Use of the multi-walled carbon nanotube electrocatalytic membrane according to claim 12 in an electrocatalytic membrane filtration system to remove pharmaceutical organic compounds in water environment, characterized in that: The initial pH value of the water environment is 3-11, and the drug-like organic compound includes but is not limited to ibuprofen.

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