Carbon nanotube-graphene oxide composite film, preparation method and water treatment method thereof

Abstract

The application discloses a carbon nanotube-graphene oxide composite film, a preparation method and a water treatment method thereof, and belongs to the technical field of nanometer materials and water treatment. The preparation method is as follows: after acid treatment, a multi-walled carbon nanotube dispersion liquid is uniformly loaded on a base film, and then a mixed solution containing a polyamine crosslinking agent and a polyanion electrolyte is mixed with a graphene oxide dispersion liquid and then loaded on the carbon nanotube single-layer film. The carbon nanotube-graphene oxide composite film can be used for electrochemically strengthening removal of organic pollutants in water, and can also be used for synergistically removing organic pollutants in water with an oxidizing agent. The composite film preparation method is simple, can realize a'screening-enrichment-catalytic oxidation' synergistic effect in water treatment, and thus achieves the purpose of efficiently removing organic pollutants.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials and water treatment technology, specifically relating to a carbon nanotube-graphene oxide composite membrane, its preparation method, and its water treatment method. Background Technology

[0002] With rapid industrial development, the types of organic pollutants in industrial wastewater are becoming increasingly diverse, and their complexity and toxicity are constantly intensifying. For example, organic pollutants such as dyes, pharmaceutical intermediates, and perfluorinated compounds are difficult to treat, posing a serious challenge to traditional water treatment technologies. Traditional polymer membranes (such as polyvinylidene fluoride membranes) suffer from low permeation flux (less than 20 L / (m²)). 2 Due to issues such as poor anti-fouling performance (·h·bar), these membranes are unable to meet the stringent requirements for current industrial wastewater treatment. Besides traditional polymer membranes, single carbon nanotube (CNT) or graphene oxide (GO) membranes also have some performance bottlenecks:

[0003] Although CNT films have high conductivity (>10), 3 While possessing high tensile strength (tensile strength > 9.6 GPa), GO membranes exhibit uneven pore size distribution (ranging from 5 to 50 nm), resulting in poor retention of small molecule pollutants (such as methylene blue, molecular weight 319.85 Da). Furthermore, GO membranes, containing oxygen functional groups, exhibit hydrophilicity, leading to swelling and increasing interlayer spacing from 0.8 nm to 1.5 nm, causing structural instability and a decrease in retention rate. Traditional crosslinking modification methods can improve stability to some extent, but at the cost of reduced water flux (by more than 50%).

[0004] Current technologies using ultrasonic dispersion to physically mix carbon nanotubes and graphene oxide rely on van der Waals forces for bonding. However, this method is prone to delamination under high temperature and pressure conditions (tensile strength <1.8 GPa), and the catalytically active sites are difficult to expose efficiently. Therefore, there is an urgent need to develop a method for preparing carbon nanotube-graphene oxide composite films suitable for treating organic pollutants. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of low permeation flux, poor antifouling ability, and insufficient retention of small molecule pollutants in traditional membrane technology when removing organic pollutants from wastewater, and to provide a carbon nanotube-graphene oxide composite membrane, its preparation method, and its water treatment method.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a carbon nanotube-graphene oxide composite film, the specific steps of which are as follows:

[0008] S1: Disperse the acidified multi-walled carbon nanotubes in water to prepare a carbon nanotube dispersion; uniformly load the carbon nanotube dispersion onto a substrate membrane to obtain a carbon nanotube monolayer membrane.

[0009] S2: Using a first mixed solution containing a polyamine crosslinking agent and a polyanionic electrolyte, the graphene oxide dispersion is mixed with the first mixed solution to obtain a second mixed solution;

[0010] S3: The second mixed solution is uniformly loaded onto the carbon nanotube monolayer film prepared in step S1 to obtain a carbon nanotube-graphene oxide composite film.

[0011] Preferably, the acidification treatment of the multi-walled carbon nanotubes is as follows: the multi-walled carbon nanotubes are soaked in a mixed solution of sulfuric acid and nitric acid with a volume ratio of (3~4):1 for 0.5~2 hours, then washed with ultrapure water until neutral, and dried for later use;

[0012] The base membrane is made of one of the following organic membranes: polyvinylidene fluoride, polysulfone, polyethersulfone, polypropylene, polyacrylonitrile, polytetrafluoroethylene, or cellulose acetate; or it can be made of inorganic ceramic membrane or stainless steel metal membrane.

[0013] Preferably, the loading method in steps S1 and S3 is coating, suspension coating, vacuum filtration or electrophoretic deposition.

[0014] Preferably, the concentration of multi-walled carbon nanotubes in the carbon nanotube dispersion is 0.2~0.8 mg / mL; and the loading of carbon nanotubes on the carbon nanotube monolayer is 0.4~1.2 mg / cm³. 2 The graphene oxide concentration in the graphene oxide dispersion is 0.02~0.2 mg / mL.

[0015] Preferably, the polyamine crosslinking agent in the first mixed solution is ethylenediamine, polyethyleneimine, or triethylenetetramine, and the polyanionic electrolyte is polystyrene sulfonate, polyacrylic acid, polyethylene sulfonic acid, layered bimetallic hydroxide, or montmorillonite.

[0016] Furthermore, the polyamine crosslinking agent in the first mixed solution is ethylenediamine, and the polyanionic electrolyte is polystyrene sulfonate; the concentration of ethylenediamine in the first mixed solution is 0.1~0.3 g / L, and the mass percentage of polystyrene sulfonate is 0.1%~0.5%; the graphene oxide dispersion is mixed with the first mixed solution at a volume ratio of 1:2.

[0017] In a second aspect, the present invention provides a carbon nanotube-graphene oxide composite film obtained by the preparation method described in the first aspect.

[0018] Thirdly, the present invention provides a method for electrochemically enhanced removal of organic pollutants from water. In a three-electrode electrochemical reaction device containing wastewater to be treated, the carbon nanotube-graphene oxide composite membrane prepared in the first aspect is used as the working electrode, Ag / AgCl is used as the reference electrode, and a platinum sheet is used as the counter electrode. An alternating current or direct current mode is used to apply a voltage of 0.5~3 V to the working electrode, and the organic pollutants in the wastewater to be treated are removed through an electrochemical reaction; the organic pollutants are methylene blue or sulfamethoxazole.

[0019] Preferably, persulfate or permanganate is added to the electrochemical reaction device as an oxidant; the amount of oxidant added is 0.1~5 mM; an electrolyte with a concentration of 1~50 mM is added to the wastewater to be treated, and the pH value of the wastewater to be treated is controlled to be 3~10.

[0020] Fourthly, the present invention provides a method for synergistic removal of organic pollutants from water by an oxidant. The method involves adding an oxidant, persulfate or permanganate, to a reaction apparatus containing wastewater to be treated, and using a carbon nanotube-graphene oxide composite membrane prepared in the first aspect as a filter membrane. The wastewater to be treated flows through the carbon nanotube-graphene oxide composite membrane under external force, and the organic pollutants in the wastewater are removed by heterogeneous catalytic oxidation. The organic pollutants are methylene blue or sulfamethoxazole.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The carbon nanotube-graphene oxide composite film prepared by the present invention uses acid treatment of carbon nanotubes (CNTs) to increase the density of carboxyl groups on their surface, thereby enhancing the hydrogen bonding and conductivity with graphene oxide (GO); the interlayer spacing of GO is controlled by intercalation of ethylenediamine (EDA) and polystyrene sulfonate (PSS), while the introduction of sulfonic acid groups increases the surface negative charge density, strengthens the coexistence of electrostatic adsorption and catalytic sites, which is conducive to the adsorption and enrichment of pollutants and provides favorable conditions for subsequent catalytic oxidation reactions.

[0023] (2) The carbon nanotube-graphene oxide composite membrane prepared by the present invention provides mechanical strength and electron transport channels for the composite membrane. The GO&EDA-PSS layer serves as the active layer, which not only achieves charge regulation and targeted enrichment of pollutants, but also has the properties of polymer materials similar to glue, which increases the adhesion of materials on the membrane, effectively solves the problem of the fragility of the simple CNT membrane, and improves the overall stability of the composite membrane.

[0024] (3) The carbon nanotube-graphene oxide composite membrane prepared by this invention can remove organic pollutants such as dyes and antibiotics through the electric field of direct current or alternating current, and is suitable for wastewater treatment of complex systems such as dyeing and printing wastewater and pharmaceutical wastewater. With carbon nanotubes as the main body, it plays a leading role in pollutant removal (adsorption and catalytic oxidation), while GO&EDA-PSS is used as an auxiliary part to improve the performance of carbon nanotube membrane, so as to achieve the synergistic effect of "screening-enrichment-catalytic oxidation", thereby achieving the purpose of efficient water treatment. Attached Figure Description

[0025] Figure 1 The graph shows the results of the linear voltammetry method in Example 2;

[0026] Figure 2 The graphs show the methylene blue removal efficiency under different voltage and pH conditions in Example 3: (a) represents a voltage difference of -1 V; (b) represents a voltage difference of -0 V; (c) represents a voltage difference of -0.5 V; (d) represents a voltage difference of 1 V; and (e) represents a voltage difference of 2 V.

[0027] Figure 3 The graph shows the methylene blue removal efficiency in Comparative Example 1 and Example 4;

[0028] Figure 4 This is a graph showing the methylene blue removal efficiency in Example 5. Detailed Implementation

[0029] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0030] Example 1

[0031] This embodiment provides a method for preparing a carbon nanotube-graphene oxide composite film, as detailed below:

[0032] (1) Add 2 g of multi-walled carbon nanotubes to 120 mL of a mixed solution of sulfuric acid and nitric acid with a volume ratio of 3:1, and stir thoroughly at 60 °C for 1 hour for acidification. After acidification, dilute the resulting carbon nanotube solution and separate it by vacuum filtration. Wash with ultrapure water until the pH of the filtrate is close to neutral (6.5-7.5). Then dry under vacuum for 12 h and collect for later use.

[0033] (2) The acidified multi-walled carbon nanotubes were dispersed in ultrapure water by ultrasound to obtain a carbon nanotube dispersion of 0.5 mg / mL.

[0034] (3) 10 mL, 15 mL, 20 mL, 25 mL and 30 mL of carbon nanotube dispersions were vacuum filtered onto polyvinylidene fluoride (PVDF) membranes and vacuum dried at 60 °C to obtain different carbon nanotube monolayer membranes. The diameter of each monolayer membrane was about 4.1 cm.

[0035] (4) Graphene oxide (GO) was ultrasonically dispersed in ultrapure water to obtain a graphene oxide dispersion of 0.1 mg / mL; 0.2 g of anhydrous ethylenediamine (EDA) and 2 g of polystyrene sulfonate (PSS) were added to 1 L of ultrapure water and completely dissolved to prepare an EDA-PSS solution (0.2 g / L EDA, 0.2 wt% PSS).

[0036] (5) Mix 5 mL of graphene oxide dispersion and 10 mL of EDA-PSS solution, and sonicate for 5 minutes to obtain a mixed solution.

[0037] (6) The mixed solution was vacuum filtered onto different carbon nanotube monolayer membranes, then rinsed by vacuum filtration with ultrapure water, and then dried at 50°C for 2 hours to obtain carbon nanotube-graphene oxide composite membranes with different CNT loadings.

[0038] Example 2

[0039] This embodiment uses linear sweep voltammetry to verify the electrochemical performance characteristics of the carbon nanotube-graphene oxide composite film prepared in Example 1, as detailed below:

[0040] Using an electrochemical workstation, the carbon nanotube-graphene oxide composite film loaded with 10 mL of carbon nanotube dispersion in Example 1 was selected as the working electrode, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode.

[0041] Set the potential scan range to -3 V to +3 V, with a scan rate gradient of 10~200 mV / s (including 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, and 200 mV / s). Current range: Adjust to ±10 A based on preliminary experiments.

[0042] Record the oxidation / reduction peak current and background current baseline at each scan rate. Focus on the potential range of -2V to +2V (the region of significant current change in the graph). Results are as follows: Figure 1 As shown. According to Figure 1It is known that the hydrogen production potential of this composite membrane is approximately -1.352 V, and the oxygen production potential is approximately 1.077 V, indicating that its electrochemical window width is approximately 2.5 V. This data limits the operating voltage range of subsequent electrochemical treatment processes, preventing voltage from exceeding this range, which could lead to water decomposition and gas production, resulting in energy waste and disturbance to the reaction system.

[0043] Furthermore, the stable current response observed at different scan rates (10–200 mV / s) confirms the high conductivity of the carbon nanotube film (current density on the order of ±10 A). This provides theoretical support for the composite film as an electrode material to rapidly transport electrons and activate oxidants (such as generating active free radicals) during electrochemical oxidation.

[0044] The absence of obvious redox peaks in the voltammetric curves indicates that the composite membrane itself does not directly participate in the Faraday reaction. Its catalytic effect mainly relies on the oxidation of surface-adsorbed pollutants induced by the electric field or the activation of external oxidants (such as persulfate) through a conductive network. This provides experimental basis for the subsequent examples employing a strategy of DC or AC driving rather than chemical polarization treatment.

[0045] These experimental data clarified the functional boundaries of the composite membrane as an electrode material: within a range below the hydrolysis voltage, pollutant degradation is achieved through an indirect electron transfer mechanism, while avoiding the performance degradation problem caused by the loss of active sites in traditional electrocatalytic materials. This lays the foundation for designing low-energy-consumption and high-stability electrochemical treatment processes in subsequent embodiments.

[0046] Example 3

[0047] This embodiment uses the carbon nanotube-graphene oxide composite film prepared in Example 1 to conduct methylene blue (MB) removal experiments under different voltage and pH conditions, as detailed below:

[0048] (1) Using the three-electrode reaction system of the electrochemical workstation, a saturated Ag / AgCl electrode was used as the reference electrode, a platinum sheet as the counter electrode, and a platinum rod sandwiching a carbon nanotube-graphene oxide composite film loaded with 10 mL of carbon nanotube dispersion as described in Example 1 was used as the working electrode. The initial reaction solution had an MB concentration of 10 μM and a sodium sulfate concentration of 1 mM, and the reaction solutions were set with pH values ​​of 4, 6, 8, and 10.

[0049] (2) First, without power on, use a syringe to take 2 mL of the initial state and 2 mL of the state after 30 min of adsorption from 50 mL of the above reaction solutions with different pH values. Filter the solution with a 0.45 μm pore size filter to obtain water samples, and measure the absorbance of the water samples at 664 nm using a UV spectrophotometer.

[0050] (3) Different voltages (-1V, 0V, 0.5V, 1V, and 2V) were applied to the working electrode to remove MB from reaction solutions at different pH values. All removal experiments were conducted in 100 mL glass beakers, which were stirred at 100 rpm on a magnetic stirrer to ensure uniform reaction. Under each voltage setting, 2 mL of solution was taken from the reaction solution at fixed time intervals (0, 2, 5, 10, 20, 30, 40, and 60 min), filtered, and the absorbance was measured using a UV spectrophotometer. Each experiment was repeated at least three times, including the control group. The results are as follows: Figure 2 As shown, Figure 2 (a) ~ Figure 2 (e) represents the MB removal efficiency in reaction solutions at different pH values ​​under voltages of -1 V, 0 V, 0.5 V, 1 V, and 2 V, respectively. Removal efficiency is expressed as C. t The ratio of C to C0 measures C t The values ​​represent the MB concentration in water samples at different times, and C0 represents the MB concentration in the initial reaction solution. The horizontal axis in the figure represents the chemical reaction time, where negative values ​​indicate the physical adsorption process in the first 30 minutes before the electrochemical reaction occurs.

[0051] according to Figure 2 It can be seen that the removal of MB by the carbon nanotube-graphene oxide composite film exhibits voltage and pH dependence, and the specific rules and mechanisms are as follows:

[0052] (1) Regarding the impact on voltage:

[0053] When the voltage is 0 V, the removal efficiency relies solely on physical adsorption and electrostatic effects. The highest removal efficiency is achieved at a reaction solution pH of 4 (C after 60 minutes). t / C0=0.3), while the lowest C was found at pH=10 (C after 60 minutes). t / C0=0.8). This indicates that in an acidic environment, positively charged MB is favored for electrostatic binding with negatively charged carbon nanotube membranes. At low voltages of 0.5 V or 1 V, electric field-assisted adsorption plays a role, and voltage-driven electroosmotic flow (EOF) accelerates mass transfer: at pH=8 and a voltage of 1 V, C0 increased significantly after 60 minutes. t When the CO value decreased to 0.2, the efficiency increased by 60% compared to the same pH and 0 V. When the voltage increased to 2 V, catalytic oxidation became the dominant mechanism, with the high voltage activating the conductive network of carbon nanotubes to produce ·OH and SO4. - Free radicals.

[0054] (2) Regarding pH regulation:

[0055] Under acidic conditions (pH 4-6), electrostatic adsorption is enhanced. Due to the increased negative charge density of the carbon nanotube film, MB becomes positively charged after protonation, but excessively high H₂ levels... + Concentration leads to the quenching of ·OH radicals, limiting free radical pathways, and removal efficiency mainly depends on adsorption. In a neutral to slightly alkaline environment (pH=8), electrostatic adsorption and free radical oxidation work synergistically to reach equilibrium. Under conditions of pH=8 and a voltage of 2 V, C... t A CO concentration of 0.1 represents optimal operating conditions. However, under strongly alkaline conditions (pH=10), the negative charge density of the carbon nanotube film decreases (Zeta potential ≈ -10 mV), causing MB to deprotonate and become neutral molecules, weakening electrostatic adsorption. However, OH... — It can promote free radical chain reactions (SO4) - ·+OH — →SO4 2- (+·OH), but requires a high voltage of ≥2 V to activate.

[0056] (3) Comprehensive analysis of key data and mechanisms:

[0057] Under conditions of pH=4 and voltage 0 V, C t The C0 ratio is 0.3, and the dominant mechanism is electrostatic adsorption, but it is easily saturated due to the lack of oxidizing capacity. Under conditions of pH=8 and voltage 1 V, C... t With a C0 value of 0.2, electroosmotic mass transfer and weak oxidation work together, but free radical generation is insufficient. Under conditions of pH=10 and voltage 2 V, C t / C0 rebounded to 0.8, limited by oxidation side reactions (such as O3). - (Generation), free radical quenching, and accumulation of byproducts.

[0058] In summary, the optimal operating window is recommended to be pH=8 and voltage 2V, under which adsorption and oxidation are balanced. t A CO = 0.1 (removal rate 90%) strikes a balance between energy consumption and stability, while avoiding pH > 10 (sharp drop in efficiency) and pH < 4 (increased side reactions). Regarding process adaptability, for low-concentration MB (<10 mg / L), an energy-saving mode with pH = 8 and voltage 1 V can be used; while for high-concentration or recalcitrant MB, an enhanced oxidation mode with pH = 4 and voltage 4 V can be used.

[0059] Comparative Example 1

[0060] This comparative example uses a carbon nanotube monolayer film to perform a methylene blue (MB) removal experiment, as detailed below:

[0061] (1) Add 2 g of multi-walled carbon nanotubes to 120 mL of a mixed solution of sulfuric acid and nitric acid with a volume ratio of 3:1, and stir thoroughly at 60 °C for 1 hour for acidification. After acidification, dilute the resulting carbon nanotube solution and separate it by vacuum filtration. Wash with ultrapure water until the pH of the filtrate is close to neutral (6.5-7.5). Then dry under vacuum for 12 h and collect for later use.

[0062] (2) The acidified multi-walled carbon nanotubes were dispersed in ultrapure water by ultrasound to obtain a carbon nanotube dispersion of 0.5 mg / mL.

[0063] (3) 10 mL and 30 mL of carbon nanotube dispersions were vacuum filtered onto polyvinylidene fluoride (PVDF) membranes and vacuum dried at 60 °C to obtain two carbon nanotube monolayers with different CNT loadings. The diameter of the monolayers was about 4.1 cm.

[0064] (4) Using a three-electrode reaction system of an electrochemical workstation, a saturated Ag / AgCl electrode was used as the reference electrode, a platinum sheet as the counter electrode, and platinum rods with carbon nanotube monolayers with different CNT loadings were used as working electrodes. A voltage of 1.6V was applied to the working electrodes to remove MB from the reaction solution. The initial reaction solution had an MB concentration of 10 μM, a sodium sulfate concentration of 1 mM, and a pH of 8.

[0065] Example 4

[0066] This embodiment uses carbon nanotube-graphene oxide composite films with different CNT loadings prepared in Example 1 to conduct methylene blue (MB) removal experiments, as detailed below:

[0067] Using a three-electrode reaction system of an electrochemical workstation, a saturated Ag / AgCl electrode was used as the reference electrode, a platinum sheet as the counter electrode, and platinum rods sandwiching carbon nanotube-graphene oxide composite films with different CNT loadings prepared in Example 1 were used as working electrodes. A voltage of 1.6V was applied to the working electrodes to remove MB from the reaction solution. The initial reaction solution had an MB concentration of 10 μM, a sodium sulfate concentration of 1 mM, and a pH of 8.

[0068] The MB removal efficiency results in Comparative Example 1 and Example 4 are as follows: Figure 3 As shown. Removal efficiency is expressed in C. t The ratio of C to C0 measures C t C represents the MB concentration in water samples at different times, and C0 represents the MB concentration in the initial reaction solution.

[0069] The results showed that the carbon nanotube monolayer membrane was more efficient at removing methylene blue (MB) than the carbon nanotube-graphene oxide composite membrane, and the removal efficiency of composite membranes with different CNT loadings did not show a significant positive correlation. This indicates that the carbon nanotube layer plays a major role in the MB removal process. However, the carbon nanotube monolayer membrane suffers from fragility and poor stability. Adding graphene oxide, ethylenediamine, and polystyrene sulfonate effectively increased the adhesion of materials on the membrane. This is because graphene oxide, ethylenediamine, and polystyrene sulfonate are polymeric materials, acting like glue on the membrane, thus providing reinforcement. Furthermore, a simple carbon nanotube layer cannot avoid electrolyte interference during the electrochemical process. The asymmetric composite membrane formed by intercalating graphene oxide (GO) / carbon nanotubes (CNTs) with ethylenediamine-polystyrene sulfonate (EDA-PSS) achieved a balance between water flux and Na+ through electrokinetic effects. + Synergistic improvement in retention rate.

[0070] Overall, carbon nanotubes, as the main material of the membrane, play a primary role in pollutant removal (including adsorption and catalytic oxidation). Graphene oxide, ethylenediamine, and polystyrene sulfonate, as auxiliary components, are mainly used to improve the performance of the carbon nanotube membrane, facilitating salt removal and enhancing membrane robustness.

[0071] Example 5

[0072] This embodiment uses the carbon nanotube-graphene oxide composite membrane prepared in Example 1, loaded with 10 mL of carbon nanotube dispersion, to conduct methylene blue (MB) removal experiments under different current modes, as detailed below:

[0073] A three-electrode reaction system was used in an electrochemical workstation, with a saturated Ag / AgCl electrode as the reference electrode, a platinum sheet as the counter electrode, and a platinum rod sandwiching a carbon nanotube-graphene oxide composite film as the working electrode. The electrochemical workstation was operated in direct current (DC), 1Hz alternating current (AC), and 400Hz alternating current (AC) modes, respectively. A voltage of 1.6V was applied to the working electrode to remove MB from the reaction solution. The initial reaction solution contained 10 μM MB, 1 mM sodium sulfate, and a pH of 8.

[0074] The results are as follows Figure 4 As shown, in direct current (DC) mode, the MB removal rate was 70% (concentration decreased from 10 mg / L to 3 mg / L) after 60 minutes, exhibiting a rapid decline in kinetics, with the removal rate exceeding 50% within the first 30 minutes. The key mechanism lies in the continuous electric field-driven electrochemical oxidation process, primarily involving ·OH and SO42-. -Free radicals play a dominant role, and the absence of polarity switching on the electrode surface allows for continuous oxidation reactions. In AC 1 Hz mode, the MB removal rate was 50% after 60 minutes (concentration decreased from 10 mg / L to 5 mg / L), exhibiting a slow, linear decline in kinetics. This is primarily because the low-frequency polarity switching (60 times per minute) allows for intermittent oxidation reactions, while some free radical generation and mass transfer effects are superimposed, thus affecting MB removal efficiency. In AC 400 Hz mode, the MB concentration decreased from 10 mg / L to 9 mg / L, with a removal rate less than 10%. The key reason is that the high-frequency polarity switching (24,000 times per minute) causes the oxidation and reduction reactions to periodically cancel each other out, and the extremely short lifetime of free radicals prevents effective MB removal, resulting in poor removal performance.

[0075] In summary, the DC power mode has the highest removal efficiency, but its energy consumption is also relatively high (0.5 kWh / m). 3 In AC 1 Hz mode, energy consumption can be reduced by 40% (0.3 kWh / m). 3 This method is suitable for treating low-concentration MB wastewater (less than 5 mg / L). It can also be used in a DC / AC coupled manner. In the initial stage (0-30 minutes), DC mode is used for rapid MB removal, while in the later stage (30-60 minutes), a 1Hz AC mode is used to maintain stability. This achieves a total MB removal rate of >80% and reduces energy consumption by 30%.

[0076] Example 6

[0077] This embodiment uses the carbon nanotube-graphene oxide composite membrane prepared in Example 1, loaded with 10 mL of carbon nanotube dispersion, to remove trace organic pollutants from surface water, as detailed below:

[0078] The electrochemical workstation employed a three-electrode reaction system, using a saturated Ag / AgCl electrode as the reference electrode, a platinum sheet as the counter electrode, and platinum rods sandwiching carbon nanotube-graphene oxide composite films as working electrodes. The electrochemical workstation was operated in direct current (DC) mode. A 4V voltage was applied to the working electrodes to remove sulfamethoxazole from the reaction solution. Other electrochemical reaction settings were identical.

[0079] The reaction solution was a sulfamethoxazole (SMX) treatment solution prepared from natural water, with an initial SMX concentration of 5 mg / L. This natural water source was a lake in Zhejiang Province, containing various coexisting interfering substances. Its basic parameters were as follows: humic acid (HA) concentration of 2.13 mg / L, conductivity of 431 µS / cm, total nitrogen content of 10.1 mg / L, and Fe... 3+ Concentration 0.012 mg / L, Cl -Concentration 0.950 mg / L, total carbon content 31.73 mg / L.

[0080] Experiments showed that at 4 V, a 4 cm diameter membrane removed 0.0025 mg of sulfamethoxazole in 60 minutes, meaning the removal rate of sulfamethoxazole (SMX) per unit area of ​​the membrane was 0.033 mg / m². -2 ·min -1 This invention demonstrates that the carbon nanotube-graphene oxide composite membrane provided by this invention helps to solve the problems of poor antifouling properties and insufficient retention of small molecule pollutants in traditional membrane technologies when removing organic pollutants from wastewater.

[0081] It should be noted that, in addition to electrochemical enhancement for removing organic pollutants from water, the carbon nanotube-graphene oxide composite membrane prepared in this invention can also be used for synergistic treatment with oxidants or electrochemical-oxidant coupling to remove organic pollutants from water, as detailed below:

[0082] I. Oxidant Synergy (Heterogeneous Catalytic Oxidation Mechanism)

[0083] (1) Oxidizing agent activation and free radical chain reaction: Addition of persulfate (PS, S2O8) 2- ) or permanganate (MnO4) - Following this, the surface properties of the composite film drive heterogeneous activation. Among these, the carbon nanotube defect sites are: sp... 2 Hybridized carbon structures act as electron transfer mediators, promoting PS decomposition; or the carbonyl groups (C=O) in the oxygen-containing groups of graphene oxide act as Lewis acid sites for MnO4 adsorption. - This triggers a reduction reaction, producing SO4. - • (Oxidation potential 2.5~3.1V) and MnO2 nanoparticles further catalyze the oxidation of pollutants.

[0084] (2) Synergistic effect of external field energy. For example, light (ultraviolet / visible light) can excite the π-π* transition of graphene oxide, generating electron-hole pairs (e-hole pairs). - -h + This can be achieved by accelerating oxidant activation (e.g., increasing the quantum efficiency of PS photolysis by 2.3 times). Heating (30~60℃), through the Arrhenius effect, can increase the reaction rate constant k by 1.8 times when the temperature is raised to 40℃. Alternatively, ultrasound (20~40kHz) can generate localized high temperature and high pressure (~5000K, 1000atm) through cavitation, promoting catalyst surface renewal and mass transfer (increasing the pollutant diffusion coefficient by 65%).

[0085] II. Electrochemical-oxidant coupling enhancement mechanism

[0086] Directed activation of oxidants by electric field: PS or MnO4 near the anode in a DC electric field of 0.5~3V.- The oxidant is preferentially activated by electrons, while the pollutants in the cathode region accumulate to form a concentration gradient, thus achieving precise spatial matching between the oxidant and the pollutants.

[0087] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for electrochemically strengthening removal of organic pollutants in water using carbon nanotube-graphene oxide composite membrane, characterized in that, In a three-electrode electrochemical reaction device containing wastewater to be treated, a carbon nanotube-graphene oxide composite film is used as a working electrode, Ag / AgCl is used as a reference electrode, and a platinum plate is used as a counter electrode; an alternating current or direct current mode is adopted to apply a voltage of 0.5-3 V to the working electrode, and organic pollutants in the wastewater to be treated are removed through electrochemical reaction; the organic pollutants are methylene blue or sulfamethoxazole; The preparation method of the carbon nanotube-graphene oxide composite film is specifically as follows: S1: dispersing the acid-treated multi-walled carbon nanotubes in water to obtain a carbon nanotube dispersion liquid; and uniformly loading the carbon nanotube dispersion liquid onto a base film to obtain a carbon nanotube monolayer film; S2: mixing a graphene oxide dispersion liquid with a first mixed solution containing a polyamine crosslinking agent and a polyanion electrolyte to obtain a second mixed solution; S3: uniformly loading the second mixed solution onto the carbon nanotube monolayer film prepared in step S1 to obtain a carbon nanotube-graphene oxide composite film.

2. The method of electrochemically enhanced removal of organic contaminants from water according to claim 1, wherein, The acid treatment of the multi-walled carbon nanotubes is specifically as follows: soaking the multi-walled carbon nanotubes in a mixed solution of sulfuric acid and nitric acid with a volume ratio of (3-4):1 for 0.5-2 hours, then washing with ultrapure water until neutral, and drying for standby use; The base film is one of polyvinylidene fluoride, polysulfone, polyethersulfone, polypropylene, polyacrylonitrile, polytetrafluoroethylene or cellulose acetate organic film, or an inorganic ceramic membrane or a stainless steel metal membrane.

3. The method of electrochemically enhanced removal of organic contaminants from water according to claim 1, wherein, The loading method in steps S1 and S3 is coating, suspension coating, vacuum filtration or electrophoretic deposition.

4. The method of electrochemically enhanced removal of organic contaminants from water according to claim 1, wherein, The concentration of multi-walled carbon nanotubes in the carbon nanotube dispersion liquid is 0.2-0.8 mg / mL; the loading of carbon nanotubes on the carbon nanotube monolayer film is 0.4-1.2 mg / cm 2 ; the concentration of graphene oxide in the graphene oxide dispersion liquid is 0.02-0.2 mg / mL.

5. The method of electrochemically enhanced removal of organic contaminants from water according to claim 1, wherein, The polyamine crosslinking agent in the first mixed solution is ethylenediamine, polyethyleneimine or triethylenetetramine, and the polyanion electrolyte is polystyrene sulfonate, polyacrylic acid, polyvinylsulfonic acid, layered double hydroxide or montmorillonite.

6. The method of electrochemically enhanced removal of organic contaminants from water according to claim 5, wherein, The polyamine crosslinking agent in the first mixed solution is ethylenediamine, and the polyanion electrolyte is polystyrene sulfonate; the concentration of ethylenediamine in the first mixed solution is 0.1-0.3 g / L, and the mass percentage of polystyrene sulfonate is 0.1%-0.5%; the graphene oxide dispersion liquid is mixed with the first mixed solution at a volume ratio of 1:

2.

7. The method of electrochemically enhanced removal of organic contaminants from water according to claim 1, wherein, An oxysulfate or permanganate is added to the electrochemical reaction device as an oxidizing agent; the addition amount of the oxidizing agent is 0.1-5 mM; an electrolyte with a concentration of 1-50 mM is additionally added to the wastewater to be treated, and the pH value of the wastewater to be treated is controlled to be 3-10.

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