CdMoO4-coated MWCNT multifunctional catalyst as well as preparation method and application thereof

Abstract

The invention discloses a CdMoO4-coated MWCNT multifunctional catalyst as well as a preparation method and application thereof, and belongs to the technical field of environmental pollutant treatment. The preparation method comprises the following steps: adding cadmium salt into ethylene glycol, dissolving to obtain a mixed solution, adding multi-walled carbon nanotubes and polyethylene glycol, and uniformly stirring; and then adding an ethylene glycol solution of Na2MoO4. 2H2O, and finally carrying out solvothermal reaction to obtain the CdMoO4-coated MWCNT multifunctional catalyst. The CdMoO4-coated MWCNT multifunctional catalyst disclosed by the invention not only can be used for detecting the concentration of EE2, but also can be used for activating PMS to catalyze and remove the EE2, so that seamless connection from monitoring to treatment is realized, and an efficient scheme is provided for comprehensive prevention and control of EE2 pollution. In the application of EE2 detection, the sensor has high sensitivity, high stability and strong anti-interference performance. The catalyst has the performance of activating PMS to efficiently degrade the EE2 in the application of catalytic removal of the EE2, and has strong anti-interference performance.

Description

Technical Field

[0001] The invention relates to a CdMoO4@MWCNT multifunctional catalyst and a preparation method and application thereof, belonging to the technical field of environmental pollutant treatment. Background Art

[0002] 17α-ethynyl estradiol (EE2) is a typical environmental endocrine disruptor (EDCs) and is widely present in water environments. It has a strong estrogenic effect and is extremely harmful to wildlife and human health. At present, the commonly used methods for detecting EE2 include high performance liquid chromatography, high performance liquid chromatography-mass spectrometry, and fluorescence spectroscopy. Although these methods have low detection limits, high sensitivity, strong anti-interference ability, and are suitable for trace analysis, they have significant disadvantages such as expensive and complex instruments, cumbersome pre-treatment techniques, and the need for professional personnel to operate, which limits their widespread application in actual water sample detection.

[0003] Electrochemical sensing technology has attracted much attention in the field of analytical chemistry due to its advantages such as simple instrumentation, low cost, fast response, simple sample pretreatment and even in-situ analysis. It is widely used in many fields such as detection of concentrations of various analytes, clinical and disease detection, environmental detection and food analysis. Advanced oxidation processes (AOPs) can use highly reactive oxygen species (ROS) to convert toxic organic matter into non-toxic or low-toxic small molecule compounds, and even achieve mineralization, and can also inactivate pathogen cells. It has the advantages of low energy consumption, simple treatment process, low treatment cost, and the ability to treat a variety of organic pollutants. It is widely used to remove EDCs in water. However, traditional AOPs have defects such as short lifetime of hydroxyl radicals and narrow pH application range. In addition, there have been no reports of bifunctional catalysts that can be used for electrochemical detection of EE2 and advanced oxidation degradation of EE2. Summary of the invention

[0004] In order to overcome the problems in the background technology, the present invention provides a bifunctional catalyst CdMoO4@MWCNT and a preparation method thereof, which can simultaneously realize high-sensitivity electrochemical detection and efficient advanced oxidation degradation of EE2 in water environment, accurately and efficiently detect and remove EE2 in water environment, and effectively solve the threat of EE2 to the environment and health.

[0005] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0006] A method for preparing a CdMoO4@MWCNT multifunctional catalyst comprises the following steps:

[0007] (1) adding cadmium salt to ethylene glycol to dissolve to obtain a mixed solution, adding multi-walled carbon nanotubes and polyethylene glycol and stirring uniformly;

[0008] (2) Then, an ethylene glycol solution of Na2MoO4·2H2O was added, and finally a solvothermal reaction was carried out to obtain the CdMoO4@MWCNT multifunctional catalyst.

[0009] As a preferred embodiment of the present invention, the cadmium salt is Cd(NO3)2·4H2O.

[0010] As a preferred embodiment of the present invention, the molar ratio of the cadmium salt to Na2MoO4·2H2O is (1-3): (3-1). The mass ratio of the cadmium salt to the multi-walled carbon nanotube is (3.08475-1.02825): 0.1.

[0011] As a preferred embodiment of the present invention, the mass ratio of polyethylene glycol to multi-walled carbon nanotubes is (0.005-0.04):0.1.

[0012] As a preferred embodiment of the present invention, the temperature of the solvent thermal reaction is 155-185°C and the time is 4-16h.

[0013] The present invention also claims to protect the CdMoO4@MWCNT multifunctional catalyst prepared by the preparation method of the CdMoO4@MWCNT multifunctional catalyst.

[0014] The present invention also claims to protect the use of the CdMoO4@MWCNT multifunctional catalyst in electrochemical detection of EE2 and activation of PMS to catalyze the removal of EE2 in water.

[0015] The application of the CdMoO4@MWCNT multifunctional catalyst in electrochemical detection of EE2 specifically includes:

[0016] The CdMoO4@MWCNT multifunctional catalyst was coated on a glassy carbon electrode to form a CdMoO4@MWCNT / GCE electrode; then a three-electrode system was constructed with the CdMoO4@MWCNT / GCE electrode as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. The current response of EE2 was detected by differential pulse voltammetry in a phosphate buffer solution containing EE2, and then the EE2 concentration was obtained based on the relationship curve between the oxidation peak current of EE2 and the EE2 concentration.

[0017] As a preferred embodiment of the present invention, when I<2.0195, the relationship curve between the oxidation peak current I of EE2 and the EE2 concentration C is I=0.144C+1.301; when I≥2.0195, the relationship curve between the oxidation peak current I of EE2 and the EE2 concentration C is I=0.0699C+1.670.

[0018] The present invention also claims to protect the use of the CdMoO4@MWCNT multifunctional catalyst for EE2 detection and removal in activating PMS to catalyze the removal of EE2 in water.

[0019] Beneficial effects of the present invention: The CdMoO4@MWCNT catalyst for EE2 detection and removal prepared by the present invention through a hydrothermal method is multifunctional in one, which can not only detect the concentration of EE2, but also activate PMS to catalyze and remove EE2, realizing seamless connection from monitoring to governance, and providing an efficient solution for the comprehensive prevention and control of EE2 pollution. In the application of EE2 detection, the linear range can reach 0.10-25.00μM, the detection limit is as low as 66nM, the sensitivity is high, and its anti-interference ability is strong. Even in the presence of 3 times the concentration of interfering substances (such as hydroquinone, urea, humic acid, etc.), the DPV current response of EE2 is slightly affected, the error is less than 5%, and it has good reproducibility, repeatability and stability. In the actual detection of Dianchi Lake water samples, the recovery rate is in the range of 94.8-107.0%, which is accurate and reliable. In the application of EE2 catalytic removal, it has the performance of activating PMS to efficiently degrade EE2 and has strong anti-interference. The degradation rate of 12μM EE2 is as high as 94.7% within 30 minutes. It can quickly and effectively remove EE2 in the water environment and significantly reduce its harm to the environment and organisms. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of materials prepared in Example 1, Comparative Example 1 and MWCNT materials, and XPS spectrum of the material prepared in Example 1; (a) is the XRD pattern; (b) is the full spectrum, (c) is the XPS spectrum of Cd 3d, (d) is the XPS spectrum of Mo 3d, (e) is the XPS spectrum of O1s, and (f) is the XPS spectrum of C 1s.

[0021] Figure 2 SEM images, element distribution diagrams and N2 adsorption-desorption curve diagrams of the materials prepared in Example 1, Comparative Example 1 and MWCNT materials; (a) is the SEM image of MWCNT, (b) is the SEM image of the material prepared in Comparative Example 1, (c) is the SEM image of the material prepared in Example 1, (d) is the energy spectrum diagram of various elements in the material prepared in Example 1, (e) is the image diagram of various elements in the material prepared in Example 1, and (f) is the N2 adsorption-desorption curve of the material prepared in Example 1.

[0022] Figure 3 CV and EIS graphs of the materials prepared in Example 1 and Comparative Example 1, MWCNT materials and glassy carbon electrode in 5.0 mM K3[Fe(CN)6] and 0.100 M KCl electrolyte solutions, respectively; (a) is the CV graph, and (b) is the EIS graph.

[0023] Figure 4 CV and DPV graphs of the materials prepared in Example 1 and Comparative Example 1, MWCNT materials and glassy carbon electrode in 0.05M PBS (pH=7.00) containing 12 μM EE2, respectively; (a) is the CV graph, and (b) is the DPV graph.

[0024] Figure 5 DPV diagram and dot-line diagram of CdMoO4@MWCNT / GCE prepared in Example 1 in PBS buffer solution containing 12 μM EE2; (a) DPV diagram of CdMoO4@MWCNT / GCE prepared in Example 1 with different concentrations in PBS buffer solution containing 12 μM EE2, (b) dot-line diagram of DPV of CdMoO4@MWCNT / GCE prepared in Example 1 with different concentrations in PBS buffer solution containing 12 μM EE2; (c) DPV diagram of CdMoO4@MWCNT / GCE prepared in Example 1 in PBS buffer solution with different pH values ​​containing 12 μM EE2, (d) oxidation potential-pH relationship diagram of CdMoO4@MWCNT / GCE prepared in Example 1 in PBS buffer solution with different pH values ​​containing 12 μM EE2.

[0025] Figure 6 (a) DPV electrochemical response of CdMoO4@MWCNT / GCE to different concentrations of EE2 (0.10-25μM) in 0.05M PBS (pH 7.14); (b) peak current response-EE2 concentration relationship diagram; (c) interference of common organic and inorganic substances on EE2 current response; (d) reproducibility analysis diagram; (e) repeatability analysis diagram; (f) storage stability analysis diagram.

[0026] Figure 7 (a) is the effect of the dosage of CdMoO4@MWCNT on the removal effect of EE2 (50mL, 12μM); (b) is the effect of the initial PMS concentration on the degradation effect; (c) is the effect of common organic and inorganic matter in the environment on the degradation effect; (d) is the effect of different reaction water qualities on the degradation effect. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0028] All chemical reagents not specified in the examples and comparative examples of the present invention were commercially available analytically pure for experiments.

[0029] Example 1

[0030] A method for preparing a CdMoO4@MWCNT multifunctional catalyst comprises the following steps:

[0031] (1) Accurately weigh 3.3 mmol (1.02825 g) of cadmium nitrate tetrahydrate, add it to the ethylene glycol solution, place it on a magnetic stirrer, and stir it at an appropriate speed for 10 minutes until the solid is completely dissolved and the solution is uniform and transparent, thereby providing a uniform cadmium source for subsequent reactions.

[0032] (2) Add 0.1000 g of multi-walled carbon nanotubes to the above solution and continue stirring for 10 minutes to ensure that the MWCNTs are evenly dispersed in the solution without agglomeration. Then add 0.0100 g of polyethylene glycol and stir again for 10 minutes. Polyethylene glycol can improve the dispersibility and stability of the system, which is conducive to the smooth progress of the subsequent composite reaction.

[0033] (3) Accurately weigh 6.6 mmol (1.6130 g) of sodium molybdate dihydrate, place it in another container, add 30 mL of ethylene glycol, and use an ultrasonic cleaner to ultrasonically treat to accelerate dissolution to form a uniform solution. Slowly add the solution to the cadmium and MWCNT solution obtained in step (2), and continue stirring for 1 hour during the addition process to ensure that the components are fully mixed and reacted to form a uniform precursor solution.

[0034] (4) The precursor solution was transferred into a 100 mL polytetrafluoroethylene reactor, the reaction temperature was set to 175°C, the reaction time was 12 hours, and the composite of CdMoO4 and MWCNT was achieved. After the reaction was completed and cooled to room temperature, the contents of the reactor were taken out and first washed by centrifugation with ultrapure water for 3 times (each time setting a suitable centrifugal speed and time, such as 8000 rpm centrifugation for 10 minutes) to remove unreacted impurities and soluble ions; then washed by centrifugation with ethanol for 2 times (centrifugation conditions were the same as ultrapure water washing) to facilitate material drying and dispersion. Finally, the washed material was placed in a 60°C oven to dry overnight, and the CdMoO4@MWCNT composite catalyst was collected.

[0035] Example 2

[0036] A method for preparing a CdMoO4@MWCNT multifunctional catalyst comprises the following steps:

[0037] (1) Accurately weigh 3.3 mmol (1.02825) of cadmium nitrate tetrahydrate, add it to the ethylene glycol solution, place it on a magnetic stirrer, and stir it at an appropriate speed for 10 minutes until the solid is completely dissolved and the solution is uniform and transparent, thereby providing a uniform cadmium source for subsequent reactions.

[0038] (2) Add 0.1000 g of multi-walled carbon nanotubes to the above solution and continue stirring for 10 minutes to ensure that the MWCNTs are evenly dispersed in the solution without agglomeration. Then add 0.0400 g of polyethylene glycol and stir again for 10 minutes. Polyethylene glycol can improve the dispersibility and stability of the system, which is conducive to the smooth progress of the subsequent composite reaction.

[0039] (3) Accurately weigh 9.9 mmol (2.4195 g) of sodium molybdate dihydrate, place it in another container, add 30 mL of ethylene glycol, and use an ultrasonic cleaner to ultrasonically treat to accelerate dissolution to form a uniform solution. Slowly add the solution to the cadmium and MWCNT solution obtained in step (2), and continue stirring for 1 hour during the addition process to ensure that the components are fully mixed and reacted to form a uniform precursor solution.

[0040] (4) The precursor solution was transferred into a 100 mL polytetrafluoroethylene reactor, and the reaction temperature was set to 155°C and the reaction time was 16 hours to achieve the composite of CdMoO4 and MWCNT. After the reaction was completed and cooled to room temperature, the contents of the reactor were taken out and first washed by centrifugation with ultrapure water for 3 times (each time setting a suitable centrifugal speed and time, such as 8000 rpm centrifugation for 10 minutes) to remove unreacted impurities and soluble ions; then washed by centrifugation with ethanol for 2 times (centrifugation conditions were the same as ultrapure water washing) to facilitate material drying and dispersion. Finally, the washed material was placed in a 60°C oven to dry overnight, and the CdMoO4@MWCNT composite catalyst was collected.

[0041] Example 3

[0042] A method for preparing a CdMoO4@MWCNT multifunctional catalyst comprises the following steps:

[0043] (1) Accurately weigh 3.3 mmol (1.02825 g) of cadmium nitrate tetrahydrate, add it to the ethylene glycol solution, place it on a magnetic stirrer, and stir it at an appropriate speed for 10 minutes until the solid is completely dissolved and the solution is uniform and transparent, thereby providing a uniform cadmium source for subsequent reactions.

[0044] (2) Add 0.1000 g of multi-walled carbon nanotubes to the above solution and continue stirring for 10 minutes to ensure that the MWCNTs are evenly dispersed in the solution without agglomeration. Then add 0.00500 g of polyethylene glycol and stir again for 10 minutes. Polyethylene glycol can improve the dispersibility and stability of the system, which is conducive to the smooth progress of the subsequent composite reaction.

[0045] (3) Accurately weigh 1.1 mmol (0.2688 g) of sodium molybdate dihydrate, place it in another container, add 30 mL of ethylene glycol, and use an ultrasonic cleaner to ultrasonically treat to accelerate dissolution to form a uniform solution. Slowly add the solution to the cadmium and MWCNT solution obtained in step (2), and continue stirring for 1 hour during the addition process to ensure that the components are fully mixed and reacted to form a uniform precursor solution.

[0046] (4) The precursor solution was transferred into a 100 mL polytetrafluoroethylene reactor, the reaction temperature was set to 185°C, the reaction time was 4 hours, and the composite of CdMoO4 and MWCNT was achieved. After the reaction was completed and cooled to room temperature, the contents of the reactor were taken out and first washed by centrifugation with ultrapure water for 3 times (each time setting a suitable centrifugal speed and time, such as 8000 rpm centrifugation for 10 minutes) to remove unreacted impurities and soluble ions; then washed by centrifugation with ethanol for 2 times (centrifugation conditions were the same as ultrapure water washing) to facilitate material drying and dispersion. Finally, the washed material was placed in a 60°C oven to dry overnight, and the CdMoO4@MWCNT composite catalyst was collected.

[0047] Comparative Example 1

[0048] A method for preparing a CdMoO4 catalyst comprises the following steps:

[0049] (1) Accurately weigh 3.3 mmol (1.02825) of cadmium nitrate tetrahydrate, add it to the ethylene glycol solution, place it on a magnetic stirrer, and stir it at an appropriate speed for 10 minutes until the solid is completely dissolved and the solution is uniform and transparent, thereby providing a uniform cadmium source for subsequent reactions.

[0050] (2) Add 0.0100 g of polyethylene glycol to the above solution and stir again for 10 minutes.

[0051] (3) Accurately weigh 6.6 mmol (1.6130 g) of sodium molybdate dihydrate, place it in another container, add 30 mL of ethylene glycol, and use an ultrasonic cleaner to ultrasonically treat to accelerate dissolution to form a uniform solution. Slowly add the solution dropwise to the cadmium-containing solution obtained in step (2), and continue stirring for 1 hour during the addition process to ensure that all components are fully mixed and reacted to form a uniform precursor solution.

[0052] (4) Transfer the precursor solution into a 100 mL polytetrafluoroethylene reactor, set the reaction temperature to 175°C, and the reaction time to 12 hours. After the reaction is completed and cooled to room temperature, take out the contents of the reactor, first centrifuge and wash with ultrapure water for 3 times (set appropriate centrifugal speed and time each time, such as 8000 rpm for 10 minutes) to remove unreacted impurities and soluble ions; then centrifuge and wash with ethanol for 2 times (centrifugal conditions are the same as ultrapure water washing) to facilitate material drying and dispersion. Finally, place the washed material in a 60°C oven to dry overnight, and collect the CdMoO4 catalyst.

[0053] according to Figure 1 It can be seen that the CdMoO4@MWCNT composite catalyst was successfully prepared in this example. Figure 1 (b) The CdMoO4@MWCNT composite catalyst prepared in this example mainly contains four elements: Cd, Mo, O and C. Figure 1 In (c), the peaks with binding energies of 421.0 eV and 405.2 eV are attributed to Cd 3d3 / 2 and Cd 3d5 / 2, respectively, which indicates that Cd exists as Cd(II). Figure 1 In (d), the peaks at 235.5 eV and 232.4 eV can be assigned to Mo 3d3 / 2 and Mo 3d5 / 2, respectively, which indicates that Mo exists as Mo(VI) in the composite. Figure 1 In (e), the two O1s peaks with different binding energies obtained at 531.6 eV and 532.1 eV correspond to the metal-oxygen atom bond and the OH bond. Figure 1 In the C1s spectrum of (f), the two peaks at 285.2eV and 286.7eV are attributed to C—C (sp2 hybridization) and C=O (carbonyl functional group), respectively. The XPS characterization results show that the nanocomposite material was successfully prepared and that the material contains oxygen-containing functional groups, which helps to improve the hydrophilicity of the material and improve the adsorption capacity of the material to a certain extent.

[0054] From Figure 2(a), it can be seen that the MWCNT without any modification treatment is in the form of long fibers with smooth surface and a fiber diameter of about 50-80 nm. Figure 2 (b) shows that the CdMoO4 material is a uniform spherical morphology with a diameter of about 10-20nm. The size is relatively uniform, but the agglomeration phenomenon is serious. After CdMoO4 is compounded on the surface of MWCNT by a one-step solvothermal method, Figure 2 As shown in (c), the agglomeration of CdMoO4 nanospheres is reduced and they are dispersed more evenly on the surface of MWCNT. EDS (2(de)) analysis of CdMoO4@MWCNT shows that the four elements Cd, Mo, C and O exist on the catalyst surface and are evenly distributed, which is consistent with the XPS analysis results.

[0055] from Figure 2 (f) It is found that MWCNT, CdMoO4 and CdMoO4@MWCNT all show typical type IV hysteresis curves at high pressure, indicating that all three materials contain mesoporous structures. The specific surface areas of MWCNT, CdMoO4 and CdMoO4@MWCNT are 40.6073 m 2 / g,41.8139m 2 / g and 97.5067m 2 / g, it can be seen that after the CdMoO4 and MWCNT are combined, the specific surface area is greatly increased, and the larger specific surface area is conducive to the adsorption of EE2 on the surface of the material. Combined with SEM morphology analysis, it can be seen that after CdMoO4 is evenly dispersed on the surface of MWCNT, it can not only increase the specific surface area of ​​the material and thus enhance its adsorption capacity, but also improve its conductivity, so it has the potential for electrochemical detection of EE2.

[0056] Effect Example 1

[0057] 1. Application of CdMoO4@MWCNT multifunctional catalyst in electrochemical detection of EE2, including:

[0058] (1) Preparation of working electrode: Accurately weigh 10 mg of CdMoO4@MWCNT multifunctional catalyst or CdMoO4 catalyst or MWCNT material prepared in Comparative Example 1, place in a centrifuge tube, add 750 μL of water and 250 μL of ethanol mixed solvent, then add 20 μL of Nafion, place the centrifuge tube in an ultrasonic cleaner for ultrasonic treatment for 20 minutes, so that the material is evenly dispersed into a stable suspension. Use a pipette to accurately pipette 5 μL of the dispersion, slowly drop it on the surface of the glassy carbon electrode (GCE), ensure that the droplets evenly cover the electrode, avoid uneven thickness or bubble defects, and then naturally air-dry at room temperature to prepare CdMoO4@MWCNT / GCE or CdMoO4 / GCE or MWCNT / GCE working electrodes, respectively.

[0059] (2) Differential pulse voltammetry (DPV) was used to detect the current response of EE2 in 0.05 M phosphate buffer solution (PBS) with a pH of 7.14: the working electrode was first immersed in a PBS solution containing different concentrations of EE2 (0.1-25.00 μM) for 240 seconds to allow EE2 to fully accumulate on the electrode surface and improve the detection sensitivity. Subsequently, a DPV test was performed with appropriate pulse amplitude (e.g., 50 mV), pulse width (e.g., 50 ms), and scan rate (e.g., 20 mV / s) set to record the oxidation peak current values ​​corresponding to different concentrations of EE2.

[0060] like Figure 6As shown in (a), within the EE2 concentration range of 0.1-25.00 μM, a very obvious oxidation peak can be observed, and as the EE2 concentration increases, the peak becomes sharper and the oxidation peak current gradually increases. Figure 6 As shown in (b), the oxidation peak current I is linearly correlated with the EE2 concentration C, and the linear regression equation is: I = 0.144C + 1.301 in the range of 0.10-5.00 μM, R 2 =0.964; in the range of 5.00-25.00 μM, I = 0.0699C + 1.670, R 2 =0.993, and the detection limit LOD is (3σ / S)33nM. The results show that CdMoO4@MWCNT / GCE has good electrocatalytic activity, a wide linear range and high sensitivity.

[0061] The oxidation peak current I of the materials prepared in Examples 2 and 3 is linearly correlated with the EE2 concentration C, which is the same as that in Example 1. They also have good electrocatalytic activity, a wide linear range and high sensitivity.

[0062] The CdMoO4 / GCE and MWCNT / GCE working electrodes prepared in Comparative Example 1 only have a weak response to EE2, and there is no linear relationship between the oxidation peak current I and the EE2 concentration C.

[0063] (3) The EE2 concentration in a liquid with unknown EE2 concentration can be estimated based on the relationship between the oxidation peak current and the EE2 concentration.

[0064] 2. After constructing the three-electrode system, place the modified electrode in 5.0 mmol L -1 K3[Fe(CN)6](containing 0.1 mol L - 1 KCl) solution, perform electrochemical impedance spectroscopy (EIS) test on electrochemical workstation, set appropriate frequency range (e.g. 100kHz-0.1Hz) and AC amplitude (e.g. 5mV), obtain electrode electron transfer resistance (Rct) data, evaluate electrode interface electron transfer capacity and adsorption performance; perform cyclic voltammetry (CV) test at the same time, scan at appropriate scan rate (e.g. 100mV / s) within the set potential window (e.g. -0.2V-0.8V), observe redox peak morphology and current response, and comprehensively analyze electrode electrochemical activity and stability. Figure 3 .

[0065] Figure 3 (a) shows a pair of typical [Fe(CN)6] 3 / 4-Redox peak, compared with bare GCE, the CV peak current of MWCNT / GCE is significantly increased, which indicates that MWCNT has excellent conductivity, but the CV peak current response of CdMoO4 / GCE is significantly reduced, which shows that the conductivity of CdMoO4 alone is poor, and its conductivity can be improved after being compounded with MWCNT. Figure 3 (b) shows the Nyquist plots of bare GCE, MWCNT / GCE, CdMoO4 / GCE and CdMoO4@MWCNT / GCE in 5.0 mM K3[Fe(CN)6] and 0.100 M KCl electrolyte solutions. The Rct value of bare GCE is about 77.81 Ω, showing a high interfacial electron transfer resistance. After surface modification of GCE, the Rct values ​​of MWCNT / GCE, CdMoO4 / GCE and CdMoO4@MWCNT / GCE are 77.31 Ω, 70.16 Ω and 65.01 Ω, respectively, indicating that MWCNT, CdMoO4 and CdMoO4@MWCNT / GCE have excellent conductivity and are conducive to electron transfer.

[0066] The electrochemical reactivity of EE2 on different electrodes was investigated by CV and DPV techniques. The electrochemical process of 12 μM EE2 on GCE and the prepared modified electrode was tested in 0.05 M PBS (pH = 7.14) solution. Figure 4 . As can be seen from the figure, bare GCE, CdMoO4 / GCE and MWCNT / GCE all have small oxidation peaks at around 0.614V, the CdMoO4 / GCE peak current is about 0.400μA, and the MWCNT / GCE oxidation peak current response is about 3.164μA, but the oxidation peak of EE2 is not obvious. The CdMoO4@MWCNT / GCE prepared in Example 1 shows an obvious EE2 oxidation peak in the potential range of 0.45-0.60V, and its peak current response is about 3.496μA, and DPV presents the same results as CV. The above electrochemical test results show that CdMoO4@MWCNT can significantly improve the conductivity of the electrode, and CdMoO4 can adsorb EE2 in the solution.

[0067] 3. A series of working electrodes with different concentrations of catalyst dispersions (such as 6, 8, 10, 12 and 14 mg / mL) were prepared, and the DPV response of 12 μM EE2 solution was detected in PBS (pH=7.14) buffer solution. Figure 5 The results of (a) and 5(b) show that when the concentration of the catalyst dispersion liquid increases from 6 mg / mL to 10 mg / mL, the oxidation peak current increases; after exceeding 10 mg / mL, it decreases. Therefore, 10 mg / mL is the optimal concentration of the modified liquid. At this concentration, the amount of catalyst on the electrode surface is moderate, the adsorption and electrocatalytic performance are best coordinated, the electron transfer is smooth, and the current response is the strongest.

[0068] 4. The CdMoO4@MWCNT / GCE working electrode prepared in Example 1 was used to detect the DPV response of 12 μM EE2 solution in PBS buffer solutions of different pH values.

[0069] Figure 5 (c) and 5(d) studied the effect of buffer solution pH, and prepared PBS buffer solutions with pH 4.01, 4.92, 5.95, 7.14 and 8.25 for detecting 12μM EE2. As the pH increased from 4.01 to 7.14, the oxidation peak became more obvious; after the pH exceeded 7.14, the current value decreased, and the optimal value was at pH = 7.14. From the fitting equation of the pH-oxidation peak potential diagram of EE2, Epa (V) = -0.0590pH + 0.960 (linear correlation coefficient is 0.997), it can be seen that the electrocatalytic oxidation of EE2 involves a proton-coupled double electron transfer process.

[0070] 5. Analysis on the anti-interference, reproducibility, repeatability and stability of the CdMoO4@MWCNT / GCE electrode constructed with the CdMoO4@MWCNT prepared in Example 1 in the application of detecting EE2.

[0071] In order to study the anti-interference ability of CdMoO4@MWCNT / GCE in detecting EE2, 36 μM hydroquinone, urea, humic acid, glucose, CaCl2, MgCl2, NaCl, and KBr were added to the PBS (pH = 7.14) solution containing 12 μM EE2 to detect the DPV response of 12 μM EE2 solution.

[0072] like Figure 6 As shown in (c), when there is a 3-fold concentration of interference, the DPV current response of EE2 is not significantly affected, and the error caused by the interference factor on the detection signal is less than 5%. Therefore, it is proved that CdMoO4@MWCNT / GCE has a high anti-interference ability for the electrochemical detection of EE2.

[0073] In the repeatability experiment, the CdMoO4@MWCNT / GCE electrode prepared in Example 1 in step S1 was tested 5 times in a 12 μM EE2 PBS (pH=6.00) solution to analyze the repeatability of the method.

[0074] like Figure 6 (d) It can be seen that the same electrode can still maintain 95.58% of the initial current after 5 consecutive measurements.

[0075] In the reproducibility experiment, five CdMoO4@MWCNT / GCE electrodes prepared in Example 1 in step S1 were prepared and DPV tests were performed in 12 μM EE2 PBS (pH=6.00) electrolyte to analyze the reproducibility of the method.

[0076] like Figure 6 (e) It can be seen that the same electrode can still maintain 95.58% of the initial current after 5 consecutive measurements.

[0077] 6. In order to investigate the storage stability of the CdMoO4@MWCNT / GCG detection method, it was stored in a 4 °C refrigerator and used for DPV detection of 12 μM EE2 in PBS buffer solution after intervals of 1, 2, 3, and 4 weeks.

[0078] The experimental results are as follows Figure 6 As shown in (f), the response current only decreased by 3.95% after 4 weeks of storage. This shows that thanks to the excellent chemical stability of CdMoO4@MWCNT, the detection has excellent storage stability.

[0079] 7. The prepared CdMoO4@MWCNT / GCE was used to detect the EE2 content in the water samples of Dianchi Lake to evaluate the practicality of the detection method. The water samples of Dianchi Lake were prepared into 0.05M PBS (pH=7.14) buffer solution. Since the EE2 content in the water samples was too low, different concentrations of EE2 were added using the standard addition method. The samples were analyzed using DPV technology, and the detection concentration and recovery rate were calculated. The results are shown in Table 1. The recovery rate of the prepared sensor is between 94.8-107.0%.

[0080] Table 1 Recovery results of EE2 in Dianchi Lake water samples

[0081]

[0082] Effect Example 2

[0083] The application of the CdMoO4@MWCNT multifunctional catalyst in activating PMS to catalyze and remove EE2 in water specifically includes:

[0084] (1) Accurate preparation of solution: Accurately weigh 0.0741g of EE2 white powder, transfer to a 25mL volumetric flask with methanol, add methanol to the scale line to make up the volume, and ultrasonicate for 15 minutes (ultrasonic power and frequency are appropriate) to ensure complete dissolution, to prepare EE2 (0.0100M) stock solution, and store in a 5℃ refrigerator to slow down the degradation or deterioration of EE2. Before each experiment, use a pipette to transfer 600μL of the stock solution to a 500mL brown volumetric flask, add ultrapure water to make up the volume, and ultrasonicate for 1 hour to fully dissolve and prepare a 12μM EE2 solution. The brown volumetric flask can be protected from light to prevent EE2 from photodegradation, ensuring that the solution concentration is accurate and stable.

[0085] (2) Degradation experiment process control: Take 30 mg of material (Examples 1-3, Comparative Example 1 or MWCNT) and 50 mL of 12 μM EE2 solution into a quartz tube, place it in Nanjing Xujiang XPA-7 photocatalytic instrument (light source off), and add an appropriate amount of potassium persulfate to start the experiment while stirring. Stirring maintains the system uniformity to promote sufficient contact and reaction between the material, PMS and EE2; the amount of potassium persulfate is determined based on the optimization of the preliminary experiment. Take 1 mL of the solution with a syringe every 5 minutes, filter it through a 0.22 μm filter head into a sample bottle, and detect the EE2 concentration with an ultra-high performance liquid chromatograph. The degradation effect is evaluated based on the concentration change to optimize the catalyst.

[0086] The degradation efficiency of EE2 by the catalysts prepared in Examples 1-3 within 30 minutes were 94.7%, 92.15% and 92.68%, respectively, which were much higher than the degradation rate of EE2 degraded by the CdMoO4 catalyst and MWCNT material activated PMS prepared in Comparative Example 1, wherein the degradation rates of EE2 degraded by the CdMoO4 catalyst and MWCNT material activated PMS were both lower than 30%.

[0087] 1. Catalyst concentration optimization

[0088] In order to achieve the best catalytic degradation effect, the effect of the amount of catalyst added on the degradation effect was studied. 0.20, 0.40, 0.60 and 0.80 g / L of catalyst were added to 50 mL, 12 μM EE2 solution, and other reaction conditions were kept the same to explore the effect of catalyst concentration on the catalytic degradation effect.

[0089] like Figure 7 As shown in (a), when 0.01 g / L of PMS is added and CdMoO4@MWCNT is not added, the EE2 solution is almost not degraded after stirring for 60 minutes. As the concentration of the catalyst increases from 0.20 g / L to 0.60 g / L, the removal rates of 12 μM EE2 are 15.5%, 60.9% and 67.0%, respectively. When the catalyst dosage is further increased to 0.80 g / L, the removal rate of EE2 does not increase significantly. This is because when the catalyst dosage is small, the adsorption is small and it cannot provide enough active sites, thus affecting the removal of EE2. However, continuing to increase the catalyst dosage has little effect on the removal effect of EE2. Considering the economic benefits, the optimal concentration of the catalyst is 0.60 g / L.

[0090] 2. Optimization of initial PMS concentration

[0091] In order to explore the effect of initial PMS concentration on the degradation of EE2 by CdMoO4@MWCNT, 0.60 g / L of CdMoO4@MWCNT was added to 50 mL, 12 μM EE2 solution, and the initial PMS concentrations were controlled to be 0.01, 0.02, 0.03 and 0.04 g / L, respectively, to investigate its degradation effect.

[0092] Figure 7 (b) shows that when only 0.02 g / L of PMS is added to the EE2 solution, the degradation rate is only 30.4% in 30 minutes, indicating that the degradation effect of PMS alone on EE2 is very poor. When only 0.60 g / L of CdMoO4@MWCNT is added, the degradation rate is 58.2%, which may be due to the excellent adsorption effect of the large specific surface area of ​​the composite material. When the catalyst and PMS are added to the degradation system at the same time, it can be seen that the degradation efficiency is greatly improved, indicating that CdMoO4@MWCNT can effectively activate PMS to produce active free radicals to degrade EE2. As the initial concentration of PMS increases from 0.01 g / L to 0.04 g / L, the degradation rates of EE2 are 92.3%, 94.7%, 93.2% and 95.9%, respectively. Introducing a large amount of PMS in the water treatment process will increase the treatment cost. Considering that the degradation rate of EE2 has not increased significantly after the PMS concentration is increased from 0.02 g / L to 0.04 g / L, the optimal initial concentration of PMS is 0.02 g / L.

[0093] 3. Effects of common coexisting substances on degradation effects

[0094] There are a lot of organic matter (such as tetracycline, urea, humic acid) and inorganic matter (MgCl2, CaCl2, NaCl, KBr) in natural water and wastewater. These coexisting substances may capture free radicals and affect the degradation of EE2 by CdMoO4@MWCNT / PMS system. Therefore, several interfering substances mentioned above were introduced into the degradation system to explore the effect of coexisting substances on the degradation of EE2. The specific results are shown in Figure 7 (c).

[0095] When MgCl2, CaCl2 and NaCl were introduced into the system, the degradation efficiency decreased to varying degrees, indicating that common inorganic substances in water had little effect on the degradation effect. When tetracycline, urea and humic acid were introduced into the system, the degradation efficiency was 76.4%, 80.9% and 79.2%, respectively, and the degradation rate decreased by 18.3%, 13.8% and 15.5%, respectively. The decrease in degradation rate may be due to the fact that the coexisting organic matter competes with EE2 for adsorption sites and active sites on the catalyst surface and consumes active free radicals.

[0096] 4. The influence of different reaction water quality

[0097] In order to explore the practical application potential of the CdMoO4@MWCNT / PMS system, EE2 degradation experiments were carried out in different water qualities.

[0098] from Figure 7 As can be seen from (d), the degradation rates of EE2 in ultrapure water, tap water and Dianchi Lake water are 94.9%, 94.0% and 78.1%, respectively. There is no obvious change in the degradation effect in tap water, while the degradation effect becomes worse in the Dianchi Lake water sample. This may be because the Dianchi Lake water sample contains a large amount of inorganic ions and organic substances, which will compete for adsorption on the CdMoO4@MWCNT surface and thus affect the activation of PMS, and compete with EE2 for the active sites and active free radicals on the catalyst surface, thereby reducing the degradation efficiency.

[0099] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing a CdMoO4@MWCNT multifunctional catalyst, characterized in that: The steps include: (1) adding cadmium salt to ethylene glycol to dissolve to obtain a mixed solution, adding multi-walled carbon nanotubes and polyethylene glycol and stirring uniformly; (2) Then, an ethylene glycol solution of Na2MoO4·2H2O was added, and finally a solvothermal reaction was carried out to obtain the CdMoO4@MWCNT multifunctional catalyst.

2. The method for preparing the CdMoO4@MWCNT multifunctional catalyst according to claim 1, characterized in that: The molar ratio of the cadmium salt to Na2MoO4·2H2O is (1-3):(3-1); the mass ratio of the cadmium salt to the multi-walled carbon nanotube is (3.08475-1.02825):0.

1.

3. The method for preparing the CdMoO4@MWCNT multifunctional catalyst according to claim 1, characterized in that: The mass ratio of the polyethylene glycol to the multi-walled carbon nanotubes is (0.005-0.04):0.

1.

4. The method for preparing the CdMoO4@MWCNT multifunctional catalyst according to claim 1, characterized in that: The temperature of the solvent thermal reaction is 155-185° C. and the time is 4-16 hours.

5. The CdMoO4@MWCNT multifunctional catalyst prepared according to the preparation method of the CdMoO4@MWCNT multifunctional catalyst according to any one of claims 1 to 4.

6. Use of the CdMoO4@MWCNT multifunctional catalyst according to claim 5 in electrochemical detection of EE2 and activation of PMS to catalyze the removal of EE2.

7. The use of the CdMoO4@MWCNT multifunctional catalyst in electrochemical detection of EE2 according to claim 5, characterized in that: Specifically include: The CdMoO4@MWCNT multifunctional catalyst was coated on a glassy carbon electrode to form a CdMoO4@MWCNT / GCE electrode; then a three-electrode system was constructed with the CdMoO4@MWCNT / GCE electrode as the working electrode, a platinum electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. The current response of EE2 was detected by differential pulse voltammetry in a phosphate buffer solution containing EE2, and then the EE2 concentration was obtained based on the relationship curve between the oxidation peak current of EE2 and the EE2 concentration.

8. The use of the CdMoO4@MWCNT multifunctional catalyst in electrochemical detection of EE2 according to claim 7, characterized in that: When I<2.0195, the relationship curve between the oxidation peak current I of EE2 and the EE2 concentration C is I=0.0699C+1.

670.

9. Use of the CdMoO4@MWCNT multifunctional catalyst according to claim 5 in activating PMS to catalyze and remove EE2 in water.

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