A method for preparing NH2-Fe3O4@Zn-MOF electrode modification material and its application in heavy metal detection in wastewater.

Abstract

This invention belongs to the field of heavy metal detection technology, and more specifically, relates to a method for preparing NH2-Fe3O4@Zn-MOF electrode modification material and its application in heavy metal detection in wastewater. This invention uses zinc salt as the base material and prepares a scalable and economical electrode modification material NH2-Fe3O4@Zn-MOF using a solvothermal method. By combining Zn-MOF with NH2-Fe3O4, the electron transfer rate of MOF nanoparticles is improved. The combination of NH2-Fe3O4 nanomaterials and electrochemical methods can lower the detection limit of metal ions, achieving detection of heavy metal ions such as Cu. 2+ and Pb 2+ Rapid and accurate identification. The working electrode prepared by the NH2-Fe3O4@Zn-MOF modified electrode of this invention provides Cu... 2+ and Pb 2+ It has good detection performance for Cu 2+ and Pb 2+ The detection limits were 1.954 × 10⁻⁶. ‑9 mol·L ‑1 and 1.560×10 ‑9 mol·L ‑1 .

Description

Technical Field

[0001] This invention belongs to the field of heavy metal detection technology, and more specifically relates to a method for preparing NH2-Fe3O4@Zn-MOF electrode modification material and its application in heavy metal detection in wastewater. Background Technology

[0002] Cu(II,Cu) in wastewater 2+ Cd(II,Cd) 2+ Pb(II,Pb) 2+ The release of heavy metal ions such as ions is constantly increasing. Most of these metal ions are highly toxic, non-degradable, and bioaccumulative. Once these pollutants enter the human body through the food chain, especially through dietary intake of plant-based foods and beverages, drinking water, or air, even trace amounts can have long-term effects on health.

[0003] Lead (Pb) can be distributed throughout the human body, causing gout, epilepsy, cancer, and acute and chronic renal failure; cadmium (Cd) mainly affects liver and kidney function, and excessive cadmium levels can lead to cardiovascular disease, liver and kidney necrosis, etc. If intracellular Cu... 2+ Disruption of this balance can damage the nervous system, leading to neurodegenerative diseases such as Parkinson's disease. Therefore, developing an efficient method for detecting heavy metal ions is of great significance.

[0004] Currently, there are various techniques for detecting heavy metal ions, including inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption / emission spectroscopy (AES), fluorescence probe methods, and electrochemical methods. Among these, electrochemical methods have shown great potential for real-time and field detection due to their simplicity, portability, fast response, and high sensitivity. However, the simultaneous detection of Cu... 2+ and Pb 2+ There are relatively few methods for quickly and accurately identifying Cu. 2+ and Pb 2+ And it can reduce Cu 2+ and Pb 2+ Determining the detection limit and achieving excellent anti-interference ability against actual samples has become a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing NH2-Fe3O4@Zn-MOF electrode modification material and its application in the detection of heavy metals in wastewater, so as to solve the problems existing in the prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] One of the technical solutions of this invention is to provide a method for preparing NH2-Fe3O4@Zn-MOF electrode modification material, the steps of which include:

[0008] Zn-MOF was prepared using zinc salt as the metal source and 1,3,5-benzenetricarboxylic acid as the ligand.

[0009] NH2-Fe3O4 was prepared by hydrothermal reaction using FeCl3·6H2O and FeCl2·4H2O as reactants, ammonia as a precipitant, and ethylenediamine as a ligand.

[0010] Using NH2-Fe3O4 and Zn-MOF as reactants, sodium acetate as a modifier, and ethylene glycol as a reaction medium, the NH2-Fe3O4@Zn-MOF electrode modification material was obtained through a solvothermal reaction.

[0011] Furthermore, the zinc salt comprises Zn(CH3COO)2·2H2O.

[0012] Furthermore, the mass ratio of the zinc salt to 1,3,5-benzenetricarboxylic acid is 0.181:0.105.

[0013] Furthermore, the ratio of FeCl3·6H2O, FeCl2·4H2O, ammonia, and ethylenediamine used is 5.41g:1.27g:10mL:40mL.

[0014] Furthermore, the ammonia solution has a mass fraction of 25%.

[0015] Furthermore, the hydrothermal reaction is carried out at a temperature of 180°C for 8 hours.

[0016] Furthermore, the mass ratio of NH2-Fe3O4, Zn-MOF and sodium acetate is 0.253:0.1209:0.7000.

[0017] Furthermore, the solvothermal reaction is carried out at a temperature of 140°C for 12 hours.

[0018] Furthermore, the process after the solvothermal reaction also includes the separation, washing, and drying of the reaction products.

[0019] Optionally, the separation is achieved by applying an external magnetic field.

[0020] Optionally, the washing process involves cleaning with ethanol.

[0021] Optionally, the drying is performed by vacuum drying at 200°C for 2 hours.

[0022] The second technical solution of the present invention provides an NH2-Fe3O4@Zn-MOF electrode modification material, wherein the NH2-Fe3O4@Zn-MOF electrode modification material is prepared by the above preparation method.

[0023] The third technical solution of the present invention provides a working electrode, wherein the working electrode uses NH2-Fe3O4@Zn-MOF electrode modification material as the active component.

[0024] Fourth technical solution of the present invention: A method for preparing the above-mentioned working electrode, comprising the following steps:

[0025] The NH2-Fe3O4@Zn-MOF electrode modification material was dispersed in Nafion solution to obtain the electrode modification solution;

[0026] The electrode modification solution is coated onto the surface of a glassy carbon electrode and dried to obtain the working electrode.

[0027] Furthermore, the mass / volume ratio of the NH2-Fe3O4@Zn-MOF electrode modification material to the Nafion solution is 8.0 mg: 800 μL.

[0028] Optionally, the Nafion solution is a Nafion solution diluted with 0.25 wt.% ethanol.

[0029] Furthermore, the peak potential difference of the glassy carbon electrode is below 70mV.

[0030] Furthermore, the amount of the electrode modification solution coated on the glassy carbon electrode surface is 3 μL.

[0031] The fifth technical solution of the present invention provides an application of the above-mentioned NH2-Fe3O4@Zn-MOF electrode modification material or the above-mentioned working electrode in the detection of heavy metals in wastewater.

[0032] Optionally, the heavy metal is Cu. 2+ and / or Pb 2+ .

[0033] The present invention discloses the following technical effects:

[0034] This invention uses zinc salt as the base material and prepares a scalable and economical electrode modification material NH2-Fe3O4@Zn-MOF using a solvothermal method. By compositing Zn-MOF with NH2-Fe3O4, the electron transfer rate of MOF nanoparticles is improved. The combination of NH2-Fe3O4 nanomaterials and electrochemical methods can lower the detection limit of metal ions, achieving the detection of heavy metal ions Cu. 2+ and Pb 2+ It provides fast and accurate identification.

[0035] The working electrode prepared by the NH2-Fe3O4@Zn-MOF modified electrode of this invention can simultaneously or independently monitor Cu in actual environmental samples. 2+ and Pb 2+ It can also detect these two metal ions separately.

[0036] The working electrode prepared by the NH2-Fe3O4@Zn-MOF modified electrode of this invention is effective against Cu. 2+ and Pb 2+ It has good detection performance for Cu 2+ and Pb 2+ The detection limits were 1.954 × 10⁻⁶. -9 mol·L -1 and 1.560×10 -9 mol·L -1 Compared with other detection methods such as single-molecule sensors, this method is economical, environmentally friendly, and effective. It has better selectivity and stronger anti-interference performance for real samples, providing a new approach for the simultaneous or individual detection of heavy metal ions and broadening the application of MOF materials in real samples and environmental analytical chemistry. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 The images show SEM images of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is a 5000x SEM image of Zn-MOF, (b) is a 5000x SEM image of NH2-Fe3O4@Zn-MOF, (c) is a 10000x SEM image of Zn-MOF, and (d) is a 10000x SEM image of NH2-Fe3O4@Zn-MOF.

[0039] Figure 2 The images show the EDS spectra of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF.

[0040] Figure 3 The image shows the XRD pattern of NH2-Fe3O4@Zn-MOF in Example 1.

[0041] Figure 4The nitrogen adsorption-desorption curves (BET) of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1 are shown, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF.

[0042] Figure 5 The images show the pore area distribution of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF.

[0043] Figure 6 The images show the pore volume distribution of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF.

[0044] Figure 7 The FTIR spectra of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1 are shown below.

[0045] Figure 8 Electrochemical impedance spectroscopy (EIS) spectra of GCE, Zn-MOF / GCE, NH2-Fe3O4 / GCE, and NH2-Fe3O4@Zn-MOF / GCE in K3Fe(CN)6 solution;

[0046] Figure 9 For GCE, Zn-MOF / GCE, and NH2-Fe3O4@Zn-MOF / GCE at 1.0×10 -6 mol·L -1 Pb 2+ and Cu 2+ The differential pulse voltammetry (DPV) curve in the figure;

[0047] Figure 10 The DPV diagrams are shown under different electrolyte solution conditions when NH2-Fe3O4@Zn-MOF / GCE is used as the working electrode.

[0048] Figure 11 The DPV diagrams of NH2-Fe3O4@Zn-MOF / GCE in acetate-sodium acetate (HAc-NaAc) electrolyte solutions at different pH values ​​are shown.

[0049] Figure 12 Cu 2+ and Pb 2+ Absolute current values ​​in acetic acid-sodium acetate electrolyte solutions at different pH values;

[0050] Figure 13 Cu 2+ and Pb 2+DPV plots under different pulse period conditions;

[0051] Figure 14 Cu 2+ and Pb 2+ Plots of absolute current values ​​under different pulse period conditions;

[0052] Figure 15 Cu 2+ and Pb 2+ DPV plots at different pulse widths;

[0053] Figure 16 Cu 2+ and Pb 2+ Plots of absolute current values ​​under different pulse widths;

[0054] Figure 17 Cu 2+ and Pb 2+ CV plots at different scan rates;

[0055] Figure 18 Cu 2+ and Pb 2+ CV fitting curves at different scan rates, where the left graph shows Cu. 2+ The right figure shows Pb. 2+ ;

[0056] Figure 19 Cu 2+ and Pb 2+ Differential pulse stripping voltammetry curves on NH2-Fe3O4@Zn-MOF / GCE;

[0057] Figure 20 For different concentrations of Cu 2+ Relationship with peak current;

[0058] Figure 21 For different concentrations of Pb 2+ Relationship with peak current. Detailed Implementation

[0059] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0060] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0061] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0062] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0063] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0064] In some specific embodiments, the preparation steps of the Zn-MOF include: adding 1,3,5-benzenetricarboxylic acid and sodium hydroxide to a mixed solvent of DMF, ethanol and water, sonicating for 30 min, then adding zinc salt, reacting for 1.5 h, centrifuging to collect the solid product after the reaction, washing the solid product alternately with water and ethanol, and vacuum drying at 140 °C for 2 h to obtain the Zn-MOF.

[0065] Optionally, the volume ratio of DMF, ethanol and water is 2:15:25.

[0066] Optionally, the mass ratio of 1,3,5-benzenetricarboxylic acid to sodium hydroxide is 21:12.

[0067] Optionally, the mass ratio of the 1,3,5-benzenetricarboxylic acid to the zinc salt is 105:181.

[0068] Optionally, the ratio of 1,3,5-benzenetricarboxylic acid to DMF is 0.105 g: 2 mL.

[0069] Unless otherwise specified, room temperature and normal temperature as referred to in the specific embodiments of the present invention refer to 20-30℃.

[0070] Example 1

[0071] The preparation steps of NH2-Fe3O4@Zn-MOF electrode modification materials include:

[0072] S1. Weigh 0.0600g NaOH and 0.1050g 1,3,5-benzenetricarboxylic acid, measure 2mL DMF, 15mL anhydrous ethanol, and 25mL deionized water, mix, and sonicate to dissolve for 30min. Then add 0.1810g Zn(CH3COO)2·2H2O, react for 1.5h, centrifuge to collect the reaction product, wash with water and ethanol three times alternately, and vacuum dry at 140℃ for 2h to obtain Zn-MOF.

[0073] S2. Weigh 5.41 g of FeCl3·6H2O and 1.27 g of FeCl2·4H2O and add them to 100 mL of aqueous solution. Under nitrogen protection and mechanical stirring, add 10 mL of 25% ammonia solution and 40 mL of ethylenediamine dropwise to the reaction solution. React in the reaction vessel at 180 °C for 8 h to form black nanoparticles. Cool to room temperature and wash the nanoparticles thoroughly with distilled water and ethanol until neutral with the help of an external magnet. Dry them in a vacuum drying oven at 50 °C to obtain NH2-Fe3O4.

[0074] S3. Weigh 0.2530g of NH2-Fe3O4 from step S2 and dissolve it in 20mL of ethylene glycol. After stirring and dissolving, add 0.7000g of CH3COONa and sonicate for 20min to obtain a mixed solution.

[0075] S4. Weigh 0.1209g of Zn-MOF from step S1 and add it to 20mL of ethylene glycol. Sonicate for 20min to obtain a dispersion.

[0076] S5. Mix the mixed solution from step S3 with the dispersion from step S4, react in a reactor at 140°C for 12 hours, cool naturally to room temperature, separate under an external magnetic field, wash three times with ethanol, and vacuum dry at 200°C for 2 hours to obtain the NH2-Fe3O4@Zn-MOF electrode modified material.

[0077] Example 2

[0078] The preparation steps of the working electrode include:

[0079] S1. Polish the glassy carbon electrode in a figure-eight pattern on a 0.3μm Al2O3 powder polishing material chamois, then rinse it with distilled water, soak it in anhydrous ethanol for 3 minutes, and then rinse it repeatedly with distilled water to obtain a glassy carbon electrode with a bright and clean mirror-like surface.

[0080] S2. Using the CV method (specific parameters: -0.3V to 1.2V) at 0.5 mol·L⁻¹ -1 The glassy carbon electrode with a bright and clean mirror-like surface was activated in H2SO4 solution. Then, a CV scan was performed in K3[Fe(CN)6] solution with the voltage set between -0.1 and 0.6V. After ten scans, the activated glassy carbon electrode was obtained when the curves completely overlapped and the peak potential difference was below 70mV. This was denoted as GCE.

[0081] S3. Disperse 8.0 mg of the NH2-Fe3O4@Zn-MOF electrode modification material prepared in Example 1 in 800 μL of Nafion solution diluted with 0.25 wt.% ethanol (ultrasonic treatment for 2 h) to obtain the electrode modification solution;

[0082] S4. Take 3 μL of the electrode modification solution from step S3 using a pipette and drop it onto the activated glassy carbon electrode surface from step S2. Let it air dry at room temperature to remove the solvent and obtain the working electrode, denoted as NH2-Fe3O4@Zn-MOF / GCE.

[0083] Comparative Example 1

[0084] The preparation steps of the working electrode include:

[0085] S1. Polish the glassy carbon electrode in a figure-eight pattern on a 0.3μm Al2O3 powder polishing material chamois, then rinse it with distilled water, soak it in anhydrous ethanol for 3 minutes, and then rinse it repeatedly with distilled water to obtain a glassy carbon electrode with a bright and clean mirror-like surface.

[0086] S2. Using the CV method (specific parameters: -0.3V to 1.2V) at 0.5 mol·L⁻¹ -1 The glassy carbon electrode with a bright and clean mirror-like surface was activated in H2SO4 solution, and then CV scanning was performed in K3[Fe(CN)6] solution with the voltage set between -0.1 and 0.6V. Ten scans were performed. When the curves completely overlapped and the peak potential difference was below 70mV, the activated glassy carbon electrode was obtained.

[0087] S3. Disperse 8.0 mg of the Zn-MOF material prepared in Example 1 in 800 μL of Nafion solution diluted with 0.25 wt.% ethanol (ultrasonic treatment for 2 h) to obtain the electrode modification solution;

[0088] S4. Use a pipette to take 3 μL of the electrode modification solution from step S3 and drop it onto the surface of the activated glassy carbon electrode from step S2. Let it air dry at room temperature to remove the solvent and obtain the working electrode, denoted as Zn-MOF / GCE.

[0089] Comparative Example 2

[0090] The preparation steps of the working electrode include:

[0091] S1. Polish the glassy carbon electrode in a figure-eight pattern on a 0.3μm Al2O3 powder polishing material chamois, then rinse it with distilled water, soak it in anhydrous ethanol for 3 minutes, and then rinse it repeatedly with distilled water to obtain a glassy carbon electrode with a bright and clean mirror-like surface.

[0092] S2. Using the CV method (specific parameters: -0.3V to 1.2V) at 0.5 mol·L⁻¹ -1 The glassy carbon electrode with a bright and clean mirror-like surface was activated in H2SO4 solution, and then CV scanning was performed in K3[Fe(CN)6] solution with the voltage set between -0.1 and 0.6V. Ten scans were performed. When the curves completely overlapped and the peak potential difference was below 70mV, the activated glassy carbon electrode was obtained.

[0093] S3. Disperse 8.0 mg NH2-Fe3O4 material in 800 μL of Nafion solution diluted with 0.25 wt.% ethanol (ultrasonic treatment for 2 h) to obtain electrode modification solution;

[0094] The preparation steps of NH2-Fe3O4 material are as follows: Fe3O4 is prepared by co-precipitation method as follows: 5.41g of FeCl3·6H2O and 1.27g of FeCl2·4H2O are added to 100mL of aqueous solution. Under nitrogen protection and mechanical stirring at 90℃, 10mL of 25wt.% ammonia aqueous solution is added dropwise to the reaction solution. The reaction is carried out for 60min, and black nanoparticles are formed. After cooling to room temperature, the nanoparticles are thoroughly washed with distilled water and ethanol until neutral with the help of an external magnet. They are then dried in a vacuum drying oven at 50℃.

[0095] S4. Use a pipette to take 3 μL of the electrode modification solution from step S3 and drop it onto the surface of the activated glassy carbon electrode from step S2. Let it air dry at room temperature to remove the solvent and obtain the working electrode, denoted as NH2-Fe3O4 / GCE.

[0096] Test case

[0097] Figure 1The images show SEM images of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is a 5000x SEM image of Zn-MOF, (b) is a 5000x SEM image of NH2-Fe3O4@Zn-MOF, (c) is a 10000x SEM image of Zn-MOF, and (d) is a 10000x SEM image of NH2-Fe3O4@Zn-MOF. As shown in the SEM images at 5000x and 10000x magnification, the Zn-MOF material exhibits an irregular sheet-like structure with frequent occurrences of triangular sheets. The particle diameter is 500 nm, and most nanosheets are in a stacked state. In the NH2-Fe3O4@Zn-MOF material, NH2-Fe3O4 particles are attached between the Zn-MOF nanosheets, and the two are observed to be tightly bonded together. This indicates that NH2-Fe3O4 has successfully modified the MOF framework and effectively composited with Zn-MOF.

[0098] Figure 2 The images show the EDS spectra of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF. As can be seen from the figures, Zn-MOF exhibits characteristic peaks for carbon (C), oxygen (O), and zinc (Zn), while NH2-Fe3O4@Zn-MOF exhibits characteristic peaks for carbon (C), nitrogen (N), oxygen (O), zinc (Zn), and iron (Fe), indicating that the NH2-Fe3O4@Zn-MOF material was successfully synthesized.

[0099] Figure 3 The image shows the XRD pattern of NH2-Fe3O4@Zn-MOF in Example 1. As can be seen from the image, the characteristic peaks of Zn-MOF material are at 11° and 32°, while the XRD diffraction peaks of NH2-Fe3O4 nanomaterial are at 30.1°, 35.5°, 43.2°, 57.8°, and 62.8°. The XRD results of NH2-Fe3O4@Zn-MOF indicate that the NH2-Fe3O4@Zn-MOF composite material was successfully synthesized.

[0100] Figure 4 The nitrogen adsorption-desorption curves (BET) of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1 are shown, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF. Figure 5 The images show the pore area distribution of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF. Figure 6The images show the pore volume distribution of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF. Figure 4-Figure 6 It can be seen that when N2 adsorption and desorption were performed on Zn-MOF and NH2-Fe3O4@Zn-MOF samples to evaluate their permanent porosity, Zn-MOF exhibited a reversible type III isotherm, and the adsorption-desorption curves almost overlapped, with no hysteresis. NH2-Fe3O4@Zn-MOF showed a type VI curve with an H3 hysteresis loop, and the isotherm exhibited hysteresis, which is a characteristic of mesoporous solid adsorption.

[0101] The specific surface area and pore volume of the adsorbent were calculated using the BET and BJH methods, and the results are shown in Table 1. From Table 1, combined with... Figure 4-Figure 6 It can be seen that the specific surface areas of Zn-MOF and NH2-Fe3O4@Zn-MOF are 13.179 m² and 13.179 m², respectively. 2 / g and 33.583m 2 / g, with pore volumes of 0.093777cm³. 3 / g and 0.045374cm 3 The pore size distribution is 14.23 nm and 2.70 nm. Compared with Zn-MOF, NH2-Fe3O4@Zn-MOF has a significantly increased specific surface area. The modification with NH2-Fe3O4 increases the specific surface area of ​​the material, enhances its physical adsorption capacity, and facilitates subsequent reactions. At the same time, because NH2-Fe3O4 is incorporated into some of the pores of Zn-MOF, its pore volume is reduced.

[0102] Table 1

[0103]

[0104] Figure 7 The figures show the FTIR spectra of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1. As can be seen from the figures, the FTIR spectrum of Zn-MOF is at 741 cm⁻¹. -1 1377~1625cm -1 The typical band of the CO vibrational mode in carboxylic acids was observed, at 1377 cm⁻¹. -1 The band at 1625 cm⁻¹ represents the COO symmetric stretching vibration. -1 The band at 741 cm⁻¹ represents the asymmetric stretching vibration of carboxylic acids, indicating that the C=O bond in the carboxylic acid of 1,3,5-benzenetricarboxylic acid has not been broken. -1 The band at 587 cm⁻¹ represents the out-of-plane bending vibration of the CH group. In the FTIR spectrum of NH₂-Fe₃O₄@Zn-MOF, the band at 587 cm⁻¹ represents the out-of-plane bending vibration of the CH group. -1The spectral band at 1618 cm⁻¹ indicates an Fe-O bond. -1 and 3434cm -1 The symmetric stretching vibration of NH2 indicates that NH2-Fe3O4 has been successfully modified on the surface of Zn-MOF material.

[0105] The impedance changes of GCE, Zn-MOF / GCE, NH2-Fe3O4 / GCE, and NH2-Fe3O4@Zn-MOF / GCE were investigated using electrostatics (EIS). The EIS measurement amplitude was 0.005 V, the voltage frequency ranged from 100 kHz to 0.01 Hz, and the applied potential was 0.2 V. The results are as follows: Figure 8 As shown.

[0106] Figure 8 The figures show the electrochemical impedance spectroscopy (EIS) spectra of GCE, Zn-MOF / GCE, NH2-Fe3O4 / GCE, and NH2-Fe3O4@Zn-MOF / GCE in K3Fe(CN)6 solution. As can be seen from the figures, NH2-Fe3O4 / GCE has the largest semicircular diameter, while Zn-MOF / GCE has the smallest. The semicircular diameter of NH2-Fe3O4@Zn-MOF / GCE is smaller than that of NH2-Fe3O4 / GCE. Therefore, NH2-Fe3O4@Zn-MOF / GCE exhibits lower impedance than NH2-Fe3O4 / GCE, indicating that NH2-Fe3O4@Zn-MOF / GCE possesses better electrochemical performance.

[0107] The electrochemical behavior was characterized and evaluated using cyclic voltammetry. GCE, Zn-MOF / GCE, and NH2-Fe3O4@Zn-MOF / GCE were simultaneously used for the detection of heavy metal ions. The DPV reaction was observed at 1.0 × 10⁻⁶. -6 mol·L -1 Pb 2+ and Cu 2+ The determination was performed in an acetate buffer solution with a pH of 5. Results are as follows: Figure 9 As shown.

[0108] Figure 9 For GCE, Zn-MOF / GCE, and NH2-Fe3O4@Zn-MOF / GCE at 1.0×10 -6 mol·L -1 Pb 2+ and Cu 2+The differential pulse voltammetry (DPV) curves show that GCE lacks good resolution and has no obvious response peak. Two response peaks with good resolution were observed simultaneously on Zn-MOF / GCE and NH2-Fe3O4@Zn-MOF / GCE, both larger than those on GCE. For Zn-MOF / GCE, the enhanced peak current response is due to the porous structure of MOF materials facilitating the diffusion and pre-enrichment of metal ions. The specific surface area and superior conductivity of MOF materials promote the enhancement of the peak current. Pb on NH2-Fe3O4@Zn-MOF / GCE... 2+ and Cu 2+ The response signal is the largest because it combines the advantages of Zn-MOF materials, with a large specific surface area, abundant active sites, and high conductivity, which is beneficial for the loading and electron transfer of heavy metal ions.

[0109] A three-electrode system was used, with NH2-Fe3O4@Zn-MOF / GCE as the working electrode, a platinum electrode as the auxiliary electrode, and a calomel electrode as the reference electrode. The system was placed in a prepared 1.0 × 10⁻⁶ ohmmeter. -6 mol·L -1 Cu 2+ and Pb 2+ Determination of Pb by DPV method in different electrolytes such as acetic acid-sodium acetate, sodium dihydrogen phosphate-disodium hydrogen phosphate, and formic acid-sodium hydroxide 2+ and Cu 2+ The concentration of electrolyte was used to determine the effect of electrolyte on the peak current of heavy metal ions, and the results are as follows: Figure 10 As shown.

[0110] Figure 10 The figures show the DPV (Distribution Potential) of Cu under different electrolyte solution conditions when using NH2-Fe3O4@Zn-MOF / GCE as the working electrode. The figures show that in sodium formate solution (formic acid-sodium hydroxide), Cu... 2+ and Pb 2+ The peak current signal is small, almost invisible; in phosphate solution (sodium dihydrogen phosphate - disodium hydrogen phosphate), Pb 2+ It exhibits a response current, but Cu 2+ The average peak current intensity is relatively weak. In contrast, in the acetate buffer solution (acetic acid-sodium acetate), the dissolution peaks of the two heavy metal ions are well separated, and the peak current intensity is significantly enhanced. 2+ and Pb 2+ The different electrochemical behaviors of heavy metal ions in the above three electrolyte solutions are due to the different degrees of complexation between heavy metal ions and electrolyte solutions.

[0111] Since pH has a significant impact on the analysis of heavy metal ions, pH value not only affects the protonation of the NH2-Fe3O4 complex functional group, but also determines the chemical properties and speciation of various heavy metal ions in solution. The effects of different pH conditions on detection are as follows: Figure 11 and Figure 12 As shown.

[0112] Figure 11 The DPV diagrams of NH2-Fe3O4@Zn-MOF / GCE in acetate-sodium acetate (HAc-NaAc) electrolyte solutions at different pH values ​​are shown. Figure 12 Cu 2+ and Pb 2+ A graph showing the absolute values ​​of current in acetate-sodium acetate electrolyte solutions at different pH values. Figures 11-12 It can be seen that at 1.0×10 -6 mol·L -1 In HAc-NaAc buffer solutions with pH values ​​of 4.4-5.2, Cu on NH2-Fe3O4@Zn-MOF / GCE 2+ and Pb 2+ The peak current. It can be seen that as the pH value increases, Cu... 2+ and Pb 2+ The peak current increases, and the peak current is the largest when the pH is 4.4.

[0113] Figure 13 Cu 2+ and Pb 2+ DPV diagrams under different pulse period conditions; Figure 14 Cu 2+ and Pb 2+ Plots of absolute current values ​​under different pulse period conditions. (From...) Figures 13-14 It can be seen that when the pulse period changes from 0.05 s to 0.1 s, the peak currents of the two ions gradually increase. However, when the pulse period increases from 0.1 s to 0.2 s, the peak currents gradually decrease as the pulse period continues to increase. The maximum peak current is reached under the condition of a pulse period of 0.1 s. Therefore, 0.1 s is chosen for simultaneous detection of Cu. 2+ and Pb 2+ .

[0114] Figure 15 Cu 2+ and Pb 2+ DPV plots at different pulse widths; Figure 16 Cu 2+ and Pb 2+ Plots of absolute current values ​​under different pulse widths. (From...) Figures 15-16It can be seen that when the pulse width is between 0.05 and 0.1 s, the current continuously increases, but when the pulse period increases from 0.1 s to 0.3 s, the current continuously decreases as the pulse period increases.

[0115] Figure 17 Cu 2+ and Pb 2+ CV plots at different scan rates; Figure 18 Cu 2+ and Pb 2+ CV fitting curves at different scan rates, where the left graph shows Cu. 2+ The right figure shows Pb. 2+ .Depend on Figures 17-18 It can be seen that the scan rate is set to 200 mV·s -1 Up to 1000mV·s -1 Cu 2+ The linear equation is Ip = 0.13 + 0.0098V, with a correlation coefficient of 0.9722. Pb 2+ The linear equation is Ip = -0.35 + 0.0087 V, with a correlation coefficient of 0.9926. The peak current and scan rate show a good linear relationship, indicating that this process is adsorption-controlled. This also confirms that NH2-Fe3O4@Zn-MOF / GCE can simultaneously determine Cu. 2+ and Pb 2+ According to Laviron's theory, the electron transfer number of the modified electrode can be calculated to be 2.3, approximately equal to 2.

[0116] Figure 19 Cu 2+ and Pb 2+ Differential pulse stripping voltammetry curves on NH2-Fe3O4@Zn-MOF / GCE; Figure 20 For different concentrations of Cu 2+ Relationship with peak current; Figure 21 For different concentrations of Pb 2+ The relationship between peak current and peak current. Figures 19-21 It can be observed that Cu 2+ and Pb 2+ The dissolution peak currents are approximately 0.532V and 0.088V respectively, and there is no interference between the two ion dissolution peaks. The peak shapes are good and the shift directions are the same. Cu 2+ and Pb 2+ Peak current increases linearly with increasing ion concentration: Cu 2 + At an ion concentration of 3.0 × 10 -8 mol·L -1 ~2.0×10 -5 mol·L -1The linear equation within the range is Ip = 0.5300c + 1.78, with a correlation coefficient of 0.9969. (Pb) 2+ At a concentration of 3.0 × 10 -8 mol·L -1 ~2.0×10 -5 mol·L -1 The linear equation within the range is Ip = 0.3791c + 1.582, with a correlation coefficient of 0.9768. Calculations show that Cu... 2+ The detection limit is 2.085 × 10⁻⁶. -9 mol·L -1 Pb 2+ The detection limit was 5.693 × 10⁻⁶. -9 mol·L -1 .

[0117] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0118] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an NH2-Fe3O4@Zn-MOF electrode modification material, characterized in that the steps include... include: Zn-MOF was prepared using zinc salt as the metal source and 1,3,5-benzenetricarboxylic acid as the ligand. NH2-Fe3O4 was prepared by hydrothermal reaction using FeCl3·6H2O and FeCl2·4H2O as reactants, ammonia as a precipitant, and ethylenediamine as a ligand. Using NH2-Fe3O4 and Zn-MOF as reactants, sodium acetate as a modifier, and ethylene glycol as a reaction medium, the NH2-Fe3O4@Zn-MOF electrode modification material was obtained through a solvothermal reaction. The zinc salt comprises Zn(CH3COO)2·2H2O; The mass ratio of the zinc salt to 1,3,5-benzenetricarboxylic acid is 0.181:0.105; The ratio of FeCl3·6H2O, FeCl2·4H2O, ammonia, and ethylenediamine used is 5.41g:1.27g:10mL:40mL; The mass fraction of the ammonia solution is 25%. The hydrothermal reaction was carried out at a temperature of 180°C for 8 hours. The mass ratio of NH2-Fe3O4, Zn-MOF, and sodium acetate is 0.253:0.1209:0.7000; The solvothermal reaction was carried out at a temperature of 140°C for 12 hours. The process after solvothermal reaction also includes the separation, washing and drying of the reaction products.

2. The preparation method according to claim 1, characterized in that, The separation is performed by an external magnetic field; and / or the washing is performed by ethanol cleaning; and / or the drying is performed by vacuum drying at 200°C for 2 hours.

3. An NH2-Fe3O4@Zn-MOF electrode modification material, characterized in that, The NH2-Fe3O4@Zn-MOF electrode modification material is prepared by the preparation method according to any one of claims 1-2.

4. A working electrode, characterized in that, The working electrode uses the NH2-Fe3O4@Zn-MOF electrode modification material as described in claim 3 as the active component.

5. A method for preparing the working electrode according to claim 4, characterized in that, step include: The NH2-Fe3O4@Zn-MOF electrode modification material was dispersed in Nafion solution to obtain the electrode modification solution; The electrode modification solution is coated onto the surface of a glassy carbon electrode and dried to obtain the working electrode.

6. The preparation method according to claim 5, characterized in that, The mass / volume ratio of the NH2-Fe3O4@Zn-MOF electrode modification material to the Nafion solution is 8.0 mg:800 μL; and / or, the peak potential difference of the glassy carbon electrode is below 70 mV; and / or, the coating amount of the electrode modification solution applied to the surface of the glassy carbon electrode is 3 μL.

7. The preparation method according to claim 5, characterized in that, The Nafion solution is a Nafion solution diluted with 0.25 wt.% ethanol.

8. The application of the NH2-Fe3O4@Zn-MOF electrode modification material of claim 3 or the working electrode of claim 4 in the detection of heavy metals in wastewater.

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