Preparation method of NH2-Fe3O4atZn-MOF electrode modification material and application of NH2-Fe3O4atZn-MOF electrode modification material in detection of heavy metals in wastewater

Abstract

The invention belongs to the technical field of heavy metal detection, and particularly relates to a preparation method of an NH2-Fe3O4Zn-MOF electrode modification material and application of the NH2-Fe3O4Zn-MOF electrode modification material in detection of heavy metals in wastewater. Zinc salt is adopted as a base material, an extensible and economical electrode modification material NH2-Fe3O4 (at) Zn-MOF is prepared through a solvothermal method, the electron transfer rate of MOFs nano-particles is increased by compounding the Zn-MOF and NH2-Fe3O4, the detection limit of metal ions can be reduced by combining the NH2-Fe3O4 nano-material with an electrochemical method, and rapid and accurate recognition of heavy metal ions Cu < 2 + > and Pb < 2 + > is achieved. The working electrode prepared from the NH2-Fe3O4 (at) Zn-MOF modified electrode has relatively good detection performance on Cu < 2 + > and Pb < 2 + >, and the detection limits on Cu < 2 + > and Pb < 2 + > are 1.954 * 10 <-9 > mol.L <-1 > and 1.560 * 10 <-9 > mol.L <-1 > respectively.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal detection, and more specifically relates to a preparation method of an NH2-Fe3O4@Zn-MOF electrode modification material and an application thereof in heavy metal detection in wastewater. Background Art

[0002] Cu(II,Cu 2+ )、Cd(II,Cd 2+ )、Pb(II,Pb 2+ ) is released in an increasing amount. 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] For example, lead (Pb) can be distributed throughout the human body, causing gout, epilepsy, cancer, and acute and chronic renal failure; cadmium (Cd) mainly affects the liver and kidney functions of the human body. When cadmium exceeds the standard, it can cause cardiovascular diseases, liver and kidney necrosis, etc. 2+ If the balance is disrupted, it will damage the human nervous system and cause neurodegenerative diseases such as Parkinson's disease. Therefore, it is of great significance to create a method for efficiently detecting heavy metal ions.

[0004] At present, there are various detection technologies for heavy metal ions, including inductively coupled plasma optical emission spectroscopy, inductively coupled plasma mass spectrometry, atomic absorption / emission spectroscopy, fluorescent probe method, electrochemical method, etc. Among them, electrochemical method has shown great potential in real-time and on-site detection due to its simple operation, portable instrument, fast response speed and high sensitivity. 2+ and Pb 2+ There are relatively few methods to quickly and accurately identify Cu 2+ and Pb 2+ , and can reduce Cu 2+ and Pb 2+ The detection limit and excellent anti-interference ability for actual samples have become problems that technical personnel in this field urgently need to solve. Summary of the invention

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

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

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

[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 with FeCl3·6H2O and FeCl2·4H2O as reactants, ammonia water as precipitant and ethylenediamine as coordination agent.

[0010] The NH2-Fe3O4 and the Zn-MOF are used as reactants, sodium acetate is used as a regulator, and ethylene glycol is used as a reaction medium. The NH2-Fe3O4@Zn-MOF electrode modification material is obtained through a solvent thermal reaction.

[0011] Furthermore, the zinc salt includes 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 usage ratio of FeCl3·6H2O, FeCl2·4H2O, aqueous ammonia and ethylenediamine is 5.41 g:1.27 g:10 mL:40 mL.

[0014] Furthermore, the mass fraction of the ammonia water is 25%.

[0015] Furthermore, the temperature of the hydrothermal reaction is 180° C. and the time is 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 temperature of the solvent thermal reaction is 140° C. and the time is 12 h.

[0018] Furthermore, after the solvent thermal reaction, the process also includes the steps of separating, washing and drying the reaction products.

[0019] Optionally, the separation is separation using an external magnetic field.

[0020] Optionally, the washing is performed using ethanol.

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

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

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

[0024] The fourth technical solution of the present invention is to provide a method for preparing the above-mentioned working electrode, the steps comprising:

[0025] Dispersing the NH2-Fe3O4@Zn-MOF electrode modification material in a Nafion solution to obtain an electrode modification solution;

[0026] The electrode modification solution is applied to the surface of the 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 and 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 70 mV.

[0030] Furthermore, the coating amount of the electrode modification liquid coated on the surface of the glassy carbon electrode 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] The present invention adopts zinc salt as the base material and adopts the solvothermal method to prepare the scalable and economical electrode modification material NH2-Fe3O4@Zn-MOF. By compounding Zn-MOF with NH2-Fe3O4, the electron transfer rate of MOFs nanoparticles is improved. The combination of NH2-Fe3O4 nanomaterials and electrochemical methods can reduce the detection limit of metal ions and realize the detection of heavy metal ions Cu 2+ and Pb 2+ Fast and accurate identification.

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

[0036] The working electrode prepared by the NH2-Fe3O4@Zn-MOF modified electrode of the present invention has good conductivity to Cu 2+ and Pb 2+ It has good detection performance for Cu 2+ and Pb 2+ The detection limits were 1.954×10 -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, with better selectivity and stronger anti-interference performance for actual samples, providing a new idea for the simultaneous or individual detection of heavy metal ions and broadening the application of MOFs materials in the field of actual samples and environmental analytical chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

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

[0039] Figure 2 The EDS spectra of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, wherein (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF;

[0040] Figure 3 is 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, wherein (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF;

[0042] Figure 5 The pore area distribution diagrams of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, wherein (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF;

[0043] Figure 6 The pore volume distribution diagrams of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, wherein (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF;

[0044] Figure 7 FTIR spectra of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1;

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

[0046] Fig. 9 For GCE, Zn-MOF / GCE, NH2-Fe3O4@Zn-MOF / GCE at 1.0×10 -6 mol·L -1 Pb 2+ and Cu 2+ Differential Pulse Voltammetry (DPV) curve in ;

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

[0048] Fig.11 DPV diagram of NH2-Fe3O4@Zn-MOF / GCE in acetic acid-sodium acetate (HAc-NaAc) electrolyte solutions with different pH values;

[0049] Fig.12 Cu 2+ and Pb 2+ Absolute value diagram of current in acetic acid-sodium acetate electrolyte solutions with different pH values;

[0050] Fig.13 Cu 2+ and Pb 2+DPV diagram under different pulse period conditions;

[0051] Fig.14 Cu 2+ and Pb 2+ Absolute value diagram of current under different pulse period conditions;

[0052] Fig.15 Cu 2+ and Pb 2+ DPV diagram at different pulse widths;

[0053] Fig.16 Cu 2+ and Pb 2+ Absolute value diagram of current at different pulse widths;

[0054] Fig.17 Cu 2+ and Pb 2+ CV graphs at different scan rates;

[0055] Fig.18 Cu 2+ and Pb 2+ CV fitting curves at different scan rates, where the left figure is Cu 2+ , the right picture is Pb 2+ ;

[0056] Fig.19 Cu 2+ and Pb 2+ Differential pulse stripping voltammetric characteristic curve on NH2-Fe3O4@Zn-MOF / GCE;

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

[0058] Fig.21 For different concentrations of Pb 2+ Relationship diagram with peak current. DETAILED DESCRIPTION

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

[0060] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0061] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0062] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[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, ultrasonically treating for 30 minutes, then adding zinc salt, reacting for 1.5 hours, collecting the solid product by centrifugation after the reaction, washing the solid product alternately with water and ethanol, and vacuum drying at 140°C for 2 hours 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 1,3,5-benzenetricarboxylic acid to zinc salt is 105:181.

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

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

[0070] Example 1

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

[0072] S1. Weigh 0.0600 g NaOH and 0.1050 g 1,3,5-benzenetricarboxylic acid, measure 2 mL DMF and 15 mL anhydrous ethanol, and 25 mL deionized water, mix, and ultrasonically dissolve for 30 min, then add 0.1810 g Zn(CH3COO)2·2H2O, react for 1.5 h, collect the reaction product by centrifugation, wash it with water and ethanol alternately three times, and vacuum dry it at 140 ° C for 2 h 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, add 10 mL of 25% ammonia solution and 40 mL of ethylenediamine dropwise to the reaction solution under mechanical stirring. React in the reactor at 180°C for 8 h to form black nanoparticles. Cool to room temperature. With the help of an external magnet, wash the nanoparticles with distilled water and ethanol until they are neutral. Dry them in a vacuum drying oven at 50°C to obtain NH2-Fe3O4.

[0074] S3, weigh 0.2530g of NH2-Fe3O4 in step S2 and dissolve it in 20mL of ethylene glycol, stir to dissolve, add 0.7000g of CH3COONa, and ultrasonicate for 20min to obtain a mixed solution;

[0075] S4, weigh 0.1209 g of the Zn-MOF prepared in step S1, add it to 20 mL of ethylene glycol, and perform ultrasonication for 20 min to obtain a dispersion;

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

[0077] Example 2

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

[0079] S1. Polish the glassy carbon electrode in a 0.3 μm Al2O3 powder polishing material suede in an 8-shaped pattern, 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 are -0.3V ~ 1.2V) at 0.5mol·L -1 The glassy carbon electrode with a bright and clean mirror surface was activated in a H2SO4 solution, and then CV scanning was performed in a K3[Fe(CN)6] solution. The voltage was set between -0.1 and 0.6 V, and the scanning was performed ten times. When the curves completely overlapped and the peak potential difference was below 70 mV, an activated glassy carbon electrode was obtained, which was recorded as GCE.

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

[0082] S4. Use a pipette to take 3 μL of the electrode modification solution in step S3 and drop it onto the surface of the activated glassy carbon electrode in step S2. Dry it at room temperature to remove the solvent to obtain a working electrode, which is recorded 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 0.3 μm Al2O3 powder polishing material suede in an 8-shaped pattern, 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 are -0.3V ~ 1.2V) at 0.5mol·L -1 The glassy carbon electrode with a bright and clean mirror-like surface is activated in a H2SO4 solution, and then CV scanning is performed in a K3[Fe(CN)6] solution, with the voltage set between -0.1 and 0.6 V, and scanned ten times. When the curves completely overlap and the peak potential difference is below 70 mV, an activated glassy carbon electrode is obtained;

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

[0088] S4. Use a pipette to take 3 μL of the electrode modification solution in step S3 and drop it onto the surface of the activated glassy carbon electrode in step S2. Dry it at room temperature to remove the solvent to obtain a working electrode, which is recorded 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 0.3 μm Al2O3 powder polishing material suede in an 8-shaped pattern, 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 are -0.3V ~ 1.2V) at 0.5mol·L -1 The glassy carbon electrode with a bright and clean mirror-like surface is activated in a H2SO4 solution, and then CV scanning is performed in a K3[Fe(CN)6] solution, with the voltage set between -0.1 and 0.6 V, and scanned ten times. When the curves completely overlap and the peak potential difference is below 70 mV, an activated glassy carbon electrode is obtained;

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

[0094] The preparation steps of NH2-Fe3O4 material are as follows: Fe3O4 is prepared by coprecipitation method as follows: 5.41g of FeCl3·6H2O and 1.27g of FeCl2·4H2O are added to 100mL of aqueous solution, 10mL of 25wt.% ammonia solution is added dropwise to the reaction solution at 90°C, nitrogen protection, and mechanical stirring, and the reaction is carried out for 60min, black nanoparticles are formed, cooled to room temperature, and with the help of an external magnet, the nanoparticles are fully washed with distilled water and ethanol to neutrality, and placed in a vacuum drying oven at 50°C for drying;

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

[0096] Test example

[0097] Figure 1These are the SEM images of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, where (a) is a 5000-fold SEM image of Zn-MOF, (b) is a 5000-fold SEM image of NH2-Fe3O4@Zn-MOF, (c) is a 10000-fold SEM image of Zn-MOF, and (d) is a 10000-fold SEM image of NH2-Fe3O4@Zn-MOF. As can be seen from the figure, in the SEM images at 5000 times and 10000 times, it can be observed that the Zn-MOF material is an irregular flake structure, triangular flakes appear frequently, the particle diameter is 500nm, and most of the nanosheets are in a stacked state; in the NH2-Fe3O4@Zn-MOF material, the NH2-Fe3O4 particles are attached between the Zn-MOF nanosheets and it can be observed that the two are tightly combined together, indicating that NH2-Fe3O4 has successfully modified the MOF skeleton and effectively composited with Zn-MOF.

[0098] Figure 2 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 figure, there are characteristic peaks of carbon (C), oxygen (O), and zinc (Zn) in Zn-MOF, and characteristic peaks of carbon (C), nitrogen (N), oxygen (O), zinc (Zn), and iron (Fe) in NH2-Fe3O4@Zn-MOF, indicating that the NH2-Fe3O4@Zn-MOF material was successfully synthesized.

[0099] Figure 3 This is the XRD diagram of NH2-Fe3O4@Zn-MOF in Example 1. It can be seen from the figure that the characteristic peaks of the Zn-MOF material are at 11° and 32°, and the XRD diffraction peaks of the NH2-Fe3O4 nanomaterial are at 30.1°, 35.5°, 43.2°, 57.8° and 62.8°. The XRD results of NH2-Fe3O4@Zn-MOF show that the NH2-Fe3O4@Zn-MOF composite material is successfully synthesized.

[0100] Figure 4 The nitrogen adsorption-desorption curves (BET) of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, wherein (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF; Figure 5 The pore area distribution diagrams of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1, wherein (a) is Zn-MOF and (b) is NH2-Fe3O4@Zn-MOF; Figure 6The pore volume distribution diagrams 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 N2 adsorption and desorption were carried out on Zn-MOF and NH2-Fe3O4@Zn-MOF samples to evaluate their permanent porosity. Zn-MOF showed a reversible type III isotherm, and the adsorption-desorption curves almost overlapped without hysteresis; NH2-Fe3O4@Zn-MOF showed a type VI curve with an H3 hysteresis loop, and the isotherm had hysteresis, which is a characteristic of mesoporous solid adsorption.

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

[0102] Table 1

[0103]

[0104] Figure 7 The FTIR spectra of Zn-MOF and NH2-Fe3O4@Zn-MOF in Example 1 are shown in the figure. As can be seen from the figure, the FTIR spectrum of Zn-MOF is at 741cm -1 1377~1625cm -1 The typical band of CO vibration mode in carboxylic acid appeared, 1377cm -1 The band at 1625 cm is the COO symmetric stretching vibration. -1 The band at 741 cm is the asymmetric stretching vibration of carboxylic acid, from which it can be inferred that the C=O bond of carboxylic acid on 1,3,5-benzenetricarboxylic acid has not been broken. -1 The band at 587cm is the out-of-plane bending vibration of the CH group. -1The band at 1618 cm is the Fe-O bond. -1 and 3434cm -1 The symmetric stretching vibration of NH2 is shown in Figure 2, indicating 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 studied by EIS. The amplitude of EIS measurement was 0.005V, the voltage frequency was 100kHz to 0.01Hz, and the applied potential was 0.2V. The results are shown in Figure 8 shown.

[0106] Figure 8 The electrochemical impedance spectra of GCE, Zn-MOF / GCE, NH2-Fe3O4 / GCE, and NH2-Fe3O4@Zn-MOF / GCE in K3Fe(CN)6 solution are shown in the figure. It can be seen that the semicircular diameter of NH2-Fe3O4 / GCE is the largest, the semicircular diameter of Zn-MOF / GCE is the smallest, and the semicircular diameter of NH2-Fe3O4@Zn-MOF / GCE is smaller than that of NH2-Fe3O4 / GCE. It can be seen that the impedance of NH2-Fe3O4@Zn-MOF / GCE is smaller than that of NH2-Fe3O4 / GCE, and NH2-Fe3O4@Zn-MOF / GCE has better electrochemical performance.

[0107] Cyclic voltammetry was used to characterize and evaluate the electrochemical behavior. GCE, Zn-MOF / GCE, and NH2-Fe3O4@Zn-MOF / GCE were simultaneously used for the detection of heavy metal ions. The DPV reaction was at 1.0×10 -6 mol·L -1 Pb 2+ and Cu 2+ The results are shown in the following table. Fig. 9 shown.

[0108] Fig. 9 For GCE, Zn-MOF / GCE, 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 shows that GCE does not have good resolution and no obvious response peak. Two well-resolved response peaks were observed simultaneously in Zn-MOF / GCE and NH2-Fe3O4@Zn-MOF / GCE, and both Zn-MOF / GCE and NH2-Fe3O4@Zn-MOF / GCE were larger than GCE. For Zn-MOF / GCE, the enhancement of the peak current response is due to the fact that the porous structure of MOFS materials is conducive to the diffusion and pre-enrichment of metal ions, and the specific surface area and superior conductivity of MOFs materials promote the enhancement of peak current. Pb on NH2-Fe3O4@Zn-MOF / GCE 2+ and Cu 2+ The response signal is the largest. This is because it combines the advantages of Zn-MOF materials, with the characteristics of large specific surface area, rich active sites and high electrical conductivity, which is conducive to the loading of heavy metal ions and electron transfer.

[0109] The three-electrode system with NH2-Fe3O4@Zn-MOF / GCE as the working electrode, platinum electrode as the auxiliary electrode and calomel electrode as the reference electrode was placed in a 1.0×10 -6 mol·L -1 Cu 2+ and Pb 2+ Determination of Pb by DPV in different electrolytes: acetic acid-sodium acetate, sodium dihydrogen phosphate-disodium hydrogen phosphate, 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. Fig.10 shown.

[0110] Fig.10 The DPV diagram of NH2-Fe3O4@Zn-MOF / GCE under different electrolyte solution conditions is shown in the figure. It can be seen that in sodium formate solution (formic acid-sodium hydroxide), Cu 2+ and Pb 2+ The peak current signal is small and almost invisible; in phosphate solution (sodium dihydrogen phosphate-disodium hydrogen phosphate), Pb 2+ showed 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 difference in electrochemical behavior of heavy metal ions in the above three electrolyte solutions is due to the different degree of complexation between heavy metal ions and electrolyte solutions.

[0111] Since pH has a significant effect on the analysis of heavy metal ions, pH value can not only affect the protonation of NH2-Fe3O4 complex functional groups, but also determine the chemical properties and forms of various heavy metal ions in the solution. The effects of different pH conditions on detection are as follows: Fig.11 and Fig.12 shown.

[0112] Fig.11 DPV diagram of NH2-Fe3O4@Zn-MOF / GCE in acetic acid-sodium acetate (HAc-NaAc) electrolyte solutions with different pH values; Fig.12 Cu 2+ and Pb 2+ Absolute current value diagram in acetic acid-sodium acetate electrolyte solutions with different pH values. Figure 11-Figure 12 It can be seen that at 1.0×10 -6 mol·L -1 In the HAc-NaAc buffer solution with a pH value of 4.4-5.2, Cu on NH2-Fe3O4@Zn-MOF / GCE 2+ and Pb 2+ It can be seen that as the pH value increases, Cu 2+ and Pb 2+ The peak current increases, and when the pH is 4.4, the peak current is the largest.

[0113] Fig.13 Cu 2+ and Pb 2+ DPV diagrams under different pulse period conditions; Fig.14 Cu 2+ and Pb 2+ The absolute value of the current under different pulse period conditions. Figure 13-14 It can be seen that when the pulse period moves from 0.05 to 0.1s, the peak current of the two ions gradually increases, but when the pulse period increases from 0.1s to 0.2s, the peak current gradually decreases as the pulse period continues to increase. The maximum peak current is reached under the condition of a pulse period of 0.1s. 0.1s is selected to simultaneously detect Cu 2+ and Pb 2+ .

[0114] Fig.15 Cu 2+ and Pb 2+ DPV diagram at different pulse widths; Fig.16 Cu 2+ and Pb 2+ The absolute value of current at different pulse widths. Figure 15-16It can be seen that when the pulse width is between 0.05 and 0.1 s, the current continues to increase, but when the pulse period increases from 0.1 s to 0.3 s, the current continues to decrease as the pulse period increases.

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

[0116] Fig.19 Cu 2+ and Pb 2+ Differential pulse stripping voltammetric characteristic curve on NH2-Fe3O4@Zn-MOF / GCE; Fig. 20 For different concentrations of Cu 2+ Relationship diagram with peak current; Fig.21 For different concentrations of Pb 2+ The relationship between the peak current and Figure 19-21 It can be observed that Cu 2+ and Pb 2+ The dissolution peak currents are around 0.532V and 0.088V respectively, and there is no interference between the two ion dissolution peaks, the peak shape is good, and the offset direction is the same. 2+ and Pb 2+ The peak current increases linearly with the increase of 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, and the correlation coefficient is 0.9969. 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, and the correlation coefficient is 0.9768. It is calculated that Cu 2+ The detection limit was 2.085×10 -9 mol·L -1 , Pb 2+ The detection limit was 5.693×10 -9 mol·L -1 .

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

[0118] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be 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 will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing NH2-Fe3O4@Zn-MOF electrode modification material, characterized in that the steps 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 with FeCl3·6H2O and FeCl2·4H2O as reactants, ammonia water as precipitant and ethylenediamine as coordination agent. The NH2-Fe3O4 and the Zn-MOF are used as reactants, sodium acetate is used as a regulator, and ethylene glycol is used as a reaction medium, and the NH2-Fe3O4@Zn-MOF electrode modification material is obtained through a solvent thermal reaction; The zinc salt includes Zn(CH3COO)2·2H2O.

2. The preparation method according to claim 1, characterized in that The mass ratio of the zinc salt to 1,3,5-benzenetricarboxylic acid is 0.181:0.105; and / or, the dosage ratio of FeCl3·6H2O, FeCl2·4H2O, ammonia water and ethylenediamine is 5.41g:1.27g:10mL:40mL; and / or, the mass fraction of ammonia water is 25%; and / or, the temperature of the hydrothermal reaction is 180°C and the time is 8h.

3. The preparation method according to claim 1, characterized in that: The mass ratio of NH2-Fe3O4, Zn-MOF and sodium acetate is 0.253:0.1209:0.7000; and / or, the temperature of the solvent thermal reaction is 140°C and the time is 12 hours; and / or, after the solvent thermal reaction, the reaction product is also separated, washed and dried.

4. The preparation method according to claim 3, characterized in that: The separation is separation by applying an external magnetic field; and / or, the washing is cleaning with ethanol; and / or, the drying is vacuum drying at 200° C. for 2 hours.

5. A NH2-Fe3O4@Zn-MOF electrode modification material, characterized in that: The NH2-Fe3O4@Zn-MOF electrode modification material is prepared by the preparation method described in any one of claims 1-4.

6. A working electrode, characterized in that The working electrode uses the NH2-Fe3O4@Zn-MOF electrode modification material described in claim 5 as an active ingredient.

7. A method for preparing a working electrode according to claim 6, characterized in that the steps include: Dispersing the NH2-Fe3O4@Zn-MOF electrode modification material in a Nafion solution to obtain an electrode modification solution; The electrode modification solution is applied to the surface of the glassy carbon electrode and dried to obtain the working electrode.

8. The preparation method according to claim 7, characterized in that: The mass / volume ratio of the NH2-Fe3O4@Zn-MOF electrode modification material and 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 liquid applied to the surface of the glassy carbon electrode is 3 μL.

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

10. Use of the NH2-Fe3O4@Zn-MOF electrode modification material according to claim 5 or the working electrode according to claim 6 in heavy metal detection in wastewater.

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