An electrochemical sensor based on metal-organic framework nanomaterials and its application in detecting nitrite and / or ammonia nitrogen

Abstract

The present invention provides an electrochemical sensor based on metal organic framework nanomaterials and its application in detecting nitrite and / or ammonia nitrogen, relating to the field of detection technology. The metal organic framework nanomaterial (Ti‑MOF / Ag / CNT) provided by the present invention has specific selectivity and sensitive current response capability to nitrite and ammonia nitrogen. As an electrochemical modification material of an electrode, it is possible to improve the current response capability of the electrode to nitrite and ammonia nitrogen. The present invention uses a Ti‑MOF / Ag / CNT modified electrode as a working electrode, a saturated calomel electrode as a reference electrode, and a platinum sheet electrode as a counter electrode to electrochemically detect nitrite and ammonia nitrogen. The Ti‑MOF / Ag / CNT modified electrode realizes simultaneous detection of nitrite and ammonia nitrogen, and has high sensitivity, high accuracy and high precision for the detection of nitrite and ammonia nitrogen.

Description

Technical Field

[0001] The present invention relates to the field of detection technology, and in particular to an electrochemical sensor based on metal organic framework nanomaterials and its application in detecting nitrite and / or ammonia nitrogen. Background Art

[0002] Ammonia is a substance widely distributed in nature and is easily accumulated in domestic sewage, industrial wastewater, and agricultural production. In the environment, ammonia nitrogen is usually present in the form of non-ionized NH3 and ionized NH4. + Ammonia nitrogen exists in two forms. Ammonia nitrogen content is an important indicator in water quality monitoring. The limit for ammonia nitrogen in the "Surface Water Environmental Quality Standard" is 0.15 mg / L (about 8.33 μM), and the limit for ammonia nitrogen in the "Fishery Water Quality Standard" is 0.02 mg / L (about 1.11 μM). When ammonia nitrogen in water is excessive, it can easily cause eutrophication and affect the metabolism, respiratory system, and immune system functions of aquatic organisms, and in severe cases, cause their death. Nitrite is another important indicator in water quality monitoring. The limit for nitrite in the "Fishery Water Quality Standard" is 0.2 mg / L (about 4.35 μM). Nitrite is a substance commonly found in food additives and preservatives, as well as in the medical and agricultural fields. Excessive concentrations of nitrite can cause protein denaturation in organisms, thereby affecting the respiratory system. How to quickly, accurately and directly monitor the content of ammonia nitrogen and nitrite nitrogen in water has become a hot topic of attention and research.

[0003] Traditional detection methods, such as gas chromatography, liquid chromatography, and colorimetry, are accurate but require complex pre-treatment and specialized instruments and equipment, making them mostly suitable for laboratory use. Electrochemical sensors are a technology that has emerged in recent years. They determine the concentration of a substance by detecting the electrical signal generated when the substance undergoes an oxidation-reduction reaction. They have short detection times, high sensitivity, and significant potential for miniaturization, making them a significant advantage in the field of in-situ online detection of substances. In electrochemical sensor detection methods, the electrode is the decisive factor affecting the detection results, and electrochemical modification is achieved by imparting functional groups with specific properties to the electrode surface, thereby accelerating the electrode reaction rate and improving the electrode selectivity and sensitivity.

[0004] The existing technology (Tang Ying. Preparation and Application of Ammonia Nitrogen and Nitrite Nitrogen Electrodes [D]. Chongqing University, 2013.) uses platinum wire microelectrodes and conventional platinum wire as base electrodes, respectively. A layer of nanoparticles of platinum is deposited on the surface of the platinum wire electrode by electrochemical modification method to obtain functionalized nPt / Pt microelectrodes and functionalized nPt / Pt conventional electrodes, respectively. The functionalized nPt / Pt microelectrodes have a large electrochemical response current to ammonia nitrogen, and the detection limit of ammonia nitrogen concentration is 4.5×10 -4The detection limit of nitrite nitrogen concentration by functionalized nPt / Pt conventional electrode is 0.3×10 -4 M. Prior art (Zhang Jiaran. Research on a Water Ammonia Nitrogen Electrode Modified with Nanocomposite Materials [D]. China Agricultural University, 2018) discloses an electrode modified with Ag2O / CNTs nanocomposite materials, which has a detection limit of 8.68 μM for ammonia nitrogen. This modified electrode can detect ammonia nitrogen or nitrite, but the detection limits for ammonia nitrogen and nitrite are high and the sensitivity is low. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide an electrochemical sensor based on metal-organic framework nanomaterials and its application in detecting nitrite and / or ammonia nitrogen. The modified electrode using the metal-organic framework nanomaterials provided by the present invention as the modified material has a low detection limit for ammonia nitrogen and nitrite and high detection sensitivity.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a metal organic framework nanomaterial, comprising a reticular porous structure material and silver nanoparticles loaded on the surface and in the pores of the reticular porous structure material; the reticular porous structure material comprises a titanium metal organic framework material and carbon nanotubes.

[0008] Preferably, the mass ratio of the titanium metal organic framework material, carbon nanotubes and silver nanoparticles is (3-5): (1-2): (0.32-0.64).

[0009] The present invention provides a method for preparing the metal organic framework nanomaterial described in the above technical solution, comprising the following steps:

[0010] Titanium metal organic framework material, silver nitrate, carbon nanotubes and dimethylformamide are mixed and subjected to solvent thermal reaction to obtain the metal organic framework nanomaterial.

[0011] The present invention provides a modified electrode, comprising a base electrode and a metal organic framework nanomaterial located on the surface of the base electrode; the metal organic framework nanomaterial is the metal organic framework nanomaterial described in the above technical solution or the metal organic framework nanomaterial prepared by the preparation method described in the above technical solution.

[0012] Preferably, the base electrode comprises a glassy carbon electrode.

[0013] The present invention provides a method for preparing the modified electrode described in the above technical solution, comprising the following steps:

[0014] mixing the metal organic framework nanomaterial, polyvinyl pyrrolidone and water to obtain a chemical modification solution;

[0015] The chemical modification solution is coated on the surface of the electrode and then dried to obtain the modified electrode.

[0016] The present invention provides an electrochemical sensor comprising a three-electrode system, wherein the three-electrode system comprises a modified electrode, a saturated calomel electrode and a platinum electrode; the modified electrode is the modified electrode described in the above technical solution or the modified electrode prepared by the preparation method described in the above technical solution.

[0017] The present invention provides the use of the metal-organic framework nanomaterial described in the above technical solution, the metal-organic framework nanomaterial prepared by the preparation method described in the above technical solution, the modified electrode described in the above technical solution, or the modified electrode prepared by the preparation method described in the above technical solution in detecting nitrite and / or ammonia nitrogen.

[0018] The present invention provides a method for detecting nitrite and / or ammonia nitrogen, comprising the following steps:

[0019] The electrochemical sensor of the above technical solution is used to perform electrochemical detection on the sample liquid to obtain the peak current of the sample to be tested; the peak current of the sample to be tested includes the nitrite peak current and / or the ammonia nitrogen peak current;

[0020] The concentration of nitrite and / or ammonia nitrogen to be measured is obtained according to the peak current of the sample to be measured and the nitrite and / or ammonia nitrogen concentration-peak current standard curve.

[0021] Preferably, the electrochemical sensor further undergoes activation before use, and the activation comprises placing the electrochemical sensor in a supporting electrolyte solution for electrochemical activation.

[0022] The present invention provides a metal-organic framework nanomaterial (denoted as Ti-MOF / Ag / CNT), comprising a reticular porous structure material and silver nanoparticles loaded on the surface and within the pores of the reticular porous structure material; the reticular porous structure material comprises a titanium metal-organic framework material and carbon nanotubes. In the present invention, the titanium metal-organic framework material (Ti-MOF) is a new type of titanium carboxylate MOF material, characterized by high porosity, large specific surface area, non-toxicity, and high stability; the carbon nanotubes (CNT) have the advantages of large specific surface area, good chemical stability, high electrical conductivity, and strong catalytic ability; the silver nanoparticles loaded on the surface and within the pores of the reticular porous structure material give the metal-organic framework nanomaterial good electrical conductivity, thereby improving the catalytic performance of the metal-organic framework nanomaterial. The Ti-MOF / Ag / CNT provided by the present invention has specific selectivity and sensitive current response for nitrite and ammonia nitrogen. As an electrochemical modification material for an electrode, it can simultaneously detect nitrite and ammonia nitrogen with a low detection limit, high sensitivity, and high accuracy and precision.

[0023] The present invention provides a method for preparing the metal-organic framework nanomaterial described in the above technical solution, comprising the steps of mixing a titanium metal-organic framework material, silver nitrate, carbon nanotubes, and dimethylformamide, and conducting a solvothermal reaction to obtain the metal-organic framework nanomaterial. The preparation method provided by the present invention is simple to operate, has low production costs, and is suitable for industrial production.

[0024] The present invention provides a modified electrode (Ti-MOF / Ag / CNT modified electrode), comprising a base electrode and a metal organic framework nanomaterial located on the surface of the base electrode; the metal organic framework nanomaterial is the metal organic framework nanomaterial described in the above technical solution or the metal organic framework nanomaterial prepared by the preparation method described in the above technical solution. In the present invention, the Ti-MOF / Ag / CNT has specific selectivity for nitrite and ammonia nitrogen. Using this material as the chemical modification material of the electrode significantly enhances the electrode's response to nitrite and ammonia nitrogen, and promotes the reaction of nitrite and ammonia nitrogen (NO2 - →NO2+e - , 2NO2+H2O→NO2 - +NO3 - +2H + ,4NH4 + +4OH - +7O2 - →NO2 + +10H2O+15e - ) can simultaneously detect nitrite and ammonia nitrogen, and the detection limit of nitrite and ammonia nitrogen is low, with high sensitivity, accuracy and precision.

[0025] The present invention provides a method for preparing the modified electrode described in the above technical solution, comprising the steps of: mixing the metal-organic framework nanomaterial, polyvinyl pyrrolidone, and water to obtain a chemical modification solution; and applying the chemical modification solution to the surface of the electrode and then drying to obtain the modified electrode. The preparation method provided by the present invention is simple to operate, has low energy consumption, low production cost, and is suitable for industrial production.

[0026] The present invention uses a Ti-MOF / Ag / CNT modified electrode as a working electrode, a saturated calomel electrode as a reference electrode, and a platinum sheet electrode as a counter electrode to perform electrochemical detection of nitrite and / or ammonia nitrogen. The Ti-MOF / Ag / CNT modified electrode has a strong response ability to nitrite and ammonia nitrogen, can simultaneously detect nitrite and ammonia nitrogen, and has high sensitivity, high accuracy, and high precision in the detection of nitrite and ammonia nitrogen.

[0027] As shown in the test results of the embodiment, the bare glassy carbon electrode has no current response to sodium nitrite and ammonium chloride; the MWCNT-modified glassy carbon electrode has a current response to sodium nitrite but no current response to ammonium chloride; and the Ti-MOF / Ag / MWCNT-modified glassy carbon electrode provided by the present invention has a current response to both sodium nitrite and ammonium chloride. This indicates that the Ti-MOF / Ag / MWCNT-modified glassy carbon electrode has the ability to simultaneously detect nitrite and ammonia nitrogen. Using the electrochemical sensor provided by the present invention for electrochemical detection, the detection range of nitrite is 10-2100 μM, the minimum detection limit is 3 μM, the recovery rate of sodium nitrite is 99.72-106%, and the RSD is 0.70-3.56%. The detection range of ammonia nitrogen is 1-130 μM, the minimum detection limit is 0.3 μM, and the recovery rate of ammonia nitrogen is 97.88-103.67%, with an RSD of 0.26-2.44%. It is shown that the electrochemical sensor provided by the present invention has high sensitivity, high accuracy and high precision in detecting nitrite and ammonia nitrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the scanning electron microscopy image of Ti-MOF / Ag / MWCNT;

[0029] Figure 2 This is a series of linear voltammetric curves of sodium nitrite and ammonium chloride with different concentrations;

[0030] Figure 3 is the nitrite concentration-peak current standard curve and fitting equation;

[0031] Figure 4 is the ammonia nitrogen concentration-peak current standard curve and fitting equation;

[0032] Figure 5 The current response effect diagram of glassy carbon electrodes with different chemical decorations to a sodium nitrite-ammonium chloride mixed aqueous solution;

[0033] Figure 6 This is the specific selectivity diagram of the electrochemical sensor for nitrite and ammonia nitrogen. DETAILED DESCRIPTION

[0034] The present invention provides a metal organic framework nanomaterial, comprising a reticular porous structure material and silver nanoparticles loaded on the surface and in the pores of the reticular porous structure material; the reticular porous structure material comprises a titanium metal organic framework material and carbon nanotubes.

[0035] In the present invention, the mass ratio of the titanium metal organic framework material, carbon nanotubes and silver nanoparticles is preferably (3-5): (1-2): (0.32-0.64), more preferably (3.5-5): (1.2-2): (0.35-0.6), and further preferably (4-4.5): (1.5-1.8): (0.4-0.5).

[0036] In the present invention, the particle size of the silver nanoparticles is preferably 2 to 10 nm, more preferably 2 to 5 nm.

[0037] In the present invention, the carbon nanotubes preferably include single-walled carbon nanotubes or multi-walled carbon nanotubes (MWCNTs).

[0038] The present invention provides a method for preparing the metal organic framework nanomaterial described in the above technical solution, comprising the following steps:

[0039] Titanium metal organic framework material, silver nitrate, carbon nanotubes and dimethylformamide are mixed and subjected to solvent thermal reaction to obtain the metal organic framework nanomaterial.

[0040] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0041] In the present invention, the preparation method of the titanium metal organic framework material (denoted as Ti-MOF) preferably includes the following steps: mixing 5-[(3,5-dicarboxyphenyl)methyl]benzene-1,3-dicarboxylic acid (H4mdip), isopropyl titanate (Ti(iPrO)4) and formic acid, and performing a coordination reaction to obtain the titanium metal organic framework material. In the present invention, the molar ratio of the 5-[(3,5-dicarboxyphenyl)methyl]benzene-1,3-dicarboxylic acid and isopropyl titanate is preferably (0.58-1.25):(1.35-2.7), more preferably (0.7-1.2):(1.5-2.5), and even more preferably (0.8-1):(2-2.2). In the present invention, the volume ratio of the amount of 5-[(3,5-dicarboxyphenyl)methyl]benzene-1,3-dicarboxylic acid to formic acid is preferably 0.01 to 0.13 mmol:1 mL, more preferably 0.05 to 0.1 mmol:1 mL. The present invention has no particular limitation on the mixing method, as long as the raw materials can be mixed evenly, such as stirring and mixing; the order of mixing is preferably: mixing 5-[(3,5-dicarboxyphenyl)methyl]benzene-1,3-dicarboxylic acid and formic acid, and adding isopropyl titanate dropwise to the resulting mixture; the present invention has no particular limitation on the speed of the addition, and it can be added dropwise. In the present invention, the temperature of the coordination reaction is preferably 150 to 180°C, more preferably 170 to 180°C. In a specific embodiment of the present invention, the coordination reaction is preferably carried out under reflux conditions; the time of the coordination reaction is preferably 12 to 24 hours, more preferably 15 to 20 hours.

[0042] After completing the coordination reaction, the present invention preferably further includes post-treatment, and the post-treatment preferably includes: cooling the coordination reaction liquid to room temperature and then separating the solid and liquid, washing the obtained solid product with alcohol and then drying it to obtain a titanium metal organic framework material. The present invention has special restrictions on the cooling method, and a cooling method well known to those skilled in the art can be adopted, such as natural cooling. The present invention has no special restrictions on the solid-liquid separation, and a solid-liquid separation method well known to those skilled in the art can be adopted, such as filtration, suction filtration or centrifugal separation. In the present invention, the alcohol washing is preferably ethanol washing, and the present invention has no special restrictions on the alcohol washing, as long as it can remove DMF in the solid product. In the present invention, the drying temperature is preferably 60-80°C, more preferably 60-65°C; the present invention has no special restrictions on the drying time, and it can be dried to constant weight.

[0043] After obtaining the titanium metal organic framework material, the present invention mixes the titanium metal organic framework material, silver nitrate, carbon nanotubes and dimethylformamide, and performs a solvent thermal reaction to obtain the metal organic framework nanomaterial (denoted as Ti-MOF / Ag / CNT).

[0044] In the present invention, the mass ratio of the titanium metal organic framework material, carbon nanotubes, and silver nitrate is preferably (3-5): (1-2): (0.5-1), more preferably (3.5-5): (1.2-2): (0.6-0.9), and even more preferably (4-4.5): (1.5-1.8): (0.7-0.8). In the present invention, the ratio of the mass of the titanium metal organic framework material to the volume of dimethylformamide is preferably 3-5 mg: 1 mL, more preferably 4 mg: 1 mL.

[0045] The present invention has no particular limitation on the mixing method, as long as the raw materials can be mixed evenly, such as stirring and mixing.

[0046] In the present invention, the temperature of the solvent thermal reaction is preferably 50-80°C, more preferably 60-70°C; the time of the solvent thermal reaction is preferably 3-5h, more preferably 4h; and the hydrothermal reaction is preferably carried out in the dark.

[0047] After the solvent reaction is completed, the present invention preferably further includes post-treatment. The post-treatment steps are preferably the same as the post-treatment steps in the preparation process of the titanium metal organic framework material, and will not be repeated here.

[0048] The present invention provides a modified electrode comprising a base electrode and a metal organic framework nanomaterial located on the surface of the base electrode; the metal organic framework nanomaterial is the metal organic framework nanomaterial described in the above technical solution or the metal organic framework nanomaterial prepared by the preparation method described in the above technical solution. In the present invention, the base electrode preferably comprises a glassy carbon electrode. In the present invention, the loading amount of the metal organic framework nanomaterial in the modified electrode is preferably 0.005 to 0.015 mg / m 2 , more preferably 0.007 to 0.014 mg / m 2 , more preferably 0.01 to 0.012 mg / m 2 .

[0049] The present invention provides a method for preparing the modified electrode described in the above technical solution, comprising the following steps:

[0050] mixing the metal organic framework nanomaterial, polyvinyl pyrrolidone and water to obtain a chemical modification solution;

[0051] The chemical modification solution is coated on the surface of the electrode and then dried to obtain the modified electrode.

[0052] The present invention mixes the metal-organic framework nanomaterial, polyvinyl pyrrolidone and water to obtain a chemical modification solution. In the present invention, the mass ratio of the metal-organic framework nanomaterial to polyvinyl pyrrolidone is preferably 1: (1 to 1.5), more preferably 1: (1 to 1.2). In the present invention, the mass ratio of the metal-organic framework nanomaterial to water is preferably 1: (1 to 1.5), more preferably 1: 1. In the present invention, the mixing is preferably: the metal-organic framework nanomaterial and polyvinyl pyrrolidone are mixed and then dispersed in water. The present invention has no special limitation on the mixing method, as long as the raw materials can be mixed evenly, such as stirring and mixing.

[0053] After obtaining the chemical modification solution, the present invention applies the chemical modification solution to the surface of the electrode and then dries it to obtain the modified electrode. In the present invention, the electrode is preferably polished to a smooth surface before use. In the present invention, the coating method is preferably dropwise application. In the present invention, the drying temperature is preferably room temperature (25°C). There is no particular limitation on the drying time; drying to constant weight is sufficient.

[0054] The present invention provides an electrochemical sensor comprising a three-electrode system, wherein the three-electrode system comprises a modified electrode, a saturated calomel electrode and a platinum electrode; the modified electrode is the modified electrode described in the above technical solution or the modified electrode prepared by the preparation method described in the above technical solution.

[0055] The present invention provides the use of the metal-organic framework nanomaterial described in the above technical solution, the metal-organic framework nanomaterial prepared by the preparation method described in the above technical solution, the modified electrode described in the above technical solution, or the modified electrode prepared by the preparation method described in the above technical solution in detecting nitrite and / or ammonia nitrogen.

[0056] The present invention provides a method for detecting nitrite and / or ammonia nitrogen, comprising the following steps:

[0057] The electrochemical sensor of the above technical solution is used to perform electrochemical detection on the sample liquid to obtain the peak current of the sample to be tested; the peak current of the sample to be tested includes the nitrite peak current and / or the ammonia nitrogen peak current;

[0058] The concentration of nitrite and / or ammonia nitrogen to be measured is obtained according to the peak current of the sample to be measured and the nitrite and / or ammonia nitrogen concentration-peak current standard curve.

[0059] The present invention utilizes the electrochemical sensor described in the above technical solution to perform electrochemical detection on the sample liquid to obtain the peak current of the sample to be tested; the peak current of the sample to be tested includes nitrite peak current and / or ammonia nitrogen peak current.

[0060] In the present invention, the electrochemical sensor preferably further includes activation before use, and the activation preferably includes: placing the electrochemical sensor in a supporting electrolyte solution, performing electrochemical activation, and obtaining an activated modified electrode. In the present invention, the supporting electrolyte in the supporting electrolyte solution is preferably sodium sulfate, and the concentration of the supporting electrolyte solution is preferably 0.05 to 0.1 mol / L, more preferably 0.1 mol / L. In the present invention, the electrochemical activation is preferably performed using an electrochemical workstation, and the electrochemical workstation is preferably a CHI660 electrochemical workstation. In the present invention, the activation is preferably linear voltammetry activation, and the working parameters of the linear voltammetry activation include: the scanning voltage is preferably 0 to 1.2 V, the scanning speed is preferably 50 mV / s, and the sensitivity is preferably 1×10 -4 μA. The present invention has no special limitation on the number of scans, and the scan can be performed until the linear voltammetric curve tends to be stable. The specific number of scans is preferably 3 to 4 times.

[0061] In the present invention, the sample liquid to be tested preferably includes nitrite and / or ammonia nitrogen, and the sample liquid to be tested is preferably a supporting electrolyte solution of nitrite and / or ammonia nitrogen; the present invention has no special limitation on the source of the sample liquid to be tested, and a water body containing nitrite and / or ammonia nitrogen can be used, such as lake water or tap water. In the present invention, the concentration of nitrite in the sample liquid to be tested is preferably 5 to 2100 μM (i.e. μmol / L), more preferably 20 to 1000 μM, and further preferably 50 to 500 μM; the source of nitrite preferably includes nitrite, more preferably sodium nitrite. In the present invention, the ammonia nitrogen (NH4 + ) is preferably 1 to 130 μM, more preferably 1.5 to 100 μM, and further preferably 2 to 52 μM; the ammonia nitrogen is preferably an ammonium salt, more preferably comprising ammonium chloride and / or ammonium sulfate. In the present invention, the concentration of the supporting electrolyte in the sample solution to be tested is preferably 0.05 to 0.1 mol / L, more preferably 0.1 mol / L. In the present invention, the sample to be tested is preferably filtered before testing, and the filtration is preferably performed using filter paper.

[0062] In a specific embodiment of the present invention, the electrochemical sensor described in the above technical solution is used to perform electrochemical detection on the sample liquid to obtain the peak current of the sample to be tested, preferably including: inserting the activated modified electrode into the sample liquid to be tested, using an activated three-electrode system to obtain a linear voltammetric curve, and obtaining the peak current of the sample to be tested based on the linear voltammetric curve.

[0063] After obtaining the peak current of the sample to be tested, the present invention obtains the concentration of the nitrite and / or ammonia nitrogen to be tested according to the peak current of the sample to be tested and a nitrite and / or ammonia nitrogen concentration-peak current standard curve.

[0064] In the present invention, the method for obtaining the concentration-peak current standard curve preferably includes the following steps: preparing a series of standard solutions; placing the modified electrode in the series of standard solutions, performing electrochemical detection using an electrochemical sensor to obtain a series of linear voltammetric curves, and drawing a nitrite concentration-peak current standard curve based on the series of linear voltammetric curves, with the nitrite concentration as the horizontal coordinate and the nitrite peak current value of the series of linear voltammetric curves as the vertical coordinate; and drawing an ammonia nitrogen concentration-peak current standard curve with the ammonia nitrogen concentration as the horizontal coordinate and the ammonia nitrogen peak current value of the series of linear voltammetric curves as the vertical coordinate.

[0065] In the present invention, the series of standard solutions are preferably a series of nitrite standard solutions, a series of ammonia nitrogen standard solutions or a series of nitrite-ammonia nitrogen mixed standard solutions; the source of nitrite in the series of nitrite standard solutions and the series of nitrite-ammonia nitrogen mixed standard solutions is preferably nitrite, more preferably sodium nitrite; the concentration of nitrite in the series of nitrite standard solutions and the series of nitrite-ammonia nitrogen mixed standard solutions is independently preferably 0 to 2100 μM (μmol / L), specifically preferably 0, 10, 100, 200, 300, 400, 500, 600, 700, 1100, 1200, 1300, 1500, 1700, 1900 and 2100 μM. In the present invention, the source of ammonia nitrogen in the series of ammonia nitrogen standard solutions and the series of nitrite-ammonia nitrogen mixed standard solutions is preferably an ammonium salt, more preferably ammonium chloride; the concentration of ammonia nitrogen in the series of ammonia nitrogen standard solutions and the series of nitrite-ammonia nitrogen mixed standard solutions is independently preferably 0 to 130 μM, specifically preferably 0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 and 130 μM. In the present invention, the concentration of the supporting electrolyte in the series of nitrite standard solutions, the series of ammonia nitrogen standard solutions or the series of nitrite-ammonia nitrogen mixed standard solutions is independently preferably 0.05 to 0.1 mol / L, more preferably 0.1 mol / L.

[0066] In the present invention, the electrochemical sensor is preferably activated before use. The activation method is preferably the same as the above activation method and will not be described in detail here. In the present invention, the detection working parameters include: using linear voltammetry, the scanning voltage is preferably 0-1.2V, the scanning speed is preferably 50mV / s, and the sensitivity is preferably 1×10 -4 μA.

[0067] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0068] Example 1

[0069] (1) Synthesis of metal-organic framework nanomaterials:

[0070] H4mdip (0.58 mmol, CAS: 10397-52-1) and formic acid (10) were mixed evenly, Ti(iPrO)4 (1.35 mmol) was added dropwise, stirred and dispersed evenly, heated under reflux for 20 h, cooled to room temperature, filtered, and the obtained solid component was washed with ethanol and dried at 60 ° C to constant weight to obtain titanium metal organic framework material (Ti-MOF);

[0071] Ti-MOF, AgNO3 and MWCNT were mixed uniformly in a mass ratio of 5:1:1, and then mixed uniformly with DMF. The resulting mixture was heated in the dark at 60°C for 4 h, cooled to room temperature, filtered, and the resulting solid product was washed with ethanol and dried at 60°C to constant weight to obtain metal organic framework nanomaterials (Ti-MOF / Ag / MWCNT), wherein the usage ratio of Ti-MOF to DMF was 5 mg:1 mL.

[0072] Figure 1 This is the SEM image of Ti-MOF / Ag / MWCNT, where the blocks are Ti-MOF, the tubes are MWCNTs, and the white dots are Ag nanoparticles.

[0073] (2) Preparation of Ti-MOF / Ag / MWCNT modified glassy carbon electrode

[0074] Ti-MOF / Ag / MWCNT and polyvinyl pyrrolidone were mixed in a 1:1 mass ratio and uniformly dispersed in deionized water to obtain a chemical modification solution. A glassy carbon electrode was polished until smooth, and 6 μL of the chemical modification solution was dropwise added to the polished surface of the glassy carbon electrode. The electrode was dried at 25°C to a constant weight to obtain a Ti-MOF / Ag / MWCNT-modified glassy carbon electrode.

[0075] (3) Construction of electrochemical sensors

[0076] The Ti-MOF / Ag / MWCNT modified glassy carbon electrode (working electrode), saturated calomel electrode (reference electrode) and platinum electrode (counter electrode) prepared in step (2) are used to construct a three-electrode system for the subsequent detection of nitrite and ammonia nitrogen.

[0077] (4) Activation of electrochemical sensors

[0078] The electrochemical sensor was placed in a 0.1 mol / L sodium sulfate solution and activated by linear voltammetry using a CHI660 electrochemical workstation to obtain an activated electrochemical sensor. The linear voltammetry activation parameters were as follows: scanning voltage of 0-1.2 V, scanning speed of 50 mV / s, and sensitivity of 1×10 -4 μA, scan until the linear voltammetric curve tends to be stable, the specific number of scans is 3 to 4 times.

[0079] Example 2

[0080] Drawing of concentration-peak current standard curve

[0081] A series of sodium nitrite-ammonium chloride mixed standard solutions were prepared, wherein the concentrations of sodium nitrite were 0, 10, 100, 200, 300, 400, 500, 600, 700, 1100, 1200, 1300, 1500, 1700, 1900 and 2100 μM, respectively; the concentrations of ammonia nitrogen were 0, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 and 130 μM, respectively; the concentrations of sodium nitrite and ammonium chloride in the series of sodium nitrite-ammonium chloride mixed standard solutions showed the same trend of change; the concentration of sodium sulfate was 0.1 mol / L, and the solvent was pure water.

[0082] The activated Ti-MOF / Ag / MWCNT modified glassy carbon electrode obtained in Example 1 was placed in a series of sodium nitrite standard solutions, and electrochemical detection was performed using an activated three-electrode washing system to obtain a series of linear voltammetric curves. According to the series of linear voltammetric curves, a nitrite concentration-peak current standard curve was drawn with the nitrite concentration as the abscissa and the peak current value of the series of linear voltammetric curves as the ordinate; wherein the working parameters of the detection were: linear voltammetry, a scanning voltage of 0-1.2 V, a scanning speed of 50 mV / s, and a sensitivity of 1×10 -4 μA;

[0083] The series of linear voltammetric curves of sodium nitrite and ammonium chloride with different concentrations are as follows: Figure 2 The peak current values of sodium nitrite and ammonium chloride at different concentrations are shown in Table 1. The nitrite concentration-peak current standard curve and fitting equation are shown in Figure 3 As shown, the ammonia nitrogen concentration-peak current standard curve and fitting equation are as follows Figure 4 shown.

[0084] The standard curves of nitrite concentration and peak current are shown in formula (1) to formula (2), and the standard curve of ammonia nitrogen concentration and peak current is shown in formula (3):

[0085] y = -0.0412x - 1.4784, where 0 ≤ x ≤ 500 (unit: μM), R 2 = 0.9791 Equation (1);

[0086] y = -0.0269x - 20.181, where 500 < x ≤ 2100 (unit: μM), R 2 = 0.9954 Equation (2);

[0087] y = -0.1051x - 0.1136, R 2 = 0.9816 Equation (3).

[0088] Table 1 Peak current values of sodium nitrite and ammonium chloride at different concentrations

[0089]

[0090] From Table 1 and Figures 2 to 4 it can be seen that the detection range of ammonia nitrogen is 1 - 130 μM, and the lowest detection limit is 0.3 μM; the detection range of nitrite is 10 - 2100 μM, and the lowest detection limit is 3 μM. It shows that the electrochemical sensor provided by the present invention has high sensitivity for the detection of nitrite and ammonia nitrogen. Among them, the lowest detection limit = 3sd / s, where sd represents the standard deviation of the blank sample, and s is the slope of the standard curve.

[0091] Example 3

[0092] (1) Place the activated Ti-MOF / Ag / MWCNT modified glassy carbon electrode in a 50 mL lake water sample filtered by filter paper, and use the activated three-electrode washing system obtained in Example 1 for electrochemical detection to obtain the linear voltammetry curves of nitrite and ammonia nitrogen. Respectively obtain the corresponding nitrite peak current value and ammonia nitrogen peak current value according to the linear voltammetry curves of nitrite and ammonia nitrogen, and substitute the nitrite peak current value and ammonia nitrogen peak current value into the corresponding nitrite concentration-peak current standard curve and ammonia nitrogen concentration-peak current standard curve respectively to calculate the corresponding nitrite concentration and ammonia nitrogen concentration. Among them, the working parameters of the detection: adopt linear voltammetry, the scanning voltage is 0 - 1.2 V, the scanning speed is 50 mV / s, and the sensitivity is 1×10 -4 μA, and obtain that the concentration of NO2 - in the lake water sample is 0 μM, and the concentration of NH4 + is 2 μM.

[0093] (2) Test the tap water sample according to step (1), and the difference from step (1) is only that the lake water sample is replaced with the tap water sample.

[0094] (3) The detection effect of the electrochemical sensor on nitrite and ammonia nitrogen was verified using the standard addition method. The specific steps are as follows: NaNO2, NH4Cl and Na2SO4 were added to the lake water sample and tap water after filter paper filtration, respectively. The addition levels of NaNO2 were 0, 50, 250 and 500 μM, and the addition levels of NH4Cl were 0, 10, 30 and 50 μM, respectively. The concentration of Na2SO4 was 0.1 mol / L. The test was carried out according to the method of step (1). The test results are shown in Table 2:

[0095] Table 2 Standard addition method test results (n=3)

[0096]

[0097]

[0098] As can be seen from Table 2, when the electrochemical sensor provided by the present invention is used for electrochemical detection, the recovery rate of sodium nitrite is 99.72-106%, and the RSD is 0.70-3.56%; the recovery rate of ammonia nitrogen is 97.88-103.67%, and the RSD is 0.26-2.44%. This shows that the electrochemical sensor provided by the present invention has high accuracy and precision in detecting nitrite and ammonia nitrogen, and the electrochemical sensor can be used to detect nitrite content and ammonia nitrogen content in the environment.

[0099] Comparative Example 1

[0100] MWCNTs and polyvinyl pyrrolidone were mixed in a 1:1 mass ratio and evenly dispersed in deionized water to obtain a chemical modification solution. The glassy carbon electrode was polished, and 6 μL of the chemical modification solution was dropwise added to the polished surface of the glassy carbon electrode. The electrode was dried at 25°C to a constant weight to obtain a MWCNT-modified glassy carbon electrode.

[0101] Example 4

[0102] Detection performance of glassy carbon electrodes with different chemical decorations

[0103] The working electrodes were: a polished bare glassy carbon electrode, a MWCNT-modified glassy carbon electrode, and the Ti-MOF / Ag / MWCNT-modified glassy carbon electrode prepared in Example 1.

[0104] Using 0.1 mol / L sodium sulfate solution as the supporting electrolyte, the three working electrodes were placed in a sodium nitrite-ammonium chloride mixed solution (sodium nitrite concentration was 250 μM, ammonium chloride concentration was 5 μM, and sodium sulfate concentration was 0.1 mol / L). Electrochemical detection was performed using a three-electrode system, and linear voltammetric curves of glassy carbon electrodes with different chemical modifications were obtained. The detection parameters were linear voltammetry, a sweep voltage of 0-1.2 V, a sweep rate of 50 mV / s, and a sensitivity of 1×10 -4 μA.

[0105] Figure 5 The current response effect of glassy carbon electrodes with different chemical modifications to sodium nitrite-ammonium chloride aqueous solution is shown in the figure. Figure 5 As can be seen, the bare glassy carbon electrode has no current response to sodium nitrite and ammonium chloride; the MWCNT-modified glassy carbon electrode has a current response to sodium nitrite but no current response to ammonium chloride; and the Ti-MOF / Ag / MWCNT-modified glassy carbon electrode has a current response to both sodium nitrite and ammonium chloride. This indicates that the Ti-MOF / Ag / MWCNT-modified glassy carbon electrode has the ability to simultaneously detect nitrite and ammonia nitrogen.

[0106] Example 5

[0107] The activated Ti-MOF / Ag / MWCNT modified glassy carbon electrode obtained in Example 1 was placed in a water sample to be tested that was filtered through filter paper. Electrochemical detection was performed using the activated three-electrode washing system obtained in Example 1 to obtain linear voltammetric curves of different analytes, as shown in Figure 6. Among them, the water samples to be tested (a total of 7 samples) are interferor solutions (a total of 6 samples), interferor-NaNO2-NH4Cl-Na2SO4 aqueous solutions, wherein the interferor solutions are KNO3-Na2SO4 aqueous solutions, KCl-Na2SO4 aqueous solutions, CaCl2-Na2SO4 aqueous solutions, urea-Na2SO4 aqueous solutions, glucose-Na2SO4 aqueous solutions and Na2CO3-Na2SO4 aqueous solutions; the concentration of NaNO2 in the interferor-NaNO2-NH4Cl-Na2SO4 aqueous solution is 200μM, and the concentration of NH4Cl is 50μM; the concentrations of KNO3, KCl, CaCl2, urea, glucose and Na2CO3 in the water samples to be tested are all 500μM, and the concentration of Na2SO4 is all 0.1mol / L. The working parameters of the detection are as follows: linear voltammetry is adopted, the scanning voltage is 0-1.2V, the scanning speed is 50mV / s, and the sensitivity is 1×10 -4 μA.

[0108] Depend on Figure 6It can be seen that the interfering substances (KNO3, KCl, CaCl2, urea, glucose and Na2CO3) do not generate a response current, indicating that the Ti-MOF / Ag / MWCNT modified electrode provided by the present invention can achieve specific and selective detection of nitrite and ammonia nitrogen.

[0109] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A metal organic framework nanomaterial, characterized in that: It comprises a mesh porous structure material and silver nanoparticles loaded on the surface and in the pores of the mesh porous structure material; the mesh porous structure material comprises a titanium metal organic framework material and carbon nanotubes; The mass ratio of the titanium metal organic framework material, carbon nanotubes and silver nanoparticles is (3-5): (1-2): (0.32-0.64).

2. The method for preparing the metal organic framework nanomaterial according to claim 1, characterized in that: The following steps are involved: Titanium metal organic framework material, silver nitrate, carbon nanotubes and dimethylformamide are mixed and subjected to solvent thermal reaction to obtain the metal organic framework nanomaterial.

3. A modified electrode, characterized in that It comprises a base electrode and a metal organic framework nanomaterial located on the surface of the electrode; the metal organic framework nanomaterial is the metal organic framework nanomaterial according to claim 1 or the metal organic framework nanomaterial prepared by the preparation method according to claim 2.

4. The modified electrode according to claim 3, characterized in that The base electrode includes a glassy carbon electrode.

5. The method for preparing the modified electrode according to claim 3 or 4, characterized in that: The following steps are involved: mixing the metal organic framework nanomaterial, polyvinyl pyrrolidone and water to obtain a chemical modification solution; The chemical modification solution is coated on the surface of the electrode and then dried to obtain the modified electrode.

6. An electrochemical sensor comprising a three-electrode system, characterized in that: The three-electrode system comprises a modified electrode, a saturated calomel electrode and a platinum electrode; the modified electrode is the modified electrode according to claim 3 or 4 or the modified electrode prepared by the preparation method according to claim 5.

7. Use of the metal-organic framework nanomaterial according to claim 1, the metal-organic framework nanomaterial obtained by the preparation method according to claim 2, the modified electrode according to claim 3 or 4, or the modified electrode obtained by the preparation method according to claim 5 in detecting nitrite and / or ammonia nitrogen.

8. A method for detecting nitrite and / or ammonia nitrogen, characterized in that: The following steps are involved: The electrochemical sensor according to claim 6 is used to perform electrochemical detection on the sample solution to obtain a peak current of the sample to be tested; the peak current of the sample to be tested includes a nitrite peak current and / or an ammonia nitrogen peak current; The concentration of nitrite and / or ammonia nitrogen to be measured is obtained according to the peak current of the sample to be measured and the nitrite and / or ammonia nitrogen concentration-peak current standard curve.

9. The detection method according to claim 8, characterized in that The electrochemical sensor further comprises activation before use, and the activation comprises: placing the electrochemical sensor in a supporting electrolyte solution for electrochemical activation.

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