Preparation method of two-dimensional cnts / mofs nanosheet composite and nitrite electrochemical sensor

Abstract

The application belongs to the technical field of electrochemical sensors, and discloses a two-dimensional CNTs / MOFs (carbon nanotube / metal organic framework) nanosheet composite material and a preparation method of a nitrite electrochemical sensor. Ligands are carried by CNTs, two-dimensional layered MOFs sheets are formed between the CNTs through one-step hydrothermal method, and the two-dimensional layered MOFs sheets are used as electrode materials and applied to the nitrite electrochemical sensor. The two-dimensional layered CNTs skeleton nanosheets have more exposed active sites than traditional three-dimensional MOFs materials, and the CNTs skeleton greatly improves the charge transport capacity of the material, thereby effectively improving the sensing performance of nitrite. The nitrite electrochemical sensor based on the CNTs skeleton MOFs nanosheet material has the advantages of fast response, high precision, wide linear range, low detection limit and low cost, and can be used for rapid and accurate detection of nitrite.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrochemical sensors, and relates to a preparation method of a two-dimensional CNTs / MOFs nanosheet composite material, a preparation method of a nitrite electrochemical sensor, and application of the nitrite electrochemical sensor in nitrite electrochemical detection. BACKGROUND

[0002] Nitrite is widely used as a food additive in pickled vegetables and cooked food, but its use is strictly limited because the harm caused by nitrite is increasingly valued by people, and many countries have therefore introduced relevant laws and regulations to control the content of nitrite in the environment and food products.

[0003] In addition, nitrite is a compound closely related to the field of corrosion and has been widely used as an inhibitor in closed water circulation systems, but at a certain concentration, it can accelerate the corrosion behavior of materials. When the amount of nitrite inhibitor is above the critical concentration, a dense passivation film can be formed on the surface of steel, and when the amount is insufficient, it can promote the corrosion of steel, especially pitting corrosion. The critical concentration increases with the increase of the concentrations of chloride ions and sulfate in water. Generally, the content of nitrite in a closed water circulation system is higher than 300 mg / L-500 mg / L. Therefore, the detection of nitrite in water environmental samples is of great significance for the safe use of metal materials.

[0004] At present, spectroscopic methods, chromatographic methods and electrochemical sensors have been widely used in the analysis and detection of nitrite. However, traditional photometric methods and chromatographic methods, although the results are relatively accurate, have the disadvantages of long detection period, complex procedure, numerous reagents required, and limited application value. Electrochemical methods have gradually become an important means for monitoring nitrite in the fields of food and environment due to their simple operation, low cost, small size, rapidness, high sensitivity and real-time monitoring. However, the current electrochemical sensors for nitrite have the problems of narrow linear range, high detection limit, complex preparation and high cost.

[0005] Two-dimensional materials have the advantages of large specific surface area, more active sites and higher catalytic activity. At present, the application of two-dimensional materials in nitrite sensors mainly focuses on graphene, transition metal sulfides and metal oxides, but there are almost no direct use of metal-organic framework (MOFs) materials as electrode materials for nitrite sensors. At present, the synthesis of MOFs is mostly limited to polyhedrons such as spheres, hexahedrons, octahedrons and dodecahedrons, and two-dimensional MOFs are rarely synthesized. Moreover, it is even rarer to use two-dimensional MOFs for nitrite sensing applications. The common synthesis method of two-dimensional MOFs has low yield and complicated operation. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a large-scale preparation method of a two-dimensional CNTs / MOFs (carbon nanotube / metal organic framework) nanosheet composite material, a preparation method of a two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor, and application of the nitrite electrochemical sensor in nitrite electrochemical detection. The two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor has an extremely wide linear range and a lower detection limit, is simple to prepare and low in cost.

[0007] The present application is realized by the following technical solutions:

[0008] A method for large-scale preparation of a two-dimensional CNTs / MOFs nanosheet composite material, the method comprising:

[0009] (1) Covalent functionalization of CNTs: a certain amount of CNTs and 4-substituted aniline are mixed, a certain amount of isoamyl nitrite is added, and heating and stirring are started for a certain time to obtain a paste, the paste is diluted with DMF (N,N-dimethylformamide) and filtered through a PTFE (polytetrafluoroethylene) membrane, the solid collected by filtration is dispersed in DMF by ultrasonic treatment, and then filtered to obtain purified functionalized carbon nanotubes CNTs-PhCOOH (carboxylated carbon nanotubes);

[0010] (2) Preparation of a two-dimensional CNTs / MOFs nanosheet composite material:

[0011] A certain amount of CNTs-PhCOOH prepared in step (1) is dispersed in DMF and ultrasonically treated for a certain time to obtain a completely dispersed solution a;

[0012] A certain amount of MOFs coordination center ions is dissolved in deionized water and added dropwise to the solution a, the mixed solution is sealed and heated in an oven, the reaction mixture is cooled to room temperature, washed in deionized water, and dried in a vacuum oven to obtain a two-dimensional CNTs / MOFs nanosheet composite material. Compared with the harsh preparation conditions of two-dimensional MOFs in the prior art, i.e., peeling two-dimensional MOFs from three-dimensional MOFs, the method provided by the present application directly forms two-dimensional MOFs on the basis of one-dimensional carbon nanotubes, which breaks away from the original preparation conditions and has the potential to realize large-scale preparation.

[0013] Further, the specific method of step (1) is: a certain amount of CNTs and 4-substituted aniline is added to a flask equipped with a reflux condenser and a magnetic stirring rod; after a certain amount of isoamyl nitrite is carefully and slowly added by a syringe, heating and vigorous stirring of the paste is started; after 20-50 min, the paste is diluted with DMF and filtered through a PTFE membrane, and the collected solid is dispersed in DMF by ultrasonic treatment, then filtered to obtain purified functionalized carbon nanotubes CNTs-PhCOOH;

[0014] wherein the addition amount of CNTs is 0.1-0.2 g, the addition amount of 4-substituted aniline is 0.4-0.8 g; the addition amount of isoamyl nitrite is 0.5-0.7 mL, the heating temperature is 50-70℃, and the heating and stirring time is 30-60 min; the pore size range of the PTFE membrane is 0.3-0.8 μm; and the ultrasonic condition is ultrasonic treatment at room temperature for 20-30 min.

[0015] Further, in step (2), the density of CNTs-PhCOOH in solution a is 5-10 mg / mL.

[0016] The mass ratio of the MOFs coordination center s-PhCOOH to the metal ion is (1-1.5):2.

[0017] wherein the mixed solution is heated in an oven at 40-50℃ for 24-48 h, and washed in deionized water for 5-8 times.

[0018] Further, in step (2), the MOFs coordination center ion is a metal ion with catalytic activity, including Ni, Co, Ce, Fe, and Cu metal ions.

[0019] A preparation method of a two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor, which is prepared by using the two-dimensional CNTs / MOFs nanosheet composite material, and the preparation of the two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor comprises the following steps:

[0020] (1) the substrate is cleaned / polished and then used;

[0021] (2) dilute the Nafion solution with ethanol to a certain concentration, mix a certain amount of Nafion solution and two-dimensional CNTs / MOFs nanosheet composite material, drop coat on the surface of the substrate electrode, and dry in an oven to obtain a two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor.

[0022] Further, in step (1), the substrate includes one of a nano-porous gold needle, a glassy carbon electrode, carbon paper, a platinum sheet, and a gold sheet; and the above-mentioned collective material is stable and has good conductivity.

[0023] Further, in step (2), the Nafion solution is diluted with ethanol to a mass fraction of 0.5-1%; and dried in an oven at 40-60°C (preferably 50°C).

[0024] The application of the two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor, the two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor prepared by the above method is used as a working electrode, Ag / AgCl is used as a reference electrode, and platinum wire is used as a counter electrode to form a three-electrode system, and the nitrite is electrochemically detected.

[0025] Further, in the electrochemical detection of the nitrite, a differential pulse voltammetry method is used.

[0026] Further, in the electrochemical detection of the nitrite, an electrolyte is 0.1M, and a pH value is 7.0 phosphate buffer solution.

[0027] The beneficial technical effects of the application are as follows:

[0028] The application provides a large-scale preparation method of a two-dimensional CNTs / MOFs nanosheet composite material, a ligand is carried by CNTs, two-dimensional layered MOFs sheets are formed between the CNTs by a one-step hydrothermal method for the first time, a two-dimensional CNTs / MOFs nanosheet composite material is prepared, and the two-dimensional CNTs / MOFs nanosheet composite material is applied to a nitrite electrochemical sensor as an electrode material. In the two-dimensional CNTs / MOFs nanosheet composite material, the two-dimensional layered CNTs skeleton nanosheet has more exposed active sites than traditional three-dimensional MOFs materials, and the CNTs skeleton greatly improves the charge transport capacity of the material, thereby effectively improving the sensing performance of the nitrite.

[0029] The nitrite electrochemical sensor based on the CNTs skeleton MOFs nanosheet material has the advantages of fast response, high precision, wide linear range, low detection limit, and low cost, and can be used for rapid and accurate detection of nitrite. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The scanning electron microscope schematic diagram of the two-dimensional CNTs / MOFs nanosheet composite material with Ce as a coordination center metal ion provided for the embodiment of the application is shown in the figure;

[0031] Figure 2 The cyclic voltammogram schematic diagram of the nitrite electrochemical sensor prepared by taking the two-dimensional CNTs / Ce-MOFs nanosheet as an electrode material in a 0.10M, pH=7.0 phosphate buffer solution is shown in the figure;

[0032] Figure 3aA schematic diagram of a linear relationship of the nitrite electrochemical sensor prepared by using the two-dimensional CNTs / Ce-MOFs nanosheet as the electrode material in the 0.10M, pH=7.0 phosphate buffer solution;

[0033] Figure 3b A schematic diagram of a linear relationship of the nitrite electrochemical sensor prepared by using the two-dimensional CNTs / Ce-MOFs nanosheet as the electrode material in the 0.10M, pH=7.0 phosphate buffer solution;

[0034] Figure 4 A schematic diagram of a linear relationship of the nitrite electrochemical sensor prepared by using the two-dimensional CNTs / Ce-MOFs nanosheet as the electrode material in the 0.10M, pH=7.0 phosphate buffer solution;

[0035] Figure 5 A schematic diagram of an anti-interference curve of the nitrite electrochemical sensor prepared by using the two-dimensional CNTs / Ce-MOFs nanosheet as the electrode material in the 0.10M, pH=7.0 phosphate buffer solution. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0037] On the contrary, the present application covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present application as defined by the claims. Further, in order to make the public have a better understanding of the present application, some specific details are described in detail in the following detailed description of the present application. The present application can also be completely understood without the description of these details by those skilled in the art.

[0038] In view of the technical problems such as narrow linear range, high detection limit and high price of the nitrite sensor on the market, the present application provides a method for large-scale preparation of two-dimensional CNTs / MOFs nanosheet composite material and a preparation method of two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor, and the two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor is applied to electrochemical detection of nitrite.

[0039] A method for large-scale preparation of two-dimensional CNTs / MOFs nanosheet composite material, characterized in that the method comprises:

[0040] (1) A certain amount of CNTs and 4-substituted aniline are mixed, a certain amount of isoamyl nitrite is added after heating and stirring for a certain time to obtain a paste, the paste is diluted with DMF and filtered through a PTFE membrane, the solid collected by filtration is dispersed in DMF by ultrasonic treatment, and then filtered to obtain purified functionalized carbon nanotubes CNTs-PhCOOH (carboxylated carbon nanotubes).

[0041] Specifically, 0.2g CNTs and 0.8g 4-substituted aniline are added to a flask equipped with a reflux condenser and a magnetic stirring rod; after carefully and slowly adding isoamyl nitrite 0.7mL by syringe, heating (heating temperature is 60℃) and stirring the paste vigorously are started; after 50min, the paste is diluted with DMF and filtered through a PTFE membrane, the collected solid is dispersed in DMF by ultrasonic treatment, and then filtered 5 times to obtain purified functionalized carbon nanotubes CNTs-PhCOOH;

[0042] (2) Preparation of two-dimensional CNTs / Ce-MOFs nanosheet composite material:

[0043] 1) 0.2g of CNTs-PhCOOH prepared in step (1) is weighed and dispersed in 20mL DMF and ultrasonically treated for 60min to obtain a solution a;

[0044] 2) 250mg CeNO3·6H2O is dissolved in 10mL deionized water, added dropwise to solution a, and the mixed solution is sealed and heated in an oven at 50℃ for 24h; next, the reaction mixture is cooled to room temperature, washed five times in deionized water, and dried in a vacuum oven to obtain a two-dimensional CNTs / Ce-MOFs nanosheet composite material, Figure 1 A scanning electron microscope schematic diagram of the two-dimensional material provided by the embodiment of the present application with Ce as the coordination center metal ion.

[0045] A preparation method of a two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor, comprising the following steps:

[0046] (1) The glassy carbon electrode is polished to a mirror surface and then used;

[0047] (2) The Nafion solution is diluted with ethanol to a mass fraction of 0.5%, a certain amount of 0.5% Nafion solution and CNTs / Ce-MOFs material are mixed, dropped on the surface of the glassy carbon electrode and dried in an oven at 50℃ to prepare a CNTs / Ce-MOFs / GCE nitrite electrochemical sensor;

[0048] The application of the two-dimensional CNTs / Ce-MOFs nanosheet-based nitrite electrochemical sensor includes the following contents:

[0049] The CNTs / Ce-MOFs / GCE nitrite electrochemical sensor was characterized by using an electrochemical workstation, and the CV curve shown in FIG. 2 was obtained. Figure 2 In a three-electrode system (saturated silver / silver chloride electrode as a reference electrode, platinum plate as a counter electrode, and the CNTs / Ce-MOFs / GCE nitrite electrochemical sensor prepared in the above example as a working electrode), at an ambient temperature of 22±3℃, the CV curve of the sensor was measured in a phosphate buffer (0.1M, pH=7) containing 0 and 0.01mol / L NaNO2, respectively, to obtain the curve shown in FIG. 2. Figure 2 It can be seen from FIG. 2 that the CNTs / Ce-MOFs / GCE nitrite electrochemical sensor prepared in the application is very sensitive to the concentration of nitrite. Figure 2

[0050] The DPV curve of the sensor was measured in a phosphate buffer (0.1M, pH=7) containing 0.65, 1.3, 6.5, 13, 26, 52, 105, 350, 700, 1400, 3500, and 7000μmol / L NaNO2, respectively, to obtain the curve shown in FIG. 3. It can be seen from FIG. 3 that the CNTs / Ce-MOFs / GCE nitrite electrochemical sensor prepared in the application has a detection limit of 0.12μM, and a linear range of 0.65-6.5μM and 6.5-7000μM.

[0051] The response time and interference ability of the sensor were measured in the cases of adding NaNO2, CaCl2, KCl, UA, DA, NaNO3, and Na2SO4 in the phosphate buffer, respectively, to obtain FIGS. 4 and 5. Figure 4 Figure 5 It can be seen from the figures that the response time is about 3.3s, and common interfering ions have no effect on the detection of sodium nitrite.​​

Claims

1. Use of a two-dimensional CNTs / MOFs nanosheet-based electrochemical sensor for detecting nitrite, characterized in that, The two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor is used as a working electrode, Ag / AgCl is used as a reference electrode, and a platinum wire is used as a counter electrode to form a three-electrode system for electrochemical detection of nitrite. The two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor is prepared by using a two-dimensional CNTs / MOFs nanosheet composite material, including the following steps: (1) The substrate is cleaned / polished and then used; (2) The Nafion solution is diluted with ethanol to a certain concentration, a certain amount of Nafion solution and two-dimensional CNTs / MOFs nanosheet composite material are mixed, and then dropped and coated on the surface of the substrate electrode and dried in an oven to obtain the two-dimensional CNTs / MOFs nanosheet nitrite electrochemical sensor, wherein the two-dimensional CNTs / MOFs nanosheet composite material is a two-dimensional CNTs / Ce-MOFs nanosheet composite material; The preparation method of the two-dimensional CNTs / MOFs nanosheet composite material comprises: (1) Covalent functionalization of CNTs: a certain amount of CNTs and 4-substituted aniline are mixed, a certain amount of isoamyl nitrite is added, and then heating and stirring are started for a certain time to obtain a paste, the paste is diluted with N,N-dimethylformamide and filtered through a PTFE membrane, the solid collected by filtration is dispersed in DMF by ultrasonic treatment, and then filtered to obtain purified functionalized carbon nanotubes CNTs-PhCOOH; (2) Preparation of two-dimensional CNTs / MOFs nanosheet composite material: A certain amount of CNTs-PhCOOH prepared in step (1) is dispersed in DMF and ultrasonically treated for a certain time to obtain a completely dispersed solution a; A certain amount of MOFs coordination center ion is dissolved in deionized water and added dropwise to the solution a, the mixed solution is heated in a sealed oven, the reaction mixture is cooled to room temperature, washed in deionized water, and dried in a vacuum oven to obtain a two-dimensional CNTs / MOFs nanosheet composite material.

2. Use according to claim 1, characterized in that, In step (1), the substrate includes one of a nanoporous gold needle, a glassy carbon electrode, carbon paper, a platinum sheet, and a gold sheet.

3. Use according to claim 1, characterized in that, In step (2), the Nafion solution is diluted with ethanol to a mass fraction of 0.5%-1%, and dried in an oven at 40-60°C.

4. The use according to claim 1, characterized in that, In the electrochemical detection of nitrite, a differential pulse voltammetry method is used.

5. The use according to claim 1, characterized in that, In the electrochemical detection of nitrite, the electrolyte is a 0.1M phosphate buffer solution with a pH value of 7.

0.

6. The use according to claim 1, characterized in that, In step (1) of the preparation method of the two-dimensional CNTs / MOFs nanosheet composite material, the addition amount of CNTs is 0.1-0.2g, the addition amount of 4-substituted aniline is 0.4-0.8g, the addition amount of isoamyl nitrite is 0.5-0.7mL, the heating temperature is 50-70°C, the heating and stirring time is 30-60min, the PTFE membrane pore size range is 0.3-0.8μm, and the ultrasonic condition is ultrasonic treatment at room temperature for 20-30min.

7. Use according to claim 6, characterized in that, In step (2), the density of CNTs-PhCOOH in solution a is 5-10mg / mL. The mass ratio of the MOFs coordination center ion and the CNTs-PhCOOH is (1-1.5):2; wherein the mixed solution is heated in a 40-50℃ oven for 24-48h, and washed in deionized water for 5-8 times.

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