CN115096976A - Silver cluster/nitrogen-doped carbon electrode material and in-situ limited synthesis method and application thereof - Google Patents

Abstract

The invention relates to a silver cluster/nitrogen-doped carbon electrode material, an in-situ limited domain synthesis method thereof and application thereof in a self-calibration electrochemical sensor, belonging to the technical field of electroanalytical chemical detection and carbon nano materials. According to the invention, the nitrogen-doped carbon sheet loaded silver nanoclusters with controllable structural morphology are synthesized after in-situ limited polymerization and subsequent carbonization of the nitrogen-containing ionic liquid and used as electrochemical signal probes, and then probe molecules are printed and pressed on the disposable silk screen printing electrode. The silver peak signal is used as a self-calibration mark peak, and the silver peak signal and the signal peak of the target object, namely the nitrite, form a good ratio type measuring electrode. Experiments show that the electrochemical sensor constructed by the method has high sensitivity, wide detection range, high specificity and good stability, shows good feasibility in the detection of actual samples, and provides a feasible method for synthesizing a stable, controllable and sensitive self-calibration sensor.

Description

Ag-cluster/nitrogen-doped carbon electrode material and its in-situ confinement synthesis method and application

technical field

The invention relates to the technical fields of electroanalytical chemical detection and carbon nanomaterials, in particular to a silver nanocluster electrode material uniformly dispersed in a nitrogen-doped carbon sheet, a synthesis method thereof, and an application thereof in a self-calibrating electrochemical sensor.

Background technique

Due to the numerous excellent properties of carbon nanomaterials, they show great potential in developing high-performance electrochemical sensors. Nanostructured carbon materials with various morphologies and structures, such as nanotubes, nanosheets, spheres, and fibers, have received extensive attention for their applications in electrocatalysis and electroanalysis. Electrochemical sensors based on carbon-based composites have the advantages of high sensitivity, simple operation, and good selectivity, and are considered as one of the most promising sensor materials. But the carbonization process is always difficult to regulate, resulting in unpredictable structural changes. Polymeric ionic liquids (PILs) provide a method for the successful synthesis of stable, controllable, and sensitive carbon-based composites due to their structural and morphological controllability and high solubility.

Polymeric ionic liquids (PILs) are prepared by incorporating cationic and/or anionic moieties into the macromolecular polymer structure. Among them, nitrogen-containing ionic liquid (IL) monomers can easily generate highly cross-linked and thermally stable nitrogen-containing skeletons. The doping of nitrogen atoms enhances the electrical conductivity, and the carbon atoms can be activated through topological defects and the electron affinity of nitrogen; and the nitrogen-containing ionic liquid monomer has excellent solubility for metal salts, and the nitrogen atoms in the carbon skeleton can stabilize the metal, Improve electrocatalytic activity. The metal precursors can be completely dispersed into the cross-linked network of ionic liquids, which are cross-linked by in-situ polymerization, resulting in solid-phase carriers. Therefore, uniformly dispersed metal clusters can be obtained through the carbonization process in a reducing atmosphere.

Based on this, the highly conductive silver nanocluster-loaded nitrogen-doped carbon sheet can be used as the electrode material of the electrochemical sensor, which can realize signal amplification, and the electrochemical signal of silver can be used as a reference signal. Therefore, the signal of the silver nanocluster is used as a ratio-type detection to make a self-calibrating electrochemical sensor, which can realize high sensitivity and accurate identification of the target. Due to the catalytic activity of silver for nitrite, highly sensitive and selective electrochemical sensors are expected to be applied to the practical monitoring of nitrite.

SUMMARY OF THE INVENTION

Based on the prior art, the purpose of the present invention is to provide an in-situ confinement synthesis method based on a uniformly dispersed silver nanocluster electrode material in a nitrogen-doped carbon sheet and a silver cluster; another purpose is to provide the composite material in self-calibration applications in electrochemical sensors.

In order to achieve the purpose of the present invention, the present invention utilizes the in-situ confinement polymerization of IL and subsequent carbonization to prepare a highly dispersed silver nanocluster composite material in a nitrogen-doped carbon sheet, and constructs a self-calibrating electrochemical sensor. for sensitive detection of nitrite.

Specifically, the following technical solutions are adopted:

(1) 1-vinylimidazole, 1,2-dibromoethane are added to the flask with ethyl acetate as solvent to react, and the solid impurities in the flask are removed; then the remaining liquid is put into another flask to continue the reaction, Obtain 3,3'-(alkene-1,2-diyl)bis(1-vinyl-1-H-imidazole) monomer (abbreviated as IL);

(2) The 3,3'-(alkene-1,2-diyl)bis(1-vinyl-1-H-imidazole) monomer obtained in step (1) was washed with ethyl acetate and evaporated The ethyl acetate solvent was removed and further evacuated with a vacuum pump to obtain purified IL monomer.

(3) The IL monomer prepared in step (2) is dissolved in water together with AgNO ₃ to remove bromide ions from the IL monomer. Then, AgNO ₃ was added to polymerize in the presence of acrylic acid and initiator to obtain poly[3,3'-(olefin-1,2-diyl)bis(1-vinyl-1-H-imidazole)] gel (referred to as PIL).

(4) The obtained silver-containing PIL gel is carbonized at high temperature to obtain a silver cluster/nitrogen-doped carbon composite (AgNC@NCS), which is then uniformly mixed with phenolic resin, conventional adhesive polyvinylidene fluoride and conductive agent acetylene black . The resulting mixed solid materials were fabricated into disposable screen printing electrodes.

Further, the amount of AgNO ₃ added for the first time in step (3) is equivalent to the amount of bromide ions in the IL monomer, and the mass of AgNO ₃ added for the second time is 30% of the total mass of the reactants.

Further, the high temperature carbonization of the silver-containing PIL gel in step (4): under the protection of Ar gas, the carbonization temperature is 500° C. and the time is 6 hours.

In step (4), the mass ratio of the phenolic resin, the conventional adhesive polyvinylidene fluoride and the conductive agent acetylene black to the material (AgNC@NCS) is 1:1:2:1.

When applied, differential pulse voltammetry is performed, and the quantitative determination of nitrite is realized through the relationship between the redox peaks of silver nanoclusters and nitrite and the concentration of nitrite.

Further, the test conditions were optimized, and the differential pulse voltammetry was preferably carried out in a 0.1 mol·L ^-1 phosphate buffer solution with pH=5.2.

The innovation of the present invention lies in that: nitrogen-doped carbon sheet-loaded silver nanoclusters with controllable structure and morphology are synthesized by in-situ confinement polymerization of nitrogen-containing ionic liquid and subsequent carbonization as electrochemical signal probes, and then the probe molecules are printed and pressed. The sheet is placed on a disposable screen-printed electrode to make an electrochemical sensor for high-sensitivity and high-selectivity quantitative determination of nitrite.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The self-calibrating electrochemical sensor prepared by using the silver cluster/nitrogen-doped carbon composite material (AgNC@NCS) of the present invention has a large effective surface area, which is 4.16 times that of conventional electrodes, thereby promoting electron conduction and providing amplified electrochemical signal.

(2) Using nitrogen-containing ionic liquid, which has excellent solubility for silver ions, and nitrogen atoms can stabilize metal clusters, the in-situ polymerization method is used to synthesize silver nanoclusters, which can achieve secondary signal amplification to a certain extent, so that the detection has good sensitivity.

(3) The present invention utilizes the silver nanocluster signal of the sensor itself as a marker signal peak for its own signal calibration, and forms a good ratio test with the target nitrite signal, so that the detection has a higher specificity sex.

(4) The electrochemical sensor of the present invention adopts a disposable screen-printed electrode, which is easy to be miniaturized, and the electrochemical signal of the silver nanocluster has high stability, so that it has high repeatability.

(5) The electrochemical sensor of the present invention realizes highly sensitive and highly selective determination of nitrite, with a detection limit of 0.38 ^{mmol·L -1} , which can be used for the determination of water and food, and is of great significance for the quantitative detection of nitrite. , is an electrochemical sensor with high sensitivity, high accuracy and high stability, and has a good development and application prospect.

Description of drawings

Figure 1 is a technical roadmap of the present invention.

Figure 2 is the energy spectrum scanning diagram and dark field scanning electron microscope of the material (AgNC@NCS) prepared by the present invention.

3 is a transmission electron microscope and a high-resolution transmission computer microscope image of the material (AgNC@NCS) prepared by the present invention.

Fig. 4 is a graph showing the impedance and cyclic voltammetry characterization during the preparation of the sensor of the present invention. In Fig. A, (1) is a conventional screen-printed electrode, (2) is a silver-free nitrogen-doped carbon (NCS) printed electrode, and (3) Electrodes were screen-printed for AgNC@NCS (inset: Randels equivalent circuit model). In Figure B, (1) is without adding 0.4 mmol·L ^-1 NaNO ₂ ; (2) is adding 0.4 mmol·L ^{- 1} NaNO ₂ , (1) and (2) are electrodes prepared by the present invention; (3) For printing electrodes on conventional screen.

Fig. 5 is the response of the sensor of the present invention to nitrite: A is the differential pulse voltammetry curve of the measurement; B is the standard curve of the current change ratio with the concentration; C is the selectivity of the electrochemical sensor of the present invention; D is the Stability diagram of the invented electrochemical sensor.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the examples. The following examples are only used to illustrate the present invention, but do not limit the scope of the present invention in any form.

Example 1 Synthesis of silver nanoclusters/nitrogen-doped carbon sheets and preparation of self-calibrating electrochemical sensors

(1) 1-vinylimidazole (0.94g, 2M), 1,2-dibromoethane (0.938g, 1M) and 5 mL of ethyl acetate were added to the eggplant flask. The reaction was carried out at 40°C for 8h, and the solid impurities in the bottle were removed. Then put the remaining liquid into a new eggplant bottle, and continue to react in an oil bath at 80 °C for 12 h to obtain 3,3`-(alkene-1,2-diyl)bis(1-vinyl-1-H- imidazole) monomer (abbreviated as IL).

(2) The 3,3'-(alkene-1,2-diyl)bis(1-vinyl-1-H-imidazole) monomer obtained in step (1) was washed three times with 90 mL of ethyl acetate , to ensure that no 1-vinylimidazole and 1,2-dibromoethane raw materials remain in the IL monomer. The ethyl acetate solvent was removed by evaporation and vacuum pumped for a further 30 minutes.

(3) The IL (1.88 g, 0.5 M) prepared in step (2) was dissolved in 10 mL H ₂ O together with AgNO ₃ (1.69 g, 1 M) to remove Br ions from the IL. Then, AgNO3 (0.307 g, 0.15 _M ) was dissolved in the IL monomer solution. The IL clear liquid was polymerized with acrylic acid (0.7206 g, 1 M) in the presence of an initiator (2,2-azobisisobutyronitrile, AIBN). After 2 hours of reaction, poly[3,3'-(alkene-1,2-diyl)bis(1-vinyl-1-H-imidazole)] gel (PIL) was obtained.

(4) The gel prepared above was placed in a tube furnace and heated at 500° C. for 6 hours under the protection of Ar gas to carbonize the silver-containing PIL. Meanwhile, during the PIL pyrolysis process, Ag ions are reduced to Ag nanoclusters. A self-calibrating electrochemical sensor (AgNC@NCS) with uniformly dispersed silver nanoclusters in nitrogen-doped carbon sheets was obtained.

(5) 8 mg of AgNC@NCS solution was uniformly dispersed in 2 mL of water and ethanol by sonication and stirring to obtain a dispersed homogenate.

(6) Preparation of modified disposable printed electrodes: add phenolic resin, conventional binder polyvinylidene fluoride and conductive agent acetylene black in a weight ratio of 1\1\2. The above disperse homogenate is uniformly mixed with it in a weight ratio of 2/8 to obtain a mixed solid material. Then, it is uniformly spread on the template surface of the printing electrode under anhydrous and oxygen-free conditions, and then fixed on the template surface of the printing electrode by pressing.

Application Example 1 The AgNC@NCS self-calibration electrochemical sensor of the present invention is applied to the determination of nitrite

A three-electrode system was used for the potential measurement, AgNC@NCS was used as the working electrode, and the carbon electrode and Ag/AgCl electrode were used as the counter electrode and the reference electrode, respectively. In 0.1mol·L ^-1 phosphate (pH=5.2) buffer solution, under the conditions of pulse amplitude of 0.004V, pulse width of 0.05μs, and sampling width of 0.0167μs, in the range of -0.2V to 1.2V The voltammetric response signal of the sensor was recorded by differential pulse voltammetry, and the ratio of the peak current of silver nanoclusters in the probe molecule to the peak current of nitrite was calculated by measuring the standard solutions of nitrite with different concentrations to calculate the ratio of the peak current to the peak current of nitrite. A standard curve was drawn from the ratio of current change-concentration. The current change ratio IP is proportional to the nitrite concentration (C) in the range of _1.12μmol·L ^-1 to 1400μmol·L ^-1 . The correlation coefficient R ² is 0.994, and the detection limit is ^0.38μmol·L -1 ¹ . It shows that this electrochemical sensor has high sensitivity for the determination of nitrite.

Application example 2 Performance investigation of the electrochemical sensor

To investigate the stability of the sensor of the present invention, the between-group precision or fabrication reproducibility was estimated in duplicate from the oxidation current density response of 1.0 mmol·L- ¹ nitrite with 4 different electrodes independently prepared in the same way. The relative standard deviation is 1.3%, which indicates that the prepared hybrid electrode has excellent reproducibility for nitrite determination. In order to study the repeatability of the sensor of the present invention, the response was maintained at 94.7, 87.2 and 85.9% of the initial voltammetric response of the electrode when the electrode was subjected to 10, 50 and 80 nitrite electrochemical signal measurements per day. Long-term stability of the assay, the current density response did not decrease significantly during the first 7 days. After 15 days, there was only about a 3% drop, and 84% of the response current density remained after two months. The results show that the sensor has good stability due to the stability and environmental compatibility of the material AgNC@NCS used for printing electrodes. In addition, the use of the electrochemical signal of silver nanoclusters as a marker peak ensures accurate and stable detection applications.

In order to evaluate the specificity of the sensor for nitrite, by adding 100 times the amount of CO ₃ ^2- , NO ₃ ^- , Fe ₃ ⁺ , Pb ²⁺ , Mg ²⁺ , PO ₄ ^3- , SO ₃ ^2- , Zn ^{2 +} and K ⁺ were in 0.1 mol·L ⁻¹ phosphate buffer at pH=5.2, in which 1.0 mmol·L ⁻¹ NO ₂ ⁻ was already present. The additive interference effect of all ions was determined to be very low (less than 1%). From the experimental data, the AgNC@NCS printed electrode showed high sensitivity and good specificity for the determination of nitrite in laboratory standard samples.

Application example 3 Determination of nitrite in actual samples

In order to evaluate the practicability of the electrochemical sensor to detect nitrite, pickled cucumbers, pickled peppers, milk, lake water, and mineral water samples were detected, and the ratio was changed according to the current. Nitrate concentration for quantitative detection. At the same time, a control experiment was done using the spectrophotometric standard method. As shown in Table 1, compared with the standard spectrophotometric method, the standard t value of the electrochemical method is lower than 1.5, which fully meets the requirements of quantitative determination. These results indicate that the electrochemical sensor has good accuracy and has potential for practical application.

Table 1. Determination of nitrite content in actual samples (n=5).

Claims (5)

1. a silver cluster/nitrogen-doped carbon electrode material, is characterized in that, is prepared by the following method: (1) 1-vinylimidazole, 1,2-dibromoethane, and ethyl acetate solvent are added to the flask to react, and the solid impurities in the flask are removed; then the remaining liquid is put into another flask, and the reaction is continued to obtain 3 ,3`-(alkene-1,2-diyl)bis(1-vinyl-1-H-imidazole)monomer (IL); (2) the IL monomer obtained in step (1) is washed with ethyl acetate, the ethyl acetate solvent is removed by evaporation, and the purified IL monomer is obtained by further vacuuming with a vacuum pump; (3) Dissolving the IL monomer obtained in step (2) together with AgNO <sub>3</sub> in water, then adding AgNO <sub>3</sub> to polymerize in the presence of acrylic acid and an initiator to obtain poly[3,3'-(olefin-1) ,2-diyl)bis(1-vinyl-1-H-imidazole)]gel (referred to as PIL); (4) The obtained silver-containing PIL is carbonized at high temperature to obtain a material (AgNC@NCS), which is then uniformly mixed with phenolic resin, adhesive polyvinylidene fluoride and conductive agent acetylene black; the obtained mixed solid material is made into disposable Screen printed electrodes. 2. The silver cluster/nitrogen-doped carbon electrode material according to claim 1, wherein, In step (3), the amount of AgNO <sub>3</sub> added for the first time is equivalent to the amount of bromide ions in the IL monomer, and the mass of AgNO <sub>3</sub> added for the second time is 30% of the total mass of the reactants. 3. The silver cluster/nitrogen-doped carbon electrode material according to claim 1, wherein in step (4), the phenolic resin, the binder polyvinylidene fluoride and the conductive agent acetylene black and the material (AgNC@NCS ) in a mass ratio of 1:1:2:1. 4. the method for preparing silver cluster/nitrogen-doped carbon electrode material as claimed in claim 1, is characterized in that, realizes through the following steps: (1) 1-vinylimidazole, 1,2-dibromoethane, and ethyl acetate solvent are added to the flask to react, and the solid impurities in the flask are removed; then the remaining liquid is put into another flask, and the reaction is continued to obtain 3 ,3`-(alkene-1,2-diyl)bis(1-vinyl-1-H-imidazole)monomer (IL); (2) the IL monomer obtained in step (1) is washed with ethyl acetate, the ethyl acetate solvent is removed by evaporation, and the purified IL monomer is obtained by further vacuuming with a vacuum pump; (3) Dissolving the IL monomer obtained in step (2) together with AgNO ₃ in water, then adding AgNO ₃ to polymerize in the presence of acrylic acid and an initiator to obtain poly[3,3'-(olefin-1) ,2-diyl)bis(1-vinyl-1-H-imidazole)] gel (referred to as (PIL); (4) The obtained silver-containing PIL is carbonized at high temperature to obtain a material (AgNC@NCS), which is then uniformly mixed with phenolic resin, adhesive polyvinylidene fluoride and conductive agent acetylene black; the obtained mixed solid material is made into disposable Screen printed electrodes. 5. The application of the silver cluster/nitrogen-doped carbon electrode material according to any one of claims 1-3 in an electrochemical sensor, characterized in that, using AgNC@NCS as the working electrode, carbon electrode and Ag/AgCl electrode Used as counter electrode and reference electrode, respectively, differential pulse voltammetry was used to quantitatively determine nitrite in water or food.

Images