CN111044588B - Electrochemical method for detecting trace lead ions by using cobalt-nitrogen doped carbon material modified working electrode - Google Patents

Electrochemical method for detecting trace lead ions by using cobalt-nitrogen doped carbon material modified working electrode Download PDF

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CN111044588B
CN111044588B CN201911204276.0A CN201911204276A CN111044588B CN 111044588 B CN111044588 B CN 111044588B CN 201911204276 A CN201911204276 A CN 201911204276A CN 111044588 B CN111044588 B CN 111044588B
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lead ions
solution
working electrode
mwcnts
cobalt
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CN111044588A (en
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袁群惠
干为
赵瑞
吴星星
高玉想
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Shenzhen Graduate School Harbin Institute of Technology
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Shenzhen Graduate School Harbin Institute of Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon

Abstract

The invention relates to an electrochemical method for detecting trace lead ions by a working electrode modified by a cobalt-nitrogen doped carbon material, belonging to the related fields of environmental monitoring, food safety and the like. The invention is mainlyThe carbon material doped with cobalt and nitrogen is prepared by integrating the advantages of a bimetallic zeolite imidazole compound and a carbon tube subjected to oxidation modification treatment through processes of chemical combination reaction, tubular furnace sintering and the like. Compared with other materials, the material is characterized in that more holes are generated by evaporation of zinc metal, so that more active sites are exposed; the existence of the carbon tube effectively improves the conductivity and the specific surface area of the material. The material is used for modifying a glassy carbon electrode, and trace lead ions in water can be efficiently detected by a differential pulse anodic stripping voltammetry. The electrode modification process is simple, and the detection limit reaches 0.4 mu g L under the optimal condition‑1Linear range 0.2-70 mu g L‑1And the electrode has good reproducibility, repeatability and stability, can quickly detect trace lead ions, and has strong popularization and application prospects.

Description

Electrochemical method for detecting trace lead ions by using cobalt-nitrogen doped carbon material modified working electrode
Technical Field
The invention relates to an electrochemical method for detecting trace lead ions by a working electrode modified by a cobalt-nitrogen doped carbon material, and relates to the field of electrochemical analysis such as environmental monitoring and food safety.
Background
Lead ions are one of the most toxic metal contaminants, which tend to cause enrichment in organisms through the food chain. Accordingly, low concentrations of lead ions may also pose a serious threat to human health and the environment. Therefore, the development of a method capable of rapidly and accurately detecting lead ions in a complex environment (e.g., natural water, industrial and biological samples) is of great significance in analytical chemistry and electrochemistry.
The current mature lead ion detection method comprises the following steps: atomic absorption spectroscopy, surface enhanced raman scattering, colorimetry, and fluorescence. However, these methods often have the defects of requiring complicated pretreatment, dedicated large-scale instruments, being difficult to operate, having high cost and the like, and cannot meet the development requirements of online and rapid detection of the environment. The electrochemical method is the means with the most application potential at present due to the advantages of simple operation, quick method, portability, easy integration, high sensitivity, low cost and the like.
Although a preparation method of a cobalt-nitrogen doped carbon material modified glassy carbon electrode is disclosed in the prior art, such as CN104282445A, the application of related materials in the electrochemical sensing field is relatively few, and during the application, problems such as low precision and insufficient detection limit may exist.
In the present invention, Co-N is usedx-C @ MWCNTs modifies a glassy carbon electrode to detect trace lead ions in tap water. Under optimum conditions, Co-NxThe detection limit of the-C @ MWCNTs modified electrode on lead ions is as low as 0.4 mu g/L, and the-C @ MWCNTs modified electrode also has extremely high stability, repeatability and anti-interference capability. Has strong popularization and application prospect.
Disclosure of Invention
The invention aims to provide an electrochemical method for detecting trace lead ions by using a working electrode modified by a cobalt-nitrogen doped carbon material, aiming at the defects of practical application of working electrode selection in the process of detecting trace lead ions by using the existing electrochemical method.
The technical scheme adopted for solving the technical problems of the invention is as follows:
firstly, the invention provides a preparation method of a Co-N doped carbon material modified working electrode for detecting trace lead ions, wherein the modified material of the working electrode is Co-Nx-C @ MWCNTs material, and the preparation method of the working electrode is as follows:
step one, preparing Nafion-H2O, mixing the solution;
step two, using nitric acid solution to carry out oxidation pretreatment on the carbon nano tube in an oil bath pan, washing by deionized water, drying and collecting the oxidized carbon nano tube;
mixing and ultrasonically treating a certain amount of processed carbon nano tubes, cobalt nitrate, zinc nitrate and methanol for a certain time, and recording as a solution A;
step four, mixing a certain amount of 2-methylimidazole and methanol to obtain a solution B;
step five, mixing the A, B solution, and putting the mixture into a microwave reactor to prepare BMZIF-67@ MWCNTs;
sixthly, calcining the BMZIF-67@ MWCNTs in a tube furnace under the protection of nitrogen flow, performing acid etching on the obtained sample by using sulfuric acid, and washing and drying to obtain the BMZIF-67@ MWCNTsFinal material Co-Nx-C@MWCNTs；
Step seven, adding proper amount of Co-Nx-C @ MWCNTs and Nafion-H prepared in step one2And mixing the O solution and ultrasonic waves to obtain a dispersion liquid, dropwise adding a certain amount of dispersion liquid onto the surface of the polished glassy carbon electrode, and drying by using an infrared lamp to obtain the working electrode.
The invention mainly utilizes the combination of bimetallic zeolite imidazole compound and carbon tube which is treated by oxidation modification, and prepares the cobalt-nitrogen doped carbon material through chemical combination reaction, tubular furnace sintering and the like. Compared with other materials, the material has the characteristics that zinc evaporation generates more holes, more active sites are exposed, and the material is combined with carbon tubes for lead ion detection.
Preferably, in the first step, Nafion mother liquor and H2The volume ratio of O is 4: 1000.
preferably, in the second step, the mass-to-volume ratio of the carbon nanotubes to the nitric acid solution is 1 g: 160mL, oil bath pan treatment conditions of 120 ℃ for 6 h.
Preferably, in the third step, the mass ratio of the oxidized carbon nanotubes to the cobalt nitrate to the zinc nitrate is 1.0: 14.5: 14.6 the mass volume ratio of the sum of the mass of the oxidized carbon nanotube, the cobalt nitrate and the zinc nitrate to the mass of the methanol is 1-1.5 g: 80 mL.
Preferably, in the fourth step, the mass-to-volume ratio of the 2-methylimidazole to the methanol is 1 to 1.5 g: 80 mL.
Preferably, in the fifth step, the microwave reactor condition is 50 ℃ for 5 min.
Preferably, in the sixth step, the sintering condition of the tube furnace is 950 ℃ for calcining for 2h, the heating rate is 5 ℃/min, the sulfuric acid concentration is 0.5mol/L, and the acid etching time is 12 h.
Preferably, in said seventh step, Co-Nx-C @ MWCNTs and Nafion-H2The mass-to-volume ratio of the O solution is 1 mg: 1 mL.
Obtained Co-NxThe glassy carbon electrode modified by the-C @ MWCNTs has excellent performance and can be used for a three-electrode system.
The selection of the aforementioned conditions is optimized according to the detection signal, and finally, an optimal value is obtained, which is important for the electrode and the detection effect.
The invention further provides an electrochemical method for detecting trace lead ions by using the working electrode modified by the cobalt-nitrogen doped carbon material.
Preferably, the electrochemical analysis method adopts stripping voltammetry, including one or more of potentiostatic method, differential pulse stripping voltammetry, cyclic voltammetry and square wave stripping voltammetry; the detected substances are trace lead ions.
The glassy carbon electrode modified by the material is applied to trace lead ion detection through differential pulse anodic stripping voltammetry. The electrode modification process is simple, and the detection limit is 0.4 mu g L under the optimal condition-1Linear range 0.2-70 mu g L-1And the method has good reproducibility, repeatability and stability, can quickly detect trace lead ions, and has strong popularization and application prospects.
Compared with the prior art, the electrochemical method has the advantages that:
1. through the addition of bimetal and calcination treatment, more holes are added in the material, the structure and the appearance of the material are optimized, more active sites are exposed, and the sensing performance of lead ions is enhanced.
2. The electrochemical test method has the advantages of simpler process, short test time, good parallelism, reproducibility and stability, and can solve the practical application problem of quickly detecting trace lead ions by the electrochemical method.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below by way of examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The first embodiment is as follows:
an electrochemical method for detecting trace lead ions by using a cobalt-nitrogen doped carbon material modified working electrode comprises the following steps:
step one, preparing Nafion-H2O mixed solution, adding 0.4 mu L Nafion mother liquor into a 2mL centrifuge tube filled with 1mL deionized water, and carrying out ultrasonic 5 minutes until the mixture is completely mixed;
step two, using nitric acid solution to carry out oxidation pretreatment on the carbon nano tube in an oil bath pot, weighing 0.25g of MWCNTs with the outer diameter of 10-30 nm into a single-neck flask, and adding 40mL of HNO with constant volume3Placing the single-mouth flask in an oil bath pot, connecting a serpentine condenser pipe above the single-mouth flask, opening the oil bath pot to enable the carbon tube to reflux for 6 hours at 120 ℃, then washing the carbon tube for 3 times by using deionized water, and then drying the carbon tube for 12 hours in vacuum at 80 ℃ to collect oxidized carbon nanotubes;
step three, 0.040g of prepared oxidized pretreated MWCNTs and 0.582g of Co (NO)3)2·6H2O、0.594g Zn(NO3)2·6H2Mixing O and 80mL of methanol in a beaker, and dispersing for 1 hour by ultrasonic to obtain a solution A;
step four, mixing a solution of 1.312g of 2-methylimidazole and 80mL of methanol in a beaker to obtain a solution B;
step five, mixing the A, B solution, putting the mixture into a microwave reactor, heating the mixture to 50 ℃, keeping the mixture for 5 minutes, washing the product with methanol for 3 times, and drying the product in a vacuum oven at 80 ℃ for 12 hours to obtain a product BMZIF-67@ MWCNTs;
step six, in N2Under the flow protection, firstly keeping a tubular furnace and introducing nitrogen for 30min, then starting a heating program, calcining BMZIF-67@ MWCNTs in the tubular furnace at 950 ℃ for 2h, and raising the temperature at 5 ℃ for min-1. The product obtained after calcination was at room temperature at 0.5M H2SO4The sample is subjected to acid etching in the solution for 12h, then washed 3 times with deionized water and dried in a vacuum oven at 80 ℃ for 12h to obtain the final material Co-Nx-C@MWCNTs；
Step seven, taking the prepared Co-Nx-C @ MWCNTs 1mg and 1mL prepared Nafion-H2Mixing the O solution and performing ultrasonic treatment to obtain a dispersion liquid, dripping 2.5 mu L of the dispersion liquid on the surface of the polished glassy carbon electrode, and drying by using an infrared lamp to obtain a working electrode Co-Nx-C@MWCNTs/GCE。
And step eight, using the electrode prepared in the step seven as a working electrode, a platinum wire as a counter electrode and an Ag/AgCl electrode as a reference electrode, connecting one end of the three electrodes to an electrochemical workstation (Shanghai Chenghua CHI660E), adding 100 mu g/L of bismuth ions and lead ions to be detected into 0.1mol/L of HAc-NaAc buffer solution, firstly adopting a timing current i-t method to enrich, setting the enrichment voltage to be-1.2V and the enrichment time to be 120 s. Running the DPASV program, DPASV program: the scanning voltage range is-1V-0V; the voltage is increased by 50 mV; pulse width 60 ms; the pulse interval is 0.5 s.
The measurement results are as follows:
for 50 mu g L under the above conditions-1The response signal of lead ion (2.6. mu.A), and the detection limit of lead ion by the electrode in the linear measurement was 0.4. mu. g L-1Linear range 0.2-70 mu g L-1The relative standard deviation was 0.9991. And has good reproducibility, repeatability and stability, and the relative standard deviation is below 5%.
Example two:
the other steps are the same as the first embodiment, except that: the amount of Nafion added in step one was adjusted to 0.8. mu.L.
The measurement results are as follows:
for 50 mu g L under the above conditions-1The response signal of lead ion (2) was 1.8. mu.A, which is inferior to that of the example, and no subsequent test was conducted.
Example three:
the other steps are the same as the first embodiment, except that: and changing the concentration of the bismuth ions in the step eight to 200 mu g/L.
The measurement results are as follows:
for 50 mu g L under the above conditions-1The response signal of lead ion (2.0. mu.A) was inferior to that of the first example, and no subsequent test was conducted.
The above description is only exemplary of the present invention and should not be taken as limiting the invention, and any modifications, equivalents, improvements, etc. that are made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A method for preparing a Co-N doped carbon material modified working electrode for detecting trace lead ions is characterized in that the modified material of the working electrode is Co-Nx-C @ MWCNTs material, and the preparation method of the working electrode is as follows:
step one, preparing Nafion-H2O, mixing the solution;
step two, using nitric acid solution to carry out oxidation pretreatment on the carbon nano tube in an oil bath pan, washing by deionized water, drying and collecting the oxidized carbon nano tube;
mixing a certain amount of oxidized carbon nano tubes, cobalt nitrate, zinc nitrate and methanol for a certain time by ultrasonic treatment, and marking as a solution A;
step four, mixing a certain amount of 2-methylimidazole and methanol to obtain a solution B;
step five, mixing the A, B solution, and putting the mixture into a microwave reactor to prepare BMZIF-67@ MWCNTs;
sixthly, calcining BMZIF-67@ MWCNTs in a tube furnace under the protection of nitrogen flow, performing acid etching on the obtained sample by using sulfuric acid, washing and drying to obtain the final material Co-Nx-C@MWCNTs；
Step seven, adding proper amount of Co-Nx-C @ MWCNTs and Nafion-H prepared in step one2And mixing the O solution and ultrasonic waves to obtain a dispersion liquid, dropwise adding a certain amount of dispersion liquid onto the surface of the polished glassy carbon electrode, and drying by using an infrared lamp to obtain the working electrode.
2. The method of claim 1, wherein in step one, Nafion mother liquor is mixed with H2The volume ratio of O is 4: 1000.
3. the method of claim 1, wherein in the second step, the mass-to-volume ratio of the carbon nanotubes to the nitric acid solution is 1 g: 160mL, oil bath pan treatment conditions of 120 ℃ for 6 h.
4. The preparation method according to claim 1, wherein in the third step, the mass ratio of the oxidized carbon nanotubes to the cobalt nitrate to the zinc nitrate is 1.0: 14.5: 14.6, the mass volume ratio of the sum of the oxidized carbon nano tube, cobalt nitrate and zinc nitrate to the methanol is 1-1.5 g: 80 mL.
5. The method according to claim 1, wherein in the fourth step, the mass-to-volume ratio of 2-methylimidazole to methanol is 1 to 1.5 g: 80 mL.
6. The method of claim 1, wherein in the fifth step, the microwave reactor conditions are maintained at 50 ℃ for 5 min.
7. The preparation method of claim 1, wherein in the sixth step, the tube furnace sintering condition is 950 ℃ for 2h, the heating rate is 5 ℃/min, the sulfuric acid concentration is 0.5mol/L, and the acid etching time is 12 h.
8. The method of claim 1, wherein in step seven, Co-Nx-C @ MWCNTs and Nafion-H2The mass-to-volume ratio of the O solution is 1 mg: 1 mL.
9. An electrochemical method for detecting trace lead ions by using a working electrode modified by a cobalt-nitrogen doped carbon material, wherein the working battery prepared by the preparation method of any one of claims 1-8 is used for detecting trace lead ions by using the electrochemical method.
10. The electrochemical method of claim 9, wherein the electrochemical analysis method employs stripping voltammetry, including one or more of potentiostatic method, differential pulse stripping voltammetry, cyclic voltammetry, square wave stripping voltammetry in combination; the detected substances are trace lead ions.
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CN108854994A (en) * 2018-06-08 2018-11-23 河南师范大学 The preparation method and applications of ZIF-67@PMMA composite material of the one kind for adsorbing Cd (II)
CN109174157B (en) * 2018-09-27 2022-02-01 合肥工业大学 Preparation method of cobalt-nitrogen co-doped biomass carbon oxidation reduction catalyst
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