CN115290723A - Preparation method and application of heavy metal ion electrochemical sensor - Google Patents
Preparation method and application of heavy metal ion electrochemical sensor Download PDFInfo
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- G—PHYSICS
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- 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
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- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
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- C—CHEMISTRY; METALLURGY
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- G01N27/3275—Sensing specific biomolecules, e.g. nucleic acid strands, based on an electrode surface reaction
- G01N27/3277—Sensing specific biomolecules, e.g. nucleic acid strands, based on an electrode surface reaction being a redox reaction, e.g. detection by cyclic voltammetry
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- G—PHYSICS
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- 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
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- G01N27/3275—Sensing specific biomolecules, e.g. nucleic acid strands, based on an electrode surface reaction
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Abstract
The invention discloses a preparation method of a heavy metal ion electrochemical sensor, the electrochemical sensor is based on a high-performance carboxylated carbon nanotube/graphene composite material, is applied to surface modification of a working electrode in a traditional three-electrode system and a composite electrode system, and realizes electrochemical detection of the sensor in cadmium and lead ion solutions with ultra-wide concentration ranges by dynamically optimizing deposition/enrichment time and mercury/bismuth ion concentration. The modification material of the working electrode of the electrochemical sensor provided by the method has the advantages of easy industrial production, strong electrochemical performance and the like; the proposed operating strategy of the electrochemical sensor has dynamic optimization capability, so that the electrochemical sensor has a linear detection range superior to that of the vast majority of products on the market.
Description
Technical Field
The invention belongs to the technical field of electrochemical sensors, and particularly relates to a heavy metal ion electrochemical sensor with an ultra-wide linear detection range and application of the electrochemical sensor in synchronous detection of heavy metal cadmium and lead ions.
Background
Cadmium ion (Cd) recommended by the World Health Organization (WHO) for index of water quality of drinking water 2+ ) And lead ion (Pb) 2+ ) The index values of (b) are 3. Mu.g/L and 10. Mu.g/L, respectively. On the other hand, in the case of industrial effluent, in particular electroplating effluent, it usually contains a high concentration of heavy metal ions (Cd) 2+ ：1.13 - 4.957 mg/L，Pb 2+ :0.06-2.626 mg/L), it is difficult to directly analyze the electrochemical sensing system developed in the past. Therefore, the development of a sensitive, simple, portable and wide-detection-range heavy metal ion analysis system is a key problem in the current environmental pollution prevention and control background.
Several analytical techniques have been reported for the simultaneous analysis of Cd 2+ And Pb 2+ Such as Atomic Absorption Spectroscopy (AAS), atomic Fluorescence Spectroscopy (AFS), inductively coupled plasma mass spectrometry (ICP-MS), however, these techniques have the disadvantages of complex equipment, cumbersome operation, long detection period and the need for professional personnel to perform the operation. Anodic Stripping Voltammetry (ASV), a simple and sensitive Electrochemical Analysis (EA) method, has proven to be very effective for the analysis of trace heavy metal ions in aqueous solutions. However, for high concentration samples to be tested, EA techniques are rarely used directly for analyzing such samples due to limited active sites of the Working Electrode (WE), and non-linear peeling caused by non-uniform deposition of the test substance on the electrode. Therefore, how to increase the linear detection range of the electrochemical sensor is closeThe research hot spot of the year. Given that the Working Electrode (WE) plays a crucial role in EA technology, an ideal WE should have multiple functions, including a highly sensitive reaction surface, a higher active surface area, good reproducibility, and low background current.
As a working electrode material of a sensor, some electrodes used for analysis of heavy metal ions use a carbon material such as glassy carbon and graphite, and a metal electrode such as gold, platinum, and silver. However, unmodified working electrodes have limited their direct analytical applications, particularly for the analysis of complex environmental samples, due to their poor electrochemical performance. Therefore, many efforts have been made to improve the heavy metal ion analysis performance of the electrochemical sensor. Among them, carbon nanomaterials are receiving increasing attention in EA technology due to their unrivaled physical/chemical properties, especially Graphene (GR) and carbon nanotubes (MWCNTs). GR is generally considered to be a single atom thick graphite layer with extremely high conductivity, electron mobility, and very large surface area. However, these properties are largely dependent on the process of preparation of the GR. In fact, past studies using rGO for electrochemical analysis have shown that the conductivity and specific surface area of rGO obtained by reduction of GO synthesized by Hummers method are much lower than expected due to the aggregation effect induced by strong pi-pi interactions between rGO nanoplates. Therefore, rGO cannot generally be used directly for analysis of heavy metal ions. MWCNTs prepared by floating catalyst chemical vapor deposition (FC-CVD) have excellent conductivity, but the low content of oxygen-containing functional groups (-OH, -COOH) makes the MWCNTs have strong hydrophobicity, so the MWCNTs are not ideal heavy metal ion sensing materials.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a preparation method of a heavy metal ion electrochemical sensor with an ultra-wide linear detection range, which comprises the following steps:
(1) Placing the carbon nano tube in a mixed solution of concentrated sulfuric acid and concentrated nitric acid, performing ultrasonic treatment for 2~6 hours at 20-80 ℃, adding deionized water after ultrasonic treatment, performing centrifugal washing until a washing solution is neutral, and performing solid freeze drying to obtain a carboxylated carbon nano tube;
the concentrated sulfuric acid-concentrated nitric acid mixed solution is prepared by mixing concentrated sulfuric acid and concentrated nitric acid according to the volume ratio of 0.5-5; nanotubes include, but are not limited to, single-walled carbon nanotubes, multi-walled carbon nanotubes;
(2) Placing the carboxylated carbon nanotube and graphene in deionized water, ultrasonically dispersing for 1~3 hours, centrifuging at 6000-15000rpm, removing supernatant, washing precipitates with the deionized water, and freeze-drying to obtain the carboxylated carbon nanotube/graphene composite material;
the mass ratio of the carboxylated carbon nanotubes to the graphene is 0.5 to 2; the graphene includes but is not limited to physical stripping method graphene, reduced graphene oxide prepared by chemical reduction method, and graphene oxide;
(3) Adding the carboxylated carbon nanotube/graphene composite material into an ethanol solution, and carrying out ultrasonic treatment for 15 to 60min to obtain 0.5 to 3mg/mL of carboxylated carbon nanotube/graphene suspension;
the ethanol solution is an ethanol water solution with the mass concentration of 15-50%;
(4) Dripping a carboxylated carbon nanotube/graphene suspension onto a working electrode, drying, dripping a Nafion dispersion liquid with the concentration of 0.1-20% on the surface of the working electrode, drying and depositing to obtain the Nafion/carboxylated carbon nanotube/graphene composite material modified electrochemical sensor;
the working electrode is an independent electrode or a working electrode in a composite electrode.
The invention also aims to apply the heavy metal ion electrochemical sensor prepared by the method to electrochemical detection of heavy metal ions in water, and the heavy metal ion electrochemical sensor in detection is used as a working electrode.
The electrochemical sensor with the ultra-wide linear detection range is used for detecting heavy metal cadmium and lead ions and comprises the following steps:
1. for the three electrode independent systems, one end of the working electrode, one end of the counter electrode and one end of the reference electrode are respectively connected to an electrochemical workstation; for a three-electrode compound system, a compound electrode is connected to an electrode interface and then connected to an electrochemical workstation; the connected three-electrode system is placed in an electrolyte containing metal ions with known concentration, the concentration ranges of cadmium ions and lead ions in the electrolyte are 0-3000 mu g/L respectively, and mercury ions or/and bismuth ions with the concentration dynamically changing along with the concentration of the cadmium ions and the lead ions (the addition amount is 10-40 times of the concentration of the metal ions to be detected) are contained, an anode stripping voltammetry is selected on an electrochemical workstation, the enrichment potential is set to-1V-1.5V, the enrichment time is dynamically changed according to the concentration of the cadmium ions and the lead ions in the solution to be detected, the electrolytic cell is mechanically stirred while carrying out enrichment, and after the enrichment is finished, the cadmium ions and the lead ions can be enriched on a working electrode and reduced into simple substances; immediately stopping stirring the solution in the electrolytic cell after the enrichment time is over, standing, loading a forward scanning voltage with the voltage range of-1.1V-0.7V on the working electrode, oxidizing the cadmium and lead simple substances enriched on the working electrode into cadmium and lead ions, stripping/dissolving the cadmium and lead ions back into the electrolyte, and recording the change condition of current-voltage by the electrochemical workstation to obtain a current-voltage curve; respectively drawing standard curves corresponding to cadmium and lead ions by taking the concentration of the cadmium and lead ions as abscissa and the peak current as ordinate, and determining the linear or nonlinear relation between the concentration of the metal ions and the peak current;
the known-concentration metal ion-containing electrolyte is prepared from an acetic acid-sodium acetate buffer solution or a PBS buffer solution, the pH value is 3.6-6.5, and the concentration is 0.1-1mol/L.
When the concentration of the metal ions is 0~5 mu g/L, the enrichment time is 480 to 800 seconds, when the concentration of the metal ions is 5 to 300 mu g/L, the enrichment time is 180 to 480 seconds, and when the concentration of the metal ions is 300 to 1500 mu g/L, the enrichment time is 30 to 180 seconds.
The stirring speed in the enrichment process is 100 to 500rpm.
Electrochemical anodic stripping voltammetry includes, but is not limited to, square wave pulsed stripping voltammetry, differential pulsed stripping voltammetry, linear stripping voltammetry, and cyclic voltammetry.
2. And (3) putting the sample to be detected into an electrolytic cell containing buffer solution, detecting the peak current respectively corresponding to the cadmium ions and the lead ions in the sample to be detected through an electrochemical workstation according to the method, substituting the peak current into a regression equation, and calculating to obtain the content of the cadmium ions and the lead ions in the sample.
The invention has the advantages and technical effects that:
the electrochemical sensor has an ultra-wide linear detection range for cadmium ions and lead ions in an aqueous solution, and the carboxylated carbon nanotube/graphene nano composite material is manufactured by a simple method. The hydrophilic carboxylated carbon nanotubes can be loaded on the graphene nanoplatelets through pi-pi interaction, so that the graphene nanoplatelets are stripped from each other and "dissolved" in water in a certain sense. The load of the carboxylated carbon nano tube inhibits the agglomeration phenomenon of the graphene nano sheet to a certain extent, the specific surface area and the conductivity of the nano sheet are increased, and the graphene also enables the originally mutually isolated carboxylated carbon nano tubes to form a staggered conductive network on the surface of the nano sheet. Therefore, the hybrid of the two materials enables the composite material to have high conductivity and high sensitivity. The advantages enable the carboxylated carbon nanotube/graphene nano composite material to become an ideal heavy metal ion sensing material, and the material is suitable for electrochemical analysis of heavy metal ions. In addition, for the limited linear detection range of the past electrochemical analysis, the linear detection of the heavy metal ions in three or more concentration ranges by the electrochemical sensor provided by the invention is realized by optimizing experimental parameters, so that the linear detection range is improved by several orders of magnitude.
Compared with other methods, the heavy metal ion electrochemical sensor provided by the invention has the function of adapting to solutions to be detected with different heavy metal ion concentrations, the ultra-wide linear range detection of cadmium ions and lead ions is realized by dynamically adjusting the enrichment/deposition time and the mercury/bismuth ion concentration, the detection performance and the technology are advanced, the method is simple, and the heavy metal electrochemical sensor is used for industrial production, the detection limits of the heavy metal cadmium ions and the lead ions are respectively 0.04 mu g/L and 0.02 mu g/L, and the linear range is 0.1 to 1350 mu g/L.
Drawings
Fig. 1 is a scanning tunneling microscope and atomic force microscope characterization result of a working electrode modified by a carboxylated carbon nanotube/graphene composite material, wherein a is an SEM image of an unmodified working electrode surface; figure b is an SEM image of the surface of the working electrode modified with the carboxylated multi-walled carbon nanotube/reduced graphene oxide composite; FIG. c is an AFM image of an unmodified working electrode surface; FIG. d is an AFM image of a carboxylated multiwalled carbon nanotube/reduced graphene oxide composite modified working electrode surface;
FIG. 2 is an electrochemical response curve diagram when the deposition/enrichment time is 480s when the concentration of cadmium ions and lead ions is 0.1 to 3.2. Mu.g/L;
FIG. 3 is a standard curve of the concentration of cadmium and lead ions versus peak current for the condition of FIG. 2;
FIG. 4 is a graph showing electrochemical response curves when the deposition/enrichment time is 180 s, when the concentrations of cadmium ions and lead ions are 3.2 to 240 μ g/L;
FIG. 5 is a standard plot of cadmium ion and lead ion concentrations versus peak current for the conditions of FIG. 4;
FIG. 6 is an electrochemical response curve diagram when the deposition/enrichment time is 30s when the concentrations of cadmium ions and lead ions are 240 to 1350 μ g/L;
FIG. 7 is a standard curve of cadmium ion and lead ion concentrations versus peak current for the conditions of FIG. 6.
Detailed Description
The present invention is further illustrated by the following figures and examples, but the scope of the present invention is not limited to the above description, and reagents and methods used in the examples are, unless otherwise specified, conventional reagents and methods are used.
Example 1: preparation method and application of heavy metal ion electrochemical sensor
(1) Putting 1g of multi-walled carbon nano-tube into 500mL of concentrated sulfuric acid-concentrated nitric acid mixed solution (the volume ratio is 3:1), performing ultrasonic treatment at 60 ℃ for 4h, cooling, and adding deionized water with the volume 4 times that of the original solution for dilution; centrifuging the diluted solution at 12000rpm, washing the black product obtained by centrifuging with deionized water until the washing liquid is neutral, freeze-drying the solid to obtain the carboxylated multi-walled carbon nanotube, and drying and storing the carboxylated multi-walled carbon nanotube at room temperature in a dark place;
(2) Placing 500mg of graphene oxide in 500mL of deionized water, then carrying out ultrasonic treatment for 2h, continuously introducing pure nitrogen into the yellow solution obtained after the ultrasonic treatment for more than 15min to remove oxygen, then adding 1g L-ascorbic acid into the solution, and continuing to carry out ultrasonic treatment for 30min; finally, stirring the solution at 60 ℃ for 36 hours under the protection of nitrogen, filtering the solution through a polytetrafluoroethylene membrane, sequentially washing and filtering the product with ethanol and deionized water, and finally freeze-drying the obtained product to obtain reduced graphene oxide, drying at room temperature and storing in a dark place;
(3) Dispersing the carboxylated multi-walled carbon nanotube and reduced graphene oxide (the mass ratio is 1:1) in deionized water, carrying out ultrasonic treatment for 2h, centrifuging the dispersion solution at 12000rpm, removing supernatant, washing precipitates with deionized water, and finally carrying out freeze drying to obtain the carboxylated multi-walled carbon nanotube/graphene composite material, drying at room temperature and storing in a dark place;
(4) Adding the carboxylated carbon nanotube/graphene composite material into an ethanol solution with the volume concentration of 20% for ultrasonic treatment for 30min to obtain 1mg/mL carboxylated carbon nanotube/graphene suspension;
(5) Dripping 5 mu L of 1mg/mL carboxylated carbon nanotube/graphene suspension on the surface of a glassy carbon electrode, drying and depositing under a nitrogen purging and infrared drying lamp, dripping 3 mu L of 0.5wt% Nafion dispersion liquid on the surface of a working electrode after the dripped suspension is completely dried, and drying and depositing under the nitrogen purging and infrared drying lamp to finally obtain a working electrode modified by the Nafion/carboxylated carbon nanotube/graphene composite material; the topography under a scanning tunneling microscope and an atomic force microscope is shown in fig. 1;
(6) Detection application of heavy metal ions
a. Testing instruments and conditions:
the electrochemical sensor comprises an electrochemical workstation, an electrolytic cell, the working electrode prepared in the step (4), a counter electrode (platinum electrode) and a silver/silver chloride reference electrode;
b. preparation of the Standard Curve
Placing 30mL of acetic acid-sodium acetate buffer solution containing cadmium with the concentration range of 0-1350 mg/L and lead ions with the concentration range of 0-1350 mg/L in the electrolytic cell, wherein the pH value of the acetic acid-sodium acetate buffer solution is 5.0, and the concentration is 0.1mol/L; simultaneously adding mercury nitrate, wherein the concentration of mercury ions is 15 times of that of ions in the electrolyte;
(1) selecting square wave pulse stripping voltammetry on an electrochemical workstation, setting an enrichment potential to be-1.3V, and setting enrichment time to be 30 seconds, 180 seconds or 480 seconds; placing an electric stirrer into an electrolytic cell, setting the stirring speed of the electric stirrer to be 300rpm, and operating an enrichment/deposition program on an electrochemical workstation to finish the enrichment time so that cadmium and lead can be enriched on a working electrode modified with a modification liquid; (2) immediately stopping stirring the solution in the electrolytic cell after the enrichment time is over, after standing for 30s, loading a forward scanning voltage with a voltage range of-1.4V to-0.5V on the working electrode, oxidizing the cadmium and lead simple substances enriched on the working electrode into cadmium and lead ions, dissolving the cadmium and lead ions back into the electrolyte, and recording the change condition of current-voltage by an electrochemical workstation to obtain a current-voltage curve (as shown in fig. 2, 4 and 6); (3) respectively drawing a standard curve corresponding to metal ions by taking the concentration of cadmium, lead and mercury ions as an abscissa and the peak current value as an ordinate, and performing linear regression to obtain a linear relation between the concentration of cadmium and lead ions and the peak current (as shown in figures 3, 5 and 7); the linear relation (standard curve) is used for quantitatively detecting the concentration of cadmium and lead ions to be detected; the linear relationship between the cadmium ion concentration and the lead ion concentration corresponding to the working electrode and the peak current is respectively as follows:
cadmium ion:
lead ion:
c. calculation of detection limits
The limit of detection was performed at a deposition/enrichment time of 480s, and was calculated by the formula CL = 3Sb/m, where CL, sb and m are the limit of detection (μ g/L), the blank standard deviation (μ a) and the standard curve slope (μ a/(μ g/L)), respectively. And c, obtaining the slope of the standard curve through the step b, wherein the slope is respectively cadmium ions: 2.43064; lead ion: 4.78996. the blank standard deviation is obtained by scanning 10 times of blank water samples to obtain the standard deviation of peak current values, and is respectively cadmium ion: 0.03241; lead ion: 0.03193; and finally, bringing the slope of the standard curve and the blank standard deviation into a formula CL = 3Sb/m to obtain the electrode detection limit as follows: 0.04 mu g/L; lead ion: 0.02. Mu.g/L.
d. Detection of sample to be tested
Detecting an acetic acid-sodium acetate buffer solution containing cadmium ions with the concentration of 105 mug/L and lead ions with the concentration of 105 mug/L, wherein the experimental method is the same as the step b, the peak currents of the cadmium ions and the lead ions are respectively 42.094 muA and 45.84 muA, then the peak current values are substituted into the linear equation of the step b, and the contents of the cadmium ions and the lead ions are respectively 103.32 mug/L and 102.78 mug/L through calculation;
(4) Electrode stability test
The same electrode is placed at room temperature for 30 days, the test current value of the same electrode is 96.2 percent and 97.3 percent of the initial value of the same electrode when the same electrode is placed for 30 days, and the test current value corresponds to cadmium ions and lead ions, so that the sensor has better stability.
Example 2: preparation method and application of heavy metal ion electrochemical sensor
(1) Placing 1g of single-walled carbon nanotube in 500mL of concentrated sulfuric acid-concentrated nitric acid mixed solution (the volume ratio is 2:1), performing ultrasonic treatment at 50 ℃ for 6 hours, cooling at room temperature, and adding deionized water with the volume 4 times that of the original solution for dilution; centrifuging the diluted solution at 14000 rpm, washing a black product obtained by centrifuging by using deionized water until washing liquor is neutral, freeze-drying to obtain the carboxylated single-walled carbon nanotube, and drying and storing in a dark place at room temperature;
(2) Placing single-layer graphene obtained by a 500mg physical stripping method in 500mL deionized water, then carrying out ultrasonic treatment for 4 hours, and drying and storing the obtained solution at 5 ℃ in a dark place after the reaction is finished;
(3) Mixing 1mg/L single-walled carbon nanotube dispersion solution and 1mg/L single-layer graphene dispersion solution (the volume ratio is 1:1), carrying out ultrasonic treatment for 3 hours, centrifuging the dispersion solution at 12000rpm, removing supernatant, washing precipitates by deionized water, and carrying out freeze drying to obtain the carboxylated single-walled carbon nanotube/single-layer graphene composite material by a physical stripping method; drying at room temperature and storing in dark place;
(4) Adding the carboxylated carbon nanotube/graphene composite material into an ethanol solution with the volume concentration of 25 percent, and carrying out ultrasonic treatment for 30min to obtain a 2mg/mL carboxylated carbon nanotube/graphene suspension;
(5) Dripping 6 mu L of 2mg/mL carboxylated carbon nanotube/graphene suspension on the surface of a working electrode in a screen-printed carbon electrode, drying and depositing under a nitrogen purging and infrared drying lamp, dripping 4 mu L of 1wt% Nafion dispersion liquid on the surface of the working electrode after the dripped suspension is completely dried, and drying and depositing under the nitrogen purging and infrared drying lamp in the same way to finally obtain the screen-printed carbon electrode modified by the Nafion/carboxylated carbon nanotube/graphene composite material;
(6) Electrochemical detection of heavy metal ions in aqueous solutions
a. Testing instruments and conditions:
the electrochemical sensor comprises an electrochemical workstation, an electrolytic cell and the modified screen-printed carbon electrode prepared in the step (4);
b. the standard curve was prepared as in example 1;
c. the detection limit was calculated as in example 1;
d. testing of samples to be tested
And (b) detecting an acetic acid-sodium acetate buffer solution containing cadmium ions with the concentration of 200 mug/L and lead ions with the concentration of 200 mug/L, wherein the experimental method is the same as the step b, the peak currents of the cadmium and the lead are 62.094 muA and 67.84 muA respectively, then the peak current values are substituted into the linear equation of the step b of the embodiment 1, and the contents of the cadmium and the lead ions are 196.43 mug/L and 197.11 mug/L respectively through calculation.
(4) Electrode stability testing
The same electrode is placed at room temperature for 30 days, and the test current value of the same electrode is 97.2 percent and 96.9 percent of the initial value of the same electrode at 30 days, which correspond to cadmium ions and lead ions, so that the sensor has better stability.
Claims (8)
1. The preparation method of the heavy metal ion electrochemical sensor is characterized by comprising the following steps:
(1) Placing the carbon nano tube in a mixed solution of concentrated sulfuric acid and concentrated nitric acid, performing ultrasonic treatment for 2~6 hours at 20-80 ℃, adding deionized water after ultrasonic treatment, performing centrifugal washing until a washing solution is neutral, and performing solid freeze drying to obtain a carboxylated carbon nano tube;
(2) Placing the carboxylated carbon nanotube and graphene in deionized water, ultrasonically dispersing for 1~3 hours, centrifuging at 6000-15000rpm, removing supernatant, washing precipitates with the deionized water, and freeze-drying to obtain the carboxylated carbon nanotube/graphene composite material;
(3) Adding the carboxylated carbon nanotube/graphene composite material into an ethanol solution, and carrying out ultrasonic treatment for 15 to 60min to obtain 0.5 to 3mg/mL of carboxylated carbon nanotube/graphene suspension;
(4) And (3) dripping the carboxylated carbon nanotube/graphene suspension onto a working electrode, drying, dripping Nafion dispersion liquid with the concentration of 0.1-20% on the surface of the working electrode, drying and depositing to obtain the Nafion/carboxylated carbon nanotube/graphene composite material modified electrochemical sensor.
2. The method for preparing a heavy metal ion electrochemical sensor according to claim 1, wherein: the concentrated sulfuric acid-concentrated nitric acid mixed solution is prepared by mixing concentrated sulfuric acid and concentrated nitric acid according to the volume ratio of 0.5-5.
3. The method for preparing a heavy metal ion electrochemical sensor according to claim 1, wherein: the ethanol solution is ethanol water solution with mass concentration of 15-50%.
4. The method for preparing a heavy metal ion electrochemical sensor according to claim 1, wherein: the mass ratio of the carboxylated carbon nanotube to the graphene is 0.5 to 2.
5. The application of the heavy metal ion electrochemical sensor prepared by the preparation method of the heavy metal ion electrochemical sensor in the electrochemical detection of the heavy metal ions in the water body, which is characterized in that: the electrochemical sensor for detecting heavy metal ions is used as a working electrode.
6. Use according to claim 5, characterized in that: respectively connecting one end of a working electrode, one end of a counter electrode and one end of a reference electrode to an electrochemical workstation, respectively placing the other ends of the working electrode, the counter electrode and the reference electrode in a metal ion-containing electrolyte with a known concentration in an electrolytic cell, detecting by using an electrochemical anodic stripping voltammetry, setting the enrichment potential to be-1V to-1.5V, stirring the solution while enriching, stopping stirring after enriching, applying a group of forward scanning voltages with a voltage scanning range of-1V to-1V on a three-electrode system after standing for 5 to 60s, recording the change condition of current-voltage by the electrochemical workstation to obtain a current-voltage curve, drawing a standard curve corresponding to metal ions by taking the concentration of the heavy metal ions as a horizontal coordinate and the peak current as a vertical coordinate, obtaining a regression equation, and determining the linear or nonlinear relation between the concentration of the metal ions and the peak current; and (3) putting the sample to be detected into an electrolytic cell, detecting the peak current corresponding to the metal ions in the sample to be detected through the electrochemical workstation according to the method, substituting the peak current into a regression equation, and calculating to obtain the content of the metal ions in the sample to be detected.
7. Use according to claim 5, characterized in that: during detection, divalent mercury ions and/or trivalent bismuth ions are dropwise added into the electrolyte, and the addition amount is 10-40 times of the concentration of the metal ions to be detected.
8. Use according to claim 5, characterized in that: when the concentration of the metal ions is 0~5 mu g/L, the enrichment time is 480 to 800 seconds, when the concentration of the metal ions is 5 to 300 mu g/L, the enrichment time is 180 to 480 seconds, and when the concentration of the metal ions is 300 to 1500 mu g/L, the enrichment time is 30 to 180 seconds.
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