CN111257386A

CN111257386A - Method for electrochemical synchronous detection of zinc, cadmium, lead, copper and mercury ions

Info

Publication number: CN111257386A
Application number: CN202010095861.8A
Authority: CN
Inventors: 张兆威; 吴文琴; 李培武; 白艺珍; 胡小风; 张奇
Original assignee: Oil Crops Research Institute of Chinese Academy of Agriculture Sciences
Current assignee: Oil Crops Research Institute of Chinese Academy of Agriculture Sciences
Priority date: 2020-02-17
Filing date: 2020-02-17
Publication date: 2020-06-09
Anticipated expiration: 2040-02-17
Also published as: CN111257386B

Abstract

The invention discloses a method for electrochemical synchronous detection of zinc, cadmium, lead, copper and mercury ions. The method can realize high-sensitivity synchronous detection of various heavy metal ions, and the detection sensitivity to zinc, cadmium, lead, copper and mercury ions is respectively as follows: 0.17,0.51,0.68,0.89,0.51 μ A μ g^‑1L^‑1cm^‑2The detection limits are respectively 0.08,0.09,0.05,0.19 and 0.01 mu g/L, and the linear ranges are respectively 6-7000,4-6000,6-5000,4-4000 and 6-5000 mu g/L. Has high sensitivity, good selectivity, wide linear range, excellent reproducibility and stabilitySimple, cheap, rapid and sensitive detection effect.

Description

Method for electrochemical synchronous detection of zinc, cadmium, lead, copper and mercury ions

Technical Field

The invention relates to the field of electrochemical sensors for detecting various heavy metals and food safety analysis, in particular to a method for synchronously detecting zinc, cadmium, lead, copper and mercury ions in agricultural products.

Background

Heavy metal contamination has become an increasingly serious problem in food safety today. Due to the large-scale development and utilization of mineral resources, the wide use of various chemical products, pesticides and fertilizers, and the unreasonable treatment of municipal waste and sludge, various heavy metals are continuously accumulated through a food chain, and finally the health and the life of human beings are threatened. As an important heavy metal migration medium, food plays an important link between heavy metal and human health, and among the heavy metals monitored by most institutions in the world, zinc, cadmium, lead, copper and mercury are the most common typical heavy metals in food. According to the world health organization, lead, mercury and cadmium are the most highly toxic heavy metals, which can lead to liver and kidney failure, lung injury, and brain death. Although copper and zinc are beneficial to human health at appropriate concentrations in the body, excessive intake of copper and zinc can lead to mental dementia, liver failure, iron deficiency anemia, acute poisoning and even death. Recent studies have shown that the coexistence of various heavy metals, in particular zinc, cadmium, lead, copper, mercury, can induce synergistic and additive toxicological effects in humans and animals. With the increasing serious problems caused by various heavy metals in the environment and food, the development of a method for simultaneously detecting various heavy metal ions rapidly, sensitively and conveniently is urgent.

At present, the main methods for detecting heavy metal ions include atomic fluorescence photometry, atomic absorption spectrometry, inductively coupled plasma mass spectrometry and the like. Problems and deficiencies of the prior art: although the methods mentioned above have good selectivity and high sensitivity, the methods require expensive equipment, large equipment volume, are not portable, and are time-consuming in preparing samples, complex in equipment operation, require professional detection, and cannot be applied to real-time online detection of heavy metal ions. The electrochemical stripping voltammetry has the advantages of high sensitivity, simple operation, low cost, low detection limit, quick response and the like, can overcome the problems encountered by the traditional technology, and is a promising method for detecting trace heavy metal ions. Among various electrochemical stripping voltammetry methods, the square wave anodic stripping voltammetry method has higher sensitivity and is more suitable for being applied to detection of heavy metal ions.

When the square wave anodic stripping voltammetry is used for detecting heavy metal ions, the key of the performance depends on the modified electrode material. At present, commonly used electrode materials comprise multi-wall carbon nanotubes, metal nano-ions, metal oxides and the like, but the performance of a sensor prepared based on the materials for detecting heavy metals such as zinc, cadmium, lead, copper and mercury ions is not obviously improved. In order to improve the performance and the practical application capability of the sensor, therefore, a nano material with good adsorption performance, high specific surface area, good catalytic performance and good electrical conductivity needs to be researched and designed to be used as a modified electrode material for detecting heavy metal ions.

Disclosure of Invention

In view of the problems in the prior art, the invention aims to provide an electrochemical sensor based on a fluorinated graphene/gold nanocage composite material and a preparation method thereof, and the electrochemical sensor is applied to synchronous detection of zinc, cadmium, lead, copper and mercury ions in agricultural products.

The invention is realized by the following technical scheme:

the gold nanocage/fluorinated graphene composite material comprises a nanoscale gold nanocage and a fluorinated graphene nanosheet, wherein: the gold nanocages are in a three-dimensional cage-shaped hollow porous shape, the fluorinated graphene nanosheets are in a folded and layered form, and the gold nanocages are uniformly attached to the fluorinated graphene nanosheets.

According to the scheme, the particle size of the gold nanocages is 30-60 nm.

The electrochemical sensor based on the gold nanocage/fluorinated graphene comprises an electrode substrate and a gold nanocage/fluorinated graphene composite material loaded on the electrode substrate.

According to the scheme, the electrode substrate is a glassy carbon electrode.

The preparation method of the electrochemical sensor based on the gold nanocage/fluorinated graphene comprises the following steps: pretreating the electrode substrate; and (3) dropwise coating the gold nanocage/fluorinated graphene composite material solution on the surface of the pretreated electrode substrate, naturally drying, and repeating for multiple times to obtain the electrochemical sensor based on the gold nanocage/fluorinated graphene.

According to the scheme, the electrode substrate is a glassy carbon electrode, and the pretreatment comprises the following steps: polishing the glassy carbon electrode, then placing the electrode in a potassium ferricyanide solution for cyclic voltammetry test to enable the redox peak potential difference of a cyclic voltammetry curve to be less than 70mV, finally performing ultrasonic cleaning on the glassy carbon electrode by using ultrapure water and absolute ethyl alcohol, and drying the glassy carbon electrode by using nitrogen.

The preparation method of the gold nanocage/fluorinated graphene composite material comprises the following steps:

(1) preparing a gold nanocage, namely mixing a precursor chloroauric acid and hexamethylenetetramine, then sequentially adding a polyvinylpyrrolidone protective agent, a silver nitrate crystal face regulating agent and an ascorbic acid reducing agent, stirring, and standing at room temperature for reaction to obtain a solution of the gold nanocage;

(2) preparing fluorinated graphene, namely placing graphene in a tube furnace, removing air and impurities, and then introducing F₂Carrying out fluorination reaction to prepare fluorinated graphene;

(3) and (2) preparing the gold nanocage/fluorinated graphene, dispersing the fluorinated graphene in an ethanol-Nafion solution, performing ultrasonic dispersion, and adding the solution into the gold nanocage solution obtained in the step (1) to perform ultrasonic treatment to obtain the gold nanocage/fluorinated graphene composite material.

According to the scheme, the reaction time is 22-26h by standing at room temperature.

According to the scheme, the molar ratio of the chloroauric acid to the hexamethylenetetramine is as follows: 1:37-1:42.

According to the scheme, the molar ratio of the chloroauric acid to the polyvinylpyrrolidone protective agent is 1:390-1: 410.

The molar ratio of the chloroauric acid to the silver nitrate crystal face regulating agent is as follows: 1:0.40-1:0.50, wherein the molar ratio of the chloroauric acid to the ascorbic acid reducing agent is as follows: 1:1.60-1:1.80.

According to the scheme, the step (2) is that graphene is placed in a reactor, then the reactor is placed in a tube furnace, and N is introduced₂Removing air and impurities in the reactor, and then introducing F₂The fluorination reaction is carried out at 165-185 ℃ for 1-2 hours, wherein the atmosphere is F₂/N₂(1:4-1:2, v/v), finally degassing to remove unreacted gas, and cooling to obtain the fluorinated graphene.

According to the scheme, in the preparation of the fluorinated graphene dispersion liquid: the mass fraction of Nafion in the ethanol-Nafion solution is 0.2-0.5 wt.%, and the ultrasonic dispersion time is 15-25 min.

According to the scheme, the volume ratio of the fluorinated graphene solution to the gold nanocage solution is 3:1-4:1, and the ultrasonic time after the gold nanocage is added is 25-35 min.

The method for synchronously detecting zinc, cadmium, lead, copper and mercury ions in agricultural products is provided, and comprises the following steps: taking the gold nanocage/graphene fluoride modified electrode, namely the graphene fluoride/gold nanocage electrochemical sensor, as a working electrode, taking a silver/silver chloride electrode as a counter electrode and a platinum column electrode as an auxiliary electrode, and scanning a solution to be detected containing zinc, cadmium, lead, copper and mercury ions by a wave anode stripping voltammetry method based on a three-electrode system, wherein: the deposition potential is: -1.15V-1.55V, deposition time of 120-160 s. Recording the current change of the square wave anode stripping voltammetry peak, and respectively calculating the contents of zinc, cadmium, lead, copper and mercury ions according to the linear relation curve of each peak current density-heavy metal ion concentration of the corresponding square wave anode stripping voltammetry characteristic peak current density and the zinc, cadmium, lead, copper and mercury ion concentrations.

According to the scheme, the electrolyte solution is 0.05-0.15M acetate buffer solution with the pH value of 4.0-6.0.

According to the scheme, the scanning window is-1.3V-0.6V.

According to the scheme, the linear relation curve of each peak current-heavy metal ion concentration of the peak current density of the square wave anode stripping voltammetry characteristic peak and the zinc, cadmium, lead, copper and mercury ion concentrations is obtained as follows: scanning standard solutions with different zinc, cadmium, lead, copper and mercury ion concentrations by using a square wave anodic stripping voltammetry, recording current changes, obtaining peak current densities of anodic stripping voltammetry peaks with corresponding characteristics under the standard solutions with different zinc, cadmium, lead, copper and mercury concentrations, and respectively fitting to obtain peak current densities-heavy metal ion concentration linear relation curves of the zinc, cadmium, lead, copper and mercury ion concentrations and the corresponding characteristic peak current densities.

The invention has the beneficial effects that:

① the gold nanocage/graphene fluoride composite material provided by the invention has excellent performances such as large specific surface area, good catalytic activity, strong adsorption capacity and the like, wherein the graphene fluoride in the gold nanocage/graphene fluoride has the characteristics of rapid electron transmission rate, large specific surface area and easy modification, and the negative charge of the graphene fluoride is enhanced due to introduction of C-F bonds in fluorination, so that the adsorption capacity to cations is enhanced, the gold nanocage has good catalytic activity and good adsorption performance to heavy metal ions, and meanwhile, the gold nanocage is uniformly dispersed on the graphene fluoride, so that the specific surface area of the composite material is large, and the electron transmission rate is good.

② the electrochemical sensor can realize high-sensitivity synchronous detection of heavy metals such as zinc, cadmium, lead, copper and mercury ions, and has detection sensitivities of 0.17,0.51,0.68,0.89 and 0.51 μ A μ g^-1L^-1cm^-2The detection limits are respectively 0.08,0.09,0.05,0.19 and 0.01 mu g/L, and the linear ranges are respectively 6-7000,4-6000,6-5000,4-4000 and 6-5000 mu g/L. Compared with other methods for detecting heavy metal ions such as zinc, cadmium, lead, copper and mercury, the electrochemical sensor has the advantages of wide detection linear range, high detection sensitivity, low detection limit, high selectivity, reproducibility and high response performance.

③ the electrochemical sensor can be used for detecting heavy metals such as zinc, cadmium, lead, copper, and mercury ions in agricultural products (such as peanut, rape moss, and tea).

Drawings

FIG. 1 is an XRD pattern of (A) FGP, AuNCs/FG; (B) XPS survey spectra of FGP, AuNCs/FG; high resolution XPS spectra of the elements in AuNCs/FG: c1s (C), F1s (D), Au4F (E). The crystal structure of the composite was determined by XRD characterization. In fig. 1A, the peaks of FGP at 14.54 °, 29.08 ° and 41.06 ° correspond to the (001), (002) and (100) crystal plane diffraction peaks of FGP standard card (JCPDS 30-0476). Diffraction peaks at 38.50 °, 44.67 °, 65.13 °, 78.35 ° and 85.78 ° of AuNCs/FG were consistent with the (111), (200), (220), (311) and (222) crystal plane diffraction peaks of AuNC standard card (JCPDS 04-0784). The XRD characterization result shows that the AuNCs/FG composite material is successfully prepared, and no other miscellaneous peak appears, which shows that the prepared AuNCs/FG has higher purity. The chemical composition and electronic structure of AuNCs/FG were studied by XPS in FIG. 1B. In FGP, we found that the peak for C1s was at 284.6eV, the peak for O1 s was at 532.7eV, and the peak for F1 was at 688.7 eV. In AuNCs/FG, Au4f shows a new peak at 86.2eV, indicating that AuNC has been successfully loaded onto FGP. The XPS characterization results are consistent with the reported FGP and AuNCs results. FIGS. 1C-E are high resolution XPS spectra for C1s, F1s, and Au4F, respectively. From the C1s spectrum (FIG. 1C), it was found that the 6 fitted peaks were located at 292.1eV, 290.3eV, 287.9eV, 286.2eV, 285.2eV, and 284.6eV, respectively, corresponding to-CF₂C-F, C ═ O, C-O, C-C and C ═ C. As is clear from the F1s spectrum (FIG. 1D), there are two different bond types, the C-F bond (689.0eV) and the-CF 2 bond (690.1 eV). The Au4f spectrum (FIG. 1E) shows two peaks of 87.2eV and 83.7eV, respectively, corresponding to the Au4f5/2 and Au4f7/2 orbitals, respectively.

In summary, XRD and XPS characterization demonstrated that gold nanocage/graphene fluoride (AuNCs/FG) nanocomposites were successfully prepared.

FIG. 2 is a scanning electron micrograph of (A) FGP, (B) AuNCs, and (C) AuNCs/FG; (D) AuNCs/FG high-resolution scanning electron microscope image; (E) AuNCs/FG, (F) C, (G) F, (H) Au. The morphology of FGP, AuNCs and AuNCs/FG was studied by field emission Scanning Electron Microscopy (SEM). In fig. 2A, FGP has a wrinkled, multilayered filamentous morphology. In FIG. 2B, AuNCs were found to be uniformly distributed hollow polygonal cage-like morphologies with a particle size of about 50 nm. Fig. 2C and 2D are low-magnification SEM images and high-magnification SEM images, respectively, of the AuNCs/FG nanocomposite material, and it can be clearly seen that the AuNCs are uniformly distributed on the FGP. By element mapping characterization, the distribution of AuNCs/FG was studied. The different colors represent C, F and Au, respectively (FIGS. 2F-H). As can be seen, C, F and Au are uniformly distributed in fig. 2E, which means that AuNC and FGP are successfully complexed and AuNCs/FG composite is successfully prepared.

FIG. 3 is a Transmission Electron Microscope (TEM) image of (A) AuNCs, (C) AuNCs/FG; (B) AuNCs, (D) high resolution transmission electron microscopy images of AuNCs/FG. The shapes of AuNCs and AuNCs/FG are further characterized by a transmission electron microscope and a high-resolution transmission electron microscope. The TEM characterization results are consistent with the SEM characterization results. As can be seen from FIG. 3A, AuNCs have good uniformity, and the corresponding high-resolution transmission electron microscope (FIG. 3B) shows that the morphology of AuNCs is a three-dimensional cage-shaped hollow porous morphology with a particle size of about 50 nm. TEM images of AuNCs/FG in fig. 3C show that FG nanoplatelets are in wrinkled and layered morphology, and that AuNCs are uniformly attached to FG. HRTEM characterization of the corresponding AuNCs/FG (fig. 3D) further showed that the AuNCs had been successfully loaded onto FG and that the hollow porous structure of the AuNCs remained intact.

FIG. 4 shows the same concentration of Zn in four different modified electrode pairs²⁺、Cd²⁺、Pb2+、Cu²⁺And Hg²⁺The square wave anodic stripping voltammetry response contrast graph of (a), wherein graphene gp (a), fluorinated graphene fgp (b), gold nanocages aunc (c) and AuNCs/fg (d); the test conditions are that the same concentration content in 20mL of 0.1M NaAc-HAc solution (pH 5.0), the deposition potential is-1.25V, the deposition time is 140s, and the scanning potential range is-1.3V-0.6V.

As shown in fig. 4, of the 4 modified electrodes gp (a), fgp (b), aunc (c) and AuNCs/FG (d), the AuNCs/FG sensor had the largest response current density to 5 heavy metal ions. Compared with other 3 modified electrodes, the response current density Zn of AuNCs/FG²⁺(378μA cm^-2),Cd²⁺(1614μAcm^-2),Pb²⁺(2012μAcm^-2),Cu²⁺(2480μA cm^-2) And Hg²⁺(1969μAcm^-2) And max. The result shows that the AuNC has a remarkable promoting effect on the catalytic performance of the FGP/AuNC composite material. The FGP/AuNC sensor has the best catalytic performance.

FIG. 5 is (A) a square wave anodic stripping voltammetry response diagram of an electrochemical sensor based on FGP/AuNCs for simultaneously detecting five metal ions; simultaneous detection of Zn²⁺(B)、Cd²⁺(C)、Pb²⁺(D)、Cu²⁺(E)、Hg²⁺(F) Linear plots of the five ions.

Method for using square wave anodic stripping voltammetry to couple Zn to AuNCs/FG sensor²⁺、Cd²⁺、Pb²⁺、Cu²⁺、Hg²⁺The electrochemical detection performance of (2) was evaluated. In FIG. 5A, potentials-1.10. + -. 0.01V, -0.77. + -. 0.03V, -0.50. + -. 0.02V, -0.01. + -. 0.01V, -0.31. + -. 0.02V are respectively attributed to Zn²⁺、Cd²⁺、Pb²⁺、Cu²⁺、Hg²⁺Characteristic peak potential of (2). Furthermore, as the concentration of heavy metal ions increases (from 1. mu.g/L to 8000. mu.g/L), the response current density increases. Zn²⁺(FIG. 5b), Cd²⁺(FIG. 5c) Pb²⁺(FIG. 5d), Cu²⁺(FIG. 5e), and Hg²⁺(FIG. 5f) are the calibration curves corresponding to the heavy metal concentration on the abscissa x (mg/L) and the corresponding ordinate y (mA cm)^-2) Is the maximum peel peak current density. Synchronous electrochemical detection of 5 heavy metals (Zn) by AuNCs/FG sensor²⁺,Cd²⁺,Pb²⁺,Cu²⁺And Hg²⁺) The detection linear ranges of (1) are respectively 6-7000 mug/L, 4-6000 mug/L, 6-5000 mug/L, 4-4000 mug/L and 6-5000 mug/L; the sensitivities were 0.17,0.51,0.68,0.89, and 0.51. mu.A. mu.g, respectively^-1L^-1cm^-2(ii) a The detection limits were 0.08,0.09,0.05,0.19, and 0.01. mu.g/L, respectively. Compared with the reported literature, the electrochemical sensor has lower detection limit, wider linear range and better correlation.

Detailed Description

Example 1

(1) Preparation of gold nanocages 6mL of 0.05M hexamethylenetetramine and 6mL of 1.25mM chloroauric acid were mixed in a 50mL beaker. Then, 6mL of 0.50M polyvinylpyrrolidone, 0.57mg of silver nitrate and 2.35mg of ascorbic acid were added to the mixed solution in this order, and stirred for 60 seconds. And finally, standing the mixture at room temperature for 24 hours to obtain a solution of the gold nanocages.

(2) Preparing fluorinated graphene, namely placing 200mg of graphene in a reactor, and introducing N₂Air and impurities were removed from the reactor. Then, F is introduced₂Fluorination at 180 ℃ for 1 hour in an atmosphere of F₂/N₂(1: 3, v/v), finally degassing to remove unreacted gas, and cooling to obtain the fluorinated graphene.

(3) Preparing the gold nanocage/fluorinated graphene, namely dispersing 3mg of fluorinated graphene in 500 mu L of ethanol-Nafion solution (wherein in the ethanol-Nafion solution, the mass fraction of Nafion is 0.5 wt.%), ultrasonically dispersing for 20min, and then adding 125 mu L of gold nanocage, and ultrasonically dispersing for 30min to obtain the gold nanocage/fluorinated graphene composite material AuNCs/FG.

Preparation method of gold nanocage/fluorinated graphene modified electrode

(1) Polishing the glassy carbon electrode by using alumina slurry with the specification of 0.3 and 0.05 mu m in sequence, then placing the electrode in a 5mmol/L potassium ferricyanide solution, scanning at a potential of-0.2-0.6V to ensure that the difference value of oxidation-reduction peak potentials is less than 70mV, finally performing ultrasonic cleaning on the glassy carbon electrode by using ultrapure water and absolute ethyl alcohol, and drying the glassy carbon electrode by using nitrogen;

(2) and (3) dropwise coating the gold nanocage/fluorinated graphene composite material on the surface of the polished glassy carbon electrode by using a liquid transfer gun, naturally drying, repeating the step three times, and dropwise coating 9 mu L in total to obtain the gold nanocage/fluorinated graphene modified electrode.

5 kinds of heavy metal ions (Zn)²⁺,Cd²⁺,Pb²⁺,Cu²⁺And Hg²⁺) Synchronous detection of

【1】 Drawing a standard curve:

(1) measuring with three-electrode system in electrochemical workstation, using the modified electrode of fluorinated graphene/gold nanocage as working electrode, silver/silver chloride electrode as counter electrode, and platinum columnThe electrode is an auxiliary electrode, a square wave anodic stripping voltammetry test is carried out on a standard solution of 5 heavy metal ions with the concentration of 0.1mol/L to 8000 mug/L in an acetate buffer solution with the concentration of 0.1mol/L, the current change is recorded (figure 5A), the enrichment voltage is-1.25V, the enrichment time is set to 140s, the scanning window is-1.3V to 0.6V, a working curve is drawn according to the linear relation between the anodic stripping voltammetry response peak current density and the concentration of the heavy metal ions, figure 5B, the synchronous electrochemical detection of the 5 heavy metals (Zn) by the AuNCs/FG modified electrode can be calculated according to a corresponding linear curve (figure 5B)²⁺,Cd²⁺,Pb²⁺,Cu²⁺And Hg²⁺) The detection linear ranges of (1) are respectively 6-7000 mug/L, 4-6000 mug/L, 6-500 mug/L, 04-4000 mug/L and 6-5000 mug/L; the sensitivities were 0.17,0.51,0.68,0.89, and 0.51. mu.A. mu.g, respectively^-1L^-1cm^-2(ii) a The detection limits were 0.08,0.09,0.05,0.19, and 0.01. mu.g/L, respectively.

【2】 Detection of the actual sample solution:

and (4) replacing the standard solution with the actual sample solution for quantitative detection.

(1) Sample preparation, 0.5g of the ground sample (tea leaves, rape bolts, peanuts) was placed in a microwave digestion apparatus, 5mL of a mixed solution of nitric acid and hydrogen peroxide (v/v ═ 1: 3) was added, and after sealing, the temperature was set at 180 ℃ and held for 30 minutes. Then removed and heating continued until near dry, and the residual digestive solution was made up to 10mL with water.

(2) And adding each heavy metal ion into the digestive juice of the actual sample according to the adding standard value of 2 mg/L. In order to verify the reliability of the sensor, AuNCs/FG electrochemical sensing detection is carried out on an actual sample and a sample subjected to labeling, and ICP-MS and AFS are used for comparing and verifying peanut, rape moss and tea samples. The experimental results are shown in table 2, the relative standard deviation of the detection results of the sensors is 0.46-5.26%, and the recovery rate reaches 93.50-105.00%. In addition, the detection result of the AuNCs/FG modified electrode has better consistency with the ICP-MS and AFS methods. Therefore, the proposed electrochemical method can simultaneously detect Zn in real samples²⁺，Cd²⁺，Pb²⁺，Cu²⁺And Hg²⁺。

TABLE 2 comparison of the actual samples for AuNCs/FG electrochemical sensor spiked recovery test with the classical method (n. 3)

Nd-not detected

Inductively coupled plasma mass spectrometry (ICP-MS)

Atomic Fluorescence Spectroscopy (AFS)

c relative standard deviation (%) -calculated from data of 3 separate tests

Claims

1. A method for electrochemical synchronous detection of zinc, cadmium, lead, copper and mercury ions is characterized in that: the method comprises the following steps: taking a gold nanocage/fluorinated graphene modified electrode as a working electrode, a silver/silver chloride electrode as a counter electrode, and a platinum column electrode as an auxiliary electrode, and scanning a solution to be detected containing zinc, cadmium, lead, copper and mercury ions by a square wave anode stripping voltammetry based on a three-electrode system, wherein: the deposition potential is: recording the current change of a square wave anode stripping voltammetry peak, and respectively calculating the contents of zinc, cadmium, lead, copper and mercury ions according to a linear relation curve of each peak current-heavy metal ion concentration of the corresponding square wave anode stripping voltammetry characteristic peak current and the concentrations of zinc, cadmium, lead, copper and mercury ions;

the gold nanocage/fluorinated graphene modified electrode comprises an electrode substrate and a gold nanocage/fluorinated graphene composite material loaded on the electrode substrate; the gold nanocage/fluorinated graphene composite material comprises a nano-scale gold nanocage and a fluorinated graphene nanosheet, wherein: the gold nanocages are in a three-dimensional cage-shaped hollow porous shape, the fluorinated graphene nanosheets are in a folded and layered form, and the gold nanocages are uniformly attached to the fluorinated graphene nanosheets.

2. The method of claim 1, wherein: the particle size of the gold nanocages is 30-60 nm.

3. The method of claim 1, wherein: the electrode substrate is a glassy carbon electrode.

4. The method of claim 1, wherein: the preparation method of the gold nanocage/fluorinated graphene composite material comprises the following steps:

(3) preparing a gold nano cage/fluorinated graphene, dispersing the fluorinated graphene in an ethanol-Nafion solution, and performing ultrasonic dispersion to obtain a fluorinated graphene dispersion solution; and (2) adding the gold nanocages obtained in the step (1), and performing ultrasonic treatment to obtain the gold nanocage/fluorinated graphene composite material.

5. The method of claim 4, wherein: standing at room temperature for 22-26 h; the molar ratio of the chloroauric acid to the hexamethylenetetramine is as follows: 1:37-1: 42; the molar ratio of the chloroauric acid to the polyvinylpyrrolidone protective agent is 1:390-1: 410; the molar ratio of the chloroauric acid to the silver nitrate crystal face regulating agent is as follows: 1:0.40-1:0.50, wherein the molar ratio of the chloroauric acid to the ascorbic acid reducing agent is as follows: 1:1.60-1:1.80.

6. The method of claim 4, wherein: the step (2) is that the graphene is placed in a reactor, then the reactor is placed in a tube furnace, and N is introduced₂Removing air and impurities in the reactor, and then introducing F₂At 165Carrying out a fluorination reaction at-185 ℃ for 1-2 hours in an atmosphere of F₂/N₂(1:4-1:2, v/v), finally degassing to remove unreacted gas, and cooling to obtain the fluorinated graphene.

7. The method of claim 4, wherein: in the preparation of the fluorinated graphene dispersion liquid: the mass fraction of Nafion in the ethanol-Nafion solution is 0.2-0.5 wt.%, and the ultrasonic dispersion time is 15-25 min.

8. The method of claim 4, wherein: the volume ratio of the fluorinated graphene dispersion liquid to the gold nanocage solution is 3:1-4:1, and the ultrasonic time after the gold nanocages are added is 25-35 min.

9. The method of claim 1, wherein: the electrolyte solution is 0.05-0.15M, and the pH value is 4.0-6.0 acetate buffer solution; the scanning window is-1.3V-0.6V.

10. The method of claim 1, wherein: the curve of the linear relation between the peak current density of the characteristic peak of the square wave anode stripping voltammetry and the concentration of each peak current-heavy metal ion of zinc, cadmium, lead, copper and mercury ions is obtained as follows: scanning standard solutions with different zinc, cadmium, lead, copper and mercury ion concentrations by using a square wave anodic stripping voltammetry, recording current changes, obtaining peak current densities of anodic stripping voltammetry peaks with corresponding characteristics under the standard solutions with different zinc, cadmium, lead, copper and mercury concentrations, and respectively fitting to obtain peak current densities-heavy metal ion concentration linear relation curves of the zinc, cadmium, lead, copper and mercury ion concentrations and the corresponding characteristic peak current densities.