CN109884143B - Electrochemical sensor for high-sensitivity synchronous detection of heavy metal cadmium, lead, mercury, copper and zinc ions and preparation method thereof - Google Patents
Electrochemical sensor for high-sensitivity synchronous detection of heavy metal cadmium, lead, mercury, copper and zinc ions and preparation method thereof Download PDFInfo
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Abstract
The invention relates to an electrochemical sensor for high-sensitivity synchronous detection of heavy metal ions of cadmium, lead, mercury, copper and zinc and a preparation method thereof. An electrochemical sensor comprising an electrochemical workstation, an electrolytic cell, and electrodes including a counter electrode, a reference electrode, and a working electrode, wherein: the active component modified on the working electrode is ferroferric oxide/fluorinated multi-walled carbon nano-tubes, and the ferroferric oxide/fluorinated multi-walled carbon nano-tubes are nano composite materials formed by fluorinated multi-walled carbon nano-tubes and ferroferric oxide nano-particles uniformly loaded on the fluorinated multi-walled carbon nano-tubes. The method can realize the synchronous detection of cadmium, lead, mercury, copper and zinc ions, simultaneously improve the synchronous detection flux, has more sensitive detection, lower detection limit and wider linear range, and is applied to the detection of cadmium, lead, mercury, copper and zinc ions in practical samples.
Description
Technical Field
The invention relates to the field of electrochemical sensors for detecting various heavy metals, in particular to an electrochemical sensor for synchronously detecting heavy metal ions such as cadmium, lead, mercury, copper and zinc ions with high sensitivity and a preparation method thereof.
Background
With the continuous development of modern society, the release of toxic heavy metals is more and more. The high content of heavy metals such as cadmium, lead, mercury, copper, zinc and the like in the environment and food is becoming a fatal threat. These heavy metals are not biodegradable and accumulate in the environment and in the food of humans and animals. Cadmium is a major carcinogen, which causes a variety of cancers, cardiovascular diseases and osteoporosis by inhibiting enzymes, producing DNA mismatches, amplifying cellular errors and mutations. Lead can cause death in children, severe damage to the brain and kidneys, manifested as kidney disease and colic. Virulent mercury threatens the brain, kidneys and lungs and causes acral pain, hunter-rocin syndrome and water deficiency. Excess copper causes chronic toxicity, such as Wilson's disease, as well as acute toxicity and even death by producing reactive oxygen species and destroying DNA. Although zinc has an important role in the human body, excessive zinc can cause the liver or kidney to lose function, thereby causing olfactory loss. Recent studies have shown that the coexistence of various heavy metals, in particular cadmium, lead, mercury, copper, zinc, 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 traditional methods for detecting heavy metal ions such as cadmium, lead, mercury, copper and zinc mainly comprise methods such as an atomic fluorescence photometry method, an atomic absorption spectrometry method, an inductively coupled plasma emission spectrometry method, an inductively coupled plasma mass spectrometry method and the like. 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 such as cadmium, lead, mercury, copper and zinc. Among various electrochemical stripping voltammetry methods, the anodic stripping voltammetry method has higher sensitivity and is more suitable for being applied to heavy metal ion detection.
The electrochemical anodic stripping voltammetry for detecting heavy metal comprises two processes of adsorption and stripping of heavy metal ions on a working electrode, and the nano material of the modified electrode plays an important role in improving the performance of an electrochemical sensor for detecting the heavy metal ions. The commonly used modified electrode materials at present comprise multi-wall carbon nanotubes, metal nano-ions, metal oxides and the like. However, the existing electrochemical detection of a plurality of heavy metals has low sensitivity, high detection limit and narrow linear range, which hinders the wide application of the electrochemical detection. Therefore, the high performance of the electrode-modified nanomaterial based on environmental friendliness and low cost in the aspect of simultaneously detecting multiple heavy metals still remains a challenge. Also, to our knowledge, many current electrochemical detection methods can measure up to 4 heavy metals.
Disclosure of Invention
In view of the problems in the prior art, the invention aims to provide an electrochemical sensor for synchronously detecting five heavy metal ions (cadmium, lead, mercury, copper and zinc ions) with high sensitivity and a preparation method thereof.
The electrode modification effective component is ferroferric oxide/fluorinated multi-walled carbon nano-tubes, and the ferroferric oxide/fluorinated multi-walled carbon nano-tubes are nano composite materials formed by fluorinated multi-walled carbon nano-tubes and ferroferric oxide nano-particles uniformly loaded on the fluorinated multi-walled carbon nano-tubes.
According to the scheme, the working electrode is a glassy carbon electrode modified by ferroferric oxide/fluorinated multi-wall carbon nano-tube/Nafion.
According to the scheme, the particle size of the ferroferric oxide nano particle is 4-8nm, and the diameter of the fluorinated multi-walled carbon nano tube is as follows: 28-32 nm and a length of less than 10 μm.
An electrochemical sensor for high-sensitivity synchronous detection of five heavy metal ions (cadmium, lead, mercury, copper and zinc ions) comprises an electrochemical workstation, an electrolytic cell and electrodes, wherein the electrodes comprise a counter electrode, a reference electrode and a working electrode.
According to the scheme, the counter electrode is a platinum wire counter electrode, and the reference electrode is silver/silver chloride.
A method for preparing a working electrode for high-sensitivity synchronous detection of five heavy metal ions (cadmium, lead, mercury, copper and zinc ions) is characterized in that a ferroferric oxide/fluorinated multi-wall carbon nano composite material is dispersed by a Nafion solution and then modified to the surface of a substrate to prepare the electrode.
Specifically, Fe3O4Adding absolute ethyl alcohol into fluorinated multi-walled carbon nanotubes for ultrasonic treatment, then performing centrifugal drying to obtain a ferroferric oxide/fluorinated multi-walled carbon nanotube nano composite material, then dispersing the ferroferric oxide/fluorinated multi-walled carbon nanotube nano composite material in a Nafion solution with the mass fraction of 0.3% -5%, and performing ultrasonic dispersion to obtain a ferroferric oxide/fluorinated multi-walled carbon nano composite material/Nafion dispersion liquid, wherein the optimal concentration of the ferroferric oxide/fluorinated carbon nanotube nano composite material is 6 mg/mL;
and (3) dropwise coating the prepared electrode modification liquid, namely ferroferric oxide/fluorinated multi-walled carbon nano composite material/Nafion dispersion liquid, on the surface of the glassy carbon electrode after polishing and cleaning treatment, and drying to obtain the glassy carbon electrode modified by the ferroferric oxide/fluorinated multi-walled carbon nano tube/Nafion composite material. The polishing and cleaning treatment can be sequentially polishing the glassy carbon electrode by using alumina slurry with the specification of 1.0, 0.3 and 0.05 mu m, ultrasonically cleaning the glassy carbon electrode by using ultrapure water and absolute ethyl alcohol, and finally drying the glassy carbon electrode by using nitrogen.
According to the scheme, the Fe3O4And the mass ratio of the fluorinated multi-walled carbon nanotube to the fluorinated multi-walled carbon nanotube is 1: 3-1: 5. The sonication time was 30 minutes, followed by centrifugation at 10000rpm for 5 minutes and finally vacuum drying at 60 ℃ overnight.
According to the scheme, the preparation of the fluorinated multi-wall carbon nanotube comprises the following steps: degassing and removing impurities from a multi-walled carbon nanotube, and then fluorinating for 24 hours at 200-450 ℃, wherein the atmosphere is F2/N2(1: 9-7: 3, v/v), finally degassing to remove unreacted gas, and cooling for standby.
According to the scheme, the degassing and impurity removing temperature is 150 ℃, and the degassing and impurity removing time is 1 hour.
According to the scheme, the synthesis of the ferroferric oxide comprises the following steps: synthesizing ferroferric oxide by a hydrothermal method, and adding 0.135g FeCl3·6H2O and 0.264g ascorbic acid in 19.7mL H2To O, then 5.3mL of 80% N was added2H4·H2And O. After stirring for about 30 minutes, the homogeneous solution was transferred to a 50mL polytetrafluoroethylene autoclave and reacted at 180 ℃ for 8 hours. The reaction solution after natural cooling was centrifuged, washed three times with ethanol and water, and freeze-dried.
The method for synchronously detecting heavy metal ions such as cadmium, lead, mercury, copper and zinc with high sensitivity comprises the following steps:
(1) by using the electrochemical sensor for synchronously and highly sensitively detecting heavy metal ions such as cadmium, lead, mercury, copper and zinc ions, one ends of a working electrode (2), a counter electrode (3) and a reference electrode (4) are respectively connected to an electrochemical workstation (1), the other ends of the working electrode (2), the counter electrode (3) and the reference electrode (4) are respectively placed in an electrolyte in an electrolytic cell (5), and the electrolyte in the electrolytic cell (5) is an acetic acid-sodium acetate buffer solution containing cadmium, lead, mercury, copper and zinc ions to be detected;
(2) selecting an anodic stripping voltammetry on an electrochemical workstation, setting an enrichment potential to be-1.25V to-1.35V, carrying out i-t enrichment, and after the enrichment is finished, enriching cadmium, lead, mercury, copper and zinc ions on a working electrode modified with a modification solution;
(3) and after the i-t enrichment time is over, immediately stopping stirring the solution in the electrolytic cell, standing, loading a forward scanning voltage with a voltage range of-1.2V-0.6V on the working electrode, oxidizing the cadmium, lead, mercury, copper and zinc elementary substances enriched on the working electrode into cadmium, lead, mercury, copper and zinc ions, dissolving the cadmium, lead, mercury, copper and zinc ions back into the electrolytic buffer solution, recording the change condition of current-voltage by an electrochemical workstation to obtain a current-voltage curve, measuring the anode dissolution peak current under different cadmium, lead, mercury, copper and zinc concentrations, and quantitatively analyzing to obtain the concentrations of the cadmium, lead, mercury, copper and zinc ions to be measured based on the linear relation between the cadmium, lead, mercury, copper and zinc ion concentrations and the peak current.
According to the scheme, the pH value of the acetic acid-sodium acetate buffer solution is 4-6, preferably 5.0, and the concentration is 0.1M.
According to the scheme, the electrolyte can be stirred while enriching, and the stirring speed is 500 rpm/min.
According to the above scheme, the enrichment potential is preferably-1.3V, and the enrichment time is preferably set to 180 s.
The beneficial effects of the invention compared with the prior art comprise:
the nano material modified by the working electrode is the ferroferric oxide/fluorinated multi-walled carbon nano tube, has better conductivity and heavy metal cation adsorption performance, can enhance the adsorption of the working electrode on the heavy metal cations under the condition of the measured potential, ensures that the heavy metal ions are easy to deposit, the working electrode does not evolve hydrogen, realizes the synchronous detection of cadmium, lead, mercury, copper and zinc ions, simultaneously improves the synchronous detection flux, and has more sensitive detection, lower detection limit and wider linear range. Specifically, the fluorinated multi-walled carbon nanotube in the ferroferric oxide/fluorinated multi-walled carbon nanotube modified electrode material introduces a C-F bond due to fluorination, and the semi-ionic C-F bond has certain negative charge, so that the surface of the fluorinated carbon nanotube is negatively charged, and the adsorption capacity on cations is enhanced. Meanwhile, the ferroferric oxide also has good adsorption performance on heavy metal ions, the adsorption performance of the ferroferric oxide and the heavy metal ions is enhanced by the synergistic effect of the ferroferric oxide and the fluorinated multi-walled carbon nano tubes, and meanwhile, the ferroferric oxide is uniformly dispersed on the fluorinated multi-walled carbon nano tubes with good conductivity, so that the specific surface area of the composite material is large, and meanwhile, the electron transfer rate is good, thereby being beneficial to realizing high-sensitivity adsorption of various heavy metal ions.
Compared with other methods, the electrochemical sensor for synchronously detecting 5 heavy metal ions with high sensitivity provided by the invention can improve the detection flux, realizes the simultaneous detection of 5 heavy metal ions, and has the advantages of green and environment-friendly materials, wide detection linear range, high detection sensitivity, low detection limit, good stability and the like, and most other documents can only simultaneously detect 1-4 heavy metal ions at present. In addition, the invention can also be used for detecting cadmium, lead, mercury, copper and zinc ions in practical samples.
The electrochemical sensor can realize high-sensitivity synchronous detection of heavy metal cadmium, lead, mercury, copper and zinc ions, and the detection sensitivity of the heavy metal cadmium, lead, mercury, copper and zinc ions is respectively as follows: 29.88,43.50,120.86,90.31 and 47.34 μ A μ M-1cm-2The detection limits are respectively 0.014,0.0084,0.0039,0.0053 and 0.012 mu M, and the linear ranges are respectively 0.048-30.0,0.028-30.0,0.013-32.5,0.017-31.5 and 0.039-32.5 mu M.
Description of the drawings:
FIG. 1 shows (A) Fe3O4XRD pattern of/F-MWCNTs; fe3O4XPS of/F-MWCNTs C1 s (B), F1 s (C), Fe 2p (D), O1 s (E).
FIG. 2 shows (A) Fe3O4，(B)F-MWCNT，(C)Fe3O4Scanning electron micrographs of/F-MWCNTs (Fe is inserted in A and B3O4And EDS map of F-MWCNT); (D) fe3O4A high-resolution scanning electron microscope image of the/F-MWCNTs; (E) fe3O4The element map of/F-MWCNTs, (F) C, (G) F, (H) Fe, and (I) O.
FIG. 3 shows (A, D) Fe3O4，(B,E)F-MWCNT，(C,F)Fe3O4Transmission electron micrographs of/F-MWCNTs; (G) fe3O4，(H)F-MWCNT，(I)Fe3O4High-resolution transmission electron microscopy of/F-MWCNTs (G, H inset is Fe respectively3O4And Fe3O4Selected area electron diffraction pattern of/F-MWCNTs).
FIG. 4(A) shows (a) GCE and (b) Fe3O4(c) F-MWCNT and (d) Fe3O4The impedance contrast diagram of the/F-MWCNT electrode shows that the working electrode is successfully modified with Fe3O4(ii)/F-MWCNT/Nafion; (B) is (a) GCE, (b) Fe3O4(c) F-MWCNT and (d) Fe3O4the/F-MWCNT electrode has a stripping voltammetry response diagram for five ions of 10 mu M zinc (II), cadmium (II), lead (II), mercury (II) and copper (II) in 0.1M NaAc-HAc buffer solution (pH value is 5.0).
FIG. 5 is a diagram showing the optimization of the reaction conditions, wherein (A) acetic acidOptimizing the pH value of the electrolyte, (B) optimizing the deposition potential, and (C) optimizing the deposition time. Experimental results show that Fe has been successfully modified on the working electrode3O4/F-MWCNT/Nafion。
FIG. 6 is Fe3O4The anode stripping voltammetry response diagram of the/F-MWCNTs/GCE for simultaneously detecting five metal ions with different concentrations shows that the peak current increases with the increase of the ion concentration, which indicates that the electrode has better sensitivity to 5 ions.
FIG. 7 is a linear graph of the simultaneous detection of five ions, namely zinc (II) (A), cadmium (II) (B), lead (II) (C), mercury (II) (D) and copper (II) (E), which are respectively shown in (A), (B), (C), (D) and (E). The detection sensitivities of cadmium, lead, mercury, copper and zinc ions can be calculated by corresponding linear curves and are respectively as follows: 29.88,43.50,120.86,90.31 and 47.34 μ A μ M-1cm-2The detection limits are respectively 0.014,0.0084,0.0039,0.0053 and 0.012 mu M, and the linear ranges are respectively 0.048-30.0,0.028-30.0,0.013-32.5,0.017-31.5 and 0.039-32.5 mu M.
Detailed Description
Example 1
A preparation method of a ferroferric oxide-fluorinated multiwalled carbon nanotube/Nafion modified glassy carbon electrode comprises the following steps:
【1】 Preparation of fluorinated multi-walled carbon nanotubes: the multi-walled carbon nanotubes were placed in a nickel reactor and degassed at 150 ℃ for 1 hour to remove impurities. Then, 0.2g of multi-walled carbon nanotubes were fluorinated at 380 ℃ for 24 hours in an atmosphere F2/N2(1: 3, v/v), finally degassing to remove unreacted gas, and cooling for standby.
【2】 And (3) synthesizing ferroferric oxide: synthesizing ferroferric oxide by a hydrothermal method, and adding 0.135g FeCl3·6H2O and 0.264g ascorbic acid in 19.7mL H2To O, then 5.3mL of 80% N was added2H4·H2And O. After stirring for about 30 minutes, the homogeneous solution was transferred to a 50mL polytetrafluoroethylene autoclave and reacted at 180 ℃ for 8 hours. The reaction solution after natural cooling was centrifuged, washed three times with ethanol and water, and freeze-dried.
【3】 Preparing a ferroferric oxide/fluorinated multi-wall carbon nano composite material: 20mg of Fe3O4And 80mg of prepared fluorinated multi-walled carbon nano-tube is added into 10mL of absolute ethyl alcohol for ultrasonic treatment for 30 minutes, then the mixture is centrifuged for 5 minutes at 10000rpm, and finally the mixture is dried in vacuum at 60 ℃ overnight to obtain the ferroferric oxide/fluorinated multi-walled carbon nano composite material (Fe)3O4/F-MWCNTs)。
【4】 Preparing ferroferric oxide-fluorinated multi-walled carbon nanotube/Nafion dispersion liquid: 1.5mg of ferroferric oxide/fluorinated multi-walled carbon nano composite material is dispersed in 250 mu L of Nafion solution (the mass fraction of Nafion is 0.5 percent by weight percent), and ultrasonic dispersion is carried out for 30 minutes to prepare electrode modification solution with the concentration of the ferroferric oxide-fluorinated multi-walled carbon nano tube of 6mg/mL and the mass fraction of Nafion of 0.5 percent.
【5】 Preparing a modified electrode: polishing the glassy carbon electrode by using alumina slurry with the specification of 1.0, 0.3 and 0.05 mu m in sequence, ultrasonically cleaning the glassy carbon electrode by using ultrapure water and absolute ethyl alcohol, and finally drying the glassy carbon electrode by using nitrogen; and d, dripping 3 mu L of the electrode modification liquid prepared in the step d by using a liquid transfer gun to the surface of the polished glassy carbon electrode, and drying the glassy carbon electrode for 3 minutes under an infrared lamp to obtain the glassy carbon electrode modified by the ferroferric oxide-fluorinated multiwalled carbon nanotube/Nafion composite material.
Fig. 1(a) is an XRD chart of the synthesized ferroferric oxide/fluorinated multi-walled carbon nanotube, which is compared with a standard PDF card to verify that the obtained ferroferric oxide/fluorinated multi-walled carbon nanotube nanocomposite has been successfully synthesized.
Fig. 1(B-E) is an XPS diagram of each element in the ferroferric oxide/fluorinated multi-walled carbon nanotube, from which the components and bonding conditions in the ferroferric oxide/fluorinated multi-walled carbon nanotube can be obtained, and the results of the test show that the ferroferric oxide/fluorinated multi-walled carbon nanotube contains a semi-ionic C-F bond. Further verifies that the ferroferric oxide/fluorinated multi-walled carbon nanotube nano composite material is successfully synthesized.
SEM test results of figures 2(A-D) show that the nano size of the ferroferric oxide is about 4-8nm, ferroferric oxide nano particles are uniformly distributed on the surface of the fluorinated multi-walled carbon nanotube, EDS graphs of the ferroferric oxide and the fluorinated multi-walled carbon nanotube are inserted in figures 2(A, B), and the proportion of atoms of the nano material is obtained through EDS test results, so that the successful preparation of the ferroferric oxide and the fluorinated multi-walled carbon nanotube is verified. FIG. 2(E-I) is an element mapping diagram of each element of the ferroferric oxide/fluorinated multi-walled carbon nanotube composite material, wherein each element is uniformly distributed, and further the successful preparation of the material is verified.
FIG. 3(A, D) Fe3O4，(B,E)F-MWCNT，(C,F)Fe3O4Transmission electron micrographs of/F-MWCNTs; (G) fe3O4，(H)F-MWCNT，(I)Fe3O4High-resolution transmission electron micrographs of/F-MWCNTs. FIG. 3 shows that the result is consistent with SEM, the nanometer size of ferroferric oxide is 4-8nm, and the surface of the fluorinated multi-wall carbon nano tube is rough, which indicates that the fluorinated multi-wall carbon nano tube is successfully fluorinated. FIG. 3(C, F, I) shows that ferroferric oxide nanoparticles are uniformly distributed on the surface of the fluorinated multi-walled carbon nanotube. The inset of fig. 3(G, I) is a selected area electron diffraction pattern of ferroferric oxide and ferroferric oxide/fluorinated multi-walled carbon nanotube composites, respectively, and the test results show that both are polycrystalline structures.
Testing instruments and conditions:
the sensor consists of an electrochemical workstation, an electrolytic cell, a working electrode, a counter electrode and a reference electrode. The platinum wire is used as a counter electrode, silver/silver chloride is used as a reference electrode, and the working electrode is a glassy carbon electrode modified by ferroferric oxide/fluorinated multi-walled carbon nano tube/Nafion, wherein the glassy carbon electrode is used as a substrate and modified by a Nafion film and a ferroferric oxide/fluorinated multi-walled carbon nano tube composite material. One ends of the working electrode, the counter electrode and the reference electrode are respectively connected to the electrochemical workstation, and the other ends of the working electrode, the counter electrode and the reference electrode are respectively placed in electrolyte in the electrolytic cell.
The electrolyte in the electrolytic cell is an acetic acid-sodium acetate buffer solution containing cadmium, lead, mercury, copper and zinc ions to be detected, the pH value of the acetic acid-sodium acetate buffer solution is 5.0, and the concentration of the acetic acid-sodium acetate buffer solution is 0.1M.
The detection method comprises the following steps:
(1) selecting an anodic stripping voltammetry on an electrochemical workstation, setting an enrichment potential to be-1.3V and setting enrichment time to be 180 s; placing an electrolytic cell on an electric stirrer, placing a stirrer in the electrolytic cell, setting the stirring speed of the electric stirrer to be 500rpm/min, and operating i-t enrichment on an electrochemical workstation, wherein cadmium, lead, mercury, copper and zinc ions to be detected can be enriched on a working electrode modified with modification liquid after the operation enrichment time is over.
(2) And after the i-t enrichment time is over, immediately stopping stirring the solution in the electrolytic cell, standing for 30s, loading a forward scanning voltage with the voltage range of-1.2V-0.6V on the working electrode, oxidizing the cadmium, lead, mercury, copper and zinc elementary substances enriched on the working electrode into cadmium, lead, mercury, copper and zinc ions, dissolving the cadmium, lead, mercury, copper and zinc ions back into the electrolytic buffer solution, recording the change condition of current-voltage by an electrochemical workstation to obtain a current-voltage curve, measuring the anode dissolution peak current under different cadmium, lead, mercury, copper and zinc concentrations, and obtaining the linear relation between the cadmium, lead, mercury, copper and zinc ion concentrations and the peak current for quantitatively detecting the concentrations of the cadmium, lead, mercury, copper and zinc ions to be detected.
FIG. 4A is a graph showing the impedance comparison between different electrodes, wherein GCE (a) and Fe3O4(b) F-MWCNT (c) and Fe3O4Impedance of the/F-MWCNT (d) electrode is compared with that of the Fe3O4The resistivity of the/F-MWCNT is higher than that of Fe3O4And F-MWCNT are small, which shows that the conductivity is improved after the material is compounded;
FIG. 4B is a comparison graph of 5 ions of the same concentration tested at the same time with different modified electrodes, from which it can be seen that Fe3O4The peak of the/F-MWCNT is best, and the peak is most sensitive to the simultaneous detection of 5 ions. Synthesizing A and B pictures to obtain Fe3O4the/F-MWCNT modified electrode is the optimal modified electrode.
FIG. 5 shows that 5 kinds of heavy metal ions with respective concentrations of 10. mu.M were measured by a controlled variable method using stripping voltammetry (SWV), and the optimum electrolyte pH, deposition potential and deposition time were selected according to the peak SWV current. (A) pH optimization with Fe3O4The method is characterized in that a/F-MWCNT/0.5% Nafion electrode is used for simultaneously detecting 5 heavy metals of 10 mu M in 0.1NaAc-HAc buffer solutions with different pH values (the pH value is 2-8)Ions, final optimum pH 5.0;
(B) with Fe3O4the/F-MWCNT/0.5% Nafion electrode is enriched in 0.1NaAc-HAc buffer solution with the pH value of 5.0 under different deposition potentials (-1.0V to-1.5V) and then detects 5 heavy metal ions with 10 mu M simultaneously, and the final optimal deposition potential is-1.3V;
(C) with Fe3O4the/F-MWCNT/0.5% Nafion electrode is used for simultaneously detecting 5 heavy metal ions of 10 mu M in a 0.1NaAc-HAc buffer solution with the pH value of 5.0 under the conditions of-1.3V deposition potential and different enrichment time (the enrichment time is 60-360 seconds), and the final optimal deposition time is 180 seconds.
FIG. 6 is Fe3O4The anode stripping voltammetry response diagram of the/F-MWCNTs/GCE for simultaneously detecting five metal ions with different concentrations shows that the peak current increases with the increase of the ion concentration, which indicates that the electrode has better sensitivity to 5 ions.
FIG. 7 is a linear graph of the simultaneous detection of five ions, namely zinc (II) (A), cadmium (II) (B), lead (II) (C), mercury (II) (D) and copper (II) (E), which are respectively shown in (A), (B), (C), (D) and (E). The detection sensitivities of cadmium, lead, mercury, copper and zinc ions can be calculated by corresponding linear curves and are respectively as follows: 29.88,43.50,120.86,90.31 and 47.34 μ A μ M-1cm-2The detection limits are respectively 0.014,0.0084,0.0039,0.0053 and 0.012 mu M, and the linear ranges are respectively 0.048-30.0,0.028-30.0,0.013-32.5,0.017-31.5 and 0.039-32.5 mu M.
Reproducibility and stability studies:
the 6 electrodes simultaneously test 5 ions with the same concentration in parallel, and the RSD is respectively 3.84%, 2.01%, 1.19%, 3.81% and 4.75%, which correspond to cadmium, lead, mercury, copper and zinc ions, thus showing that the electrode has better reproducibility.
The same electrode is placed at room temperature for 30 days, and the test current values of the same electrode at 30 days are 93.2%, 94.3%, 96.4%, 93.1% and 93.5% of the initial values, which correspond to cadmium, lead, mercury, copper and zinc ions, so that the sensor has better stability.
And (3) actual sample detection:
lake water collected from local cities and experimentsThe cell tap water sample was filtered through a water filtration membrane (0.45 μm). 200 mu LHNO3(68.0%, v/w) was added to a 10mL water sample for acidification for 3 hours, and the mixture was heated to remove acid and then tested. For the rice sample, 1g of the rice sample was digested with microwaves in a microwave oven after being sealed in a digestion tank with 10mL of nitric acid. Finally, use 5mL of H2The samples were diluted and tested after acid removal with a hot plate.
The original actual samples were tested by classical methods (ICP-MS and AFS) followed by spiking recovery assays in the original samples, which would use Fe3O4The detection result of the/F-MWCNTs electrochemical sensor is compared with that of the classical method. Specific results are shown in table 1.
TABLE 1 Fe3O4Comparison of practical sample for recovery detection of/F-MWCNT electrochemical sensor by adding standard and classical method
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
The results show that: with Fe3O4the/F-MWCNTs electrochemical sensor and typical methods (ICP-MS and AFS) detect actual samples, and the results have better consistency, the RSD is less than 5.63%, and the recovery rate is 96.0% and 101.5% (Table 1). In the classical method, Cd (II), Pb (II), Cu (II) and Zn (II) are measured by ICP-MS, Hg (II) is measured by AFS, and the test parameters of ICP-MS and AFS are shown in GB/T5750.6-2006 (Chinese drinking water-metal parameter standard test method). The detailed operating conditions are as follows: 【1】 ICP-MS: pump speed: 29 r.min-1The flow rate of the atomizer: 0.86 L.min-1The power: 1300w, assist gas: 0.7 L.min-1Sample washing time: 40s, scanning: peak jump and sampling depth: 180. 【2】 AFS: the measuring method comprises the following steps: cold atoms, lamp current: 30mA, furnace temperature: 100 ℃, high pressure: 230V, carrier gas flow rate: 800L·min-1。
Claims (8)
1. A method for synchronously detecting heavy metal ions of cadmium, lead, mercury, copper and zinc with high sensitivity comprises the following steps:
(1) one end of a working electrode, one end of a counter electrode and one end of a reference electrode of an electrochemical sensor for synchronously detecting heavy metal ions such as cadmium, lead, mercury, copper and zinc ions with high sensitivity are respectively connected to an electrochemical workstation, the other ends of the working electrode, the counter electrode and the reference electrode are respectively placed in electrolyte in an electrolytic cell, the electrolyte in the electrolytic cell is acetic acid-sodium acetate buffer solution containing cadmium, lead, mercury, copper and zinc ions to be detected,
the electrochemical sensor for synchronously detecting heavy metal ions such as cadmium, lead, mercury, copper and zinc ions with high sensitivity comprises an electrochemical workstation, an electrolytic cell and electrodes, wherein the electrodes comprise a counter electrode, a reference electrode and a working electrode, active components modified on the working electrode are ferroferric oxide/fluorinated multi-walled carbon nanotubes, and the ferroferric oxide/fluorinated multi-walled carbon nanotubes are a nano composite material formed by fluorinated multi-walled carbon nanotubes and ferroferric oxide nano particles uniformly loaded on the fluorinated multi-walled carbon nanotubes;
(2) selecting an anodic stripping voltammetry on an electrochemical workstation, setting an enrichment potential to be-1.25V to-1.35V, carrying out i-t enrichment, and after the enrichment is finished, enriching cadmium, lead, mercury, copper and zinc ions on a working electrode modified with a modification solution;
(3) and after the i-t enrichment time is over, immediately stopping stirring the solution in the electrolytic cell, standing, loading a forward scanning voltage with a voltage range of-1.2V-0.6V on the working electrode, oxidizing the cadmium, lead, mercury, copper and zinc elementary substances enriched on the working electrode into cadmium, lead, mercury, copper and zinc ions, dissolving the cadmium, lead, mercury, copper and zinc ions back into the electrolytic buffer solution, recording the change condition of current-voltage by an electrochemical workstation to obtain a current-voltage curve, measuring the anode dissolution peak current under different cadmium, lead, mercury, copper and zinc concentrations, and quantitatively analyzing to obtain the concentrations of the cadmium, lead, mercury, copper and zinc ions to be measured based on the linear relation between the cadmium, lead, mercury, copper and zinc ion concentrations and the peak current.
2. The method of claim 1, wherein: the pH value of the acetic acid-sodium acetate buffer solution is 4-6.
3. The method of claim 1, wherein: the counter electrode is a platinum wire counter electrode, and the reference electrode is silver/silver chloride.
4. The method of claim 1, wherein: the working electrode is a glassy carbon electrode modified by ferroferric oxide/fluorinated multi-wall carbon nano-tube/Nafion.
5. The method of claim 1, wherein: the mass ratio of the ferroferric oxide nano particles to the fluorinated multi-walled carbon nano tubes is 1: 3-1: 5; the particle size of the ferroferric oxide nano particles is 4-8nm, the diameter of the fluorinated multi-walled carbon nano tube is 28-32 nm, and the length of the fluorinated multi-walled carbon nano tube is less than 10 mu m.
6. The method of claim 1, wherein: and dispersing the ferroferric oxide/fluorinated multi-wall carbon nano composite material by using a Nafion solution, and then modifying the dispersed ferroferric oxide/fluorinated multi-wall carbon nano composite material to the surface of a substrate to prepare the electrode.
7. The method of claim 6, wherein: adding absolute ethyl alcohol into ferroferric oxide and fluorinated multi-walled carbon nano-tubes for ultrasonic treatment, then carrying out centrifugal drying to obtain a ferroferric oxide/fluorinated multi-walled carbon nano-tube nano-composite material, then dispersing the ferroferric oxide/fluorinated multi-walled carbon nano-composite material in a Nafion solution with the mass fraction of 0.3% -5%, carrying out ultrasonic dispersion to obtain a ferroferric oxide/fluorinated multi-walled carbon nano-composite material/Nafion dispersion liquid, and modifying the dispersion liquid to the surface of a substrate to prepare an electrode.
8. The method of claim 5, wherein: the preparation of the fluorinated multi-wall carbon nano-tube comprises the following steps: degassing multi-wall carbon nanotube to remove impurities, and then removing impurities in the multi-wall carbon nanotubeFluorinating for 24 hours at 200-450 ℃, wherein the atmosphere is F2 / N2，F2And N2The volume ratio of (1: 9) - (7: 3), finally degassing to remove unreacted gas, and cooling for later use.
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