CN107356656B - Cadmium-lead electrochemical detection method based on sulfur-doped graphene - Google Patents
Cadmium-lead electrochemical detection method based on sulfur-doped graphene Download PDFInfo
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Abstract
The invention discloses a cadmium-lead electrochemical detection method based on sulfur-doped graphene, wherein an electrochemical sensor involved in the method consists of a polysulfide/graphene-Nafion modified working electrode, an Ag/AgCl reference electrode, a Pt filament counter electrode, an electrolytic cell and an electrochemical workstation, and the electrochemical technology comprises the following steps: differential pulsed anodic stripping voltammetry. The detection range of the sensor to cadmium ions is 2.0-300 mu gL‑1The detection range of the lead ions is 1.0-300 mu gL‑1(ii) a The detection limit is 0.67 mu gL respectively‑1And 0.17. mu.gL‑1Both below 4.5 and 59 times the drinking water standards given by the world health organization; simultaneously, the high-frequency-conversion-rate optical fiber has better reproducibility, stability and anti-interference performance; in the detection of the cadmium and lead ion content of tap water, the sensor shows good sensitivity and repeatability. The sensor can accurately, quickly and simultaneously detect the content of cadmium and lead ions on site, thereby having better practical application prospect.
Description
Technical Field
The invention relates to a cadmium-lead electrochemical detection method based on sulfur-doped graphene, which comprises the following steps: differential pulsed anodic stripping voltammetry.
Background
Due to the advantages of good conductivity, large specific surface area, many active sites and the like, graphene is widely concerned in the field of electrochemical analysis of highly toxic heavy metal ions. However, most of the functionalized modification active sites of the graphene are positioned at the edge of the graphite, and the basal plane carbon occupying most of the atoms of the graphene does not participate in the effective enrichment of heavy metals. Aiming at the problem of full utilization of the graphene carbon base surface, the research on high-sensitivity heavy metal electrochemical sensing based on the graphene composite nano material is developed. The polysulfide with low cost is a functional modifier of graphene, the heavy metal ions are quickly and effectively enriched by utilizing the strong chemical adsorption effect between sulfur and the heavy metal ions, the influence of the functional modification process on the sensing performance, sensitivity, selectivity and the like of a graphene sensor is researched by investigating the factors such as the enrichment capacity, selectivity, stability and the like of polysulfide compounds with different chain lengths for modifying the graphene material on the heavy metal ions, the adsorption mechanism and the electron transfer mechanism of the polysulfide functional graphene material on the heavy metal ions are revealed on the molecular level, a new high-sensitivity and high-selectivity heavy metal electrochemical sensing material and a method technology are established, and new theoretical clues and experimental bases are provided for the detection and treatment of the highly toxic heavy metal ions in the environment.
Heavy metal (mercury, lead, cadmium, arsenic, cadmium, thallium, etc.) pollution has become one of the most serious environmental pollution problems in the world today. With the rapid development of industrial and agricultural production and the increasing population, the discharge of various industrial and mining industry and domestic wastewater, waste residues and the like, the environments such as soil, water and the like which human beings live in all suffer from heavy metal pollution to different degrees, the pollution of the heavy metal to the environment has the characteristics of irreversibility, long-term property, accumulation, latency and the like, and the pollution treatment cost is extremely high.
According to relevant statistics, 1/6 cultivated land in China is polluted by heavy metal (3 hundred million mu), the quantity of polluted grains reaches 1200 million tons every year, and the direct economic loss reaches 200 hundred million RMB in 2006. One of the important means for alleviating the threat caused by heavy metal pollution is to establish an efficient, rapid and sensitive detection technology, meet the requirement of environmental real-time monitoring, and be the urgent need of a multi-stage inspection and detection department.
The mainstream heavy metal testing method at present is an absorption spectrum and emission spectrum method based on atomic spectrum technology, and an analysis method for measuring element content by utilizing atomic or ion absorption or emission specific spectrum has the advantages of high sensitivity, good selectivity, high analysis speed, strong anti-interference capability and the like, and gradually becomes one of standard methods for heavy metal detection from the middle of the last century. The method has the characteristics of simple instrument, reliable method, wide application range and the like, and becomes one of the methods with wider popularity. In addition, biochemical analysis, mass spectrometry, high performance liquid chromatography, and the like are available. Although the detection method has the advantages, the detection method also has the defects of expensive required instruments, high operation cost, long detection time and the like, and the actual requirement of rapid and in-situ detection of the heavy metal is difficult to meet. Compared with the traditional instrument analysis technology, the electrochemical method is used for measuring by utilizing the fact that a certain relation exists between the change of certain electrical parameters (resistance, current, potential, electric quantity and the like) of heavy metal ions in a chemical pool and the concentration of a substance to be measured, has the advantages of simple instrument, high sensitivity, low price, real-time online monitoring and the like, is easy to miniaturize, integrate and automate, and can meet the development direction and requirements of on-site, quick, real-time, online, continuous and automated measurement of heavy metal detection. The core component for electrochemically determining the content of the heavy metal is to design and manufacture an electrode sensing material with high selectivity and high sensitivity. Early polarographic voltammetry based on metal mercury electrode technology can determine more than 10 heavy metal elements such As cadmium (Cd), lead (Pb), copper (Cu), arsenic (As), chromium (Cr) and the like, and the detection limit also reaches the ng/mL level. Because of using the highly toxic metal mercury electrode, the method has certain harm to the health of operators and is easy to cause secondary environmental pollution. In recent years, development of a novel electrode which is green, pollution-free and meets the modern environmental protection requirements becomes a research hotspot in the field of electrochemical detection of heavy metals. Therefore, a bismuth membrane electrode which partially replaces a mercury membrane electrode is successfully developed and applied to the ultra-sensitive anodic stripping voltammetry measurement of cadmium and lead. Compared with bulk phase materials, the nano material has the advantages of large specific surface area, high surface energy, more active sites and the like, and has higher heavy metal enrichment capacity. The nano-scale bismuth nano-particle modified membrane electrode can detect 0.03ppb thallium ions. The Wuhan university Husheng water subject group successfully realizes the electrochemical simultaneous determination of the lead and the cadmium at ppb concentration level by using the anthraquinone/clay nano composite material; pandan Dai et al realizes iodine ion-induced high-sensitivity lead ion detection by using a ferroferric oxide iron oxide nanoparticle modified electrode, and reduces the detection limit to 0.04 nM; hou huina et al successfully achieved simultaneous electrochemical determination of lead and copper using gold/silicon nanowire modified electrodes. The conductivity of the nano material is not ideal, and the nano material needs to be uniformly loaded on the surface of an electrode to meet the electrode conductivity test requirement, so that the electrode material has higher preparation technical requirement. Carbon nanomaterials have the advantages of easy preparation, good conductivity, etc., in addition to the general characteristics of nanomaterials, and have recently received much attention in the field of heavy metal electroanalytical chemistry. Research of Hongqun Luo et al finds that the carbon nano tube can effectively improve the electrochemical response signal of the bismuth film electrode to cadmium ions; the adsorption analysis performance of heavy metals can be effectively improved based on the carbon nanotube composite material.
Graphene in the carbon nanomaterial is a high-conductivity single-layer carbon atom layer discovered by Geim in 2004, and has ultrahigh electron migration rate and large specific surface area (2600 m)2In terms of/g). The heterogeneous electron transfer rate, the local state density, the structural defects and the number of functional groups of the boundary carbon atoms of the graphene are all higher than those of the carbon atoms in the middle part, and the graphene serving as an active site of an electrochemical catalytic organic micromolecule is applied to electrochemical sensing research. The edge carboxylated graphene can be applied to simultaneous pulse voltammetry determination of heavy metal lead and cadmium, the detection limit reaches 0.02 nM and 0.2nM respectively, but the bottom surface carbon atom in the middle of the single-layer graphene does not participate in the heavy metal ion enrichment process. Abraham et al apply 1, 2-bis (diphenylphosphinophenyl) functionalized graphene to the construction of a potential lead ion sensor of graphene, the detection limit reaches 25nM, and the sensitivity is improved by two orders of magnitude. In addition, inorganic nano materials such as gold, bismuth, carbon nano tubes and graphene composite materials can improve the detection sensitivity of the graphene heavy metal sensor. The sensing performance of the graphene electrochemical heavy metal sensor can also be improved by organic high-molecular polymers such as polydopamine, Nafion and chitosan, but the situation that the aggregation of the high-molecular polymers on the surface of graphene affects the transmission of electrons on the surface of the graphene, so that the heavy metal sensing performance of the graphene electrochemical heavy metal sensor cannot reach the optimal performance, is difficult to avoid.
Based on the analysis, in order to improve the sensitivity of the heavy metal electrochemical sensor, the heavy metal capturing groups need to be fixed on the graphene basal plane in a monodisperse mode, and the capturing groups have strong adsorption bonding effect on heavy metal ions. If the sulfur-containing compound is adopted to perform monodisperse functionalized modification on the graphene basal plane, and heavy metal ions are adsorbed based on the strong interaction of sulfur atoms and heavy metal elements, the heavy metal atoms are effectively enriched on the graphene surface, the sensitivity of the heavy metal sensor is greatly enhanced, and thus some very valuable results can be obtained. Although few reports exist on modification of polysulfide compounds on the surface of graphene, no relevant report exists so far on the modification principle of polysulfide compounds with different chain lengths on graphene-based surface carbon, and research on electrochemical sensing performance and electron transfer mechanism of heavy metals.
Aiming at the current problems, the invention provides a preparation method of a polysulfide/graphene cadmium-lead electrochemical sensor, which adopts a wet chemical method to prepare a graphene material, and adjusts and controls the chain length of polysulfide by adjusting the adding amount of a sulfur simple substance, the reaction time and the reaction temperature to form polysulfide (S) with different chain lengths2，S3，S4And S5) The modified graphene composite material explores the optimal structure-activity relationship between the sulfur chain length and the graphene loading amount, inspects the conductivity, the specific surface, the hydrophobicity and the chemical stability of the composite material, and regulates the conductivity, the hydrophilicity and the hydrophobicity of the composite material and the loading amount of polysulfide on the graphene surface.
By comparing the electrochemical sensing performance of the graphene, polysulfide and polysulfide/graphene composite material on the heavy metal ions, the structure-activity relationship between the physicochemical characteristics of the carbon on the base surface of the composite material and the electrochemical sensing performance of the heavy metal ions is researched, and the objective rules of the sensitivity and selectivity of the sulfur chain length and the loading capacity on different heavy metal ions are disclosed. By optimizing a solution buffer system and adjusting the pH value of the solution, the stability and selectivity of the heavy metal sensor are optimized, and a new method and technology for real-time and online sensing of heavy metal ions based on a new material is established.
Disclosure of Invention
The invention aims to provide a cadmium-lead electrochemical detection method based on sulfur-doped graphene, and an electrochemical sensor involved in the method is a polysulfide/graphene-Nafion modified working electrode, an Ag/AgCl reference electrode and a Pt wire counter electrodeThe electrode, the electrolytic cell and the electrochemical workstation, the electrochemical technology is as follows: differential pulsed anodic stripping voltammetry. The detection range of the sensor to cadmium ions is 2.0-300 mu gL-1The detection range of the lead ions is 1.0-300 mu gL-1(ii) a The detection limit is 0.67 mu gL respectively-1And 0.17. mu.gL-1Both below 4.5 and 59 times the drinking water standards given by the world health organization; simultaneously, the high-frequency-conversion-rate optical fiber has better reproducibility, stability and anti-interference performance; in the detection of the cadmium and lead ion content of tap water, the sensor shows good sensitivity and repeatability. The sensor can accurately, quickly and simultaneously detect the content of cadmium and lead ions on site, thereby having better practical application prospect.
The invention relates to a cadmium-lead electrochemical detection method based on sulfur-doped graphene, wherein an electrochemical sensor involved in the method consists of a polysulfide/graphene-Nafion modified working electrode, an Ag/AgCl reference electrode, a Pt filament counter electrode, an electrolytic cell and an electrochemical workstation, and the specific operation is carried out according to the following steps:
a. preparing a graphene oxide carrier:
the preparation method of the graphite oxide Hummers comprises the following steps: under the conditions of ice-water bath and stirring, adding a mixture of 1g of sodium nitrate and 2g of high-purity flake graphite into 46mL of concentrated sulfuric acid, then slowly adding 6g of potassium permanganate under the condition of ice-water bath, keeping the temperature of the solution at 0 ℃, then controlling the temperature at 35 ℃ and stirring in an oil bath for 30 minutes, then slowly adding 88mL of deionized water, then controlling the temperature of the solution at 98 ℃, stirring in the oil bath for 15 minutes, adding 10mL of 30% hydrogen peroxide solution under the stirring state, cooling to room temperature, finally filtering, washing and freeze-drying the mixture to obtain graphite oxide powder;
b. preparing a graphene oxide suspension:
accurately weighing 80.0mg of graphite oxide obtained in the step a, dissolving the graphite oxide in 40mL of deionized water to prepare 2mg/mL of suspension, ultrasonically stirring and dispersing for 50 minutes, and adjusting the pH value to 7-8 by using 1mol/L potassium hydroxide solution;
c. preparation of polysulfide/graphene composite material:
0.385g of sodium sulfide is dissolved into 7mL of deionized water to form a sodium sulfide water solution, 0.1536g of sulfur powder is added, and ultrasonic stirring is carried out until the solution becomes clear and transparent, wherein the reaction equation is as follows:
Na2S+(x-1)S＝Na2Sx(x＝2，3，4，5)
then, under the protection of nitrogen, dropwise adding the transparent solution into the graphene oxide suspension subjected to ultrasonic dispersion in the step b, refluxing for 24 hours at the temperature of 80 ℃, carrying out suction filtration and washing on the obtained solution, then carrying out ultrasonic dispersion on the solution in 80mL of water, adding 0.7mL of hydrazine hydrate under the protection of nitrogen, continuously refluxing for 24 hours at the temperature of 80 ℃, washing the obtained product, and carrying out vacuum drying at the temperature of 110 ℃ for 12 hours to obtain a sulfur-doped graphene composite material;
d. preparing a sulfur-doped graphene electrode:
the bare electrode was treated with 1.0, 0.3 and 0.05 μm Al, respectively2O3Polishing the powder, ultrasonic cleaning in ethanol and deionized water for 3min, and adding N2Drying water on the surface of the electrode, dispersing 1.5mg of the sulfur-doped graphene composite material obtained in the step c in isopropanol and water in a volume ratio of 1:4, performing ultrasonic treatment for 30min to prepare 1.5mg/ml suspension, dripping 4 mu L of the suspension on the surface of the pyrolytic graphite electrode, and naturally drying at room temperature to obtain a sulfur-doped graphene electrode (1);
f. cadmium-lead determination by using sulfur-doped graphene electrode
Respectively connecting one end of a sulfur-doped graphene electrode (1), an Ag/AgCl reference electrode (2) and a Pt wire counter electrode (3) to an electrochemical workstation (1), respectively placing the other ends of the sulfur-doped graphene electrode (1), the Ag/AgCl reference electrode (2) and the Pt wire counter electrode (3) in an electrolytic cell (4), adding 0.1M 10ml HAc-NaAc electrolyte with pH of 4.5 into the electrolytic cell (4), and respectively dropwise adding 50 mu g/L Cd electrolyte2+And Pb2+Solution, with chronoamperometry, parameters set: the enrichment potential is-1.2V; enrichment time 240s, stirring rate: 400 r/min, standing for 10s, setting parameters of differential pulse anodic stripping voltammetry: initial potential-1.0V; termination potential: -0.4V, Cd2+、Pb2+The peak positions of the dissolution peaks are-0.82V and-0.58V respectively, and the concentration Cd is recorded2+、Pb2+The dissolution peak current intensity, the cleaning timing current and the parameter setting: cleaning potential is 0.6V; the cleaning time is 60s, and Cd is continuously increased after cleaning2+、Pb2+And (4) recording the peak current intensities of different concentrations, sequentially and circularly measuring, and drawing an electrochemical analysis cadmium and lead working curve according to the peak current intensities and the concentrations.
The invention discloses a cadmium-lead electrochemical detection method based on sulfur-doped graphene, which uses differential pulse anodic stripping voltammetry. The soft template method for synthesizing mesoporous carbon needs a large amount of reagents and has complicated steps. The detection range of the sensor to cadmium ions is 2.0-300 mu gL-1The detection range of the lead ions is 1.0-300 mu gL-1(ii) a The detection limit is respectively lower than 4.5 times and 59 times of the drinking water standard value given by WHO; simultaneously, the high-frequency-conversion-rate optical fiber has better reproducibility, stability and anti-interference performance; in the detection of the contents of cadmium and lead ions in tap water, the sensor shows good sensitivity and accuracy. The sensor can accurately, quickly and simultaneously detect the content of cadmium and lead ions on site, so the sensor has better practical application prospect, and the used reaction materials are industrial common raw materials, thereby being convenient, easy to obtain and low in cost.
Determining heavy metal ions by using the sulfur-doped graphene composite material modified electrode:
fixing the sulfur-doped graphene composite material on the surface of a glassy carbon electrode, adding heavy metal ions with fixed concentration into an electrolyte buffer solution, performing electrochemical measurement on the heavy metal ions by adopting an electrochemical anodic stripping voltammetry or a pulse voltammetry, and detecting the corresponding relation between the stripping voltammetry current intensity of the heavy metal ions and the concentration of the heavy metal ions.
The sulfur-doped graphene composite material has the following influence on the selectivity and stability of highly toxic heavy metal ions:
investigating different metal cations (such as Fe) of the sulfur-doped graphene composite material under various environmental conditions2+/3+，Cu2+，Co2 +，Pb2+，Cd2+，Ni2+，Ca2+，Mg2+，Al3+Etc.) whether to generate serious interference on the modified membrane electrode of the sulfur-doped graphene composite materialHow to affect the sensitivity of the electrochemical test and the selectivity of the sensor. The stability (service life) of the sulfur-doped graphene composite material electrode is an important condition for determining the practical value of the electrode: and (3) investigating the structure-activity relationship between the response signal of the sulfur-doped graphene composite material electrode and the storage time and the use frequency, and evaluating the practicability of the sulfur-doped graphene composite material electrode.
Compared with the prior art, the method of the invention has obvious differences:
1. utilizing a graphene basal plane:
the sensing performance of the graphene electrochemical heavy metal sensor can be improved by organic high-molecular polymers such as polydopamine, Nafion and chitosan, but the situation that the aggregation of the high-molecular polymers on the surface of graphene affects the transmission of electrons on the surface of the graphene, so that the heavy metal sensing performance of the graphene electrochemical heavy metal sensor cannot reach the optimal performance, is difficult to avoid. In addition, some small molecular compounds, such as cyclodextrin, L-cysteine, ionic liquid and the like, can effectively improve the heavy metal detection performance of the graphene sensor through the action of covalent bonding or strong physical adsorption with functional groups on the edge carbon of the graphene. However, most of the carbon atoms of the groups on the graphene basal plane are not fully utilized, so that in order to improve the sensitivity of the heavy metal electrochemical sensor, the heavy metal capturing groups need to be monodispersed and fixed on the graphene basal plane, and the capturing groups also retain strong adsorption bonding effect on heavy metal ions.
2. The polysulfide/graphene heavy metal sensor method is established as follows:
the sulfur-containing compound is adopted to perform monodisperse functionalized modification on the graphene basal plane, and heavy metal ions are adsorbed based on the strong interaction of sulfur atoms and heavy metal elements, so that the heavy metal atoms are effectively enriched on the graphene surface, the sensitivity of the heavy metal sensor is greatly enhanced, and some very valuable results are obtained. Few reports are reported on polysulfide modification on the surface of graphene, but no relevant report is found so far on the research on the electrochemical sensing performance of heavy metal modified by polysulfide on graphene-based planar carbon.
3. Low detection limit of the sensor:
the maximum acceptable concentration of cadmium and lead in drinking water given by WHO is 3 mu gL respectively-1And 10. mu.gL-1The lowest detection limits of cadmium and lead of the sensor are respectively 0.67 mu gL-1And 0.17. mu.gL-1. The detection limits of cadmium and lead are respectively 4.5 times and 59 times lower than the maximum acceptable concentration of cadmium and lead in drinking water.
Description of the drawings:
FIG. 1 is a flow chart of the synthesis and electrochemical detection of the sulfur-doped graphene composite material of the invention
FIG. 2 is an electron micrograph of the sulfur-doped graphene composite material of the present invention, wherein (a) is a scanning electron micrograph, (b) is a transmission electron micrograph, and (c) is an EDS energy spectrum
FIG. 3 is a photoelectron spectrum of the sulfur-doped graphene composite material of the present invention, wherein (a) the photoelectron spectrum of X and (b) the high resolution S2 p diagram
FIG. 4 is a differential pulse anodic stripping voltammetry diagram for cadmium and lead in accordance with the present invention, wherein (a) is a cadmium working curve of a sensor, and (b) is a cadmium-lead working curve
Detailed Description
The invention is further illustrated by the following specific examples:
a. preparing a graphene oxide carrier:
the preparation method of the graphite oxide Hummers comprises the following steps: under the conditions of ice-water bath and stirring, adding a mixture of 1g of sodium nitrate and 2g of high-purity crystalline flake graphite into 46mL of concentrated sulfuric acid, then slowly adding 6g of potassium permanganate under the condition of ice-water bath, keeping the temperature of the solution at 0 ℃, then controlling the temperature at 35 ℃, stirring in an oil bath for 30 minutes, then slowly adding 88mL of deionized water, keeping the temperature of the solution at 98 ℃, stirring in the oil bath for 15 minutes, adding 10mL of 30% hydrogen peroxide solution under the stirring state, cooling to room temperature, and finally filtering, washing and freeze-drying the mixture to obtain graphite oxide powder;
b. preparing a graphene oxide suspension:
accurately weighing 80mg of graphite oxide powder obtained in the step a, dissolving the graphite oxide powder in 40mL of deionized water to prepare 2mg/mL suspension, ultrasonically dispersing for 50 minutes, and adjusting the pH value to 7-8 by using 1mol/L potassium hydroxide solution;
c. preparation of polysulfide/graphene composite material:
0.385g of sodium sulfide is dissolved into 7mL of deionized water to form a sodium sulfide water solution, 0.1536g of sulfur powder is added, and ultrasonic stirring is carried out until the solution is clear and transparent, wherein the reaction equation is as follows:
Na2S+(x-1)S＝Na2Sx(x＝2，3，4，5)
and then, under the protection of nitrogen, dropwise adding the transparent solution into the graphene oxide suspension subjected to ultrasonic dispersion in the step b, refluxing for 24 hours at the temperature of 80 ℃, filtering and washing the obtained solution for 3-5 times by deionized water, then performing ultrasonic dispersion in 80mL of water, adding 0.7mL of hydrazine hydrate under the protection of nitrogen, continuously refluxing for 24 hours at the temperature of 80 ℃, washing the obtained product, and performing vacuum drying at the temperature of 110 ℃ for 12 hours to obtain the sulfur-doped graphene composite material, wherein the material synthesis diagram is shown in figure 1, and the characteristics are shown in figure 2 and figure 3
d. Preparing a sulfur-doped graphene electrode:
bare electrodes were made with 1.0, 0.3 and 0.05 μm Al, respectively2O3Polishing the powder, ultrasonic cleaning in ethanol and deionized water for 3min, and adding N2Drying water on the surface of the electrode, dispersing 1.5mg of the sulfur-doped graphene composite material obtained in the step c in isopropanol and water in a volume ratio of 1:4, performing ultrasonic treatment for 30min to prepare 1.5mg/ml suspension, dripping 4 mu L of the suspension on the surface of the pyrolytic graphite electrode, and naturally drying at room temperature to obtain a sulfur-doped graphene electrode 1;
f. and (3) measuring cadmium and lead by using the sulfur-doped graphene electrode:
respectively connecting one end of a sulfur-doped graphene electrode 1, an Ag/AgCl reference electrode 2 and a Pt wire counter electrode 3 to an electrochemical workstation 1, respectively placing the other ends of the sulfur-doped graphene electrode 1, the Ag/AgCl reference electrode 2 and the Pt wire counter electrode 3 in an electrolytic cell 4, adding 0.1M 10ml HAc-NaAc electrolyte with pH4.5 into the electrolytic cell 4, and respectively dropwise adding 50 mu g/L Cd2+And Pb2+Solution, with chronoamperometry, parameters set: the enrichment potential is-1.2V; enrichment time 240s, stirring rate: standing for 10s at 400 r/min, and dissolving with differential pulse anodeAnd (3) performing voltammetry parameter setting: initial potential-1.0V; termination potential: -0.4V, Cd2+、Pb2+The peak positions of the dissolution peaks are-0.82V and-0.58V respectively, and the concentration Cd is recorded2+、Pb2+The dissolution peak current intensity, the cleaning timing current and the parameter setting: cleaning potential is 0.6V; the cleaning time is 60s, and Cd is continuously increased after cleaning2+、Pb2+And (3) recording the peak current intensities of different concentrations, sequentially and circularly measuring, and drawing an electrochemical analysis cadmium and lead working curve according to the peak current intensities and the concentrations, wherein the working curve is shown in a table 1:
TABLE 1
Example 2
The method of the invention is used for detecting the water sample:
preparing a HAc-NaAc solution with the pH value of 5.0 by using a laboratory tap water sample, taking 10mL, and adding heavy metals in an amount (mu g/L): 0. 50, 100, recording peak current intensity under different concentrations, respectively measuring for 3 times, and calculating the recovery rate and the relative standard deviation according to a linear equation, wherein the recovery rate and the relative standard deviation are shown in a table 2;
TABLE 2
As can be seen from the table: the recovery rate of heavy metals is between 95.8% and 103.8%, which shows that the cadmium-lead electrochemical detection method based on the sulfur-doped graphene can be used for detecting the concentration of cadmium and lead in a water sample, and has a better result.
Claims (1)
1. The cadmium-lead electrochemical detection method based on sulfur-doped graphene is characterized in that an electrochemical sensor involved in the method consists of a polysulfide/graphene-Nafion modified working electrode, an Ag/AgCl reference electrode, a Pt wire counter electrode, an electrolytic cell and an electrochemical workstation, and the specific operation is carried out according to the following steps:
a. preparing a graphene oxide carrier:
the preparation method of the graphite oxide Hummers comprises the following steps: under the conditions of ice-water bath and stirring, adding a mixture of 1g of sodium nitrate and 2g of high-purity flake graphite into 46mL of concentrated sulfuric acid, then slowly adding 6g of potassium permanganate under the condition of ice-water bath, keeping the temperature of the solution at 0 ℃, then controlling the temperature at 35 ℃ and stirring in an oil bath for 30 minutes, then slowly adding 88mL of deionized water, then controlling the temperature of the solution at 98 ℃, stirring in the oil bath for 15 minutes, adding 10mL of 30% hydrogen peroxide solution under the stirring state, cooling to room temperature, finally filtering, washing and freeze-drying the mixture to obtain graphite oxide powder;
b. preparing a graphene oxide suspension:
accurately weighing 80.0mg of graphite oxide obtained in the step a, dissolving the graphite oxide in 40mL of deionized water to prepare 2mg/mL suspension, ultrasonically stirring and dispersing for 50 minutes, and adjusting the pH value to 7-8 by using 1mol/L potassium hydroxide solution;
c. preparation of polysulfide/graphene composite material:
0.385g of sodium sulfide is dissolved into 7mL of deionized water to form a sodium sulfide water solution, 0.1536g of sulfur powder is added, and ultrasonic stirring is carried out until the solution becomes clear and transparent, wherein the reaction equation is as follows:
Na2S+（x-1）S=Na2Sx(x =2,3,4, 5), dropwise adding the transparent solution into the graphene oxide suspension subjected to ultrasonic dispersion in the step b under the protection of nitrogen, refluxing for 24 hours at the temperature of 80 ℃, filtering and washing the obtained solution, performing ultrasonic dispersion in 80mL of water, adding 0.7mL of hydrazine hydrate under the protection of nitrogen, continuously refluxing for 24 hours at the temperature of 80 ℃, washing the obtained product, and performing vacuum drying at the temperature of 110 ℃ for 12 hours to obtain the sulfur-doped graphene composite material;
d. preparing a sulfur-doped graphene electrode:
the bare electrode was treated with 1.0, 0.3 and 0.05 μm Al, respectively2O3Polishing the powder, ultrasonic cleaning in ethanol and deionized water for 3min, and adding N2Drying the water on the surface of the electrode, dispersing 1.5mg of the sulfur-doped graphene composite material obtained in the step c into isopropanol and water in a volume ratio of 1:4, performing ultrasonic treatment for 30min,preparing 1.5mg/ml suspension, dripping 4 mu L of suspension on the surface of a pyrolytic graphite electrode, and naturally drying at room temperature to obtain a sulfur-doped graphene electrode (1);
f. cadmium-lead determination by using sulfur-doped graphene electrode
Respectively connecting one end of a sulfur-doped graphene electrode (1), an Ag/AgCl reference electrode (2) and a Pt wire counter electrode (3) to an electrochemical workstation, respectively placing the other ends of the sulfur-doped graphene electrode (1), the Ag/AgCl reference electrode (2) and the Pt wire counter electrode (3) in an electrolytic cell (4), adding 0.1M 10ml HAc-NaAc electrolyte with pH4.5 into the electrolytic cell (4), and respectively dropwise adding 50 mu g/L Cd2+And Pb2+Solution, with chronoamperometry, parameters set: the enrichment potential is-1.2V; enrichment time 240s, stirring rate: 400 r/min, standing for 10s, setting parameters of differential pulse anodic stripping voltammetry: initial potential-1.0V; termination potential: -0.4V, Cd2+、Pb2+The peak positions of the dissolution peaks are-0.82V and-0.58V respectively, and the concentration Cd is recorded2+、Pb2+The dissolution peak current intensity, the cleaning timing current and the parameter setting: cleaning potential is 0.6V; the cleaning time is 60s, and Cd is continuously increased after cleaning2+、Pb2+And (4) recording the peak current intensities of different concentrations, sequentially and circularly measuring, and drawing an electrochemical analysis cadmium and lead working curve according to the peak current intensities and the concentrations.
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