CN113702458A

CN113702458A - rGO-ZVI nano composite material, application and detection equipment

Info

Publication number: CN113702458A
Application number: CN202110995249.0A
Authority: CN
Inventors: 陈星�; 鲍钱鑫; 吴玉程; 丁兆罡
Original assignee: Hefei University of Technology
Current assignee: Hefei University of Technology
Priority date: 2021-08-27
Filing date: 2021-08-27
Publication date: 2021-11-26
Anticipated expiration: 2041-08-27
Also published as: CN113702458B

Abstract

The invention relates to an rGO-ZVI nano composite material, application and detection equipment. The preparation method of the rGO-ZVI nano composite material comprises the following steps: dissolving graphene oxide powder in deionized water, and performing ultrasonic dispersion to obtain a mixed solution I; adding tea polyphenol into the mixed solution I and fully stirring to obtain mixed solution II; adding ferrous sulfate into the mixed solution II, and stirring for a certain time to obtain a mixed solution III; adding tea polyphenol into deionized water, and uniformly stirring to obtain a mixed solution IV; and finally, adding the mixed solution IV into the mixed solution III, stirring for a certain time to obtain a mixed solution V, and washing and drying the mixed solution V in sequence to obtain the rGO-ZVI nano composite material. The rGO-ZVI nano composite material is prepared by adopting a green route, the tea polyphenol is simultaneously used as a reducing agent and a sealing agent of zero-valent iron, the nano zero-valent iron with good dispersibility is prepared on a reduced graphene oxide framework, the self-aggregation phenomenon of the zero-valent iron is reduced, and the application of the nano zero-valent iron in water pollution detection is expanded.

Description

rGO-ZVI nano composite material, application and detection equipment

Technical Field

The invention relates to water pollution detection, in particular to an rGO-ZVI nano composite material, application and detection equipment.

Background

With the accelerated development of social industry, the environmental pollution is becoming more severe, wherein the heavy metal pollution is particularly prominent, and industrial wastewater discharged by the industries such as electroplating, mining, papermaking and the like is one of the main causes of heavy metal ion pollution. Common heavy metal ions include mercury, lead, cadmium, chromium, etc., which can cause serious damage to the human body at very low concentrations. Because the heavy metal ions can not be naturally degraded by the environment, the generated heavy metal ions are easy to accumulate in fishes, algae and plants and finally reach the human body through a food chain to destroy various organs and nerve centers of the human body. Therefore, a rapid, simple and efficient method for detecting the concentration of heavy metal ions in the water body is needed. The traditional detection methods for heavy metal ions comprise high performance liquid chromatography, colorimetric detection method, atomic absorption spectrometry and the like, and although the methods can accurately detect the content of the heavy metal ions in the water body, the methods often face the problems of expensive equipment, complex operation and the like, and are not suitable for on-site in-situ detection.

The square wave anodic stripping voltammetry is used for detecting heavy metal ions (such as mercury ions and the like) in a water environment, is a common electrochemical detection method, has the advantages of simplicity in operation, easiness in carrying, low detection limit, high sensitivity and the like, and is considered to be an effective replacement method for the traditional detection method. In the detection of the stripping voltammetry, the surface of an electrode needs to be subjected to material modification treatment firstly, so that the electrode surface is provided with a large specific surface area and unique surface properties. Generally, the performance of the electrode modified by noble metal materials is better, because these noble metal materials (including gold, palladium, platinum, etc.) can form a large number of effective active sites on the surface of the electrode, and the electrochemical response capability of the electrode is greatly improved. However, these noble metal materials often face problems such as high cost.

Zero-valent iron is a nano material with high catalytic activity, low cost and no toxicity, is commonly used for detecting and adsorbing heavy metal ions in a water environment, but is easily oxidized and agglomerated in an external environment, and faces a plurality of limitations in practical use. This further limits its application in the field of water pollution detection.

Disclosure of Invention

Based on this, the invention provides an rGO-ZVI nanocomposite, an application and a detection device, aiming at the technical problem that zero-valent iron is easily oxidized and agglomerated in an external environment in the prior art, so that the zero-valent iron is limited in the field of water pollution detection.

The invention provides an rGO-ZVI nano composite material, and a preparation method thereof comprises the following steps:

(1) according to the mass portion ratio, 5 portions of graphene oxide powder, 10 portions of tea polyphenol, 2000 portions of deionized water and 69.5 portions of ferrous sulfate are respectively prepared.

(2) And adding 5 parts of graphene oxide powder into 1000 parts of deionized water, and performing ultrasonic dispersion for 20min to obtain a first mixed solution for later use.

(3) And adding 5 parts of tea polyphenol into the mixed solution I which is kept stirring, and fully reacting to obtain mixed solution II for later use.

(4) Adding 69.5 parts of ferrous sulfate into the second mixed solution, and stirring for 1 hour to obtain a third mixed solution for later use.

(5) And adding 5 parts of tea polyphenol into 1000 parts of deionized water, and uniformly stirring to obtain a mixed solution IV for later use.

(6) And adding the mixed solution IV into the mixed solution III, and stirring for 24 hours to form a mixed solution V.

(7) And washing and drying the mixed solution V in sequence to prepare the rGO-ZVI nano composite material.

In one embodiment, in the step (1), graphene oxide is prepared by a Hummers method, and graphene oxide powder is obtained after vacuum drying treatment.

In one embodiment, in step (3), it is determined whether the tea polyphenol fully reacts with the mixed solution by the color change, and when the color change shows that the color changes from brown yellow to black, it is determined that the tea polyphenol fully reacts with the mixed solution.

In one embodiment, in step (7), the washing treatment process is as follows:

and adding a proper amount of ethanol into the mixed solution five, centrifuging the mixed solution five through a centrifuge, pouring out the supernatant, repeating the steps for three times, adding a proper amount of deionized water into the mixed solution five, centrifuging the mixed solution five through the centrifuge, pouring out the supernatant, and repeating the steps for three times again to fully remove impurities in the mixed solution five.

In one embodiment, the drying process is as follows: and (3) vacuum drying for 6h at 65 ℃ to obtain the rGO-ZVI solid material.

The invention also provides an application of the rGO-ZVI nanocomposite in detecting trace mercury ions in a water environment, wherein the rGO-ZVI nanocomposite is any one of the rGO-ZVI nanocomposites.

The invention also provides a detection device for trace mercury ions in a water environment, and the detection device adopts a square wave anodic stripping voltammetry to detect the concentration of mercury ions in a water sample. The detection device includes:

the three-electrode system comprises a glassy carbon electrode, a silver-silver chloride electrode and a platinum wire electrode. The glassy carbon electrode is used as a working electrode in a three-electrode system and is used for generating corresponding electrochemical response according to the concentration of mercury ions in a water sample under an optimized condition. The glassy carbon electrode is modified by an rGO-ZVI nano composite material. The silver-silver chloride electrode serves as a reference electrode in a three-electrode system. The platinum wire electrode served as the counter electrode in the three-electrode system.

And the current acquisition module is used for acquiring the response current value when the glassy carbon electrode generates electrochemical response.

And the controller is used for inquiring a preset mapping function of the response current and the mercury ion concentration according to the response current value so as to calculate the mercury ion concentration in the water sample corresponding to the response current value.

Wherein, the optimization conditions are as follows: the buffer solution for electrochemical reaction was phosphate buffer solution with a concentration of 0.1M and pH 5. The water sample was mixed with the buffer at a ratio of 1: 9. The enrichment voltage and time of the first stage are set at-1.2V and 180s, respectively. The rGO-ZVI nanocomposite is any one of the rGO-ZVI nanocomposites.

In one embodiment, the modification method for modifying glassy carbon electrode by using rGO-ZVI nano composite material comprises the following steps:

s1, pretreatment of the electrode surface: and polishing the glassy carbon electrode to enable the surface of the glassy carbon electrode to be a mirror surface, then continuously carrying out ultrasonic treatment on the glassy carbon electrode for 2min by using ethanol and deionized water in sequence, and naturally drying for later use.

S2, preparation of a modification liquid: according to the mass part ratio, 0.1 part of rGO-ZVI nano composite material is dissolved in 94.5 parts of dimethylformamide solution, the solution is placed in ultrasonic equipment for ultrasonic treatment for 30min after being stirred, and modification liquid is obtained and taken out for later use.

S3, modification of the electrode: and (3) uniformly dripping a proper amount of modification liquid on the surface of the pretreated glassy carbon electrode by using a trace liquid transfer gun, and naturally drying to obtain the glassy carbon electrode modified by the rGO-ZVI nano composite material.

In one embodiment, in step S1, the polishing process for the glassy carbon electrode is as follows:

and sequentially using alumina powder with the grain diameters of 1.0um, 0.3um and 0.05um to polish the glassy carbon electrode.

In one embodiment, the response current-mercury ion concentration function is obtained by an external standard method.

Compared with the prior art, the rGO-ZVI nanocomposite material, the application and the detection equipment provided by the invention have the following beneficial effects:

1. according to the invention, the rGO-ZVI (zero-valent iron-reduced graphite oxide) nano material is synthesized by adopting a green route, and in the preparation process, tea polyphenol is simultaneously used as a reducing agent and a sealing agent of zero-valent iron, so that nano zero-valent iron with good dispersibility is prepared on a reduced graphene oxide framework. The green synthesis method not only effectively avoids the pollution of the traditional reducing agent to the environment, but also effectively reduces the aggregation and oxidation of zero-valent iron. The zero-valent iron is loaded on the surface of the graphene to form a large number of effective active sites, and the self-aggregation phenomenon of the zero-valent iron is further reduced by utilizing the unique properties of folds, porosity and the like of the graphene, so that the limitation of the traditional zero-valent iron in the actual use is broken through, and the application of the zero-valent iron in the field of water pollution detection can be expanded.

2. According to the invention, tea polyphenol and graphene framework are utilized to carry out double protection on zero-valent iron, so that nano zero-valent iron with good dispersibility can be obtained, and oxygen is not easy to contact. The preparation method not only effectively avoids the aggregation and oxidation of zero-valent iron, but also has large specific surface area and a large number of active sites of the prepared hybrid material, and the performance of the prepared hybrid material is comparable to that of a noble metal material. In addition, the cost of the hybrid material is obviously reduced compared with that of the noble metal, and the marketization is facilitated.

3. The rGO-ZVI nano composite material prepared by the invention can be modified on the surface of an electrode to detect heavy metal ions in water, and due to the good synergistic effect of zero-valent iron and graphene, detection equipment shows a lower detection limit (1.2nM) and a higher sensitivity (41.422 (nA/mu M)), and still shows unique affinity to mercury ions under the interference of other cations.

4. The invention optimizes the electrochemical detection method of the rGO-ZVI modified electrode, and obtains the optimal conditions for detecting mercury ions by the rGO-ZVI modified electrode through a series of experiments on the type of buffer solution, the pH value of the buffer solution, the first-stage ion enrichment time and the enrichment voltage: the buffer was selected as 0.1M phosphate buffer (pH 5) and the enrichment voltage and time for the first stage were set to-1.2V and 180s, respectively.

Drawings

FIG. 1 is a schematic flow diagram of the preparation process of rGO-ZVI nanocomposites in example 1 of the present invention;

FIG. 2 is a graph showing typical stripping curves for 0.5 μ M mercury ions detected by different electrodes in example 2 of the present invention;

FIG. 3 is a schematic representation of the experimental results of the rGO-ZVI modified electrode in example 2 of the present invention under certain optimization conditions; wherein, (a) is buffer type, (b) is solution PH value, (c) is enrichment voltage, and (d) is enrichment time;

FIG. 4 is a schematic diagram of the detection and analysis of mercury ion solutions with different concentrations under optimized conditions in example 2 of the present invention; wherein, (a) is a SWASV response schematic diagram of a rGO-ZVI modified electrode; (b) fitting a calibration curve to the response of (a);

FIG. 5 is a SWASV response graph of rGO-ZVI modified electrodes to a series of concentrations of mercury ions under single ion or multi-ion interference conditions in example 2 of the present invention;

FIG. 6 is a graph of various linear fits corresponding to various interference conditions of FIG. 5;

FIG. 7 is a SWASV response graph and a linear fitting curve graph of the rGO-ZVI modified electrode in the detection of mercury ions in an actual water sample in example 2 of the present invention;

FIG. 8 shows XPS total spectra of rGO-ZVI and high resolution spectra of three elements, iron, oxygen and carbon, in example 2 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "or/and" includes any and all combinations of one or more of the associated listed items.

Example 1

Referring to fig. 1, the present embodiment provides an rGO-ZVI nanocomposite, and the preparation method of the rGO-ZVI nanocomposite includes the following steps, i.e., steps (1) to (7).

(1) 0.5g of graphene oxide powder, 1g of tea polyphenol, 200mL of deionized water, and 6.95g of ferrous sulfate were prepared, respectively. In this embodiment, graphene oxide may be prepared by Hummers method, and the prepared graphene oxide may be vacuum-dried to obtain graphene oxide powder.

Graphene is a common two-dimensional nano material, is paid attention to due to its huge specific surface area and excellent heat conduction and electrical conductivity, and is commonly used in the fields of supercapacitors, sensors and the like. However, the electrochemical response of the electrode cannot be greatly improved by modifying the single graphene material on the surface of the electrode, because the limited number of active sites on the surface of the graphene material limits the capture of heavy metal ions in a water environment, and the difficulty can be well solved by performing corresponding modification treatment on the graphene material.

(2) And adding 0.5g of graphene oxide powder into 100mL of deionized water, and performing ultrasonic dispersion for 20min to obtain a first mixed solution for later use. Due to ultrasonic dispersion treatment, graphene oxide powder can be uniformly dispersed in deionized water, and the mixed solution I is in a suspension state.

(3) Adding 0.5g of tea polyphenol into the mixed solution I which is kept stirring, and obtaining mixed solution II after full reaction for later use. In this embodiment, whether the tea polyphenol and the first mixed liquid sufficiently react can be determined according to the color change mode, and when the color change changes from brown to black, the tea polyphenol and the first mixed liquid can be determined to have sufficiently reacted.

(4) And 6.95g of ferrous sulfate in parts by mass is added into the second mixed solution, and the mixture is stirred for 1 hour to obtain a third mixed solution for later use.

(5) And adding 0.5g of tea polyphenol into 100mL of deionized water, and uniformly stirring to obtain a mixed solution IV for later use.

In this embodiment, the washing treatment process may be as follows: and adding a proper amount of ethanol into the mixed solution five, centrifuging the mixed solution five through a centrifuge, pouring out the supernatant, repeating the steps for three times, adding a proper amount of deionized water into the mixed solution five, centrifuging the mixed solution five through the centrifuge, pouring out the supernatant, and repeating the steps for three times again to fully remove impurities in the mixed solution five. The centrifugation treatment in the step (7) is to remove impurities in the mixed solution five, so that relatively pure solid substances are obtained.

The drying treatment process can be as follows: and (3) drying the solid material for 6 hours in vacuum at the temperature of 65 ℃ to obtain the rGO-ZVI solid material. In this embodiment, the drying may be performed by a vacuum oven.

In the embodiment, a green route is adopted to synthesize the rGO-ZVI (zero-valent iron-reduced graphene oxide) nano material, and in the preparation process, tea polyphenol is simultaneously used as a reducing agent and a sealing agent of zero-valent iron to prepare nano zero-valent iron with good dispersibility on a reduced graphene oxide framework. The green synthesis method not only effectively avoids the pollution of the traditional reducing agent to the environment, but also effectively reduces the aggregation and oxidation of zero-valent iron. The zero-valent iron is loaded on the surface of the graphene to form a large number of effective active sites, and the self-aggregation phenomenon of the zero-valent iron is further reduced by utilizing the unique properties of folds, porosity and the like of the graphene, so that the limitation of the traditional zero-valent iron in the actual use is broken through, and the application of the zero-valent iron in the field of water pollution detection can be expanded.

The traditional preparation method of the zero-valent iron often faces the problem that the zero-valent iron is easy to oxidize and agglomerate, and the embodiment utilizes tea polyphenol and a graphene framework to carry out double protection on the zero-valent iron, so that nano iron ions with good activity and dispersibility can be obtained, and oxygen is not easy to contact. In the embodiment, tea polyphenol is used as a reducing agent, zero-valent iron nanoparticles are prepared on a reduced graphene oxide framework by adopting a green route, and the rGO-ZVI nano material is successfully synthesized. In addition, the cost of the hybrid material is obviously reduced compared with that of the noble metal, and the marketization is facilitated.

Example 2

The rGO-ZVI nanocomposite material in the embodiment 1 can be applied to detection of trace mercury ions in a water environment, and the rGO-ZVI nanocomposite material has a large specific surface area and a large number of active sites, so that mercury ions in the water environment can be effectively adsorbed in the process of detecting the trace mercury ions in the water environment, and the detection of the concentration of the mercury ions in the water environment is facilitated.

The embodiment provides a detection device for trace mercury ions in a water environment, and the detection device detects the concentration of mercury ions in a water sample by adopting a square wave anodic stripping voltammetry method. The detection apparatus includes:

And the controller is used for inquiring a preset response current-mercury ion concentration function according to the response current value and calculating the mercury ion concentration in the water sample corresponding to the response current value. It should be noted here that the mapping function of the response current-mercury ion concentration may be obtained by an external standard method, and before detecting the mercury ion concentration in the water sample, the detection device in this embodiment may perform detection analysis on mercury ion solutions with different concentrations under an optimized condition, and may obtain the sensitivity of the working electrode and calculate a linear fitting coefficient through linear fitting analysis, thereby obtaining the mapping function of the response current-mercury ion concentration.

Wherein, the optimization conditions are as follows: the buffer solution of the electrochemical reaction selects a phosphate buffer solution with the concentration of 0.1M and the pH value of 5, and the enrichment voltage and the time of the first stage are respectively set at-1.2V and 180 s. The rGO-ZVI nanocomposite was the rGO-ZVI nanocomposite used in example 1.

In this embodiment, the method for modifying a glassy carbon electrode by using an rGO-ZVI nanocomposite material may include the following steps:

s1, pretreatment of the electrode surface: and sequentially polishing the glassy carbon electrode by using alumina powder with the grain diameters of 1.0um, 0.3um and 0.05um to enable the surface of the glassy carbon electrode to present a mirror surface, sequentially and continuously carrying out ultrasonic treatment on the glassy carbon electrode for 2min by using ethanol and deionized water, and naturally drying for later use.

S2, preparation of a modification liquid: according to the mass ratio, 10mg of rGO-ZVI nano composite material is dissolved in 10mL of dimethylformamide solution, the solution is placed in ultrasonic equipment for ultrasonic treatment for 30min after stirring, and modification liquid is obtained and taken out for later use.

S3, modification of the electrode: and (3) uniformly dripping 6 mu L of modification liquid by using a micro liquid transfer gun on the surface of the pretreated glassy carbon electrode, and naturally drying to obtain the glassy carbon electrode modified by the rGO-ZVI nano composite material.

In order to verify the effectiveness of the detection apparatus of the present embodiment, the present embodiment further performs a plurality of sets of experiments.

Experiment one:

under the condition that other variables are not changed, working electrodes in a three-electrode system of the detection device are respectively arranged into a glassy carbon electrode (unmodified), a glassy carbon electrode modified by a graphene material and a glassy carbon electrode modified by the rGO-ZVI nano composite material in the embodiment 1 under the optimized condition, the three glassy carbon electrodes are used as three working electrodes, and Hg with the concentration of 0.5 mu M is respectively detected²⁺Different electrochemical response values.

Referring to fig. 2, fig. 2 shows that 0.5 μ M Hg is detected by three electrodes, namely a glassy carbon electrode modified by a graphene material, and a glassy carbon electrode modified by a graphene material loaded with zero-valent iron²⁺Typical peel curve of (a). The effect of detecting mercury ions by the zero-valent iron-loaded graphene material is obviously better than that of a zero-valent iron-unloaded graphene material, and is better than that of a glassy carbon electrode which is not modified by the material. This indicates that the zero-valent iron can provide a large number of effective active sites for the graphene material, and the graphene material enables electricityThe polar surface has a larger specific surface area, and the electrode modified by the hybrid material shows a stronger response current peak to mercury ions due to the synergistic effect of the polar surface and the electrode.

In this embodiment, when the detection device detects the concentration of mercury ions in the solution, the conditions such as the type of buffer, the pH value of the solution, the enrichment voltage, and the enrichment time can also be determined by experiments to be optimal. Thus, a set of experiments is provided below to explore the determination of the optimization conditions.

Experiment two:

the experiment can be divided into a plurality of groups of experiments, and variables in each group of experiments are controlled in a variable control mode. They are respectively: (1) buffer type experiment, (2) solution pH value experiment, (3) enrichment voltage experiment and (4) enrichment time experiment.

(1) Buffer type experiments:

0.1M Acetate Buffer (ABS), 0.1M Phosphate Buffer (PBS) and 0.1M citrate buffer (CPBS) are respectively selected as buffers of three control groups, other conditions are unchanged, and the influence of different buffer types on the response current of the working electrode under the same mercury ion concentration is observed. Referring to fig. 3, it is the effect of different buffer types on the response current of the working electrode that is characterized by (a) in fig. 3. As can be seen from the figure, in this experiment, the working electrode showed the strongest peak of response current to mercury ions when phosphate buffer was selected. (Note: 0.1M acetic Acid Buffer (ABS) was prepared by mixing 0.1M acetic acid and sodium acetate solutions; 0.1M Phosphate Buffer (PBS) was prepared by mixing 0.1M disodium hydrogen phosphate and potassium dihydrogen phosphate solutions; 0.1M citrate buffer (CPBS) was prepared by mixing 0.1M citric acid and sodium citrate solutions; all solutions were prepared from deionized water)

(2) Solution pH value test

The pH of the buffer was set to 3, 4, 5, 6, respectively, and other conditions were unchanged, and the effect of different pH on the response current of the working electrode (rGO-ZVI modified electrode) was observed.

Continuing with FIG. 3, FIG. 3 (b) illustrates the effect of different pH on the response current of the working electrode. As can be seen from the figure, the response current of the working electrode peaked when the pH was 5.

(3) Experiment of enrichment Voltage

The magnitude of the enrichment voltage of a plurality of control groups is respectively-1.5V, -1.4V, -1.3V, -1.2V, -1.1V and-1.0, other conditions are unchanged, and the influence of different enrichment voltages on the response current is observed.

Continuing with FIG. 3, (c) of FIG. 3 illustrates the effect of different accumulation voltages on the response current, and it can be seen that the response current of the working electrode is the largest when the accumulation voltage is at-1.2V.

(4) Experiment of enrichment time

The lengths of the enrichment times of the multiple control groups are respectively set to be unchanged at 90s, 120s, 150s, 180s, 210s and 240s, and the influence of the enrichment times with different lengths on the response current of the working electrode is observed.

Continuing with FIG. 3, FIG. 3 (d) illustrates the effect of different lengths of the enrichment time on the response current of the working electrode. As can be seen, the response current of the working electrode is relatively high when the enrichment time is set at 180s-240 s.

In conclusion, the optimization conditions of the rGO-ZVI modified electrode can be judged by a plurality of experiments of the second experiment.

In the present embodiment, after determining the optimization condition, the aforementioned current-mercury ion concentration function can be obtained through experiments. A set of experiments is provided below for validation:

experiment three:

under the optimized condition, a square wave anodic stripping voltammetry method is adopted to detect mercury ions in a water environment, and a certain amount of mercury ions are added into a water sample in an equivalent manner from low concentration through an external standard method. In this example, the concentration of mercury ions was gradually increased from 0.05 μ M to 0.6 μ M, and the response current of the working electrode was recorded after each addition of a fixed amount of mercury ions, and the voltammogram of the response was plotted accordingly.

Referring to fig. 4, (a) of fig. 4 represents the change of the response current of the working electrode at different concentrations of mercury ions. Figure 4 (b) characterizes a fitted calibration curve that responds to current as a function of concentration. As can be seen from the figure, the modified electrode modified by rGO-ZVI can show electrochemical response when the concentration of mercury ions is only 0.05 μ M, and the sensitivity of the electrode is 41.422(nA/μ M) through linear fitting analysis, and the linear fitting coefficient is 0.999.

In this embodiment, in order to verify the anti-interference capability of the detection device provided in this embodiment under the interference condition of multiple heavy metal ions in practical application, this embodiment further provides a set of experiments.

Experiment four:

four control groups were set up, each control group initially containing the same detection base fluid. A fixed amount of cadmium ions was added to the first control group, a fixed amount of copper ions was added to the second control group, a fixed amount of lead ions was added to the third control group, and the same amounts of cadmium ions, copper ions, and lead ions were simultaneously added to the fourth control group. Equal amounts of mercury ions can be added simultaneously to the four control groups starting from low concentrations after the start of the experiment.

Referring to fig. 5, fig. 5 shows SWASV response graphs of the rGO-ZVI modified electrode of the present embodiment to a series of concentrations of mercury ions under single ion interference or multiple ion interference conditions, where (a), (b), (c), and (d) in fig. 5 correspond to the four control groups in the experiment. As can be seen from the figure, the response current peak value of the rGO-ZVI modified electrode provided by the embodiment can achieve a relatively high level and has high response sensitivity no matter under the condition of single ion interference or multi-ion interference.

Referring to fig. 6, fig. 6 illustrates the corresponding linear fit curves for the multiple anti-interference condition control groups of the present experiment, and fig. 6 corresponds to fig. 5. As can be obtained by combining the graph shown in FIG. 5 and the graph shown in FIG. 6, the rGO-ZVI modified electrode still shows a higher response current peak and a good linear fitting (R)²0.999), which shows that the rGO-ZVI modified electrode has excellent anti-interference capability and still shows unique affinity for mercury ions even in the presence of other ions.

In order to further verify the effectiveness of the detection device provided by the embodiment in practical application, a water sample of south \28125ofHefei city is taken in the embodiment to perform detection on an actual water sample, and the sampling point of the actual water sample is one of domestic water sources of local residents. In this example, an actual water sample was mixed with ABS (pH 5.0) at a ratio of 1:9, and mercury ions in the water environment were detected using square wave anodic stripping voltammetry.

Referring to fig. 7, fig. 7 is a SWASV response diagram of the rGO-ZVI modified electrode for detecting mercury ions in an actual water sample. As can be seen from the figure, since the original mercury ion concentration in the actual water sample is relatively low, after a series of equivalent mercury ions are added into the solution, the hybrid material modified electrode shows an electrochemical response similar to the optimized condition (as shown in FIG. 4), and it can be obtained that the detection sensitivity of the working electrode in the actual water sample is 40.956(nA/μ M), and the linear fitting coefficient is 0.999. Therefore, the detection device provided by the embodiment can still exert better detection sensitivity in practical application.

Referring to fig. 8, (a) in fig. 8 is the XPS total spectrum of the rGO-ZVI nanocomposite of the present embodiment; (b) high resolution spectra for the corresponding Fe2 p; (c) high resolution spectra for the corresponding O1 s; (d) high resolution spectrum of C1 s. As can be seen from the figure, the rGO-ZVI nanocomposite respectively comprises three elements of iron, oxygen, carbon and the like, wherein the two elements of carbon and oxygen are derived from tea polyphenol and graphene, and the iron element is derived from zero-valent iron reduced by the tea polyphenol.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above examples are merely illustrative of several embodiments of the present invention, and the description thereof is more specific and detailed, but not to be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. An rGO-ZVI nanocomposite, wherein the preparation method of the rGO-ZVI nanocomposite comprises the following steps:

(1) respectively preparing 5 parts of graphene oxide powder, 10 parts of tea polyphenol, 2000 parts of deionized water and 69.5 parts of ferrous sulfate according to the mass part ratio;

(2) adding 5 parts of graphene oxide powder into 1000 parts of deionized water, and performing ultrasonic dispersion for 20min to obtain a first mixed solution for later use;

(3) adding 5 parts of tea polyphenol into the mixed solution I which is kept stirring, and obtaining mixed solution II for later use after full reaction;

(4) adding 69.5 parts of ferrous sulfate into the second mixed solution, and stirring for 1 hour to obtain a third mixed solution for later use;

(5) adding 5 parts of tea polyphenol into 1000 parts of deionized water, and uniformly stirring to obtain a mixed solution IV;

(6) adding the mixed solution IV into the mixed solution III, and stirring for 24 hours to form a mixed solution V;

2. The rGO-ZVI nanocomposite material of claim 1, wherein in the step (1), graphene oxide is prepared by a Hummers method, and graphene oxide powder is obtained after vacuum drying treatment.

3. The rGO-ZVI nanocomposite of claim 1, wherein in step (3), the color change is used to determine whether the tea polyphenol fully reacts with the first mixed solution, and when the color change appears to change from brown to black, the tea polyphenol fully reacts with the first mixed solution.

4. The rGO-ZVI nanocomposite of claim 1, wherein in step (7), the washing treatment process is as follows:

and adding a proper amount of ethanol into the mixed solution V, centrifuging the mixed solution V by using a centrifuge, pouring out the supernatant, repeating the steps for three times, adding a proper amount of deionized water into the mixed solution V, centrifuging the mixed solution V by using the centrifuge, pouring out the supernatant, and repeating the steps for three times to fully remove the impurities in the mixed solution V.

5. The rGO-ZVI nanocomposite of claim 1, wherein in step (7), the drying process is as follows:

and (3) vacuum drying for 6h at 65 ℃ to obtain the rGO-ZVI solid material.

6. The application of the rGO-ZVI nanocomposite material in detection of trace mercury ions in water environment is characterized in that the rGO-ZVI nanocomposite material is the rGO-ZVI nanocomposite material as claimed in any one of claims 1 to 5.

7. The detection equipment for the trace mercury ions in the water environment is characterized by detecting the concentration of the mercury ions in a water sample by adopting a square wave anodic stripping voltammetry; the detection apparatus includes:

the three-electrode system comprises a glassy carbon electrode, a silver-silver chloride electrode and a platinum wire electrode; the glassy carbon electrode is used as a working electrode in the three-electrode system and is used for generating corresponding electrochemical response according to the concentration of mercury ions in the water sample under an optimized condition; the glassy carbon electrode is modified by an rGO-ZVI nano composite material; the silver-silver chloride electrode is used as a reference electrode in the three-electrode system; the platinum wire electrode is used as a counter electrode in the three-electrode system;

the current acquisition module is used for acquiring a response current value when the glassy carbon electrode generates electrochemical response;

the controller is used for inquiring a preset response current-mercury ion concentration mapping function according to the response current value so as to calculate the mercury ion concentration in the water sample corresponding to the response current value;

wherein the optimization conditions are as follows: the buffer solution of the electrochemical reaction selects a phosphate buffer solution with the concentration of 0.1M and the pH value of 5; mixing the water sample with a buffer solution in a ratio of 1: 9; the enrichment voltage and time of the first stage are respectively set at-1.2V and 180 s; the rGO-ZVI nanocomposite material is prepared by using the rGO-ZVI nanocomposite material as claimed in any one of claims 1 to 5.

8. The apparatus for detecting the trace mercury ions in the water environment according to claim 7, wherein the method for modifying the glassy carbon electrode by the rGO-ZVI nanocomposite material comprises the following steps:

s1, pretreatment of the electrode surface: polishing the glassy carbon electrode to enable the surface of the glassy carbon electrode to be a mirror surface, then sequentially carrying out continuous ultrasonic treatment on the glassy carbon electrode for 2min by using ethanol and deionized water, and naturally drying for later use;

s2, preparation of a modification liquid: according to the mass part ratio, 0.1 part of rGO-ZVI nano composite material is dissolved in 94.5 parts of dimethylformamide solution, the solution is placed in ultrasonic equipment for ultrasonic treatment for 30min after being stirred, and modification liquid is obtained and taken out for later use;

s3, modification of the electrode: and (3) uniformly dripping a proper amount of modification liquid on the surface of the pretreated glassy carbon electrode by using a trace liquid transfer gun, and naturally air-drying to obtain the glassy carbon electrode modified by the rGO-ZVI nano composite material.

9. The apparatus for detecting the trace mercury ions in the water environment according to claim 8, wherein in step S1, the polishing process of the glassy carbon electrode comprises the following steps:

10. The apparatus for detecting the trace mercury ions in the water environment according to claim 7, wherein the mapping function of the response current to the concentration of the mercury ions is obtained by an external standard method.