CN111458388A - Preparation method of GSH @ AuNCs/MgAl-E L DH modified electrode - Google Patents
Preparation method of GSH @ AuNCs/MgAl-E L DH modified electrode Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 31
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- YIXJRHPUWRPCBB-UHFFFAOYSA-N magnesium nitrate Inorganic materials [Mg+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O YIXJRHPUWRPCBB-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y40/00—Manufacture or treatment of nanostructures
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/78—Compounds containing aluminium and two or more other elements, with the exception of oxygen and hydrogen
- C01F7/784—Layered double hydroxide, e.g. comprising nitrate, sulfate or carbonate ions as intercalating anions
- C01F7/785—Hydrotalcite
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
- B22F2009/245—Reduction reaction in an Ionic Liquid [IL]
Abstract
The invention discloses a preparation method of a GSH @ AuNCs/MgAl-E L DH modified electrode, which comprises the following specific steps of S1, preparation of glutathione-coated gold nanocluster GSH @ AuNCs, preparation of a GSH @ AuNCs sample by using glutathione GSH as a stabilizing agent and a reducing agent and a chemical reduction method, S2, preparation of a magnesium-aluminum hydrotalcite MgAl-L DH and magnesium-aluminum hydrotalcite nanosheet MgAl-E L DH by using a coprecipitation and formamide stripping method, S3, preparation of the GSH @ AuNCs/MgAl-E L DH, S4, preparation of the GSH @ AuNCs/MgAl-E L DH modified electrode, preparation of the GSH @ AuNCs/MgAl-E L DH modified electrode, preparation of the modified electrode, increase of the electrochemical activity of the electrode, and simultaneous determination of the GSH @ AuNCs/MgAl-E L modified electrode on isoprocarb and isoprocarb.
Description
Technical Field
The invention relates to the field of modified electrode preparation, in particular to a preparation method and detection application of a GSH @ AuNCs/MgAl-E L DH modified electrode.
Background
The carbamate pesticide is an ester (R) derived from carbamate1-O-CO-NR2R3) Or thioesters (R)1-S-CO-NR2R3) The composition is used for controlling plant diseases and insect pests and increasing crop yield. Most carbamate pesticides (such as carbaryl and isoprocarb) are directly sprayed on crops, but residual pesticides are diffused into ecosystems such as soil and water. Pesticides are among the most toxic chemicals to any organism, causing problems with cancer, the urinary system and nervous system, and ultimately death from continued exposure to pesticides. Therefore, it is very necessary to detect the residue of pesticides such as carbaryl and isoprocarb in vegetables to ensure food safety.
In the past, many conventional methods have been applied to the detection of carbaryl and isoprocarb, including liquid chromatography, fluorescence, gas chromatography, electrochemical sensors, and polarography. Most of these methods are sensitive and efficient. The electrochemical sensor is an important tool for environmental monitoring and food safety detection due to the characteristics of nondestructive detection, low detection limit and strong universality. However, the unmodified electrode has slow reaction kinetics and poor catalytic activity, and is not enough to meet the requirements of an electrochemical sensor. Therefore, the exploration of an efficient electrode modification material has important significance for improving the catalytic detection performance of carbaryl and isoprocarb.
The hydrotalcite-like nano-sheet is an important two-dimensional nano-material, has the characteristics of high catalytic activity, good mechanical strength and the like, and is applied to the aspects of electrochemical sensors, energy conversion, energy storage, catalysis and the like. For an electrochemical sensor, the hydrotalcite-like nanosheet can provide an effective mass transfer path and more active sites. However, the single hydrotalcite-like nano-sheet can generate agglomeration phenomenon in the preparation and application processes to cause the loss of active area and active sites, and meanwhile, the single hydrotalcite-like nano-sheet also has the problem of poor conductivity, thereby limiting the application range of the single hydrotalcite-like nano-sheet.
The gold nanocluster is proved to be a high-activity high-selectivity catalyst due to the advantages of good conductivity, small size, controllability and the like. In electrochemical detection, the gold nanoclusters can improve the conductivity of the electrode, improve the transfer speed of electrons and provide a large number of active sites. However, the small size of the gold nanoclusters causes problems of instability, easy aggregation and the like when the sensor is constructed, and the electrochemical performance of the gold nanoclusters is influenced.
In order to solve the defects existing when the materials are used independently, the invention adopts the positively charged stripped magnalium hydrotalcite nanosheet (MgAl-E L DH) and the gold nanocluster (GSH @ AuNCs) with stable glutathione and containing sulfydryl, carboxyl and other groups to synthesize the glutathione coated gold nanocluster/magnalium hydrotalcite nanosheet compound (GSH @ AuNCs/MgAl-E L DH) through the action of positive and negative charge electrostatic attraction, prepare the modified electrode and use the modified electrode for simultaneous detection of carbaryl and isoprocarb, the MgAl-E L nanosheet DH prepared by adopting the formamide stripping method has thin thickness and small size, the GSH @ AuNCs synthesized by the chemical reduction method are regular spherical shapes and small and uniform sizes, in the composite material, the MgAl-E L serves as a main support body, a larger dispersion ratio is provided, an active site with full exposure is provided, the GSH @ AuNCs are uniformly adsorbed on the support body, the conductivity of the material is improved, the synergistic effect between two groups of the electronic interaction plays a role of inhibiting each other, the stability of enhancing the modified GSH @ AuNCs, the electrochemical detection of the GSH @ NCs has a good sense of electrochemical detection of improving the electrochemical detection of the MgAl-Almoccasin which makes up the MgAl-Alkanba 2 and the electrochemical detection of the MgH @ AuNCHs @ AuNCs.
Disclosure of Invention
In view of the above, the invention provides a preparation method of a GSH @ AuNCs/MgAl-E L DH modified electrode, which comprises the steps of preparing hydrotalcite-like compound L DH, coating gold nanoclusters GSH @ AuNCs with glutathione to form GSH @ AuNCs/MgAl-E L DH, preparing the modified electrode, increasing the electrochemical activity of the electrode, and successfully fixing the GSH @ AuNCs/MgAl-E L DH on the surface of the electrode.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a preparation method of a GSH @ AuNCs/MgAl-E L DH modified electrode comprises the following specific steps:
s1, preparation of the glutathione-coated gold nanocluster GSH @ AuNCs:
pipetting HAuCl with pipette4Placing the solution and glutathione solution in a beaker, adding NaOH solution after vigorously stirring for 5min, placing at room temperature and reacting for 19h with slow stirring to obtain light yellow solution GSH @ AuNCs, dialyzing and purifying with a dialysis bag of 1KDa, placing in a refrigerator at 4 ℃, and keeping the whole operation process away from light;
s2, preparing the magnesium-aluminum hydrotalcite material:
preparation of magnesium-aluminum hydrotalcite MgAl-L DH by weighing Mg (NO)3)2·6H2O、Al(NO3)3·9H2Adding deionized water into a round-bottom flask to completely dissolve O and urea, stirring the mixed solution at room temperature for two hours, heating to 97 ℃, refluxing for 48 hours to obtain a white MgAl-L DH solid, centrifuging at 8000r for 5min, and washing with deionized water and absolute ethyl alcohol for three times respectively;
preparing magnesium-aluminum hydrotalcite nanosheet MgAl-E L DH, namely measuring the solid content of a MgAl-L DH wet sample, accurately weighing the MgAl-L DH wet sample, dissolving the MgAl-L DH wet sample in formamide, and ultrasonically stripping for 48 hours to obtain the magnesium-aluminum hydrotalcite nanosheet MgAl-E L DH;
s3, preparing GSH @ AuNCs/MgAl-E L DH;
adopting an electrostatic adsorption method, mixing a GSH @ AuNCs solution and a MgAl-E L DH solution according to the volume ratio of GSH @ AuNCs to MgAl-E L DH being 1:1, slowly stirring for 30min at room temperature, and then incubating for 6h to obtain a suspension of the GSH @ AuNCs/MgAl-E L DH nanosheet compound, respectively preparing the GSH @ AuNCs/MgAl-E L DH being 2:1, 1:2, 1:3 and 1:4 GSH @ AuNCs/MgAl-E L DH nanosheet compound with different solution volume ratios under the same step and condition, and keeping the whole process away from light;
s4, preparation of modified electrode:
polishing and grinding a glassy carbon electrode GCE with the diameter of 3mm to a mirror surface by using alumina powder, respectively ultrasonically washing the polished glassy carbon electrode GCE in a mixed solution of dilute nitric acid and ethanol, washing the polished glassy carbon electrode GCE with deionized water, transferring a GSH @ AuNCs/MgAl-E L DH suspension liquid drop of 2 mu L by using a liquid transfer gun, coating the suspension liquid drop on the surface of the pretreated naked GCE, covering a beaker with the solution, drying the solution at room temperature, and marking the solution as GSH @ AuNCs/MgAl-E L DH/GCE, and preparing the GSH @ AuNCs/GCE and the MgAl-E L DH/GCE by using the same conditions and steps.
Preferably, in the step S1, HAuCl4The concentration of the solution, the concentration of the glutathione solution and the concentration of the NaOH solution are respectively 10mM, 15mM and 1M, and 5-15M L HAuCl is removed by using a pipette gun4The solution and 6-18m L glutathione solution are put into a beaker and stirred vigorously for reaction for 5min, and then 1-5m L NaOH solution is added.
Preferably, in the step S2, 0.11 to 0.15g of Mg (NO) is accurately weighed when preparing the MgAl-L DH sample3)2·6H2O、0.0937g Al(NO3)3·9H2Placing O and 0.05-0.10g urea in 80m L round-bottom flask, and measuring solid content by taking three empty dry 1.5m L centrifuge tubes, respectively labeled with numerals 1, 2 and 3, and weighing with tray balance and marking as m1Empty, m2Empty, m3Respectively placing proper amount of prepared MgAl-L DH wet sample into a centrifugal tube with a label, weighing and recording as m1Wet, m2Wet, m3And (5) wetting. Drying the three centrifuge tubes containing the wet sample in a 50 ℃ oven, taking out the centrifuge tubes after the wet sample is completely dried, weighing again and recording as m1Dry, m2Dry, m3And (d) drying, and calculating by using a calculation formula of (m dry-m empty)/(m wet-m empty) 100% to obtain the solid content of MgAl-L DH.
Preferably, in the step S3, the MgAl-L DH suspension is calculated and weighed, and a MgAl-L DH wet sample with a solid content of 2-7mg is added into 10m L deionized water, and the mixture is fully stirred and dispersed under ultrasonic conditions.
Preferably, in the step S3, AuNCs in the prepared GSH @ AuNCs/MgAl-E L DH nanosheet composite are uniformly distributed on the surface of the MgAl-E L DH nanosheet, are smaller in size and are more regularly and circularly shaped at 2-3nm, and the GSH @ AuNCs and MgAl-E L DH do not have an aggregation phenomenon and have better dispersibility.
The application of the preparation method of the GSH @ AuNCs/MgAl-E L DH modified electrode is characterized in that the modified electrode prepared by the method is used for simultaneously detecting pesticides carbaryl and isoprocarb.
By adopting the technical scheme, the invention has the following beneficial effects:
the electrode material of the GSH @ AuNCs/MgAl-E L DH nanosheet composite modified electrode is prepared by firstly preparing MgAl-L DH by adopting a coprecipitation method, ultrasonically stripping the MgAl-L DH in formamide to obtain MgAl-E L DH, synthesizing the GSH @ AuNCs at room temperature by utilizing a chemical reduction method, and then preparing the electrode material by utilizing an electrostatic adsorption method, wherein the preparation method is simple.
The GSH @ AuNCs/MgAl-E L DH nanosheet composite modified electrode plays a synergistic effect of GSH @ AuNCs and MgAl-E L DH in the aspects of electrocatalysis of carbaryl and isoprocarb, MgAl-E L DH nanosheets obtained by a formamide stripping method are thin and have small sizes and active sites fully exposed, a carrier is provided for adsorption of the GSH @ AuNCs in the composite, the GSH @ AuNCs obtained by a chemical reduction method are regular spherical in shape and small and uniform in size, the electrical conductivity of the composite material is improved by doping, the stability of the GSH @ AuNCs is improved by the synergistic effect of the GSH @ AuNCs and the MgAl-E L DH, the mutual aggregation is inhibited, and the adsorption and capture capacities of the modified electrode on a detected object are improved.
The GSH @ AuNCs/MgAl-E L DH nanosheet composite modified electrode has the advantages that a wider linear range (0.01-30 mu M) and lower detection limits (5.73 nM for carbaryl and 6.39nM for isoprocarb) are obtained in the aspect of simultaneous detection of carbaryl and isoprocarb, and the oxidation peak potential difference is larger, so that simultaneous detection of carbaryl and isoprocarb can be well realized, the detection method is good in stability and high in sensitivity.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the description of the embodiments are briefly introduced below, the drawings in the description below are merely the embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a transmission electron micrograph of GSH @ AuNCs (A) and a diameter distribution histogram (B) thereof, and a transmission electron micrograph of GSH @ AuNCs/MgAl-E L DH (C) and a partial magnification (D) thereof;
FIG. 2 is a graph of the IR spectra of pure GSH, MgAl-E L DH and GSH @ AuNCs/MgAl-E L DH (A), and the UV-vis spectra of pure GSH and GSH @ AuNCs (B);
FIG. 3 is an XRD pattern of GSH @ AuNCs/MgAl-E L DH;
FIG. 4 shows different materials in [ Fe (CN) ]6]3-/4-Cyclic voltammogram (a) and impedance plot (B) in solution;
FIG. 5 shows different materials at 5mM [ Fe (CN) ] containing 0.1M KCl6]3-/4-Cyclic voltammogram (a) and impedance plot (B) in solution;
FIG. 6 shows CV diagrams (A) for different materials in KOH solution (0.2M) containing 0.1mM carbaryl and isoprocarb and CV diagrams (B) for GSH @ AuNCs/MgAl-E L DH/GCE in blank (a), solution (c) containing 0.1mM carbaryl, solution (B) containing 0.1mM isoprocarb, and solution (d) containing 0.1mM carbaryl and isoprocarb;
FIG. 7 is a graph of the effect of GSH @ AuNCs/MgAl-E L DH modification on the peak currents for carbaryl (a) and isoprocarb (b);
FIG. 8 is a graph of the effect of accumulation time (A) and accumulation potential (B) on the peak current of carbaryl (a) and isoprocarb (B);
FIG. 9 is a CV diagram (A) and the effect on peak current (B) of carbaryl (a) and isoprocarb (B) in different concentrations of KOH solutions (a to e: 0.1, 0.2, 0.3, 0.4, 0.5M);
FIG. 10 is a DPV curve (A) of carbaryl at various concentrations (0.01-30 μ M) in a 0.2M KOH solution containing 50nM isoprocarb, with an enlargement (B) of the DPV curve for carbaryl over the 0.01-1 μ M concentration range; DPV curves (C) for isoprocarb at various concentrations (0.01-30 μ M) in 0.2M KOH solutions containing 50nM carbaryl, and a magnified plot (D) of the DPV curves for isoprocarb over the 0.01-1 μ M concentration range. The inset is a calibration curve of carbaryl and isoprocarb;
FIG. 11 shows the reproducibility (A) and stability (B) of GSH @ AuNCs/MgAl-E L DH/GCE;
FIG. 12 shows the anti-interference detection of GSH @ AuNCs/MgAl-E L DH/GCE.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all 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.
The GSH @ AuNCs/MgAl-E L DH/GCE for the electrode is prepared by the method, and data in the GSH @ AuNCs/MgAl-E L DH/GCE are optimized, and the specific preparation and experimental processes are as follows:
a preparation method of GSH @ AuNCs/MgAl-E L DH/GCE for an electrode comprises the following specific steps:
s1, formulation GSH @ AuNCs reagent:
preparation of HAuCl4The concentrations of the solution, the glutathione solution and the NaOH solution are respectively 10mM, 15mM and 1M;
s2, preparation of GSH @ AuNCs:
adopting chemical reduction method, and using pipette to transfer 5-15m L HAuCl4Placing the solution and 6-18m L glutathione solution in a beaker, violently stirring for reaction for 5min, adding 1-5m L NaOH solution, placing at room temperature and reacting for 19h with slow stirring to obtain light yellow solution GSH @ AuNCs, dialyzing and purifying by using a dialysis bag of 1KDa, and placing in a refrigerator for 4 ℃, and keeping the whole operation process away from light;
s3, preparing MgAl-L DH reagent:
accurately weigh 0.11-0.15g Mg (NO)3)2·6H2O、0.0937g Al(NO3)3·9H2O and 0.05-0.10g of urea are put into an 80m L round-bottom flask, and 50m L deionized water is added to completely dissolve the O and the urea;
s4, preparation of MgAl-L DH:
Mg(NO3)2·6H2O、Al(NO3)3·9H2stirring the mixed solution of O and urea at room temperature for two hours, heating to 97 ℃, refluxing for 48 hours to obtain a white MgAl-L DH solid, centrifuging for 5min at 8000r, and washing with deionized water and absolute ethyl alcohol for three times respectively;
s5, preparation of MgAl-E L DH:
taking an MgAl-L DH wet sample to measure the solid content, taking three empty dry 1.5m L centrifuge tubes to carry out labels 1, 2 and 3 respectively, weighing the weight by a tray balance and recording the weight as m1Empty, m2Empty, m3Respectively placing proper amount of prepared MgAl-L DH wet sample into a centrifugal tube with a label, weighing and recording as m1Wet, m2Wet, m3And (5) wetting. Drying the three centrifuge tubes containing the wet sample in a 50 ℃ oven, taking out the centrifuge tubes after the wet sample is completely dried, weighing again and recording as m1Dry, m2Dry, m3Calculating the solid content of MgAl-L DH by using a calculation formula of (m dry-m empty)/(m wet-m empty) 100%, calculating a MgAl-L DH wet sample required by 50mg of dry sample according to the solid content, accurately weighing the MgAl-L DH wet sample, dissolving the MgAl-L DH in 100m L formamide, and ultrasonically stripping for 48 hours to obtain a magnesium-aluminum hydrotalcite nanosheet MgAl-E L DH;
s6, preparing GSH @ AuNCs/MgAl-E L DH/GCE for electrodes:
polishing and grinding a glassy carbon electrode GCE with the diameter of 3mm by using alumina powder, ultrasonically washing the glassy carbon electrode GCE in a mixed solution of dilute nitric acid and ethanol, washing the glassy carbon electrode GCE clean by using deionized water, transferring 2 mu L GSH @ AuNCs/MgAl-E L DH suspension by using a liquid transfer gun, dropwise coating the suspension on the surface of a clean naked GCE, covering a beaker, airing the surface of the naked GCE at room temperature, and then using the suspension as a working electrode GSH @ AuNCs/MgAl-E L DH/GCE, wherein the GSH @ AuNCs/GCE and the MgAl-E L DH/GCE are prepared under the same condition.
Structure and shape characterization analysis
(1) The TEM is shown in FIG. 1, it can be seen from the graph (A) that the synthesized GSH @ AuNCs are in a more regular spherical shape, uniform in size and better in dispersion degree, and large-area aggregation and large-size particles do not occur, the diameter distribution histogram (B) can see that the particle sizes of AuNCs are mostly distributed in 2-3nm, and the graph (C) (D) is a GSH @ AuNCs/MgAl-E L DH nanosheet compound and a local amplified TEM result thereof, and it can be seen that AuNCs are uniformly distributed on the surface of MgAl-E L DH nanosheet and are more regular in shape.
(2) Fourier Infrared Spectroscopy (FT-IR) and ultraviolet Spectroscopy (UV-Vis) are shown in FIG. 2, and FIG. A shows the IR spectra of pure GSH, MgAl-E L DH and GSH @ AuNCs/MgAl-E L DH from the IR spectra of pure GSH, at 2524cm-1There is an absorption band characteristic of stretching vibration of-SH, and the absorption band disappears in the infrared result of GSH @ AgNCs/MgAl-E L DH due to deprotonation of-SH groups and binding of the generated AuNCs to GSH via Au-S bonds-1) The disappearance in the complex is due to deprotonation of the carbonyl group. Simultaneous nanosheet complexes 1627 and 1356cm-1The peak of GSH due to COO-asymmetric stretching, which also fully confirms the binding of GSH to AuNCs, GSH acts both as a reducing agent and as a stabilizer for AuNCs during synthesis, the characteristic absorption bands of hydrotalcite-like compounds in the composite can be found for the infrared spectra of contrast GSH @ AuNCs/MgAl-E L DH and MgAl-E L DH, and 800cm in the composite-1The following is a wave change that illustrates the interaction between AuNCs and MgAl-E L DH in the composite, graph (B) is an ultraviolet spectrum of pure GSH and GSH @ AuNCs, the maximum absorption wavelength of the synthesized AuNCs is 500nm, and the size of the synthesized gold nanoclusters is less than 3 nm.
(3) The X-ray diffraction (XRD) pattern is shown in fig. 3, where 2 θ 11.73 ° (003), 23.84 ° (006), 35.02 ° (012), 40.23 ° (015), 47.44 ° (018), 60.74 ° (110) and 62.86 ° (113) are all attributed to MgAl-E L DH compound, while the weak, unapparent diffraction peaks appearing at 38.48 ° (111) and 64.58 ° (220) are attributed to GSH @ AuNCs in the composite, and the reason for the weak diffraction peaks in the composite may be that the synthesized AuNCs have a small particle size and do not have properties of intact metal crystals.
(II) electrochemical characterization analysis
Electrochemical testing was performed on the GSH @ AuNCs/MgAl-E L DH of the examples, as follows:
inserting a three-electrode system into a KOH solution, taking GSH @ AuNCs/MgAl-E L DH as a working electrode, researching electrochemical behaviors of carbaryl and isoprocarb with different modification amounts and different concentrations of the KOH solution by CV within a potential range of 0-0.8V, measuring DPV of the carbaryl and isoprocarb solutions with different concentrations under the optimal experimental condition, and finally measuring a recovery rate experiment.
(1) Electrochemical characterization of differently modified electrodes
Fig. 4(a) shows that the four electrodes all exhibit a better pair of redox peaks in the target, the peak current for bare GCE and MgAl-E L DH/GCE is smaller, while the redox peak current response for GSH @ AuNCs/GCE is significantly enhanced, approximately 1.53 times that of bare GCE and 1.22 times that of MgAl-E L DH/GCE, because the modification of GSH @ AuNCs shortens the electron transport path, increasing the conductivity of the electrode, and thus increasing the response to the peak current, in the modified electrode, the current response for GSH @ AuNCs/MgAl-E L DH/GCE is stronger than the current response for MgAl-E L/GCE and GSH @ AuNCs/GCE alone, which is attributed to the greater surface area and better catalytic activity of MgAl-E L DH, providing support for loading of AuNCs, and the enhanced transfer of mgh @ AuNCs/GCE modified materials, which is due to the synergistic effect of the enhanced electrochemical transfer of the MgAl-E loading, which results are a graph with the minimum electrical resistance of the electrode, a comparable map, the electrochemical transfer of the MgAl-E4625.
(2) Electrochemical characterization of GSH @ AuNCs/MgAl-E L DH at different doping volume ratios
As shown in figure 5, in order to explore the influence of the doping ratio of GSH @ AuNCs to MgAl-E L DH nanosheets on the performance of the composite material, five GSH @ AuNCs/MgAl-E L DH nanocomposites with different volume ratios are prepared and tested for electrochemical properties, wherein the graph (A) is a CV graph of a composite material modified electrode with different volume ratios, and when the doping volume ratio of the GSH @ AuNCs to MgAl-E L DH is 2:1, the electrochemical signal is strongest6]3-/4-Adsorption and electron transfer at the electrode surface. On the one hand, GSH @ AuNCs improves the conductivity of the composite,graph (B) is a response modified electrode impedance graph, and the impedance is the minimum when the volume ratio of GSH-AuNCs to MgAl-E L DH is 2:1, which fully proves that the doping ratio of the two components can influence the performance of the composite material, and the optimal volume ratio of the synthesized GSH @ AuNCs/MgAl-E L DH nanosheet composite material is GSH @ AuNCs: MgAl-E L DH-2: 1.
(3) Electrochemical behavior of carbaryl and isoprocarb
The response to carbaryl/MgAl-E L DH/GCE (d) is significantly higher than that of MgAl-E L DH/GCE (b) and GSH @ AuNCs/GCE (c) alone, indicating that GSH @ AuNCs and MgAl-E L/GCE interact synergistically with each other and that electrocatalysis of the target occurs simultaneously on the modified electrode surface.
FIG. B is a CV diagram of GSH @ AuNCs/MgAl-E L DH/GCE in blank 0.2M KOH solution, 0.2M KOH solution containing 0.1mM carbaryl, 0.2M KOH solution containing 0.1mM isoprocarb, and mixed solution containing 0.1mM carbaryl and isoprocarb, respectively.
The data optimization process is as follows:
(1) influence of modification amount
FIG. 7 shows the optimization results of GSH @ AuNCs/MgAl-E L DH, in the range of modification amount from 0 to 8 mu L, the peak current response of the modified electrode to carbaryl and isoprocarb is gradually enhanced along with the increase of the modification amount, and when the modification amount exceeds 8 mu L, the oxidation peak current of carbaryl and isoprocarb tends to be stable, therefore, 8 mu L is taken as the optimal modification amount.
(2) Influence of accumulation time and accumulation potential
FIG. 8 is an optimization of accumulation time and accumulation potential, in which graph (A) shows the effect of the change of accumulation time on the peak current response of carbaryl and isoprocarb, and as the accumulation time increases, the number of molecules of carbaryl and isoprocarb adsorbed on the surface of the electrode increases, the oxidation peak current response of the modified electrode increases, the oxidation peak current of carbaryl and isoprocarb reaches the maximum at 120s, and then the accumulation time continues to increase, and the current does not change significantly, so 120s is taken as the optimal accumulation time, and in which graph (B) is an optimization of accumulation potential, from which GSH @ AuNCs/MgAl-E L DH/GCE shows the strongest electrochemical signal at-0.2V, so the optimal accumulation potential of the experiment is-0.2V.
(3) Effect of different concentration of KOH solution
The carbaryl and isoprocarb belong to carbamate pesticides, which are unstable and easily hydrolyzed under alkaline conditions, and the hydrolysis process is shown in the following formula. The hydrolysis products are the corresponding phenols and the electrochemical signal is stronger than that measured directly for carbaryl and isoprocarb. According to previous reports, the hydrolysis speed of the carbamate pesticide is increased by about ten times for every pH increase, so that electrochemical detection of carbaryl and isoprocarb is carried out at a higher pH value. The concentration of the KOH solution is optimized. As shown in fig. 9, the oxidation peak currents of carbaryl and isoprocarb were greatest at a KOH solution concentration of 0.2M. When the KOH concentration is too small, hydrolysis is not favorably carried out, and when the KOH concentration is too high, the activity of the electrode material is lowered. Therefore, 0.2M KOH solution was chosen for the optimal buffer concentration for this experiment.
(4) Differential Pulse Voltammetry (DPV)
GSH @ AuNCs/MgAl-E L DH/GCE quantitatively detects carbaryl and isoprocarb in 0.2M KOH solution by DPV.FIG. 10(A) is a DPV graph in which 50nM isoprocarb is fixed and the concentration of carbaryl is continuously increased in 0.2M KOH solution.FIG. 10(A) is a DPV graph in which 50nM carbaryl is fixed and the concentration of isoprocarb is continuously increased in 0.2M KOH solution.As can be seen from the graph, the current response of the modified electrode to carbaryl and isoprocarb linearly increases with the increase in concentration (0.01-30. mu.M). The graph (B) and graph (D) are an enlarged view of the DPV response of carbaryl and isoprocarb in the concentration range of 0.01-1. mu.M, respectively, and the current response of the modified electrode still exhibits better linearity when quantitatively detecting carbaryl and isoprocarb at lower concentrations.33. mu.M.82. mu.82 R.82. the regression equation is obtained by calculation20.997), detection limit 5.73 nM. Isoprocarb: ipa (μ a) ═ 1.07C (μ M) -0.42 (R)20.998), detection limit 6.39 nM.
Table 1 shows the comparison of detection limits of carbaryl and isoprocarb at different modified electrodes
As shown in Table 1, compared with electrochemical detection methods reported in many literatures, the method has wider linear range and lower detection limit when used for simultaneously detecting carbaryl and isoprocarb.
(5) Study of reproducibility, stability and interference
FIG. 11(A) is a graph which illustrates the reproducibility of GSH @ AuNCs/MgAl-E L DH/GCE electrodes, and which records the current responses of 5 μ M modified electrodes prepared under the same conditions in 0.2M KOH solution, with continuous measurements, the Relative Standard Deviation (RSD) being less than 2.6%, showing that the GSH @ AuNCs/MgAl-E L DH/GCE electrode has good reproducibility in detecting both carbaryl and isoprocarb, and in addition, the graph (B) shows that the prepared electrodes are stored at 4 ℃ for two weeks, and the stability of the electrodes is studied, and that the DPV currents of carbaryl and isoprocarb still retain 94.2% and 92.7% of the initial values, demonstrating that the sensor has satisfactory stability.
FIG. 12 is a study of the anti-interference ability of GSH @ AuNCs/MgAl-E L DH/GCE in the determination of carbaryl and isoprocarb, and this experiment selects several possible interfering phenolic compounds and pesticides to evaluate the anti-interference ability of GSH @ AuNCs/MgAl-E L DH/GCE electrode, and 500. mu.M phenol, naphthol, bisphenol A, propoxur, methomyl and carbendazim are added to 0.2M KOH solution containing 5. mu.M carbaryl and isoprocarb
(5) Sample detection
The GSH @ AuNCs/MgAl-E L DH/GCE is applied to detecting carbaryl and isoprocarb in actual samples of watermelon, cucumber and pumpkin purchased from Yan mountain market (Shandong Qingdao). 10g of watermelon, cucumber and pumpkin are accurately weighed respectively, cut into small pieces and put into a beaker to be mashed into a paste, 10.0m of L absolute ethyl alcohol is added into the beaker, the mixture is uniformly stirred for 20min and then soaked for 10 h, the mixture is centrifuged for 5min at 8000r, and supernatant is collected to determine the concentrations of the carbaryl and isoprocarb by a standard addition method.A recovery rate range shown in Table 2 is from 97.8% to 100.1%, which indicates that the electrochemical sensor is reliable in actual sample detection.
TABLE 2
a watermelon, cucumber and pumpkin purchased from Yan jiashan markets; b five replicates
In conclusion, the MgAl-L DH is prepared by a coprecipitation method, the MgAl-E L DH is obtained by ultrasonic stripping in formamide, GSH @ AuNCs is synthesized by a chemical reduction method, a GSH @ AuNCs/MgAl-E L DH nanosheet compound is prepared by an electrostatic adsorption method, a modified electrode is prepared, and simultaneous detection of carbaryl and isoprocarb is realized, the MgAl-E L DH nanosheet prepared by the formamide stripping method is thin in thickness and small in size, active sites are fully exposed, the GSH @ AuNCs synthesized by the chemical reduction method is regular and spherical in shape and small in size and uniform, the GSH AuNCs/MgAl-E L nanosheet compound not only can fully utilize the large specific surface area and the fully exposed active sites of the MgAl-E2 nanosheet DH, but also improves the conductivity of the material by the adsorbed GSH AuNCs, the electrostatic interaction of the GSH @ AuNCs and the MgAl-E L DH is effectively solved, the problem of mutual aggregation is enhanced, the stability of the GSH @ AuNCs, the AuNCs of the AuNCs is improved, the high dispersion degree of the MgH @ AlnC @ AlC @ AlCl @ AlO-Al.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (6)
1. A preparation method of a GSH @ AuNCs/MgAl-E L DH modified electrode is characterized by comprising the following specific steps:
s1, preparation of the glutathione-coated gold nanocluster GSH @ AuNCs:
pipetting HAuCl with pipette4Placing the solution and glutathione solution in a beaker, adding NaOH solution after vigorously stirring for 5min, placing at room temperature and reacting for 19h with slow stirring to obtain light yellow solution GSH @ AuNCs, dialyzing and purifying with a dialysis bag of 1KDa, placing in a refrigerator at 4 ℃, and keeping the whole operation process away from light;
s2, preparing the magnesium-aluminum hydrotalcite material:
preparation of magnesium-aluminum hydrotalcite MgAl-L DH by weighing Mg (NO)3)2·6H2O、Al(NO3)3·9H2Adding deionized water into a round-bottom flask to completely dissolve O and urea, stirring the mixed solution at room temperature for two hours, heating to 97 ℃, refluxing for 48 hours to obtain a white MgAl-L DH solid, centrifuging at 8000r for 5min, and washing with deionized water and absolute ethyl alcohol for three times respectively;
preparing magnesium-aluminum hydrotalcite nano-sheet MgAl-E L DH, namely measuring the solid content of a MgAl-L DH wet sample, accurately weighing the MgAl-L DH wet sample, dissolving the MgAl-L DH wet sample in formamide, and ultrasonically stripping for 48 hours to obtain the magnesium-aluminum hydrotalcite nano-sheet MgAl-E L DH;
s3, preparing GSH @ AuNCs/MgAl-E L DH;
adopting an electrostatic adsorption method, mixing a GSH @ AuNCs solution and a MgAl-E L DH solution according to the volume ratio of GSH @ AuNCs to MgAl-E L DH being 1:1, slowly stirring for 30min at room temperature, and then incubating for 6h to obtain a suspension of the GSH @ AuNCs/MgAl-E L DH nanosheet compound, respectively preparing the GSH @ AuNCs/MgAl-E L DH being 2:1, 1:2, 1:3 and 1:4 GSH @ AuNCs/MgAl-E L DH nanosheet compound with different solution volume ratios under the same step and condition, and keeping the whole process away from light;
s4, preparation of modified electrode:
polishing and grinding a glassy carbon electrode GCE with the diameter of 3mm to a mirror surface by using alumina powder, respectively ultrasonically washing the polished glassy carbon electrode GCE in a mixed solution of dilute nitric acid and ethanol, washing the polished glassy carbon electrode GCE with deionized water, transferring a GSH @ AuNCs/MgAl-E L DH suspension liquid drop of 2 mu L by using a liquid transfer gun, coating the suspension liquid drop on the surface of the pretreated naked GCE, covering a beaker with the solution, drying the solution at room temperature, and marking the solution as GSH @ AuNCs/MgAl-E L DH/GCE, and preparing the GSH @ AuNCs/GCE and the MgAl-E L DH/GCE by using the same conditions and steps.
2. A method as claimed in claim 1The preparation method of the GSH @ AuNCs/MgAl-E L DH modified electrode is characterized in that in the step S1, HAuCl is adopted4The concentration of the solution, the concentration of the glutathione solution and the concentration of the NaOH solution are respectively 10mM, 15mM and 1M, and 5-15M L HAuCl is removed by using a pipette gun4The solution and 6-18m L glutathione solution are put into a beaker and stirred vigorously for reaction for 5min, and then 1-5m L NaOH solution is added.
3. The method of claim 1, wherein the MgAl-L DH sample is prepared by accurately weighing 0.11-0.15g Mg (NO) in the step S23)2·6H2O、0.0937g Al(NO3)3·9H2Placing O and 0.05-0.10g urea in 80m L round-bottom flask, and measuring solid content by taking three empty dry 1.5m L centrifuge tubes, respectively labeled with numerals 1, 2 and 3, and weighing with tray balance and marking as m1Empty, m2Empty, m3Empty, respectively putting the MgAl-L DH wet samples prepared in proper amount into a centrifugal tube with a label, weighing and recording as m1Wet, m2Wet, m3Wetting, drying the three centrifuge tubes containing the wet sample in a 50 ℃ oven, taking out the centrifuge tubes after the wet sample is completely dried, weighing again and recording as m1Dry, m2Dry, m3And (d) drying, and calculating by using a calculation formula of (m dry-m empty)/(m wet-m empty) 100% to obtain the solid content of MgAl-L DH.
4. The method of claim 1, wherein in step S3, the MgAl-L DH suspension is prepared by calculating and weighing MgAl-L DH with a solid content of 2-7mg, adding 10m L deionized water in a wet sample, and fully stirring and dispersing under ultrasonic conditions.
5. The method for preparing the GSH @ AuNCs/MgAl-E L DH modified electrode according to claim 1, wherein in the step S3, AuNCs in the prepared GSH @ AuNCs/MgAl-E L DH nanosheet composite are uniformly distributed on the surface of the MgAl-E L DH nanosheet, have smaller size and more regular and circular shape at 2-3nm, and have better dispersibility due to no aggregation phenomenon of two components of the GSH @ AuNCs and the MgAl-E L DH.
6. The use of the GSH @ AuNCs/MgAl-E L DH modified electrode as claimed in any one of claims 1 to 5, wherein the modified electrode prepared by the method is used for detecting the pesticides carbaryl and isoprocarb simultaneously.
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Application publication date: 20200728 |