AuNps / rGO / L-cysteine-FTO electrode and preparation method and application thereof

Abstract

The invention belongs to the technical field of cadmium ion detection, and particularly relates to an AuNps / rGO / L-cysteine-FTO electrode and a preparation method and application thereof.The preparation method includes the following steps that firstly, a certain amount of graphene oxide is dispersed in water to form graphene oxide colloid; adding HAuCl4 into the graphene oxide colloid to form a mixed solution; 2, the mixed solution is adopted as an electro-deposition solution, graphene oxide is electrochemically reduced into reduced graphene oxide, AuNPs is electrodeposited on an FTO bare electrode, and an AuNPs / rGO-FTO electrode is obtained; and step 3, the obtained AuNps / rGO-FTO electrode is cleaned, the cleaned AuNps / rGO-FTO electrode is soaked in an L-cysteine solution, and then the AuNps / rGO / L-cysteine-FTO electrode is obtained. The electrochemical sensor has good analysis performance such as wide linear range, high sensitivity, low detection limit and good repeatability.

Description

Technical Field

[0001] The present invention belongs to the technical field of cadmium ion detection, and particularly relates to an AuNps / rGO / L-cysteine-FTO electrode and a preparation method and application thereof. Background Art

[0002] Cadmium is one of the most toxic heavy metal ions. Once it enters the human body, it binds to proteins containing hydroxyl, amino, and sulfhydryl groups, thereby inhibiting various enzyme systems and affecting the normal function of organs. Long-term exposure to cadmium can lead to serious health risks, such as kidney dysfunction, bone degeneration, itai-itai disease, and certain cancers. The World Health Organization (WHO) and the U.S. Environmental Protection Agency (EPA) have set a maximum permissible concentration of cadmium (II) in drinking water at 5 μg / L.

[0003] In the related prior art, Cd 2+ Detection methods include flame atomic absorption spectrometry (FAAS), X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectrometry (ICP-AES), etc. Although these methods have high sensitivity and appropriate selectivity, they still have the disadvantages of high implementation and maintenance costs, long time consumption, and are not suitable for on-site analysis.

[0004] Electrochemical sensing offers advantages such as accuracy, simplicity, low cost, high sensitivity, multimodal detection efficiency, and on-site detection capabilities. Electrode surface modification is key to improving the performance of heavy metal ion electrochemical sensors. Gold nanoparticles (AuNPs) are undoubtedly the most widely studied nanomaterial across various research fields. Gold nanoparticles possess excellent conductivity, high surface area, good chemical stability, biocompatibility, and low toxicity.

[0005] In order to improve the performance of electrochemical sensors, carbon nanomaterials such as graphene oxide are used to detect heavy metal ions. Graphene oxide is a highly oxygenated form of GP. These oxygenated groups also produce defects in graphene oxide, such as the introduction of some five-membered and six-membered rings. These defects hinder the ballistic electron transport properties and electron localization of graphene oxide, resulting in extremely low conductivity and extremely high sheet resistance of graphene oxide, about 10 12 Ω·sq -1 This makes it less suitable as an electrode modifier compared to other GPs.

[0006] Cadmium ion is one of the most toxic heavy metal ions in the environment, but the Cd 2+ The detection has disadvantages such as complex operation, high detection cost and slow detection speed. Therefore, it is urgent to develop a fast, selective, sensitive and convenient analytical method for measuring trace cadmium in the environment. Summary of the Invention

[0007] One of the objects of the present invention is to provide a method for preparing an AuNps / rGO / L-cysteine-FTO electrode, comprising the following steps:

[0008] Step 1: dispersing a certain amount of graphene oxide in water to form a graphene oxide colloid, and adding HAuCl4 to the above-mentioned graphene oxide colloid to form a mixed solution;

[0009] Step 2: using the mixed solution prepared in step 1 as an electrodeposition solution, electrochemically reducing graphene oxide to reduced graphene oxide, and electrodepositing AuNPs on the FTO bare electrode to obtain an AuNps / rGO-FTO electrode;

[0010] Step 3: Clean the obtained AuNps / rGO-FTO electrode, and soak the cleaned AuNps / rGO-FTO electrode in L-cysteine ​​solution to obtain AuNps / rGO / L-cysteine-FTO electrode.

[0011] As a preferred solution, in step 2, the electrodeposition solution is 0.2-0.3 mM HAuCl4 and 0.4-0.6 mg·L -1 Graphene oxide mixed solution.

[0012] As a preferred solution, in the step 2, GO is electrochemically reduced to reduced graphene oxide (rGO) at a voltage of -1.1 to -0.9 V for 140 to 160 s, and AuNPs are electrodeposited on FTO.

[0013] As a preferred solution, in step three, the AuNps / rGO / L-cysteine-FTO electrode is obtained by soaking in a 0.09-0.11M L-cysteine ​​solution for 45-75 minutes.

[0014] A second object of the present invention is to provide an AuNps / rGO / L-cysteine-FTO electrode, which is prepared by the preparation method of the AuNps / rGO / L-cysteine-FTO electrode described in any of the above.

[0015] The third object of the present invention is to provide a AuNps / rGO / L-cysteine-FTO electrode on Cd 2+ Application in detection.

[0016] As a preferred solution, the following steps are included:

[0017] Step 1: Using a platinum electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and the AuNps / rGO / L-cysteine-FTO electrode as the working electrode, the DPASV method was used to2+ Determination of Cd in buffer solution 2+ concentration;

[0018] Step 2: Pre-deposit Cd by stirring for a certain time under certain potential conditions 2+ , change Cd 2+ The Cd deposited on the surface of AuNps / rGO / L-cysteine-FTO electrode was reduced and deposited. 2+ Then it is stripped to Cd through oxidation 2+ ;

[0019] Step 3: Remove the residual metal on the electrode surface and perform cyclic voltammetry and electrochemical impedance spectroscopy in a mixed solution of K3[Fe(CN)6] / K4[Fe(CN)6] and KCl to obtain Cd 2+ content.

[0020] As a preferred solution, in the step 2, the potential condition ranges from -0.4V to -1.4V.

[0021] As a preferred solution, in step 2, Cd 2+ The deposition time is 120 to 480 seconds.

[0022] As a preferred embodiment, in step 1, the buffer solution is acetate buffer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the preparation of AuNps / rGO / L-cysteine-FTO electrode;

[0024] Figure 2 (a) SEM image of AuNps-FTO electrode sample;

[0025] Figure 3 FESEM image of AuNps-FTO electrode sample (b);

[0026] Figure 4 SEM image of AuNps / rGO-FTO electrode sample (c);

[0027] Figure 5 FESEM image of AuNps / rGO / L-cysteine-FTO electrode sample (d);

[0028] Figure 6 FT-IR spectra of GO, AuNps / rGO, L-cys, and AuNps / rGO / L-cysteine;

[0029] Figure 7XPS analysis of AuNps / rGO / L-cysteine-FTO electrode: measured spectrum (a); Figure 8-12 They are Au4f(b), C1s(C), N1s(d), O1s(e) and S2p(f) respectively;

[0030] Figure 13 、 14 Cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) of bare FTO, AuNps-FTO, AuNps / rGO-FTO, and AuNps / rGO / L-cysteine-FTO electrodes in 50 mM K3[Fe(CN)6] / K4[Fe(CN)6] solution containing 0.1 M KCl (pH = 5.0), respectively;

[0031] Figure 15 Cd 2+ DPASV curves on bare FTO, AuNps-FTO, AuNps / rGO-FTO, and AuNps / rGO / L-cysteine-FTO electrodes;

[0032] Figure 16 、 17 This is a diagram showing the effect of different deposition potentials on peak current;

[0033] Figure 18 、 19 The effect of different deposition times on Cd 2+ The influence diagram of peak current in the range of 120 to 480 seconds;

[0034] Figure 20 、 21 This is the effect of different buffer solution pH on peak current;

[0035] Figure 22 、 23 This is a diagram showing the effect of different buffer solutions on peak current;

[0036] Figure 24 In 0.1M acetate buffer solution (different Cd 2+ concentration), DPASV curve of AuNps / rGO / L-cysteine-FTO electrode;

[0037] Figure 25 is the fitting curve of the dissolution peak current versus cadmium ion concentration;

[0038] Figure 26 、 27 Schematic diagram of the repeatability and stability of the AuNps / rGO / L-cysteine-FTO electrode.

[0039] Figure 281 is a comparison diagram of the electrodes of Example 1 and Comparative Examples 1 to 4; from left to right in the figure are Comparative Example 1, Comparative Example 2, Example 1, Comparative Example 3, and Comparative Example 4;

[0040] Figure 29 1 is a comparison diagram of the electrodes of Example 1 and Comparative Examples 5 to 8: from left to right in the figure are Comparative Example 5, Comparative Example 6, Example 1, Comparative Example 7, and Comparative Example 8;

[0041] Figure 30 This is a comparison diagram of the electrodes of Example 1 and Comparative Examples 9 to 12, where from left to right are Comparative Example 9, Comparative Example 10, Example 1, Comparative Example 11, and Comparative Example 12.

[0042] The present invention has the following beneficial effects:

[0043] First, this scheme provides a method for preparing AuNps / rGO / L-cysteine-FTO electrode. The electrode prepared by this preparation method is used to perform reduced graphene oxide / nano-gold (rGO / AuNPs) electrodeposition on FTO substrate, and the FTO electrode modified with L-cysteine ​​is used as DPASV to detect Cd 2+ A novel electrochemical sensor was developed. RGO / AuNPs enhance the conductivity of the electrode surface. Gold nanoparticles possess excellent electron transfer capabilities, enabling interfacial charge transfer through the adsorption and coordination of heavy metals by L-cysteine ​​and reduced graphene oxide, thereby enhancing conductivity and sensing performance.

[0044] Secondly, this scheme provides a AuNps / rGO / L-cysteine-FTO electrode on Cd 2+ Under the optimal conditions, the AuNps / rGO / L-cysteine-FTO electrode can effectively detect Cd 2+ The sensor has good linear range, low detection limit, high sensitivity and selectivity. 2+ The detection limit was 0.013 nM, lower than the World Health Organization standard. The sensor maintained its selectivity even in the presence of various interfering ions. In real-world samples, the sensor achieved recoveries ranging from 95.4% to 103.7%, demonstrating excellent accuracy. DETAILED DESCRIPTION

[0045] In order to make the technical means, creative features, objectives and beneficial effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0046] In addition, in order to better illustrate the present invention, numerous specific details are given in the specific embodiments below. Those skilled in the art should understand that the present invention can also be implemented without certain specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present invention.

[0047] like Figure 1 As shown, this embodiment provides a method for preparing an AuNps / rGO / L-cysteine-FTO electrode, comprising the following steps: firstly, dispersing graphene oxide in ultrapure water, and then ultrasonically treating it at room temperature for 60 minutes to form a 0.5 mg·L -1 Graphene oxide (GO) colloid. The above colloid was used to prepare 0.20-0.30 mM HAuCl4 and 0.4-0.6 mg·L -1 A mixed solution of GO was used for potentiostatic deposition. Using this mixed solution as the electrodeposition solution, potentiostatic deposition was performed at -1.1 to -0.9 V for 140 to 160 seconds to electrochemically reduce GO to reduced graphene oxide (rGO) and electrodeposit AuNPs on FTO. The AuNPs / rGO-FTO electrode was then carefully rinsed in ultrapure water and soaked in a 0.09 to 0.11 M L-cysteine ​​solution for 45 to 75 minutes to obtain the AuNPs / rGO / L-cysteine-FTO electrode.

[0048] Example 1

[0049] Graphene oxide was first dispersed in ultrapure water and then ultrasonicated at room temperature for 60 min to form a 0.5 mg·L -1 Graphene oxide (GO) colloid. The above colloid was used to prepare 0.25mM HAuCl4 and 0.5mg·L -1 The mixed solution of GO was used for constant potential deposition. The above 0.25mM HAuCl4 and 0.5mg·L -1 The GO mixed solution was used as the electrodeposition solution, and GO was electrochemically reduced to reduced graphene oxide (rGO) at a voltage of -1.0 V for 150 seconds, and AuNPs were electrodeposited on FTO. The AuNPs / rGO-FTO electrode was then carefully rinsed in ultrapure water and immersed in a 0.1 M L-cysteine ​​solution for 60 minutes to obtain the AuNPs / rGO / L-cysteine-FTO electrode.

[0050] Example 2

[0051] The AuNps / rGO / L-cysteine-FTO electrode was prepared by the preparation process conditions and steps of Example 1, except that 0.5 mg·L -1Preparation of graphene oxide (GO) colloids 0.2 mM HAuCl4 and 0.5 mg·L -1 Mixed solution of GO.

[0052] Example 3

[0053] The AuNps / rGO / L-cysteine-FTO electrode was prepared by the preparation process conditions and steps of Example 1, except that 0.5 mg·L -1 Preparation of graphene oxide (GO) colloids 0.3 mM HAuCl4 and 0.5 mg·L -1 Mixed solution of GO.

[0054] Example 4

[0055] The AuNps / rGO / L-cysteine-FTO electrode was prepared by the preparation process conditions and steps of Example 1, except that 0.4 mg·L -1 Preparation of graphene oxide (GO) colloids 0.25 mM HAuCl4 and 0.4 mg·L -1 Mixed solution of GO.

[0056] Example 5

[0057] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that 0.6 mg·L -1 Preparation of graphene oxide (GO) colloids 0.25 mM HAuCl4 and 0.6 mg·L -1 Mixed solution of GO.

[0058] Example 6

[0059] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that constant potential deposition was continued at a voltage of -1.1 V for 150 s to electrochemically reduce GO to reduced graphene oxide (rGO).

[0060] Example 7

[0061] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that constant potential deposition was continued at a voltage of -0.9 V for 150 s to electrochemically reduce GO to reduced graphene oxide (rGO).

[0062] Example 8

[0063] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that constant potential deposition was continued at a voltage of -1.0 V for 140 s to electrochemically reduce GO to reduced graphene oxide (rGO), and AuNPs were electrodeposited on FTO.

[0064] Example 9

[0065] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that constant potential deposition was continued at a voltage of -1.0 V for 160 s to electrochemically reduce GO to reduced graphene oxide (rGO), and AuNPs were electrodeposited on FTO.

[0066] Example 10

[0067] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that the AuNps / rGO-FTO electrode was immersed in a 0.09 M L-cysteine ​​solution for 60 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0068] Example 11

[0069] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that the AuNps / rGO-FTO electrode was immersed in a 0.11 M L-cysteine ​​solution for 60 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0070] Example 12

[0071] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that the AuNps / rGO-FTO electrode was immersed in 0.1 M L-cysteine ​​solution for 45 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0072] Example 13

[0073] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that the AuNps / rGO-FTO electrode was immersed in 0.1 M L-cysteine ​​solution for 75 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0074] The preparation method of the mixed solution of Examples 1-13 is as follows: taking a 23.5% mass fraction HAuCl4 solution as an example, the HAuCl4 solution is mixed evenly with the graphene oxide (GO) colloid / solution prepared in the previous step to obtain 0.2-0.3 mM HAuCl4 and 0.4-0.6 mg·L -1 mixture of GO.

[0075] Comparative Example 1

[0076] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the same process conditions and steps as in Example 1, except that the electrodeposition solution was 0.1 mM HAuCl4 and 0.5 mg·L -1 Graphene oxide mixed solution.

[0077] Comparative Example 2

[0078] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the same process conditions and steps as in Example 1, except that the electrodeposition solution consisted of 0.5 mM HAuCl4 and 0.5 mg·L -1 Mixed solution of graphene oxide.

[0079] According to the results of Comparative Examples 1, 2 and Example 1, although a low concentration of HAuCl4 can make AuNps grow uniformly, it also reduces the deposition rate of AuNps. After the deposition process, the amount of AuNps deposited on the FTO electrode is also reduced; and although a high concentration of HAuCl4 promotes the deposition of AuNPs on FTO, the excessively high concentration causes AuNPs to agglomerate on the FTO electrode.

[0080] Comparative Example 3

[0081] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the same process conditions and steps as in Example 1, except that the electrodeposition solution was 0.25 mM HAuCl4 and 0.25 mg·L -1 GO mixed solution.

[0082] Comparative Example 4

[0083] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1.

[0084] The only difference is that the electrodeposition solution is 0.25mM HAuCl4 and 1mg·L -1 GO solution.

[0085] The results of Comparative Examples 3, 4 and Example 1 show that when 0.25 mM HAuCl4 and 0.25 mg·L -1 In the GO mixed solution, due to the low GO content, a thinner reduced graphene oxide (rGO) layer was formed on the surface of AuNps, and the overall conductivity of the electrode may be reduced due to the reduction of the rGO layer; when using 0.25mM HAuCl4 and 1mg·L -1 GO mixed solution mg·L -1 When GO solution was added, a thicker rGO layer was formed on the surface of AuNps, which affected the electron transfer performance of the composite structure.

[0086] Comparative Example 5

[0087] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that GO was electrochemically reduced to reduced graphene oxide (rGO) at a voltage of -1.2 V for 150 s.

[0088] Comparative Example 6

[0089] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that GO was electrochemically reduced to reduced graphene oxide (rGO) at a voltage of -0.8 V for 150 s.

[0090] According to the results of Comparative Examples 5, 6 and Example 1, it was found that a more negative voltage (-1.2 V) would increase the Au 3+ ion deposition rate, but too fast a rate leads to uneven dispersion of AuNps (i.e., agglomeration); a more positive voltage (-0.8 V) weakens the electrochemical reduction of GO on the one hand, and on the other hand reduces the deposition rate of AuNps, and even forms larger AuNps nanoparticles.

[0091] Comparative Example 7

[0092] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that GO was electrochemically reduced to reduced graphene oxide (rGO) at a voltage of -1.0 V for 120 s, and AuNPs were electrodeposited on FTO.

[0093] Comparative Example 8

[0094] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that GO was electrochemically reduced to reduced graphene oxide (rGO) at a voltage of -1.0 V for 180 s, and AuNPs were electrodeposited on FTO.

[0095] The results of Comparative Examples 7, 8 and Example 1 show that too short a deposition time shortens the Au 3+ The time of ion deposition will not make the deposition amount of AuNps reach the expected level, and it will also lead to incomplete GO reduction and incomplete structure, and the rGO layer formed on the electrode surface will be thinner; too long deposition time increases the Au 3+ The ion deposition process increases the deposition amount, but the size of AuNps also increases, causing agglomeration and making the rGO layer too thick.

[0096] Comparative Example 9

[0097] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, except that the AuNps / rGO-FTO electrode was immersed in a 0.05 M L-cysteine ​​solution for 60 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0098] Comparative Example 10

[0099] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that the AuNps / rGO-FTO electrode was immersed in a 0.15 M L-cysteine ​​solution for 60 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0100] According to the results of Comparative Examples 9 and 10 and Example 1, the low concentration of L-cysteine ​​solution has a low content of L-cysteine, which leads to a weakened interaction with the AuNPs / rGO surface, reduces the stability of the modified layer, and the modification effect of the electrode is not as good as that of the 0.1 M solution; although the high concentration of L-cysteine ​​solution improves the modification effect and helps the growth of the modified layer, the excessive growth of the modified layer reduces the conductivity of the electrode, reduces electron transfer, and thus reduces the overall performance of the electrode.

[0101] Comparative Example 11

[0102] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that the AuNps / rGO-FTO electrode was immersed in 0.1 M L-cysteine ​​solution for 30 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0103] Comparative Example 12

[0104] The AuNps / rGO / L-cysteine-FTO electrode was prepared using the preparation process conditions and steps of Example 1, with the only difference being that the AuNps / rGO-FTO electrode was immersed in 0.1 M L-cysteine ​​solution for 120 min to obtain the AuNps / rGO / L-cysteine-FTO electrode.

[0105] The results of Comparative Examples 11 and 12 and Example 1 show that a 30-min immersion time may not be sufficient for cysteine ​​to fully react with the active sites on the AuNPs / rGO surface. This may lead to incomplete surface modification, insufficient cysteine ​​adsorption, and poor stability of the modified layer, which is prone to shedding during subsequent testing. A 120-min immersion time may lead to excessive adsorption of cysteine, forming an overly thick adsorption layer, which may block the active sites on the electrode surface and reduce the performance of the electrode. Long-term immersion may also cause the modified layer structure to become unstable, and excessive cysteine ​​adsorption may cause internal stress in the layer, resulting in shedding of the modified layer.

[0106] In this solution, in Examples 1-13 and Comparative Examples 1-12, the FTO cleaning and drying steps are as follows: Use an ultrasonic cleaner to thoroughly soak the FTO in acetone, anhydrous ethanol, hydrogen peroxide, and ultrapure water for 15 minutes, and then dry it in an oven:

[0107] (1) Acetone cleaning (cleaning grease and most organic matter on the FTO surface): Gently place the FTO glass sheet into the cleaning tank of the ultrasonic cleaning machine, add enough acetone to the cleaning tank to ensure that the FTO glass sheet is completely immersed, turn on the ultrasonic cleaning machine, and set the cleaning time to 15 minutes.

[0108] (2) Cleaning with anhydrous ethanol (to further clean residual acetone and organic matter): After 15 minutes, remove the FTO glass slide, pour out the acetone, rinse the cleaning tank with a small amount of anhydrous ethanol, add sufficient anhydrous ethanol to the cleaning tank, ensure that the FTO glass slide is completely immersed again, turn on the ultrasonic cleaning machine, and continue cleaning for 15 minutes.

[0109] (3) Hydrogen peroxide cleaning (using the strong oxidizing property of hydrogen peroxide to oxidize and remove insoluble organic matter and bacteria): Take out the FTO glass piece, pour out the anhydrous ethanol, and rinse the cleaning tank with a small amount of ultrapure water. Add 30% hydrogen peroxide to the cleaning tank to completely immerse the FTO glass piece, turn on the ultrasonic cleaning machine, and clean for 15 minutes.

[0110] (4) Ultrapure water cleaning (for cleaning residual cleaning agents and ions): Take out the FTO glass sheet, pour out the hydrogen peroxide mixture, and rinse the cleaning tank with ultrapure water. Add ultrapure water to the cleaning tank to ensure that the FTO glass sheet is completely immersed. Turn on the ultrasonic cleaning machine and clean for 15 minutes.

[0111] (5) Drying step: After cleaning, carefully remove the FTO glass sheet, try to avoid direct contact with your hands, and place the FTO glass sheet on a clean tray in the oven, taking care not to overlap. Set the oven temperature (100-120℃) to avoid damage to the FTO surface caused by high temperature. Dry the FTO glass sheet in the oven for at least 30 minutes, or until it is completely dry. After drying, wait for the FTO glass sheet to cool naturally to room temperature in the oven, then take it out for use.

[0112] Comparative Example 13

[0113] The AuNps-FTO electrode was prepared as follows: A FTO electrode cleaned as described above was used as the working electrode, along with a platinum counter electrode and an Ag / AgCl reference electrode, to construct a three-electrode test system. In this system, 20 mL of a 0.25 mM HAuCl₄ solution was used as the electrodeposition medium. Gold nanoparticles were electrochemically deposited using chronoamperometry by applying a constant voltage of -1.0 V for 150 seconds. After the deposition process, the AuNps-FTO electrode was prepared.

[0114] Comparative Example 14

[0115] The preparation method of AuNps / rGO-FTO electrode is as follows: the FTO electrode cleaned as described above is used as the working electrode, together with the platinum counter electrode and the Ag / AgCl reference electrode to construct a three-electrode test system. In this system, 20 mL of 0.25 mM HAuCl4 and 0.5 mg·L -1 GO solution served as the electrodeposition medium. Chronoamperometry was used to electrochemically deposit gold nanoparticles by applying a constant voltage of -1.0 V for 150 seconds. After the deposition process, an AuNp / rGO-FTO electrode was prepared.

[0116] The surface morphologies of the AuNps-FTO electrode (a, b), AuNps / rGO-FTO electrode (c) and AuNps / rGO / L-cysteine-FTO electrode (d) samples prepared in Examples 13, 14 and Example 1 were characterized by SEM.

[0117] from Figure 2 、 3 It can be seen that a large amount of dispersed AuNps are deposited on the surface of the AuNps / FTO electrode. After further co-deposition of rGO and AuNps, Figure 4 Wrinkled rGO and AuNps can be seen deposited on the electrode surface. The wrinkles create a larger specific surface area, which can provide additional Cd 2+ Adsorption active points. Figure 5 It can be seen from the figure that due to the combination of L-cysteine ​​and AuNps through S-Au bonds, the surface of AuNps is no longer smooth but becomes rough.

[0118] In order to study the surface characteristic functional groups of the prepared samples, FT-IR analysis was performed. FT-IR spectra of the prepared GO, AuNps / rGO, L-cysteine ​​(L-cys) and AuNps / rGO / L-cysteine ​​materials, as shown in Figure 2 Figure 6 As shown, the KBr method was used at wave numbers of 4000 to 400 cm -1 The C=O (1597.78 cm -1 )、-OH(1400.27cm -1 )、CO(1090.77cm -1 ) peak. L-cysteine ​​is at 3408.21 cm -1 、2547.77cm -1 and 2081.54cm -1 The stretching vibrations of -OH, -SH and -NH3 groups are shown at the positions. It can also be seen that these functional groups also exist in AuNps / rGO / L-cysteine.

[0119] The XPS spectrum of the composite material is shown in Figure 7 The characteristic peaks of Au4f, C1s, N1s, O1s and S2p are shown in Figure 8-12As shown. The C1XPS spectrum peaks at 284.8, 286.5, and 287.8 eV correspond to C-C, C-OH, and C-N bonds, respectively. For the N1s spectrum, the peak at 399.8 eV is attributed to the NH bond, while for the O1s spectrum, the peaks at 531.6 eV and 532.7 eV are attributed to the CO / OC=O, Sn-O bonds. In the S2p spectrum, the peaks at 162.1 eV and 167.4 eV indicate that sulfur atoms have been incorporated into the nanocomposite through the grafting of AuNPs. The peaks at 162.9 eV and 168.5 eV are likely attributed to the C-SH bond.

[0120] In order to investigate the performance of the prepared electrochemical sensor, cyclic voltammetry tests were carried out on BareFTO, AuNps-FTO, AuNps / rGO-FTO, and AuNps / rGO / L-cysteine-FTO electrodes in 50 mM K3[Fe(CN)6] / K4[Fe(CN)6] solution containing 0.1 mM KCl. The cyclic voltammetry curves are shown in Figure 2. Figure 13 As shown. Compared with the bare FTO electrode, the redox peak current of the AuNps-FTO electrode increased slightly, which is due to the fact that the AuNps with high conductivity increased the electron transfer rate. Since rGO has a higher specific surface area, it further increases the electron transfer rate, improves the conductivity and sensitivity of the electrode, and thus increases the redox peak current of the AuNps / rGO-FTO electrode. Compared with the other three electrodes, the redox peak current of the AuNps / rGO / L-cysteine-FTO electrode increased significantly. Due to the presence of amino nitrogen, sulfhydryl (-SH) and carboxyl oxygen groups in the L-cysteine ​​molecule, which interact with Cd 2+ A stable coordination compound is formed, thereby increasing the redox peak current.

[0121] Figure 14 The Nyquist plots of various modified electrodes are shown. Generally speaking, a Nyquist plot consists of a high-frequency semicircle and a low-frequency straight line, which are closely related to electron transfer and diffusion-limited processes, respectively. The diameter of the semicircle represents the charge transfer resistance (Rct). As shown in Table 1, the bare FTO electrode has the highest Rct value (11.340Ω). After the GCE is modified with AuNps-FTO (3.619Ω), AuNps / rGO-FTO (2.863Ω), and AuNps / rGO / L-cysteine-FTO (2.938Ω), the corresponding Rct values ​​decrease. This is because rGO and AuNps modify the electrode's conductivity; lower Rct values ​​indicate a higher reaction rate. Furthermore, the slight increase in Rct for the AuNps / rGO / L-cysteine-FTO electrode is due to the introduction of L-cysteine, which has a lower conductivity and reduces the electrode's conductivity.

[0122] Table 1 EIS data fitting table

[0123]

[0124]

[0125] *This refers to the basic electronic or electrochemical components used in equivalent circuits to simulate the behavior of actual electrochemical systems.

[0126] In this scheme, the above composite electrodes are used to 2+ The results of electrochemical studies are as follows:

[0127] In 0.1 M acetate buffer solution, Cd 2+ The concentration is 150 μg·L -1 , at a deposition potential of -1.0 V, the DPASV responses of bare FTO, AuNps-FTO, AuNps / rGO-FTO, and AuNps / rGO / L-cysteine-FTO electrodes were measured, as shown in Figure 15 As shown. It can be seen that the bare FTO electrode Cd 2+ The peak current corresponding to DPASV was only -20.22 μA. After modification with AuNps, AuNps / rGO, and AuNps / rGO / L-cysteine, the peak current was significantly increased. The peak current of the AuNps / rGO / L-cysteine-modified electrode was -82.80 μA, higher than the peak currents of the AuNps-modified electrode (-55.82 μA) and the AuNps / rGO-modified electrode (-63.63 μA), indicating that the AuNps / rGO / L-cysteine-modified electrode enhanced the response to DPASV better than AuNps and AuNps / rGO. This indicates that modification with AuNps / rGO / L-cysteine ​​effectively enhanced the detection capability. This is partly because the co-deposition of gold nanoparticles and reduced graphene oxide significantly increased the peak current of DPASV. AuNps have excellent conductivity, catalysis, and biocompatibility, effectively enhancing the electron transfer capacity of the electrode surface. Reduced graphene oxide is a versatile two-dimensional carbon material with a high specific surface area and excellent electrocatalytic activity. Compared with graphite, its surface is rich in various oxygen-containing active groups such as -COOH and -OH, which can provide specific active sites for interaction with metal ions during adsorption. On the other hand, L-cysteine ​​is a Cd 2+ The pre-enriched selective molecules can form stable coordination compounds due to the amino N, sulfhydryl (-SH) and carboxyl oxygen groups in the L-cysteine ​​molecule.

[0128] Table 2 Cd described in this protocol 2+ Comparison of the detection method with other reported methods

[0129]

[0130]

[0131] This embodiment also provides an application of an AuNps / rGO / L-cysteine-FTO electrode, and the specific steps are as follows:

[0132] A platinum electrode was used as the counter electrode, an Ag / AgCl electrode was used as the reference electrode, and the modified electrode prepared in Example 1 was used as the working electrode. The DPASV method was used to determine the Cd 2+ First, Cd was pre-deposited at -1.0 V with stirring for 360 s. 2+ , change Cd 2+ Then, the electrodeposited Cd 2+ Cd is stripped to Cd through reoxidation 2+ Finally, the working electrode was stirred and cleaned for 120 s at a potential of -0.3 V to remove any metal deposits that may remain on the surface. CV and electrochemical impedance spectroscopy (EIS) analyses were performed in a mixed solution of 50 mM K3[Fe(CN)6] / K4[Fe(CN)6] and 0.1 M KCl. The cyclic voltammetry (CV) scan rate was 0.10 V·s -1 Electrochemical impedance spectroscopy (EIS) analysis was performed under the conditions of a DC potential of 0 V, an AC amplitude of 5 mV, a starting frequency of 100 kHz, and an ending frequency of 0.1 Hz. All experiments were performed in an air environment at room temperature.

[0133] Application Example 1

[0134] A platinum electrode was used as the counter electrode, an Ag / AgCl electrode was used as the reference electrode, and the modified electrode prepared in Example 1 was used as the working electrode. The DPASV method was used to determine the Cd 2+ First, Cd was pre-deposited at -1.0 V with stirring for 360 s. 2+ , change Cd 2+ Then, the electrodeposited Cd 2+ Cd is stripped to Cd through reoxidation 2+, a stripping current with a potential range of -1.0 to -0.3 V, a potential increment of 4 mV, an amplitude of 50 mV, a pulse width of 0.05 s, and a pulse period of 0.2 s was obtained. Finally, the working electrode was stirred and cleaned for 120 s at a potential of -0.3 V to remove any metal deposits that may remain on the surface. CV and electrochemical impedance spectroscopy (EIS) analysis were performed in a mixed solution of 50 mM K3[Fe(CN)6] / K4[Fe(CN)6] and 0.1 M KCl. The cyclic voltammetry (CV) scan rate was 0.10 V·s -1 Electrochemical impedance spectroscopy (EIS) analysis was performed under the conditions of a DC potential of 0 V, an AC amplitude of 5 mV, a starting frequency of 100 kHz, and an ending frequency of 0.1 Hz. All experiments were performed in an air environment at room temperature.

[0135] Application Example 2-7

[0136] The other conditions are the same as those in Application Example 1, with the only difference being that the deposition potential of -1.0 V is changed to -0.4 V, -0.6 V, -0.8 V, -1.0 V, -1.2 V, and -1.4 V, respectively.

[0137] like Figure 16 、 17 As shown, at 220 μg·L -1 CD 2+ In acetic acid buffer, the effect of deposition potential was studied in the range of -0.4V to -1.4V, and the deposition time was 360s. When the deposition potential increased from -0.4V to -1.0V, Cd 2+ The current increases and reaches its maximum value at -1.0V. The target metal ion reaches its maximum peak current at -1.0V. At higher potentials, the stripping current peak intensity decreases. This phenomenon is due to the more pronounced hydrogen evolution in the acetate buffer. In this scheme, a deposition potential of -1.0V is selected as the optimal deposition potential.

[0138] Application Examples 8-15

[0139] The other conditions are the same as those in Application Example 1, with the only difference being that the deposition time is changed to 120S, 180S, 240S, 300S, 340S, 360S, 420S, and 480S.

[0140] Figure 18 、 19 As shown, the deposition time is affected by the cd at the same deposition potential of -1.0V. 2+ The peak current increases with the increase of deposition time and reaches the maximum value when the deposition time is 360S, indicating that Cd 2+Deposition on the AuNps / rGO / L-cysteine-FTO electrode increased with increasing deposition time. However, the peak current barely increased at 420 and 480 s, likely due to saturation of the surface active sites on the AuNps / rGO / L-cysteine-FTO electrode. Therefore, a deposition time of 360 s was selected as the optimal deposition time.

[0141] Application Examples 16-20

[0142] The other conditions are the same as those in Application Example 1, except that the pH value is changed to 3, 4, 5, 6, and 7.

[0143] The pH value of the loaded electrolyte affects the acidic or basic functional groups present in the cavities of L-cysteine ​​and rGO, thereby affecting the adsorption and capture of target ions. The peak current intensity in the DPASV of the AuNps / rGO / L-cysteine-FTO electrode is affected by the pH value, and an acetate buffer with a pH value of 3.0 to 7.0 was used for the study. Figure 20 、 21 As shown in the figure, when the pH value is lower than 5.0, the peak current increases with the increase of pH value; when the pH value is higher than 5.0, the peak current decreases with the increase of pH value. When the pH value is lower than 5.0, the number of active sites for cation coupling and coordination decreases due to the protonation of N-containing groups in a strong acidic medium, resulting in the decrease of the number of active sites for cation coupling and coordination of AuNps / rGO / L-cysteine-FTO to Cd 2+ In addition, the more positive charges of the protonated groups, the better the adsorption of AuNps / rGO / L-cysteine-FTO and Cd 2+ The stronger the repulsive interaction between them, the more unfavorable it is for Cd 2+ Penetrate the interlayers and cavities of AuNps / rGO / L-cysteine-FTO. As the pH value continues to increase, the peak current decreases at higher pH values, which may be due to the Cd 2+ Therefore, pH = 5.0 was finally selected as the optimal condition.

[0144] Application Examples 21-23

[0145] The other conditions were the same as those in Application Example 1, with the only difference being that the buffer solutions used were 0.1 M citric acid buffer (pH 5.0), 0.1 M acetate buffer (pH 5.0), and 0.1 M PBS (pH 5.0).

[0146] By analyzing the Cd 2+The effects of carrier electrolytes on DPASV response were investigated. The voltammetric responses of the AuNps / rGO / L-cysteine-FTO electrode were recorded in three different electrolytes, namely 0.1 M acetate buffer (pH 5.0), 0.1 M PBS (pH 5.0) and 0.1 M citric acid buffer (pH 5.0). Figure 22 、 23 As shown in Figure 3 . In PBS (phosphate buffered saline) and citrate buffer, the peak current response is smaller, which may be due to the interaction between metal ions and phosphate and citrate ions. As can be seen, the current peak is highest in sodium acetate buffer. Therefore, acetate buffer is preferred in this protocol.

[0147] Interference Study Example

[0148] Anti-interference is an important performance indicator of heavy ion sensors. Generally speaking, during the DPASV process, interfering ions and target metal ions are deposited on the electrode almost simultaneously. If the interfering ions seriously affect the response current of the target ions, the quantitative detection will be invalid. In order to demonstrate the selectivity and anti-interference ability of the sensor, the AuNps / rGO / L-cysteine-FTO sensor electrode was tested for interference from other interfering metal ions under the above optimal experimental conditions. -1 The interfering ion Cl - 、Na + , K + 、SO4 2- 、NO3 - Mg 2+ 、Mn 2+ , Ca 2+ 、Zn 2+ 、Al 3+ 、Fe 3+ 、Hg 2+ At the same time, 220 μg·L -1 Cd 2+ The changes in the response current were observed in the solution. The evaluation results showed that the interference effect was less than ±5%, and the changes in the peak current with the relative signal change are shown in Table 3. Since repeated testing of the AuNps / rGO / L-cysteine-FTO electrode will also produce deviations in the response current, the 5% response current fluctuation is not necessarily caused by interfering ions. It is well known that ions with higher reduction potentials may interrupt the detection of ions with low reduction potentials. Here, all interfering ions have lower or equivalent standard reduction potentials than the target metal ions, which indicates that the AuNps / rGO / L-cysteine-FTO electrode has a good sensitivity to Cd 2+ The test conditions were the optimal experimental conditions, that is, the DPASV method was used to determine 220 μg·L in 0.1 M acetate buffer solution (pH = 5.0).-1 Cd 2+ The deposition potential was -1.0 to -0.3 V, the potential increment was 4 mV, the amplitude was 50 mV, the pulse width was 0.05 s, and the pulse period was 0.2 s.

[0149] Table 3 Effects of the presence of alien species on metal ion currents and changes in their relative signals

[0150]

[0151] Stability, reusability and repeatability

[0152] The repeatability and stability of the electrode are also important parameters for evaluating the performance of the electrode. The concentration was selected as 350 μg·L -1 CD 2+ Under the optimal experimental conditions, a single electrode was used to detect Cd for 10 consecutive times. 2+ level, the results of each repeated test are almost the same. Figure 26 、 27 As shown in Table 4, the response current was almost unchanged at 1, 3, 5, 10, 15, 20 and 30 days. 2+ The electrode was subjected to DPASV test. After 30 days, the response current of the electrode did not decrease significantly. The above results show that the AuNps / rGO / L-cysteine-FTO electrode has good reproducibility and stability. The test conditions are the optimal experimental conditions, that is, the DPASV method is used to measure 350μg·L in 0.1M acetate buffer solution (pH=5.0). -1 Cd 2+ The deposition potential was -1.0 to -0.3 V, the potential increment was 4 mV, the amplitude was 50 mV, the pulse width was 0.05 s, and the pulse period was 0.2 s.

[0153] Table 4 Reproducibility and stability analysis of AuNps / rGO / L-cysteine-FTO

[0154]

[0155] Real water sample testing

[0156] Since Cd is a highly toxic and non-biodegradable element to humans, Cd in water sources 2+ The content of Cd can be used as an important indicator to evaluate the safety of drinking water. Table 5 shows the Cd content of wastewater, river water (Luoyang Luohe River) and lake water (Luoyang Qinhu Lake) samples. 2+The applicability of the proposed AuNps / rGO / L-cysteine-FTO was investigated. All samples were filtered through a 0.20 μm membrane before testing. No Cd was found in these water samples. 2+ The reaction of Cd 2+ Therefore, different concentrations of Cd were added to the samples. 2+ Perform recovery evaluation.

[0157] The statistical evaluation results are shown in Table 5. 2+ The recovery rate was between 95.4% and 103.7%, indicating good accuracy. 2+ The analytical requirements of the test are high and the reliability is high.

[0158] Table 5 shows the DPASV method for detecting cadmium ions in water

[0159]

[0160]

[0161] L means not detected and below the detection limit

[0162] All electrochemical studies in this protocol, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse anodic stripping voltammetry (DPASV) tests, were performed on a CS350M electrochemical workstation (cortest Instruments, Wuhan, China).

[0163] In this study, a scanning electron microscope (SEM, ZEISS Gemini SEM 300, Germany) was used to characterize the sample morphology. X-ray diffraction (XRD, Rigaku Ultima IV, Japan) was used to determine the sample structure, and X-ray photoelectron spectroscopy (XPS, ThermoScientific K-AlpHa, United States) was used to analyze the chemical composition and valence state of the sample. Functional groups were recorded using a Fourier transform infrared spectrometer (FT-IR, Shimadzu, Japan).

[0164] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an AuNps / rGO / L-cysteine-FTO electrode, characterized by: The steps include: Step 1: dispersing a certain amount of graphene oxide in water to form a graphene oxide colloid, and adding HAuCl4 to the above-mentioned graphene oxide colloid to form a mixed solution; Step 2: using the mixed solution prepared in step 1 as an electrodeposition solution, electrochemically reducing graphene oxide to reduced graphene oxide, and electrodepositing AuNPs on the FTO bare electrode to obtain an AuNps / rGO-FTO electrode; Step 3: Clean the obtained AuNps / rGO-FTO electrode, and soak the cleaned AuNps / rGO-FTO electrode in L-cysteine ​​solution to obtain AuNps / rGO / L-cysteine-FTO electrode.

2. The method for preparing an AuNps / rGO / L-cysteine-FTO electrode according to claim 1, wherein: In the step 2, the electrodeposition solution is 0.2-0.3 mM HAuCl4 and 0.4-0.6 mg·L -1 Graphene oxide mixed solution.

3. The method for preparing an AuNps / rGO / L-cysteine-FTO electrode according to claim 1, wherein: In the second step, GO is electrochemically reduced to reduced graphene oxide (rGO) at a voltage of -1.1 to -0.9 V for 140 to 160 seconds, and AuNPs are electrodeposited on the FTO.

4. The method for preparing an AuNps / rGO / L-cysteine-FTO electrode according to claim 1, wherein: In the step 3, the AuNps / rGO / L-cysteine-FTO electrode is obtained by soaking in a 0.09-0.11M L-cysteine ​​solution for 45-75 minutes.

5. An AuNps / rGO / L-cysteine-FTO electrode, characterized by: The AuNps / rGO / L-cysteine-FTO electrode is prepared by the preparation method of any one of claims 1 to 4.

6. The AuNps / rGO / L-cysteine-FTO electrode as claimed in claim 5 is 2+ Application in detection.

7. The AuNps / rGO / L-cysteine-FTO electrode as claimed in claim 6 is 2+ The application in detection is characterized by: The steps include: Step 1: Using a platinum electrode as a counter electrode, an Ag / AgCl electrode as a reference electrode, and the AuNps / rGO / L-cysteine-FTO electrode as claimed in claim 5 as a working electrode, the DPASV method is used to 2+ Determination of Cd in buffer solution 2+ ; Step 2: Pre-deposit Cd by stirring for a certain time under certain potential conditions 2+ , change Cd 2+ The Cd deposited on the surface of AuNps / rGO / L-cysteine-FTO electrode was reduced and deposited. 2+ Then it is stripped to Cd through oxidation 2+ ; Step 3: Remove the residual metal on the electrode surface and perform cyclic voltammetry and electrochemical impedance spectroscopy in a mixed solution of K3[Fe(CN)6] / K4[Fe(CN)6] and KCl to obtain Cd 2+ content.

8. The AuNps / rGO / L-cysteine-FTO electrode as claimed in claim 7 is 2+ The application in detection is characterized by: In the step 2, the potential condition range is: -0.4V to -1.4V.

9. The AuNps / rGO / L-cysteine-FTO electrode as claimed in claim 7 is 2+ The application in detection is characterized by: In the step 2, Cd 2+ The deposition time is 120 to 480 seconds.

10. The AuNps / rGO / L-cysteine-FTO electrode as claimed in claim 7 is 2+ The application in detection is characterized by: In the step 1, the buffer solution is acetate buffer.

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