Ag-CuO / Cu electrode, preparation method and passion fruit juice detection application

Abstract

The invention provides an Ag-CuO / Cu electrode, a preparation method and passion fruit juice detection application, and the preparation method comprises the following steps: cleaning a copper electrode, and then grinding and polishing; the copper electrode obtained after primary treatment is immersed in a 0.5-1.5 M H2SO4 solution, square wave pulse treatment is carried out, and a pretreated copper electrode is obtained; the pretreated copper electrode is placed in a 0.5-1.5 M KOH solution, cyclic voltammetry scanning is carried out, and an activated copper electrode is obtained; and the activated copper electrode is placed in a 0.005-0.05 M AgNO3 solution, and Ag < + > is reduced and deposited on the surface of the copper electrode by adopting a constant potential deposition method to form an Ag modification layer. The Ag-CuO / Cu electrode prepared by the invention is used for detecting ascorbic acid in passion fruit juice, and is high in sensitivity, good in repeatability and reproducibility, excellent in long-term stability and strong in anti-interference capability; and the electrode preparation process is simple.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of substance detection, in particular to an Ag-CuO / Cu electrode, a preparation method and a passion fruit juice detection application. BACKGROUND

[0002] The passion fruit juice is rich in nutritional components such as glucose, citric acid and ascorbic acid, and these substances jointly determine the sensory quality and antioxidant activity of the juice. As a core functional component, ascorbic acid directly affects the nutritional value, oxidation stability and shelf life of the juice, and therefore accurate detection of ascorbic acid is of great significance for product quality control and process optimization.

[0003] The existing detection methods of ascorbic acid mainly include titration, spectrophotometry and chromatography. However, the passion fruit juice matrix is complex, containing high concentrations of reducing sugars such as glucose and fructose, as well as various organic acids, inorganic salts and pigments, which are prone to interference in conventional detection: the reducing sugars may compete with the reagent, the organic acids and ions affect the pH and ionic strength of the system, and the pigments interfere with the light signal detection, resulting in problems such as low sensitivity, poor repeatability and complicated operation.

[0004] In recent years, electrochemical sensing technology based on nanomaterials has provided a new way for ascorbic acid detection, and bimetallic composite nanomaterials have attracted much attention due to their synergistic catalytic effect. However, there are still significant challenges in applying them to actual passion fruit juice samples: (1) the components such as fructose, glucose, polyphenols and pigments in the juice are complex, and are prone to competitive adsorption or side reactions with ascorbic acid on the electrode surface, resulting in decreased selectivity of the sensor; (2) the preparation of traditional composite nanomaterials often relies on high temperature, high pressure or complex templates, which is complicated and costly, and is not conducive to large-scale application; (3) the existing materials still have deficiencies in dimension matching and structure design, the active sites are not fully exposed, and the conductivity and catalytic performance are difficult to balance, which restricts the rapid and sensitive detection of low-concentration target substances in complex matrix.

[0005] Therefore, it is urgent to establish an ascorbic acid detection method with good selectivity, strong anti-interference ability, simple operation and reliable results to meet the analysis needs of passion fruit juice, a special matrix, and provide reliable technical support for its quality evaluation and deep processing. SUMMARY

[0006] In view of the above technical problems, the application discloses an Ag-CuO / Cu electrode, a preparation method and a passion fruit juice detection application, which is used for ascorbic acid detection in passion fruit juice, has high sensitivity, good repeatability and reproducibility, excellent long-term stability, and strong anti-interference ability to coexisting interference substances such as glucose, fructose and inorganic salts in passion fruit juice; and the electrode preparation process is simple.

[0007] The technical solution adopted by this invention is as follows:

[0008] A method for preparing an Ag-CuO / Cu electrode includes the following steps:

[0009] Step S1: Clean the copper electrode, then grind and polish it.

[0010] Step S2: Immerse the copper electrode after the initial treatment in step S1 in a 0.5-1.5M H2SO4 solution and perform square wave pulse treatment to remove the surface oxide layer and activate the surface, providing an attachment point for the next step of generating a two-dimensional copper oxide structure. After treatment, rinse it with ultrapure water to obtain the pretreated copper electrode.

[0011] Step S3: The pretreated copper electrode is then placed in a 0.5-1.5M KOH solution and subjected to cyclic voltammetry scanning. During the induced deposition process, CuO grows in layers, forming a porous "flower cluster" morphology. After the process is completed, the electrode is rinsed with ultrapure water and dried to obtain the activated copper electrode.

[0012] Step S4: The activated copper electrode is placed in a 0.005-0.05M AgNO3 solution, and Ag+ is reduced and deposited on the surface of the copper electrode using a constant potential deposition method to form an Ag modification layer. After deposition, the unadsorbed Ag+ on the surface is rinsed with ultrapure water, and the water is dried to obtain an Ag-CuO / Cu electrode. The deposition potential is -1.5-0.5V, and the deposition time is 50-300s.

[0013] The Ag-CuO / Cu electrode obtained using this technical solution has a strong anti-interference ability against coexisting interfering substances such as glucose, fructose, and inorganic salts in passion fruit juice, and exhibits excellent repeatability, reproducibility, and long-term stability.

[0014] As a further improvement of the present invention, in step S2, the pulse potential of the square wave pulse is -1.8 V ~ -0.4 V, the frequency is 50-100 Hz, and the pulse width is 100-300 s.

[0015] As a further improvement of the present invention, in step S3, the scanning voltage of the cyclic voltammetric scan is -1.2 ~ -0.1V, the scan speed is 30-100 mV / s, and the number of scan cycles is 5-60.

[0016] As a further improvement of the present invention, in step S1, the cleaning includes acid washing of the copper electrode and then ultrasonic cleaning with clean water; the polishing includes polishing with 5000 grit and 8000 grit sandpaper in sequence; the polishing includes polishing the copper electrode to a mirror finish on a chamois with alumina powder, and then ultrasonically cleaning it in deionized water for 3-5 minutes and then air drying it naturally.

[0017] As a further improvement of the present invention, the pickling includes immersing the copper electrode in 1-2M hydrochloric acid for 2-5 minutes; the alumina powder has a particle size of 30-80 nm.

[0018] As a further improvement of the present invention, in step S1, the diameter of the copper electrode is 1~3mm and the purity is ≥99.99%; in steps S2 and S3, the copper electrode is the working electrode, the platinum sheet is the counter electrode, and the saturated calomel electrode is the reference electrode.

[0019] As a further improvement of the present invention, in step S4, the deposition time is 100-200 s. This technical solution forms a porous heterostructure of "two-dimensional substrate-zero-dimensional particles", which has maximized specific surface area and catalytic active sites.

[0020] As a further improvement of the present invention, in step S4, the concentration of the AgNO3 solution is 0.01M.

[0021] As a further improvement of the present invention, in step S4, the deposition potential is -0.84 V and the deposition time is set to 200 s.

[0022] This invention discloses an Ag-CuO / Cu electrode, which is prepared using the Ag-CuO / Cu electrode preparation method described above.

[0023] As a further improvement of the present invention, the composition and mass ratio of the Ag-CuO / Cu electrode membrane electrode are as follows: C element 8.46%-11.12%, O element 7.05%-9.05%, Cu element 28.27%-29.9%, Ag element 49.93%-55.78%.

[0024] This invention discloses the application of the Ag-CuO / Cu electrode described above in the detection of passion fruit juice, wherein the Ag-CuO / Cu electrode is used as the working electrode to detect the content of ascorbic acid in passion fruit juice.

[0025] This invention discloses a sensor for detecting ascorbic acid in passion fruit juice, comprising the Ag-CuO / Cu electrode as described above.

[0026] This invention discloses a method for detecting ascorbic acid in passion fruit juice, comprising the following steps:

[0027] Step S10: Using the Ag-CuO / Cu electrode as the working electrode, immerse it in a 0.1M sodium hydroxide solution, use a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode, apply a voltage for testing, and then add different concentrations of ascorbic acid to obtain the it curve of the working electrode to different concentrations of ascorbic acid. Further fit to obtain the linear regression equation of the steady-state current value of ascorbic acid and its concentration.

[0028] In step S20, the sample is immersed in a 0.1M sodium hydroxide solution. A platinum sheet is used as the counter electrode and a saturated calomel electrode is used as the reference electrode. A voltage is applied for testing. Then, the passion fruit juice to be tested is added to obtain the steady-state current value. The concentration of ascorbic acid is calculated using the linear regression equation obtained in step S10.

[0029] As a further improvement of the present invention, the linear regression equation is y = 1.6384x + 0.60015.

[0030] As a further improvement of the present invention, the voltage is 0.6V. Using this technical solution, at this detection potential, the method exhibits a linear detection range of 2 μM to 9.11 mM for AA, a response time of less than 3 s in the low concentration range (2 to 40 μM), and a sensitivity of 1638.4 μA•mM. -1 •cm -2 The detection limit was 0.0046 μM.

[0031] The Ag-CuO / Cu nanocomposite electrode prepared by this invention exhibits excellent comprehensive performance in the detection of ascorbic acid (AA) in passion fruit juice, and its beneficial effects are specifically reflected in the following aspects:

[0032] First, charge transfer and catalytic performance are significantly enhanced. Modification with Ag reduces the charge transfer resistance of the electrode by over 96%, indicating that Ag, as a highly efficient catalytic active site, greatly promotes electron transport at the electrode / electrolyte interface, thereby significantly improving electrochemical reaction kinetics. In the system containing AA, the electrode oxidation peak current after Ag deposition increases significantly, and the reduction peak characteristics are obvious, demonstrating a significant synergistic catalytic effect between Ag and CuO. This composite structure exhibits superior electrocatalytic oxidation activity and selectivity for AA compared to the control system.

[0033] Secondly, it possesses a wide linear range and ultra-high sensitivity. At the optimal detection potential of 0.6 V, the sensor exhibits a wide linear detection range for AA, ranging from 2 μM to 9.11 mM, covering the possible concentration range of AA in actual samples. Its sensitivity reaches as high as 1638.4 μA·mM. -1 ·cm -2 With a detection limit as low as 0.0046 μM (4.6 nM) and a response time of less than 3 seconds in the low concentration range (2 ~ 40 μM), it achieves rapid and highly sensitive quantitative detection.

[0034] Third, it exhibits excellent selectivity and anti-interference capabilities. Anti-interference tests show that when common interfering substances found in passion fruit juice (such as 0.1 mM glucose, fructose, sucrose, citrate, NaCl, Na₂SO₄, NaH₂PO₄, CaCl₂, and 0.02 mM uric acid) are continuously added, the current response shows no significant change; only when AA is added does the current show a significant stepwise increase. This confirms that the electrode has high specificity for the oxidation of AA, and the complex matrix components in passion fruit juice, such as sugars, organic acids, and inorganic salts, hardly produce interfering signals, demonstrating extremely strong applicability for practical sample detection.

[0035] Fourth, it exhibits good reproducibility, repeatability, and stability. The electrode fabrication process is stable, with a relative standard deviation (RSD) of 2.5% for repeated tests and an RSD of 6.7% for reproducibility between different electrodes. It also demonstrates good long-term stability, meeting the reliability and durability requirements of practical testing.

[0036] In summary, the Ag-CuO / Cu nanocomposite electrode provided by this invention successfully solves the technical problems of low sensitivity, poor selectivity, and susceptibility to interference from coexisting substances in the detection of ascorbic acid in passion fruit juice through the dimensional and catalytic synergy of Ag and CuO. It provides a high-performance electrochemical sensing solution for the rapid and accurate detection of ascorbic acid in fruit juice and other complex food matrices. Attached Figure Description

[0037] Figure 1 These are SEM images of the Ag-CuO / Cu electrode obtained in Example 1 of this invention; where A to D are SEM images at different magnifications.

[0038] Figure 2 This is a surface microstructure diagram of the Ag-CuO / Cu electrode obtained in Example 1 of the present invention.

[0039] Figure 3 This is an elemental analysis diagram of the surface film electrode of the Ag-CuO / Cu electrode obtained in Example 1 of the present invention.

[0040] Figure 4 This is the XPS image of the surface film electrode of the Ag-CuO / Cu electrode obtained in Example 1 of the present invention; wherein, A is the full spectrum, B is the peak spectrum of Cu 2p, C is the Ag 3d orbital peak, and D is the peak spectrum of O.

[0041] Figure 5 These are the electrochemical impedance test results of the Ag-CuO / Cu electrode of Example 1 of the present invention and the CuO / Cu electrode of the control sample.

[0042] Figure 6The results are cyclic voltammetry test results of the Ag-CuO / Cu electrode of Example 1 of the present invention and the CuO / Cu electrode of the control sample, respectively immersed in 0.1M NaOH solution and 0.1M NaOH+10mM AA solution.

[0043] Figure 7 The results are cyclic voltammetry test results of the Ag-CuO / Cu electrode in Example 1 of this invention; where A is the cyclic voltammetry test results at different scan rates, and B is the fitting graph.

[0044] Figure 8 These are the electrochemical performance results of the Ag-CuO / Cu electrode in AA solutions of different concentrations according to Example 1 of the present invention; wherein, A is the it curve of the Ag-CuO / Cu electrode in AA solutions of different concentrations, B is the it fitting linear graph of A, C is the cyclic voltammetry test results of the Ag-CuO / Cu electrode in AA solutions of different concentrations, and D is the CV fitting linear graph of C.

[0045] Figure 9 The results are obtained by using the chronoamperometry method to test the Ag-CuO / Cu electrode of Embodiment 1 of the present invention at different potentials.

[0046] Figure 10 These are the anti-interference test results of the Ag-CuO / Cu electrode in Example 1 of the present invention; wherein, A is the it curve of adding different concentrations of AA from 2μM to 10 mM, B is an enlarged view of the continuous addition of low concentration AA in Figure A, C is the linear relationship between the fitted response current and the AA concentration, and D is the anti-interference it curve.

[0047] Figure 11 These are the repeatability, reproducibility, and stability test results of the Ag-CuO / Cu electrode in Example 1 of this invention; where A is the repeatability test result, B is the reproducibility test result, and C is the stability test result.

[0048] Figure 12 Figure A shows the detection results of the Ag-CuO / Cu electrode in actual samples in Example 1 of this invention. Among them, A is the chronoamperometry response graph of the Ag-CuO / Cu electrode at 0.6 V, with 1 M AA standard solution added dropwise to a continuously stirred 0.1 M NaOH solution, followed by the continuous addition of 1 mM passion fruit test solution; B is the standard curve graph of AA and current in 1 M AA standard solution determined by the standard addition method in Figure A.

[0049] Figure 13 These are the cyclic voltammetry test results of electrodes obtained at different deposition times in steps (4) of Examples 1 to 4 of the present invention.

[0050] Figure 14The results are cyclic voltammetry test results of electrodes obtained with different AgNO3 solutions in steps (4) of Examples 1, 5 to 7 of this invention. Detailed Implementation

[0051] The preferred embodiments of the present invention will be described in further detail below.

[0052] A method for preparing an Ag-CuO / Cu electrode includes the following steps:

[0053] (1) Preparation. Before preparation, the copper electrode (diameter 2 mm, purity ≥99.99%) was soaked in 1-2M hydrochloric acid for 2-5 min, then ultrasonicated with water for 2-5 min, and air-dried naturally. It was then polished with 5000 grit and 8000 grit sandpaper until the surface was smooth, and then polished with alumina powder (50 nm) on chamois leather until it was mirror-like. After that, it was ultrasonically cleaned in deionized water for 3-5 min and then air-dried naturally.

[0054] (2) The electrode surface is further cleaned and active sites are created by square wave pulse treatment in 0.5-1.5M H2SO4 solution, providing attachment points for the growth of CuO layer and Ag particles; square wave pulse, pulse potential -1.8 V ~ -0.4 V, frequency 50-100Hz, pulse width 100-300 s;

[0055] (3) The pretreated copper electrode is then placed in 0.5-1.5M KOH solution and cyclic voltammetry (CV) scan is performed. The scan range is -1.2 ~ -0.1 V, the scan rate is 30-100 mV / s, and the number of scans is 5-60. This further optimizes the surface morphology of the electrode and enhances the uniformity of subsequent deposition. After the scan is completed, the electrode is rinsed with ultrapure water and dried with a paper towel.

[0056] (4) The activated copper electrode is placed in 0.005-0.05M AgNO3 solution and the constant potential deposition method is used (deposition potential -1.5-0.5V, deposition time set to 50-300 s) to reduce and deposit Ag+ on the surface of the copper electrode to form an Ag-modified layer. After deposition, the unadsorbed Ag+ on the surface is rinsed with ultrapure water and dried with paper towel to obtain silver nitrate modified copper electrode (Ag-CuO / Cu).

[0057] The obtained Ag-CuO / Cu nanoelectrode membrane electrode contains 8.46%-11.12% C, 7.05%-9.05% O, 28.27%-29.9% Cu, and 49.93%-55.78% Ag (mass ratio).

[0058] The following description is based on specific embodiments.

[0059] Example 1

[0060] A method for preparing an Ag-CuO / Cu electrode includes the following steps:

[0061] (1) Immerse the copper electrode (diameter 2 mm, purity ≥99.99%) in 1M hydrochloric acid for 3 min, and then clean it with water using ultrasonic cleaning. Then polish it with 5000 grit and 8000 grit sandpaper until the surface is smooth. Finally, polish it with alumina powder (50 nm) on chamois leather until it is mirror-like. Then place it in deionized water for ultrasonic cleaning for 3 min and let it air dry naturally.

[0062] (2) The Ag-CuO / Cu electrode was prepared in a self-made electrolytic cell, with a copper electrode as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The pretreated copper electrode was immersed in 1 M H2SO4 solution and treated with square wave pulse technology (parameters: pulse potential -1.8 V ~ -0.4 V, frequency 50 Hz, pulse width 200 s) to remove the surface oxide layer and activate the surface. After treatment, it was rinsed with ultrapure water to obtain the pretreated copper electrode.

[0063] (3) The pretreated copper electrode was then placed in 1 M KOH solution and cyclic voltammetry (CV) scan was performed (scan range -1.2 ~ -0.1 V, scan rate 50 mV / s, scan number 10 cycles) to further optimize the surface morphology of the electrode and enhance the uniformity of subsequent deposition. After the process, the electrode was rinsed with ultrapure water and dried with a paper towel to obtain the activated copper electrode.

[0064] (4) The activated copper electrode was placed in 0.01 M AgNO3 solution and the constant potential deposition method (deposition potential -0.84 V, deposition time set to 200 s) was used to reduce and deposit Ag+ on the surface of the copper electrode to form an Ag-modified layer. After deposition, the unadsorbed Ag+ on the surface was rinsed with ultrapure water and dried with paper towel to obtain silver nitrate modified copper electrode (Ag-CuO / Cu).

[0065] For comparison, CuO / Cu electrodes without silver nitrate deposition were prepared simultaneously under the same conditions as a control.

[0066] The surface microstructure of the Ag-CuO / Cu electrode obtained in this embodiment is as follows: Figure 1 As shown, the surface of the Ag-CuO / Cu electrode exhibits a uniform porous "flower-like" morphology; microscopic particles of 10-50 nm in size and interstitial pores approximately 30-40 nm wide are visible. The abundant "flower-like" morphology increases the electrode's specific surface area and the amount of ascorbic acid present, making the electrode more sensitive in detecting electrical signals. The numerous 30-40 nm interstitial pores allow for the entry of more ascorbic acid, facilitating adsorption and chemical reactions.

[0067] like Figure 2 As shown in the surface microstructure diagram, the black Cu and white C elements are in an alternating cluster state, and the O and Ag elements are grown on the black Cu and white C elements.

[0068] like Figure 3 As shown in Table 1, the elemental analysis data of the Ag-CuO / Cu electrode are as follows.

[0069] Table 1 Elemental Analysis Data

[0070] The X-ray photoelectron spectroscopy (XPS) image of the Ag-CuO / Cu electrode membrane electrode is shown below. Figure 4 As shown, Figure 4 The characteristic peaks of Cu 2p, Ag 3d, and O 1s were clearly detected in the full spectrum, and a C 1s peak (284.8 eV) was also present. The core elemental composition of the material is Cu, Ag, O, and C. Figure 4 B shows the peak-separated spectrum of Cu 2p. The Cu 2p orbital exhibits characteristic main peaks at 2p¹ / ² (955 eV) and 2p³ / ² (935 eV), as well as two pairs of strong satellite peaks at 940.7 eV and 943.3 eV nearby, which are typical XPS signals of Cu²⁺, corresponding to the CuO phase. Additionally, the spectrum also shows main peaks with binding energies at 932.6 eV (Cu 2p³ / ²) and 952.6 eV (Cu 2p¹ / ²), corresponding to CuO or Cu. + Cu 2+ Cu is a nano-copper-based material whose surface inevitably oxidizes when exposed to air. Figure 4 In C, the Ag 3d orbitals exhibit characteristic peaks of 3d³ / 2 (374 eV) and 3d⁵ / 2 (368 eV), with peak positions perfectly matching the standard binding energy of metallic Ag without significant shift. Therefore, Ag in the material mainly exists in the form of elemental silver without oxidation. Its metallic structure ensures high electronic conductivity of the electrode, which is a key factor in enhancing electrochemical performance and strengthening the current signal.

[0071] The CuO / Cu electrode of the control sample and the Ag-CuO / Cu electrode of Example 1 were placed in 10 mL of 0.1 M K3[Fe(CN)6] solution, and their impedance was studied by electrochemical impedance spectroscopy. The parameters were set as follows: open circuit potential of CuO / Cu electrode was 0.03637 V, and open circuit potential of Ag-CuO / Cu was 0.20027 V. The results are as follows. Figure 5As shown, for the CuO / Cu electrode (black curve), its capacitive arc covers a wide range from Z′≈0 to 20000 Ω, with a corresponding Rct of approximately 18000 Ω. This indicates that the charge transfer process on the CuO / Cu electrode surface faces significant resistance, resulting in sluggish electrochemical reaction kinetics. For the Ag-CuO / Cu electrode (red curve), its capacitive arc diameter is significantly reduced, with the maximum extension range of Z′ being only about 800 Ω, corresponding to a decrease in Rct to approximately 700 Ω. The modification with Ag reduced the charge transfer resistance by more than 96%, indicating that Ag, as a catalytically active site, effectively promoted charge transfer at the electrode-electrolyte interface, significantly increasing the electrochemical reaction rate. Furthermore, neither curve exhibits Warburg impedance, representing diffusion control, in the low-frequency region, indicating that the electrode process in this system is primarily controlled by charge transfer, further validating the dominant influence of Rct on electrode activity.

[0072] Cyclic voltammetry tests were performed using the Ag-CuO / Cu electrode from Example 1 and the CuO / Cu electrode from the control sample, respectively, immersed in 0.1M NaOH solution and 0.1M NaOH + 10mM AA solution. The results are as follows: Figure 6 As shown, curve a (CuO / Cu): Without Ag deposition and without AA, the background current is low and there are no obvious redox peaks, indicating that the CuO / Cu electrode has weak electrochemical activity in the NaOH system. Curve b (CuO / Cu): Without Ag deposition but containing AA, the current is significantly higher than curve a and an AA oxidation peak appears, indicating that CuO / Cu has a certain catalytic oxidation ability for AA, but the response intensity is limited. Curve c (Ag-CuO / Cu): With Ag deposition but without AA, the current is slightly higher than curve a, reflecting the improvement in electrode conductivity after Ag modification, but no strong electrochemical response is shown without AA. Curve d (Ag-CuO / Cu): After Ag deposition and containing AA, the current (especially the oxidation peak) increases significantly and the reduction peak is obvious, indicating that the synergistic effect of Ag and CuO significantly enhances the catalytic activity of the electrode for AA. It is the group with the strongest electrochemical response among the four systems, and this composite structure exhibits excellent electrocatalytic oxidation performance and selectivity for AA.

[0073] Cyclic voltammetry tests were performed on the Ag-CuO / Cu electrode of Example 1 at different scan rates increasing from 10 mV / s to 140 mV / s. The results are as follows: Figure 7 As shown in Figure A, it can be seen that the currents of both the oxidation and reduction peaks of AA increase significantly with increasing scan rate. Using the peak currents at 0.63 V, 0.21 V, 0.061 V, and 0.27 V as the ordinate and the square root of the corresponding scan rate as the abscissa, a fitting was performed to obtain... Figure 7B. It can be seen that the oxidation and reduction peak currents at different potentials are related to υ. 1 / 2 All showed a good linear relationship. The goodness of fit R for the 0.63 V oxidation peak was... 2 =0.9953, 0.27 V oxidation peak R 2 =0.9991, 0.21 V reduction peak R 2 =0.9799, 0.061 V reduction peak R 2 =0.9975, all close to 1. This indicates that the redox reaction of AA on the Ag-CuO / Cu electrode is controlled by diffusion, which is beneficial for the electrochemical testing of AA on the Ag-CuO / Cu electrode.

[0074] The Ag-CuO / Cu electrode from Example 1 was immersed in 0.1M NaOH solution, 0.1M NaOH+1M AA solution, 0.1M NaOH+2M AA solution, 0.1M NaOH+3M AA solution, 0.1M NaOH+4M AA solution, and 0.1M NaOH+5M AA solution, respectively. A platinum sheet was used as the counter electrode, and a saturated calomel electrode as the reference electrode. A detection potential of 0.6V was applied, and the it curves were obtained as shown below. Figure 8 As shown in Figure A, the fitted linear graph of it is as follows: Figure 8 As shown in B.

[0075] The Ag-CuO / Cu electrode from Example 1 was immersed in 0.1M NaOH solution, 0.1M NaOH+1M AA solution, 0.1M NaOH+2M AA solution, 0.1M NaOH+3M AA solution, 0.1M NaOH+4M AA solution, and 0.1M NaOH+5M AA solution, respectively, and cyclic voltammetry was performed at a scan rate of 50 mV / s. The results are as follows: Figure 8 As shown in C, the CV fitting linear plot is as follows: Figure 8 As shown in D.

[0076] As can be seen, Ipa = 6.794C AA 1 / 2 -6.523 (R) 2 =0.9816), the oxidation peak current is linearly related to the square root of the AA concentration, rather than being directly proportional to the concentration itself. This strongly suggests that the oxidation process of AA on the Ag-CuO / Cu electrode is controlled by the mass diffusion step.

[0077] Using the Ag-CuO / Cu electrode from Example 1 as the working electrode, the sample was immersed in the passion fruit juice to be tested. Detection potentials of 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, and 0.8V were applied. Tests were performed at different potentials using the chronoamperometry method. The results are as follows: Figure 9As shown, when performing AA detection, a suitable operating potential can effectively improve the sensitivity and catalytic effect of the sensor. When the potential is 0.6 V, the generated current is relatively stable and the current gradient is the largest.

[0078] The detection experiment of the Ag-CuO / Cu electrode for AA in Example 1 specifically included: immersing the Ag-CuO / Cu electrode in a solution containing 2 μM AA, using a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode, applying a detection potential of 0.6 V, and continuously adding AA to the solution to obtain it curves of different concentrations of AA from 2 μM to 10 mM versus the current value, as shown below. Figure 10 As shown in Figure A, a magnified diagram of the continuous addition of low-concentration AA is shown below. Figure 10 As shown in Figure B, the linear relationship between the fitted response current and the AA concentration is as follows: Figure 10 As shown in Figure C, within the concentration range of 2 μM to 10 mM, the steady-state current value of AA exhibits a good linear relationship with its concentration. The linear fitting equation is y = 1.6384x + 0.60015. Calculations show that the response range of the Ag-CuO / Cu electrode to AA is 2 μM to 9.11 mM, with a sensitivity of 1638.4 μA·mM. -1 ·cm -2 The detection limit was 0.0046 μM.

[0079] Passion fruit juice contains, in addition to acetic acid (AA), sugars such as glucose, fructose, and sucrose, inorganic salts such as NaCl, CaCl2, Na2SO4, and NaH2PO4, and organic acids such as citric acid, which can interfere with digestion. The Ag-CuO / Cu electrode of Example 1 was subjected to... Figure 10 D. Adding an anti-interference substance, the resulting anti-interference it curve is as follows: Figure 10 As shown in Figure D, the anti-interference test curves reveal that when 1 mM AA, 0.1 mM glucose, 0.02 mM uric acid (UA), 0.1 mM sodium citrate, 0.1 mM NaCl, 0.1 mM Na2SO4, 0.1 mM NaH2PO4, 0.1 mM fructose, 0.1 mM sucrose, and 0.1 mM CaCl2 were added to the detection system sequentially, the current response showed no significant fluctuations; only when 1 mM AA was added multiple times did the current increase significantly. This indicates that the various sugars, inorganic salts, and organic acids in passion fruit juice generate extremely weak electrochemical signals when detecting AA, and the Ag-CuO / Cu electrode exhibits strong anti-interference capability for AA detection.

[0080] This embodiment also conducted performance tests on the repeatability, reproducibility, and stability of the obtained Ag-CuO / Cu electrode for the AA sensor. This included immersing the Ag-CuO / Cu electrode in a 0.1 M NaOH solution, using a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode, applying a detection potential of 0.6 V, and continuously adding 1 mM AA five times. The resulting response current is shown below. Figure 11 As shown in Figure A, the response currents of the five tests are very similar, with a relative standard deviation (RSD) of 2.5%, indicating that the Ag-CuO / Cu electrode has excellent repeatability.

[0081] Five Ag-CuO / Cu electrodes were prepared under the same conditions and immersed in 0.1 M NaOH solution. A platinum sheet was used as the counter electrode, and a saturated calomel electrode as the reference electrode. A detection potential of 0.6 V was applied, and 1 mM AA was added. The resulting response currents were as follows: Figure 11 As shown in B, the relative standard deviation (RSD) is 6.7%, indicating good reproducibility among different electrodes.

[0082] Then, long-term stability testing of the Ag-CuO / Cu nanoelectrode was conducted, including: storing the prepared Ag-CuO / Cu electrode in a 4°C refrigerator, and performing chronoamperometry (it) tests every 7 days in an AA solution (1 mM) of the same concentration, using the same method as above. The test results are as follows. Figure 11 As shown in Figure C, after 35 days of storage (a total of 5 detection cycles), the electrode current response value still maintains more than 97% of the initial response value, indicating that the Ag-CuO / Cu electrode prepared in the experiment has excellent stability.

[0083] To verify the practicality of the Ag-CuO / Cu electrode, the content of AA in fresh passion fruit juice samples was further investigated. The accuracy of the results was assessed using the standard addition method, and the electrochemical detection of the spiked samples was performed using the coulometric method. The specific procedure was as follows: Fresh passion fruit was taken, washed, and cut open. The pulp (peeled and pitted) was scooped out with a spoon and ground into a fine pulp in a clean mortar. The pulp was transferred to a PP tube, 10 mL of deionized water was added, and the mixture was ultrasonically dispersed for 10 min. Then, it was centrifuged at 8000 rpm for 10 min, and the supernatant was collected as the test solution. 0.176 g of analytical grade AA was ultrasonically dispersed in 10 mL of deionized water as the standard solution. The Ag-CuO / Cu electrode was immersed in a continuously stirred 0.1 M NaOH solution, with a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode. A detection potential of 0.6 V was applied, and 1 M AA standard solution was added dropwise. Then, 1 mM passion fruit test solution was continuously added. The chronoamperotropic response graph is shown in the figure. Figure 12As shown in Figure A, the standard curve of AA and current in a 1 M AA standard solution determined by the standard addition method is shown in Figure A. Figure 12 As shown in Figure B, the concentration of AA in passion fruit juice was measured to be 8.071 mM (the actual AA content in passion fruit juice is found to be 2 ~ 8 mM), indicating that the prepared Ag-CuO / Cu electrode can be used for the actual analysis and detection of passion fruit juice.

[0084] Example 2

[0085] Based on Example 1, the difference in this example is that the deposition time in step (4) is different. In this example, the deposition time is 50s.

[0086] Example 3

[0087] Based on Example 1, the difference in this example is that the deposition time in step (4) is different. In this example, the deposition time is 100s.

[0088] Example 4

[0089] Based on Example 1, the difference in this example is that the deposition time in step (4) is different. In this example, the deposition time is 300s.

[0090] The electrodes obtained in Examples 1 to 4 were immersed in a 0.1M NaOH + 10mM AA solution, and cyclic voltammetry tests were performed. The results are as follows: Figure 13 As shown, Example 1 has the best effect, followed by Example 3.

[0091] Example 5

[0092] Based on Example 1, the difference in this example is that the concentration of AgNO3 solution in step (4) is different. In this example, the concentration of AgNO3 solution is 0.005M.

[0093] Example 6

[0094] Based on Example 1, the difference in this example is that the concentration of AgNO3 solution in step (4) is different. In this example, the concentration of AgNO3 solution is 0.03M.

[0095] Example 7

[0096] Based on Example 1, the difference in this example is that the concentration of AgNO3 solution in step (4) is different. In this example, the concentration of AgNO3 solution is 0.05M.

[0097] The electrodes obtained in Examples 1, 5-7 were immersed in a 0.1M NaOH + 10mM AA solution and cyclic voltammetry tests were performed. The results are as follows:Figure 14 As shown, Example 1 has the best effect, followed by Example 6 and Example 7.

[0098] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an Ag-CuO / Cu electrode, characterized in that: Includes the following steps: Step S1: Clean the copper electrode, then grind and polish it; Step S2: Immerse the copper electrode after the initial treatment in step S1 in a 0.5-1.5M H2SO4 solution and perform square wave pulse treatment to remove the surface oxide layer and activate the surface, providing an attachment point for the next step of generating a two-dimensional copper oxide structure; after treatment, rinse it with ultrapure water to obtain the pretreated copper electrode. Step S3: The pretreated copper electrode is then placed in a 0.5-1.5M KOH solution and subjected to cyclic voltammetry scanning. During the induced deposition process, CuO grows in layers, forming a porous "flower cluster" morphology. After the process is completed, the electrode is rinsed with ultrapure water and dried to obtain the activated copper electrode. Step S4: Place the activated copper electrode in a 0.005-0.05M AgNO3 solution and use a potentiostatic deposition method to deposit Ag... + An Ag-modified layer was formed by reduction and deposition on the surface of a copper electrode. After deposition, the unadsorbed Ag+ on the surface was rinsed with ultrapure water, and the water was dried to obtain an Ag-CuO / Cu electrode. The deposition potential was -1.5 to 0.5 V, and the deposition time was 50 to 300 s.

2. The method for preparing the Ag-CuO / Cu electrode according to claim 1, characterized in that: In step S2, the square wave pulse has a pulse potential of -1.8 V to -0.4 V, a frequency of 50-100 Hz, and a pulse width of 100-300 s; in step S3, the cyclic voltammetric scan has a scanning voltage of -1.2 V to -0.1 V, a scan speed of 30-100 mV / s, and a scan number of 5-60 cycles.

3. The method for preparing the Ag-CuO / Cu electrode according to claim 1, characterized in that: In step S1, the cleaning includes acid washing of the copper electrode, followed by ultrasonic cleaning with clean water; the polishing includes polishing with 5000-grit and 8000-grit sandpaper in sequence; the polishing includes polishing the copper electrode to a mirror finish on chamois leather with alumina powder, followed by ultrasonic cleaning in deionized water for 3-5 minutes and then air drying.

4. The method for preparing the Ag-CuO / Cu electrode according to claim 3, characterized in that: The pickling process involves immersing the copper electrode in 1-2M hydrochloric acid for 2-5 minutes; the alumina powder has a particle size of 30-80 nm. In step S1, the diameter of the copper electrode is 1~3mm and the purity is ≥99.99%; in steps S2 and S3, the copper electrode is the working electrode, the platinum sheet is the counter electrode, and the saturated calomel electrode is the reference electrode; in step S4, the deposition time is 100-200s.

5. An Ag-CuO / Cu electrode, characterized in that: It was prepared using the method described in any one of claims 1 to 4 for preparing the Ag-CuO / Cu electrode.

6. The Ag-CuO / Cu electrode according to claim 5, characterized in that: The composition and mass ratio of the Ag-CuO / Cu electrode membrane electrode are as follows: C element 8.46%-11.12%, O element 7.05%-9.05%, Cu element 28.27%-29.9%, Ag element 49.93%-55.78%.

7. The application of the Ag-CuO / Cu electrode as described in claim 5 or 6 for passion fruit juice detection, characterized in that: The Ag-CuO / Cu electrode was used as the working electrode to detect the ascorbic acid content in passion fruit juice.

8. A sensor for detecting ascorbic acid in passion fruit juice, characterized in that: Includes the Ag-CuO / Cu electrode as described in claim 5 or 6.

9. A method for detecting ascorbic acid in passion fruit juice, characterized in that, Includes the following steps: Step S10: Using the Ag-CuO / Cu electrode as the working electrode, immerse it in a 0.1M sodium hydroxide solution, use a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode, apply a voltage for testing, and then add different concentrations of ascorbic acid to obtain the it curve of the working electrode to different concentrations of ascorbic acid. Further fit to obtain the linear regression equation of the steady-state current value of ascorbic acid and its concentration. In step S20, the Ag-CuO / Cu electrode is used as the working electrode and immersed in a 0.1M sodium hydroxide solution. A platinum sheet is used as the counter electrode and a saturated calomel electrode is used as the reference electrode. A voltage is applied for testing, and then passion fruit juice to be tested is added to obtain a steady-state current value. The concentration of ascorbic acid is calculated using the linear regression equation obtained in step S10.

10. The method for detecting ascorbic acid in passion fruit juice according to claim 9, characterized in that: The potential is 0.6V.

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