CuO / Cu (OH) 2-Ni (OH) 2 / Ni electrode and application thereof in passion fruit juice detection

Abstract

The invention provides a CuO / Cu (OH) 2-Ni (OH) 2 / Ni electrode and application of the CuO / Cu (OH) 2-Ni (OH) 2 / Ni electrode in passion fruit juice detection. The CuO / Cu (OH) 2-Ni (OH) 2 / Ni electrode is prepared through the following steps that a nickel electrode is pretreated, the treated nickel electrode is placed in a mixed solution containing hydrochloric acid and copper chloride, electrochemical deposition is conducted through a square wave pulse method, and a deposition layer is formed on the surface of the nickel electrode; and placing the obtained electrode in an alkaline solution containing sodium hydroxide and glucose, and carrying out electrochemical activation treatment by adopting cyclic voltammetry to obtain the CuO / Cu (OH) 2-Ni (OH) 2 / Ni electrode. The electrode shows excellent electrocatalytic oxidation performance on glucose, is wide in linear detection range, high in sensitivity and low in detection limit, has good anti-interference performance, repeatability and long-term stability, and can realize rapid, accurate and quantitative detection of glucose in a passion fruit juice matrix.

Description

Technical Field

[0001] This invention relates to the field of electrochemical sensor technology, and in particular to a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode and its application in passion fruit juice detection. Background Technology

[0002] Passion fruit, a tropical and subtropical fruit, is rich in various nutrients, and its juice quality is closely related to its glucose content. Glucose is the main soluble sugar in passion fruit juice, and its content directly determines the sweetness, flavor, and nutritional value of the juice. It is a core indicator for juice quality grading, process optimization, and adulteration detection. Therefore, establishing a rapid, accurate, and sensitive glucose detection method is of significant practical importance.

[0003] Currently, glucose detection methods mainly include high-performance liquid chromatography (HPLC), gas chromatography (GC), spectrophotometry, and electrochemical sensor methods. While GC offers high precision, it suffers from drawbacks such as cumbersome sample pretreatment, long detection cycles, and high instrument costs. Spectrophotometry is simple to operate but has limited selectivity and sensitivity. Electrochemical sensor methods, due to their rapid response, ease of operation, low cost, high sensitivity, and ease of miniaturization, have become the ideal technical solution for glucose detection.

[0004] In electrochemical sensors, enzyme-free glucose sensors have attracted widespread attention due to their high stability and low cost. Nickel-based and copper-based materials, in particular, have been extensively studied for their excellent catalytic performance. However, the catalytic activity and stability of single-component electrode materials still need improvement. Furthermore, passion fruit juice contains complex components such as fructose, glucose, polyphenols, and pigments, which can easily compete with ascorbic acid for adsorption or undergo side reactions on the electrode surface, leading to decreased sensor selectivity. Moreover, existing materials suffer from insufficient exposure of active sites in terms of dimensional matching and structural design, making it difficult to balance conductivity and catalytic performance, thus limiting their ability to rapidly and sensitively detect low-concentration target analytes in complex matrices.

[0005] Therefore, developing a composite electrode material with simple preparation process, high sensitivity, good stability, strong anti-interference ability, easy operation and reliable results, and applying it to the rapid and accurate detection of glucose in complex matrices (such as fruit juice) has important application value. Summary of the Invention

[0006] To address the above technical problems, this invention discloses a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode and its application in passion fruit juice detection. This electrode has a wide linear detection range, high sensitivity, low detection limit, and excellent anti-interference, stability, repeatability, and reproducibility. It solves the technical problem that the sensitivity, stability, and anti-interference ability of glucose detection electrodes in the prior art need to be improved, and realizes rapid and accurate quantitative detection of glucose in passion fruit juice matrix.

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

[0008] A method for preparing a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode includes the following steps:

[0009] Step S1: Pre-treat the nickel electrode to obtain a clean nickel electrode;

[0010] Step S2: The nickel electrode treated in step S1 is placed in a mixed solution containing hydrochloric acid and copper chloride, and electrochemical deposition is performed using a square wave pulse method to form a deposition layer on the surface of the nickel electrode; the concentration of hydrochloric acid in the mixed solution is 0.05~2.0 mol / L, and the concentration of copper chloride is 0.05~2.0 mol / L; the potential range of the square wave pulse method is -0.6 V to 0 V, and the deposition time is 20~200 seconds;

[0011] Step S3: The electrode obtained in step S2 is placed in an alkaline solution containing sodium hydroxide and glucose, and electrochemical activation is performed using cyclic voltammetry to obtain a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode; the concentration of sodium hydroxide in the alkaline solution is 0.05~0.2 mol / L, and the concentration of glucose is 0.1~10 mmol / L.

[0012] Using this technique, a Cu(OH)₂ nanofilm was formed on the surface of a Ni electrode via a square-wave pulse method. Then, through cyclic voltammetry activation, a CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode was successfully constructed on a nickel substrate. This electrode possesses a unique porous structure composed of nanoparticles, increasing its specific surface area and providing abundant catalytic active sites. XPS and EDS analyses confirmed the simultaneous presence of Ni(OH)₂, CuO, and Cu(OH)₂ active components on the electrode surface, forming a highly efficient synergistic catalytic system. This electrode exhibits excellent electrocatalytic oxidation performance for glucose. Electrochemical tests show that it has a wide linear range (0.002 mmol / L ~ 9.11 mmol / L) and high sensitivity (3170 μA·mM). -1 ·cm -2 It exhibits a low detection limit (0.0014 μmol / L), as well as good anti-interference, repeatability, reproducibility, and long-term stability (5 weeks). Moreover, the entire preparation method is simple and the conditions are controllable, making it suitable for large-scale preparation.

[0013] As a further improvement of the present invention, the preparation method of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode further includes step S4, in which the obtained CuO / Cu(OH)2-Ni(OH)2 / Ni electrode is soaked in deionized water for 5-10 minutes to wash away the residual liquid on the electrode surface, ultrasonically cleaned for 5-20 seconds, and then taken out and dried.

[0014] As a further improvement of the present invention, the pretreatment in step S1 includes: first, polishing the nickel electrode with sandpaper, then polishing it to a mirror finish on a polishing cloth with aluminum oxide powder, and finally ultrasonically cleaning it in distilled water. Further, the ultrasonic cleaning time is 3 minutes. Ultrasonic cleaning provides a better cleaning effect and does not damage the electrode surface.

[0015] As a further improvement of the present invention, in step S2, the concentration of hydrochloric acid is 0.1~1 mol / L, the concentration of copper chloride is 0.1~0.5 mol / L, and the deposition time is 50~100 seconds.

[0016] As a further improvement of the present invention, in step S2, the concentration of hydrochloric acid is 0.1 mol / L, the concentration of copper chloride is 0.3 mol / L, and the deposition time is 100 seconds. Using this technical solution, the electrode exhibits the strongest catalytic oxidation ability for glucose, and the current response reaches its maximum value.

[0017] As a further improvement of the present invention, in step S3, the scanning rate of the cyclic voltammetry is 10~150 mV / s, and the number of scanning cycles is 1~30 cycles.

[0018] As a further improvement of the present invention, in step S3, the concentration of sodium hydroxide is 0.1 mol / L and the concentration of glucose is 10 mmol / L; the scanning rate of the cyclic voltammetry is 50 mV / s, and the number of scan cycles is 10. Under these conditions, a porous nanocomposite electrode with abundant active sites and significantly improved electrocatalytic activity can be prepared.

[0019] This invention discloses a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode, which is prepared by the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode preparation method described above.

[0020] As a further improvement of the present invention, the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode has a porous structure composed of nanoparticles, and the electrode surface simultaneously contains active components of Ni(OH)2, CuO, and Cu(OH)2. The Ni electrode surface is covered with a CuO / Cu(OH)2-Ni(OH)2 nanofilm. In the electrode, Cu elements mainly exist in the form of CuO and Cu(OH)2, and Ni elements mainly exist in the form of Ni(OH)2. The porous structure provides abundant active sites for the catalytic oxidation of glucose, accelerating the adsorption, activation, and electron transfer processes of glucose.

[0021] This invention discloses the application of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode described above in the detection of passion fruit juice. Specifically, it is used for the quantitative detection of glucose in the passion fruit juice matrix. This electrode is adapted to the complex matrix of passion fruit juice, effectively avoiding interference from other components in the juice and achieving accurate glucose detection.

[0022] This invention discloses a method for detecting glucose content in passion fruit juice, using the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode as described above as the working electrode, and employing electrochemical analysis to quantitatively detect glucose in passion fruit juice samples.

[0023] Preferably, the working potential during detection is 0.6 V, and enzyme-free amperometric detection is performed using the chronoamperometry method; 0.6 V is the optimal working potential, at which point the electrode baseline is low, the current increment is large, the current response is stable, the current step is the largest, and the detection sensitivity is the highest.

[0024] The CuO / Cu(OH)2-Ni(OH)2 / Ni electrode exhibits a linear detection range of 0.002 mmol / L to 9.11 mmol / L for glucose, with a sensitivity of 3170 μA·mM. -1 ·cm -2 The detection limit was 0.0014 μmol / L; within the concentration range of 2 μmol / L to 10 mol / L, the steady-state current value of glucose showed a good linear relationship with its concentration, and the linear fitting equation was y=3.1695x+0.5526 (R²=0.9964).

[0025] As a further improvement of the present invention, the passion fruit juice is pretreated before detection. The pretreatment steps are as follows: take passion fruit juice, add distilled water for ultrasonic extraction, centrifuge, take the supernatant, dilute with 0.1 mol / L NaOH solution, and then perform detection. More preferably, the ultrasonic extraction time is 20 min, the centrifugation speed is 8000 r / min, and the centrifugation time is 10 min. This pretreatment method can effectively remove impurities such as pulp residue in passion fruit juice, avoid matrix interference, and at the same time ensure the glucose dissolution rate and improve the detection accuracy.

[0026] When glucose in passion fruit juice was detected using the above method, the spiked recovery rate was 95.61%, and the detection results were accurate and reliable, meeting the actual needs of passion fruit juice quality testing.

[0027] The CuO / Cu(OH)2-Ni(OH)2 / Ni electrode of the present invention also has excellent anti-interference, repeatability, reproducibility and stability:

[0028] Anti-interference ability: It has good anti-interference ability against common interfering substances in passion fruit juice, such as ascorbic acid, uric acid, sodium citrate, sodium chloride, sucrose, fructose, sodium dihydrogen phosphate, etc. It can still produce obvious specific current signals to glucose when interfering substances are present.

[0029] Repeatability: The relative standard deviation (RSD) of glucose response current was only 2.294% after five consecutive measurements using the same electrode.

[0030] Reproducibility: When five electrodes were prepared under the same conditions to measure the response current of glucose, the relative standard deviation (RSD) was only 2.441%.

[0031] Stability: After the electrode was stored at room temperature for 5 weeks, the response current to glucose remained at 96% of the original value, demonstrating good long-term storage capability.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] First, the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode of this invention exhibits excellent electrocatalytic performance, with a wide linear detection range, high sensitivity, and low detection limit for glucose. It also demonstrates excellent anti-interference, repeatability, reproducibility, and long-term stability, solving the problems of poor adaptability and insufficient detection performance of existing electrodes. It enables rapid and accurate quantitative detection of glucose in passion fruit juice matrix, requiring simple sample pretreatment, offering fast detection speed, accurate and reliable results, and a spiked recovery rate of 95.61%. This electrode provides an effective detection tool for quality grading, process optimization, and adulteration identification of passion fruit juice, which is of significant practical importance for ensuring the quality and safety of passion fruit products and regulating market order. Furthermore, it has potential application value in glucose detection in other fields such as food testing and biomedicine.

[0034] Secondly, the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode preparation method of the present invention is simple, easy to control, and convenient to operate. No complicated instruments are required during the preparation process, making it suitable for large-scale preparation. By optimizing the process parameters of square wave pulse deposition and cyclic voltammetry modification, a nanocomposite electrode with uniform particle size, high crystallinity, and porous structure with abundant active sites can be prepared. Attached Figure Description

[0035] Figure 1 These are microscopic morphology images of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1 of this invention, where A and B are scanning electron microscope images at different magnifications, and C is an EDS energy spectrum.

[0036] Figure 2 The above are XPS images of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1 of this invention, where A is the full XPS spectrum, B is the Ni 2p spectrum, and C and D are the high-resolution XPS spectra of Cu 2p and O 1s, respectively.

[0037] Figure 3 These are the electrochemical impedance curves of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1 of this invention in 0.1 mol / L K3[Fe(CN)6]+10 mmol / L glucose solution.

[0038] Figure 4 This is a cyclic voltammetry (CV) diagram of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode and the Ni(OH)2 / Ni electrode in 0.1 mol / L NaOH and 0.1 mol / L NaOH + 10 mmol / L glucose solution in Example 3 of the present invention; wherein, A is the Ni(OH)2 / Ni electrode and B is the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode.

[0039] Figure 5 This is the result of the electro-oxidation kinetics of glucose using the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in Example 3 of the present invention; wherein, A is the CV diagram of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in 0.1 mol / L NaOH solution with different scan rates, and B is the oxidation peak current, reduction peak current and scan number υ in diagram A. 1 / 2 Relationship diagram.

[0040] Figure 6 This refers to the linear range and sensitivity results of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in Example 3 of this invention based on cyclic voltammetry and chronoamperometry; wherein, A is the cyclic voltammetric curve of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in 0.1 mol / L NaOH solutions containing different concentrations of glucose, and B is the I in A. glu / I0 and C glu 1 / 2 The linear relationship is shown in the graph. C is the chronoamperometry curve of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in 0.1 mol / L NaOH solution containing different concentrations of glucose, and D is the Ig in C. glu / I0 and C glu 1 / 2 Linear relationship graph.

[0041] Figure 7 This is the enzyme-free amperometric detection result of glucose using the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in Example 3 of the present invention; wherein A is the current response of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode to 10 mmol / L glucose in 0.1 mol / L NaOH at different potentials, B is the it curve of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode with different concentrations of glucose continuously added to 0.1 mol / L NaOH solution, C is an enlarged view of the continuous addition of low concentration glucose in Figure A, and D is the standard curve relationship between the corresponding current and glucose concentration in Figure A.

[0042] Figure 8 This is the current response diagram of adding interfering substances to the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in Example 4 of the present invention.

[0043] Figure 9The results of repeatability, reproducibility, and stability tests of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode in Example 4 of this invention in 0.1 mol / L NaOH and 1 mmol / L glucose solutions are shown, where A represents repeatability, B represents reproducibility, and C represents stability.

[0044] Figure 10 Example 5 of the present invention provides the chronoamperometry response diagram and standard curve for determining glucose in passion fruit juice. A is the chronoamperometry response diagram of a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode at 0.6 V, where passion fruit juice is added dropwise once to a continuously stirred 0.1 mol / L NaOH solution, followed by the addition of 1 mmol / L glu. B is the standard curve of glucose and current in passion fruit juice determined using the standard addition method in Figure A.

[0045] Figure 11 The image shows the CV curves of CuO / Cu(OH)2-Ni(OH)2 / Ni electrodes obtained by deposition in NaOH for different times in Example 6 of this invention in 0.1 mol / L NaOH + 10 mmol / L glucose solution.

[0046] Figure 12 The image shows the CV curves of CuO / Cu(OH)2-Ni(OH)2 / Ni electrodes obtained by deposition in HCl of different concentrations for 100 s in 0.1 mol / L NaOH + 10 mmol / L glucose solution in Example 7 of this invention.

[0047] Figure 13 This is the CV diagram of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode obtained by deposition for 100 s in CuCl2 of different concentrations under the same HCl concentration in Example 8 of the present invention in 0.1 mol / L NaOH + 10 mmol / L glucose solution. Detailed Implementation

[0048] The preferred embodiments of the present invention will be described in further detail below.

[0049] Example 1

[0050] A method for preparing a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode, the specific steps of which are as follows:

[0051] Step S1, Electrode Pretreatment: The nickel electrode is polished smooth with 5000-grit and 8000-grit sandpaper, then polished with aluminum oxide powder on a polishing cloth until the electrode surface has a smooth mirror finish. Afterward, the electrode is placed in distilled water and cleaned with an ultrasonic cleaner for 3 minutes, then removed and air-dried for later use.

[0052] Step S2, Square Wave Pulse Deposition: The pretreated nickel electrode was placed in a mixed solution containing 1 mol / L HCl and 0.1 mol / L CuCl2. Deposition was performed using the square wave pulse method, with parameters set as follows: potential range -0.6 V to 0 V, deposition time 100 seconds. After deposition, a brown film adhered to the surface of the nickel electrode, indicating that copper nanoparticles were successfully deposited on the nickel electrode surface.

[0053] Step S3, Cyclic voltammetric activation: The deposited electrode was placed in 0.1 mol / L NaOH solution and 0.1 mol / L NaOH + 10 mmol / L glucose solution, respectively, and activated using cyclic voltammetry. The scan rate was 50 mV / s, and the number of scan cycles was 10, resulting in the modified electrode.

[0054] Step S4, post-processing: Soak the modified electrode in deionized water for 8 minutes, ultrasonically clean it for 10 seconds, and then remove it and air dry it to obtain CuO / Cu(OH)2-Ni(OH)2 / Ni nanocomposite electrode.

[0055] The electrodes prepared in this embodiment were characterized by SEM and EDS. Figure 1 As shown in Figures A and B, the electrode surface has a porous structure composed of nanoparticles, which are formed by the aggregation of many nanoparticles. After being treated by the square wave pulse method, the surface of Ni is covered with a thin film, indicating that Cu nanoparticles have modified the surface of Ni. Figure 1 The EDS spectrum of the C figure in the figure confirms the presence of Cu, Ni, C and O elements in the electrode. The C and O elements in the spectrum may be due to the adsorption of C-containing and O-containing substances in the air on the electrode surface, while the Ni and Cu elements come from the electrode itself.

[0056] Furthermore, the composition of the electrode surface was analyzed by XPS, and the results are as follows: Figure 2 As shown, Figure 2 The full spectrum of Figure A shows the presence of Cu, Ni, O, and C elements, which is consistent with the EDS characterization results. Figure 2 The characteristic peaks and satellite peaks at 855.8 eV (2p3 / 2) and 873.6 eV (2p1 / 2) in the high-resolution Ni 2p spectrum of Figure B confirm that Ni mainly exists in the Ni(OH)2 valence state. Figure 2 The high-resolution spectrum of the Cu 2p orbital in Figure C shows typical Cu 2p characteristic peaks at 932.6 eV and 934 eV, corresponding to CuO and Cu(OH)2, confirming that Cu mainly exists in the form of CuO and Cu(OH)2. Figure 2The high-resolution spectrum of O1s in the D diagram shows a strong peak at 531.2 eV, corresponding to the oxygen in the hydroxyl group (-OH) in the hydroxide, further verifying the successful construction of the Cu(OH)2-Ni(OH)2 / Ni composite structure. These results demonstrate the successful construction of the CuO / Cu(OH)2-Ni(OH)2 / Ni composite structure.

[0057] Example 2

[0058] Electrochemical impedance spectroscopy (EIS), a powerful technique for studying the interfacial properties of electrode surfaces, is used to monitor impedance changes during the modification of electrodes with different surfaces. A typical Nyquist plot consists of a high-frequency semicircular portion and a low-frequency linear portion, where the diameter of the semicircular portion is related to the electron transfer resistance, which represents conductivity. A Ni(OH)₂ / Ni electrode was used as a control; Ni(OH)₂ / Ni was obtained by adding a nickel electrode to a NaOH solution for 3 minutes.

[0059] The Ni(OH)₂ / Ni electrode and the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode prepared in Example 1 were placed in 10 mL of 0.1 mol / L K₃[Fe(CN)₆] solution, and their impedance was studied by electrochemical impedance spectroscopy. The parameters were set as follows: the open-circuit potential of the Ni(OH)₂ / Ni electrode was 0.35988 V. The results are as follows. Figure 3 As shown, the open-circuit potential of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode is -0.01458 V. The conductivity of the CuO / Cu(OH)2-Ni(OH)2 / Ni composite nanoelectrode is improved after modification.

[0060] Example 3

[0061] The Ni(OH)₂ / Ni electrode from Example 2 and the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode prepared in Example 1 were immersed in 0.1 mol / L NaOH solution and 0.1 mol / L NaOH + 10 mmol / L glu (glucose) solution, respectively, and CV scans were performed with and without glucose at a scan rate of 50 mV / s. The results are as follows. Figure 4 As shown.

[0062] like Figure 4As shown in Figure A, in a 0.1 mol / L NaOH electrolyte without glucose, the Ni(OH)₂ / Ni electrode exhibits an oxidation peak in the 0.6 V to 0.8 V range as the potential is swept from -1 V to 0.8 V. The weak peak current corresponding to the electrode's oxidation indicates low redox activity of the Ni(OH)₂ / Ni electrode in 0.1 mol / L NaOH. Curve b shows a significantly enhanced electrode reaction due to the presence of glucose, reflecting the catalytic oxidation process of glucose on the Ni(OH)₂ / Ni electrode.

[0063] like Figure 4 As shown in Figure B, a significant oxidation peak is observed at a potential of 0.45 V. This is the Ni(ɪɪɪ) / Cu(ɪɪɪ) peak formed by the electrocatalytic oxidation of glucose. Literature review indicates that this is related to the conversion between Ni(OH)₂ → NiOOH and CuO → CuOOH, with reaction equations shown in equations (1) and (3). However, the corresponding reduction peak current at approximately 0.71 V (related to NiOOH→Ni(OH)₂ and CuOOH→CuO) weakens. This is due to the co-mediation effect of Ni(OH)₂ / NiOOH and CuO / CuOOH, which leads to the electrocatalytic oxidation of glucose, with reaction equations shown in equations (2) and (4). This demonstrates that the electrode modified with CuO / Cu(OH)₂-Ni(OH)₂ / Ni nanomaterials exhibits significant electrocatalytic activity for glucose oxidation.

[0064]

[0065] It is evident that the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode more readily forms highly active copper-based compounds (such as Cu2O, CuO, or Cu nanocrystals). These substances inherently possess strong redox activity in alkaline environments, thus exhibiting a significant redox peak in 0.1 mol / L NaOH. As shown by curve b in the figure, the current peak value is increased in the glucose-containing system, and the oxidation peak potential is higher, approximately 0.6 ~ 0.8 V. Figure 4 In Figure B, the current response in the glucose-containing system (red curve) is significantly enhanced, and the oxidation peak potential is markedly reduced, indicating that the electrocatalytic activity of the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode for glucose is greatly improved. It is evident that the square-wave pulse method constructs abundant active sites, enabling efficient catalysis of the glucose oxidation reaction. These active sites accelerate the adsorption, activation, and electron transfer processes of glucose, allowing the reaction to occur at a lower potential, with a significantly increased current density and accelerated reaction kinetics.

[0066] pass Figure 4 The comparison shows that Figure 4In Figure A, the current of the Ni(OH)2 / Ni electrode (curve a) and the glucose response (curve b) are poorly distinguishable. This may be because it lacks active sites for glucose oxidation and can only generate current through its own weak electrochemical activity or non-specific reactions of ions in the solution. The reaction kinetics of glucose oxidation are slow, requiring a higher potential to drive the reaction, and the current density is low.

[0067] Furthermore, the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode obtained in Example 1 was immersed in a 0.1 mol / L NaOH solution, and the scan rate was varied to study the electrocatalytic oxidation ability of glucose on the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode. The results are as follows: Figure 5 As shown, within the scan rate range of 10 ~ 140 mV / s, with the increase of scan rate, due to the ohmic voltage drop, the oxidation peak current shifts slightly positively while the reduction peak current shifts slightly negatively. Furthermore, the redox peak currents are related to the square root of the scan rate, υ. 1 / 2 A good linear relationship exists: R² - 0.0492 = 0.99873, R² - 0.7312 = 0.99901, proving that the electrocatalytic oxidation of glucose by the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode is controlled by the diffusion process. Furthermore, with increasing scan rate, the oxidation peak potential shifts to the right, while the reduction peak potential shifts to the left, indicating that electrochemical relaxation occurs in this electrochemical process. This is beneficial for the electrochemical detection of glucose on the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode.

[0068] The CuO / Cu(OH)2-Ni(OH)2 / Ni electrode obtained in Example 1 was immersed in a 0.1 mol / L NaOH solution containing different concentrations of glu (glucose), and cyclic voltammetry was performed at a working potential of 0.6 V with a scan rate of 50 mV / s.

[0069] The results are as follows Figure 6 As shown, in a 0.1 mol / L NaOH substrate solution, the oxidation peak current exhibits a regular increase with increasing glucose concentration (1 ~ 5 mmol / L), and the peak potential remains stable, indicating that the electrode has good catalytic activity and reversible reaction for glucose. For further quantitative analysis, the relationship between the response current and concentration was fitted. The results show that the oxidation peak current exhibits an excellent linear relationship with the square root of the glucose concentration in the range of 1 ~ 5 mmol / L (linear equation: y = 1.6293x - 0.1414, R0). 2=0.9962). This linear relationship conforms to the diffusion-controlled electrode process kinetics, indicating that the oxidation reaction of glucose at the electrode is controlled by the mass transfer step. These data fully demonstrate the high sensitivity and good linear response of this electrode in glucose detection, laying a solid foundation for constructing a reliable glucose electrochemical sensor. Chronoamperometry was also performed to obtain the electrocatalytic oxidation rate constant of glucose (κ). cat ),like Figure 6 As shown in Figure C, when the oxidation current is controlled by the electrocatalytic reaction rate, the catalytic current (IC) glu This can be expressed by the formula:

[0070]

[0071] In the formula I glu I0 and Ik are the currents with and without glucose, respectively, and κ is the current. cat It is the catalytic rate constant (mol / L)⁻¹ / s, t is the running time (s), and c is the catalytic rate constant. glu This is the concentration of glucose (mol / L). According to I... glu / I0 compared to c glu 1 / 2 The slope (R) 2 =0.9936), the κ of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode was calculated. cat The value is 220.4 (mol / L)⁻¹ / s (t=100 s).

[0072] The above experiments demonstrate that as the concentration of glucose increases, the oxidation peak current in the high potential region increases significantly, indicating that glucose undergoes an oxidation reaction at this potential, and the oxidation current is positively correlated with the glucose concentration.

[0073] In addition, chronoamperometry was used to detect glucose without enzymes using a CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode. When detecting glucose, a suitable operating potential can effectively improve the sensor's sensitivity and catalytic effect. Firstly, the operating potential for glucose was optimized, including immersing the CuO / Cu(OH)₂-Ni(OH)₂ / Ni electrode in a 0.1 mol / L NaOH + 10 mmol / L glucose solution and performing CV scans at different potentials at a scan rate of 50 mV / s to obtain the amperometric current response of the electrode at operating potentials of 0.3–0.7 V. Figure 7 As can be seen from A, since the baseline is low at 0.6 V and the current increment is large, the current generated is relatively stable and the current gradient is the largest when the potential is 0.6 V. Therefore, 0.6 V is chosen to continue to examine the enzyme-free detection of glucose. Figure 7Figure B shows the it current curves of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode at the optimal potential of 0.6 V for different concentrations of glucose. It can be seen that with the continuous addition of different glucose concentrations (2 μmol / L ~ 10 mmol / L), the current curve increases in a stepwise manner. However, after repeated additions of high-concentration glucose, the baseline of the glucose response current shows a slight shift. This may be because the consumption of glucose is faster than its diffusion, resulting in minor local pH changes. Figure 7 C represents the it curves of the working electrode at low concentrations of glucose to different concentrations. It can be seen that it exhibits excellent response performance to low concentrations of glucose, with a response time of less than 2 s. From... Figure 7 As can be seen from D, within the concentration range of 2 μmol / L to 10 mmol / L, the steady-state current of glucose exhibits a good linear relationship with its concentration, and the linear fitting equation is y = 3.1695x + 0.5526(R²). 2 =0.9964), and through calculation, it can be seen that the response range of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode to glucose is 0.002 mmol / L ~ 9.11 mmol / L, and the sensitivity is 3170 μA·mM. -1 ·cm -2 The detection limit was 0.0014 μmol / L.

[0074] Table 1 shows a comparative analysis of the electrochemical sensing performance of the electrode in this embodiment and other Ni-containing composite electrodes in the prior art. It can be seen that the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode has advantages such as low detection limit, wide linear range and high sensitivity.

[0075] Table 1. Comparison of electrochemical sensing performance between Example 1 and other Ni-containing composite electrodes.

[0076]

[0077] Example 4

[0078] In actual sample determination, the main interfering factors for enzyme-free glucose detection are easily oxidized compounds such as ascorbic acid (AA) and uric acid (UA). Therefore, this experiment conducted an anti-interference test on the electrode obtained by the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1, including: selecting ascorbic acid, uric acid, sodium citrate, sodium chloride, sucrose, fructose, and sodium dihydrogen phosphate as interfering substances, setting the ratio of interfering substances to glucose to be 1:10, detecting the current response at a working potential of 0.6 V, with a scan rate of 50 mV / s, and observing the changes in interfering substances and response current when the electrode material was changed.

[0079] The results are as follows Figure 8As shown, at a potential of 0.6 V, compared with other interfering substances, the addition of glucose produces a significant current signal, indicating that the electrode can overcome the interference problem and has good anti-interference ability.

[0080] The electrode obtained from the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1 was subjected to repeatability experiments, including: measuring the response current of 1 mmol / L glucose five consecutive times using the same electrode in a NaOH solution containing 10 mmol / L glucose (i.e., 0.1 mol / L NaOH + 10 mmol / L glucose solution). The results are as follows. Figure 9 As shown in Figure A, the relative standard deviation of five consecutive measurements using the same electrode is 2.294%, indicating good electrode repeatability.

[0081] The reproducibility test of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1 was performed, including: preparing 5 electrodes under the same conditions as in Example 1, immersing each electrode in a 0.1 mol / L NaOH solution containing 1 mmol / L glucose (0.1 mol / L NaOH + 1 mmol / L glucose solution), and measuring the response current at 1 mmol / L glucose. The results are as follows. Figure 9 As shown in Figure B, the relative standard deviation of the measurements for the five independently prepared electrodes is 2.441%, indicating good electrode reproducibility.

[0082] The stability of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1 was tested, including weekly testing with a 1 mmol / L glucose solution, i.e., weekly immersion in a 0.1 mol / L NaOH solution containing 1 mmol / L glucose. The results are as follows. Figure 9 As shown in Figure C, after the electrode was stored at room temperature for 5 weeks, the response current to glucose remained at 96% of its original value, demonstrating excellent long-term stability of the electrode.

[0083] Example 5

[0084] The glucose content in passion fruit juice was detected using the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode prepared in Example 1. The specific steps are as follows:

[0085] (1) Pretreatment of passion fruit juice: Take fresh passion fruit, peel it and take the pulp, filter it with a filter screen and take the juice. Accurately weigh 5.0 g of juice, add 10 mL of distilled water, extract by ultrasonication for 20 min, then centrifuge at 8000 r / min for 10 min, take the supernatant, dilute it with 0.1 mol / L NaOH solution to an appropriate number of times to obtain the test solution;

[0086] (2) Electrochemical detection: The electrode of Example 1 was placed in the test solution. The working potential for detection was 0.6 V and the scan rate was 50 mV / s. The CuO / Cu(OH)2-Ni(OH)2 / Ni electrode was placed in a 0.1 mol / L NaOH solution with continuous stirring. Passion fruit juice was added once, and then 1 mmol / L glucose was added. The chronocurrent response signal was recorded. The optimized method was used for detection. Each sample was measured in parallel 3 times. At the same time, a spike recovery experiment was performed to calculate the spike recovery rate.

[0087] The chronoamperometry response graphs for three parallel additions of 1 mol / L glucose standard solution using the standard addition method are shown below. Figure 10 As shown, the glucose content in passion fruit juice was measured to be 102.54 mmol / L, with a spiked recovery rate of 95.61%, proving that the electrode can be used for accurate detection of glucose in actual samples.

[0088] Example 6

[0089] Based on Example 1, the difference in this example is that the time of square wave pulse deposition in step S2 is changed, and set to 20s, 50s, 100s, and 200s respectively. The results are as follows. Figure 11 As shown, the electrode’s catalytic oxidation ability for glucose increases with the increase of the square wave pulse deposition time. The current response is the largest when the time is 100 s, and the catalytic ability for glucose is the strongest. When the time exceeds 100 s, the current decreases significantly.

[0090] Example 7

[0091] Based on Example 1, the difference in this example is that the concentration of hydrochloric acid in step S2 is changed, using 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, and 2 mol / L respectively, and CuCl2 is not added. The results are as follows. Figure 12 As shown, the response current of the electrode to glucose increases with the increase of HCl concentration. The response current is the largest when the HCl concentration is 0.1 mol / L. When the HCl concentration is greater than 0.1 mol / L, the response current decreases. The response current is the lowest when the HCl concentration is 2 mol / L, which is lower than the case when the HCl concentration is 0.05 mol / L.

[0092] Example 8

[0093] Based on Example 1, the concentration of hydrochloric acid in the mixed solution of step S2 is 0.1 mol / L. The difference in this example is that the concentration of CuCl2 is changed, using 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, and 2 mol / L respectively. The results are as follows. Figure 13 As shown, the response current of the electrode to glucose increases with the increase of CuCl2 concentration, and the response current is the largest when the concentration of CuCl2 is 0.3 mol / L.

[0094] In summary, the CuO / Cu(OH)2-Ni(OH)2 / Ni composite electrode prepared by this invention is simple to prepare and has excellent performance, and has high practical value in the field of glucose electrochemical detection.

[0095] 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 a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode, characterized in that, Includes the following steps: Step S1: Pre-treat the nickel electrode to obtain a clean nickel electrode; Step S2: The nickel electrode treated in step S1 is placed in a mixed solution containing hydrochloric acid and copper chloride, and electrochemical deposition is performed using a square wave pulse method to form a deposition layer on the surface of the nickel electrode; the concentration of hydrochloric acid in the mixed solution is 0.05~2.0 mol / L, and the concentration of copper chloride is 0.05~2.0 mol / L; the potential range of the square wave pulse method is -0.6 V to 0 V, and the deposition time is 20~200 seconds; Step S3: The electrode obtained in step S2 is placed in an alkaline solution containing sodium hydroxide and glucose, and electrochemical activation is performed using cyclic voltammetry to obtain a CuO / Cu(OH)2-Ni(OH)2 / Ni electrode; the concentration of sodium hydroxide in the alkaline solution is 0.05~0.2 mol / L, and the concentration of glucose is 0.1~10 mmol / L.

2. The method for preparing the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode according to claim 1, characterized in that: The process also includes step S4, in which the obtained CuO / Cu(OH)2-Ni(OH)2 / Ni electrode is soaked in deionized water for 5-10 minutes to remove residual liquid from the electrode surface, ultrasonically cleaned for 5-20 seconds, and then removed and air-dried.

3. The method for preparing the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode according to claim 1, characterized in that: The pretreatment described in step S1 includes: first, polishing the nickel electrode with sandpaper, then polishing it to a mirror finish on a polishing cloth with aluminum oxide powder, and finally ultrasonically cleaning it in distilled water; in step S2, the concentration of hydrochloric acid is 0.1~1 mol / L, the concentration of copper chloride is 0.1~0.5 mol / L, and the deposition time is 50~100 seconds.

4. The method for preparing the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode according to claim 3, characterized in that: In step S2, the concentration of hydrochloric acid is 0.1 mol / L, the concentration of copper chloride is 0.3 mol / L, and the deposition time is 100 seconds.

5. The method for preparing the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode according to claim 1, characterized in that: In step S3, the scanning rate of the cyclic voltammetry is 10~150 mV / s, and the number of scans is 1~30.

6. The method for preparing the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode according to claim 5, characterized in that: In step S3, the concentration of sodium hydroxide is 0.1 mol / L and the concentration of glucose is 10 mmol / L; the scanning rate of cyclic voltammetry is 50 mV / s and the number of scans is 10.

7. A CuO / Cu(OH)2-Ni(OH)2 / Ni electrode, characterized in that: The CuO / Cu(OH)2-Ni(OH)2 / Ni electrode was prepared using the method described in any one of claims 1 to 6.

8. The CuO / Cu(OH)2-Ni(OH)2 / Ni electrode according to claim 7, characterized in that: The CuO / Cu(OH)2-Ni(OH)2 / Ni electrode has a porous structure composed of nanoparticles, and the electrode surface simultaneously contains active components of Ni(OH)2, CuO and Cu(OH)2.

9. The application of the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode as described in claim 7 or 8 in the detection of passion fruit juice.

10. A method for detecting glucose content in passion fruit juice, characterized in that: Using the CuO / Cu(OH)2-Ni(OH)2 / Ni electrode as described in claim 7 or 8 as the working electrode, an electrochemical analysis method was used to quantitatively detect glucose in passion fruit juice samples.

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