Flower-like difunctional Zn / Cu / Co-ZIF material and preparation method and application thereof

Abstract

The invention belongs to the technical field of electrochemical sensing detection, and particularly relates to a flower-like bifunctional Zn / Cu / Co-ZIF material and a preparation method and ratio detection application thereof. The method comprises the following steps: dissolving Cu (OAc) 2. H2O, Zn (OAc) 2. 2H2O and Co (NO3) 2. 6H2O in water to obtain a solution A; and then adding a 2-methylimidazole solution into the solution A, and carrying out ultrasonic treatment, stirring, washing and drying to obtain the product. The preparation method provided by the invention does not need high-temperature heating, does not need an organic solvent, can prepare through simple stirring, and is simple, convenient, low in cost and more environment-friendly. The Zn / Cu / Co-ZIF material for electrochemical sensing, provided by the invention, can provide an endogenous reference signal and also can enhance response current of electrochemical active components, and sensitive and reliable electrochemical ratio detection of some electrochemical active components can be realized without additionally introducing an electrochemical catalyst and a conductive material.

Description

Technical Field

[0001] This application belongs to the field of electrochemical sensing and detection technology, specifically relating to a flower-like bifunctional Zn / Cu / Co-ZIF material, its preparation method, and its application. Background Technology

[0002] Electrochemical sensors are a highly sensitive analytical technique; however, traditional electrochemical analysis relies on a single signal response induced by the analyte. This single-signal detection mode can easily lead to the response signal being affected by internal and external factors such as the electrode preparation process (e.g., electrode material loading, loading method), the detection environment (temperature, acidity, etc.), and the sample matrix. This often results in poor stability and reproducibility, severely impacting the reliability of analytical results and sometimes even leading to false negatives or false positives. To reduce the influence of these external factors and improve signal reproducibility and reliability, researchers, inspired by ratiometric fluorescence methods, have developed ratiometric electrochemical detection methods. This involves introducing electrochemically active molecules at the sensing interface, using their response as a reference signal to internally calibrate the analyte's response signal (usually a ratio of two signals). The analyte concentration is then accurately determined by the ratio of these two signals, rather than relying on a single analyte signal. In this measurement mode, any signal intensity change caused by external factors, rather than the target concentration, should equally affect both the internal reference signal and the analyte signal. Therefore, when calculating the analyte concentration based on the ratio of the two peaks, the aforementioned external influences are canceled out. This ratio measurement method achieves an enhanced signal-to-noise ratio, overcomes the typical drawbacks of single-signal detection, and improves the reproducibility and reliability of electrochemical methods.

[0003] Currently, most reference signals (or ratiometric probes) are exogenous electrochemically redox-active molecules, such as thionine (TH), ferrocene (Fc), and methylene blue (MB). These are either placed in electrolyte solutions or introduced into electrode modification materials through covalent bonding or physical adsorption to act as internal controls. Placing the reference signal in the electrolyte is the simplest approach, but this method cannot improve the electrochemical response of the analyte, is not convenient for portable, rapid, in-situ analysis, and has limited utilization methods. Immobilizing the reference signal on the surface of the identification component or electrode material facilitates miniaturization, portable detection, and diversification of detection schemes. Currently, ratiometric electrochemical sensors have been applied in many fields, including small biomolecules, proteins, nucleic acids, metal ions, and in vivo pH sensing.

[0004] However, most electrochemical ratiometric probes introduce electrochemically redox-active molecules into electrode materials or sensing interfaces via covalent bonding or physical adsorption. Covalent bonding is a complex process, often requiring specialized reagents, resulting in high costs and time consumption. Physical adsorption is simpler, but internal reference signal molecules may leak during detection, causing signal instability. Furthermore, these ratiometric probes often need to be combined with electrocatalytically active materials (such as gold nanoparticles) to ensure both reliability and sensitivity, further complicating the construction of sensing interfaces, increasing costs, and adding uncertainties. In recent years, porous framework materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have attracted considerable attention for constructing ratiometric electrochemical probes due to their porosity and structural tunability. While encapsulating reference signal molecules within MOFs can increase the loading capacity, this encapsulation lacks stability, and most MOFs are polyhedral with poor electrochemical activity. They require combination with other conductive functional materials (such as graphene) or electrocatalytically active materials (such as nanoparticles) to generate an internal reference signal and improve sensing performance. Introducing reference signal molecules into COFs involves numerous organic synthesis processes. Furthermore, the synthesis of MOF or COF materials in reported ratiometric electrochemical sensing generally requires high temperature, high pressure, and organic solvents, resulting in complex, costly, environmentally unfriendly, and inefficient operations. Therefore, it is essential to prepare an electrochemical ratiometric probe material that is easy to synthesize, possesses a significant and stable internal reference signal, and can improve the response signal of the target analyte. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a flower-like bifunctional Zn / Cu / Co-ZIF material, its preparation method, and its applications. Specifically, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing a flower-like bifunctional Zn / Cu / Co-ZIF material, comprising the following steps: Cu(OAc)2·H2O, Zn(OAc)2·2H2O and Co(NO3)2·6H2O were dissolved in water to obtain solution A; then 2-methylimidazole solution was added to solution A, and the mixture was sonicated, stirred, washed and dried to obtain the flower-shaped dual-active Zn / Cu / Co-ZIF material.

[0006] This invention provides a Cu-doped ZIF material (Zn) that combines the functions of an internal reference signal and improving the electrochemical response signal of the analyte. x Cu 1-xCo-ZIF and its simple preparation method. On the one hand, its own Cu redox signal can be used as an internal standard signal for the ratiometric electrochemical detection of analytes without the need to introduce external electroactive molecules. Moreover, the material preparation can be completed in aqueous solution at room temperature, thus making the material preparation and sensor interface construction simpler and less expensive. On the other hand, compared with common polyhedral MOFs such as Zn / Co-ZIF, the Cu-doped ZIF material of this invention has better conductivity and a larger specific surface area, which can improve the redox current response of electrochemically active analytes without the need to add additional conductive and electrocatalytic materials. This helps to simplify the construction of ratiometric electrochemical sensor interfaces. Based on this material, ratiometric electrochemical sensors can be conveniently and quickly constructed for the detection of electrochemically active substances (the examples take catechol and acetaminophen as examples). The aqueous synthesis scheme provided by this invention is not only more environmentally friendly, but also adjusts the product morphology from polyhedral to flower-like structures composed of thin sheets, resulting in higher conductivity and electrochemical activity. This invention employs a simple and environmentally friendly "one-pot method" to prepare high-yield bifunctional MOF materials at room temperature using water as a solvent. This method effectively reduces energy consumption, is easy to operate, highly reproducible, and suitable for practical applications.

[0007] As a further preferred embodiment, the molar ratio of Cu(OAc)2·H2O to Zn(OAc)2·2H2O is 0.25-0.75:0.25-0.75.

[0008] As a further preferred embodiment, the molar ratio of Cu(OAc)2·H2O and Zn(OAc)2·2H2O is 0.5:0.5.

[0009] As a further preferred embodiment, the ultrasound duration is 25 min-35 min.

[0010] As a further preferred embodiment, the stirring time is 12 h-24 h.

[0011] Secondly, the present invention provides a flower-like bifunctional Zn / Cu / Co-ZIF material, which is prepared by the above-described preparation method.

[0012] As a further preferred embodiment, the elements in the flower-like bifunctional Zn / Cu / Co-ZIF material include C, N, O, Co, Cu, and Zn.

[0013] As a further preferred embodiment, the Cu content is 5.15 wt%.

[0014] Thirdly, the present invention provides the application of the above-mentioned flower-like bifunctional Zn / Cu / Co-ZIF material in the detection of phenolic pollutants.

[0015] As a further preferred embodiment, the phenolic pollutants include catechol and acetaminophen.

[0016] The beneficial effects of this invention are as follows: (1) The preparation method provided by the present invention does not require high temperature heating or organic solvents. It can be prepared by simple stirring. The preparation method is simple, low cost and more environmentally friendly.

[0017] (2) When the MOF material provided by this invention is used as a ratiometric probe to detect phenolic pollutants, the internal reference signal it provides comes from the metal Cu in the MOF material. It does not require the introduction of externally introduced electrochemically active molecules (such as ferrocene, methylene blue, etc.) nor the introduction of electrochemically active molecules (such as thionine, etc.) into the MOF or COF ligands. Its preparation is simple, feasible, and stable. This method avoids the complex ligand modification process and high organic synthesis process requirements (covalent access method) often involved in the prior art when the reference signal molecule needs to be introduced from the outside. It significantly reduces the problem of reference signal molecule leakage during use (physical adsorption method or coating access method). The method of this invention utilizes the coordination effect between the ligand and the metal. It does not require organic ligand modification or the introduction of additional reference signal molecules. It does not involve complex processes and does not have the risk of internal reference signal molecule leakage.

[0018] (3) The MOF material for electrochemical sensing provided by the present invention not only has the function of providing an intrinsic reference signal, but also has the function of improving the current response signal of the analyte. It can realize highly sensitive electrochemical ratio detection of some electrochemical active components without the need to introduce additional electrochemical catalysts and conductive materials, which is beneficial to simplifying the construction process of ratio electrochemical sensors. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The diagram shows the preparation and testing of Zn / Cu / Co-ZIF materials; Figure 2 The image shows the Zn prepared in Example 1. 0.5 / Cu 0.5 Scanning electron microscope (SEM) images (ab), EDS elemental analysis diagram (c), and solid image (d) of the Co-ZIF (i.e., Zn / Cu molar ratio of 0.5:0.5) material. Figure 3The images shown are SEM images of Zn / Co-ZIF (i.e., Zn / Cu molar ratio of 1:0) prepared by Comparative Examples 1 (a, b) and 2 (c, d). Figure 4 The figure shows Zn prepared at different Zn / Cu molar ratios. x / Cu 1-x SEM images of / Co-ZIF materials; the corresponding Zn / Cu molar ratios for each image are: (a) 0.75:0.25; (b) 0.25:0.75; (c) 0:1.

[0021] Figure 5 The image shows Zn. 0.5 / Cu 0.5 EIS response curves of / Co-ZIF / GCE, Cu / Co-ZIF / GCE, and Zn / Co-ZIF / GCE in (a) 5 mM potassium ferricyanide / potassium ferrocyanide solution and (b) cyclic voltammetry (CV) response curves in blank phosphate buffer solution (0.2 M, pH=7.0).

[0022] Figure 6 The image shows Zn. 0.5 / Cu 0.5 The CV response of / Co / GCE, Zn / Co-ZIF / GCE and bare glassy carbon electrode GCE in phosphate buffer to (a) 100 μM CC; (b) CV response of 100 μM AP; (c) CV response of solution containing 100 μM AP and 100 μM CC; (d) differential pulse voltammetry (DPV) response of blank phosphate buffer; (e) DPV response of 100 μM CC + 100 μM AP; (f) Zn / Co / GCE and Zn / Co-ZIF / GCE when the concentration of CC and AP in solution changes from low concentration (10 μM) to high concentration (100 μM). 0.5 / Cu 0.5 DPV response on / Co-ZIF / GCE.

[0023] Figure 7 The image shows (a) Zn in a phosphate buffer solution. 0.5 / Cu 0.5 The CV response of / Co-ZIF / GCE to different concentrations of CC and (b) CC response current I CC With CC concentration C CC (c) The linear relationship between CC and Cu response currents I CC / I Cu With CC concentration C CC The linear relationship; (d) Zn 0.5 / Cu 0.5 CV response and (e)AP response current of / Co-ZIF / GCE to different concentrations of AP I AP With AP concentration C AP (f) The linear relationship between AP and Cu response currents; I AP / I Cu With AP concentration C AP The linear relationship.

[0024] Figure 8 The figure shows the effect of simultaneous and continuous addition of CC and AP to phosphate buffer, (a) Zn 0.5 / Cu 0.5 DPV response and (b, c) corresponding to / Co-ZIF / GCE I CC / I Cu and I AP / I Cu Linear relationship with CC or AP concentration.

[0025] Figure 9 The image shows a comparison of the electrochemical responses of CC (50 µM) and AP (50 µM) on a bare glassy carbon electrode (GCE) before (black line) and after (red line) the addition of methylene blue MB as a ratio probe in phosphate buffer solution. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Example 1 A method for preparing a flower-like dual-active Zn / Cu / Co-ZIF material, specifically comprising the following steps: (1) Dissolve 0.110 g Cu(OAc)2·H2O, 0.120 g Zn(OAc)2·2H2O and 0.007 g Co(NO3)2·6H2O in 20 mL of aqueous solution to form homogeneous solution A; (2) Dissolve 0.984 g of 2-methylimidazole in 20 mL of aqueous solution to obtain solution B; (3) Quickly add solution B to solution A, sonicate the solution for 30 minutes (ultrasonic exfoliation to form a multi-layered two-dimensional structure), stir vigorously at room temperature for 12 hours, wash several times with deionized water and ethanol, and dry to obtain a light green powder (e.g. Figure 2 As shown in d), this is a bifunctional active material (Zn). 0.5 / Cu 0.5 / Co-ZIF).

[0028] The Zn prepared above 0.5 / Cu 0.5 Scanning electron microscope images and real-world images of / Co-ZIF, and EDS spectra, are shown below. Figure 2 As shown; where by Figure 2 From a and b in the image, we can see that the SEM electron microscope image shows the material as a nanoflower-like structure formed by the assembly of two-dimensional nanosheets; from Figure 2 The 'c' in the equation indicates that the material contains the elements C, N, O, Co, Cu, and Zn.

[0029] Example 2 A method for preparing a flower-like dual-active Zn / Cu / Co-ZIF material is described. The specific preparation process is similar to that of Example 1, except that the molar ratio of Zn(OAc)₂·2H₂O and Cu(OAc)₂·H₂O in step 1 of Example 1 (0.50:0.50) is replaced with 0.75:0.25. The total molar number of Zn and Cu remains unchanged, and other steps remain the same, yielding Zn… 0.75 / Cu 0.25 / Co-ZIF.

[0030] SEM images of the prepared materials are as follows: Figure 4 As shown in Figure a, many layered ZIF materials are stacked around the center in a petal-like shape.

[0031] Example 3 A method for preparing a flower-like dual-active Zn / Cu / Co-ZIF material is disclosed. The specific preparation process is similar to that of Example 1, except that the molar ratio of Zn(OAc)₂·2H₂O and Cu(OAc)₂·H₂O in step 1 of Example 1, which was 0.50:0.50, is replaced with 0.25:0.75. The total molar number of Zn and Cu remains unchanged, and other steps are kept the same, yielding Zn… 0.25 / Cu 0.75 / Co-ZIF.

[0032] SEM images of the prepared materials are as follows: Figure 4 As shown in b, many layered ZIF materials are stacked around the center to form a dense flower-like shape.

[0033] Comparative Example 1 A method for preparing a polyhedral Zn / Co-ZIF material is described. The specific preparation process is similar to that of Example 1, except that in step (1) of Example 1, all Cu(OAc)₂·H₂O is replaced with Zn(OAc)₂·H₂O (i.e., the Zn / Cu ratio is 1:0), and the aqueous solution in step (1) is replaced with a methanol solution. All other steps remain unchanged, resulting in the Zn / Co-ZIF material. The electron micrograph of the material is shown below. Figure 3 a and Figure 3 As shown in Figure b, the material exhibits a polyhedral shape. In this type of polyhedral MOF, metal ions are embedded inside the MOF, resulting in relatively low conductivity and electrochemical activity of the MOF material.

[0034] Comparative Example 2 A method for preparing sheet-like stacked Zn / Co-ZIF material is described. The specific preparation process is similar to that of Example 1, except that in step (1) of Example 1, Cu(OAc)₂·H₂O is completely replaced by Zn(OAc)₂·H₂O (i.e., the Zn / Cu ratio is 1:0). All other steps remain unchanged, resulting in the Zn / Co-ZIF material. The electron microscope image of the material is shown below. Figure 3 c and Figure 3 As shown in Figure d, the material exhibits a two-dimensional layered stacked structure. The two-dimensional structure allows for a more complete exposure of the metal center, thus improving conductivity and electrochemical activity.

[0035] The comparison results between Comparative Examples 1 and 2 show that the solvent used in the preparation of the material affects the morphology of the ZIF material. Traditional imidazole organic ligands and metal ions dispersed in organic solvents (methanol, ethanol) will form a polyhedral structure. By changing the solvent, using an all-aqueous solvent can transform the ZIF material into a two-dimensional nanosheet structure.

[0036] Comparative Example 3 A method for preparing Cu / Co-ZIF material is described. The specific preparation process is similar to that of Example 1, except that in step (1) of Example 1, Zn(OAc)2·H2O is completely replaced by Cu(OAc)2·H2O (i.e., the Zn / Cu ratio is 0:1), while the other steps remain unchanged, and Cu / Co-ZIF material is obtained.

[0037] SEM images of its Cu / Co-ZIF material are as follows: Figure 4 As shown in c, it is a stacked layered ZIF material.

[0038] according to Figure 2 and Figure 4 The above results show that the amount of copper salt can change the Zn content. x / Cu 1-xThe morphology of the / Co-ZIF material showed that with increasing copper salt content, more plate-like products transformed into flower-like products. Subsequent characterization indicated that the addition of copper helped improve the electrochemical response signal of the analyte and also provided an internal reference signal. The Zn prepared at a Zn:Cu ratio of 0.5:0.5... 0.5 / Cu 0.5 / Co-ZIF exhibits the strongest response current and is the most stable electrochemical internal reference signal peak.

[0039] Example 4 The Zn prepared in Example 1 0.5 / Cu 0.5 Electrochemical impedance spectroscopy was performed using / Co-ZIF, with Zn / Co-ZIF and Cu / Co-ZIF used as controls.

[0040] Preparation of modified electrodes: The prepared Zn / Co-ZIF, Cu / Co-ZIF, and Zn... 0.5 / Cu 0.5 10 mg of / Co-ZIF material was ultrasonically dispersed in 10 mL of aqueous solution to form a suspension with a concentration of 1 mg / mL. Then, 5 μL of the suspension was drop-coated onto a polished glassy carbon electrode. After drying at room temperature, the modified electrode was obtained, denoted as Zn / Co-ZIF / GCE, Cu / Co-ZIF / GCE, and Zn... 0.5 / Cu 0.5 / Co-ZIF / GCE.

[0041] Impedance spectroscopy scanning: The modified electrode was used as the working electrode, the platinum wire electrode as the counter electrode, the saturated calomel electrode as the reference electrode, and 0.1 M KCl solution as the electrolyte solution with 5 mM K3Fe(CN)6 added. The electrochemical impedance spectroscopy (EIS) curve was scanned in the range of 0.1 Hz to 100 kHz.

[0042] The result is as follows Figure 5 As shown in Figure a, Zn / Co-ZIF / GCE (Comparative Example 2), Cu / Co-ZIF / GCE (Comparative Example 3), and Zn were calculated and fitted from the EIS curve results of the materials. 0.5 / Cu 0.5 The electrochemical impedances of Zn / Co-ZIF / GCE (Example 1) were 2165 Ω, 5012 Ω, and 1378 Ω, respectively. This indicates that the impedance of Zn / Co-ZIF is relatively large, and Zn... 0.5 / Cu 0.5 The / Co-ZIF exhibits a lower charge transfer resistance, with the impedance reaching its maximum when Zn is completely replaced by Cu. This indicates that only by appropriately controlling the amount of Cu introduced can the charge transfer capability of the material be improved, and the impedance is relatively low when the Zn / Cu ratio is 0.5:0.5.

[0043] Example 5 The Zn material prepared in Example 1 0.5 / Cu 0.5 Cyclic voltammetry (CV) scans were performed on / Co-ZIF to confirm its electrochemical activity and the source of the reference signal. Zn / Co-ZIF and Cu / Co-ZIF were used as controls.

[0044] Preparation of modified electrode: Same as the procedure in “Preparation of modified electrode” in Example 4.

[0045] Cyclic voltammetry scan: Modified electrode Zn x / Cu 1-x Using Co-ZIF / GCE as the working electrode, a platinum wire electrode as the counter electrode, a saturated calomel electrode as the reference electrode, and a 0.2 mol / L phosphate buffer solution at pH 7 as the electrolyte solution, cyclic voltammetry curves were scanned in the range of -0.6 V to 0.8 V.

[0046] The result is as follows Figure 5 As shown in b, the Zn / Co-ZIF / GCE electrode did not exhibit a significant redox response peak in the blank phosphate buffer solution, and the baseline value of the current signal was also relatively small. Compared to the Zn / Co-ZIF / GCE electrode, Zn... 0.5 / Cu 0.5 The / Co-ZIF@GCE electrode exhibits a distinct Cu oxidation peak at +0.02V, and a corresponding Cu reduction peak is observed at -0.13V. This Cu redox peak (the oxidation peak in this pair will be used as an internal standard signal for ratiometric detection using the DPV method) will be used as the reference signal peak for internal standard calibration. The Cu / Co-ZIF electrode also shows a pair of redox peaks, but with a larger peak potential difference, due to its poor conductivity. Figure 5 The result is consistent with a.

[0047] Example 6 The Zn material prepared in Example 1 0.5 / Cu 0.5 The response signals of phenolic substances catechol (CC) and acetaminophen (AP) on the electrode surface were investigated using a Zn / Co-ZIF modified glassy carbon electrode and a bare glassy carbon electrode (GCE) as comparisons.

[0048] Preparation of modified electrodes: The prepared Zn 0.5 / Cu 0.5Weigh 10 mg of Zn / Co-ZIF or Zn / Co-ZIF material and ultrasonically disperse it in 10 mL of aqueous solution to form a suspension with a concentration of 1 mg / mL. Then, take 5 μL of the suspension and drop it onto a polished glassy carbon electrode. After drying at room temperature, the modified electrode is obtained, denoted as Zn. 0.5 / Cu 0.5 / Co-ZIF / GCE or Zn / Co-ZIF / GCE.

[0049] Cyclic voltammetry scan: Modified electrode Zn 0.5 / Cu 0.5 Using / Co-ZIF / GCE or Zn / Co-ZIF / GCE or GCE as the working electrode, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, a 0.2 mol / L phosphate buffer solution at pH=7 was used as the electrolyte solution, with 100 µM CC and / or 100 µM AP added. Cyclic voltammetry curves were scanned in the range of -0.3 V to 0.8 V.

[0050] The result is as follows Figure 6 a, Figure 6 As shown in the CV curve in b, in a solution containing a certain concentration of CC (… Figure 6 a) or AP ( Figure 6 In solution b), it can be known that Zn 0.5 / Cu 0.5 The / Co-ZIF / GCE modified electrode exhibits the highest oxidation current for both CC and AP, while the unmodified GCE electrode shows the lowest response for both CC and AP. The current response on the Zn / Co-ZIF / GCE modified electrode is significantly different from that on the Zn electrode. 0.5 / Cu 0.5 The current response of the / Co-ZIF / GCE modified electrode is also smaller. The above results indicate that this copper-doped flower-like ZIFs material Zn 0.5 / Cu 0.5 / Co-ZIF has a better amplification effect on the electrochemical response signals of CC and AP, providing a better guarantee for improving the sensitivity of phenolic substances detection alone.

[0051] in addition Figure 6 The results showed that when CC and AP were added to the solution simultaneously, their effect on Zn... 0.5 / Cu 0.5 The response current on / Co-ZIF / GCE is much larger than that on GCE and Zn / Co-ZIF / GCE, and the oxidation peaks of CC and AP can be clearly distinguished, indicating that Zn 0.5 / Cu 0.5 / Co-ZIF can also be used for simultaneous detection of CC and AP.

[0052] Example 7 The Zn material prepared in Example 1 0.5 / Cu 0.5 The electrochemical responses of CC and AP on the Zn / Co-ZIF modified electrode were investigated using differential pulse voltammetry (DPV). The Zn / Co-ZIF modified electrode and the bare glassy carbon electrode GCE were used as comparisons.

[0053] Preparation of modified electrode: Same as the preparation of modified electrode in Example 6.

[0054] DPV scan: Zn 0.5 / Cu 0.5 Using / Co-ZIF / GCE or Zn / Co-ZIF / GCE or GCE as the working electrode, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, a 0.2 mol / L phosphate buffer solution at pH=7 was used as the electrolyte solution. Blank DPV response curves were scanned in the range of -0.3 V to 0.8 V. After adding 100 µM CC and 100 µM AP, the DPV response curves were recorded again, and the changes in the Cu response peak and the CC and AP response peaks were observed. The result is as follows Figure 6 d- Figure 6 As shown in f. Figure 6 d indicates that in blank phosphate buffer solution, GCE and Zn / Co-ZIF / GCE did not exhibit significant redox signals, while Zn 0.5 / Cu 0.5 / Co-ZIF / GCE exhibits a significant oxidation peak at -0.1V, corresponding to Cu 2+ / Cu + The transformation. Figure 6 e indicates that both CC and AP can generate electrochemical DPV signals on all three electrodes, but not on Zn. 0.5 / Cu 0.5 The maximum current response is observed on / Co-ZIF / GCE, further demonstrating that Zn 0.5 / Cu 0.5 / Co-ZIF has a significant effect on enhancing the electrochemical response signals of analytes CC and AP. This is consistent with... Figure 6 The CV test results for c are consistent.

[0055] contrast Figure 6 As can be seen from d and 6e, when CC and AP are added, in Zn 0.5 / Cu 0.5 The DPV curve on / Co-ZIF / GCE still shows a Cu signal peak, but the current response is much weaker. Figure 6The results show that increasing the concentrations of CC and AP gradually decreases the electrochemical response signal of Cu. This indicates that the oxidation signal peak of Cu at around -0.1 V is negatively correlated with CC or AP, which is consistent with the OFF-On type ratiometric electrochemical response model. This suggests that Zn... 0.5 / Cu 0.5 / Co-ZIF can be used as an internal reference signal to construct a ratiometric electrochemical sensor for detecting CC and AP.

[0056] Example 8 The Zn material prepared in Example 1 0.5 / Cu 0.5 / Co-ZIF was used as a modified electrode material to construct an electrochemical sensor for the ratiometric detection of catechol (CC), and its practicality for ratiometric electrochemical detection was verified.

[0057] Preparation of modified electrodes: The prepared Zn 0.5 / Cu 0.5 10 mg of / Co-ZIF material was ultrasonically dispersed in 10 mL of aqueous solution to form a suspension with a concentration of 1 mg / mL. Then, 5 μL of the suspension was drop-coated onto a polished glassy carbon electrode and dried at room temperature to obtain the modified electrode, denoted as Zn. 0.5 / Cu 0.5 / Co-ZIF / GCE.

[0058] DPV detection: Zn 0.5 / Cu 0.5 Using / Co-ZIF / GCE as the working electrode, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, a 0.2 mol / L phosphate buffer solution with pH=7 was used as the electrolyte solution. After continuously adding CC to the solution, the DPV curve was scanned in the range of -0.3 V to 0.6 V.

[0059] The result is as follows Figure 7 As shown in Figure 7a, it can be seen that as the concentration of CC increases, the response current also increases continuously, and there is a certain pattern of change between the two variables. Figure 7 b and Figure 7 c is a graph representing the linear relationship between variables using two different fitting methods, with the linear correlation coefficient as the key indicator. R 2 Assuming >=0.99, Figure 7 b indicates the concentration of CC ( C CC ) and response current ( I CC It exhibits a good linear relationship in the range of 0.5–20 μM, with the square of the correlation coefficient being... R 2=0.9961, the current response above 20 μM deviates significantly from this linearity; therefore, the linear range of direct detection of CC is very narrow, only 0.5-20 μM, and the detection limit is 0.3 μM. Figure 7 c is the concentration of CC ( C CC The ratio of the peak current signals of CC and Cu () I CC / I Cu The linear relationship between them is shown to be very good across the entire concentration range (0.5-150 μM), and the linear relationship equation is as follows: I CC / I Cu = 0.01055 C CC + 0.12536, R 2 = 0.9907, the linear range for detecting CC is 0.5 μM-150 μM, and the detection limit is 0.12 μM (S / N = 3). Compared to directly using the response peak of CC to determine the linear relationship, using the oxidation peak response value of Cu as an internal reference yields better results. This allows the sensor to have a strong linear correlation with high concentrations of CC, thus achieving a lower detection limit and a wider linear range.

[0060] Example 9 The Zn material prepared in Example 1 0.5 / Cu 0.5 / Co-ZIF was used as a modified electrode material to construct an electrochemical sensor for the ratiometric detection of acetaminophen (AP), and its practicality for ratiometric electrochemical detection was verified.

[0061] The preparation of the modified electrode and the DPV test were performed in the same manner as in Example 8, except that the analyte was changed from CC to AP.

[0062] Figure 7 d is the DPV response curve with different concentrations of AP added. Figure 7 e is the linear fit result of AP response current and AP concentration (direct detection). Figure 7 f represents the result of fitting the linear relationship between the peak ratio of AP and Cu and the AP concentration (ratio detection). The ratio detection method is calculated as follows: Zn 0.5 / Cu 0.5 The / Co-ZIF / GCE electrode exhibits a linear range of 0.2 μM–300 μM for AP detection, with a detection limit of 0.04 μM (S / N = 3). R 2=0.9953. The direct detection method has a slightly narrower linear response range (6-300 μM) and a smaller linear correlation coefficient. R 2 =0.9901, detection limit 0.12 μM. This indicates that when using the Cu response as a reference, the ratiometric method achieves a wider linear range and a lower detection limit compared to directly using the AP signal for quantification. This result is consistent with the results of Example 8. Furthermore, comparing the error bars of the corresponding signals in the figure, it can be seen that the error bar of the ratiometric method's vertical axis signal is smaller than that of the direct method, which also indicates that the ratiometric method improves the sensor's response reliability to some extent.

[0063] Example 10 The Zn material prepared in Example 1 0.5 / Cu 0.5 / Co-ZIF was used as a modified electrode material to construct an electrochemical sensor for the simultaneous ratiometric detection of catechol (CC) and acetaminophen (AP), and its practicality for ratiometric electrochemical detection was verified.

[0064] The preparation of the modified electrode and the DPV test were performed in the same manner as in Example 8, except that the analyte CC was replaced with a mixed solution of CC and AP.

[0065] Figure 8 The results show that when CC and AP are added simultaneously, Zn 0.5 / Cu 0.5 The signal peaks of CC, AP and Cu can still be clearly observed on the / Co-ZIF / GCE electrode, and the Cu peak intensity decreases with increasing CC and AP concentrations, still exhibiting an OFF-On dependence. Figure 8 b, Figure 8 The results showed that the concentration of CC or AP was related to... I CC / I Cu or I AP / I Cu Proportional. This indicates that the ratio detection method is also applicable to the simultaneous detection of CC and AP.

[0066] Comparative Example 4 The effect of adding MB on the current response of CC and AP was investigated using methylene blue (MB), a traditional electrochemically active molecule, as a ratio probe.

[0067] Using a bare glassy carbon electrode (GCE) as the working electrode, a platinum wire electrode as the counter electrode, and a saturated calomel electrode as the reference electrode, and a 0.2 mol / L phosphate buffer solution at pH 7 as the electrolyte solution, 50 µM CC and 50 µMAP were added, and the DPV current response was recorded in the range of -0.3 V to 0.6 V. Then, 10 µM methylene blue (a typical electrochemical ratio probe) was added to the solution, and the DPV curve was scanned and recorded again.

[0068] Figure 9 The results show that, compared to the response at GCE, the addition of the electrochemical ratio probe MB, while generating a reference signal peak (-0.23V), does not increase the current response of CC and AP; in fact, it slightly weakens them, and the oxidation peak potential also shifts slightly in the positive direction. This indicates that although this electrochemically redox-active molecule can serve as a ratio detection probe, it does not enhance the electrochemical response signal of the analyte.

[0069] Further comparison Figure 6 The results of e and 6f highlight the dual-functional advantages of the ratio probe prepared in this scheme: while providing an internal reference signal, it can also amplify the electrochemical response signal of the analyte, thereby improving both signal reliability and detection sensitivity.

[0070] The embodiments of this application have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the core ideas of this application. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a bifunctional flower-like Zn / Cu / Co-ZIF material, characterized in that, Includes the following steps: Cu(OAc)2·H2O, Zn(OAc)2·2H2O and Co(NO3)2·6H2O were dissolved in water to obtain solution A; then 2-methylimidazole solution was added to solution A, and the mixture was sonicated, stirred, washed and dried to obtain the flower-shaped dual-active Zn / Cu / Co-ZIF material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of Cu(OAc)2·H2O to Zn(OAc)2·2H2O is 0.25-0.75:0.25-0.

75.

3. The preparation method according to claim 2, characterized in that, The molar ratio of Cu(OAc)2·H2O and Zn(OAc)2·2H2O is 0.5:0.

5.

4. The preparation method according to claim 1, characterized in that, The ultrasound session lasted 25-35 minutes.

5. The preparation method according to claim 1, characterized in that, The stirring time is 12 h-24 h.

6. A flower-like bifunctional Zn / Cu / Co-ZIF material, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. The flower-like bifunctional Zn / Cu / Co-ZIF material according to claim 6, characterized in that, The elements in the flower-shaped bifunctional Zn / Cu / Co-ZIF material include C, N, O, Co, Cu, and Zn.

8. The flower-like bifunctional Zn / Cu / Co-ZIF material according to claim 7, characterized in that, The Cu content is 5.15 wt%.

9. The application of the flower-like bifunctional Zn / Cu / Co-ZIF material according to any one of claims 6-8 in the detection of phenolic pollutants.

10. The application according to claim 9, characterized in that, The phenolic pollutants include catechol and acetaminophen.

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