An electrochemical sensor based on bimetallic MOFs material and its preparation method and application

Abstract

The present invention discloses an electrochemical sensor based on a bimetallic MOF material and a method for preparing the same. The electrochemical sensor comprises an oxide derived from a bimetallic MOF as a modifying material, doped with Fe and loaded onto a hydrophilic carbon cloth to form a CeO2 / Co3O4-Fe2O3@CC working electrode. The electrode is placed in a three-electrode system and connected to an electrochemical workstation to form an electrochemical sensor for detecting phenolic substances. The present invention uses bimetallic MOFs as precursors and calcines them to generate metal oxides. This retains the high surface area and high porosity characteristics of the MOF material while also improving its electrical conductivity. By incorporating the Fe metal element, the sensor's performance is enhanced, resulting in high sensitivity, a wide linear range, and a low detection limit. This highly efficient and economical electrochemical sensor material can be used to detect phenolic pollutants.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical sensing technology, and in particular to an electrochemical sensor based on a bimetallic MOFs material, and a preparation method and application thereof. Background Art

[0002] Phenolic compounds are widely used in food preservatives, plastics, dyes, and household cleaners due to their anti-inflammatory, antioxidant, and antimicrobial properties. However, phenolic compounds are aromatic organic compounds, such as phenol, bisphenol A, catechol, and hydroquinone, many of which have acute toxicity, genotoxicity, and endocrine-disrupting effects. Most phenolic compounds and their derivatives are highly soluble in water, making them susceptible to entering wastewater from pharmaceuticals and production processes and subsequently into natural aquatic environments, causing water pollution. In recent years, phenolic compounds have been detected in water bodies in an increasing number of countries, including China, the United States, France, and Japan. Phenolic compounds migrate through water bodies and readily enter groundwater and soil, significantly impacting ecosystems. Therefore, the persistence of phenolic compounds and other harmful substances in water bodies has attracted global attention. According to the United States Environmental Protection Agency (USEPA) regulations, the permitted limit for phenol in surface water is less than 1 ppb. Human exposure to higher doses of phenolic compounds can lead to chronic respiratory problems. According to research reports, the standard level of the permissible limit of phenolic compounds in drinking water is 0.002 mg / L. Phenolic compounds above the permissible concentration level in drinking water are considered toxic to humans, so there is a great need to use appropriate analytical techniques to monitor these compounds.

[0003] Common methods for detecting phenolic compounds include high-performance liquid chromatography (HPLC), liquid chromatography / gas chromatography-mass spectrometry (LC / GC-MS), enzyme-linked immunosorbent assay (ELISA), molecular imprinting, spectrophotometry, and electrochemical methods. Among these methods, chromatography and spectrophotometry require large instruments, are complex to operate, have high solvent costs, and take a long time to detect. Electrochemical methods, on the other hand, have attracted widespread attention due to their simplicity, lack of need for complex instrumentation, short response time, and high sensitivity. However, pure electrodes such as glassy carbon electrodes (GCE), FTO, and carbon cloth (CC) cannot meet the requirements for detecting phenolic compounds. Therefore, functional materials are needed to modify the electrodes to enable them to selectively detect phenolic substances and achieve a higher electrochemical response and superior sensitivity.

[0004] Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials formed by organic ligands and metal ions. They have been widely studied due to their large surface area and high porosity. MOFs materials are widely used in electrochemical fields such as water electrolysis, electrochemical reduction of carbon dioxide, energy storage, batteries and electrochemical sensors. In the past few decades, many sensors based on MOFs materials have been reported, including those for the detection of H2O2, glucose, heavy metal ions and phenolic substances. However, the disadvantages of MOFs materials such as low conductivity, slow diffusion and slow mass transfer rate limit their practical application in the field of electrochemistry. Therefore, it is necessary to modify MOFs materials to meet the requirements for the detection of various pollutants.

[0005] A common method for improving the conductivity of MOFs is to combine them with other conductive materials, such as carbon nanotubes (CNTs), graphene, conductive polymers, and metal oxides. This integration of various functional materials enhances the performance of MOFs. Another approach is to use MOFs as precursors and synthesize derivatives through calcination and doping to improve their electrochemical properties.

[0006] Bimetallic MOFs are pure compounds formed by the reaction of organic ligands with two different metal ions. Previous studies have shown that the unique properties of bimetallic MOFs are due to the ratio of metal ions and the synergistic effects between the different components. Bimetallic MOFs exhibit higher activity, selectivity, and stability than monometallic MOFs, and their properties can be tuned by adjusting the metal ratio. Consequently, bimetallic MOFs have attracted increasing attention. Summary of the Invention

[0007] The present invention aims to prepare an electrochemical sensor with high sensitivity for detecting phenolic pollutants (taking bisphenol A as an example) and its preparation method. The prepared material has high sensitivity, low detection limit, and the preparation method is simple and economical.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A three-electrode system was prepared using a modified hydrophilic carbon cloth (CC) as the working electrode. CeO2 / Co3O4-Fe2O3 was loaded onto the surface of the modified hydrophilic carbon cloth electrode, where CeO2 / Co3O4 is a bimetallic CeCo-MOFs-derived metal oxide. This electrode system was connected to an electrochemical workstation to form an electrochemical sensor for the detection of phenolic pollutants. The working electrode preparation steps are as follows:

[0010] (1) Dissolve soluble cerium salt and soluble cobalt salt in N,N-dimethylformamide to form solution A. Dissolve 1,3,5-benzenetricarboxylic acid in anhydrous ethanol to form solution B. Slowly add solution A to solution B and stir evenly. Then transfer the solution to a high-pressure reactor for hydrothermal reaction. After the reaction is completed, cool to room temperature, wash and dry to obtain CeCo-MOFs powder.

[0011] (2) Dispersing the bimetallic CeCo-MOFs powder prepared in step (1) on Fe 2+ The precursor solution is stirred to be evenly dispersed, and the solid particles are separated from the solution, centrifuged, washed, and dried to obtain a MOFs-based Fe-doped composite material;

[0012] (3) calcining the composite material obtained in step (2) at a certain temperature and cooling it to room temperature to obtain CeO2 / Co3O4-Fe2O3 powder;

[0013] (4) The CeO2 / Co3O4-Fe2O3 powder in step (3) was dispersed in a solvent and Nafion solution was added to prepare a suspension. The obtained suspension was drop-coated on a pretreated hydrophilic carbon cloth conductive substrate and dried to obtain a CeO2 / Co3O4-Fe2O3@CC sensor working electrode.

[0014] The present invention prepares bimetallic MOFs via a hydrothermal method. By stirring and incorporating Fe, the resulting composite material forms a ternary metal oxide and exhibits excellent electrical conductivity. Furthermore, Fe doping can significantly enhance electrochemical response and detection performance for phenolic compounds.

[0015] In the preparation method of the present invention, the metal ratio, hydrothermal temperature, hydrothermal time, calcination temperature, calcination time, etc. will directly affect the crystallization state of the catalyst, and the concentration of the catalyst and the amount of binder in the dispersion will also affect the electrochemical properties and detection performance of the prepared sensor.

[0016] The performance of the sensor can be controlled by adjusting the metal ratio, hydrothermal parameters and calcination parameters.

[0017] In the above preparation route, the specific process conditions of each step are as follows:

[0018] (1) In step (1):

[0019] The soluble cerium salt may be cerium chloride, cerium nitrate, cerium sulfate, cerium acetate, etc., and the soluble cobalt salt may be cobalt nitrate, cobalt chloride, cobalt bromide or cobalt acetate, etc. Preferably, the soluble cerium salt is cerium nitrate, and the soluble cobalt salt is cobalt nitrate.

[0020] The molar ratio of the metal salt to 1,3,5-benzenetricarboxylic acid is (0.1-1):1; the molar ratio of the cerium salt to the cobalt salt is (0.05-12):1; the molar ratio of the metal salt to N,N-dimethylformamide is 1:(50-400); and the molar ratio of 1,3,5-benzenetricarboxylic acid to anhydrous ethanol is 1:(100-500).

[0021] Further preferably, the molar ratio of the cerium salt to the cobalt salt is (0.1-10):1; the molar ratio of the metal salt to N,N-dimethylformamide is 1:(100-300); and the molar ratio of 1,3,5-benzenetricarboxylic acid to anhydrous ethanol is 1:(200-400).

[0022] The hydrothermal temperature is 70-180° C., and the hydrothermal time is 5-24 hours. More preferably, the hydrothermal temperature is 90-140° C., and the hydrothermal time is 8-15 hours.

[0023] (2) In step (2):

[0024] The Fe 2+ The precursor solution is prepared from a soluble ferrous salt and a solvent. The soluble ferrous salt can be ferrous nitrate, ferrous chloride, ferrous sulfate, ferrous acetate, or ferrous oxalate, and the solvent can be one or more of ethylene glycol, methanol, ethanol, and water. Preferably, the soluble ferrous salt is ferrous chloride, and the solvent is a mixture of ethylene glycol and water, with a volume ratio of ethylene glycol to water of 1:(4-15).

[0025] Preferably, the Fe 2+ Fe in the precursor solution 2+ The molar concentration is 0.01~0.2M.

[0026] Preferably, the Fe 2+ In the precursor solution, the concentration of the bimetallic CeCo-MOFs powder is 2 to 20 mg / mL; more preferably, the concentration of the bimetallic CeCo-MOFs powder is 5 to 10 mg / mL.

[0027] (III) In step (3):

[0028] The muffle furnace calcination temperature and time will affect the crystallization state of CeO2 / Co3O4-Fe2O3.

[0029] The calcination temperature is 400-600°C for 0.5-5 hours; preferably, the calcination temperature is 450-550°C for 1-3 hours. Controlling the calcination temperature and time allows for the regulation of the crystallinity of the catalytic film. At the optimal calcination temperature, the material exhibits excellent crystallinity and high activity for detecting phenolic substances. Lower calcination temperatures result in poor crystallinity.

[0030] (IV) In step (4):

[0031] The conductive substrate is a hydrophilic carbon cloth (CC), and the conductive substrate needs to be pre-cleaned and dried before the catalyst is drop-coated.

[0032] The pretreatment of the hydrophilic carbon cloth is to cut the conductive carbon cloth into small pieces, wash them with acetone, ethanol and deionized water, and then dry the hydrophilic carbon cloth in an oven after removing surface impurities.

[0033] The CeO2 / Co3O4-Fe2O3 powder is added at a concentration of 2 to 50 mg / mL; preferably, the CeO2 / Co3O4-Fe2O3 powder is added at a concentration of 5 to 30 mg / mL. Excessive CeO2 / Co3O4-Fe2O3 powder content in the suspension can easily cause problems such as agglomeration and aggregation, resulting in uneven dispersion. Excessive powder content can result in a low electrochemical response and fail to meet detection requirements.

[0034] Preferably, the solvent in step (4) is deionized water, anhydrous ethanol, N,N-dimethylformamide, etc.

[0035] Preferably, the amount of suspension applied in step (4) is 20 to 400 μL; more preferably, the amount of suspension applied is 50 to 300 μL. The amount of suspension applied will affect the film thickness of the electrode surface material, thereby affecting the detection performance of the sensor. Too much application will result in a film that is too thick and easily falls off, resulting in unstable electrodes.

[0036] The CeO2 / Co3O4-Fe2O3@CC sensor prepared by the present invention integrates the advantages of MOFs materials and hydrophilic carbon cloth substrate, and has good conductivity, low detection limit and high sensitivity.

[0037] The present invention uses a hydrothermal method to prepare bimetallic CeCo-MOFs, then dopes them with Fe and calcines them to form ternary metal oxides. By adjusting the metal ratio, hydrothermal time, hydrothermal temperature, calcination time, calcination temperature and modification amount, the most suitable CeO2 / Co3O4-Fe2O3@CC sensor material is obtained for the detection of phenolic pollutants.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention uses bimetallic CeCo-MOFs, and uses bimetallic MOFs as precursors to generate metal oxides through calcination. This not only retains the high surface area and high porosity characteristics of MOFs materials, but also improves their electrical conductivity, resulting in a higher response to phenol detection.

[0040] (2) By incorporating Fe metal elements, the electrochemical performance and active surface area of the sensor are improved.

[0041] (3) The catalytic electrode prepared by the present invention has high sensitivity, wide linear range and low detection limit (as low as 8.7 nM).

[0042] (4) The electrode proposed in the present invention can be used as an efficient and economical electrochemical sensor material to detect phenol pollutants in tap water and lake water, and is feasible in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the SEM image of the CeO2 / Co3O4-Fe2O3 composite material prepared in Example 1;

[0044] Figure 2 XRD patterns of the CeO2 / Co3O4-Fe2O3 material prepared in Example 1, the CeO2 / Co3O4 material prepared in Comparative Example 1, the CeO2 material prepared in Comparative Example 2, and the Co3O4 material prepared in Comparative Example 4;

[0045] Figure 3 The CeO2 / Co3O4-Fe2O3@CC sensor electrode prepared in Example 1, the CeO2 / Co3O4@CC sensor electrode prepared in Comparative Example 1, and the pure CC electrode prepared in Comparative Example 6 were heated to 5.0 mM [Fe(CN)6] 3- / 4- Cyclic voltammetry (CV) diagram containing 0.1 M KCl as supporting electrolyte;

[0046] Figure 4 The CeO2 / Co3O4-Fe2O3@CC sensor electrode prepared in Example 1, the CeO2 / Co3O4@CC sensor electrode prepared in Comparative Example 1, and the pure CC electrode prepared in Comparative Example 6 were heated to 5.0 mM [Fe(CN)6] 3- / 4- Electrochemical impedance spectroscopy (EIS) spectrum containing 0.1M KCl as supporting electrolyte;

[0047] Figure 5 Cyclic voltammograms (CV graphs) of the CeO2 / Co3O4-Fe2O3@CC sensor prepared in Example 1 in 0.2 M phosphate buffer solution with and without bisphenol A added;

[0048] Figure 6a Differential pulse voltammetry curves (DPV graphs) of the CeO2 / Co3O4-Fe2O3@CC sensor prepared in Example 1 in 0.2 M phosphate buffer solution to study the changes in bisphenol A at different concentrations;

[0049] Figure 6bThe linear relationship between the peak current and concentration change of the CeO2 / Co3O4-Fe2O3@CC sensor prepared in Example 1 was studied in 0.2 M phosphate buffer solution at different concentrations of bisphenol A;

[0050] Figure 7a Cyclic voltammograms (CV diagrams) of the CeO2 / Co3O4-Fe2O3@CC modified electrode prepared in Example 1 for bisphenol A at different scan rates;

[0051] Figure 7b This is a linear relationship diagram of the peak current of the CeO2 / Co3O4-Fe2O3@CC modified electrode prepared in Example 1 for bisphenol A at different scan rates;

[0052] FIG8 is a bar graph showing the effect of the CeO2 / Co3O4-Fe2O3@CC modified electrode prepared in Example 1 on the current of bisphenol A detection in the presence of common inorganic ions and organic pollutants. DETAILED DESCRIPTION

[0053] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] The preparation method of CeO2 / Co3O4-Fe2O3@CC in this embodiment includes the following steps:

[0055] (1) A soluble cerium salt and a soluble cobalt salt are dissolved in N,N-dimethylformamide to form solution A. 1,3,5-benzenetricarboxylic acid is dissolved in anhydrous ethanol to form solution B. Solution A is slowly added to solution B and stirred evenly. The solution is then transferred to a high-pressure reactor for a hydrothermal reaction. After the reaction is completed, the solution is cooled to room temperature, and the precipitate is collected, centrifuged, washed, and dried to obtain CeCo-MOFs powder.

[0056] In this example, the soluble cerium salt is Ce(NO₃)₃·6H₂O, and the soluble cobalt salt is Co(NO₃)₂·6H₂O. The molar ratio of the cerium salt to the cobalt salt is 4:6; the molar ratio of the metal salt to N,N-dimethylformamide is 1:233; the molar ratio of the metal salt to 1,3,5-benzenetricarboxylic acid is 1:2; and the molar ratio of 1,3,5-benzenetricarboxylic acid to anhydrous ethanol is 1:307. This solution is prepared by the following method: a certain amount of Ce(NO₃)₃·6H₂O and Co(NO₃)₂·6H₂O are dissolved in 18 mL of N,N-dimethylformamide to form a homogeneous solution A; a certain amount of 1,3,5-benzenetricarboxylic acid is dissolved in 18 mL of anhydrous ethanol and stirred thoroughly to form a homogeneous solution B. Solution A is slowly added to solution B, stirred thoroughly to form a homogeneous mixed solution, and then the mixed solution is transferred to a high-pressure hydrothermal autoclave.

[0057] The hydrothermal reaction process parameters in this example were: a hydrothermal temperature of 120°C and a hydrothermal time of 10 hours. The hydrothermal solution was cooled to room temperature, and the resulting precipitate was collected by centrifugation. The resulting precipitate was washed several times with DMF and anhydrous ethanol, and then dried at 60°C to obtain CeCo-MOFs powder.

[0058] (2) Dispersing the bimetallic CeCo-MOFs powder prepared in step (1) on Fe 2+ The precursor solution is stirred to make it evenly dispersed, and the solid particles are separated from the solution, centrifuged, washed and dried to obtain a MOF-based Fe-doped composite material.

[0059] The amount of bimetallic CeCo-MOFs powder used in this example is 500 mg;

[0060] In this embodiment, Fe 2+ The precursor solution is an ethylene glycol solution containing FeCl2·4H2O, Fe 2+ In the precursor solution, Fe 2+ The molar concentration of the catalyst is 0.04M, the solvent is a mixture of ethylene glycol and distilled water, and the volume ratio of ethylene glycol to distilled water is 1:8. It is prepared by the following method: take a certain amount of FeCl2·4H2O in a beaker, pipette ethylene glycol, and then add distilled water to dissolve it fully. The bimetallic CeCo-MOFs powder is dispersed in Fe 2+ The precursor solution was stirred, the powder was collected, and dried to obtain a MOF-based Fe-doped composite material.

[0061] (3) The composite material obtained in step (2) is placed in a muffle furnace and calcined for a period of time, cooled to room temperature, and the calcined powder is collected to obtain CeO2 / Co3O4-Fe2O3 powder.

[0062] In this embodiment, the calcination temperature in the muffle furnace is 500° C., the calcination time is 2 h, and the calcined powder obtained after cooling to room temperature is collected, namely CeO 2 / Co 3 O 4 -Fe 2 O 3 .

[0063] (4) The CeO2 / Co3O4-Fe2O3 powder prepared in step (3) was dispersed in a solvent and Nation solution was added to prepare a suspension. The obtained suspension was drop-coated on a pretreated conductive substrate and dried to obtain a CeO2 / Co3O4-Fe2O3@CC sensor electrode.

[0064] In this example, the suspension contained CeO2 / Co3O4-Fe2O3 powder at a concentration of 15 mg / mL, and the solvent was N,N-dimethylformamide. The specific implementation steps were as follows: Weigh a certain amount of CeO2 / Co3O4-Fe2O3 powder and ultrasonically disperse it in N,N-dimethylformamide (containing a Nation solution) to obtain a uniform suspension.

[0065] The conductive substrate in this embodiment is a conductive hydrophilic carbon cloth. The carbon cloth is cut into a size of 1 cm×1 cm, ultrasonically washed in acetone, ethanol, and deionized water for 15 minutes respectively to remove surface impurities, and then dried at 60° C. for use.

[0066] In this embodiment, the drop coating amount is 150 μL. 150 μL of the dispersed suspension is slowly drop coated on the pretreated hydrophilic carbon cloth and dried at 60° C. to obtain a CeO 2 / Co 3 O 4 -Fe 2 O 3 @CC electrode.

[0067] Comparative Example 1

[0068] To facilitate performance comparison, the operating steps of Example 1 were repeated, with the only difference being that no Fe element was introduced in step (2) and direct calcination was performed. Other experimental conditions were the same, and CeO2 / Co3O4@CC was prepared.

[0069] Comparative Example 2

[0070] To facilitate performance comparison, CeO2 was prepared by the following method. The specific preparation method is as follows:

[0071] A soluble cerium salt was dissolved in N,N-dimethylformamide to form solution A. 1,3,5-benzenetricarboxylic acid was dissolved in anhydrous ethanol to form solution B. Solution A was slowly added to solution B and stirred evenly. The solution was then transferred to an autoclave for a hydrothermal reaction. After the reaction was completed, the solution was cooled to room temperature, and the precipitate was collected, centrifuged, washed, and dried to obtain Ce-MOF powder.

[0072] In this example, the soluble cerium salt is Ce(NO₃)₃·6H₂O. The molar ratio of the metal salt to N,N-dimethylformamide is 1:233; the molar ratio of the metal salt to 1,3,5-benzenetricarboxylic acid is 1:2; and the molar ratio of 1,3,5-benzenetricarboxylic acid to anhydrous ethanol is 1:307. This is prepared by the following method: dissolving a certain amount of Ce(NO₃)₃·6H₂O in 18 mL of N,N-dimethylformamide to form a homogeneous solution A; dissolving a certain amount of 1,3,5-benzenetricarboxylic acid in 18 mL of anhydrous ethanol, and stirring thoroughly to form a homogeneous solution B. Solution A is slowly added to solution B, stirring thoroughly to form a homogeneous mixed solution. The mixed solution is then transferred to a high-pressure hydrothermal autoclave and hydrothermalized at 120°C for 10 hours. The mixture is centrifuged, washed with DMF and anhydrous ethanol, and then dried at 60°C to obtain a powder, which is Ce-MOF.

[0073] The above Ce-MOF is placed in a muffle furnace for calcination. In this embodiment, the calcination temperature of the muffle furnace is 500°C and the calcination time is 2 hours. After cooling to room temperature, the calcined powder is collected, which is CeO2.

[0074] The remaining steps in this embodiment are the same as those in embodiment 1.

[0075] Comparative Example 3

[0076] In order to compare the performance, the steps of Comparative Example 2 were repeated except that the obtained Ce-MOF was placed on Fe 2+ The precursor solution was stirred, the powder was collected and dried, and the other experimental steps were the same to obtain CeO2-Fe2O3@CC.

[0077] In this embodiment, Fe 2+ The method for preparing the precursor solution is the same as that in Example 1.

[0078] Comparative Example 4

[0079] To facilitate performance comparison, Co3O4 was prepared by the following method. The specific preparation method is as follows:

[0080] In this example, the soluble cobalt salt is Co(NO₃)₂·6H₂O. The molar ratio of the metal salt to N,N-dimethylformamide is 1:233; the molar ratio of the metal salt to 1,3,5-benzenetricarboxylic acid is 1:2; and the molar ratio of 1,3,5-benzenetricarboxylic acid to anhydrous ethanol is 1:307. The preparation method is as follows: a certain amount of Co(NO₃)₂·6H₂O is dissolved in 18 mL of N,N-dimethylformamide to form a homogeneous solution A; a certain amount of 1,3,5-benzenetricarboxylic acid is dissolved in 18 mL of anhydrous ethanol and stirred thoroughly to form a homogeneous solution B. Solution A is slowly added to solution B, stirred thoroughly to form a homogeneous mixed solution, and then the mixed solution is transferred to a high-pressure hydrothermal autoclave and hydrothermalized at 120°C for 10 hours. The mixture is centrifuged, washed with DMF and anhydrous ethanol, and then dried at 60°C to obtain a powder, which is Co-MOF.

[0081] The obtained Co-MOF is placed in a muffle furnace for calcination, and the powder collected after cooling is Co3O4.

[0082] The calcination conditions in this example are the same as those in Example 1.

[0083] Comparative Example 5

[0084] In order to compare the performance, the steps of Comparative Example 4 were repeated except that the obtained Co-MOF was placed on Fe 2+ The precursor solution was stirred, the powder was collected and dried, and the other experimental steps were the same to obtain Co3O4-Fe2O3@CC.

[0085] In this embodiment, Fe 2+ The method for preparing the precursor solution is the same as that in Example 1.

[0086] Comparative Example 6

[0087] In order to compare the performance, the hydrophilic carbon cloth was cut into 1 cm × 1 cm size, ultrasonically washed with acetone, anhydrous ethanol, and deionized water for 15 min, and then dried at 60 °C to obtain a pure CC electrode.

[0088] Figure 1 (ab) are scanning electron microscope (SEM) images of the CeO2 / Co3O4-Fe2O3 material prepared in Example 1. It can be seen from the figure that CeO2 / Co3O4-Fe2O3 is a nanorod-like structure, which increases the specific surface area of the material and exposes more active sites.

[0089] Figure 2The XRD patterns of the CeO2 / Co3O4-Fe2O3 material prepared in Example 1, the CeO2 / Co3O4 material prepared in Comparative Example 1, the CeO2 material prepared in Comparative Example 2, and the Co3O4 material prepared in Comparative Example 4 show that the XRD patterns all show corresponding crystal planes, and the response peak of the material CeO2 / Co3O4 is reduced, indicating that the CeO2 / Co3O4 material is successfully composited. Compared with the CeO2 / Co3O4 in Comparative Example 1, the corresponding crystal plane peak of the material CeO2 / Co3O4-Fe2O3 is also reduced and Fe2O3 appears, indicating that Fe is successfully doped.

[0090] Figure 3 The CeO2 / Co3O4-Fe2O3@CC sensor electrode prepared in Example 1, the CeO2 / Co3O4@CC sensor electrode prepared in Comparative Example 1, and the pure CC electrode prepared in Comparative Example 6 were heated to 5.0 mM [Fe(CN)6] 3- / 4- Cyclic voltammetry (CV) diagram containing 0.1 M KCl as supporting electrolyte. Figure 3 The redox peak current of the carbon cloth modified with CeO2 / Co3O4 is higher than that of the pure carbon cloth, indicating that the electrode modified with CeO2 / Co3O4 has a higher electron transfer efficiency; the electrode modified with CeO2 / Co3O4-Fe2O3 has a higher redox peak current, indicating that the incorporation of Fe can further improve the electrochemical performance of the electrode.

[0091] Figure 4 The CeO2 / Co3O4-Fe2O3@CC sensor electrode prepared in Example 1, the CeO2 / Co3O4@CC sensor electrode prepared in Comparative Example 1, and the pure CC electrode prepared in Comparative Example 6 were heated to 5.0 mM [Fe(CN)6] 3- / 4- Electrochemical impedance spectroscopy (EIS) spectrum obtained with 0.1 M KCl as the supporting electrolyte. Figure 4 The arc radius of the EIS spectra of the CeO2 / Co3O4-Fe2O3@CC and CeO2 / Co3O4@CC electrodes shows a decreasing trend compared to the pure CC electrode. In electrochemical impedance spectroscopy, a smaller impedance loop radius indicates a lower resistance and stronger charge transfer capability. This further demonstrates that modification of CeO2 / Co3O4 can reduce electrode resistance, and that incorporation of Fe further reduces the electron transfer resistance.

[0092] Figure 5The cyclic voltammograms of the CeO2 / Co3O4-Fe2O3@CC prepared in Example 1 are shown in 0.2M phosphate buffer (pH = 7.0) as the supporting electrolyte with and without the addition of 20μM bisphenol A. As can be seen, no oxidation peak is observed when no bisphenol A is added, but a significant oxidation peak appears with the addition of 20μM bisphenol A, demonstrating that the sensor can be used to detect bisphenol A.

[0093] Example 2

[0094] This example is an experiment of using a MOFs-based electrochemical sensor to detect bisphenol A.

[0095] The specific detection process of CeO2 / Co3O4-Fe2O3@CC prepared in this embodiment based on Example 1 is as follows:

[0096] A three-electrode system was adopted, with the CeO2 / Co3O4-Fe2O3@CC prepared in Example 1 as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. Electrochemical detection of bisphenol A standard solutions of different concentrations was carried out by differential pulse stripping voltammetry in 0.2 M phosphate buffer (pH = 7.0). Based on the relationship between peak current and concentration, the standard working solution was plotted, and the linear range, sensitivity, and detection limit of bisphenol A were determined.

[0097] Figure 6 shows that the linear relationship is as follows when the BPA concentration is 0.5-10 μM: I p (μA)=20.489C(μM)+84.908, the linear correlation coefficient is R 2 =0.996; when the concentration is 10-30μM, the linear relationship is: I p (μA)=7.839C(μM)+223.920, the linear correlation coefficient is R 2 =0.993. Therefore, the sensitivity of the sensor is 20.489μA / μM·cm 2 The detection range is 0.5-10 μM, and the calculated LOD is 8.7 nM (S / N = 3). The decrease in the peak current growth rate with increasing BPA concentration at high concentrations is due to the adsorption of a certain amount of pollutants on the detection electrode surface at high concentrations, which affects mass transfer and leads to a decrease in the peak current growth rate.

[0098] Example 3

[0099] In this example, the detection performance of the CeO2 / Co3O4-Fe2O3@CC modified electrode for bisphenol A at different scan rates was studied by changing the scan rate and drawing cyclic voltammetry curves.

[0100] In this example, the CeO2 / Co3O4-Fe2O3@CC prepared in Example 1 was used as the working electrode, a platinum sheet was used as the counter electrode, and a saturated calomel electrode (SCE) was used as the reference electrode. Cyclic voltammetry was used to study the changes in peak current at different scan rates in 0.2 M phosphate buffer (pH = 7.0) (containing 20 μM bisphenol A).

[0101] Figure 7-a shows the cyclic voltammograms of the CeO2 / Co3O4-Fe2O3@CC electrode in the presence of 20 μM bisphenol A at different scan rates (20 mV / s to 250 mV / s). As shown, with increasing scan rate, the peak oxidation current gradually increases, and the peak oxidation potential shifts toward the positive potential. Figure 7-b shows the linear relationship between the peak oxidation current and scan rate. As can be seen from the figure, the peak current of the CeO2 / Co3O4-Fe2O3@CC electrode for detecting BPA shows a good linear relationship with the scan rate, indicating that the electrochemical reaction of bisphenol A on the CeO2 / Co3O4-Fe2O3@CC electrode is an adsorption-controlled process.

[0102] Example 4

[0103] This example studies the stability, selectivity and reproducibility of CeO2 / Co3O4-Fe2O3@CC electrode.

[0104] In this example, the CeO2 / Co3O4-Fe2O3@CC prepared in Example 1 was used as the working electrode, a platinum sheet was used as the counter electrode, and a saturated calomel electrode (SCE) was used as the reference electrode. The selectivity, stability, and reproducibility of the sensor for detecting bisphenol A were studied in 0.2 M phosphate buffer (pH = 7.0).

[0105] Selectivity is one of the important parameters of electrochemical sensors used in actual sample analysis. In order to study the selectivity of the modified electrode, the changes in the peak current response value of bisphenol A were studied in the absence or presence of common interfering substances ( Figure 8a -b). When 100 times the concentration of the target substance Na + Mg 2+ NH4 + 、NO3 - 、Cl - 、SO4 2- , and HCO3 - The influence on the detection of bisphenol A can be ignored. The specific current changes are as follows: Figure 8a As shown. Similarly, Figure 8bIt shows that when phenol (Ph), catechol (CC), p-nitrophenol (p-NP), resorcinol (RC), and hydroquinone (HQ) are added at the same concentration as the target pollutants, the impact on the peak current of bisphenol A detection is less than ±5%, indicating that the CeO2 / Co3O4-Fe2O3@CC modified electrode has good selectivity for the detection of bisphenol A.

[0106] Reproducibility and stability are also important indicators for evaluating electrochemical sensors. The CeO2 / Co3O4-Fe2O3@CC composite electrochemical sensor was tested five times against a mixed standard solution of bisphenol A, and the relative standard deviation of the peak current was 1.99%. Furthermore, when the CeO2 / Co3O4-Fe2O3@CC composite electrochemical sensor was stored at 4°C for 10 days and then used to detect bisphenol A, the current response signal was 96.84% of the initial detection value, demonstrating the excellent stability of the electrochemical sensor constructed using this composite. Furthermore, five identical modified electrodes were prepared using the same method and tested at the same concentration of bisphenol A, with a relative standard deviation of 1.84%. Therefore, the CeO2 / Co3O4-Fe2O3@CC modified electrode demonstrated excellent reproducibility and stability in the detection of bisphenol A.

[0107] Example 5

[0108] Repeat steps (1) (2) (3) (4) in Example 1 and the operating steps of Example 2, except that in the process of preparing CeO2 / Co3O4-Fe2O3@CC electrode, in step (1), the soluble cerium salt used is cerium chloride, and the soluble cobalt salt is cobalt chloride. The remaining steps are the same as Examples 1 and 2.

[0109] The CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of this example had lower detection performance for bisphenol A than the CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of Example 1. The linear range for bisphenol A was 5-20 μM, and the limit of detection (LOD) was 38 nM.

[0110] Example 6

[0111] Repeat the steps (1) (2) (3) (4) in Example 1 and the operating steps of Example 2, except that in the process of preparing CeO2 / Co3O4-Fe2O3@CC electrode, in step (2), Fe 2+ The concentration of the precursor solution was 0.02 M, and the remaining steps were the same as those in Example 1 and Example 2.

[0112] The detection performance of the CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of this example for bisphenol A was inferior to that of the CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of Example 1. The linear range for bisphenol A was 5-25 μM, and the limit of detection (LOD) was 20 nM.

[0113] Example 7

[0114] Repeat steps (1) (2) (3) (4) in Example 1 and the operating steps of Example 2, except that in the process of preparing the CeO2 / Co3O4-Fe2O3@CC electrode, in step (1), the molar ratio of metal cerium to metal cobalt is 1:1, and the remaining steps are the same as Examples 1 and 2.

[0115] The detection performance of the CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of this example for bisphenol A was inferior to that of the CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of Example 1. The linear range for bisphenol A was 5-25 μM, and the limit of detection (LOD) was 30 nM.

[0116] Example 8

[0117] Repeat steps (1) (2) (3) (4) in Example 1 and the operating steps of Example 2, except that in the process of preparing CeO2 / Co3O4-Fe2O3@CC electrode, in step (1), the hydrothermal condition is 100℃ and the hydrothermal temperature is 10h, and the remaining steps are the same as Examples 1 and 2.

[0118] The detection performance of the CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of this example for bisphenol A was inferior to that of the CeO2 / Co3O4-Fe2O3@CC electrode prepared under the conditions of Example 1. The linear range for bisphenol A was 5-20 μM, and the limit of detection (LOD) was 34 nM.

[0119] It can be seen from the above examples that the CeO2 / Co3O4-Fe2O3@CC electrochemical sensor prepared in the present invention has excellent electrochemical performance, low detection limit and stability.

[0120] The specific implementation methods described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An electrochemical sensor based on bimetallic MOFs material, characterized in that: The electrochemical sensor comprises a working electrode, a counter electrode, a reference electrode, and a buffer solution, adopting a three-electrode system and connected to an electrochemical workstation to form an electrochemical sensor for detecting phenolic substances; the working electrode is a CeO2 / Co3O4-Fe2O3@CC formed by using a bimetallic MOFs-derived oxide as a modified material and doped with Fe and loaded on a hydrophilic carbon cloth; the preparation method of the CeO2 / Co3O4-Fe2O3@CC sensor working electrode comprises the following steps: (1) Soluble cerium salt and soluble cobalt salt are dissolved in N, N-dimethylformamide to form solution A, 1, 3, 5-benzenetricarboxylic acid is dissolved in anhydrous ethanol to form solution B, solution A is slowly added to solution B and stirred evenly, and then the solution is transferred to a high-pressure reactor for hydrothermal reaction. After the reaction is completed, it is cooled to room temperature, washed and dried to obtain CeCo-MOFs powder; (2) Disperse the bimetallic CeCo-MOFs powder prepared in step (1) on Fe 2+ The precursor solution is stirred to be evenly dispersed, and the solid particles are separated from the solution, centrifuged, washed, and dried to obtain a MOFs-based Fe-doped composite material; (3) calcining the composite material obtained in step (2) at a certain temperature and cooling it to room temperature to obtain CeO2 / Co3O4-Fe2O3 powder; (4) The CeO2 / Co3O4-Fe2O3 powder prepared in step (3) was dispersed in a solvent and Nafion solution was added to prepare a suspension. The obtained suspension was drop-coated on a pretreated hydrophilic carbon cloth conductive substrate and dried to obtain a CeO2 / Co3O4-Fe2O3@CC sensor working electrode.

2. An electrochemical sensor based on bimetallic MOFs material according to claim 1, characterized in that: In step (1), the soluble cerium salt may be one or more of cerium chloride, cerium nitrate, cerium sulfate, and cerium acetate, and the soluble cobalt salt may be one or more of cobalt nitrate, cobalt chloride, cobalt bromide, and cobalt acetate.

3. An electrochemical sensor based on bimetallic MOFs material according to claim 1, characterized in that: In step (1), the molar ratio of cerium salt to cobalt salt is (0.05-12):1; the molar ratio of 1,3,5-benzenetricarboxylic acid to anhydrous ethanol is 1:(100-500).

4. The electrochemical sensor based on bimetallic MOFs material according to claim 1, characterized in that: In step (1), the hydrothermal temperature is 70-180°C, and the hydrothermal time is 5-24 h.

5. The electrochemical sensor based on bimetallic MOFs material according to claim 1, characterized in that: In step (2), the Fe 2+ The precursor solution is prepared from a soluble ferrous salt and a solvent. The soluble ferrous salt can be one or more of ferrous nitrate, ferrous chloride, ferrous sulfate, ferrous acetate or ferrous oxalate. The solvent can be one or more of ethylene glycol, methanol, ethanol and water.

6. The electrochemical sensor based on bimetallic MOFs material according to claim 1, characterized in that: In step (2), the Fe 2+ Fe in the precursor solution 2+ The molar concentration is 0.01~0.2 M, and the bimetallic CeCo-MOFs powder is dispersed in Fe 2+ The concentration in the precursor solution is 2~20 mg / mL.

7. The electrochemical sensor based on bimetallic MOFs material according to claim 1, characterized in that: In step (3), the calcination temperature is 400-600°C, and the calcination time is 0.5-5 h.

8. The electrochemical sensor based on bimetallic MOFs material according to claim 1, characterized in that: In step (4), the concentration of CeO2 / Co3O4-Fe2O3 powder added to the suspension is 2~50 mg / mL, and the amount of the drop-coated suspension is 20~400 μL.

9. Use of the electrochemical sensor based on the bimetallic MOFs material according to claim 1 in detecting phenolic pollutants.

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