ZIF-8 (at) MWCNTs (at) CeO2 composite material, preparation method thereof and application thereof in electrochemical sensor

Abstract

The invention discloses a ZIF-8 (at) MWCNTs (at) CeO2 composite material as well as a preparation method and application thereof in an electrochemical sensor, and particularly relates to the technical field of food detection. Wherein the ZIF-8 (at) MWCNTs (at) CeO2 composite material is prepared from zinc nitrate hexahydrate, 2-methylimidazole, cerium nitrate hexahydrate and MWCNTs (multi-walled carbon nanotubes); wherein on the basis of zinc nitrate hexahydrate, the mass ratio of the zinc nitrate hexahydrate to the 2-methylimidazole is 0.36-0.91, and the mass ratio of the zinc nitrate hexahydrate to the 2-methylimidazole to the zinc nitrate hexahydrate to the 2-methylimidazole is 0.36-0.91. The mass ratio of the zinc nitrate hexahydrate to the cerium nitrate hexahydrate is 1.37-13.7; the mass of the MWCNTs accounts for 5%-20% of the total mass. According to the scheme, a high-performance Xa and Hx detection sensor is provided through material optimization, and a valuable practical scheme is provided for application and development of the MOFs-based composite material in the field of rapid food freshness detection.

Description

Technical Field

[0001] This application relates to the field of food detection technology, and in particular to ZIF-8@MWCNTs@CeO2 composite material, its preparation method and its application in electrochemical sensors. Background Technology

[0002] As an important economic fish species in my country, the freshness of large yellow croaker directly affects its food safety and economic value. Xanthine and hypoxanthine are key products in the ATP degradation process after fish death, and their content is widely considered an objective indicator of the freshness of aquatic products. Currently, the mainstream methods for detecting these purine substances rely on large-scale instrumental analysis techniques such as high-performance liquid chromatography (HPLC). While these methods are highly accurate, they have inherent limitations, including expensive equipment, complex sample pretreatment, long analysis cycles, and difficulty in meeting the needs of rapid on-site detection.

[0003] Electrochemical sensors, with their advantages of rapid response, high sensitivity, low cost, and ease of miniaturization, provide an effective method for the rapid detection of food freshness indicators. However, due to the limited catalytic activity of ordinary electrode materials, the detection sensitivity is not high, and they are easily interfered with by other coexisting substances in actual samples. Therefore, ordinary electrode materials cannot obtain accurate results when used to simultaneously detect xanthine and hypoxanthine.

[0004] Therefore, how to construct composite materials with excellent electrochemical response to xanthine and hypoxanthine is a problem that testing technicians urgently need to solve. Summary of the Invention

[0005] This invention provides a ZIF-8@MWCNTs@CeO2 composite material, its preparation method, and its application in electrochemical sensors. This solution not only provides a high-performance Xa and Hx detection sensor through material optimization, but also offers a valuable practical solution for the development and application of MOF-based composite materials in the rapid detection of food freshness.

[0006] The objective of this invention is achieved through the following technical solution: The ZIF-8@MWCNTs@CeO2 composite material is prepared from zinc nitrate hexahydrate, 2-methylimidazole, cerium nitrate hexahydrate, and MWCNTs. The mass ratios of zinc nitrate hexahydrate to the above components are as follows: zinc nitrate hexahydrate to 2-methylimidazole is 0.36-0.91; zinc nitrate hexahydrate to cerium nitrate hexahydrate is 1.37-13.7; and MWCNTs account for 5%-20% of the total mass.

[0007] Preferably, the mass ratio between zinc nitrate hexahydrate and the above components is as follows: the mass ratio of zinc nitrate hexahydrate to 2-methylimidazole is 0.45; the mass ratio of zinc nitrate hexahydrate to cerium nitrate hexahydrate is 3.42; and the mass of MWCNTs accounts for 20% of the total mass.

[0008] This invention also provides a method for preparing ZIF-8@MWCNTs@CeO2 composite material, the method comprising the following steps: S01. Dissolve zinc nitrate hexahydrate and cerium nitrate hexahydrate together in 20 mL of methanol, then add MWCNTs, sonicate at 40 kHz for 5 min, and disperse to form a uniform suspension. S02. Dissolve 2-methylimidazole in 20 mL of methanol in another container and then quickly pour it into the above suspension. Let it stand at room temperature for 24 hours to react. S03. After the reaction is complete, the product is centrifuged at 10000 rpm / min for 15 min, washed with methanol, and vacuum dried at 60℃ to obtain the ZIF-8@MWCNTs@CeO2 composite material.

[0009] This invention also provides a method for preparing an electrochemical sensor using ZIF-8@MWCNTs@CeO2 composite material, the method comprising the following steps: (1) After pretreatment, the glassy carbon electrode is ultrasonically cleaned in anhydrous ethanol and ultrapure water in sequence; (2) The ZIF-8@MWCNTs@CeO2 composite material was dispersed in ultrapure water and sonicated to obtain a modified suspension; (3) The modified suspension was drop-coated onto the surface of the pretreated glassy carbon electrode and allowed to dry naturally at room temperature to obtain the ZIF-8@MWCNTs@CeO2 electrochemical sensor.

[0010] Preferably, in step (1), the pretreatment process of the glassy carbon electrode is as follows: the glassy carbon electrode is polished to a mirror finish on chamois leather with 0.3 μm and 0.05 μm alumina pastes in sequence.

[0011] Preferably, in step (1), the cleaning time for the glassy carbon electrode is 1 minute.

[0012] Preferably, in step (2), the ultrasonic time is 30 minutes and the ultrasonic power is 40 kHz.

[0013] Preferably, the ZIF-8@MWCNTs@CeO2 electrochemical sensor prepared in step (3) can be used for the simultaneous detection of a mixture of xanthine and hypoxanthine.

[0014] Compared with the prior art, the advantages or beneficial effects of the technical solution of this application include: 1. This invention confirms a significant synergistic effect among ZIF-8, MWCNTs, and CeO2. ZIF-8 plays a crucial role in enhancing sensitivity by providing a powerful enrichment function for the target analyte; MWCNTs offer efficient electron transport channels; and CeO2 contributes to catalytic activity. This synergistic effect overcomes the limitations of single materials.

[0015] 2. The sensor exhibits high sensitivity, wide linear range (0.01-40 μg / mL), and low detection limit for xanthine (Xa) and hypoxanthine (Hx), and can achieve simultaneous and highly selective detection of the two substances in mixed solutions, with good separation of oxidation peaks.

[0016] 3. The sensor performs excellently in terms of selectivity, storage stability, repeatability, and reproducibility, meeting the core reliability requirements of practical applications.

[0017] 4. In the spiked recovery experiment on actual large yellow croaker samples, the average recovery rate was between 91.5% and 105.2%, and the results were accurate and reliable, fully demonstrating the sensor's ability to accurately quantify complex real samples. Attached Figure Description

[0018] Figure 1 The results of the orthogonal experiment are shown in the figure. Figure 2 Infrared spectra of ZIF-8, MWCNTs, CeO2, and the target composite material; Figure 3 The electrochemical performance curves of sensors with different modified materials were obtained by cyclic voltammetry testing. Figure 4 Impedance plots of sensors with different modified materials Figure 5 The response of sensors with different modified materials to a mixed solution of xanthine and hypoxanthine; Figure 6 The sensor's current response to different concentrations of xanthine is shown in the graph. Figure 7 This is a linear graph showing the relationship between the sensor and peak current for different concentrations of xanthine. Figure 8 The current response of the sensor to different concentrations of hypoxanthine is shown in the graph. Figure 9 The graph shows the linear relationship between the sensor and peak current for different concentrations of hypoxanthine. Figure 10 The current response of the sensor to different concentrations of hypoxanthine and xanthine is shown in the graph. Figure 11 The graph shows the linear relationship between the sensor and peak current for different concentrations of hypoxanthine. Figure 12 This is a linear graph showing the relationship between the sensor and peak current for different concentrations of xanthine. Figure 13 This is a graph showing the relationship between the sensor's storage time and current response ratio. Figure 14 A statistical chart showing the repeatability results of the sensor; Figure 15 A statistical chart showing the reproducibility results of the sensor; Figure 16 A statistical chart showing the sensor's anti-interference performance. Figure 17 Statistical table of spiked recovery of actual samples of large yellow croaker. Detailed Implementation

[0019] The following detailed description of the embodiments of this application, in conjunction with the accompanying drawings, will provide a thorough understanding of how this application uses technical means to solve technical problems and achieve corresponding technical effects, enabling its implementation. The embodiments of this application and the various features within them can be combined with each other without conflict, and all resulting technical solutions are within the protection scope of this application.

[0020] It should be clearly stated that the embodiments described below are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] Example 1: Optimization of Orthogonal Experiment To optimize the properties of ZIF-8@MWCNTs@CeO2 composites, this study employed L 16 (4 5 An orthogonal experimental design was used to systematically investigate the effects of six factors—ZIF-8 feed ratio (A), MWCNTs feed ratio (B), CeO2 precursor feed ratio (C), pH value (D), casting volume (E), and concentration (F)—on the sensor response signal (oxidation peak current of xanthine and hypoxanthine). Range analysis showed that for xanthine detection, the order of influence of each factor was C > A > E > F > D > B, with the theoretical optimal combination being A3B4C3D4E3F3; for hypoxanthine detection, the order was E > F > C > A > B > D, with the theoretical optimal combination being A2B4C3D4E3F3. To balance the sensor's overall detection performance for both purines, the optimal combination was ultimately determined to be A3B4C3D4E3F3, meaning the optimal ratio for the material synthesis was: ZIF-8 feed ratio (Zn... 2+: 2-Methylimidazole) 1:8 (A3), MWCNTs feed ratio 20% (B4), CeO2 precursor feed ratio (Ce 3+ :Zn 2+ ) 1:5 (C3), orthogonal experimental table as follows Figure 1 As shown.

[0022] Based on this optimal ratio, and using a fixed 60.0 mg of zinc nitrate hexahydrate as a baseline, the amounts of the remaining components were accurately calculated and weighed: According to Zn 2+ Weigh out 132.5 mg of 2-methylimidazole at a molar ratio of 1:8; according to Ce... 3+ With Zn 2+ Weigh 17.5 mg of cerium nitrate hexahydrate at a molar ratio of 1:5; calculate and weigh 52.5 mg of MWCNTs based on the MWCNTs content of 20% of the total mass.

[0023] The specific preparation process is as follows: Zinc nitrate hexahydrate and cerium nitrate hexahydrate were dissolved together in 20 mL of methanol, and then MWCNTs were added and ultrasonically dispersed to form a uniform suspension. In another container, 2-methylimidazole was dissolved in 20 mL of methanol and then quickly poured into the above suspension. The mixture was allowed to stand at room temperature for 24 hours. After the reaction was completed, the mixture was centrifuged, washed with methanol, and vacuum dried at 60 °C to finally obtain the high-performance ZIF-8@MWCNTs@CeO2 composite material.

[0024] Subsequent sensor fabrication and performance testing were all based on these optimal conditions (material ratio A3B4C3, detection condition D4E3F3).

[0025] Example 2: Characterization of composite materials To confirm the successful preparation of the ZIF-8@MWCNTs@CeO2 ternary composite material and to explore its structural characteristics, Fourier transform infrared spectroscopy analysis was performed on ZIF-8, MWCNTs, CeO2, and the target composite material. The analysis results are as follows: Figure 2 The results show that the spectral characteristics of the various materials differ significantly. Pure ZIF-8 exhibits significant differences at 1580 cm⁻¹. -1 The peak at 1350-500 cm⁻¹ shows a strong characteristic peak attributable to the stretching vibration of the C=N bond in the imidazole ring. -1 A series of sharp absorption peaks were observed in the fingerprint region. The spectrum of MWCNTs showed high transmittance and a flat curve across the entire scanning range, indicating a weak infrared signal. The spectrum of CeO2 showed relatively weak characteristic absorption peaks within the test range. Analysis of the spectrum of the ZIF-8@MWCNTs@CeO2 composite material was crucial. This spectrum clearly reproduced the ZIF-8 peak at 1580 cm⁻¹. -1The presence of the main characteristic absorption peaks in the fingerprint region directly proves that the ZIF-8 framework was successfully retained after composite formation. However, compared with pure ZIF-8, the intensity of all characteristic absorption peaks of ZIF-8 in the composite material was significantly weakened, and some peaks broadened. This phenomenon cannot be caused by simple physical mixing, but strongly reveals a close interaction (such as coating effect or interfacial bonding) between ZIF-8 and components such as MWCNTs and CeO2. The introduction of MWCNTs and CeO2 effectively modulates the interfacial properties of the composite material. In summary, FTIR spectroscopy not only confirms the successful loading of ZIF-8 into the composite material, but more importantly, reveals the effective composite formation and interaction among multiple components. This provides crucial structural evidence for the formation of a stable composite structure and the subsequent excellent synergistic electrochemical performance.

[0026] Example 3: Fabrication of ZIF-8@MWCNTs@CeO2 electrochemical sensor The glassy carbon electrode was polished to a mirror finish on chamois leather using 0.3 μm and 0.05 μm alumina pastes, respectively, and then ultrasonically cleaned for 1 minute each in anhydrous ethanol and ultrapure water. Accurately weigh the material as described above. Figure 1 1.5 mg of ZIF-8@MWCNTs@CeO2 composite powder (corresponding to the optimal level F3 determined by orthogonal experiment: concentration 1.5 mg / mL) synthesized with the optimal ratio (A3B4C3) described above was dispersed in 1.0 mL of ultrapure water and sonicated for 30 minutes to form a uniform and stable black modification solution suspension. 9.0 μL (corresponding to the optimal level E3 determined by orthogonal experiment: casting volume 9 μL) of the above modification solution was accurately transferred and carefully and completely drop-coated onto the pretreated clean glassy carbon electrode surface, ensuring complete coverage of the electrode's working area. Subsequently, the electrode was allowed to air dry at room temperature. After the solvent completely evaporated, the composite material firmly adhered to the electrode surface, thus obtaining the ZIF-8@MWCNTs@CeO2 sensor for later use.

[0027] Example 4: Study on Electrode Interface Performance and Sensing Response Characteristics To evaluate the electrochemical properties of the ZIF-8@MWCNTs@CeO2 composite material, we first used potassium ferricyanide ([Fe(CN)6]), a standard electrochemical probe molecule. 3- / 4- The test was conducted in the solution.

[0028] Figure 3Cyclic voltammetry (CV) curves showed that the bare electrode exhibited the lowest redox peak current. The peak currents of the electrodes modified with ZIF-8 and CeO2 alone only increased slightly, indicating moderate conductivity. Notably, the MWCNTs-modified electrode displayed the sharpest redox peak with the highest current response among all electrodes, fully demonstrating the excellent conductivity of MWCNTs themselves. While the peak current of the ZIF-8@MWCNTs@CeO2 ternary composite modified electrode was slightly lower than that of the MWCNTs electrode, its peak shape was broader and the peak potential difference was reduced, indicating that its electrochemically effective area may have increased significantly due to the loading of ZIF-8, making the reaction process more reversible.

[0029] Figure 4 Electrochemical impedance spectroscopy (EIS) provided crucial information for understanding this phenomenon. MWCNTs exhibited the smallest impedance arc diameter, corresponding to their optimal conductivity. The increased impedance of ZIF-8@MWCNTs@CeO2 is primarily attributed to the poor conductivity of ZIF-8 itself, which, when coated on the MWCNT surface, increases the resistance to electron transport. Both CV and EIS results demonstrate that the preparation of ternary composite materials significantly alters the interfacial properties of the electrodes while sacrificing some conductivity. This change in interface properties plays a decisive role in the detection of target objects. Figure 5 Clearly, in a mixed solution containing 20 μg / mL xanthine (Hx) and hypoxanthine (Xa), the oxidation peak current response of ZIF-8@MWCNTs@CeO2 to both purines was significantly higher than that of MWCNTs and all other comparative electrodes. This result is crucial, demonstrating that despite a decrease in the background conductivity of the composite material, its detection sensitivity for the target analyte was greatly enhanced. This is mainly due to the highly efficient enrichment of xanthine and hypoxanthine molecules by ZIF-8's ultra-high specific surface area and porous structure, resulting in a reactant concentration on the electrode surface that is much higher than in the bulk solution, thus generating a stronger current signal. Simultaneously, the catalytic activity potentially provided by CeO2 synergistically promotes the electrochemical oxidation of the target analyte with the conductive substrate of MWCNTs.

[0030] In summary, although the introduction of ZIF-8 increases interfacial impedance, its strong enrichment capacity is the dominant factor in improving sensor sensitivity. The results show that the ZIF-8@MWCNTs@CeO2 composite material successfully prepared in this study, through functional complementarity (MWCNTs ensure conductivity, ZIF-8 provides enrichment capacity, and CeO2 may enhance catalysis), successfully optimizes the interfacial properties to a form more conducive to specific detection, rather than simply pursuing high conductivity, ultimately achieving a significant breakthrough in target analyte detection performance.

[0031] Example 5: Sensor Analysis Performance Study Under optimal conditions, we systematically evaluated the quantitative detection capabilities of the ZIF-8@MWCNTs@CeO2 sensor for xanthine (Xa) and hypoxanthine (Hx), including both individual and simultaneous detection.

[0032] Detection performance for xanthine (Xa): The sensor's response to Xa was studied using differential pulse voltammetry (DPV). Figure 6 As shown, in 0.1 M PBS (pH 7.4), the oxidation peak current at approximately 0.65 V significantly and regularly increases with increasing Xa concentration (0.01–40 μg / mL). The peak current exhibits a good linear relationship with Xa concentration within this range. Figure 7 The linear regression equation is I(μA) = 0.2444C(μg / mL) + 0.7248, and the correlation coefficient (R²) is... 2 The signal-to-noise ratio (S / N = 3) was 0.9877. The limit of detection (LOD) was calculated to be 0.02 μg / mL. This linear relationship indicates that the sensor has excellent quantitative analysis capabilities for Xa, and its wide linear range and low LOD meet the needs of practical sample detection.

[0033] Detection performance for hypoxanthine (Hx): The DPV method was also used to evaluate the sensor's response to Hx, such as... Figure 8 As shown, Hx exhibits a distinct oxidation peak at approximately 1.0 V, with its peak current increasing with increasing concentration (0.01–40 μg / mL). The calibration curves show good linearity between the peak current and Hx concentration in the range of 0.01–40 μg / mL. Figure 9 The linear equation is I(μA) = 0.2010C(μg / mL) + 0.6209, and the correlation coefficient R0 is... 2 The value was 0.9886, and the calculated detection limit was 0.03 μg / mL. The results indicate that the sensor also exhibits high sensitivity and a wide linear range for the detection of Hx.

[0034] Simultaneous detection of mixtures of Xa and Hx: such as Figure 10 As shown, in a mixed solution of xanthine (Xa) and hypoxanthine (Hx), the sensor successfully achieved simultaneous quantitative detection of the two substances. Quantitative analysis is as follows: Figure 11 and Figure 12 The results show that, within the concentration range of 0.01 to 40 μg / mL, the oxidation peak currents of both Xa and Hx exhibit a good linear relationship with their concentrations. For hypoxanthine (Hx), the linear regression equation is I(A) = 2.021 × 10⁻⁶. -7 C (μg / mL) + 3.403×10 -7 Correlation coefficient (R)2 The linear equation for xanthine (Xa) is 0.9782; for xanthine (Xa), the linear equation is I(A) = 1.991 × 10⁻⁶. -7 C (μg / mL) +4.2664×10 -7 Correlation coefficient (R) 2 The standard deviation of the multiple parallel measurements at each concentration point was 0.9435. The small standard deviation demonstrates the excellent reproducibility and stability of this method. This result clearly shows that the sensor can overcome the mutual interference between the two substances, achieving simultaneous, stable, and accurate detection of Xa and Hx in a mixed system, providing a solid foundation for its application in the analysis of complex real-world samples.

[0035] Example 6: Sensor Storage Stability Such as storage stability curve Figure 13 The data shows the performance changes of the sensor after storage at 4°C for different periods (1, 3, 5, 7, 10 days). The data indicates that during the 10-day test period, the mean current response of the sensor to xanthine (Xa) and hypoxanthine (Hx) (relative to the initial value) slowly decreased from 100% to 93.15% and 93.68%, respectively. Throughout the process, the response signal retention rate remained above 93%, and the standard deviation of measurements at each time point was small. This demonstrates that the sensor has excellent storage stability and can meet the requirements of short-term storage and multiple uses in practical applications.

[0036] Example 7: Repeatability and Reproducibility of Sensors Repeatability was examined by measuring the fluctuations of the same sensor in 10 consecutive measurements of the same concentration of sample. The results are as follows: Figure 14 The data shows that the average current response ratios of Xa and Hx are as high as 91.8% and 88.7%, respectively, and the RSD values ​​of 10 measurements are less than 7.5% and 7%, respectively, indicating that the single sensor has extremely high measurement precision.

[0037] Reproducibility was assessed by evaluating the differences in response to the same sample from 10 sensors prepared in different batches. Data are as follows: Figure 15 The results show that the mean response ratios of Xa and Hx are 96.2% and 95.5%, respectively, with batch-to-batch standard deviations of less than 7.6% and 5%, respectively. This indicates that the sensor fabrication method of the present invention has good reproducibility, and the performance of different batches of sensors is consistent, which is beneficial for standardized applications.

[0038] Example 7: Anti-interference capability The results of the anti-interference test were the most significant. For example... Figure 16As shown, in solutions containing the same concentrations of interfering substances (including ATP, various amino acids such as Cys, Ala, Gly, His, Asp, Glu, Pro, and biogenic amines such as histamine, TMA, DMA, etc.), the sensor's current response ratios to Xa and Hx did not change significantly. More importantly, the mean current response caused by all interfering substances themselves was below 15.98% (most were far below 10%, for example, ATP was only 4.63% and 6.00%), and their standard deviations were very small. This result strongly demonstrates that the sensor has extremely high specificity and selectivity for Xa and Hx, effectively avoiding interference from complex matrices in real samples, and ensuring the accuracy and reliability of the detection results.

[0039] Based on the comprehensive performance evaluation conducted in sections 4-7, the ZIF-8@MWCNTs@CeO2 sensor prepared in this study not only demonstrated high sensitivity and a wide linear range for the detection of xanthine and hypoxanthine, but also exhibited superior performance in key practical indicators such as selectivity, stability, and reproducibility. This lays a solid foundation for its reliable application in complex real-world samples, such as the detection of freshness in aquatic products. Example

[0040] To evaluate the reliability of the constructed ZIF-8@MWCNTs@CeO2 sensor in practical applications, we used it to detect the content of xanthine (Xa) and hypoxanthine (Hx) in real large yellow croaker samples, and conducted spiked recovery experiments using the standard addition method.

[0041] The actual sample processing procedure was as follows: Fresh large yellow croaker dorsal muscle tissue was taken from the market and subjected to standard pretreatment steps such as homogenization and centrifugation. The supernatant was then appropriately diluted with 0.1 M PBS (pH 7.4) to prepare the sample solution. First, the background value of the sample solution was directly measured using the sensor (Xa and Hx were not detected). Subsequently, three concentration levels (1, 20, and 40 μg / mL) of Xa and Hx standards were precisely added to a known volume of sample solution. After mixing, the samples were immediately detected using the sensor. Each spiked level was measured in triplicate, and the average detection amount, average recovery rate, and average standard error were calculated.

[0042] Experimental results are as follows Figure 17As shown in the figure, for xanthine (Xa), the average recoveries at three spiking levels of 1, 20, and 40 μg / mL were 91.5%, 100.5%, and 99.5%, respectively. For hypoxanthine (Hx), the corresponding average recoveries were 105.2%, 99.5%, and 96.9%. All recovery results fell within the ideal range of 91.5%–105.2%, indicating very high detection accuracy of the sensor. Furthermore, the average standard error of most parallel determinations was less than 5% (only slightly higher at the lowest concentration of 1 μg / mL), demonstrating good repeatability of the method. These data fully demonstrate that this sensor can effectively overcome the interference of complex matrices in real samples and achieve accurate quantification of the target analyte.

[0043] The ZIF-8@MWCNTs@CeO2 sensor was successfully applied to the detection of xanthine and hypoxanthine in real large yellow croaker samples. The spiked recovery experiment yielded satisfactory results, with good recovery rate and excellent parallelism, strongly validating the sensor's high accuracy, high precision, and strong anti-interference capability in practical sample analysis, demonstrating its great application potential in the rapid detection of food freshness.

Claims

1. A ZIF-8@MWCNTs@CeO2 composite material, characterized in that, It was prepared from zinc nitrate hexahydrate, 2-methylimidazole, cerium nitrate hexahydrate, and MWCNTs; wherein, based on zinc nitrate hexahydrate, the mass ratio between zinc nitrate hexahydrate and the above components was: The mass ratio of zinc nitrate hexahydrate to 2-methylimidazole is 0.36-0.91; the mass ratio of zinc nitrate hexahydrate to cerium nitrate hexahydrate is 1.37-13.7; and MWCNTs account for 5%-20% of the total mass.

2. The ZIF-8@MWCNTs@CeO2 composite material according to claim 1, characterized in that, The specific mass ratio between zinc nitrate hexahydrate and the above components is as follows: The mass ratio of zinc nitrate hexahydrate to 2-methylimidazole was 0.45; the mass ratio of zinc nitrate hexahydrate to cerium nitrate hexahydrate was 3.42; and MWCNTs accounted for 20% of the total mass.

3. A method for preparing ZIF-8@MWCNTs@CeO2 composite material, characterized in that, Includes the following steps: S01. Dissolve zinc nitrate hexahydrate and cerium nitrate hexahydrate together in 20 mL of methanol, then add MWCNTs and disperse by sonication at 40 kHz for 5 min to form a uniform suspension. S02. Dissolve 2-methylimidazole in 20 mL of methanol in another container and then quickly pour it into the above suspension. Let it stand at room temperature for 24 hours to react. S03. After the reaction is complete, the product is centrifuged at 10000 rpm / min for 15 min, washed with methanol, and vacuum dried at 60℃ to obtain the ZIF-8@MWCNTs@CeO2 composite material.

4. A method for preparing an electrochemical sensor using the ZIF-8@MWCNTs@CeO2 composite material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) After pretreatment, the glassy carbon electrode is ultrasonically cleaned in anhydrous ethanol and ultrapure water in sequence; (2) The ZIF-8@MWCNTs@CeO2 composite material was dispersed in ultrapure water and sonicated to obtain a modified suspension; (3) The modified suspension was drop-coated onto the surface of the pretreated glassy carbon electrode and allowed to dry naturally at room temperature to obtain the ZIF-8@MWCNTs@CeO2 electrochemical sensor.

5. The method according to claim 4, characterized in that, In step (1), the glassy carbon electrode is pretreated by polishing it to a mirror finish on chamois leather with 0.3 μm and 0.05 μm alumina pastes in sequence.

6. The method according to claim 4, characterized in that, In step (1), the cleaning time for the glassy carbon electrode is 1 minute.

7. The method according to claim 4, characterized in that, In step (2), the ultrasound time is 30 minutes and the ultrasound power is 40 kHz.

8. The method according to claim 4, characterized in that, The ZIF-8@MWCNTs@CeO2 electrochemical sensor prepared in step (3) can be used for the simultaneous detection of a mixture of xanthine and hypoxanthine.

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