Method for detecting hydrogen peroxide by using a CD@Mn-MOF composite material modified electrode

Abstract

The invention discloses a method for detecting hydrogen peroxide by using a CD@Mn-MOF composite material modified electrode. The composite material CD@Mn-MOF is prepared by a one-pot method. The CD@Mn-MOF composite material can detect hydrogen peroxide in an aqueous solution. There is a good linear relationship between the concentration of H2O2 and the current value, enabling quantitative detection of hydrogen peroxide. Moreover, it has good anti-interference performance, sensitivity, stability and reversibility. The composite of carbon quantum dots and MOF is a good method to improve the performance of MOF materials. The lowest detection limit for H2O2 reaches 14.7 μM, which is about 5 times higher than that of Mn-MOF.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical detection, and particularly relates to a method for detecting hydrogen peroxide by using a CD@Mn-MOF composite material modified electrode. Background Art

[0002] H2O2 is an important molecule. It is used as a mediator in biological systems and is also an oxidant in many fields, such as food safety, environmental monitoring, clinical applications, etc., and is an important trace gas that plays an important role in the troposphere. The determination of H2O2 is very important in enzyme reactions, and the detection of trace H2O2 also has quite important significance in clinical and environmental applications. In the prior art, various methods, such as titration, chromatography, spectroscopy, and electrochemistry, have been successfully used to detect H2O2. In the past few decades, enzyme-based electrochemical biosensors have received increasing research due to their high sensitivity and excellent selectivity. However, enzyme-based electrochemical biosensors usually have disadvantages such as complexity, high cost, and strong dependence on pH and temperature. Non-enzyme electrochemical biosensors are considered very promising candidate materials for detecting H2O2 due to their high sensitivity, no strict pH requirement, long-term stability, and fast responsiveness. In recent years, transition metals, transition metal oxides or hydroxides, and carbon-based materials have been widely studied as active materials for non-enzymatic H2O2 sensors. However, although high-performance H2O2 sensors have been rapidly developed, their applications are limited by low toxicity, poor operational stability, or limited electronic conductivity. To solve these problems, it is crucial to develop new high-performance H2O2 detection electrode materials.

[0003] MOF is a porous crystalline material constructed from organic ligands and inorganic metal ions or metal clusters. It has come into the view of researchers due to its advantages such as high specific surface area, high porosity, high chemical and thermal stability, etc., and has been widely studied and applied in the fields of sensing, adsorption, separation, energy storage, etc. Among them, 2D metal-organic frameworks (MOFs) have many unique physical and chemical properties due to their layered structure, such as significant electron transport ability, large surface area, and high density of accessible active sites on the surface, and have been widely explored. These advantages of 2D MOFs enable them to be used as electrode catalytic materials for electrochemical sensors. In the present invention, layered two-dimensional Mn-MOF was prepared by a solvothermal method under the condition of 160 °C, and the composite material CD@Mn-MOF was prepared by a one-pot method. The material was characterized by means of scanning electron microscopy, PXRD, thermogravimetric analysis, XPS, cyclic voltammetry, EIS, etc. Experiments have proved that the CD@Mn-MOF composite material can detect hydrogen peroxide in aqueous solution and has good anti-interference performance and sensitivity. The experiments of the invention also show that the composite of carbon quantum dots and MOF is a good method to improve the performance of MOF materials. Summary of the Invention

[0004] The object of the present invention is to provide a method for detecting hydrogen peroxide by using a CD@Mn-MOF composite material modified electrode.

[0005] I. Preparation of CD@Mn-MOF

[0006] 1,3,5-triimidazolylbenzene, terephthalic acid, and manganese acetate are dissolved in a mixed solvent of ethanol and distilled water, and a carbon quantum dot solution is added. After ultrasonic treatment, it is completely dissolved, heated to 130-150 °C within 3 h, and then slowly cooled to room temperature within 48-72 h. After washing, it is filtered to obtain CD@Mn-MOF. Among them, the molar ratio of 1,3,5-triimidazolylbenzene, terephthalic acid, and manganese acetate is 1:1:1 to 1:3:3. The preparation method of Mn-MOF is the same as that of CD@Mn-MOF except that the carbon quantum dot solution is not added.

[0007] The preparation method of the carbon quantum dot solution is as follows: 1 mmol of urea and 3 mmol of ethylenediamine are dissolved in 10 ml of deionized water. After ultrasonic treatment for 5 min, it is completely dissolved, placed in a sealed 23.0 mL Teflon-lined autoclave, and placed in a constant temperature drying oven at 140 °C for 6 h, and then naturally cooled to room temperature to obtain a brown-yellow carbon quantum dot solution. The mass-volume ratio of manganese acetate to the carbon quantum dot solution is 0.2-1 mg / μL.

[0008] II. Structure of CD@Mn-MOF

[0009] 1. Structural Characteristics and Composition

[0010] Single crystal X-ray diffraction analysis shows that this Mn-MOF belongs to the triclinic system and is located in the P -1 space group. As Figure 1 shown in a, the smallest asymmetric unit includes 1 Mn(II) ion, 1 1,3,5-triimidazolylbenzene, 3 coordinated H2O molecules, 2 free water molecules, and one molecule of crystalline terephthalic acid. The central metal Mn forms a six-coordinate hexahedral configuration with the surrounding oxygen and nitrogen (as Figure 1b) Among them, O6, O7, N2, and N6 form the plane of the octahedron, and N4 and O5 form the axial positions of the octahedron. The coordinating atoms are respectively the nitrogen from three 1,3,5-trimidazolylbenzenes and the oxygen from three H2O molecules. The bond lengths of the Mn-O bonds range from 2.1741(10) Å to 2.2087(9) Å, and the bond lengths of the Mn-N bonds range from 2.2004(11) Å to 2.2850(11) Å. To simplify the crystal structure of Mn-MOF, we analyzed Mn-MOF topologically. With metal Mn as the node and 1,3,5-trimidazolylbenzene as the linker, the entire structure of the 2D sheet-like structure Mn-MOF can be simplified to Figure 1 the topological structure shown in Fig. d.

[0011] Figure 2 The SEM and EDS spectra of Mn-MOF are given. In the corresponding Mn-MOF material, in addition to the signal peaks of elements C, O, and N being observable, the signal peak of element Mn can also be observed. The elemental compositions in Mn-MOF are as shown in the following table:

[0012]

[0013] 2. PXRD powder diffraction pattern, thermogravimetric analysis

[0014] The PXRD pattern analysis shows that Mn-MOF has good phase purity. The CD@Mn-MOF composite shows the same diffraction peaks as the original Mn-MOF, with narrow and sharp peak shapes, indicating that the synthesized composite has the same crystal structure as the original material and a very high purity (as shown in Figure 3 Fig. a). After grinding the composite CD@Mn-MOF and soaking it in aqueous solutions with pH values of 2, 7, and 12 respectively, after 24 hours, the measured PXRD patterns are as shown in Figure 3 Fig. b. It can be seen that the pattern of CD@Mn-MOF remains consistent with that before soaking, proving that the composite has good pH stability and water stability in the pH range of 2 - 12. Analyzing the thermogravimetric curve of Mn-MOF ( Figure 3 Fig. c), it can be known that during the heating of the sample to 800 °C, due to the departure of free water molecules and coordinated water molecules (the calculated value is 17.9%), Mn-MOF loses approximately 17.23% of its initial weight in the temperature range of 35 °C to 170.83 °C. There is no weight loss in the temperature range of 177.1 °C to 404.58 °C, indicating that Mn-MOF is stable in this temperature range. Then, when further heated from 404.58 °C to 800 °C, the Mn-MOF framework completely collapses. Generally speaking, below 404.58 °C, Mn-MOF remains stable in a nitrogen atmosphere, indicating its high thermal stability.

[0015] 3. Electrochemical, Infrared, and XPS Characterizations

[0016] The synthesized Mn-MOF and CD@Mn-MOF were electrochemically characterized. The electrolyte was a 0.1 M KCl solution containing 5 mM [Fe(CN)6], the scan rate was 0.1 V / s, and the voltage window was -0.2 V - 0.9 V. As shown in 3- / 4- Figure a, there are obvious differences in the cyclic voltammograms of Mn-MOF and CD@Mn-MOF. The height of the redox peaks of the composite material CD@Mn-MOF is significantly higher than that of Mn-MOF. In Figure 4 Figure b, the R value of the CD@Mn-MOF composite material is lower than that of Mn-MOF. These results prove that CD@Mn-MOF has a lower electron transfer resistance. Thus, it can be proved that carbon quantum dots have been successfully introduced into Mn-MOF. Figure 4 Figure b shows that the R value of the CD@Mn-MOF composite material is lower than that of Mn-MOF. ct These results prove that CD@Mn-MOF has a lower electron transfer resistance. Thus, it can be proved that carbon quantum dots have been successfully introduced into Mn-MOF.

[0017] Figure 5 Figures c and d are the infrared spectra of Mn-MOF and CD@Mn-MOF. Except for the difference at 3500 cm -1 , the other positions are basically the same. The materials and methods used to prepare carbon quantum dots in this invention are exactly the same as those used by the Gan Ziyu research group. In the papers of that research group, the infrared characterization of carbon quantum dots has been carried out. The results show that carbon quantum dots contain a large number of carboxyl and amino groups. Correspondingly, in the infrared spectrum of the composite material CD@Mn-MOF prepared in this invention, a stretching vibration peak of -NH appears at 3500 cm -1 again, further proving that carbon quantum dots have been successfully loaded into Mn-MOF. The peaks corresponding to other positions mainly include: the stretching vibration peak of the C-N bond between 1254 cm -1 and 1369 cm -1 ; the vibration peak of the benzene ring between 1510 cm -1 and 1624 cm -1 ; the peak between 2500 cm -1 and 3421 cm -1 is the stretching vibration peak of the -OH bond in the crystal water and coordinated water and the vibration peak of the carboxyl group.

[0018] Figure 6 Figure e is the X-ray photoelectron spectrum. The high-magnification scanning spectra of cobalt and manganese elements on the surface of the CD@Mn-MOF material were fitted and analyzed. The binding energies located at 653.34 eV and 641.75 eV correspond to the spin-orbit doublets of Mn2p 3 / 2 and Mn2p 1 / 2 respectively. Each peak is also split into two small peaks, corresponding to Mn 2+ and Mn 4+Two valence states. The peak with a binding energy of 646.66 eV corresponds to the satellite peak of Mn2p.

[0019] III. Applications of CD@Mn-MOF

[0020] H2O2 is an important molecule. It is not only used as a mediator in biological systems but also an oxidant in many fields such as food safety, environmental monitoring, and clinical applications. Therefore, the analysis and detection of H2O2 are very important. To study the electrochemical properties of Mn-MOF and CD@Mn-MOF, a glassy carbon bare electrode (GEC) was modified with them, and cyclic voltammetry curve tests were carried out.

[0021] The preparation process of the working electrode is as follows:

[0022] The three-electrode system was mainly used to test the electrochemical performance of the prepared materials. Among them, a platinum sheet was used as the counter electrode, a saturated calomel electrode was used as the reference electrode, and a glassy carbon electrode modified with the composite material was used as the working electrode (d = 3 mm). The modification of the working electrode was mainly divided into three steps;

[0023] a. The glassy carbon electrode was polished with three different specifications of alumina polishing powders, ultrasonically treated in ethanol and ultrapure water respectively, and air-dried naturally;

[0024] b. Weighed 4 mg of the composite material and dissolved it in 0.375 mL of water, then added 50 μL of a 5w% conductive binder (Nafion membrane solution) and 0.125 mL of ethanol solution, and ultrasonically dispersed for 1 h;

[0025] c. Pipetted 6 μL of the above solution and dropped it on the surface of the glassy carbon electrode, and air-dried naturally. During the coating process, it must be ensured that the composite material evenly covers the electrode surface without overflowing.

[0026] The electrochemical test method is as follows:

[0027] The electrochemical performance tests mainly include cyclic voltammetry tests and potentiostatic chronoamperometry tests.

[0028] a. Cyclic voltammetry test

[0029] The redox activity of the electrode material was studied through cyclic voltammetry curves, and the activity strengths of the composite materials with different carbon quantum dot contents were compared during the detection process. And the mechanism and control process of the electrochemical detection of hydrogen peroxide were analyzed by cyclic voltammetry test method to further determine the potential for the potentiostatic chronoamperometric detection of hydrogen peroxide;

[0030] b. Potentiostatic chronoamperometry test method

[0031] The main electrochemical parameters of the probe during the electrochemical detection, namely sensitivity, response time, detection limit, and detection range, were detected by the potentiostatic amperometry method. The operation method was to slowly stir a 0.1 M PBS buffer solution and successively add different amounts of hydrogen peroxide to it to obtain a stepped current response, and then obtain an i-t curve. Further fitting the i-c curve, the above main parameters were obtained from the i-t curve.

[0032] As Figure 7 Figure 1 shows the cyclic voltammograms of the GEC bare electrode, Mn-MOF modified electrode, and CD@Mn-MOF modified electrode in a 0.1 M PBS buffer solution with a scan rate of 0.1 v / s. As shown in the figure, after gradually adding hydrogen peroxide, within the potential range of -0.2 V to 0.9 V, there was no obvious current change for the glassy carbon bare electrode. However, for the Mn-MOF modified electrode, when the concentrations of hydrogen peroxide added were 5 mM, 8 mM, 13 mM, and 18 mM respectively, at the electrode potential of 0.8 V, the oxidation peak current increased significantly. That is, within the potential range of -0.2 V to 0.9 V, an irreversible oxidation-reduction process of hydrogen peroxide oxidation could be observed through a single peak passing through the electrode. The cyclic voltammogram records in the presence and absence of hydrogen peroxide showed that no obvious peak was found without hydrogen peroxide, while in the presence of hydrogen peroxide, a strong and obvious peak was obtained at 0.8 V, and the oxidation peak current gradually increased with the increase in the concentration of hydrogen peroxide. By comparing the cyclic voltammograms of the Mn-MOF and CD@Mn-MOFs modified electrodes, it could be observed that after adding the same concentration of hydrogen peroxide, the increase in the oxidation peak current of the cyclic voltammogram obtained by the composite material modified electrode was more significant, and the increase amount was significantly greater than that of Mn-MOF. Thus, it was preliminarily inferred that this composite material could be used to detect hydrogen peroxide in aqueous solution.

[0033] To determine the optimal composite amount of carbon quantum dots, CD 2μL @Mn-MOF, CD 4μL @Mn-MOF, CD 6μL @Mn-MOF composites with three different carbon quantum dot contents were prepared. The electrocatalytic activity of different samples for the reduction of H2O2 was evaluated by the typical cyclic voltammetry method. After preparing the electrodes from these three materials respectively, 10 μL of hydrogen peroxide with the same concentration (0.2 mol / L) was added to 20 ml of PBS (0.1 M) buffer solution, and the corresponding current magnitudes were recorded respectively. The experimental results are as Figure 8 shown. When the addition amount of carbon quantum dots was 4 μL, the corresponding oxidation peak current intensity was the largest. However, when the content of carbon quantum dots was further increased, the oxidation peak current decreased instead. This might be due to the aggregation of carbon quantum dots leading to a decrease in the electron transfer rate. It indicated that when preparing the composite material, the optimal addition amount of carbon quantum was 4 μL.

[0034] Subsequently, cyclic voltammetry was used to study the effect of different pH values of PBS (0.1 M) buffer solution (pH range from 4 to 10) on the oxidation peak current of H2O2 at the CD 4μL @Mn-MOF electrode. As Figure 9 shown, the oxidation peak current intensity increased with the increase of pH from 4 to 9. When pH > 9, the current decreased significantly, indicating that the optimal pH condition for CD 4μL @Mn-MOF to detect hydrogen peroxide is 9. Therefore, PBS buffer solution with pH 9 was selected for subsequent experiments.

[0035] To further explore the kinetic mechanism of electrocatalytic recognition and oxidation of hydrogen peroxide by the CD 4μL @Mn-MOF modified electrode, cyclic voltammograms of the CD 4μL @Mn-MOF modified electrode were analyzed at different scanning rates in a hydrogen peroxide electrolyte solution with a concentration of 5 mM (pH = 9). The results are as Figure 10 shown in a. It can be seen that a pair of redox peaks appeared in the potential range of -0.2 - 0.9 V, and with the increase of the scanning rate, the peak current increased correspondingly. As Figure 10 shown in b, the oxidation peak current was linearly fitted with the square root of the scanning rate (V 1 / 2 ), and it can be seen that the oxidation peak current intensity has a linear relationship with the square root of the scanning rate, indicating that the redox reaction of hydrogen peroxide on the surface of the working electrode modified with CD 4μL @Mn-MOF is a diffusion-controlled process, and diffusion control is beneficial to the quantitative detection and analysis of hydrogen peroxide.

[0036] In cyclic voltammetry, the electrochemical behavior of hydrogen peroxide indicates that the Mn 4+ and Mn 2+ redox couple participates in the oxidation of hydrogen peroxide. The network structure of two-dimensional MOF helps electron transfer, and the incorporation of carbon quantum dots helps to improve the electron transfer rate. Mn 4+ can act as an electron transfer medium, and the electrochemical oxidation of hydrogen peroxide in the presence of the oxide Mn 4+ causes a large current response in alkaline medium. In addition, during the electrochemical reaction process, Mn 2+ may be converted to Mn 4+ . At the same time, hydrogen peroxide is further oxidized to oxygen and water, and Mn 4+ is reduced. Therefore, CD 4μL @Mn-MOF can be in the redox couple (Mn 4+ / Mn 2+Under the support of transformation, it promotes the maximum electrocatalytic activity for the oxidation of hydrogen peroxide under alkaline conditions. This excellent performance is achieved by the synergistic effect of the large porosity, large surface area, and excellent electron transfer network structure of the material.

[0037] In addition to general sensing parameters, anti-interference performance is another important factor for evaluating sensing materials. Electrochemically active carbon quantum dots are combined with Mn-MOF, and the prepared CD 4μL @Mn-MOF shows good anti-interference performance. As Figure 11 shown for the current response of CD 4μL @Mn-MOF to other different analytes. First, H2O2 was added to a PBS (0.1 M) buffer solution with pH = 9. To further demonstrate the excellent selectivity of the prepared CD 4μL @Mn-MOF, other physiological substances with a concentration of 0.2 M (such as glucose, proline, ascorbic acid, sodium chloride, calcium chloride) were successively added to the buffer solution as interfering substances, and the corresponding current intensity values were recorded to study the anti-interference performance of the sensor. The results showed that the successive addition of interfering substances did not have any effect on the oxidation peak current, which proved that CD 4μL @Mn-MOF material has excellent anti-interference performance in recognizing hydrogen peroxide.

[0038] At an applied potential of 0.8 V (because it can be seen from the cyclic voltammetry curve that the strongest current response is shown at this voltage with different concentrations of hydrogen peroxide added), as Figure 12 shown in a, when different concentrations of hydrogen peroxide were added dropwise to a 0.1 M PBS (pH = 9) buffer solution and stirred continuously, a stable current response appeared, and the stable current appeared about 13 s after the addition of hydrogen peroxide. This phenomenon indicates that the time required for hydrogen peroxide to transfer from the electrolyte to the electrocatalytic site is very short. It also shows that CD 4μL @Mn-MOF has good timeliness in the detection of hydrogen peroxide. At the same time, the calibration curve of the oxidation current varying with the H2O2 concentration is as Figure 12 shown in b. The results show that both Mn-MOF and CD 4μL @Mn-MOF have a linear range of 0.1 to 1.6 mM. The H2O2 concentration and the corresponding current values show a good linear relationship because the regression equations are I = 1.946×10 -4 C + 1.226×10 -6 and I = 0.001C + 1.043×10 -6 respectively, both with relatively high linear correlation coefficients (0.99361 and 0.99185). The detection limit (LOD) calculation formula is as follows:

[0039] I = 1 + b [M]

[0040] LOD=k×SB / b

[0041] wherein, SB is the blank standard deviation, b is the sensitivity of the method (determined as the slope of the calibration curve), k is a statistical constant (a widely accepted value is 3).

[0042] The calculated LOD (Mn-MOF) = 75.4 μM, LOD (CD 4μL @Mn-MOF) = 14.7 μM. It can be seen that the addition of carbon quantum dots increases the lowest detection limit of Mn-MOF by about 5 times. b CD4μL@Mn-MOF > b Mn-MOF , that is, the sensitivity of the composite material is higher than that of the single Mn-MOF material. Thus, it can be proved that the composite of carbon quantum dots and MOF is an effective method to improve the performance of MOF.

[0043] The reversibility of the sensor is an important factor in practical applications. The reversibility of the CD 4μL @Mn-MOF electrode was studied by cyclic voltammetry. The cyclic voltammogram of 1 mM H2O2 at a scan rate of 0.1 V s −1 in the presence of 0.1 M PBS (pH = 9) showed a distinct oxidation peak in the range of -0.2 to 0.9 V ( Figure 13 a), and this peak remained after reverse scanning (30 cycles at the same scan rate), indicating good reversibility of the electrode process. In addition, the stability of CD 4μL @Mn-MOF for the determination of 5 mM H2O2 over seven days was measured. The prepared CD 4μL @Mn-MOF electrode material solution was coated on the surface of the glassy carbon electrode every 24 hours, and the current response of a 5 mM hydrogen peroxide solution was measured. The obtained results are as Figure 13 shown in b. The current response of the working electrode to hydrogen peroxide remained relatively stable within 7 days. By the last day, the current intensity could reach 90.8% of the initial current value, proving that CD 4μL @Mn-MOF has a certain stability as an electrode material.

[0044] In summary, a two-dimensional structured Mn-MOF was synthesized in this invention, and the composite material CD@Mn-MOF was prepared by a one-pot method. The material was characterized by means such as electron microscopy scanning, PXRD, thermogravimetric analysis, XPS, cyclic voltammetry, and EIS. Experiments have proved that the CD@Mn-MOF composite material can detect hydrogen peroxide in aqueous solution, and there is a good linear relationship between the concentration of H2O2 and the current value, enabling quantitative detection of hydrogen peroxide, and having good anti-interference performance, sensitivity, stability, and reversibility. Combining carbon quantum dots with MOF is a good method to improve the performance of MOF materials. The lowest detection limit for H2O2 reached 14.7 μM, which is about 5 times higher than that of Mn-MOF. Description of the Drawings

[0045] Figure 1 is the crystal structure of Mn-MOF: a) the smallest asymmetric unit of Mn-MOF; b) the seven-coordinate octahedral structure of the central metal Tb; c) the two-dimensional structure of Tb-MOF; d) the topology diagram of Mn-MOF (hydrogen atoms have been omitted, blue lines are 1,3,5-triimidazolylbenzene);

[0046] Figure 2 are the SEM and EDS of Mn-MOF;

[0047] Figure 3 a) PXRD patterns of Mn-MOF and the composite material CD@Mn-MOF; b) stability test of CD@Mn-MOF at different pH values; c) thermogravimetric curve of CD@Mn-MOF

[0048] Figure 4 a) CV characterization diagrams of Mn-MOF and the composite material CD@Mn-MOF; b) impedance characterization diagrams of Mn-MOF and the composite material CD@Mn-MOF;

[0049] Figure 5 are the infrared spectra of Mn-MOF and CD@Mn-MOF;

[0050] Figure 6 a) XPS full-spectrum analysis of CD@Mn-MOF; b) high-resolution spectrum analysis of Mn2p of the CD@Mn-MOF material

[0051] Figure 7 a) Influence of hydrogen peroxide with different concentrations on the CV curve of the bare electrode; b) Influence of hydrogen peroxide with different concentrations on the CV curve of Mn-MOF; c) Influence of hydrogen peroxide with different concentrations on the CV curve of the composite material CD@Mn-MOF;

[0052] Figure 8CV curves obtained with different doping amounts of carbon quantum dots;

[0053] Figure 9 Cyclic voltammograms of the CD4μL@Mn-MOF modified electrode in 0.1 M PBS buffer solution (with 5 mM hydrogen peroxide added) at different pH values;

[0054] Figure 10 a) CD 4μL Cyclic voltammograms of the @Mn-MOF modified electrode under different scan rate conditions (0.1 M PBS buffer solution with 5 mM hydrogen peroxide added); b) Relationship curve between oxidation peak current and square root of scan rate

[0055] Figure 11 Amperometric responses of the CD4μL @Mn-MOF modified electrode after sequentially adding hydrogen peroxide, proline, glucose, ascorbic acid, sodium chloride, sodium perchlorate, calcium chloride, and hydrogen peroxide to 0.1 M PBS buffer solution

[0056] Figure 12 a) Amperometric responses of the Mn-MOF and CD4μL @Mn-MOF modified electrodes after gradually adding hydrogen peroxide to 0.1 M PBS (pH = 9) buffer solution (the inset is a partial enlarged view from 800 - 1600 s); b) Linear fitting curve between hydrogen peroxide concentration and current intensity

[0057] Figure 13 a) CD 4μL @Mn-MOF CV cyclic curve; b) Histogram of current responses (0.8 V) of the composite material within 7 days Specific implementation manners

[0058] The following specifically describes the specific implementation manners of the present invention in combination with specific embodiments.

[0059] The drugs and instruments used in the present invention are as follows:

[0060] 1,3,5-triimidazolylbenzene, terephthalic acid, manganese acetate, sodium chloride, potassium ferricyanide, and potassium chloride were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Urea and ethylenediamine were purchased from Energy Chemical Co., Ltd. Ethanol and other reagents were all of analytical reagent grade and provided by local commercial suppliers. The chemical reagents purchased in this experiment were directly used without further purification and separation.

[0061] Rigaku-Oxford Supernova CCD diffractometer for single crystal diffraction. Hitachi (Japan) F-7000 fluorescence spectrophotometer was used to record fluorescence spectra; DHG-9036A electrothermal constant temperature forced air drying oven from Shanghai Jinghong Experimental Equipment Co., Ltd.; AK-060SD ultrasonic cleaner from Shenzhen Jieqing Cleaning Equipment Co., Ltd.; CHI760E electrochemical workstation from Shanghai Chenhua; UV-3900 ultraviolet spectrophotometer from Hitachi, Japan.

[0062] Example 1 Preparation of CD@Mn-MOF

[0063] (1) Preparation of carbon quantum dots

[0064] Carbon quantum dots were prepared according to the method reported in previous literature. 1 mmol of urea and 3 mmol of ethylenediamine were dissolved in 10 ml of deionized water, completely dissolved after ultrasonic treatment for 5 min, placed in a sealed 23.0 mL Teflon-lined autoclave, and placed in a constant temperature drying oven at 140 °C for 6 h and then naturally cooled to room temperature to obtain a brown-yellow carbon quantum dot solution.

[0065] (2) Preparation of CD@Mn-MOF

[0066] 1,3,5-Triimidazolylbenzene (4.9 mg, 0.02 mmol), terephthalic acid (3.3 mg, 0.02 mmol), and manganese acetate (3.58 mg, 0.02 mmol) were dissolved in a mixed solvent of 1.0 ml of ethanol and 9.0 mL of distilled water. 4 μL, 6 μL, and 8 μL of the carbon quantum dot solution prepared in step (2) were added respectively, completely dissolved after ultrasonic treatment for 5 min, placed in a sealed 23.0 mL Teflon-lined autoclave, heated to 140 °C in a constant temperature drying oven, and then slowly cooled to room temperature within 72 hours. After washing with water in small amounts and multiple times and then filtering, colorless block crystals with different carbon quantum dot contents, namely Mn-MOF, CD 4μL @Mn-MOF, CD 6μL @Mn-MOF, CD 8μL @Mn-MOF.

[0067] Preparation of Mn-MOF

[0068] The Mn-MOF was synthesized by the solvothermal method. Exactly weigh 1,3,5-tris(imidazol-1-yl)benzene (4.9 mg, 0.02 mmol), terephthalic acid (4.1 mg, 0.02 mmol), and manganese acetate (3.58 mg, 0.02 mmol) with an analytical balance and dissolve them in a mixed solvent of 1.0 mL of methanol and 5.0 mL of distilled water. Ultrasonic for 5 min, then put it into a sealed 23.0 mL Teflon-lined autoclave and place it in a constant-temperature drying oven and heat it to 140 °C, and then slowly cool it to room temperature within 72 hours. After washing with water in small amounts and multiple times, filter to obtain colorless block crystals, namely Mn-MOF.

[0069] Example 2 Preparation of Composite Material Modified Electrode and Detection of Hydrogen Peroxide

[0070] (1)Preparation of Composite Material Modified Electrode

[0071] a. Polish the glassy carbon electrode with three different specifications of alumina polishing powders, place it in ethanol and ultrapure water for ultrasonic treatment respectively, and air-dry it naturally in the air;

[0072] b. Weigh 4 mg of the composite material and dissolve and disperse it in 0.375 mL of water, then add 50 μL of a 5w% conductive adhesive (Nafion membrane solution) and 0.125 mL of ethanol solution, and ultrasonic disperse for 1 h;

[0073] c. Pipette 6 μL of the above solution and drop-coat it on the surface of the glassy carbon electrode, and air-dry it naturally. During the coating process, it must be ensured that the composite material evenly covers the electrode surface and does not overflow.

[0074] (2)Detection of Hydrogen Peroxide

[0075] Using a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, and the composite material modified electrode as the working electrode, and 0.1 M PBS buffer solution with a pH of 9 as the electrolyte. Add the H2O2 solution to the PBS buffer solution and detect it by the constant potential chronoamperometry method at a potential of 0.8 V to obtain the current value. Utilize the linear relationship between the H2O2 concentration and the current value to quantitatively detect the concentration of H2O2; the linear relationship between the hydrogen peroxide concentration and the current value is as follows:

[0076] In the linear range of hydrogen peroxide concentration from 0.1 mM to 1.6 mM, the H2O2 concentration and the corresponding current value show a good linear relationship. The linear relationship is I = 0.001C + 1.043×10 -6 , R 2 = 0.99185, and the detection limit is 14.7 μM; I is the current value, with the unit of mA, and C is the H2O2 concentration, with the unit of mM.

Claims

1. A method for detecting hydrogen peroxide using a CD@Mn-MOF composite material modified electrode, comprising the following steps: (1)Preparation of CD@Mn-MOF 1,3,5-triimidazolylbenzene, terephthalic acid, and manganese acetate were dissolved in a mixed solvent of ethanol and distilled water. The carbon quantum dot solution was added, and after ultrasonic treatment, it was completely dissolved. Then it was heated to 130 - 150 °C and slowly cooled to room temperature within 48 - 72 h. After washing and filtration, the CD@Mn-MOF composite material was obtained; (2)Preparation of the composite material modified electrode The CD@Mn-MOF composite material was dispersed in water, and then the conductive binder Nafion membrane solution and ethanol solution were added for ultrasonic dispersion. The dispersed solution was taken and drop-coated on the surface of the polished glassy carbon electrode, and it was naturally dried in air to obtain the composite material modified electrode; (3)Detection of hydrogen peroxide Using a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, the composite material modified electrode as the working electrode, and a PBS buffer solution with a pH of 9 as the electrolyte. The H2O2 solution was added to the PBS buffer solution, and at a fixed potential of 0.8 V, it was detected by the constant potential chronoamperometry method to obtain the current value. Using the linear relationship between the H2O2 concentration and the current value, the concentration of H2O2 was quantitatively detected; The linear relationship between the hydrogen peroxide concentration and the current value is as follows: In the linear range of hydrogen peroxide concentration from 0.1 mM to 1.6 mM, the H2O2 concentration and the corresponding current value show a good linear relationship, and the linear relationship is I = 0.001C + 1.043×10 -6 , R 2 = 0.99185; I is the current value in mA, and C is the H2O2 concentration in mM.

2. The method for detecting hydrogen peroxide using the CD@Mn-MOF composite material modified electrode according to claim 1, wherein: In step (1), the molar ratio of 1,3,5-triimidazolylbenzene, terephthalic acid, and manganese acetate is 1:1:1 - 1:3:

3.

3. The method for detecting hydrogen peroxide using the CD@Mn-MOF composite material modified electrode according to claim 1, wherein: In step (1), the preparation method of the carbon quantum dot solution is as follows: 1 mmol of urea and 3 mmol of ethylenediamine were dissolved in 10 ml of deionized water. After ultrasonic treatment for 5 min, it was completely dissolved, placed in a sealed 23.0 mL Teflon-lined autoclave, and placed in a constant temperature drying oven at 140 °C for 6 h and then naturally cooled to room temperature to obtain the carbon quantum dot solution; The mass-volume ratio of manganese acetate to the carbon quantum dot solution is 0.2 - 1 mg / μL.

4. The method for detecting hydrogen peroxide using the CD@Mn-MOF composite material modified electrode according to claim 1, wherein: The concentration of the PBS described in step (3) is 0.1 M.

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