MnO2 (at) SiO2 (at) CTS modified electrode, preparation method and application

Abstract

The invention discloses a MnO2 (at) SiO2 (at) CTS modified electrode, a preparation method and application, and the preparation method comprises the following steps: step 1, under the ultrasonic action, dropwise adding a potassium permanganate solution into a manganese sulfate solution, and carrying out a hydrothermal reaction to obtain MnO2 nanorods; step 2, coating the surface of the MnO2 nanorod with SiO2 through an in-situ reaction, so as to obtain MnO2 coated SiO2 with a core-shell structure; 3, MnO2 (at) SiO2 and chitosan are fully and evenly mixed under the ultrasonic action, and a MnO2 (at) SiO2 (at) CTS composite material is obtained; and 4, dispensing the MnO2 (at) SiO2 (at) CTS composite material on the surface of the activated glassy carbon electrode, and refrigerating to obtain the required modified electrode. The sensor prepared from the modified electrode has a wide linear range and has good anti-interference performance and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural residue detection, and particularly to a MnO2@SiO2@CTS modified electrode, a preparation method and an application thereof. Background Art

[0002] Hydrogen peroxide (H2O2) is an inorganic strong oxidant. At room temperature, it is a light blue viscous liquid, easily soluble in water to form a colorless transparent solution (commonly known as hydrogen peroxide solution), and is widely used in food processing, medical sterilization and industrial fields. In the food industry, hydrogen peroxide is commonly used in the bleaching of livestock hooves and poultry claws, the cleaning of dairy product processing equipment, and the preservation of fruits and vegetables. However, its residue may enter the human body through animal-derived foods or environmental emissions. Long-term low-dose exposure may cause health risks such as digestive tract mucosal damage and cellular oxidative stress, and accelerate the generation of microbial drug resistance. Although the "National Food Safety Standard" in China clearly stipulates the residue limit of hydrogen peroxide in foods (for example, the detection limit is 1.6 mg / kg as specified in GB5009.226-2016), due to its low cost and significant effect, there are still some illegal abuse phenomena. In particular, the residue problems in bulk aquatic products, soy products and other fields are prominent, and highly sensitive detection methods are required for accurate monitoring.

[0003] For the detection of hydrogen peroxide residues, currently, mainly iodometry, titanium salt colorimetry and rapid colorimetry are used. Iodometry titrates the iodine released by the oxidation reaction with sodium thiosulfate, and can quantitatively detect the residue amount above 3 mg / kg, but the operation is cumbersome; titanium salt colorimetry uses the property that hydrogen peroxide reacts with titanium ions to form an orange complex, and is detected by spectrophotometry, with higher sensitivity (quantitative limit 1.6 mg / kg), suitable for trace analysis. In addition, the rapid detection method based on the color reaction principle of potassium iodide-starch (such as the colorimetry method in the disinfection verification of the purified water system) has the advantages of strong instantaneity and low cost, and can qualitatively judge the residue below 0.05%, but its stability is greatly affected by environmental factors. In contrast, electrochemical technology has received extensive attention due to its simple operation, fast analysis speed, low cost and high sensitivity. Summary of the Invention

[0004] The present invention provides a MnO2@SiO2@CTS modified electrode, a preparation method and an application thereof in view of the problems existing in the prior art.

[0005] The technical solution adopted by the present invention is: a preparation method of a MnO2@SiO2@CTS modified electrode, comprising the following steps:

[0006] Step 1: Under ultrasonic action, drop the potassium permanganate solution into the manganese sulfate solution, and perform a hydrothermal reaction to obtain MnO2 nanorods;

[0007] Step 2: Coating SiO2 on the surface of MnO2 nanorods through in-situ reaction to obtain core-shell structured MnO2@SiO2;

[0008] Step 3: Mixing the MnO2@SiO2 obtained in Step 2 and chitosan thoroughly under ultrasonic action to obtain MnO2@SiO2@CTS composite material;

[0009] Step 4: Drop-coating the MnO2@SiO2@CTS composite material obtained in Step 3 on the surface of the activated glassy carbon electrode, and refrigerating to obtain the required modified electrode.

[0010] Further, the hydrothermal reaction conditions in Step 1 are as follows:

[0011] The reaction temperature is 140 °C, and the reaction time is 12 h.

[0012] Further, the molar ratio of potassium permanganate to manganese sulfate in Step 1 is 2:3.

[0013] Further, the concentration of the potassium permanganate solution in Step 1 is 0.1 mol / L, the concentration of the manganese sulfate solution is 0.15 mol / L; the dropping rate is 0.5 mL / min.

[0014] Further, the preparation process of the core-shell structured MnO2@SiO2 in Step 2 is as follows:

[0015] Mixing the MnO2 nanorod suspension and cetyltrimethylammonium bromide solution thoroughly, and dropping tetraethyl orthosilicate; the SiO2 coating can be completed after sufficient reaction; the mass ratio of MnO2 nanorods to cetyltrimethylammonium bromide is 2:3.

[0016] Further, after the in-situ coating reaction is completed, centrifuge, disperse in a solvent, carry out condensation reflux, and dry to obtain the core-shell structured MnO2@SiO2.

[0017] Further, the dropping rate of tetraethyl orthosilicate is 0.2 mL / min.

[0018] A MnO2@SiO2@CTS modified electrode.

[0019] An application of a MnO2@SiO2@CTS modified electrode, and the modified electrode is used for preparing a sensor for detecting hydrogen peroxide.

[0020] Further, the modified electrode serves as a working electrode.

[0021] The beneficial effects of the present invention are:

[0022] The modified electrode obtained by the present invention is used as a sensor for detecting hydrogen peroxide at 0.3996×10-12 mol / L to 0.89597×10 -12 mol / L and 0.99443×10 -12 mol / L to 17.5507×10 -12 mol / L all have a relatively wide linear range, a detection limit of 3.69×10 -12 mol / L; and have good anti-interference and stability; the sensor obtained by the present invention has good performance, providing an idea for the detection of hydrogen peroxide in food. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 SEM image of the MnO2 nanorods obtained in Example 1 of the present invention.

[0024] Figure 2 SEM image of the MnO2@SiO2 obtained in Example 1 of the present invention.

[0025] Figure 3 XRD schematic diagram of the MnO2 nanorods and MnO2@SiO2 obtained in Example 1 of the present invention.

[0026] Figure 4 CV diagram of the sensor obtained in Example 1 of the present invention.

[0027] Figure 5 EIS diagram of the sensor obtained in Example 1 of the present invention.

[0028] Figure 6 CV diagrams of the sensors obtained in Example 1 of the present invention and the comparative example and after adding H2O2.

[0029] Figure 7 EIS diagrams of the sensors obtained in Example 1 of the present invention and the comparative example and after adding H2O2.

[0030] Figure 8 Linear diagram of the sensor obtained in Example 1 of the present invention for detecting hydrogen peroxide. a shows the results of 0.4 - 0.9 pM and 1 - 18 pM, b shows the results of 0.3996×10 -12 mol / L to 0.89597×10 -12 mol / L, and c shows the results of 0.99443×10 -12 mol / L to 17.5507×10 -12 mol / L. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described below with reference to the drawings and specific embodiments.

[0032] A preparation method of a MnO2@SiO2@CTS modified electrode, comprising the following steps:

[0033] Step 1: Under ultrasonic action, a potassium permanganate solution is dropped into a manganese sulfate solution, and a hydrothermal reaction is carried out to obtain MnO2 nanorods; the concentration of the potassium permanganate solution is 0.1 mol / L, the concentration of the manganese sulfate solution is 0.15 mol / L; the dropping rate is 0.5 mL / min. Dropping the potassium permanganate solution at this rate, combined with ultrasonic oscillation, synchronously eliminates the local concentration gradient to achieve the directional growth of MnO2 nanorods.

[0034] Step 2: Through an in-situ reaction, SiO2 is coated on the surface of the MnO2 nanorods to obtain a core-shell structured MnO2@SiO2; the MnO2 nanorod suspension is fully mixed with a cetyltrimethylammonium bromide solution, and tetraethyl orthosilicate is dropped; after sufficient reaction, the SiO2 coating can be completed; the mass ratio of the MnO2 nanorods to the cetyltrimethylammonium bromide is 2:3.

[0035] Step 3: Distilled water is added to the MnO2@SiO2 obtained in Step 2 and chitosan, and it is continuously vibrated for 30 min with an ultrasonic cleaner and fully mixed evenly to obtain a MnO2@SiO2@CTS composite material; the SiO2 shell surface is rich in hydroxyl groups (-OH) and may be negatively charged in the solution, and the amino group (-NH2) of chitosan is protonated to -NH3 + with a positive charge, and the negatively charged SiO2 and the positively charged CTS are combined through electrostatic attraction to form a stable complex. The hydroxyl group (-OH) and amino group (-NH2) of CTS can form hydrogen bonds with the hydroxyl group of SiO2 to further enhance the interfacial binding.

[0036] Step 4: The MnO2@SiO2@CTS composite material obtained in Step 3 is drop-coated on the surface of the activated glassy carbon electrode, and stored at 4 - 8 °C for about 4 h to form a uniform solid film, and the required modified electrode can be obtained.

[0037] The electrode activation process is as follows:

[0038] The glassy carbon electrode is polished with 0.02 μm alumina powder, the polished glassy carbon electrode is rinsed clean with deionized water, placed in deionized water for ultrasonic cleaning for 3 min, then placed in absolute ethanol for ultrasonic cleaning for 3 min, and then placed in deionized water for ultrasonic cleaning for 3 min.

[0039] The cleaned glassy carbon electrode is placed in a 0.5 M sulfuric acid solution, and the electrode is activated by cyclic voltammetry with a potential range of -0.6 to 1.0 V for 50 cycles.

[0040] After activation, it is rinsed clean with deionized water and placed in deionized water for standby.

[0041] The obtained modified electrode is used as the working electrode, and the specific detection process is as follows:

[0042] S1: Prepare a PBS buffer solution with pH = 7.00;

[0043] S2: Weigh a certain amount of hydrogen peroxide into a beaker, make up the volume to prepare a solution with a concentration of 10 mM, and use ultrapure water to perform gradient dilution to prepare the standard solution for detection;

[0044] S3: Weigh a certain amount of potassium ferricyanide and dissolve it in ultrapure water, make up the volume to prepare a 5 mM potassium ferricyanide solution;

[0045] S4: Use the PBS buffer solution with pH = 7.03 obtained in S1 and the potassium ferricyanide solution obtained in step 3 as the base solution, and perform detection using a three-electrode system, and set the working conditions; in the three-electrode system, the glassy carbon electrode modified with the manganese dioxide / silicon dioxide / chitosan composite material obtained in the present invention is used as the working electrode, the platinum wire electrode is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode.

[0046] S5: Pipette 9 mL of PBS (pH = 7) into the electrolytic cell, add 10 μL of hydrogen peroxide (0.01 M) and 1 mL of potassium ferricyanide solution (5 mM), and use cyclic voltammetry to optimize the material ratio of the modified electrode. The optimal ratio is MnO2@SiO2:CTS = 2:1;

[0047] S6: Pipette 9 mL of PBS into the electrolytic cell, add 10 μL of hydrogen peroxide (0.01 M) and 1 mL of potassium ferricyanide solution (5 mM), and use cyclic voltammetry to optimize the pH of PBS under the condition of the optimal material ratio. The best pH is 6.5;

[0048] S7: Pipette 9 mL of PBS (pH = 6.5) into the electrolytic cell, add 10 μL of hydrogen peroxide (0.01 M) and 1 mL of potassium ferricyanide solution (5 mM), and use cyclic voltammetry to characterize the electrochemical properties of the electrode modification process;

[0049] S8: Pipette 9 mL of PBS (pH = 6.5) into the electrolytic cell, add 1 mL of potassium ferricyanide solution (5 mM), and successively take the hydrogen peroxide standard solution (10-9 M and 10-8 M) starting from the lowest concentration. Take 1 μL each time for 10 times for each concentration and measure once and accumulate it into the base solution, and use DPV method to find the linearity.

[0050] Example 1

[0051] A preparation method of an MnO2@SiO2@CTS modified electrode includes the following steps:

[0052] Step 1: MnO2 nanorods

[0053] Dissolve 1.014 g of manganese sulfate monohydrate (MnSO4·H2O) in 40 mL of deionized water to form solution A;

[0054] Dissolve 0.632 g of potassium permanganate (KMnO4) in 40 mL of deionized water to form solution B;

[0055] Ultrasonically disperse solutions A and B (for 10 min), and slowly drip the KMnO4 solution into the MnSO4 solution at a rate of 0.5 mL / min. Combine ultrasonic oscillation to synchronously eliminate the local concentration gradient and achieve the directional growth of MnO2 nanorods;

[0056] Transfer the mixed solution to a 100 mL polytetrafluoroethylene-lined hydrothermal autoclave, react at 140 °C for 12 h, and after centrifugal washing and drying at 60 °C, obtain MnO2 nanorods.

[0057] The SEM image of the nanorods obtained in this example is as Figure 1 shown. It can be seen from the figure that the obtained MnO2 is a uniform nanorod-like structure, and this structure can greatly improve the electron transfer efficiency.

[0058] Step 2: Core-shell structured MnO2@SiO2

[0059] Disperse 0.2 g of MnO2 in 40 mL of deionized water and ultrasonically treat for 10 min to obtain suspension C;

[0060] Dissolve 0.3 g of cetyltrimethylammonium bromide (CTAB) in a mixed solvent containing 40 mL of distilled water, 120 mL of absolute ethanol, and 6 mL of 28 wt% ammonia water, and ultrasonically treat for 10 min to obtain solution D;

[0061] Mix C and D in a 250 mL three-necked flask, stir at a constant temperature of 35 °C, and dropwise add 6 mL of tetraethyl orthosilicate (TEOS) at a rate of 0.2 mL / min, then react for 12 h for in-situ coating reaction to complete the SiO2 coating under mild conditions;

[0062] After centrifugation, the product is dispersed in 100 mL of ethanol, and condensed and refluxed at 70 °C and 4000 rpm for 12 h (repeated twice), and dried at 60 °C for 12 h to obtain the core-shell structured MnO2@SiO2.

[0063] The SEM image of the MnO2@SiO2 obtained in this example is as Figure 2 shown. It can be seen from the figure that SiO2 is uniformly coated on the surface of MnO2 and MnO2@SiO2 is a uniformly distributed nanorod-like structure.

[0064] The XRD patterns of MnO2 nanorods and MnO2@SiO2 are as Figure 3As shown, it can be seen from the figure that the crystal form of the synthesized MnO₂ is α-MnO₂, which has a high specific surface area. The significantly large tunnel structure and nano-morphology are beneficial to the rapid diffusion of ions and reduce the charge transfer resistance.

[0065] Step 3: MnO₂@SiO₂@CTS composite material

[0066] Take 0.001 g of MnO₂@SiO₂ powder and add the MnO₂@SiO₂ powder to 0.0005 g of chitosan (CTS);

[0067] Add 0.5 mL of distilled water to the chitosan and MnO₂@SiO₂ mixture, and continuously vibrate it with an ultrasonic cleaner for 30 min to make the MnO₂@SiO₂ powder and chitosan mix evenly. After dispersion, the MnO₂@SiO₂@CTS composite material is obtained.

[0068] Step 4: Modified electrode

[0069] Take 3 μL of the MnO₂@SiO₂@CTS composite material prepared in Step 3 and drop-coat it on the surface of the activated glassy carbon electrode, and place it in a refrigerator at 4 - 8 °C for about 4 h to form a uniform solid film MnO₂@SiO₂ / CTS / GCE-2.

[0070] Use the modified electrode obtained above as the working electrode to prepare a hydrogen peroxide sensor. The preparation process is as described above. Add 9 mL of PBS (pH = 6.5) and 1 mL of a solution of K₃[Fe(CN)₆] with a concentration of 5 mM to the electrolytic cell, and measure the oxidation peak potential and reduction peak potential of the bare GCE and the GCE with MnO₂@SiO₂@CTS dropped on it by CV. The CV and EIS diagrams are as Figure 4 and Figure 5 shown. In the figure, bare GCE is the unmodified electrode.

[0071] It can be seen from the figure that the oxidation-reduction peak current of the electrode with MnO₂@SiO₂@CTS dropped on it is significantly enhanced; add 9 mL of PBS (pH = 6.5) and 1 mL of a solution of K₃[Fe(CN)₆] with a concentration of 5 mM to the electrolytic cell.

[0072] The resistance value of the electrode with MnO₂@SiO₂@CTS dropped on it is less than that of the bare GCE.

[0073] From Figure 4 and Figure 5 it can be seen that the conductivity of the modified electrode obtained in this example is stronger than that of the bare GCE, and MnO₂@SiO₂@CTS can enhance the electron transfer efficiency.

[0074] Comparative example

[0075] To illustrate the effects of the present invention, a comparative example was set up.

[0076] The preparation process of this comparative example was the same as that of Example 1, except that step 2 was not included, and the modified electrode obtained was MnO2 / CTS / GCE.

[0077] A hydrogen peroxide sensor was prepared using the modified electrode obtained from the above comparative example.

[0078] First, 9 mL of PBS (pH = 6.5) and 1 mL of a 5 mM K3[Fe(CN)6] solution were added to the electrolytic cell, and the CV tests of the bare GCE, MnO2@CTS@GCE, and MnO2@SiO2@CTS@GCE were carried out. Their CV and EIS diagrams are as Figure 6 and 7 shown.

[0079] The oxidation peak current value of MnO2@CTS@GCE was the highest, and the reduction peak current value of MnO2@SiO2@CTS@GCE was the highest. Then, a hydrogen peroxide solution was added to the electrolytic cell, and the CV tests of MnO2@CTS@GCE and MnO2@SiO2@CTS@GCE were carried out. It can be seen that the oxidation-reduction current decreased, indicating that MnO2@CTS@GCE and MnO2@SiO2@CTS@GCE had an obvious response to hydrogen peroxide. Due to the binding of the existing SiO2 and CTS to hydrogen peroxide, the response of the sensor to potassium ferricyanide decreased. And the current response change of MnO2@SiO2@CTS@GCE to hydrogen peroxide was the most obvious; 9 mL of PBS (pH = 6.5) and 1 mL of a 5 mM K3[Fe(CN)6] solution were added to the electrolytic cell, and the charge transfer resistance of the bare GCE, MnO2@CTS@GCE, and MnO2@SiO2@CTS@GCE was measured by EIS. The resistance value of MnO2@SiO2@CTS@GCE was the smallest, indicating the strongest electron transfer efficiency. Then, a hydrogen peroxide solution was added to the electrolytic cell, and it could be observed that the resistance values of the MnO2@CTS@GCE and MnO2@SiO2@CTS@GCE sensors increased. The addition of H2O2 might slightly change the ionic strength or dielectric constant of the electrolyte, thereby increasing the solution resistance value. Both methods could prove that the sensor had good electro-sensing performance.

[0080] 9 mL of PBS (pH = 6.5) and 1 mL of a 5 mM K3[Fe(CN)6] solution were pipetted, and hydrogen peroxide standard solutions (10 -9 mol / L and 10 -8 mol / L) were taken in sequence starting from the lowest concentration. 1 μL of each concentration was taken 10 times in sequence and measured once each time and accumulated into the bottom solution, and the oxidation peak current was detected by DPV method. The results are as Figure 8 shown.

[0081] Figure 8 As can be seen from a, there is a good linear relationship between the oxidation peak current and its concentration at 0.4 - 0.9 pM and 1 - 18 pM. Figure 8 As can be seen from b, the concentration is in the range of 0.3996×10 -12 mol / L to 0.89597×10 -12 mol / L, the linear regression equation is y = -0.26598x + 1.48354, and the correlation coefficient is R 2 = 0.99116. Figure 8 As can be seen from c, the concentration is in the range of 0.99443×10 - 12 mol / L to 17.5507×10 -12 mol / L, the linear regression equation is y = -0.00656x + 1.25237, and the correlation coefficient is R 2 = 0.99221. In the low concentration range, the lowest concentration detection limit is 3.69×10 -12 mol / L.

[0082] The silica-coated manganese dioxide (MnO2@SiO2) particles with core-shell nanostructure synthesized in this invention and chitosan are used to construct a nano-composite electrode. The MnO2@SiO2 core-shell nano-material with high active sites combines with CTS. The negatively charged SiO2 and the positively charged CTS are combined through electrostatic attraction to form a stable complex. The amino and hydroxyl groups of CTS can provide adsorption sites for H2O2, and cooperate with the catalytic activity of MnO2 to improve the sensor sensitivity. The constructed sensor has a wide linear range for hydrogen peroxide detection at 0.3996×10 -12 mol / L to 0.89597×10 -12 mol / L and 0.99443×10 -12 mol / L to 17.5507×10 -12 mol / L, and the detection limit is 3.69×10 -12 mol / L. The sensor has good anti-interference performance (the current change in the presence of L-histidine < 2%), reproducibility (RSD = 2.87%) and stability, and has been successfully applied to tripe samples, with the spiked recovery rate between 92% and 102%. In summary, the obtained sensor has good performance, provides an idea for the detection of hydrogen peroxide in food, and also provides a new idea for the detection of hydrogen peroxide in living cells.

Claims

1. A preparation method of a MnO2@SiO2@CTS modified electrode, characterized in that, It includes the following steps: Step 1: Under the action of ultrasound, potassium permanganate solution is dropped into manganese sulfate solution, and hydrothermal reaction is carried out to obtain MnO2 nanorods; Step 2: Through in-situ reaction, SiO2 is coated on the surface of MnO2 nanorods to obtain MnO2@SiO2 with a core-shell structure; Step 3: The MnO2@SiO2 obtained in Step 2 and chitosan are fully mixed evenly under the action of ultrasound to obtain MnO2@SiO2@CTS composite material; Step 4: The MnO2@SiO2@CTS composite material obtained in Step 3 is drop-coated on the surface of the activated glassy carbon electrode, and the required modified electrode can be obtained after refrigeration.

2. The preparation method of a MnO2@SiO2@CTS modified electrode according to claim 1, characterized in that, The hydrothermal reaction conditions in Step 1 are as follows: The reaction temperature is 140 °C, and the reaction time is 12 h.

3. The preparation method of a MnO2@SiO2@CTS modified electrode according to claim 1, characterized in that, The molar ratio of potassium permanganate to manganese sulfate in Step 1 is 2:

3.

4. The preparation method of a MnO2@SiO2@CTS modified electrode according to claim 1, characterized in that, The concentration of potassium permanganate solution in Step 1 is 0.1 mol / L, the concentration of manganese sulfate solution is 0.15 mol / L; the dropping rate is 0.5 mL / min.

5. The preparation method of a MnO2@SiO2@CTS modified electrode according to claim 1, characterized in that, The preparation process of MnO2@SiO2 with a core-shell structure in Step 2 is as follows: The MnO2 nanorod suspension is fully mixed with cetyltrimethylammonium bromide solution, and tetraethyl orthosilicate is dropped; the SiO2 coating can be completed after sufficient reaction; the mass ratio of MnO2 nanorods to cetyltrimethylammonium bromide is 2:

3.

6. The preparation method of a MnO2@SiO2@CTS modified electrode according to claim 5, characterized in that, After the in-situ coating reaction is completed, it is centrifuged, dispersed in a solvent, condensed and refluxed, and dried to obtain MnO2@SiO2 with a core-shell structure.

7. The preparation method of a MnO2@SiO2@CTS modified electrode according to claim 5, characterized in that, The dropping rate of tetraethyl orthosilicate is 0.2 mL / min.

8. The preparation method of the MnO2@SiO2@CTS modified electrode obtained by using the preparation method according to any one of claims 1 to 7.

9. The application of a MnO2@SiO2@CTS modified electrode according to claim 8, characterized in that, The modified electrode is used for preparing a sensor for detecting hydrogen peroxide.

10. Application of a MnO2@SiO2@CTS modified electrode according to claim 9, characterized in that, The modified electrode serves as a working electrode.

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