A waste coffee fruit shell derived manganese-doped porous carbon nanomaterial, a preparation method and application thereof

Abstract

This invention provides a manganese-doped porous carbon nanomaterial derived from waste coffee husks, its preparation method, and its application, belonging to the field of electrochemical sensor technology. The preparation method of this manganese-doped porous carbon nanomaterial includes the following steps: mixing biomass raw materials with water uniformly, adding a manganese source and a zinc source, carrying out an adsorption reaction, and then collecting the solid product; carbonizing the solid product to obtain the manganese-doped porous carbon nanomaterial. When used as an electrode modification material for electrochemical sensors, the manganese-doped porous carbon nanomaterial provided by this invention exhibits extremely high sensitivity and a wide detection range, enabling accurate and rapid detection of salicylic acid content in plants.

Description

Technical Field

[0001] This invention relates to the field of electrochemical sensor technology, and in particular to a manganese-doped porous carbon nanomaterial derived from waste coffee shells, its preparation method, and its application. Background Technology

[0002] Salicylic acid (SA) is a class of small-molecule phenolic compounds with various physiological functions in plants, including regulating plant growth and enhancing plant stress and disease resistance. SA can induce resistance in various plants to pests, viruses, fungi, and bacterial diseases (such as spider mites and Fusarium wilt pathogens that cause avocado root rot). The dynamic concentration of SA can reflect the activation status of the plant's immune system in real time, providing a biomarker for early warning of pests and diseases. Studies have shown that exogenous SA treatment can significantly improve the resistance of avocados to pests and diseases. Therefore, accurate, rapid, portable, and low-cost detection methods for monitoring SA levels in plants play a crucial role in determining whether plants are affected by pests and diseases.

[0003] Existing techniques for detecting SA have significant limitations: (1) While mass spectrometry / high-performance liquid chromatography (HPLC) is widely used and highly sensitive, it has a high detection limit and relies on large instruments. Sample pretreatment is complex and requires professional personnel, resulting in high personnel training and detection costs. (2) Fluorescence / colorimetric methods are easily affected by factors such as sample turbidity, color, and chlorophyll, resulting in a large detection limit that cannot meet detection requirements. (3) Traditional electrochemical sensor detection methods are limited by a finite temperature range, low catalytic activity of materials, and limited specific surface area, resulting in a high detection limit. Summary of the Invention

[0004] In view of this, the present invention aims to provide a manganese-doped porous carbon nanomaterial (PC-Mn) derived from waste coffee husks, its preparation method, and its applications. When used as an electrode modification material for electrochemical sensors, the PC-Mn provided by this invention exhibits extremely high sensitivity and a wide detection range, enabling accurate and rapid detection of SA content in plants.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of this invention is a method for preparing manganese-doped porous carbon nanomaterials, comprising the following steps:

[0007] After the biomass raw material is mixed evenly with water, manganese source and zinc source are added to carry out the adsorption reaction, and then the solid product is collected.

[0008] The solid product is carbonized to obtain the manganese-doped porous carbon nanomaterial.

[0009] In a preferred embodiment of the present invention, the biomass raw material is coffee fruit shells; before the biomass raw material is mixed evenly with water, the method further includes the steps of crushing and sieving the biomass raw material.

[0010] In a preferred embodiment of the present invention, the manganese source is manganese acetate tetrahydrate; the zinc source is zinc nitrate hexahydrate; and the ratio of manganese in the biomass raw material, manganese source, and zinc in the zinc source is 80g:10-40mmol:40mmol.

[0011] Specifically, the ratio of manganese in the biomass raw material, manganese in the manganese source, and zinc in the zinc source is 80g:10mmol:40mmol, 80g:20mmol:40mmol, 80g:30mmol:40mmol, or 80g:40mmol:40mmol.

[0012] In a preferred embodiment of the present invention, the adsorption reaction is specifically performed as follows: stirring at room temperature first, followed by sealing and aging at room temperature; the stirring time at room temperature is preferably 1 hour, and the aging time is preferably 12 hours.

[0013] In a preferred embodiment of the present invention, the carbonization temperature is 700–1000°C, the time is 0.5–2 hours, and the heating rate is 2–5°C / min. -1 An inert atmosphere.

[0014] Specifically, the carbonization temperature is 700℃, 800℃, 900℃, or 1000℃, the time is 0.5h, 1h, 1.5h, or 2h, and the heating rate is 2℃ / min. -1 3℃min -1 4℃min -1 or 5℃min -1 .

[0015] In this invention, the parameters of the carbonization reaction affect the catalytic performance of the final material. Low temperature and short time will affect the degree of graphitization and conductivity. Too fast a heating rate or too high a temperature will cause structural collapse, reduced porosity, reduced exposure of catalytic active centers, and thus reduced catalytic activity.

[0016] The second technical solution of the present invention is a manganese-doped porous carbon nanomaterial prepared by the above preparation method.

[0017] The third technical solution of the present invention is an electrochemical sensor in which the electrode modification material of the working electrode is the aforementioned manganese-doped porous carbon nanomaterial.

[0018] In a preferred embodiment of the present invention, the working electrode is prepared by: mixing the above-mentioned manganese-doped porous carbon nanomaterial with water to obtain a suspension; coating the suspension onto the electrode surface, drying it, and then coating it with Nafion ethanol solution to obtain the working electrode.

[0019] In a preferred embodiment of the present invention, the mass-to-volume ratio of the manganese-doped porous carbon nanomaterial to water is 0.5-2 mg:1 mL; and the amount of the suspension is 5-9 μL.

[0020] Specifically, the mass-to-volume ratio of the manganese-doped porous carbon nanomaterial to water is 0.5 mg:1 mL, 1 mg:1 mL, 1.5 mg:1 mL, or 2 mg:1 mL; the volume of the suspension is 5 μL, 6 μL, 7 μL, 8 μL, or 9 μL.

[0021] In a preferred embodiment of the present invention, the electrode is a screen-printed electrode (SPE) with a diameter of 4 mm; the concentration of the Nafion ethanol solution is 0.5 wt%.

[0022] The fourth technical solution of the present invention is the application of the above-mentioned manganese-doped porous carbon nanomaterial or the above-mentioned electrochemical sensor in the detection of salicylic acid.

[0023] The present invention discloses the following technical effects:

[0024] The manganese-doped porous carbon nanomaterial of the present invention uses waste coffee husks as a carbon source and also as a nitrogen source. It is inexpensive and readily available, realizing the utilization of coffee husk biomass resources.

[0025] The electrochemical sensor of the present invention utilizes Mn 3+ / Mn 2+ The redox center catalyzes the SA reaction, exhibiting a wide linear range (16.67 nmol / L–250 μmol / L) and strong anti-interference ability in pH 7.0 PBS, with a low detection limit (16.67 nmol / L). Practical application revealed that the SA content in leaves infested with spider mites (96.82 μmol / L) was 122 times higher than that in healthy leaves (0.79 μmol / L), confirming the reliability of SA as an early biomarker of pest stress and providing new technological support for green early warning of avocado diseases and the resource utilization of agricultural waste. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 X-ray diffraction (XRD) patterns of the different materials prepared in Examples 1-4;

[0028] Figure 2 The images show the Raman spectra of the different materials prepared in Examples 1-4.

[0029] Figure 3 The image shows a scanning electron microscope (SEM) image of PC-Mn20 prepared in Example 1.

[0030] Figure 4 Elemental mapping of PC-Mn20 prepared in Example 1;

[0031] Figure 5 The X-ray photoelectron spectroscopy (XPS) full spectra of the different materials prepared in Examples 1, 3, and 4 are shown.

[0032] Figure 6 High-resolution XPS images of C1s elements in different materials prepared in Examples 1, 3, and 4;

[0033] Figure 7 High-resolution XPS images of Mn 2p elements in different materials prepared in Examples 1, 3, and 4;

[0034] Figure 8 High-resolution XPS images of N1s elements in different materials prepared in Examples 1, 3, and 4;

[0035] Figure 9 The N2 adsorption-desorption isotherm of PC-Mn0 prepared in Example 2;

[0036] Figure 10 The pore size distribution diagram of PC-MnO prepared in Example 2;

[0037] Figure 11 The N2 adsorption-desorption isotherm of PC-Mn10 prepared in Example 3;

[0038] Figure 12 The pore size distribution diagram of PC-Mn10 prepared in Example 3;

[0039] Figure 13 The N2 adsorption-desorption isotherm of PC-Mn20 prepared in Example 1;

[0040] Figure 14 The pore size distribution diagram of PC-Mn20 prepared in Example 1;

[0041] Figure 15 The N2 adsorption-desorption isotherm of PC-Mn40 prepared in Example 4;

[0042] Figure 16 The pore size distribution diagram of PC-Mn40 prepared in Example 4;

[0043] Figure 17 This is a superimposed graph of cyclic voltammetry (CV) curves for detecting 250 μmmol / L SA using different modified electrodes prepared in Examples 1-4;

[0044] Figure 18 Electrochemical impedance spectroscopy (EIS) spectra of the different modified electrodes prepared in Examples 1-4;

[0045] Figure 19 The graphs show the relationship between current density and scan rate for electrodes modified with different materials prepared in Examples 1-4;

[0046] Figure 20 The left image shows the CV curves (left) and the right image shows the SA oxidation peak current versus PC-Mn20 concentration (right) of the Nafion / PC-Mn20 modified electrodes with different concentrations in Example 1.

[0047] Figure 21 The left image shows the CV curves (left) and the right image shows the SA oxidation peak current versus the PC-Mn20 coating amount (right) of the modified electrodes with different PC-Mn20 coating amounts in Example 1.

[0048] Figure 22 The image shows a superimposed plot of cyclic voltammetry (CV) curves of the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 detecting 250 μmmol / L SA in PBS at different pH values ​​(left) and a dotted line graph of SA oxidation peak current versus PBS pH value (right).

[0049] Figure 23 The image shows the CV stack-up plots of 250 μmmol / L SA detected by the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 at different scan rates.

[0050] Figure 24 The graphs show the linear relationship between Ipc and scan rate and the relationship between Epa and scan rate in 250 μmmol / L SA using the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 at different scan rates (left) and (right).

[0051] Figure 25 The image shows the differential pulse voltammetry (DPV) overlay plot (left) and the linear relationship between current and concentration (right) for detecting salicylic acid at different concentrations (50-900 nmol / L) using the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1.

[0052] Figure 26 The image shows the differential pulse voltammetry (DPV) overlay plot (left) and the linear relationship between current and concentration (right) for detecting salicylic acid at different concentrations (50-900 μmol / L) using the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1.

[0053] Figure 27 A bar chart showing the parallelism test of the same 7 modified electrodes Nafion / PC-Mn20 / SPE prepared using the method in Example 1;

[0054] Figure 28 The bar chart shows the response of the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 to interfering substances when detecting SA. Detailed Implementation

[0055] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0056] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0057] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0058] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0059] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0060] Unless otherwise specified, room temperature in this invention refers to 25±5℃.

[0061] This invention utilizes biomass-derived manganese-doped porous carbon nanomaterials (PC-Mn) to modify the surface of a screen-printed electrode (SPE). Combined with a micro-workstation featuring wireless transmission capabilities, a smart electrochemical sensor is constructed for detecting salicylic acid (SA) in plant leaves infested by spider mites. The structure and morphology of PC-Mn were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and N2 adsorption-desorption techniques. The electrochemical sensing performance of SA on the modified electrode surface was analyzed using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). This invention provides a portable, compact, low-cost, and easy-to-operate method that can offer insights for the resource utilization of agricultural waste (coffee fruit peel) and the early monitoring of plant disease resistance signaling molecules.

[0062] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0063] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0064] Example 1

[0065] The preparation of PC-Mn20 includes the following steps:

[0066] Step 1: Crush the coffee fruit shells (Lujiangba Coffee Processing Company, Baoshan City, Yunnan Province) using a high-speed grinder, pass them through an 80-mesh sieve, weigh out 8.0g of coffee fruit shell powder, mix it with 100mL of deionized water, and magnetically stir at 400rpm for 1 hour to fully disperse the fibers and obtain a mixture.

[0067] Step 2: Add 20 mmol manganese acetate tetrahydrate and 40 mmol zinc nitrate hexahydrate to the mixture, continue stirring for 1 hour, seal and let stand at room temperature for 12 hours to promote uniform adsorption of metal ions; then centrifuge and collect the solid product.

[0068] Step 3: After drying the solid product, grind it into a fine powder using an agate mortar and pestle, transfer it to a porcelain boat, place it in the constant temperature zone of a tube furnace, and carbonize it for 2 hours under a N2 flow at 900℃ (heating rate of 5℃ / min). -1 The target sample PC-Mn20 was obtained.

[0069] 1.5 mg PC-Mn20 was mixed with 1 mL of water to obtain a suspension. 8 μL of the suspension was coated onto the surface of a screen-printed electrode (SPE, 4 mm in diameter), dried, and then coated with Nafion ethanol solution (0.5 wt%) to obtain a working electrode, denoted as Nafion / PC-Mn20 / SPE.

[0070] The optimal ratio of PC-Mn20 to water and the optimal amount of suspension were investigated separately:

[0071] (1) When the ratio of PC-Mn20 to water is 0.5mg:1mL, 1mg:1mL, 1.5mg:1mL, and 2mg:1mL, the volume of the suspension is fixed at 8μL to explore the optimal ratio of PC-Mn20 to water.

[0072] Figure 20 The left image shows the CV curves (left) and the right image shows the SA oxidation peak current versus PC-Mn20 concentration (right) of the electrodes modified with different concentrations of PC-Mn20 in Example 1. As shown in the figure, the SA oxidation peak current is the highest when the PC-Mn20 concentration is 1.5 mg / L. Therefore, 1.5 mg / L was selected as the optimal modification concentration of PC-Mn20 (the ratio of PC-Mn20 to water is 1.5 mg:1 mL).

[0073] (2) The ratio of PC-Mn20 to water was fixed at 1.5 mg: 1 mL, and the amount of suspension used was 5 μL, 6 μL, 7 μL, 8 μL and 9 μL, respectively, to explore the optimal amount of suspension.

[0074] Figure 21 The figures show the CV curves (left) and the dotted-line graph (right) of the SA oxidation peak current versus the PC-Mn20 coating amount for the electrodes modified with different PC-Mn20 coating amounts in Example 1. As can be seen from the figures, the SA oxidation peak current is the largest when the PC-Mn20 coating amount is 8 μL. Therefore, 8 μL was selected as the optimal coating amount for PC-Mn20.

[0075] Example 2

[0076] The preparation of PC-Mn0 includes the following steps:

[0077] The only difference between this method and the preparation method of PC-Mn20 in Example 1 is that the addition of manganese acetate tetrahydrate is omitted; all other steps and parameters are the same as in Example 1. The target sample PC-Mn0 was obtained.

[0078] 1.5 mg PC-MnO was mixed with 1 mL of water to obtain a suspension; 8 μL of the suspension was coated onto the surface of a screen-printed electrode (SPE, 4 mm in diameter), dried, and then coated with Nafion ethanol solution (0.5 wt%) to obtain a working electrode, denoted as Nafion / PC-MnO / SPE.

[0079] Example 3

[0080] The preparation of PC-Mn10 includes the following steps:

[0081] The only difference between this method and the preparation method of PC-Mn20 in Example 1 is that the amount of manganese acetate tetrahydrate was adjusted from 20 mmol to 10 mmol. All other steps and parameters are the same as in Example 1. The target sample PC-Mn10 was obtained.

[0082] 1.5 mg PC-Mn10 was mixed with 1 mL of water to obtain a suspension. 8 μL of the suspension was coated onto the surface of a screen-printed electrode (SPE, 4 mm in diameter), dried, and then coated with Nafion ethanol solution (0.5 wt%) to obtain a working electrode, denoted as Nafion / PC-Mn10 / SPE.

[0083] Example 4

[0084] The preparation of PC-Mn40 includes the following steps:

[0085] The only difference between this method and the preparation method of PC-Mn20 in Example 1 is that the amount of manganese acetate tetrahydrate was adjusted from 20 mmol to 40 mmol. All other steps and parameters are the same as in Example 1. The target sample PC-Mn40 was obtained.

[0086] 1.5 mg PC-Mn20 was mixed with 1 mL of water to obtain a suspension. 8 μL of the suspension was coated onto the surface of a screen-printed electrode (SPE, 4 mm in diameter), dried, and then coated with Nafion ethanol solution (0.5 wt%) to obtain a working electrode, denoted as Nafion / PC-Mn20 / SPE.

[0087] Characterization and effect verification:

[0088] Figure 1 The XRD patterns of the different materials prepared in Examples 1-4 with diffraction angles 2θ ranging from 20° to 90° are shown. The patterns show that the samples have a typical faceted cubic crystal structure (FCC), with strong diffraction peaks at 34.9° and 40.5°, corresponding to the (111) and (200) planes of Mn (PDF#07-0230).

[0089] Figure 2The figures show the Raman spectra of the different materials prepared in Examples 1-4. As can be seen from the figures, the 530 cm⁻¹ peak value of PC-Mn₂O is... -1 This is a characteristic peak of Mn-O, while PC-Mn0 does not have a characteristic Mn peak. 1350 cm⁻¹ -1 The Raman characteristic peak is the D peak, corresponding to the characteristic peak of sp3 hybridized carbon atoms. The appearance of the D peak is due to the vibration of defective or disordered carbon atoms in carbon materials; 1584 cm⁻¹ -1 The Raman characteristic peak is the G peak, which originates from the stretching vibration of the C-C bonds in the graphite layered structure. D / I G Used to assess the defect density of materials, corresponding to I D / I G The values ​​are 0.91, 0.41, and 0.81, respectively. Among them, the I of PC-Mn20... D / I G The smallest value indicates fewer defects and a high degree of graphitization.

[0090] Figure 3 The image shows a scanning electron microscope (SEM) image of PC-Mn20 prepared in Example 1. As can be seen from the image, the SEM image of PC-Mn20 exhibits a typical honeycomb porous structure. The material surface is rough, with numerous uneven areas.

[0091] Figure 4 The image shows the elemental mapping of PC-Mn20 prepared in Example 1. As can be seen from the image, PC-Mn20 is composed of C, Mn, N and O elements, and they are uniformly distributed.

[0092] Figure 5 The images show the full X-ray photoelectron spectroscopy (XPS) spectra of the different materials prepared in Examples 1, 3, and 4. As can be seen from the figures, C, N, and Mn elements are present in all three samples.

[0093] Figure 6 The figures show the high-resolution XPS spectra of C1s elements in the different materials prepared in Examples 1, 3, and 4. As can be seen from the figures, the C1 XPS spectra of the three samples all show three characteristic peaks: the peak at 284.8 eV represents the carbon skeleton (CC / C=C), and the peak at 286.5 eV represents the CO / CN bond.

[0094] Figure 7 High-resolution XPS spectra of Mn 2p elements in different materials prepared in Examples 1, 3, and 4. The Mn 2p spectra of the three samples show that the peaks at 641.1 eV and 652.5 eV correspond to Mn, respectively. 2+ 2P 3 / 2 and Mn 2+ 2P 1 / 2 .

[0095] Figure 8 The images show high-resolution XPS spectra of N1s elements in the different materials prepared in Examples 1, 3, and 4. The high-resolution N1s spectra of the three samples all show three peaks, located at 398.3 eV (pyridine-N), 400.5 eV (pyrrole-N), and 401.9 eV (graphite-N), which further confirms the N doping in the carbon support.

[0096] Figure 9 , 11 Figures 13 and 15 show the N2 adsorption-desorption isotherms of PC-Mn0, PC-Mn10, PC-Mn20, and PC-Mn40 prepared in Examples 1-4. As can be seen from the figures, all three samples exhibit typical Type IV isotherms, with a significant hysteresis loop in the relative pressure range of 0.4–1.0, indicating the presence of mesoporous structures in the materials. The BET specific surface area of ​​PC-Mn20 is 536.9 × 10⁶ m². 2 The specific surface areas of PC-Mn0, PC-Mn10, and PC-Mn40 per g were 777.4781 m², respectively. 2 / g、543.1772m 2 / g and 365.5264m 2 / g.

[0097] Figure 10 , 12 Figures 14 and 16 show the pore size distribution of PC-Mn0, PC-Mn10, PC-Mn20, and PC-Mn40 prepared in Examples 1-4. PC-Mn20 is predominantly mesoporous at 3-4 nm, indicating its high specific surface area and good pore structure, making it suitable for catalysis, adsorption, and other applications. The pores around 4 nm likely originate from the carbon matrix, while the remainder are packing pores of Mn nanoparticles. The pore sizes of PC-Mn0, PC-Mn10, and PC-Mn40 are also mainly concentrated in the 3-4 nm range, and they also exhibit packing pores. The mesoporous structure of the samples can promote solution diffusion, thereby improving their catalytic performance, and the large specific surface area can expose more active sites, further enhancing the catalytic effect.

[0098] Figure 17Superimposed cyclic voltammetry (CV) curves of different modified electrodes prepared in Examples 1-4 for detecting 250 μmmol / L SA. As can be seen from the figure, oxidation peaks appear on different modified electrodes, which is due to the oxidation reaction occurring in the SA molecule. The oxidation peak current (Ipa) on the surface of Nafion / PC-Mn20 / SPE is the highest, at 99.61 μA, while no oxidation peak appears on the surface of the Nafion / PC-Mn0 / SPE electrode. This is because Mn is the catalytic active center for the electrochemical oxidation of SA and is prone to oxidation reactions during CV testing, thus generating obvious oxidation peaks. Such active substances are lacking in the nanomaterials without Mn, resulting in no oxidation peaks.

[0099] Figure 18 Electrochemical impedance spectroscopy diagrams of different modified electrodes prepared in Examples 1-4. As can be seen from the figure, the order of charge transfer impedance of the four electrodes is Nafion / PC-Mn20 / SPE < Nafion / PC-Mn10 / SPE < Nafion / PC-Mn40 / SPE < Nafion / PC-Mn0 / SPE, indicating that Nafion / PC-Mn20 / SPE has good conductivity, improves the electron transfer rate, and reduces the resistance.

[0100] Figure 19 Relationship diagram of current density and scan rate of different material modified electrodes prepared in Examples 1-4. As can be seen from the figure, at a given scan rate (0.01 V / s to 0.10 V / s), the electrochemical double-layer capacitance (C dl ) can be calculated by fitting the linear diagram of the current density difference and the scan rate. The C dl values of Nafion / PC-Mn0 / SPE, Nafion / PC-Mn10 / SPE, Nafion / PC-Mn20 / SPE, and Nafion / PC-Mn40 / SPE are 0.30 mF, 5.31 mF, 5.60 mF, and 4.00 mF respectively. The ECSA can be calculated by dividing Cdl by Cs, where Cs represents the specific capacitance of the material. The Cs of the screen-printed electrode is 0.04 mF cm -2 . The calculated ECSA values of Nafion / PC-Mn0 / SPE, Nafion / PC-Mn10 / SPE, Nafion / PC-Mn20 / SPE, and Nafion / PC-Mn40 / SPE are 7.5 cm 2 , 132.75 cm 2 , 140 cm 2 and 100 cm 2 respectively. Consistent with the change trend of the peak current of different nanomaterial modified electrodes, therefore, the larger ECSA of PC-Mn20 helps to expose the active centers during the electrocatalytic process and improve the catalytic effect.

[0101] Figure 22 The left image shows a superimposed cyclic voltammetry (CV) curve of the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 detecting 250 μmmol / L SA in PBS at different pH values, and the right image shows a dotted line plot of the SA oxidation peak current versus the pH value of PBS. As can be seen from the figure, the SA oxidation peak current is largest when the pH of PBS is 7. Therefore, PBS at pH 7 was used as the experimental condition for subsequent experiments.

[0102] Figure 23 The image shows the CV stack-up of the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 at different scan rates for detecting 250 μmmol / L SA. As can be seen from the image, the oxidation peak current of SA varies with different scan rates.

[0103] Figure 24 The graphs show the linear relationship between Ipc and scan rate (left) and Epa and scan rate (right) for the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 at different scan rates in the detection of 250 μmmol / L SA. Under optimal conditions, the effect of scan rate (ν) on the electrochemical oxidation process was investigated. The peak current of salicylic acid oxidation increased with increasing ν (0.03 to 0.10 V / s), showing a good linear relationship (left graph). The linear relationship between peak current and scan rate is Ipa (μA) = 1841.03lnν (V / s) + 73.00 (n = 8, R 2 =0.995), showing a typical diffusion-controlled electrochemical behavior. The relationship between peak potential and scan rate was also investigated (right figure), and a good linear relationship was found between the two. The linear regression equation was Epa = 1.43lnν(V / s) + 1.10 (n = 8, R2 = 0.962).

[0104] Figure 25 , 26 The figure shows the differential pulse voltammetry (DPV) overlay plot and the linear relationship between current and concentration for detecting different concentrations of salicylic acid using the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1. As shown in the figure, I pa The linear range increases with increasing salicylic acid concentration, and can be divided into two segments: I pa (μA)=0.01912C(nmol / L)+2.389(n=6, R 2 =0.993) and I pa (μA)=0.02829C(μmol / L)+21.031(n=6, R 2 =0.994), and the sensitivity is 152.23 mA / (cm). 2nmol / L) and 225.24 mA / (cm 2 The limit of detection (LOD) was 16.67 nmol / L.

[0105] Figure 27 A bar chart was prepared to demonstrate the parallelism of the seven modified electrodes (Nafion / PC-Mn20 / SPE) prepared using the method described in Example 1. The figure shows that the relative standard deviation (RSD) of the oxidation peak current of 250 μmmol / L SA measured by the seven modified electrodes (Nafion / PC-Mn20 / SPE) was 0.87%, indicating that the working electrode exhibits good parallelism.

[0106] Figure 28 The bar chart shows the response of the modified electrode Nafion / PC-Mn20 / SPE prepared in Example 1 to interfering substances when detecting salicylic acid (SA). As shown in the figure, the use of indoleacetic acid, glucose, caffeine, and inorganic ions for the determination of 250.0 μmol / LSA revealed that these interfering substances had no significant effect on the determination of salicylic acid.

[0107] To verify the reliability of this experimental method in detecting salicylic acid in actual samples, the standard addition method was used to quantitatively detect salicylic acid in healthy and mite-infested leaves of avocado. The results are shown in Table 1. The constructed Nafion / PC-Mn20 / SPE electrochemical sensor showed a salicylic acid recovery rate ranging from 97.51% to 103.92%, with an RSD of less than 5%, indicating satisfactory results. Importantly, practical application revealed that the salicylic acid (SA) content in mite-infested leaves (96.82 μmol / L) was 122 times higher than that in healthy leaves (0.79 μmol / L), confirming the reliability of SA as an early biomarker of pest stress and providing new technological support for green early warning of avocado diseases and the resource utilization of agricultural waste.

[0108] Table 1

[0109]

[0110] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An application of manganese-doped porous carbon nanomaterial in salicylic acid detection, characterized in that, The manganese-doped porous carbon nanomaterial is used as an electrode modification material for the working electrode of the electrochemical sensor. The preparation method of the manganese-doped porous carbon nanomaterial includes the following steps: The coffee husks were crushed and passed through an 80-mesh sieve. 8.0 g of coffee husk powder was mixed evenly with water, and then 20 mmol of manganese acetate tetrahydrate and 40 mmol of zinc nitrate hexahydrate were added to carry out the adsorption reaction. The solid product was then collected. The solid product is carbonized to obtain the manganese-doped porous carbon nanomaterial. The carbonization temperature is 700~1000 ℃, the time is 0.5~2 h, and the heating rate is 2~5 ℃ min. -1 Inert atmosphere; The adsorption reaction is specifically carried out by stirring at room temperature first, followed by sealing and aging at room temperature.

2. The application according to claim 1, characterized in that, The working electrode is prepared by mixing the manganese-doped porous carbon nanomaterial with water to obtain a suspension; coating the suspension onto the electrode surface, drying it, and then coating it with Nafion ethanol solution to obtain the working electrode.

3. The application according to claim 2, characterized in that, The mass-to-volume ratio of the manganese-doped porous carbon nanomaterial to water is 0.5-2 mg:1 mL; the amount of the suspension used is 5-9 μL.

Images