Preparation method, product and application of waste coffee residue derived in-situ monatomic iron loaded nitrogen-doped carbon nanomaterial

Abstract

The invention relates to the fields of green energy materials, electrochemical sensing detection, food and medicine, in particular to a preparation method, a product and application of a waste coffee residue derived in-situ monatomic iron loaded nitrogen-doped carbon nanomaterial. The preparation method of the waste coffee residue derived in-situ monatomic iron loaded nitrogen-doped carbon nanomaterial comprises the following steps: carbonizing coffee residues in an argon atmosphere to obtain the waste coffee residue derived in-situ monatomic iron loaded nitrogen-doped carbon nanomaterial, the carbonization specifically comprises the step of heating to 800-1000 DEG C at the rate of 5 DEG C / min and carbonizing for 2 hours. The waste coffee residue derived in-situ monatomic iron loaded nitrogen-doped carbon nanomaterial prepared by the method has selectivity and high efficiency on chlorogenic acid detection, and the detection limit of chlorogenic acid is as low as 66.67 nmol / L.

Description

Technical Field

[0001] The present invention relates to the fields of green energy materials, electrochemical sensing detection, food and medicine, and in particular to a preparation method, product and application of an in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial derived from waste coffee grounds. Background Art

[0002] Chlorogenic acid, a natural polyphenol compound widely found in plants such as coffee and tea, is widely used in medicine, food and other fields due to its significant anti-inflammatory, anti-cancer, antioxidant and potential antiviral activities. With the intensification of environmental pollution and the frequent occurrence of food safety incidents, the rapid detection of natural antioxidant components in food is crucial to protecting human health. However, traditional detection methods such as high performance liquid chromatography (HPLC), UV-visible spectrophotometry and fluorescence sensor methods generally have problems such as cumbersome operation and expensive instruments, which make it difficult to meet the needs of on-site real-time monitoring. In contrast, electrochemical sensing technology has become an emerging direction for the detection of bioactive substances due to its advantages of simple operation, rapid response and high sensitivity. In the field of electrochemical sensing, carbon-based nanomaterials have become an ideal substrate for building high-performance sensors because of their excellent conductivity, chemical stability and rich surface active sites. By applying sp 2 Introducing heteroatoms into the hybrid carbon skeleton for structural regulation can significantly change the electron cloud distribution of the material, thereby improving its electrocatalytic activity and selectivity.

[0003] Single-atom catalysts excel in the field of electrocatalysis due to their high atomic utilization rate and unique electronic structure, and have achieved remarkable results in fields such as energy conversion. Although single-atom iron-doped carbon materials based on MOFs or polymers have excellent performance, their synthesis process is complex and the cost is high, and green and efficient preparation strategies are urgently needed. Coffee grounds are the main solid waste of the coffee industry, with an annual global output of more than 10 million tons. Currently, most of them are treated as organic waste, resulting in waste of resources and environmental burden. How to achieve high-value utilization of coffee grounds, how to simplify the process of single-atom catalysts and reduce their costs are technical problems that those skilled in the art urgently need to solve. Summary of the Invention

[0004] In view of this, the present invention provides a preparation method, product and application of in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial (SAFe-NC) derived from waste coffee grounds.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for preparing in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterials derived from waste coffee grounds, comprising the following steps:

[0007] Carbonizing coffee grounds in an argon atmosphere to obtain the waste coffee grounds-derived in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial;

[0008] The carbonization is specifically carried out by heating the material to 800-1000° C. at a rate of 5° C. / min and carbonizing the material for 2 hours.

[0009] The second technical solution of the present invention is an in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial derived from waste coffee grounds prepared according to the above-mentioned preparation method.

[0010] A third technical solution of the present invention is a method for preparing an electrochemical sensor, comprising the following steps:

[0011] The above-mentioned waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterial is mixed with water to prepare a dispersion, and the dispersion is drop-coated on the electrode surface. After drying, Nafion ethanol solution is continuously drop-coated and dried to obtain the electrochemical sensor.

[0012] A fourth technical solution of the present invention is an electrochemical sensor prepared according to the above-mentioned method for preparing an electrochemical sensor.

[0013] A fifth technical solution of the present invention is the use of the above-mentioned electrochemical sensor in detecting chlorogenic acid.

[0014] The present invention discloses the following technical effects:

[0015] This invention uses waste coffee grounds as a biomass precursor and prepares waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterials (SAFe-NC) through high-temperature carbonization. During the carbonization process, nitrogen and oxygen more effectively bond to the carbon backbone. SAFe-NC features single-atomically dispersed Fe atoms and a hierarchical pore structure, making it suitable for applications such as adsorption and catalysis.

[0016] The waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterial prepared by the method of the present invention has selectivity and high efficiency for the detection of chlorogenic acid, and the detection limit of chlorogenic acid is as low as 66.67 nmol / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 The SEM images of SAFe-NC-900 prepared in Example 1 at different magnifications are shown;

[0019] Figure 2 TEM image of SAFe-NC-900 prepared in Example 1;

[0020] Figure 3 This is a spherical aberration corrected electron microscope image of SAFe-NC-900 prepared in Example 1;

[0021] Figure 4 EDS elemental mapping of SAFe-NC-900 prepared in Example 1;

[0022] Figure 5 XRD spectra of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 prepared in Example 1 and Comparative Examples 1-2;

[0023] Figure 6 Raman spectra of SAFe-NC-800, SAFe-NC-900, and SAFe-NC-1000 prepared in Example 1 and Comparative Examples 1-2;

[0024] Figure 7 The full XPS spectra of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 prepared in Example 1 and Comparative Examples 1-2;

[0025] Figure 8 The C element XPS graphs of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 prepared in Example 1 and Comparative Examples 1-2;

[0026] Figure 9 The N element XPS graphs of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 prepared in Example 1 and Comparative Examples 1-2;

[0027] Figure 10 BET diagrams of SAFe-NC-800, SAFe-NC-900, and SAFe-NC-1000 prepared in Example 1 and Comparative Examples 1-2;

[0028] Figure 11 BET pore size diagrams of (a) SAFe-NC-800, (b) SAFe-NC-900, and (b) SAFe-NC-1000 prepared in Example 1 and Comparative Examples 1-2;

[0029] Figure 12 The superposition of CV curves of SPE electrodes modified with different SAFe-NC-900 concentrations in PBS (pH = 7) containing 500 μmol / L chlorogenic acid;

[0030] Figure 13 The CV curves of SAFe-NC-900 modified SPE with different coating amounts for the determination of 500 μmol / L chlorogenic acid are overlaid;

[0031] Figure 14 The CV curves of Nafion / SAFe-NC-900 / SPE in PBS with different pH values ​​containing 500 μmol / L chlorogenic acid are superimposed.

[0032] Figure 15 The linear relationship between the redox potential of 500 μmol / L chlorogenic acid and pH;

[0033] Figure 16 is the relationship between the oxidation current of 500 μmol / L chlorogenic acid and pH;

[0034] Figure 17 This is an overlay of the CV curves of Nafion / SAFe-NC-900 / SPE detecting 500 μmol / L chlorogenic acid at different scan rates;

[0035] Figure 18 The linear relationship between the redox peak current and the scan rate of 500 μmol / L chlorogenic acid on the Nafion / SAFe-NC-900 / SPE surface;

[0036] Figure 19 is the linear relationship diagram between the redox potential and lnν of chlorogenic acid;

[0037] Figure 20 The CV curves of Nafion / SAFe-NC-900 / SPE in pH 4 PBS containing 500 μmol / L chlorogenic acid and without chlorogenic acid are superimposed.

[0038] Figure 21 CV curves of Nafion / SAFe-NC-800 / SPE, Nafion / SAFe-NC-900 / SPE, and Nafion / SAFe-NC-1000 / SPE in PBS containing 500 μmol / L chlorogenic acid at pH = 4;

[0039] Figure 22 The impedance spectroscopy of Nafion / SAFe-NC-800 / SPE, Nafion / SAFe-NC-900 / SPE, and Nafion / SAFe-NC-1000 / SPE;

[0040] Figure 23This is the linear relationship diagram between the current density and scan rate of Nafion / SAFe-NC-800 / SPE, Nafion / SAFe-NC-900 / SPE, and Nafion / SAFe-NC-1000 / SPE.

[0041] Figure 24 This is the parallelism bar graph of Nafion / SAFe-NC-900 / SPE detecting 500 μmol / L chlorogenic acid;

[0042] Figure 25 This is a bar graph showing the repeatability of Nafion / SAFe-NC-900 / SPE in detecting 500 μmol / L chlorogenic acid.

[0043] Figure 26 This is a bar graph showing the storage stability of chlorogenic acid at 500 μmol / L detected by Nafion / SAFe-NC-900 / SPE.

[0044] Figure 27 Interference test diagram for the detection of chlorogenic acid using Nafion / SAFe-NC-900 / SPE;

[0045] Figure 28 DPV response diagram of different concentrations of chlorogenic acid on the Nafion / SAFe-NC-900 / SPE surface;

[0046] Figure 29 This is the linear relationship between the current and concentration of Nafion / SAFe-NC-900 / SPE. DETAILED DESCRIPTION

[0047] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0048] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0049] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0050] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0051] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0052] Since coffee grounds are rich in natural carbon, nitrogen precursors and trace iron elements, they are an ideal biomass carbon source. At the same time, coffee grounds are widely available, inexpensive and green and renewable. Converting them into single-atom iron-doped carbon nanomaterials can not only achieve high-value utilization of waste, but also open up new avenues for the preparation of high-performance carbon-based materials. However, current research on carbon materials based on coffee grounds is mainly focused on adsorption, energy storage and other fields. Research on using them to construct single-atom iron-doped carbon nanomaterials and apply them to electrochemical sensing of bioactive substances (such as chlorogenic acid) is still in its infancy. The preparation of most single-atom catalysts comes from the introduction of exogenous metal sources rather than intrinsically rich metal sources, and since most of them require acid treatment, they have poor biocompatibility, which limits their practical application.

[0053] This study utilizes waste coffee grounds, which are inherently rich in elements such as C, Fe, and N, to prepare in situ single-atom iron-loaded nitrogen-doped carbon nanomaterials (SAFe-NC). SAFe-NC is modified on a SPE surface using a single-atom catalyst and combined with a portable electrochemical workstation to construct an intelligent electrochemical sensor for on-site detection of chlorogenic acid. This approach has important scientific significance and application value for promoting waste resource utilization and enabling rapid and accurate detection of bioactive components.

[0054] A first aspect of the present invention provides a method for preparing in situ single-atom iron-loaded nitrogen-doped carbon nanomaterials derived from waste coffee grounds, comprising the following steps:

[0055] Carbonizing coffee grounds in an argon atmosphere to obtain the waste coffee grounds-derived in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial;

[0056] The carbonization is specifically carried out by heating the material to 800-1000° C. at a rate of 5° C. / min and carbonizing the material for 2 hours.

[0057] In the present invention, a carbonization heating rate that is too fast will cause the structure of the in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial to collapse, resulting in a decrease in pores and a reduction in specific surface area. A carbonization time that is too short will result in a low degree of graphitization and poor conductivity, while a carbonization time that is too long will increase costs. Based on a comprehensive consideration of product performance and cost, the present invention preferably limits the carbonization parameters to the above range.

[0058] In a preferred embodiment of the present invention, the inert atmosphere is an argon atmosphere.

[0059] In a preferred embodiment of the present invention, the coffee grounds are dry coffee grounds from which impurities have been removed.

[0060] In a preferred embodiment of the present invention, the step of grinding to a particle size of no more than 0.5 μm is further included after the carbonization is completed.

[0061] A second aspect of the present invention provides a waste coffee grounds-derived in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial prepared according to the above-mentioned preparation method.

[0062] A third aspect of the present invention provides a method for preparing an electrochemical sensor, comprising the following steps:

[0063] The above-mentioned waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterial is mixed with water to prepare a dispersion, and the dispersion is drop-coated on the electrode surface. After drying, Nafion ethanol solution is continuously drop-coated and dried to obtain the electrochemical sensor.

[0064] In a preferred embodiment of the present invention, the concentration of the dispersion is 0.5-2 mg / mL; the mass concentration of the Nafion ethanol solution is 0.5%; the electrode is a glassy carbon electrode or a screen-printed electrode; the drop amount of the dispersion on the electrode surface is 0.5-0.7 μL / mm 2 The amount of Nafion ethanol solution applied to the electrode surface is 0.3 to 0.4 μL / mm 2 .

[0065] A fourth aspect of the present invention provides an electrochemical sensor prepared according to the above-mentioned method for preparing an electrochemical sensor.

[0066] A fifth aspect of the present invention provides a use of the above-mentioned electrochemical sensor in detecting chlorogenic acid.

[0067] The present invention uses waste coffee grounds, which are intrinsically rich in C, Fe, and N elements, as a biomass precursor to prepare in situ single-atom iron-loaded nitrogen-doped carbon nanomaterials (SAFe-NC). Spherical aberration electron microscopy (HAADF-STEM) confirmed that Fe was evenly distributed on the surface of the C carrier in the form of single atoms, without forming clusters or particles, significantly improving atomic utilization. The electrochemical sensor constructed with in situ single-atom iron-loaded nitrogen-doped carbon nanomaterials (SAFe-NC) derived from waste coffee grounds has a wide detection range (200.0-800.0 nmol / L and 0.8-500.0 μmol / L) and a low detection limit (66.67 nmol / L). It was also verified that the sensor has strong anti-interference ability, good repeatability and stability. When testing actual sample coffee bean samples, the spiked recovery rate was between 100.84% ​​and 106.02%, which fully demonstrated the reliability and practicality of the portable intelligent electrochemical sensor. It is expected to provide a new and effective way for the rapid and accurate detection of chlorogenic acid, and has broad application prospects in the detection of chlorogenic acid content in food, medicine and other fields.

[0068] In summary, the present invention provides a method for preparing in situ single-atom iron-loaded nitrogen-doped carbon nanomaterials (SAFe-NC) by high-temperature pyrolysis using waste coffee grounds as a biomass precursor. The method is simple and convenient, does not require the addition of additional metal sources and nitrogen sources, and does not require acid treatment, thereby increasing biocompatibility. This design is intended to provide relevant companies and universities with a method for preparing single-atom catalysts with low preparation cost and simple steps. By using the method for preparing single-atom catalysts of the present invention, the development and application of waste resource utilization and electrochemical sensing technology can be further promoted, contributing to the development of my country's food, medical and electrochemical sensing fields.

[0069] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0070] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0071] Example 1

[0072] This embodiment provides a method for preparing in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterials derived from waste coffee grounds, the steps of which are as follows:

[0073] 5.0 g of decontaminated, dry coffee grounds were weighed and placed in a porcelain boat. The boat was then placed in a quartz tube furnace and heated to 900°C at a rate of 5°C / min under an argon atmosphere for carbonization for 2 hours. The mixture was then cooled naturally to room temperature to produce a brownish-black powder. This brownish-black powder was then ball-milled to a particle size of 0.5 μm, yielding a waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterial, designated SAFe-NC-900.

[0074] Comparative Example 1

[0075] The only difference from Example 1 is that the carbonization temperature is 800° C.; the remaining steps and parameters are the same as Example 1. The obtained waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterial is denoted as SAFe-NC-800.

[0076] Comparative Example 2

[0077] The only difference from Example 1 is that the carbonization temperature is 1000° C.; the remaining steps and parameters are the same as Example 1. The obtained waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterial is denoted as SAFe-NC-1000.

[0078] Effect Example 1

[0079] The waste coffee grounds-derived in situ single-atom iron-loaded nitrogen-doped carbon nanomaterials (SAFe-NCs) prepared in the Examples and Comparative Examples were used to construct electrochemical sensors: a 1.0 mg / mL SAFe-NC dispersion was prepared and sonicated for 30 minutes. 8.0 μL of this dispersion was then drop-coated on a clean, polished screen-printed electrode (SPE) (working electrode diameter: 4 mm). After air drying, 5.0 μL of a 0.5% Nafion ethanol solution was drop-coated on the modified electrode surface. After air drying, the resulting electrochemical sensor, Nafion / SAFe-NC / SPE, was used for electrochemical detection of chlorogenic acid. Electrochemical sensors constructed with different SAFe-NCs (SAFe-NC-800, SAFe-NC-900, and SAFe-NC-1000) were labeled Nafion / SAFe-NC-800 / SPE, Nafion / SAFe-NC-900 / SPE, and Nafion / SAFe-NC-1000 / SPE, respectively.

[0080] The electrochemical detection method for chlorogenic acid is as follows: Arabica coffee beans (medium roast) from the Lujiangba coffee plantation were ground into a powder using a grinder. Accurately weigh 5.0 g of the powder and disperse it in 200 mL of 100°C hot water. Extraction was performed for 10 minutes. After cooling to room temperature, the mixture was filtered through filter paper, and the coffee extract was retained for later use. The extract was diluted 20-fold with PBS buffer (pH 4).

[0081] The constructed electrochemical sensor was used to determine the chlorogenic acid content in coffee bean extract. Chlorogenic acid standard solutions (50, 100, and 200 μmol / L) were added to 10 mL of coffee extract, and the recovery rate was determined using the standard addition method. The results are shown below.

[0082] Figure 1 The SEM images of SAFe-NC-900 at different magnifications are shown in Figure 2. Figure 1 It can be seen that SAFe-NC-900 presents an irregular block structure and a rough surface.

[0083] Figure 2 TEM image of SAFe-NC-900. Figure 2 It can be seen that SAFe-NC-900 has no nanoparticle aggregation.

[0084] Figure 3 This is the spherical aberration corrected electron microscope image of SAFe-NC-900. Figure 3 It can be seen that Fe exists in a single-atom distribution mode.

[0085] Figure 4 The EDS element mapping spectrum of the prepared SAFe-NC-900. Figure 4 It can be seen that C, Fe, and N elements are evenly distributed in SAFe-NC-900.

[0086] Figure 5 The XRD spectra of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 are shown in Figure 2. Figure 5 It can be seen that SAFe-NC-900, SAFe-NC-800, and SAFe-NC-1000 all exhibit peaks at around 44.29°, corresponding to the characteristic diffraction peak of the (111) plane of metal C (PDF#80-0017). This indicates that during the treatment at different temperatures, the main crystal structure of the material did not change significantly, and the carbon phase also existed stably, with the presence of (111) crystal plane-related diffraction peaks and carbon phase diffraction peaks.

[0087] Figure 6 The full Raman spectra of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 are shown in Figure 2. Figure 6 It can be seen that the wave number is 1345cm -1 The D peak is the disorder peak, due to sp 3 The second-order resonance Raman scattering process of hybrid carbon atoms is caused by this process, and its intensity reflects the degree of defects in carbon materials. It is located at a higher wave number of 1586cm -l The strong peak at the peak position is the G peak, which is due to the sp2 Hybrid bond vibration is a characteristic peak of graphene or graphite-phase carbon, reflecting the material's order and degree of graphitization. The intensity ratio of the D and G peaks (ID / IG) is used to measure the number of structural defects in a carbon material. The ID / IG values ​​for SAFe-NC-1000, SAFe-NC-900, and SAFe-NC-800 are 0.97, 0.94, and 0.91, respectively. SAFe-NC-1000 has the highest ID / IG value, indicating a higher proportion of defects or disordered structures in this carbon material.

[0088] Figure 7 The full XPS spectra of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 are shown in Figure 2. Figure 7 It can be seen that C and N elements exist in all three samples.

[0089] Figure 8 The C element XPS patterns of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 are shown in Figure 2. Figure 8 It can be seen that the C1s XPS spectra of the three samples all show four peaks. The peak at 295.71 eV represents the typical K 2p1 / 2 bond, the peak at 292.96 eV corresponds to K 2p3 / 2, the peak at 285.4 V corresponds to CO / CN, which indicates the effective bonding of nitrogen and oxygen to the carbon skeleton, and the peak at 284.64 eV corresponds to CC / C=C / CH.

[0090] Figure 9 The N element XPS diagrams of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 are shown in Figure 2. Figure 9 It can be seen that all three samples show three peaks, located at 400.05 eV (graphene-type-N), 399.1 eV (pyrrole-type-N), and 398 eV (pyridine-type-N), which further verifies the N doping in the carbon support.

[0091] Figure 10 The BET diagrams of SAFe-NC-900, SAFe-NC-800 and SAFe-NC-1000 are shown in Figure 2. Figure 10 It can be seen that the BET specific surface areas of SAFe-NC-800, SAFe-NC-900 and SAFe-NC-1000 are 68.84 m 2 / g,52.89m 2 / g and 39.45m 2 / g.

[0092] Figure 11The BET pore size diagrams of SAFe-NC-900, SAFe-NC-800 and SAFe-NC-1000 are shown in Figure 2. Figure 11 It can be seen that SAFe-NC-800 is mainly composed of large pores, while SAFe-NC-900 and SAFe-NC-1000 have hierarchical pore structures.

[0093] Figure 12 This is an overlay of the CV curves of SPE modified with different SAFe-NC-900 concentrations (0.5 mg / L to 2.0 mg / L) in PBS (pH = 7) containing 500 μmol / L chlorogenic acid. The figure shows that the redox current of chlorogenic acid is the largest when the concentration is 1.0 mg / L. Therefore, the optimal SAFe-NC-900 concentration is determined to be 1.0 mg / L.

[0094] Figure 13 This is an overlay of the CV curves of the determination of 500 μmol / L chlorogenic acid by SAFe-NC-900 modified SPE with different drop amounts. It can be seen from the figure that when the SAFe-NC-900 drop amount is 9 μL, the redox peak current of chlorogenic acid is the largest, so the optimal drop amount is determined to be 9 μL.

[0095] Figure 14 This is an overlay of the CV curves of Nafion / SAFe-NC-900 / SPE in PBS with different pH values ​​containing 500 μmol / L chlorogenic acid. It can be seen from the figure that the redox peak current and potential of chlorogenic acid are different at different pH values.

[0096] Figure 15 This is a linear relationship diagram between the redox potential of 500 μmol / L chlorogenic acid and pH. It can be seen from the figure that the redox potential of chlorogenic acid decreases with increasing pH.

[0097] Figure 16 The graph shows the relationship between the oxidation peak current of 500 μmol / L chlorogenic acid and pH. As can be seen from the graph, the oxidation peak current of chlorogenic acid is the largest at pH 4. Therefore, the optimal pH is determined to be 4.

[0098] Figure 17 This is an overlay of the CV curves of Nafion / SAFe-NC-900 / SPE detecting 500 μmol / L chlorogenic acid at different scan rates. It can be seen from the figure that the redox peak current of chlorogenic acid increases with the increase of the scan rate.

[0099] Figure 18The figure shows the linear relationship between the redox peak current and the scan rate of 500 μmol / L chlorogenic acid on the Nafion / SAFe-NC-900 / SPE surface. It can be seen from the figure that Ipa, Ipc and the scan rate have a good linear relationship, revealing that the redox process of chlorogenic acid on the SAFe-NC-900 / SPE surface is an adsorption-controlled process.

[0100] Figure 19 This is the linear relationship diagram between the redox potential of chlorogenic acid and lnν. It can be seen from the figure that there is a linear relationship between the redox potential of chlorogenic acid and lnν.

[0101] Figure 20 The CV curves of Nafion / SAFe-NC-900 / SPE in 500 μmol / L chlorogenic acid and pH 4 PBS without chlorogenic acid are superimposed. Figure 21 It can be seen that no redox peak appears on the modified electrode in pH = 4.0 PBS (without chlorogenic acid), but there is an obvious redox peak at a potential of 0.4 V in PBS containing chlorogenic acid, indicating that redox reaction of chlorogenic acid occurs on the electrode surface.

[0102] Figure 21 The CV curves of Nafion / SAFe-NC-800 / SPE, Nafion / SAFe-NC-900 / SPE, and Nafion / SAFe-NC-1000 / SPE (corresponding to SAFe-NC-800, SAFe-NC-900, and SAFe-NC-1000 in the figure, respectively, the same below) in PBS containing 500 μmol / L chlorogenic acid at pH = 4 are shown. Figure 21 It can be seen that the redox peak current of chlorogenic acid is the largest in Nafion / SAFe-NC-900 / SPE, which means that SAFe-NC-900 has the strongest catalytic ability for chlorogenic acid.

[0103] Figure 22 The AC impedance spectra of Nafion / SAFe-NC-800 / SPE, Nafion / SAFe-NC-900 / SPE, and Nafion / SAFe-NC-1000 / SPE are shown in Figure 2. Figure 22 It can be seen that SAFe-NC-900 has the smallest semicircle diameter in the high-frequency region and the largest slope in the low-frequency region, which proves that its charge transfer resistance is the smallest and its mass transfer capacity is the strongest, which is consistent with the Figure 21 consistent.

[0104] Figure 23The linear relationship between current density and scan rate of Nafion / SAFe-NC-800 / SPE, Nafion / SAFe-NC-900 / SPE, and Nafion / SAFe-NC-1000 / SPE is shown in Figure 2. Figure 23 It can be seen that SAFe-NC-900 exhibits a Cdl of 1.80F. Compared with SAFe-NC-800 (1.50F) and SAFe-NC-1000 (1.01F), SAFe-NC-900 has a larger ECSA, which improves its electrochemical performance and exhibits higher electrocatalytic activity towards chlorogenic acid.

[0105] Figure 24 This is the parallelism bar graph of chlorogenic acid detection by Nafion / SAFe-NC-900 / SPE. Figure 24 It can be seen that the current difference is less than 5%, indicating that SAFe-NC-900 / SPE has good parallelism.

[0106] Figure 25 The repeatability bar graph of chlorogenic acid detection by Nafion / SAFe-NC-900 / SPE is shown in the figure. Figure 25 It can be seen that for the same electrode, the test was repeated 5 times based on 100 cycles. After 5 cycle tests, the current response of the sensor to chlorogenic acid remained within 90% of the initial value, demonstrating the good cycle stability of Nafion / SAFe-NC-900 / SPE.

[0107] Figure 26 The storage stability bar graph of chlorogenic acid at 500 μmol / L detected by Nafion / SAFe-NC-900 / SPE. Figure 26 It can be seen that after an electrode was stored in a refrigerator at around 4°C for one week, the current remained at 98.7% of the initial current. After two weeks, the oxidation peak current of chlorogenic acid showed a downward trend and remained at 73.1% of the initial current.

[0108] Figure 27 This is the interference test diagram for the detection of chlorogenic acid by Nafion / SAFe-NC-900 / SPE. Figure 27 It can be seen that the anti-interference performance of Nafion / SA Fe-NC-900 / SPE is 100 μmol / L Na + 、C1 - Ascorbic acid had little effect on the determination of 100 μmol / L chlorogenic acid, and the allowable relative error was within +5% of the oxidation peak signal intensity, indicating that SAFe-NC-900 has good anti-interference ability.

[0109] Figure 28The DPV response diagram of Nafion / SAFe-NC-900 / SPE with different concentrations of chlorogenic acid. Figure 28 It can be seen that with the increase of the concentration of chlorogenic acid solution, the Ipa value gradually increases.

[0110] Figure 29 The linear relationship between the redox peak current and concentration of chlorogenic acid on the surface of Nafion / SAFe-NC-900 / SPE is shown in Figure 2. Figure 29 It can be seen that Ipa and chlorogenic acid concentrations showed good linear relationships in the range of 200.0-800.0 nmol / L and 0.8-500.0 μmol / L, respectively, Ipa (μA) = 2.77168 C (nmol / L) -0.38657 (n = 5, R2 = 0.99444) and Ipa (μA) = 0.16032 C (μmol / L) -2.82852, (n = 7, R 2 =0.99307), and the minimum detection limit was 66.67nmo1 / L(3S0 / S).

[0111] Table 1 shows the content of chlorogenic acid in coffee beans detected by the spike recovery method. The results show that the recovery rate of coffee beans determined by the electrochemical sensor based on SAFe-NC-900 is in the range of 100.84% ​​to 106.02%, and the RSD value is less than 5%.

[0112] Table 1

[0113]

[0114]

[0115] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterials derived from waste coffee grounds, characterized in that: The following steps are involved: Carbonizing coffee grounds in an argon atmosphere to obtain the waste coffee grounds-derived in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial; The carbonization is specifically carried out by heating the material to 800-1000° C. at a rate of 5° C. / min and carbonizing the material for 2 hours.

2. The method for preparing in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterials derived from waste coffee grounds according to claim 1, characterized in that: The inert atmosphere is an argon atmosphere.

3. The method for preparing in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterials derived from waste coffee grounds according to claim 1, characterized in that: The coffee grounds are dry coffee grounds from which impurities have been removed.

4. The method for preparing in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterials derived from waste coffee grounds according to claim 1, characterized in that: After the carbonization is completed, the step of grinding the particles to a size no greater than 0.5 μm is also included.

5. An in situ single-atom iron-loaded nitrogen-doped carbon nanomaterial derived from waste coffee grounds prepared according to the preparation method according to any one of claims 1 to 4.

6. A method for preparing an electrochemical sensor, characterized in that: The following steps are involved: The waste coffee grounds-derived in-situ single-atom iron-loaded nitrogen-doped carbon nanomaterial according to claim 5 is mixed with water to prepare a dispersion, the dispersion is drop-coated on the electrode surface, and after drying, a Nafion ethanol solution is continuously drop-coated and dried to obtain the electrochemical sensor.

7. The method for preparing an electrochemical sensor according to claim 6, wherein: The concentration of the dispersion is 0.5-2 mg / mL; the mass concentration of the Nafion ethanol solution is 0.5%; the electrode is a glassy carbon electrode or a screen-printed electrode; the drop amount of the dispersion on the electrode surface is 0.5-0.7 μL / mm 2 The amount of Nafion ethanol solution applied to the electrode surface is 0.3 to 0.4 μL / mm 2 .

8. An electrochemical sensor prepared according to the method for preparing an electrochemical sensor according to claim 6 or 7.

9. Use of the electrochemical sensor according to claim 8 in detecting chlorogenic acid.

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