Potassium ion working electrode based on eggshell-shaped hollow carbon microspheres as well as preparation method and application of potassium ion working electrode

Abstract

The invention discloses a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres and a preparation method and application thereof, the electrode comprises a glassy carbon substrate and an ESHCMS layer modified on the surface of the glassy carbon substrate, and the ESHCMS layer is composed of eggshell-shaped hollow carbon microspheres. The eggshell-shaped hollow carbon microspheres are synthesized through a simple hydrothermal method, the prepared eggshell-shaped hollow carbon microspheres are good in graphitization degree, the large specific surface area, the excellent electronic conductivity and the excellent chemical stability of the eggshell-shaped hollow carbon microspheres and the high electric capacity and the good hydrophobicity when the eggshell-shaped hollow carbon microspheres serve as double electric layers are utilized, and the graphitization degree of the eggshell-shaped hollow carbon microspheres is improved. The potassium ion selective electrode is introduced between a polymer film and a glassy carbon substrate, so that a water layer between a conductive substrate and the polymer film is effectively eliminated, the potential of the potassium ion selective electrode is stabilized, and the sensitivity, selectivity and response speed of the working electrode are improved.

Description

Technical Field

[0001] The present invention belongs to the field of chemical / biological sensing technology, and relates to a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres, a preparation method and application thereof, and more particularly to a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres as ion-electron converters and its application in potassium ion detection. Background Art

[0002] From nature to industrial production, potassium is a widely existing and very important element. In nature, the amount of potassium in the soil is directly related to the normal growth of plants. In the human body, potassium ions are widely present in body fluids, playing a key role in activities such as nerve impulse transmission and osmotic regulation. The imbalance of its content in the body is often closely related to the occurrence of some diseases, including non-seborrheic hyperkalemia, obesity, heart disease, diabetes and Addison's disease. In the cigarette paper industry, potassium salts are adsorbed on the surface of cigarette paper fibers in the form of ions, catalyzing the combustion and decomposition of cellulose, thereby affecting the combustion temperature, combustion rate and combustion products of cigarette paper. The quality of cigarette products can be improved by adjusting the content and type of potassium salts. Moreover, potassium salts are usually added to cigarette paper as an organic potassium salt as a combustion aid. Different batches of cigarette paper have different potassium salt addition requirements due to their different product quality preferences. In this production link, the significance of monitoring and controlling potassium salt content is self-evident. At the same time, it is also of great development significance to realize rapid and on-site detection of potassium ions in industrial production workshops. In traditional K + Detection methods such as fluorescence, chromatography, and atomic absorption spectrometry often require complex pre-processing, expensive instrumentation, and complex operation and maintenance. Furthermore, rapid on-site monitoring is difficult to achieve. Therefore, further development of potassium ion monitoring methods is needed in environments such as cigarette paper production workshops and living systems.

[0003] Ion-selective electrodes (ISEs) based on potentiometry offer advantages such as low cost, high reliability, and simple operation, and are widely used in clinical analysis, environmental monitoring, process control, and other fields. To enhance the potential stability of all-solid-state ion-selective electrodes, researchers initially added electroactive substances during the electrode preparation process, finding that this effectively improved the ion-electron conductivity at the interface between the thin film and the conductive substrate, thereby enhancing electrode stability. Although these electrodes still face the problem of water layer interference, this has sparked research on solid-state transduction layers. Currently, the transduction material is often introduced by first forming an intermediate layer on a conductive substrate through drop coating or electrodeposition, followed by drop casting of an ion-selective carrier membrane onto the surface of the intermediate layer. However, this method still suffers from limitations such as insufficient electrode potential stability and sensitivity degradation over long-term use. In addition to exploring methods for introducing transduction materials, the synthesis of novel solid-state transduction materials is also a hot research topic. Summary of the Invention

[0004] In view of the shortcomings of the potassium ion working electrode in the prior art, the first object of the present invention is to provide a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres. The electrode introduces the eggshell-shaped hollow carbon microspheres between the polymer membrane and the glassy carbon electrode, effectively eliminating the water layer between the conductive substrate and the polymer membrane, stabilizing the potential of the potassium ion selective electrode, and improving the selectivity and response speed of the working electrode.

[0005] The second object of the present invention is to provide a method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres with simple operation, mild conditions and low production cost.

[0006] A third object of the present invention is to provide an application of a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres, which is applied to the detection of potassium ions and has good linear response capability, fast response speed, high sensitivity and stability, can accurately measure potassium ion concentrations over a wide range, maintains stability after long-term performance testing, and has high accuracy and reproducibility in on-site rapid detection.

[0007] In order to achieve the above technical objectives, the present invention provides a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres, which includes a glassy carbon matrix 5 and an ESHCMS layer 6 modified on the surface of the glassy carbon matrix; the ESHCMS layer is loaded with K + ICM film layer 7; the K + There is K in the ICM film + ICM unit 9, the K + ICM units can bind to target K + 8, there is ESHCMS unit 10 in the ESHCMS layer; the K + The ICM unit is a cyclic 12-peptide, and its structural formula is shown in Formula I:

[0008]

[0009] As a preferred solution, the ESHCMS unit is an eggshell-shaped hollow carbon microsphere.

[0010] The present invention uses 1-hydroxy-3-aminobenzene and formaldehyde as raw materials, uses acetone to promote the homogeneous reaction to be complete, and after selectively removing the inhomogeneous components inside the resin ball, obtains eggshell-shaped hollow carbon microspheres (ESHCMS units) after high-temperature carbonization. The degree of graphitization of these microspheres is well improved by hydrothermal preparation. Then, these eggshell-shaped hollow carbon microspheres are drop-coated on a glassy carbon matrix (GCE) and covered with a polymer potassium ion selective membrane to form the working electrode of the present invention. The key to the present invention is to utilize the excellent properties of eggshell-shaped hollow carbon microspheres, including their large specific surface area, good hydrophobicity, large interfacial capacitance, excellent conductivity and chemical stability. These properties help to effectively eliminate the water layer between the conductive substrate and the polymer membrane, stabilize the potential of the potassium ion selective electrode, thereby improving the selectivity and response speed of the working electrode. In addition, the electrode of the present invention is also embedded with a K that is sensitive to potassium ions. + The ICM unit is a cyclic 12-peptide with an optimal size and shape. The diameter of the cavity formed by its six adjacent oxygen atoms matches the size of potassium ions, allowing potassium ions to move freely through the membrane medium while other ions of mismatched sizes are unable to pass through, thus achieving high selectivity for potassium ions. The cyclic 12-peptide, combined with the solid-state conductive layer of the ESHCMS unit, can form a more stable potential signal, further enhancing the performance of the electrode.

[0011] As a preferred solution, the thickness of the glassy carbon matrix is ​​1.0 to 5.0 mm; the thickness of the ESHCMS layer is 400 to 2000 nm; the K + The thickness of the ICM film layer is 200 to 2000 nm.

[0012] The thickness of the glassy carbon matrix in the present invention affects the conductivity and stability of the electrode. Too thick may cause the electrode response speed to slow down, while too thin may affect the stability of the electrode. The thickness of the ESHCMS layer affects the hydrophobicity and interface capacitance of the electrode. An appropriate thickness helps to stabilize the potential and eliminate the water layer between the conductive matrix and the polymer film. + The thickness of the ICM film layer affects the selectivity and response speed of the electrode. A thinner film layer is beneficial to improving the selectivity of the electrode, but may affect the response speed. An appropriate thickness helps to balance the selectivity and response speed. Therefore, the glassy carbon matrix, ESHCMS layer and K + The thickness of the ICM film layer needs to be reasonably optimized to obtain the best electrode performance.

[0013] As a preferred solution, the outer diameter of the eggshell-shaped hollow carbon microspheres is 433±13nm and the thickness is 19.4±1.7nm. The outer diameter and thickness of the hollow carbon microspheres directly affect the electron transfer efficiency, and thus directly affect the response performance of the electrode. Within a certain size range, the smaller outer diameter of the hollow carbon microspheres gives the material a larger specific surface area, enabling the electrode to obtain a large double-layer capacitance and stably carry out ion-electron conversion, thereby improving the potential stability of the electrode; at the same time, the small thickness of the hollow shell can shorten the propagation path of the electrons, accelerate the propagation of the electrons, and thus help the electrode to respond quickly to the target ions.

[0014] As a preferred solution, the K + The ICM film is made of K + The ICM membrane solution is drop-coated and dried.

[0015] As a preferred solution, the K + The ICM membrane solution includes the following raw materials in parts by weight: 1 to 5 parts K + ICM unit; 1 to 5 parts of potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate; 50 to 100 parts of modified polyvinyl chloride; 60 to 150 parts of o-nitrophenyl octyl ether; 1 to 2 parts of anhydrous tetrahydrofuran (solvent). + In the ICM membrane solution, K + The ICM unit is an active carrier material, highly selective for potassium ions. Potassium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate acts as an anion localizer, inhibiting interfering ions from penetrating the sensitive membrane and improving the response to the target ion. Modified polyvinyl chloride serves as an inert matrix for the carrier, and o-nitrophenyl octyl ether acts as a plasticizer, enhancing sensitivity to the target ion. High potassium ion selectivity and rapid response are achieved only through coordinated control of the types and amounts of these components.

[0016] As a preferred solution, the modified polyvinyl chloride is obtained by irradiating polyvinyl chloride with ultraviolet light in the wavelength range of 320-400 nm for 1-10 hours. Ultraviolet light modification of polyvinyl chloride can improve the performance of the inert matrix and further enhance the response to target ions.

[0017] As a preferred solution, the degree of polymerization of the polyvinyl chloride is 1200-1400.

[0018] The present invention also provides a method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres, comprising grinding an ESHCMS unit and dissolving and dispersing it in tetrahydrofuran to obtain an ESHCMS solution; drop-coating the ESHCMS solution on the surface of a glassy carbon electrode to obtain an ESHCMS-GCE composite electrode; and drop-coating the surface of the ESHCMS-GCE composite electrode with K +ICM membrane solution was dried and activated with potassium ions to obtain K + ISM-ESHCMS-GCE composite electrode.

[0019] As a preferred solution, during the preparation of the ESHCMS-GCE composite electrode, if the weather is relatively humid, an infrared lamp can be used to bake the electrode surface to achieve rapid loading and avoid moisture absorption.

[0020] As a preferred solution, the K + The ICM membrane solution contains K + The raw materials including ICM unit, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, modified polyvinyl chloride, o-nitrophenyl octyl ether and anhydrous tetrahydrofuran are shaken and mixed to obtain the product.

[0021] As a preferred solution, the ESHCMS unit is obtained by polycondensing an aqueous phase containing 1-hydroxy-3-aminobenzene with formaldehyde under the action of ammonia catalyst to obtain phenolic resin microspheres; the phenolic resin microspheres are obtained by selectively dissolving in acetone, centrifuging, drying and carbonizing.

[0022] As a preferred solution, the potassium ion activated solution is 1.0×10 -3 ~1.0×10 -7 mol / L potassium ion standard solution, the activation time is 2 to 24 hours.

[0023] As a preferred solution, the concentration of the ESHCMS solution is 0.05-2.0 mg / mL, and the dosage is 5.0-50 μL.

[0024] As a preferred solution, the K + The ICM membrane solution is applied 3 to 4 times, with a single application volume of 5 to 20 μL.

[0025] As a preferred solution, the solid-liquid ratio of the 1-hydroxy-3-aminobenzene, formaldehyde and ammonia water is (80-150) mg: (20-120) μL: (10-100) μL; the concentration of the formaldehyde is 8-10 mol / L; and the amount of the ammonia water is 8-10 mol / L.

[0026] As a preferred solution, the conditions for the polycondensation reaction are: temperature of 25 to 60° C. and time of 10 to 30 minutes.

[0027] As a preferred solution, the carbonization conditions are: under a protective atmosphere, a temperature of 800 to 1200° C., and a time of 1 to 12 hours.

[0028] As a preferred solution, the formaldehyde is added dropwise at a dropping rate of 10 to 60 drops / min.

[0029] As a preferred embodiment, the glassy carbon electrode is polished with alumina powder before use until the surface is smooth and the resistance is less than 100 ohms. Further preferably, the surface of the glassy carbon electrode is polished with 0.1μm, 0.3μm, and 0.05μm alumina powder before use, and then ultrasonically cleaned. The cleaning steps include ultrasonic cleaning with ultrapure water, ethanol, and ultrapure water for 0.5 to 5.0 minutes in sequence; and the surface of the glassy carbon electrode substrate is blown dry under a nitrogen flow.

[0030] Finally, the present invention also provides an application of a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres, which is applied to the detection of potassium ions. During the detection process, a working standard curve is first drawn, and then the potassium ions in the sample to be tested are detected. + There is a good linear relationship between the concentrations of -6 ~1.0×10 -2 mol / L, the optimal linear response slope was 55.53mV / decade (±1.6mV / decade), and the detection limit was as low as 1.4×10 -6 mol / L.

[0031] As a preferred solution, the potassium ion detection process is carried out with K + The ICM-ESHCMS-GCE composite electrode was used as the working electrode, the double-junction calomel electrode was used as the reference electrode, and the LiOAc buffer solution constituted a potential detection circuit, and a direct potential test method was adopted.

[0032] As a preferred solution, the composition of the double-junction calomel electrode is Hg / Hg2Cl2 / saturated KCl solution / LiOAc, and its external salt bridge solution is 0.5-3.0MLiOAc.

[0033] As a preferred solution, the LiOAc buffer solution comprises 0.5-3.0 mol / L LiOH solution and 0.5-3.0% dilute acetic acid solution in a volume ratio of (3-9):(30-40), and its pH value is 6-8.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) The present invention synthesizes eggshell-shaped hollow carbon microspheres by a simple hydrothermal method. The prepared eggshell-shaped hollow carbon microspheres have a good degree of graphitization. The eggshell-shaped hollow carbon microspheres are introduced between a polymer membrane and a glassy carbon electrode by utilizing their large specific surface area, excellent electrical conductivity, excellent chemical stability, high capacitance when acting as a double layer, and good hydrophobicity. This effectively eliminates the water layer between the conductive substrate and the polymer membrane, stabilizes the potential of the potassium ion selective electrode, and improves the selectivity and response speed of the working electrode.

[0036] 2) The all-solid-state potassium ion selective electrode prepared by the present invention. The electrode is -5 ~1.0×10 -2 It has good linearity within the range of mol / L, with the best linear response slope of 55.53mV / decade (±1.6mV / decade), and the detection limit is as low as 1.4×10 -6 mol / L. The electrode exhibits fast response, high sensitivity, and excellent stability and reproducibility. During a four-month performance test of the electrode, the electrode's response slope decreased by 4.34% compared to the initial value, demonstrating its stable performance and long life.

[0037] 3) The prepared electrode was applied to potassium ion detection. The detection results were consistent with those of traditional ion chromatography, with spiked recoveries ranging from 93.5% to 105.8%. However, it has the advantage of rapid on-site detection compared with traditional methods.

[0038] 4) The preparation process of the present invention is simple, the electrode is easy to prepare, and the prepared electrode has high application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A potassium ion electrode (K) based on eggshell-shaped hollow carbon microspheres as ion-electron converters + Schematic diagram of the working structure of ICM-ESHCMS-GCE, where: 1-reference electrode; 2-working electrode; 3-test solution; 4-detection cell; 5-glassy carbon matrix; 6-eggshell hollow carbon microsphere (ESHCMS) layer; 7-K + ICM film; 8-K + ; 9-potassium ionophore (K + ICM, cyclic 12 peptide); 10-eggshell hollow carbon microspheres (ESHCMS).

[0040] Figure 2 The structure diagram of eggshell-shaped hollow carbon microspheres, where d1 is the outer diameter, d2 is the inner diameter, and h is the thickness.

[0041] Figure 3These are high-resolution electron microscopy images of the eggshell-shaped hollow carbon microspheres, where A, B, C, and D are SEM images, and E and F are TEM images.

[0042] Figure 4 This is the EDS spectrum analysis of eggshell-shaped hollow carbon microspheres.

[0043] Figure 5 (A) XRD pattern and (B) Raman spectrum of eggshell-shaped hollow carbon microspheres.

[0044] Figure 6 For composite electrode (K + ICM-ESHCMS1-GCE, K + ICM-ESHCMS2-GCE, K + ICM-ESHCMS3-GCE and K + (A) Calibration curve of ICM-GCE for potassium ion; and (B) K + Dynamic potential response of ICM-ESH CMS1-GCE.

[0045] Figure 7 K + ICM-ESHCMS1-GCE with K + Electrochemical impedance spectroscopy of the ICM-GCE electrode in 0.01 mol / L KCl solution.

[0046] Figure 8 K + ICM-ESHCMS1-GCE and K + Chronopotentiometry test spectrum of ICM-GCE; I is ±1 nA, each lasting 60 s, and the electrolyte solution is 0.01 M KCl solution.

[0047] Figure 9 K + ICM-ESHCMS1-GCE and K + Water layer test diagram of ICM-GCE in 0.01mol / L KCl solution and NaCl solution.

[0048] Figure 10 K + Service life test curve of ICM-ESHCMS1-GCE electrode. DETAILED DESCRIPTION

[0049] The present invention is further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without making creative efforts are still within the scope of protection of the present invention.

[0050] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0051] Example 1

[0052] This embodiment is a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres. Figure 1 It can be seen that its structure includes a glassy carbon matrix 5 and an ESHCMS layer 6 modified on the surface of the glassy carbon matrix 5; the ESHCMS layer 6 is loaded with K + ICM film layer 7; K + There is K in ICM layer 7 + ICM Unit 9, K + ICM unit 9 can combine with target K + 8, ESHCMS unit 10 exists in ESHCMS layer 6. The glassy carbon matrix is ​​3mm, the ESHCMS layer is 850nm and K + ICM film layer 1120nm. Figure 2 It can be seen that the outer diameter of the eggshell-shaped hollow carbon microspheres (ESHCMS unit) is 422 nm and the thickness is 20.4 nm.

[0053] The preparation method of a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres in this embodiment is as follows:

[0054] 1) Preparation of eggshell-shaped hollow carbon microspheres (ESHCMS units)

[0055] Place 110 mg of 1-hydroxy-3-aminobenzene in a 100 mL round-bottom flask, add 25 mL of distilled water, and place in a 32°C waterbath with constant stirring. Take 120 μL of formaldehyde solution (10 mol / L), dilute it with 10 mL of distilled water, and add it dropwise to the round-bottom flask at a rate of 25 drops / min. Add 50 μL of ammonia solution (10 mol / L) as a catalyst, and react in a 32°C waterbath for 25 min. After the reaction, centrifuge and collect the precipitate. Add 25 mL of acetone to promote complete homogeneous reaction. After centrifugation, wash three times with distilled water, and collect the precipitate. Place the solid in a vacuum drying oven at 110°C for 12 h. Place the dried solid in an alumina boat, place it in a tube furnace, and calcine it at 1000°C for 6 h under a nitrogen atmosphere to obtain ESHCMS1.

[0056] 2) Preparation of potassium ion carrier (K + ICM) membrane solution

[0057] Take 2.2mg potassium ion carrier (K +ICM, cyclic 12 peptide), 1.2 mg of potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, 70 mg of modified polyvinyl chloride powder, 135 mg of o-nitrophenyl octyl ether (o-NPOE), dissolved in 1.5 mL of anhydrous tetrahydrofuran. The degree of polymerization of the modified polyvinyl chloride is 1350, and the powder is modified by irradiating ultraviolet light for 6 hours, and the wavelength range of ultraviolet light is 350 nm. + The structural formula of ICM is shown below.

[0058]

[0059] Since o-NPOE (ρ = 1.04 g / mL) is a liquid, convert the mass to volume before pipetting. Shake thoroughly until completely dissolved to obtain a light yellow, transparent film solution. Store in the refrigerator when not in use.

[0060] 3) Preparation of K + ICM-ESHCMS1-GCE composite electrode

[0061] First, place a glassy carbon electrode (GCE, with a diameter of 3 mm) on a polishing velvet cloth and polish it with alumina powder with diameters of 0.1, 0.3 and 0.05 μm in turn, wherein the resistance after polishing is less than 100 ohms; then perform ultrasonic cleaning, and the cleaning steps are ultrasonic cleaning with ultrapure water, ethanol and ultrapure water for 1.0 min in turn; blow dry the surface of the glassy carbon electrode substrate under a nitrogen flow and set aside. Then, the ESHCMS1 prepared above was placed in a mortar and ground for 3 minutes, 1 mg was weighed and dissolved in 2 mL of tetrahydrofuran, and ultrasonically dispersed for 15 minutes to mix it completely. 25 μL of the uniform mixture was aspirated with a pipette and carefully dripped onto the surface of the glassy carbon electrode so that it completely covered the conductive substrate to obtain an ESHCMS1-GCE composite electrode; then, 12 μL of the potassium ion carrier (K + ICM) membrane solution was drop-coated on the surface of the ESHCMS1-GCE composite electrode, once every 10 minutes, for a total of three times. After the drop-coating was completed, the newly prepared electrode was transferred to a fume hood and covered to avoid surface contamination. It was dried at room temperature for 12 hours. After drying, the electrode was transferred to a 1.0×10 -3 mol / L potassium ion standard solution for more than 12 h, and then placed in 1.0×10 -7 If not used for a long time, store it in a dry place at room temperature.

[0062] Example 2

[0063] The only difference between this embodiment and embodiment 1 is that the preparation method of the ESHCMS unit is changed to: 100 mg of 1-hydroxy-3-aminobenzene is placed in a 100 mL round-bottom flask, 20 mL of distilled water is added, and the mixture is placed in a 35°C water bath with constant stirring. Take 110 μL of formaldehyde solution (10 mol / L), dilute it with 10 mL of distilled water, and add it dropwise to the round-bottom flask at a rate of 15 drops / min. Add 80 μL of ammonia solution (10 mol / L) as a catalyst and react for 20 minutes in a 35°C water bath. After the reaction is completed, centrifuge and collect the precipitate, add 30 mL of acetone to promote complete homogeneous reaction, and wash it three times with distilled water after centrifugation to collect the precipitate. Place the solid in a vacuum drying oven and vacuum dry it at 120°C for 4 hours. Place the dried solid in an alumina porcelain boat, place it in a tubular furnace, and calcine it at 950°C for 8 hours under a N2 environment to obtain ESHCMS2. The remaining steps and conditions are the same to obtain K + ICM-ESHCMS2-GCE composite electrode, performance test see Figure 6 The outer diameter of the eggshell-shaped hollow carbon microspheres (ESHCMS units) is 438 nm and the thickness is 20.8 nm.

[0064] Example 3

[0065] The only difference between this embodiment and embodiment 1 is that the preparation method of the ESHCMS unit is changed to: 80 mg of 1-hydroxy-3-aminobenzene is placed in a 100 mL round-bottom flask, 15 mL of distilled water is added, and the mixture is placed in a 40°C water bath with constant stirring. Take 90 μL of formaldehyde solution (10 mol / L), dilute it with 10 mL of distilled water, and add it dropwise to the round-bottom flask at a rate of 35 drops / min. Add 40 μL of ammonia solution (10 mol / L) as a catalyst and react for 15 minutes in a 40°C water bath. After the reaction is completed, centrifuge and collect the precipitate, add 50 mL of acetone to promote complete homogeneous reaction, and wash it three times with distilled water after centrifugation to collect the precipitate. Place the solid in a vacuum drying oven and vacuum dry it at 90°C for 8 hours. Place the dried solid in an alumina porcelain boat, place it in a tubular furnace, and calcine it at 1050°C for 4 hours under a N2 environment to obtain ESHCMS3. The remaining conditions and steps are the same, and K is obtained. + ICM-ESHCMS3-GCE composite electrode, performance test see Figure 6 The outer diameter of the eggshell-shaped hollow carbon microspheres (ESHCMS units) is 444 nm and the thickness is 21.1 nm.

[0066] Comparative Example 1

[0067] This comparative example is a solid-state transfer layer without the same amount of K + Glassy carbon electrode for selective membrane solution (K+ ICM-GCE), the preparation method of this comparative example is the same as that of Example 1, except that the potassium ion carrier (K + ICM) membrane solution was added dropwise to obtain a glassy carbon electrode without a solid transfer layer (K + ICM-GCE).

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 1 is that the potassium ion carrier (K + Unmodified polyvinyl chloride (PVC) was used for the ICM membrane solution, with all other conditions remaining the same. During the process, unmodified PVC has insufficient adhesion, allowing the plasticizer and ion carrier to leak easily. Furthermore, the sensitive membrane can fall off during electrode activation, preventing it from being fixed to the electrode.

[0070] The eggshell hollow carbon microspheres (ESHCMS1 unit) obtained in Example 1 were subjected to electron microscope scanning, and the results are shown in FIG. Figure 2 and Figure 3 .from Figure 3 ( Figure 3 AD) shows that the outer diameter of the sphere is 422nm, the thickness is 20.4nm, the overall structure is three-dimensional, the size distribution is uniform, and it shows good dispersion. The eggshell-shaped hollow carbon microspheres are complete and independent, with basically no adhesion. At the same time, there are a small number of broken carbon microspheres in the synthesized carbon microspheres, and it can be clearly observed that they are eggshell-shaped hollow structures, proving that the synthesized carbon microspheres are eggshell-shaped hollow carbon microspheres. Figure 3 ( Figure 3 E and F), the spherical particles are intact, but the surface is not smooth and dense, confirming the presence of a microporous structure. The hollow shell and spherical micropores give the material a large specific surface area, enabling the electrode to achieve a large double-layer capacitance and stable ion-electron conversion, thereby improving the electrode's potential stability. Furthermore, the hollow shell and spherical micropores shorten the electron propagation path, accelerating electron propagation and promoting a rapid response of the electrode to target ions.

[0071] The eggshell hollow carbon microspheres (ESHCMS1 unit) obtained in Example 1 were subjected to EDS spectrum analysis, and the results are shown in Figure 4 and Table 1. Figure 4 As shown in the figure, it can be seen that the main element composition of the eggshell-shaped hollow carbon microspheres is C, containing a small amount of N and O elements. Generally, the C element in the material is conducive to the conductivity of the material, while the O element is related to the affinity for the electrolyte. From the results in Table 1, it can be seen that the C element content accounts for more than 90%, indicating that the eggshell-shaped hollow carbon microspheres have good electrochemical properties.

[0072] Table 1 Contents of elements in ESHCMS1 unit

[0073]

[0074] The eggshell-shaped hollow carbon microspheres (ESHCMS1 unit) obtained in Example 1 were subjected to X-ray diffraction and Raman spectroscopy analysis. Figure 5 As shown in (A), the eggshell-shaped hollow carbon microspheres (ESHCMS1 unit) have obvious diffraction peaks at 22.4° and 43.6°, corresponding to the (002) crystal plane and (101) diffraction crystal plane of pure graphite, respectively, which indicates that the degree of graphitization of ESHCMS1 unit is high. The Raman spectrum of ESHCMS1 unit is shown in Figure 5 As shown in (B), the ESHCMS1 unit is at 1580 cm -1 The peak that appears corresponds to the G absorption band, while at 1340 cm -1 The peak shown corresponds to the D absorption band. Located at 1580 cm -1 The G absorption band at 1340 cm is caused by the stretching vibration between sp2 carbon atoms, while the -1 The D absorption band at [Number] represents the aromatic ring breathing mode, which typically occurs when the material contains defects. Therefore, the peak intensity of the D absorption band can also serve as a reference for the material's disorder. The Raman spectrum shows distinct G and D absorption bands, indicating that the prepared ESHCMS unit is well graphitized.

[0075] The electrodes obtained in Examples (1, 2, and 3) were used as working electrodes and a double-junction calomel electrode (Hg / Hg2Cl2 / saturated KCl solution / LiOAc) was used as a reference electrode to form a potential detection circuit. The structure of the primary cell was: Hg / Hg2Cl2 / saturated KCl solution / LiOAc / sample solution / K + ICM-ESHCMS-GCE composite electrode. The external salt bridge solution is 1.0M LiOAc. The composition of the LiOAc buffer solution is a mixture of 6.0mL 1.0mol / L LiOH solution (Solution A) and 34.0mL 1.0% dilute acetic acid solution (Solution B). The pH value of the LiOAc buffer solution is pH 7.0. -8 to 1.0×10 - 2 mol / L KCl solution to test K + The ion response performance of the ICM-ESHCMS-GCE composite electrode, where the low concentration solution was prepared by diluting the high concentration solution 10 times. Figure 6 The prepared electrode has a potassium ion concentration of 1.0×10 -5 ~1.0×10 -2It has a good linear response relationship within mol / L, and its performance parameters are shown in Table 2.

[0076] Table 2 Comparison of performance of composite potassium ion selective electrodes

[0077]

[0078] The impedance of the electrodes obtained in Example 1 and Comparative Example 1 was compared, that is, the impedance test was carried out in a 0.01 mol / L KCl solution. The results are shown in FIG. Figure 7 The impedance spectrum can reflect the resistance and capacitance properties of the material to a certain extent. The semicircle diameter in the high-frequency amplification area of ​​the spectrum represents the charge transfer resistance Rct, that is, the transfer resistance of ions across the membrane interface to the transduction layer. The larger the semicircle diameter, the greater the material resistance, and the more difficult it is to achieve rapid ion-electron conversion. Figure 7 It can be seen that after adding eggshell-shaped hollow carbon microspheres (ESHCMS1 unit), K + The resistance of the selective electrode improves the transmission efficiency of electrons. Since the ESHCMS1 unit has a large specific surface area, the contact area of ​​the electrode is increased, thereby accelerating the ion-electron conversion rate during potassium ion testing and obtaining a fast and stable response signal.

[0079] The electrodes obtained in Example 1 and Comparative Example 1 were subjected to chronopotentiometry analysis and testing, respectively. + ICM-ESHCMS1-GCE composite electrode and electrode K prepared in Comparative Example 1 + ICM-GCE applies a +1nA constant current for 60s, and then applies a constant direction current for 60s. Figure 8 As shown in the figure, when a constant current is applied in the forward direction for 60s, the electrode potential has a certain drift; when the current is reversed, the potential has an instantaneous downward step. The main reason is that the electrode may have a "membrane volume resistance". Through calculation and analysis, it can be obtained that the electrode without a solid transfer layer K + The potential of ICM-GCE changed by 51.9 mV within 60 s; however, when the solid-state transduction layer ESHCMS unit was introduced, the electrode K + The potential of the ICM-ESHCMS1-GCE composite electrode changed by 2.7 mV within 60 s. According to the formula, K + The capacitance of the ICM-ESHCMS1-GCE composite electrode is 22.2 μF, which is much larger than the electrode K + The capacitance of ICM-GCE is 1.15 μF. It can be seen that the addition of the solid-state transduction layer of eggshell-shaped hollow carbon microspheres improves the electrode's potential stability, increases capacitance, improves electron transfer efficiency, and significantly improves electrode response speed.

[0080] The electrodes obtained in Example 1 and Comparative Example 1 were subjected to water layer test, and the K + ICM-ESHCMS1-GCE composite electrode and electrode K prepared in Comparative Example 1 + After the ICM-GCE was subjected to continuous open circuit potential testing in 0.01 mol / L KCl solution for 1.0 h, the electrode was transferred to 0.01 mol / L NaCl solution for continuous open circuit potential testing for 1.0 h, and then transferred back to 0.01 mol / L KCl solution for testing for 3.0 h. The test results are shown in Figure 9 .Depend on Figure 9 It can be seen that K + The ICM-ESHCMS1-GCE composite electrode showed only a slight potential drift, while the electrode K + The ICM-GCE showed a significant potential drop. This experimental result shows that the introduction of the ESHCMS unit solid contact layer can effectively prevent the accumulation of a large amount of water layer between the ion-selective membrane and the glassy carbon matrix, thereby enhancing the stability of the ion-selective electrode.

[0081] The electrode prepared in Example 1 was subjected to ion selectivity detection, and the selectivity coefficient was As an important characterization parameter of ion-selective electrodes, it is used to measure the ability of the electrode to distinguish specific ions in the presence of multiple interfering substances. The smaller the value, the stronger the selectivity of the electrode to the i ion, that is, the greater the anti-interference ability of the j ion. + The anti-interference ability of ICM-ESHCMS1-GCE composite electrode to other ions was tested by separate solution method. + ICM-ESHCMS1-GCE composite electrode for Na + Mg 2+ NH4 + , Ca 2+ 、Ba 2+ Potential tests were performed on various metal ions. The concentration of each solution was 0.01 mol / L. The selectivity coefficient was calculated using the following formula.

[0082]

[0083] Where i represents the main ion K + ; j represents the interfering ion, E is the potential of the solution to be measured, F is the Faraday constant, which is 96500C / mol, R is the gas constant, whose value is 8.314J / (K·mol), T is the thermodynamic temperature, Z represents the ion charge number, and a is the ion activity in the solution.

[0084] Selectivity coefficient The smaller the value, the higher the selectivity of the electrode to the measured ion. Table 3 lists the selectivity coefficients of the electrode in lithium acetate buffer solution. + The selectivity coefficient is greater than 10 -1 , has a certain influence on the electrode, this is because Cs + With K + The standard electrode potential of ions is close to that of ions, but this ion is not usually found in common test environments. Therefore, the electrode has good selectivity and can meet the requirements of actual sample testing.

[0085] Table 3 Selectivity of potassium ion selective electrodes for common interfering ions

[0086]

[0087]

[0088] The electrode prepared in Example 1 was tested for service life. -7 mol / L KCl solution, regularly test the response performance of the electrode and record its response. Figure 10 As shown, the electrodes are at 10 -5 ~10 -2 The electrode showed a stable linear response within the range of mol / L, and the response results are shown in Table 4. During the entire monitoring period, the slope value of the electrode did not change much, and the electrode performance was stable, indicating that the electrode has a long service life of more than 4 months, meeting the requirements of long-term use and having the ability to detect potassium ions for a long time.

[0089] Table 4 Service life of electrodes

[0090]

[0091] Application Examples

[0092] The K prepared in Example 1 + An ICM-ESHCMS1-GCE composite electrode was used as the working electrode, an XR314 double salt bridge electrode was used as the reference electrode, and the internal filling solution was 0.1 mol / L lithium acetate solution. The standard addition method was used to test the potassium content in cigarette paper at open circuit voltage. The cigarette paper preparation method and potassium content calculation were based on the Hunan China Tobacco Industry Co., Ltd. corporate standard: "Determination of Inorganic Cations in Cigarette Paper - Ion Chromatography Method: HNZY / JS-CF-CL-0061.00-211103."

[0093] Cigarette Paper Treatment Method: Weigh 0.10-0.12g of cigarette paper sample, cut into pieces, place in a plastic conical flask, add 100mL of 1% acetic acid solution, and ultrasonically extract for 30 minutes. Accurately measure 34.0mL of the treatment solution and add 6.0mL of 1.0mol / L LiOH solution to prepare the test solution. Transfer to a plastic centrifuge tube for storage.

[0094] According to the tobacco industry standard calculation method, the potassium content is calculated according to the following formula.

[0095]

[0096] Where:

[0097] χ——potassium content in the sample, %;

[0098] C——mass concentration of potassium in the sample, mg / L;

[0099] V——total volume of sample digestion solution, mL;

[0100] n——dilution multiple of sample digestion solution;

[0101] m——sample mass, g;

[0102] ω——moisture content of sample, %.

[0103] After the test, the calculated results were compared with the ion chromatography test data provided by the cigarette factory, as shown in Table 5.

[0104] Table 5 Comparison of potassium ion content in different samples determined by ion selective electrode method and ion chromatography test data

[0105]

[0106] From Table 5, we can see that using K + The average relative deviation (RD) of potassium content data from cigarette paper samples collected at different times, measured using the ICM-ESHCMS1-GCE composite electrode and ion chromatography, was 3.65% (n=6), indicating consistent results with no significant difference. Therefore, the solid-state contact potassium ion-selective electrode based on ESHCMS cell transduction can be used as a novel technique for potassium ion detection and analysis in cigarette paper.

[0107] Select lithium acetate buffer solution, use the potassium ion selective electrode K + The ICM-ESHCMS1-GCE composite electrode was used to determine the spike recovery of potassium in cigarette paper. The standard addition method was used: a known potassium ion solution was added to the actual sample, the potential change was measured, and the measured content was calculated using the working curve and compared with the actual added value.

[0108] As shown in Table 6, K + The ICM-ESHCMS1-GCE composite electrode was used to test the recovery rate of cigarette paper samples 1#, 8#, 21#, 22#, and 31#. The ion chromatography data was set as the standard value, and potassium chloride solutions of different standard concentrations were added to the sample solution. The potassium ion content in the sample was measured using the ion selective electrode. The recovery rate of the potassium ion selective electrode method was 93.5% to 105.8%, indicating that K + The ICM-ESHCMS1-GCE composite electrode can be used to determine the potassium content in cigarette paper.

[0109] Table 6 Determination of potassium ion content and recovery rate in different samples by ion selective electrode method

[0110]

[0111] Note: IC is the value measured by ion chromatography, Spiked is the amount added, and Measured is the value measured by electrode

[0112] In summary, the present invention prepared eggshell-shaped hollow carbon microspheres (ESHCMS units) with excellent performance and successfully used them as a solid-state transduction layer to prepare a solid-state potassium ion-selective electrode. The addition of ESHCMS units increases both electron transport efficiency and ion-electron conversion efficiency. The large specific surface area and high capacitance also stabilize the electrode potential. After optimizing the conditions, a calibration curve was obtained under the optimal conditions, with a linear range of 5.0×10 -6 ~1.0×10 -2 mol / L, the linear equation is E(mV)=55.53C(mol / L)+348.57(R 2 =0.9995), and the detection limit was 1.4×10 -6 mol / L. In actual sample testing, the test results were not much different from those of ion chromatography, and the electrode performed well in the selective testing process, and can be used for on-site rapid testing of actual samples in cigarette workshops.

Claims

1. A potassium ion working electrode based on eggshell-shaped hollow carbon microspheres, characterized by: The invention comprises a glassy carbon matrix (5) and an ESHCMS layer (6) modified on the surface of the glassy carbon matrix (5); the ESHCMS layer (6) is loaded with K + ICM membrane layer (7); said K + There is K in the ICM film (7) + ICM unit (9), the K + ICM unit (9) can bind to target K + (8), an ESHCMS unit (10) exists in the ESHCMS layer (6); The K + The ICM unit is a cyclic 12-peptide, and its structural formula is shown in Formula I: The ESHCMS unit is an eggshell-shaped hollow carbon microsphere.

2. The potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 1, characterized in that: The thickness of the glassy carbon matrix (5) is 1.0 to 5.0 mm; The thickness of the ESHCMS layer (6) is 400 to 2000 nm; The K + The thickness of the ICM film layer (7) is 200-2000 nm.

3. The potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 2, characterized in that: The outer diameter of the eggshell-shaped hollow carbon microspheres is 433±13 nm and the thickness is 19.4±1.7 nm.

4. The potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 1, characterized in that: The K + ICM film (7) is made of K + The ICM membrane solution was drop-coated and dried; The K + The ICM membrane solution includes the following raw materials in parts by weight: 1 to 5 parts K + ICM unit; 1 to 5 parts of potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate; 50 to 100 parts of modified polyvinyl chloride; 60 to 150 parts of o-nitrophenyl octyl ether; and 1 to 2 parts of anhydrous tetrahydrofuran.

5. The potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 4, characterized in that: The modified polyvinyl chloride is obtained by irradiating polyvinyl chloride with ultraviolet light having a wavelength range of 320 to 400 nm for 1 to 10 hours.

6. The potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 5, characterized in that: The polymerization degree of the polyvinyl chloride is 1200-1400.

7. The method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to any one of claims 1 to 6, characterized in that: The ESHCMS unit was ground and dissolved in tetrahydrofuran to obtain an ESHCMS solution; the ESHCMS solution was drop-coated on the surface of the glassy carbon substrate to obtain an ESHCMS-GCE composite electrode; the surface of the ESHCMS-GCE composite electrode was drop-coated with K + ICM membrane solution was dried and activated with potassium ions to obtain K + ICM-ESHCMS-GCE composite electrode; The K + The ISM membrane solution contains K + The raw materials including ICM unit, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, modified polyvinyl chloride, o-nitrophenyl octyl ether and anhydrous tetrahydrofuran are shaken and mixed to obtain the product; The ESHCMS unit is prepared by polycondensing an aqueous phase containing 1-hydroxy-3-aminobenzene with formaldehyde under the action of an ammonia catalyst to obtain phenolic resin microspheres; the phenolic resin microspheres are obtained by selectively dissolving in acetone, centrifuging, drying and carbonizing.

8. The method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 7, characterized in that: The concentration of the ESHCMS solution is 0.05-2.0 mg / mL, and the dosage is 5.0-50 μL; The K + The ICM membrane solution is applied 3 to 4 times, with a single application volume of 5 to 20 μL.

9. The method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 7, characterized in that: The solid-liquid ratio of the 1-hydroxy-3-aminobenzene, formaldehyde and ammonia water is (80-150) mg: (20-120) μL: (10-100) μL; The concentration of the formaldehyde is 8 to 10 mol / L; The concentration of the ammonia water is 8-10 mol / L.

10. The method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 9, characterized in that: The conditions for the polycondensation reaction are: temperature of 25-60° C., time of 10-30 min; the conditions for the carbonization are: temperature of 800-1200° C., time of 1-12 h under a protective atmosphere.

11. The method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 10, characterized in that: The formaldehyde is added dropwise at a rate of 10 to 60 drops / min.

12. The method for preparing a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 7, characterized in that: The glassy carbon electrode is polished with aluminum oxide powder before use until the surface is smooth and the resistance is less than 100 ohms.

13. Use of a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to any one of claims 1 to 6, characterized in that: Used for the detection of potassium ions.

14. The use of a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 13, characterized in that: The potassium ion detection process is based on K + The ICM-ESHCMS-GCE composite electrode was used as the working electrode, the double-junction calomel electrode was used as the reference electrode, and the LiOAc buffer solution constituted a potential detection circuit, and a direct potential test method was adopted.

15. The use of a potassium ion working electrode based on eggshell-shaped hollow carbon microspheres according to claim 14, characterized in that: The LiOAc buffer solution comprises 0.5-3.0 mol / L LiOH solution and 0.5-3.0% dilute acetic acid solution in a volume ratio of (3-9):(30-40), and its pH value is 6-8.

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