An ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum, its preparation method and application

Abstract

This invention relates to the field of sensor fabrication technology, and discloses an ammonia nitrogen electrochemical sensor constructed based on platinum supported by ZIF-8-derived carbon NC, its fabrication method, and its application. The ammonia nitrogen electrochemical sensor based on platinum supported by ZIF-8-derived carbon NC comprises: a glassy carbon electrode; a ZIF-8-derived carbon NC material layer modified on the surface of the glassy carbon electrode; and platinum nanoparticles electrodeposited and loaded on the NC material layer. This invention utilizes the high specific surface area, abundant pore structure, and good conductivity of ZIF-8-derived carbon NC as an ideal carrier for platinum nanoparticles, effectively improving the dispersibility of platinum nanoparticles and the effective specific surface area of ​​the electrode. The electrodeposited platinum nanoparticles exhibit excellent electrocatalytic activity, showing a significant signal amplification effect on the oxidation reaction of ammonia nitrogen, thereby achieving high-sensitivity detection of ammonia nitrogen with a linear range of 50 μmol / L to 55000 μmol / L.

Description

Technical Field

[0001] This invention relates to the field of sensor fabrication technology, specifically to an ammonia nitrogen electrochemical sensor constructed based on ZIF-8 derived carbon NC-loaded platinum, its fabrication method, and its application. Background Technology

[0002] Ammonia nitrogen (NH3-N) is one of the most significant nitrogenous pollutants in water bodies, primarily originating from human activities such as agricultural fertilization, industrial wastewater discharge, domestic sewage, and aquaculture wastewater. Ammonia nitrogen in water exists primarily as ammonium ions (NH4+). + Ammonia exists in two forms: chlorine nitrogen (NH3) and free ammonia nitrogen (NH4+). Their distribution ratio is significantly regulated by water pH and temperature. When pH > 9.75, the proportion of the more toxic free ammonia nitrogen (NH3) increases sharply, posing a direct threat to aquatic ecosystems. On the one hand, ammonia nitrogen can cause eutrophication, leading to abnormal algal blooms, dissolved oxygen depletion, and severely disrupting the aquatic ecological balance. On the other hand, free ammonia nitrogen has a strong toxic effect on the gill tissues of fish and other aquatic animals, potentially causing mass fish deaths. In the field of drinking water safety, the presence of ammonia nitrogen increases chlorine consumption during disinfection and promotes the formation of carcinogenic disinfection byproducts such as trihalomethanes, directly endangering public health. Therefore, achieving rapid, accurate, and on-site detection of ammonia nitrogen in water bodies is of significant practical importance for environmental monitoring, water quality assurance, and pollution control.

[0003] Currently, methods for detecting ammonia nitrogen mainly include Nessler's reagent spectrophotometry, salicylic acid-hypochlorite spectrophotometry, distillation-titration, and ion-selective electrode methods. While Nessler's reagent spectrophotometry and salicylic acid spectrophotometry offer high sensitivity and are national standard methods, the former requires mercury-containing reagents, which can easily cause secondary pollution, and the latter involves cumbersome procedures and long color development times. Both methods require complex pretreatment of water samples, such as pre-distillation, making them unsuitable for rapid on-site detection. Distillation-titration is lengthy and consumes large amounts of reagents, limiting its application to laboratory analysis. Although ion-selective electrode methods are relatively simple to operate, their electrode response is easily affected by coexisting ions such as potassium and sodium ions in the water, and they have high detection limits, making accurate quantitative analysis of low-concentration ammonia nitrogen difficult.

[0004] In recent years, electrochemical detection technology has shown great application potential in the field of rapid on-site detection of ammonia nitrogen due to its outstanding advantages such as high sensitivity, fast response speed, simple operation, low cost, and ease of miniaturization and automation. The core of electrochemical sensor detection of ammonia nitrogen lies in the material design and interface construction of the working electrode. Its detection principle is mainly based on the electrocatalytic oxidation reaction of ammonia nitrogen on the modified electrode surface. Among various electrode substrates, glassy carbon (GCE) electrodes are widely used as the substrate electrode for electrochemical sensors due to their good chemical stability, excellent conductivity, wide potential window, and ease of surface modification. By modifying the GCE surface with functional materials to construct a modified electrode (i.e., a GCE electrochemical sensor), the detection performance of ammonia nitrogen can be significantly improved.

[0005] Research on ammonia nitrogen electrochemical sensors based on GCEs has made some progress. Previous studies have shown that noble metal nanoparticles such as platinum (Pt), gold (Au), and palladium (Pd) exhibit high catalytic activity for the electrocatalytic oxidation of ammonia nitrogen, with platinum nanoparticles (PtNPs) being widely studied due to their excellent electrocatalytic performance. For example, some studies have constructed PtNPs / GCE electrodes by directly electrodepositing platinum nanoparticles onto bare GCE surfaces, demonstrating a certain electrocatalytic oxidation response to ammonia nitrogen. However, these electrodes have limited specific surface area and a small number of active sites, leaving considerable room for improvement in detection sensitivity. To improve the specific surface area and catalytic activity of the electrodes, researchers have attempted to load platinum nanoparticles onto various carbon material substrates, such as carbon nanotubes, graphene, and activated carbon. While these carbon materials can improve the dispersion of platinum nanoparticles and the effective specific surface area of ​​the electrode, their preparation processes are usually complex, or suffer from problems such as uncontrollable pore structure and insufficient surface functional groups, making it difficult to effectively achieve uniform loading of platinum nanoparticles and interfacial enrichment of ammonia nitrogen while simultaneously increasing the specific surface area.

[0006] Metal-organic framework (MOF)-derived carbon materials are a new type of porous carbon material that has emerged in recent years. Among them, ZIF-8-derived carbon (NC), obtained by high-temperature carbonization of the zeolite imidazolium ester framework material ZIF-8, not only fully inherits the high specific surface area and regular porous structure of the precursor, but also retains the nitrogen element in the precursor, forming a nitrogen-doped carbon framework. Abundant nitrogen-containing functional groups (such as pyridine nitrogen and graphitic nitrogen) endow NC with excellent surface chemical activity, and the regular microporous-mesoporous structure is conducive to the adsorption and mass transfer of target molecules. These properties give NC unique advantages in the field of electrochemical sensing. However, research on the composite of ZIF-8-derived carbon and platinum nanoparticles for the construction of ammonia-nitrogen electrochemical sensors is currently lacking.

[0007] In summary, existing GCE electrochemical sensors still have the following shortcomings in ammonia nitrogen detection: (1) GCEs using bare GCEs or those modified with a single material have limited electrocatalytic activity for ammonia nitrogen, resulting in low detection sensitivity; (2) Existing carbon material supports lack sufficient dispersion, loading uniformity, and interfacial enrichment capacity for platinum nanoparticles, making it difficult to achieve synergistic enhancement of catalytic activity and adsorption enrichment; (3) The preparation processes of some modified materials are complex and have poor controllability, which is not conducive to the mass production and practical application of sensors. Therefore, how to construct an ammonia nitrogen electrochemical sensor with high sensitivity, wide linear range, good stability, and simple preparation through reasonable material selection and structural design is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to provide an ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC supported platinum, its preparation method and application, so as to overcome the problems of insufficient sensitivity of existing GCE electrochemical sensors for ammonia nitrogen detection, narrow linear range and complex preparation of modified materials.

[0009] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides an ammonia nitrogen electrochemical sensor based on ZIF-8-derived carbon NC loaded platinum, comprising: a glassy carbon electrode; a ZIF-8-derived carbon NC material layer modified on the surface of the glassy carbon electrode; and platinum nanoparticles electrodeposited on the ZIF-8-derived carbon NC material layer. The ZIF-8 derived carbon NC material is obtained by dissolving zinc nitrate hexahydrate and 2-methylimidazole in methanol at a molar ratio of 1:4-1:8, stirring the reaction at room temperature, washing, centrifuging and drying to obtain a ZIF-8 precursor, and then calcining the ZIF-8 precursor at 900℃-1000℃ for 3-5 hours under a protective atmosphere to obtain a nitrogen-doped porous carbon material. The ZIF-8 derived carbon NC material is modified onto the surface of a glassy carbon electrode through the following steps: The ZIF-8 derived carbon NC material is dispersed in a mixed solvent consisting of deionized water, isopropanol and Nafion solution with a volume ratio of 8-12:2-7:0.05-1, and then drop-coated onto the pretreated glassy carbon electrode surface and dried to obtain the final product. The electrodeposition was carried out in a 0.1-1 mol / L HCl solution containing 2-15 mmol / L H2PtCl6·6H2O, with a deposition potential of -1.2 to -0.5 V and a deposition time of 200-800 s.

[0010] In some embodiments, the intensity ratio of the D band to the G band in the Raman spectrum of the ZIF-8 derived carbon NC material is ID / IG, which is 0.8 to 1.2.

[0011] In some embodiments, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:8; the ZIF-8 precursor is calcined at 900°C for 3 hours under a protective atmosphere; the solvent is a mixed solvent consisting of deionized water, isopropanol, and 5 wt.% Nafion solution in a volume ratio of 8:2:0.05; and the electrodeposition is carried out in a 0.5 mol / L HCl solution containing 15 mmol / L H2PtCl6·6H2O, with a deposition potential of -1.0 V and a deposition time of 800 s.

[0012] In some embodiments, when the sensor is used for ammonia nitrogen detection, it is in an environment containing 0.1 mol / L NH4. + In a 1 mol / L KOH solution, the peak current of ammonia nitrogen oxidation per unit electrochemically active surface area is at least 50 times higher than that of a platinum-modified glassy carbon electrode without NC. The ammonia nitrogen electrochemical sensor provided by this invention uses ZIF-8 derived carbon NC as the substrate material, leveraging its excellent electrochemical performance and stability to provide a solid foundation for the electrochemical sensor. Simultaneously, platinum nanoparticles are loaded onto the surface of the ZIF-8 derived carbon NC using electrodeposition technology, forming a PtNPs / NC composite structure. This composite structure not only increases the specific surface area of ​​the electrode, improving the contact opportunity between the electrode and the analyte, but also utilizes the excellent catalytic performance of platinum in the electro-oxidation of ammonia nitrogen, enhancing the sensor's detection sensitivity for ammonia nitrogen.

[0013] Secondly, the present invention provides a method for preparing an ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC supported platinum, comprising the following steps: S1. Preparation of ZIF-8 derived carbon NC material: Zinc nitrate hexahydrate and 2-methylimidazolium were dissolved in methanol at a molar ratio of 1:4-1:8. After stirring at room temperature, the mixture was washed, centrifuged, and dried to obtain the ZIF-8 precursor. The ZIF-8 precursor was calcined at 900℃-1000℃ for 3-5 hours under a protective atmosphere to obtain the ZIF-8 derived carbon NC material. S2. Preparation of NC / GCE modified electrode: The ZIF-8 derived carbon NC material is dispersed in a solvent, drop-coated onto the surface of a pretreated glassy carbon electrode, and dried to obtain the NC / GCE modified electrode. S3. Electrodeposition of platinum nanoparticles: Using the NC / GCE as the working electrode, PtNPs / NC / GCE electrochemical sensor is obtained by constant potential electrodeposition in an electrolyte containing platinum precursor.

[0014] In some embodiments, in step S1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:4-1:6; the ZIF-8 precursor is calcined at 900℃-950℃ for 3-4 hours under a protective atmosphere.

[0015] The preferred method is that the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:8; the calcination temperature is 900℃ and the time is 3 hours.

[0016] In some embodiments, the solvent in step S2 is a mixed solvent consisting of deionized water, isopropanol and Nafion solution with a volume ratio of 8-12:2-7:0.05-1.

[0017] The preferred method is to use a mixed solvent consisting of deionized water, isopropanol and 5 wt.% Nafion solution in a volume ratio of 8:2:0.05.

[0018] In some embodiments, in step S3, the electrolyte is a 0.1-1 mol / L HCl solution containing 2-15 mmol / L H2PtCl6·6H2O, the deposition potential is -1.2 to -0.5 V, and the deposition time is 200-800 s.

[0019] The preferred method is that the electrolyte is a 0.5 mol / L HCl solution containing 15 mmol / L H2PtCl6·6H2O, the deposition potential is -1.0 V, and the deposition time is 800 s.

[0020] Thirdly, this invention provides an application of an ammonia nitrogen electrochemical sensor constructed based on ZIF-8 derived carbon NC-supported platinum, which is used to detect the ammonia nitrogen content in water.

[0021] In some embodiments, the sensor detects ammonia nitrogen in a linear range of 50 μmol / L to 55000 μmol / L.

[0022] In some embodiments, the detection of ammonia nitrogen content in the water body includes: Step 1: Take 1-5 mL of the water sample to be tested, dilute it 10-20 times with 0.5-1.5 mol / L KOH electrolyte, mix well, and obtain the sample solution to be tested; Step 2: Using the sensor as the working electrode, a reference electrode suitable for alkaline systems, and a platinum sheet as the auxiliary electrode, insert the three electrodes into the sample solution to be tested and let it stand for 1-2 minutes. Step 3: Use cyclic voltammetry for detection. The scanning potential range is -0.8 V to 0.2 V, the scanning rate is 100 mV / s, the current response signal is recorded, and the ammonia nitrogen concentration is calculated according to the standard curve.

[0023] In some embodiments, the reference electrode is preferably a saturated Hg / HgO electrode.

[0024] In this invention, ZIF-8 derived carbon NC (hereinafter referred to as NC), glassy carbon electrode (hereinafter referred to as GCE) and platinum nanoparticles (PtNPs) produce a synergistic effect.

[0025] NC is the core functional layer of the sensor, and its main functions are: (1) Physical adsorption enrichment (specific surface area effect): After carbonization, ZIF-8 retains the microporous / mesoporous structure of the MOF precursor, and the BET specific surface area can reach hundreds or even thousands of m² / g. This rich pore structure forms an adsorption layer similar to a molecular sieve on the electrode surface. Through van der Waals forces and pore confinement effect, it can adsorb ammonia nitrogen molecules (NH3 / NH4) in the solution. + It is captured from the liquid phase and enriched near the electrode surface.

[0026] (2) Chemisorption enrichment (nitrogen doping effect): A large number of 2-methylimidazolium ligands in the ZIF-8 framework are converted in situ into various nitrogen-containing functional groups during carbonization: Pyridine nitrogen: sp² hybridized, with its lone pair of electrons exposed, it can bind to ammonia nitrogen molecules via hydrogen bonds (N···H-NH2). Graphite nitrogen: It replaces carbon atoms in the carbon skeleton, alters the electron density of adjacent carbon sites, and enhances the dipole-induced dipole interaction with polar molecules (such as NH3). Pyrrole nitrogen: provides a weakly Brønsted basic site, which can react with NH4+. + Acid-base interaction occurs These nitrogen-containing sites act as anchors, chemically adsorbing ammonia nitrogen molecules, which is the core chemical driving force for NC / GCE to achieve ammonia nitrogen pre-enrichment.

[0027] (3) Conductive network, the carbonized NC forms sp 2 The carbon framework exhibits good electronic conductivity. Its Raman ID / IG ratio is approximately 1.02, indicating a moderate degree of graphitization. This balances the presence of sufficient defect sites for platinum anchoring and ammonia nitrogen adsorption while also providing the conductivity to rapidly transport electrons from catalytic sites to the GCE surface. In this invention, platinum nanoparticles are the active centers for the electrocatalytic oxidation of ammonia nitrogen, and their main function is the electrocatalytic oxidation of ammonia nitrogen.

[0028] In this invention, the glassy carbon electrode (GCE) is the "foundation" of the entire sensor, serving to conduct electricity and provide support.

[0029] Synergy between GCE, NC, and PtNPs: NC is drop-coated onto the GCE surface using a Nafion-isopropanol-water mixed solvent system. Nafion acts as a film-forming binder, forming a stable modification layer. The NC layer transforms the GCE from a two-dimensional planar electrode into a three-dimensional porous electrode, significantly increasing the effective area. During electrodeposition, PtCl6... 2- It is electrochemically reduced to Pt on the GCE surface. 0 Atoms nucleate and grow into nanoparticles; the active specific surface area of ​​PtNPs / GCE is lower than that of NC / GCE loaded with platinum. This is because the two-dimensional plane of GCE makes platinum particles more likely to aggregate, while the NC layer transforms GCE from a two-dimensional planar electrode into a three-dimensional porous electrode, which greatly increases the effective area.

[0030] Synergy between NC and PtNPs: (1) NC provides highly dispersed anchoring sites for PtNPs, and the nitrogen-containing defects on the NC surface (provided by the nitrogen-doped carbon framework) are strong adsorption sites for platinum ions. During electrodeposition, PtCl6 2- Platinum nanoparticles preferentially adsorb near the pyridine nitrogen and graphitic nitrogen sites on NC and are reduced in situ to Pt atoms, forming uniformly dispersed, fine-sized platinum nanoparticles. This contrasts sharply with the uneven nucleation and coarse particles on smooth GCE surfaces due to the lack of anchoring sites.

[0031] (2) NC pumps ammonia nitrogen to the PtNPs catalytic site. Through the dual effects of physical adsorption and chemical adsorption, NC forms a local high-concentration ammonia nitrogen enrichment zone around the Pt nanoparticles. This pre-concentration effect makes the ammonia nitrogen concentration at the Pt catalytic site much higher than the bulk concentration. According to the law of mass action, the electrocatalytic oxidation rate is greatly increased.

[0032] (3) PtNPs provide an electron conduction channel. PtNPs deposited on the NC framework form a good electrical contact with the sp² carbon framework. Electrons released by the catalytic reaction are quickly conducted to the GCE substrate through the NC conductive framework, which reduces the electron transport impedance (EIS data show that the resistance of PtNPs / NC / GCE is significantly lower than that of NC / GCE).

[0033] Based on the above technical solution, the embodiments of the present invention can produce at least the following technical effects: (1) The synergistic effect between NC and Pt makes the PtNPs / NC / GCE electrochemical sensor produce a significant effect on the electrochemical redox response of ammonia nitrogen: After the introduction of NC, the peak current of ammonia nitrogen oxidation of the electrode increased by as much as 76.5 times from 37.4 μA and 2861 μA. This signal amplification factor is much higher than the area growth factor, which is unpredictable by conventional material loading.

[0034] (2) High sensitivity and wide linear range: The ZIF-8 derived carbon NC of this invention provides a triple function of enrichment, conductivity and platinum anchoring. Utilizing the high specific surface area, abundant pore structure and good conductivity of ZIF-8 derived carbon NC, it serves as an ideal carrier for platinum nanoparticles, effectively improving the dispersion of platinum nanoparticles and the effective specific surface area of ​​the electrode. The electrodeposited platinum nanoparticles exhibit excellent electrocatalytic activity, showing a significant signal amplification effect on the oxidation reaction of ammonia nitrogen, thus achieving high-sensitivity detection of ammonia nitrogen in water, with a linear range of 50 μmol / L to 55000 μmol / L, while NC / GCE shows no response and PtNPs / GCE shows a very small response.

[0035] (3) Excellent anti-interference ability: The PtNPs / NC / GCE electrochemical sensor provided by this invention has good selectivity for ammonia nitrogen within a scanning potential window of -0.8 V to 0.2 V, and can handle common coexisting ions (such as Cl). - Na + CO3 2- HCO3 - SO4 2- NO3 - (etc.) does not produce significant interference and is suitable for direct detection of complex water samples.

[0036] (4) The preparation process is simple and controllable: the present invention can complete the loading of platinum nanoparticles at room temperature through a simple electrodeposition method, avoiding the use of complex and expensive chemical reducing agents or high temperature heat treatment. The process is green and efficient.

[0037] (5) Good stability and reusability: Thanks to the stable structure of the ZIF-8 derived carbon NC support and the strong interaction between platinum nanoparticles and carbon substrate, the prepared PtNPs / NC / GCE electrochemical sensor can be recycled multiple times, reducing detection costs.

[0038] (6) Strong applicability: The PtNPs / NC / GCE electrochemical sensor provided by this invention can be directly applied to the rapid on-site detection of ammonia nitrogen in various water bodies such as surface water, domestic sewage and industrial wastewater. It is simple to operate, responds quickly, and has broad application prospects. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0040] Figure 1This is a flowchart illustrating the fabrication process of the PtNPs / NC / GCE electrochemical sensor in Example 1 of this invention.

[0041] Figure 2 The images are field emission transmission electron microscopy (TEM) images of ZIF-8 and ZIF-8-derived carbon NC obtained in Example 1 of this invention.

[0042] Figure 3 The images shown are transmission electron microscopy (TEM) images and lattice fringes of the PtNPs / NCs prepared in Example 1 of this invention.

[0043] Figure 4 The BET test diagrams of the specific surface area of ​​ZIF-8 and ZIF-8-derived carbon NC obtained in Example 1 of this invention are shown, where (A) is the N2 adsorption-desorption isotherm and (B) is the pore size distribution diagram.

[0044] Figure 5 The images show the structural characterization diagrams of ZIF-8, ZIF-8-derived carbon NC, and PtNPs / NC obtained in Example 1 of this invention, where (A) is a Raman spectrum and (B) is an X-ray powder diffraction (XRD) spectrum.

[0045] Figure 6 The different electrodes used in Example 2 of this invention were at 5 mmol / L [Fe(CN)6] 3- / 4- Electrochemical performance test results in +0.1 mol / L KCl solution, where (A) is the cyclic voltammetry (CV) curve, (B) is the electrochemical impedance spectroscopy (EIS) curve, (C) is the CV curve of PtNPs / NC / GCE electrode at different scan rates, and (D) is the linear relationship between peak current and the square root of scan rate.

[0046] Figure 7 The figures show the electrochemical response test results of different electrodes to ammonia nitrogen in Example 3 of this invention. (A) is the CV curve of different electrodes in 1 mol / L KOH solution, (B) is the CV curve of different electrodes in 1 mol / L KOH + 0.1 mol / L NH4Cl solution, (C) is the CV curve of PtNPs / GCE in 1 mol / L KOH and 1 mol / L KOH + 0.1 mol / L NH4Cl, and (D) is the CV curve of PtNPs / NC / GCE in 1 mol / L KOH and 1 mol / L KOH + 0.1 mol / L NH4Cl.

[0047] Figure 8 This is an orthogonal experiment for optimizing the conditions of the PtNPs / NC / GCE electrode in Example 3 of the present invention, where (A) is a data statistics graph and (B) is a range analysis graph.

[0048] Figure 9 The following is an electrochemical test diagram of ammonia nitrogen by the PtNPs / NC / GCE electrode in Example 3 of the present invention. (A) is the CV curve of the PtNPs / NC / GCE electrode at different NH4Cl concentrations in 1 mol / L KOH solution, (B) is the linear relationship between concentration and peak current, (C) is the CV curve at different scan rates, and (D) is the relationship between scan rate and peak current.

[0049] Figure 10 This is an anti-interference stability experiment of the PtNPs / NC / GCE electrode in Embodiment 3 of the present invention, wherein (A) is an anti-interference experiment and (B) is a stability test. Detailed Implementation

[0050] 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.

[0051] 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. Every smaller range between any stated value or intermediate value within a stated range, and 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Example 1 Figure 1 This is a flowchart illustrating the fabrication process of the PtNPs / NC / GCE electrochemical sensor in Example 1 of this invention; as shown. Figure 1 As shown, a method for fabricating an ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC supported platinum is described, with the following specific steps: S1. Accurately weigh 3.700 g of 2-methylimidazole and place it in a beaker. Add 60 mL of methanol and stir thoroughly to dissolve, obtaining a 2-methylimidazole-methanol solution. Accurately weigh 1.676 g of Zn(NO3)2·6H2O and place it in another beaker. Add 60 mL of anhydrous methanol and sonicate until completely dissolved, obtaining a zinc nitrate-methanol solution. Pour the zinc nitrate-methanol solution into the 2-methylimidazole-methanol solution and stir evenly. Stir at room temperature for 24 h, then centrifuge. Wash three times with anhydrous ethanol and centrifuge. Place the product in a 60℃ forced-air drying oven to dry, obtaining a white ZIF-8 precursor powder. Place the precursor powder in a quartz boat and calcine it at 900℃ for 3 h under nitrogen protection at a flow rate of 100 mL / min, with a heating rate of 5℃ / min. Then cool it at a rate of 2℃ / min. The resulting black powder is ZIF-8 derived carbon NC (hereinafter referred to as NC).

[0056] Preparation of S2 and NC / GCE A 3 mm diameter glassy carbon electrode was sequentially polished on a polishing cloth using 0.3 μm and 0.05 μm alumina polishing powders. After polishing, the electrode was sonicated in ultrapure water for 10 minutes, then transferred to anhydrous ethanol and sonicated for another 10 minutes. The electrode surface was then dried with nitrogen gas. 8 mg of the prepared NC was weighed and added to a mixed solution of 600 μL deionized water, 50 μL of 5% Nafion, and 350 μL of isopropanol. The solution was sonicated for 30 minutes to obtain a homogeneous and stable 8 mg / mL NC dispersion. 2.5 μL of the NC dispersion was pipetted onto the pretreated glassy carbon electrode surface and then dried in an 80°C oven until the solvent completely evaporated. This process was repeated four times to obtain the final NC / GCE.

[0057] Fabrication of S3, PtNPs / NC / GCE electrochemical sensors Electrodeposition was performed using a three-electrode system. The prepared NC / GCE electrode was used as the working electrode, the Ag / AgCl electrode as the reference electrode, and a platinum sheet as the auxiliary electrode. A 0.5 mol / L HCl solution containing 15 mmol / L H₂PtCl₆·6H₂O was used as the deposition electrolyte. The constant potential was set to -1 V, and the electrodeposition time was 800 s. After electrodeposition, the electrode was removed, rinsed with ultrapure water to remove residual electrolyte, and allowed to air dry at room temperature to obtain the PtNPs / NC / GCE electrochemical sensor.

[0058] Material structure characterization: TEM characterization of ZIF-8 and NC: The surface morphology of the prepared ZIF-8 and NC was examined using TEM. Figure 2 It can be seen that after carbonization, the ZIF-8-derived carbon NC still retains some of the inherent structure of ZIF-8.

[0059] Preparation of PtNPs / NC: PtNPs / NC were obtained by scraping directly from the surface of the PtNPs / NC / GCE electrochemical sensor and used for subsequent characterization such as TEM and XRD.

[0060] TEM characterization of PtNPs / NC: PtNPs / NC were subjected to material testing using TEM, from... Figure 3 The lattice spacing indicates that Pt(111) was successfully modified on NC.

[0061] BET testing of ZIF-8 and NC: Their porous properties were characterized by nitrogen adsorption-desorption isotherms. Figure 4 As can be seen, both ZIF-8 and NC exhibit the typical Type I isotherm of microporous materials. They retain a good porous structure even after carbonization, providing ample space for the loading of platinum nanoparticles and facilitating mass transport during electrochemical reactions.

[0062] Raman spectroscopy and XRD analysis of ZIF-8, NC, and PtNPs / NC: To verify the successful preparation of ZIF-8, NC, and PtNPs / NC, Raman spectroscopy and XRD analysis were performed. From the Raman spectroscopy results... Figure 5 As shown in (A), the original ZIF-8 material exhibits typical 2-methylimidazolium ligand characteristic peaks, confirming its intact skeletal structure. After carbonization, these characteristic peaks disappear and reappear at ~1330 cm⁻¹. -1 (D band) and ~1580 cm -1 Two broad peaks appear at the (G band), indicating that carbonaceous material has formed and NC preparation was successful. The calculated ID / IG ratio of NC is 1.02, reflecting a moderate defect density, which is beneficial for platinum metal fixation and ammonia nitrogen adsorption while maintaining good conductivity. XRD tests ( Figure 5As shown in (B) of the diagram, ZIF-8 exhibits characteristic peaks consistent with the simulated spectrum, confirming the successful synthesis of ZIF-8. These peaks disappear after carbonization, and a broad peak appears at approximately 21, which is a characteristic peak of amorphous carbon, further indicating successful carbonization. For PtNPs / NC, additional diffraction peaks were observed at 39.8, 46.2, 67.5, 81.3, and 85.7, corresponding to the (111), (200), (220), (311), and (222) crystal planes of platinum, respectively, proving that PtNPs were successfully deposited on the NC surface.

[0063] Example 2: Electrochemical performance testing of the PtNPs / NC / GCE electrochemical sensor: (1) An electrochemical workstation three-electrode system was used, with a saturated Ag / AgCl electrode as the reference electrode and a platinum sheet electrode as the auxiliary electrode, in 40 mL of 5 mmol / L Fe(CN)6 containing 0.1 mol / L KCl. 3- / 4- Electrochemical tests were conducted in solution. (2) Characterization of electrodes GCE, PtNPs / GCE, NC / GCE, and PtNPs / NC / GCE in potassium ferricyanide solution by cyclic voltammetry: Preparation of PtNPs / GCE: The pretreated bare glassy carbon electrode was directly used as the working electrode, and platinum nanoparticles were electrodeposited under the same electrodeposition conditions as in step S3 to obtain the PtNPs / GCE electrode.

[0064] For comparison, cyclic voltammetry was performed on different modified electrodes in potassium ferricyanide solution. Figure 6 In the figure (A), different modified electrodes are used in a solution containing 0.1 mol / L KCl and 5 mmol / L Fe(CN)6. 3- / 4- Cyclic voltammograms in solution; GCE has a pair of symmetrical and reversible redox peaks; when NC is modified onto GCE, due to Nafion, NC / GCE has no obvious redox peaks; after Pt electrodeposition onto the GCE surface, due to the high catalytic activity of Pt, electron transfer is promoted, resulting in a significant increase in the PtNPs / GCE peak current; when Pt is modified onto NC / GCE, the formed PtNPs / NC / GCE electrode also has a pair of redox peaks comparable to those of PtNPs / GCE.

[0065] (3) Electrochemical impedance spectroscopy characterization of electrodes GCE, PtNPs / GCE, NC / GCE, and PtNPs / NC / GCE in potassium ferricyanide solution: In order to further evaluate the conductivity and electron transport capability of the electrodes, electrochemical impedance spectroscopy tests were performed on the modified electrodes in potassium ferricyanide solution. Figure 6(B) shows GCE, PtNPs / GCE, NC / GCE, and PtNPs / NC / GCE in 5 mmol / L Fe(CN)6 containing 0.1 mol / L KCl. 3- / 4- AC impedance diagram in solution; as shown in the diagram, the resistance values ​​Rct are: NC / GCE>GCE>PtNPs / NC / GCE>PtNPs / GCE.

[0066] (4) Active specific surface area test of electrodes GCE, PtNPs / GCE, and PtNPs / NC / GCE: In order to evaluate the number of active sites and the catalytic ability of the electrode, the active specific surface area of ​​electrodes GCE, PtNPs / GCE, and PtNPs / NC / GCE was tested. Figure 6 (C) Figure 6 As shown in (D), the RS equation method was used in a solution containing 0.1 mol / L KCl and 5 mmol / L Fe(CN)6. 3- / 4- In solution, the Faraday current was scanned at different scan rates (20-200 mV / s), and the active specific surface area of ​​different electrodes was calculated. The ratio of PtNPs / NC / GCE (0.149 cm⁻¹) was calculated. 2 PtNPs / GCE (0.114cm) 2 GCE (0.067 cm) 2 NC / GCE has poor conductivity, and its active surface area cannot be measured by the RS equation method, which is 0.

[0067] Example 3: Used for the detection of ammonia nitrogen in water: (1) Using an electrochemical workstation with a three-electrode system, saturated Hg / HgO electrode as reference electrode and platinum sheet electrode as auxiliary electrode, a feasibility test was conducted in 40 mL of 1 mol / L KOH solution with and without ammonia nitrogen: the electrodes GCE, Pt / GCE, NC / GCE, and PtNPs / NC / GCE were tested by cyclic voltammetry with and without ammonia nitrogen. Figure 7 (A) in the figure represents the CV curves of GCE, Pt / GCE, NC / GCE, and PtNPs / NC / GCE prepared in this embodiment in 1 mol / L KOH solution, respectively. Figure 7 (B) shows the CV curves of GCE, Pt / GCE, NC / GCE, and PtNPs / NC / GCE prepared in this embodiment in 1 mol / L KOH + 0.1 mol / L NH4Cl solution. Figure 7 (C) and Figure 7(D) shows the CV curves of PtNPs / GCE and PtNPs / NC / GCE in 1 mol / L KOH and 1 mol / L KOH + 0.1 mol / L NH4Cl, respectively. The comparison shows that GCE and NC / GCE have no obvious redox response to ammonia nitrogen. After electrodeposition modification with Pt, PtNPs / GCE and PtNPs / NC / GCE show obvious oxidation peaks for ammonia nitrogen at -0.19 V and -0.14 V, respectively, with oxidation peak currents of 37.4 μA and 2861 μA, corresponding to the oxidation process from NH3 to N2. Compared with GCE and NC / GCE, the electrochemical electrode sensor shows a significant redox response to NH3 after electrodeposition with Pt. Modification with NC can increase the oxidation peak current of the electrode, effectively promoting the electrocatalytic oxidation of NH3. This may be due to the strong hydrogen evolution performance of Pt, which can catalyze the oxidation of NH3 to N2. Meanwhile, NC possesses abundant porous structures and nitrogen-containing functional groups (such as pyridine nitrogen and graphitic nitrogen), which is beneficial for the adsorption and enrichment of ammonia nitrogen in water, promoting the electrochemical oxidation-reduction of ammonia nitrogen by PtNPs / NC / GCE. After introducing NC, the peak oxidation current of ammonia nitrogen on the electrode increased by as much as 76.5 times from 37.4 μA to 2861 μA. This signal amplification factor is far greater than the area growth factor, a phenomenon unpredictable with conventional material loading. This significant difference demonstrates a synergistic effect of "1+1>2" between NC and Pt in this invention, resulting in a significant effect on the electrochemical oxidation-reduction response of ammonia nitrogen by PtNPs / NC / GCE.

[0068] (2) Orthogonal experiment for optimizing the conditions of PtNPs / NC / GCE electrodes: an orthogonal array design L16(4 5 Five key preparation parameters were systematically optimized, as shown in Table 1. The selected factors and their four levels are as follows: A: NC concentration (2 mg / mL, 4 mg / mL, 6 mg / mL, 8 mg / mL), B: Number of drops (1, 2, 3, 4), C: Electrodeposition time (200 s, 400 s, 600 s, 800 s), D: H2PtCl6 concentration (2 mmol / L, 5 mmol / L, 10 mmol / L, 15 mmol / L), and E: Drying temperature (25, 40, 60, 80℃). The response variable is the anodic peak current measured in a 1 mol / L KOH solution containing 0.1 mol / L NH4Cl (e.g., NC concentration). Figure 8 As shown in (A)), all experiments were repeated three times to ensure reproducibility. A range analysis plot was drawn based on the experimental data (as shown in Figure 1). Figure 8As shown in (B) in the figure, the optimal modification conditions were determined to be 8 mg / ml NC, 4 drop coats, electrodeposition time of 800 s, H2PtCl6 concentration of 15 mmol / L, and drying temperature of 80℃.

[0069] Table 1. Different Levels of Five Influencing Factors

[0070] The PtNPs / NC / GCE electrodes prepared under the above experimental conditions can all be used for ammonia nitrogen detection. The optimal conditions are 8 mg / ml NC, 4 drop coatings, electrodeposition time of 800 s, H2PtCl6 concentration of 15 mmol / L, and drying temperature of 80℃.

[0071] (3) Detection range of ammonia nitrogen by the PtNPs / NC / GCE electrochemical sensor: First, cyclic voltammetry (CV) was used to test the CV values ​​of different ammonia nitrogen concentrations, such as... Figure 9 As shown in (A) above. Based on the linear relationship between the obtained oxidation peak current and NH3 concentration, a working curve was plotted, as shown below. Figure 9 As shown in (B), the fitting equation for the low concentration region is y = 0.000171x + 0.0143, R0 2 =0.965, the fitting equation for the high concentration region is y=0.508logx-1.410, R 2 =0.985, the linear range was measured to be 50-55000 μmol / L, and the detection limit was calculated to be 15.71 μmol / L based on the signal-to-noise ratio (S / N=3).

[0072] (4) Mass transfer mechanism of ammonia nitrogen in the electrochemical redox reaction of PtNPs / NC / GCE: The CV of PtNPs / NC / GCE was tested at different scan rates (range 20-200 mV / s) in 1 mol / L KOH + 0.1 mol / L NH4Cl solution, such as... Figure 9 (C) Figure 9 As shown in (D), it was found that the peak current is linearly related to the square root of the scan rate. Therefore, ammonia nitrogen is mainly transferred through diffusion in the electrochemical redox reaction of ammonia nitrogen in PtNPs / NC / GCE.

[0073] (5) Electrode Anti-interference Stability Test: To evaluate the practical performance of the PtNPs / NC / GCE electrode, an anti-interference stability test was conducted on water samples containing ammonia nitrogen. For example... Figure 10 As shown in (A), the anti-interference test was conducted by adding 5 mmol / L Cl to a 1 mol / L KOH + 100 μmol / L NH4Cl solution. - Na+ CO3 2- HCO3 - SO4 2- NO3 - Common coexisting ions are used to record the sensor's current response. For example... Figure 10 As shown in (B), stability test: after five consecutive measurements in 1 mol / L KOH + 1 mmol / L NH4Cl solution, the response current of the electrode remained basically unchanged, indicating that the electrode has good stability.

[0074] The above results demonstrate that the effect of "1+1>2" has been achieved: GCE active specific surface area: 0.067 cm² 2 The specific surface area of ​​NC / GCE activity is 0, and the specific surface area of ​​PtNPs / GCE activity is 0.114 cm². 2 The active specific surface area of ​​PtNPs / NC / GCE is 0.149 cm². 2 GCE and NC / GCE showed no significant redox response to ammonia nitrogen, while the oxidation peak currents of PtNPs / GCE and PtNPs / NC / GCE were 37.4 μA and 2861 μA, respectively. The active area increased by only 30%, yet the intrinsic catalytic activity per unit area increased by 58.5 times, a highly significant superaddition effect in conventional carbon-supported noble metal catalytic systems. The fundamental reason lies in the "enrichment-catalysis" functional coupling formed between NC and Pt.

[0075] After introducing nitrogen doping (NC), the peak current for ammonia nitrogen oxidation at the electrode increased by a staggering 76.5 times, from 37.4 μA to 2861 μA; while the active specific surface area of ​​the electrode only increased from 0.114 cm² to 0.149 cm², a mere 1.3-fold increase. This phenomenon, where the signal amplification factor far exceeds the area growth factor, is unpredictable with conventional material loading. This significant difference demonstrates that the introduction of NC not only provides Pt with a larger specific surface area but also, through its nitrogen-doped sites and porous structure, exhibits a strong adsorption and enrichment effect on ammonia nitrogen, potentially altering the electronic states of Pt and significantly enhancing the intrinsic catalytic activity of Pt nanoparticles (the switching frequency of each active site). NC "enriches" ammonia nitrogen around platinum, creating a locally high-concentration environment and amplifying the electrocatalytic oxidation signal of platinum.

[0076] Alternative embodiments: The following steps were performed in Example 1: Step S1 was replaced with a calcination of zinc nitrate hexahydrate and 2-methylimidazole at a molar ratio of 1:4, at 1000℃ for 3 hours; Step S2 was replaced with 8 mg of the prepared NC solution added to a mixed solution of 800 μL deionized water, 50 μL of 5% Nafion, and 200 μL of isopropanol; Step S3 was replaced with a 0.1 mol / L HCl solution containing 2 mmol / L H2PtCl6·6H2O as the deposition electrolyte. The constant potential was set to -0.5 V, and the electrodeposition time was 200 s. The obtained product was characterized, and the PtNPs / NC / GCE electrochemical sensor was successfully prepared.

[0077] The following steps were performed in Example 1: Step S1 was replaced with a calcination of zinc nitrate hexahydrate and 2-methylimidazole at a molar ratio of 1:6, at 950°C for 5 hours; Step S2 was replaced with 8 mg of the prepared NC solution added to a mixed solution of 1000 μL deionized water, 80 μL of 5% Nafion, and 500 μL of isopropanol; Step S3 was replaced with a 1 mol / L HCl solution containing 10 mmol / L H2PtCl6·6H2O as the deposition electrolyte. A constant potential of -1.2 V and a deposition time of 600 s were set. The resulting product was characterized, and a PtNPs / NC / GCE electrochemical sensor was successfully fabricated.

[0078] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. An ammonia nitrogen electrochemical sensor constructed based on ZIF-8 derived carbon NC-supported platinum, characterized in that, include: Glassy carbon electrode; A ZIF-8-derived carbon NC material layer modified on the surface of the glassy carbon electrode; And platinum nanoparticles electrodeposited and loaded on the ZIF-8 derived carbon NC material layer; The ZIF-8 derived carbon NC material is obtained by dissolving zinc nitrate hexahydrate and 2-methylimidazole in methanol at a molar ratio of 1:4-1:8, stirring the reaction at room temperature, washing, centrifuging and drying to obtain a ZIF-8 precursor, and then calcining the ZIF-8 precursor at 900℃-1000℃ for 3-5 hours under a protective atmosphere to obtain a nitrogen-doped porous carbon material. The ZIF-8 derived carbon NC material is modified onto the surface of a glassy carbon electrode through the following steps: The ZIF-8 derived carbon NC material is dispersed in a mixed solvent consisting of deionized water, isopropanol and Nafion solution with a volume ratio of 8-12:2-7:0.05-1, and then drop-coated onto the pretreated glassy carbon electrode surface and dried to obtain the final product. The electrodeposition was carried out in a 0.1-1 mol / L HCl solution containing 2-15 mmol / L H2PtCl6·6H2O, with a deposition potential of -1.2 to -0.5 V and a deposition time of 200-800 s.

2. The ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum as described in claim 1, characterized in that, The intensity ratio of the D band to the G band in the Raman spectrum of the ZIF-8 derived carbon NC material is ID / IG, which is 0.8 to 1.

2.

3. The ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum as described in claim 1, characterized in that, The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:8; the ZIF-8 precursor is calcined at 900°C for 3 hours under a protective atmosphere; the solvent is a mixed solvent consisting of deionized water, isopropanol, and 5 wt.% Nafion solution in a volume ratio of 8:2:0.05; the electrodeposition is carried out in a 0.5 mol / L HCl solution containing 15 mmol / L H2PtCl6·6H2O, with a deposition potential of -1.0 V and a deposition time of 800 s.

4. The ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum as described in claim 1, characterized in that, When the sensor is used for ammonia nitrogen detection, it operates in an environment containing 0.1 mol / L NH4+. + In a 1 mol / L KOH solution, the peak current of ammonia nitrogen oxidation per unit electrochemically active surface area is increased by at least 50 times compared with that of a platinum-modified glassy carbon electrode without NC.

5. A method for preparing an ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of ZIF-8 derived carbon NC material: Zinc nitrate hexahydrate and 2-methylimidazolium were dissolved in methanol at a molar ratio of 1:4-1:

8. After stirring at room temperature, the mixture was washed, centrifuged, and dried to obtain the ZIF-8 precursor. The ZIF-8 precursor was calcined at 900℃-1000℃ for 3-5 hours under a protective atmosphere to obtain the ZIF-8 derived carbon NC material. S2. Preparation of NC / GCE modified electrode: The ZIF-8 derived carbon NC material is dispersed in a solvent, drop-coated onto the surface of a pretreated glassy carbon electrode, and dried to obtain the NC / GCE modified electrode. S3. Electrodeposition of platinum nanoparticles: Using the NC / GCE as the working electrode, PtNPs / NC / GCE electrochemical sensor is obtained by constant potential electrodeposition in an electrolyte containing platinum precursor.

6. The method for preparing an ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum according to claim 5, characterized in that, In step S1, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:4-1:6; the ZIF-8 precursor is calcined at 900℃-950℃ for 3-4 hours under a protective atmosphere.

7. The method for preparing an ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum according to claim 5, characterized in that, In step S2, the solvent is a mixed solvent consisting of deionized water, isopropanol and Nafion solution with a volume ratio of 8-12:2-7:0.05-1.

8. The method for preparing an ammonia nitrogen electrochemical sensor based on ZIF-8 derived carbon NC-supported platinum according to claim 5, characterized in that, In step S3, the electrolyte is a 0.1-1 mol / L HCl solution containing 2-15 mmol / L H2PtCl6·6H2O, the deposition potential is -1.2 to -0.5 V, and the deposition time is 200-800 s.

9. The application of the sensor according to any one of claims 1-8 in detecting ammonia nitrogen content in water.

10. The application according to claim 9, characterized in that, The detection of ammonia nitrogen content in the water body includes: Step 1: Take 1-5 mL of the water sample to be tested, dilute it 10-20 times with 0.5-1.5 mol / L KOH electrolyte, mix well, and obtain the sample solution to be tested; Step 2: Using the sensor as the working electrode, a reference electrode suitable for alkaline systems, and a platinum sheet as the auxiliary electrode, insert the three electrodes into the sample solution to be tested and let it stand for 1-2 minutes. Step 3: Use cyclic voltammetry for detection. The scanning potential range is -0.8 V to 0.2 V, and the scanning rate is 20-200 mV / s. Record the current response signal and calculate the ammonia nitrogen concentration based on the standard curve.

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