AuNPs@NiCo2O4 composite electrode material, gas sensing electrode and preparation method and application

Abstract

The application relates to the technical field of gas sensors, in particular to an AuNPs@NiCo2O4 composite material, a gas sensing electrode and a preparation method and application thereof. The AuNPs@NiCo2O4 composite material is composed of Au nanoparticles with a particle size of 2nm+ / -0.5nm uniformly dispersed on the surface of NiCo2O4, the loading amount of the Au nanoparticles is 0.3%-0.9% of the mass of the NiCo2O4, and the particle size of the composite material is 500nm-600nm. The composite material has a high specific surface area, a multi-stage pore structure and rich active sites, and a resistance type trimethylamine sensor constructed by using the composite material as a substrate is characterized by a detection range of 0.5ppm-15ppm, a detection limit of 0.12ppm, a working temperature of room temperature, excellent response-recovery speed, a wide detection range and high selectivity, and has a wide application prospect in the field of on-site rapid detection of food freshness.

Description

Technical Field

[0001] This invention relates to the field of electrochemical sensors and gas detection technology, specifically to an AuNPs@NiCo2O4 composite material, a gas sensing electrode, its preparation method, and its application. Background Technology

[0002] Trimethylamine is a low-molecular-weight volatile organic amine that is a colorless gas with a strong fishy odor at room temperature and pressure. As a characteristic biomarker of protein spoilage and fish degradation, trimethylamine is widely present in spoiled aquatic products, fermented foods, and biological metabolic processes. Because its vapor is highly irritating to the eyes, nose, throat, and respiratory tract, and long-term exposure can cause mucosal dryness, inflammation, and damage to the nervous system, establishing a rapid, sensitive, and accurate method for detecting trimethylamine is of great significance for food safety monitoring, drug quality control, and public health protection.

[0003] Currently, traditional methods for detecting trimethylamine mainly include spectrophotometry, gas chromatography, and ion chromatography. While these methods offer advantages in quantitative detection, they also suffer from drawbacks such as high cost, complex operation, and long detection time, severely limiting the demand for rapid detection. Therefore, developing low-cost, easy-to-operate, and fast-response on-site rapid detection technologies has become an urgent need in this field.

[0004] In recent years, sensors based on bimetallic oxide resistive gas sensing electrodes have shown broad application prospects in the detection of volatile organic amines due to their outstanding advantages such as fast response speed, low preparation cost, portable equipment, and real-time monitoring. For example, the resistive sensor based on manganese-doped zinc ferrite (Mn-ZnFe2O4) bimetallic oxide prepared by Thangavel Ravikumar et al. showed a sensitivity of only 6.24 for 10 ppm trimethylamine at ambient temperature, and the response-recovery speed needs further optimization. This indicates that existing sensors based on bimetallic oxide gas sensing electrodes still fall short of meeting the requirements for rapid and accurate detection of trimethylamine in practical applications in terms of detection sensitivity, response speed, and recovery characteristics. Summary of the Invention

[0005] To address the problems of low sensitivity, slow response, and high-temperature operation required for existing bimetallic oxide gas sensors in detecting trimethylamine, which make them unsuitable for rapid on-site detection of food freshness, this invention provides an AuNPs@NiCo2O4 composite material, a gas sensing electrode, its preparation method, and its applications. Using porous NiCo2O4 as a substrate, small-diameter Au nanoparticles are loaded onto it. The high specific surface area and oxygen vacancies of NiCo2O4 provide active sites, while AuNPs exhibit electron sensitization effects, promoting electron transfer and lowering the reaction activation energy. This enables highly sensitive and rapid detection of trimethylamine at room temperature.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] This invention provides an AuNPs@NiCo2O4 composite material, wherein the AuNPs@NiCo2O4 composite material is composed of Au nanoparticles uniformly dispersed on the surface of NiCo2O4; the particle size of the Au nanoparticles is 2nm±0.5nm; the loading of the Au nanoparticles is 0.3% to 0.9% of the mass of NiCo2O4; and the particle size of the AuNPs@NiCo2O4 composite material is 500nm to 600nm.

[0008] Preferably, the NiCo2O4 is obtained by calcining ZIF-67-derived nickel-cobalt double hydroxide powder at 300°C to 400°C for 120 to 180 minutes in air.

[0009] Preferably, the ZIF-67-derived nickel-cobalt bimetallic hydroxide powder is obtained by heating ZIF-67 with nickel nitrate in an ethanol solution.

[0010] Preferably, the ZIF-67 is synthesized from a methanol solution of cobalt nitrate and 2-methylimidazole.

[0011] The second objective of this invention is to provide a method for preparing AuNPs@NiCo2O4 composite materials, comprising the following steps: NiCo2O4 was dispersed in water, and a gold source solution and a reducing agent were added to carry out an in-situ reduction reaction to form dispersed Au nanoparticles on the surface of NiCo2O4, thus obtaining AuNPs@NiCo2O4 composite material.

[0012] Preferably, the ratio of the gold source to NiCo2O4 is 40mg:12.5mmol~37.5mmol.

[0013] Preferably, the gold source is a gold-containing acid, salt, or complex.

[0014] Preferably, the gold source is chloroauric acid, and the concentration of the gold source solution is 12.5 mmol / L to 37.5 mmol / L; the reducing agent is sodium borohydride solution, and the concentration of the sodium borohydride solution is 0.05 mol / L to 0.15 mol / L.

[0015] The third objective of this invention is to provide a gas sensing electrode, which is formed by modifying the surface of an interdigitated electrode with an AuNPs@NiCo2O4 composite material.

[0016] Preferably, the preparation method of the gas sensing electrode includes the following steps: dispersing AuNPs@NiCo2O4 composite material in a solvent to obtain a dispersion, coating the dispersion on the surface of an interdigitated electrode, drying it, and then heat-treating it at 180°C to obtain the gas sensing electrode.

[0017] The fourth objective of this invention is to provide a gas sensing electrode for the application of an electrode sensor in the detection of trimethylamine. The method for preparing the electrode sensor includes the following steps: welding platinum wire as a lead in the pad area of ​​the gas sensing electrode, fixing the gas sensing electrode with the lead wire connected to it on a ceramic substrate, and aging it at 150°C to 200°C for 2 to 3 hours to obtain the electrode sensor.

[0018] The application method is as follows: place the electrode sensor in a mixed atmosphere containing trimethylamine, obtain the initial resistance value of the electrode sensor and the actual resistance value after the mixed atmosphere containing trimethylamine is introduced, and obtain the ratio of the actual resistance value to the initial resistance value; based on the ratio of the actual resistance value to the initial resistance value and the concentration of trimethylamine in the mixed atmosphere, obtain the relationship curve between the ratio of the actual resistance value to the initial resistance value and the concentration of trimethylamine in the mixed atmosphere, so as to realize the detection of the concentration of trimethylamine in the mixed atmosphere.

[0019] Preferably, the gas sensor has a detection range of 0.5ppm to 15ppm, a detection limit of 0.12ppm, and an operating temperature of room temperature.

[0020] Among them, the AuNPs@NiCo2O4 composite material provided in this application has the following advantages compared with other sensing substrates: (1) Oxygen vacancies, as natural "electron donors," provide a large number of electrons that can be captured by adsorbed oxygen, which greatly increases the concentration of adsorbed oxygen on the surface and improves sensitivity. (2) The electron sensitization effect of AuNPs can promote electron transfer and reduce the activation energy of the reaction. (3) AuNPs can significantly reduce the operating temperature of the sensor, thereby ensuring the stability of the sensor during operation.

[0021] The gas sensor provided by this invention has the following specific mechanism for detecting trimethylamine: Oxygen molecules in the air adsorb onto the surface of AuNPs@NiCo2O4 composite material (p-type semiconductor) and capture electrons from the material, forming chemisorbed oxygen species (such as O2). - O - This leads to a significant increase in the concentration of charge carrier "holes," resulting in a relatively low overall resistivity of the material. When trimethylamine is present in the environment, it reacts with oxygen species (such as O2) adsorbed on its surface. -A redox reaction occurs, and electrons that were originally captured by oxygen species are released back into the sensing material, resulting in a significant increase in resistance. Finally, the detection of trimethylamine gas molecules is achieved by recording the change in sensor resistance before and after the gas is introduced.

[0022] Specifically, NiCo2O4, as a bimetallic oxide sensing material, possesses a high specific surface area and a hierarchical porous structure, providing abundant surface active sites and effective mass transport channels. This facilitates the adsorption and diffusion of reactants, thereby enhancing the detection signal response. Furthermore, NiCo2O4 itself exhibits good electronic conductivity and structural stability, providing reliable substrate support for the sensing process.

[0023] The AuNPs introduced into the composite material possess electron sensitization properties. With their excellent catalytic activity, they can significantly reduce the activation energy of the target analyte in the trimethylamine detection process, accelerating the oxidation reaction kinetics. Simultaneously, the catalytic effect of AuNPs allows detection to be performed at relatively low operating temperatures, which is beneficial for reducing energy consumption and improving device stability.

[0024] The beneficial effects of this application include at least the following: 1. This invention controls the particle size of Au nanoparticles to 2nm ± 0.5nm and the loading to 0.3%–0.9% of the mass of NiCo2O4, while limiting the particle size of the composite material to 500nm–600nm, thus forming an AuNPs@NiCo2O4 composite material with high specific surface area and hierarchical porous structure. The electronic sensitization effect of AuNPs can reduce the reaction activation energy, and the hierarchical porous structure of the composite material provides abundant surface active sites and effective gas molecule transport channels for the target trimethylamine. The synergistic effect of these two factors allows the target to fully contact the sensitive material and induces a significant change in resistance, thereby achieving highly sensitive and rapid detection of trimethylamine at room temperature.

[0025] 2. The present invention constructs a gas sensing electrode based on the above-mentioned AuNPs@NiCo2O4 composite material modified interdigitated electrode. The sensor has the advantages of simple operation, small size and portability, which meets the needs of on-site detection.

[0026] 3. This invention successfully constructed a resistive trimethylamine sensor using the above-mentioned AuNPs@NiCo2O4 composite material. The detection range is 0.5ppm to 15ppm, and the detection limit is 0.12ppm. The sensor exhibits excellent response-recovery speed, wide detection range, and high selectivity, and has broad application prospects in the field of rapid on-site detection of food freshness. Attached Figure Description

[0027] Figure 1Transmission electron microscopy image of the AuNPs@NiCo2O4 composite material with an AuNPs loading of 0.6% prepared in Example 2.

[0028] Figure 2 The images show the dynamic response-recovery curves of the AuNPs@NiCo2O4 composite gas sensors prepared in Examples 1 to 3. (a) represents Example 2; (b) represents Example 1; and (c) represents Example 3.

[0029] Figure 3 The sensitivity of the AuNPs@NiCo2O4 composite material with an AuNPs loading of 0.6% prepared in Example 2 was tested in the range of 0.5ppm to 15ppm.

[0030] Figure 4 Linear fitting curves of the AuNPs@NiCo2O4 composite material with an AuNPs loading of 0.6% prepared in Example 2 in the range of 1ppm to 15ppm. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The technical solution of the present invention will be further described below through specific embodiments.

[0034] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0035] Example 1 A method for preparing AuNPs@NiCo2O4 composite material includes the following steps: Preparation of S1 and ZIF-67: 1.31 g of 2-methylimidazole (2-MI) and 1.16 g of Co(NO3)2·6H2O were dissolved in 100 mL of methanol, respectively, and defined as solutions A and B. Solution A was then rapidly added to solution B with stirring for 30 min. The mixed solution was then aged at room temperature for 24 h. Finally, it was washed three times with anhydrous methanol and dried under vacuum at 70°C for 24 h to obtain the purple solid product ZIF-67.

[0036] Preparation of S2 and NiCo-LDH: A certain amount of ZIF-67 was weighed and dissolved in a polar solution. A purple solution was obtained by magnetic stirring. Then, a Ni ion nitric acid solution was added to the purple solution, and the mixture was stirred to obtain a homogeneous solution. The solution was then transferred to an oil bath and heated to 80°C. o The reaction was carried out at C for 1 hour. The product was washed with a polar solvent and dried to obtain the green product NiCo-LDH.

[0037] Preparation of S3 and NiCo2O4: 40 mg of the prepared NiCo-LDH was placed in a porcelain boat and calcined at 300°C for 180 min at a heating rate of 5°C / min under an oxygen atmosphere; the mixture was cooled to room temperature and the black solid powder was collected to obtain NiCo2O4.

[0038] Preparation of S4, 0.6% AuNPs@NiCo2O4: 40 mg of NiCo2O4 sample was suspended in 15 mL of deionized water. Then, 50 μL of chloroauric acid solution (25 mM) was added and the mixture was sonicated for 30 min. Next, 1 mL of a solution containing NaBH4 (0.1 M) and NaOH (0.2 M) was rapidly injected into the mixture and stirred for 1 h. Finally, the precipitate was separated by centrifugation, washed with deionized water and ethanol, and then vacuum dried at 60°C for 24 h to obtain 0.6% AuNPs@NiCo2O4.

[0039] Example 2 A method for preparing AuNPs@NiCo2O4 composite material differs from Example 1 in that the loading of AuNPs is 0.3% of the mass of NiCo2O4. Preparation methods S1 to S4 are the same as in Example 1.

[0040] Example 3 A method for preparing AuNPs@NiCo2O4 composite material differs from Example 1 in that the loading of AuNPs is 0.9% of the mass of NiCo2O4. Preparation methods S1 to S4 are the same as in Example 1.

[0041] Application Example 1 A method for fabricating a gas sensor includes the following steps: Interdigitated electrodes were used as signal acquisition units, and these electrodes were fabricated by depositing metallic silver on a PET substrate. 5 mg of the AuNPs@NiCo2O4 composite material prepared in Examples 1-3 was dispersed in 1 mL of ultrapure water and subjected to ultrasonic treatment to obtain a homogeneous suspension. 10 μL of this suspension was measured using a micropipette and drop-coated onto the clean surface of the interdigitated electrodes. The suspension was dried at 75°C to form a sensing film on the electrode surface. Subsequently, heat treatment at 180°C for 5 h yielded a stable gas-sensitive material, ultimately producing a gas sensor.

[0042] The gas sensor described above is used to detect trimethylamine. The detection method is as follows:

[0043] The gas sensing test uses the static gas mixing method. To obtain the required gas, trimethylamine liquid is added to the test chamber using a micro-syringe and evaporated directly to form trimethylamine gas. The trimethylamine gas is then mixed with air to obtain a mixed gas. The gas sensor is placed in the test chamber, and the resistance change of the gas sensor before and after the mixed gas is introduced is recorded to detect the concentration of trimethylamine gas molecules in the mixed gas.

[0044] The initial resistance of the gas sensor in air is recorded as Ra. Mixed gases containing different concentrations of trimethylamine (where the concentrations of trimethylamine in the mixed gases are 0, 1 ppm, 5 ppm, 7.5 ppm, 11.5 ppm, and 15 ppm, respectively) are introduced into the test chamber, and the resistance when the mixed gas is introduced is recorded as Rg. The working curve is plotted based on the relationship between the ratio of Rg to Ra and the concentration of trimethylamine gas molecules.

[0045] The gas sensor has a detection range of 0.5ppm to 15ppm, a detection limit of 0.12ppm, and an operating temperature of room temperature.

[0046] Transmission electron microscopy (TEM) was performed on the AuNPs@NiCo2O4 composite material prepared in Example 1 with an AuNPs loading of 0.6%. The results are as follows: Figure 1 As shown. (Through) Figure 1 It can be seen that AuNPs@NiCo2O4 exhibits a nano-hollow cage-like structure with a particle size of 500nm to 600nm. At the same time, AuNPs are uniformly distributed on the surface of NiCo2O4. This structure has a large specific surface area, which can increase the reaction sites between the detected target gas trimethylamine and the sensing material, thus facilitating the rapid response of the sensor.

[0047] Dynamic response-recovery tests were performed on the gas sensors prepared using the AuNPs@NiCo2O4 composite materials prepared in Examples 1 to 3. The results are as follows: Figure 2 As shown. (Through) Figure 2It can be seen that at a trimethylamine concentration of 0.5 ppm, compared with AuNPs@NiCo2O4 composites with AuNPs loadings of 0.3% and 0.9%, the AuNPs@NiCo2O4 composite with AuNPs loading of 0.6% exhibits the fastest response / recovery time (14.5 s / 12.5 s) and the highest signal response. This further demonstrates that the abundant active sites and hollow nanocage structure in the AuNPs@NiCo2O4 composite with AuNPs loading of 0.6% can achieve rapid identification and signal amplification of the target gas trimethylamine. Furthermore, AuNPs can provide an electronic sensitization effect, thereby enabling real-time room temperature monitoring of trimethylamine.

[0048] The sensitivity of the AuNPs@NiCo2O4 composite material with an AuNPs loading of 0.6% prepared in Example 1 was tested in the range of trimethylamine concentration from 0.5 ppm to 15 ppm. The results are as follows: Figure 3 As shown. (Through) Figure 3 It can be seen that the AuNPs@NiCo2O4 composite material with an AuNPs loading of 0.6% exhibits excellent sensing performance for trimethylamine. Within the concentration range of 0.5ppm to 15ppm, the response value (Rg / Ra) of the gas sensor increases with increasing concentration, demonstrating excellent sensitivity and real-time monitoring capability.

[0049] The linear fitting curves of the AuNPs@NiCo2O4 composite material with an AuNPs loading of 0.6% prepared in Example 1 in the range of 1ppm to 15ppm are shown in the following figures. Figure 4 As shown. (Through) Figure 4 The linear fit between the response value (Rg / Ra) and the gas concentration can be observed at trimethylamine concentrations of 1 ppm to 15 ppm. 2 =0.992, showing a good concentration-response linear relationship. This result verifies that the unique hollow cage structure and electronic sensitization effect of the gas sensing material prepared in this study can provide efficient gas diffusion channels and abundant active sites, enabling efficient real-time monitoring of trimethylamine gas.

[0050] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An AuNPs@NiCo2O4 composite material, characterized in that, The AuNPs@NiCo2O4 composite material is obtained by uniformly dispersing Au nanoparticles on the surface of NiCo2O4; the particle size of the Au nanoparticles is 2nm±0.5nm; the loading of the Au nanoparticles is 0.3% to 0.9% of the mass of NiCo2O4; and the particle size of the AuNPs@NiCo2O4 composite material is 500nm to 600nm.

2. The AuNPs@NiCo2O4 composite material according to claim 1, characterized in that, The NiCo2O4 was obtained by calcining ZIF-67-derived nickel-cobalt bimetallic hydroxide powder at 300°C–400°C for 120–180 min in air.

3. A method for preparing the AuNPs@NiCo2O4 composite material according to claim 1 or 2, characterized in that, Includes the following steps: NiCo2O4 was dispersed in water, and a gold source solution and a reducing agent were added to carry out an in-situ reduction reaction to form dispersed Au nanoparticles on the surface of NiCo2O4, thus obtaining AuNPs@NiCo2O4 composite material.

4. The method for preparing the AuNPs@NiCo2O4 composite material according to claim 3, characterized in that, The ratio of NiCo2O4 to gold source is 40mg:12.5mmol~37.5mmol.

5. The method for preparing the AuNPs@NiCo2O4 composite material according to claim 3, characterized in that, The gold source is an acid, salt, or complex of gold.

6. The method for preparing the AuNPs@NiCo2O4 composite material according to claim 3, characterized in that, The gold source solution is a chloroauric acid solution, and the concentration of the gold source solution is 12.5 mmol / L to 37.5 mmol / L; The reducing agent is a sodium borohydride solution, and the concentration of the sodium borohydride solution is 0.05 mol / L to 0.15 mol / L.

7. A gas sensing electrode, characterized in that, The gas sensing electrode is formed by modifying the surface of the substrate with AuNPs@NiCo2O4 composite material, which is based on an interdigitated electrode. The AuNPs@NiCo2O4 composite material is the AuNPs@NiCo2O4 composite material as described in claim 1 or 2.

8. The gas sensing electrode according to claim 7, characterized in that, The method for preparing the gas sensing electrode includes the following steps: AuNPs@NiCo2O4 composite material was dispersed in a solvent to obtain a dispersion. The dispersion was coated on the surface of an interdigitated electrode, dried, and then heat-treated at 180°C to obtain a gas sensing electrode.

9. The application of the gas sensing electrode of claim 8 in the preparation of an electrode sensor for detecting trimethylamine, characterized in that, The method for fabricating an electrode sensor includes the following steps: In the pad area of ​​the gas sensing electrode, platinum wire is soldered as a lead wire, and the gas sensing electrode with the lead wire connected is fixed on the ceramic base. It is then aged at 150°C to 200°C for 2 to 3 hours to obtain the electrode sensor. The application method is as follows: place the electrode sensor in a mixed atmosphere containing trimethylamine, obtain the initial resistance value of the electrode sensor and the actual resistance value after the mixed atmosphere containing trimethylamine is introduced, and obtain the ratio of the actual resistance value to the initial resistance value; based on the ratio of the actual resistance value to the initial resistance value and the concentration of trimethylamine in the mixed atmosphere, obtain the relationship curve between the ratio of the actual resistance value to the initial resistance value and the concentration of trimethylamine in the mixed atmosphere, so as to realize the detection of the concentration of trimethylamine in the mixed atmosphere.

10. The application of the gas sensing electrode according to claim 9, characterized in that, The gas sensor has a detection range of 0.5 ppm to 15 ppm for the concentration of trimethylamine in the mixed atmosphere.

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