A hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material and its preparation method and application

Abstract

The present invention relates to a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material, and its preparation method and application. The method uses dimethyl imidazole cobalt as a structure-directing agent, combined with a nickel-cobalt layered double hydroxide derivatization method and a chemical reduction method, to simultaneously achieve triple optimization of the material's microstructure, interface energy band gap, and composition. The unique hollow nanocage structure of the prepared composite material greatly increases its contact area with the gas being detected; the interface heterojunction formed by nickel cobaltate and nickel oxide in the material accelerates the efficiency of interfacial electron transmission; and silver doping increases the number of electron transitions during the detection process. Gas-sensing experiments have shown that the composite material has high selectivity, sensitivity, and stability for the volatile organic gas n-butanol at a relatively low operating temperature, and is suitable for the detection of trace n-butanol in complex environments. The preparation method has mild conditions, low cost, and good industrialization prospects, and has broad application prospects in the field of gas-sensitive material preparation.

Description

Technical Field

[0001] The invention relates to a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material and a preparation method and application thereof, belonging to the technical field of gas sensor preparation. Background Art

[0002] Gas sensors play a vital role in environmental monitoring, industrial production, home safety and other fields. Compared with traditional gas detection methods, gas sensors have the advantages of low power consumption, small size, fast response and easy integration, and have become one of the mainstream technologies for gas detection. Semiconductor gas sensors are an important branch of this, which mainly use the physical or chemical interaction between the surface of semiconductor materials and gas molecules to achieve gas detection. Semiconductor oxide gas sensors are divided into two types: n-type and p-type, with different electronic structures and gas response characteristics, which are suitable for different detection needs. However, existing semiconductor gas sensors have some limitations, such as the need for higher operating temperatures in high-sensitivity detection and insufficient selectivity for certain gases, which has a certain impact on their wide application in practical applications. Therefore, how to improve the sensitivity and selectivity of semiconductor gas-sensitive materials while reducing the operating temperature has become a key challenge in the current research and development of gas sensors.

[0003] Among many gas-sensitive materials, nickel cobalt oxide (NiCo2O4) is a typical p-type semiconductor material. With its bimetallic components (Ni and Co) and its reversible redox couple (Ni 3+ / Ni 2+ ,Co 3+ / Co 2+ ), showing excellent oxidation catalytic performance. These characteristics make nickel cobalt oxide have good response performance in the detection of toxic gases such as volatile organic compounds (VOCs). However, due to its p-type conductive properties, nickel cobalt oxide has low sensitivity and is difficult to effectively detect low-concentration gas molecules, which has become the main bottleneck for improving its performance. It is reported that by constructing nanoscale structures in structural design, such as nanosheets and hollow microspheres, the specific surface area of ​​the material can be significantly increased, thereby increasing the number of active sites and promoting the adsorption and surface reaction of gas molecules; by constructing pn heterojunctions or doping precious metals, the electronic structure of nickel cobalt oxide can also be effectively regulated, thereby improving conductivity and reaction rate. For example, Chen et al. used Ni-Co-BTC bimetallic organic framework (MOF) as a template and prepared NiO / NiCo2O4 hollow microspheres by annealing treatment, and the response value to 100ppm acetone gas reached 17.86 (Chen Q, Zhang YH, MaS Y, et al. Multishelled NiO / NiCo2O 4:hollow microspheres derived from bimetal-organic frameworks as high-performance sensing material for acetone detection[J].Journal of Hazardous Materials,2021,415:125662). Liang et al. constructed a ZnO@NiCo2O4 core-shell porous structure and formed a pn heterojunction between NiCo2O4 nanosheets and ZnO nanofibers, significantly improving the gas-sensing performance of the material (Liang Y,Liu WH,Hu W,et al.Synthesis and gas-sensing propertiesof ZnO@NiCo2O4 core@shell nanofibers[J].Materials Research Bulletin,2019,114:1-9). In summary, through reasonable structural design and composition modification, the comprehensive performance of nickel cobalt oxide-based gas-sensitive materials has been significantly improved, providing broad prospects for its application in the field of high sensitivity and low temperature detection.

[0004] Although nickel cobalt oxide has made some progress in improving its gas-sensing performance, current technical solutions still have bottlenecks and shortcomings. Nickel cobalt oxide-based gas-sensing materials typically need to operate at higher temperatures when detecting gases, which increases power consumption and offers limited improvement in detection sensitivity, making it difficult to meet the needs of high-precision detection. In addition, existing modification methods mostly rely on single structural designs or element doping, making it difficult to balance the coordinated optimization of multiple properties. Typically, only a single structure of nickel cobalt oxide is produced, making it difficult to achieve deeper optimization of the microstructure and functional components, thus limiting the material's gas-sensing performance. Summary of the Invention

[0005] The purpose of the present invention is to address the shortcomings of the technology and provide a hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material and its preparation method and application. The method uses dimethyl imidazole cobalt (ZIF-67) as a structure-directing agent to generate a nickel cobalt layered double hydroxide (NiCoLDH) precursor material with nickel salt through a solvent thermal method. After a one-step calcination method, NiCoLDH is used to derive and synthesize a nickel cobaltate / nickel oxide composite material (NiCo2O4 / NiO) with a hollow nanocage structure. Silver nanoparticles are then uniformly doped on its surface through a sodium borohydride reduction method, and finally a hollow nanocage structure silver-doped nickel cobaltate / nickel oxide (Ag-NiCo2O4 / NiO) composite gas-sensitive material is obtained. The preparation conditions of the method of the present invention are mild and controllable. The dual optimization of material structure and composition is achieved simultaneously by using ZIF-67 structure directing agent combined with NiCoLDH derivatization. The material is subsequently subjected to simple chemical reduction silver doping to further improve the gas-sensing performance of the material. The Ag-NiCo2O4 / NiO composite gas-sensitive material prepared by this method is used for n-butanol detection and has the characteristics of low operating temperature, good selectivity, high sensitivity, etc.

[0006] In order to achieve the above invention purpose, the present invention adopts the following technical solutions:

[0007] One of the technical solutions of the present application provides a method for preparing a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material, comprising the following steps:

[0008] a. Weigh nickel nitrate hexahydrate into ethanol, sonicate, then add cobalt dimethylimidazole (ZIF-67), and continue sonicating to obtain a uniform mixed solution;

[0009] b The mixed solution obtained in step a above was transferred to a polytetrafluoroethylene-lined autoclave, placed in an oven, and heated to react;

[0010] c. After the reaction is completed, the product is cooled naturally, and the green solid is separated by centrifugation and washed 3 to 5 times with anhydrous ethanol. The resulting solid product is placed in a vacuum oven and dried to obtain a nickel-cobalt layered double hydroxide (NiCoLDH) precursor material;

[0011] d. The nickel cobalt layered double hydroxide (NiCoLDH) precursor material prepared in step c was ground evenly with a mortar and placed in a quartz crucible. The crucible was wrapped with tin foil, and several small holes were punched in the tin foil. It was placed in a muffle furnace and heated to 300-500°C at a rate of 1-5°C / min and maintained at this temperature for 1-3h to obtain a black powder of nickel cobaltate / nickel oxide composite material (NiCo2O4 / NiO);

[0012] e. Weigh the NiCo2O4 / NiO obtained in step d, dissolve it in anhydrous ethanol solution by ultrasonication, add an aqueous silver nitrate solution, and stir for 10 to 30 minutes to obtain a mixed solution;

[0013] f. The sodium borohydride solution was added to the mixed solution obtained in step e above, and stirring was continued for 5 to 15 minutes to obtain a black solution;

[0014] g. The black solution obtained in step f was centrifuged to collect the black solid, which was washed 3 to 5 times with anhydrous ethanol and then dried in a vacuum oven to obtain a black solid hollow nanocage structure silver-doped nickel cobaltate / nickel oxide composite material.

[0015] Furthermore, the usage ratio of nickel nitrate hexahydrate, ethanol and dimethylimidazolium cobalt (ZIF-67) in step a is 0.1-0.3 g: 50 mL: 0.1 g;

[0016] Furthermore, the duration of the two ultrasounds in step a is 5-15 minutes;

[0017] Furthermore, the dimethyl imidazole cobalt (ZIF-67) in step a is used as a structure directing agent.

[0018] In some specific embodiments, the volume of the high-pressure reactor in step b is 100 mL;

[0019] Furthermore, the temperature of the heating reaction in step b is 100-150° C., and the reaction time is 4-8 hours.

[0020] Furthermore, the centrifugal speed in step c is 6000-10000 rpm, and the time is 3-5 min; the drying temperature is 50-70° C., and the time is 7-9 h;

[0021] Furthermore, in step e, the dosage of NiCo2O4 / NiO, anhydrous ethanol solution, and silver nitrate aqueous solution is 20 mg:50 mL:0.1-2 mL; the concentration of the silver nitrate aqueous solution is 1 mg / mL;

[0022] Furthermore, the amount of the sodium borohydride solution in step f and the mixed solution obtained in step e is 0.5-2 mL: 50.1-52 mL; the concentration of the sodium borohydride solution is 1 mg / mL;

[0023] Furthermore, the centrifugal speed in step g is 6000-10000 rpm, and the time is 3-5 min; the drying temperature is 40-80° C., and the time is 6-10 h.

[0024] The second technical solution of the present application provides a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material obtained by the above-mentioned preparation method.

[0025] The third technical solution of the present application provides an application of the above-mentioned hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material. The hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material is used as a gas sensor device for detecting volatile organic gases (such as n-butanol, formaldehyde, ethanol, etc.) and is suitable for detecting trace gases in complex environments.

[0026] Compared with the prior art, the method of the present invention has the following obvious outstanding substantial features and significant advantages:

[0027] (1) The preparation conditions of the method of the present invention are mild and controllable. The ZIF-67 structure-directing agent is combined with NiCoLDH derivatization to achieve dual optimization of material structure and composition, and the material is subsequently subjected to simple chemical reduction silver doping.

[0028] (2) This preparation method uses simple synthetic steps to simultaneously modify the material through structural optimization, heterostructure construction, and noble metal doping, significantly improving the material's gas-sensing performance. The unique hollow nanocage structure of the Ag-NiCo2O4 / NiO composite gas-sensing material prepared by this invention provides a large specific surface area and abundant pores, thereby improving the material's gas detection sensitivity.

[0029] (3) In addition, the heterojunction formation of NiCo2O4 and NiO and the doping of Ag, as dual factors, greatly accelerate the electron transfer rate between the material interfaces, while reducing the working temperature of the material and significantly improving its gas sensing selectivity, sensitivity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a transmission electron microscope (TEM) image of the Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in Example 1 of the present invention;

[0031] Figure 2 This is the energy spectrum analysis (EDS) diagram of the Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in Example 1 of the present invention;

[0032] Figure 3 This is a test chart of the gas-sensing performance of the Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in Example 1 of the present invention to gases of different concentrations at 170°C;

[0033] Figure 4 This is a test graph of the selectivity of the Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in Example 1 of the present invention to n-butanol under the condition of 100 ppm mixed gas;

[0034] Figure 5 This is a graph showing the stability of the Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in an embodiment of the present invention to 100 ppm n-butanol gas; DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below with reference to specific embodiments. It should be noted that the following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0036] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0037] Example 1

[0038] In this embodiment, a method for preparing a hollow nanocage structured silver-doped nickel cobalt oxide / nickel oxide gas-sensitive material comprises the following steps:

[0039] a. Weigh 0.2 g of nickel nitrate hexahydrate into 50 mL of ethanol and sonicate for 5 minutes. Then, add 0.1 g of dimethylimidazolium cobalt (ZIF-67) and continue sonicating for 10 minutes to mix the solution evenly to obtain a mixed solution; the dimethylimidazolium cobalt (ZIF-67) acts as a structure-directing agent.

[0040] b. The mixed solution obtained in step a was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, placed in an oven, heated to 120°C, and reacted for 6 h.

[0041] c. After the reaction is completed, the product is cooled naturally, and the green solid is separated by centrifugation and washed three times with anhydrous ethanol. The resulting solid product is placed in a vacuum oven and dried at 60°C for 8 hours to obtain a nickel-cobalt layered double hydroxide (NiCoLDH) precursor material.

[0042] d. The nickel cobalt layered double hydroxide (NiCoLDH) precursor material prepared in step c was ground evenly with a mortar and placed in a quartz crucible. The crucible was wrapped with tin foil, and several small holes were punched in the tin foil. It was placed in a muffle furnace and heated to 400°C at a rate of 2°C / min and maintained at this temperature for 2h to obtain a black powder of nickel cobaltate / nickel oxide composite material (NiCo2O4 / NiO).

[0043] e. Weigh 20 mg of NiCo2O4 / NiO obtained in step d and dissolve it in 50 mL of anhydrous ethanol solution by ultrasonication. Add 1 mL of a 1 mg / mL aqueous silver nitrate solution and stir for 10 min to obtain a mixed solution.

[0044] f. 1 mL of a 1 mg / mL sodium borohydride solution was added to the mixed solution obtained in step e above, and stirring was continued for 10 min to obtain a black solution.

[0045] g. The black solution obtained in step f was centrifuged to collect the black solid, which was washed three times with anhydrous ethanol and then placed in a vacuum oven at 60 ° C for 8 h to obtain a black solid hollow nanocage structure silver-doped nickel cobaltate / nickel oxide composite material Ag-NiCo2O4 / NiO.

[0046] In order to verify the successful synthesis of a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide composite gas-sensitive material in the present invention, its morphology and composition were characterized. Figure 1 This is the transmission electron microscope image of Ag-NiCo2O4 / NiO, which further confirms that the material is composed of hollow nanocages with a rough surface. This structure has a large specific surface area, which is conducive to the material adsorbing more gas during the gas sensing process. Figure 2 This is the energy spectrum analysis diagram of the Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in accordance with the present invention. In the diagram, uniform distribution of Ni, Co, O and Ag elements can be observed on the sample surface, which proves the successful synthesis of the Ag-NiCo2O4 / NiO material.

[0047] Gas sensing performance test:

[0048] (1) Preparation of a Gas Sensor Device: To verify the performance of the Ag-NiCo2O4 / NiO composite gas-sensitive material of the present invention, 1 mg of the prepared material was added to an agate mortar and an appropriate amount of ethanol was added to grind the mixture evenly and mix it into a paste. The paste was then evenly coated on the surface of an Al2O3 ceramic tube using a spatula to form a film of suitable thickness. The ceramic tube was then transferred to a 60°C air drying oven and removed after 2 hours. The solder was melted using an electric soldering iron, and the Pt wires at the four corners of the ceramic tube were fixed to the metal base of the sensor using solder. After completing the above steps, a heating wire was passed through the ceramic tube and the ends of the heating wire were soldered to the metal base using solder. This completed the preparation of the gas sensor device.

[0049] (2) Test method: Insert the prepared device into the test circuit board, age the component at 300℃ for 48h on the aging table, and then use the WS-30A gas sensor test system to perform gas sensing test. The test system mainly reflects the characteristics of the gas sensor by measuring the voltage on the load resistor connected in series with the gas sensor, so as to obtain the resistance and other parameters of the gas sensitive material. First, insert the test circuit board, select the appropriate load resistor, then turn on the power, set the measurement voltage and heating voltage, and let the instrument run smoothly for a period of time so that the resistance of the gas sensor in the air tends to be stable. After the output voltage on the computer software interface stabilizes, cover the gas distribution box, inject a certain amount of the liquid to be tested into the evaporator from the back, press the evaporation button, turn on the fan, and evenly distribute the volatile organic compounds in the gas distribution box. When the gas sensor contacts the target gas, its resistance changes, which causes the voltage of the load resistor to change. After the voltage stabilizes, open the gas distribution box, the gas escapes from the gas distribution box, and the output voltage returns to the level when it is in the air.

[0050] (3) Analysis of experimental test results: Figure 2 The Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in the embodiment of the present invention responds to different concentrations of gas and different concentrations of n-butanol at 170°C. It can be found that the gas-sensitive response of the material increases with the increase of n-butanol concentration. Through calculation, its detection limit is 0.27ppm. Figure 3 The response value of the Ag-NiCo2O4 / NiO composite gas-sensitive material prepared by this method to a 100 ppm mixed gas at 170°C is significantly higher for n-butanol than for other gases, indicating that the sensor has better selectivity for n-butanol. Figure 4 The Ag-NiCo2O4 / NiO composite gas-sensitive material prepared in this embodiment was tested for stability of 100 ppm n-butanol gas under the same conditions. It can be seen that at 170°C, the Ag-NiCo2O4 / NiO composite gas-sensitive material has a response value of 31.41 for 100 ppm n-butanol gas, and still maintains a response value of 84.68% after 14 days, indicating that the sensor has ideal long-term stability.

[0051] Example 2

[0052] The process of this embodiment is basically the same as that of embodiment 1, the main difference is the amount of material added, and the special feature is:

[0053] a. Weigh 0.1 g of nickel nitrate hexahydrate into 50 mL of ethanol and sonicate for 5 minutes. Then, add 0.1 g of dimethylimidazolium cobalt (ZIF-67) and continue sonicating for 5 minutes to mix the solution evenly to obtain a mixed solution; the dimethylimidazolium cobalt (ZIF-67) acts as a structure-directing agent.

[0054] b. The mixed solution obtained in step a was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, placed in an oven, heated to 100°C, and reacted for 4 h.

[0055] c. After the reaction is completed, the product is cooled naturally, and the green solid is separated by centrifugation and washed three times with anhydrous ethanol. The resulting solid product is placed in a vacuum oven and dried at 50°C for 7 hours to obtain a nickel-cobalt layered double hydroxide (NiCoLDH) precursor material.

[0056] d. The nickel cobalt layered double hydroxide (NiCoLDH) precursor material prepared in step c was ground evenly with a mortar and placed in a quartz crucible. The crucible was wrapped with tin foil, and several small holes were punched in the tin foil. It was placed in a muffle furnace and heated to 300°C at a rate of 1°C / min and maintained at this temperature for 1 hour to obtain a black powder of nickel cobaltate / nickel oxide composite material (NiCo2O4 / NiO).

[0057] e. Weigh 20 mg of NiCo2O4 / NiO obtained in step d and dissolve it in 50 mL of anhydrous ethanol solution by ultrasonication. Add 0.1 mL of a 1 mg / mL aqueous silver nitrate solution and stir for 10 min to obtain a mixed solution.

[0058] f. 0.5 mL of a 1 mg / mL sodium borohydride solution was added to the mixed solution obtained in step e above, and stirring was continued for 5 min to obtain a black solution.

[0059] g. The black solution obtained in step f was centrifuged to collect the black solid, which was washed three times with anhydrous ethanol and then placed in a vacuum oven at 40 ° C for 6 h to obtain a black solid hollow nanocage structure silver-doped nickel cobaltate / nickel oxide composite material Ag-NiCo2O4 / NiO.

[0060] The preparation and performance testing of the gas sensor device were the same as in Example 1. The Ag-NiCo2O4 / NiO composite gas-sensitive material prepared using the process of this example was subjected to gas-sensing performance testing, demonstrating excellent gas-sensing performance. The test results showed that, in a 100 ppm mixed gas test at 170°C, the material's response to n-butanol was significantly higher than its response to other gases, indicating excellent selectivity for n-butanol. Furthermore, the material also demonstrated good performance in stability testing. Under the same test conditions for 100 ppm n-butanol gas, the material's response value was 30.12, and after 14 days, it still maintained a response value of 82.95%, demonstrating excellent long-term stability.

[0061] Comparative Example 1

[0062] Preparation of a hollow nanocage structured nickel cobalt oxide / nickel oxide composite gas-sensing material:

[0063] a. Weigh 0.2 g of nickel nitrate hexahydrate into 50 mL of ethanol and sonicate for 5 minutes. Then, add 0.1 g of dimethylimidazolium cobalt (ZIF-67) and continue sonicating for 10 minutes to mix the solution evenly to obtain a mixed solution; the dimethylimidazolium cobalt (ZIF-67) acts as a structure-directing agent.

[0064] b. The mixed solution obtained in step a was transferred to a 100 mL polytetrafluoroethylene-lined autoclave, placed in an oven, heated to 120°C, and reacted for 6 h.

[0065] c. After the reaction is completed, the product is cooled naturally, and the green solid is separated by centrifugation and washed three times with anhydrous ethanol. The resulting solid product is placed in a vacuum oven and dried at 60°C for 8 hours to obtain a nickel-cobalt layered double hydroxide (NiCoLDH) precursor material.

[0066] d. The nickel cobalt layered double hydroxide (NiCoLDH) precursor material prepared in step c was ground evenly with a mortar and placed in a quartz crucible. The crucible was wrapped with tin foil, and several small holes were punched in the tin foil. It was placed in a muffle furnace and heated to 400°C at a rate of 2°C / min and maintained at this temperature for 2h to obtain a black powder of nickel cobaltate / nickel oxide composite material (NiCo2O4 / NiO).

[0067] e. The black solution obtained in step f was centrifuged to collect the black solid, which was washed three times with anhydrous ethanol and then placed in a vacuum oven at 60 ° C for 8 h to obtain a black solid hollow nanocage structure silver-doped nickel cobaltate / nickel oxide composite material.

[0068] The preparation and performance testing of the gas sensor device were similar to those in Example 1. The NiCo2O4 / NiO composite gas-sensitive material prepared using the comparative example's preparation process was tested for gas-sensing performance. The response to 100 ppm n-butanol gas was measured, and the results showed a response value of only 3.81. Compared to the material in the example, the comparative example material exhibits a lower response value, indicating some deficiencies in its gas-sensing performance.

[0069] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material, characterized in that: The following steps are involved: a. Weigh nickel nitrate hexahydrate into ethanol, sonicate, then add cobalt dimethylimidazole ZIF-67, and continue sonication to obtain a uniform mixed solution; b. The mixed solution obtained in step a was transferred to a high pressure reactor and heated to react; c. After the reaction is completed, the mixture is cooled naturally, and the green solid is separated by centrifugation and washed and dried to obtain a nickel-cobalt layered double hydroxide precursor material NiCoLDH; d. The nickel-cobalt layered double hydroxide precursor prepared in step c was ground evenly and placed in a crucible and heated to react to obtain a black powder of nickel cobaltate / nickel oxide composite material NiCo2O4 / NiO; e Weigh the NiCo2O4 / NiO obtained in step d, ultrasonically dissolve it in anhydrous ethanol solution, add an aqueous silver nitrate solution, and stir to obtain a mixed solution; f. The sodium borohydride solution was added to the mixed solution obtained in step e, and stirring was continued to obtain a black solution; g. The black solution obtained in step f was centrifuged to collect the black solid, washed and dried to obtain a black solid hollow nanocage structure silver-doped nickel cobaltate / nickel oxide composite material.

2. The method for preparing a hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material according to claim 1, characterized in that: The usage ratio of nickel nitrate hexahydrate, ethanol and cobalt dimethylimidazole in step a is 0.1-0.3 g:50 mL:0.1 g; and the two ultrasonic times in step a are both 5-15 min.

3. The method for preparing a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material according to claim 1, characterized in that: The temperature of the heating reaction in step b is 100-150° C., and the reaction time is 4-8 hours; the high-pressure reactor in step b is lined with polytetrafluoroethylene.

4. The method for preparing a hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material according to claim 1, characterized in that: In step c, the centrifugal speed is 6000-10000 rpm and the time is 3-5 minutes; the washing and drying is washing with anhydrous ethanol 3-5 times, and the obtained solid product is placed in a vacuum oven for drying; the drying temperature is 50-70° C. and the time is 7-9 hours.

5. The method for preparing a hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material according to claim 1, characterized in that: The heating reaction in step d is to wrap the crucible with tin foil, poke several small holes in the tin foil, place it in a muffle furnace, heat it to 300-500°C at a rate of 1-5°C / min, and maintain it at this temperature for 1-3h.

6. The method for preparing a hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material according to claim 1, characterized in that: The dosage of NiCo2O4 / NiO, anhydrous ethanol solution, and silver nitrate aqueous solution in step e is 20 mg:50 mL:0.1-2 mL; the concentration of the silver nitrate aqueous solution is 1 mg / mL; and the stirring time is 10-30 min.

7. The method for preparing a hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material according to claim 1, characterized in that: The amount of the sodium borohydride solution in step f and the mixed solution obtained in step e is 0.5-2 mL:50.1-52 mL; the concentration of the sodium borohydride solution is 1 mg / mL; and the stirring time is 5-15 min.

8. The method for preparing a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material according to claim 1, characterized in that: In step g, the centrifugal speed is 6000-10000 rpm and the time is 3-5 min; the washing and drying is washing with anhydrous ethanol 3-5 times, and then the black solid is placed in a vacuum oven for drying; the drying temperature is 40-80° C. and the time is 6-10 h.

9. A hollow nanocage structure silver-doped nickel cobaltate / nickel oxide gas-sensitive material, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 8.

10. Application of a hollow nanocage structured silver-doped nickel cobaltate / nickel oxide gas-sensitive material, characterized in that: The hollow nanocage structured silver-doped nickel cobalt oxide / nickel oxide gas-sensitive material is used as a gas sensor device to detect volatile organic gases and is suitable for detecting trace gases in complex environments; the volatile organic gases include but are not limited to n-butanol, methanol or ethanol.

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