Polymer-coated non-metallic element doped metal oxide multistage branch-shaped composite material, preparation method and application

Abstract

The invention discloses a macromolecule coated non-metallic element doped metal oxide multi-stage branch-shaped composite material, a preparation method and application of the macromolecule coated non-metallic element doped metal oxide multi-stage branch-shaped composite material. A non-metallic element doped metal oxide is prepared by combining a solvothermal method with an annealing process, and then the polymer-coated non-metallic element doped metal oxide composite material is prepared by using an in-situ polymerization process. The composite material is in a multi-stage branch-shaped morphology and comprises a macromolecular coating layer and a trunk-branch-secondary branch carrier layer formed by non-metallic element doped metal oxide, nanopores and defect oxygen are enriched on the surface of the composite material, and high volume / surface area and reaction adsorption sites can be provided. The composite material obtains good sensing performance by utilizing ternary synergistic modification of a multi-stage branch-shaped structure, polymer coating and non-metallic element doping, can be widely applied to the fields of gas sensing, biological sensing, photoelectric sensing, pressure sensing and electrochemical sensing, and has important application value in the scenes of environmental monitoring, biological detection and intelligent equipment manufacturing.

Description

Technical Field

[0001] The present invention relates to a polymer-coated non-metallic element-doped metal oxide multi-level branched composite material, a preparation method and an application. Specifically, the composite material is designed through a multi-level branched structure, combined with surface polymer coating and non-metallic element doping modification means, to construct a microstructure with high volume / surface area and abundant sensing adsorption sites; the preparation method of the composite material adopts a solvent thermal method combined with an annealing process to obtain non-metallic element-doped metal oxide, and coats the polymer through an in-situ polymerization method to establish a structure-activity relationship between the material morphology and sensing performance. The composite material exhibits excellent performance in the fields of gas sensing, biosensing, and photoelectric sensing, and provides innovative ideas and technical solutions for the design and preparation of sensing materials. The present invention is a function-oriented sensing material design and modification technology, belonging to the field of sensing technology. Background Art

[0002] Against the backdrop of the deep integration of digital and intelligent technologies, intelligent sensing technology is the core driving force behind the rapid development of the Internet of Things (IoT) industry. Sensors, as core components of the IoT's perception layer, play a vital role. For example, gas sensors are a crucial line of defense in preventing toxic and hazardous gas leaks and explosions in industrial production (Nano-MicroLetters 2025, 17, 54). In medical diagnostics, gas sensors can detect exhaled breath, enabling early screening and non-invasive diagnosis of diseases. Furthermore, gas sensors can effectively detect biomarker gases produced during food spoilage, safeguarding public food safety (Advanced Functional Materials 2022, 32, 2107439). Therefore, improving the performance and industrialization of gas sensors holds significant practical significance and holds broad market prospects.

[0003] Chemiresistive gas sensors, due to their ease of miniaturization and integration, have become a research hotspot in the field of gas sensing. Their sensing performance depends on the microstructure, surface chemistry, and electron transport properties of the core sensing material. In recent years, researchers have conducted extensive innovative research on novel sensing materials. For example, in 2022, the Chemical Engineering Journal reported a chemiresistive gas sensor based on palladium / palladium oxide-coated iron oxide core-shell nanoparticles. This sensor exhibited rapid response to hydrogen, excellent stability, and a ppb-level detection limit (Chemical Engineering Journal 2022, 457, 141258). Another example, in 2025, the journal Sensors and Actuators B: Chemical reported on palladium- and polypyrrole-modified iron vanadate nanorods, which reliably detected indole, a metabolic biomarker for Escherichia coli (Sensors and Actuators B: Chemical 2025, 433, 137590).

[0004] While the aforementioned research has made some progress, existing technologies still face challenges in promoting the industrial application of gas sensors. On the one hand, sensing materials must simultaneously meet multiple performance requirements, including reliable detection within a specific operating temperature range and extremely low detection limits. On the other hand, industrial applications require sensing materials to exhibit excellent long-term stability and high selectivity, and their preparation processes require the regulation of key performance parameters (specific surface area, pore size distribution, defect concentration) and the surface sensing layer. Therefore, the development of new sensing materials and preparation methods that combine excellent sensing performance with the requirements of industrial application is an urgent challenge in this field. Summary of the Invention

[0005] To address the limitations of existing technologies, the present invention provides a polymer-coated, non-metallic element-doped metal oxide multi-level branched composite material, along with its preparation method and application. This composite material is prepared by a solvothermal method combined with an annealing process to form the non-metallic element-doped metal oxide. This composite material is then uniformly coated with a polymer layer through in-situ polymerization, resulting in a high-performance sensing composite material with a multi-level branched structure and controlled surface defects. To achieve these objectives, the present invention employs the following technical solutions.

[0006] The present invention provides a polymer-coated non-metallic element-doped metal oxide multi-level branched composite material, wherein the composite material has a multi-level branched morphology and includes a polymer coating layer and a trunk-branch-sub-branch carrier layer composed of a non-metallic element-doped metal oxide. The preparation method thereof is as follows: (1) Preparation of non-metallic element doped metal oxides by solvent thermal method combined with annealing process: 0.02-0.25 M cyanometallic complex and 0.01-0.1 M other metal salts were added to deionized water and stirred for 0.5-2 h to obtain solution A; solution A was transferred to a reactor and placed in an oven at 100-200 °C for 1-10 h, and precipitated product B was obtained after centrifugal washing and drying; precipitated product B was calcined in a muffle furnace at 300-600 °C at a heating rate of 1-5 °C / min and a calcination time of 1-8 h to obtain non-metallic element doped metal oxide C; (2) Preparation of polymer-coated non-metallic element-doped metal oxide composite materials by in situ polymerization process: the above-mentioned non-metallic element-doped metal oxide C, 0.05-0.5 M monomer and 0.05-1 M pH regulator are added to deionized water and ultrasonically dispersed for 0.1-1 h to obtain dispersion D; 0.05-1 M initiator is added to the dispersion D, and stirred in a water bath at 0-60 °C for 1-10 h. After centrifugal washing and drying, the polymer-coated non-metallic element-doped metal oxide composite material is obtained.

[0007] In the trunk-branch-sub-branch carrier layer composed of the non-metallic element doped metal oxide, the branches are distributed on the trunk and the sub-branches are distributed on the branches; the trunk branch diameter is 0.5-15 um, the branch branch diameter is 0.05-5 um, and the sub-branch branch diameter is 5-50 nm; the number of branches per unit trunk is 20-80, and the number of sub-branches per unit branch is 2-30; the angle between the branch and the trunk is 35°-65°, and the angle between the sub-branch and the branch is 35°-65°.

[0008] The polymer coating layer is uniformly coated on the surface of the trunk-branch-sub-branch carrier layer composed of non-metallic elements doped with metal oxides, and the thickness of the polymer coating layer is 2-100 nm.

[0009] The surface of the composite material is enriched with nanopores and defective oxygen, the pore diameter is 1-30 nm, and the proportion of the defective oxygen in the oxygen element content of the material is 15-55 at.%.

[0010] The non-metallic element includes at least one of carbon and nitrogen, and the total doping amount is 0.5-5 wt.%.

[0011] Preferably, the preparation method of the composite material is characterized by: in step (1), the cyanometallic complex includes any one of potassium ferrocyanide (K3[Fe(CN)6]), potassium cobalt cyanide (K3[Co(CN)6]) and potassium tetracyanopalladate (K2[Pd(CN)4]).

[0012] Preferably, the preparation method of the composite material is characterized by: in step (1), the other metal salts include any one of ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3), ferric sulfate (Fe2(SO4)3), cobaltous chloride (CoCl2), cobalt nitrate (Co(NO3)2), cobalt sulfate (CoSO4), palladium chloride (PdCl2) and palladium nitrate (Pd(NO3)2), and the metal element in the other metal salts must be the same element as the central metal element of the cyanometallic complex.

[0013] Preferably, the preparation method of the composite material is characterized by: in step (2), the monomer is selected from any one of aniline, pyrrole, 3,4-ethylenedioxythiophene, dopamine and indole.

[0014] Preferably, the preparation method of the composite material is characterized in that: in step (2), the pH regulator includes any one of hydrochloric acid (HCl), sulfuric acid (H2SO4), p-toluenesulfonic acid (C7H8O3S), citric acid (C6H8O7), ammonia water (NH3·H2O), sodium carbonate (Na2CO3), sodium hydroxide (NaOH) and potassium hydroxide (KOH).

[0015] Preferably, the preparation method of the composite material is characterized in that in step (2), the initiator includes any one of ammonium persulfate ((NH4)2S2O8), potassium persulfate (K2S2O8), sodium persulfate (Na2S2O8), ferric chloride (FeCl3), ferric nitrate (Fe (NO3)3) and ferric sulfate (Fe2(SO4)3).

[0016] The preparation method of the composite material is characterized by: in steps (1) and (2), the centrifugal washing is carried out by alternating deionized water and anhydrous ethanol for 2-6 times, the centrifugal speed is 3000-10000 rpm, and the centrifugal time is 3-10 min; the drying treatment is carried out in an oven, the drying temperature is 40-80 ° C, and the drying time is 5-24 h.

[0017] Preferably, the metal oxide includes at least one of ferric oxide (Fe2O3), ferrosoferric oxide (Fe3O4), cobalt oxide (CoO), cobalt oxide (Co3O4) and palladium oxide (PdO).

[0018] Preferably, the polymer is formed by polymerization of corresponding monomers, including at least one of polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), polydopamine and polyindole.

[0019] The present invention provides a polymer-coated, non-metallic element-doped metal oxide multi-level branched composite material for sensing applications. The composite material can be used for gas sensing, biosensing, photoelectric sensing, pressure sensing, and electrochemical sensing of ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), volatile organic compounds (VOCs), and biomarkers. The application of a polyaniline-coated carbon-doped ferric oxide composite material (PANI@C-Fe2O3) in gas sensing is described as follows: (1) Preparation of gas sensing components: Weigh an appropriate amount (10-50 mg) of PANI@C-Fe2O3 sensing material, add appropriate amounts of deionized water and ethanol, and drop the mixed liquid onto the interdigital electrodes. Then, perform the sensing performance test at room temperature. (2) Sensing applications: The PANI@C-Fe2O3 sensing material in the present invention has a multi-level branched morphology and is enriched with nanopores and defective oxygen on the surface, which helps to provide abundant gas diffusion paths and adsorption sites. It has excellent sensing response to ammonia and has important application prospects in industrial production, food safety and medical diagnosis. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 (a) Schematic diagram of the morphology and (b) scanning electron microscope image of PANI@C-Fe2O3, showing the existence of a multi-level branched structure, a PANI coating layer, and a trunk-branch-sub-branch support layer composed of C-Fe2O3.

[0021] Figure 2 This is a scanning electron microscope image of PANI@C-Fe2O3, showing the large-area batch preparation of PANI@C-Fe2O3.

[0022] Figure 3 (ab) Transmission electron microscopy images, (c) high-resolution transmission electron microscopy images, and (d-d4) element distribution maps of PANI@C-Fe2O3. The characterization results show that the material has a multi-level branched morphology, a nanoporous structure, and the presence of a PANI coating layer and a C-Fe2O3 carrier layer.

[0023] Figure 4 (a) X-ray photoelectron spectrum full spectrum and (b) X-ray photoelectron spectrum C 1s fine scan spectrum of PANI@C-Fe2O3. The characterization results confirm the presence of C-doped components in the material.

[0024] Figure 5 This is the X-ray diffraction pattern of PANI@C-Fe2O3. The results show that there are amorphous C-doped phase, PANI and Fe2O3 phase with good crystallinity in the composite material.

[0025] Figure 6 Sensing response curves of PANI@C-Fe2O3 to (a) NH3 and (b) H2S at room temperature. DETAILED DESCRIPTION

[0026] The present invention is described below by way of specific embodiments. Unless otherwise specified, the technical means used in the present invention are methods well known to those skilled in the art. In addition, the embodiments should be understood to be illustrative rather than limiting the scope of the present invention, the spirit and scope of the present invention being limited only by the claims. For those skilled in the art, various changes or modifications to the material components and dosages in these embodiments, without departing from the spirit and scope of the present invention, also fall within the scope of protection of the present invention. The raw materials and reagents used in the present invention are all commercially available.

[0027] Example 1 (1) Preparation of carbon-doped iron oxide by solvothermal method combined with annealing process: 0.2 M K3[Fe(CN)6] and 0.05 MFeCl3 were added to deionized water and stirred for 0.5 h to obtain solution A; solution A was transferred to a reactor and placed in an oven at 180 °C for 6 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 300 °C at a heating rate of 1 °C / min for 2 h to obtain carbon-doped iron oxide C; (2) Preparation of polyaniline-coated carbon-doped iron oxide composites by in situ polymerization process: the above-mentioned carbon-doped iron oxide C, 0.2 M aniline monomer and M HCl were added to deionized water and ultrasonically dispersed for 0.5 h to obtain dispersion D; 0.6 M (NH4)2S2O8 was added to the dispersion D, and stirred in a water bath at 25 °C for 3 h. After centrifugal washing and drying, the polyaniline-coated carbon-doped iron oxide composite was obtained.

[0028] Example 2 (1) Preparation of carbon-doped cobalt oxide by solvothermal method combined with annealing process: 0.05 M K3[Co(CN)6] and 0.4 MCo(NO3)2 were added to deionized water and stirred for 2 h to obtain solution A; solution A was transferred to a reactor and placed in a 150 °C oven for 6 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 500 °C at a heating rate of 2 °C / min for 3 h to obtain carbon-doped cobalt oxide C; (2) Preparation of polypyrrole-coated carbon-doped cobalt oxide composite materials by in situ polymerization process: the above-mentioned carbon-doped cobalt oxide C, 0.5 M pyrrole and 0.05 M C7H8O3S were added to deionized water and ultrasonically dispersed for 0.5 h to obtain dispersion D; 1 M FeCl3 was added to the dispersion D, and the mixture was stirred in a water bath at 5 °C for 6 h. After centrifugal washing and drying, the polypyrrole-coated carbon-doped cobalt oxide composite material was obtained.

[0029] Example 3 (1) Preparation of carbon-nitrogen doped iron oxide by solvothermal method combined with annealing process: 0.1 M K3[Fe(CN)6] and 0.05 M Fe2(SO4)3 were added to deionized water and stirred for 0.7 h to obtain solution A; solution A was transferred to a reactor and placed in a 120 °C oven for 4 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 300 °C with a heating rate of 5 °C / min and a calcination time of 6 h to obtain carbon-nitrogen doped iron oxide C; (2) Preparation of poly (3,4-ethylenedioxythiophene) coated carbon-doped iron oxide composite material by in situ polymerization process: the above carbon-nitrogen doped iron oxide C, 0.1 M 3,4-ethylenedioxythiophene and 0.5 M H2SO4 were added to deionized water and ultrasonically dispersed for 0.8 h to obtain dispersion D; 1 M Fe2(SO4)3 was added to the dispersion D, and the mixture was stirred in a water bath at 40 °C for 8 h. After centrifugal washing and drying, the poly (3,4-ethylenedioxythiophene) coated carbon-nitrogen doped iron oxide composite material was obtained.

[0030] Example 4 (1) Preparation of nitrogen-doped palladium oxide by solvothermal method combined with annealing process: 0.15 M K2[Pd(CN)4] and 0.1 MPdCl2 were added to deionized water and stirred for 1.5 h to obtain solution A; solution A was transferred to a reactor and placed in a 200 °C oven for 5 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 350 °C at a heating rate of 3 °C / min for 1 h to obtain nitrogen-doped palladium oxide C; (2) Preparation of poly (3,4-ethylenedioxythiophene) coated nitrogen-doped palladium oxide composite material by in situ polymerization process: the above nitrogen-doped palladium oxide C, 0.3 M 3,4-ethylenedioxythiophene and 0.2 M C7H8O3S were added to deionized water and ultrasonically dispersed for 0.5 h to obtain dispersion D; 0.5 M (NH4)2S2O8 was added to the dispersion D, and the mixture was stirred in a water bath at 25 °C for 3 h. After centrifugal washing and drying, the poly (3,4-ethylenedioxythiophene) coated nitrogen-doped palladium oxide composite material was obtained.

[0031] Example 5 (1) Preparation of nitrogen-doped cobalt oxide by solvothermal method combined with annealing process: 0.05 M K3[Co(CN)6] and 0.05 MCoSO4 were added to deionized water and stirred for 1.5 h to obtain solution A; solution A was transferred to a reactor and placed in a 150 °C oven for 5 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 400 °C at a heating rate of 4 °C / min for 2 h to obtain nitrogen-doped cobalt oxide C; (2) Preparation of polyaniline-coated nitrogen-doped cobalt oxide composite materials by in situ polymerization process: the above-mentioned nitrogen-doped cobalt oxide C, 0.15 M aniline and 1 M C7H8O3S were added to deionized water and ultrasonically dispersed for 1 h to obtain dispersion D; 1 M Na2S2O8 was added to the dispersion D, and the mixture was stirred in a water bath at 20 °C for 4 h. After centrifugal washing and drying, the polyaniline-coated nitrogen-doped cobalt oxide composite material was obtained.

[0032] Example 6 (1) Preparation of carbon-doped palladium oxide by solvothermal method combined with annealing process: 0.1 M K2[Pd(CN)4] and 0.05 M Pd(NO3)2 were added to deionized water and stirred for 0.8 h to obtain solution A; solution A was transferred to a reactor and placed in an oven at 180 °C for 3 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 350 °C with a heating rate of 2 °C / min and a calcination time of 3 h to obtain carbon-doped palladium oxide C; (2) Preparation of polyindole-coated carbon-doped palladium oxide composite material by in situ polymerization process: the above-mentioned carbon-doped palladium oxide C, 0.4 M indole and 0.1 M HCl were added to deionized water and ultrasonically dispersed for 0.5 h to obtain dispersion D; 0.5 M Fe (NO3)3 was added to the dispersion D, and the mixture was stirred in a water bath at 40 °C for 6 h. After centrifugal washing and drying, the polyindole-coated carbon-doped palladium oxide composite material was obtained.

[0033] Example 7 (1) Preparation of carbon-nitrogen doped iron oxide by solvothermal method combined with annealing process: 0.02 M K3[Fe(CN)6] and 0.01 M Fe(NO3)3 were added to deionized water and stirred for 1.5 h to obtain solution A; solution A was transferred to a reactor and placed in a 160 °C oven for 7 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 450 °C with a heating rate of 3 °C / min and a calcination time of 5 h to obtain carbon-nitrogen doped iron oxide C; (2) Preparation of polydopamine-coated carbon-nitrogen-doped iron oxide composites by in situ polymerization process: the carbon-nitrogen-doped iron oxide C, 0.01 M dopamine and 0.1 M NH3·H2O were added to deionized water and ultrasonically dispersed for 0.5 h to obtain dispersion D; 0.1 M (NH4)2S2O8 was added to the dispersion D, and the mixture was stirred in a water bath at 25 °C for 9 h. After centrifugal washing and drying, the polydopamine-coated carbon-nitrogen-doped iron oxide composites were obtained.

[0034] Example 8 (1) Preparation of nitrogen-doped cobalt oxide by solvothermal method combined with annealing process: 0.2 M K3[Co(CN)6] and 0.05 MCo(NO3)2 were added to deionized water and stirred for 1 h to obtain solution A; solution A was transferred to a reactor and placed in a 120 °C oven for 5 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 400 °C with a heating rate of 1 °C / min and a calcination time of 7.5 h to obtain nitrogen-doped cobalt oxide C; (2) Preparation of conductive polymer-coated nitrogen-doped cobalt oxide composite materials by in situ polymerization process: the above-mentioned nitrogen-doped cobalt oxide C, 0.5 M pyrrole and 1 M H2SO4 were added to deionized water and ultrasonically dispersed for 0.5 h to obtain dispersion D; 0.3 M Na2S2O8 was added to the dispersion D, and stirred in a water bath at 5 °C for 10 h. After centrifugal washing and drying, a polypyrrole-coated nitrogen-doped cobalt oxide composite material was obtained.

[0035] Example 9 (1) Preparation of nitrogen-doped iron oxide by solvothermal method combined with annealing process: 0.04 M K3[Fe(CN)6] and 0.02 MFeCl3 were added to deionized water and stirred for 0.5 h to obtain solution A; solution A was transferred to a reactor and placed in a 150 °C oven for 6 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 350 °C with a heating rate of 2 °C / min for 6 h to obtain nitrogen-doped iron oxide C; (2) Preparation of poly (3,4-ethylenedioxythiophene)-coated nitrogen-doped iron oxide composite material by in situ polymerization process: the above nitrogen-doped iron oxide C, 0.06 M 3,4-ethylenedioxythiophene and 0.1 M H2SO4 were added to deionized water and ultrasonically dispersed for 0.5 h to obtain dispersion D; 0.4 M K2S2O8 was added to the dispersion D, and the mixture was stirred in a water bath at 25 °C for 8 h. After centrifugal washing and drying, the poly (3,4-ethylenedioxythiophene)-coated nitrogen-doped iron oxide composite material was obtained.

[0036] Example 10 (1) Preparation of carbon-doped palladium oxide by solvothermal method combined with annealing process: 0.05 M K2[Pd(CN)4] and 0.05 MPdCl2 were added to deionized water and stirred for 2 h to obtain solution A; solution A was transferred to a reactor and placed in a 200 °C oven for 9 h. After centrifugal washing and drying, precipitate product B was obtained; precipitate product B was calcined in a muffle furnace at 400 °C with a heating rate of 2 °C / min and a calcination time of 8 h to obtain carbon-doped palladium oxide C; (2) Preparation of polydopamine-coated carbon-doped palladium oxide composite material by in situ polymerization process: the above-mentioned carbon-doped palladium oxide C, 0.3 M dopamine and 1 M NaOH were added to deionized water and ultrasonically dispersed for 1 h to obtain dispersion D; 0.5 M FeCl3 was added to the dispersion D, and the mixture was stirred in a water bath at 60 °C for 10 h. After centrifugal washing and drying, the polydopamine-coated carbon-doped palladium oxide composite material was obtained.

Claims

1. A polymer-coated non-metallic element-doped metal oxide multi-level branched composite material, characterized by: The composite material has a multi-level branched structure, consisting of a polymer coating layer and a trunk-branch-sub-branch carrier layer composed of a non-metallic element doped metal oxide. The preparation method is as follows: (1) Preparation of non-metallic element-doped metal oxides by solvothermal method combined with annealing process: 0.02-0.25 M cyanometallic complex and 0.01-0.1 M other metal salts were added to deionized water and stirred for 0.5-2 h to obtain solution A; Solution A is transferred to a reactor, placed in an oven at 100-200°C for 1-10 hours, and subjected to centrifugal washing and drying to obtain a precipitated product B. The precipitated product B is calcined in a muffle furnace at 300-600°C at a heating rate of 1-5°C / min for 1-8 hours to obtain a non-metallic element-doped metal oxide C. (2) Preparation of polymer-coated non-metallic element-doped metal oxide composite materials by in situ polymerization process: the above-mentioned non-metallic element-doped metal oxide C, 0.05-0.5 M monomer and 0.05-1 M pH regulator are added to deionized water and ultrasonically dispersed for 0.1-1 h to obtain dispersion D; 0.05-1 M initiator is added to the dispersion D, and the mixture is stirred in a water bath at 0-60 °C for 1-10 h. After centrifugal washing and drying, the polymer-coated non-metallic element-doped metal oxide composite material is obtained.

2. The polymer-coated non-metallic element-doped metal oxide multi-level branched composite material according to claim 1, characterized in that: In the trunk-branch-sub-branch carrier layer composed of the non-metallic element doped metal oxide, the branches are distributed on the trunk and the sub-branches are distributed on the branches; the trunk branch diameter is 0.5-15 um, the branch branch diameter is 0.05-5 um, and the sub-branch branch diameter is 5-50 nm; the number of branches per unit trunk is 20-80, and the number of sub-branches per unit branch is 2-30; the angle between the branch and the trunk is 35°-65°, and the angle between the sub-branch and the branch is 35°-65°.

3. The polymer-coated non-metallic element-doped metal oxide multi-level branched composite material according to claim 1, characterized in that: The polymer coating layer is uniformly coated on the surface of the trunk-branch-sub-branch carrier layer composed of non-metallic elements doped with metal oxides, and the thickness of the polymer coating layer is 2-100 nm.

4. The polymer-coated non-metallic element-doped metal oxide multi-level branched composite material according to claim 1, characterized in that: The surface of the composite material is enriched with nanopores and defective oxygen, the pore diameter is 1-30 nm, and the proportion of the defective oxygen to the oxygen content in the material is 15-55 at.%; the non-metallic element includes at least one of carbon and nitrogen, and the total doping amount is 0.5-5 wt.%.

5. The method for preparing a polymer-coated non-metallic element-doped metal oxide multi-level branched composite material according to claim 1, characterized in that: In step (1), the cyanometallic complex includes any one of potassium ferricyanide (K3[Fe(CN)6]), potassium cobalt cyanide (K3[Co(CN)6]) and potassium tetracyanopalladate (K2[Pd(CN)4]); the other metal salts include any one of ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3), ferric sulfate (Fe2(SO4)3), cobaltous chloride (CoCl2), cobalt nitrate (Co(NO3)2), cobalt sulfate (CoSO4), palladium chloride (PdCl2) and palladium nitrate (Pd(NO3)2), and the metal element in the other metal salts must be the same element as the central metal element of the cyanometallic complex.

6. The method for preparing a polymer-coated non-metallic element-doped metal oxide multi-level branched composite material according to claim 1, characterized in that: In step (2), the monomer is selected from any one of aniline, pyrrole, 3,4-ethylenedioxythiophene, dopamine and indole; the pH regulator includes any one of hydrochloric acid (HCl), sulfuric acid (H2SO4), p-toluenesulfonic acid (C7H8O3S), citric acid (C6H8O7), ammonia (NH3·H2O), sodium carbonate (Na2CO3), sodium hydroxide (NaOH) and potassium hydroxide (KOH); the initiator includes any one of ammonium persulfate ((NH4)2S2O8), potassium persulfate (K2S2O8), sodium persulfate (Na2S2O8), ferric chloride (FeCl3), ferric nitrate (Fe (NO3)3) and ferric sulfate (Fe2(SO4)3); in steps (1) and (2), the centrifugal washing is performed by alternating deionized water and anhydrous ethanol for 2-6 times, the centrifugal speed is 3000-10000 rpm, and the centrifugal time is 3-10 min; the drying process is carried out in an oven at a drying temperature of 40-80°C and a drying time of 5-24 h.

7. The polymer-coated non-metallic element-doped metal oxide multi-level branched composite material according to claim 1, characterized in that: The metal oxide includes at least one of ferric oxide (Fe2O3), ferrosoferric oxide (Fe3O4), cobalt oxide (CoO), cobalt trioxide (Co3O4) and palladium oxide (PdO); the polymer is formed by polymerization of corresponding monomers, including at least one of polyaniline, polypyrrole, poly (3,4-ethylenedioxythiophene), polydopamine and polyindole.

8. The use of a polymer-coated non-metallic element-doped metal oxide multi-stage branched composite material according to claim 1, characterized in that: Used in the fields of gas sensing, biosensing, photoelectric sensing, pressure sensing and electrochemical sensing for detecting ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), volatile organic compounds (VOCs) and biomarkers.

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