阅读说明：本技术 一种氮掺杂的金属氧化物气敏材料、气敏元件及其制备方法与应用 (Nitrogen-doped metal oxide gas-sensitive material, gas-sensitive element, and preparation method and application thereof ) 是由 刘久荣 杜文静 吴莉莉 刘伟 王凤龙 汪宙 王�琦 陈国文 于 2019-08-29 设计创作，主要内容包括：本发明提供一种氮掺杂的金属氧化物气敏材料、气敏元件及其制备方法与应用,属于气敏材料技术领域。所述氮掺杂的金属氧化物气敏材料是由金属氧化物经表面掺氮处理后获得,所述的气敏材料为小颗粒组成的多孔纳米球,直径为300-700nm,小颗粒的尺寸为10-30nm。本发明的氮掺杂的金属氧化物气敏材料在氮源提供氮的气氛下在不同温度下进行表面掺氮处理,掺杂浓度可调,且制备方法方便简单,将其制备为气敏元件,研究表明该气敏元件在较低温度下对低浓度NO<Sub>2</Sub>气体的响应值高、选择性好,因此具有良好的实际应用之价值。(The invention provides a nitrogen-doped metal oxide gas-sensitive material, a gas-sensitive element, and a preparation method and application thereof, and belongs to the technical field of gas-sensitive materials. The nitrogen-doped metal oxide gas-sensitive material is obtained by carrying out surface nitrogen doping treatment on metal oxide, and the gas-sensitive material is a porous nanosphere consisting of small particles, the diameter of the nanosphere is 300-700nm, and the size of the small particles is 10-30 nm. The nitrogen-doped metal oxide gas-sensitive material is subjected to surface nitrogen doping treatment at different temperatures under the atmosphere of nitrogen provided by a nitrogen source, the doping concentration is adjustable, the preparation method is convenient and simple, the nitrogen-doped metal oxide gas-sensitive material is prepared into a gas-sensitive element, and researches show that the gas-sensitive element can be used for preparing low-concentration NO at a lower temperature 2 The gas has high response value and good selectivity, thereby having good practical application value.)

1. The nitrogen-doped metal oxide gas-sensitive material is characterized in that the nitrogen-doped metal oxide gas-sensitive material is monodisperse porous nanospheres consisting of small particles, and the specific surface area of the monodisperse porous nanospheres is 10m²g^-1-50m²g^-1(ii) a The average sphere diameter of the monodisperse porous nanospheres is 400-700nm, and the small particle size is 20-30 nm.

2. The nitrogen-doped metal oxide gas-sensitive material of claim 1, wherein the metal oxide is tin oxide.

3. The method for preparing the nitrogen-doped metal oxide gas-sensitive material according to claim 1 or 2, which comprises calcining the metal oxide material in an atmosphere of nitrogen provided by a nitrogen source to obtain the nitrogen-doped metal oxide gas-sensitive material;

preferably, the metal oxide material is a metal oxide porous nanosphere.

4. The method of preparing the nitrogen-doped metal oxide gas-sensitive material of claim 3, wherein the method comprises:

(1) dissolving a metal salt raw material and a surfactant in an organic solvent; carrying out a chemical synthesis reaction on the obtained clarified liquid under the conditions of high temperature and high pressure to obtain a metal oxide precursor;

(2) centrifuging the product obtained in the step (1), washing with methanol, drying and calcining to obtain the porous metal oxide nanospheres;

(3) calcining the porous nanospheres of the metal oxide in an atmosphere of nitrogen provided by a nitrogen source, and carrying out nitrogen doping treatment on the surface of the metal oxide to obtain the nano-spheres.

5. The method according to claim 4, wherein in the step (1),

the metal salt is SnCl₄ ^.5H₂O; the surfactant is polyvinylpyrrolidone;

preferably, the dosage of the surfactant is 1-2 times of the mass of the metal salt raw material;

preferably, the high-temperature and high-pressure condition is specifically that the temperature is kept for 2 to 6 hours (preferably 3 hours) at 180 ℃;

preferably, the organic solvent is methanol.

6. The method according to claim 4, wherein in the step (2),

the calcination temperature is controlled to be 400-600 ℃, and the calcination time is 1-3h (preferably 2 h).

7. The production method according to claim 4, wherein in the step (3),

the nitrogen source is selected from: n is a radical of₂、NH₃Or any one or more of urea;

preferably, the calcination temperature of nitrogen doping is 100-700 ℃; further preferably, the calcination temperature is 100-400 ℃; the calcination time is 1-3 h.

8. Use of the nitrogen-doped metal oxide gas-sensitive material according to any one of claims 1 to 2 and/or the nitrogen-doped metal oxide gas-sensitive material prepared by the preparation method according to any one of claims 3 to 7 in preparation of a nitrogen-doped metal oxide gas-sensitive element.

9. A nitrogen-doped metal oxide gas sensor is characterized in that the preparation method of the nitrogen-doped metal oxide gas sensor comprises the following steps: preparing the metal oxide porous nanospheres of claim 3 or 4 into a gas-sensitive layer slurry, attaching the gas-sensitive layer slurry to a carrier, drying and calcining to prepare a metal oxide gas-sensitive element, and calcining the metal oxide gas-sensitive element in an atmosphere of nitrogen provided by a nitrogen source to obtain a nitrogen-doped metal oxide gas-sensitive element;

preferably, in the step of preparing the metal oxide gas-sensitive element after drying and calcining, the calcining temperature is 400-;

preferably, in the step of calcining the metal oxide gas sensor in the atmosphere of nitrogen provided by the nitrogen source, the calcining temperature is 100-400 ℃; the calcination time is 1-3 h;

preferably, the attachment mode can be realized by adopting a spin coating, smearing or printing process;

preferably, the carrier is a ceramic substrate;

preferably, the gas-sensitive layer slurry further comprises ethyl cellulose and terpineol.

10. The use of the nitrogen-doped metal oxide gas-sensitive material according to any one of claims 1 to 2, the nitrogen-doped metal oxide gas-sensitive material prepared by the preparation method according to any one of claims 3 to 7 and/or the nitrogen-doped metal oxide gas-sensitive element according to claim 9 in gas detection;

preferably, the application mode is specifically to detect low-concentration NO in low-temperature environment₂A gas;

the low temperature is not higher than 120 ℃, further 50-120 ℃, and further 50-80 ℃; said NO₂The gas concentration ranges from 0.5 to 50 ppm.

Technical Field

The invention belongs to the technical field of gas-sensitive materials, and particularly relates to a nitrogen-doped metal oxide gas-sensitive material, a gas-sensitive element, and a preparation method and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

With the increasing development of science and technology, the living standard of people is continuously improved, and industrial waste gas and living waste gas (such as NO) are generated₂、SO₂、H₂S, CO, etc.) and the environmental pollution problems (such as haze, acid rain, greenhouse effect, etc.) faced by people are also increasing. Therefore, effective monitoring and management of the emission of the polluted gas become an indispensable treatment means at present. Gas detection technologies led by gas sensitive materials are receiving high attention worldwide. NO₂The gas is a typical pollution gas in industrial waste gas and domestic waste gas, has high chemical activity and strong corrosivity, can react with moisture or hydrocarbon in the air, is a main source for forming secondary pollutants such as acid rain, photochemical smog, haze and the like, and seriously threatens the health of people and living environment where people live. Therefore, the gas-sensitive sensing material with high sensitivity and selectivity is designed for detecting low-concentration NO₂Gas is of great significance.

SnO₂As a common N-type semiconductor material, NO has been widely used due to its unique physicochemical properties₂And (4) detecting the gas. The detection is mainly based on NO₂Gas and SnO₂The principle that the material surface generates electron exchange to cause the resistance of the material to change is realized by detecting SnO in the test process₂Thereby achieving the effect of NO₂The purpose of gas detection. SnO in general₂The gas-sensitive performance mainly comprises the diffusion and adsorption of the gas to be detected on the surface of the material and the generation of electronic exchange. Thus, SnO₂The gas-sensitive performance of (a) is mainly determined by three factors of the following materials: geometric effects, electronic effects, and chemical effects. The geometric effect mainly refers to the geometric structure of the material, and the porous structure with high specific surface area can provide more diffusion channels and active positions for the diffusion and adsorption of the gas to be detected on the surface of the material; the electronic effect means that the energy band structure, the electronic structure and the electrical property of the material are changed due to external factors such as semiconductor compounding, metal ion doping, laser or illumination and the like, so that the effective electron transfer and resistance change of the material are promoted in the detection process; the chemical effect means that the surface defects caused by element doping or material surface reduction and catalyst modification reduce the activation energy required by gas-sensitive reaction on the material surface, and effectively promote the adsorption of the gas to be detected on the material surface and the generation of electronic exchange. However, pure metal oxide has many disadvantages in low-temperature detection of low-concentration gas, such as low sensitivity, poor selectivity, high working temperature, etc., which limits its application in the field of low-temperature gas detection.

Disclosure of Invention

In view of the above prior art, the present invention provides a method for treating low concentration NO₂The gas-sensitive material of metal oxide is processed by surface nitrogen doping treatment at different temperatures in the atmosphere of nitrogen provided by nitrogen source through a temperature-controllable tubular furnace, the doping concentration is adjustable, the preparation method is convenient and simple, and the metal oxide can carry out low-concentration NO treatment at lower temperature₂The gas response value is high, the selectivity is good, and therefore, the method has good practical application value.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

in a first aspect of the invention, a nitrogen-doped metal oxide gas-sensitive material is provided, wherein the nitrogen-doped metal oxide gas-sensitive material is monodisperse porous nanospheres composed of small particles, the diameter of the nanospheres is 200-700nm, and the size of the small particles is 10-30 nm.

Further, the metal oxide is tin oxide.

In a second aspect of the present invention, a method for preparing the nitrogen-doped metal oxide gas-sensitive material is provided, where the method includes calcining the metal oxide material in an atmosphere of nitrogen provided by a nitrogen source to obtain the nitrogen-doped metal oxide gas-sensitive material. The invention discovers that: the nitrogen-doped treatment method can effectively improve the NO of the material at lower temperature₂Sensitivity and selectivity of the gas.

In a third aspect of the invention, the application of the nitrogen-doped metal oxide gas-sensitive material in preparing a nitrogen-doped metal oxide gas-sensitive element is provided.

In a fourth aspect of the present invention, there is provided a nitrogen-doped metal oxide gas sensor, wherein the preparation method of the nitrogen-doped metal oxide gas sensor comprises: preparing the metal oxide material into gas-sensitive layer slurry, attaching the gas-sensitive layer slurry to a carrier to prepare a metal oxide gas-sensitive element, and calcining the metal oxide gas-sensitive element in an atmosphere of nitrogen provided by a nitrogen source to obtain the nitrogen-doped metal oxide gas-sensitive element.

In a fifth aspect of the present invention, there is provided the use of the above-mentioned nitrogen-doped metal oxide gas-sensitive material and/or nitrogen-doped metal oxide gas-sensitive element in gas detection.

The application is particularly to detecting low-concentration NO in low-temperature environment₂Application in gas. The low temperature is not higher than 120 ℃, further 50-120 ℃, and further 50-80 ℃; said NO₂The gas concentration is 0.5-50 ppm.

The invention has the beneficial effects that:

(1) the invention provides a method for treating low-concentration NO at low temperature₂The gas has excellent gas-sensitive performance. The synthesized material is porous nanosphere composed of small particles and has extremely high specific surface area. The high specific surface area being gas on the surface of the materialThe adsorption provides more active sites, and the porous structure provides abundant channels for the diffusion of gas on the surface of the material, which is beneficial to improving the sensitivity and response recovery speed of the material. The nitrogen doping causes defects on the surface of the oxide, and the defect positions on the surface have lower adsorption energy on the nitrogen dioxide gas, so that more nitrogen dioxide gas molecules are favorably adsorbed on the surface of the gas sensitive material; secondly, nitrogen doping revises the electronic structure of the metal oxide, improves the electrical property of the material, increases the number of surface free electrons, optimizes the electron transfer efficiency of the metal oxide, and plays an important role in improving the gas-sensitive property of the metal oxide gas-sensitive material at low temperature.

(2) The nitrogen-doped metal oxide semiconductor gas-sensitive material effectively solves a series of problems of the existing pure oxide semiconductor gas-sensitive material, such as low sensitivity, poor selectivity, high working temperature and the like, and expands the application range of the pure oxide semiconductor gas-sensitive material. The gas sensor of the invention aims at low concentration NO₂The gas has high sensitivity and selectivity, can work at a lower temperature of 50-120 ℃ and has a higher response value, namely sensitivity.

(3) The nitrogen-doped metal oxide semiconductor gas-sensitive material has good dispersibility, and avoids the problem of uneven smearing caused by agglomeration in the preparation process of a gas-sensitive element.

(4) The invention provides a safe and convenient method for obtaining the nitrogen-doped metal oxide semiconductor gas-sensitive material, and the nitrogen-doped metal oxide semiconductor gas-sensitive material is subjected to nitrogen doping treatment in a tubular furnace under the atmosphere of nitrogen provided by a nitrogen source, so that the temperature is controllable, the doping concentration is adjustable, and subsequent treatment is not required.

(5) The invention provides a safe and effective method for preparing a nitrogen-doped metal oxide semiconductor gas-sensitive element, which is characterized in that the prepared pure metal oxide gas-sensitive element is placed in a tube furnace, and nitrogen doping treatment is carried out under the atmosphere of nitrogen provided by a nitrogen source to obtain the nitrogen-doped metal oxide semiconductor gas-sensitive element.

(6) The preparation method of the invention is safe and effective, the required equipment is simple and easy to operate, the process parameters are convenient to control, the use cost of raw materials and instruments and equipment is low, and the like, and the preparation method has good value of practical application.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a scanning electron microscope photograph of pure tin oxide porous nanoballs prepared in comparative example 1;

fig. 2 is a scanning electron microscope photograph of the nitrogen-doped tin oxide porous nanoball prepared in example 1;

fig. 3 is a transmission electron microscope photograph (high magnification) of the nitrogen-doped tin oxide porous nanoball prepared in example 1;

fig. 4 is a full spectrum of X-ray photoelectron diffraction spectra of pure tin oxide prepared in comparative example 1 and nitrogen-doped tin oxide porous nanospheres prepared in example 1;

FIG. 5 is an O1s peak energy spectrum of X-ray photoelectron diffraction of the nitrogen-doped tin oxide porous nanospheres prepared in example 1;

fig. 6 is free electron density and electron mobility of pure tin oxide prepared in comparative example 1 and nitrogen-doped tin oxide porous nanospheres prepared in examples 1 and 2;

FIG. 7 is a graph of pure tin oxide prepared in comparative example 1 and nitrogen-doped tin oxide porous nanospheres prepared in examples 1 and 2 versus 5ppm NO at 80 deg.C₂The response value of the gas;

FIG. 8 is the nitrogen doped tin oxide porous nanospheres prepared in example 1 for NO at different concentrations₂Gas-sensitive performance test chart of gas at 80 ℃;

FIG. 9 is a bar graph of the response values of the nitrogen-doped tin oxide porous nanospheres prepared in example 1 to different gases at 80 ℃;

FIG. 10 is a schematic view of a gas sensor made of the oxygen vacancy modified metal oxide gas sensing material prepared in example 1: 1. an alumina ceramic substrate; 2. a test electrode; 3. heating the electrode; 4. a platinum wire; 5. a Ni-Cr alloy; 6. and coating the gas sensitive material.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise. It is to be understood that the scope of the invention is not to be limited to the specific embodiments described below; it is also to be understood that the terminology used in the examples is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention.

As mentioned above, the current pure metal oxide semiconductor gas sensitive material can be used for low concentration NO₂The problems of low sensitivity, poor selectivity, high working temperature and the like are reflected.

In view of the above, in one embodiment of the present invention, there is provided a nitrogen-doped metal oxide gas-sensitive material, which is monodisperse porous nanospheres composed of small particles, and has a specific surface area of 10m²g^-1-50m²g^-1(ii) a The whole size distribution is uniform, the average ball diameter of the monodisperse porous nanospheres is between about 400 nm and 700nm, and the small particle size is 20-30 nm.

In yet another embodiment of the present invention, the metal oxide is tin oxide.

In still another embodiment of the present invention, there is provided the above nitrogenThe preparation method of the doped metal oxide gas-sensitive material comprises the step of calcining the metal oxide material under the atmosphere of nitrogen provided by a nitrogen source to obtain the nitrogen-doped metal oxide gas-sensitive material. The invention discovers that: the nitrogen-doped treatment method can effectively improve the NO of the material at lower temperature₂Sensitivity and selectivity of the gas.

In another embodiment of the present invention, the metal oxide material is a metal oxide porous nanosphere, and the porous structure is favorable for gas diffusion and adsorption due to its multiple active sites and diffusion channels, and formation of nitrogen doping, thereby improving the sensitivity of the material at low temperature. Specifically, the metal oxide porous nanospheres of the present invention are tin oxide porous nanospheres.

In another embodiment of the present invention, there is provided a method for preparing the metal oxide material, including: uniformly mixing metal salt, a surfactant and an organic solvent, and synthesizing a metal oxide precursor material by a solvothermal method; and separating, drying and calcining the metal oxide precursor material to obtain the metal oxide porous nanospheres.

In another embodiment of the present invention, there is provided a method for preparing the above nitrogen-doped metal oxide gas-sensitive material, the method comprising:

(1) dissolving a metal salt raw material and a surfactant in an organic solvent; and carrying out a chemical combination reaction on the obtained clarified liquid under the conditions of high temperature and high pressure to obtain a metal oxide precursor.

(2) And (2) centrifuging the product obtained in the step (1), washing with methanol, drying and calcining to obtain the metal oxide porous nanospheres.

(3) Calcining the porous nanospheres of the metal oxide in an atmosphere of nitrogen provided by a nitrogen source, and carrying out nitrogen doping treatment on the surface of the metal oxide to obtain the nano-spheres.

In another embodiment of the present invention, the metal salt raw material in step (1) is SnCl₄ ^.5H₂O; the surfactant is polyvinylpyrrolidone;

in still another embodiment of the present invention, the amount of the surfactant is 1 to 2 times the mass of the metal salt raw material.

In another embodiment of the present invention, the high temperature and high pressure condition is specifically a heat preservation at 180 ℃ for 2-6h (preferably 3 h); the high-temperature high-pressure reaction can be carried out in a high-pressure reaction kettle.

In another embodiment of the present invention, the organic solvent is methanol; the amount of the solvent is the dissolved amount.

In still another embodiment of the present invention, the calcination temperature in step (2) is controlled to be 400-600 ℃, and the calcination time is 1-3h (preferably 2 h). Step (2) can be carried out in a muffle furnace.

In still another embodiment of the present invention, the nitrogen source in step (3) is selected from the group consisting of: n is a radical of₂、NH₃Or any one or more of urea.

In another embodiment of the present invention, the calcination temperature of the nitrogen doping is 100-700 ℃; further preferably, the calcination temperature is 100-400 ℃; the calcination time is 1-4 h; step (3) can be carried out in a tube furnace. The change of the structure of the nitrogen-doped metal oxide caused by air calcination is avoided, and the excellent gas-sensitive performance of the gas-sensitive material is ensured. Meanwhile, the calcination temperature and the calcination time are controlled, so that the nitrogen doping treatment of different degrees on the surface of the metal oxide porous nanospheres is realized.

In yet another embodiment of the present invention, the amount of nitrogen source is an amount useful to provide a nitrogen-containing atmosphere.

In another embodiment of the present invention, there is provided a use of the above-described nitrogen-doped metal oxide gas sensing material in the preparation of a nitrogen-doped metal oxide gas sensor.

In another embodiment of the present invention, a nitrogen-doped metal oxide gas sensor is provided, and the preparation method of the nitrogen-doped metal oxide gas sensor comprises: preparing the metal oxide porous nanospheres into gas-sensitive layer slurry, coating the gas-sensitive layer slurry on an alumina ceramic substrate, drying and calcining to prepare a metal oxide gas-sensitive element, and calcining the metal oxide gas-sensitive element under the nitrogen atmosphere provided by a nitrogen source to obtain the nitrogen-doped metal oxide gas-sensitive element.

In another embodiment of the invention, in the step of preparing the metal oxide gas sensor after drying and calcining, the calcining temperature is 400-600 ℃; the calcination time is 1-3 h.

In another embodiment of the present invention, in the step of calcining the metal oxide gas sensor under the nitrogen-supplied nitrogen atmosphere, the calcining temperature is 100-700 ℃; further preferably, the calcination temperature is 100-400 ℃; the calcination time is 1-4 h.

In another embodiment of the present invention, the attaching means may be implemented by spin coating, painting or printing, and the carrier may be a ceramic substrate.

In another embodiment of the present invention, the gas-sensitive layer slurry further comprises ethyl cellulose and terpineol.

In another embodiment of the present invention, there is provided the use of the above-described nitrogen-doped metal oxide gas sensing material and/or nitrogen-doped metal oxide gas sensing element in gas detection.

In yet another embodiment of the present invention, the application is specifically to the detection of low concentration NO in low temperature environment₂Application in gas. The low temperature is not higher than 120 ℃, further 50-120 ℃, and further 50-80 ℃; said NO₂The gas concentration is 0.5-50 ppm.

The nitrogen-doped metal oxide porous nanosphere gas-sensitive material can be used for treating low-concentration NO at lower temperature₂The gas has high sensitivity and selectivity to NO₂Application in gas sensitive detection. The working temperature is 50-120 ℃, the detection concentration range is 0.5-50ppm, wherein the low concentration is 0.5ppm NO₂The gas has a high response value (the ratio of the resistance of the material in the environment to the resistance in air) calculated to be 4.

The nitrogen-doped metal oxide porous nanosphere gas-sensitive material is a porous nanosphere which is composed of small particles and has uniform size, and a large number of pore channels are distributed on the surface of the nanosphere; nitrogen doping of metal oxide surfaces not only in metal oxidationOxygen vacancy and nitrogen-containing active site are formed on the surface of the substance, and NO is increased₂The adsorption of gas on the surface of the material changes the electronic structure of the material, increases the free electron density of the material and optimizes the electron transfer efficiency. After being made into gas sensor, low concentration NO is treated at low temperature₂The gas has high sensitivity and selectivity, the optimal working temperature is reduced to 50-120 ℃, and the response value reaches 3-5 times of that of an unmodified matrix material.

The invention is further illustrated by the following examples, which are not to be construed as limiting the invention thereto. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The raw materials used in the implementation all adopt the commercial analytical pure reagents.