1. A tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material is characterized in that: has gas sensing performance, is a tin oxide/polyacid/tungsten oxide composite material with a molecular formula of SnO₂@[email protected]₃The polyacid is Keggin type phosphomolybdic acid, phosphotungstic acid and silicotungstic acid.

2. The tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material of claim 1, characterized in that: the gas sensor can be prepared by a coaxial electrostatic spinning technology and a calcining oxidation mode, and can be manufactured by coating a sensitive material film.

3. The tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material according to claim 1, characterized in that: under a certain working temperature, the change of an electrochemical signal can be utilized to detect the existence of gases such as ethanol in the air, thereby realizing gas sensing.

4. The tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material according to claim 1, characterized in that: the main body is three layers of coaxial nanofiber materials, a core layer is tin oxide, a middle layer is polyacid, a shell layer is tungsten oxide, the three materials are distributed in a three-layer cable shape, and the composition and the structure of the materials are determined; the material can stably exist on the electrode of the ceramic tube in the form of a film, so that the gas-sensitive reaction can be directly carried out in the air; the gas-sensitive reaction method is simple, the recovery is complete, and the environment is not polluted; the gas-sensitive film can be repeatedly used, and the gas sensitivity can still be maintained.

Background

Ethanol, commonly known as ethanol, is an organic substance, of formula C₂H₆O, ethanol is a flammable, volatile, colorless and transparent liquid at normal temperature and pressure. The ethanol vapor can form an explosive mixture with air and can be mutually soluble with water in any proportion. The ethanol has wide application range, and can be used for preparing acetic acid, beverages, essence, fuels, fuel and the like. In medical treatment, 70-75% volume fraction ethanol is also commonly used as a disinfectant, and has wide application in national defense chemical industry, medical treatment and health, food industry, industrial and agricultural production. Because ethanol is volatile, the vapor and air can form explosive mixture, and the explosion caused by open fire and high heat energy is easy to cause combustion. Contact with the oxidant causes a chemical reaction or combustion. The ethanol gas can easily enter human body through inhalation, ingestion, percutaneous absorption and other ways. The human body inhales excessive ethanol to cause life risks such as loss of consciousness, dilated pupils, irregular breathing, shock, heart circulation failure, respiratory arrest and the like; more serious patients may cause polyneuropathy, chronic gastritis, fatty liver, liver cirrhosis, myocardial damage, and organic psychosis. Prolonged contact with the skin can cause dryness, desquamation, chapping and dermatitis. Based on the above analysis, it is important to detect ethanol gas.

A gas sensor is a device that can convert certain information of a gas, including concentration and species, into data information that can be utilized. The physical and chemical properties of various gases are used to convert the change of the monitored gas into electric signals which can be easily processed, so that people can control and apply the gas correctly and effectively. Is the first link for realizing automatic detection and automatic control. The semiconductor material is one of the cores of the gas sensor, and has high sensitivity and simple operation. The practical application of the gas sensitive material with low cost and high performance is realized, and the development of a novel semiconductor material is urgently needed. To date, over more than half a centuryIn the research, tens of gas sensitive materials are successively developed, developed and applied. However, the research focus is still on metal oxide semiconductors, wherein SnO₂、ZnO、TiO₂、WO₃、In₂O₃And alpha-Fe₂O₃The n-type semiconductor material occupies more than 90% of the research field of gas sensing. However, the single-component semiconductor material has a high carrier recombination rate, which limits the performance of the gas-sensitive material. This also becomes a scientific problem limiting the development of gas sensitive materials. With the continuous and deep research of semiconductor gas sensors, people find that the gas-sensitive performance of semiconductor materials can be obviously improved by constructing a reasonable heterojunction. In the material of the zero-dimensional nanoparticles, at the grain boundaries, a large amount of recombination of electron and hole pairs can occur due to the presence of defects; at the same time, there are long carrier migration paths with random directions, which limit the gas-sensitive performance of the material. The material with the one-dimensional structure, such as the nanotube, the nanorod and the nanofiber, can provide a preferential directional migration path for a current carrier, and effectively promotes the separation of electrons and holes, thereby improving the photoelectric performance of the material.

Polyoxometalates (i.e. polyacids, Polyoxometalates, POMs) are polynuclear complexes, have a history of development for nearly two hundred years so far, and have become an important research field in inorganic chemistry. In recent years, polyacid has been studied in gas sensing. In 2011, Suzhou professor combined ascorbic acid and silicotungstic acid, and the subject group showed a significant color change in ammonia. In 2013, Khan and the like prepare polyvanadate with a frame structure, and have certain electrochemical response to the existence of nitrogen oxides. Respectively introducing polyacid into SnO by professor of Shanxi university in northeast China₂、BiVO₃And TiO₂In addition, the sensor has sensing function on gases such as formaldehyde, toluene and the like. In addition, polyoxometallate (polyacid for short) is a good electron acceptor, and can inhibit the recombination of photon-generated carriers and promote the migration of the photon-generated carriers by capturing photon-generated electrons of a semiconductor conduction band, thereby being beneficial to electron transfer. However, in previous studies, electricity using polyacids was mainly usedSubaceptor properties, in simple molecularly doped form, for introduction of polyacids into SnO₂And the like, in order to improve the gas-sensitive performance of the original semiconductor. The polyacid in the semiconductor material has low content, plays a main role in the original semiconductor material, is in a disordered state, is distributed on the surface and bulk phase of the semiconductor material, and cannot form a polyacid/semiconductor heterojunction. There has been no report on the study of polyacids to form heterojunctions with semiconductor materials and to be used as gas sensing. Therefore, the deep research on the gas sensing performance of the polyacid/semiconductor heterojunction material has become a key scientific problem for developing the application of the polyacid in devices such as gas sensors and the like. In addition, the influence of the structure of polyacid on gas sensing performance has not been fully revealed and studied, which limits the development and application of polyacid/semiconductor materials in the field of devices such as gas sensors. Thus, we introduced the polyacid to SnO₂@WO₃Two heterojunctions are formed, thereby obviously improving WO₃The detection performance of the gas sensor.

Disclosure of Invention

The invention aims to provide a semiconductor/polyacid/semiconductor series heterojunction material and a preparation method thereof for the first time. Wherein the material is SnO₂@[email protected]₃The structure of the three-layer coaxial nanofiber is shown in figure 1, a core layer is tin oxide, a middle layer is polyacid, a shell layer is tungsten oxide, and the three substances are distributed in a three-layer cable shape. Phosphomolybdic acid (PMo) with a polyacid of the Keggin type₁₂) Phosphotungstic acid (PW)₁₂) And silicotungstic acid (SiW)₁₂) The preparation method can be prepared by a coaxial electrostatic spinning technology and a calcining oxidation mode.

The second purpose of the invention is to solve the scientific problem of high electron hole recombination rate of the semiconductor gas-sensitive material. The material prepared by the invention has two series-connected heterogeneous interfaces, can promote the migration of current carriers and inhibit the electron hole recombination, thereby improving the gas-sensitive performance of the material. And SnO without addition of polyacid₂@WO₃Fiber-to-fiber ratio, SnO₂@[email protected]₃The three-layer coaxial nanofiber has more excellent gas-sensitive performance.

The third purpose of the invention is to react the polyacid for the first timeFor use in connection with WO₃The gas sensor of (1) is used for investigating the promotion effect of polyacid on the gas-sensitive performance of organic gases such as ethanol, acetone and the like.

SnO provided by the invention₂@[email protected]₃The three-layer coaxial nanofiber gas sensing material can be prepared by the following method:

firstly, dissolving a certain amount of ammonium metatungstate and PVP in an organic solvent, and stirring at room temperature to obtain a transparent and uniform shell precursor solution; then dissolving a certain amount of stannic chloride and PVP in an organic solvent, and stirring at room temperature to obtain a uniform and transparent core layer precursor solution; and dissolving a certain amount of polyacid and PVP in an organic solvent, and stirring at room temperature to obtain a transparent and uniform intermediate layer precursor solution. Then the solution is spun under a certain voltage by a coaxial electrostatic spinning technology to obtain SnO₂@[email protected]₃Precursor fiber is calcined at high temperature to prepare SnO₂@[email protected]₃Three layers of coaxial nanofibers (the morphology is shown in figure 2).

SnO prepared by the method₂@[email protected]₃The three-layer coaxial nanofiber is characterized by X-ray powder diffraction (PXRD, shown in figure 3) to determine the composition. It was found that the peak positions and peak intensities of the synthesized material and tin oxide pentoxide were consistent in the XRD spectrum, which confirmed that the material synthesized by the above-mentioned method was indeed tin oxide and tungsten oxide, and the presence of polyacid was not observed in the XRD spectrum due to the small amount of polyacid.

SnO provided by the invention₂@[email protected]₃The application of the three-layer coaxial nanofiber gas sensing material in gas sensing has the following working conditions:

the above materials can be coated on the gas sensor shown in fig. 4. The gas sensor consists of Al with a pair of gold electrodes on the outer surface₂O₃Insulating ceramic tube, through Al₂O₃Ni-Gr alloy heating wire and four Pt wires in insulating ceramic tube and Al-coated Ni-Gr alloy heating wire₂O₃A hexagonal base consisting of the external surface of the insulating ceramic tube and the sensitive material film on a pair of gold electrodes, and four posts of the hexagonal base connected with four platinum wiresConnected to four signal lines and the remaining two columns connecting two heater lines, the sensor exposed to air has a stable resistance value when a certain current is applied, and when the sensitive material film comes into contact with a certain amount of the gas to be measured (ethanol), the resistance value is reduced until a stable value is reached. According to the principle, when the sensor works under a certain current and a corresponding certain temperature, if the resistance value is reduced, the existence of the gas to be measured is indicated.

The tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material provided by the invention has the following characteristics:

1. the tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material has a SnO main body₂@[email protected]₃The three-layer coaxial nanofiber comprises a core layer made of tin oxide, a middle layer made of polyacid, a shell layer made of tungsten oxide and three substances distributed in a three-layer cable shape.

2. The tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material is coated on a ceramic tube electrode and has a sensing effect on ethanol gas at a certain working temperature. The first application of the polyacid to the composition based on WO₃The gas sensor of (1) is used for investigating the promotion effect of polyacid on the gas-sensitive performance of organic gases such as ethanol, acetone and the like. .

3. The tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material has the advantages of optimal response performance to 100ppm ethanol, high sensitivity, quick response and recovery rate, good selectivity to ethanol gas and good long-term stability.

Drawings

Fig. 1 is a structural schematic diagram of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material.

FIG. 2 is a transmission electron microscope image and a high-power transmission electron microscope image of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material.

Fig. 3 is an X-ray powder diffraction pattern of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material.

Fig. 4 is a schematic structural diagram of the tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensor.

FIG. 5 is a curve diagram of response amplitude of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material to 100ppm ethanol at different temperatures.

FIG. 6 is a graph of the dynamic response and recovery characteristics of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material at 280 ℃ for 5ppm to 100ppm ethanol gas.

FIG. 7 is a graph of the dynamic response and recovery time of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material to 100ppm ethanol gas at 280 ℃.

FIG. 8 is a bar graph of response characteristics of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material to 100ppm of different types of gases at 280 ℃.

FIG. 9 is a graph of the response amplitude change of a tin oxide/polyacid/tungsten oxide three-layer coaxial nanofiber gas sensing material to 100ppm ethanol gas within 30 days.

Detailed Description

To further illustrate the present invention, the following examples are set forth without limiting the scope of the invention as defined by the appended claims.

This example is an SnO with the best content of the three groups of polyacids prepared in the summary of the invention₂@POMs(PMo₁₂、PW₁₂、SiW₁₂)@WO₃Testing the performance of the gas sensor by adding SnO₂@POMs(1％PMo₁₂、3％PW₁₂、3％SiW₁₂)@WO₃Gas sensor and SnO₂@WO₃The gas sensor is subjected to a comparative experiment to test the performance; here, the gas response amplitude of the gas sensor is defined as S ═ R_a/R_gWhere Ra is the resistance in air and Rg is the resistance in the gas to be measured, and further, the response or recovery time is 90% of the time it takes for the resistance value of the gas sensor to stabilize after being added or removed from the gas bottle to be measured.

Specific example 1:

SnO is reacted as shown in FIG. 5₂@POMs(1％PMo₁₂、3％PW₁₂、3％SiW₁₂)@WO₃Gas sensor and SnO₂@WO₃The gas sensor tests the response performance of 100ppm ethanol at different temperatures of 240-360 ℃; as can be seen from the figure, four groups of sensors all showed temperature-dependent sensing characteristics, SnO₂@POMs(1％PMo₁₂、3％PW₁₂、3％SiW₁₂)@WO₃Gas sensor and SnO₂@WO₃The response of the gas sensor reaches the maximum value at 280 ℃; therefore, the following other gas sensitive performance tests were all performed at the optimum temperature of 280 ℃.

As shown in FIG. 6, SnO₂@POMs(1％PMo₁₂、3％PW₁₂、3％SiW₁₂)@WO₃Gas sensor and SnO₂@WO₃The gas sensor is used for testing the dynamic response and recovery characteristics of ethanol gas with different concentrations of 5ppm to 100ppm at 280 ℃: the results show that the response value is gradually increased along with the increase of the ethanol concentration, and SnO₂@3％PW₁₂@WO₃The gas sensor has the best sensitivity to ethanol, and the response can reach 8.8 at 100 ppm.

As shown in FIG. 7, by reacting SnO₂@POMs(1％PMo₁₂、3％PW₁₂、3％SiW₁₂)@WO₃Gas sensor and SnO₂@WO₃The gas sensor carries out response recovery characteristic test on 100ppm ethanol at 280 ℃, and the result shows that SnO₂@1％PMo₁₂@WO₃The response time and recovery time of the gas sensor are 1.8s and 69.1s respectively, and the response recovery time is fastest, which indicates that SnO₂@1％PMo₁₂@WO₃The gas sensor has a rapid response and recovery rate to ethanol gas.

As shown in FIG. 8, by reacting SnO₂@POMs(1％PMo₁₂、3％PW₁₂、3％SiW₁₂)@WO₃Gas sensor and SnO₂@WO₃The gas sensor is used for testing the response characteristics of 100ppm different types of gases at 280 ℃, wherein SnO₂@3％PW₁₂@WO₃Gas response of gas sensor to 100ppm ethanol gasThe amplitude is up to 9, which shows that SnO₂@3％PW₁₂@WO₃The gas sensor has good selectivity to ethanol gas.

As shown in FIG. 9, by reacting SnO₂@POMs(1％PMo₁₂、3％PW₁₂、3％SiW₁₂)@WO₃The gas sensor is subjected to a stability test for 30 days, and the result shows that SnO₂@3％SiW₁₂@WO₃The response amplitude to the ethanol gas is always kept at about 5.5, which shows that SnO₂@3％SiW₁₂@WO₃The gas sensor has good long-term stability to ethanol.