A porous In2O3 nanofiber embedded with octahedral hollow Fe2O3 and its preparation and application

Abstract

The present invention provides a porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, its preparation method and application. The porous In2O3 nanofiber embedded with octahedral hollow Fe2O3 comprises a porous In2O3 nanofiber and octahedral hollow Fe2O3 uniformly embedded in the porous In2O3 nanofiber. The porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, its preparation method and application provided by the present invention form a large number of unique heterojunctions and provide abundant active sites by embedding octahedral hollow Fe2O3 with a specific nanostructure into the porous In2O3 nanofiber, thereby effectively improving the adsorption capacity for triethylamine and enhancing the sensitivity of gas detection. When used in a gas sensor, a highly sensitive response to triethylamine in a wide concentration range can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, and its preparation and application. Background Art

[0002] With the development of industry in recent years, a large amount of toxic and harmful volatile gases have been discharged. Triethylamine is an amine organic compound, which is flammable, and its vapor can form an explosive mixture with air. It is not only used in industry, but also used as preservatives, surfactants, organic solvents, catalysts, etc. However, it is also very harmful to the human body. Once we are exposed to triethylamine for a long time, it will cause strong irritation to the skin, mucous membranes and central nervous system, and even lead to death. According to the recommendations of the National Institute for Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH), the concentration limit of exposure to triethylamine within one hour is 10 ppm. Therefore, it is extremely important and urgent to produce high-performance triethylamine sensors for environmental monitoring and human health protection.

[0003] Semiconductor gas sensors are widely used in gas detection because of their high sensitivity, real-time detection, light weight, easy integration, low cost, intelligence, and integration of detection and conversion. According to different sensing principles, they are divided into resistance sensors, optical sensors, micro surface plasmon resonance sensors, surface acoustic sensors, and microwave sensors. Resistance sensors are widely used in gas leak detection, public safety, and medical diagnosis because of their high sensitivity, good repeatability, and excellent selectivity. The commonly used materials are generally metal oxide materials, such as ZnO, In2O3, SnO2, WO3, ɑ-Fe2O3, NiO, Co3O4, etc.

[0004] Among them, In2O3 is a typical n-type metal oxide semiconductor with a band gap of 3.55 - 3.75 eV. However, its weak selectivity, low sensitivity, and high working temperature have hindered its practical application as a high-performance gas sensor. As a resistance gas sensor, the working principle of In2O3 is related to the change of surface resistance with temperature and gas atmosphere. Gas molecules adsorbed on the surface of In2O3 act as electron donors or acceptors, and the change of carrier concentration near the semiconductor surface leads to the change of resistance, and an oxidation-reduction reaction occurs. In order to further improve the sensing performance, the morphology of In2O3 is usually adjusted and noble metals are loaded, such as thin films, nanowires, nanocrystals, hollow microspheres, and nanofibers, but the effect is not obvious. Electrospinning is a simple, easy-to-operate, and low-cost technology that can be used to manufacture flexible nanofibers and nanotubes with nano-scale size, significant length, and uniform diameter. It can maximize the specific surface area and further improve the gas adsorption capacity. Summary of the Invention

[0005] Based on the technical problems existing in the background art, the present invention proposes a porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, its preparation method and application. By embedding octahedral hollow Fe2O3 with a specific nanostructure into In2O3 nanofibers, a large number of unique heterojunctions are formed, providing abundant active sites, thereby effectively improving the adsorption capacity for triethylamine and enhancing the sensitivity of gas detection; when used in a gas sensor, high-sensitivity response to triethylamine in a wide concentration range can be achieved.

[0006] A porous In2O3 nanofiber embedded with octahedral hollow Fe2O3 proposed by the present invention includes porous In2O3 nanofibers and octahedral hollow Fe2O3 uniformly embedded in the porous In2O3 nanofibers.

[0007] In the present invention, due to the large specific surface area, high porosity, adjustable pore size and easy modification of octahedral hollow Fe2O3, after embedding it into In2O3 nanofibers, a unique heterojunction can be formed between the two, thereby improving the gas-sensing performance of triethylamine.

[0008] Preferably, the diameter of the porous In2O3 nanofibers is 100 - 150 nm.

[0009] The present invention also proposes a preparation method of a porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, including: mixing MIL-101(Fe) and trivalent indium salt to make a precursor spinning solution, then making precursor fibers through electrospinning, and finally obtaining the porous In2O3 nanofiber embedded with octahedral hollow Fe2O3 after high-temperature calcination.

[0010] In the present invention, by using electrospinning technology to embed MIL-101(Fe) with an octahedral structure into porous In2O3 nanofibers, after high-temperature calcination, not only can the morphology before calcination be still maintained, but the corresponding organic ligands are decomposed into carbon dioxide and water. Therefore, it can be used as a perfect sacrificial template to fabricate metal oxide nanostructures with adjustable morphology, and finally obtain the porous In2O3 nanofiber embedded with octahedral hollow Fe2O3.

[0011] Preferably, the MIL-101(Fe) is obtained by reacting ferric chloride hexahydrate as an iron source and terephthalic acid as a ligand in a mixed solvent of water and N,N-dimethylformamide;

[0012] Preferably, the particle size of the MIL-101(Fe) is 400 - 500 nm.

[0013] Preferably, the precursor spinning solution is obtained by uniformly dispersing MIL-101(Fe), indium(III) salt, and polyvinylpyrrolidone in an organic solvent by stirring.

[0014] Preferably, the indium(III) salt is indium nitrate, and the organic solvent is N,N-dimethylformamide.

[0015] Preferably, the molar ratio of MIL-101(Fe) to indium(III) salt is 0.05 - 0.3:1.

[0016] Preferably, the molar ratio of polyvinylpyrrolidone to indium(III) salt is 4 - 6:1, where the molar amount of polyvinylpyrrolidone is calculated based on the molar amount of its polymerization monomer, which is 111.

[0017] Preferably, the electrospinning voltage is 12 - 18 kV, the distance between the nozzle and the collecting end is 12 - 18 cm, the advancing speed of the syringe is 0.002 - 0.004 mm / s, and the reaction humidity is 20 - 40%RH.

[0018] Preferably, the high-temperature calcination is carried out in an air atmosphere.

[0019] Preferably, the temperature of the high-temperature calcination is 400 - 600 °C, and the time is 1 - 3 h.

[0020] The present invention also provides a gas sensor, which is made of the above-mentioned porous In2O3 nanofibers or the porous In2O3 nanofibers prepared by the above-mentioned preparation method.

[0021] Preferably, the gas sensor is used for detecting toxic and harmful gases.

[0022] Preferably, the toxic and harmful gas is triethylamine.

[0023] A porous In2O3 nanofiber embedded with octahedral hollow Fe2O3 proposed by the present invention. In2O3 is a typical wide-bandgap n-type semiconductor, insoluble in water, soluble in inorganic acids, with the characteristics of small resistivity, good optical transparency, and good catalytic activity, and is the most representative semiconductor gas-sensitive material. The octahedral hollow Fe2O3 belongs to nanoscale α-Fe2O3. As an inexpensive and easily obtainable wide-bandgap semiconductor, its conductivity is very sensitive to the gases in its environment, and its carriers are mostly electrons. Therefore, it can be used as an efficient gas-sensing material. In the present invention, the octahedral hollow Fe2O3 with a specific morphology and structure is embedded in the In2O3 nanofiber. Compared with the prior art of directly mixing iron salts and indium salts to react to form α-Fe2O3 / In2O3 composite nanofibers, the former has the characteristics of large specific surface area, high porosity, adjustable pore size, and easy modification due to the octahedral hollow Fe2O3. When it is embedded in the In2O3 nanofiber, the combination of the two can form a unique heterojunction, thereby more effectively improving the gas-sensing performance to triethylamine.

[0024] The present invention also proposes a preparation method for a porous In2O3 nanofiber embedded with octahedral hollow Fe2O3. This preparation method uses In2O3 nanofibers as the precursor and N-N dimethylformamide as the solvent to disperse MIL-101(Fe), which is beneficial to the full and uniform dispersion of the two. When MIL-101(Fe) is added to the precursor solution containing trivalent indium salt, since MIL-101(Fe) has a framework structure, uniform particle size, and uniform dispersion as the calcination precursor, the adsorption specific surface area of the obtained porous In2O3 nanofibers after calcination can be increased. Therefore, the nanofiber material prepared by the preparation method of the present invention has a great improvement effect on the sensitivity of the sensor.

[0025] In fact, through testing, it is found that the gas-sensing performance of the gas sensor has been significantly improved by the porous In2O3 nanofiber (Fe2O3 / In2O3 NFs) embedded with octahedral hollow Fe2O3 of the present invention. Simply put, when the Fe2O3 / In2O3 NFs sensor is exposed to air, O2 molecules in the air will be adsorbed on the surface of the Fe2O3 / In2O3 NFs and capture electrons from the conduction band on the surface of the Fe2O3 / In2O3 NFs, and are ionized into O - , thereby reducing the concentration of free electrons in the conduction band and forming a depletion layer. When the sensor is exposed to triethylamine, the triethylamine molecules adsorbed on the surface of the Fe2O3 / In2O3 NFs will provide electrons to reduce the oxygen anions (O -), and then the captured electrons are released back to the conduction band of Fe2O3 / In2O3 NFs, thereby increasing the concentration of free electrons, narrowing the width of the depletion layer, and thus reducing the resistance of the sensor. When the sensor returns from triethylamine to air, the triethylamine molecules on the surface of Fe2O3 / In2O3 NFs begin to desorb, and the conduction band of Fe2O3 / In2O3 NFs absorbs electrons, reducing the concentration of free electrons in the conduction band of Fe2O3 / In2O3 NFs, thereby increasing the sensor resistance, and then achieving a highly sensitive response to triethylamine, and finally effectively solving the long-existing problem of low sensitivity of gas sensors to triethylamine. Description of the Drawings

[0026] Figure 1 Scanning electron microscope images of the octahedral hollow Fe2O3 before and after calcination in Example 1 of the present invention: (a) is the scanning electron microscope image of the octahedral hollow Fe2O3 before calcination, i.e., MIL-101(Fe); (b) is the scanning electron microscope image of the octahedral hollow Fe2O3 after calcination;

[0027] Figure 2 Scanning electron microscope images of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 before and after calcination in Example 2 of the present invention: (a) is the scanning electron microscope image of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 before calcination; (b) is the scanning electron microscope image of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 after calcination;

[0028] Figure 3 Transmission electron microscope images of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 in Example 2 of the present invention: (a) is the transmission electron microscope image of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3; (b) is the single-strand structure diagram of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3;

[0029] Figure 4 X-ray photoelectron spectroscopy analysis diagram of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 in Example 2 of the present invention;

[0030] Figure 5 X-ray single crystal powder diffraction diagram of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 in Example 2 of the present invention;

[0031] Figure 6Radar charts of the sensitivity responses of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Example 2 of the present invention, the octahedral hollow Fe₂O₃ described in Example 1, and the porous In₂O₃ nanofibers described in Comparative Example 1 to different gases;

[0032] Figure 7 Sensitivity detection chart of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Example 2 of the present invention to triethylamine: (a) Sensitivity response curves of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Examples 2-8, the octahedral hollow Fe₂O₃ described in Example 1, and the porous In₂O₃ nanofibers described in Comparative Example 1 to 10 ppm triethylamine at different temperatures; (b) Multiple cycle test curves of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Example 2 to 10 ppm triethylamine. Detailed implementation manners

[0033] Next, the technical solutions of the present invention will be described in detail through specific examples. However, it should be clearly stated that these examples are for illustrative purposes only and are not construed as limiting the scope of the present invention.

[0034] Example 1

[0035] This example presents an octahedral hollow Fe₂O₃, which is prepared by the following method:

[0036] (1) First, add 1.667 mL of deionized water and 3.33 mL of DMF to a round-bottom flask as the initial solution, heat it in a water bath to 65 °C, and control the rotation speed at 550 rpm; then weigh 0.21624 g (0.8 mmol) of FeCl₃·6H₂O, dissolve it in 20 mL of deionized water as the metal stock solution, and then weigh 0.1329 g (0.8 mmol) of terephthalic acid (PTA), dissolve it in 20 mL of DMF as the ligand stock solution; feed the metal stock solution and the ligand stock solution into the initial solution through two separate channels of PFA (perfluoroalkoxy material, inner diameter: 0.8 mm tube) and a microfluidic syringe of model TYD01-01 for reaction, and control the feeding rates respectively as follows: first feed 1 mL at 0.12 mL / min, and then feed 16.5 mL at 0.25 mL / min. The obtained product is washed 3 times with absolute ethanol and DMF respectively to obtain the calcination precursor of octahedral hollow Fe₂O₃, that is, MIL-101(Fe);

[0037] (2) Calcinate the above MIL-101(Fe) in air, control the calcination temperature at 500 °C, the heating rate at 2 °C / min, and after calcining for 2 h, cool it to room temperature to obtain brick-red octahedral hollow Fe₂O₃.

[0038] The octahedral hollow Fe2O3 prepared in Example 1 was respectively subjected to scanning electron microscopy (SEM) detection before and after calcination. The results are as Figure 1 shown, Figure 1 which are the SEM images of the octahedral hollow Fe2O3 described in Example 1 of the present invention before and after calcination. Figure 1 (a) is the SEM image of the MIL-101(Fe), and (b) is the SEM image of the octahedral hollow Fe2O3 obtained after calcination of the MIL-101(Fe). Referring to Figure 1 (a), it can be seen that the morphology of the MIL-101(Fe) is octahedral, with a smooth surface, uniform particle size, and the particle size is about 400 - 500 nm. Referring to Fig. (b), it can be seen that for the octahedral hollow Fe2O3 obtained after calcination of the MIL-101(Fe), its particle size is reduced to about 200 nm, the surface is rough and porous, the morphology is slightly collapsed, and the edges are blurred.

[0039] Example 2

[0040] This example presents a porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, which is prepared by the following method:

[0041] (1) 1.5 mmol of indium nitrate hydrate was added to 4.5 mL of N,N-dimethylformamide. After stirring and dissolving, 60 mg of the MIL-101(Fe) prepared in Example 1 was added thereto. After ultrasonic treatment for 10 min, it was stirred for another 10 min. Then, 0.9 g of polyvinylpyrrolidone was added, and the rotation speed was controlled at 120 rpm and stirred for 8 h to obtain a precursor spinning solution.

[0042] (2) The above precursor spinning solution was electrospun under the conditions of a humidity of 20 - 40 RH%, a voltage of 15 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe propulsion speed of 0.0003 mm / s to obtain precursor fibers.

[0043] (3) The above precursor fibers were calcined in air. Under the conditions of a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min, they were calcined for 2 h. After cooling to room temperature, a porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, namely Fe2O3@In2O3-60, was obtained.

[0044] The porous In2O3 nanofiber embedded with octahedral hollow Fe2O3 prepared in Example 2 was respectively subjected to SEM detection before and after calcination. The results are as Figure 2 shown, Figure 2Scanning electron microscope images of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ before and after calcination in Example 2 of the present invention. Figure 2 (a) Scanning electron microscope image of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ before calcination. Figure 2 (b) Scanning electron microscope image of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ after calcination.

[0045] Referring to Figure 2 (a), it can be seen that the surface structure of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ is smooth before calcination, with a diameter of about 400 nm. The nanostructure can be clearly seen being coated therein and is evenly dispersed. Referring to Figure 2 (b), it can be seen that the fiber diameter of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ shrinks to about 100 nm after calcination, presenting a porous and rough shape.

[0046] The porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ prepared in Example 2 were analyzed by transmission electron microscopy. Figure 3 Transmission electron microscope image of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ in Example 2 of the present invention. Figure 3 (a) Transmission electron microscope image of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃. Figure 3 (b) Structure diagram of a single fiber of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃. Referring to Figure 3 It can be seen that the octahedral hollow Fe₂O₃ nanostructure is well embedded in the nanofibers, and the In element is evenly distributed.

[0047] The porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ prepared in Example 2 were analyzed by X-ray photoelectron spectroscopy. Figure 4 X-ray photoelectron spectroscopy analysis diagram of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ in Example 2 of the present invention. Referring to Figure 4 It can be seen that the peak positions of the obtained porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ coincide with the peak positions of In₂O₃ (444.1 eV and 451.6 eV) and Fe₂O₃ (710.3 eV and 723.9 eV), and it can be clearly determined that the obtained product is the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃.

[0048] The porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ prepared in Example 2 were subjected to X-ray single crystal powder diffraction. Figure 5This is the X-ray single crystal powder diffraction pattern of the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 described in Example 2 of the present invention. Referring to Figure 5 it can be seen that the peaks of the obtained product coincide with the peaks of In2O3 (PDF#06-0416) and Fe2O3 (PDF#33-0664), and it can be clearly determined that the obtained product is the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3.

[0049] Example 3

[0050] This example presents a kind of porous In2O3 nanofibers embedded with octahedral hollow Fe2O3, which is prepared by the following method:

[0051] (1) Add 1.5 mmol of indium nitrate hydrate to 4.5 mL of N-N dimethylformamide. After stirring and dissolving, add 20 mg of MIL-101(Fe) prepared in Example 1 thereto. After ultrasonic treatment for 10 min, stir for another 10 min. Then add 0.9 g of polyvinylpyrrolidone, control the rotation speed at 120 rpm, and stir for 8 h to obtain a precursor spinning solution;

[0052] (2) Carry out electrospinning on the above precursor spinning solution under the conditions of a humidity of 20-40% RH, a voltage of 15 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe feeding speed of 0.0003 mm / s to obtain precursor fibers;

[0053] (3) Place the above precursor fibers in the air for calcination. Calcinate at a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min for 2 h. After cooling to room temperature, obtain the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3, namely Fe2O3@In2O3-20.

[0054] Example 4

[0055] This example presents a kind of porous In2O3 nanofibers embedded with octahedral hollow Fe2O3, which is prepared by the following method:

[0056] (1) Add 1.5 mmol of indium nitrate hydrate to 4.5 mL of N-N dimethylformamide. After stirring and dissolving, add 40 mg of MIL-101(Fe) prepared in Example 1 thereto. After ultrasonic treatment for 10 min, stir for another 10 min. Then add 0.9 g of polyvinylpyrrolidone, control the rotation speed at 120 rpm, and stir for 8 h to obtain a precursor spinning solution;

[0057] (2) Electrospin the above precursor spinning solution under the conditions of a humidity of 20 - 40% RH, a voltage of 15 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe propulsion speed of 0.0003 mm / s to obtain precursor fibers;

[0058] (3) Place the above precursor fibers in air for calcination. Calcinate them at a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min for 2 h. After cooling to room temperature, obtain porous In2O3 nanofibers with octahedral hollow Fe2O3 embedded, namely Fe2O3@In2O3 - 40.

[0059] Example 5

[0060] This example presents a porous In2O3 nanofiber with octahedral hollow Fe2O3 embedded, which is prepared by the following method:

[0061] (1) Add 1.5 mmol of indium nitrate hydrate to 4.5 mL of N - N dimethylformamide. After stirring and dissolving, add 50 mg of MIL - 101(Fe) prepared in Example 1 to it. After ultrasonic treatment for 10 min, stir for another 10 min. Then add 0.9 g of polyvinylpyrrolidone, control the rotation speed at 120 rpm, and stir for 8 h to obtain a precursor spinning solution;

[0062] (2) Electrospin the above precursor spinning solution under the conditions of a humidity of 20 - 40% RH, a voltage of l5 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe propulsion speed of 0.0003 mm / s to obtain precursor fibers;

[0063] (3) Place the above precursor fibers in air for calcination. Calcinate them at a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min for 2 h. After cooling to room temperature, obtain porous In2O3 nanofibers with octahedral hollow Fe2O3 embedded, namely Fe2O3@In2O3 - 50.

[0064] Example 6

[0065] This example presents a porous In2O3 nanofiber with octahedral hollow Fe2O3 embedded, which is prepared by the following method:

[0066] (1) Add 1.5 mmol of indium nitrate hydrate to 4.5 mL of N - N dimethylformamide. After stirring and dissolving, add 70 mg of MIL - 101(Fe) prepared in Example 1 to it. After ultrasonic treatment for 10 min, stir for another 10 min. Then add 0.9 g of polyvinylpyrrolidone, control the rotation speed at 120 rpm, and stir for 8 h to obtain a precursor spinning solution;

[0067] (2) Electrospin the above precursor spinning solution under the conditions of a humidity of 20 - 40% RH, a voltage of 15 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe propulsion speed of 0.0003 mm / s to obtain precursor fibers;

[0068] (3) Calcinate the above precursor fibers in air at a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min for 2 h. After cooling to room temperature, porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃, namely Fe₂O₃@In₂O₃ - 70, are obtained.

[0069] Example 7

[0070] This example presents a porous In₂O₃ nanofiber embedded with octahedral hollow Fe₂O₃, which is prepared by the following method:

[0071] (1) Add 1.5 mmol of indium nitrate hydrate to 4.5 mL of N,N - dimethylformamide. After stirring and dissolving, add 80 mg of MIL - 101(Fe) prepared in Example 1. After ultrasonic treatment for 10 min, stir for another 10 min. Then add 0.9 g of polyvinylpyrrolidone, control the rotation speed at 120 rpm, and stir for 8 h to obtain a precursor spinning solution;

[0072] (2) Electrospin the above precursor spinning solution under the conditions of a humidity of 20 - 40% RH, a voltage of 15 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe propulsion speed of 0.0003 mm / s to obtain precursor fibers;

[0073] (3) Calcinate the above precursor fibers in air at a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min for 2 h. After cooling to room temperature, porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃, namely Fe₂O₃@In₂O₃ - 80, are obtained.

[0074] Example 8

[0075] This example presents a porous In₂O₃ nanofiber embedded with octahedral hollow Fe₂O₃, which is prepared by the following method:

[0076] (1) 1.5 mmol of indium nitrate hydrate was added to 4.5 mL of N,N-dimethylformamide. After stirring to dissolve, 100 mg of MIL-101(Fe) prepared in Example 1 was added thereto. After ultrasonic treatment for 10 min, stirring was continued for 10 min. Then, 0.9 g of polyvinylpyrrolidone was added, the rotation speed was controlled at 120 rpm, and stirring was carried out for 8 h to obtain a precursor spinning solution;

[0077] (2) The above precursor spinning solution was subjected to electrospinning under the conditions of a humidity of 20 - 40% RH, a voltage of 15 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe propulsion speed of 0.0003 mm / s to obtain precursor fibers;

[0078] (3) The above precursor fibers were calcined in air at a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min for 2 h. After cooling to room temperature, porous In2O3 nanofibers embedded with octahedral hollow Fe2O3, namely Fe2O3@In2O3-100, were obtained.

[0079] Comparative Example 1

[0080] This comparative example presents a kind of porous In2O3 nanofibers, which are prepared by the following method:

[0081] (1) 1.5 mmol of indium nitrate hydrate was added to 4.5 mL of N,N-dimethylformamide. After ultrasonic treatment for 10 min, stirring was continued for 10 min. Then, 0.9 g of polyvinylpyrrolidone was added, the rotation speed was controlled at 120 rpm, and stirring was carried out for 8 h to obtain a precursor spinning solution;

[0082] (2) The above precursor spinning solution was subjected to electrospinning under the conditions of a humidity of 20 - 40% RH, a voltage of 15 kV, a distance between the nozzle and the collection end of 15 cm, and a syringe propulsion speed of 0.0003 mm / s to obtain precursor fibers;

[0083] (3) The above precursor fibers were calcined in air at a calcination temperature of 500 °C and a calcination heating rate of 2 °C / min for 2 h. After cooling to room temperature, porous In2O3 nanofibers were obtained.

[0084] Performance test:

[0085] The porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ obtained in Examples 2 - 8, Example 1, and Comparative Example 1 (represented by MIL-101(Fe) addition amount - Fe₂O₃ / In₂O₃ respectively), octahedral hollow Fe₂O₃ (represented by Fe₂O₃), and porous In₂O₃ nanofibers (represented by In₂O₃) were respectively adhered to the surface of ceramic chips with deionized water. After the materials were dried, gas sensors with different doping amounts were obtained;

[0086] The gas sensors were tested for gas sensitivity. At 150 - 400 °C, different gases and 10 ppm triethylamine were introduced for testing. The results are as Figure 6 and Figure 7 shown:

[0087] Figure 6 For the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Example 2 of the present invention, the octahedral hollow Fe₂O₃ described in Example 1, and the porous In₂O₃ nanofibers described in Comparative Example 1 when used in gas sensors, the sensitivity response radar charts (250 °C) for various gases such as benzene, toluene, n-butanol, and acetone are respectively shown.

[0088] Figure 7 The sensitivity detection chart of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Example 2 of the present invention to triethylamine is as follows: Figure 7 (a) The sensitivity response curves of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Examples 2 - 8, the octahedral hollow Fe₂O₃ described in Example 1, and the porous In₂O₃ nanofibers described in Comparative Example 1 to 10 ppm triethylamine at different temperatures; Figure 7 (b) The multiple-cycle test curve (250 °C) of the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Example 2 to 10 ppm triethylamine. Referring to Figure 7 it can be seen that the porous In₂O₃ nanofibers embedded with octahedral hollow Fe₂O₃ described in Example 2 have the highest sensitivity to 10 ppm triethylamine.

[0089] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A porous In2O3 nanofiber embedded with octahedral hollow Fe2O3, characterized in that It includes porous In2O3 nanofibers and octahedral hollow Fe2O3 uniformly embedded in the porous In2O3 nanofibers; The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 are prepared by the following method: After mixing MIL-101(Fe) and trivalent indium salt to form a precursor spinning solution, electrospinning is carried out to obtain precursor fibers, and then high-temperature calcination is carried out to obtain the porous In2O3 nanofibers embedded with octahedral hollow Fe2O3; The MIL-101(Fe) is obtained by reacting ferric chloride hexahydrate as an iron source and terephthalic acid as a ligand in a mixed solvent of water and N,N-dimethylformamide.

2. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 1, wherein The diameter of the porous In2O3 nanofibers is 100-150 nm.

3. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 1, wherein The particle size of the MIL-101(Fe) is 400-500 nm.

4. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 1, characterized in that, The precursor spinning solution is obtained by dispersing MIL-101(Fe), trivalent indium salt and polyvinylpyrrolidone in an organic solvent and stirring evenly.

5. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 4, wherein the trivalent indium salt is indium nitrate and the organic solvent is N,N-dimethylformamide.

6. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 4, wherein The molar ratio of the MIL-101(Fe) to the trivalent indium salt is 0.05-0.3:

1.

7. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 4, characterized in that, The molar ratio of the polyvinylpyrrolidone to the trivalent indium salt is 4-6:1, wherein the molar amount of the polyvinylpyrrolidone is calculated according to the molar amount of its polymerization monomer of 111.

8. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 1, characterized in that The electrospinning voltage is 12-18 kV, the distance between the nozzle and the collection end is 12-18 cm, the injection speed of the syringe is 0.002-0.004 mm / s, and the reaction humidity is 20-40%RH.

9. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 1, characterized in that, The high-temperature calcination is carried out in an air atmosphere.

10. The porous In2O3 nanofibers embedded with octahedral hollow Fe2O3 according to claim 1, wherein the temperature of the high-temperature calcination is 400-600 °C and the time is 1-3 h.

11. A gas sensor, characterized in that, It uses the porous In2O3 nanofibers according to any one of claims 1-10.

12. The gas sensor according to claim 11, characterized in that, It is used for the detection of toxic and harmful gases.

13. The gas sensor according to claim 12, characterized in that, The toxic and harmful gas is triethylamine.

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