CN104422716B - Preparation method of gas sensor gas sensitive film based on In2O3 nanowire - Google Patents

Abstract

This patent relates to a method for preparing a gas-sensing film for a gas sensor based on In ₂ O ₃ nanowires. The porous semiconductor In ₂ O ₃ nanometer material is synthesized by a two-step chemical conversion method, and the In ₂ O ₃ nanowire with high purity is obtained after preliminary separation and purification, and is used as a gas-sensitive material to assemble a semiconductor gas sensor. The working principle of the gas sensor is based on the detection and analysis of the electrical signal (resistance, voltage, current, etc.) changes of the semiconductor In ₂ O ₃ nanowire material exposed to the air and the gas to be measured. Gas sensors can respond well to common organic volatile gases (VOCs) such as ethanol, acetone, and formaldehyde, as well as toxic and harmful environmental pollutants such as ammonia and hydrogen sulfide, and their response (ie sensitivity) is comparable to that of the gas to be measured. It is directly related to the concentration (or content) of the gas and can be used for online detection of gas.

Description

Preparation method of gas sensor film based on In2O3 nanowires

technical field

The invention relates to a method for preparing a gas-sensitive film of a semiconductor gas sensor. Specifically, In ₂ O ₃ nanowires are used as a gas-sensitive material and assembled into a semiconductor gas sensor to realize gas analysis and detection.

Background technique

With the improvement of human safety and health awareness, it is urgent to monitor flammable, explosive and toxic gases in the atmosphere, family and various production and living places, so as to prevent safety accidents and ensure the safety of people and property. At present, the detection and analysis of gas is still mainly based on large-scale instrument analysis, such as gas chromatography, infrared absorption, thermal conductivity analysis and other analytical instruments. monitor. Therefore, it is imminent to develop low-cost, high-sensitivity, portable gas sensors. The performance of gas sensors is closely related to gas-sensing materials, so high-performance gas-sensing materials have attracted more and more attention. Although various semiconducting metal oxide materials have been widely used as gas-sensing materials for gas sensors, their low sensitivity limits their popularization to some extent.

The nanowire structure of metal oxide is very sensitive to the surrounding environment due to its large specific surface area and high surface activity, and is expected to show excellent gas-sensing performance for the gas to be measured. Moreover, the nanomaterials of these metal oxides have a simple manufacturing process, low cost, and are easy to implement, which lays the foundation for their large-scale promotion.

Based on these advantages of metal oxide nanomaterials, it is designed as a semiconductor gas sensor gas-sensing film, which can improve the detection sensitivity of gas and shorten the response and recovery time.

Contents of the invention

The object of the present invention is to propose a method for preparing a gas sensor film based on In ₂ O ₃ nanowires, so as to improve the detection sensitivity of gas and shorten the response and recovery time. In order to achieve the above purpose, the technical scheme adopted in this design is:

In ₂ O ₃ nanomaterials were prepared from commercially available In ₂ O ₃ powders, and the porous In ₂ O ₃ one-dimensional nanowire materials were isolated and used as gas-sensing membranes for sensors.

Including the preparation of In ₂ O ₃ nanomaterials, the separation of In ₂ O ₃ nanowires, and the assembly of gas-sensitive membranes for gas sensors;

(1) Spread the commercialized In ₂ O ₃ powder prepared into a paste with water evenly on the inner wall of the quartz boat, put it into the center of the quartz tube furnace after drying, and react at high temperature in the ammonia flow for 3-8 hours; the reaction is over Finally, the quartz tube is slowly cooled to room temperature; the product obtained in the quartz boat is calcined at a high temperature for 2-5 hours in an air atmosphere, and after the reaction is completed, it is slowly cooled to room temperature;

(2) Disperse the remaining nanomaterials and metal indium powder in an organic solvent from the product obtained in step (1) except the metal indium spheres with a diameter of more than 2 mm; suck out all the dispersion solution, and stir the suctioned dispersion solution After 6-12 hours, centrifuge to collect the obtained supernatant, and after the supernatant is centrifuged again, collect the obtained precipitate, and disperse all the precipitate in absolute ethanol;

(3) A Ni-Cr heating wire is passed through a ceramic tube with a pair of gold electrodes and a platinum lead wire; the nanowire ethanol dispersion solution is slowly drip-coated between a pair of gold electrodes on the outer surface of the ceramic tube to form a film, Aging for 24h.

The commercialized In ₂ O ₃ is In ₂ O ₃ with a mass purity greater than or equal to 99.99%.

The flow rate of the ammonia gas flow in step (1) is 100-500mL/min; the high temperature in the ammonia gas refers to 600-800°C.

The air atmosphere in step (1) is an air flow with a flow rate of 100-500mL/min; the high temperature in the air atmosphere refers to 500-700°C.

The centrifugation speed in step (2) is 2000-5000rpm, and the centrifugation time is 1-10min.

The organic solvent in step (2) is one or more of ethanol, toluene, hexane, n-hexane, ethylene glycol, trichlorophenol, chloroform and the like.

In step (3), the nanowire ethanol dispersion solution coated on the outer surface of the ceramic tube with a length×outer diameter of 4 mm×1.2 mm has a volume of 5-200 μL.

The aging temperature in step (3) is controlled at 400-500°C.

The gas-sensitive film can be used for real-time detection of organic volatile gases.

The nanowires were synthesized using a two-step chemical transformation method. First, In ₂ O ₃ is nitrided in NH ₃ atmosphere to prepare InN nanowires, and then the InN nanowires are oxidized into In ₂ O ₃ nanowires in the air flow. Due to the Kirkendall effect, the metal is nitrided by ammonia gas The oxide forms a metal nitride, which oxidizes back to a metal oxide in air. The newly formed metal oxide is coated on the surface of the unreacted metal nitride, and the nitrogen generated by the reaction gathers under the metal oxide layer, and finally breaks through the metal oxide layer to form an ultrafine nanopore structure, and more oxygen flows from the pores Enter in the middle, react with the metal nitride of the next layer, and go round and round to form a porous material with an ultra-fine nanoporous structure, further increasing the specific surface area of the nanowire material.

Among the obtained products, in addition to In ₂ O ₃ nanowires, there are metal indium powder, indium spheres, In ₂ O ₃ micro-sheets, micro-tubes, etc. After centrifugal separation, In ₂ O ₃ nanowires with higher purity can be separated under different centrifugal forces according to the difference in density and viscosity of different products in chloroform.

The isolated porous In ₂ O ₃ nanowires are dispersed by ethanol and drop-coated on the ceramic tube, which is convenient to make and easy to repeat.

The invention relates to a method for preparing a gas sensitive film of a gas sensor based on In ₂ O ₃ nanowires. The porous semiconductor In ₂ O ₃ nanometer material is synthesized by a two-step chemical conversion method, and the In ₂ O ₃ nanowire with high purity is obtained after preliminary separation and purification, and is used as a gas-sensitive material to assemble a semiconductor gas sensor. The working principle of the gas sensor is based on the detection and analysis of the electrical signal (resistance, voltage, current, etc.) changes of the semiconductor In ₂ O ₃ nanowire material exposed to the air and the gas to be measured. The gas sensor can respond well to common organic volatile gases (VOCs) such as ethanol, acetone, and formaldehyde, and toxic and harmful environmental pollutants such as ammonia and hydrogen sulfide, and its response degree (ie sensitivity) is comparable to that of the gas to be measured. It is directly related to the concentration (or content) of the gas and can be used for online detection of gas.

Advantages of the invention

1. In ₂ O ₃ used to prepare semiconductor gas sensors is a porous nanowire one-dimensional material, which improves the sensitivity to gases and shortens the response and recovery time.

2. The manufacturing process of the sensor gas sensitive film is simple, low in cost and easy to implement.

Instructions attached

Figure 1. Scanning electron microscope pictures of the prepared In ₂ O ₃ nanomaterials.

Figure 2. SEM images of (a) relatively pure In ₂ O ₃ nanowires; (b) other structures obtained after separation.

Fig. 3. (a) Schematic diagram of semiconductor gas sensor; (b) Schematic diagram of circuit used for gas sensing performance test; (c) Response curves of different concentrations of ethanol.

detailed description

(1) Preparation of In ₂ O ₃ nanomaterials. Weigh 1.5 g of In ₂ O ₃ powder (Aladdin Company, 99.99%) in a quartz boat (5 cm×2.8 cm×1.4 cm). Add a few drops of distilled water to the quartz boat, adjust the In ₂ O ₃ powder into a paste, apply it evenly on the inner wall of the quartz boat with a medicine spoon, and put it in a fume hood to dry slowly. Then put the quartz boat into the center of the quartz tube furnace (60cm×3.535cm×3.106cm). Ammonia gas was introduced into the quartz tube at a flow rate of 200 mL/min for 30 min to remove the air in the quartz tube. Then, the quartz tube was rapidly heated from room temperature to 730° C. in 200 mL/min of ammonia gas, and the reaction was kept for 6 h. After the reaction, the quartz tube furnace was closed, and the quartz tube was slowly cooled to room temperature. Finally, the product obtained in the quartz boat was heated from room temperature to 600 °C in an air atmosphere of 200 mL/min and kept for 3 h. After the reaction was completed, the quartz tube furnace was closed and slowly cooled to room temperature.

(2) Separation of In ₂ O ₃ nanowires. Remove the metal indium spheres with a diameter of more than 2mm from the material obtained in step (1), and the remaining nanomaterials and metal indium powder (Figure 1) can be dispersed in 20mL of chloroform. Metal indium powder settles very quickly in chloroform, but the nanomaterials are too late to deposit, so the dispersion can be sucked out with a pipette gun and placed in another 20mL vial. The dispersion in the vial was stirred on a magnetic stirrer for 12 hours, then placed in a high-speed centrifuge, centrifuged at 2000 rpm for 3 minutes, and the supernatant was sucked out. Collect the obtained supernatant, centrifuge at 9000rpm for 5min, pour off the supernatant completely, collect the precipitate (Figure 2), and finally disperse all the precipitate in absolute ethanol.

(3) Assembly of the gas detector. As shown in Fig. 3a, a Ni-Cr heating wire 1 is passed through a ceramic tube 4 (length×outer diameter×inner diameter is 4mm×1.2mm×0.8mm) with a pair of gold electrodes 3 and platinum lead wire 2 to provide The temperature required for the test; a pair of gold electrodes 3 are wound on the outer surface of the ceramic tube 4 at intervals, a pair of gold electrodes 3 are respectively provided with platinum lead wires 2, and a Ni-Cr heater is inserted in the ceramic tube 4 silk1. The platinum lead wire and the Ni-Cr heating wire were respectively welded and fixed on the base. Figure 3b is a schematic diagram of the circuit used. Take 200 μL of nanowire ethanol dispersion solution, and slowly drop-coat it between a pair of gold electrodes 3 on the outer surface of the ceramic tube to form a gas-sensitive film 5 . Then, the entire sensor was connected to a gas sensor testing system (WS-30A, Zhengzhou Weisheng) for aging at 400-500°C for 24h, and the heating voltage during aging was controlled at 4V.

(4) Gas sensitivity test experiment. According to the calculation, absorb a certain amount of absolute ethanol solution and place it in a closed system, and wait for it to completely evaporate to obtain the required concentration of ethanol.

The specific operation is as follows: first turn on the WS-30A gas sensitive test system, expose it to the air, plug in the load card, and start the test. After the electrical signal is stable, quantitatively absorb 1 μL, 2 μL, 3 μL, 4 μL, and 5 μL of absolute ethanol and place them on the evaporator of the gas-sensing test system, cover the gas distribution box, and press the "evaporation" button on the front control panel , do not loosen it, the liquid will be completely volatilized after a few seconds, and then loosened, the static gas distribution method is adopted, in a closed container, the required concentration of the gas is obtained by calculating the ideal gas state equation, and the corresponding is 20ppm, 40ppm, 60ppm, 80ppm, 100ppm. The WS-30A gas-sensing test system automatically records the change curve of the electrical signal generated by the gas-sensing film corresponding to different concentrations of absolute ethanol in the airtight container (as shown in Figure 3c).

Claims (9)

1. In is based on₂O₃The preparation method of the gas sensor air-sensitive film of nano wire, it is characterised in that：By commercialization In₂O₃Powder End prepares In₂O₃Nano material, isolated porous In₂O₃1-dimention nano wire material, and as preparing the air-sensitive film of sensor；

Include In₂O₃The preparation of nano material, In₂O₃The separation of nano wire and the assembling of gas sensor air-sensitive film；

(1) the commercialization In of pasty state will be modulated into water₂O₃Powder uniform application puts into stone in the inwall of quartz boat after being dried The center of English tube furnace, in ammonia flow high temperature 3～8h is reacted；After reaction terminates, it is slowly cooled to room temperature quartz ampoule；Will The product obtained in quartz boat calcines 2～5h in air atmosphere high temperature, after reaction terminates, is slowly cooled to room temperature；

(2) product for being obtained step (1) removes the oarse-grained metal indium pellet of more than diameter 2mm, remaining nano material It is scattered in organic solvent with Metallic Indium Powder；Dispersion soln is all suctioned out, the dispersion soln of sucking-off is stirred after 6～12h, from The heart, collects gained supernatant, after supernatant recentrifuge, collects the precipitation for obtaining, and precipitation is all scattered in dehydrated alcohol；

(3) a Ni-Cr heater strip will be passed through in the earthenware with a pair of gold electrodes and platinum lead；Take the dispersion of nano wire ethanol Solution, slow drop coating film forming, aging 24h between a pair of gold electrodes of ceramic tube outer surface.

2. method according to claim 1, it is characterised in that：The commercialization In₂O₃It is more than or equal to for quality purity 99.99% In₂O₃。

3. method according to claim 1, it is characterised in that：The flow velocity of step (1) ammonia flow is 100～500mL/ min；Ammonia high temperature refers to 600～800 DEG C.

4. preparation method according to claim 1, it is characterised in that：Step (1) air atmosphere be flow velocity be 100～ The air stream of 500mL/min；Air atmosphere high temperature refers to 500～700 DEG C.

5. preparation method according to claim 1, it is characterised in that：Step (2) centrifugal speed be 2000～ 5000rpm, centrifugation time is 1～10min.

6. preparation method according to claim 1, it is characterised in that：Step (2) organic solvent be ethanol, toluene, One or two or more kinds in hexane, normal hexane, ethylene glycol, trichlorophenol, 2,4,6,-T, chloroform.

7. preparation method according to claim 1, it is characterised in that：Step (3) is described be coated in length × external diameter be 4mm × The nano wire ethanol dispersion soln volume of 1.2mm ceramics tube outer surfaces is 5～200 μ L.

8. preparation method according to claim 1, it is characterised in that：The control of step (3) aging temperature 400～ 500℃。

9. preparation method according to claim 1, it is characterised in that：Air-sensitive film can be used for the real-time of volatile organic compoundses Detection.