Ag-doped nano In2O3 ozone sensing material and preparation method thereof

Abstract

The invention belongs to the technical field of metal oxides, and discloses an Ag-doped nano In2O3 ozone sensing material and a preparation method thereof, and the preparation method comprises the following steps: preparing a precursor solution of an In element; preparing a precursor solution of an Ag element; synthesizing and preparing In2O3 semiconductor O3 sensing materials doped with different contents of Ag by using a CSHS reaction device; after the reaction is finished, collecting and settling nano turbid liquid for 12-24 hours, centrifuging and washing repeatedly for 6 times, freezing for 4 hours by using a freeze-drying machine, freeze-drying for 24 hours, taking out powder, grinding, putting into a glass container, exhausting air in the bottle by using argon, and sealing and storing an edge opening by using a sealing tape, so as to obtain nano In2O3 semiconductor O3 sensing material powder doped with different contents of Ag; and drying by using a heating table at 70 DEG C, and standing for 30 minutes to obtain the pole piece capable of being used for testing the O3 sensing performance. The Ag-doped nano In2O3 semiconductor O3 sensing material prepared by the method is good in structural consistency and excellent in sensing performance. The preparation method is green, energy-saving and efficient, can realize 24-hour continuous preparation, and is high in material yield.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal oxides, and particularly relates to an Ag-doped nano In2O3 ozone sensing material and a preparation method thereof. BACKGROUND

[0002] Ozone (O3) is a pale blue gas with a fishy smell. With the increasing attention of the country to the air environmental quality, especially the attention to O3 pollution problems, the demand for O3 sensing and monitoring technology in China will rapidly grow. Under such a background, the environmental protection industry also puts forward higher requirements for the performance of O3 sensors. Not only should they have high sensitivity and high selectivity to ensure accurate monitoring of O3, but also should be stable and reliable under various environmental conditions. In addition, the response speed of the sensor should be further improved and the recovery time should be shortened so as to timely capture the changes of O3 concentration and provide real-time data support for environmental protection and pollution control. Therefore, it is urgent to develop a sensing material that can be used for real-time monitoring of O3 in the atmospheric environment.

[0003] A semiconductor O3 sensor uses gas-sensitive semiconductor materials to make sensitive elements. When O3 molecules are adsorbed on the surface of these materials, a redox reaction occurs, causing changes in the resistance or temperature of the sensitive element. This change is related to the concentration of O3, and by measuring the change in resistance or temperature, the concentration of O3 can be inferred. O3 sensors based on metal oxide semiconductor materials have the advantages of high sensitivity, short response time, low cost, light weight, etc., and are the development frontier of the current gas sensor industry.

[0004] Continuous supercritical hydrothermal synthesis (CSHS) technology has the characteristics of environmental protection, suitable for preparing multi-element composite metal oxide materials, continuous and rapid preparation, controllable reaction conditions, and low production cost conducive to industrialization. Therefore, by using the CSHS technology to realize the preparation of nano In2O3 semiconductor O3 sensing material, and by adjusting the type and concentration of the precursor solution, adjusting the reaction conditions, etc., a trace amount of Ag element is introduced into the synthesis process to simultaneously dope and modify the nano In2O3 semiconductor O3 sensing material, which has important value for improving the O3 sensing performance of the In2O3 semiconductor material. SUMMARY

[0005] In view of the problems existing in the prior art, the application provides an Ag-doped nano In2O3 ozone sensing material and a preparation method thereof.

[0006] The application is implemented as follows: an Ag-doped nano In2O3 ozone sensing material and a preparation method thereof, the method comprising: S1: configuring a precursor solution of In element.

[0007] S2: configure the precursor solution of Ag element.

[0008] S3: use the self-built CSHS reaction device to synthesize and prepare In2O3 semiconductor O3 sensing material doped with different contents of Ag.

[0009] S4: after the reaction, the nanometer suspension is collected and settled for 12-24 hours. After centrifugation, washing and repetition for 6 times, the powder is taken out, ground and placed in a glass container. The air in the bottle is exhausted using argon, sealed with adhesive tape and stored. Different content of Ag-doped nano In2O3 semiconductor O3 sensing material powder is obtained.

[0010] S5: 100 mg of Ag-doped nano In2O3 semiconductor O3 sensing material powder obtained in step four is weighed using a balance. 500 μL of ultrapure water is measured using a pipette and placed in a sample tube. The mixture is mixed uniformly, and 2.5 μL of the mixture is sucked using a pipette and dropped on the gold substrate of the interdigital electrode sheet. After drying using a 70°C heating table, the electrode sheet is obtained which can be used for testing O3 sensing performance.

[0011] Further, the S1 specifically comprises: The target volume of ultrapure water is accurately measured using a graduated cylinder and placed in a reagent bottle. A certain amount of In(NO3)3·H2O solid is accurately weighed using a balance and dissolved in ultrapure water. After the solute is dissolved, the reagent bottle is placed on a magnetic stirrer to obtain the precursor solution of In element.

[0012] Further, the S2 specifically comprises: The target volume of ultrapure water is accurately measured using a graduated cylinder and placed in a reagent bottle. A certain amount of AgNO3 powder is accurately weighed using a balance and dissolved in ultrapure water. After the solute is dissolved, the reagent bottle is placed on a magnetic stirrer at a stirring speed of 600 r / min for 30 min to obtain the precursor solution of Ag element. The total concentration of metal ions in the two precursor solutions is controlled at 0.02 mol / L. The specific concentration is adjusted according to the doping ratio of Ag. The molar percentage of Ag element in the total concentration of metal ions in the two precursor solutions is 0.5%-5%, and the molar percentage of In element in the total concentration of metal ions in the two solutions is 99.5%-95%.

[0013] Further, the CSHS reaction device mainly consists of four parts: liquid phase delivery system, reaction system, temperature control system and sample collection system.

[0014] Liquid phase delivery system: composed of three high-pressure delivery pumps for liquid chromatography and corresponding liquid phase pipelines and adapters, respectively used for delivering deionized water, precursor solution and additive solution.

[0015] Reaction system: composed of two sets of electric heating devices and corresponding liquid phase pipelines and adapters, the electric heating device (large) is used for heating normal temperature high pressure deionized water to 450-550 DEG C, so that it reaches supercritical state. The electric heating device (small) is used for heat preservation of the straight pipe section at the outlet of the mixer, so as to ensure that the contact time of the mixed solution of the precursor and the additive with the supercritical water reaches more than 2s.

[0016] Temperature control system: control two sets of electric heating devices to program temperature and stabilize the temperature above 450 DEG C.

[0017] Sample collection system: composed of water cooling device, filter and back pressure valve, the prepared nanomaterials flow out of the system in the form of suspension after cooling and pressure relief.

[0018] Further, the S3 specifically comprises: Three liquid chromatography high pressure delivery pumps pump ultrapure water, Sn element precursor solution and Sb element precursor solution at a certain flow rate at normal temperature and give the three-way pipeline an initial pressure above 20 Mpa-23 Mpa, rely on the back pressure valve at the end of the system outlet to maintain the internal pressure of the whole system stable; The normal temperature high pressure In and Ag element precursor solution is mixed in a three-way for the first time, while the normal temperature high pressure ultrapure water flows through the electric heating device (large) and is heated to 450-550 DEG C to reach supercritical state, and then the In and Ag element precursor mixed solution and the supercritical water are mixed in a four-way mixer for the second time, and after sufficient mixing, it flows into the electric heating device (small), the temperature is still maintained at 450-550 DEG C, and the In and Ag element precursor mixed solution and the supercritical water are fully contacted for more than 2s for reaction, the In and Ag element precursor mixed solution and the supercritical water are rapidly reacted and crystallized to generate nanometer oxide after contacting, the reaction liquid flows out of the electric heating device (small) and enters the sample collection system after cooling, pressure relief and filtration, and finally the suspension of the Ag doped nanometer In2O3 semiconductor O3 sensing material with different contents is obtained.

[0019] The application aims to provide an Ag doped nanometer In2O3 ozone sensing material and a preparation method thereof.

[0020] In combination with the above technical solutions and the technical problems solved, the technical solution to be protected by the application has the following advantages and positive effects: Firstly, the application provides an Ag doped nanometer In2O3 semiconductor O3 sensing material and a preparation method thereof, the Ag doped nanometer In2O3 semiconductor O3 sensing material prepared by using the method has good structural consistency and excellent sensing performance. The preparation method is green, energy-saving and efficient, and can realize 24h continuous preparation, and the material yield is large.

[0021] Second, as the invention of the claim of the creation of auxiliary evidence, but also embodied in the following several important aspects: (1) the expected income and commercial value of the technical scheme of the present application after transformation is: The continuous supercritical hydrothermal synthesis technology process is environmentally friendly, suitable for preparing multi-component composite metal oxide materials, can realize continuous and rapid preparation, and the reaction conditions are controllable. The production cost is low and conducive to industrialization. The preparation method can effectively reduce the energy consumption and water consumption of the synthesis process, thereby reducing the preparation cost of O3 sensing materials.

[0022] (2) the technical scheme of the present application fills the domestic and foreign industry technical blank: At present, there is no micro indoor environment O3 sensor on the domestic market, only a few sensing devices are integrated as core components in air purifiers, fresh air machines and other whole machine products. Or as a handheld independent device, although the function is complete, the display is intuitive, the precision is relatively high, but the main application scene is professional test, and it is not aimed at indoor environment ozone monitoring and the cost is high. Therefore, the present application can effectively fill the technical blank of low-cost indoor environment ozone sensor core material.

[0023] (3) the technical scheme of the present application solves the technical problems that people have been eager to solve but have always failed to succeed: In the preparation technology, the metal oxide semiconductor O3 sensing material can be prepared by various methods such as solution method, gas phase method, thermal decomposition method, deposition method and the like. These preparation methods make the metal oxide semiconductor O3 sensing material have more possibilities in morphology and structure, and the sensing performance is also improved to a certain extent. However, the above preparation methods still face the difficulties of long preparation time, unstable control of the structure and surface properties of the prepared material and difficulty in industrialization. The supercritical fluid state refers to a special state reached when the temperature and pressure of a substance exceed the critical value. In this state, the substance is neither gaseous nor liquid, but a new phase with both phase properties, for example, the rapid diffusion property of gas phase and the dissolution and adsorption characteristics of liquid phase. Due to the special physicochemical properties of this phase state, the application of supercritical fluid in chemical reaction medium has attracted widespread attention. For water, when the temperature and pressure exceed the critical temperature of 374 DEG C and the critical pressure of 22.1 Mpa, it enters the supercritical state. Supercritical water has some properties of gaseous water and liquid water, and shows significant changes in density, dielectric constant, ion product, hydrogen bond and heat capacity, resulting in a decrease in solubility of supercritical water and strong oxidizing property. After the precursor salt solution of different metal elements is contacted with supercritical water, the metal oxide or elemental substance is rapidly oxidized and decomposed to form metal oxide or elemental substance and continuously nucleate and grow, and the nanometer particles are crystallized and precipitated. By using the special physicochemical properties of this phase state, the green, rapid and controllable preparation of nanometer metal oxide materials can be realized, and the doping modification and surface property regulation of nanometer metal oxide materials can be realized simultaneously in the preparation process. This not only opens up a new way for the synthesis and performance improvement of O3 sensing materials, but also provides an effective solution to the pollution problem in traditional preparation technology. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of a CSHS device provided by an embodiment of the present application.

[0025] Figure 2 is a response curve of a 1% Ag-doped nanometer In2O3 semiconductor O3 sensing material at different temperatures to 1 ppm O3.

[0026] Figure 3 is a sensing performance repeatability result of a 1% Ag-doped nanometer In2O3 semiconductor O3 sensing material at 200 DEG C to 1 ppm O3.

[0027] Figure 4 is an XRD spectrum of a nanometer In2O3 semiconductor O3 sensing material doped with different contents of Ag.

[0028] Figure 5The sensing selectivity performance results of the 1% Ag-doped nano In2O3 semiconductor O3 sensing material provided by the embodiment of the application to different polluted gases at 200 DEG C are shown in the following table. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the application clearer, the application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not used to limit the application.

[0030] The embodiment of the application provides an Ag-doped nano In2O3 ozone sensing material and a preparation method thereof, and the method comprises the following steps: S1: configuring a precursor solution of In element.

[0031] S2: configuring a precursor solution of Ag element.

[0032] S3: using a self-built CSHS reaction device to synthesize and prepare the In2O3 semiconductor O3 sensing material doped with different contents of Ag.

[0033] S4: after the reaction, the nano suspension liquid is collected and settled for 12-24 hours, after centrifugation, washing and repetition for 6 times, the nano suspension liquid is frozen for 4 hours by using a freeze dryer, and then is freeze-dried for 24 hours, the powder is taken out, grinded, placed in a glass container, the air in the bottle is exhausted by using argon, and the glass container is sealed by using a sealing tape, thereby obtaining the nano In2O3 semiconductor O3 sensing material powder doped with different contents of Ag.

[0034] S5: 100 mg of the nano In2O3 semiconductor O3 sensing material powder doped with different contents of Ag obtained in step four is weighed by using a balance, 500 muL of ultrapure water is taken by using a pipette, and then is placed in a sample tube, the mixture is uniformly mixed, 2.5 muL of the mixture is taken by using the pipette, and then is dropped and coated on a gold-based interdigital electrode sheet; after drying by using a 70 DEG C heating table, the electrode sheet is placed for 30 minutes, thereby obtaining an electrode sheet that can be used for testing the O3 sensing performance.

[0035] The S1 specifically comprises the following steps: A target volume of ultrapure water is accurately measured by using a measuring cylinder, and then is placed in a reagent bottle, a certain amount of In(NO3)3·H2O solid is accurately weighed by using a balance, and then is dissolved in the ultrapure water, after the solute is dissolved, the reagent bottle is placed on a magnetic stirrer, thereby obtaining the precursor solution of In element.

[0036] The S2 specifically comprises the following steps: Accurately measure the target volume of ultrapure water in a reagent bottle with a measuring cylinder, accurately weigh a certain amount of AgNO3 powder with a balance, and dissolve it in ultrapure water; after the solute is dissolved, place the reagent bottle on a magnetic stirrer and stir at a speed of 600 r / min for 30 min to obtain a precursor solution of Ag element; control the total concentration of metal ions in the two bottles of precursor solution to be 0.02 mol / L; adjust the specific concentration according to the doping ratio of Ag, and the molar percentage of Ag element in the total concentration of metal ions in the two bottles of precursor solution is 0.5%-5%, and the molar percentage of In element in the total concentration of metal ions in the two bottles of solution is 99.5%-95%.

[0037] As shown in Figure 1 The CSHS reaction device mainly consists of four parts: a liquid phase delivery system, a reaction system, a temperature control system, and a sample collection system.

[0038] The liquid phase delivery system consists of three identical high-pressure delivery pumps for liquid chromatography and corresponding liquid phase pipelines and adapters, which are used to deliver deionized water, precursor solution, and auxiliary solution, respectively.

[0039] The reaction system consists of two sets of electric heating devices and corresponding liquid phase pipelines and adapters. The electric heating device (large) is used to heat the normal temperature high-pressure deionized water to 450-550°C to achieve a supercritical state. The electric heating device (small) is used to heat the straight pipe section of the mixer outlet to ensure that the contact time of the mixed solution of the precursor and the auxiliary agent with the supercritical water reaches more than 2s.

[0040] The temperature control system controls the two sets of electric heating devices to program the temperature and stabilize the temperature above 450°C.

[0041] The sample collection system consists of a water cooling device, a filter, and a back pressure valve. The prepared nanomaterials flow out of the system in the form of a suspension after cooling and pressure relief.

[0042] Figure 1 The CSHS reaction device shown is a typical continuous supercritical water synthesis system, which consists of a liquid phase delivery system, a reaction system, a temperature control system, and a sample collection system. Each part is coupled in a closed manner through high-pressure fluid pipelines and interfaces to form a continuous flow reaction system. The detailed working principle is as follows.

[0043] After the system is started, the three high-pressure delivery pumps extract deionized water, precursor solution, and auxiliary solution from independent liquid storage bottles, respectively, and stably send them into the reaction system through high-pressure stainless steel pipelines according to the set flow rate. The flow rate of each pump is accurately adjusted by the control module to ensure that the volume ratio and molar ratio of the three liquids at the mixing point meet the process requirements, providing a guarantee for the controllability and repeatability of the reaction.

[0044] The deionized water delivered first enters the first set of high-power electric heating device, and is heated to 450-550 DEG C under high pressure conditions, so that it enters the supercritical state. At this time, the dielectric constant of water is significantly reduced, and the diffusion coefficient is similar to that of gas, which has the mass transfer characteristics of gas phase and the dissolution capacity of liquid phase, creating a high-reactivity environment for rapid hydrolysis and nucleation of metal salts or organic precursors.

[0045] The precursor solution and the auxiliary solution are mixed into the supercritical water flow at the inlet of the mixer, and the three streams are mixed uniformly and undergo intense hydrothermal reaction in a very short time. To avoid the temperature drop of the mixed reaction stream causing the system to deviate from the supercritical region, a small electric heating device is provided to continuously heat the straight pipe section of the mixing outlet, so that the reaction temperature is stably maintained above 450 DEG C, ensuring that the solution reacts in the supercritical state for at least 2 s, thereby realizing the continuous generation of nano materials with controllable particle size.

[0046] The entire reaction system is monitored and feedback-adjusted in real time by the temperature control system, and the temperature rising rate and steady temperature of the two-stage electric heating device are accurately controlled by the PID algorithm. The temperature control unit is provided with a temperature sensor and a safety interlocking mechanism, which automatically corrects the power output or triggers the protection shutdown when the temperature deviates from the set value, ensuring the safety of the reaction and the consistency of the product.

[0047] The high-temperature and high-pressure fluid after the reaction passes through the water cooling device, the filter and the back pressure valve in turn. The fluid is rapidly cooled in the cooling process and is reduced to atmospheric pressure at the back pressure valve, so that the generated nano materials are discharged in the form of stable suspension. The cooling device recovers part of the heat to improve the energy efficiency of the system, and the filter is used to remove unreacted particles or impurities. The final product is collected in a sample bottle for subsequent analysis and application.

[0048] The CSHS system realizes the controllable synthesis of nano materials through continuous high-pressure pumping, rapid supercritical reaction and precise temperature control, and has the technical advantages of short reaction time, narrow particle size distribution, continuous and high degree of automation.

[0049] The S3 specifically includes: Three high-pressure transfer pumps for liquid chromatography pump ultrapure water, Sn precursor solution, and Sb precursor solution at specific flow rates at room temperature, respectively, applying an initial pressure of 20-23 MPa to the three pipelines. The system's internal pressure is maintained by a back pressure valve at the system's outlet. The room-temperature, high-pressure In and Ag precursor solutions are initially mixed in a three-way valve. Simultaneously, the room-temperature, high-pressure ultrapure water is heated to 450-550°C by a large electric heater, reaching a supercritical state. The In and Ag precursor mixture is then mixed with the supercritical water in a four-way mixer for a second mixing. After thorough mixing, the mixture flows into a small electric heater, maintaining the temperature at 450-550°C, ensuring sufficient contact between the In and Ag precursor mixture and the supercritical water. The reaction proceeds above s. After the mixed solution of In and Ag precursors comes into contact with supercritical water, it reacts rapidly and crystallizes to form nano-oxides. The reaction liquid flows out of the electric heating device (small) and enters the sample collection system. After cooling, depressurization, and filtration, a suspension of nano-In2O3 semiconductor O3 sensing materials with different Ag doping contents is finally obtained.

[0050] Example 1 Step 1: Prepare 1 L of In element precursor solution. Accurately measure 1 L of ultrapure water using a graduated cylinder and place it in a reagent bottle. Take 6351 mg of In(NO3)3·H2O solid and dissolve it in ultrapure water. After the solute is dissolved, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of In element precursor solution.

[0051] Step 2: Prepare 1 L of Ag precursor solution. Accurately measure 1 L of ultrapure water into a reagent bottle using a graduated cylinder. Precisely weigh 17 mg of AgNO3 powder using a balance and dissolve it in the ultrapure water. After dissolving the solute, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of Ag precursor solution. Control the total metal ion concentration in both precursor solutions to 0.02 mol / L. At this point, the molar percentage of Ag in the total metal ion concentration of both precursor solutions is 0.5%, and the molar percentage of In in the total metal ion concentration of both solutions is 99.5%.

[0052] Step 3: Synthesize and prepare 0.5% Ag-doped In2O3 semiconductor O3 sensing material using a self-built CSHS reaction apparatus.

[0053] The process of preparing 0.5% Ag-doped In2O3 semiconductor O3 sensing material using a CSHS device: Three high-pressure transfer pumps for liquid chromatography pump ultrapure water, In element precursor solution, and Ag element precursor solution at room temperature at 20 mL / min, 10 mL / min, and 10 mL / min respectively, and apply an initial pressure of 23 MPa to the three pipelines. The internal pressure of the entire system is maintained by relying on the back pressure valve at the end of the system outlet. Precursor solutions of In and Ag elements at room temperature and high pressure are initially mixed in a three-way mixer. Simultaneously, ultrapure water at room temperature and high pressure is heated to 450°C and reaches a supercritical state by an electric heating device (large). Then, the In and Ag element precursor solution and the supercritical water are mixed in a four-way mixer for a second mixing. After thorough mixing, the mixture flows into an electric heating device (small), where the temperature is maintained at 450°C. The In and Ag element precursor solution is allowed to fully contact the supercritical water for more than 2 seconds to react. Upon contact with the supercritical water, the In and Ag element precursor solution reacts rapidly and crystallizes to form nano-oxides. The reaction liquid flows out of the electric heating device (small) and enters the sample collection system. After cooling, depressurization, and filtration, a suspension of 0.5% Ag-doped In2O3 semiconductor O3 sensing material is finally obtained.

[0054] Step 4: After the reaction is complete, the nano suspension is collected and allowed to settle for 12 hours. After centrifugation and washing are repeated 6 times, the powder is frozen for 4 hours and freeze-dried for 24 hours. The powder is then removed, ground, and placed in a glass container. The air inside the container is purged with argon gas, and the container is sealed with tape to preserve the powder. 0.5% Ag-doped In2O3 semiconductor O3 sensing material powder is obtained.

[0055] Step 5: Weigh 100 mg of the 0.5% Ag-doped In₂O₃ semiconductor O₃ sensing material powder obtained in Step 4 using a balance. Measure 500 μL of ultrapure water using a pipette and place it in a sample tube. Mix thoroughly. Use a pipette to draw 2.5 μL of the mixture and drop it onto the gold-based interdigitated electrode sheet. Dry the electrode sheet using a 70°C heating stage and let it stand for 30 min to obtain an electrode sheet suitable for testing O₃ sensing performance.

[0056] Example 2 Step 1: Prepare 1 L of In element precursor solution. Accurately measure 1 L of ultrapure water using a graduated cylinder and place it in a reagent bottle. Take 6319 mg of In(NO3)3·H2O solid and dissolve it in ultrapure water. After the solute is dissolved, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of In element precursor solution.

[0057] Step 2: Prepare 1 L of Ag precursor solution. Accurately measure 1 L of ultrapure water into a reagent bottle using a graduated cylinder. Precisely weigh 34 mg of AgNO3 powder using a balance and dissolve it in the ultrapure water. After the solute is dissolved, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of Ag precursor solution. Control the total metal ion concentration in both precursor solutions to 0.02 mol / L. At this point, the molar percentage of Ag in the total metal ion concentration of both precursor solutions is 1%, and the molar percentage of In in the total metal ion concentration of both solutions is 99%.

[0058] Step 3: Synthesize and prepare 1% Ag-doped In2O3 semiconductor O3 sensing material using a self-built CSHS reaction apparatus.

[0059] The process of preparing 1% Ag-doped In2O3 semiconductor O3 sensing material using a CSHS device: Three high-pressure transfer pumps for liquid chromatography pump ultrapure water, In element precursor solution, and Ag element precursor solution at room temperature at 20 mL / min, 10 mL / min, and 10 mL / min respectively, and apply an initial pressure of 23 MPa to the three pipelines. The internal pressure of the entire system is maintained by relying on the back pressure valve at the end of the system outlet. Precursor solutions of In and Ag elements at room temperature and high pressure are initially mixed in a three-way valve. Simultaneously, ultrapure water at room temperature and high pressure is heated to 450°C and reaches a supercritical state by an electric heating device (large). Then, the In and Ag element precursor solution and the supercritical water are mixed in a four-way mixer for a second mixing. After thorough mixing, the mixture flows into an electric heating device (small), where the temperature is maintained at 450°C. The In and Ag element precursor solution is allowed to fully contact the supercritical water for more than 2 seconds to react. After contact with the supercritical water, the In and Ag element precursor solution reacts rapidly and crystallizes to form nano-oxides. The reaction liquid flows out of the electric heating device (small) and enters the sample collection system. After cooling, depressurization, and filtration, a suspension of 1% Ag-doped In2O3 semiconductor O3 sensing material is finally obtained.

[0060] Step 4: After the reaction is complete, the nano suspension is collected and allowed to settle for 12 hours. After centrifugation and washing are repeated 6 times, the powder is frozen for 4 hours and freeze-dried for 24 hours. The powder is then removed, ground, and placed in a glass container. The air inside the container is purged with argon gas, and the container is sealed with tape to preserve the powder, thus obtaining 1% Ag-doped In2O3 semiconductor O3 sensing material powder.

[0061] Step 5: Weigh 100 mg of the 1% Ag-doped In₂O₃ semiconductor O₃ sensing material powder obtained in Step 4 using a balance. Measure 500 μL of ultrapure water using a pipette and place it in a sample tube. Mix thoroughly. Use a pipette to draw 2.5 μL of the mixture and drop it onto the gold-based interdigitated electrode sheet. Dry the electrode sheet using a 70°C heating stage and let it stand for 30 min to obtain an electrode sheet suitable for testing O₃ sensing performance.

[0062] Example 3 Step 1: Prepare 1 L of In precursor solution. Accurately measure 1 L of ultrapure water using a graduated cylinder and place it in a reagent bottle. Take 6191 mg of In(NO3)3·H2O solid and dissolve it in ultrapure water. After the solute is dissolved, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of In precursor solution.

[0063] Step 2: Prepare 1 L of Ag precursor solution. Accurately measure 1 L of ultrapure water into a reagent bottle using a graduated cylinder. Precisely weigh 102 mg of AgNO3 powder using a balance and dissolve it in the ultrapure water. After dissolving the solute, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of Ag precursor solution. Control the total metal ion concentration in both precursor solutions to 0.02 mol / L. At this point, the molar percentage of Ag in the total metal ion concentration of both precursor solutions is 3%, and the molar percentage of In in the total metal ion concentration of both solutions is 97%.

[0064] Step 3: Synthesize and prepare 3% Ag-doped In2O3 semiconductor O3 sensing material using a self-built CSHS reaction apparatus.

[0065] The process of preparing 3% Ag-doped In2O3 semiconductor O3 sensing material using a CSHS device: Three high-pressure transfer pumps for liquid chromatography pump ultrapure water, In element precursor solution, and Ag element precursor solution at room temperature at 20 mL / min, 10 mL / min, and 10 mL / min respectively, and apply an initial pressure of 23 MPa to the three pipelines. The internal pressure of the entire system is maintained by relying on the back pressure valve at the end of the system outlet. Precursor solutions of In and Ag elements at room temperature and high pressure are initially mixed in a three-way valve. Simultaneously, ultrapure water at room temperature and high pressure is heated to 450°C and reaches a supercritical state by an electric heating device (large). Then, the In and Ag element precursor solution and the supercritical water are mixed in a four-way mixer for secondary mixing. After thorough mixing, the mixture flows into an electric heating device (small), where the temperature is maintained at 450°C. The In and Ag element precursor solution and the supercritical water are brought into full contact for more than 2 seconds to react. After contact with the supercritical water, the In and Ag element precursor solution reacts rapidly and crystallizes to form nano-oxides. The reaction liquid flows out of the electric heating device (small) and enters the sample collection system. After cooling, depressurization, and filtration, a suspension of 3% Ag-doped In2O3 semiconductor O3 sensing material is finally obtained.

[0066] Step 4: After the reaction is complete, the nano suspension is collected and allowed to settle for 12 hours. After centrifugation and washing are repeated 6 times, the powder is frozen for 4 hours and freeze-dried for 24 hours. The powder is then removed, ground, and placed in a glass container. The air inside the container is purged with argon gas, and the container is sealed with tape to preserve the powder. 3% Ag-doped In2O3 semiconductor O3 sensing material powder is obtained.

[0067] Step 5: Weigh 100 mg of the 3% Ag-doped In₂O₃ semiconductor O₃ sensing material powder obtained in Step 4 using a balance. Measure 500 μL of ultrapure water using a pipette and place it in a sample tube. Mix thoroughly. Use a pipette to draw 2.5 μL of the mixture and drop it onto the gold-based interdigitated electrode sheet. Dry the electrode sheet using a 70°C heating stage and let it stand for 30 min to obtain an electrode sheet suitable for testing O₃ sensing performance.

[0068] Example 4 Step 1: Prepare 1 L of In precursor solution. Accurately measure 1 L of ultrapure water using a graduated cylinder and place it in a reagent bottle. Take 6064 mg of In(NO3)3·H2O solid and dissolve it in ultrapure water. After the solute is dissolved, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of In precursor solution.

[0069] Step 2: Prepare 1 L of Ag precursor solution. Accurately measure 1 L of ultrapure water into a reagent bottle using a graduated cylinder. Precisely weigh 170 mg of AgNO3 powder using a balance and dissolve it in the ultrapure water. After dissolving the solute, place the reagent bottle on a magnetic stirrer and stir at 600 r / min for 30 min to obtain 1 L of Ag precursor solution. Control the total metal ion concentration in both precursor solutions to 0.02 mol / L. At this point, Ag accounts for 5% of the total metal ion concentration in both precursor solutions, and In accounts for 95% of the total metal ion concentration.

[0070] Step 3: Synthesize and prepare 5% Ag-doped In2O3 semiconductor O3 sensing material using a self-built CSHS reaction device.

[0071] The process of preparing 5% Ag-doped In2O3 semiconductor O3 sensing material using a CSHS device: Three high-pressure transfer pumps for liquid chromatography pump ultrapure water, In element precursor solution, and Ag element precursor solution at room temperature at 20 mL / min, 10 mL / min, and 10 mL / min respectively, and apply an initial pressure of 23 MPa to the three pipelines. The internal pressure of the entire system is maintained by relying on the back pressure valve at the end of the system outlet. Precursor solutions of In and Ag elements at room temperature and high pressure are initially mixed in a three-way valve. Simultaneously, ultrapure water at room temperature and high pressure is heated to 450°C and reaches a supercritical state by an electric heating device (large). Then, the In and Ag element precursor solution and the supercritical water are mixed in a four-way mixer for a second time. After thorough mixing, the mixture flows into an electric heating device (small), where the temperature is maintained at 450°C. The In and Ag element precursor solution and the supercritical water are brought into full contact for more than 2 seconds to react. After contact with the supercritical water, the In and Ag element precursor solution reacts rapidly and crystallizes to form nano-oxides. The reaction liquid flows out of the electric heating device (small) and enters the sample collection system. After cooling, depressurization, and filtration, a suspension of 5% Ag-doped In2O3 semiconductor O3 sensing material is finally obtained.

[0072] Step 4: After the reaction is complete, the nano suspension is collected and allowed to settle for 12 hours. After centrifugation and washing are repeated 6 times, the powder is frozen for 4 hours and freeze-dried for 24 hours. The powder is then removed, ground, and placed in a glass container. The air inside the container is purged with argon gas, and the container is sealed with tape to preserve the powder. This yields 5% Ag-doped In2O3 semiconductor O3 sensing material powder.

[0073] Step 5: Weigh 100 mg of the 5% Ag-doped In₂O₃ semiconductor O₃ sensing material powder obtained in Step 4 using a balance. Measure 500 μL of ultrapure water using a pipette and place it in a sample tube. Mix thoroughly. Use a pipette to draw 2.5 μL of the mixture and drop it onto the gold-based interdigitated electrode sheet. Dry the electrode sheet using a 70°C heating stage and let it stand for 30 min to obtain an electrode sheet suitable for testing O₃ sensing performance.

[0074] like Figure 2 As shown, the 1% Ag-doped nano-In₂O₃ semiconductor O₃ sensing material exhibits the optimal response value for 1 ppm O₃ at 200 °C. Test conditions: O₃ concentration: 1 ppm, O₂ concentration: 20%, N₂ as makeup gas, total flow rate: 1 L / min, reaction temperature 50–250 °C.

[0075] like Figure 3 As shown, the 1% Ag-doped nano-In2O3 semiconductor O3 sensing material in Example 2 exhibits good repeatability for 1 ppm O3 at 200°C.

[0076] like Figure 4 As shown, the XRD patterns of the nano-In₂O₃ semiconductor O₃ sensing materials with different Ag doping contents in Examples 1–4 did not show any impurity peaks of other phases, which is consistent with the standard card. The average particle size of the prepared materials was calculated to be around 10 nm according to the Scherrer equation.

[0077] This invention provides an Ag-doped nano-In2O3 ozone sensing material and its preparation method.

[0078] The embodiments of this invention are implemented using a self-made CSHS device. XRD tests were performed on the samples prepared in Examples 1–4. Calculations using the Scherrer equation showed that the average particle size of the prepared material was approximately 10 nm, indicating that the prepared material is a nanomaterial. O3 sensing performance tests were conducted on the material prepared in Example 2. The results showed that it had a response value of approximately 30 for 1 ppm O3 at 50°C, and the optimal response value was approximately 110 for 1 ppm O3 at 200°C. The test results also showed good repeatability, indicating that the material has excellent O3 sensing performance. Furthermore, the material exhibited good selectivity for O3, with its absolute response value being more than 10 times that of other gases.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing Ag-doped nano-In₂O₃ ozone sensing material, characterized in that, Includes the following steps: (1) Prepare an In element precursor solution by dissolving In(NO3)3·H2O in ultrapure water and stirring with magnetic force to form a uniform and transparent solution. (2) Prepare Ag precursor solution by dissolving AgNO3 in ultrapure water and stirring at 600 rpm for 30 minutes; control the total concentration of metal ions in the two solutions to be 0.02 mol per liter, the molar percentage of Ag to be 0.5 to 5, and the molar percentage of In to be 99.5 to 95. (3) Using a continuous hydrothermal synthesis device, the In and Ag precursor solutions are reacted with supercritical water for more than 2 seconds at 450 to 550 degrees Celsius and 20 to 23 MPa. (4) Cool, depressurize, centrifuge, wash and freeze dry the resulting reaction suspension to obtain Ag-doped nano-In2O3 powder; (5) Take 100 mg of the powder and mix it with 500 μL of ultrapure water. Spread the mixture onto a gold-based finger electrode sheet. After drying at 70 degrees Celsius, let it stand for 30 minutes to obtain a sensor electrode sheet for ozone detection.

2. The method according to claim 1, characterized in that, The continuous hydrothermal synthesis apparatus includes a liquid phase delivery system, a reaction system, a temperature control system, and a sample collection system. The liquid phase delivery system includes three high-pressure pumps, which are used to deliver deionized water, precursor solution, and auxiliary agent solution, respectively. The sample collection system includes a water cooling device, a filter, and a back pressure valve.

3. The method according to claim 1, characterized in that, The reaction system includes two sets of electric heating devices. The large heating device is used to heat the high-pressure deionized water to a supercritical state, and the small heating device is used to maintain the temperature of the reaction outlet section and extend the reaction contact time.

4. The method according to claim 1, characterized in that, The Ag-doped nano-In2O3 powder was centrifuged and washed six times, each time using ultrapure water as the washing solution to remove residual ions and unreacted precursors.

5. The method according to claim 1, characterized in that, The freeze-drying step includes: first in... Freeze at 20 degrees Celsius for 4 hours, then... Dry at 50 degrees Celsius and under low pressure for 24 hours.

6. An Ag-doped nano-In₂O₃ ozone sensing material, characterized in that, The material consists of an In2O3 lattice and doped Ag ions, which are dissolved in the In2O3 lattice in the form of substitution for In sites. The molar fraction of Ag atoms is 0.5 to 5, and the average grain size is 10 to 50 nanometers.

7. The Ag-doped nano-In₂O₃ ozone sensing material according to claim 6, characterized in that, The material has a cubic bixbyite structure, and Ag ion doping increases the lattice constant by 0.1% to 0.3%.

8. The Ag-doped nano-In₂O₃ ozone sensing material according to claim 6, characterized in that, The material has a specific surface area of ​​50 to 120 square meters per gram and a response value of more than 200% to 100 to 300 micrograms per cubic meter of ozone gas at room temperature.

9. An ozone gas sensor constructed based on the Ag-doped nano-In₂O₃ material as described in claim 6, characterized in that, include: Conductive substrate, interdigitated electrodes, sensitive layer, and signal output circuit; The sensitive layer is formed by drop-coating Ag-doped nano-In2O3 powder. After curing at 70 degrees Celsius, it is tightly bonded to the interdigitated electrode to realize ozone gas adsorption and resistance change detection.

10. The ozone gas sensor according to claim 9, characterized in that, The thickness of the sensitive layer is 2 to 10 micrometers, the electrode spacing is 50 to 100 micrometers, the sensing response time is less than 5 seconds, and the recovery time is less than 15 seconds.

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