Ni-doped nano SnO2 semiconductor HCHO sensing material as well as preparation method and application thereof

Abstract

The invention discloses a Ni-doped nano SnO2 semiconductor HCHO sensing material as well as a preparation method and application thereof. The preparation method of the sensing material comprises the following steps: step 1, preparing a Sn salt-Ni salt solution; and 2, carrying out a contact reaction on the Sn salt-Ni salt solution and supercritical water by using a supercritical hydrothermal synthesis (CSHS) reaction device, crystallizing and separating out a nano doped oxide, discharging and collecting a reaction solution, cooling, and separating out a crystal substance, thereby obtaining the Ni-doped nano SnO2 semiconductor HCHO sensing material. The Ni-doped nano SnO2 semiconductor HCHO sensing material prepared by the method disclosed by the invention is good in structural consistency and excellent in sensing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of metal oxide semiconductor gas sensing materials, and particularly to a method for preparing Ni-doped nano-SnO2 semiconductor HCHO sensing materials using CSHS technology and its application. Technical Background

[0002] HCHO is a colorless organic compound with a pungent odor. When the concentration of HCHO is higher than 0.1 mg / m 3 3, long-term exposure will pose potential hazards to human health, and people pay much attention to low-concentration HCHO in indoor and other environments. However, low-concentration HCHO sensors often become poisoned and inactivated in high-concentration HCHO environments. And in some factories, there may be a risk of leakage of higher-concentration HCHO (above 1 mg / m 3 3), and HCHO alarms also need attention because higher-concentration HCHO can cause people in the environment to cough, gasp, and even die. Therefore, it is necessary to develop an HCHO sensor that can adapt to a higher concentration range, and the market prospect of such real-time monitoring sensing materials is huge.

[0003] Metal oxide semiconductor gas sensors have been widely used in the fields of environmental monitoring, pollution control, and safety warning due to their excellent sensing characteristics, easy integration advantages, and significant cost-effectiveness, and have become an important technical means for detecting toxic and harmful gases. However, in the application of real-time HCHO detection, this type of sensor has limitations such as insufficient stability and low selectivity. Based on this, developing HCHO gas sensing materials with excellent stability and high selectivity has become a key topic and research focus that urgently needs to be overcome in the field of environmental air detection technology. Summary of the Invention

[0004] Aiming at the above technical problems existing in the prior art, the purpose of the present invention is to provide a Ni-doped nano-SnO2 semiconductor HCHO sensing material, its preparation method, and its application.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A supercritical hydrothermal preparation method of a Ni-doped nano-SnO2 semiconductor HCHO sensing material, characterized by comprising the following steps:

[0007] 1) Prepare a precursor aqueous solution containing SnCl4 and NiCl2, denoted as Sn salt-Ni salt solution;

[0008] 2) Preparation is carried out using a CSHS reaction device. The Sn salt-Ni salt solution and ultrapure water described in step 1) are respectively transported by high-pressure delivery pumps, merged and premixed in a three-way joint, and then the Sn salt-Ni salt premixed solution and supercritical water at 450°C - 550°C transported under high pressure are merged into a four-way mixer for secondary mixing. After sufficient mixing, heating and insulation are carried out through an electric heating device, so that the SnCl4 / NiCl2 solution reacts rapidly after contacting the supercritical water, and nanodoped oxides are crystallized and precipitated. The reaction solution is discharged, collected, and cooled, and the crystallized substances are separated to obtain the Ni-doped nanosized SnO2 semiconductor HCHO sensing material.

[0009] Further, for a hydrothermal synthesis method of a Ni-doped nanosized SnO2 semiconductor HCHO sensing material as described in step 1), it is characterized in that in the Sn-Ni mixed solution prepared in step 1), the molar concentration of the Sn salt is 0.01 - 0.03 mol / L, and the molar concentration of the Ni salt is 0.1 - 5% of the molar concentration of the Sn salt, preferably 1%.

[0010] Further, for a hydrothermal synthesis method of a Ni-doped nanosized SnO2 semiconductor HCHO sensing material as described in step 1), it is characterized in that the Sn salt is SnCl4 and the Ni salt is NiCl2.

[0011] Further, for a hydrothermal synthesis method of a Ni-doped nanosized SnO2 semiconductor HCHO sensing material as described in step 2), it is characterized in that the specific operation of step 2) includes the following process:

[0012] Three high-pressure delivery pumps for liquid chromatography pump ultrapure water, precursor solution, and ultrapure water respectively at a certain flow rate at room temperature, and an initial pressure of more than 22 Mpa - 25 Mpa is given to the three pipelines. The first path of room-temperature high-pressure ultrapure water is merged into a three-way joint for primary mixing with the second path of room-temperature high-pressure Sn salt-Ni salt solution. At the same time, the third path of room-temperature high-pressure ultrapure water flows through the first set of electric heating devices and is heated to 450°C - 550°C to reach the supercritical state. Then the Sn salt-Ni salt solution and supercritical water are merged into a four-way mixer for secondary mixing. After sufficient mixing, it flows into the second set of electric heating devices, and the heating temperature remains at 450°C - 550°C. The SnCl4 / NiCl2 solution and supercritical water are allowed to react for more than 2 s. After the Sn salt-Ni salt solution contacts the supercritical water, it reacts rapidly and nanodoped oxides are crystallized and precipitated. The reaction solution flows out of the second set of electric heating devices, is collected, cooled, and filtered, and finally the Ni-doped nanosized SnO2 semiconductor HCHO sensing material is obtained.

[0013] Further, in the supercritical hydrothermal preparation method of a Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in step 2), it is characterized in that the volume flow ratio of the second path of room-temperature and high-pressure Sn salt-Ni salt solution to the first path of room-temperature and high-pressure ultrapure water is 1:1.8 - 2.5, preferably 1:2; the volume flow ratio of the second path of room-temperature and high-pressure SnCl4 / NiCl2 solution to the third path of room-temperature and high-pressure ultrapure water is 1:0.8 - 1.2, preferably 1:1.

[0014] Further, in the supercritical hydrothermal preparation method of a Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in step 2), it is characterized in that after the reaction, the nano-suspension is collected and sedimented for 12–24 h. After centrifugation and repeated washing with ultrapure water 4 - 6 times, it is frozen for 4 h using a freeze dryer, freeze-dried for 24 h, the powder is taken out, ground, placed in a glass container, the air in the bottle is exhausted using argon, and the mouth is sealed with adhesive tape for storage, obtaining nano-SnO2 semiconductor HCHO sensing material powders with different Ni doping contents.

[0015] Further, a HCHO sensor is prepared, which is characterized in that the HCHO sensor includes a substrate, a heating plate, interdigital electrodes, and a gas-sensitive material layer stacked in sequence, and the gas-sensitive material layer includes a Ni-doped nano-SnO2 semiconductor HCHO sensing material of the present invention.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) The CSHS technology is very suitable for preparing various nano-metal oxides because it can precisely control reaction parameters such as reaction temperature, reaction pressure, reaction time, and pH value. In a high-temperature and high-pressure environment, materials usually finally form in the most stable state. Therefore, each batch of materials prepared has highly uniform physical and chemical properties, including microscopic morphology, particle size, crystal plane, etc. Due to these similar microscopic properties, in terms of macroscopic sensing performance, the stability of the resistance value and response value of these materials is very excellent, and the life of the prepared sensor is relatively long, which makes it have extremely high application value in the field of gas detection. In addition, by skillfully introducing a trace amount of Ni element during the synthesis process, doping and modification of the nano-SnO2 semiconductor material are carried out, and the test temperature is adjusted, which can greatly improve the HCHO sensing performance of the SnO2 semiconductor material and show a better application prospect in the field of air quality control.

[0018] (2) The supercritical hydrothermal preparation method of the Ni-doped nano-SnO2 semiconductor HCHO sensing material of the present invention has not only achieved a breakthrough in technology, but also demonstrated excellent performance in practical applications. Through experimental verification, the Ni-doped nano-SnO2 material of the present invention is particularly suitable for the detection of higher concentrations of HCHO (1 mg / m 3 or more), and has a high response value in the detection.

[0019] Another major highlight of the CSHS technology is that it makes full use of the unique properties of supercritical water and can achieve continuous preparation for 24 hours without interruption. This means a significant improvement in production efficiency and meets the requirements of modern industry for high-efficiency production. From an economic perspective, the production cost of the CSHS technology is also relatively low, which has inestimable value for promoting its industrialization process and realizing large-scale production. More importantly, no acids, alkalis, or organic ligands are used as precipitants or pH regulators in this preparation method, which has the characteristics of being green and energy-saving. At the same time, due to the precise control of reaction conditions and the ability of continuous preparation, the quality and yield of the materials have been significantly improved simultaneously, which is of great significance for meeting market demand and promoting the industrialization process.

[0020] In summary, by introducing the CSHS technology and skillfully applying it to the preparation of nano-SnO2 semiconductor HCHO sensing materials, the present invention has not only achieved controllability, high efficiency, and greenness in the preparation process, but also significantly improved the sensing performance and application value of the materials, injecting new vitality into the development of materials science and sensor technology, and providing more reliable technical support for fields such as environmental monitoring and air quality control. Brief Description of the Drawings

[0021] Figure 1 : Schematic diagram of the CSHS device.

[0022] Figure 2 : Response curve of the 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material in Example 1 tested at 50°C - 200°C for 8 ppm HCHO; test conditions: HCHO concentration: 8 ppm, O2 concentration: 20%, N2 as the supplementary gas, total flow rate: 3 L / min, reaction temperature 50°C - 200°C.

[0023] Figure 3 : Response-recovery curve of the 0.1 - 5% Ni-doped nano-SnO2 semiconductor HCHO sensing material in Examples 1 - 2 tested at 175°C for 8 ppm HCHO; test conditions: HCHO concentration: 8 ppm, O2 concentration: 20%, N2 as the supplementary gas, total flow rate: 3 L / min, reaction temperature 175°C.

[0024] Figure 4: The sensor response value of the 0.1-5% Ni-doped nano-SnO2 semiconductor HCHO sensor material in Example 1-2 to 8ppm HCHO at 175°C; test conditions: HCHO concentration: 8ppm, O2 concentration: 20%, N2 as supplementary gas, total flow rate: 3L / min, reaction temperature 175°C.

[0025] Figure 5 : Sensing response recovery curve of 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material in Example 1 tested at 175°C for 1-8ppm HCHO; test conditions: HCHO concentration: 8ppm, O2 concentration: 20%, N2 as supplementary gas, total flow rate: 1L / min, reaction temperature 175°C.

[0026] Figure 6 : The stability test results of the 1% Ni-doped nano-SnO2 semiconductor HCHO sensor material in Example 1 in response to 8ppm HCHO at 175°C; test conditions: HCHO concentration: 8ppm, O2 concentration: 20%, N2 as supplementary gas, total flow rate: 3L / min, reaction temperature 175°C.

[0027] Figure 7 : The selective response results of the 1% Ni-doped nano-SnO2 semiconductor HCHO sensor material to five test gases at 175°C in Example 1; Test conditions: each gas concentration: 8ppm, O2 concentration: 20%, N2 as supplementary gas, total flow rate: 3L / min, reaction temperature 175°C.

[0028] Figure 8 The sensor response values ​​of the 1% Ni-doped nano-SnO2 semiconductor HCHO sensor material in Example 1 and the 1% antimony (Sb)-doped nano-SnO2 semiconductor HCHO sensor material in Example 3 to 5-20ppm HCHO test; test conditions: HCHO concentration: 5-20ppm, O2 concentration: 20%, N2 as supplementary gas, total flow rate: 3L / min, reaction temperature 175°C.

[0029] Figure 9 : XRD patterns of nano-SnO2 semiconductor HCHO sensing materials doped with different contents of Ni in Example 1 and Example 2.

[0030] The Ni-doped nano SnO2 semiconductor HCHO sensing material prepared in the present invention is an N-type semiconductor. For an N-type semiconductor, the sensitivity S is defined as the ratio of the resistance value (Ra) of the gas sensor element in clean air to the resistance value (Rg) in the target gas, that is, S=Ra / Rg.

[0031] $R_a$ is the resistance value of the device after being stabilized in clean air, and $R_g$ is the resistance value of the device after being stabilized in the gas to be measured; the response time is the time required for the device resistance value to change by 90% during the response stage, and the recovery time is the time required for the device resistance to change by 90% during the recovery stage. Detailed implementation manners

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. On the contrary, the present invention covers any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present invention defined by the claims. Further, in order to enable the public to have a better understanding of the present invention, in the following detailed description of the present invention, some specific details are described in detail. Those skilled in the art can also fully understand the present invention without the description of these details.

[0033] Embodiment 1

[0034] A supercritical hydrothermal preparation method of a Ni-doped nano-SnO₂ semiconductor HCHO sensing material, comprising the following steps:

[0035] Step 1: Dissolve a certain amount of SnCl₄ and NiCl₂ in ultrapure water to prepare an aqueous solution with a molar concentration of SnCl₄ of 0.02 mol / L and a molar concentration of NiCl₂ of 0.0002 mol / L, and stir it at a speed of 600 r / min for 30 min to obtain a SnCl₄ / NiCl₂ solution. The molar concentration of NiCl₂ is 1% of the molar concentration of SnCl₄.

[0036] Step 2: Use a CSHS reaction device to synthesize and prepare a 1% Ni-doped SnO₂ semiconductor HCHO sensing material. 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, as Figure 1 shown.

[0037] Liquid-phase delivery system: It consists of three identical high-pressure delivery pumps for liquid chromatography and corresponding liquid-phase pipelines and adapters, which are respectively used to deliver ultrapure water, SnCl₄ / NiCl₂ solution, and ultrapure water.

[0038] Reaction system: It consists of two sets of electric heating devices and corresponding liquid-phase pipelines and adapters. The electric heating device (large) is used to heat normal-temperature high-pressure ultrapure water to 450 °C to make it reach the supercritical state. The electric heating device (small) is used to keep the straight pipe section at the outlet of the mixer warm to ensure that the contact time between the SnCl₄ / NiCl₂ solution and supercritical water at 450 °C is more than 2 s.

[0039] Temperature control system: Control two sets of electric heating devices to increase the temperature in a programmed manner and stabilize the temperature above 450 °C.

[0040] Sample collection system: Composed 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.

[0041] Process of preparing 1% Ni-doped SnO2 semiconductor HCHO sensing material using the CSHS device: Three high-pressure delivery pumps for liquid chromatography pump ultrapure water, SnCl4 / NiCl2 solution, and ultrapure water at 20 mL / min, 10 mL / min, and 10 mL / min respectively at room temperature, and apply an initial pressure of 23 Mpa to the three pipelines. Rely on the back pressure valve at the end of the system to maintain the internal pressure stability of the whole system. The room-temperature high-pressure ultrapure water and the room-temperature high-pressure SnCl4 / NiCl2 solution are mixed for the first time in a three-way joint. At the same time, the room-temperature high-pressure ultrapure water flows through the large electric heating device and is heated to 450 °C to reach the supercritical state. Then the SnCl4 / NiCl2 solution and the supercritical water are mixed for the second time in a four-way mixer. After sufficient mixing, it flows into the small electric heating device, and the temperature still remains at 450 °C. And make the SnCl4 / NiCl2 solution and the supercritical water contact sufficiently at 450 °C for more than 2 s to react. After the SnCl4 / NiCl2 solution contacts the supercritical water, it reacts rapidly and crystallizes and precipitates to generate nano-oxides. After the reaction solution flows out of the small electric heating device, it enters the sample collection system, undergoes cooling, pressure relief, and collection to obtain a suspension of 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material.

[0042] Step 3: After the reaction is completed, collect and sediment the nano-suspension for 12 h. After centrifugation and repeated washing with ultrapure water 6 times, use a freeze dryer to freeze at -70 °C for 4 h and dry for 24 h. Take out the powder, grind it and place it in a glass container. Use argon to exhaust the air in the bottle, and seal the mouth with adhesive tape to obtain the powder of 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material.

[0043] Step 4: Weigh 100 mg of the 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material powder obtained in Step 3 using an analytical balance, measure 500 μL of ultrapure water using a pipette, place them in a sample tube, mix evenly. Use a pipette to suck 2.5 μL of the mixed solution and drop it on the interdigitated electrode sheet on the gold substrate. The interdigitated spacing and the interdigitated width are both 200 μm. After drying on a 70 °C heating table and standing for 30 min, the coating thickness after drying is about 50 μm to obtain a pole piece that can be used to test the HCHO sensing performance, which is the gas sensor.

[0044] Example 2

[0045] Supercritical hydrothermal preparation of nano-SnO2 semiconductor HCHO sensing materials with Ni doping amounts of 0.1%, 0.5%, 3% and 5% respectively. The preparation method steps are repeated as in Example 1, with the difference only being that "in the preparation process of the SnCl4 / NiCl2 solution in Step 1, the molar concentration of NiCl2 in the solution is adjusted to 0.00002 mol / L, 0.0001 mol / L, 0.0006 mol / L and 0.001 mol / L respectively, so that the molar concentration of NiCl2 is 0.1%, 0.5%, 3% and 5% of the molar concentration of SnCl4", and the other conditions remain unchanged. Finally, SnO2 semiconductor HCHO sensing materials doped with 0.1%, 0.5%, 3% and 5% Ni are obtained respectively.

[0046] Example 3

[0047] Preparation of 1% Sb-doped nano-SnO2 semiconductor HCHO sensing material. The preparation method is repeated as in Example 1, with the difference only being that "in the preparation process of the SnCl4 / NiCl2 solution in Step 1, NiCl2 is replaced with SbCl3 of the same molar concentration", and the other conditions remain unchanged. Finally, 1% Sb-doped nano-SnO2 semiconductor HCHO sensing material is obtained.

[0048] The HCHO sensing materials prepared in Examples 1-3 are respectively made into gas sensors according to the method in Step 4 of Example 1, and relevant gas sensing performance tests are carried out on HCHO gas:

[0049] As Figure 2 shown, the performance of the 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material is significantly improved at 175 °C and is similar to that at 200 °C. Considering the low-temperature principle, it is considered that it has the optimal response performance for 8 ppm HCHO at 175 °C.

[0050] As Figure 3 shown, for the 0.1–5% Ni-doped nano-SnO2 semiconductor HCHO sensing materials at 175 °C, the response and recovery times for 8 ppm HCHO are both less than 50 s, and their HCHO sensing performance is excellent.

[0051] As Figure 4 shown, for the 0.1–5% Ni-doped nano-SnO2 semiconductor HCHO sensing materials in Example 1 at 175 °C for the sensing response value of 8 ppm HCHO, when the Ni doping amount is 1%, the performance is optimal.

[0052] As Figure 5 ​As shown, the 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material in Example 1 exhibits excellent sensing performance. As the concentration of HCHO gas increases, the sensitivity of the sensing material in Example 1 increases significantly, and there is a good linear growth relationship between the sensitivity and the concentration.

[0053] As Figure 6 shown, the 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material in Example 1 exhibits excellent stability. The response value remains at about 8.2, the response time is about 56 s, and the recovery time is about 215 s. After continuous testing, the response value to HCHO does not show obvious fluctuations.

[0054] As Figure 7 shown, the 1% Ni-doped nano-SnO2 semiconductor HCHO sensing material in Example 1 exhibits excellent gas selectivity.

[0055] As Figure 8 shown, two kinds of doped materials of SnO2 with 1% Ni and 1% Sb were prepared and their performances were compared. The results show that when testing 5–20 ppm HCHO, the response value of the Ni-doped SnO2 material to HCHO is about 4 times that of the Sb-doped SnO2 material.

[0056] As Figure 9 shown, there are no impurity peaks of other phases in the XRD patterns of the nano-SnO2 semiconductor HCHO sensing materials with different Ni doping contents in Example 1 and Example 2, which is consistent with the standard card. The space group is p42mm, and each peak can point to the tetragonal phase of SnO2. It can be seen that the crystal form of the material prepared by the supercritical hydrothermal technology is very uniform, and its crystal planes are the stable (101) and (110) crystal planes, which is also related to its stable performance to a certain extent. According to the Scherrer formula, the average particle size of the prepared material is about 5 nm.

Claims

1. A supercritical hydrothermal preparation method of Ni-doped nano-SnO2 semiconductor HCHO sensing material, characterized in that, It includes the following steps: 1) Prepare an aqueous precursor solution containing tin (Sn) salt and Ni salt, denoted as the Sn salt-Ni salt solution; 2) Use a CSHS reaction device for preparation. The Sn salt-Ni salt solution and ultrapure water in step 1) are respectively transported by high-pressure delivery pumps, merged and premixed in a three-way joint, and then the Sn salt-Ni salt premixed solution and supercritical water at 450 °C–550 °C transported under high pressure are merged into a four-way mixer for secondary mixing. After sufficient mixing, it is heated and kept warm by an electric heating device, so that the Sn salt-Ni salt solution reacts rapidly after contacting with supercritical water, and nanodoped oxides are crystallized and precipitated. After the reaction solution is discharged and collected, it is cooled, and the crystals are separated to obtain the Ni-doped nano-SnO2 semiconductor HCHO sensing material.

2. The supercritical hydrothermal preparation method of a Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in claim 1, characterized in that, In the Sn-Ni mixed solution prepared in step 1), the molar concentration of the Sn salt is 0.01-0.03 mol / L, and the molar concentration of the Ni salt is 0.1-5% of the molar concentration of the Sn salt, preferably 1%.

3. The supercritical hydrothermal preparation method of a Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in claim 1, characterized in that, The Sn salt is tin tetrachloride SnCl4, and the Ni salt is nickel dichloride NiCl2.

4. The hydrothermal preparation method of a Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in claim 1, characterized in that, The specific operation of step 2) includes the following process: Three high-pressure delivery pumps for liquid chromatography pump ultrapure water, precursor solution, and ultrapure water at a certain flow rate at room temperature, and an initial pressure of 22 Mpa–25 Mpa or more is given to the three pipelines. The first-way ultrapure water at room temperature and high pressure is merged into a three-way joint for primary mixing with the second-way Sn salt-Ni salt solution at room temperature and high pressure. At the same time, the third-way ultrapure water at room temperature and high pressure flows through the first set of electric heating devices and is heated to 450 °C-550 °C to reach the supercritical state. Then the Sn salt-Ni salt solution and supercritical water are merged into a four-way mixer for secondary mixing. After sufficient mixing, it flows into the second set of electric heating devices, and the heating temperature remains at 450 °C-550 °C, and the Sn salt-Ni salt solution and supercritical water are allowed to contact sufficiently for more than 2 s for reaction. After the Sn salt-Ni salt solution contacts with supercritical water, it reacts rapidly and nanodoped oxides are crystallized and precipitated. After the reaction solution flows out of the second set of electric heating devices, it is collected, cooled, and filtered. Finally, the Ni-doped nano-SnO2 semiconductor HCHO sensing material is obtained.

5. The supercritical hydrothermal preparation method of a Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in claim 4, characterized in that, The volume flow ratio of the second-way Sn salt-Ni salt solution at room temperature and high pressure to the first-way ultrapure water at room temperature and high pressure is 1:1.8–2.5, preferably 1:2; the volume flow ratio of the second-way Sn salt-Ni salt solution at room temperature and high pressure to the third-way ultrapure water at room temperature and high pressure is 1:0.8–1.2, preferably 1:

1.

6. The hydrothermal preparation method of Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in claim 4, characterized in that After the reaction, the nano-suspension is collected and sedimented for 12–24 h. After centrifugation and washing are repeated 4-6 times, it is freeze-dried. The powder is taken out, ground, placed in a glass container, and the air in the bottle is exhausted with argon, and the mouth is sealed with a sealing tape for storage to obtain Ni-doped nano-SnO2 semiconductor HCHO sensing material powder with different contents of Ni.

7. A Ni-doped nano-SnO2 semiconductor HCHO sensing material prepared by the method according to any one of claims 1–6.

8. A HCHO sensor, characterized in that, The HCHO sensor includes a substrate, a heating plate, interdigital electrodes, and a gas-sensitive material layer that are sequentially stacked. The gas-sensitive material layer includes a Ni-doped nano-SnO2 semiconductor HCHO sensing material as described in Claim 7.

9. Use of an HCHO sensor as described in claim 8, characterized in that, It is used to detect HCHO in the gas.

10. The application according to claim 9, characterized in that The concentration of HCHO in the gas to be measured is 1 ppm or more, preferably 1–10 ppm.

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