A HEOs / SnO2 nanocomposite material and a gas sensor based thereon

Abstract

This invention discloses a HEOs / SnO2 nanocomposite material and a gas sensor based thereon. The preparation method is as follows: HEOs (high entropy oxide) powder is prepared by solvothermal reaction and high-temperature calcination using manganese(II), iron(III), cobalt(III), nickel(II), and copper(II) acetylacetone as precursors; the HEOs powder is then ultrasonically combined with SnO2 powder to obtain the HEOs / SnO2 nanocomposite material. The gas sensor of this invention uses the HEOs / SnO2 nanocomposite material as the gas-sensitive material, effectively solving the technical problems of low response and poor selectivity in traditional metal oxide sensors. At a relatively low operating temperature of 130℃, the response value to 0.5 ppm nitrogen dioxide can reach 747 (R0). g / R a It combines high responsiveness, strong selectivity and excellent stability, and has great application potential in the field of low temperature and low concentration NO2 monitoring.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, specifically relating to an HEOs / SnO2 nanocomposite material and a gas sensor based thereon. Background Technology

[0002] With the rapid development of society and economy and the continuous improvement of people's living standards, ambient air quality monitoring has received increasing attention, among which the accurate monitoring of toxic and harmful gases is becoming increasingly important. Nitrogen oxides (NOx) x ), sulfur oxides (SO x Ozone (O3) and other major air pollutants can cause serious harm to human health and the ecological environment if exposed to them for a long time. Among them, nitrogen dioxide (NO2) has become a key target in the field of gas monitoring due to its wide range of sources and high toxicity.

[0003] NO2 emissions come from diverse sources, including not only major pollutants such as vehicle exhaust and industrial production activities, but also low-concentration but persistent NO2 releases from residential gas combustion, cooking processes, and the volatilization of indoor decoration materials. This gas not only triggers or exacerbates asthma and other respiratory diseases, harming human respiratory health, but also participates in the formation of ground-level ozone and photochemical smog, disrupting the ecological balance and posing a serious challenge to human health, safety, and sustainable development. Therefore, developing inexpensive, highly sensitive, and highly stable NO2 gas sensors to achieve accurate monitoring of low-concentration NO2 is of significant practical importance and application value for protecting human health and improving environmental quality.

[0004] A gas sensor is an electrical signal converter that transforms the concentration information of a target gas into a detectable electrical signal through physical or chemical processes. Currently, various sensing technologies are applied to NO2 gas detection, including optical sensing, electrochemical sensing, absorption spectroscopy, and resistive sensing. Among these technologies, resistive gas sensors based on metal oxides have been widely researched and applied in the field of NO2 detection due to their outstanding advantages, such as high sensitivity (capable of detecting gases at the ppb to ppm level), low manufacturing cost, small size, fast response speed, and good stability.

[0005] To further improve the performance of metal oxide resistive sensors, researchers have developed various metal semiconductor oxide gas-sensitive materials, including n-type semiconductor oxides (such as In₂O₃ and SnO₂) and p-type semiconductor oxides (such as NiO and CuO). However, existing NO₂ sensors based on single metal oxides still have significant technical shortcomings, making it difficult to meet practical application requirements: First, they have poor selectivity and are easily affected by interfering gases coexisting in the environment, such as methane (CH₄), hydrogen (H₂), and carbon monoxide (CO), leading to a decrease in detection accuracy; second, their response values ​​to low concentrations of NO₂ are low, and the response recovery speed is slow, making it impossible to achieve rapid and accurate detection of low concentrations of NO₂; third, some sensors require higher operating temperatures to achieve effective detection, increasing equipment power consumption and failure rate.

[0006] To address the shortcomings of the existing technologies, developing a sensor based on novel metal oxide composite materials that possesses high responsivity, strong selectivity, and excellent stability, and can achieve efficient detection of low-concentration NO2, has become a key technological challenge that urgently needs to be overcome in the field of gas-sensitive materials and devices. Summary of the Invention

[0007] The purpose of this invention is to provide a HEOs / SnO2 nanocomposite material and a gas sensor based thereon, so as to solve the shortcomings of existing nitrogen dioxide gas sensors based on simple oxides, such as high operating temperature, poor selectivity and stability.

[0008] To achieve its objectives, the present invention employs the following technical solution: This invention first discloses a method for preparing HEOs / SnO2 nanocomposite materials, comprising the following steps: Step 1: Using manganese acetylacetone (II), iron acetylacetone (III), cobalt acetylacetone (III), nickel acetylacetone (II), and copper acetylacetone (II) as raw materials, an intermediate product is first obtained through a solvothermal method. Then, the intermediate product is calcined at high temperature to obtain high-entropy oxide powder, i.e., HEOs powder. The specific operation method is as follows: Manganese acetylacetone (II), iron acetylacetone (III), cobalt acetylacetone (III), nickel acetylacetone (II), and copper acetylacetone (II) are each mixed at 5 × 10⁻⁶... -3 ~8×10 -3 Add M to the reaction vessel, mix ethanol and acetone at a volume ratio of 1:1 to 3 and add to the reaction vessel. React at a constant temperature of 180 to 200°C in an air-atmosphere oven for 12 to 18 hours. After the reaction is completed, allow it to cool naturally to room temperature, open the reaction vessel and filter. Dry the filtered product under vacuum at 40 to 60°C for 10 to 12 hours. Finally, place the dried powder in a tube furnace under an air-atmosphere atmosphere and calcine at a constant temperature of 600 to 800°C for 2 to 4 hours to obtain HEOs powder.

[0009] Step 2: HEOs powder and SnO2 powder are ultrasonically mixed, allowed to stand, filtered, and dried to obtain HEOs / SnO2 nanocomposite materials. The specific procedure is as follows: 0.0003–0.006 g of HEOs powder and 0.097–0.094 g of SnO2 powder are added to 30–50 mL of water, ultrasonically treated for 1–3 hours, then allowed to stand for 10–14 hours. The product is then filtered and vacuum-dried at 40–60°C for 10–12 hours to obtain the HEOs / SnO2 nanocomposite material. The mass percentage of HEOs in the obtained HEOs / SnO2 nanocomposite material is controlled by adjusting the amounts of HEOs powder and SnO2 powder.

[0010] This invention also discloses the application of the HEOs / SnO2 nanocomposite material prepared according to the above method in a gas sensor. This gas sensor uses the HEOs / SnO2 nanocomposite material as the gas-sensitive material for the detection of nitrogen dioxide gas. The preparation method of this sensor is as follows: the HEOs / SnO2 nanocomposite material is ultrasonically dispersed uniformly in ethanol to obtain an HEOs / SnO2 slurry; the HEOs / SnO2 slurry is then coated onto the surface of an interdigitated electrode using a drop-coating method to obtain the gas sensor.

[0011] Compared with the prior art, the beneficial effects of the present invention are that it provides a sensor with high response and high selectivity, and the ability to detect low concentrations of NO2 gas, specifically in the following aspects: (1) The method of synthesizing HEOs / SnO2 nanocomposite material of the present invention is simple to operate and low in cost. Moreover, the nanocomposite material prepared has relatively uniform bonding between the components and has excellent performance.

[0012] (2) In the nanocomposite material synthesized in this invention, by controlling the combination of trace amounts of HEOs and SnO2, the performance of the gas sensor based on the composite material is significantly improved, overcoming the disadvantage of low response of single oxides to NO2.

[0013] (3) In view of the fact that existing nitrogen dioxide gas sensors mostly use a single oxide as the gas-sensitive sensing layer and can only achieve effective detection at a high operating temperature, which leads to increased power consumption, higher failure rate, and poor selectivity and stability, the HEOs / SnO2 nanocomposite material provided by the present invention can enable the gas sensor to operate stably at a lower operating temperature. This not only reduces power consumption and failure rate, but also further improves the selectivity and stability of the sensor, showing great application potential in the field of low temperature and low concentration NO2 monitoring. Attached Figure Description

[0014] Figure 1The images shown are scanning electron microscope (SEM) images of (a) pure SnO2 powder and (b) 1 wt% HEOs / SnO2 nanocomposite material in the embodiments of the present invention.

[0015] Figure 2 The X-ray diffraction (XRD) patterns of the synthesized materials in this embodiment are as follows: (a) is the XRD pattern of HEOs powder; (b) is the XRD pattern of pure SnO2 and 0.3 wt%, 0.6 wt%, 1 wt%, 3 wt%, and 6 wt% HEOs / SnO2 nanocomposites.

[0016] Figure 3 This is a schematic diagram of the structure of the interdigitated electrode and the gas sensor coated with HEOs / SnO2 nanocomposite material in an embodiment of the present invention.

[0017] Figure 4 The images show the response curves of a sensor based on a single-component SnO2 and different HEOs loadings (0.3 wt%, 0.6 wt%, 1 wt%, 3 wt%, 6 wt%) HEOs / SnO2 nanocomposite materials to 0.5 ppm NO2 at different temperatures in embodiments of the present invention.

[0018] Figure 5 This is a response-recovery curve of a sensor based on a single component SnO2 constructed in an embodiment of the present invention at 130°C for 0.5 ppm NO2.

[0019] Figure 6 The image shows the response-recovery curve of the sensor constructed based on 1 wt% HEOs / SnO2 nanocomposite material in this embodiment of the invention at 130°C to 0.5 ppm NO2.

[0020] Figure 7 This is a dynamic response diagram of a sensor based on 1 wt% HEOs / SnO2 nanocomposite material in an embodiment of the present invention to 0.1~0.3 ppm NO2 at 130℃.

[0021] Figure 8 This is a dynamic response diagram of a sensor based on 1 wt% HEOs / SnO2 nanocomposite material in an embodiment of the present invention to 0.5~10 ppm NO2 at 130℃.

[0022] Figure 9 This is a repeatability response diagram of the sensor based on 1 wt% HEOs / SnO2 nanocomposite material in an embodiment of the present invention to 0.5 ppm NO2 at 130°C.

[0023] Figure 10This is a test curve of 0.5 ppm NO2 by a sensor based on 1 wt% HEOs / SnO2 nanocomposite material in an embodiment of the present invention at different humidity and 130℃.

[0024] Figure 11 This is a bar chart showing the selectivity test of a sensor based on 1 wt% HEOs / SnO2 nanocomposite material for different gases at 130°C in an embodiment of the present invention.

[0025] Figure 12 This is a graph showing the response differences of four different sensors based on 1 wt% HEOs / SnO2 nanocomposite material to 0.5 ppm NO2 at 130°C in an embodiment of the present invention.

[0026] Figure 13 This is a graph showing the long-term stability test of the sensor based on 1 wt% HEOs / SnO2 nanocomposite material in an embodiment of the present invention. Detailed Implementation

[0027] To more clearly illustrate the purpose, features, and advantages of this invention, the synthesis method of the HEOs / SnO2 nanocomposite material and the fabrication and gas-sensing testing of a gas sensor based on this material will be described in detail below with reference to illustrations and implementation examples. The following content is merely an example and explanation of the innovative ideas of this invention. Any modifications, additions, or similar alternatives made by those skilled in the art to the specific implementation, as long as they do not deviate from the innovative ideas or exceed the limits defined by this invention, should be considered within the scope of protection of this invention.

[0028] Example 1 In this embodiment, HEOs / SnO2 nanocomposite materials were prepared according to the following steps: 1. Preparation of HEOs powder: Manganese acetylacetone (II), iron acetylacetone (III), cobalt acetylacetone (III), nickel acetylacetone (II), and copper acetylacetone (II) were each 5 × 10⁻⁶ -3 The concentration of M was added to the reaction vessel. Ethanol and acetone were mixed at a volume ratio of 1:1 and added to the reaction vessel. The mixture was then reacted at a constant temperature of 200°C for 12 hours in an oven under air atmosphere. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The reaction vessel was then opened for filtration. The filtered product was dried in a vacuum drying oven at 60°C for 12 hours. Finally, the dried powder was placed in a tube furnace under air atmosphere and calcined at a constant temperature of 600°C for 2 hours to obtain HEOs powder.

[0029] 2. Preparation of HEOs / SnO2 nanocomposites: 0.1 g of HEOs powder and SnO2 powder were added to 30 mL of water, sonicated for 1 hour, and then allowed to stand for 12 hours. The product was then filtered and dried in a vacuum oven at 60°C for 12 hours to obtain HEOs / SnO2 nanocomposite materials. The amount of HEOs powder was controlled to be 0.0003 g, 0.0006 g, 0.001 g, and 0.003 g, respectively, and the resulting composite materials were 0.3 wt% HEOs / SnO2, 0.6 wt% HEOs / SnO2, 1 wt% HEOs / SnO2, 3 wt% HEOs / SnO2, and 6 wt% HEOs / SnO2, respectively.

[0030] Figure 1 These are scanning electron microscope (SEM) images of (a) pure SnO2 powder and (b) a 1 wt% HEOs / SnO2 nanocomposite material in this embodiment. As can be seen from the images, both samples exhibit a coral-like porous morphology formed by the aggregation of nanoparticles. The primary particle size is approximately 20–50 nm, and the overall particle size and pore distribution are uniform, without obvious dense masses or abnormally large grains, indicating a loose structure. Comparing (a) and (b), it can be found that compared to pure SnO2, the overall morphology of the sample did not change significantly after incorporating 1 wt% HEOs. This is mainly attributed to the extremely low amount of HEOs added, which did not significantly affect the bulk growth process of SnO2.

[0031] Figure 2 The X-ray diffraction (XRD) patterns of the materials synthesized in this embodiment are as follows: (a) is the XRD pattern of HEOs powder, whose characteristic diffraction peaks are basically consistent with the characteristic peaks of the standard card CuMn2O4 (PDF #84-0543), indicating that the target high-entropy oxide was successfully prepared; (b) are the XRD patterns of pure SnO2 and 0.3 wt%, 0.6 wt%, 1 wt%, 3 wt%, and 6 wt% HEOs / SnO2 nanocomposites. It can be seen that the diffraction peaks of all composite materials are dominated by the characteristic peaks of SnO2, and no obvious HEOs characteristic peaks appear. This is because the content of HEOs in the composite materials is low, below the detection limit of XRD, and therefore cannot be clearly observed in the spectrum.

[0032] 3. Preparation of HEOs / SnO2 nanocomposite gas sensor: 10 mg of HEOs / SnO2 powder was dissolved in 20 μL of ethanol, and the mixture was sonicated for 25 min to obtain a uniform HEOs / SnO2 slurry. The HEOs / SnO2 slurry was pipetted and uniformly drop-coated onto the surface of the interdigitated electrode. After standing, it was dried in a vacuum drying oven at 70℃ for 6 h to obtain the gas sensor. Figure 3This is a schematic diagram of the structure of the interdigitated electrode and the gas sensor coated with HEOs / SnO2 nanocomposite material in this embodiment.

[0033] Take 10 mg of SnO2 powder and prepare a gas sensor using the same method as described above as a comparison.

[0034] 4. Gas Sensitivity Test The gas-sensing performance was tested using a multi-channel dynamic gas detector. The dynamic gas mixing system was equipped with five mass flow meters of different ranges. High-purity dry air was used as the background gas, and different concentrations of gas could be mixed by automatically adjusting the flow rate ratio of each gas path. The resistance changes of the gas-sensing element within the test chamber were then acquired in real time using a Keithley 2612B source meter. The responsivity of the tested sensor was defined as S = R. g / R a , where R a and R g These represent the room temperature resistance of the gas sensor exposed to air and the target gas, respectively. Response time / recovery time is the time it takes for the sensor to recover from its initial / saturated state to 90% of its total resistance change during the response / recovery process. The target gas used in the gas-sensing performance tests was always dry.

[0035] (1) Different operating temperatures (T) w Response performance test under ) To investigate the optimal addition amount of HEOs and the optimal operating temperature of the sensor, the response performance of gas sensors based on single-component SnO2 and different HEOs loadings (0.3 wt%, 0.6 wt%, 1 wt%, 3 wt%, 6 wt%) HEOs / SnO2 nanocomposites was tested within a temperature range of 100–170 °C (directly heated via a hot-cold stage) for 0.5 ppm NO2. The results are as follows: Figure 4 As shown, the response values ​​of all sensors exhibit a typical "volcano-shaped" relationship with operating temperature: the response value first increases and then decreases with increasing temperature, with an optimal operating temperature at which the response reaches its peak. Among them, the 1 wt% HEOs / SnO2 sensor has the highest response value for 0.5 ppm NO2 at 130℃, which is the optimal value among all samples. Therefore, this temperature was used as the operating temperature for subsequent tests.

[0036] (2) Comparison of gas-sensing performance between pure SnO2 and 1 wt% HEOs / SnO2 To verify the performance enhancement effect of trace HEOs composites on SnO2-based sensors, the response-recovery curves of sensors based on pure SnO2 and 1 wt% HEOs / SnO2 were tested at 130℃ and 0.5 ppm NO2 (e.g., Figure 5 , Figure 6 As shown): The response value R of the pure SnO2 sensor g / R a The response time and recovery time are 1866 s and 263 s, respectively; the response value R of the 1% HEOs / SnO2 sensor is 23. g / R a The response time was 747, and the recovery time was 142 s and 60 s, respectively. These results indicate that the introduction of trace amounts of HEOs significantly improved the sensitivity of the SnO2-based sensor to NO2 and substantially shortened the response / recovery time.

[0037] (3) Detection performance of low concentration NO2 (0.1~0.3 ppm) To evaluate the sensor's ability to detect trace NO2, the dynamic response of a 1 wt% HEOs / SnO2 sensor to 0.1 ppm, 0.2 ppm, and 0.3 ppm NO2 at 130℃ was tested (e.g., ...). Figure 7 As shown in the figure). The results show that when the NO2 concentration is as low as 0.1 ppm, the sensor's response value (R) is... g / R a The value remains as high as 130, indicating that it has excellent detection sensitivity for ppb-level NO2 and can meet the needs of low-concentration NO2 monitoring.

[0038] (4) Wide concentration range response performance (0.5~10 ppm) The dynamic response of the 1 wt% HEOs / SnO2 sensor to 0.5–10 ppm NO2 at 130 °C was further tested (e.g., Figure 8 (As shown in the figure). The results show that the sensor's response value is significantly positively correlated with the increase of NO2 concentration, exhibits a good response gradient within the test concentration range, and has the ability to detect NO2 at different concentrations.

[0039] (5) Repeatability testing The 1 wt% HEOs / SnO2 sensor was subjected to seven consecutive response-recovery cycles at 130℃ and 0.5 ppm NO2. The results are as follows: Figure 9 As shown, the sensor's response value showed no significant decay during multiple cycles, and the curve repeatability was good, indicating that the sensor has excellent operational stability and repeatability.

[0040] (6) Moisture resistance test To evaluate the impact of ambient humidity on sensor performance, the response performance of a 1 wt% HEOs / SnO2 sensor to 0.5 ppm NO2 at 130℃ was tested under relative humidity conditions of 11%, 25%, 33%, 57%, and 86%. Figure 10(As shown in the figure). The results show that the sensor response value decreases slightly with increasing humidity. This is because water molecules compete with NO2 for adsorption sites on the material surface in high humidity environments, while diluting the concentration of the target gas and weakening the response to NO2. However, at 86% humidity, the sensor still maintains a high response level, indicating that it has good moisture resistance.

[0041] (7) Selective testing To verify the sensor's anti-interference capability, the response of a 1 wt% HEOs / SnO2 sensor to different gases was tested at 130℃: the target gas was 0.5 ppm NO2, and the interfering gases included 20 ppm H2, 20 ppm NH3, 20 ppm ethanol, 50 ppm CO, 50 ppm CH4, and 50 ppm ethylene. The results are as follows: Figure 11 As shown.

[0042] Although the concentration of interfering gases is 40 to 100 times that of NO2, the sensor's response value to NO2 (>700) is still much higher than that to all interfering gases, indicating that the sensor has excellent selectivity to NO2 and can effectively avoid interference from common coexisting gases.

[0043] (8) Device conformance testing To verify the reliability and versatility of the preparation process, four independent 1 wt% HEOs / SnO2 sensors were prepared using the same process, and their response performance to 0.5 ppm NO2 was tested under the same conditions (e.g., Figure 12 (As shown in the figure). The results show that the response curves of the four sensors highly overlap, and the performance differences are negligible, indicating that the fabrication process can stably produce devices with consistent performance, and has good repeatability and industrial application potential.

[0044] (9) Long-term stability test A long-term stability test was conducted on a 1 wt% HEOs / SnO2 sensor for 40 days: the response performance was tested every 5 days at 130℃ and 0.5 ppm NO2. The results are as follows: Figure 13 As shown in the figure, during the test, the sensor's response value did not decrease significantly and the change was minimal, indicating that the sensor has excellent long-term stability and can meet the application requirements for long-term monitoring.

[0045] In summary, this embodiment prepared a series of HEOs / SnO2 nanocomposites and constructed gas sensors by controlling the amount of HEOs added. Among them, the 1 wt% HEOs / SnO2 sensor exhibited comprehensive performance advantages: at a relatively low operating temperature of 130℃, it achieved a response value as high as 747 for 0.5 ppm NO2, with a response time of only 142 s and a recovery time of only 60 s; it maintained high sensitivity even for NO2 concentrations as low as 0.1 ppm, while also possessing excellent repeatability, moisture resistance, selectivity, and long-term stability. These characteristics indicate that the 1 wt% HEOs / SnO2 composite material has broad application prospects in the field of low-temperature, low-concentration NO2 gas detection.

[0046] The above description is merely a preferred embodiment of the present invention and does not imply any limitation thereof. Without departing from the spirit and principles of the present invention, those skilled in the art can make various modifications and improvements to the present invention, and all such modifications and improvements should be included within the scope of protection of the present invention.

Claims

1. A method for preparing HEOs / SnO2 nanocomposite materials, characterized in that, Includes the following steps: Step 1: Using manganese acetylacetone (II), iron acetylacetone (III), cobalt acetylacetone (III), nickel acetylacetone (II) and copper acetylacetone (II) as raw materials, an intermediate product is first obtained by solvothermal method, and then the intermediate product is calcined at high temperature to obtain high entropy oxide powder, namely HEOs powder. Step 2: HEOs powder and SnO2 powder are ultrasonically mixed, allowed to stand, filtered and dried to obtain HEOs / SnO2 nanocomposite material.

2. The method for preparing HEOs / SnO2 nanocomposite material according to claim 1, characterized in that, The specific operation method of step 1 is as follows: Mix manganese acetylacetone (II), iron acetylacetone (III), cobalt acetylacetone (III), nickel acetylacetone (II), and copper acetylacetone (II) at a ratio of 5 × 10⁻⁶. -3 ~8×10 -3 Add M to the reaction vessel, mix ethanol and acetone at a volume ratio of 1:1 to 3 and add them to the reaction vessel, and react at a constant temperature of 180 to 200°C in air for 12 to 18 hours. After the reaction is completed, allow it to cool naturally to room temperature, open the reaction vessel and filter it. Dry the filtered product under vacuum at 40 to 60°C for 10 to 12 hours. Finally, calcine the dried powder at a constant temperature of 600 to 800°C in air for 2 to 4 hours to obtain HEOs powder.

3. The method for preparing the HEOs / SnO2 nanocomposite material according to claim 1, characterized in that, The specific operation method of step 2 is as follows: Add 0.0003~0.006 g HEOs powder and 0.097~0.094 g SnO2 powder to 30~50 mL of water, sonicate for 1~3 hours, then let stand for 10~14 hours, filter the product after standing, and then vacuum dry the filtered product at 40~60℃ for 10~12 hours to obtain HEOs / SnO2 nanocomposite material.

4. A HEOs / SnO2 nanocomposite material prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the HEOs / SnO2 nanocomposite material as described in claim 4 in a gas sensor.

6. A gas sensor, characterized in that, The gas sensor uses the HEOs / SnO2 nanocomposite material as described in claim 4 as the gas-sensitive material.

7. The gas sensor according to claim 6, characterized in that, The gas sensor is used to detect NO2 gas.

8. The gas sensor according to claim 6, characterized in that, HEOs / SnO2 nanocomposite material was ultrasonically dispersed in ethanol to obtain HEOs / SnO2 slurry; the HEOs / SnO2 slurry was then coated onto the surface of interdigital electrodes using a drop-coating method to obtain a gas sensor.

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