A method for preparing a high-sensitivity gas sensor based on waste catalyst recovery ZnO

Abstract

ZnO was extracted from waste Zn metal-based catalysts by acid leaching and used to fabricate sensors for the detection of ammonia at room temperature. The response of the recovered ZnO-based sensor to 500 ppm ammonia at room temperature reached 101, with a response / recovery time of only 8 / 3 s, thus enabling fast detection of NH3. In addition, it also has excellent selectivity and excellent long-term stability. The successful conversion of waste catalysts into high-performance gas sensors has far-reaching significance for sustainable development and green manufacturing practices. The combination of cost-effective material recycling and excellent sensing performance makes this strategy particularly important for the development of next-generation new gas sensors.

Description

Technical Field

[0001] This invention relates to the field of gas sensors, specifically to a method for preparing a ZnO gas sensor using waste Zn metal-based catalyst and the application of this sensor in the detection of ammonia. Background Technology

[0002] Zn-based metal catalysts possess numerous advantages, including high catalytic activity, good selectivity, and strong stability, leading to their widespread application in organic synthesis, chemical industry, coatings and inks, new energy, and many other fields. However, the activity of these catalysts gradually decreases or even completely disappears over time. Deactivated catalysts become solid waste, occupying land resources and potentially generating harmful wastewater and exhaust gases that pollute the environment. Recycling these catalysts can achieve efficient utilization of metal resources, reduce energy consumption and production costs, decrease waste and environmental pollution, promote resource recycling, and create economic benefits.

[0003] Zinc is the main metallic component in Zn metal catalysts. Through recycling, high-purity metallic zinc and zinc oxide can be obtained. Zinc oxide is an important N-type semiconductor metal oxide with advantages such as stable physicochemical properties and non-toxicity. It possesses a wide bandgap, high electron mobility, and excellent chemical and thermal stability, making it a potential candidate for ideal sensors. Therefore, recovering ZnO from waste zinc-based catalysts and processing it for use in gas sensors is a promising secondary source. This not only conserves limited zinc resources and reduces the mining and consumption of new resources but also reduces environmental pollution from catalyst waste and lowers processing costs.

[0004] Ammonia is a colorless, toxic gas with a strong, pungent odor. Its main sources include industrial production, construction, agricultural activities, and interior decoration. The hazards of ammonia are multifaceted. Long-term exposure to ammonia can cause irreversible damage to the human respiratory system, nervous system, liver and kidney function, and it also affects the ecological and atmospheric environment. Therefore, effective detection of ammonia during its production, storage, transportation, and use to prevent leaks and environmental pollution is becoming increasingly important. The high response speed and sensitivity of ammonia gas sensors typically rely on high operating temperatures (120-300 °C). However, with the rapid development of IoT systems, the performance requirements for gas sensors have significantly increased in terms of stringency and versatility. Modern applications demand that sensors be miniaturized, flexible, and wearable, while also adapting to complex and dynamic working environments. Sensors packaged on flexible substrates, due to their excellent mechanical deformation adaptability, have become an effective solution for meeting these requirements.

[0005] To address the aforementioned issues, this invention proposes an innovative scheme for extracting ZnO semiconductors from spent catalysts for gas sensing. ZnO is extracted from spent Zn metal-based catalysts using an acid leaching method, and a sensor is fabricated and applied to detect ammonia at room temperature. Based on the recovered ZnO sample, the sensor achieves a response of 10¹ to 500 ppm ammonia at room temperature, with a response / recovery time of only 8 / 3 s, thus enabling rapid detection of NH₃. Furthermore, it exhibits excellent selectivity and superior long-term stability. The successful conversion of spent catalysts into high-performance gas sensors has profound implications for sustainable development and green manufacturing practices. The combination of cost-effective material recycling and superior sensing performance makes this strategy particularly important for developing next-generation gas sensors. Summary of the Invention

[0006] This invention discloses a scheme for extracting ZnO semiconductors from spent catalysts for gas-sensitive performance sensing. ZnO was extracted from spent Zn metal-based catalysts using an acid leaching method, and a sensor was fabricated and applied to detect ammonia at room temperature. Based on the recovered sample ZnO-based sensor, the response of the sensor to 500 ppm ammonia at room temperature reaches 101, with a response / recovery time of only 8 / 3 s, thus enabling rapid detection of NH3. Furthermore, it exhibits excellent selectivity and superior long-term stability.

[0007] To achieve the above objectives, the present invention provides the following technical solution: Preparation methods of gas-sensitive materials and sensors: a. Grind the waste catalyst in a planetary ball mill; b. Place the sample ground in step a into a crucible and calcine it in a muffle furnace at 600°C for 2 hours; c. Take 50 g of the spent catalyst treated in step b, add it to 500 ml of 15 wt% sulfuric acid solution, and mechanically stir at 45°C for 60 minutes. d. Filter the mixed solution obtained in step c to separate solid impurities, obtaining a filtrate containing zinc ions (Zn²⁺). e. Adjust the pH of the filtrate obtained in step d to 7 using ammonia water; f. Filter and evaporate the mixed solution from step e. The resulting crystals are treated with Zn. 2+ Recycling in the form of [unclear]; g. The sample evaporated in step f is calcined at 700°C for 2 h in a tube furnace with oxygen introduced. h. Take out the sample obtained after annealing in step g, grind it thoroughly in an agate mortar for 20 minutes to obtain powder, then mix it with deionized water in a certain ratio (powder to water ratio 4:1) and continue grinding to obtain a uniformly dispersed solution. Use a dropper to evenly drop it onto the interdigital electrode plate, and after drying at room temperature for 24 hours, a gas sensor based on metal oxide semiconductor is made.

[0008] The first aspect of this invention application provides a high-sensitivity gas sensor prepared by recovering ZnO from waste catalyst, which is prepared according to the above method.

[0009] The second aspect of this invention application provides an application of a high-sensitivity gas sensor prepared by recovering ZnO from waste catalyst in the detection of ammonia.

[0010] Beneficial technical effects of the present invention: This invention focuses on the efficient recovery of valuable metals from waste catalysts and successfully transforms them into high-performance metal oxide semiconductor (MOS) gas-sensitive materials, achieving efficient recycling of waste resources. Traditionally, waste catalysts are disposed of through landfill or incineration, but both methods have numerous drawbacks. Landfilling not only occupies a large amount of valuable land resources, but heavy metals from waste catalysts may also leach into the soil, severely damaging soil quality and threatening the entire ecological environment. Incineration, on the other hand, emits toxic gases, posing a serious pollution risk to the atmosphere. This invention uses waste catalysts as raw materials, eliminating reliance on traditional high-purity minerals. Throughout the entire process of preparing the high-performance gas-sensitive material, the emission of harmful substances is effectively controlled and significantly reduced. This not only mitigates the potential environmental harm of heavy metals at the source but also significantly alleviates the pressure caused by the large accumulation of waste catalysts. This "waste-to-treasure" technology route, which transforms waste catalysts into high-performance gas-sensitive materials, has profound significance. On the one hand, it endows waste resources with new functional value, allowing waste catalysts to play an important role again in new product fields; on the other hand, this technical route is deeply in line with the concept of circular economy, providing a practical and feasible solution for the green transformation of the industrial sector, and has important value in the process of sustainable industrial development.

[0011] This invention extracts ZnO semiconductors from spent catalysts for ammonia detection at room temperature, reducing environmental pollution and lowering costs. Based on the recycled ZnO sample, the sensor achieves a response of 10¹ to 500 ppm ammonia at room temperature, with a response / recovery time of only 8 / 3 seconds, enabling rapid detection of NH₃. Furthermore, it exhibits excellent selectivity and superior long-term stability. The successful conversion of spent catalysts into high-performance gas sensors has profound implications for sustainable development and green manufacturing practices. The combination of cost-effective material recycling and superior sensing performance makes this strategy particularly important for developing next-generation gas sensors. Attached Figure Description

[0012] Figure 1 Scanning electron microscope (SEM) images of ZnO materials prepared for this invention. Figure 2 Transmission electron microscope (TEM) images of ZnO materials prepared for this invention. Figure 3 X-ray diffraction (XRD) pattern of ZnO material prepared according to the present invention Figure 4 The Fourier transform infrared (FTIR) spectrum of the ZnO material prepared in this invention is shown below. Figure 5 Selectivity radar image of the ZnO material prepared for this invention for multiple gases at room temperature (25 °C); Figure 6 The response recovery curve of the ZnO material prepared in this invention to ammonia gas is shown. Figure 7 The response curves of the ZnO material prepared for this invention to ammonia concentration gradients from 10 ppm to 500 ppm; Figure 8 The response fitting curves of the ZnO material prepared in this invention for ammonia concentration gradients from 10 ppm to 500 ppm. Detailed Implementation

[0013] The following is a detailed description of various exemplary embodiments of this invention. This description illustrates alternative embodiments of this invention; however, it is more clearly stated that this invention can be implemented in various forms and is not intended to limit the invention. Rather, these specific embodiments are provided to increase the completeness and thoroughness of the invention and to clearly and fully convey the scope of this invention to those skilled in the art.

[0014] The terminology used in this application is not intended to limit the scope of the application, but is merely for describing the embodiments. The singular forms “a,” “the,” etc., used in this application and the claims are intended to represent more than one form, but to encompass multiple forms. Open-ended terms such as “having,” “comprising,” etc., used herein mean including but not limited to, unless specifically stated otherwise.

[0015] The numerical ranges used herein do not specifically refer to or represent any particular intermediate value, but rather encompass every intermediate value within that specific range. Any stated value or every smaller range within a stated range is also included in this application.

[0016] Unless otherwise specified herein, all technical and scientific terms used herein have the same meaning as understood by one of ordinary skill in the art. While only preferred materials and embodiments have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0017] The following is a detailed description of a method for preparing a high-sensitivity gas sensor based on the recovery of ZnO from waste catalysts, in conjunction with the accompanying drawings: Example

[0018] The method for preparing a high-sensitivity gas sensor by recovering ZnO from waste catalysts in this invention application includes: a. Grind the waste catalyst in a planetary ball mill; b. Place the sample ground in step a into a crucible and calcine it in a muffle furnace at 600°C for 2 hours; c. Take 50 g of the spent catalyst treated in step b, add it to 500 ml of 15 wt% sulfuric acid solution, and mechanically stir at 45°C for 60 minutes. d. Filter the mixed solution obtained in step c to separate solid impurities, obtaining a filtrate containing zinc ions (Zn²⁺). e. Adjust the pH of the filtrate obtained in step d to 7 using ammonia water; f. Filter and evaporate the mixed solution from step e. The resulting crystals are treated with Zn. 2+ Recycling in the form of [unclear]; g. The sample evaporated in step f is calcined at 700°C for 2 h in a tube furnace with oxygen introduced. h. Take out the sample obtained after annealing in step g, grind it thoroughly in an agate mortar for 20 minutes to obtain powder, then mix it with a certain ratio (powder to water ratio 4:1) of deionized water and continue grinding to obtain a uniformly dispersed solution. Use a dropper to evenly drop it onto the interdigitated electrode sheet, and after drying at room temperature for 24 hours, a gas sensor based on metal oxide semiconductor is made. Example

[0019] like Figure 1 The SEM images shown reveal the morphology of the material. Figure ac displays the SEM image of the recovered ZnO sample, which shows that the ZnO sample consists of a large number of irregular lumps, the size of which is approximately between 100-500 nm. This irregular lumpy morphology increases the gas contact area, which is beneficial for gas adsorption.

[0020] Example 3 Figure 2 ab are TEM images of the recovered ZnO sample. It can be seen that the TEM characterization is consistent with SEM, and the recovered ZnO sample is composed of a large number of bulk particles. Figure 2 c is the high-resolution transmission electron microscopy (HRTEM) characterization of Z2. The lattice spacings of 0.245 nm and 0.282 nm are clearly observed in the image, corresponding to the (10 1) and (1 0 0) crystal planes of the hexagonal wurtzite ZnO (PDF#99-0111). This is consistent with XRD analysis. Furthermore, in Figure 2 d is the annular SEAD plot of the recovered sample Z2, which reveals the polycrystalline nature of the sample.

[0021] Example 4 Figure 3 The XRD characterization of the recovered sample is shown, revealing a series of sharp diffraction peaks. The diffraction peaks at 31.7°, 34.4°, 36.2°, and 56.5° correspond to the (100), (002), 101, and (110) crystal planes of hexagonal wurtzite ZnO (PDF#99-0111), respectively. All diffraction peaks of the sample closely match the hexagonal wurtzite structure (PDF#99-0111) of ZnO, and no diffraction peaks corresponding to impurities were observed, indicating that a single zinc oxide phase is predominantly present in the recovered sample.

[0022] Example 5 Figure 4 The Fourier transform infrared spectrum was used to study the functional groups of the sample. The sample has abundant functional groups, which provide active sites for gas adsorption, thus exhibiting high sensitivity.

[0023] Example 6 Figure 5 To connect the AES-4SD power supply of the optoelectronic integrated test platform, the sensor's response to target gases such as ethylene glycol, ethanol, aniline, formaldehyde, ammonia, toluene, acetone, and trimethylamine at 500 ppm was tested at room temperature (25°C, 30% relative humidity) under a bias voltage of 4 V. It was found that the gas sensor prepared in this invention exhibits high sensitivity and selectivity to ammonia.

[0024] Example 7 pass Figure 6 It can be seen that the sample's response intensity to 500 ppm ammonia is 101, and the response and recovery times are 8 seconds and 3 seconds, respectively.

[0025] Example 8 pass Figure 7 It can be seen that the sample's sensing limit for ammonia reaches 10 ppm, with a response value of 2.1.

[0026] Example 9 pass Figure 8 It can be seen that the sample fits the ammonia concentration gradient very well, with a fitting function y = 0.21x ± 3.12 and R0. 2 =0.996.

Claims

1. Preparation method of gas-sensitive materials: a. Grind the waste catalyst in a planetary ball mill; b. Place the sample ground in step a into a crucible and calcine it in a muffle furnace at 600°C for 2 hours; c. Take 50 g of the spent catalyst treated in step b, add it to 500 ml of 15 wt% sulfuric acid solution, and mechanically stir at 45°C for 60 minutes. d. Filter the mixed solution obtained in step c to separate solid impurities, obtaining a filtrate containing zinc ions (Zn²⁺). e. Adjust the pH of the filtrate obtained in step d to 7 using ammonia water; f. Filter and evaporate the mixed solution from step e. The resulting crystals are treated with Zn. 2+ Recycling in the form of [unclear]; g. The sample evaporated in step f is calcined at 700°C for 2 h in a tube furnace with oxygen introduced. h. Take out the sample obtained after annealing in step g, grind it thoroughly in an agate mortar for 20 minutes to obtain powder, then mix it with deionized water in a certain ratio (powder to water ratio 4:1) and continue grinding to obtain a uniformly dispersed solution. Use a dropper to evenly drop it onto the interdigital electrode plate, and after drying at room temperature for 24 hours, a gas sensor based on metal oxide semiconductor is made.

2. The method for preparing a highly sensitive and selective gas sensor based on the recovery of ZnO from waste catalysts according to claim 1, characterized in that... Step c involves leaching Zn²⁺ in a 15wt% sulfuric acid solution, along with other impurities to inhibit leaching, in order to extract pure zinc oxide.

3. A highly sensitive and selective gas sensor prepared based on the recovery of ZnO from waste catalysts, characterized in that, Prepared according to the preparation method according to any one of claims 1 to 2.

4. The waste catalyst ZnO recovery method according to claim 3 is used to prepare a high-sensitivity gas sensor, which has the application of efficient and rapid detection of ammonia gas.

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