| In the past few decades,nanostructure-based metal oxide gas sensors have attracted great interest due to their low cost,ease of manufacture,high sensor response and short response/recovery time.Traditional MOS-based gas sensors usually need to work at higher temperatures,which increases the risk of gas sensors for flammable and explosive gas detection.Therefore,it is necessary to develop efficient and reliable gas sensors that can work at low/room temperature.Metal oxide heterojunction is often used to improve the gas sensitivity of resistive MOS gas sensors due to Fermi level effect and synergy between different components.In this paper,a novel n-type semiconductor(Sr0.6Bi0.305)2Bi2O7(SBO)with hydrophobic properties is developed as the base material,and the gas-sensitive performance of MOS sensor is improved by heterostructure construction and photoactivation modulation.The specific research contents are as follows:1.Exploring novel sensing materials enabling selective discrimination of trace ambient H2S at lower temperature is of utmost importance for diverse practical applications.Herein,heterostructural ZnO/SBO nanomaterials were proposed.Synergetic effect of promoting analyte adsorption(via multiplying oxygen vacancy defects)and reversible sulfuration-desulfuration reaction induced unique band alignment among ZnO/SBO/ZnS,contributes to the sensitive and selective response toward H2S molecules.Novel ZnO/SBO(10%)sensor possesses excellent sensing H2S performances,including a high response(107.6 for 10 ppm),low limit of detection of 20 ppb,good selectivity and long-term stability.Together with the merits of low operation temperature of 75℃ and weak humidity dependence(endowed by the hydrophobic SBO),present heterostructural ZnO/SBO sensor paves the way for the practical monitoring of trace H2S pollutants in diverse workplaces including petroleum and natural gas industries.2.Methyl mercaptan(MM)and H2S have similar origins and should be distinguished due to their different odor thresholds and health effects.Therefore,it is necessary to design a novel heterostructure gas sensor for high sensitivity and selective detection of MM.The nanoscale CdS/SBO heterostructure material was prepared by a facile chemical precipitation method,and the gas sensor made of this material can have a high response to MM at a lower operating temperature of 100℃.The gas sensing test results show that the heterostructure CdS/SBO(SBO compound molar weight is 0.05%)gas sensor has a response value of 114.7 to 100 ppm MM,which is about 36 times and 9 times higher than that of pure SBO and CdS,respectively,And the sensor has a weak response to a variety of volatile organic compounds,especially volatile sulfide.At the same concentration,the sensor’s response to MM is also greater than that of H2S,with excellent selectivity.In addition,which effectively overcomes the problem of poor stability of conventional oxide sensors due to irreversible sulfuration,thus showing good long-term stability.Furthermore,the analysis of the gas-sensing enhancement mechanism shows that abundant oxygen vacancies,reversible sulfurization-desulfurization reactions,and the formation of a large number of n-n heterojunctions at the interface promote the redox reactions of surface active species,making the CdS/SBO gas sensor with excellent sensing properties.3.With the development trend of low power consumption and low risk operation of the Internet of Things,it is urgent to develop high-performance room temperature gas sensors based on metal oxide nanostructures.Photoactivated gas sensing technology has high efficiency in improving the room temperature gas sensing performance of MOS.Though UV illumination has been widely adopted to activate the room temperature response of metal oxide based chemiresistors,photoexcited abundant carriers(low base resistance)induced low response,and UV induced hydrophilicity caused degradation or even poisoning in ambient humid air atmosphere,pose a challenge for real applications.Herein,15 mol%(optimized ratio)ZnO nanoparticles have been coupled into hydrophobic SBO matrix,hydrophobic ZnO/SBO chemiresistor has been proposed.Visible 455 nm light could not only trigger the gas/oxide interfacial charge exchange,but also substantially reduce the carrier concentration of gas sensor in comparison with UV 365 nm light,and therefore noticeably boosts trimethylamine(TMA)response at room temperature,including an enlarged sensitivity,extremely high limit of detection(LoD)(10 ppb),good selectivity,reproducibility and long-term stability.More importantly,present hydrophobic ZnO/SBO chemiresistor could be operated under high relative humidity(RH 90%)with a slight decline(17%)of response with respect to dry air background,opening an opportunity for the practical applications of oxide chemiresistors in ambient humid atmosphere. |
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