Preparation And Gas Sensing Properties Of MoO₃-based Gas Sensing Materials

Due to the continuous progress of the society,people’s quality of life has become more beautiful with the continuous change of industrialization and science and technology,but the air pollution problem in life has become more and more obvious.Factory exhaust and automobile exhaust emissions,the incineration of household waste,indoor decoration of toxic gases,etc.all inadvertently flow into the atmosphere,leading to the deterioration of gas quality.These toxic and harmful gases will enter the blood,organs and respiratory tract of the gas,causing inestimable impact on human physical and mental health.Hydrogen sulfide（H₂S）is a highly toxic gas with rotten egg taste.High concentration of H₂S will cause sudden death（"electric shock"death）.Even low concentration of H₂S gas will cause serious damage to human trachea and respiratory tract.Therefore,it is particularly necessary to design an H₂S gas sensor with high gas sensitivity and lower detection limit.To date,numerous gas sensors including acoustic,electrochemical,optical and electrical resistance have been developed based on their working principles;However,resistive gas sensors based on metal oxides（MO_x）are superior to other materials due to their high sensitivity,ease of manufacture,light weight,low manufacturing cost and simple detection methods.Therefore,in this paper,the lower cost and more convenient hydrothermal-solvothermal method was used to prepare MoO₃-based gas-sensitive materials,and various instruments were used to characterize the material’s micro-morphology,composition,chemical state of elements,specific surface area and other parameters in detail.The influences of the micro-morphology,specific surface area,composite modification,g-C₃N₄ and ambient humidity on the gas-sensitive properties of the gas-sensitive materials are studied in detail.Then the sensing mechanism and mechanism of the gas sensor are further discussed.Finally,the internal and external mechanisms of various gas-sensitive properties are analyzed and summarized.It provides a better solution for the rapid detection of trace H₂S gas at room temperature,and contributes a new strategy for the subsequent research of metal oxide semiconductor（MOS）gas sensors.The research content of this paper is as follows:（1）The H₂S sensor based on MoO₃ with different morphologies were presented,and the MoO₃ were synthesized by a low-cost and environment-friendly hydrothermal method.The products are characterized by XRD,SEM,TEM,XPS and BET techniques.The results show that MoO₃ exhibits irregular nanoparticle shape and nanobelt shape,respectively,and the nanobelts have the width of 100～300 nm and the length of 2～5μm.Compared to MoO₃nanobelts,MoO₃ nanoparticles possess a larger specific surface area,and have more adsorbed oxygen and oxygen vacancy.The gas sensing test results show that the response of MoO₃nanoparticle sensor to 100 ppm H₂S is 3.73 at room temperature,which is 2.85 times of MoO₃nanobelt sensor（1.31）.In addition,MoO₃ nanoparticle sensor has an excellent selectivity to H₂S gas against other gases（such as NH₃,H₂,CO and SO₂）,and still maintains high response under continuous test for 5 weeks.The excellent gas sensing properties of MoO₃ nanoparticle sensor are due to the larger specific surface area that can enable more gases to be adsorbed on the material surface.In addition,the oxygen vacancy reduces the energy required to adsorb the target gas.Therefore,the synergistic effect strengthens the physical and chemical adsorption of MoO₃ nanoparticles,which will enhance the gas sensing performance of MoO₃ nanoparticle sensor.Our work will create a new idea for the application of room-temperature H₂S sensors based on MoO₃ with different morphologies.（2）The detection of H₂S for biomarkers or special occasions often requires a lower detection limit.The ppb-level H₂S sensor based on MoO₃/CuO/g-C₃N₄（MCC）was presented by a simple method.The characterized results show that MCC-2 possesses a larger specific surface area,and has more adsorbed oxygen and oxygen vacancy compared to MoO₃ and MoO₃/CuO.The gas-sensitive test results show that the response of the MCC-2 sensor to 1000ppb H₂S is up to 8.24 at room temperature,which is 1.31 times of MoO₃/CuO（6.28）.More importantly,the theoretical detection limit of the MCC-2 sensor is as low as 1.1 ppb,which is the lowest in the recent H₂S sensor.In addition,the MCC-2 sensor has reliable repeatability,excellent selectivity to H₂S,and still maintains a high response after continuous test for 5 weeks.Simultaneously,the MCC-2 sensor also keeps an outstanding response at high relative humidity.The excellent gas sensing properties are due to the larger specific surface area that can enable more gases to be adsorbed on the material surface.In addition,the oxygen vacancy reduces the energy required to adsorb the target gas and the formed heterojunctions by MoO₃/CuO/g-C₃N₄expedite carrier migration.