Oxide Nanostructure Gas Sensor And Application In Ammonia Detection

Ammonia plays an integral role in our industry,agriculture and life as a colorless,irritating,volatile gas.The traditional sensors generally have the disadvantages of low sensitivity and poor selectivity,but,semiconductor metal oxide sensors can solve these defects well.The main research contents are as follows.WO3 has been widely used in gas sensing tests as a wide bandgap semiconductor metal oxide gas sensing material.However,the existing WO3 gas sensor generally has low response,which limits the application of the sensor in low concentration ammonia.Ag nanoparticles are deposited on the surface of WO3 by in-situ photoreduction.The microstructure and crystal structure of the gas sensing materials were analyzed by scanning electron microscopy,transmission electron microscopy and XRD.The characterization results show that Ag nanoparticles are successfully deposited on the surface of WO3 nanorods.The gas response test results show that the minimum ammonia concentration detected is 50 ppb by the Ag/WO3 sensor,which greatly increases the lower limit of detection of ammonia by the semiconductor metal oxide sensor.It is worth noting that although the Ag/WO3 sensor increases the lower limit of detection of ammonia,it has low response to ammonia when the sensor is operating at the optimum operating temperature.Based on this defect,the WO3/MoO3 high response sensor was prepared by a two-step hydrothermal method.The characterization results show that the WO3 nanoparticles are dispersed on the surface of the MoO3 hollow spheres after the WO3 nanorods are ultrasonically stripped.Due to the difference in the work functions of the two semiconductor metal oxides,electron transfer occurs at the interface,resulting in a depletion layer.The experimental results show that the WO3/MoO3 sensor greatly improves the gas response to ammonia when the sensor is operating at the optimum operating temperature.The sensor’s response is 28000 to 100 ppm ammonia,which is the highest response in existing sensors.Although Ag/WO3 and WO3/MoO3 sensors improve the detection limit and response of ammonia gas,the sensor will show the error when the sensor is in a complex environment containing multiple gases due to other gases.In order to solve this problem,the MoO3 sensor was obtained by high temperature oxidation using MoS2 as a template.The high temperature oxidation not only maintained the porous hollow structure of MoS2,but also improved the selectivity of the sensor to ammonia.The MoO3 has substantially no response to other gases except for a high response to ammonia in a variable temperature range.The normal operation of the three sensors requires high temperature heating.Industrial production needs to be safe and reliable,which limits the use of the sensor in some flammable and explosive places.Graphene and MoS2 are typical two-dimensional materials,and have been widely used in gas sensing tests in combination with metal oxides.It can adsorb more test gas molecules to contact with the gas sensitive material due to the graphene surface has defects and functional groups,and MoS2 as a transition metal dihaloalkane plays a significant role in reducing the operating temperature of the sensor.The MoO3/MoS2/rGO rose-like composites were prepared based on the excellent properties of graphene and MoS2.The new material not only progresses in microscopic morphology,but also greatly reduces the operating temperature of the sensor.