Study On The Direct Construction And Performance Of MoS₂ Based Composite Gas Sensors With Hierarchical Nanostructure

Two dimensional?2D?semiconductor materials,such as molybdenum disulfide?MoS₂?,are one of the hot spots in the research of gas sensing materials.Due to its special 2D structure,MoS₂ has a large specific surface area.At the same time,a large number of defects exist on the surface of MoS₂,which benefit to the excellent sensing response.However,there still are some defects for the MoS₂ gas sensor,such as the high working temperature and insensitivity to low concentration gas,which limits its development.Therefore,we proposed to modify the sensing properties of MoS₂ by compositing the noble metals and metal oxides on the surface,which could build Schottky contacts and n-n heterojunction to enhance its gas sensing properties.At present,the researchers focus on the fabrication and investigation of layered MoS₂ gas sensor due to its special 2D sturcture.And there is few works major in the preparison of MoS₂ gas sensitive materials with special hierarchical morphology through chemical methods.In addition,in order to avoid the uneven distribution and easy shedding of the material on the surface of the ceramic tube,which caused by the manual coating,the MoS₂ sensing material was directly grown on the surface of the ceramic tube by simple hydrothermal method.In this way,the sensing matierals with whole structures are stably attached on the surface of ceramic tube.The details of work are described as follows:1.First of all,in order to obtain the MoS₂ nano materials with regular morphology,the different raw materials were used to prepare MoS₂ by simple hydrothermal method.Finally,when using thiourea,sodium molybdate,and citric acid as the row reagents,the MoS₂ nanoflowers hierarchical structure are synthesized.Under the auxiliary of seed layer,the MoS₂ nanoflowers were directly grown on the surface of the ceramic tube.Toward100 ppm of triethylamine,the sensing response of pristine MoS₂ nanoflowers sensors could reach about 27 at 300 oC.Moreover,the sensor exist good selectivity to triethylamine.The sensor is also very sensitive to change of gas concentration.However,it is found that the pure the MoS₂ nanoflowers sensors exhibit high operating temperature and are not sensitive to the low concentration of gas.Therefore,it is necessary to put forward some improvement measures to optimize the sensing performances of MoS₂.2.Constructing the Schottky contact and using the sensitization of noble metals to improve the sensing properties of Mo S2 nanoflowers.Au nanoparticles are deposited on the surface of MoS₂ nanoflowers by vacuum ion plating.After that,the sensors were fabricated and tested.The results of sensing performancs show that,during several groups of sensors,the MoS₂ nanoflowers puttered with 50 s Au nanoparticles exhibited the best gas sensing response.At 300 oC,the sensing response could reach up to 50 taward 50 ppm of triethylamine.It was found that,toward the low concentration of triethylamine?2¹0 ppm?,there were significant fluctuations showing in the responsing curves.It was proved that the gas sensing properties of MoS₂ nanoflowers were enhanced by compositing Au nanoparticles.But the results of sensing test also show that the sensors still can't work at low temperature.Therefore,the following work was carried out.3.Constructing n-n heterojunction and Schottky contact to improve the sensing properties of MoS₂ nanoflowers.A certain quantum of SnO₂ nanoparticles are deposited on the surface of MoS₂ nanoflowers by pulsed laser deposition.And the Au nanoparticles are composited on them to form the ternary Au@SnO₂/MoS₂ nanoflowers sensing materials.The results of sensing test show that,after depositing SnO₂ and Au nanoparticles,the sensing properties of MoS₂ has been effectively improved.Especially for the ternary Au@SnO₂/MoS₂ nanoflowers,its device can work at lower temperature.At 300 oC,the sensing response of the ternary Au@SnO₂/MoS₂ nanoflowers can reach up to nearly 100 to 100 ppm of triethylamine.Moreover,during the continuity test of different concentration of triethylamine,the sensing response of ternary Au@SnO₂/MoS₂ nanoflowers could reach to 6 toward 2 ppm of triethylamine.