Study On The Preparation Of ?-MoO₃ Nanowires Paper And Its Hydrogen Sensing Properties At Room Temperature

Hydrogen?H₂?is a clean energy carrier,and which was widely used in medical,petrochemical,electronics,aerospace and ship and other fields.However,hydrogen is a flammable and explosive gas,and the explosive concentration limit in the air at room temperature is 4.65%.Therefore,it is of great significance to study a sensor with fast respond speed,good reliability,safety and wide hydrogen detection and low cost.The Molybdenum oxide?MoO₃?,a transition metal oxide with a wide bandgap?3.2ev?,has excellent optical,electrical and catalytic properties,and is also commonly used hydrogen sensitive materials at room temperature.In this paper,the molybdenum oxide nanowires paper hydrogen sensor was prepared by hydrothermal method and self-assembly technique.The effects of hydrothermal reaction temperature and hydrothermal reaction time on the phase and morphology of molybdenum oxide nanowires were also studied.Hydrogen sensitive properties was enhanced after the nanowire paper modified by Pd,and at the same time,the hydrogen sensing mechanism also was discussed in detail.The main results obtained are as follows:1.The use of hydrothermal method by controlling the hydrothermal temperature and hydrothermal time can obtain different sizes of molybdenum oxide nanowires.The results show that the length of the obtained molybdenum oxide nanowires is becoming longer with the increase of the hydrothermal reaction temperature.At 96h hydrothermal reaction time,nanowires diameter is about 200nm and the length is⁵00um at 230^oC reaction temperature,however the length of the nanowires could reach 3mm when the reaction temperature increased to 260^oC.And what is more,the surface area of the molybdenum oxide nanowires increases and the internal stress of the molybdenum oxide crystal increased with the crystal space becoming small when the reaction temperature becoming higher.At the same time,the length of the molybdenum oxide nanowires increased sharply with the increase of the time of hydrothermal reaction under a certain hydrothermal reaction temperature?260 ^oC?.Under the condition of 12h reaction time,the molybdenum oxide nanowires only a few hundred nanometers,but after 96h reaction time,the length of molybdenum oxide nanowires can reach up 3mm.2.The molybdenum oxide nanowires obtained after 96 hours reaction at 260^oC were completely dispersed,and A4-sized molybdenum oxide nanowire paper with a certain porosity was prepared on the hydrophobic substrate by self-assembly process.By adjusting the concentration of molybdenum oxide nanowires,the temperature and time of self-assembly process,the thickness of the nanowire paper can be changed.The results of the tensile test showed that the nanowire paper prepared by the molybdenum oxide nanowires obtained after the 260^oC reaction temperature for 96 hours had excellent flexibility and ductility.3.The use of magnetron sputtering method,in the size of 10mm×10mm molybdenum oxide deposition of Ti/Pt electrode,constituted a simple molybdenum oxide nanowires paper hydrogen sensor.The obtained sensor showed a good hydrogen sensitive response to hydrogen at a concentration of 500 ppm to 1.5%hydrogen concentration.When the hydrogen concentration is 1.5%,the response time is 3.0s,the recovery time is 2.7s,the relative sensitivity factor is 84%,and the reproducibility and selectivity are also still good.The device can work for 5.16 years continuously.Compared with the traditional metal oxide semiconductor sensor,MoO₃ nanowires with more Mo⁵⁺content have more adsorbed oxygen on the surface of nanowires.As the target gases contact with MoO₃ nanowires,which would prefer to react with adsorbed oxygen on the surface of nanowires to release most electrons to lead the résistance decreasing of the sensor device.Therefore,the sensing performance of our sensors to all the target gases could be attributed to the redox reaction with the adsorbed oxygen molecules..4.The effect of Pd quantum dot modification on the microstructure surface and hydrogen sensing performance of the sensor was studied by using Pd quantum dots to modify the surface of molybdenum oxide nanowire paper.The results show that the introduction of an appropriate amount of Pd quantum dots can effectively accelerate the response speed of molybdenum oxide nanometer paper sensor,increase the concentration range of hydrogen concentration and improve the sensitivity.The sensor to the concentration of 1.0%of the hydrogen response time is shortened to 2.0s,repeatability is good,and the detection mix limit of hydrogen can reach 50ppm.