Study On The Effects Of MoO₃ Microstructure And Sensor Type On The Gas Sensing Properties

Sensing layer is the core part of a gas sensor,thus,the selection of materials as well as the structure for sensing layer becomes the key precondition and foundation to meet the needs of technology revolution and product innovation.MoO₃ is a promising material for sensing layers as its nice selectivity,fast response and recovery,good linear relationship between response and concentration.However,it also shows the shortage of high operating temperature and pure ability of detecting trace target gas.Thus,further improvements in the sensing behaviors are needed.In this study,we choose one-dimensional MoO₃ nanomaterials as the research object,using Cu,Zn and Ti doping as well as design of sensor structure to solve the problems above.We study the change of structure,phase,morphology,defect and energy level structure,so as to study their influence and mechanism on the final gas sensing performance.Gas sensors based on single MoO₃ nanobelt and MoO₃ array are also fabricated,and the relationship between structures of gas sensors and gas sensing properties are studied.Cu doped MoO₃ nanobelts are prepared via hydrothermal method,and discussions on the relationship between structures and gas sensing properties are carried out.The reason for the improved gas sensing properties are found out by comparing the ability of absorbing and decomposing ammonia and ethanol.As the operating temperature of ethanol and ammonia are in different zone,the selectivity to ammonia and ethanol could be realized by adjusting the temperatures.The response of Cu doped MoO₃ nanobelts to trace gas is improved,and the operating temperature to ammonia is reduced by about 80^?C compared with pure MoO₃ nanobelts.It is found that Cu contributes not only to the absorbance but also to the catalytic decomposition of gas,which leads to the improvement of gas sensing properties.Ti doped MoO3-x nanobundles are successfully prepared by hydrothermal method,and the progress of growth and optimum annealing temperature is studied.The influence of compositions,morphologies and structures of Ti doped MoO3-x nanobundles are stdied as well to concern the reasons for the improvement of gas sensing properties.Gas sensors based on Ti doped MoO_3-x nanobundles are fabricated on ceramic tubes.The sensors have responses to 0.25 ppm ethanol,which indicates that the ability of detecting trace ethanol is greatly improved.After the great band bending as the large surface state density,the Femi level is close to valence band and the sample change to p type,which is the main reason for the response of ethanol at room temperature.In view of the characteristic that electrons could transport along the axis of one dimensional materials,ultralong MoO₃ nanobelts are prepared via hydrothermal method.Gas sensors based on ultralong MoO₃ nanobelts are fabricated on ceramic tubes,and they have good response and selectivity to TMA from 100^?C to 380^?C.To check the reason for the outstanding gas sensing properties of ultralong MoO₃,we test the decompositions of TMA with and without the existence of ultralong MoO₃nanobelts.The results show that ultralong MoO₃ nanobelts play as a catalyst in the decompositions of TMA.Besids,the situation of absorbtion and the electrons released after TMA interact with MoO₃ are also studied to analysis the factors that leading to the outstanding gas sensing response to TMA.As surface Zn atom could help absorbing ethanol and decrease the probability of recombination of ethoxy and hydroxyl,Zn doped MoO₃ nanobelts are prepared via hydrothermal method in order to accelerate the key step——proton transfer progress during the decomposing of ethanol.The relationship between the doping amount of Zn and the final gas sensing properties as well as the optimum doping amount are studied.Gas sensors based on Zn doped MoO₃ nanobelts have good gas sensing properties to ethanol from 100^?C to 380^?C.The highest response value to 1000 ppm ethanol is 321,which is 15 times higher than pure ultralong MoO₃ nanobelts.Finally,in order to take the advantage of one dimensional nanomaterials and promote the transporting of electrons between electrodes,gas sensors based on single and multiple ultralong MoO₃ nanobelts are fabricated.The imfluence of grain boundary barriers to the final gas sensing properties are studied.Besides,sensors based on MoO₃ arrays that prepared via liquid phase method and physical vapor deposition method are assembled to increase the contact area between sensing materials and gas molecules.The influence of preparation conditions on the final structure and morphology of MoO₃ arrays are studied,the optimum preparation conditions is obtained as well.Sensors based on single MoO3 nanobelt and MoO3arrays could have gas sensing response to target gas at roon temperature,which imply that the improving of gas sensing properties could be realized via appropriate design and fabrication of gas sensors.