Doping And Modification Of Hollow SnO₂Nanofibers And Their Gas Sensing Properties

Sensing material is a key factor for gas sensors, because it should contact and react with analyte gases directly so as to feedback information to the gas sensing system. For the advantages of fast response-recovery time and excellent stability, semiconductor metal oxide with a low cost has become one of the most important gas sensing materials. However, pure semiconductor metal oxides always have a low sensitivity and a poor selectivity, so some modifications should be made in order to improve gas sensing properties.In this thesis, we improved the gas sensing properties of SnO2in two aspects. First, through combination of electrospinning and appropriate calcination, we prepared hollow SnO2nanofibers with a high active surface area. Then, hollow SnO2nanofibers were doped with Ni and modified with a-Fe2O3, forming heterojunctions in the interfaces to improve gas sensing properties.1. SnO2nanofibers with different morphologies and compositions were synthesized.,With a heating rate of10℃/min, hollow nanofibers would form. Two types of comparative investigation of sensor materials were studied.(I) Pure and Ni-doped SnO2hollow nanofibers were fabricated to examine the effect of Ni doping on the sensing properties. By comparison, Ni doped SnO2hollow nanofibers with different loadings displayed enhanced performances than pure ones, and5at.%Ni doped SnO2have the most excellent properties. Then,5at.%Ni was chosen as an optimum doping content.(II) SnO2nanofibers with hollows and those with solid cores were prepared in order to investigate the influence of the hollow structure. As the hollows can provide more active surface areas, they exhibited better properties when compared with the solid ones. Thus,5at.%Ni doped SnO2hollow nanofibers had the best performance, when operated at340℃. The sensors can have a response to64.9towards100ppm acetone. And when exposed to as low as2ppm acetone, the response can reach13.5.2. One dimensional hierarchically hollow SnO2/a-Fe2O3core-shell nanofibers were synthesized by using electrospun SnO2hollow nanofibers as core followed by the hydrothermal growth and calcination of a-FeOOH nanorods on the outer surface of SnO2nanofibers. The gas sensing measurement results showed that the hierarchical nanofibers performed well when detecting volatile organic compounds, such as acetone, ethanol at340℃, and that the sensitivities to100ppm acetone and ethanol could be30.363and20.370, respectively. The hierarchical samples also had shorter response-recovery time when compared with the sensors made by any single components, i.e., pure SnO2and a-Fe2O3nanostructures. All these improvement can be attributed to the unique hierarchical structure and the heterojunctions formed in the interfaces of SnO2and α-Fe2O3.