Microstructure Control Of Electrospinning SnO₂ Nanotubes And Its Influence On Gas-Sensing Performance

As the serious air pollution situation in China, it is urgent to apply ultra-sensitive and high-responsive gas sensors in air monitoring. Metal oxide semiconductor gas sensor is regarded as a promising air monitoring device due to its wide application, high sensitivity, easily testing method and so on. The gas-sensing reaction relies on the catalytic reaction in the solid-gas interface. Thus the gas-sensing properties is closely related to the microstructure properties of metal oxide including surface area, grain size, porous structure, defects, heterointerface and so on. This paper focuses on the influence of mictructure properties on the gas-sensing performance through controlling microstructure of SnO2 nanotubes using electrospinning. Consequently, the relation between microstructure parameters and sensing performance is builted.Firstly, the formation mechanism of SnO2 nanotubes fabricated by electrospinning was studied. Experimental results revealed the sequential structural evolution from solid fiber to wire-in-tube to nanotube for PVP/SnCl2 electrospun fibers during calcining process. A PVP assisted Ostwald ripening was proposed for the formantion of SnO2 nanotubes by comparing and analyzing the calcining residue and volatile products and the structural evolution. The mechanism inspired us to fabricate SnO2 wire-in-tube(WIT) and nanotubes(NTs) by controlling the calcining temperature. Gas-sensing tests revelaed that SnO2 WIT showed good response to toluene while SnO2 NTs showed good reponse to formaldehyde. Thus the different architecture of SnO2 may affectits selectivity.To investigate the effect of defects of SnO2 nanotubes on sensing performance, we fabricated Al-doped SnO2 NTs and attempted to find the relationship between oxygen vacancy and gas-sensing properties. As the Al content increased, the grain size of SnO2 varied little, but the oxygen vacancies gradually increased and showed the highest amount when Al/(Al+Sn) was 8%. At the meantime, this specimen exhibited the highest response to formadelyde. The dependence of gas response of Al-doped SnO2 NTs on the amount of oxygen vacancies illustrated that the sensing performance of SnO2 strongly depended on oxygen vacancy.To resolve the drawback of overlarge grain size of electrospinning SnO2 nanotubes and enhance their gas-sensing properties, Si was doped into the SnO2 WIT. It was demonstrated that 1% Si-doped SnO2 showed the smallest the grain size which was 8.6 nm and the highest response to 80 ppm formaldehyde at a low operature temperature of 120°C. Additionally, 1%Si-Sn showed fast response and recovery rate at 120°C. Furthermore, the effect of CeO2 on gas-sensing performance of SnO2 WIT was investigated. We proposed an electronic sensitization mechanism for the improved sensing performance of CeO2-modified SnO2 in which the localization depletion region was enhanced. This work provided new evidence for the research on the effect of rare earth on the catalytic reaction of SnO2.