The Influence Of Metal Doping On The Microstructure And Gas Sensing Properties Of SnO₂ Nanomaterials

SnO₂ is an important direct band gap oxide semiconductor, which has band gap of 3.6 eV at room temperature, and the exciton binding energyas high as 130 meV. Because of its nanomaterials with unique electricity, optical and chemical properties, which has an important application value in solar cells, laser diode, ultraviolet laser piezoelectric sensors, surface acoustic wave device, gas sensor, etc. But the system study of the morphology for different gas response of the research is still lacking. Therefore, we can further through grow parameter optimization, such as doping, surface modification, and semiconductor or metal composite methods, thus achieve the purpose of modification for SnO₂ nanomaterials. Our thinking was mainly base on hydrothermal method preparation porous hierarchical 3D nanoflower and electrospinning method to construct nanoparticles, 1D nanotube, to synthesize small size of Y doped SnO₂ nanoparticle, Y doped Sn O2 nanotube, TiO2-SnO₂ composite nanotube and 3D porous SnO₂ nanoflower, their gas sensitive properties are also discussed. Mainly works and results are as following:1. Porous coral-like pure and Y-doped SnO₂ nanoparticles were fabricated by electrospinning method and calcination procedure. The porous coral-like SnO₂ nanostructure and morphology were characterized. The results indicated that the coral-like structure was composed of 5 wt% Y-doped SnO₂ nanoparticles had smaller particle size and bigger surface-to-volume area. In addition, through the gas sensitive tests found that 5 wt% Y-doped SnO₂ based sensor has better response, shorter response-recovery time and selectivity than pure SnO₂ for the same acetic acid concentration at 300°C. And through the analysis of the structure and morphology, the acetic acid sensing mechanism of SnO₂ rectangular nanoparticles was also investigated. These results demonstrate that the coral-like Y-doped SnO₂ nanoparticles exhibited excellent sensing properties are due to the decreasing of the particle size, the porous surface structure and the promoting effects of Y-doping. Thus, porous Y-doped SnO₂ coral-like nanostructure can be used as a promising material for acetic acid sensors.2. Pure and Y-doped SnO₂ hollow nanofibers with porous structures were fabricated via electrospinning technique and calcination procedure. The porous SnO₂ hollow nanofibers were characterized. Acetone sensing properties of the hollow nanofibers were also investigated. The results indicated that the Y-doped SnO₂ hollow nanostructure was compared to pure SnO₂ hollow nanofibers had bigger surface-to-volume area. The grain size of pure and 0.7 wt% Y-doped SnO₂ nanostructures were about 21.8 nm and 20 nm, respectively. Therefore, according to the XPS analysis, the Y is successfully incorporated into SnO₂ lattices. Compared with pure SnO₂ hollow nanofibers, Y doped SnO₂ nanostructure exhibited excellent sensing performances toward acetone. Y-doped SnO₂ hollow nanofibers showed high gas response, fast response-recovery time, excellent selectivity and long-term stability to acetone at 300°C, which were attributed to the 1D hollow nanostructure. The formation mechanism and the acetone sensing mechanism of SnO₂ hollow nanofibers were also discussed. It was worth mentioned that 1D porous prismatic structure of SnO₂ hollow nanofibers and the Y-doping improved the gas sensing performances, so Y-doped SnO₂ hollow nanofibers has significant improvement for selective detection of acetone.3. On the basis of the previous chapter, the TiO2-SnO₂ composite nanotubes（NTs） have been fabricated, and the morphology and structure of all samples were characterized. The results indicated that both the average diameter and surface roughness of TiO2-SnO₂ composite NTs were bigger than these of Y-doped SnO₂ NTs. In addition, the responses of all samples to acetone were tested. We found that the gas sensing performance of TiO2-SnO₂ composite NTs have improved significantly in comparison with Y-doped SnO₂ NTs. The main reason is the construction of heterojunction can enhance the surface reaction between adsorbed oxygen and current-carrying electrons. As is known to all, to improve the gas-sensing properties of materials mainly achieved by the following two aspects:（1） Reduce the grain size and increase the surface active area of material, build porous materials（hollow, mesoporous materials, etc.） to increase the interactive surface, which can provide more active site for gas adsorption.（2） The modification of rare-earth elements and precious metals is used to change the intrinsic electrical characteristics of semiconductor, optimize material morphology and increase surface carrier concentration. Through the improvement of these two aspects, the TiO2-SnO₂ composite NTs with an enhanced gas sensing performance to acetone were successfully synthesised.4. 3D hierarchical porous flower-like SnO₂ architectures have been successfully synthesized by the hydrothermal method and followed by calcination. The microstructure of SnO₂ nanoflower was characterized using XRD, SEM and TEM. The results show that the hierarchical flower-like architectures are found to be composed of well ordered 2D porous nanosheets, and the thickness of nanosheets was about 20 nm. Mixed SnO₂ nanoflower with deionized water and then coated on a ceramic tube with electrode to fabricate gas sensors. From the gas sensitive test, we found that compared with the previous results, the acetone-sensing performance of porous SnO₂ nanoflower was further enhanced.