| With the development of economy and technology, environmental problems have been the major challenges for the human beings. The series of environmental problems, such as, air pollution, ozone depletion, acid rain, and global warming were generally generated by the toxic and harmful gases, it is very important to prepare gas sensors with excellent properties to detect the toxic gases. It is reported that the gas sensing properties are correlated to the size, morphology and composition of the materials. Small size nanoparticles have been attracted great attentions due to its high surface energy and specific surface area; however, their aggregation will lead to the decreases of the activity and stability. It is of great interesting to self-assembling the small size nanoparticles into hierarchical structures, which will not only inherit the properties of nanoparticle but also take advantages of the interactions between neighboring nanoparticles, which makes it exhibits optimal properties in the application of gas sensor, photocatalysis, solar cells, and Li-ion battery. In addition, the modification of the gas sensing materials with noble metal will lead to the enhancement of the gas sensing performance. This work will focus on the preparation and gas sensing properties of the gas sensing materials, and the gas sensing mechanism will also be discussed.1. The small size nanoparticles of ZnO and SnO2 have been successfully prepared, and the particle size could be controlled via annealing the as-synthesised precursor at different temperature. The gas sensing performance of the obtained samples has been detected, and the results indicate that with the decreasing of the particles size the gas sensing response increases. The ZnO nanoparticles with small size show high sensing response, fast response and recovery, and good sensing selectivity to the NO2. The SnO2 quantum dots exhibit excellent sensing performance to the ethanol, and both of the response and recovery time could down to 1 s, which are shorter than that of reported materials.2. As the small size nanoparticles are easy to be aggregated because of its high surface energy, it is of great interesting to fabricate the nanoparticles into hierarchical structures. Hierarchical ZnO with dandelion-like and tubular structure has been successfully prepared. These hierarchical structures were constructed by nanoparticles and have highly open-ended and porous structures, and larger specific surface area. The nanoparticles size could be controlled by altering the annealing temperature. Those hierarchical structures exhibit excellent gas sensing performance due to the highly open-ended and porous structures, larger specific surface area, and small nanoparticles size. Furthermore, those hierarchical structures have showed good repeatability due to their good structural stability.3. The hierarchical spherical SnO2 has been prepared by a simple hydrothermal method. The obtained SnO2 was composed by porous nanosheets with the thickness of 3～6 nm. By comparing with the SnO2 nanosheet, those hierarchical spherical SnO2 exhibits higher sensing response and higher limits of concentration that could be detected, this is because the nanosheets stand on the sphere which could favor to the gas diffusion and support more active sites for the gas adsorption; on the other hand, the thin and porous nanosheets will facilitate the diffusion of gas and the capture of electrons.4. Considering the fact that the facets of the Pd nanoparticles have influences on the gases adsorption and catalysis performance, the Pd nanoparticles with different exposed facets has been prepared and decorated onto the ZnO nanorods. The gas sensing performance of the Pd decorated ZnO to H2 has been studied, and the results indicates that the cube Pd nanoparticles with (100) facet exposed decorated ZnO has showed the highest and the fastest response, but shortest recovery to H2 due to the strong adsorption of H2 onto the (100) facet.5. Based on the excellent properties of the bimetal in the application of catalysis, the PtAu bimetallic nanoparticles with Pt and Au highly dispersed and with the atomic ratio of 1:1 have been prepared. The gas sensing performance of the PtAu decorated ZnO nanorods response to the H2 has been studied, and the results indicates that the PtAu decorated ZnO shows the highest sensing response to H2 compared with the Pt decorated ZnO, Au decorated ZnO, and Pt and Au co-decorated ZnO. The reasons for the excellent sensing performance of the PtAu decorated ZnO nanorods are that the easy and strong adsorption of the H2 onto the PtAu alloys. In addition, the PtAu decorated ZnO shows good sensing selectivity to H2 and could detect the H2 at relatively low operating temperature. What more, the PtAu decorated ZnO shows high sensing response to H2 even with low concentration. |
