Yuxiang Qin

First principles study on the surface- and orientation-dependent electronic structure of a WO3 nanowire

The effects of the surface and orientation of a WO3 nanowire on the electronic structure are investigated by using first principles calculation based on density functional theory (DFT). The surface of the WO3 nanowire was terminated by a bare or hydrogenated oxygen monolayer or bare WO2 plane, and the [010]- and [001]-oriented nanowires with different sizes were introduced into the theoretical calculation to further study the dependence of electronic band structure on the wire size and orientation. The calculated results reveal that the surface structure, wire size and orientation have significant effects on the electronic band structure, bandgap, and density of states (DOS) of the WO3 nanowire. The optimized WO3 nanowire with different surface structures showed a markedly dissimilar band structure due to the different electronic states near the Fermi level, and the O-terminated [001] WO3 nanowire with hydrogenation can exhibit a reasonable indirect bandgap of 2.340 eV due to the quantum confinement effect, which is 0.257 eV wider than bulk WO3. Besides, the bandgap change is also related to the orientation-resulted surface reconstructed structure as well as wire size.

Synthesis and NO 2 -sensing properties of one-dimensional tungsten oxide nanowire bundles

Nanowire bundles of tungsten oxide were synthesized by solvothermal method with tungsten hexachloride (WCl 6 ) as precursor and 1-propanol as solvent. The synthesis processes were preformed at different WCl 6 concentration. Long W 18 O 49 nanowire bundles with effective surface area of 89.89 m2/g was synthesized at a WCl 6 concentration of 0.01M. With concentration increasing, the nanowire bundles became shorter and thicker and finally a nanoplates structure formed. The measurements for NO 2 -sensing properties indicated that the longer and thinner W 18 O 49 nanowire bundles showed the quickest response/recovery and the highest sensitivity to different concentration NO 2 gas due to their special structural feature, and the response time, recovery time and sensitivity are 19 s, 112 s and 123.6 to 5 ppm NO 2 , respectively.