Ruosong Wang,Huaqiao Tan,Zhao Zhao,Guoqiang Zhang,Laiwen Song,Wenfei Dong,Zaicheng Sun
Nanostructured metal oxides such as ZnO and TiO2 have been extensively employed as self-cleaning coatings due to their large band gaps as well as their hydrophilic and photocatalytic properties. We have developed a simple hydrothermal method to coat thin TiO2 nanosheets with exposed (001) facets onto a ZnO nanorod array. The chemical stability of the ZnO nanorods was great improved due to the existence of the TiO2 layer. Owing to the porous structure of the ZnO@TiO2 nanorod arrays, this thin coating layer possesses anti-reflective properties. A transmittance improvement of ∼5% was observed for one-side coated FTO glass. This coating also exhibits good hydrophilic properties, after addition of the TiO2 nanosheets. More importantly, these ZnO@TiO2 nanorod arrays display excellent photocatalytic properties for the degradation of dye molecules, due to the heterojunction between the ZnO nanorods and TiO2 nanosheets. This heterojunction facilitates the charge separation of photo generated carriers. Based on the above features, the ZnO@TiO2 core/shell nanorod array film has many advantages as a self-cleaning coating.
Constructing heterostructures with efficient modulation of electron transfer at the heterointerface affords great opportunity for electronic devices. Herein, a high performance nanosensor based on core-shell ZnO@TiO 2 nanorods is successfully realized for n-butanol detection. The n-n heterointerface formed between TiO 2 and ZnO allows for vast variation of conductivity due to electron confinement induced by their different works functions and enhances the response on exposure to gaseous molecules. Studies reveals that the shell thickness of TiO 2 has a great impact on the sensor performances, and the sensor based on ZnO@TiO 2 nanorods with 6.4 nm-thick TiO 2 shell delivers outstanding gas sensing properties in terms of high sensitivity, low detection limit (133 ppb), fast response-recovery, and excellent selectivity towards n-butanol detection. The mechanism for the improved gas sensing function is ascribed to the heterojunctions of core-shell nanostructure, the enhanced oxygen adsorption due to the TiO 2 shell and the fully electron-depleted TiO 2 shell layer with a thickness comparable to the Debye length. The strategy presented here is generally applicable and can provide some hints to design efficient electronic sensors with optimized performances.
The regularly ordered core–shell nanorods provide an effective transport channel for the adsorption and desorption of the target molecules. However, it remains a great challenge to precisely control the shell thickness of the ordered core–shell nanorods and improve the catalytic activity of their surfaces due to the complexity of the reaction system, especially by enhancing their selectivity to short-chain alcohols. Herein, we propose ZnO/TiO2 core–shell nanorod arrays (NRs) with different shell thicknesses prepared by electron beam evaporation and found that they possess advanced selectivity for short-chain alcohols. The response time of a ZnO/TiO2 core–shell NR with a TiO2 shell of 30 nm to 100 ppm isoamyl alcohol is 17 s. Its response to 100 ppm of isoamyl alcohol is 807, which is approximately 158 times that of the pure ZnO NR. The ZnO/TiO2 NR (30 nm) sensor exhibited excellent selectivity for methanol, ethanol, isopropanol, n-butanol, and isoamyl alcohol. The response to alcohols increased with the increase of the alcohols’ chain length. Its sensing mechanism for short-chain alcohols is explained in terms of adsorption energy, acidity, and electronegativity of H in organic groups by density functional theory in detail. Our results open an alternative route for the design of sensitive materials for the selective detection of short-chain alcohols.
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