| ZnO as semiconductor materials, has been widely applied to photocatalytic degradation of pollutants and gas sensor, due to its high electron mobility and special physical and chemical properties. While the morphology of materials and the corresponding exposed active surfaces have an important influence for its application. Therefore, it is urgent to synthesize special morphology with high exposed active facet and take measures to improve the gas sensing charasteristies and photocatalysis properties of ZnO nanomaterials. The mechanisms for photocatalysis and gas sensing process are with distinct emphasis. In this work, three different kinds of morpholog ies for ZnO nanostructures were synthesized, then diverse sensitizers, such as Au, Ag2Se and CdSe, were adopted to sensitized as-prepared ZnO to improve the gas sensing and photocatalysis properties. The content and results are shown as follows:(1) Hierarchically ZnO nest-like architectures (ZnO NAs) composed of nanosheets (thickness of 60 nm) were successfully synthesized by a facile hydrothermal method. The results show that ZnO NAs are wurtzite phase and the exposed facet is (001) and (110) with high specific surface area (63.46 m2/g), and the exposure rate for (100) is 95%. ZnO NAs exhibit high sensitivity (R=23), low detection limit (10 ppm), fast response (19 s) and good selectivity to ethanol at the low working temperature (105 ℃). Moreover, ZnO NAs can more effectively degradate rhodamine Bunder under ultraviolet light, which is 1.2 times than P25. The good gas sensing properties are due to mounts of oxygen vacancy and high exposed active facet (001) and (110), which are benefit to absorb more ethanol molecules and following reactions. And the good photocatalysis properties are due to oxygen vacancies can capture more excited electrons and inhibition the of composite electron-hole pairs under UV irradiation.(2) Dumbbell ZnO (ZDs) was prepared using liquid phase deposition on the surface of conductive glass ITO, and Ag2Se quantum dots (QDs) sensitized dumbbell ZnO (ASZDs) were prepared by the method of ion exchange. Compared to ZDs, the proportion of O- in the surface of ASZDs has improved significantly for the ASZDs (2.6 times), which is good for the adsorption of acetone molecules and following reactions. The sensitivity to acetone for ASZD increased 6 times compared with that for ZDs and response time is only 9 s at the working temperature as low as 105℃.(3) CdSe QDs sensitized dumbbell ZnO (CSZDs) were prepared by the method same as (2) above. Compared to ZDs, the proportion of reactive oxygen species O" has increased 1.13 times, which is benefit to adsorpt more ethanol molecules and the oxideation of ethanol. The CSZDs gas sensing to ethanol shows excellent response: high sensitivity (7 times higher than ZDs), short response time (12 s), low working temperature(110℃) and good selectivity. Moreover, the optical absorption of the CSZDs can be controllably tuned to visible spectrum via CdSe QDs sensitized. And effectively suppresses the photoproduction electron-holes of the compound, enhancing the photoproduction carrier transmission efficiency, then improving the photocatalysis properties. Moreover, the external quantum efficiency for CSZDs increced 1.5 times than ZDs and it owns great photo-electric response, which has potential use as anode materials in solar cell.(4) Small-size nest like ZnO architectures (ZnO Ss, about 2μm) composed of nanosheets were successfully synthesized by a facile hydrothermal method on the surface of ITO, then Au nanoparticles (about 6nm) is utilized to be sensitized onto ZnO Ss by high temperature reduction method. After sensitized, ZnO As effectively decreases the composition of electron-hole pairs and enhances the visible-light absorption of ZnO As. Moreover, the work function of ZnO As is reduced and electrons from ZnO off to adsorbed oxygen (Oads) were accelerated, then the photocatalytic active substances (·OH) were formed, so pollutants were degradated. |
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