| ZnO-based nanocomposites are widely applied as catalysts in the fields of detection of toxic and harmful gas in air pollutant and photocatalytic degradation of pollutants in the environment. Compared with pure ZnO, ZnO-based nanocomposites usually have excellent properties due to the synergistic effects between different components. This paper focused on the synthesis of various semiconductor nanocomposites based on ZnO through various routes in order to improve the gas sensing and photocatalytic properties. In addition, the effects of morphologies and structures of as-prepared nanostructures on the properties were also investigated. The main contents and conclusions are described as follows:(1) Using CTAB as surfactant, urea as mineralizer, Zn2SnO4 three-dimensional (3D) flower-like hierarchical nanostructures was successfully synthesized via a simple one-step hydrothermal method. SEM and TEM results revealed that the Zn2SnO4 flower-like structures were assembled with nanorods. Gas sensing test results showed that the hierarchical Zn2SnO4 sensor exhibited significantly higher sensitivity and better sensing properties as well as short response-recovery time to ethanol vapor than the compact Zn2SnO4 structures. The optimum operating temperature of the sensors to ethanol was 380?, the responses of hierarchical Zn2SnO4 sensor to 50 ppm ethanol was 30.8, and the time of response and recovery was 10 s and 7 s, respectively. The improvement of the sensing performance of the flow-like Zn2SnO4 may be attributed to the contact surface area between Zn2SnO4 and target gases, and hierarchical nanostructures provided more channels for gas diffusion, which was of great benefit to the response.(2) Graphene oxide (GO) was obtained by oxidation of graphite powders by the modified Hummers' method. A composite photocatalyst of zinc oxide (ZnO) nanoparticles decorated with different contents of graphene (rGO) was prepared via a one-step method. The structure, morphology and optical properties of as-synthesized products were characterized by XRD, SEM, TEM, Raman and UV-vis DRS. The results showed the aggregation degree of ZnO nanoparticles could be effectively alleviated due to the introduction of rGO, light absorption ability was increased in comparison with pure ZnO. The photocatalytic performance for the degradation of methyl orange (MO) was investigated under simulated sunlight irradiation. It was revealed that rGO-ZnO composite showed a high catalytic ability,when the percentage of rGO was up to 1.0 wt.%, the degradation rate of optimal rGO-ZnO composite on MO was 15.17 times as great as that of pure ZnO. The enhanced photocatalytic activity mainly benefited from the enhanced adsorption capacity, the extended optical absorption range and the effective separation of photoinduced electron-hole pairs.(3) Here, A series of Sn-doped ZnO samples with various doping concentration (mole fraction) were prepared by alcohol-thermal method. XRD, SEM, TEM, EDS and UV-vis DRS were used to investigated the crystal structure, morphology, element composition and optical properties of the prepared Sn-doped ZnO composites. The effects of the Sn-doped amount on the photocatalytic activity of ZnO were also discussed. The results showed that Sn doping did not affect the morphology of ZnO, but the size of the ZnO grain decreased significantly with the increment of Sn amount and the band gap of ZnO decreased. Methyl orange was used as a probe molecule to evaluate the photocatalytic activity of pure ZnO and Sn-doped ZnO. The resulted showed that 5% Sn-ZnO sample showed the highest photocatalytic performance, the degradation rate of ZnO on MO was 1.83 times as great as that of pure ZnO. The enhanced photocatalytic activity of Sn-doped ZnO was mainly due to the decrease of the grain size of ZnO and the increase of specific surface area. Besides, the introduced impurity level reduced the excitation energy and promoted the effective separation of photoinduced electron-hole pairs. |
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