Hydrothermal synthesis of CeO2 nanowires and WO3-CeO2 core/shell nanorods for gas sensing applications

Autor: Peng-Wen Wang, 王芃文
Rok vydání: 2012
Druh dokumentu: 學位論文 ; thesis
Popis: 100
We synthesized CeO2-WO3 core/shell nanowires and WO3- CeO2 core/shell nanorods by a two-step hydrothermal method. The CeO2 nanowire and WO3 nanorod core structures were synthesized in the first step, and then the WO3 and CeO2 shell structures were deposited on the CeO2 and WO3 core nanostructures. The growth mechanism of CeO2 nanowires was investigated by observing the structure evolution during the synthesis process. The crystalline structures and morphologies of as-synthesized products were identified by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) analysis. In addition, gas sensors based on CeO2 nanowires, WO3 nanorods, CeO2-WO3 core/shell nanowires and WO3- CeO2 core/shell nanorods were fabricated and their gas sensing properties to different concentrations of CO and NO2 were measured. The results show that the formation of single-crystalline CeO2 nanowires is governed by the Ostwald ripening (OR) mechanism. Ce(OH)3 nuclei are formed by homogeneous nucleation as soon as the Ce3+ ions are mixed with NaOH. Ce(OH)3 will first oxidize into in the basic solution environment and then Ce(OH)4 will transfer to CeO2 nanopaticles under high temperature and pressure. The increase of dissolution and recrystallization rate will promote the anisotropic growth of CeO2 along the [110] direction and finally form CeO2 nanowires. For NO2, the WO3 nanorods exhibited the best sensitivity, while the WO3-CeO2 core/shell nanorods had lowest sensitivity. The sensitivities of CeO2 nanowires and CeO2-WO3 core/shell nanowires are in between WO3 nanorods and WO3-CeO2 core/shell nanorods. For CO, only CeO2 nanowires had noticeable sensitivity, while others had limited or no response.
Databáze: Networked Digital Library of Theses & Dissertations
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