以溶解水熱製程製備奈米二氧化鈰結晶

Abstract

本論文提出了一改良型之水熱法製程以合成高結晶性之奈米二氧化鈰(CeO2)晶體。本論文先以水熱法製備碳酸氧氧鈰(CeOHCO3)，再以合成得之碳酸氫氧鈰粉體作為鈰離子來源、雙氧水(H2O2)作為氧化劑，進行第二次水熱反應合成奈米氧化鈰晶體。本論文成功合成得到晶粒大小超過30 nm之奈米氧化鈰晶體，且合成所需之反應溫度僅為180°C，反應時間僅需6小時。在水熱環境下，鈰三價離子可以自碳酸氫氧鈰粉體當中釋出，並進一步行氧化-水解-脫水反應來形成二氧化鈰晶體。碳酸氫氧鈰粉體的緩慢溶解特性可以控制鈰離子的釋放速率，並控制成核點的產生速率，進而能有助於成長高結晶性之二氧化鈰晶體。本論文所提出之奈米氧化鈰晶體合成機制可解釋為一「自催化溶解-氧化-結晶」機制，質子在反應中有催化的效果，可促進碳酸氫氧鈰粉體溶解並製造有利於奈米氧化鈰晶體成長的環境。本論文所提出之奈米氧化鈰晶體合成製程可有效降低合成大晶粒大小之氧化鈰晶體所需要之反應溫度，並縮短反應所需之時間，且有潛力可用以合成不同種之金屬氧化物材料。

A modified hydrothermal route was successfully developed to synthesize cerium oxide (CeO2) nanocrystals with high crystallinity. Cerium carbonate hydroxide (CeOHCO3) and hydrogen peroxide (H2O2) were used as the source of cerium ions and oxidizer, respectively, and CeO2 nanocrystals with crystallite size of more than 30 nm were successfully synthesized at 180 °C within 6 h. Ce3+ ions are released from CeOHCO3 particles under hydrothermal condition, and forming CeO2 via the following oxidization-hydrolysis-dehydration process. The slow dissolution of CeOHCO3 particles controls the releasing rate of cerium ions, which can control the formation nuclei and would be benign to grow CeO2 nanocrystals with large crystallite size. The growth mechanism of the CeO2 nanocrystals is elucidated as an autocatalytic dissolution-oxidization-crystallization process, and protons are proved to have catalytic effects. The present protocol can significantly reduce the reaction time and the reaction temperature for synthesizing CeO2 nanocrystals with high crystallinity, and could potentially be applied to synthesize other oxide materials.