Morphological Mapping and Growth Mechanisms of Ceria Nanocrystals

Abstract

The morphologies of ceria nanocrystals play an essential role in determining their redox performance in many applications, yet the effect of synthesis variables on the formation of ceria nanoparticles of different morphologies and their related growth mechanisms are poorly understood. The present thesis investigates the morphological development of nanoceria through the examination of the key processing variables for precipitation and hydrothermal synthesis at high Ce and NaOH concentrations. The characterization included the analytical techniques XRD, TEM, HRTEM, XPS, BET, and laser Raman microspectroscopy.

A comprehensive survey of the effects of experimental conditions on the resultant morphologies of nanoceria during precipitation and hydrothermal synthesis is presented. The key experimental variables [Ce], [NaOH], temperature, and time are observed to have significant effects on the morphological evolution and grain growth. Detailed schematic mapping of nanoceria in the form of nanorods and nanocubes indicates that high [Ce] and low temperature facilitate chain formation and subsequent coalescence into hexagonal nanorods. With increasing temperature and time, these structurally destabilise and re-form into nanospheres and nanocubes.

The present work is elucidated through a range of mechanistic interpretations that underpin a new morphological map for high [Ce]; this incorporates not only morphological development but also grain growth effects of nanoceria. The experimental data and morphological map have allowed the derivation of the comprehensive schematic mapping that explains, for the first time, the effects of the four key experimental variables on the generation of the different morphologies that have been observed and reported in the literature.