Morphological Mapping of Hydrothermally Synthesised Nanoceria at High Ce Concentrations

Abstract Synthesis methods for different nanoparticulate morphologies are of increasing importance since the morphological features determine the redox performance in many applications. However, the effects of synthesis variables on the formation of these morphologies are not well understood and previous work has been limited to relatively low [Ce] and [NaOH]. The present work reports an investigation of the morphological development of nanoceria through the examination of the key processing variables for precipitation and hydrothermal synthesis at high [Ce] and [NaOH]. Characterisation included XRD, Raman, TEM, HRTEM, SAED, XPS, and BET. The resultant refined morphological map delineates the effects of [NaOH] and temperature on the morphological evolution of ceria nanoparticles synthesised from Ce(NO₃)₃ aqueous solutions in terms of morphology and grain size. The data show that temperature dominates the morphology but elevated [NaOH] and temperature both increase the nanoparticle size. Compared to synthesis at low concentrations, high [Ce] also promotes grain growth, although this is secondary to the effect of [NaOH]. Significantly, the increased grain sizes also enhance the concentrations of catalytically active sites (Ce³⁺ and charge‐compensating oxygen vacancies). The present work provides a platform of fundamental concepts for the control of experimental variables to synthesise predictable nanoparticulate characteristics.