Study of a Facile Cerium Oxide Nanoparticles Hydrothermal Synthesis by Ceric Ammonium Nitrate

Cerium oxide nanoparticles (CNPs) are a well-known functional material with broad applications in catalysis, gas sensor, and nanomedicine due to their unique shape-dependent properties. In recent years, solutions-based, sol-gel, and template-assisted synthesis routes have been explored for CNPs synthesis. Among these methods, hydrothermal synthesis has been considered one of the most effective and scalable routes thanks to its merit of single-step, one-pot synthesis. Regarding hydrothermal synthesis, cerium (III) nitrate/chloride/sulfate, sodium hydroxide, and ammonium hydroxide are the most commonly used precursor and oxidizers in CeO₂ hydrothermal synthesis. However, the application of the nanoparticles synthesized from a harsh high-pH alkaline synthetic environment usually suffers from vigorous nanoparticle aggregation, which could severely affect their performance.<br/>In this study, we report a facile hydrothermal synthesis method to fabricate cerium oxide nanoparticles with different shapes. The ceric ammonium nitrate (CAN) was used as a cerium precursor to synthesize a highly dispersed CNPs in a low-pH acidic environment to obtain a cubic fluorite structure with narrow size distribution. The octahedron shape of CNP was synthesized by introducing only CAN into the aqueous precursor. The strong shape transformation of CNPs from octahedron to truncated octahedron to cubical is achieved by controlling the introduction of acetic ion which is done by varying the concentration between sodium acetate and acetate acid in precursor. CNP synthesized in pH &gt;10 environments was considered a control in this study to compare the physiochemical properties difference between CNPs synthesized in acidic or alkaline precursor environments. One of the key properties of CNPs is its cyclic change of redox potential Ce³⁺/ Ce⁴⁺ on its surface. Hence the variation in the morphology of CNPs changed its redox potential, which was measured and analyzed using X-Ray photoelectron spectroscopy. CNP's change in size and shape affects its superoxide dismutase activity (SOD). The result, which showed better SOD activity, will be studied for their application in biomedical therapy.