Controlled One-Step Synthesis of Monodisperse CeO2 Octahedra in a Binary Solvent System with Waste Liquid Recycling.

To overcome the limitations of template-dependent and anion-assisted methods, this work presents a solvent-controlled strategy for the one-step solvothermal synthesis of octahedral CeO2. Using only Ce(NO3)3·6H2O in methanol/water (MeOH/H2O) mixtures without the addition of auxiliary templates or surfactants, phase-pure cubic CeO2 was obtained. Well-defined octahedra were exclusively formed in a 15 mL MeOH/5 mL H2O system at 180 °C for 12 h, whereas other alcohols (including ethanol (EtOH), n-propanol (n-PrOH), and iso-propanol (i-PrOH)) yielded irregular aggregates. Time-dependent evolution revealed continuous crystallinity optimization between 3 and 24 h, beyond which surface dissolution occurred. The solvothermal mother liquor could be recycled four times without compromising phase purity or octahedral morphology, as confirmed by XRD and SEM. This work provides a green and practical route for morphology-controlled oxide synthesis while significantly reducing solvent consumption.