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.