Hydrothermal synthesis and multifunctional performance of cerium oxide nanoparticles for sunlight-driven photocatalytic and supercapacitor applications

Cerium oxide (CeO2) nanoparticles were synthesized via a low-temperature hydrothermal method using cerium(III) acetate hydrate as the precursor, followed by calcination at 600–800 °C to elucidate the effect of thermal treatment on their defect chemistry and multifunctional performance. X-ray diffraction confirmed the formation of phase-pure cubic fluorite CeO2, while Fourier-transform infrared spectroscopy verified the characteristic Ce–O bonding. Electron microscopic analyses revealed nearly spherical, uniformly distributed nanoparticles with good crystallinity. Among the prepared samples, C2-700 exhibited the most favorable balance between crystallinity and defect-related features, as reflected by its reduced optical band gap of 2.44 eV obtained from UV–Vis diffuse reflectance spectra using the Kubelka–Munk model. Photoluminescence studies showed a defect-associated emission at 663 nm, indicative of oxygen-vacancy-related states. Electrochemical measurements demonstrated pseudocapacitive behavior with high specific capacitance at 1 A g−1 and 94% retention after 2000 cycles. The nanoparticles also exhibited appreciable sunlight-driven photocatalytic degradation of the cationic dyes methylene blue and brilliant green, with degradation efficiencies of 75% and 69%. These findings highlight the importance of calcination-temperature-controlled defect engineering in tuning the structural and functional properties of CeO2 nanoparticles for environmental and energy-storage applications.