Ce3+-ion, Surface Oxygen Vacancy, and Visible Light-induced Photocatalytic Dye Degradation and Photocapacitive Performance of CeO2-Graphene Nanostructures

Cerium oxide nanoparticles (CeO₂ NPs) were fabricated and grown on graphene sheets using a facile, low cost hydrothermal approach and subsequently characterized using different standard characterization techniques. X-ray photoelectron spectroscopy and electron paramagnetic resonance revealed the changes in surface states, composition, changes in Ce⁴⁺ to Ce³⁺ ratio, and other defects. Transmission electron microscopy (TEM) and high resolution TEM revealed that the fabricated CeO₂ NPs to be spherical with particle size of ~10-12 nm. Combination of defects in CeO₂ NPs with optimal amount of two-dimensional graphene sheets had a significant effect on the properties of the resulting hybrid CeO₂-Graphene nanostructures, such as improved optical, photocatalytic, and photocapacitive performance. The excellent photocatalytic degradation performances were examined by monitoring their ability to degrade Congo red ~94.5% and methylene blue dye ~98% under visible light irradiation. The photoelectrode performance had a maximum photocapacitance of 177.54 Fg^-1 and exhibited regular capacitive behavior. Therefore, the Ce³⁺-ion, surface-oxygen-vacancies, and defects-induced behavior can be attributed to the suppression of the recombination of photo-generated electron-hole pairs due to the rapid charge transfer between the CeO₂ NPs and graphene sheets. These findings will have a profound effect on the use of CeO₂-Graphene nanostructures for future energy and environment-related applications.