CeO2 nanoscale particles: Synthesis, characterization and photocatalytic activity under UVA light irradiation

Abstract

CeO2 nanoparticles (NPs) were synthesized in alkaline medium via the homogeneous precipitation method and were subsequently calcined at 80 °C/24 h (assigned as CeO2-80) and 500 °C/2 h (assigned as CeO2-500). The as-prepared materials and the commercial ceria (assigned as CeO2-com) were characterized using TGA-MS, XRD, SEM-EDX, UV–vis DRS and IEP techniques. The photocatalytic performances of all obtained photocatalysts were assessed by the degradation of Congo red azo-dye (CR) under UVA-light irradiation at various environmental key factors (e.g., reaction time and calcination temperature). Results reveal that CeO2 compounds crystalize with cubic phase. CeO2-500 exhibits smaller crystallite size (9 nm vs 117 nm) than that of bare CeO2-com. SEM analysis shows that the materials are spherical-like in shape NPs with strong assembly of CeO2 NPs observed in the CeO2-500 NPs. EDX analysis confirms the stoichiometry of CeO2 NPs. UV–vis DRS measurement reveals that, CeO2-500 NPs exhibits a red-shift of absorption band and a more narrow bandgap (2.6 eV vs 3.20 eV) than that of bare CeO2-com. On the contrary, Urbach energy of Eu is found to be increased from 0.12 eV (CeO2-com) to 0.17 eV (CeO2-500), highlighting an increase of crystalline size and internal microstrain in the CeO2-500 NPs sample. Zeta potential (IEP) of CeO2-500 NPs is found to be 7.2. UVA-light-responsive photocatalytic activity is observed with CeO2-500 NPs at a rate constant of 10 × 10−3 min−1, which is four times higher than that of CeO2-com (Kapp = 2.4 × 10−3 min−1) for the degradation of CR. Pseudo-first-order kinetic model gives the best fit. On the basis of the energy band diagram positions, the enhanced photocatalytic performance of CeO2-500 nano-catalyst can be ascribed to O2·−, O·H and R·+ as the primary oxidative species involved in the degradation of RC under UVA-light irradiation.