Green Synthesis, Structural Characterization and Kinetics of Photocatalytic Degradation of Reactive Blue 19 Dye Using CeO2-doped Reduced Graphene Oxide Nanohybrid

The development of visible-light-active photocatalysts through sustainable synthetic routes remains a critical challenge in wastewater remediation. In this study, a CeO₂-doped reduced graphene oxide (CeO₂/rGO) nanohybrid was synthesized using Carica papaya leaf extract as a green reducing agent. The resulting catalyst exhibited a surface area of 95 m²/g, a narrowed optical band gap of 2.91 eV, and uniformly distributed CeO₂ nanoparticles with an average size of 4–8 nm as confirmed by HRTEM. Structural and spectroscopic analyses validated the formation of a stable CeO₂/rGO hybrid with enhanced charge separation efficiency. The photocatalytic activity was evaluated through the degradation of Reactive Blue 19 (RB19) under UV and solar irradiation. Nonlinear regression using a fractional-order Langmuir–Hinshelwood kinetic model achieved superior fitting accuracy over conventional linearized models, with reaction orders ranging from 0.30–0.58 under varying irradiation conditions. Notably, this approach provides enhanced insight into non-ideal surface reaction behavior, highlighting its advantage over commonly applied integer-order kinetic analyses. The nanohybrid retained more than 95% degradation efficiency after four successive cycles, demonstrating excellent stability. These results indicate that green-synthesized CeO₂/rGO is a promising, sustainable photocatalyst for treatment of dye-laden wastewater.