Green synthesis and sunlight-driven photocatalytic degradation of diclofenac using biogenic Co₃O₄ nanoparticles derived from Carica papaya peel waste

The increasing presence of pharmaceutical contaminants such as diclofenac in aquatic environments poses serious ecological and health risks, necessitating efficient and sustainable degradation approaches. In this study, Co₃O₄ nanoparticles were green-synthesized using Carica papaya peel waste extract as a natural reducing and stabilizing agent and calcinated at temperatures ranging from 300 to 900 °C . XRD analysis confirmed the formation of a highly crystalline cubic spinel Co₃O₄ phase, while FESEM images showed quasi-spherical, porous nanoparticles with sizes of 50–70 nm. Elemental analysis revealed dominant cobalt (65.26 wt%) and oxygen (28.52 wt%), consistent with Co₃O₄ stoichiometry, with only trace amounts of phosphorus and magnesium originating from intrinsic phytochemical constituents. FTIR verified Co–O vibrations and removal of organic residues, and UV-Vis/DRS analyses showed strong visible-light absorption with a tunable band gap (1.69–1.49 eV). The photocatalytic degradation of diclofenac under natural sunlight achieved 93 % efficiency at pH 2 within 270 min for the 900 °C sample (1 mg/mL dosage), following pseudo-first-order kinetics. These results demonstrate that biogenic Co₃O₄ nanoparticles serve as efficient, cost-effective, and sustainable photocatalysts for solar-assisted degradation of pharmaceutical pollutants in wastewater.