Temperature dependent microstructural defects and surface charge effects on antioxidant activity of green synthesized nanoceria.

This study reports a novel eco-friendly route for synthesizing cerium dioxide nanoparticles (nanoceria) that converts waste coffee husks into both reagent and process medium. Polyphenol rich phytochemicals chelate Ce, guide hydrolysis, and locally modulate redox conditions, imprinting abundant surface Ce and oxygen vacancies that underpin activity. Reuse of the clarified supernatant in successive cycles boosts yield exponentially without added metal oxide precursor, highlighting intrinsic process efficiency. Subsequent calcination turns the bio templated precipitate into phase pure fluorite CeO₂ whose crystallite size, strain, and defect concentration can be tuned by temperature alone. Higher temperatures enlarge particles and improve crystallinity while removing vacancies and strain. Radical scavenging assays show the highest activity in uncalcined material and a steady decline with increasing temperature that parallels the loss of surface Ce and vacancies. Statistical analysis confirms that antioxidant performance depends on defect density, quantum confinement, and surface charge, whereas external morphology and residual organics are negligible. The unique mechanism is phytochemical-directed defect engineering, which couples the use of agricultural waste with precise control of redox-active sites to deliver tuneable nanoceria for biomedical, agricultural, and environmental remediation applications.