Influence of Size on Biological and Catalytic Functions of Chitosan‐Coated Copper Oxide Particles Synthesized With Paris Polyphylla Extract

ABSTRACT To study the influence of size, copper particles synthesized using Paris polyphylla extract and coated with chitosan (CS) to get CuO‐PP‐CS MPs (microparticles) and CuO‐PP‐CS NPs (nanoparticles) were compared using biological (antibacterial, antioxidant, and dissolution) and catalytic activity (discoloration of methylene blue (MB), and methyl orange (MO)). Particles were characterized by FTIR, FE‐SEM, XRD, EDX, PSD, and zeta potential analysis to study size, CS/extract integration, structure, phase purity, and stability. CuO‐PP‐CS NPs demonstrated superior antibacterial efficacy, exhibiting lower IC 50 values (147.11–192.52 µg/mL) than CuO‐PP‐CS MPs (188.76–282.05 µg/mL) across all tested strains, with Bacillus cereus being the most susceptible. Dissolution profiles followed the Weibull 4‐parameter model with R 2 >0.99 for both particles, despite differing release behavior. Both particles exhibited weak antioxidant activity, attributed to copper's prooxidant nature. Similar catalytic activity for both the particles with best fit to Langmuir–Hinshelwood model, with ≈95% degradation, but CuO‐PP‐CS NPs showed better reusability, retaining 89.5% and 87.6% viability after the fifth cycle for MB and MO, while CuO‐PP‐CS MPs retained 87.4% and 71.6%, respectively. Overall, these multifunctional micro‐ and nano‐materials promise use as antimicrobial coating, catalytic pollutant discoloration, and for future therapeutic delivery.