Opuntia ficus-indica-Loaded Chitosan/Zinc Oxide Nanocomposites: Physicochemical Characterization, Antibacterial, Antioxidant  and Photocatalytic Degradation Investigation

The present study focuses on developing Opuntia ficus indica (OFI) loaded chitosan/zinc oxide (CS/ZnO) nanocomposites. Box-Behnken design was used to optimize and analyse the formulation conditions. The physicochemical nature of the prepared nanocomposite was examined and confirmed using XRD, FTIR, SEM coupled with EDS, and TEM. The formulations exhibited significant radical-scavenging activity in both DPPH and ABTS assays, with CS/OFI-ZnONCs showing markedly lower IC₅₀ (DPPH – 140 µg/mL, ABTS – 185 µg/mL) values than ZnONPs, OFI, and OFI-ZnONPs, indicating enhanced antioxidant activity. The formulations also demonstrated concentration-dependent antibacterial activity against Escherichia coli and Psuedomonas aeruginosa, with CS/OFI-ZnONCs exhibiting the highest zone of inhibition of 18.33 ± 1.15 mm and 17.33 ± 0.58 mm at 300 µg/mL, respectively. In photocatalytic degradation studies, CS/OFI-ZnONCs demonstrated excellent methylene blue degradation efficiency of 96.03% after 50 min of visible-light irradiation, significantly outperforming OFI-ZnONPs (80.23%) and OFI extract (61.12%). The enhanced photocatalytic performance was further supported by the highest apparent rate constant (0.02957 min⁻¹), which was 2.16- and 1.44-fold higher than those of OFI extract and OFI-ZnONPs, respectively. Overall, the findings demonstrate that incorporating OFI-derived bioactive constituents and ZnO nanoparticles into chitosan produces a multifunctional nanocomposite with enhanced antioxidant, antibacterial, and photocatalytic properties, highlighting its promising potential for sustainable environmental and functional material applications.