Light-Mediated Antibacterial Activity of Composites of Polypyrrole and Green Zinc Oxide Nanoparticles Synthesized using Sarcomphalus joazeiro Extract

The preparation of zinc oxide nanoparticles and zinc oxide-polypyrrole (ZnONPs@PPy) composites can be considered a critical step for enhancement in the antibacterial activity of the synthesized material, established by its electrostatic interactions with the bacterial cell wall. Herein, the reported novelty is based on the biosynthesis of ZnONPs by Sarcomphalus joazeiro and their subsequent incorporation into a composite with polypyrrole for impregnation into cotton fibers, enabling their use in wound dressing applications. The samples were characterized using HPLC, FTIR, SEM, TEM, XRD, and UV–visible spectroscopy, with the band gap determined by the Tauc method. HPLC analysis confirmed the presence of phenolic compounds in the extract applied to reduce ZnONPs. At the same time, FTIR indicated the presence of specific bonds of Zn–O in the synthesized ZnONPs. XRD assays indicated a hexagonal structure of ZnO, with crystallites of 46.69 nm, and TEM showed a distribution of particles with diameters ranging from 12 to 38 nm. By comparison, the UV–vis spectrum confirmed a plasmon band at 368 nm and a reduction in the band gap from 2.97 to 2.88 eV in the composite (ZnONPs@PPy). Antibacterial tests against Escherichia coli and Staphylococcus aureus demonstrated good efficacy of compounds under sunlight exposure, indicating that the smaller band gap width favored the interaction of ZnONPs and PPy with bacterial membranes, with the release of reactive oxygen species enhancing the antimicrobial action, resulting in significant bacterial cell damage and killing.