Chitosan Composites Functionalized with Green-Synthesized Silver Nanoparticles from Manacá-da-Serra Flowers for the Disinfection of Industrial Wastewater

Green silver nanoparticles (AgNPs) have been increasingly recognized for their antimicrobial properties and environmental compatibility. In this study, AgNPs were synthesized using an aqueous extract of Manacá-da-Serra (Pleroma sellowianum) flowers as a natural reducing and stabilizing agent and subsequently incorporated into a chitosan matrix to produce functionalized composites for industrial wastewater disinfection. Optimal synthesis conditions were achieved at pH 12.0, 25 °C, and 0.01 mol/L AgNO3, yielding uniformly dispersed spherical NPs (20–30 nm) with moderate colloidal stability (zeta potential ≈ −14 mV) and a minimum inhibitory concentration of 5 μL/mL against Escherichia coli and Staphylococcus aureus. The effective integration of AgNPs into the biopolymer was verified by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The interaction between AgNPs and chitosan was confirmed by the data, while successful NP incorporation was further supported by homogeneous Ag distribution and improved thermal stability. Inhibition zones of 11 ± 1 mm (S. aureus) and 9 ± 1 mm (E. coli) were revealed by antimicrobial assays. For industrial wastewater disinfection, a total coliform reduction of >99.9% was achieved within 180 min, with Ag release remaining at 0.01 mg/L, below the regulatory threshold. The synergistic effect between chitosan and green-synthesized AgNPs was highlighted by these findings, demonstrating the potential of this environmentally friendly material for efficient, safe, and sustainable wastewater disinfection and reuse.