Bio-based in situ fabrication of silver nanoparticles on silk threads using discarded immature Punica granatum L. fruit extract.

For years, the susceptibility of silk to microbial attack has been a considerable disadvantage to the material applications in clothing, textile industries and medical practices. To address this drawback, nano-functionalization utilizing plant-based reducing agents has become an interesting approach. In this study, the application of aqueous extract from immature fruits of pomegranate (Punica granatum), a discarded agricultural by-product, for the in situ preparation of silver nanoparticle (AgNP)-functionalized silk thread was described. The residual AgNP colloid was characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD), showing the successful synthesis of spherical, well-dispersed, and stable AgNPs with an average hydrodynamic size of 37.7 nm under the optimal conditions of pH 9.0, 8 g L-1 extract, and 12 mM AgNO3. The distribution of AgNPs on the silk surface was validated by energy dispersive X-ray (EDX) spectroscopy, field-emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS). The effects of AgNP-functionalization on the silk thread's color and mechanical properties were also evaluated. Significant enhancement in antibacterial effects of AgNP-functionalized silk thread in comparison with the pristine and extract-treated samples was confirmed by the inhibitory efficiencies of over 99.90% against Staphylococcus aureus and Escherichia coli, whose insignificant reduction after 5-, 10-, and 20-washing cycles indicated the good washing durability. These findings suggest the potential applicability of the discarded immature pomegranate fruit for the preparation of antibacterial nanoparticle-functionalized silk.