Environmentally sustainable route to SiO₂@Au-Ag nanocomposites for biomedical and catalytic applications

A facile, sustainable, operationally simple and mild method for the synthesis of SiO₂@Au-Ag nanocomposites (NCs) using Nephrolepis cordifolia tuber extract is described and its catalytic, antibacterial and cytotoxic properties were investigated. The fabricated SiO₂@Au-Ag NCs were well characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) to determine the optical activity, size and morphology, elemental composition, functional groups present, crystallinity, thermal stability and chemical state respectively. The obtained SiO₂@Au-Ag NCs exhibited spherical shape SiO₂ decorated with Au and Ag nanoparticles. The diameter of the SiO₂ nanoparticles ranges from 200-246 with average 3 nm diameter of Au and Ag NPs. Synthetic utility of this protocol has been demonstrated by exploring its effective catalytic activities for the solvent-free amidation of carboxylic acid with a primary amine with excellent yields. Moreover, the synthesized nanocomposite exhibited as noticeable antibacterial effect against Gram negative and Gram positive bacteria and better bio-compatibility against human keratinocytes. Thus, additive free SiO₂@Au-Ag NCs display the potential for catalysis and biomedical applications.