Eco-friendly synthesis of silver and gold nanoparticles with enhanced bactericidal activity and study of silver catalyzed reduction of 4-nitrophenol

•Synthetic method is robust and rapidly produces nano silver and gold particles.•Larger volume of root extract increases metal interaction yielding smaller spherical nanoparticles.•Silver and gold nanoparticles show excellent activity against clinically isolated bacteria.•Silver nanoparticles work as efficient green catalyst for the reduction of 4-nitrophenol.

The present study reports a simple and robust method for synthesis of silver and gold nanoparticles using Coleus forskohlii root extract as reducing and stabilizing agent. Stable silver nanoparticles (AgNPs) and gold nanopoarticles (AuNPs) were formed on treatment of an aqueous silver nitrate (AgNO3) and chloroauric acid (HAuCl4) solutions with the root extract. The nanoparticles obtained were characterized by UV–Visible spectroscopy, Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). UV–Vis and TEM analysis indicate that with higher quantities of root extract, the interaction is enhanced leading to size reduction of spherical metal nanoparticles. XRD confirms face-centered cubic phase and the diffraction peaks can be attributed to (1 1 1), (2 0 0), (2 2 2) and (3 1 1) planes for these nanoparticles. These synthesized Ag and Au nanoparticles were found to exhibit excellent bactericidal activity against clinically isolated selected pathogens such as Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus). The synthesized AgNPs were also found to function as an efficient green catalyst in the reduction of anthropogenic pollutant 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride, which was apparent from the periodical color change from bright yellow to colorless, after the addition of AgNPs.

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