Influence of temperature on the structural, optical, morphological and antibacterial properties of biosynthesized silver nanoparticles

Abstract

This present investigated the effect of synthesis temperature on size and shape of silver nanoparticles biosynthesized using aqueous leaf extract Tridax procumbens and their evaluate of antibacterial activities. Silver nanoparticles synthesized at four different temperatures (200 to 500 °C) were characterized by X-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) and scanning electron microscopy (SEM) analysis. Silver nanoparticles with crystalline sizes ranging from 18 to 25 nm and narrow size distributions were synthesized. We show that as the temperature rises, the size does not increase in a linear fashion. Micrographs of silver nanoparticles synthesized at 300 °C showed that synthesis temperature affected the sizes and shapes of silver nanoparticles. The FT-IR spectra at different temperatures revealed that the characteristic band for silver at 470 cm⁻¹ became more prominent with increasing temperature as a result of the conversion of precursor into silver nanoparticles. The UV–Vis absorbance of silver nanoparticles shows that as the temperature rises, the absorption peak shifts to a longer wavelength and the bandgap energy decreases. The antibacterial activities of synthesized nanoparticles were determined using a disk diffusion method against gram-positive (B. subtilis and S. aureus) and gram-negative (E. coli and P. aeruginosa) bacteria. Synthesized nanoparticles calcined at 300 °C are more effective at killing E. coli (29 mm) bacteria than other temperatures at 20 µg/mL. Bacterial activity of silver nanoparticles depends on their size, morphology and structural which are affected by their calcination temperature.