Comparative evaluation of green synthesized silver nanoparticles using Psidium guajava and Azadirachta indica leaf extracts for photocatalytic and antibacterial applications

The biosynthesized silver nanoparticles (AgNPs) have attracted significant attention due to their eco-friendly synthesis and multifunctional properties. In this study, AgNPs were synthesized via a green approach using aqueous leaf extracts of Psidium guajava and Azadirachta indica . The synthesized nanoparticles were characterized using UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), and zeta potential analysis. UV-Vis spectra exhibited surface plasmon resonance peaks at 450 nm and 437 nm with corresponding band gap energies of 3.57 eV and 3.47 eV for Psidium guajava and Azadirachta indica respectively. XRD analysis confirmed the face-centred cubic (FCC) crystalline structure with an average crystallite size of ∼11 nm. FTIR results indicated the presence of phytochemicals which are responsible for reduction and stabilization of nanoparticles. SEM and HR-TEM analysis revealed predominantly the spherical nanoparticles with sizes ranging from 22 to 23 nm. DLS measurements showed hydrodynamic diameters of 249.3 nm and 264 nm, while zeta potential values of –21.97 mV and –13.77 mV for Psidium guajava and Azadirachta indica respectively that indicates moderate colloidal stability with some degree of aggregation. The photocatalytic performance demonstrated maximum degradation efficiencies of 96.54% for methylene blue (MB) and 92.64% for malachite green (MG) under sunlight irradiation. Antibacterial studies against Escherichia coli and Staphylococcus aureus confirmed significant antimicrobial activity, with Azadirachta indica -mediated AgNPs showing relatively higher efficacy against S. aureus , while Psidium guajava -mediated AgNPs exhibited superior photocatalytic performance. These findings highlight the critical role of plant-derived phytochemicals in tailoring the nanoparticles properties and demonstrate the potential of green-synthesized AgNPs for environmental remediation and antimicrobial applications. This study presents a novel comparative approach combining both the photocatalytic and antibacterial evaluations of the prepared nanoparticles for sustainable nanomaterial development.