Green Synthesis of Silver Nanoparticles Using Syzygium gratum Branch Extract: Physicochemical Characterization, and Antibacterial Activities

Abstract

Green synthesis offers a sustainable alternative for producing metal nanoparticles with controlled structural and functional properties. In this study, silver nanoparticles (AgNPs) were successfully synthesized using Syzygium gratum branch extract as a natural reducing and stabilizing agent. The formation of AgNPs was confirmed by the emergence of a characteristic surface plasmon resonance band at 436 nm. Systematic optimization of reaction parameters, including silver nitrate concentration, extract volume, and incubation time, enabled reproducible nanoparticle formation under ambient conditions. Comprehensive physicochemical characterization using UV–Vis spectroscopy, FT-IR, XRD, SEM, HRTEM, EDX, dynamic light scattering, and zeta-potential analysis revealed the formation of crystalline silver nanostructures with a face-centered cubic lattice. XRD analysis indicated an average crystallite size of 11.64 nm, while electron microscopy showed predominantly quasi-spherical nanoparticles with sizes ranging from 2 to 50 nm. The hydrodynamic particle size was 66.64 nm with a polydispersity index of 0.239, and a negative zeta potential value of −35 mV demonstrated good colloidal stability. FT-IR spectral shifts associated with hydroxyl, carbonyl/amide, and C–O functional groups confirmed the involvement of plant-derived phytochemicals in silver ion reduction and nanoparticle surface capping. The biosynthesized AgNPs exhibited pronounced antibacterial activity against both Gram-positive and Gram-negative bacterial strains. At a concentration of 10 mM, inhibition zones ranging from 12.67 ± 1.15 to 18.67 ± 0.58 mm were observed, with statistically significant differences (p < 0.05) for five of the six tested strains. The enhanced antibacterial performance is attributed to the small particle size, high surface area, and stable dispersion of the AgNPs. Therefore, this work demonstrates that Syzygium gratum branch extract effectively governs nanoparticle nucleation, growth, and stabilization. The proposed environmentally benign synthesis route provides a reproducible strategy for producing functional silver nanomaterials with potential applications in antimicrobial and biointerface-related fields.

HIGHLIGHTS

• A green and reproducible strategy was developed to synthesize silver nanoparticles using Syzygium gratum branch extract as a dual reducing and stabilizing agent.
• The biosynthesized AgNPs exhibited a stable face-centered cubic crystalline structure with an average crystallite size of 11.64 nm and a negative zeta potential (−35 mV), indicating good colloidal stability.
• Plant-derived functional groups (O–H, C=O/amide, and C–O) played a key role in directing nanoparticle nucleation, growth, and surface stabilization.
• The AgNPs showed pronounced antibacterial activity against both Gram-positive and Gram-negative bacteria, producing inhibition zones up to 18.67 ± 0.58 mm with statistically significant effects (p < 0.05).
• This environmentally benign synthesis route provides mechanistic insight and a scalable platform for producing functional silver nanomaterials for antimicrobial applications.

GRAPHICAL ABSTRACT