Antibacterial Activity of Silver–Graphene Composites Against Escherichia coli

Abstract

Silver nanoparticle-incorporated three-dimensional graphene (AgNP–3D graphene) composites were synthesised and evaluated for antibacterial activity against Escherichia coli. Graphene oxide was prepared using a modified Hummers’ method and subsequently reduced to form a three-dimensional graphene framework. Silver nanoparticles were incorporated in situ using silver nitrate as the precursor, while citrate or sodium bisulfite served as reducing agents in the presence or absence of ammonia. The structural and morphological characteristics of the prepared composites were assessed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). XRD confirmed the formation of crystalline metallic silver within the graphene framework, and SEM revealed differences in nanoparticle size and distribution according to the synthesis route. EDX analysis showed silver contents ranging from 17.25 to 20.22 wt.% among the silver-containing composites. Antibacterial performance was examined using batch and continuous-flow disinfection experiments with E. coli-contaminated water. In batch studies, the SC composite achieved a maximum log reduction value of 5.1 after 720 min, whereas comparative evaluation showed strong antibacterial activity for the SBA composite. Continuous-flow experiments indicated that the SCA composite had the highest apparent antibacterial activity rate constant under the tested conditions. Silver leaching remained low during the experimental period. These findings indicate that AgNP–3D graphene composites have measurable antibacterial potential against E. coli, with performance influenced by nanoparticle dispersion, graphene architecture, and synthesis conditions.