One-step sonochemical synthesis of a reduced graphene oxide - ZnO nanocomposite with antibacterial and antibiofouling properties

Microbial contamination and biofilm formation present major challenges in numerous applications. Many types of nanoparticles possess high antibacterial activity and thus are being investigated to combat environmental microbial contamination, limit bacterial deposition, and inhibit or destroy biofilms. In addition to finding nanoparticles with high and broad antibacterial activity, the synthesis of nanoparticles must also be sustainable and the nanoparticles should have low toxicity and low environmental impact. In this study, we developed a simple one-step probe sonication method to synthesize a ZnO nanoparticle functionalized reduced graphene oxide (rGO-ZnO) nanocomposite by exfoliating oxidized graphite in the presence of Zn2+. The antibacterial activity of the nanocomposite was higher than that of graphene oxide (GO) and rGO against Gram-negative (Escherichia coli and Serratia marcescens) and Gram-positive (Bacillus subtilis) bacteria. Direct intracellular reactive oxygen species (ROS) and Zn2+ leaching measurements indicated that the high antibacterial activity against different bacteria of the nanocomposite arises from the formation of ROS, whereas the effect of Zn2+ is negligible. Furthermore, incorporating rGO-ZnO nanocomposite into a polyethersulfone (PES) membrane inhibited biofilm growth compared with a pristine PES membrane. Leaching experiments of Zn2+ from the incorporated rGO-ZnO membrane during synthetic wastewater filtration revealed that Zn2+ concentration in the effluent was below the environmental standards for potable and non-potable uses. Our research presents an effective, fast, and low-cost preparation method for developing nanocomposites with high antimicrobial activities. Also, it shows that a nanocomposite incorporated polymeric membrane can be safely applied for water and wastewater treatment with minimum environmental impact.