Enhanced antimicrobial activity of Cu-decorated graphene nanoplatelets and carbon nanotubes

Abstract

New materials with antimicrobial properties are necessary to combat the proliferation and transmission of pathogenic microorganisms. In this work, graphene nanoplatelets (GPN) and multi-walled carbon nanotubes (CNT) decorated with Cu nanoparticles (Cu NPs) were synthetized by microwave-assisted hydrothermal method, varying the Cu content from 1 to 10 wt.%. These materials were characterized by X-ray diffraction (XRD), Raman spectroscopy, and scanning and transmission electron microscopy (SEM and TEM) and their antimicrobial activity against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) were evaluated. The sample with 10 wt.% Cu at CNTs is more effective compared to GPNs. Then, brass coatings with pure and Cu-decorated (10 wt.%) CNTs and GPNs were prepared by spin coating to evaluate the antimicrobial activity of these surfaces. It was observed that coatings with the carbon matrices reduced microbial growth by 2 logs, whereas decoration with Cu NPs amplified this value, especially for the Cu/CNT coating, achieving up to a 6-log reduction after 24 h of contact. The stability of the antimicrobial activity of these coatings was evaluated over 5 successive 24-h cycles, demonstrating high stability. DFT calculations on a simplified model, based on a Cu atom adsorbed on GPN and CNT, reveal a thermodynamically favorable pathway to explain the antibacterial activity. The results show a mechanism that could promote the formation of the precursors of hydroxyl (⦁OH), superoxide (⦁O₂⁻), and hydroperoxyl (⦁OOH) radicals, which are adsorbed strongly on GPN and CNT surfaces. This study highlighted the critical role of Cu NPs-loaded on carbon materials, GPN and CNT, in enhancing the antibacterial activity.