Copper Precursor Salt‐Dependent Antimicrobial Activity of Graphite Oxide Composites Against Escherichia coli and Staphylococcus Aureus: Synthesis and Characterization

Abstract

Graphite oxide (GrO) is doped with Cu(NO3)2 (CuN/GrO) and CuSO4 (CuS/GrO). Face‐centered cubic Cu, monoclinic CuO, and cubic Cu2O mixed crystalline phases are observed. The ID/IG ratio on average is 1.0 for all composites, associated with similar structural disorders and defects. CuN/GrO and CuS/GrO composites increase the C:O ratio by 30% compared to GrO. In Cu(NO3)2‐ and CuSO4‐doped GrO composites, the copper particle dispersion is on the GrO surface and GrO edges, respectively. By agarwell diffusion assay, the CuN/GrO composite presents only inhibition against the Staphylococcus aureus microorganism at 10 mg mL−1 per well. However, using the CuS/GrO composite, the minimum inhibitory concentration is 5 mg mL−1 per well against Escherichia coli and S. aureus microorganisms. In general, the copper precursor salt influences the copper particle localization in the GrO matrix in a different way, modulating the antimicrobial behavior. In this way, it is possible to establish a possible electrostatic adsorption caused by the Cu+ or Cu2+ ions and the negative charges of the bacterial cell membrane, where the adsorption and mass diffusion mechanisms between charged composites and Gram‐positive and Gram‐negative microorganisms are affected by the copper particle arrangement in the composites.