Green solid-state synthesis of Cu4O3/biochar composites with high antimicrobial activity†

Infectious diseases caused by pathogenic microorganisms pose severe challenges to human society. In this study, we successfully developed Cu₄O₃/biochar composites with highly effective antimicrobial properties using an eco-friendly green solid-state synthesis strategy involving ball milling and sintering processes. Our mechanistic investigation revealed that biochar, derived from plant materials, such as corn stover, serves multiple physicochemical roles, including acting as a support carrier, dispersant, and reducing agent. This allowed for precise regulation of the stoichiometric ratio between Cu₂O and CuO, which were critical to the successful preparation of pure Cu₄O₃. The antimicrobial efficacy of the Cu₄O₃/biochar composite was demonstrated against E. coli, S. aureus, and methicillin-resistant Staphylococcus aureus (MRSA) through minimum inhibitory concentration (MIC) testing, which showed remarkably low MIC values, particularly against the Gram-positive strains S. aureus and MRSA. Further experimental and computational investigations into the antibacterial mechanisms revealed a synergistic effect between the controlled release of Cu(I)/Cu(II) ions and the generation of reactive oxygen species, which enhances the composite's antimicrobial activity. This work is the first report on solid-state symproportionation reaction of CuO_x for the preparation of high-purity Cu₄O₃, stabilized by biochar. This method offers several advantages, including simplicity, low cost, brevity, mild reaction conditions, and environmental friendliness. The Cu₄O₃/biochar composite shows promise for use as an additive in antibacterial materials to combat harmful microbial infections, including antibiotic-resistant superbugs.