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

Abstract

Infectious diseases caused by pathogenic microorganisms have inflicted significant calamities upon human society. The Cu₄O₃/biochar composites with high efficacy of antimicrobial properties are developed for the first time via a green solid synthesis strategy of ball milling and sintering processes in this work. The mechanistic investigation revealed that the biochar, e.g. corn stover, plays multiple physiochemical roles as a support carrier, dispersant, and reducing agent, regulating elegantly the stoichiometric ratio of Cu₂O and CuO. The potent antimicrobial activities of the Cu₄O₃/biochar composite were confirmed against E. coli, S. aureus, and methicillin-resistant Staphylococcus aureus MRSA through minimum inhibitory concentration (MIC) testing, exhibiting extremely low MIC values against the Gram-positive strains S. aureus and MRSA. Furthermore, the antibacterial mechanisms of the Cu₄O₃/biochar composite were studied through the experiments and quantum mechanical computations, showing the enhanced effects between the successive release of Cu(I)/Cu(II) ions and the generation of reactive oxygen species. This work reports the first solid-state symproportionation reactions of CuO_x to prepare high-purity Cu₄O₃, stabilized by biochar with the advantages of simplicity, low cost, brevity, mild reaction conditions, and eco-friendliness. The Cu₄O₃/biochar composite can be applied as additives in anti-bacterial materials to protect against harmful microbial infections including superbugs.