Importance of Surface Functionalities for Antibacterial Properties of Carbon Spheres

Abstract Carbon spheres (CS) are interesting materials for antibacterial applications. Herein, CS are produced by a green process utilizing microwave‐assisted hydrothermal treatment of cellulose. The CS are then postmodified in acidic and basic solutions to evaluate the influence of different functionalities on antibacterial properties. CS contain OH/COOH, CC, and CO functionalities, while O‐CS produced by acid treatment of CS have additional COOH, and NH/NH₂ groups, resulting in carbon spheres with negatively and positively charged groups in dispersion. Treatment with base (Na‐CS) removes low molecular weight species with oxygen and results in carbon spheres with the highest C/O ratio. CS, O‐CS, and Na‐CS have nonporous morphology and are in micro/nanometer sizes, although, smaller sized spheres, hollow spheres, and fragments are also attained in the case of O‐CS. O‐CS show antibacterial activity toward both Gram‐positive Staphylococcus aureus (S. aureus) and Gram‐negative Pseudomonas aeruginosa (P. aeruginosa). The minimum inhibitory concentration is 200 and 400 µg mL⁻¹ for S. aureus and P. aeruginosa, respectively, and is achieved only after 3 h of incubation. Neither CS nor Na‐CS exhibit antibacterial activity. The antibacterial activity is suggested to originate from electrostatic interactions between O‐CS and the bacteria.