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.

Oxidized Carbonized Cellulose-Coated Filters for Environmental Contaminant Adsorption and Detection

“…Thus, the carbonization process introduced CC bonds and resulted in different oxygen functionalities in the carbonized products. The spectrum of OCC showed in addition a probable organic nitrogen stretch at 1540 cm –1 as previously observed after oxidation of carbon spheres by H 2 SO 4 /HNO 3 …”

“…According to SEM, OCC consisted of flake-like structures, and some collapsed hollow carbon spheres (HCS) were also encountered. Previously, a milder oxidation of CS compared to this study was also shown to lead to formation of HCS in addition to spheres and other fragments . Further TEM analysis of the isolated flake-like structures displayed that their lateral sizes were from few μm down to 500 nm (Figure c and Figure S1).…”

“…The intensity ratio I (D)/ I (G) was slightly higher for OCC as compared to CS, i.e., 0.42 compared to 0.37, corresponding to an increment of 14%. Previously, oxidation of carbon spheres using milder oxidation conditions displayed an I (D)/ I (G) increment of 4% …”

Carbon Dot-Triggered Photocatalytic Degradation of Cellulose Acetate

“…The spectrum of CDs showed further an absorption band at 1540 cm –1 , indicating organic nitrogen originating from the oxidation with HNO 3 . 42 …”

Osteoconductive and Antibacterial Poly(lactic acid) Fibrous Membranes Impregnated with Biobased Nanocarbons for Biodegradable Bone Regenerative Scaffolds

“…In general, metal particles such as zinc oxide, silver, and even hybrid nanoparticles are impregnated into electrospun polymer fibers to render antibacterial functions. − Herein, by direct incorporation of coffee-ground-derived QDs, the electrospun PLA composite membranes were endowed with immediate and broad-spectrum antibacterial performance. A variety of carbon-based nanoallotropes, e.g., graphene, carbon spheres, and carbon nanotubes, have been found to exert high efficacy of killing bacteria. By a series of comparative studies in terms of aggregation morphology and surface chemistry, a consensus has been made that the synergy of membrane stress and oxidative stress likely contributes to the antibacterial mechanisms. , The antibacterial effect of QDs can presumably be ascribed to the ultralow dimensions and high surface activity of enabling rapid attachment and accumulation onto bacterial cells, which contributed to the effective destruction of bacterial membranes by large contact stress and ultimate death of bacteria. , This mechanism can be further enhanced by the existence of plentiful oxygen functional groups carried by QDs that could chemically induce cellular oxidative stress, which is hypothesized to disrupt a specific microbial process by oxidizing or disturbing a vital cellular structure or component without reactive oxygen species production. , This implies that the QD-modified membranes offer prominent improvements in osteoconductive and antibacterial properties of the electrospun fibers, holding potential for serving as biodegradable bone regenerative scaffolds and for meeting the clinical demands. , …”