Synthesis of reduced graphene oxide from onion peel waste by single-stage pyrolysis, characterization and evaluation of its antibacterial activity

Two types of reduced graphene oxides (rGO) were synthesized from onion (Allium cepa L.) peel waste by single-stage pyrolysis at 500 °C; one with ferrocene catalyst and the other without the catalyst. The crystalline size of both ranged from 13.2 to 35.67 nm as per XRD and Raman. The specific surface area ranged from 97 to 2652 m² g⁻¹ as per BET. TEM revealed that the rGO prepared with catalyst had ultrathin nanosheets of graphene oxides resulting from the stacking of many nanostructured graphene oxides and graphene layers. The rGO prepared without the catalyst showed disordered carbon structure containing randomly oriented graphene sheets with minimum stacking. The zone of inhibition method and colony counting method together inferred that both the rGOs could fight successfully against chosen infectious human pathogens Streptococcus pyogenes, Staphylococcus aureus, Escherichia. coli and Klebsiella pneumoniae which had been posting strong resistance to conventional antibiotics. The rGO prepared with catalyst had 38.5 percent higher antibacterial activity than that of the other. The activity in both was higher at a conc. of 200 μg mL⁻¹. The rGO is now emerging as a tangible option in the context of bacterial resistance to conventional antibiotics.