Visible light-driven ZnO nanoparticles/carbon nanodots hybrid for broad-spectrum antimicrobial activity

Abstract

A Hybrid composite of zinc oxide nanoparticles (ZnO-NPs) and carbon nanodots (CNDs) was synthesized by the sol–gel method. CNDs were obtained from olive solid wastes by pyrolysis and chemical oxidation methods. The combination of CNDs and ZnO materials led to the formation of a hybrid nanocomposite, where CNDs adsorbed on the surface of ZnO particles leading to an increase of its ζ- potential to be −28 mV; this refers to the hydroxyl and carboxyl groups attached on CNDs, which localized on the surface of ZnO after the hybridization, as well their sizes have been enlarged from 23.5 to 105 nm which is an indication of the successful hybridization of those moieties. Additionally, the CNDs enhance the visible-light photocatalytic activity of ZnO, showing a decrease in the energy band gap from 3.1 to 2.8 eV, where CNDs play as an intermediate energy level above the valence band of ZnO. Antimicrobial activity tests were also performed against Gram-positive and Gram-negative bacterial and fungal strains under dark and sunlight modes. The hybrid exhibits excellent antimicrobial activity within minimal inhibitory concentrations (7.8–62.5) µg/L, and the inhibition growth percentage was 99.9%, an inhibition zone ranged from (19 to 38) mm, and the kill time kinetic was one to two hours. The antimicrobial activity mechanism was also studied by the glutathione oxidation test showing that the broad-spectrum antimicrobial is directly related to its ROS-forming ability with a percent glutathione deficiency oxidation percentage of (88.2%) for dark mode and (95%) for sunlight mode. The findings of this study demonstrate the ability of synthesized hybrid nanocomposite as an antimicrobial active material for broad-spectrum microbial strains and other environmental solutions.