One-pot wet ball milling synthesis of CdO@GO nanocomposites with antimicrobial characteristics: Experimental and DFT studies

Numerous nanomaterials with strong antibacterial properties have been developed to address microbial contamination and biofilm formation. In this work, cadmium oxide nanoparticles (CdO NPs) were immobilized on graphene oxide (GO) sheets via a simple one-step wet ball milling technique, resulting in CdO@GO nanocomposites (0.25 g CdO: CdO@GO-1, and 0.50 g CdO: CdO@GO-2). The CdO@GO nanocomposites exhibit a uniform distribution of CdO nanoparticles on the wrinkled and flake-like GO nanosheets, with denser coverage at higher CdO content. The antibacterial activity of the CdO@GO nanocomposite was superior to that of its individual components, CdO and GO, against both Gram-negative bacteria (Escherichia coli (EC), Klebsiella pneumoniae (KP), and S. typhimurium (ST)) and Gram-positive bacteria (Bacillus subtilis (BS), Listeria monocytogenes (LM), and Staphylococcus aureus (SA)). CdO@GO-2, with approximately 47 wt.% of Cd atoms, showed the highest antibacterial activity, with the lowest minimum inhibitory concentrations (MICs) for EC (3.25 ± 0.15 μg/mL), BS (3.51 ± 0.72 μg/mL), and LM (4.11 ± 0.34 μg/mL). However, SA (5.67 ± 0.28 μg/mL), ST (6.49 ± 0.36 μg/mL), and KP (7.08 ± 0.83 μg/mL) were less susceptible. Density-functional theory (DFT) calculations indicated that CdO@GO-2 has the best antimicrobial properties, attributed to its high electrophilicity index (62.16), low electronic bandgap (0.38 eV), favorable chemical potential (−4.86 eV), low chemical hardness (0.19 eV), and a highly negative electrostatic potential (−2.45 eV), making it highly reactive and effective at disrupting microbial cells.