Physics of Ce3+↔Ce4+ electronic transition in phytosynthesized CeO2/CePO4 nanocomposites and its antibacterial activities

The interplay between physics and chemistry of nanoparticles dictate many useful properties for their practical applications. In this context, we synthesized well controlled CeO2/CePO4 nanocomposites using Artocarpus heterophyllus aqueous leaf extract as reducing agent. The as-synthesized nanocomposites were annealed at elevated temperatures (500–900 °C) for 3 h under air atmosphere and their characterizations were performed using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Differential Scanning Calorimetry (DSC) –Thermo Gravimetric (TG) analysis, Raman, Fourier Transform Infrared (FTIR) and UV–Visible spectroscopy analysis. The formation of the CeO2/CePO4 nanocomposites could be realized by the presence of phosphate ions in aqueous leaf extract which has been confirmed by Gas Chromatography – Mass Spectrometry (GC-MS) analysis. Such stabilization of Ce3+ ions as CePO4 phase on the surface of nanoceria induced the reduction of grain growth and lowering of the bandgap of the nanocomposites. The antibacterial efficacy against both gram positive (S. aureus and B. cereus) and gram negative (S. typhimurium and E. coli) bacteria is attributed to the redox cycling between Ce3+ and Ce4+ ions at the oxide-phosphate interface of CeO2/CePO4 nanocomposites. The cytotoxicity analysis observed on two mammalian cell lines (HeLa and Vero) shows that the functional nanocomposites were non–toxic up to higher concentration (3 g/L). Our findings have implication that the phyto-synthesized CeO2/CePO4 nanocomposites could provide novel insights for mimicking multienzymes’ activities and safe for antibacterial applications in terms of in vitro cytotoxicity.