Fully crystalline single phase multi-component fluorite oxide (Gd_0.2La_0.2Y_0.2Hf_0.2Zr_0.2O₂ and Gd_0.2La_0.2Ce_0.2Hf_0.2Zr_0.2O₂) nanoparticle sols were synthesized at low temperature (≤80 °C) by co-precipitation followed by peptization in acidic medium.

Background: Cerium oxide nanoparticles (CeO₂) have been shown to be a novel therapeutic in many biomedical applications. Gold (Au) nanoparticles have also attracted widespread interest due to their chemical stability and unique optical properties. Thus, decorating Au on CeO₂ nanoparticles would have potential for exploitation in the biomedical field. Methods: In the present work, CeO₂ nanoparticles synthesized by a chemical combustion method were supported with 3.5% Au (Au/CeO₂) by a deposition-precipitation method. The as-synthesized Au, CeO₂, and Au/CeO₂ nanoparticles were evaluated for antibacterial activity and cytotoxicity in RAW 264.7 normal cells and A549 lung cancer cells. Results: The as-synthesized nanoparticles were characterized by X-ray diffraction, scanning and transmission electron microscopy, and ultraviolet-visible measurements. The X-ray diffraction study confirmed the formation of cubic fluorite-structured CeO₂ nanoparticles with a size of 10 nm. All synthesized nanoparticles were nontoxic towards RAW 264.7 cells at doses of 0–1,000 µM except for Au at >100 µM. For A549 cancer cells, Au/CeO₂ had the highest inhibitory effect, followed by both Au and CeO₂ which showed a similar effect at 500 and 1,000 µM. Initial binding of nanoparticles occurred through localized positively charged sites in A549 cells as shown by a shift in zeta potential from positive to negative after 24 hours of incubation. A dose-dependent elevation in reactive oxygen species indicated that the pro-oxidant activity of the nanoparticles was responsible for their cytotoxicity towards A549 cells. In addition, cellular uptake seen on transmission electron microscopic images indicated predominant localization of nanoparticles in the cytoplasmic matrix and mitochondrial damage due to oxidative stress. With regard to antibacterial activity, both types of nanoparticles had the strongest inhibitory effect on Bacillus subtilis in monoculture systems, followed by Salmonella enteritidis, Escherichia coli, and Staphylococcus aureus, while, in coculture tests with Lactobacillus plantarum, S. aureus was inhibited to a greater extent than the other bacteria. Conclusion: Gold-supported CeO₂ nanoparticles may be a potential nanomaterial for in vivo application owing to their biocompatible and antibacterial properties.

Recently, the conversion of 4-nitrophenol to 4-aminophenol via metal-supported oxide catalysts has attracted significant attention because of its potential applications. The main objective of this study was to demonstrate the crucial role of support materials in heterogeneous catalysts with inherent redox cycling features. The metals supported on these redox active materials can significantly alter the catalytic performance in a synergistic manner. For this, the catalytic hydrogenation of Au–ceria, prepared by altering the annealing–impregnation procedures, was investigated in terms of the size of gold and support material and their redox chemistry. The study clearly shows the variation in the catalytic activity of gold supported on the as-prepared and annealed ceria surface. This variation was due to the fact that the mutual interactions at the interface between absorbed Au and cerium oxide were certainly different in the as-prepared and annealed ceria surfaces with respect to surface chemistry and size of the particles. The redox nature of ceria and partial oxidation of gold on the surface of CeO₂ were involved in the catalytic reduction process.