Direct Room Temperature Synthesis of Valence State Engineered Ultra-Small Ceria Nanoparticles: Investigation on the Role of Ethylenediamine as a Capping Agent

Direct room temperature synthesis of ultrasmall (2.5 +/- 0.2 nm), water dispersible ceria nanoparticles are reported for the first time. Nanopafticles were synthesized directly in ethylenediamine that served as a catalyst as well as capping agent. Larger particles could be obtained by solvothermal synthesis keeping other parameters identical. X-ray photoelectron spectroscopic studies indicated the formation of valence state engineered (a mixed valence state of Ce(3+) and Ce(4+)) ceria nanoparticles. The proportion of the valence states could be tuned by varying the solvothermal synthesis temperature and solvent composition by introducing water along with ethylenediamine. UV-visible transmission studies revealed antioxidant properties of the nanoparticles that could lead to possible therapeutic applications of the nanoparticles in biomedicine. It was observed that the ultra small ceria nanoparticles having mixed valence state prevent photobleaching of organic dyes by scavenging free radicals