Redox-Ligand Complexation Controlled Chemical Fate of Ceria Nanoparticles in an Agricultural Soil

Ceria (CeO₂) has received much attention in the global nanotechnology market due to its useful industrial applications. Because of its release to the environment, the chemical fate of ceria nanoparticles (NPs) becomes important in protecting the agricultural and food systems. Using experimental biogeochemistry and synchrotron-based X-ray techniques, the fate of ceria NPs (30 and 78 nm) in an agricultural soil (mildly acidic Taccoa entisols) was investigated as a function of exchangeable Ce(III) concentration (0.3 and 1.56 mM/kg in small and large NPs, respectively) under anoxic and oxic conditions. Both ceria NPs strongly adsorbed (>98%) in soils. Under the anoxic condition, the reduction of Ce(IV) was more pronounced in small NPs, whereas the greater concentration of exchangeable Ce(III) in large NPs facilitated the formation of Ce(III) phosphate/oxalate surface precipitates that suppressed the electron transfer reaction. The study shows the importance of redox-ligand complexation controlled chemical fate of ceria NPs in an agricultural soil.