Engineering of Oxygen-Deficient Nano-CeO_2–<i>x</i> with Tunable Biocidal and Antioxidant Activity

Biocidal activity and radical scavenging capacity (RSC), two seemingly opposing concepts, can coexist in engineered nanoceria (CeO2) materials. In the present study, a series of CeO2–x (x = 0–0.75) nanoparticles have been engineered utilizing the anoxic-flame spray pyrolysis (A-FSP) technology. A-FSP allows for tuning of the physicochemical and structural properties of CeO2–x arising from lattice defects (Ce3+ and Vos) while maintaining minimal carbon incorporation. Our study aimed to understand the complex relationships between the biocidal and antioxidant activities of CeO2–x, concepts whose origin was not sufficiently detangled in the bibliography. The biocide profiles of CeO2–x nanoparticles toward the marine bacterium Aliivibrio fischeri were studied in tandem with their reactive oxygen species (ROS) scavenging capacity. A key finding of the present study is that the A-FSP process allows selective engineering of cluster-type Ce3+ and Vo defects, while typical, nonanoxic nanoceria structures (code-named ox-CeO2) present mainly monomeric Ce3+ defects. The type of Ce3+ defects directly impacts the ROS scavenging efficiency. In addition, structural modifications that occur from the presence of cluster-type Ce3+ defects, such as larger particle sizes, are directly associated with lower biocidal activity. Thus, the findings of this study indicate that biocidal and ROS antioxidant activities are not mutually exclusive properties