Plasmon-induced tuning of cerium oxidation states in Au@CeO<i>x</i> core@shell nanoparticles

Abstract

CeOx-based nanoforms are widely used in catalysis, or biomedical applications due to their redox activity and oxygen storage capacity. The key parameters determining their surface chemistry are the Ce3+/Ce4+ ratio and the ability to transition between Ce4+ and Ce3+ states. We synthesized Au@CeOx core@shell nanoparticles with different thicknesses of CeOx shells and different Ce3+/Ce4+ ratios through a photothermal reaction driven by localized surface plasmon resonances (LSPRs) at the Au nanoparticle surface induced by visible light. We introduce a way to further enhance the Ce3+/Ce4+ ratio in the shell by exposing the Au@CeOx nanoparticles to visible light using a green laser (532 nm, 50 mW). Our findings based on photoelectron spectroscopy indicate that the Ce4+-to-Ce3+ transition results from LSPR-induced superheating of the Au/CeOx interface, leading to the formation of oxygen vacancies and reduction of Ce4+ ions. This process is reversible upon air exposure suggesting that the ability to transition between the Ce4+ and Ce3+ states is retained in the Au@CeOx nanoparticles. Our study presents the CeOx-based nanoforms with a tunable cerium valence state ratio, highlighting the potential of plasmonic control in optimizing their photocatalytic and enzyme-mimetic properties.