CeO$_x$-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 Ce$^{ 3+}$/Ce$^{ 4+}$ ratio and the ability to transition between Ce$^{ 4+}$ and Ce$^{ 3+}$ states. We synthesized Au@CeO$_x$ core@shell nanoparticles with different thicknesses of CeO$_x$ shells and different Ce$^{ 3+}$/Ce$^{ 4+}$ 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 Ce$^{ 3+}$/Ce$^{ 4+}$ ratio in the shell by exposing the Au@CeO$_x$ nanoparticles to visible light using a green laser (532 nm, 50 mW). Our findings based on photoelectron spectroscopy indicate that the Ce$^{ 4+}$-to-Ce$^{ 3+}$ transition results from LSPR-induced superheating of the Au@CeO$_x$ interface, leading to the formation of oxygen vacancies and reduction of Ce$^{ 4+}$ ions. This process is reversible upon air exposure suggesting that the ability to transition between the Ce$^{ 4+}$ and Ce$^{ 3+}$ states is retained in the Au@CeO$_x$ nanoparticles. Our study presents the CeO$_x$-based nanoforms with a tunable cerium valence state ratio, highlighting the potential of plasmonic control in optimizing their photocatalytic and enzyme-mimetic properties.
Categories: cond-mat.mtrl-sci