Silver Nanocubes Coated in Ceria: Core/Shell Size Effects on Light-Induced Charge Transfer

Plasmonic sensitization of semiconductors is an attractive
approach to increase light-induced photocatalytic performance; one
method is to use plasmonic nanostructures in core@shell geometry.
The occurrence and mechanism of synergetic effects in photocatalysis
of such geometries are under intense debate and proposed to occur
either through light-induced charge transfer (CT) or through thermal
effects. This study focuses on the relation between the dimensions
of Ag@CeO2 nanocubes, the wavelength-dependent efficiency,
and the mechanism of light-induced direct CT. A 4-mercaptobenzoic
acid (4-MBA) linker between core and shell acts as a Raman probe for
CT. For all Ag@CeO2 nanocubes, CT increases with decreasing
excitation wavelength, with notable increase at and below 514 nm.
This is fully explainable by CT from silver to the 4-MBA LUMO, with
the increase for excitation wavelengths that exceed the Ag/4-MBA LUMO
gap of 2.28 eV (543 nm). A second general trend observed is an increase
in CT yield with ceria shell thickness, which is assigned to relaxation
of the excited electron further into the ceria conduction band, potentially
producing defects.