Gold/Ceria Nanostructures for Plasmon-Enhanced Catalytic Reactions Under Visible Light
Authors: Yang Jianhua , Jia Henglei , Li Benxia , Wang Jianfang 
Published: February 2020

Driving catalytic reactions with sunlight is an excellent example of sustainable chemistry. Gold nanocrystals have proven promising in harvesting solar energy for chemical reactions due to their extraordinary and tailorable localized surface plasmon resonance (LSPR) properties. Gold/semiconductor hybrid nanostructures have recently attracted much attention because of LSPR-induced light focusing in the vicinity of Au nanocrystals and/or plasmon induced charge transfer across the interface. CeO2 has shown great potential in catalysis due to its attractive chemical and physical properties, including its unique 4f electron configuration and oxygen ion conductivity. Intimate integration of CeO2 with Au nanocrystals at nanoscale is therefore expected to enable Au/CeO2 to function as an excellent photocatalyst for desired catalytic reactions. However, the rational preparation of plasmonic Au/CeO2 nanostructures has yet remained challenging. In addition, to fully improve the catalytic activity of Au/CeO2 requires a thorough fundamental understanding of the underlying plasmon-enhanced mechanisms. We have recently performed systematic studies on the design of Au/CeO2 with enhanced activities for the oxidation of alcohols and carried out investigations on the plasmon-enhanced mechanisms.

First, we developed a versatile approach for coating CeO2 on monometallic Au and bimetallic Au@Pt, Au@Pd nanocrystals to produce multifunctional core@shell nanostructures with plasmon resonance wavelengths tunable from the visible to near-infrared region. The calcined (Au core)@(CeO2 shell) nanostructures display high photocatalytic activities toward the oxidation of benzyl alcohol to benzaldehyde under the illumination of visible light. The enhanced photocatalytic activities are attributed to the synergistic effect between the Au nanocrystal core acting as a plasmonic component for efficient light harvesting and the CeO2 shell providing catalytically active sites for the oxidation reaction.

Second, for core@shell structures, the effective accessibility of the active metal core by reactants is of particular importance. Dense shells might hinder hot holes in the Au core from being accessed by reactant molecules, which leads to the recombination of electrons and holes and therefore the reduction of photocatalytic activities. In this regard, mesoporous shell is of great promise since it offers a large number of continuous channels, high specific surface areas, and versatile pore structures. We successfully prepared mesoporous Au/CeO2 microsphere photocatalysts with different Au loading amounts using an aerosol spray method. The mesoporous nature of CeO2 endows the Au/CeO2 sample with drastically boosted activities that are about 23 times larger than those of (Au nanosphere core)@(CeO2 dense shell) nanostructures.

[1] B. X. Li, T. Gu, T. Ming, J. X. Wang, P. Wang, and J. F. Wang,* J. C. Yu, ACS Nano, 8 (2014), 8152-8162.

[2] H. L. Jia, X. M. Zhu, R. B. Jiang, and J. F. Wang,* ACS Appl. Mater. Interfaces (2017), 9, 2560-2571.