Surface-Structure Sensitivity of CeO2 Nanocrystals in Photocatalysis and Enhancing the Reactivity with Nanogold

• Published in: ACS catalysis 2015-07, Vol.5 (7), p.4385-4393
• Main Authors: Lei, Wanying, Zhang, Tingting, Gu, Lin, Liu, Ping, Rodriguez, José A, Liu, Gang, Liu, Minghua
• Format: Article
• Language: English
• Subjects: aberration-corrected STEM; CeO2; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; nanogold; photocatalysis; surface plasmon resonance; surface structure
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.5b00620

Structure–function correlations are a central theme in heterogeneous (photo)­catalysis. In this study, using aberration-corrected scanning transmission electron microscopy (STEM), the atomic surface structures of well-defined one-dimensional (1D) CeO2 nanorods (NRs) and 3D nanocubes (NCs) are directly visualized at subangstrom resolution. CeO2 NCs predominantly expose the {100} facet, with {110} and {111} as minor cutoff facets at the respective edges and corners. Notably, the outermost surface layer of the {100} facet is nearly O-terminated. Neither surface relaxations nor reconstructions on {100} are observed, indicating unusual polarity compensation, which is primarily mediated by near-surface oxygen vacancies. In contrast, the surface of CeO2 NRs is highly stepped, with the enclosed {110} facet exposing Ce cations and O anions on terraces. On the basis of STEM profile-view imaging and electronic structure analysis, the photoreactivity of CeO2 nanocrystals toward aqueous methyl orange degradation under UV is revealed to be surface-structure-sensitive, following the order: {110} ≫ {100}. The underlying surface-structure sensitivity can be attributed to the variation in low-coordinate surface cerium cations between {110} and {100} facets. To further enhance light absorption, Au nanoparticles (NPs) are deposited on CeO2 NRs to form Au/CeO2 plasmonic nanocomposites, which dramatically promotes the photoreactivity that is Au particle size- and excitation light wavelength-dependent. The mechanisms responsible for the enhancement of photocatalytic activity are discussed, highlighting the crucial role of photoexcited charge carrier transfer.