Insights into the Surface-Defect Dependence of Photoreactivity over CeO₂ Nanocrystals with Well-Defined Crystal Facets

Abstract

Crystal facet engineering (CFE) has been widely employed to regulate the photoreactivity of crystalline materials, mostly concerning the surface atomic and electronic structures. However, surface defects ubiquitous in real catalysts have long been less recognized. An integrated examination of various influence factors is necessary for the elucidation of an accurate structure–function relationship. Herein, we carefully studied the heterogeneous photoreactivity of CeO2 nanocrystals (NCs) with well-defined crystal facets in multiple processes, including photocatalytic oxidation of volatile organic compounds (VOCs), O2 evolution, and ·OH generation. Variable reactivity priorities were found between different nanoshapes as well as samples of identical nanoshapes. With integrated examinations of the coexisting surface factors (i.e., atomic, electronic, and defect structures), surface defects were evidently proved to compete with other surface factors in deciding the final photoreactivity orders. Surface-defect structure (e.g., Ce3+ ions and O vacancies) was suggested to greatly influence the surface properties of ceria NCs, including the activation of reactants as well as the mobility of surface lattice oxygen. The results clearly confirm the surface-defect dependence of photoreactivity and provide further insights into the complex surface effects in semiconductor photocatalysis. It also underscores the significance of surface-defect structure as an essential supplement to the traditional CFE strategy for achieving desired solar energy utilization.

Recent Progress in Well‐Controlled Synthesis of Ceria‐Based Nanocatalysts towards Enhanced Catalytic Performance

“…[ 206 ] By preventing the recombination of charge carriers, the photocatalytic activity of metal oxide catalysts can be remarkably improved. [ 211 ] They suggested the surface-defect structure consisting of the presence of Ce(III) ions and oxygen vacancies can modify the surface properties of ceria nanoparticles, including the activation of reactants together with the mobility of surface lattice oxygen. In other words, the oxygen vacancies can play the role of electron capture centers.…”

Tuning the structural properties of CeO2 by Pr and Fe codoping for enhanced visible‐light catalytic activity

“…First, some Pr may exist in the form of Pr 4+ , having a slightly smaller ionic radius (0.96 Å) compared with Ce 4+ (0.97 Å) . Second, there are probably more oxygen vacancies in the Pr doped CeO 2 , which shrink the cell . The average crystal size showed the same trend as the lattice parameter changed with the doping Pr concentration.…”

“…PFC5 has the highest value of 1.09% whereas that for PFC9 is only 0.41%. The oxygen vacancies can generate intermediate energy levels, shrink the cell and trap the photogenerated electrons, whereas the peroxide species on the CeO 2 surface may participate in the oxidation reaction . Hence, the oxygen vacancies and the peroxide species on the CeO 2 surface even in small amounts may play significant roles in the reactivity of CeO 2 for the photocatalytic degradation of pollutants.…”

“…(a). As discussed above, more Ce 3+ or oxygen vacancies can widen the light absorption wavelength and promote the separation of electron and hole pairs, which might enhance the visible‐light catalytic activity of CeO 2 samples. The experimental and fitted O1s XPS spectra are presented in Fig.…”

“…Then the oxygen vacancy can shrink the cell and result in lattice deformation. Also, the oxygen vacancy can trap the photogenerated electrons and promote the separation of electron and hole pairs . In addition, Fe 3+ is a shallow electron or hole trap due to its stable half‐filled electronic configuration of 3d 5 .…”