Abstract
Oxygen vacancies (OVs) have critical effects on the photoelectric characterizations and photocatalytic activity of nanoceria, but the contributions of surface OVs on the promoted photocatalytic properties are not clear yet. In this work, we synthesized ceria nanopolyhedron (P-CeO2), ceria nanocube (C-CeO2) and ceria nanorod (R-CeO2), respectively, and annealed them at 600 °C in air, 30%, 60% or pure H2. After annealing, the surface OVs concentration of ceria elevates with the rising of H2 concentration. Photocatalytic activity of annealed ceria is promoted with the increasing of surface OVs, the methylene blue photodegradation ratio with pure hydrogen annealed of P-CeO2, C-CeO2 or R-CeO2 is 93.82%, 85.15% and 90.09%, respectively. Band gap of annealed ceria expands first and then tends to narrow slightly with the rising of surface OVs, while the valence band (VB) and conductive band (CB) of annealed ceria changed slightly. Both of photoluminescence spectra and photocurrent results indicate that the separation efficiency of photoinduced electron-hole pairs is significantly enhanced with the increasing of the surface OVs concentration. The notable weakened recombination of photogenerated carrier is suggested to attribute a momentous contribution on the enhanced photocatalytic activity of ceria which contains surface OVs.
Highlights
Published: 29 April 2021Cerium is the first element in the periodic table to possess a ground state electron in a 4f orbital (Xe 4f1 5d1 6s2 ), which is responsible for the powerful redox behavior between its two ionic states, Ce4+ and Ce3+ (Xe 4f1 ) [1]
XRD patterns of synthesized nanoceria are exhibited in Figure 1, it can be seen that all samples show the typical diffraction peaks of CeO2 with a fluorite-type structure and Fm3m space group (PDF: #03-065-2975)
We found that the BET surface area of all samples decreased after calcining in H2, which further indicates that the surface Oxygen vacancies (OVs) concentration is the major factor on the photocatalytic properties of ceria in this study
Summary
Published: 29 April 2021Cerium is the first element in the periodic table to possess a ground state electron in a 4f orbital (Xe 4f1 5d1 6s2 ), which is responsible for the powerful redox behavior between its two ionic states, Ce4+ (the Xe ground state) and Ce3+ (Xe 4f1 ) [1]. Cerium dioxide is known for its excellent redox ability, outstanding oxygen storage capacity and stable chemical properties, which make ceria a prominent function material for various applications, e.g., threeway catalysis [2], water gas shift reaction (WGS) [3,4], solar energy conversion [5,6], gas sensor [7] and chemical-mechanical polishing [8]. It is generally accepted that the photocatalytic application of ceria is impeded by its wide band gap ~3.2 eV and a quick recombination of photogenerated electrons (e− ). Oxygen vacancies (OVs) or Ce3+ have been reported to affect both band structure and recombination of photocarriers significantly, and promote the photocatalytic activity of ceria [20,21,22,23]. It is believed that the OVs are favorable for reducing the e- /h+ pairs recombination rate [24,25]
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