Self-assembly of structured CeCO3OH and its decomposition in H2 for a novel tactic to obtain CeO2-x with excellent photocatalytic property

Highlights: • Various new morphologies of CeCO₃OH were synthesized by a facile hydrothermal route. • Ce₂(CO₃)₃⋅6H₂O was found as an intermediate product in studied synthetic process. • Decomposition behaviors of CeCO₃OH in H₂/Ar atmosphere are revealed. • Ceria with higher photocatalytic activity was obtained by decomposing CeCO₃OH in H₂. -- Abstract: In this work, various new-observed structured CeCO₃OH were synthesized by a self-assembly hydrothermal method, and a novel tactic to produce CeO_2-x with excellent photocatalytic activity by decomposing CeCO₃OH in H₂ was proposed and identified. By controlling the synthetic conditions, almond-like, subglobose shape and hollow-sphere of CeCO₃OH, 3D-broom-like of Ce₂O₃·2CO₂·nH₂O (n = (1–2)), and sheet-like of Ce₂(CO₃)₃·6H₂O were synthesized. The crystal growth and formation of the cerium carbonate compounds were carefully studied using XRD, SEM and TEM. TG, thermodynamic calculation and in-situ XRD were employed to reveal the decomposition behavior of almond-like CeCO₃OH in air, Ar and H₂. The results show that the decomposition temperatures of CeCO₃OH in Ar and H₂ are higher than that of in air, and suggest that Ce₂O₃ has a low thermodynamic stability during the decomposition of CeCO₃OH in Ar and H₂, and Ce³⁺ will be mostly oxidized by H₂O firstly and then by both of H₂O and CO₂. The ceria samples obtained by decomposing from CeCO₃OH in different atmosphere maintain indistinguishable shape and particle size. The XPS, Raman spectra and ESR results indicate that the one obtained in H₂ has the richest surface oxygen vacancies (OVs), narrowest band gap of 3.12 eV, lowest intensity in PL spectra and a significantly enhanced photodegradation ratio of methylene blue. The MB photodegradation ratio after 120 min reaction with the catalysts of CeO₂-Air, CeO₂-Ar and CeO₂-H₂ is 43.14%, 54.43% and 73.41%, with a calculated reaction rate constant of 0.00539, 0.00652 and 0.01097 min^-1, respectively. The offered novel tactic of decomposing CeCO₃OH in H₂ is an efficient and facile technique for active CeO_2-x production.