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The structure of doped ceria plays an important role in its chemical reactivity and catalytic performance. However, for the majority of the dopants studied, whether a monophasic solid solution is formed or not is typically determined only by standard X-ray diffraction (XRD). In-depth structural characterization is lacking. In this paper we have prepared Zn-doped ceria nanocrystals exhibiting twice the oxygen storage capacity (OSC) of pure ceria. X-ray photoelectron spectroscopy (XPS) shows that the material is chemically inhomogeneous with zinc enrichment in the surface layer. X-ray fluorescence (XRF) reveals significant compositional inhomogeneity of the material after annealing in air at 1300 °C for 24 h. The standard structural characterization of this material using room temperature XRD and transmission electron microscopy (TEM) fails to reveal its correct phase composition. Based on clear evidence from in situ high temperature XRD we show that, after calcination at 500 °C, the material is not monophasic: X-ray amorphous ZnO is present within the material. The amorphous ZnO crystallizes at 800 °C and undergoes second-stage incorporation at even higher temperatures. This second-stage incorporation is not complete after annealing and trace amounts of ZnO remain according to synchrotron-based XRD. Our work provides valuable insight into the incorporation mechanism of zinc into the ceria lattice, and in particular, raises some doubts on the phase compositions reported in many previous studies on doped ceria. [ABSTRACT FROM AUTHOR]

Nanosheet-assembled yolk–shell anatase TiO2 microspheres were synthesized utilizing the slow hydrolysis of K2TiO(C2O4)2 in a mixed solution of H2O2 and HNO3. Under a temperature near to the ambient one, microspheres assembled with nanoparticles were firstly obtained at the early reaction stage. Prolonging the reaction duration led to the formation of urchin-like microspheres, which further developed into nanosheet-assembled yolk–shell microspheres through a dissolution–precipitation procedure. The intermediate acid washing and final calcination transformed the microspheres to phase-pure anatase TiO2. The yolk–shell anatase microspheres exhibited a photocatalytic activity twice that of the urchin-like microspheres when utilized to assist the photodegradation of both rhodamine B and phenol in water under the illumination of UV light. [ABSTRACT FROM AUTHOR]

Shape-controlled synthesis of CoCO3 crystals is achieved by a mild template- and surfactant-free solvothermal process. On switching the volume ratio of ethylene glycol (EG) in the mixed solvent, the structures of the CoCO3 crystals change from cantaloupe-like patterns to microcubes. The formation pathway of CoCO3 was discussed from the viewpoint of Ksp and the equilibrium of water ionization. After calcination in air at 500 °C, the as-prepared CoCO3 crystals convert to porous Co3O4 microstructures. When used as negative electrodes of alkaline rechargeable batteries, these Co3O4 samples display high discharge capacities and good cycle stability. The electrochemical reactions occurring on the Co3O4 electrode are investigated by XRD, cyclic voltammetry (CV) and charge–discharge curves. In the activation process for about 20 cycles, Co3O4 transforms to Co(OH)2 in the charged process, then a large discharge capacity is obtained through Faradaic reaction between Co and Co(OH)2. Experimental results indicate that the discharge capacities of the obtained Co3O4 samples are significantly influenced by their surface area and microstructures. Through lowering the calcination temperature to 300 °C, a mesoporous sample with a high BET surface area of 105 m2 g−1 and narrow particle size distribution is obtained. At a current density of 100 mA g−1, the discharge capacity of this Co3O4 sample reaches 490.2 mA h g−1. After 50 cycles it can still achieve 436.9 mA h g−1. Meanwhile, the Co3O4 sample shows enhanced rate performance, indicating great potential application in alkaline rechargeable batteries. [ABSTRACT FROM AUTHOR]