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Amongst the most popular methods for the production of metal oxide nanostructures is hydrothermal synthesis. For producing ZnO nanostructures, a nitrate-based precursor reaction with equimolar amounts of hexamethylenetetramine (HMTA) is commonly used. In these reactions, zinc nitrate provides the source of Zn2+ ions, and HMTA produces the desired amount of OH− ions. The growth process occurs due to a dissolution-secondary precipitation mechanism. ZnO nanostructures are characterized by anisotropic growth with different growth rates of the individual faces, where (v(0001) > v(101¯0) > v(101¯1¯) > v(101¯1) > v(0001¯)). Therefore, considering the principle of energy minimization, the most favorable is vertical growth perpendicular to the (0001) plane, which ensures the formation of characteristic rod-like nanostruchtures of ZnO. The mentioned process takes place when chemical reactions are in equilibrium. Shifting from the equilibrium conditions by varying the parameters of reaction, or using capping agents, makes it possible to change the growth rate of individual crystallographic planes and, as result, affect the morphology of the obtained nanostructure. In this paper the influence of concentration and composition of the reagents, growth time and temperature, pH of the solution, and the presence of different capping agents on the growth process of nanostructured ZnO were investigated. Optimal synthesis parameters for obtaining nine independent ZnO morphologies have been determined. The distinctive feature of these experiments is the fact that the samples were obtained as durable, homogeneous, epitaxial coatings on hard surfaces. This can be especially interesting for the development of sensors and other fields where surface area is crucial, and it opens up more possibilities than use of the nanostructured ZnO powders. [ABSTRACT FROM AUTHOR]

The exposure of the crystallographic facets of CeO2 nanocrystals may alter their surface structure and composition, leading to significant discrepancies in their reactivity with respect to catalyzing different reactions. In this paper, a facile strategy of etching hollow CeO2 spheres (@CeO2) with a fluorine-containing ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), under hydrothermal conditions was developed to achieve surface-fluorinated @CeO2 nanoparticles with exposed active high-energy facets, which were further assembled in situ into @CeO2 nanoparticle assemblies. The IL, [Bmim][BF4], is believed to play an important role in determining the formation of CeO2 nanoparticles, and the mild release of fluorine species from [Bmim][BF4] may account for the surface-fluorination and the exposure of active high-energy facets of CeO2. The CeO2 nanoparticle assemblies are ideal model materials for studying crystal facet-dependent catalytic behavior. By loading well-dispersed Au nanoparticles via a sol-impregnation method, @CeO2/Au nanoparticle assemblies were achieved, which showed an enhanced catalytic performance for benzyl alcohol aerobic oxidation. In comparison with @CeO2/Au nanoparticle assemblies obtained by etching @CeO2 spheres with other fluorine-containing agents, NH4BF4, NaBF4, and NH4F, under identical reaction conditions, @CeO2/Au nanoparticle assemblies achieved by etching with [Bmim][BF4] exhibited the highest catalytic activity for benzyl alcohol aerobic oxidation. The surface-fluorination and the exposure of active high-energy facets of CeO2 nanoparticles are believed to be responsible for the enhancement of their catalytic activity. This methodology provides a robust strategy to create CeO2 materials with the active high-energy facets exposed and afford model materials for investigating crystal facet-dependent catalytic behavior, which currently represents an exciting issue in the nanocatalysis community. [ABSTRACT FROM AUTHOR]

This paper reports on a facile hydrothermal route that has been developed to synthesize a precursor Gd(OH)2.14F0.86 and a novel phosphor host Gd6O5F8. The morphology of the micro-sized Gd(OH)2.14F0.86/Gd6O5F8 can be easily tuned in a controlled manner by altering the fluorine sources, alkali solutions, reaction time and the pH values of the initial solution. Under ultraviolet (UV) light, vacuum ultraviolet (VUV) light and low-voltage electron beam excitation, the Gd(OH)2.14F0.86/Gd6O5F8:Ln3+ (Eu, Tb and Tm) samples show the characteristic f–f transitions of the Ln3+ ions and give bright red, green and blue emissions, respectively. The results prove that the as-synthesized Gd6O5F8 are excellent host lattices for rare earth luminescence, which may find potential applications in solid-state light, field emission displays (FEDs). [ABSTRACT FROM AUTHOR]

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]