Phosphate ions play a crucial role not only for the formation of the spindlelike precursors of the single‐crystalline hematite nanotubes that were synthesized by a facile hydrothermal method. They are also important for the adsorption and coordination effects. The mechanism of tube formation was deduced through EM observations as a coordination‐assisted dissolution process (see picture).
Pure monoclinic (m-) and tetragonal phased (t-) LaVO(4) nanocrystals could be obtained by a hydrothermal method in a controllable way with additives. It is found that chelating ligands, such as ethylenediaminetetraacetic acid [EDTA or H(4)L, where L(4-) = (CH(2)COO)(2)N(CH(2))(2)N(CH(2)COO)(2)(4-)], favor the formation of t-LaVO(4) and can induce the polymorph transformation from stable m-LaVO(4) to metastable t-LaVO(4). Further studies demonstrated the important roles of chelating ligands in this transformation process. Careful investigation over the phase transition from t- to m-LaVO(4) was also conducted with high-temperature X-ray diffraction (HTXRD) studies. The phase transition occurred at 850 degrees C, which is about 250 degrees C higher than for the bulk. The enhanced thermal stability of the nanosized metastable t-LaVO(4) may come from the small size effect. Our capability of obtaining and stabilizing t-LaVO(4) not only benefits the wider applications based on LaVO(4) due to the improved luminescent and catalytic performance but also provides a new idea in the studies of polymorph control and selective synthesis of inorganic materials.
Single-crystalline hematite tube-in-tube nanostructures were prepared by a facile one-step hydrothermal method. The structure, shape, and formation mechanism of the tube-in-tube nanostructures were investigated. The results disclosed that the hematite tube-in-tube nanostructures were formed through a multisite dissolution process of the ellipsoid precursors. What is more, the tube-in-tube nanostructure is a single crystal in nature, and a simple combination of a small tube filling into a big one can be excluded. Single-crystalline magnetite and maghemite tube-in-tube nanostructures were also obtained via a simple reduction or reduction and reoxidation process with the hematite as the precursor. The facile and mild reaction route could be useful for the fabrication of complex tubular nanostructures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.