ABSTRACT
CeVO(4) nanocrystals doped by heteroions were prepared via a hydrothermal method without the presence of surfactants or templates. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), solid state (51)V NMR, and inductively coupled plasma (ICP) were used to characterize the morphology, structure, and compositions of the materials. X-ray photoelectron spectroscopy (XPS) results confirmed that there is a valence change from Ce(3+) to Ce(4+) for a fraction of cerium atoms whereas the vanadium atoms remain in the pentavalent state V(5+) upon the substitution of Ca(2+) into CeVO(4). Raman spectroscopy was used to monitor the effects of the doping ion on the CeVO(4) lattice contraction and distortion. The appearance of the shifted and broadened Raman peaks for the doped CeVO(4) was interpreted by theoretical calculations performed with Vienna ab initio simulation package. The redox properties and photocatalytic activities of the obtained nanocrystals were also investigated and discussed in detail.
ABSTRACT
Mechanistic investigation on spherical assembly of the unique one-dimensional ZnO nanorods, solid nanocones, or hollow prisms with the closed -c end, directed by poly ethylene glycol (PEG) with different molecular weights, has been carried out using spectroscopic methods. The single crystalline ZnO nanoprisms, hollow along the c axis but closed at the -c end, aggregate to urchin-type globules in the microscale when PEG 2000 is used as directing reagent, while spherical aggregates of single crystalline ZnO nanocones are obtained under the direction of PEG 200. Studies reveal that both the PEG molecules aggregate to globules by interacting with zinc species in suitable solvents and englobe the zinc species. By the short time of ultrasonic pretreatment on the solution, a kind of flagellum structure is induced around the globules, in long tubular shapes for PEG 2000 but as shorter wedges for PEG 200. The globules with flagellums are templates for the assembly of the ZnO nanotubes or ZnO nanocones in the hydrothermal treatment. The tiny ZnO crystallites, produced in the hydrothermal process, stack to the templates and amalgamate to single crystalline nanotubes or nanocones, similar to the oriented attachment mechanism. The PEG 2000 template is included in the ZnO cavity of nanotubes, while PEG 200 is excluded from the ZnO nanocones due to the different intertwist properties between the two PEG molecules. Both the urchin-type assemblies, possessing the same external crystalline plane, compose a isotropic powder and emit very strong yellow light, centered at approximately 2.1 eV, under the excitation of the He-Cd laser at 325 nm, which has been correlated to the specific crystal plane. The special powders will be easily coated onto any type of surface for the decoration of a large area of surfaces for future applications.
