Formation of CeO2 nanotubes from Ce(OH)CO3 nanorods through Kirkendall diffusion.

In this paper, CeO(2) nanotubes based on the Kirkendall effect (for simplicity, this type of nanotubes is denoted as K-type CeO(2) nanotubes) are fabricated through a solid-liquid interface reaction between Ce(OH)CO(3) nanorods and NaOH solutions. Our studies indicate the formation mechanism of K-type CeO(2) nanotubes is quite different from those of CeO(2) nanotubes subjected to template (T-type CeO(2) nanotubes) and lamellar rolling (L-type CeO(2) nanotubes) reported previously by our group. The K-type CeO(2) nanotubes are prepared by congregating Kirkendall voids and subsequent calcinations. The time evolution processes are imaged by TEM, and the results show that as the reaction processes, interior spaces are formed and enlarged in Ce(OH)CO(3) nanorods to form K-type CeO(2) nanotubes. In contrast, the interior space in T-type CeO(2) nanotubes decreases with reaction time. XRD is applied to study the phase transformation in the formation process of K-type CeO(2) nanotubes. Our study also indicates NaOH and reaction temperature are two key factors responsible for formation of K-type CeO(2) nanotubes. Combined with the T- and L-type nanotubes, three types of CeO(2) nanotubes with different formation mechanisms are successfully synthesized in one reaction system, which might afford some guidance for the synthesis of other inorganic nanotubes.

Synthesis and characterization of a new metal-organic NLO material: dibromo bis(triphenylphosphine oxide) mercury(II).

A new metal-organic nonlinear optical dibromo bis(triphenylphosphine oxide) mercury(II) (HgBr(2)(TPPO)(2), TPPO=triphenylphosphine oxide) crystal has been synthesized. Single-crystal X-ray diffraction reveals that HgBr(2)(TPPO)(2) crystallizes in the orthorhombic system, space group Pna2(1), a=21.174A, b=9.1979A, c=17.468A, and Z=4. The crystal was also characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), thermal gravity analysis (TGA), and UV-vis-IR spectroscopy. Thermal analyses confirmed that the crystal is stable up to 151 degrees C. The transmission spectrum of the crystal shows that the lower cut off wavelength lies at 340nm. The nonlinear optical (NLO) property of HgBr(2)(TPPO)(2) has been estimated by Kurtz-powder second harmonic generation (SHG) test.

Densely stacked multilamellar and oligovesicular vesicles, bilayer cylinders, and tubes joining with vesicles of a salt-free catanionic extractant and surfactant system.

In the phase diagram of an excellent extractant of rare earth metal ions, di(2-ethylhexyl) phosphate (HDEHP, commercial name P204), mixing with a cationic trimethyltetradecylammonium hydroxide (TTAOH) in water, a birefringent Lalpha phase was found, which consists of densely stacked multilamellar vesicles. The densely stacked multilamellar vesicles are remarkably deformed, as observed by means of cryotransmission electron microscopy (cryo-TEM). Further, self-assembled structures-oligovesicular vesicles, bilayer cylinders, and tubes joining with vesicles-were also observed. The self-assembled phase is transparent, anisotropic, and highly viscous, possessing elastic properties determined by rheological measurements. This is the first time that birefringent Lalpha phase with remarkably deformed amphiphilic bilayer membranes has been constructed through combining a hydrophobic organic extractant having double chains with a water-soluble surfactant having a single chain, which may direct primarily toward acquiring an understanding of the mechanism of salt-free catanionic vesicles and secondarily to determine if vesicle-extraction technology utilizing extractants is possible.

Selected-control hydrothermal synthesis and formation mechanism of monazite- and zircon-type LaVO(4) nanocrystals.

Selective-controlled structure and shape of LaVO(4) nanocrystals were successfully synthesized by a simple hydrothermal method without the presence of catalysts or templates. It was found that tuning the pH of the growth solution was a crucial step for the control of the structure transformation, that is, from monoclinic (m-) to tetragonal (t-) phase, and morphology evolution of LaVO(4) nanocrystals. Further studies demonstrated that the morphology of the product had a strong dependence on the initial lanthanum sources. In the La(NO(3))(3) or LaCl(3) reaction system, pure t-LaVO(4) nanorods with uniform diameters about 10 nm could be obtained. But when using La(2)(SO(4))(3) as the lanthanum source, we can get t-LaVO(4) nanowiskers with broomlike morphology. The detailed systematic study had shown that a special dissolution-recrystallization transformation mechanism as well as an Ostwald ripening process was responsible for the phase control and anisotropic morphology evolution of the LaVO(4) nanocrystals. As a result, the controlled synthesis of m- and t-LaVO(4) not only has great theoretical significance in studying the polymorph control and selective synthesis of inorganic materials but also benefits the potential applications based on LaVO(4) nanocrystals owing to the unusual luminescent properties induced by structural transformation.

One-step preparation of single-crystalline beta-MnO2 nanotubes.

Single-crystal beta-MnO(2) nanotubes with diameters in the range 200-500 nm and lengths up to several micrometers were successfully prepared by a simple hydrothermal method through oxidizing MnSO(4) with NaClO(3) in the presence of poly(vinyl pyrrolidone) (PVP). It was found that the formation process of beta-MnO(2) nanotubes included two primary evolution stages over time: (1) the MnOOH nanoparticles initially formed in the hydrothermal system and anisotropic growth to nanorods and nanorod aggregates, and (2) the MnOOH nanorods transformed into beta-MnO(2) tubular structure and grown into beta-MnO(2) nanotubes due to continuous growth through a dissolution-recrystallization process eventually. Based on a series of experimental analysis, the formation mechanism of these nanostructures was discussed briefly. The present study has enlarged the family of nanotubes available and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials.

Single-crystalline CuO nanobelts fabricated by a convenient route.

A reverse micelle-assisted route for preparing CuO nanobelts from precursor Cu(OH)2- 4 is reported. The reverse micelles were used as microreactors, which led to anisotropic growth crystals during a simple solvothermal process. The formation conditions of the CuO nanobelts were also studied.

A method for the synthesis of spherical copper nanoparticles in the organic phase.

In this paper, stable metallic copper nanoparticles protected by bis(ethylhexyl)hydrogen phosphate (HDEHP) were prepared in the organic phase. In the synthesis of copper nanoparticles, the bis(ethylhexyl)hydrogen phosphate (HDEHP) acted as both a phase-transfer agent and a particle protector. It was also found that the protective ability of HDEHP was different with different diluent polarities. Despite zero valent Cu initially forming in all the solvents studied, it has been found that the zero valent Cu can easily transform into oxides in those solvents with high dipole moments under ambient conditions. Only in those nonpolar solvents, the metallic copper nanoparticles are stable in air. In addition, theoretical analyses were made in order to interpret the interaction mode between the copper nanoparticles and the surfactant HDEHP.

Interface reaction route to two different kinds of CeO2 nanotubes.

CeO(2) nanotubes have been synthesized with a simple solid-liquid interface reaction route in the absence of any surfactants. Although the basic reaction principles are similar, two kinds of nanotubes with completely different morphologies and structures can be generated by slightly tuning the postprocessing conditions. The first formation involves employing Ce(OH)CO(3) nanorods as both the physical and chemical templates, and the other requires layered Ce(OH)3 as an anisotropic intermediate species. During this process, NaOH and reaction temperature were demonstrated as the key factors responsible for the formation of Ce(OH)(3) intermediate and final CeO(2) nanotubes with well-defined structures. The structural details were provided by a combination of XRD, SEM, TEM, and HRTEM investigations. Catalytic measurement shows that both nanotubes are very active for CO oxidation, and at 250 degrees C, the conversion rates of CeO(2) nanotubes are 3 times higher than that of the bulk counterpart.

Microemulsion-based synthesis of titanium phosphate nanotubes via amine extraction system.

The first titanium phosphate nanotubes with alternating interlayer spacings have been successfully prepared and characterized. The synthesis is accomplished in a reverse microemulsion formed in an amine extraction system. TEM data from samples made after different times of reaction suggest a scrolling-formation mechanism.