A simple route to lanthanum hydroxide nanorods

This letter first describes a facile, low-cost, solution-phase approach to the large-scale preparation of lanthanum hydroxide single crystal nanorods at 60 °C without any template and surfactant. X-ray diffraction (XRD) shows that the nanorods are of pure hexagonal structure. The size and morphology of the products were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Lanthanum hydroxide single crystal nanorods are with diameters of approximately 20 nm and lengths of 150-200 nm. The processes of formation and decomposition for the as-prepared lanthanum hydroxide nanorods were discussed.     

Microwave-assisted synthesis of praseodymium hydroxide nanorods and thermal conversion to oxide nanorod

Pr(OH)₃ nanorods with uniform diameter of 12 nm and different lengths ranging from 50 to 220 nm were successfully prepared via a facile and rapid microwave-assisted hydrothermal method. Pr₆O₁₁ nanorods were also obtained from calcination of the as-prepared hydroxide nanorods as precursors at 500 °C for 6 h. The results showed that the Pr(OH)₃ with hexagonal phase and Pr₆O₁₁ nanorods with cubic phase have high crystallinity and purity. The mechanism for the microwave-assisted hydrothermal synthesis of Pr(OH)₃ nanorods was preliminarily presented.     

Synthesis and formation process of zirconium dioxide nanorods

Crystalline zirconium dioxide nanorods have been prepared by a simple hydrothermal process using zirconium hydroxide as the zirconium raw material. Zirconium dioxide nanorods are composed of monoclinic zirconium dioxide phase, which has been confirmed by the X-ray diffraction analysis. Electron microscopy observations show that the zirconium dioxide nanorods have a single crystal structure, with the rod diameter of less than 100 nm and length of 1–2 μm. Hydrothermal temperature and reaction time play essential roles in the formation and growth of the zirconium dioxide nanorods. Nucleation and crystal growth process are proposed to explain the formation and growth of the zirconium dioxide nanorods.     

Hydrothermal in-situ growth of Tris(8-hydroxyquinolate) aluminum nanorods thin films

Tris(8-hydroxyquinolate) aluminum(Alq₃) thin films assembled with large-scaled nanorods have been fabricated on Al substrates through hydrothermal in-situ growth method assisted by the surfactant of sodium dodecylbenzenesulfonate. The obtained Alq₃ thin film is composed of uniformly sized (500-800nm × 4-10 μm) nanorods with regular hexagonal cross section, which are assembled to form dense nanorod arrays perpendicularly to the Al substrate. X-ray diffraction revealed that the prepared Alq₃ nanorods were the α-phase. Photoluminescence spectra showed that the Alq₃ nanorods thin film possessed a spectral blue-shift (10 nm) compared with the Alq₃ solution. The hydrothermal growth mechanism of nanorods was studied, which implied that the hydrothermal in-situ growth process on the metal substrate played an important role in the formation of the Alq₃ nanorods thin film. This simple hydrothermal method provides a convenient fabrication approach for nanocrystalline functional organic/metal interface.     

Hydrothermal deposition and characterization of ultrafine ZrO2 thin films

Ultrafine ZrO₂ thin films (0.6 μm) have been prepared by a hydrothermal method on polycrystalline alumina substrates (α-Al₂O₃). The hydrothermal treatment of zirconium hydroxide sol in the temperature range of 100–240 °C for 6–72 h results in the formation of monoclinic single-phase films. The resulting films have a white appearance and are homogeneous, without visible pores and defects, and the average grain size in the film is 18 nm.     

Selected-control synthesis of dysprosium hydroxide and oxide nanorods by adjusting hydrothermal temperature

Dysprosium hydroxide and oxide nanorods were prepared directly from commercial bulk Dy₂O₃ crystals by facile hydrothermal process at 130 and 210 °C, respectively. The as-synthesized dysprosium hydroxide and oxide nanorods were investigated by various techniques of XRD, TEM, SEM, and EDS. In the process, the temperature was found to play important roles in determining produce dysprosium hydroxide and oxide nanorods.     

PEG-directed hydrothermal synthesis of alumina nanorods with mesoporous structure via AACH nanorod precursors

Al₂O₃ nanorods with mesoporous structures are successfully synthesized from a hydrothermal and thermal decomposition process via the ammonium aluminum carbonate hydroxide (denoted as AACH) precursors. TEM images show that the average diameter of Al₂O₃ nanorods is about 60 nm, and the length is around 1–2 μm. The experimental results show that well-crystallized mesopores with hierarchically distributed pore sizes are embedded in the Al₂O₃ nanorods. The N₂ adsorption–desorption experiment indicates that the as-synthesized alumina nanorods have large surface area (ca. 176 m²/g) and narrow pore-size distributions. At the same time, the as-prepared Al₂O₃ nanorods exhibit strong photoluminescent properties at room temperature. A plausible surfactant-induced nanorod formation mechanism using the poly ethylene glycols as the template agent for the nanorod assembly is also proposed.     

The formation of WO3 nanorods using the surfactant-assisted hydrothermal reaction

Monoclinic tungsten oxide (WO₃) nanorods were grown using the hydrothermal method on a seeded W foil. The seed layer was formed by thermal oxidation of W foil at 400°C for 30 min. Cetyltrimethylammonium bromide (CTAB) or hexamethylamine (HMT) was used in the reactive hydrothermal bath, along with sodium tungstate dihydrate (Na₂WO₄.2H₂O) and hydrochloric acid (HCl). The concentration of CTAB was varied from 0.01 M to 0.07 M and the concentration of HMT was varied from 0.01 M and 0.05 M. The result showed that CTAB-assisted hydrothermal reaction produced WO₃ nanorods with 4–7 nm diameter, and provided that CTAB concentration was less than 0.07 M. WO₃ nanorods could not be obtained when CTAB concentration was 0.07 M. Columnar structured WO₃ was produced with the presence of HMT in the hydrothermal bath. This was due to decomposition of HMT to form hydroxyl ions (OH^?) that inhibited the growth of nanorods. Cyclic voltammetry (CV) analysis showed better electrochromic property of WO₃ nanorods compared to columnar structured WO₃.     

Synthesis and characterization of bundle-like structures consisting of single crystal Ce(OH)CO3 nanorods

Bundle-like structures consisting of single crystal cerium hydroxide carbonate (Ce(OH)CO₃) nanorods have been synthesized successfully by a hydrothermal method at 100 °C using cerium nitrate (Ce(NO₃)₃·6H₂O) as the cerium source, aqueous carbamide both as an alkaline and carbon source and cetyltrimethylammonium bromide (CTAB) as surfactant. X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to characterize such bundle-like structures. SEM and TEM images show that Ce(OH)CO₃ bundle-like structures were composed of nanorods with diameters of ∼ 100 nm. The XRD pattern and electron diffraction (ED) pattern indicate that Ce(OH)CO₃ has a pure orthorhombic single crystal structure.     

Surfactant-assisted hydrothermal synthesis and characterization of WS2 nanorods

WS₂ nanorods with diameters of about 20–100 nm and lengths of about 0.1–2 μm were successfully synthesized by a simple hydrothermal method with the help of the surfactant Cetyltrimethylammonium Bromide (CTAB). As-prepared WS₂ samples are characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Moreover, the influence of surfactant CTAB on the formation of WS₂ nanorods was investigated. A possible three-step growth mechanism of WS₂ nanorods, in which initial nucleation, self-assembly (oriented aggregation), and subsequent crystal growth (Ostwald ripening) is involved, is proposed to explain the formation of WS₂ nanorods on the basis of observations of a time-dependent morphology evolution process.     

Polymer-assisted hydrothermal synthesis of single crystal Pb1 − xLaxTiO3 nanorods

Single-crystal Pb_xLa_1 − xTiO₃ (PLT) nanorods of various La concentrations have been synthesized by polymer-assisted hydrothermal method. The nanorods have diameters of 25-60 nm and average lengths of 3 μm. With tetragonal lattices structures, the PLT nanorods grow along the (001) direction. As La concentration increasing, the tetragonality c/a decreases and the Raman mode E(1TO) becomes softening. PLT nanorods with various lengths and diameters have been prepared by using different polymer additives. To fabricate well-crystallized nanorods, an annealing process after the hydrothermal treatment is proved to be necessary.     

Hydrothermal synthesis,characterization, and luminescence of BaWO4 nanorods

Barium tungstate (BaWO₄) nanorods were synthesized by a hydrothermal process with the assistant of cetyltrimethyl ammonium bromide (CTAB). The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and photoluminescence measurements. The XRD and FT-IR results show that BaWO₄ samples can be indexed as a pure tetragonal scheelite structure. The SEM results show that the morphologies are nanorods with a diameter about 45 nm and a length exceeding 1 μm. The CTAB and “oriented attachment” play key roles in the growth of BaWO₄ nanorods in the hydrothermal process. When excited at 265 nm, BaWO₄ nanorods show the intrinsic emission band centered at 467 nm. The calculated luminescence lifetime of WO₄ ^2? in BaWO₄ is 8.9 μs.     

pH-dependant structural and morphology evolution of Ni(OH)2 nanostructures and their morphology retention upon thermal annealing to NiO

Nickel hydroxide nanosheets, nanobelts and nanorods were prepared by hydrothermal treatment of the precipitates obtained at different pH values. The morphology and crystal structure of the products could be controlled simply by adjusting the pH value at precipitation. Interconnected nanosheets of hexagonal β-Ni(OH)₂ with thickness around 10–20 nm were formed at pH ∼ 11, whereas nanobelts with typical widths around 40–80 nm, and nanorods with diameters around 50–60 nm of phase pure α-Ni(OH)₂ containing intercalated sulphate ions were obtained in the pH range ∼9.5–8.5. Thermal annealing of the hydroxides at 500 °C yielded cubic phase NiO with morphologies similar to their hydroxide precursors. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and energy dispersive X-ray (EDX) analysis were used to characterize the as-prepared products. The role of pH in controlling the phase and morphology of the products was discussed.     

Synthesis of α-Sb2O4 nanorods by a facile hydrothermal route

α-Sb₂O₄ nanorods with diameter of 50–150 nm and length of 100–300 nm have been successfully synthesized by a hydrothermal method using SbCl₃ and I₂ as reaction reagents. The obtained sample is characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and selected-area electron diffraction. The results confirm that the product is pure single-crystalline α-Sb₂O₄ nanorods with few dislocations and defects. The vibrational property of the nanorods is investigated by Raman spectroscopy. Raman spectrum of α-Sb₂O₄ nanorods has a small red shifts compared with that of the bulk α-Sb₂O₄ powders. A possible growth mechanism of α-Sb₂O₄ nanorods is proposed as three stages: the hydrolyzation of SbCl₃ under strong acid condition, the oxidation of Sb₄O₅Cl₂ and the growth of α-Sb₂O₄ nanorods with the aid of iodine transport.     

Synthesis of highly-active single-crystalline TiO2 nanorods and its application in environmental photocatalysis

Highly-active anatase TiO₂ nanorods have been successfully synthesized via a simple two-step method, hydrothermal treatment of anatase/rutile titanium dioxide nanoparticle powder in a composite-hydroxide eutectic system of 1:1 M KOH/NaOH, followed by acid post-treatment. The morphology and crystalline structure of the obtained nanorods were characterized using XRD, TEM, SEM/EDX and BET surface area analyzer. The obtained TiO₂ nanorods have a good crystallinity and a size distribution (about 4-16 nm); with the dimensions of 200-300 nm length and of 30-50 nm diameter. Compared with its precursor anatase/rutile TiO₂ nanoparticles and the titanate nanotubes, the pure anatase TiO₂ nanorods have a large specific surface area with a mesoporous structure. The photocatalytic performance of the prepared nanorods was tested in the degradation of the commercial Cibacrown Red (FN-R) textile dye, under UV irradiation. Single-crystalline anatase TiO₂ nanorods are more efficient for the dye removal.     

White-light-controlled resistive switching and photovoltaic effects in TiO2/ZnO composite nanorods array at room temperature

White-light-controlled resistance switching and photovoltaic effects in TiO₂/ZnO composite nanorods array grown on fluorine-doped tin oxide (FTO) substrate by hydrothermal process were investigated. The average length of TiO₂/ZnO nanorods is about 3 μm, and the average diameter is about 200 nm. ZnO nanoparticles with size 5–10 nm are embedded in TiO₂ base material. The current–voltage characteristics of Ag/[TiO₂/ZnO]/FTO device demonstrate an outstanding rectifying property and bipolar resistive switching behavior. Specially, the resistive switching behavior can be regulated by white-light illuminating. In addition, this structure also exhibits a substantial white-light photovoltaic effect. This study is helpful for exploring the multifunctional materials and their applications in nonvolatile multistate memory devices and solar cells.     

Surfactant-assisted synthesis and characterization of lanthanum oxide nanostructures

By a simple hydrothermal process, we have synthesized lanthanum oxide nanoneedles, nanorods, and nanorod bundles. The porosity of the obtained materials was found. The structure and morphology of the maintained products were studied by XRD, TG/DTA, TEM, and SAED. The porosity was illustrated by N₂ absorption–desorption, BET, and BJH curves. Moreover, the influence factors and the mechanism for the morphology control of lanthanum oxide have also been preliminarily presented.     

Syntheses and gas-sensing properties of CuO nanostructures by using [Cu(pbbt)Cl2]2·CH3OH as a precursor

The rod-like and dandelion-like CuO nanomaterials have been prepared by the decomposition of a copper complex [Cu(pbbt)Cl₂]₂·CH₃OH (pbbt = 1,1′-(1,3-propylene)-bis-1H-benzotriazole) in the presence of suitable surfactants and alkalies under hydrothermal conditions. The CuO nanorods are about 50 nm in diameter and up to 500-700 nm in length; the average diameter of the dandelion-like CuO microspheres is of 2 μm. A formation mechanism for the CuO nanomaterial was proposed. The gas-sensing properties of as-prepared CuO nanomaterial were studied. The sensitivity of the as-prepared CuO nanorods was better than that of dandelion-like CuO particles, and the CuO nanorods displayed special sensitivity to alcohol.     

A facile low temperature hydrothermal route to CdSO4 nanotubes/rods

Cadmium sulphate nanotubes/rods have been synthesized by hydrothermal treatment using CdSO₄ powder as precursor and hexadecylamine (HDA) as surfactant at 180 °C for 7 days. The powder X-ray diffraction (PXRD) pattern reveals that the CdSO₄ nanotubes/rods are of orthorhombic phase. Fourier transform infrared (FTIR) spectrum shows characteristic bands due to the sulfate ion in 1114 cm^? 1 and 617 cm^? 1 region, besides bands due to the amine moiety. Transmission electron micrograph (TEM) images reveal the nanorods are of 10–15 nm in thickness and nanotubes of wall thickness 5–8 nm. UV–visible absorption spectrum of CdSO₄ nanotubes/rods shows the peak at 221 nm. Photoluminescence (PL) spectrum exhibits an intense UV band at 372 nm and weak green band at 484 nm.     

Large scale hydrothermal synthesis of PbS nanorods

PbS nanorods with a diameter of 20-50 nm have been synthesized successfully by surfactant-assisted hydrothermal route. The product was over 90% yield according to the amount of Pb(CH₃CHOO)₂ used. Experiments showed that the concentration of N-cetyl-N,N,N-trimethyl- ammonium bromide (CTAB) and thiourea (Tu), reaction time and sulfur sources played important roles in the formation of the PbS nanorods. A reasonable mechanism for the formation of the PbS nanorods is also discussed.