Facile synthesis of solution-disposable carbon nanotube-TiO2 hybrids in organic media

Oleic acid-capped TiO₂ nanoparticles (NPs) were directly grown on untreated multiwalled carbon nanotubes (MWCNTs) from a stable titanium carboxylate complex through a solvothermal aminolysis process in organic media. The shape of the TiO₂ NPs loaded on the MWCNTs can be controlled from nanodots (∼ 3 nm in diameter) to nanorods (∼ 5 nm in diameter, 30-40 nm in length) by changing solvent components and by Co²⁺ doping. The resulting hybrids can be well dispersed in apolar organic solvents, which may provide possibilities for manipulating them in solutions for widespread applications.     

Morphology effect on the performances of SnO2 nanorod arrays as anodes for Li-ion batteries

Ni foam suppported-SnO₂ nanorod arrays with controllable diameter were prepared via a template-free growth method, which was a convenient route for the large-scale growth of pure-phase metal oxide nanorod arrays on metal substrates. The relationship between electrochemical behavior and the shape of SnO₂ nanorod arrays has been investigated in detail. SnO₂ nanorod arrays with diameter of about 25 nm, as anode materials for Li-ion batteries revealed a capacity of 607 mAh g⁻¹ (at 0.2 C) up to 50 cycles. The superior performance of the SnO₂ nanorods can be mainly attributed to small size of nanorods which reduce volume expansion and lithium diffusion length.     

A comparative study on the NO2 gas sensing properties of ZnO thin films, nanowires and nanorods

ZnO thin films were fabricated using the spin coating method, ZnO nanowires by cathodically induced sol-gel deposition by the means of an anodic aluminum oxide (AAO) template, and ZnO nanorods with the hydrothermal technique. For thin film preparation, a clear, homogeneous and stable ZnO solution was prepared by the sol-gel method using zinc acetate (ZnAc) precursor which was then coated on a glass substrate with a spin coater. Vertically aligned ZnO nanowires which were approximately 65 nm in diameter and 10 μm in length were grown in an AAO template by applying a cathodic voltage in aqueous zinc nitrate solution at room temperature. For fabrication of the ZnO nanorods, the sol-gel ZnO solution was coated on glass substrate by spin coating as a seed layer. Then ZnO nanorods were grown in zinc nitrate and hexamthylenetetramine aqueous solution. The ZnO nanorods are approximately 30 nm in diameter and 500 nm in length. The ZnO thin film, ZnO nanowires and nanorods were characterized by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). The NO₂ gas sensing properties of ZnO thin films, nanowires and nanorods were investigated in a dark chamber at 200 °C in the concentration range of 100 ppb-10 ppm. It was found that the response times of both ZnO thin films and ZnO nanorods were approximately 30 s, and the sensor response was depended on shape and size of ZnO nanostructures and electrode configurations.     

Ni-doped vertically aligned zinc oxide nanorods prepared by hybrid wet chemical route

Ni-doped zinc oxide (Ni:ZnO) nanorods were synthesized by incorporating nickel in vertically aligned ZnO nanorods. Ni was evaporated onto ZnO nanorods and the composite structure was subjected to rapid thermal annealing for dispersing Ni in ZnO nanorods. The optical band gap decreased with increasing amount of Ni incorporation. The origin of the photoluminescence peak at ∼ 400 nm was related to the defect levels introduced due to substitution of Ni²⁺ in the Zn²⁺ site with annealing. The Raman spectra indicated the presence of the characteristic peak at ∼ 436 cm^− 1 which was identified as high frequency branch of E₂ mode of ZnO. The Fourier Transformed Infrared spectra indicated the existence of the distinct characteristic absorption peak at 481 cm^− 1 for ZnO stretching modes. Current-voltage characteristics indicated that the current changed linearly with voltage for both the doped and undoped samples.     

Mass-synthesized anatase titania nanocrystals with tunable size and shape via sol-gel in organic solvents with adsorbing ligands

High-quality anatase titania (TiO₂) nanoparticles, nanowires, and nanorods have been mass-synthesized by the modified sol-gel method in the saturated fatty alcohol, acid, and amine systems with adsorbing ligands, respectively. These obtained quasi-spherical TiO₂ nanoparticles showed the mean size of 16.5 nm with a narrow size-distribution. These resulting TiO₂ nanowires had the uniform diameter of 3.8 nm with the length range of 80-180 nm, and TiO₂ nanorods had the uniform diameter of 7.5 nm with the length range of 40-70 nm, respectively. We demonstrated that the shapes, sizes and morphology of these anatase TiO₂ nanocrystals could be controlled systematically by adjusting certain reaction parameters, such as the kind of organic solvents, the alkyl length of organic solvents, and the reaction time. It has been found that the shape of the products was primarily determined by the kind of organic solvents. However, their sizes, size-distributions, and morphology could be controlled by adjusting the alkyl length of organic solvents and the reaction time. Based on the analysis of all experiment results, we have investigated the growth mechanism of these TiO₂ nanocrystals with the different shape. Meanwhile, this synthetic method can be extended further for the preparation of other oxides nanocrystals.     

In situ formation of β-silicon carbide nanorods from the hybrid of an organic moiety and methyltriethoxysilane

Silicon carbide (SiC) nanorods were prepared by the pyrolysis of a hybrid of organic moiety (1,3-propanediamine) and methyltriethoxysilane (MTEOS). The organic-inorganic hybrid was developed using a sol-gel process and blending it with the organic moiety. The nanostructures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which revealed the continuous formation of β-SiC nanorods having a 30-100 nm diameter and a length of a few micrometers. The unreacted silica agglomerated to form lumps with the release of excess carbon during oxidation. Electron diffraction patterns from the nanowires revealed them to have the cubic β-SiC structure. This was in agreement with XRD data. There were found to be many periodically twinned or stacking faulted regions observed along the length of the nanowires. While this yielded a zig-zag pattern to the outside of the core and changes to the local internal diameter of the nanowires, there was no correspondence to the changes to the diameter of the outer sheaf. The Raman shifts for β-SiC appeared as small peaks at 795.6 and 983.1 cm⁻¹ respectively. The characteristic vibration of SiC at 795 cm⁻¹ in Fourier Transform Infrared Spectroscopy (FTIR) was also observed.     

Selective synthesis, characterization, and photoluminescence study of YPO4:Eu nanorods and nanoparticles

Two different morphological varieties of YPO₄:Eu³⁺ (nanorods and nanoparticles) have been synthesized by convenient template-assisted routes. A surfactant-mediated synthesis route generated the nanorods, while a complex based precursor solution method led to the formation of the nanoparticles. The nanorods have an average diameter of ∼33 nm and an average length of ∼290 nm, whereas the spherical nanoparticles show an average diameter of ∼34 nm. Upon photoluminescence study of the as-prepared samples, the chromaticity of the dopant ion was found to be sensitive to the host morphology as well as the preparative strategy adopted for sample fabrication.     

One-step hydrothermal synthesis of CdTe nanowires with amorphous carbon sheaths

CdTe nanowires with carbon sheaths were synthesized via a one-step hydrothermal process using ascorbic acid as a reducing agent and carbonization source. The average diameter of CdTe core nanowires and thickness of amorphous carbon sheaths are about 20 nm and 10 nm, respectively. During this process, carbon-coated Te nanowires were formed and then reacted with Cd²⁺ ions, resulting in the formation of carbon-coated CdTe nanowires. Additionally, the size and shape of the CdTe nanowires were determined during the initial stage of Te formation.     

Facile synthesis of prickly CoNi microwires

Novel prickly CoNi microwires have been successfully synthesized via a hydrothermal synthetic route. The samples prepared at 120 °C for 6 h were made up of large-scale wire-like assemblies with the diameter of about 3 μm and length up to several dozens microns. These wires exhibited hierarchical structure, which was constructed by thornlike crystals with the length of 300-500 nm. The morphology of the wires could be adjusted by the NaOH contents in the system. The magnetic hysteresis measurement revealed that the CoNi microwires displayed ferromagnetic behaviors with a saturation magnetization (Ms) of 83.90 emu/g and a coercivity (Hc) of 119.1 Oe.     

Potentiometric cholesterol biosensor based on ZnO nanorods chemically grown on Ag wire

An electrochemical biosensor based on ZnO nanorods for potentiometric cholesterol determination is proposed. Hexagon-shaped ZnO nanorods were directly grown on a silver wire having a diameter of 250 μm using low temperature aqueous chemical approach that produced ZnO nanorods with a diameter of 125-250 nm and a length of ~ 1 μm. Cholesterol oxidase (ChOx) was immobilized by a physical adsorption method onto ZnO nanorods. The electrochemical response of the ChOx/ZnO/Ag biosensor against a standard reference electrode (Ag/AgCl) was investigated as a logarithmic function of the cholesterol concentration (1 × 10⁻⁶ M to 1 × 10⁻² M) showing good linearity with a sensitivity of 35.2 mV per decade and the stable output signal was attained at around 10 s.     

Photo-initiated growth of zinc oxide (ZnO) nanorods

A photo-initiated process via femtosecond pulse-induced heterogeneous nucleation in zinc ammine complex (Zn(NH₃)₄²⁺)-based aqueous solution without catalyst and surfactant, followed by hydrothermal treatments for crystal growth into zinc oxide (ZnO) nanorods, was investigated. Flat-top hexagonal ZnO nanorods with smooth planes of diameter ≥ 100 nm and length ≤ 1 μm were grown with laser irradiation, compared to porous rod-like structures without irradiation. The flat-top planes indicate slow growth rate, due to the intermediate step of Zn(NH₃)₄²⁺ decomposition to Zn(OH)₄²⁻, before dehydration to ZnO. Prolonged hydrothermal treatment produced nanotubes and lateral splits due to OH⁻ erosion of the crystal faces. XRD analysis showed a hexagonal crystal structure while photoluminescence study indicated a peak at about 380 nm.     

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.     

Vertically aligned Mn-doped zinc oxide nanorods by hybrid wet chemical route

Mn-doped zinc oxide (Mn:ZnO) nanorods were synthesized by incorporating manganese in aligned ZnO nanorods. For this, Mn was evaporated onto ZnO nanorods and the composite structure was subjected to rapid thermal annealing. The nanorods were preferentially oriented in (0 0 2) direction as indicated by the XRD measurement. Optical band gap was seen to decrease with increasing amount of Mn incorporation. XPS studies indicated that incorporated Mn was in Mn²⁺ and Mn⁴⁺ states. Mn²⁺ atomic concentration was found to be larger than Mn⁴⁺ concentration in all the samples. The Raman spectra of the Mn:ZnO nanorods indicated the presence of the characteristic peak at ∼438 cm⁻¹ for high frequency branch of E₂ mode of ZnO. The PL peak at ∼376 nm (∼3.29 eV) was ascribed to the band edge luminescence while the peak at ∼394 nm (∼3.15 eV) was assigned to the donor bound exciton (D^oX) and free exciton transition related to Mn²⁺ states.     

Optical properties of water-soluble Co:ZnS semiconductor nanocrystals synthesized by a hydrothermal process

Water-soluble ZnS:Co²⁺ nanocrystals (NCs) were synthesized by a low temperature hydrothermal process using 3-mercaptopropionic acid (MPA) as capping agent and the influence of doping on the optical properties of ZnS:Co²⁺ NCs was investigated. It was found that the ZnS:Co²⁺ NCs are highly crystalline and show zinc blende structure with an average particle size of about 7 nm. The lattice constant of the ZnS:Co²⁺ NCs decreases slightly by the introduction of Co²⁺. The Co dopants were well doped into the ZnS:Co²⁺ NCs, as confirmed by X-ray photoelectron spectroscopy(XPS) and the ⁴A₂(F) → ⁴T₁(P) transition of Co²⁺ was detected from the UV-vis absorption spectra. The absorption edge of the ZnS:Co²⁺ NCs is blue-shifted as compared with that of bulk ZnS, indicating the quantum confinement effect. The PL intensity of the NCs shows the maximum value when the Fe-doping concentration is 0.5 at.%.     

Growth and characterization of germanium nanowires by electron beam evaporation

Germanium nanowires were grown on Au coated Si substrates at 380 °C in a high vacuum (5 × 10^− 5 Torr) by e-beam evaporation of Germanium (Ge). The morphology observation by a field emission scanning electron microscope (FESEM) shows that the grown nanowires are randomly oriented with an average length and diameter of 600 nm and 120 nm respectively for a deposition time of 60 min. The nanowire growth rate was measured to be ∼ 10 nm/min. Transmission electron microscope (TEM) studies revealed that the Ge nanowires were single crystalline in nature and further energy dispersive X-ray analysis (EDAX) has shown that the tip of the grown nanowires was capped with Au nanoparticles, this shows that the growth of the Ge nanowires occurs by the vapour liquid solid (VLS) mechanism. HRTEM studies on the grown Ge nanowire show that they are single crystalline in nature and the growth direction was identified to be along [110].     

Self-assembly of polyaniline nanowires into polyaniline microspheres

High quality microspheres self-assembled from nanowires of polyaniline (PANI) are prepared by a self-assembly process using ammonium peroxydisulfate as oxidant in aqueous solution. The microspheres of about 2.6 μm average diameter are composed of uniform nanowires with 40-60 nm in diameter. The formation process of PANI microsphere indicates that its evolution of morphologies can be divided into three stages. First, a large quantity of PANI nanowires form, then porous microspheres develop, and finally most of nanowires transform into microspheres. The morphology and uniformity of the PANI microspheres mainly depend on the mole ratio of aniline to ammonium peroxydisulfate. The BET specific surface area and conductivity of the polyaniline porous microsphere at room temperature are 53 m² g^− 1 and 3.3 × 10⁻¹ S cm^− 1, respectively.     

Fabrication of single-crystalline Co3O4 nanorods via a low-temperature solvothermal process

Co₃O₄ nanorods with average diameter and length of ∼ 50 nm and 1 μm were successfully prepared via a simple surfactant-assisted solvothermal method at 160 °C for 12 h. The formation of Co₃O₄ nanorods is attributed to alcoholysis of cobalt ions dispersed in ethanol in the presence of a capping agent—CTAB. The composition and purity of the sample were characterized by X-ray diffraction (XRD). Transmission and scanning electron microscopy images show that the particles are homogenous and have the shape of rods. The mechanism of forming Co₃O₄ nanorods is also discussed.     

Chemical vapor deposition and electrical characterization of sub-10 nm diameter InSb nanowires and field-effect transistors

Synthesis of InSb nanowires using a chemical vapor deposition technique, as a function of growth temperature and time, was investigated. High aspect ratio InSb nanowires, having a diameter of about 5–10 nm, were grown at 400 °C for 1 h on InSb (1 1 1) substrate onto which 60 nm Au particle was used as a metal catalyst. The synthesized InSb nanowires had zinc blend single crystal structure without any stacking faults, and they were covered with a thin (∼1 nm thick) amorphous layer. Electrical characterization of InSb nanowires was conducted utilizing a back-gated SNWFET. Device characterization demonstrated that NWs were n-type and exhibited a high I_on/I_off ratio of 10⁶ and device resistance of 250 kΩ.     

Hydrothermal synthesis and photoluminescence properties of Gd2Zr2O7:Tb phosphors

This paper presents hydrothermal synthesis, characterization, and photoluminescence (PL) properties of novel green-emitting phosphors, Gd₂Zr₂O₇:Tb³⁺. Their crystal structure, morphology and photoluminescence properties were investigated by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and fluorescence spectrophotometer. The results revealed that one-dimensional Gd₂Zr₂O₇:Tb³⁺ nanorods with diameter of about 30 nm and length of 150-300 nm were formed, and the products exhibited a fluorite-type structure. PL study revealed that Gd₂Zr₂O₇:Tb³⁺ phosphors presented dominant green emission luminescence, which was attributed to the transitions from ⁵D₄ excited states to ⁷F_J (J = 3-6) ground states of Tb³⁺. The luminescence intensity of Gd₂Zr₂O₇:Tb³⁺ with different Tb³⁺ concentration was also investigated and reported, and an obvious concentration quenching was observed when Tb³⁺ ion concentration was 5 at.%.     

Y2O3:Eu microstructures: Hydrothermal synthesis and photoluminescence properties

Hexagonal microprisms of yttrium hydroxide (Y(OH)₃) with tuned diameter and height have been successfully prepared for the first time via a facile hydrothermal process using sodium citrate as the shape modifying agent. Y(OH)₃ microspheres with diameter of ca. 2.5 μm and microtubes with an average length about 13 μm, outer diameter about 3 μm and tube thickness about 800 nm were also obtained in current reaction systems. The possible formation mechanism for the Y(OH)₃ microstructures was briefly proposed. Y₂O₃:Eu³⁺ (5%) microstructures with similar morphologies was obtained after thermal treatment of the as-prepared Y(OH)₃:Eu³⁺ microstructures at 700 °C for 4 h. Results show that the relative emission intensity of the Y₂O₃:Eu³⁺ microprisms is about 8 times as those of the Y₂O₃:Eu³⁺ microtubes and microspheres under excitation of 259 nm ultraviolet light. The products were characterized by XRD, SEM, and EDS.