A facile synthesis of novel nanorod-assembling hollow nanowires of cadmium sulfide/DBTU nanocomposite

Novel nanorod-assembling hollow nanowires of cadmium sulfide/DBTU (N,N′-dibutylthiourea) nanocomposite were synthesized by reacting CdCl₂ with in situ produced H₂S from reaction of butylamine and carbon disulfide at molar ratio 3:3 of CS₂:BuNH₂ at 50 °C. This product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SEAD), energy dispersive X-ray spectroscopy (EDAX), thermogravimetric (TG), Fourier transform infrared (FTIR) and UV-vis absorption spectra. A plausible mechanism that the extending DBTU molecules in solvent of CS₂ induce the formation of CdS/DBTU nanorods by coordinating with the formed CdS particles, and construct these nanorods to hollow nanowires via molecular interactions is proposed and discussed on the basis of experimental results. Photoluminescence (PL) of CdS/DBTU nanocomposite exhibits increasing emission intensity largely.     

Photocatalytic hydrogen production over Na2Ti2O4(OH)2 nanotube sensitized by CdS nanoparticles

Na₂Ti₂O₄(OH)₂ nanotubes were obtained by hydrothermal reaction of TiO₂ with concentrated NaOH solution. CdS nanoparticles were then decorated on Na₂Ti₂O₄(OH)₂ nanotubes through partial ion-exchange method. The composite photocatalysts were characterized by X-ray diffraction (XRD), ultraviolet-visible spectra (UV-vis), transmission electron microscope (TEM), etc. The results showed that CdS nanoparticles of 5-6 nm were anchored on the surface of the Na₂Ti₂O₄(OH)₂ nanotubes. Under irradiation of visible light (λ ≥ 430 nm), the prepared CdS/Na₂Ti₂O₄(OH)₂ showed high photoactivity for hydrogen production.     

Optical switches based on CdS single nanowire

CdS nanowires have been synthesized by a composite-hydroxide-mediated approach. The characterization of the nanowire with X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated a single-crystalline hexagonal structure growing along direction with length up to 100 μm. The UV-visible reflection spectrum demonstrated a band gap of 2.36 eV. A strong light emission centered at 543 nm was observed under different excitation wavelengths of 300, 320, 360 and 400 nm, which was further confirmed by a bright fluorescent imaging of a single CdS nanowire. The photocurrent response based on a single CdS nanowire showed distinct optical switch under the intermittent illumination of white light. The rise and decay time were less than 1.0 and 0.2 s, respectively, indicating high crystallization with fewer trap centers in the CdS nanowires. It is possible that the undesirable trapping effects on grain-boundaries for photoconductors could be avoided thanks to the single-crystalline nature of the CdS nanowires.     

Synthesis of size tuneable cadmium sulphide nanoparticles from a single source precursor using ammonia as the solvent

Size tuneable cadmium sulphide nanoparticles of a few nanometres in size were prepared by thermolysis of a single source precursor of cadmium xanthates with variable carbon chain length (Cd(ROCS₂)₂, where R denotes -C₂H₅, -C₄H₉, -C₈H₁₇ and -C₁₂H₂₅, respectively) in an ammonia solution. The particle size, morphology and crystallinity of these nanoparticles were characterized using X-ray powder diffractometry, transmission electron microscopy, and nitrogen adsorption/desorption techniques. The results show that hexagonal CdS nanoparticles can be produced by thermolysis of cadmium alkyl xanthate in an ammonia solution at a temperature as low as 100 °C. The size of CdS particles (between 5.60 nm and 3.71 nm) decreases with increasing length of carbon chain in the precursor, as further confirmed by UV-visible and fluorescence spectrophotometric measurements. The size tuning mechanism of CdS from cadmium alkyl xanthate is also discussed.     

Preparation of VO2 nanowires and their electric characterization

Large-scale VO₂ nanowires have been synthesized by two-step method. First, we have been obtained (NH₄)_0.5V₂O₅ nanowire precursors by hydrothermal treatment of ammonium metavanadate solution at 170 °C. Secondly, the precursors have been sealed in quartz tube in vacuum and annealed to form VO₂ nanowires at 570 °C. Scanning electron microscope and transmission electron microscope analysis show that the nanowires have self-assembling nanostructure with the diameter of about 80-200 nm, length up to125 μm. Electrical transport measurements show that it is semiconductor with conduction activate energy of 0.128 eV. A metal-semiconductor transition can be observed around 341 K.     

Fabrication, structural and electrical characterization of VO2 nanowires

The structural and electrical properties of VO₂ nanowires synthesized on Si₃N₄/Si substrates or molybdenum grids by a catalyst-free vapour transport method were investigated. The grown VO₂ nanowires are single crystalline and rectangular-shaped with a preferential axial growth direction of [1 0 0], as examined with various structural analyses such as transmission electron microscopy, electron diffraction, X-ray diffraction, and X-ray photoelectron spectroscopy. In particular, it was found that growing VO₂ nanowires directly on Si₃N₄ deposited molybdenum transmission electron microscopy grids is advantageous for direct transmission electron microscopy and electron diffraction characterizations, because it does not involve a nanowire-detachment step from the substrates that may cause chemical residue contamination. In addition to structural analyses, VO₂ nanowires were also fabricated into field effect transistor devices to characterize their electrical properties. The transistor characteristics and metal-insulator transition effects of VO₂ nanowires were investigated.     

Low temperature growth of single crystalline germanium nanowires

Ge nanowires have been prepared at a low temperature by a simple hydrothermal deposition process using Ge and GeO₂ powders as the starting materials. These as-prepared Ge nanowires are single crystalline with the diameter ranging from 150 nm to 600 nm and length of several dozens of micrometers. The photoluminescence spectrum under excitation at 330 nm shows a strong blue light emission at 441 nm. The results of the pressure and GeO₂ content dependences on the formation and growth of Ge nanowires show that the hydrothermal pressure and GeO₂ content play an essential role on the formation and growth of Ge nanowires under hydrothermal deposition conditions. The growth of Ge nanowires is proposed as a solid state growth mechanism.     

Ag-catalyzed synthesis of europium borate Eu(BO2)3 nanowires, growth mechanism and luminescent properties

Eu(BO₂)₃ nanowires with diameters of 10-20 nm were fabricated through direct sintering Eu(NO₃)₃·6H₂O and H₃BO₃ with Ag as catalyst. The result of X-ray diffraction (XRD) indicated that the nanowire was single-crystalline with body-centered monoclinic structure. Based on the fact that Ag nanoparticles attached to the tips and middles of nanowires, a vapor-liquid-solid (VLS) growth mechanism of the Eu(BO₂)₃ nanowires is proposed. Three well-defined stages have been clearly identified during the process: Ag-Eu-B-O cluster process, crystal nucleation, and axial growth. The photoluminescence characteristics under UV excitation were investigated. The dominated Eu³⁺ orange-red emission corresponding to the magnetic dipole transition ⁵D₀ → ⁷F₁ is centered at 591 nm, indicating that Eu³⁺ is located at high symmetry crystal field with inversion center.     

Synthesis of aluminium borate nanowires by sol-gel method

A sol-gel process followed by annealing was employed to fabricate single crystal aluminium borate (Al₄B₂O₉ and Al₁₈B₄O₃₃) nanowires. The diameter of Al₄B₂O₉ nanowires synthesized at 750 °C annealing is ranging from 7 to 17 nm, and that of Al₁₈B₄O₃₃ nanowires synthesized at 1050 °C annealing is about 38 nm. Instead of the well-known vapor-liquid-solid (VLS) mechanism, self-catalytic mechanism was used to explain the growth of the nanowires.     

Growth of quantum-confined CdS nanoparticles inside Ti-MCM-41 as a visible light photocatalyst

CdS nanocrystallites have been successfully incorporated into the mesopores of Ti-MCM-41 by a two-step method involving ion-exchange and sulfidation. The X-ray diffraction patterns (XRD), UV-vis absorption spectra (UV-vis), photoluminescence spectra (PL), Raman spectra and N₂ adsorption-desorption isotherms were used to characterize the structure of the composite materials. It is found that most of the CdS nanocrystallites are about 2.6 nm, less than the pore diameter of Ti-MCM-41. The CdS nanocrystallites inside the mesopores of Ti-MCM-41 host show a significant blue shift in the UV-vis absorption spectrum. Under irradiation of visible light (λ > 430 nm), the composite material has greater and more stable photocatalytic activity for hydrogen evolution than bulk CdS, which can be explained by the effective charge separation between the CdS nanocrystallites and mesoporous Ti-MCM-41.     

Enhancement of photocatalytic H2 evolution on hexagonal CdS by a simple calcination method under visible light irradiation

An easy-handling calcination method has been used to eliminate the trap energy levels of hexagonal cadmium sulfide (CdS). The treated CdS exhibited extremely high photocatalytic activity for H₂ production under visible light irradiation. The rate of photocatalytic H₂ evolution has been dramatically enhanced by 55.8 times to 118 μmol h⁻¹ and further improved by 6.3 times to 749 μmol h⁻¹ after loading with 0.2 wt% Pt co-catalyst.     

Control of growth orientation and shape for epitaxially grown In2O3 nanowires on a-plane sapphire

Vertically aligned indium oxide nanowires were grown on a-plane sapphire substrate by the method of catalyst-assisted carbothermal reduction. The morphology and crystal structure of the nanowires are determined by X-ray diffraction, transmission electron microscopy and field-emission scanning electron microscopy. Two types of In₂O₃ nanowires were found by controlling the growth conditions. The nanowires with a hexagonal cross-section were shown to grow in [1 1 1] direction, whereas those with a square cross-section grow in [0 0 1] direction. In addition to the temperature effects, the concept of supersaturation in Au catalyst is proposed to explain the formation of these two types of nanowires. Besides, tapering, which is explained with the interplay between the vapor-liquid-solid and vapor-solid growth mechanisms, is observed in the nanowires.     

Low-temperature performance of Al4B2O9 nanowires

In this paper we report on the synthetic investigation of single-crystalline aluminum borate (Al₄B₂O₉) nanowires in large scale by a direct calcination of a precursor powder made of Na₂B₄O₇·10H₂O and Al (NO₃)₃·9H₂O at a low temperature of 850 °C. The nanowires, with the diameter of 20-40 nm and the length up to several micrometers, possess smooth surfaces and uniform sizes along the entire wire. The growth mechanism of the nanowires is attributed to a solid-liquid-solid process, which controls the nanowire morphology.     

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.     

Electrochemical fabrication of ordered Ag2S nanowire arrays

We have successfully fabricated ordered crystalline Ag₂S nanowire arrays by direct current electrodeposition into the nanochannels of porous anodic aluminum oxide templates from a dimethylsulfoxide solution containing AgNO₃ and elemental S. X-ray diffraction and the selected area electron diffraction investigations demonstrate that the Ag₂S nanowires are a uniform actanthite structure. Electromicroscopy results show that the nanowires are quite ordered with diameters of about 40 nm and lengths up to 5 μm. X-ray energy dispersion analysis indicates that the atomic composition of Ag and S is very close to a 2:1 stoichiometry. Furthermore, a possible mechanism for the formation of the Ag₂S nanowires is proposed.     

Characteristics of gold/cadmium sulfide nanowire Schottky diodes

Schottky diode junctions were formed between nanowires of cadmium sulfide and nanowires of gold, through sequential cathodic electrodeposition into the pores of anodized aluminum oxide (AAO) templates. Lengths of CdS and Au nanowires were 100-500 nm and 300-400 nm respectively, while the diameter was 30 nm, each. Analysis of Schottky diodes yielded an effective reverse saturation current (J_o), of 0.32 mA/cm² and an effective diode ideality factor (A) of 8.1 in the dark. Corresponding values under one sun illumination were, J_o = 0.92 mA/cm² and A = 10.0. Dominant junction current mechanisms are thought to be tunneling and/or interface state recombination.     

Polyol method synthesis and characterization of nanoscale Sb2Se3 wires

Sb₂Se₃ nanowires ([0 0 1] orientation) with diameter of ∼100 nm and high aspect ratio were successfully synthesized in large scale by a facile nonaqueous polyol method, where home-prepared NaHSe alcohol solution is used as selenium source and PEG-400 serves as an excellent solvent and structure director. The product was characterized by XRD, TEM, SAED, HRTEM, EDS and diffuses reflectance spectroscopy, respectively. The effects of the experimental conditions on the final morphologies were also investigated. The method is promising to be extended to synthesize other V₂VI₃ compound semiconductor 1D nanostructure.     

Synthesis of La0.5A0.5MnO3 (A = Sr, Ba) by a hydrothermal method at low temperature

A mild hydrothermal method has been adopted to prepare La_0.5Sr_0.5MnO₃ and La_0.5Ba_0.5MnO₃, which is of interest for a number of possible applications. The results from X-ray diffraction (XRD) indicate that in the present work the temperature of 200 and 240 °C are sufficient to prepare phase pure La_0.5Sr_0.5MnO₃ and La_0.5Ba_0.5MnO₃ crystals. At 200 °C, La_0.5Sr_0.5MnO₃ nanowires are obtained. The average width and length of the nanowires are 40 nm and 4 μm, respectively. At 240 °C, La_0.5Ba_0.5MnO₃ powders obtained have a cubic structure with the average size of 3-5 μm.     

Preparation and characterization of Chitosan/Konjac glucomannan/CdS nanocomposite film with low infrared emissivity

Novel organic-inorganic nanocomposite films were prepared with Chitosan (CS), Konjac glucomannan (KGM) and CdS by one-step synthesis. As-prepared films were characterized by IR spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and infrared emissometer (IR). The results indicated that grown CdS dendrites were formed with reaction time of 12 h for Cd²⁺ and CS/KGM, and were well dispersed in CS/KGM with an average diameter of 40 nm. The CS/KGM/CdS nanocomposite films had significantly low infrared emissivity. When the mole ratio of CdS to summation of CS&KGM construction units was 1.0 with CdS size of 10-20 nm, the film got the lowest infrared emissivity value of 0.011, which could be attributed to the strong synergism effect existing between CS/KGM and CdS dendrites.     

Characterization of nanostructured photosensitive (NiS)x(CdS)(1−x) composite thin films grown by successive ionic layer adsorption and reaction (SILAR) route

Recently ternary semiconductor nanostructured composite materials have attracted the interest of researchers because of their photovoltaic applications. Thin films of (NiS)_x(CdS)_(1−x) with variable composition (x = 1-0) had been deposited onto glass substrates by the successive ionic layer adsorption and reaction (SILAR) method. As grown and annealed films were characterised by X-ray diffraction, scanning electron microscopy and EDAX to investigate structural and morphological properties. The (NiS)_x(CdS)_(1−x) films were polycrystalline in nature having mixed phase of rhombohedral and hexagonal crystal structure due to NiS and CdS respectively. The optical and electrical properties of (NiS)_x(CdS)_(1−x) thin films were studied to determine compsition dependent bandgap, activation energy and photconductivity. The bandgap and activation energy of annealed (NiS)_x(CdS)_(1−x) film decrease with improvement in photosensitive nature.