One-Dimensional （1D） ZnS Nanomaterials and Nanostructures

One-dimensional （1D） nanomaterials and nanostructures have received much attention due to their potential interest for understanding fundamental physical concepts and for applications in constructing nanoscale electric and optoelectronic devices. Zinc sulfide （ZnS） is an important semiconductor compound of Ⅱ-Ⅵ group, and the synthesis of 1D ZnS nanomaterials and nanostructures has been of growing interest owing to their promising application in nanoscale optoelectronic devices. This paper reviews the recent progress on 1D ZnS nanomaterials and nanostructures, including nanowires, nanowire arrays, nanorods, nanobelts or nanoribbons, nanocables, and hierarchical nanostructures etc. This article begins with a survey of various methods that have been developed for generating 1D nanomaterials and nanostructures, and then mainly focuses on structures, synthesis, characterization, formation mechanisms and optical property tuning, and luminescence mechanisms of 1D ZnS nanomaterials and nanostructures. Finally, this review concludes with personal views towards future research on 1D ZnS nanomaterials and nanostructures.     

Synthesis of CdS nanorods by reacting CdCl2 nanorods with H2S at room temperature

We report the synthesis of CdS nanorods by reacting CdCl₂ nanorods with H₂S at room temperature. The preparation method was based on CdCl₂ nanorods employed as chemical template. The length and the diameter of the obtained CdS nanorods are about tens micron and 120−300 nm, respectively. The phase and the crystallographic structure of the products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The composition of the products was investigated by X-ray photoelectron spectroscopy (XPS).     

Synthesis of magnesium borate nanorods

Single-crystalline magnesium borate Mg₂B₂O₅ nanorods have been synthesized via a simple route based on the calcinations of mixed powders containing Mg(OH)₂ and H₃BO₃. The nanorods have the typical diameters in the range of 70-120 nm and the lengths up to a few micrometers. An optimal synthesis temperature for Mg₂B₂O₅ nanorods was obtained, and the possible growth mechanism was also presented.     

Mixed-solvothermal synthesis of hybrid nanostructures of alkaline earth phenylphosphonates

Hybrid nanostructures such as nanoflowers, nanosheets and nanoribbons of the alkali earth phenylphosphonates were prepared via mixed-solvothermal approaches by reaction of alkali earth metal salt with phenylphosphonate in ethylene glycol. The final products have been characterized with X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Fourier-Transform Infrared Spectroscopy (FT-IR), and Thermogravimetry (TG). Effects of reaction parameters on the formation of two-dimensional nanostructure were discussed. This work may provide a simple and effective approach to control the microstructures of the metal phenylphosphonates, which will be of great importance for the controlled synthesis of hybrid nanostructures and further applications.     

Synthesis of silica nanoboxes via a simple hard-template method and their application in controlled release

Silica nanoboxes have been successfully synthesized via a simple hard-template method at room temperature. The MnCO₃ nanocubes are firstly employed as the hard template. Scanning electron microscopy (SEM) is used to characterize silica nanoboxes and indicates the hollow structure of products. The shell thickness of nanoboxes can be well controlled by the amount of tetraethylorthosilicate (TEOS) and the surface area is calculated through the N₂ adsorption-desorption isotherm. Based on these results, a plausible mechanism is proposed to explain the formation of silica nanoboxes. In addition, preliminary tests demonstrate that the silica nanoboxes are capable of being loaded and releasing Rhodamine B, thus showing a great potential in the controlled delivery applications.     

BaTiO3 nanocubes: Size-selective formation and structure analysis

Single crystalline BaTiO₃ nanoparticles starting from BaCO₃ and TiO₂ have been synthesized by a composite-hydroxide-mediated method. The influence of reaction time and temperature was investigated systematically. The as-synthesized samples were characterized by XRD, SEM and TEM. The result showed that all BaTiO₃ samples were cubic phase with size from 70 to100 nm under different reaction temperature (165-220 °C) and time (24-72 h); higher temperature and longer time clearly favored the increase of particle size. The widened FWHM in XRD and the peak blue shift in UV-vis absorption spectrum with the decrease of the nanocube size demonstrated the quantum size effect.     

Surfactant mediated optical properties of cytosine capped CdSe quantum dots

This letter demonstrates the use of one of the nucleobases, ‘cytosine’ as a new capping agent in controlling the size of the nanoparticles. A size dependent blue shift in optical absorption with enhanced luminescence is observed. Since the calculated density of states do not show any change in the band gap of as-prepared quantum dots after capping, the observed blue shift of the absorption peak can solely be attributed to the so-called size-effect whereas the enhancement in luminescence to surfactant mediated defect passivation. It is expected that the observed properties of the cytosine capped CdSe quantum dots would facilitate a better bio-compatibility of tailor-made nanoparticles for bio-imaging applications.     

Controllable growth of Se nanotubes and nanowires from different solvent during the sonochemical process

Selenium (Se) nanotubes and nanowires have been controllably prepared by a solution-phase approach consisting of hydrothermal process and subsequent sonochemical process in different solvent including methanol, ethanol, acetone, dimethyl formamide, water, isopropanol and ethylene glycol. It is revealed that the formation of the Se nanotubes or nanowires is dependent on the breakage or not of the in-situ generated Se nanoparticles. The effects of the solvents on the morphology of Se nanostructures have been preliminarily discussed. Finally, Se nanotubes and nanowires have been characterized by X-ray powder diffraction (XRD), field emission scan electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy.     

Synthesis and characterization of bismuth sulfide nanowires through microwave solvothermal technique

One-dimensional (1D) bismuth sulfide (Bi₂S₃) semiconducting nanowires have been successfully synthesized through mircrowave assisted solvothermal technique. The obtained product was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and UV-vis spectrophotometry. The result shows that the Bi₂S₃ nanowires are single crystals grown along the [001] (c-axis) direction. The growth of Bi₂S₃ nanofibers with a preferential direction of c-axis can be ascribed to its particular structure. The optical measurement shows a blue shift relative to the bulk orthorhombic Bi₂S₃, which might be ascribed to the high aspect ratio of the nanowires.     

Growth behavior of GaN nanoneedles with changing HCl/NH3 flow ratio

We grew one-dimensional GaN nanoneedles on AlN/Si(111) substrates at HCl/NH₃ gas-flow ratios of 1/20, 1/30, and 1/50 using the hydride vapor-phase epitaxy (HVPE) method. Field emission-scanning electron microscopy (FE-SEM) images of GaN nanoneedles show that the vertical growth rate of GaN nanoneedles increases with increasing gas-flow ratio, but there is little growth in the lateral direction. X-ray diffraction patterns indicate that GaN nanoneedles grew with c-axes oriented perpendicular to the substrate. The room-temperature PL spectrum of GaN nanoneedles was detected at 3.237 eV of near-band-edge transitions.     

Facile and large-scale synthesis of hollow TiO2 nanostructures from TiCl3 solution

Hollow TiO₂ nanostructures were successfully synthesized by a hydrothermal process using TiCl₃ solution as Ti sources. The as-obtained product consists of quasi-spherical hollow nanostructures in the diameter of about 500 nm with anatase phase. The control experiments indicated that the synergism of H₂O₂ and KBF₄ plays an important role in the formation of hollow TiO₂ nanostructures. Compared with solid TiO₂ nanostructures, the photocatalytic property of hollow TiO₂ nanostructures has been markedly improved in degradation of methyl orange under UV light. This synthesis procedure is facile and thus promotes large-scale production of hollow TiO₂ nanostructures.     

Synthesis and photocatalytic characterization of porous cuprous oxide octahedra

Porous cuprous oxide octahedra with a mean diameter of 1 μm have been successfully prepared with high yield via a hydrothermal reduction process at a low temperature. The growth mechanism and the influences of the poly(vinylpyrrolidone) (PVP) and citric acid have been discussed. And then, the samples were used as photocatalytic in the degradation of methyl red (MR). Thanks to the 3D architecture of the product, the photocatalytic performance has been significantly improved. We believe that the present work will open up to systematically explore ways to fabricate porous nanostructures and thus find use in a variety of applications.     

Controllable synthesis of pentagonal silver nanowires via a simple alcohol-thermal method

Pentagonal silver nanowires with diameters in range of 20-40 nm, and lengths up to ~ 10 µm were successfully synthesized via a simple and effective alcohol-thermal route. These nanowires were prepared by reducing silver nitrate in ethanol solution with dodecylamine which acted as complexing, reducing and capping agent. The molar ratio of dodecylamine to AgNO₃ played an important role in controlling aspect ratio of the products. Samples were characterized in detail by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) technologies. UV-vis absorption spectrum of the nanowires in solution has been taken to study their optical properties. Based on the analysis of the experimental results, the possible formation mechanism of nanowires was proposed as well.     

Self-catalytic growth of silicon nanowires on stainless steel

Silicon nanowires were grown on a stainless steel substrate using a vapor-liquid-solid mechanism in self-catalytic mode. The multi-component Fe-Cr-Ni-Mn-Si catalyst that was formed from the substrate leads the growth of single-crystal Si nanowires with lengths of several micrometers and diameters ranging from 100 to 150 nm. A systematic investigation of the processing parameters revealed that the hydrogen flow rate is critical to the growth of the nanowires. At a high flow rate that exceeds 1000 sccm, the substrate is embrittled by H₂, and liquid droplets, which lead the growth of nanowires by the vapor-liquid-solid mechanism, are formed on the substrate. Electrical transport measurements indicated that the nanowires grown with the multi-component catalyst have electrical properties comparable to those grown by a single-component Ti catalyst.     

Formation of crystalline AlN nanotubes by a roll-up approach

In this study, aluminum nitride (h-AlN) nanotubes with high crystallinity and yield have been prepared by AlP and NaN₃ in a stainless steel autoclave at 350 °C. The samples were studied by powder X-ray diffraction pattern (XRD), transmission electron microscopy (TEM) and HRTEM in detail. The lengths of the AlN nanotubes are about 1 μm with most of the tube ends are open. The AlN nanotube preferentially grow along the [001] direction. The results demonstrate that the bending and roll-up of a thin layer to form tubular nanoscrolls is a thermally driven process. One-dimensional preferential growth was explained in terms of the crystallographic feature of hexagonal AlN.     

Preparation of Sb2S3 nanostructures by the [BMIM][BF4] ionic liquid assisted low power sonochemical method

Sb₂S₃ nanorods were successfully synthesized by the ionic liquid assisted sonochemical method (ILASM). The starting reagents were Sb₂Cl₃, Thioacetamide, absolute ethanol (ETA) and the selected ionic liquid (IL) was 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). The synthesized materials were subjected to 200 °C annealing treatment under controlled vacuum conditions. X-ray powder diffraction analysis showed that ultrasound irradiation played a key role on the crystallization degree of Sb₂S₃, whilst Scanning Electron Microscopy analysis showed that the addition of IL was fundamental for the formation of 1-D Sb₂S₃ nanostructures. XPS confirmed the formation of Sb₂S₃.The optical properties (band gap) were similar to previously reported for bulk Sb₂S₃.     

Effect of solvent type on the formation of tubular fullerene nanofibers

1D Fullerene C₆₀ nanofibers (FNFs) were prepared via liquid-liquid interfacial precipitation (LLIP) using toluene, m-xylene, pyridine and/or N-methyl-2-pyrrolidone (NMP) as solvents and isopropyl alcohol as the precipitation agent at 8 °C. C₆₀-saturated solutions were exposed to visible light to promote the growth of FNFs. When the solvents were toluene and m-xylene, it was difficult to synthesize hollow C₆₀ fullerene nanotubes (FNTs). By contrast, the hollow FNTs were easily grown in the C₆₀-pyridine solution or C₆₀-NMP solution upon exposure to visible light. It is found that there is a critical correlation between the adducts of the solvents with C₆₀ molecules and the tubular structure of FNFs.     

Synthesis of hierarchical barium tungstate corns and their shape evolution process

Barium tungstate nanocorns with lengths of 200-800 nm and with diameters of 20-50 nm in the middle section were synthesized by a facile stepwise solution-phase method. Various comparison experiments showed that several experimental parameters, such as the volume ratio of DMF/H₂O, and the quantity of urea and CTAB, played important roles for the morphological control of BaWO₄ nanostructures. A possible mechanism is offered for the formation of the hierarchical nanostructures. The obtained samples are characterized by means of X-ray diffraction, energy dispersion X-ray spectrometry, scanning electron microscopy, and transmission electron microscopy.