Synthesis and kinetics research of ZnS nanoparticles prepared by sonochemical process

Abstract

ZnS nanocrystallites have been successfully prepared by a sonochemical process. The reaction kinetics of the process was also investigated. The as prepared ZnS nanocrystallites were characterised by XRD and TEM. Results show that ZnS nanoparticles can be obtained by sonochemical process using ZnCl₂ and thiacetamide as raw materials. It is found that the as prepared ZnS nanoparticles are hexagonal phase with spherical or spherical-like morphologies. The grain size decreases with increasing ultrasonic irradiation power. Reaction kinetics shows that the weight content of ZnS nanoparticles increases linearly with reaction time at different temperatures. The synthesis activation energy of ZnS nanoparticles is calculated to be 27·80 kJ mol^–1.     

A simple solution route to controlled synthesis of ZnS submicrospheres, nanosheets and nanorods

ZnS nanostructures with different morphologies of submicrospheres, nanosheets and nanorods were synthesized by solution precipitation of thiourea with Zn(NO(3))(2) in the presence of block copolymer at low temperature. The sizes and morphologies of ZnS can be controlled simply by?changing the processing parameters. The results show that the ZnS submicrospheres are of 250-500?nm in diameter, nanosheets are 2.5?μm × 5.5?μm with an estimated thickness of 20-30?nm, and nanorods are 2-5?nm in diameter and 10-30?nm in length. Keeping the precursor system in an autoclave at 105?°C results in the formation of ZnS submicrospheres; ultrasonication and keeping the system at room temperature leads to the formation of ZnS nanosheets; and long-time continuous ultrasonication and keeping the system in an autoclave at 105?°C induces the formation of uniform ZnS nanorods. We argue that the reaction temperature and P123 may play crucial roles in the formation of three ZnS structures in this work. The morphologically controllable synthesis strategies may be extended to the shape-controlled production of nanostructures of other inorganic materials.     

Preparation and field emission study of low-dimensional ZnS arrays and tubules

In the present work, freestanding ZnS nanotipped arrays and hollow tubules have been generated using an electrodeposition technique via template synthesis. The structures and morphologies of the arrays and tubules were investigated using X-ray diffraction and scanning electron microscopy, respectively. Electron field emission properties of the ZnS nanotipped arrays and tubules have been studied in a good vacuum condition at room temperature and current–voltage characteristics were found to follow the Fowler–Nordheim theory.

It is found that ZnS tubules show good electron field emission properties at low voltage with large field enhancement factor compared to ZnS solid arrays. Optical properties of such synthesised structures were also studied using ultraviolet–visible spectrophotometery.     

Synthesis and characterization of shaped ZnS nanocrystals in water in oil microemulsions

Shaped zinc sulfide nanocrystals were synthesized in W/O microemulsions by using cyclohexane/Triton X-100/n-pentanol/water system. Under different synthetic conditions appearance of two distinct morphologies of ZnS nanocrystals, either cubes or nanowires, was proven by transmission electron microscopy (TEM). The ZnS cubes have an average size of about 25 nm, while the ZnS nanowires have 25 Å diameter and length ranging from several hundred nanometers up to a few microns. The X-ray diffraction analysis (XRD) revealed formation of ZnS with cubic zinc blende crystal structure. Due to two dimensional confinement the exciton of ZnS nanowires is blue shifted compared to the bulk material. Four well-resolved photoluminescence bands in visible spectral region were observed upon excitation of cubic ZnS particles, while in the case of ZnS nanowires emission band was observed at 421 nm. The origin of photoluminescence bands was discussed in details.     

Inside Front Cover: Self‐Assembled Highly Faceted Wurtzite‐Type ZnS Single‐Crystalline Nanotubes with Hexagonal Cross‐Sections (Adv. Mater. 16/2005)

Highly faceted wurtzite‐type ZnS nanotubes with hexagonal cross‐section morphologies have been self‐assembled via a controllable high‐temperature thermal‐chemical reaction route in work reported by Yin and co‐workers on p. 1972. The self‐assembly growth along c‐axis to highly hexagonal‐faceted ZnS single‐crystalline nanotubes is associated with the crystallographic characteristics, such as the non‐central and polar surfaces of the wurtzite‐type ZnS structure. The faceted ZnS nanotubes grow along the <0001> direction, and are closed by low‐index faces of non‐polar {1000} faces. The inside cover and insets show electron microscopy and scanning electron microscopy images of the faceted ZnS nanotubes.     

Biomolecule-assisted synthesis of ZnS nanocorals and open-benzene ring in supercritical carbon dioxide

The nanostructured ZnS of cubic nanocorals and open-benzene ring has been synthesized by the biomolecule-assisted method in mixture of supercritical carbon dioxide and water as reaction medium at 150 °C and 28 MPa. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectrum of sample were characterized. The sodium tripoly phosphate and CO₂ as well as high-pressure condition might be the key factors for formation of the particular morphologies and nanostructures of ZnS. This synthesis method could be employed for preparation of other semiconductor nanomaterials.     

Plasmon assisted intense blue-green emission from ZnO/ZnS nanocrystallites

Excellent luminescence properties of ZnO/ZnS nanocrystallites prepared using simple wet chemical approach at room temperature have been reported. ZnS coating on the surface of ZnO nanocrystallites enhanced the green emission (around 500 nm) by a factor of 2. The intensity of the blue emission around 450 nm of ZnO/ZnS nanocrystallites is observed to be as high as three times the emission intensity of pure ZnO nanocrystallites. A further overall increase by a factor of ∼2.5 has also been observed in the intensity of wide blue-green emission when the sample was prepared onto grating compared to that of the samples prepared onto uncoated as well as gold coated quartz. The enhanced emission is thought to be due to plasmon assisted electromagnetic field enhancement near nanocrystallites-metal interface. This is supported by power dependent photoluminescence measurements. The strong enhanced blue-green emission covering a wide spectral range of ∼375-650 nm signifies potential optoelectronic applications in near UV and VIS wavelength regimes.     

Synthesis of aligned zinc sulfide nanostructures and the influence of experimental conditions on their morphologies and phase

A novel aligned flower-like array and single-crystal nanosheets composed of ZnS quantum wires were fabricated via a simple solution route. In the method, ZnCl2 chemicals reacted with Na2S in 50 ml of ethylenediamine (en) solution containing different amounts of hydrochloric acid (HCl) at 70-80 degrees C. After annealing at 500 degrees C for 1.5 h, wurtzite phase ZnS nanoscaled materials were synthesized. When the amount of HCl was 2 ml and 3 ml, respectively, flower-like structure and nanosheets were obtained. The products were characterized by X-ray diffraction, transmission electron microscopy, high-resolution electron microscopy (HREM), and electron diffraction (ED). The influences of concentration, temperature, and reaction time on the morphologies and phase of ZnS nanostructures were also studied. The photoluminescence peaks are located at approximately 308 nm and approximately 410 nm. The formation mechanism is also discussed here.     

Phase and morphology controlled synthesis of high-quality ZnS nanocrystals

Through a facile solvothermal method, the controlled preparation of ZnS nanocrystals with different phases and morphologies was achieved only by changing the organic additives. By adding the surfactant of sodium dodecyl benzene sulfonate (SDBS) into the reaction, the cubic heart-like ZnS nanoparticles with uniform size were obtained in a large scale. While, with the assistance of the biomolecule of alginic acid, the pure phase of hexagonal ZnS nanospheres assembled from small ZnS nanoparticles were synthesized. The optical properties of the obtained ZnS nanocrystals were investigated by ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) spectra. The quantum confinement effect could be observed clearly in ZnS nanoparticles.     

Monolayer Silane‐Coated,Water‐Soluble Quantum Dots

A one‐step method to produce ≈12 nm hydrodynamic diameter water‐soluble CdSe/ZnS quantum dots (QDs), as well as CdS/ZnS, ZnSe/ZnMnS/ZnS, AgInS₂/ZnS, and CuInS₂/ZnS QDs, by ligand exchange with a near‐monolayer of organosilane caps is reported. The method cross‐links the surface‐bound silane ligands such that the samples are stable on the order of months under ambient conditions. Furthermore, the samples may retain a high quantum yield (60%) over this time. Several methods to functionalize aqueous QD dispersions with proteins and fluorescent dyes have been developed with reaction yields as high as 97%.     

Recent Progress in One-dimensional ZnS Nanostructures:Syntheses and Novel Properties

In this review, the progress made during the last two years with respect to the syntheses and novel properties of one-dimensional （1D） ZnS nanostructures is presented. Primarily the research on 1D ZnS nanostructures has been of growing interest owing to their promising applications in nanoscale optoelectronic devices. Diverse 1D ZnS nanostructures with delicately-tuned morphologies, sizes, and microstructures have been synthesized through relatively simple and well-controlled techniques. Some novel properties of the nanomaterials have been explored and the relationships between their structural features and functions have been understood gradually.     

Preparation and characterization of ZnS nanocrystalline thin films by low cost dip technique

Nanocrystalline ZnS semiconducting nanopowder and thin films have been deposited by simple low cost technique based on combination of dip coating and thermal reaction process. The deposited films and the prepared nanopowder have been characterized in the structurally, optically and electrically point of views. The effect of preparation conditions has been also optimized for good quality films. X-ray diffraction analysis performed the ZnS cubic phase in the reaction temperatures in the range 473–593 K. Above 593 K mixed cubic and hexagonal crystallographic phases have been resolved. Crystallite size and micro strain have been calculated to be 2.65 and 0.011 nm, respectively. The deposited film surface and cross section morphologies show that neither cracks nor peels have been observed and good film adhesion with the substrate was performed. Energy dispersive X-ray measurements of the film agree well with the calculated concentrations of the precursor components. Optical measurements confirm the optical characteristics of nanocrystalline ZnS film such as absorption and dispersion properties. Copper doped ZnS reduces the band gap while indium doped ZnS increases the band gap. Electrical characterization shows that copper doped ZnS increases the resistivity by one order of magnitude due to electron compensation process while indium doped ZnS decreases the resistivity three orders of magnitude due to increase of the carriers concentration. Hot probe thermoelectric quick test of ZnS:Cu and ZnS:In show opposite sign of thermoelectric voltage due to bipolar p and n types, respectively.     

Substrate temperature influence on ZnS thin films prepared by ultrasonic spray

ZnS thin films were deposited by ultrasonic spray technique. The starting solution is a mixture of 0.1 M zinc chloride as source of Zn and 0.05 M thiourea as source of S. The glass substrate temperature was varied in the range of 250 °C-400 °C to investigate the influence of substrate temperature on the structure, chemical composition and optical properties of ZnS films. The DRX analyses indicated that ZnS films have nanocrystalline hexagonal structure with (002) preferential orientation and grain size varied from 20 to 50 nm, increasing with substrate temperature. The optical films characterization was carried out by the UV-visible transmission. The optical gap and films disorder were deduced from the absorption spectra and the refractive indices of the films were determined by ellipsometric measurements. It is shown that the obtained films are generally composed of ZnO and ZnS phases with varied proportion, while at deposition temperature of 400 °C, they are near stoichiometric ZnS.     

以ZnO纳米结构为前驱体制备空心ZnS纳米结构

以ZnO纳米粒子和纳米棒为前驱体制备出空心ZnS纳米粒子和纳米管,详细研究了反应温度和时间对产物形貌的影响。结果表明,反应温度是决定产物空心状况的最重要因素,其次是反应时间。生成空心产物的机理与产生Kirkendall效应的原理相似,是由参与反应的微观粒子的扩散速率不同而导致的。     

温度对化学水浴法制备ZnS薄膜的影响

采用化学水浴法在玻璃上制备了太阳能电池中的ZnS缓冲层。采用SEM、EDS、XRD和nkd-分光光度计等手段研究了水浴温度对ZnS薄膜的表面形貌、结构和光学性能的影响。结果表明,升高温度不能明显改变薄膜的结晶性、形貌和沉积生长方式,能否成膜与温度的关系也不大,但成膜速率对温度的依赖性较大。随温度的升高,薄膜的透过率先减小后增大,反射率则先增大后减小。对同一试样而言,透过率和反射率对应较好。当温度为70℃时,可制得禁带宽度为3.83eV、符合化学计量比、平整的非晶ZnS薄膜。     

High refractive index films of ZnS/PVP nanocomposite by in situ thermolysis

A simple and rapid process for deposition of high refractive index films of ZnS/PVP nanocomposite (NC) is described. Precursor films are dip-coated on glass/quartz substrates from methanolic solution of polyvinylpyrrolidone (PVP) containing Zn⁺²–thiourea (TU) complex. ZnS/PVP nanocomposite films are produced by heating the solid precursor at 200°C for 10 min in air. Heat treatment converts the Zn⁺²–TU complex to ZnS by thermolysis in situ PVP. The transmission spectra of the films (typically 700 nm thickness) in the wavelength range of 200–1000 nm showed an absorption edge near 300 nm due to ZnS nanoparticles and high transmission of 97% beyond 400 nm. ZnS nanoparticles are uniformly dispersed in PVP matrix having sizes of about 3–4 nm. For ZnS loading of 45% by weight, the refractive index of ZnS/PVP is 1.65 which is in between that of PVP (1.48) and ZnS (2.36). Fourier Transform Infrared (FTIR) spectroscopy of the composite showed that there is a strong interaction between ZnS nanocrystals and PVP. The root mean square (RMS) roughness of the films is about 3 nm as determined by atomic force microscope (AFM).     

Effect of the thickness of Bi2Se3 sheets on the morphologies of Bi2Se3–ZnS nanocomposites and improved photoresponsive characteristic

Bi₂Se₃–ZnS nanocomposites were synthesized with different morphologies and their photoluminescence were investigated. The compounds formed hexagonal rods as the thickness of Bi₂Se₃ sheets stayed about a few nanometers; while the Bi₂Se₃ sheets’ thickness increased to tens of nanometers, the compounds formed novel morphologies of Bi₂Se₃–ZnS nanocomposites with small ZnS nanoparticles randomly decorated onto Bi₂Se₃ sheets. The formation mechanism was proposed based on the different thickness of Bi₂Se₃ sheets used in experimental processes. In addition, the significant fluorescence quench and obvious improvement in photoresponsive characteristic were shown after the integration of ZnS with Bi₂Se₃ sheets, which showed potential application in optoelectronic devices.     

Hydrothermal synthesis of spindle-like ZnS hollow nanostructures

Spindle-like hollow nanostructures of zinc sulfide (ZnS) have been successfully synthesized by hydrothermal process using a simple surfactant emulsion template. The morphologies of ZnS nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy (FE-SEM). It is found that most of the products including twin ellipsoids with connected hollow cores are reminiscent of spindle-like structures. The lengths, widths and the thickness of the shell are in the range of 1-2 μm, 300-450 nm and 20-40 nm, respectively. Selected area electron diffraction (SAED) and X-ray powder diffraction (XRD) patterns show that the shell is composed of sphalerite ZnS polycrystals.     

Synthesis of wurtzite ZnS nanorods by microwave assisted chemical route

ZnS nanorods were synthesized by microwave assisted chemical method. Polyvinylpyrrolidone (PVP) was used as a capping agent to stabilize the nanostructure. Synthesized ZnS nanorods were characterized by X-ray diffraction (XRD), Energy dispersive X-ray analysis (EDAX), Transmission Electron Microscopy (TEM), UV-visible spectrophotometry (UV), photoluminescence spectroscopy (PL) and Fourier transform Infra-red spectroscopy (FTIR). The results showed that the nanorods have wurtzite phase crystal structure and exhibits near band edge luminescence in the ultra violet region. The diameter of the synthesized PVP capped ZnS nanorods is about 600 nm. The possible growth mechanism of the ZnS nanorods could be attributed to the oriented attachment effect.