Spectroscopic studies on Zn-doped CdS nanopowders prepared by simple coprecipitation method

Abstract  

A series of Zn-doped cadmium sulfide (CdS:Zn) nanopowders were prepared by a simple coprecipitation method at room temperature, mixing the stoichiometric amount of reactants in a Milli-Q water solvent. The composition of nanopowders was accurately adjusted by controlling the molar ratio of Cd, Zn acetate in the mixed reactants. Spectroscopic studies on as prepared nanopowders were investigated by using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy, Raman, UV–Vis absorption, Field emission–scanning electron microscope–energy-dispersive X-ray analysis, and photoluminescence. Broad nature of XRD peaks confirms that as prepared powders are in nanosize and cubic structure at room temperature. Doping with Zn in CdS does not lead to any structural phase transformation but introduces a decrease in the lattice constants. Raman spectrum of Zn-doped CdS nanopowders shifts slightly toward higher energy side compared with their pure CdS nanopowders. Exciton–phonon confinement factor (S) varies in between 0.3 and 0.4. At lower wavelength excitation, we observed a broad emission peak maximum centered at 404 nm is attributed to localized band edge emission.     

Novel method to control the size of well-crystalline ceria particles by hydrothermal method

Well-crystalline ceria particles were synthesized by heating peptized ceria sol as precursor under hydrothermal conditions. The morphology and the crystallites size of hydrothermal ceria particles were controlled by varying the dielectric property of solvent used in preparation of the ceria precursor. The synthesized particles exhibit cubic fluorite structure with size ranged from 20 to 400 nm without the formation of hard aggregates. In this work, the relationships between dielectric property of the solvent and particle size were investigated in terms of the supersaturation of solute. In addition, the influences of precipitation participating anions (OH⁻) and acidic hydrothermal medium on crystallites size of ceria particles were studied.     

Synthesis,characterization and optical properties of CdS nanorods by a simple solution chemistry method

In this paper, we prepared CdS nanorods with controllable size via a facile wet route. Cadmium acetate and sulfur powder were used as precursors and alkylamine and trioctylphosphine (TOP) as solvents in the reactions. Transmission electron microscopy (TEM) studies showed that the length of the nanorods could be controlled by varying ripening time and the amount and types of organic surfactants. Moreover, the result of spectral characterizations demonstrated that the as-prepared nanorods had strong absorption and two photoluminescence emissions in the visible region.     

Novel approach to the synthesis of core-shell particles by sacrificial polymer shell method

In this work a new approach has been developed for the synthesis of SiO₂@Y₂O₃ particles with core-shell structure. The method is based on the synthesis of a covalently bonded sacrificial polymer shell grown onto silica particles. It is suitable to promote and stabilize the adsorption of different ions, namely Yttrium from its nitrate solution. After calcination and consequent elimination of the sacrificial polymer shell, the SiO₂@Y₂O₃ core-shell particles are obtained. Results reveal that the shell thickness of these core-shell particles is higher and more uniform than that of particles prepared without sacrificial polymer shell.     

Synthesis of CdS nanoplates by PAA-assisted hydrothermal approach

Triangular and hexagonal CdS nanoplates, with average size about 100 nm and average thickness range from 10 to 30 nm, have been synthesized in the presence of poly (acrylic acid) (PAA) assisted hydrothermal process at 180 °C. The structural characteristics, morphology, and optical properties of the as-prepared CdS products were investigated. UV–vis spectroscopy measurement reveals that the products show a strong quantum size effect. Based on the experiment results, the possible formation mechanism of CdS nanoplates has been proposed.     

A hydrothermal approach to flake-shaped CdS single crystals

The morphological transformation process from CdS nanorods to hexagonal CdS flakes was investigated in detail by transmission electron microscope (TEM). The CdS flakes were liable to form with the alkalinity being increased and the reaction time being prolonged. Using this transformation, hexagonal CdS flakes with diameters of 0.3 cm were grown via a recrystallization process in 6 mol/L sodium hydroxide solution at 250 °C. And the formation mechanism of CdS flakes is suggested based on the growth habits of polar crystals under proper basic hydrothermal conditions.     

水热法制备CdS纳米结构

利用氯化镉(CdC12)、硫脲(CO(NH2)2)和聚乙烯吡咯烷酮(PVP),在水热条件下获得了玉米棒状和花状等不同形貌的CdS纳米结构.采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、荧光发光光谱(PL)、紫外可见光分光光度计(UV-vis)对产物进行表征.结果表明:PVP对不同形貌CdS纳米结构的形成起关键作用,随着PVP量的增加,PVP选择性地吸附(102)晶面,抑制了该(102)晶面方向的生长,使产物的形貌由玉米棒状转变为花状;而花状纳米结构的紫外的吸收产生了红移现象,荧光性能无明显变化.     

Melnikov method approach to control of homoclinic/heteroclinic chaos by weak harmonic excitations

A review on the application of Melnikov's method to control homoclinic and heteroclinic chaos in low-dimensional, non-autonomous and dissipative oscillator systems by weak harmonic excitations is presented, including diverse applications, such as chaotic escape from a potential well, chaotic solitons in Frenkel-Kontorova chains and chaotic-charged particles in the field of an electrostatic wave packet.     

一种无水无氧制备CdS纳米晶的新方法

以醋酸镉和硫为原料,采用二硫化四乙基秋兰姆TETD和2,2-二硫代二苯并噻唑为成核剂,利用无水无氧系统在ODE的溶液中制备了尺寸可控、单分散、均一的半导体CdS纳米材料.采用XRD、粒度分析、SEM技术分别表征产物的结构、粒度和形貌.通过改变两种成核剂的使用量及反应时间可以得到不同粒径的CdS纳米晶.研究表明,在一定范围内,成核剂使用量增加或者反应时间延长都会导致产物的粒度变大,因此通过调节成核荆的使用量和反应时间从而实现对CdS纳米晶的可控生长.     

反胶团法制备CdS半导体纳米粒子

以十六烷基三甲基溴化铵(CTAB)为表面活性剂、正己醇为助表面活性剂制备了水/CTAB/正己醇/正庚烷的四元反相胶束体系,利用该体系制备了尺寸可控、均一、单分散的半导体CdS纳米材料,其中反相胶束体系被认为是一个"微反应器".获得了一个CdS纳米微粒的最佳制备条件.通过研究CTAB四元反相胶团体系的成相区域、稳定性、微液滴大小和尺寸分布和胶团组成,得出了反相胶团组成与胶团中微液滴大小的关系,采用TEM、XRD等分析技术对所制备的CdS纳米颗粒进行了性能表征.     

Synthesis and optical properties of CdS nanowires by a simple chemical deposition

CdS nanowires were prepared by a paired cell method, using highly ordered porous anodic alumina (PAA) membranes as templates. The morphology, structure, and composition of these nanowires were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) pattern. SEM images indicated that nanowires arrays are highly ordered and coincide with the contours of PAA. The EDS analysis, combined with HRTEM images and SEAD patterns, confirmed the formation of CdS. The formation and growth mechanism of CdS nanowires, as well as the optical properties, were also analyzed in details. The results indicated that the formation and growth of CdS nanowires experience from initial nuclei, nanoparticles, linear pearl-chain structures to final nanowires, attributed to electrostatic adsorption and ions diffusion. A strong emission with a maximum around 430 nm was observed from the synthesized CdS nanowires, which was attributed to the recombination of trapped electron/hole pairs. The absorption edge in UV–Vis spectrum of CdS/PAA nanoarrays showed a blue shift due to the quantum confinement effects. The technique can be used to fabricate other compound nanowires and newly light-emitting semiconductor materials.     

Novel electromagnetic approach to photonic crystals with use of the C method

We introduce a new method allowing rigorous electromagnetic analysis of scattering through photonic crystals comprising polygonal or round rods. For this purpose, we reformulate the C method with adaptive spatial resolution by utilizing the hybrid-spectrum connection method, permitting the use of nonidentical trapezoidal profiles. Considering polygonal rods as gratings consisting of different piecewise-differentiable surfaces, we are able to analyze the reflection and the transmittance of crystals by means of the C method. To enhance computational efficiency, we apply the recursive S-matrix approach with Redheffer's star product to solve the transfer matrix for structures of numerous successive layers of rods.     

Characterisation of one-dimensional CdS nanorods synthesised by solvothermal method

One-dimensional (1D) cadmium sulfide nanorods were successfully synthesised using cadmium nitrate and sulfur powder as starting materials and polyvinyl alcohol (PVA, MW = 1 25,000) as a capping agent in ethylenediamine as a solvent by solvothermal method at 200°C for 24 and 72 h. X-ray diffraction patterns (XRD) indicated a single phase of hexagonal wurtzite CdS structure, of which the results are in accordance with those of selected area electron diffraction (SAED). The morphologies of CdS were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which showed 1D nanorods. The length and diameter of CdS nanorods were increased when PVA was added and the reaction times were prolonged. High resolution transmission electron microscopy (HRTEM) showed that growth direction of wurtzite CdS nanorods is along [001] direction or c-axis. Raman spectra presented the 1LO and 2LO at 299.36 and 600.72 cm^?1, respectively. The 2LO/1LO intensity ratios were increased when the length of CdS nanorods became longer.     

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.     

Novel fabrication of silica nanotube by selective photoetching of CdS nanorod template

CdS/silica core–shell nanorod was prepared by silica coating over the CdS nanorod template of which the surface was initially capped by (3-mercaptopropyl)trimethoxysilane. The silica nanotube with both ends closed was fabricated from the core–shell nanorod by selective photoetching of the core CdS nanorod template with controlled photon energy in the oxygen-saturated aqueous solution including methyl viologen.     

Histidine functionalised biocompatible CdS quantum dots synthesised by sonochemical method

Histidine functionalised CdS quantum dots (QDs) have been synthesised by sonochemical method. Transmission Electron Microscopy (TEM) observation shows that the histidine functionalised CdS QDs are well-defined, nearly spherical particles. The X-ray diffraction pattern indicates formation of cubic phase of CdS/histidine QDs. The absorption spectra confirm quantum confinement of histidine functionalised CdS QDs. The photoluminescence property of CdS/histidine QDs is found better than that of CdS QDs. Histidine functionalised CdS QDs, in which histidine acts as a biocompatibiliser, can find potential applications in the biological fields.