Formation Of CdS Nanocrystals Research Articles

Simple and green synthesis of protein-conjugated CdS nanoparticles and spectroscopic study on the interaction between CdS and zein

The present study demonstrates the role of zein molecules in synthesizing CdS nanoassemblies through protein-directed, green synthetic approach. Zein molecules can as capping ligand and stabilizing agent to regulate the nucleation and growth of CdS nanocrystals, and the obtained products are organic–inorganic nanocomposites. The analysis of surface charge and conductivity indicates that strong electrostatic force restricts mobility of ions, which creates a local supersaturation surrounding the binding sites of zein and reduces the activated energy of nucleation. The interaction between Cd2+/CdS and zein molecules was systematically investigated through spectroscopy techniques. Fourier transform infrared (FT-IR) spectra were used to envisage the binding of the functional groups of zein with the surface of CdS nanoparticles. Ultraviolet visible (UV–Vis) and photoluminescence (PL) spectra results show that Cd2+/CdS might interact with the aromatic amino acids of protein molecules and change its chemical microenvironment. The quantum-confined effect of nanocrystals is confirmed by optical absorption spectrum due to the small size (3–5 nm) of CdS particles. The data of circular dichroism (CD) spectra indicate that the formation of CdS nanocrystals could lead to the conformational change of zein molecules. Moreover, the possible mechanism of CdS nanocrystals growth in zein solution was also discussed. The weak interactions such as Van der Waals, hydrophobic forces and hydrogen bonds in zein molecules should play a crucial factor in the self-assembly of small nanoparticles.

Synthesis and characterization of CdS nanocrystals in Maleic anhydride–Octene-1–Vinylbutyl Ether terpolymer matrix

A Maleic anhydride–Octene-1–Vinylbutyl Ether terpolymer was synthesized via the radical terpolymerization method in order to prepare a new matrix for CdS nanocrystal synthesis. CdS nanocrystals were synthesized through the reaction of thiourea with cadmium chloride. The synthesized terpolymer/CdS nanocrystal composites were characterized by several methods. Energy Dispersive X-ray analysis, Raman spectroscopy and powder X-ray diffraction methods. The room temperature UV–visible absorption spectra show a shift of the absorption edge towards higher energies. The band gap of the CdS nanocomposite is bigger than that of bulk CdS. Raman spectrum exhibits characteristic peaks of CdS. Images of the nanocomposite obtained with Atomic Force Microscopy and Transmission Electron Microscopy are the evidences of CdS nanocrystal formation in the terpolymer. Thermal investigation shows that the nanocomposite is more thermostable than the terpolymer which could be useful for application in thermo aggressive medium.

Peculiarities of CdS nanocrystal formation at annealing of a Langmuir‐Blodgett matrix

AbstractFormation and assembling of CdS nanocrystals (NC) on highly‐ordered pyrolytic graphite (HOPG) and on oxidized silicon substrates have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). NC were initially formed within a Langmuir‐Blodgett (LB) matrix of cadmium behenate. The LB matrix was then removed by annealing in an ammonia atmosphere. It is shown that the NC self‐assembling is mainly determined by the LB matrix wetting properties. In case of wettable HOPG substrate homogeneous matrix evaporation occurs that leads to coarsening of the NC arrays as the main self‐assembly process. Otherwise, NC prepared on non‐wettable SiO2‐Si substrate demonstrate arrays formation determined by the LB matrix dewetting process. For the both cases, the influence of kinetic limitations connected with matrix evaporation rate on the self‐assembly process is observed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Role of Defects in Carbon Nanotube Walls in Deposition of CdS Nanoparticles from a Chemical Bath

Multiwall carbon nanotubes (MWCNTs), as-prepared and annealed in an inert atmosphere, have been used as templates for growth of CdS nanoparticles from an aqueous ammonium solution of cadmium chloride and thiourea. Transmission electron microscopy and Raman spectroscopy revealed that formation of CdS nanocrystals on the raw MWCNT surface proceeds markedly faster than on the annealed one. X-ray photoelectron spectroscopy showed a strong difference in the chemical state of the deposited CdS depending on the defect density in the MWCNTs. An interaction of Cd2+ ions and mixed Cd(II) complexes with a defective graphene fragment was studied using density functional theory. The calculations indicated that, for attachment of Cd-containing species to the graphitic surface, defects with the dangling carbon bonds are needed. By combining the experimental and theoretical results, a model of CdS nucleation on the MWCNTs was proposed.

Step-by-step build-up of ordered p–n heterojunctions at nanoscale for efficient light harvesting

A simple “grafting from” strategy is reported to graft polymer brushes bearing thiophene groups onto TiO2 nanowires via a surface initiated polymerization and FeCl3 catalytic oxidized polymerization. Subsequently, the in situ CdS nanocrystals can be fabricated along the conductive polymer network, enabling highly ordered p–n heterojunctions to be prepared on the nanoscale. Polynorbornene bearing thiophene was grafted onto TiO2 nanowires via surface-initiated ring-opening metathesis polymerization (SI-ROMP), and then the oxidization polymerization of the thiophene derivative was performed to prepare conductive conjugated polythiophene brushes. The carboxyl groups in conductive polymer brushes can be used as the source precursor to coordinate cadmium cations for templating CdS nanocrystal formation, meanwhile creating intimate interfacial contact between nanocrystals and conjugated polymers. This novel approach offered a superior platform to the step-by-step build-up of ordered heterojunctions on the nanometer scale and has great advantages in precisely controlling the detailed nano-morphology and dispersion of nanocrystals within conductive polymers.

Enzyme-polymers conjugated to quantum-dots for sensing applications.

In the present research, the concept of developing a novel system based on polymer-enzyme macromolecules was tested by coupling carboxylic acid functionalized poly(vinyl alcohol) (PVA-COOH) to glucose oxidase (GOx) followed by the bioconjugation with CdS quantum-dots (QD). The resulting organic-inorganic nanohybrids were characterized by UV-visible spectroscopy, infrared spectroscopy, Photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). The spectroscopy results have clearly shown that the polymer-enzyme macromolecules (PVA-COOH/GOx) were synthesized by the proposed zero-length linker route. Moreover, they have performed as successful capping agents for the nucleation and constrained growth of CdS quantum-dots via aqueous colloidal chemistry. The TEM images associated with the optical absorption results have indicated the formation of CdS nanocrystals with estimated diameters of about 3.0 nm. The “blue-shift” in the visible absorption spectra and the PL values have provided strong evidence that the fluorescent CdS nanoparticles were produced in the quantum-size confinement regime. Finally, the hybrid system was biochemically assayed by injecting the glucose substrate and detecting the formation of peroxide with the enzyme horseradish peroxidase (HRP). Thus, the polymer-enzyme-QD hybrid has behaved as a nanostructured sensor for glucose detecting.

Correlation of CdS Nanocrystal Formation with Elemental Sulfur Activation and Its Implication in Synthetic Development

Formation of CdS nanocrystals in the classic approach (with octadecene (ODE) as the solvent and elemental sulfur and cadmium carboxylate as the precursors) was found to be kinetically dependent on reduction of elemental sulfur by ODE, which possessed a critical temperature (~180 °C). After elemental sulfur was activated by ODE, the formation reaction of CdS followed closely. 2-tetradecylthiophene from the activation of S by ODE and fatty acids from the formation reaction of CdS were found to be the only soluble side products. The overall reaction stoichiometry further suggested that oxidation of each ODE molecule generated two molecules of H(2)S, which in turn reacted with two molecules of cadmium carboxylate molecules to yield two CdS molecular units and four molecules of fatty acids. In comparison to alkanes, octadecene was found to be substantially more active as a reductant for elemental sulfur. To the best of our knowledge, this is the first example of quantitative correlation between chemical reactions and formation of high-quality nanocrystals under synthetic conditions. To demonstrate the importance of such discovery, we designed two independent and simplified synthetic approaches for synthesis of CdS nanocrystals. One approach with its reaction temperature at the critical temperature of S activation (180 °C) used the same reactant composition as the classic approach but without any hot injection. The other approach performed at an ordinary laboratory temperature (≤100 °C) and in a common organic solvent (toluene) was achieved by addition of fatty amine as activation reagent of elemental sulfur.

Theoretical study on influence of ligand and solvent to CdS clusters

AbstractBased on the experimental zinc blende and wurtzite structures of CdS nanocrystals, five new CdS clusters (Cd3S3, (Cd3S3)2, (Cd3S3)3, Cd4S4 with C2V, and Cd4S4 with TD symmetry) are investigated via optimization of their original structures at B3LYP/Lanl2dz theoretical level. Through considering integration influence of solvent and ligand, our calculated Raman and absorption spectra can be consistent with the reported experimental results. First, our calculated Raman peaks of Cd3S3, Cd4S4 (TD), (Cd3S3)2, and (Cd3S3)3 are within the range of 260–290 cm−1, which is also reported by experiment. Subsequently, for deep researching five clusters, the absorption spectra of them are calculated using time‐dependent DFT method. The wavelengths of the absorption peaks, which is calculated in solvent, increase in the order Cd3S3, Cd4S4 (TD), (Cd3S3)2, and (Cd3S3)3. Moreover, the wavelengths of absorption peaks shift to blue in solvent, compared with those without solvent. Furthermore, our clusters are smaller than the size of the smallest CdS nanocrystals, the calculated absorption spectra of five clusters in solvent show obvious blue shift than the wavelengths of absorption spectra of reported CdS nanocrystals. This is induced by the quantum size effect. Besides, we further investigated the influence of ligands to CdS unit in aqueous condition. Through structures and characters analysis of SCdSR, we discovered that ligands took important role during the formation of CdS nanocrystals in aqueous synthesis. Calculated results of spectra, bond length, and Wiberg bond index (WBI) values show that different ligands have similar influence on CdS unit. Moreover, using WBI values, we also confirm that Cd atom has stronger interaction with S in nanocrystals than that with S atom in ligand. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Enzyme mediated synthesis of phytochelatin-capped CdS nanocrystals

We reported the enzyme mediated synthesis of CdS nanocrystals by immobilized phytochelatin synthase, which converts glutathione into the metal-binding peptide phytochelatin (PC). Formation of CdS nanocrystals were observed upon the addition of CdCl2 and Na2S with PC as the capping agent. By varying the reaction times, different compositions of PCs (form PC2 to PC3) can be synthesized, resulting in the formation of highly stable nanocrystals with tunable sizes (from 2.0 to 1.6 nm diameter). This approach may be generalized to guide the in vitro self assembly of a wide range of nanocrystals with different compositions and sizes.

The Effect of Irradiation Wavelength on the Quality of CdS Nanocrystals Formed Directly into PMMA Matrix

UV laser irradiation of PMMA films containing Cd thiolate precursors results in the spatially selective formation of CdS crystalline nanoparticles in the host matrix. Here we investigate the effect of the irradiation wavelength on the quality of the formed nanocrystals. Fluorescence topography and XPS studies reveal that the polymer matrix contributes to the trap states formation on the surface of the nanocrystals. When the latter are formed upon irradiation at 266 nm, they exhibit broad emission spectra, ascribed to the high degree of photodegradation of the polymer. In contrast, the irradiation at 355 nm does not chemically modify the matrix, resulting in the formation of CdS nanocrystals with narrow emission, i.e. high emission quality. This is further confirmed by fluorescence lifetime topography studies giving a mean fluorescence nanocrystal lifetime as short as 200 ps at room temperature. Thus, the optimized combination of irradiation wavelength with polymer matrix gives nanocomposite materials incorporating nanocrystals of high quality, ready to be used in various optical applications.

Patterned structures of in situ size controlled CdS nanocrystals in a polymer matrix underUV irradiation

A method of in situ formation of patterns of size controlled CdS nanocrystals in a polymermatrix by pulsed UV irradiation is presented. The films consist of Cd thiolate precursorswith different carbon chain lengths embedded in TOPAS polymer matrices. Under UVirradiation the precursors are photolyzed, driving to the formation of CdS nanocrystals inthe quantum size regime, with size and concentration defined by the number of incidentUV pulses, while the host polymer remains macroscopically/microscopically unaffected.The emission of the formed nanocomposite materials strongly depends on thedimensions of the CdS nanocrystals, thus, their growth at the different phases of theirradiation is monitored using spatially resolved photoluminescence by meansof a confocal microscope. X-ray diffraction measurements verified the existenceof the CdS nanocrystals, and defined their crystal structure for all the studiedcases. The results are reinforced by transmission electron microscopy. It is provedthat the selection of the precursor determines the efficiency of the procedure,and the quality of the formed nanocrystals. Moreover it is demonstrated thatthere is the possibility of laser induced formation of well-defined patterns of CdSnanocrystals, opening up new perspectives in the development of nanodevices.

Facile Cd−Thiourea Complex Thermolysis Synthesis of Phase-Controlled CdS Nanocrystals for Photocatalytic Hydrogen Production under Visible Light

We describe a simple cadmium−thiourea complex thermolysis route for the formation of CdS nanocrystals with controlled dispersity, crystalline phase, composition, average grain size, and band gap. Visible-light-driven photocatalytic activities for hydrogen production over the different CdS products have been compared. Phase structure and composition of the obtained CdS nanocrystals has been optimized either by changing the ratio of thiourea to Cd or by changing the annealing temperature. Over a broad annealing temperature range of 150−500 °C, either cubic, a mixture of cubic and hexagonal, or hexagonal CdS nanocrystals are obtained at thiourea/Cd molar ratios of <1.0, 1.5−2.5, and 3.0−4.5, respectively. Nanocrystalline cubic CdS is stable at temperatures as high as 500 °C for 0.5 h, and is converted to hexagonal CdS for annealing time longer than 1 h. The phase transition from cubic to hexagonal CdS occurs at temperatures of 200−300 °C, and pure hexagonal CdS is formed at annealing temperatures higher than...

Photon-induced formation of CdS nanocrystals in selected areas of polymer matrices

We demonstrate light-induced formation of semiconductor quantum dots in TOPAS® polymer matrix with very high control of their size and their spatial localization. Irradiation with UV laser pulses of polymer films embedding Cd thiolate precursors results in the formation of cadmium sulfide nanocrystals well confined in the irradiation area, through a macroscopically nondestructive procedure for the host matrix. With increasing number of laser pulses, we accomplish the formation of nanoparticles with gradually increasing dimensions, resulting in the dynamic change of the spectra emitted by the formed nanocomposite areas. The findings are supported by x-ray diffraction and transmission electron microscopy measurements.

Growth kinetics and characterization of fluorescent CdS nanocrystals synthesized with different sulfur precursors in paraffin hot-matrix

The present paper describes the influence of the sulfur precursor on the nanocrystal growth rate and optical properties of cadmium sulfide nanocrystals in a hot-paraffin matrix. One of the precursors used is tributylphosphine sulfide; the other one is elemental sulfur. The growth kinetics is studied at various temperatures to estimate the activation energy for the formation of CdS nanocrystals from the temperature dependence of model kinetic parameters. The different sulfur precursors lead to different trends in the limiting nanocrystal radii and the time-constant of growth. The obtained nanocrystals are characterized by UV-absorption and photoluminescence spectroscopy, electrophoresis, X-ray powder diffraction and transmission electron microscopy. The nanocrystals prepared from tributylphosphine sulfide have fewer surface defects and their spectra exhibit a band-edge emission only. In this case the limiting radii of the nanocrystals increase with increasing the temperature of growth. The nanocrystals synthesized from elemental sulfur show in addition a trap-state emission due to much more surface defects. Here the limiting radii of nanocrystals decrease with increasing temperature in contrast to the previous case. In both cases, the semiconductor nanocrystals can be sterically and electrostatically stabilized in non-polar organic solvents by post-capping with tributylphosphine. Our findings are important for the controlled manufacturing of CdS nanocrystals with pre-determined properties and their utilization in a variety of optical devices.

Laser-induced nanocomposite formation for printed nanoelectronics

CdS nanocrystals are formed by regioselective thermal decomposition of metal alkanethiolates in a polymer matrix by selective heating of a polystyrene foil filled with the cadmium-(bis)-thiolate precursor using focused laser beam irradiation. CdS nanocrystal formation in the polymer was investigated by photoluminescence emission and excitation (PL and PLE) spectroscopy and transmission electron microscopy (TEM). The PLE spectra show a band edge at 420 nm for the irradiated area, indicating the presence of nanocrystalline CdS of size of about 2–3 nm. The PL exhibits an emission band at 535 nm that is also characteristic of nanometer-sized CdS. TEM images confirm the presence and size of CdS nanoparticles. The surface temperature was estimated theoretically considering the relationships between the temperature, time and power of the laser pulses. Nanoparticle formation via laser probe is also discussed in terms of possible utilization of other probes (e.g., electrons, etc.), inducing nanocrystal formation for the realization of conducting nanowires embedded in non-conductive matrix materials useful for nanoelectronic devices or conductive plastic.

A Spray-Based Method for the Production of Semiconductor Nanocrystals

We present a spray based-method for the formation and production of semiconductor nanocrystals that provides an attractive alternative to the commonly used epitaxial and colloidal procedures. According to this spray-based method, mainly thermospray, solutions of semiconductor salts are first sprayed into monodispersed droplets, which subsequently become solid nanocrystals by solvent evaporation. A semiconductor nanocrystal is produced from a single spray droplet upon the full vaporization of the solvent. The average diameter and size distribution of the final nanocrystals are controlled and determined by the solute concentration of the sprayed solution and by the droplet size, hence by the spray production parameters. The spray-produced nanocrystals are collected on any selected solid support. Representative results, shown in this letter, reveal the formation of CdS nanocrystals in the size range of 3 to 6 nanometers and with a size distribution of as low as five percent. A further structural analysis of these nanocrystals showed that they were formed in the zinc blend phase with a high degree of crystallinity.

A Novel Spray Based Method for the Production of Semiconductor Nanocrystals

AbstractWe present a novel spray based method for the formation and production of semiconductor nanocrystals that provides an attractive alternative to the commonly used epitaxial and colloidal procedures. According to this spray-based method, mainly thermospray, solutions of semiconductor salts are first sprayed into monodispersed droplets, which subsequently become solid nanoparticles by solvent evaporation. A semiconductor nanoparticle is produced from a single spray droplet upon the full vaporization of the solvent. The average diameter and size distribution of the final nanocrystals are controlled and determined by the solute concentration of the sprayed solution and by the droplet size, hence by the spray production parameters. The spray-produced nanocrystals are collected on any selected solid support. Representative results, shown in this paper, reveal the formation of CdS nanocrystals in the size range of 3 to 6 nanometer and with a size distribution of as low as five percents. A further structural analysis of these nanocrystals showed that they were formed in the zinc blend phase with high degree of crystallinity.

Temperature dependent studies of CdS nanoparticles in viscous matrix

We report the formation of CdS nanocrystals in colloidal solution of glycerin at various temperatures. A detailed systematic study on the size variation of these particles with temperature has been carried out using the UV/VIS spectroscopy in these colloids. Particle size variation as a function of temperature has been observed. The temperature dependent spectra showed a red shift indicating an increase in size of the CdS nanocrystals with the increase of temperature.

Synthesis and Characterization of Bifunctionalized Ordered Mesoporous Materials

AbstractDirect synthesis (co‐condensation reaction) and post‐synthesis reaction (grafting) are combined for the first time to efficiently fabricate bifunctionalized ordered mesoporous materials (OMMs). Ethylenediamine‐containing OMMs (ED‐MCM‐41) were first synthesized via direct synthesis and then further modified by the phenyl (PH) group in a supercritical fluid (SCF) medium via grafting reaction, resulting in OMMs with ED and PH groups (PH‐ED‐MCM‐41). X‐ray diffraction (XRD) patterns, N2 sorption properties, transmission electron microscopy (TEM), 29Si and 13C magic angle spinning (MAS) NMR, chemical analysis, and hydrothermal treatment were used to characterize the bifunctionalized materials. Experiments show that bifunctionalized OMMs can be efficiently prepared by modifying the directly synthesized monofunctionalized OMMs via grafting reaction in a supercritical fluid medium. Both functional groups are distributed uniformly at the surfaces. The advantage of bifunctionalized OMMs over monofunctionalized OMMs was illustrated by introducing thiol groups into ED‐MCM‐41 materials and the subsequent formation of CdS nanocrystals inside thiol‐ and ED‐functionalized MCM‐41 (HS‐ED‐MC‐41). Because of the variety of the functional groups that can be introduced into OMMs by direct synthesis or post‐synthesis reaction, it is expected that the present strategy could provide a generally applicable approach to the design of OMMs with two functional groups.

The formation of CdS nanocrystals in silica gels by gamma-irradiation and their opticalproperties

Silica gels dispersed with nanoscale CdS particles were prepared by the sol–gel process combined withγ-irradiation at room temperature and in ambient pressure. X-ray diffraction (XRD) andtransmission electron microscopy have revealed the existence of CdS nanocrystals, as wellas their structures and size distributions. The silica matrix affects the crystal structure ofthe CdS particles produced. A prominent quantum size effect was observed through theabsorption and luminescence spectra of samples irradiated for different periods of time. Themost interesting phenomenon is that on increasing the irradiation time, the surface-stateemission disappears, and simultaneously band edge emission appears and becomes evenstronger with longer irradiation: this is thought to be due to the passivation effect by thesurrounding matrix through the interface electrostatic interactions around the particles.