Optical and electroluminescent characteristics of CdS nanoparticles stabilized by guanidine-containing dendrimers

Colloidal CdS nanoparticles measuring 1.9-2.3 nm and stabilized by guanidine-containing dendrimers were produced. It was established that such nanoparticles are characterized by photoluminescence in a wide spectral range (2.1-3.2 eV) with an average radiative lifetime of 55-85 ns depending on the energy of the emitted quanta and also by electroluminescence in the visible region of the spectrum (1.8-2.8 eV).     

Synthesis, structural and photocatalytic studies of Mn-doped CdS nanoparticles

Mn-doped CdS nanoparticles (Cd_1?x Mn _x S; where x = 0.00–0.10) were synthesized by a chemical precipitation method. The synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscope (TEM), and UV–Vis spectrometer. The XRD and TEM measurements show that the size of crystallites is in the range of 10–40 nm. Optical measurements indicated a red shift in the absorption band edge upon Mn doping. The direct allowed band gaps of undoped and Mn-doped CdS nanoparticles measured by UV–Vis spectrometer were 2.3 and 2.4 eV at 400 °C, respectively. Photocatalytic activities of CdS and Mn-doped CdS were evaluated by irradiating the solution to ultraviolet light and taking methyl orange (MO) as organic dye. It was found that 5 mol% Mn-doped CdS bleaches MO much faster than undoped CdS upon its exposure to the ultraviolet light. The experiment demonstrated that the photo-degradation efficiency of 5 mol% Mn-doped CdS was significantly higher than that of undoped CdS.     

Solid state morphology and band gap studies of ETS-10 supported CdS nanoparticles

Engelhard titanosilicate (ETS-10) supported cadmium sulphide (CdS) nanoparticles were synthesized and characterized by various solid state techniques including: XRD, DR UV-Vis, TEM and FESEM. The effect of different synthesis routes of CdS nanoparticles on its physicochemical character was studied. It was observed that CdS nanoparticles prepared by both in situ sulphur reduction (CdS-IS) and reverse micelle (CdS-RM) methods showed similar roperties. However, CdS-IS nanoparticles are more feasible and economically practical. The reflectance measurements of the as-synthesized CdS nanoparticles are apparently blue-shifted compared to bulk CdS. This phenomenon of blue-shifted absorption edge has been ascribed to an increase in bandgap energy with a decrease in particle sizes. The bandgap of the as-synthesized CdS samples was calculated from the linear correlation of [F(R) hν]² and hν. The bandgap of CdS in ETS-10 was noticeably slightly reduced when compared with the as-synthesized CdS (8 nm) due to the formation of cluster arrays on the pores of ETS-10.     

Synthesis and kinetic studies of PMMA nanoparticles by non-conventionally initiated emulsion polymerization

The aqueous emulsifier-free emulsion polymerization of methyl methacrylate (MMA) was studied under the catalytic effect of in situ developed bivalent transition metal-EDTA complex with ammonium persulfate (APS, (NH₄)₂S₂O₈) as initiator. Out of these, Cu(II)-EDTA system was selected for detailed kinetic and spectrometric study of polymerization. The apparent activation energy E_a, 34.5 kJ/mol, activation energy of initiator decomposition E_d, 26.9 kJ/mol, energy of propagation E_p, 29 kJ/mol and energy of termination E_t, 16 kJ/mol were reported. The emulsion polymer (PMMA) latex was characterized through the determination of the size and morphology by scanning electron microscopy, the average molecular weight by GPC and viscosity methods and the sound velocity by ultrasonic interferometer. From the kinetic results, the rate of polymerization, R_p at 50 °C was expressed by

     

Bimetallic nanoparticles: kinetic control matters

Morphologies à la carte: A kinetic control strategy has been utilized to fabricate bimetallic nanoparticles. Using cubic Pd nanocrystals as seeds and a syringe pump that enables precise control over precursor injection rate, it is possible to synthesize Pd-Ag bimetallic nanoparticles with tailored shapes (see picture: dimers, eccentric hybrid bars, and core-shell structures) and tunable localized surface plasmon resonances.     

Color kinetic nanoparticles

Eu3+ doped LaF3 nanoparticles functionalized with a 3-4 formylphenyl benzoic acid ligand were synthesized. Excitation energy-dependent energy transfer from the ligand to Eu3+ yields color tunability from the red to greenish-blue as a function of excitation wavelengths. This synthetic approach provides large shifts in the resultant chromaticity with an excitation wavelength including the generation of white light.     

CdS量子点的合成及其光学性能

以硝酸镉和硫代乙酰胺为原料,以N-乙酰-L-半胱氨酸(NAC)为稳定剂,在水溶液中合成了Cd S量子点(Cd S QDs)。通过考察稳定剂的配比、反应温度、反应时间、p H和搅拌时间对Cd S QDs的影响,研究Cd S QDs的光学性能。结果表明:当n(Cd2+)/n(NAC)=2/1,p H=7,搅拌10 min,于80℃反应2 h制得的Cd S QDS荧光性能较好。     

CdS纳米粒子的表面修饰及其对光学性质的影响

用反胶束法合成了用表面活性剂分子磺基焉珀酸双－２－乙基已酯钠盐（ＡＯＴ）进行表面修饰的ＣｄＳ纳米粒子（记为ＣｄＳ／ＡＯＴ－ＳＯ３＾－）,研究了这种纳米粒子在正庚烷（ｈｅｐｔａｅ）和吡啶（Ｐｙ）溶剂中的荧肖及光解行为,发现其在正庚烷中荧光很强,而Ｐｙ却强烈地猝灭ＣｄＳ纳一子的荧光,用电荷转移猝灭机制进行了解释,这种解释为ＣｄＳ纳米粒子在Ｐｙ中光解实验进一步证实。     

Direct electrochemistry of hemoglobin immobilized on CdS:Mn nanoparticles

The First International Congress of Applied Chemistry was organised by the Association of Belgian Chemists in 1894, the eighth and last was held in Washington and New York in 1912. These congresses, unlike the early congresses on pure chemistry, were very successful and held with the highest patronage in the host countries. The ninth planned for St. Petersburg in 1915 was not held due to the intervention of the First World War. The initiative passed to IUPAC but due to political and financial restraints the International Congresses of Pure and Applied Chemistry did not commence till 1934.     

Thermoluminescence study of ZnS:Cu nanoparticles

In this paper, we report on the TL glow curves and kinetic parameters, activation energy, order of kinetics, and the frequency factor of copper-doped zinc sulfide nanophosphor under UV irradiations. The sample was prepared by the chemical precipitation method; thereafter, the TL glow curves were recorded for different doses of UV exposure at a heating rate of 10 °C/s. The synthesized nanophosphor exhibited TL glow peaks at 241, 255, and 281 °C for the heating rate 10 °C/s at different doses of 5, 10, and 15 min of UV exposure. The kinetic parameters activation energy E, the order of kinetics b, and the frequency factor S of synthesized nanophosphor of ZnS:Cu have been calculated by using a peak shape method while the trap depth was determined using different formulae. The sample was characterized by XRD (X-ray diffraction) and SEM (scanning electron microscope).     

Optical absorption enhancement of CdS nanometer crystallites

An elementary model and analytical theory on optical absorption enhancement phenomena with decreasing the nanometer crystallite size is proposed by using the effective mass theory of excitons and taking into account the tunneling effect and the frequency change. With decreasing particle size, the confinement imposed on the relative motion of electron—hole pair enhances the oscillator strength, and the change of transition frequency due to the size quantization blue shift weakens the oscillator strength. For larger band gap materials, the former is dominant, thus the absorption coefficient tends to enhancement as the particle size decreases. Good agreement between the theoretical and the experimental absorption coefficient of CdS is achieved.     

Preparation and characterization of polyaniline microwires containing CdS nanoparticles

Polyaniline(PANI) microwires containing CdS nanoparticles have been prepared by introducing hydrogen bonding and/or electrostatic interaction between mercaptocarboxylic acid capped CdS nanoparticles and PANI. SEM and TEM proved them to be wire-like structures. PL spectra of the PANI/CdS complex is blue-shifted by 14 nm compared to CdS nanoparticles in N-methylpyrrolidinone(NMP).     

CdS semiconductor nanoparticles in silica sonogel matrices

SiO₂ gels obtained by sonocatalytic method combined with DCCA were used as host-matrices for extremely fine dispersions of CdS semiconductor particles. Small crystallites were produced in situ by H₂S gas diffusion method. The particles were characterized by TEM and HRTEM, EXAFS, UV-Vis and Raman spectroscopies. The size of crystallites ranged from 5 to 10 nm. The optical transmission spectra showed the characteristic blue shift as a function of the particles size, as predicted by the theory. The optical and mechanical qualities of the samples were substantially improved by an infiltration method using a sono-sol which sealed the superficial pores thus ensuring greater longevity and the possibility of obtaining transparent gels by polishing.     

Chemical effects of size quantization of CdS nanoparticles

The behaviour of photoreaction occurring on the superfine duster interface of semiconductor CdS has been studied. The results indicated that the size quantization effect of semiconductor nanoparticles was obviously reflected not only in their physical properties, but also in the interfacial photocatalysis reactions initiated by superfine nanopartides. This means that the direction and mechanisms in photoreactions of the compounds adsorbed on the surface of nanopartides could vary with the alteration of particle size because the redox potential values of semiconductor particles could be changed with the variation of particle size. Doubtlessly, this effect could play an important role in controlling the interfacial reaction mechanisms and raising the selectivity to photoreaction paths.     

Proton-coupled electron transfer from photo-excited CdS nanoparticles

Abstract

Polyoxometalate (POM) cluster anions form monolayers on metal(0) nanoparticles (NPs) in water, serve as protecting ligands for binary-salt nanocrystals (such as AgCl), and as covalently attached ligands on anatase TiO₂ nanocrystals. We now show that the lacunary-Keggin ion [α-AlW₁₁O₃₉]^9? (1) binds strongly to Cd²⁺ in water, providing control over the growth and stability of CdS nanoparticles (NPs) that form upon addition of sulfide. When reduced by a single electron, the already highly negatively charged POM, 1 is protonated by water, and 1-protected CdS NPs were used as visible-light driven electron donors to assess whether combined reduction and protonation of 1 occurred via sequential electron- and proton-transfer steps (an ETPT mechanism), or simultaneously, via concerted proton-electron transfer (CPET). Comparison of the kinetic profiles for reduction of 1 in D₂O and in H₂O showed the absence of a kinetic isotopic effect (KIE), characteristic of ETPT mechanisms.     

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt_2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S~(2-) to St~- (stearate ion). Characterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i. e. CdS particle inserts in the CdSt_2 molecular layers to form a sandwich-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.