Photochemistry at the surface of colloidal cadmium sulfide

Pulsed laser studies of surfactant stabilized CdS colloids indicate a rapid (<10^?9 s) c^? transfer from CdS to methylviologen adsorbed on the colloids. A rapid (≈ 10^?6 s) subsequent back reaction of some of the reduced methylviologen is observed. pH, solute concentration, etc., affect the reaction.     

Electrochemical deposition of cadmium sulfide from DMSO solution

Semiconducting films of CdS are produced by the cathodic deposition of Cd on inert electrodes in the presence of dissolved S₈ in dimethylsulfoxide solution. Linear potential scans and potential pulse measurements show that the first layers are formed by underpotential deposits of Cd reacting with S₈ from the solution. With increasing coverage of the surface the mechanism changes to a mixed reduction of Cd and a reduction of S₈ to sulfide, which forms the deposit with Cd²⁺ from the solution. Photoeffects are observed with deposits greater than three or four equivalent monolayers of CdS, demonstrating the n-type character of the deposits. The photocurrent spectrum of films in the micrometer range differs considerably from that of single-crystal CdS. Films produced in this way need further treatment before they could be useful as low-cost electrodes for solar cells.     

Synthesis of stable cadmium sulfide nanoparticles using surfactin produced by Bacillus amyloliquifaciens strain KSU-109

In this study, a surfactin was extracted from a novel surfactant producing bacterial strain Bacillus amyloliquifaciens KSU-109, isolated from rhizosphere of date palm (Phoenix dactylifera), and characterized based on 16Sr RNA and sfp genes using Blastn, Blastx and phylogenetic analyses. The study was performed to obtain a renewable bioresource for surfactin production, and its application in nanotechnology as a non-hazardous and environmentally compatible nanoparticle (NP) stabilizer. The strain KSU-109 produced the surfactin with an average yield of 160 mg/L with strong surfactant activity, reducing the surface tension of the medium from 72 mN/m to 29.3 mN/m. The surfactin preparation was used for synthesizing the cadmium sulfide nanoparticles (CdS-NPs) by mixing 0.005% surfactin with 1mM Cd(NO(3))(2) in 1:1 ratio (v/v) and 10mM Na(2)S solution at pH 7.2 and ambient temperature, which were stable up to 120 days. The surfactin stabilized CdS-NPs were characterized using XRD, TEM, and spectroscopic techniques. The data revealed a significant role of surfactin as a stabilizer and capping agent, which also causes phase transition to yield the cubic/hexagonal CdS-NPs of average size of 3-4 nm. The results elucidated the significance of biocompatible and biodegradable surfactin as an effective and inexpensive stabilizing agent for developing stable CdS nanoparticles.     

Preparation of uniform colloidal cadmium and lead selenide particles

Colloidal cadmium selenide and lead selenide particles of narrow size distribution were prepared by decomposition of selenourea in solutions of corresponding metal salts. While both salts were crystalline, CdSe powders showed nearly spherical morphology whereas PbSe consisted of particles of cubic symmetry. In the latter case greater uniformity was achieved if homogeneous precipitation was carried out in methanol-water mixtures.     

Stability of colloidal solutions containing various surface-modified cadmium sulfide particles under stationary illumination

Stability of the various colloidal solutions containing CdS particles with the surface modified by thiols such as thioglycerol (TG-CdS), mercaptophenyltetrazole (MPT-CdS), mercaptobenzimidazole (MBI-CdS), and mercaptoacetate (MA-CdS) (capped CdS particles) under the stationary illumination was studied by monitoring the changes in the absorption spectra to obtain knowledge about the influence of these capping agents on photocatalytic events such as electron and hole transfer processes at the capped semiconductor particle-solution interface. By the stationary illumination of the capped CdS particles, the photo-aggregation of the particles was observed in water and the photo-dissolution in organic solvents. The observed difference may be ascribed to the oxidative elimination of the capping agents from the CdS particles which occurs assisted by proton dissociation from the agents in water but not in organic solvents with aprotic nature. Addition of iodide which is known as a hole scavenger enhanced the photo-dissolution of both the capped and ordinary non-capped CdS particles, contrary to the expected photo-aggregation.     

Preparation of cadmium sulfide nanoparticles in self-reproducing reversed micelles

Octyl octanoate (O-OL) underwent hydrolysis in sodium octanoate (NaOA) reversed micelles in 85:15 = isooctane:octanol (OL) (v/v), containing w = [H2O]/[NaOA] = 40. The products of the hydrolysis, octanoic acid (OA) and octanol (OL), lead to the formation of additional (albeit smaller) reversed micelles; hence the process is considered to be self-reproducing. Self-reproduction was found to be catalyzed by lithium hydroxide, solubilized in the water pools, as well as by hydrogen sulfide, added to the solution of the reversed micelles. Addition of hydrogen sulfide to cadmium perchlorate containing self-reproducing reversed micelles resulted in the formation of cadmium sulfide (CdS) nanoparticles. Diameters of the CdS containing nanoparticles could be altered from 5.4 to 1.8 nm by changing the [Cd2+]/[H2S] ratios from 0.25 to 10. The CdS nanoparticles formed were capped by mercaptopropionic acid, isolated as solids, and could be repeatedly redispersed in water without changing their sizes. Additional CdS nanoparticles were generated in the supernatants removed from the precipitated capped CdS nanoparticles.     

Preparation and properties of uniform amorphous and crystalline colloidal nickel sulfide

 Amorphous spherical particles of nickel sulfide of 10 nm in diameter were synthesized by the controlled double-jet precipitation (CDJP) technique using nickel sulfate and sodium sulfide. Cubic crystalline particles of ∼200 nm were obtained by aging dispersions of amorphous particles at 80 °C for more than a week, as long as the pH was kept between 3 and 3.5. Electrokinetic mobilities of these particles are reported, as well as color properties of their dispersions in liquids and in poly(vinyl alcohol) films are described. Received: 20 January 1997 Accepted: 21 January 1997     

Preparation of mesoporous cadmium sulfide nanoparticles with moderate pore size

The preparation of cadmium sulfide nanoparticles that have a moderate pore size is reported. This preparation method involves a hydrothermal process that produces a precursor mixture and a following acid treatment of the precursor to get the porous material. The majority of the particles have a pore size close to 20 nm, which complements and fills in the gap between the existing cadmium sulfide materials, which usually have a pore size either less than 10 nm or are well above 100 nm.     

Creation of cadmium sulfide nanostructures using AFM dip-pen nanolithography

A dip-pen nanolithography (DPN) process capable of depositing nanoscaled structures of semiconducting CdS materials was developed by careful control of the reaction speed between the precursors. The new development expanded the scope of the powerful DPN process and provided more insight in the deposition mechanism. Features ranging from several hundreds of nanometers to sub-50 nanometers were generated and characterized. The effects of the surface property of the substrate, the relative humidity, the translating rate, and the temperature were systematically investigated. X-ray photoelectron spectroscopy (XPS) was used to verify the chemical composition of the patterns. In principle, this simple and convenient method should be applicable to deposit various metal sulfides on suitable substrates.     

Synthesis of quasi-two-dimensional colloidal cadmium selenide nanoparticles and formation of sulfide monolayer on their surfaces

We have carried out a solution synthesis of quasi-two-dimensional CdSe nanoparticles (nanoplates) using oleic acid as a stabilizer. Three populations of CdSe nanoplates with different thicknesses quantified by one CdSe monolayer were obtained. The absorption spectra of CdSe nanoplates exhibit narrow excitonic bands (with bandwidths of ～60 meV), whose positions are determined by the nanoplate thickness and are 461, 503, and 551 nm for the three populations. We have systematically studied how formation of sulfide monolayer on the surface of CdSe nanoplates affects their optical properties. The red shift and significant broadening of absorption bands was shown.     

One- and two-photon induced polymerization of methylmethacrylate using colloidal CdS semiconductor quantum dots

The development of one- and two-photon induced polymerization using CdS semiconductor quantum dots (QDs) and amine co-initiators to promote radical generation and subsequent polymerization is presented. Two-photon absorption (TPA) cross-section measurements, linear absorption, and transmission electron microscopy are used to characterize the QDs. The effectiveness of the co-initiators in increasing the efficiency of photopolymerization (polymer chains formed per excitation) is examined. Triethylamine was observed to be most effective, yielding quantum efficiencies of initiation of >5%. The interactions between the co-initiators and QDs are investigated with steady-state photoluminescence and infrared spectroscopies. Possible initiation mechanisms are discussed and supported by electrochemical data. Making use of the surface chemistry developed here and the large QD TPA cross-sections, two-photon induced polymerization is demonstrated. The large TPA cross-sections coupled with modest quantum efficiencies for initiation reveal the unique potential of molecularly passivated QDs as efficient two-photon photosensitizers for polymerization.     

Preparation of a stable injection solution of barvinkan hydrochloride

Summary A method has been developed for obtaining a stable 1% injection solution of barvinkan hydrochloride with the aid of a complex stabilizer.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 601–603, September–October, 1978.     

Preparation of aqueous CdS colloids in the presence of cadmium complexonates: effect of complexonates on the size of CdS nanoparticles

The results of a systematic study of the preparation of CdS colloids in aqueous solutions containing different Cd²⁺ complexonates are presented. The effects of the ratio of the reagents and the nature and concentration of various stabilizing surfactants and Cd²⁺ complexonates, including those of some sulfur-containing compounds, on the size of the colloidal particles have been studied. Thermodynamic calculation of the expected equilibrium size of the colloidal particles as a function of the solvent composition, taking into account the increase in the solubility of the CdS phase as the particle size decreases, has been performed. Comparison of the calculated results with the experimental data shows that the size of colloidal particles is determined to a great extent by kinetic factors of their growth rather than by thermodynamic factors. It has been established that when the size of colloidal particles is less than a critical value, their dissolution by adding strong compexing agents to the system does not result in a change in the observed mean-volume size of the particles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1739–1746, September, 1995.The authors are grateful to A. L. Chuvilin (G. K. Boreskov Institute of Catalysis, SB of the RAS) for help in preparing the electron photomicrographs.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-4816).     

Synthesis of hybrid gold-gold sulfide colloidal particles

The nucleation and growth mechanism of nanometer size gold onto gold sulfide colloidal particles by irradiation-induced reduction is reported. The process is characterized by ultraviolet-visible spectroscopy, electronic diffraction, and high-resolution transmission electron microscopy, allowing for observation of several key intermediates and characteristics of the growth mechanism. The formation mechanism of gold on the surface of the gold sulfide particles is shown to depend strongly on the deposition rate. At low dose rate, gold nucleates preferentially onto specific gold-rich Au2S facets {110}, resulting in epitaxial growth. The gold crystal lattice plastically deforms near the interface to accommodate a substantial lattice mismatch. Upon increasing gold precursor concentration, this low dose rate results in growth of elongated gold island on the gold sulfide surface. At a high dose rate, several randomly oriented gold particles are simultaneously produced on gold sulfide, resulting in a layered structure. The absorption spectra of these particles show a dominant surface plasmon band, whose peak wavelength shifts markedly to the red as layered structure is formed.     

Preparation and optical properties of blue-emitting colloidal CdS nanocrystallines by the solvothermal process using poly (ethylene oxide) as the stabilizer

Blue-emitting colloidal CdS nanocrystals have been synthesized through the solvothermal reaction of cadmium acetate and thiourea in N,N-dimethylformamide using poly(ethylene oxide; PEO) as the stabilizing polymer. The as-prepared CdS colloids were stable at ambient conditions for several weeks. The PEO-stabilized CdS colloids showed a narrow fluorescence band with the maximum at about 420 nm and thus emitting blue fluorescence under the ultraviolet (UV) lamp. A common red shift of fluorescence band is not detected for the prepared CdS colloids in the study, indicating that PEO-stabilized CdS NCs possess few crystalline defects on their surface. In addition, transmission electron microscope micrographs reveal that the sizes of CdS NCs are between 4.4 to 5.4 nm with small standard deviations from 0.5 to 0.7 nm. The particle growth kinetics was studied by monitoring UV-visible absorption onsets versus the reaction time and was found to nearly follow the Lifshitz–Slyozov–Wagner theory for the Ostwald ripening mechanism.     

Preparation of colloidal CdSe and CdS/CdSe nanoparticles from sodium selenosulfate in aqueous polymers solutions

Cadmium selenide nanoparticles formation at the interaction between CdCl2 and Na2SeSO3 in aqueous solutions of sodium polyphosphate and gelatin has been studied. Structural and optical properties of CdSe nanoparticles have been characterized. It has been shown that the temperature and the ratio of reagents concentrations are the basic parameters, controlling the size of CdSe nanoparticles. Photocatalytic activity of CdS nanoparticles in Na2SeSO3 reduction has been found and investigated; structural and optical properties of binary CdS/CdSe nanoparticles have been characterized. This photoreaction, when carried out in the presence of CdCl2, results in the formation of composite CdS/CdSe nanoparticles. It has been shown that slow interaction of adsorbed selenosulfate with surface-trapped CdS conduction band electrons is the limiting stage of the photocatalytic reaction.     

Synthesis of small-sized rhenium sulfide colloidal nanoparticles

Rhenium sulfide colloidal nanoparticles with average size 5.5 nm were synthesized. Characterizations by ultraviolet-visible spectrophotometry, transmission electron microscopy, energy dispersive X-ray spectrum, and X-ray powder diffraction verified the formation of ReS(2) rhenium sulfide colloidal nanoparticles. The colloidal nanoparticles had good stability and they could be stored stably for 1 week in water. Surface modification by organic molecules improved the stability of the rhenium sulfide nanoparticles. The small-sized rhenium sulfide nanoparticles may be useful for their promising applications in tracing diagnosis and therapy of tumor diseases.     

CdS/TiO2 composite films for methylene blue photodecomposition under visible light irradiation and non-photocorrosion of cadmium sulfide

Cadmium sulfide/titanium dioxide (CdS/TiO₂) composite films were grown on glass by the chemical bath deposition (DBQ) and sol-gel/dip coating methods, respectively, in order to increase the photocatalytic activity of TiO₂ in photodegradation processes. The influence of the CdS deposition time on the morphology, optical absorption, and phononic modes of the composites were examined. Scanning electron microscopy (SEM) images showed clearly the CdS deposit on the TiO₂ surface. The absorbance spectra indicated that the absorption of composites depends on the CdS deposition time and the absorption edges are shifted to the visible range. Micro Raman spectra exhibited the phonons associated with the TiO₂ anatase and the longitudinal optic (LO) phonon of CdS whose intensity increases with the CdS deposition time. Photodegradation of methylene blue (MB) under visible light irradiation was observed in all films and the results were compared with those obtained with TiO₂ films. The decomposition is higher for the composite with the CdS deposition time of 15 min. This optimal deposition time allows maximal enhancement of the charge carriers transfer to TiO₂ involved in the photocatalysis. No signal associated with cadmium was detected by the atomic absorption spectroscopy (AAS), which means that the CdS photocorrosion does not occur since trap centers such as OH-Cd-S and Cl^?, which trap holes and inhibit the photocorrosion, are produced during the growth process.