Luminescence of polymer composite materials with cadmium sulfide nanoparticles

The structure and optical characteristics of CdS nanoparticles synthesized in low-density polyethylene were studied. The particles have a hexagonal structure of the greenockite type; the presence of the cubic phase is also possible. The position of the absorption edge slightly depends on the average size of particles because of their polydispersity. It has been shown that the luminescence spectra of nanoparticles are strongly distorted by scattering and self-adsorption in the samples. To correct the spectra, a program for Monte-Carlo simulation of luminescence propagation in the samples was developed. It was shown that the luminescence band at 500–550 nm in the experimental spectra might be spurious because of luminescence absorption in the edge region.     

Synthesis and barrier properties of a film polymer nanocomposite based on polystyrene and cadmium sulfide nanoparticles

A film polymer nanocomposite with nanoparticles of a chalcogenide semiconductor, CdS, in a polystyrene matrix was prepared on the surface of 08kp steel. The barrier properties of the synthesized two-layer film nanomaterial in a 3 wt % aqueous NaCl solution were evaluated by measuring the electrode potential of coated and uncoated specimens and were compared with those of polymer films without nanofiller and with Fe₃O₄ nanoparticles. Introduction of hydrophobic CdS nanoparticles into the polymer matrix leads to significant enhancement (by ～20%, as compared to Fe₃O₄) of the barrier properties of the polymer nanocomposite.     

Cyclic allylic sulfide based photopolymer for holographic recording showing high refractive index modulation

The development and characterization of a new holographic photopolymer system showing high refractive index modulation (∆n) is presented. It exploits the ring-opening polymerization reaction of a cyclic allylic sulfide (CAS) monomer, which is dispersed in a cellulose acetate butyrate (CAB) polymer matrix together with a blue sensitive radical photoinitiator. Volume Phase Holographic Gratings (VPHGs) obtained using these films show a very good fidelity of the transferred pattern, without deviations from the theoretical curves. A high ∆n is obtained due to the addition to this system of a tetrafunctional thiol crosslinker, which maximizes the material potential (formula limit) of the formulation. It also allows for a thermal post process of the gratings, further enhancing the ∆n. The photopolymer properties are evaluated as function of the monomer and thiol concentration to determine the optimal composition, at which a ∆n greater than 0.03 is obtained. This is a considerably high value in the field of photopolymers for holography and it enables the manufacturing of efficient holograms.     

Photochemical synthesis of cadmium sulfide nanoparticles

The formation of cadmium sulfide nanoparticles upon UV irradiation of aqueous solutions of cadmium thiosulfates was established on the basis of spectroscopic and macroscopic data. The yield and size of the cadmium sulfide nanoparticles depend on the ratio of cadmium to thiosulfate ions in solution, the concentration of the solution, and the irradiation duration. The cadmium sulfide nanoparticles with a diameter of 4 nm were obtained by the photolysis of solutions with a concentration of 10⁻³ mol L⁻¹ at the ratio S₂O₃ ²⁻: Cd²⁺ = 2: 1.     

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.     

Properties and biocompatibility of colloid cadmium sulfide nanoparticles

The properties and cytotoxicity of aqueous colloidal solutions of cadmium sulfide CdS nanoparticles obtained by chemical condensation were explored. Dynamic light scattering and optical spectroscopy were used to study the hydrodynamic diameter, size distribution, zeta-potential and optical properties of the CdS nanoparticles in solution. The cytotoxicity of colloidal CdS nanoparticles at different concentrations was assessed on cultures of human dermal fibroblasts and the cancer HeLa line.     

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.     

Determination of ciprofloxacin with functionalized cadmium sulfide nanoparticles as a fluorescence probe

A novel assay of ciprofloxacin with a sensitivity at the microgram level is proposed based on the measurement of enhanced fluorescence intensity signals resulting from the interaction of functionalized nano-CdS with ciprofloxacin. The CdS nanoparticles was synthesized by thioacetamide (TAA) and cadmium nitrate (Cd(NO(3))(2)) in the alkaline solution. At pH 7.4, the fluorescence signals of functionalized nano-CdS were greatly enhanced by ciprofloxacin with the increase concentration of ciprofloxacin. Linear relationship can be established between the enhanced fluorescence intensity and ciprofloxacin concentration in the range of (1.25-8.75)x10(-4) mg mL(-1) ((3.77-26.4) x 10(-4)mmol L(-1)) or (8.75-1200) x 10(-4)mg mL(-1) ((26.4-3625) x 10(-4) mmol L(-1)). The limit of detection is 7.64 x 10(-6) mg mL(-1) (2.31 x 10(-5)mmol L(-1)). Based on this, a new direct quantitative determination method for ciprofloxacin in human serum samples without separation of foreign substances was established. The contents of ciprofloxacin in human serum samples were determined with recovery of 95-105% and relative standard deviation (R.S.D.) of 1.5-2.5%. This method was proved to be very sensitive, rapid, simple and tolerance of most interfering substances.     

Electric conductivity of polymer films filled with magnetic nanoparticles

The conductivity of polymer composites with magnetic nanoparticles (MNP) containing magnetite and other MNP (Ni, Cu–Ni) in the layers and planar cells with Al electrodes is studied. For soluble polymers (polyvinylpyrrolidone and polyvinyl alcohol) containing 1–10 wt % of magnetite MNP, a substantial effect of MNP on surface conductivity is detected over a wide range (from 10^–10 to 10^–3 Ω^–1). It is shown that the addition of magnetite MNP not only results in a considerable change in cell conductivity, but also leads to its partially irreversible variation (by an order of magnitude or more) via minor modifications of the experimental conditions (temperature, electric field). For high-resistance samples with low probabilities of conducting chain formation, temperature current peaks are observed upon moderate heating (up to 350 K). These peaks are similar to the maxima observed upon polymer electret thermodischarges when the charges are captured by the deep centers associated with separate MNP or MNP aggregates. The type and position of the maxima are determined by the characteristics of the polymer matrix. For polyvinylpyrrolidone composites, the maxima are observed some time after heating (the echo effect). With composites based on solventborne polymers (polyalkanesterimides, soluble polyimide) and Ni, Cu–Ni MNP, no change in film conductivity measured electrophotographically is observed, due to the formation of a dielectric coating formed by polymer macromolecules adsorbed on the MNP surface. An explanation based on the possible formation of magnetic aggregates of magnetite MNP and conducting chains is proposed. Magnetic aggregation IPM is proposed as one way of controlling cell conductivity.     

Nanostructural composite photocatalysts based on polycrystalline cadmium sulfide

The results of studies of new photocatalysts—composites of cadmium sulfide with nanoparticles or thin layers of copper(I), silver(I), mercury(I), copper(II), bismuth(III), antimony(III) and iron(III) sulfides—are reviewed. The optical and electrophysical characteristics, the ranges of photosensitivity, the nature of the increased activity and the peculiarities of the photocatalytic effects are discussed. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 22039 Kiev, Science Prosp., 31. Translated from Teoreticheskiya i éksperimental'naya Khimiya, Vol. 33, No. 5, pp. 306–321, September–October, 1997.     

Corona-inhibited photochemical dissolution of aluminum films by polymer compositions

A change in electric conductivity of the polyepoxypropylcarbazole-CBr₄ polymer composition applied onto a vapor-deposited aluminum layer was considered. Under exposure to UV radiation, a photochemical reaction resulting in the dissolution of aluminum and the formation of organometal complexes in the bulk of the polymer composition takes place. It was found that the aluminum dissolution was inhibited by a positive charge induced on the polymer surface by a corona discharge.     

Polarization holographic optical recording based on a new photochromic diarylethene compound

A new unsymmetrical photochromic diarylethene, namely1-[2-methyl-5-(p-N,N-dimethylaminophenyl)-3-thienyl]-2-[2-methyl-5-(3-methoxylphenyl)-3-thienyl] perfluorocyclopentene (1a), was synthesized. The compound showed good photochromism, high sensitivity and remarkable fatigue-resistance both in solution and in poly(methyl methacrylate) (PMMA) matrix with UV/Vis light irradiation. The absorption maximum of its closed-ring isomer was observed at 624 nm in PMMA amorphous film. It is a nice match for the wavelength of the recording laser (633 nm). Using this target compound as recording medium, four types of polarization holographic optical recordings were performed successfully using a He-Ne laser. The results showed that only the orthogonal circular polarization recording could obtain a hologram with high diffraction efficiency and high signal-to noise-ratio. With multiplexing recording technology, three types of polarization multiplexing holographic optical recordings, including angular multiplexing, polarization multiplexing, and angular plus polarization multiplexing holographic recording, were also carried out perfectly based on its photoinduced anisotropic phenomenon accompanying the photochromic reaction by photoirradiation. The results demonstrate that the multiplexing recording technology is an effective method to improve recording capacity when using diarylethene 1 as recording medium.     

Microplate electrochemical DNA detection for phosphinothricin acetyltransferase gene sequence with cadmium sulfide nanoparticles

An electrochemical DNA detection method for the phosphinothricin acetyltransferase (PAT) gene sequence from the transgenetic plants was established by using a microplate hybridization assay with cadmium sulfide (CdS) nanoparticles as oligonucleotides label. The experiment included the following procedures. Firstly target PAT ssDNA sequences were immobilized on the polystyrene microplate by physical adsorption. Then CdS nanoparticle labeled oligonucleotide probes were added into the microplate and the hybridization reaction with target ssDNA sequences took place in the microplate. After washing the microplate for three times, certain amounts of HNO₃ were added into the microplate to dissolve the CdS nanoparticles anchored on the hybrids and a solution containing Cd²⁺ ion was obtained. At last differential pulse anodic stripping voltammetry (DPASV) was used for the sensitive detection of released Cd²⁺ ion. Based on this principle a sensitive electrochemical method for the PAT gene sequences detection was established. The voltammetric currents of Cd²⁺ were in linear range with the target ssDNA concentration from 5.0 × 10^− 13 to 1.0 × 10^− 10 mol/L and the detection limit was estimated to be 8.9 × 10^− 14 mol/L (3σ). The proposed method showed a good promise for the sensitive detection of specific gene sequences with good selectivity for the discrimination of the mismatched sequences.     

A heterostructure composed of conjugated polymer and copper sulfide nanoparticles

A heterostructure formed by a conjugated polymer and semiconducting nanoparticles was produced. The conjugated polymer was synthesized by oxidative copolymerization of 3-thiopheneacetic acid and 3-hexylthiophene, thus obtaining an amphiphilic polythiophene that allows the formation of a stable polymer layer at the air-water interface. Different numbers of monolayers were deposited on solid substrates. CuS nanoparticles were grown directly in the polymeric matrix using the carboxylic groups as nucleation centers. The reactions were monitored by quartz crystal microbalance, Brewster angle, and fluorescence microscopy. The heterostructure showed increased conductivity as compared to the pristine polymer.     

Photoelectrochemical behavior of nanostructural composites based on polycrystalline cadmium sulfide

Nanostructural composites can be used as suspension electrodes; they are made by substitution cadmium(II) at the surfaces of CdS microcrystals for Cu(I, II), Fe(III), Bi(III), and Sb(III). Features are considered in the photoelectrochemical action mechanism of the various nanocomposites. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 79–82, March–April, 1999.     

Rate constant of free electron-hole recombination in thin cadmium sulfide films

The transient decay kinetics of electrons generated in thin cadmium sulfide films by short laser pulses was studied by the microwave photoconductivity method (9 and 36 GHz) at 295 K. The films were prepared by the pulverization method from thiocarbamide coordination compounds. At the high light intensity I ₀ > 10¹⁴ photon cm^–2 per pulse, the decay kinetics of photoelectrons corresponded to a reaction of the second order. Analysis of the kinetic data made it possible to determine the rate constant of recombination of free electrons and holes: k ₃ 2(±1)·10^–13 cm³ s^–1.     

Structural and optical characterization of thermally evaporated cadmium sulfide thin films

The article reports the structural and optical properties of vacuum‐evaporated cadmium sulfide (CdS) films with different thicknesses at room temperature. The structural investigations performed by means of X‐ray diffraction (XRD) technique have showed that all the films have the zinc‐blende structure, a face‐centered cubic form with lattice constants a = b = c = 5.82 Å and point group F4 3m. Crystallite sizes calculated from Scherrer relation are in the range of 173–345 Å. So far, because the optical parameters of the metastable cubic CdS have not been so well known, we apply spectroscopic ellipsometry to determine the thickness, optical constants and energy band gap of CdS thin film deposited by thermal evaporation onto opaque gold substrate, a perfect reflectivity and inert metal. As shown the measured spectral behavior of the optical constants and the band gap value of CdS thin film are in agreement with those obtained by the reflectance and transmittance methods. The energy band gap of CdS thin film determined from the spectral behavior of the absorption coefficient is about 2.46 eV. Copyright © 2008 John Wiley & Sons, Ltd.