SummaryThis work describes a fast, clean and low-cost approach to synthesize ZnS–PVA nanofluids consisting of ZnS nanoparticles homogeneously distributed in a PVA solution. The ZnS nanoparticles were formed by the electrostatic force between zinc and sulfur ions induced by gamma irradiation at a dose range from 10 to 50 kGy. Several experimental characterizations were conducted to investigate the physical and chemical properties of the samples. Fourier transform infrared spectroscopy (FTIR) was used to determine the chemical structure and bonding conditions of the final products, transmission electron microscopy (TEM) for determining the shape morphology and average particle size, powder X-ray diffraction (XRD) for confirming the formation and crystalline structure of ZnS nanoparticles, UV–visible spectroscopy for measuring the electronic absorption characteristics, transient hot wire (THW) and photoacoustic measurements for measuring the thermal conductivity and thermal effusivity of the samples, from which, for the first time, the values of specific heat and thermal diffusivity of the samples were then calculated.

Colloidal silver nanoparticles were synthesized by γ-irradiation-induced reduction method of an aqueous solution containing silver nitrate as a precursor in various concentrations between 7.40×10−4 and 1.84×10−3 M, polyvinyl pyrrolidone for capping colloidal nanoparticles, isopropanol as radical scavenger of hydroxyl radicals and deionised water as a solvent. The irradiations were carried out in a 60Co γ source chamber at doses up to 70 kGy. The optical absorption spectra were measured using UV-vis spectrophotometer and used to study the particle distribution and electronic structure of silver nanoparticles. As the radiation dose increases from 10 to 70 kGy, the absorption intensity increases with increasing dose. The absorption peak λmax blue shifted from 410 to 403 nm correspond to the increase of absorption conduction electron energy from 3.02 to 3.08 eV, indicating the particle size decreases with increasing dose. The particle size was determined by photon cross correlation spectroscopy and the results showed that the particle diameter decreases exponentially with the increase of dose. The transmission electron microscopy images were taken at doses of 20 and 60 kGy and the results confirmed that as the dose increases the diameter of colloidal silver nanoparticle decreases and the particle distribution increases.

ABSTRACT:The electrochemical preparation of polypyrrole (PPY)-poly(vinyl alcohol) (PVA) conducting polymer composite films on an indium-tin oxide glass electrode from an aqueous solution containing a pyrrole monomer, a ptoluene sulfonate electrolyte, and a PVA insulating polymer is reported. The prepared PPY-PVA composite films were characterized by Fourier Transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and conductivity measurements. The FTIR study showed that the composite of PPY and PVA formed through bond formation between PVA and the p-toluene sulfonate dopant anion. The conductivity data of PPY-PVA showed that with increasing PVA concentration in the pyrrole solution, the conductivity of the prepared PPY-PVA film increased up to a certain level due to an increase in conjugation length, and later, it decreased with further increases in the PVA concentration in the solution due to a decrease in conjugation length. This was supported by the FTIR band intensity I 1560 /I 1480 . The TGA results show that the PPY-PVA polymer composite film was thermally more stable than the PPY film. A shielding effectiveness of 45.6 dB was exhibited by the PPY-PVA composite film in the microwave frequency range.

Photocatalysis based on semiconductor quantum dots which utilize the solar energy can be used for the elimination of pollutants from aqueous media and applied for water purification. Degradation of dyes is a standard method to check the photocatalytic activity of any type of photocatalyst. In this paper polyvinyl pyrrolidone (PVP)-capped ZnS and CdS nanoparticles were prepared by a simple microwave irradiation method and studied in detail for their photocatalytic activity in visible range. The obtained nanoparticles were characterized by XRD, TEM, UV-Vis and EDX. The prepared PVP-capped ZnS and CdS nanoparticles have average sizes of $5.1 and 18.3 nm with cubic and hexagonal crystalline structures, respectively. PVP capped CdS nanoparticles exhibited a unique property of optical absorption in visible region with a wave length below than 460 nm followed by a clear long tail up to 700 nm and showed excellent activity toward degradation of dye under visible light illumination. The photocatalytic activity of PVP-capped CdS nanoparticles was found to be improved by mixing with appropriate amount of PVP-capped ZnS nanoprticles. From the study of variation in weight percentages of PVP-capped ZnS nanoparticles, the physical mixture with 20% of PVP-capped ZnS nanoparticles was found to be very efficient for degradation of methylene blue. In this case the degradation efficiency after 6 h illumination was about 81%.

A new sensing area for a sensor based on surface plasmon resonance (SPR) was fabricated to detect trace amounts of mercury and lead ions. The gold surface used for SPR measurements were modified with polypyrrole-chitosan (PPy-CHI) conducting polymer composite. The polymer layer was deposited on the gold surface by electrodeposition. This optical sensor was used for monitoring toxic metal ions with and without sensitivity enhancement by chitosan in water samples. The higher amounts of resonance angle unit (ΔRU) were obtained for PPy-CHI film due to a specific binding of chitosan with Pb2+ and Hg2+ ions. The Pb2+ ion bind to the polymer films most strongly, and the sensor was more sensitive to Pb2+ compared to Hg2+. The concentrations of ions in the parts per million range produced the changes in the SPR angle minimum in the region of 0.03 to 0.07. Data analysis was done by Matlab software using Fresnel formula for multilayer system.

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The crosslinked chitosan thin film had been studied as a sensor element of surface plasmon resonance (SPR) optical sensor. Crosslinked chitosan solution was synthesized by homogeneous reaction of medium molecular weight chitosan in aqueous acetic acid solution with glutaraldehyde as crosslinking agent. It was deposited on gold film by spin coating. Using SPR technique, the optical properties of crosslinked chitosan thin film before and after contacting with different concentration of Pb(II) ion in a range of 0.5-100 ppm had been obtained by fitting. The resonance angle shifted to lower value as the Pb(II) ion concentration increased. Changes in the resonance angle (Δθ) are directly proportional to the concentration of Pb(II) ion solution. X-ray photoelectron spectroscopy (XPS) had been employed to confirm chemical elements and their bonding of the thin film prior to adsorption, as well as chemical interactions involved between Pb(II) ion and the thin film. Keyword: Crosslinked chitosan; Pb(II) ion; Surface plasmon resonance (SPR); X-ray photoelectron spectroscopy (XPS).

Coating of ZnS and CdS nanoparticles with organic and inorganic materials can extend their light absorption in the visible region and their stability against photo-corrosion. Such materials could emerge as excellent photocatalysts for the elimination of pollutants from aqueous media using solar energy. In this study, PVP (polyvinyl pyrrolidone)-capped ZnS and CdS nanoparticles, ZnS/CdS and CdS/ZnS core shell nanoparticles were synthesized by microwave irradiation method and characterized using different techniques. The XRD patterns exhibited cubic and hexagonal structures for coated ZnS and CdS nanoparticles, respectively. Morphological evaluation of TEM images showed that the nanoparticles are generally spherical in shape. The UV-visible spectra confirmed a shift in the band gap of coated nanoparticles to longer or shorter wavelengths due to size and potential-well effects. The photocatalytic activity of nanoparticles toward dye degradation under visible light was found to be improved after coating. PVP-capped ZnS and CdS exhibited an enhancement in the initial methylene blue degradation efficiency by a factor of about 1.3. ZnS nanoparticles coated by CdS displayed the initial efficiency 3.2 times higher than bare ZnS. The maximum dye removal was obtained in presence of CdS/ZnS core shells which is 1.4 times more efficient than bare CdS.