No abstract

Zinc oxide (ZnO) nanoparticles are synthesized using a simple chemical method at room temperature. A variation in molar concentration of the precursor, potassium hydroxide, from 0.25 to 0.01 mol L −1 is accompanied by a decrease in the average size of the nanoparticles. These nanoparticles are used for the preparation of polystyrene/ZnO nanocomposite films using the spin-coating technique. These films are found to be highly transparent throughout the visible region and absorb UV light in the region from 395 to190 nm, almost covering the near and middle UV ranges (400 to 200 nm). This observation highlights the possible prospects of these films in UV shielding applications. The wavelength corresponding to the onset of UV absorption is found to be blue shifted with a decrease in size of the ZnO particles in the composite films due to confinement effects. The photoluminescence spectra of the composite films also change as a function of particle size. The emissions at longer wavelength due to defects and impurity-related states in ZnO are almost quenched as a result of surface modification by the polymer matrix. The observed band-gap enlargement with a decrease in size of the ZnO particles in the composite films is significant for band-gap engineering of nanoparticles for various applications.

Composites of nanocrystalline iron disulfide (FeS2) coated with poly(vinyl pyrrolidone) (PVP) or poly(vinyl alcohol) (PVA) have been successfully synthesized using a solvothermal process, in which PVP and PVA serve as soft templates. Transparent, flexible thin films of these nanocomposites were prepared from homogeneous solution using a solution‐casting approach. X‐ray diffraction and thermogravimetric analysis and energy‐dispersive X‐ray, Fourier transform infrared and UV‐visible absorption spectroscopic techniques were employed to study the structural and optical properties of these nanocomposite films. UV‐visible spectra in transmission mode reveal the UV‐shielding efficiency of these nanocomposite films and the films are found to be exceptionally good for UV‐shielding applications in the wavelength range 200 to 400 nm. The present work aims at developing transparent and flexible UV‐shielding materials and colour filters using cost‐effective and non‐toxic inorganic–polymer nanocomposites. © 2012 Society of Chemical Industry

Biocompatible and highly luminescent manganese doped zinc sulfide (ZnS:Mn) nanocrystals of average particle size 10 nm have been synthesized by capping with a novel amino acid ligand, L-citrulline. Though there are many reports on the bioimaging applications of nanostructured semiconductors, the present study focused on the detection of a special type of metal accumulating bacteria, Lysinibacillus fusiformis. This bacterium has significant applications in the disposal of metal components from industrial effluents. In this context, the detection of this bacterium is quite important and the present work demonstrates a novel technique for this bacterial detection. The synthesized nanocrystals were attached to Lysinibacillus fusiformis and characteristics of the bioconjugated system were studied. The blue shift observed in the ultraviolet-visible absorption and photoluminescence spectra of the bioconjugated system, confirms conjugation of the Lysinibacillus fusiformis with L-citrulline-capped ZnS:Mn. When the bioconjugated system (capped ZnS:Mn + bacteria) was observed using a fluorescent microscope under excitation wavelengths 365.4 nm (ultraviolet), 435.8 nm (blue) and 546.1 nm (green), fluorescence emissions were obtained in yellow, green and red regions respectively. The study of relative growth of Lysinibacillus fusiformis in the presence of L-citrulline-capped ZnS:Mn proves biocompatible property of these nanocrystals and their tunable color properties under different excitation wavelengths make them ideal for biolabeling applications.