Anca Dumbrava

Dependence of ZnO-based dye-sensitized solar cell characteristics on the layer deposition method

The selection of a proper method for the semiconductor layer deposition is an important requirement towards a high efficiency for dye-sensitized solar cells (DSSCs). We compared three techniques for deposition of the semiconductor thin layer in ZnO-based DSSCs, in order to determine the dependence between the deposition method, the ZnO film properties and finally the DSSCs characteristics. For this purpose, we varied the method used for deposition of the semiconductor film and we replaced ZnO with Al-doped ZnO. The nanostructured films morphology was analysed by transmission electron microscopy, high-resolution transmission electron microscopy and selected area electron diffraction. The optical properties were examined by UV–visible spectroscopy and the bandgap energies were calculated using the Tauc equation. The higher fill factor value was registered for DSSCs based on the ZnO film obtained by electrochemical method, but the higher efficiency was registered for doctor-blading method.

Considerations about the Dependence of PEGylated ZnS Nanoparticles Properties on the Synthesis Method

Abstract We studied the dependence between properties and synthesis method for PEGylated ZnS nanoparticles. Thus, we proposed the PEGylation of ZnS nanopowder, in non-aqueous medium, by a facile one-pot synthesis in very mild conditions, as an alternative for the chemical precipitation of PEGylated ZnS in an aqueous solution, and we compared the properties of zinc sulfide obtained by both methods. The structure and morphology of PEGylated ZnS nanopowders were investigated by X-ray diffraction and transmission electron microscopy, and the FTIR spectra confirmed the PEGylation of ZnS nanoparticles. The values for band gap energy are in good accordance with the quantum confinement effect for nanocrystals. The mean dimension of particles was calculated, on the basis of UV–Vis spectra, by using the Brus equation and it is in good agreement with the crystallites size, determined from X-ray diffraction. The photocatalytic properties of synthesized nanopowders were tested in the degradation of Congo red azo dye, demonstrating a faster bleaching of dye in the presence of PEGylated ZnS prepared in non-aqueous medium. The photoluminescence properties are also dependent on the synthesis method and can be correlated with the surface modifications by PEG.

Seasonal variation and speciation of dissolved iron in an artificial surface water body

Abstract The aquatic chemistry of iron is an important issue since iron is a micronutrient for the growth of phytoplankton. Its concentration in surface waters involves many environmental aspects, from the quality of a particular water to the control of atmospheric carbon dioxide. Dissolved iron can exist in water as ferrous and ferric iron, and the equilibrium between these two forms, as well as the precipitation and solubilization of iron, depends on many natural and anthropic factors. We studied the variation for an year of Fe(II) and total iron concentration into Poarta Alba - Midia Navodari Canal, an artificial surface water which connects Danube River with Black Sea. The results indicate a high iron concentration in surface water and a seasonal variation of iron concentration and speciation, which can be correlated with the oxidable matter content.