Mechanochemical Solvent-Free Synthesis of Quaternary Semiconductor Cu-Fe-Sn-S Nanocrystals.

In this study, we demonstrate a one-pot mechanochemical synthesis of the nanocomposite composed of stannite Cu2FeSnS4 and rhodostannite Cu2FeSn3S8 nanocrystals using a planetary ball mill and elemental precursors (Cu, Fe, Sn, S). By this approach, unique nanostructures with interesting properties can be obtained. Methods of XRD, Raman spectroscopy, UV-Vis, nitrogen adsorption, SEM, EDX, HRTEM, STEM, and SQUID magnetometry were applied. Quaternary tetragonal phases of stannite and rhodostannite with crystallite sizes 18-19 nm were obtained. The dominant Raman peaks corresponding to the tetragonal stannite structure corresponding to A-symmetry optical modes were identified in the spectra. The bandgap 1.25 eV calculated from UV-Vis absorption spectrum is very well-acceptable value for the application of the synthesized material. The SEM micrographs illustrate the clusters of particles in micron and submicron range. The formation of agglomerates is also illustrated on the TEM micrographs. Weak ferromagnetic properties of the synthesized nanocrystals were documented.

CdS/ZnS nanocomposites: from mechanochemical synthesis to cytotoxicity issues.

CdS/ZnS nanocomposites have been prepared by a two-step solid-state mechanochemical synthesis. CdS has been prepared from cadmium acetate and sodium sulfide precursors in the first step. The obtained cubic CdS (hawleyite, JCPDS 00-010-0454) was then mixed in the second step with the cubic ZnS (sphalerite, JCPDS 00-005-0566) synthesized mechanochemically from the analogous precursors. The crystallite sizes of the new type CdS/ZnS nanocomposite, calculated based on the XRD data, were 3-4 nm for both phases. The synthesized nanoparticles have been further characterized by high-resolution transmission electron microscopy (HRTEM) and micro-photoluminescence (µPL) spectroscopy. The PL emission peaks in the PL spectra are attributed to the recombination of holes/electrons in the nanocomposites occurring in depth associated with Cd, Zn vacancies and S interstitials. Their photocatalytic activity was also measured. In the photocatalytic activity tests to decolorize Methyl Orange dye aqueous solution, the process is faster and its effectivity is higher when using CdS/ZnS nanocomposite, compared to single phase CdS. Very low cytotoxic activity (high viability) of the cancer cell lines (selected as models of living cells) has been evidenced for CdS/ZnS in comparison with CdS alone. This fact is in a close relationship with Cd(II) ions dissolution tested in a physiological solution. The concentration of cadmium dissolved from CdS/ZnS nanocomposites with variable Cd:Zn ratio was 2.5-5.0 µg.mL(-1), whereas the concentration for pure CdS was much higher - 53 µg.ml(-1). The presence of ZnS in the nanocrystalline composite strongly reduced the release of cadmium into the physiological solution, which simulated the environment in the human body. The obtained CdS/ZnS quantum dots can serve as labeling media and co-agents in future anti-cancer drugs, because of their potential in theranostic applications.

Preparation of CuO/ZnO nanocomposite and its application as a cysteine/homocysteine colorimetric and fluorescence detector.

Cysteine and homocysteine play a crucial role in many biological functions but abnormal levels of these amino acids may lead to various forms of pathogenesis. Therefore, selective and easy-to-use methods for the detection of cysteine and homocysteine are essential for the early diagnosis of developing diseases. In this paper we report on a rapid, straightforward and highly selective method for the detection of cysteine (Cys) and homocysteine (Hcy) which uses a CuO/ZnO nanocomposite as a dual colorimetric and fluorometric assay. The presence of Cys and Hcy in a solution of these nanorods (NRs) induces a change in its color from light blue to dark grey which is visible to the naked eye. This is accompanied by a blue shift in the absorption spectra from 725 nm to 650 nm and a decrease in the intensity of CuO/ZnO nanocomposite emission. These changes are ascribed to the reduction of Cu(II) to Cu(0), and the oxidation of cysteine (homocysteine) and subsequent formation of the disulfide bond. This novel assay method does not respond to any other amino-acid which is present in living organisms; therefore the selective determination of cysteine (homocysteine) with a lower analyte limit of 40 µM (4.8 µg mL(-1)) can be carried out in aqueous solutions without the need for any sophisticated instrumentation, fluorophore molecules or complicated procedures.

The dual role of sulfur-containing amino acids in the synthesis of IV-VI semiconductor nanocrystals: a mechanochemical approach.

PbS@cystine nanocrystals were synthesized mechanochemically, with lead acetate and L-cystine being used as the lead and sulfur precursors, respectively. The resulting nanocrystals are 22-34 nm in size, well-faceted and octahedral in shape. Characterization by XRD, FT-IR, NMR, FE-SEM, EDS, TEM (HRTEM) and surface area measurement methods showed that the particles are single, defect-free crystals with a high crystallinity. Furthermore, the crystals were prepared using a solvent-free procedure that was performed under ambient temperature and atmospheric pressure.