T. A. Lastovina

Copper-based nanoparticles prepared from copper(II) acetate bipyridine complex

The syntheses of CuO, Cu/Cu2O and Cu2O/CuO nanoparticles (NPs) from a single copper(II) acetate bipyridine complex by three different methods, microwave-assisted, solvothermal and borohydride, are reported. The presence of the bipyridine ligand in the copper complex would impose no necessity for additional stabilization during synthesis. The phases of formed NPs were ident- ified by X-ray diffraction. The CuO NPs obtained via solvothermal synthesis from alkaline solution at 160 °C were of ≈11 nm in size. Cu/Cu2O NPs of ≈80 nm were produced via a microwave-assisted polyol procedure at 185-200 °C, where ethylene glycol could play a triple role as a solvent, a reducing agent and a surfactant. Cu2O/CuO NPs of ≈16 nm were synthesized by a borohydride method at room temperature. The interplanar spacing calculated from selected- -area electron diffraction data confirmed the formation of Cu, CuO and Cu2O phases in the respective samples. All NPs were stable and could be used for various applications, including biomedicine.

Structural studies of magnetic nanoparticles doped with rare-earth elements

Magnetic nanoparticles and those doped with rare-earth metal ions having spinel structure were synthesized, possessing the average particles size of 11.3-13.4 nm. According to Mössbauer spectroscopy data it can be concluded that prepared iron oxide nanoparticles are γ-Fe2O3. For materials containing rare-earth elements the decrease of octahedral component surface was observed in comparison to non-doped material, what can be explained by Eu3+, Sm3+ и Gd3+ ions occupying the octahedral position.

Synthesis and structure modeling of ZnS based quantum dots

Quantum dots (QDs) based on zinc sulfide are synthesized by a microwave method in an aqueous medium using dioctyl sodium sulfosuccinate (DS) or 4,4′-bipyridine (BP). Based on the analysis of X-ray diffraction profiles the conclusion is drawn that QDs obtained have a structure of cubic zinc blende with an average particle size of 5.6 nm for the ZnSDS sample and 4.8 nm for ZnSBP. Transmission electron microscopy images show the presence of spherical aggregates of particles only for ZnSDS. FTIR data indicate the presence of sulfate ions in both samples; DS remains in the sample, facilitating the QD agglomeration, while BP is effectively washed out. From the optical diffuse reflectance spectra the band gap is estimated, which turns out to be larger than the expected one due to the presence of elemental sulfur in the samples and partial oxidation of the QD surface. The QD structure based on ZnS particles is also modeled in the work. The possibility to employ X-ray absorption near-edge spectroscopy for the verification of atomic structural parameters around zinc sites in QDs based on zinc sulfide is demonstrated.

Local atomic and electronic structure of quantum dots based on Mn- and Co-doped ZnS

Solid solutions of zinc sulfide with manganese and cobalt are synthesized. Based on the analysis of X-ray diffraction profiles the conclusion is drawn about the formation of a hexagonal wurtzite type structure in the synthesized quantum dot (QD) solutions. The average crystallite sizes are 8 nm and 22 nm for the samples with manganese and cobalt respectively. Results of IR and optical spectroscopy are consistent with the powder X-ray diffraction and X-ray fluorescence data. The question about particle aggregation in isopropanol and DMF solutions is considered. The QD structures based on ZnS particles doped with Mn and Co transition metal atoms are modeled. The possibility to apply X-ray absorption near edge structure (XANES) spectroscopy to verify the atomic structure parameters around the positions of doping transition metal atoms in QDs of the ZnS family is shown. Partial densities of ZnS:Mn and ZnS:Co electronic states are calculated.

Platinum-free catalysts for low temperature fuel cells

In this work, we have successfully prepared Zn/Co-N/C and Zn/Co-Fe/N/C composites, both derived from single zeolitic imidazolate framework (ZIF) precursor Zn/Co-ZIF containing equivalent quantities of Zn and Co metal sites. The composites were formed by pyrolysis of the precursor at 700 °C in inert gas atmosphere as such and after mixing it with Fe(II) salt and 1,10-phenontraline in ethanol. Catalytic tests for oxygen reduction reaction (ORR) in electrochemical cell demonstrated promising results allowing us to consider these composites as potential Pt-free catalysts for low temperature fuel cells.

Novel insight into the effect of disappearance of the Morin transition in hematite nanoparticles

An alternative treatment of the well-known effect of a decrease in the Morin transition temperature in hematite with a decrease in the size of crystallites to the complete disappearance of the transition for nanoparticles smaller than 20 nm is proposed. In contrast to the standard speculative explanation of this effect in terms of the effect of surface and defectiveness of grains, we suggest that the decisive factor is an increase in the contribution of the shape anisotropy of particles with a decrease in their size, which is responsible for the spread of orientations of the axes of the resulting magnetic anisotropy with respect to the crystallographic axes. Our reasons are confirmed by a numerical analysis of Mössbauer spectra of hematite nanoparticles within the continuous model of magnetic dynamics of an ensemble of antiferromagnetic nanoparticles in the two-sublattice approximation generalized to the existence of weak ferromagnetism (Dzyaloshinskii interaction).

Low toxic maghemite nanoparticles for theranostic applications

Background Iron oxide nanoparticles have numerous and versatile biological properties, ranging from direct and immediate biochemical effects to prolonged influences on tissues. Most applications have strict requirements with respect to the chemical and physical properties of such agents. Therefore, developing rational design methods of synthesis of iron oxide nanoparticles remains of vital importance in nanobiomedicine. Methods Low toxic superparamagnetic iron oxide nanoparticles (SPIONs) for theranostic applications in oncology having spherical shape and maghemite structure were produced using the fast microwave synthesis technique and were fully characterized by several complementary methods (transmission electron microscopy [TEM], X-ray diffraction [XRD], dynamic light scattering [DLS], X-ray photoelectron spectroscopy [XPS], X-ray absorption near edge structure [XANES], Mossbauer spectroscopy, and HeLa cells toxicity testing). Results TEM showed that the majority of the obtained nanoparticles were almost spherical and did not exceed 20 nm in diameter. The averaged DLS hydrodynamic size was found to be ~33 nm, while that of nanocrystallites estimated by XRD waŝ16 nm. Both XRD and XPS studies evidenced the maghemite (γ-Fe2O3) atomic and electronic structure of the synthesized nanoparticles. The XANES data analysis demonstrated the structure of the nanoparticles being similar to that of macroscopic maghemite. The Mossbauer spectroscopy revealed the γ-Fe2O3 phase of the nanoparticles and vibration magnetometry study showed that reactive oxygen species in HeLa cells are generated both in the cytoplasm and the nucleus. Conclusion Quasispherical Fe3+ SPIONs having the maghemite structure with the average size of 16 nm obtained by using the fast microwave synthesis technique are expected to be of great value for theranostic applications in oncology and multimodal anticancer therapy.

Theoretical and experimental study of mononuclear Cu(II) acetate-bipyridine complex

Cu(II) acetate-bipyridine complex has been synthesized. A series of experimental and theoretical spectroscopic studies was carried out for the freshly prepared sample. The local atomic and electronic structure was theoretically analyzed based on functional density theory and the structural models of the complex was obtained for various solvents. IR and XANES spectra were experimentally measured and modelled in the framework of functional density theory in a generalized gradient approximation to provide information on the chemical bond and local surroundings of copper. The powder X-ray pattern of the Cu(II) complex was obtained. The measured ESR spectra of the acetate-bipyridine complex at room temperature for the solid sample and solution in DMF confirms the formation of the mononuclear square planar complex.

Gd3+-Doped Magnetic Nanoparticles for Biomedical Applications

Magnetic nanoparticles (MNPs) made of iron oxides with cubic symmetry (Fe3O4, γ-Fe2O3) are demanded objects for multipurpose in biomedical applications as contrast agents for magnetic resonance imaging, magnetically driven carriers for drug delivery, and heaters in hyperthermia cancer treatment. An optimum balance between the right particle size and good magnetic response can be reached by a selection of a synthesis method and by doping with rare earth elements. Here, we present a microwave-assisted polyol synthesis of iron oxide MNPs with actual gadolinium (III) doping from 0.5 to 5.1 mol.%. The resulting MNPs have an average size of 14 nm with narrow size distribution. Their surface was covered by a glycol layer, which prevents aggregation and improves biocompatibility. The magnetic hyperthermia test was performed on 1 and 2 mg/ml aqueous colloidal solutions of MNPs and demonstrated their ability to rise the temperature by 3°C during a 20–30 min run. Therefore, the obtained Gd3+ MNPs are the promising material for biomedicine.

The Atomic Structure of Cu(II) Acetate-Bipyridine Under Thermal Decomposition: An X-Ray Spectroscopy Study

A number of experimental techniques were used to study the changes in the atomic structure of copper(II) acetate-bipyridine under thermal decomposition between 25°C and 700°C to form copper-containing nanoparticles. The dynamics of structural changes during decomposition in a thermogravimetric chamber is compared with X-ray absorption spectra, IR spectra, and diffraction patterns for a sequence of annealing temperatures. The experimental results were used to construct theoretical structural models of the complex under thermal decomposition.