Katarzyna Balin

Conversion of Natural Tannin to Hydrothermal and Graphene-Like Carbons Studied by Wide-Angle X-ray Scattering

The atomic structure of carbon materials prepared from natural tannin by two different techniques, high-temperature pyrolysis and low-temperature hydrothermal carbonization, was studied by wide-angle X-ray scattering. The obtained diffraction data were converted to the real space representation in the form of pair distribution functions. The X-ray photoelectron spectroscopy measurements provided information about the chemical state of carbon in tannin-based materials that was used to construct final structural models of the investigated samples. The results of the experimental data in both reciprocal and real spaces were compared with computer simulations based on the PM7 semiempirical quantum chemical method. Using the collected detailed information, structural models of the tannin-based carbons were proposed. The characteristics of the investigated materials at the atomic level were discussed in relation to their preparation method. The rearrangement of the tannin molecular structure and its transformation to graphene-like structure was described. The structure of tannin-based carbons pyrolyzed at 900 °C exhibited coherently scattering domains about 20 Å in size, consisting of two defected atomic layers and resembling a graphene-like arrangement.

Unique properties of silver and copper silica-based nanocomposites as antimicrobial agents

The paper reports a new route for the fabrication and determination of physicochemical properties and biological activity, of metallic silica-based nanostructure (Ag/SiO2, Cu/SiO2). A research studies shows mono-dispersed nanoparticles in silica matrix with an average size of 12 nm for silver, as well as 12 nm and 4 nm, respectively for copper in hydrophobic and hydrophilic silica composites. The chemical analysis highlights metallic silver and copper ions heterogeneously distributed in the composite as well as metallic oxides such as Ag2O, Cu2O and CuO in hydrophobic system, and CuO in hydrophilic one. Structural research evidences the presence of amorphous, stoichiometric and non-stoichiometric crystalline phase of silica. Biological studies reveal potentially inhibition of growth gram-positive and gram-negative bacteria as well as microscopic fungi. The size of metal nanoparticles and level of silica hydrophobicity show the highest inhibition bacterial growth for hydrophilic system with embedding inside them, 4 nm in size copper nanoparticles. Finally, cytotoxic interaction against human cells with respect to silver and copper silica-based nanocomposites was not found.

Ni-Supported Pd Nanoparticles with Ca Promoter: A New Catalyst for Low-Temperature Ammonia Cracking.

In this paper we report a new nanometallic, self-activating catalyst, namely, Ni-supported Pd nanoparticles (PdNPs/Ni) for low temperature ammonia cracking, which was prepared using a novel approach involving the transfer of nanoparticles from the intermediate carrier, i.e. nano-spherical SiO2, to the target carrier technical grade Ni (t-Ni) or high purity Ni (p-Ni) grains. The method that was developed allows a uniform nanoparticle size distribution (4,4±0.8 nm) to be obtained. Unexpectedly, the t-Ni-supported Pd NPs, which seemed to have a surface Ca impurity, appeared to be more active than the Ca-free (p-Ni) system. A comparison of the novel PdNPs/Ni catalyst with these reported in the literature clearly indicates the much better hydrogen productivity of the new system, which seems to be a highly efficient, flexible and durable catalyst for gas-phase heterogeneous ammonia cracking in which the TOF reaches a value of 2615 mmolH2/gPd min (10,570 molNH3/molPd(NP) h) at 600°C under a flow of 12 dm3/h (t-Ni).

Catalytic Gas-Phase Glycerol Processing over SiO2-, Cu-, Ni- and Fe- Supported Au Nanoparticles.

In this study, we investigated different metal pairings of Au nanoparticles (NPs) as potential catalysts for glycerol dehydration for the first time. All of the systems preferred the formation of hydroxyacetone (HYNE). Although the bimetallics that were tested, i.e., Au NPs supported on Ni, Fe and Cu appeared to be more active than the Au/SiO2 system, only Cu supported Au NPs gave high conversion (ca. 63%) and selectivity (ca. 70%) to HYNE.

Reduced fecundity and cellular changes in Acheta domesticus after multigenerational exposure to graphene oxide nanoparticles in food

Despite the fact that the demand for graphene and its derivatives in commercial applications is still growing, many aspects of its toxicity and biocompatibility are still poorly understood. Graphene oxide, which is released into the environment (air, soil and water) as so-called nanowaste or nanopollution, is able to penetrate living organisms. It is highly probable that, due to its specific nature, it can migrate along food chains thereby causing negative consequences. Our previous studies reported that short-term exposure to graphene oxide may increase the antioxidative defense parameters, level of DNA damage, which results in numerous degenerative changes in the gut and gonads. The presented research focuses on reproductive dysfunction and cellular changes in Acheta domesticus after exposure to GO nanoparticles in food (concentrations of 20 and 200 μg·g-1 of food) throughout their entire life cycle. The results showed that long-term exposure to GO caused a significant decrease in the reproductive capabilities of the animals. Moreover, the next generation of A. domesticus had a lower cell vitality compared to their parental generation. It is possible that graphene oxide can cause multigenerational harmful effects.

Magnetic properties of Eu-Fe thin films

We studied the formation of alloys and compounds of the Eu-Fe binary system, in the form of thin films, prepared using molecular beam epitaxy. Diffraction and photoelectron spectroscopy investigations revealed mixing of the elements during the annealing at relatively low temperature. Magnetic studies showed ferromagnetic behavior up to 400 K, and strong thermomagnetic effects and exchange bias indicating the presence of an antiferromagnetic phase and superparamagnetic particles. X-ray photoemission microscopy with dichroic contrast confirmed this hypothesis, showing two types of Eu-Fe alloys with various stoichiometries and showing ferromagnetically ordered particles of 100–500 nm in size. Ferromagnetic particles contain divalent Eu atoms, whereas the antiferromagnetic alloy is probably composed of the trivalent Eu atoms detected in the photoelectron spectra.