Leszek Stobinski

Molecular hydrogen interactions with discontinuous and continuous thin gold films

Abstract The influence of thin gold film surface nanostructure on H2 chemisorption on unsintered gold films at 78 K was studied. Three classes of thin Au films of different thicknesses were chosen for these experiments, as follows: (i) very thin, purplish colour, transparent film formed by isolated Au islands, (ii) violet–green colour film formed by Au islands joined together and creating a kind of golden net, (iii) non-transparent, continuous Au film of golden colour. It has been found that H2 chemisorption occurs only in the case when the thin Au films are deposited at low temperatures (78 K) and unsintered. It has been suggested that this chemisorption occurs on surface Au atoms of low coordination number as a result of formation of AuH2 complexes, similarly to the compounds arising due to H2 interaction with isolated Au atoms.

Effects of hydrogen, oxygen, and ammonia low-pressure glow plasma on granular starches

Cassava, corn, high amylose corn, potato, rice Indica, rice Japonica, sweet potato, waxy corn, and wheat starches were exposed to low-pressure ammonia, hydrogen, and oxygen plasma. In every case, depolymerization of the starch polysaccharides was noted. The extent of the depolymerization depended on the nature of the starch as well as the type of plasma applied. Among three fractions of polysaccharides distinguished by their molecular weight average, the fraction of the highest molecular weight suffered the most efficient depolymerization. The relative depolymerization for the middle- and low-molecular fractions of polysaccharides was found to be starch and plasma specific. The chemical character of the plasma had very little influence on the starch polysaccharides. Only subtle oxidation effects were observed in oxygen plasma. Low-pressure glow plasma treatment appeared to be a convenient tool for a waste-less dextrinization of starch. Manipulation of the plasma variety and the time of exposure resulted in a wide spectrum of dextrins of various molecular weights and paste-forming properties.

Single-walled carbon nanotube—potato amylose complex

Single-walled carbon nanotubes are wetted in aqueous solution of pure potato amylose and separated into homogenous suspension of nanotubes and sediment of bundled nanotubes. Similarly microcrystalline and colloidal graphite is wetted in the amylose solution whereas C60 fullerenes remained non-wetted. In the micro-Raman spectra of the amylose complexes with single-walled nanotubes, a relatively large shift of the ωD and ωG modes towards a higher wave number was observed. In such a spectra of complexes of microcrystalline and colloidal graphite corresponding shifts were much subtler. These changes in the spectra of nanotubes were accompanied by clear changes in the ratio of the integrated intensities of both the modes. No such changes could be noted in the spectra of amylose complexes with graphite. Optical, SEM and AFM microscopic observations of solidified complexes suggest that small nanotubes could be enveloped by amylose helices.

Single-walled carbon nanotube-amylopectin complexes

Single-walled carbon nanotubes (SWCNTs) are wetted in aqueous solution of pure potato and waxy corn amylopectins. Formation of weak sorption complexes of amylopectins on carbon nanotubes is postulated based on the micro-Raman spectra, differential scanning calorimetric and thermogravimetric studies as well as scanning electron micrographs and atomic force microscope images. Under an influence of ultrasounds bundles of SWCNTs disintegrated much more readily in aqueous solution of waxy corn amylopectin. In the solid state resulting from evaporation of suspensions to dryness interactions of SWCNTs with waxy corn amylopectin were also stronger than with potato amylopectin.

DFT studies of COOH tip-functionalized zigzag and armchair single wall carbon nanotubes

AbstractStructure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory. From 1 to 9 COOH groups were added at the end of the nanotube. The differences in structure and energetics of partially and fully functionalized SWCNTs at one end of the nanotube are observed. Up to nine COOH groups could be added at one end of (9,0) zigzag SWCNT in case of full functionalization. However, for (5,5) armchair SWCNT, the full functionalization was impossible due to steric crowding and rim deformation. The dependence of substituent attachment energy on the number of substituents at the carbon nanotube rim was observed. FigureStructure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory and from 1 to 9 COOH groups was added at the end of the nanotube

Atomic hydrogen solubility in thin gold films and its influence on hydrogen thermal desorption spectra from the surface

Abstract Atomic hydrogen solubility in thin gold films within the temperature interval 250–380 K has been studied, and the exothermic heat of the solution (9 kJ/mol H) has been determined. The influence of predissolved hydrogen concentration on TD spectra from the surface has been shown.

Efficient Modeling of NMR Parameters in Carbon Nanosystems.

Rapid growth of nanoscience and nanotechnology requires new and more powerful modeling tools. Efficient theoretical modeling of large molecular systems at the ab initio and Density Functional Theory (DFT) levels of theory depends critically on the size and completeness of the basis set used. The recently designed variants of STO-3G basis set (STO-3Gel, STO-3Gmag), modified to correctly predict electronic and magnetic properties were tested on simple models of pristine and functionalized carbon nanotube (CNT) systems and fullerenes using the B3LYP and VSXC density functionals. Predicted geometries, vibrational properties, and HOMO/LUMO gaps of the model systems, calculated with typical 6-31G* and modified STO-3G basis sets, were comparable. The (13)C nuclear isotropic shieldings, calculated with STO-3Gmag and Jensens polarization consistent pcS-2 basis sets, were also identical. The STO-3Gmag basis sets, being half the size of the latter one, are promising alternative for studying (13)C nuclear magnetic shieldings in larger size CNTs and fullerenes.

Carbon encapsulated iron oxide nanoparticles surface engineered with polyethylene glycol-folic acid to induce selective hyperthermia in folate over expressed cancer cells.

Carbon encapsulated iron oxide nanoparticles (CEIO-NPs) prepared by carbon arc method were successfully applied for in vitro magnetic hyperthermia. The CEIO-NPs were chemically oxidized and surface modified with PEG-FA for selective tumor localization in cancer cells that over expresses the folate receptors (FR(+)). The size, morphology, heating efficiency, biocompatibility and in vitro cell uptake of CEIO-PEG-FA NPs are extensively characterized. The as-prepared nanoparticles have generated quick heating (43-45°C) upon exposure to an alternating magnetic field (AMF) with the saturation magnetization of 25emu/g. The LDH cytotoxic assay demonstrated that the nanoparticle did not affect the viability of normal human fibroblast. The quantitative and cellular uptake studies by TEM confirmed the selective and increased uptake of CEIO-PEG-FA NPs when compared to the CEIO-nanoparticles. In conclusion, CEIO-PEG-FA NPs have the potential to induce magnetic hyperthermia in FR(+) cells via the receptor mediated endocytosis uptake mechanism.

Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter

We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solutions concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8–1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.

Exposure of granular starches to low-pressure glow ethylene plasma

Polymerization of ethylene was initiated by low-pressure glow plasma generated in this gas. Depending on starch present in this plasma polymerization could be considered either as graft-polymerization of ethylene onto starch or homopolymerization. Result of the treatment of cassava, corn, potato, rice Indica, sweet potato, and waxy corn starches with ethylene plasma was analyzed by means of high-performance size exclusion chromatography, X-ray powder diffraction, thermogravimetry, digestion with β-amylase, and scanning electron microscopy. Analyses suggested that graft-polymerization occurred on sweet potato and rice starch. With other starches homopolymerization of ethylene on granules took place.