ABSTRACT
In this work, we studied the local adsorption properties of gold, nickel, and platinum nanoparticles. A correlation was established between the chemical properties of massive and nanosized particles of these metals. The formation of a stable adsorption complex M-Aads on the nanoparticles' surface was described. It was shown that the difference in local adsorption properties is caused by specific contributions of nanoparticle charging, the deformation of its atomic lattice near the M-C interface, and the hybridization of the surface s- and p-states. The contribution of each factor to the formation of the M-Aads chemical bond was described in terms of the Newns-Anderson chemisorption model.
ABSTRACT
The oxidation of Ni nanoparticles supported on highly oriented pyrolytic graphite was investigated under conditions of low exposure to oxygen by methods of scanning tunneling microscopy and spectroscopy. It was found that charge transfer effects at the Ni-C interface influenced the surface activity of the nanoparticles. The O2 dissociation and the Ni oxidation were shown to occur only at the top of the nanoparticle, while the border of the Ni-C interface was the less preferable area for these processes. The O2 dissociation was inhibited, and atomic oxygen diffusion was suppressed in the given nanosystem, due to the decrease in holes concentration.
ABSTRACT
Because of the effort to preserve petroleum resources and promote the development of eco-friendly materials, bio-based polymers produced from sustainable resources have attracted great attention. Among them, polylactide (PLA) and natural rubber (NR) present prominent polymers with unique barrier and mechanical features. A series of samples with improved phase compatibility were obtained by blending PLA and NR using a double-rotor mixer. A plasticizing and enhancing effect on the polymers' compatibility was achieved by using epoxidized soybean oil (ESO) as a natural plasticizer and compatibilizer. ESO compounding in the PLA-NR blends increased the mobility of the biopolymer's molecular chains and improved the thermal stability of the novel material. The size of the NR domains embedded in the continuous PLA matrix decreased with the ESO content increment. The combination of thermal analysis and scanning electron microscopy enabled the authors to determine the features of potential packaging material and the optimal content of PLA-NR-ESO for the best mechanical properties.
ABSTRACT
The adsorption of CO on the surface of Cu-based nanoparticles was studied in the presence of an external electric field by means of scanning tunneling microscopy (STM) and spectroscopy (STS). Nanoparticles were synthesized on the surface of a graphite support by the impregnation-precipitation method. The chemical composition of the surface of the nanoparticles was determined as a mixture of Cu2O, Cu4O3 and CuO oxides. CO was adsorbed from the gas phase onto the surface of the nanoparticles. During the adsorption process, the potential differences ΔV = +1 or -1 V were applied to the vacuum gap between the sample and the grounded tip. Thus, the system of the STM tip and sample surface formed an asymmetric capacitor, inside which an inhomogeneous electric field existed. The CO adsorption process is accompanied by the partial reduction of nanoparticles. Due to the orientation of the CO molecule in the electric field, the reduction was weak in the case of a positive potential difference, while in the case of a negative potential difference, the reduction rate increased significantly. The ability to control the adsorption process of CO by means of an external electric field was demonstrated. The size of the nanoparticle was shown to be the key factor affecting the adsorption process, and particularly, the strength of the local electric field close to the nanoparticle surface.
ABSTRACT
Compositions of polylactide (PLA) and poly(3-hydroxybutyrate) (PHB) thermoplastic polyesters originated from the nature raw have been obtained by blending under shear deformations and electrospinning methods in the form of films and nanofibers as well as unwoven nanofibrous materials, respectively. The degrees of crystallinity calculated on the base of melting enthalpies and thermal transition temperatures for glassy state, cold crystallization, and melting point for individual biopolymers and ternary polymer blends PLA-PHB- poly(ethyleneglycol) (PEG) have been evaluated. It has been shown that the mechanical properties of compositions depend on the presence of plasticizers PEG with different molar masses in interval of 400-1000. The experiments on the action of mold fungi on the films have shown that PHB is a fully biodegradable polymer unlike PLA, whereas the biodegradability of the obtained composites is determined by their composition. The sorption activity of PLA-PHB nanofibers and unwoven nanofibrous PLA-PHB composites relative to water and oil has been studied and the possibility of their use as absorbents in wastewater treatment from petroleum products has been demonstrated.
ABSTRACT
An experimental study of molecular hydrogen adsorption on single gold nanoparticles of various sizes deposited on the surface of highly oriented pyrolytic graphite (HOPG) was carried out by means of scanning tunneling microscopy and spectroscopy. The effect of size on the HOPG/Au system was established. Hydrogen was dissociatively chemisorbed on the surface of gold nanoparticles with an average size of 5â»6 nanometers. An increase in the size of nanoparticles to 10 nm or more led to hydrogen chemisorption being inhibited and unable to be detected.
