Catalytic Activity of Ni Nanotubes Covered with Nanostructured Gold

Ni nanotubes (NTs) were produced by the template method in the pores of ion-track membranes and then were successfully functionalized with gold nanoparticles (Ni@Au NTs) using electroless wet-chemical deposition with the aim to demonstrate their high catalytic activity. The fabricated NTs were characterized using a variety of techniques in order to determine their morphology and dimensions, crystalline structure, and magnetic properties. The morphology of Au coating depended on the concentration of gold chloride aqueous solution used for Au deposition. The catalytic activity was evaluated by a model reaction of the reduction of 4-nitrophenol by borohydride ions in the presence of Ni and Ni@Au NTs. The reaction was monitored spectrophotometrically in real time by detecting the decrease in the absorption peaks. It was found that gold coating with needle-like structure formed at a higher Au-ions concentration had the strongest catalytic effect, while bare Ni NTs had little effect. The presence of a magnetic core allowed the extraction of the catalyst with the help of a magnetic field for reusable applications.

Quartz Tuning Fork Sensor-Based Dosimetry for Sensitive Detection of Gamma Radiation

This study generally relates to nuclear sensors and specifically to detecting nuclear and electromagnetic radiation using an ultrasensitive quartz tuning fork (QTF) sensor. We aim to detect low doses of gamma radiation with fast response time using QTF. Three different types of QTFs (uncoated and gold coated) were used in this study in order to investigate their sensitivity to gamma radiations. Our results show that a thick gold coating on QTF can enhance the quality factor and increase the resonance frequency from 32.7 to 32.9 kHz as compared to uncoated QTF. The results also show that increasing the surface area of the gold coating on the QTF can significantly enhance the sensitivity of the QTF to radiation. We investigated the properties of gold-coated and uncoated QTFs before and after irradiation by scanning electron microscopy. We further investigated the optical properties of SiO2 wafers (quartz) by spectroscopic ellipsometry (SE). The SE studies revealed that even a small change in the microstructure of the material caused by gamma radiation would have an impact on mechanical properties of QTF, resulting in a shift in resonance frequency. Overall, the results of the experiments demonstrated the feasibility of using QTF sensors as an easy to use, low-cost, and sensitive radiation detector.

ACCELERATION OF ELECTRON BUNCHES USING PERIODIC DIELECTRIC STRUCTURES WITH AND WITHOUT COATING

The numerical studies of high acceleration gradients obtaining for the dielectric laser accelerators (DLA) based on-chip structures with one-sided laser excitation at a wavelength of 800 nm are presented. The electron flight heights of 200 and 400 nm over a structure are presented. The influence of the geometric parameters of the structures on the acceleration gradients was also investigated. A study of changes in the acceleration gradients of structures, when applying a gold coating on these types of structures, has been carried out.

Enhanced Microsphere-Assisted Picosecond Laser Processing for Nanohole Fabrication on Silicon via Thin Gold Coating

The nanohole arrays on the silicon substrate can effectively enhance the light absorption in thin film silicon solar cells. In order to optimize the solar energy absorption, polystyrene microspheres with diameters of 1 μm are used to assist picosecond laser with a wavelength of 1064 nm to fabricate nanohole arrays on silicon substrate. The experimental results show that the morphology and size of the silicon nanoholes strongly depend on the laser fluence. At 1.19–1.59 J/cm2 laser fluences, well-ordered arrays of nanoholes were fabricated on silicon substrate, with diameters domain from 250 to 549 nm and depths ranging from 60 to 99 nm. However, large amounts of sputtered nanoparticles appeared around the silicon nanoholes. To improve the surface morphology of silicon nanoholes, a nanolayered gold coating is applied on silicon surface to assist laser processing. The results show that, for gold-coated silicon substrate, sputtered nanoparticles around the nanoholes are almost invisible and the cross-sectional profiles of the nanoholes are smoother. Moreover, the ablation rate of the nanoholes on the gold-coated silicon substrate have increased compared to that of the nanoholes on the uncoated one. This simple method allows fast fabrication of well-ordered nanoholes on silicon substrate without sputtered nanoparticles and with smooth inner surface.

Phase composition of autoclave oxidation products and its effect on gold coating

This paper describes the mineralogical studies of the solid products of autoclave oxidation. These products were obtained during autoclave pilot tests at a temperature of 225 oС and total pressure 3.25 МPa. Autoclave tests were carried out on the samples of sulfide gold-bearing concentrate of the Malomyr deposit. Mineralogical studies were provided using Mossbauer spectrometry, scanning electron microscope, X-ray fluorescence and X-ray diffraction analysis. It was found that the solid autoclave residues consist of basic ferric arsenate sulfate (Fe(AsO4)x(SO4)y(OH)z·wH2O), sodium jarosite (KFe3(SO4)2(OH)6), basic ferric sulfate (Fe(OH)SO4) and gangue minerals (muscovite, quartz, feldspars and others). The main relationships of the phase transformations in the autoclave oxidation process were described. Data obtained during these studies shows that some part of the gold may be associated with a secondary arsenic-containing phase formed in the autoclave oxidation process. This gold may be isolated from cyanidation solution and remain in the tailings. It was considered to subject the autoclave slurry to an additional treatment — Hot Cure process. This can minimize the loss of the precious metal during autoclave aftertreatment. As a result, a part of the secondary soluble phases (up to 10–50%) decomposes and dissolves. After that gold becomes accessible to the cyanide solution during sorption cyanidation. The increase in precious metal recovery is 2–5% for various samples.

Почему наночастицы магнетит/золото со структурой ядро-оболочка недостаточно хороши и как их улучшить

In this paper a short review of experimental and theoretical recent researches of magnetic core-shell nanoparticles with noble metals shell is given. Magnetic nanoparticles of Fe3O4 coated with a gold shell are in demand in many biomedical applications. However, there are practically no good nanoparticles completely and uniformly coated with gold. In this paper, we investigated the formation of a chemical bond at the magnetite/gold interface. In the framework of DFT-GGA calculations, the geometric structure, electronic and magnetic properties of flat layers consisting of Fe3O4 magnetite, titanium, and gold are studied. It is established that the specific energy and wetting parameters of the magnetite-gold interface are negative, while these values of the magnetite-titanium (for thin Ti layers) and magnetite-titanium-gold boundaries are positive. This allows us to hope that an intermediate thin layer of titanium at the boundary between the surface of the magnetite nanoparticle and the gold layer will stabilize this three-layer structure and allow obtaining magnetite nanoparticles coated with a solid gold coating.