Platinum nanoparticles on the antimony-doped tin dioxide surface: Quantum-chemical modeling

The interaction of Pt₂₉ nanoparticles with pristine and reduced (110) and (100) SnO₂ surfaces doped with Sb has been modeled using the density functional theory method within the generalized gradient approximation (GGA). It has been demonstrated that the introduction of antimony contributes to dispersion of substrate particles and, in some cases, leads to an increase in the energy of interaction with platinum and to the fixation of platinum nanoparticles on the surface.     

醋酸盐共沉淀法制备锑掺杂二氧化锡(ATO)粉体

在较低的温度下将锡粉和三氧化二锑溶于冰醋酸并通过共沉淀,成功制备了锑掺杂二氧化锡(ATO)纳米粉体.采用XRD、SEM、TEM、N_2等温吸/脱附及粉末电阻率测试仪等对其结构、形貎和导电性进行表征,并研究了锑掺杂浓度对ATO导电性能的影响.结果表明:随着锑掺杂量的增加,ATO粉体电阻率有一最低值,即在锑掺杂浓度为8%时,ATO粉体电阻率可达0.4Ω·cm;ATO粉体的一次粒径约为5nm,其比表面高达85.9m~2/g.     

An electron microscope study of some titanium sulphides

Crystals of titanium sulphides of nominal composition Ti_1.25S₂ (Ti₅S₈), Ti_1.50S₂ (Ti₃S₄), and Ti_1.60S₂ (Ti₄S₅) have been prepared and studied by transmission electron microscopy. Lattice fringe resolution has shown faulting to be commonplace in the Ti_1.25S₂ and Ti_1.50S₂ compositions, but infrequent in the Ti_1.60S₂ material. In all crystals, repeat distances between lattice fringes have been found which do not correspond to previously reported titanium sulphides and are considered to arise from new structures. Diffraction evidence supports this view. Although it is likely that the existence of these new structures is due to different titanium to sulphur stoichiometries, the possibility that they are polytypes or due to impurities is also considered.     

An electron microscope study of some nonstoichiometric tungsten oxides

Large crystals of WO₃ have been reduced to a composition of approximately WO_2.91 at 3 different temperatures, 950, 1000, and 1070°C. After reduction the crystals were examined by optical microscopy and transmission electron microscopy. The crystals were faulted in a variety of ways and rarely perfectly ordered. Large crystals heated at 1070°C supported oxygen loss by formation of {103} CS planes while crystals heated at 950°C contained {102} CS planes. At 1000°C {102} and {103} CS planes coexisted. It was found that the way in which the WO₃ structure accommodated oxygen loss was a function of composition and of temperature. In all experiments, some vapour transport also took place, resulting in the growth of needle shaped crystals. These were always members of the W_xO_3n?2 homologous series of oxides, and contained {103} CS planes, irrespective of the formation temperature.     

Adsorption study of micropore structure of tin dioxide

The micropore structure of xerogels of tin dioxide prepared by precipitation is studied by the physical adsorption of N₂, O₂, and H₂ at -195.6°C. The parameters of the microstructure as a whole depend on the adsorbate. The specific surface area of supermicropores measured by the oxygen adsorption exceeds that measured by nitrogen adsorption, and the extent of excess increases linearly with an increase in the supermicropore volume. The samples of tin dioxides have molecular-sieve properties, but they do not contain ultramicropores measurable by the adsorption of molecular hydrogen.     

Effect of drying periods on antimony-doped tin dioxide-coated titanium electrode

The present work investigated the drying period effect on the activity, morphology, crystallinity, and other properties of antimony-doped tin dioxide-coated titanium electrodes prepared by coating pyrolysis method. The drying period is found to be an important factor affecting the electrode activity. The antimony content in the electrode decreased when the drying period increased. Simultaneously, crack width, Sn3d_5/2 binding energy, crystallite size, catalyst loading, and resistivity increased with the drying time. The results showed that the electrode prepared with the drying time of 10 min had the highest activity towards phenol degradation in the series under study.     

Spectroelectrochemistry of cytochrome c and azurin immobilized in nanoporous antimony-doped tin oxide

Stable immobilization of two redox proteins, cytochrome c and azurin, in a thin film of highly mesoporous antimony-doped tin oxide is demonstrated via UV-vis spectroscopic and electrochemical investigation.     

Planar defects in Mo2BC. An electron microscope study

Structural relationships between Mo₂BC, σ-MoB, β-MoB, and β-MoC_1?x are described and possibilities for planar intergrowth defects (Wadsley defects) and nonstoichiometry are considered. The term chemical stacking fault is proposed. Electron microscopy of Mo₂BC specimens revealed crystals that were rich in planar defects with widths consistent with the defects postulated.     

The effect of dopant’s valence (+III and +V) on the anion/cation uptake properties of antimony-doped tin dioxide

Antimony is perhaps the most frequently used doping element of tin dioxide. Although antimony of different oxidation states have been used in the synthesis, the effect of dopant’s valence on ion exchange properties has not been investigated critically. In our study the valence of antimony had clear effects on the metal uptake properties of Sb-doped SnO₂ materials. Extremely high Tc uptake (Kd > 100 000 mL g⁻¹) on Sb(III)-doped material was observed in conditions under which Sb(V)-doped material did not show any Tc uptake. However, the Sb(V)-doped material showed good Ni²⁺ uptake properties (Kd up to 33 000 mL g⁻¹), even at pH values below the material’s point of zero charge (pzc), while the Sb(III)-doped material showed Ni²⁺ uptake only at pH above its pzc. The cation uptake of Sb-doped SnO₂ resembles typical weakly acidic cation exchanger character but the uptake of TcO₄- does not follow a typical anion exchange pattern. Instead, we propose a sorption process related to redox reactions as the probable Tc uptake process.     

An electron microscope study of perovskite-related oxides in the SrTiO system

In order to investigate the relationship between nonstoichiometry and the static dielectric constant, phases in the SrOTiO₂ pseudo-binary system have been studied by X-ray diffraction and electron microscopy. Three ternary oxides were found in the temperature interval 1373–1673°K, Sr₂TiO₄, Sr₃Ti₂O₇, and SrTiO₃. In all of these oxides, nonstoichiometry seems to be taken up by coherent intergrowth of lamellae of various homologous oxides Sr_n+1Ti_nO_3n+1 The results are discussed in terms of the crystal chemistry of the perovskite oxides and factors which influence the magnitude of the static dielectric constant of solids.     

An improved visual tracking method in scanning electron microscope

Since their invention, nanomanipulation systems in scanning electron microscopes (SEMs) have provided researchers with an increasing ability to interact with objects at the nanoscale. However, most nanomanipulators that are capable of generating nanometer displacement operate in an open-loop without suitable feedback mechanisms. In this article, a robust and effective tracking framework for visual servoing applications is presented inside an SEM to achieve more precise tracking manipulation and measurement. A subpixel template matching tracking algorithm based on contour models in the SEM has been developed to improve the tracking accuracy. A feed-forward controller is integrated into the control system to improve the response time. Experimental results demonstrate that a subpixel tracking accuracy is realized. Furthermore, the robustness against clutter can be achieved even in a challenging tracking environment.     

Dopants in nanocrystalline tin dioxide

The review surveys studies aimed at constructing new materials for gas sensors based on nanocrystalline tin dioxide. The influence of doping with various impurities (Pt, Pd, Ru, Rh, Cu, Ni, or Fe) on the composition, microstructure, and electrophysical and sensor properties of nanocrystalline SnO₂ was discussed. The conditions for the preparation of powders and thick and thin SnO₂ films by the wet chemical method and aerosol pyrolysis of organometallic compounds are reported. The mechanism of interaction of pure and doped nanocrystalline SnO₂ with a gas phase was analyzed based on the data from Mossbauer, Auger electron, and X-ray photoelectron spectroscopy and the results of in situ Raman spectroscopy, XANES, and conductivity measurements.     

Formation of tin dioxide pore structure

Formation of tin dioxide pore structure has been studied under various hydrogel precipitation conditions. Desired volumes of micro-and mesopores can be obtained when the pH and precipitation temperature are controlled. A relationship between the initial salt hydrolysis rate and the oxide phase nucleation rate appears to be of key importance. Peculiarities of thermal treatment of tin dioxide xerogel are shown.     

Structure and dehydration of hydrous tin dioxide xerogel

Hydrous tin dioxide xerogel with the composition SnO2 · 1.75H₂O is built of tin-oxygen-hydroxide fragments. Water molecules (no more than 1 mol) in the grain structure are kept by hydrogen bonds. Xerogel is dehydrated in the range 50–890°C in two stages. Below 123°C, molecular water is removed and the polycondensation of ≡Sn-O(H)-Sn≡ bridge groups occurs. There also takes place the transition of some water molecules from the molecular to hydroxide form as follows: ≡Sn-O-Sn≡ + H₂O → 2≡Sn-O-H. All processes occur within individual grains. Above 123°C, water removal is due to the polycondensation of tin-oxygen groups. As a result, grains are coarsen. After 200°C, their structure is determined as cassiterite coated by tin oxyhydrate.     

Physicochemical and functional properties of modified tin dioxide

Specimens of tin dioxide with modifying Sb and Pt additives are synthesized. Their physicochemical properties (specific surface area, porosity, and conductivity), chemisorption and catalytic activity in the model reaction of CO oxidation are studied. A considerable chemisorption of CO on SnO₂ and SnO₂-SbO _x is observed at 150–180°C. The oxidation of CO in the flow of gases starts in the same temperature range. An addition of platinum leads to a significant increase in the rate of CO oxidation, the reaction starts at 80°C. It is proposed that the process proceeds at the SnO₂/Pt interface.     

Vanadium doped tin dioxide as a novel sulfur dioxide sensor

Considering the short-term exposure limit of SO2 to be 5 ppm, we first time report that semiconductor sensors based on vanadium doped SnO2 can be used for SO2 leak detection because of their good sensitivity towards SO2 at concentrations down to 5 ppm. Such sensors are quite selective in presence of other gases like carbon monoxide, methane and butane. The high sensitivity of vanadium doped tin dioxide towards SO2 may be understood by considering the oxidation of sulfur dioxide to sulfur trioxide on SnO2 surface through redox cycles of vanadium-sulfur-oxygen adsorbed species.     

Mechanochemical synthesis of nanosize tin dioxide powders

Structural parameters, dispersity, morphology, and magnetic properties of a tin dioxide-magnetite nanosize composite material mechanochemically synthesized from salt systems were studied. The possibility of using the composite nanopowder as a sorbent for nucleic acids was analyzed.     

Preparation of stable aqueous suspensions of antimony-doped tin oxide nanoparticles used for transparent and thermal insulation fluorocarbon coating

In order to prepare the highly stable aqueous suspensions of antimony-doped tin oxide (ATO) used for the transparent and thermal insulation fluorocarbon coating, the effect of sodium polyacrylate (PAAS) and polyvinyl alcohol (PVA) on the stability of the suspensions was investigated. The stability and dispersity of the suspensions were characterized using zeta potential analyzer, ultraviolet–visible spectrophotometer, and scanning electron microscope. No sediments were observed after 6-month storage of the ATO suspensions containing 0.1 wt% PAAS and 2.0 wt% PVA. The reason why aqueous suspensions were capable of stabilization was explained from a theoretical perspective. A new model of steric hindrance for colloid particles stabilized by binary dispersant was proposed, which may have positive contribution to other colloid system containing two dispersants. A nano-composite fluorocarbon coating, exhibiting a good thermal insulation and high transmittance, was formed after ATO suspensions were added in fluorocarbon emulsion. The temperature inside the chamber was decreased by 6.0 °C, and 75.0 % visible light rays could pass through the coating.