A novel method of electrodepositing highly dispersed nano palladium particles on glassy carbon electrode

The volumetric behavior of a chloride complex of palladium was studied at a glassy carbon electrode (GCE). The Pd-IV complex existing on the GCE surface was found, which was proposed to form an octahedral surface complex through coordination to the oxygen atom of an oxygen functional group on the pretreated GCE surface. The ferri/ferrocyanide redox couple was used as a probe to examine the activity of the GCE. X-ray photoelectron spectroscopy provided the evidence of the surface complex existing on the GCE. Highly dispersed Pd particles can be obtained when the surface complexes were reduced electrochemically to Pd atoms. The Pd particles obtained in this way were in nanometer scale and exhibit high catalytic activity towards the oxidation of hydrazine. (C) 1997 Elsevier Science Ltd.

Low-temperature molten salt synthesis and characterization of CoWO4 nano-particles

CoWO4 nano-particles were successfully synthesized at a low temperature of 270 degrees C by a molten salt method, and effects of such processing parameters as holding time and salt quantity on the crystallization and development Of CoWO4 crystallites were initially studied. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). and photoluminescent spectra techniques (PL), respectively. Experimental results showed that the well-crystallized CoWO4 nano-particles with ca. 45 nm in diameter could be obtained at 270 degrees C for a holding time of 8 h with 6:1 mass ratio of the salt to CoWO4 precursor, and XRD analysis evidenced that the as-prepared sample was a pure monoclinic phase Of CoWO4 with wolframite structure. Their PL spectra revealed that the CoWO4 nano-particles displayed a very strong PL peak at 453 nm with the excitation wavelength of 230 nm, and PL properties of CoWO4 crystallites relied on their crystalline state, especially on their particle size. (C) 2009 Elsevier B.V. All rights reserved.

Synthesis of NiWO4 nano-particles in low-temperature molten salt medium

Nickel tungstate (NiWO4) nano-particles were successfully synthesized at low temperatures by a molten salt method, and characterized by Xray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet visible spectra techniques (UV-vis), respectively. The effects of calcining temperature and salt quantity on the crystallization and development of NiWO4 crystallites were studied. Experimental results showed that the well-crystallized NiWO4 nano-particles with about 30 nm in diameter could be prepared at 270 degrees C with 6:1 mass ratio of the salt to NiWO4 precursor. XRD analysis confirmed that the product was a pure monoclinic phase of NiWO4 with wolframite structure. UV-vis spectrum revealed that NiWO4 nano-particles had good light absorption properties in both ultraviolet and visible light region. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Formation of nano-crystalline corrosion products on Zn-Al alloy coating exposed to seawater

Hot dip Zn-Al alloy coating performs better than hot dip galvanized coating and 55% Al-Zn-Si coating as well with regard to general seawater corrosion protection. A characterization of the corrosion products on Zn-Al alloy coating immersed in dynamic aerated seawater has been performed mainly based on transmission electron microscopy (TEM) for morphological analysis and X-ray diffraction (XRD) technique for crystalline phase identification. The XRD and TEM analyses showed that the corrosion products mainly were typical nanometer Zn4CO3(OH)(6).H2O, Zn-5(OH)(8)Cl-2 and Zn6Al2CO3(OH)(16). 4H(2)O microcrystals. This probably is connected to the co-precipitation of Zn2+ and Al3+ ions caused by adsorption. Zn-Al alloy coating being suffered seawater attacks, AI(OH)(3) gel was first produced on the coating surface. Zn and Al hydroxides would co-precipitate and form double-hydroxide when the concentration of adsorbed Zn2+ ions by the newly produced gel exceeded the critical degree of supersaturation of the interphase nucleation. However, because the growth of the crystals was too low to keep in step with the nucleation, a layer of nano-crystalline corrosion products were produced on the surface of the coating finally. (C) 2001 Elsevier Science Ltd. All rights reserved.

Effect of nano-TiO(2)on MP-25 resin

MP-25 resin is a chlorine-containing polymer widely used in coatings. The effects of two types of nano-TiO2 (P-25 and RM301 LP) on MP-25 were studied with saline immersion, UV irradiation, and electrochemical impedance spectroscopy. UV irradiation was evaluated in terms of gloss change and X-ray photoelectron spectroscopy (XPS). The results indicate that, compared to pigment R-930 TiO2, P-25 reduced the immersion resistance and accelerated UV aging of the MP-25 coating, whereas RM301 LP showed the opposite effects. XPS analysis showed that MP-25 resin degraded under UV irradiation via dechlorination and C-C bond breakage, similarly to poly(vinyl chloride), but RM301 LP could inhibit the aging of MP-25 to a certain extent. A skin effect of oxygen and chlorine was identified in MP-25 resin by XPS. RM301 LP could improve the impedance of the MP-25 coating because of its excellent fill capacity. Hence, rutile nano-TiO2 RM301 LP represents an excellent additive for MP-25 resin. (c) 2007 Wiley Periodicals, Inc.

Thermal stability of nano-KH particles and their chemical reactivities

The variation of specific surface area and chemical reactivity of nano-KH particles treated at different temperatures has been studied, The BET surface area of nano-KH decreases with the increase of heat treatment temperature, while the chemical reactivity per unit surface increases steadily. These results indicate that the state of KH surface is changed after heat treatment. Large specific surface area of nano-KH is a major factor for its high chemical reactivity, nevertheless, the surface in an activated state with high surface energy is also an important factor for its high chemical reactivity. Nano-KH alone can polymerize styrene rapidly with the formation of polystyrene.

A high-resolution solid-state NMR study on nano-structured HZSM-5 zeolite

Variations in the structure and acidity properties of HZSM-5 zeolites with reduction in crystal sizes down to nanoscale (less than 100 nm) have been investigated by XRD, TEM and solid-state NMR with a system capable of in situ sample pretreatment. As evidenced by a combination of Al-27 MAS NMR, Si-29 MAS, CP/MAS NMR and H-1 MAS NMR techniques, the downsize of the zeolite crystal leads to an obvious line broadening of the Al-27, Si-29 MAS NMR spectrum, an increasing of the silanol concentration on the external surface, and a pronounced alteration of the acidity distribution between the external and internal surfaces of the zeolite. In a HZSM-5 zeolite with an average size at about 70 nm, the nonacidic hydroxyl groups (silanols) are about 14% with respect to the total amount of Si, while only 4% of such hydroxyl groups exist in the same kind of zeolite at 1000 nm crystal size. The result of H-1 MAS NMR obtained using Fluorinert(R) FC-43 (perfluorotributyl amine) as a probe molecule demonstrates that most of the silanols are located on the external surface of the zeolite. Moreover, the concentration of Bronsted acid sites on the external surface of the nano-structured zeolite appears to be distinctly higher than that of the microsized zeolite.

Characterizations and activities of the nano-sized Ni/Al2O3 and Ni/La-Al2O3 catalysts for NH3 decomposition

A series of nano-sized Ni/Al2O3 and Ni/La-Al2O3 catalysts that possess high activities for NH3 decomposition have been successfully synthesized by a coprecipitation method. The catalytic performance was investigated under the atmospheric conditions and a significant enhancement in the activity after the introduction of La was observed. Aiming to study the influence of La promoter on the physicochemical properties, we characterized the catalysts by N-2 adsorption/desorption, XRD, H-2-TPR, chemisorption and TEM techniques. Physisorption results suggested a high specific surface area and XRD spectra showed that nickel particles are in a highly dispersed state. A combination of XRD, TEM and chemisorption showed that Ni-0 particles with the average size lower, than 5.0 nm are always obtained even though the Ni loading ranged widely from 4 to 63 %. Compared with the Ni/Al2O3 catalysts, the Ni/La-Al2O3 ones with an appropriate amount of promoter enjoy a more open mesoporous structure and higher dispersion of Ni. Reduction kinetic studies of prepared catalysts were investigated by temperature-programmed reduction (TPR) method and the fact that La additive partially destroyed the metastable Ni-Al mixed oxide phase was detailed. (c) 2005 Elsevier B.V. All rights reserved.