Electrochemical modification of Bi2S3 coatings in a nickel plating electrolyte

The electrochemical behavior of Bi₂S₃ coatings in Watts nickel plating electrolyte was investigated using the cyclic voltammetry, electrochemical quartz crystal microbalance, X-ray diffraction, and energy dispersive X-ray analysis methods. During the bismuth sulfide coating reduction in Watts background electrolyte in the potential region from −0.4 to −0.6 V, the Bi₂S₃ and Bi(III) oxygen compounds are reduced to metallic Bi, and the decrease in coating mass is related to the transfer of S²⁻ ions from the electrode surface. When the bismuth sulfide coating is reduced in Watts nickel plating electrolyte, the observed increase in coating mass in the potential region −0.1 to −0.4 V is conditioned by Ni²⁺ ions reduction before the bulk deposition of Ni, initiated by Bi₂S₃. In this potential region, the reduction of Bi(III) oxygen compounds can occur. After the treatment of as-deposited bismuth sulfide coating in nickel plating electrolyte at E = −0.3 V, the sheet resistance of the layer decreases from 10¹³ to 500–700 Ω cm. A metal-rich mixed sulfide Ni₃Bi₂S₂–parkerite is obtained when as-deposited bismuth sulfide coating is treated in Watts nickel plating electrolyte at a potential close to the equilibrium potential of the Ni/Ni²⁺ system and then annealed at temperatures higher than 120 °C.     

Spontaneous Bi-modification of polycrystalline Pt electrode: fabrication, characterization, and performance in formic acid electrooxidation

Spontaneous modification of polycrystalline Pt by irreversibly adsorbed bismuth was performed in BiCl₃ solution in concentrated hydrochloric acid under open-circuit conditions. After spontaneous modification, followed by extensive rinsing with water and drying, the surface was characterized using X-ray photoelectron spectroscopy and electrochemistry. Bi-oxy(chloride), oxide species, and metallic Bi were found at a submonolayer coverage on the Pt surface after spontaneous modification. The electrochemical response of Bi-modified polycrystalline Pt electrode in sulfuric acid solution exhibits a complex multi-peak feature, which is resulting in about constant redox charge (Bi species coverage) in the potential region from 0 to 0.9 V (vs. a standard hydrogen electrode). The spontaneously Bi-modified Pt catalyst in model studies exhibits a superior activity towards formic acid oxidation at fuel cell anode relevant potentials. The catalytic effect of bismuth oxy-species is explained in terms of both inhibition of CO_ad formation and oxidation of CO_ad in reaction with Bi-oxy-species.     

Wada index based on the weighted and truncated Shannon entropy

Nonlinear Dynamics - The Wada index based on the weighted and truncated Shannon entropy is presented in this paper. The proposed Wada index can detect if a given basin boundary is a Wada boundary....     

Platinum–tin complexes as catalysts for the anodic oxidation of borohydride

Platinum–tin complexes were prepared by the reduction of Pt(IV) with Sn(II) in HCl media and studied by light absorption spectrometry, X-ray photoelectron spectroscopy (XPS), and electron microscopy. The formation of three complexes, H₃[Pt(SnCl₃)₅], H₂[Pt(SnCl₃)₂Cl₂], and H₂[Pt₃(SnCl₃)₈], depending on HCl and SnCl₂ concentrations, has been shown. The glassy carbon (GC) electrode modified in the complexes solutions was found to be an electrocatalyst for borohydride oxidation in a 1.0-M NaOH solution. Comparison of BH₄ ⁻ electrooxidation on Pt and on GC modified with platinum–tin complexes has shown that catalytic hydrolysis of BH₄ ⁻ did not proceed in the latter case in contrast to its oxidation on the Pt electrode, and only direct BH₄ ⁻ oxidation has been observed in the positive potentials scan. The activity of Pt–Sn complexes for BH₄ ⁻ oxidation changes with time and eventually decreases due to Sn(II), bound in the complex with Pt(II), oxidation by atmospheric oxygen. The complexes may be renewed by addition of missing amounts of SnCl₂ and HCl.     

Connected generalised Sierpiński carpets

Generalised Sierpiński carpets are planar sets that generalise the well-known Sierpiński carpet and are defined by means of sequences of patterns. We present necessary and sufficient conditions, under which generalised Sierpiński carpets are connected, with respect to Euclidean topology.     

Chemometric analysis of volatiles of propolis from different regions using static headspace GC-MS

Six samples of propolis were analyzed in the paper: a sample from Brazil, Estonia, China and three samples from different locations of Uruguay. Static headspace technique coupled with gas chromatography-mass spectrometry analysis has been applied for the determination of the characteristic volatile profile with the aim to differentiate the propolis from different regions. Monoterpenes (α- and β-pinenes) were predominant in all samples, except the sample from China. This sample separated itself by the alcohols 3-methyl-3-buten-1-ol and 3-methyl-2-buten-1-ol, (40.33% and 11.57%, respectively) and ester 4-penten-1-yl acetate (9.04%). α-Pinene and β-pinene composed 64.59–77.56% of volatiles in Brazilian and Uruguayan propolis, and 29.43% in Estonian propolis. Brazilian propolis was distinguished by a high amount of β-methyl crotonaldehyde (10.11%), one of Uruguayan samples 3- by limonene (15.58%), and the Estonian sample — by eucalyptol (25.95%). Statistical investigation of the samples was made applying principal component, hierarchical cluster and K-Means cluster analyses. Various data pre-processing techniques were proposed and used to study and obtain the important volatile compounds contributed to the differentiation of the propolis samples from different regions to separate clusters.      

Interpretation of fringes produced by time average reflection moiré on a circular disk

Inverse problem of reconstruction of dynamic displacements from the fringe pattern generated by time average reflection moiré is investigated in this paper. A technique for numerical simulation of time average smoothed reflection moiré fringes is proposed. The smoothing procedure is incorporated into the finite element formulation of the problem. Reconstruction of the field of deflections is illustrated for a centrally clamped disk. Such techniques can be effectively exploited in hybrid numerical–experimental procedures for different objects and grating geometries.     

ATRP synthesis and association properties of temperature responsive dextran copolymers grafted with poly(N-isopropylacrylamide)

Temperature responsive copolymers of dextran grafted with poly(N-isopropylacrylamide) (Dex-g-PNIPAAM) were prepared by atom transfer radical polymerization (ATRP) in homogeneous mild conditions without using protecting group chemistry. Dextran macroinitiator was synthesized by reaction of dextran with 2-chloropropionyl chloride at room temperature in DMF containing 2% LiCl. ATRP was carried out in DMF:water 50:50 (v/v) mixtures at room temperature with CuBr/Tris(2-dimethylaminoethyl)amine (Me₆TREN) as catalyst. Several grafted copolymers with well defined number and length of low polydispersity grafted chains were prepared. Temperature induced association properties in aqueous solution were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy and atomic force microscopy (AFM). LCST, ranging from 35 to 41 °C, was significantly affected by number and length of grafted chains. The fine tuning of LCST around body temperature is an important characteristic not obtainable by conventional radical grafting of PNIPAAM. Well defined spherical nanoparticles were formed above the LCST of PNIPAAM. Hydrodynamic diameter was in the range 73-98 nm.