Thermogravimetric analysis of layered double hydroxides intercalated with sulfate and alkaline cations [M62+Al3(OH)18][A+(SO4)2] 12H2O (M2+ = Mn,Mg, Zn; A+ = Li,Na, K)

Journal of Thermal Analysis and Calorimetry - The synthesized phases with chemical composition $$\left[ {{\text{M}}^{2 + }_{6} {\text{Al}}_{3} \left( {\text{OH}} \right)_{18} } \right]\left[...     

Improvement of the electrochemical properties of “as-grown” boron-doped polycrystalline diamond electrodes deposited on tungsten wires using ethanol

The electrochemical properties of boron-doped diamond (BDD) polycrystalline films grown on tungsten wire substrates using ethanol as a precursor are described. The results obtained show that the use of ethanol improves the electrochemistry properties of “as-grown” BDD, as it minimizes the graphitic phase upon the surface of BDD, during the growth process. The BDD electrodes were characterized by Raman spectroscopy, scanning electronic microscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The boron-doping levels of the films were estimated to be ∼10²⁰ B/cm³. The electrochemical behavior was evaluated using the and redox couples and dopamine. Apparent heterogeneous electro-transfer rate constants were determined for these redox systems using the CV and EIS techniques. values in the range of 0.01–0.1 cm s⁻¹ were observed for the and redox couples, while in the special case of dopamine, a lower value of 10⁻⁵ cm s⁻¹ was found. The obtained results showed that the use of CH₃CH₂OH (ethanol) as a carbon source constitutes a promising alternative for manufacturing BDD electrodes for electroanalytical applications.     

Photoelectrode characteristics of an organic bilayer in water phase containing a redox molecule

We have recently reported that the organic bilayer of 3,4,9,10-perylenetetracarboxyl-bisbenzimidazole (PTCBI, n-type semiconductor) and 29H,31H-phthalocyanine (H₂Pc, p-type semiconductor), which is a part of a photovoltaic cell, acts as a photoanode in the water phase (Abe et al., ChemPhysChem 5:716, [2004]); in that case, the generation of the photocurrent involving an irreversible thiol oxidation at the H₂Pc/water interface took place to be coupled with hole conduction through the H₂Pc layer, based on the photophysical character of the bilayer. In the present work, the photoelectrode characteristics of the bilayer were investigated in the water phase containing a redox molecule , where the photo-induced oxidation and reduction for the couple were found to take place at the bilayer. The photoanodic current involving the oxidation efficiently occurred at the interface of H₂Pc/water, similar to the previous example. In the view of the voltammograms obtained, it was noted that there are pin-holes in the H₂Pc layer of the bilayer, leading to a cathodic reaction with at the PTCBI surface especially in the dark; that is, the band bending at the PTCBI/water interface can essentially be reduced by applying a negative potential [e.g., < ∼ 0 V (vs Ag/AgCl)] to the PTCBI, when the cathodic reaction may take place through the conduction band of the PTCBI. Moreover, under that applied potential condition of irradiation, the photogenerated electron carrier part can move to the PTCBI surface, thus enhancing the reduction of .     

Mechanism of the catalyzed by cysteine electroreduction of the insoluble in water cobalt(II) salt as a component of carbon paste electrode

The mechanism of the Co(II) catalytic electroreduction of water insoluble CoR₂ salt in the presence of cysteine was developed. CoR₂ = cobalt(II) cyclohexylbutyrate is the component of a carbon paste electrode. Electrode surface consecutive reactions are: (a) fast (equilibrium) reaction of the complex formation, (b) rate-determining reversible reaction of the promoting process of CoR(Ac⁺) complex formation, (c) rate-determining irreversible reaction of the electroactive complex formation with ligand-induced adsorption, and (d) fast irreversible reaction of the electroreduction. Reactions (a,b) connected with CoR₂ dissolution and reactions (c,d) connected with CoR₂ electroreduction are catalyzed by . Regeneration of (reactions “b,d”) and accumulation of atomic Co(0) (reaction “d”) take place. Experimental data [Sugawara et al., Bioelectrochem Bioenergetics 26:469, 1991]: i _a vs E (i _a is anodic peak, E is cathodic accumulation potential), i _a vs , and i _a vs pH have been quantitatively explained.     

Extraction kinetics of Uranium(VI) and Thorium(IV) with Tri-iso-amyl phosphate from nitric acid using a Lewis Cell

The extraction kinetics of uranium(VI) and thorium(IV) with Tri-iso-amyl phosphate (TiAP) from nitric acid medium has been investigated using a Lewis Cell. Especially, dependences of the extraction rate on stirring speed, temperature, interfacial area were firstly measured to elucidate the extraction kinetics regimes. The experimental results demonstrated that extraction kinetic of U(VI) is governed by chemical reactions at interface with an activation energy, E_a, of 43.41 kJ/mol, while the rate of Th(IV) extraction is proved to be intermediate controlled, of which the E_a is 23.20 kJ/mol. Reaction orders with respect to the influencing parameters of the extraction rate are determined, and the rate equations of U(VI) and Th(IV) at 293 K have been proposed as $$ {\text{r}} = - {\text{dcUO}}_{ 2} \left( {{\text{NO}}_{ 3} } \right)_{ 2} /{\text{dt}} = 1. 80 \times 10^{ - 3} \left[ {{\text{UO}}_{ 2} \left( {{\text{NO}}_{ 3} } \right)_{ 2} } \right]^{ 1.0 1} \left[ {\text{TiAP}} \right]^{0. 5 5} , $$ $$ {\text{r}} = - {\text{dcTh }}\left( {{\text{NO}}_{ 3} } \right)_{ 4} /{\text{dt}} = 1. 8 8\times 10^{ - 3} \left[ {{\text{Th }}\left( {{\text{NO}}_{ 3} } \right)_{ 4} } \right]^{ 1.0 4} \left[ {\text{TiAP}} \right]^{ 1. 7 7} \left[ {{\text{HNO}}_{ 3} } \right]^{0. 3 8} , $$ respectively.     

Influence of Substituents in β-Cyclodextrin on the Interaction of Levofloxacin–β-Cyclodextrin Complexes with Liposomal Membrane

Colloid Journal - The effect of substituents (polar CH2CH(OH)CH3, hydrophobic CH3, and charged $${{\left( {{\text{C}}{{{\text{H}}}_{{\text{2}}}}} \right)}_{{\text{4}}}}{\text{SO}}_{3}^{ - }$$ ) in...     

On the charge storage mechanism at RuO<Subscript>2</Subscript>/0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript> interface

Comparative study of capacitative properties of RuO₂/0.5 M H₂SO₄ and Ru/0.5 M H₂SO₄ interfaces has been performed with a view to find out the nature of electrochemical processes involved in the charge storage mechanism of ruthenium (IV) oxide. The methods of cyclic voltammetry and scanning electron microscopy (SEM) were employed for the investigation of electrochemical behavior and surface morphology of RuO₂ electrodes. It has been suggested that supercapacitor behavior of RuO₂ phase in the potential E range between 0.4 and 1.4 V vs reference hydrogen electrode (RHE) should be attributed to double-layer-type capacitance, related to non-faradaic highly reversible process of ionic pair formation and annihilation at RuO₂/electrolyte interface as described by following summary equation:

Thermal investigations of SmFeTeO6 and SmCrTeO6 compounds

SmFeTeO₆ and SmCrTeO₆ were synthesized by heating the respective oxides in molar quantities and characterized by X-ray technique. Thermogravimetric studies suggested that SmFeTeO₆ and SmCrTeO₆ vapourize incongruently according to the reactions: $$ \begin{aligned} {\text{SmFeTeO}}_{ 6}{({\text{s}})} & \to {\text{SmFeO}}_{ 3} {( {\text{s}})} + {\text{TeO}}_{ 2} {( {\text{g}})} + \left( { 1/ 2} \right){\text{O}}_{ 2}{( {\text{g}})} \\ {\text{SmCrTeO}}_{ 6} {( {\text{s}})} & \to {\text{SmCrO}}_{ 3} {( {\text{s}})} + {\text{TeO}}_{ 2}{( {\text{g}})} + \left( { 1/ 2} \right){\text{O}}_{ 2}{( {\text{g}})}. \\ \end{aligned} $$ X-ray diffraction data of both the compounds have been indexed on the hexagonal system. Partial pressures of TeO₂(g) were measured over SmFeO₃(s) and SmCrO₃(s) by employing the Knudsen effusion mass loss technique. The standard Gibbs free energy of formation of (Δ_f G°) SmFeTeO₆(s) and SmCrTeO₆(s) were obtained from partial pressures and represented by the following relations: $$\Updelta_{\text{f}} G^{\circ} \left( {{\text{SmFeTeO}}_{6}{( {{\text{s}},\,T})}} \right) \pm 2 5\,{\text{kJ}}\,{\text{mol}}^{ - 1} = - 1 5 1. 6 5+ 0. 1 5\left(T \right)\quad \left( 1 ,0 90{-} 1,1 80\,{\text{K}} \right) \\ \Updelta_{\text{f}} G^{\circ } \left( {{\text{SmCrTeO}}_{ 6} {( {{\text{s}},\,T})}} \right) \pm 2 5\,{\text{kJ}}\,{\text{mole}}^{ - 1} = - 2 5 2. 8 6+ 0. 1 2(T)\quad \left( { 1,100 {-} 1 , 1 7 5\,{\text{K}}} \right).$$      

Efficient strategy for quality control of screen-printed carbon ink disposable sensor electrodes based on simultaneous evaluation of resistance,capacitance and Faradaic current by Fourier transform AC voltammetry

Two types of mass-produced, screen-printed carbon ink-based macrodisc electrodes suitable for routine sensing applications have been fabricated. Microscopic examination of these carbon ink electrode surfaces reveals that their surfaces are both rough and highly heterogeneous, consisting of random arrays of carbon particles of different sizes, as well as binder. Consequently, they may suffer from a lack of reproducibility in their performance because of variable resistance, capacitance or electroactive area. Use of a Fourier transform AC voltammetric protocol involving application of periodic waveform obtained from summation of five sine waves of variable frequency enabled resistance and capacitance, as well as DC and AC Faradaic currents associated with the model processes or (where FcMeOH is ferrocene methanol) to be assessed from a single experiment. Such data, which may be obtained rapidly via this approach, are highly suitable for quality control assessment.     

System Zn–Rh–O: heat capacity and Gibbs free energy of formation using differential scanning calorimeter and electrochemical cell

The standard molar Gibbs free energy of formation of ZnRh₂O₄(s) has been determined using an oxide solid-state electrochemical cell wherein calcia-stabilized zirconia (CSZ) was used as an electrolyte. The oxide cell can be represented by: . The electromotive force was measured in the temperature range from 943.9 to 1,114.2 K. The standard molar Gibbs energy of formation of ZnRh₂O₄(s) from elements in their standard state using the oxide electrochemical cell has been calculated and can be represented by: . Standard molar heat capacity C ^o _p,m(T) of ZnRh₂O₄(s) was measured using a heat flux-type differential scanning calorimeter in two different temperature ranges, from 127 to 299 and 307 to 845 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: . The heat capacity of ZnRh₂O₄(s), was used along with the data obtained from the oxide electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K.     

Investigations on NH4VO3 thermal decomposition in dry air

The results of investigations on thermal decomposition of NH₄VO₃ in dry air have been presented. TG?CDSC measurements were carried out under non-isothermal conditions at linear change of samples temperature in time and under isothermal conditions. Characterization of the products structure was performed by XRD method. MS method was used to determine evolved gaseous products. The decomposition of NH₄VO₃ was described by the following equation: $$ 6 {\text{NH}}_{ 4} {\text{VO}}_{ 3} \to \, \left( {{\text{NH}}_{ 4} } \right)_{ 3} {\text{V}}_{ 6} {\text{O}}_{ 1 6} \to \, \left( {{\text{NH}}_{ 4} } \right)_{ 2} {\text{V}}_{ 6} {\text{O}}_{ 1 6} \to {\text{ V}}_{ 2} {\text{O}}_{ 5}.$$      

Binuclear cobalt(II/II) and cobalt(II/III) chelates with O<Subscript>2</Subscript>N<Subscript>2</Subscript> ligands: synthesis,structure and magnetic studies

Abstract  The title complexes and have been synthesized in excellent yields by reacting Co(OAc)₂·4H₂O with H₂L¹ and H₂L², respectively, in acetonitrile solution. Here, [L¹]²⁻ and [L²]²⁻ are the deprotonated forms of N,N-bis(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine and N,N-bis(2-hydroxybenzyl)-2-picolylamine, respectively. The crystal structures of and were determined by x-ray crystallography. In , each cobalt atom has distorted trigonal bipyramid geometry, while in , each cobalt atom has distorted octahedral geometry. Variable temperature magnetic moment measurements show weak antiferromagnetic interaction in . The magnetic characterization for is in agreement with the presence of Co(II) and Co(III) centers. Graphical Abstract  The title complexes and have been synthesized in excellent yields by reacting Co(OAc)₂·4H₂O with dianionic N₂O₂ coordinating ligands. In complex 1, each cobalt atom has distorted trigonal bipyramid geometry, while in complex 2, each cobalt atom has distorted octahedral geometry. Variable temperature magnetic moment measurements show weak antiferromagnetic interaction in complex 1. The magnetic characterization for complex 2 is in agreement with the presence of Co(II) and Co(III) centers. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Reaction graphs and a construction of reaction networks

Summary A general definition of reaction graphs is presented. For a pair of isomeric molecular graphs and , related by a chemical transformation , the reaction graph is determined using a maximal common subgraph defined for vertex mapping . A binary operation defined for graphs constructed over the same vertex set enables us to decompose the reaction graph into the sum of prototype reaction graphs. A decomposition of an overall reaction graph can be advantageously used for the construction of a reaction network. An oriented path in this network beginning at and ending at corresponds to a breakdown of the transformation into a sequence of intermediates.     

Thermal decomposition kinetics of bis(pyridine)manganese(II) chloride

The thermal stability and the decomposition steps of bis(pyridine)manganese(II) chloride (Mn(py)₂Cl₂) were determined by thermogravimetry and derivative thermogravimetry. The initial compound and the solid compounds resulted from each step of decomposition were characterized by FT-IR spectroscopy and RX diffraction. It was pointed out that at the progressive heating of Mn(py)₂Cl₂, the following decomposition reactions occur: I $$ {\text{Mn}}\left( {\text{py}} \right)_{ 2} {\text{Cl}}_{ 2} \left( {\text{s}} \right) \, \to {\text{ Mn}}\left( {\text{py}} \right){\text{Cl}}_{ 2} \;\left( {\text{s}} \right) \, + {\text{ Py }}\left( {\text{g}} \right) $$ II $$ {\text{Mn}}\left( {\text{py}} \right){\text{Cl}}_{ 2} \left( {\text{s}} \right) \, \to {\text{ Mn}}\left( {\text{py}} \right)_{ 2/ 3} {\text{Cl}}_{ 2} \;\left( {\text{s}} \right) \, + { 1}/ 3 {\text{ Py }}\left( {\text{g}} \right) $$ III $$ {\text{Mn}}\left( {\text{py}} \right)_{ 2/ 3} {\text{Cl}}_{ 2} \left( {\text{s}} \right) \, \to {\text{ MnCl}}_{ 2} \left( {\text{s}} \right) \, + { 2}/ 3 {\text{ Py }}\left( {\text{g}} \right) $$ The dependence of the activation energy of these decompositions steps on the conversion degree, evaluated by isoconversional methods, shows that all decomposition reactions are complex. The mechanism and the corresponding kinetic parameters of reaction (I) were determined by multivariate non-linear regression program and checked for quasi-isothermal data. It was pointed out that the reaction (I) consists of three elementary steps, each step having a specific kinetic triplet.     

Electrodeposition of metals on anodized thin Nb films

The influence of the electronic properties of oxidized Nb surfaces on the electrodeposition of metals (Me=Co, Cu, Ag) with different equilibrium potentials is studied by conventional electrochemical techniques and atomic force microscopy. The results show that relatively thin anodic Nb₂O₅ films (thickness <11 nm) present a frequency-dependent n-type semiconductor behavior, which can be described by the theory of amorphous semiconductor. The Schottky barrier, formed at the a-Nb₂O₅/electrolyte interface, affects the deposition rate of metals with equilibrium potentials more positive than the flat band potential Then, the dependence of density of states on the oxide thickness and anodization conditions leads to different extents of the band bending, affecting directly the rate of electron transfer.     

Paradigms and Paradoxes: Diazomethane and Ethyl Diazoacetate: The Role of Substituent Effects on Stability

Diazomethane and ethyl diazoacetate are highly reactive and highly versatile synthetic reagents that undergo numerous related reactions. However, while the former is highly dangerous because of its toxicity and explosive behavior; the latter is much more benign. This is usually ascribed to resonance stabilization in ethyl diazoacetate involving an extra carbonyl group that is absent in diazomethane, cf. $$\begin{gathered} {\text{EtOOC}}---{\text{CH}} = {\rm N}^ + = {\rm N}^ - \leftrightarrow {\rm E}{\text{tOOC}}---{\text{CH}}^ - ---{\text{N}}^{\text{ + }} \equiv {\text{N}} \leftrightarrow {\text{EtOC(O}}^ - {\text{)}} = {\text{CH}}---{\text{N}}^{\text{ + }} \equiv {\rm N} \hfill \\ {\text{CH}}_{\text{2}} = {\rm N}^ + = {\rm N}^ - \leftrightarrow {\text{CH}}_{\text{2}}^ - ---{\text{N}}^{\text{ + }} \equiv {\rm N} \hfill \\ \end{gathered}$$ The additional resonance stabilization is derived using a recent literature measurement of the enthalpy of an ethyl diazoacetate/aldehyde reaction, key enthalpies of formation, also from the literature, and some simplifying assumptions. The resonance stabilization is deduced to be but 16 kJ/mol, merely 4 kcal/mol. But, oh how grateful we are for this!     

Electrochemical study of the thermodynamics and kinetics of hydrophilic ion transfers across water | <Emphasis Type="Italic">n</Emphasis>-octanol interface

Thermodynamics and kinetics of hydrophilic ion transfers across water|n-octanol (W|OCT) interface have been electrochemically studied by means of novel three-phase and thin-film electrodes. Three-phase electrodes used for thermodynamics measurements comprise edge plane pyrolytic graphite, the surface of which was partly modified with an ultrathin film of OCT, containing hydrophobic lutetium bis(tetra-tert-butylphthalocyaninato) (Lu[tBu₄Pc]₂) as a redox probe. The transfers of anions and cations from W to OCT were electrochemically driven by reversible redox transformations of Lu[tBu₄Pc]₂ to chemically stable lipophilic monovalent cation and anion , respectively. Upon reduction of Lu[tBu₄Pc]₂, the transfers of alkali metal cations from W to OCT have been studied for the first time, enabling estimation of their Gibbs transfer energies. For kinetic measurements, a thin-film electrode configuration has been used, consisting of the same electrode covered completely with a thin layer of OCT that contained the redox probe and a suitable electrolyte. Combining the fast and sensitive square-wave voltammetry with thin-film electrodes, the kinetics of , , and Cl⁻ transfers have been estimated. Dedicated to Professor Dr. Yakov I. Tur’yan on the occasion of his 85th birthday.     

It spectroscopic study of the interaction of chlorosilanes with the surface of aerosil

The surface-chemical reactions of the chlorosilanes

$$\left( {\begin{array}{*{20}c} {} & {} & {} & {{\text{CH}}_{\text{3}} } & {} & {} & {{\text{CH}}_{\text{3}} } & {} \\ {} & {} & {} & {} & {} & {} & {} & {} \\ {{\text{CL}}_{\text{3}} {\text{SiH,}}} & {{\text{CL}}_{\text{3}} {\text{Si}}} & {} & {} & {,{\text{ ClSi}}} & {} & {} & {\text{H}} \\ {} & {} & {} & {} & {} & {} & {} & {} \\ {} & {} & {} & {\text{H}} & {} & {} & {{\text{CH}}_{\text{3}} } & {} \\ {} & {} & {} & {} & {} & {} & {} & {} \\ \end{array} } \right)$$     

Palladized aluminum as a novel substrate for electrosynthesis of polyaniline in sulfuric acid solutions

The electropolymerization of aniline on a palladized aluminum electrode (Pd/Al) by potentiodynamic as well as potentiostatic methods is described. The effect of the monomer concentration between 0.01 and 0.4 M on the polyaniline (PANI) formation and its growth on the Pd/Al electrode was investigated and a suitable concentration of 0.2 M is suggested. A similar study was carried out to investigate the effect of sulfuric acid concentration and 0.1 M sulfuric acid was chosen. A study on the influence of electropalladization time on the polymer formation and its growth suggested a convenient time of 40 s. The stability of the PANI film on the Pd/Al electrode was studied as function of the potential imposed on the electrode. For applied electrode potentials of 0.1–0.7 V, the first-order degradation rate constant, k, of PANI film varies between 1×10⁻⁶ and 2×10⁻⁵ s⁻¹, and a relatively low slope (i.e., 2.2) was obtained for the plot of log k versus E. The coatings were characterized by scanning electron microscopy (SEM), and cyclic voltammetric behavior of the PANI-deposited Pd/Al electrode is discussed. The electrocatalytic activity of the PANI-deposited Pd/Al electrode against para-benzoquinone/hydroquinone (Q/H₂Q) and redox systems were investigated and on the basis of of the corresponding cyclic voltammograms and the redox systems were identified as the reversible and quasi-reversible systems, respectively.     

Thermal properties of Na2TeO4(s) and TiTe3O8(s)

Molar heat capacity measurement on Na₂TeO₄(s) and TiTe₃O₈(s) were carried out using differential scanning calorimeter. The molar heat capacity values were least squares analyzed and the dependence of molar heat capacity with temperature for Na₂TeO₄(s) and TiTe₃O₈(s) can be given as, $$ \begin{gathered} {\text{C}}^{\text{o}}_{{{\text{p}},{\text{m}}}} \left\{ {{\text{Na}}_{ 2} {\text{TeO}}_{ 4} \left( {\text{s}} \right)} \right\} \,={159}.17 { } + 1.2\,\times\,10^{-4}T-{55}.34\,\times\,10^{5}/T^{2};\hfill \\ C^{\text{o}}_{{{\text{p}},{\text{m}}}} \left\{ {{\text{TiTe}}_{ 3} {\text{O}}_{ 8} \left( {\text{s}} \right)} \right\}\,=\,{ 275}.22{ }+{4}.0\,\times\, 10^{-5}T-{58}.28\,\times\,10^{5}/T^{2};\hfill \\ \end{gathered} $$ From this data, other thermodynamic functions were evaluated.