SBA-Pr-IS-MN synthesis and its application as Ag+ optical sensor in aqueous media

Research on Chemical Intermediates - A new functionalized mesoporous silica entitled SBA-Pr-IS-MN was produced and characterized by diverse techniques like FT-IR, TGA, XRD, SEM, TEM, and BET....     

Simultaneous Raman spectroscopic and differential double-layer capacitance measurements of pyridine adsorbed on roughened silver electrodes

It is shown that differential double-layer capacitance data can be obtained simultaneously with the recording of the Raman spectra of adsorbates at a roughened silver microelectrode. The use of such data to provide information about the structure of the silver electrode/aqueous KCl (0.1 M)/pyridine (0.1 M) interface is demonstrated.     

Electrochemical behavior of small biological molecules at organic donor—acceptor electrodes in aqueous media

The electrochemical behavior of NADH, xanthine, uric acid, 6-mercaptopurine, 6-thioxanthine, dopamine and ascorbic acid was investigated at the organic metal-like polymer paste electrodes, tetrathiafulvalene- and N-methylphenazene-tetracyanoquinodimethane. The reactivity of small biological molecules at polymer paste electrodes is generally lower than at most active graphite electrodes. Typical detection limits of about 10^?5 M and the typical upper limit of linearity of 10^?3 M are observed for the compounds studied.     

Estimation of chloride in oxidizing media by means of ion-selective electrodes

Chloride concentrations down to the ppm level in a large excess of chlorate or perchlorate can be quantitatively estimated by use of chloride ion-selective electrodes (ISEs). Similarly traces of chloride in chromic acid solutions can be estimated with a heterogeneous silicone-rubber based chloride ISE. However, homogeneous chloride ISEs pose a problem for practical applications, because their response in chromic acid solutions changes with time owing to chemical attack on the membrane surface. In permanganate solutions, both homogeneous and heterogeneous type electrodes can be used for monitoring chloride ions. The Orion electrode, however, was found to show a slightly super-Nernstian response in such solutions. The presence of 10(-3)M iron(III) had no adverse effect on the performance of these electrodes in permanganate solutions.     

Rayleigh relaxation of pyrazine,pyridine and piperidine molecules adsorbed on the roughened Ag electrode by light beating technique

The light beating technique (intensity correlation algorithm) was employed to analyze the Rayleigh scattering from the roughened Ag electrode in very dilute (10^?4 M) pyrazine, pyridine and piperidine aqueous solutions containing KC1 (0.1 M). The relaxation time is longer when the applied voltages are between ?0.4 V and ?0.8 V (vs. SCE) where the Raman effect also shows greater surface enhancement. Also observed was that for the piperidine case the relaxation time reaches its maximum at the more negative applied voltage. The origin of the relaxation is attributed mainly to the desorption process of the pyrazine, pyridine and piperidine molecules off the roughened Ag electrode. An electrostatic model was also proposed for the interpretation of these experimental observations.     

Long-term stability of glass electrodes in aqueous media

The stability of the potential of glass electrodes has been studied. The potential changes only slightly during the hydration of freshly etched electrodes. With glass electrodes previously used in alkaline solutions, structural transformations within the gel-layer give rise to large potential drifts in neutral or acidic test solutions. In alkaline solutions all glass electrodes are attacked, especially the low-temperature type, and the potential changes with time. Drying hydrated electrodes affects the stability only slightly. Alternating transfers between acidic and basic solutions decrease the stability. Recommendations for precise measurements with glass electrodes are given.     

Electroreduction of some pyridine carboxamides on carbon electrodes in aqueous solutions

The electroreductions of the NAD⁺ model compounds nicotinamide (I), N₁-methyl nicotinamide (II), N′-methyl nicotinamide (III) and isonicotinamide (IV) on carbon electrodes have been studied in aqueous media in the pH range 0–12 by linear-sweep cyclic voltammetry (Scheme 1, I-IV). Logarithmic analyses of the reduction peaks were performed by computing the convolution of the current with time as a function of the potential. On the basis of the experimental results it was concluded that the irreversibility of the electron transfers increased when a glassy carbon electrode was used, and this irreversibility being more marked when a plastic formed carbon electrode was employed. The reduction processes occurred with more difficulty on carbon electrodes than on mercury electrodes. Both the reduction and the reoxidation (when occurred) processes changed with respect to those observed on mercury electrodes, being irreversible electron transfers the rate-determining steps in most cases. Thus, for compounds I, II and III at pH < 2 the reductions occurred by the uptake of two electrons and two H⁺ ions, and the rate determining step was found to be the first one-electron transfer, for I and III, and the irreversible second electron transfer, preceded by the uptake of an H+ ion, for II. At pH>3 the processes consisted of electrodimerization reactions, preceded by the protonation of the heterocyclic nitrogen in cases I and III. The second electron transfer of the electroreduction of IV always appeared irreversible, in contrast with that found for mercury electrodes.     

Electrochemical behavior of phthaloyl peroxide in aqueous media

The electrochemical behavior of phthaloyl peroxide C₈H₄O₄ on an Au disk electrode in a 0.05 M aqueous solution of Na₂SO₄ was studied by cyclic voltammetry (CVA). It demonstrated a high activity in cathodic reduction with the formation of an irreversible peak on the CVA curve at E =–0.81 V. Additionally, during the anodic oxidation of C₈H₄O₄, the surface of the Au electrode became passivated by compounds which prevented its oxidation during the registration of repeated cycles. Apparently, these compounds are surface complexes of phthaloyl peroxide with a gold cation.     

Rotaxanes capable of recognising chloride in aqueous media

A new, versatile chloride-anion-templating synthetic pathway is exploited for the preparation of a series of eight new [2]rotaxane host molecules, including the first sulfonamide interlocked system. (1)H NMR spectroscopic titration investigations demonstrate the rotaxanes' capability to selectively recognise the chloride anion in competitive aqueous solvent media. The interlocked host's halide binding affinity can be further enhanced and tuned through the attachment of electron-withdrawing substituents and by increasing its positive charge. A dicationic rotaxane selectively binds chloride in 35% water, wherein no evidence of oxoanion binding is observed. NMR spectroscopy, X-ray structural analysis and computational molecular dynamics simulations are used to account for rotaxane formation yields, anion binding strengths and selectivity trends.     

Electrochemical and structural characterization of lithium titanate electrodes

Lithium titanate (LTO) materials of different particle size, surface area, and morphology were characterized by constant current cycling and cyclic voltammetry. By examining the particles and electrodes with scanning electron microscopy, we show that particle morphology, in addition to particle size, has important implications for high-rate performance. Large agglomerates, even when porous and made of small crystallites, cannot effectively form homogenous electrodes with the polymer binder and carbon conducting diluents; hence, low power performance results. Another nanostructured LTO of very high surface area was found to have poor electrochemical performance most likely due to its high concentration of structural defects. We recommend further development in nanoparticles of LTO of optimal crystallinity as well as improved electrode homogeneity through the use of more compatible binders and conducting diluents and better electrode processing techniques. Simultaneous realization of these imperatives should facilitate the development of LTO-based high-power batteries for automotive applications.     

Electrochemical reduction of substituted cobalticinium cations in aqueous media

Summary In aqueous base, polarography, coulometry and cyclic voltammetry show that the cobalticinium skeleton is reduced in two monoelectronic and reversible steps, leading successively to cobaltocenes and cobaltocene anions. In acid solutions, the second reduction step is only observed for derivatives having electron withdrawing substituents. The height of the second reduction wave is pH dependent. Two different schemes are discussed for the reduction in acid solution.     

Cyclic voltammetry responses of metastable gold electrodes in aqueous media

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Electrochemical generation of ferrate in acidic media at boron-doped diamond electrodes

An extremely strong oxidant, ferrate (Fe(VI) or FeO4(2-), has been produced electrochemically in an acidic aqueous medium for the first time.     

Efficient gold and silver electrodes for surface enchanced raman spectral studies of electrochemical systems: The behaviour of pyridine and naphthalene adsorbed on roughened gold electrodes

A method is described whereby surface enhanced Raman (SER) active electrode surfaces of gold and silver may be made without recourse to the oxidation—reduction techniques which have been used hitherto. This method involves electroplating at low current density from dilute (< 10^?2M) solutions of a suitable salt or complex in the absence of supporting electrolyte.Scanning electron microscopy shows the surfaces to consist of small spherical particles of fairly constant diameter packed together on the electrode. The sphere diameters are typically 70 nm (gold) and 180 nm (silver) for electrodes prepared in this manner. These electrodes exhibit intense SER scattering and have advantages over oxidation—reduction roughened electrodes. As examples of their utility some results are presented relating to the gold/pyridine and gold/naphthalene systems and these are discussed in relation to results obtained by other workers in similar systems using different methods, i.e., ellipsometry and differential capacitance variation.     

Electrochemical characterization of self-assembled thiol-porphyrin monolayers on gold electrodes by SECM.

Herein, the scanning electrochemical microscopy (SECM) approach is applied to study the formation of thiol-porphyrin self-assembled monolayer (SAMs). Using cyclic voltammetry (CV), the formation process is characterized adopting different probe molecules. The observed phenomena indicate that the formation process is affected by solution properties and the molecular structure of the probe molecules. In K(3)Fe(CN)(6) , the SAMs show a strong electron-transfer (ET) blocking effect on a pure porphyrin-modified electrode. However, addition of metal ions to the porphyrin molecules leads to ET. A consistent tendency is observed throughout the modification process using CV and SECM methods. Furthermore, k(eff) values, the apparent heterogeneous rate constants, obtained for different modification periods affirm the validity of these results. SECM images are used to collect surface information in the course of the modification process when the substrate potential is 0.5 V versus Ag/AgCl. The effect of the substrate potential indicates that the oxidation of the porphyrin molecules is supported by more positive potentials because of the similar bimolecular reaction of the porphyrin ring with positive charge and the probe molecules with negative charge.