Anodic oxidation of selenadiazoloquinolones in alkaline media

Newly synthesized derivatives of 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinoline variously substituted at position 7 (R = H, COOH, COCH(3), CN, COOC(2)H(5) and COOCH(3)) are established in strongly alkaline aqueous solutions (0.1 M NaOH; pH ～ 13) as N(9)-deprotonated structures, but in less alkaline solutions (0.001 M NaOH; pH ～ 11) the N(9)-protonated oxo tautomeric forms dominate. Upon their anodic oxidation in alkaline solutions, the selenadiazole ring is replaced, forming instead the paramagnetic species analogous to the ortho semiquinone radical anions as monitored by in situ EPR spectroscopy. The quantum chemical calculations for two representative selenadiazoloquinolones (R = H and COOH) and their anodic oxidation products presented are in agreement with experiments.     

Electrocatalysis of oxygen reduction and small alcohol oxidation in alkaline media

We present here a critical review of several technologically important electrocatalytic systems operating in alkaline electrolytes. These include the oxygen reduction reaction (ORR) occurring on catalysts containing Pt, Pd, Ir, Ru, or Ag, the methanol oxidation reaction (MOR) occurring on Pt-containing catalysts, and the ethanol oxidation reaction (EOR) occurring on Ni-Co-Fe alloy catalysts. Each of these catalytic systems is relevant to alkaline fuel cell (AFC) technology, while the ORR systems are also relevant to chlor-alkali electrolysis and metal-air batteries. The use of alkaline media presents advantages both in electrocatalytic activity and in materials stability and corrosion. Therefore, prospects for the continued development of alkaline electrocatalytic systems, including alkaline fuel cells, seem very promising.     

Electrocatalytic oxidation of methanol on Pt/NiZn electrode in alkaline medium

In this study, a platinum electrode was coated with NiZn layer (Pt/NiZn) in a nickel-zinc bath by electrodeposition for use as anode material for methanol electrooxidation in alkaline solution. The electrode prepared was etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the methanol electrooxidation (Pt/NiZn). The surface morphologies and compositions of coating before and after alkaline leaching were determined by energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) techniques. The effect of NiZn coated platinum electrode for methanol electrooxidation was investigated in 1 M NaOH solution by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Methanol electrooxidation on Pt/NiZn electrode was studied at various temperatures and potential scan rates. The results showed that Pt/NiZn electrode behaved as an efficient catalyst for the electrooxidation of methanol in alkaline medium.     

Microbalance study of gold dissolution in alkaline sulfite-thiocarbamide electrolytes

It is shown that gold does not virtually dissolve in alkaline (pH 12.5) solutions containing either thiocarbamide or sodium sulfite. Gold dissolves in alkaline solutions simultaneously containing thiocarbamide (0.1 M) and sodium sulfite (0.5 M). The gold dissolution rate increases with the increase in the contents of thiocarbamide and sodium sulfite. The methods of microbalance and voltammetry are used in studying the mechanism of gold dissolution in a solution containing 0.5 M sodium sulfite, 0.1 M thiocarbamide, and 0.03 M KOH. The found relationships are explained based on the assumption that the gold dissolution in alkaline sulfite-thiocarbamide electrolytes affords gold sulfite complexes.     

Spectrophotometric determination of rhenium with dithio-oxamide in strongly alkaline medium

The interaction between rhenium(VII) and dithio-oxamide in strongly alkaline medium in presence of tin(II) chloride as reluctant has been studied. A purple complex is obtained, with lambda(max) 526 nm and (max) = 4.0 x 10(3) l.mole(-1).cm(-1). The reaction has been applied to the determination of rhenium in tungsten-rhenium alloy after its anodic electrochemical dissolution in alkaline medium. A 1000-fold excess of molybdenum or tungsten does not interfere. A modification of the proposed method can be used as a spot-test for rapid control of rhenium content in industrial solutions.     

Corrosion mechanism of pure aluminium in aqueous alkaline solution

The corrosion of pure aluminium in alkaline solution has been explored using an open circuit potential transient, potentiodynamic polarization experiment and a.c. impedance spectroscopy. The steady-state value of the open circuit potential (E _ocp ^ss ) of pure aluminium in alkaline solution was observed to decrease with increasing rotation rate of the specimen, which is ascribed to the enhanced anodic reaction. The extent of anodic polarization for the aluminium dissolution reaction on pure aluminium at E _ocp ^ss was found to be greater than that of cathodic polarization for the water reduction reaction. This indicates that the rate of corrosion of pure aluminium is mainly determined by the anodic reaction in alkaline solution. Based upon the experimental results, a corrosion mechanism for pure aluminium has been proposed in the presence of the native surface oxide film in alkaline solution, involving consecutive oxide film formation and dissolution, and simultaneous water reduction.     

Sample preparation in alkaline media

The use of tetramethylammonium hydroxide, tertiary amines and strongly alkaline reagents for sample treatment involving extraction and digestion procedures is discussed in this review. The preparation of slurries is also discussed. Based on literature data, alkaline media offer a good alternative for sample preparation involving an appreciable group of analytes in different types of samples. These reagents are also successfully employed in tailored speciation procedures wherein there is a critical dependence on maintenance of chemical forms. The effects of these reagents on measurements performed using spectroanalytical techniques are discussed. Several undesirable effects on transport and atomization processes necessitate use of the method of standard additions to obtain accurate results. It is also evident that alkaline media can improve the performance of techniques such as inductively coupled plasma mass spectrometry and accessories, such as autosamplers coupled to graphite furnace atomic absorption spectrometers.     

Encapsulation of curcumin in cationic micelles suppresses alkaline hydrolysis

The alkaline hydrolysis of curcumin was studied in three types of micelles composed of the cationic surfactants cetyl trimethylammonium bromide (CTAB) and dodecyl trimethylammonium bromide (DTAB) and the anionic surfactant sodium dodecyl sulfate (SDS). At pH 13, curcumin undergoes rapid degradation by alkaline hydrolysis in the SDS micellar solution. In contrast, alkaline hydrolysis of curcumin is greatly suppressed in the presence of either CTAB or DTAB micelles, with a yield of suppression close to 90%. The results from fluorescence spectroscopic studies reveal that while curcumin remains encapsulated in CTAB and DTAB micelles at pH 13, curcumin is dissociated from the SDS micelles to the aqueous phase at this pH. The absence of encapsulation and stabilization in the SDS micellar solution results in rapid hydrolysis of curcumin.     

Identification of condensed-phase species on the thermal transformation of alkaline and alkaline earth metal sulphates on a graphite platform

Thermal treatment of alkaline and alkaline earth metal sulphates on a graphite platform was performed over the temperature range 200–2000 °C. The solid residues produced at each temperature were located by scanning electron microscopy (SEM) and then identified by energy-dispersive (ED) X-ray spectroscopy and Raman microanalysis. Additional experiments involved the dissolution of the residues from the platform and analysis by ion chromatography to determine the concentration of sulphate and other ions. A decomposition pattern was derived for the alkaline and alkaline earth metal sulphates. The transformation of the metal sulphates was dependent on temperature and the cation present. In general, the metal sulphates do not undergo significant decomposition to other species at temperatures less than 900 °C, with the exception of magnesium and beryllium sulphates, which are transformed into metal oxides to some extent. Above 900 °C, major transformations occur mainly for sodium, magnesium, and beryllium sulphates. For all the salts studied, there is evidence of the formation of species such as metal sulphides and elemental sulphur.     

Deposition yield of nickel in alkaline bath for synthesizing Ni-63 beta source

Nickel (Ni) and Ni-63 films were synthesized by direct current electrodeposition. The composition of an alkaline electrolyte was ammonium citrate (25 g/l), hydrazine hydrate (25 g/l), and ammonium solution (25%) for adjusting the pH to 10. The acidic electrolyte at pH 4 was prepared using a full chloride bath. A higher deposition yield (92%) of the citrate electrolyte (pH 10) than 73% of acidic electrolyte (pH4) was measured using ICP. The deposition yield of radioactive Ni-63 in a citrate bath was also same as natural Ni in alkaline electrolyte. A newly prepared alkaline bath for the deposition of Ni-63 can be a solution for an extremely decreased radio-activity in the waste after plating.     

Rapid precipitation-reduction synthesis of carbon-supported silver for efficient oxygen reduction reaction in alkaline solution

Journal of Solid State Electrochemistry - Silver has emerged as a promising electrocatalyst for oxygen reduction reaction (ORR) in alkaline membrane fuel cell for its high stability in alkaline...     

Properties of Zinc alloy electrodeposits produced from acid and alkaline electrolytes

Zinc–cobalt (Zn–Co) and zinc–nickel (Zn–Ni) alloy electrodeposits each prepared from acid and alkaline formulations were compared for their properties. Compared to alkaline baths, acid baths offer higher metal percent of the alloying element and higher current efficiency. In alkaline baths, the variation of metal percent in deposit with current density is less significant, but that of current efficiency with current density is more. Electrolyte pH does not change significantly in alkaline solutions compared to acid solutions. X-ray diffraction evaluation of Zn–Co deposits from both electrolytes indicated their presence in the η-phase, while Zn–Ni shows pure γ-phase for deposits obtained from alkaline solutions and the existence of γ-phase with traces of η-phase of zinc for deposits obtained from the acid electrolytes. Scanning electron microscope examination shows finer grain structure for deposits obtained from alkaline solutions, and atomic force microscope studies confirm their nanostructure with reduced surface roughness. Deposits obtained from the alkaline baths exhibited higher corrosion resistance probably due to their nanostructure.     

Carbon exchange in hot alkaline degradation of glucose

The decomposition of 1-13C-D-glucose, 6-13C-D-glucose, and 1-13C-sodium lactate has been studied in hot (145 +/- 3 degrees C) alkaline (3.5 M) sodium hydroxide solution in order to understand the mechanisms of carbon exchange in the alkaline degradation of glucose. The results show that in the formation of lactate from glucose the carboxylate (COO-) carbon is formed preferentially from C1 carbons but methyl (CH3) carbon is formed preferentially from C6 carbons. However, on further decomposition of lactate to ethanol and carbonate, 13C-labeled carboxylate (COO-) is scrambled equally among carbonate and both carbons in product ethanol molecules. In the production of glycolate, the labeled C1 carbon mainly ends up as carboxylate (COO-) carbon, while for C6-labeled glucose the labeled carbon mainly ends up as alcoholic (CH2OH) carbon. In the production of acetate and formate there is also discrimination between C1 and C6 label.     

铂电极在碱性含氧溶液中的预还原处理对鲁米诺电 致化学发光的影响

研究了铂电极的不同预极化处理过程对碱性鲁米诺阳极电致化学发光(ECL)和阳极极化曲线的影响,发现在碱性含氧溶液中预还原处理的铂电极可增强0.22V(vs.SCE)处发光峰强度,且催化产生1.07V(vs.SCE)附近氧气析出过程并伴随产生明显的ECL发光峰;在酸性溶液中预处理电极可抑制这些活性。给出了催化氧气析出的可能作用机理：在碱性溶液中溶解氧还原生成了吸附在铂电极表面的(OH^-)~a~d~s,从而回忆了氧气的析出过程。同时给出了在碱性含氧溶液中预还原的铂电极上两个可能的ECL反应通道：(1)在0.22V鲁米诺阴离子氧化为鲁米诺自由基,然后与溶解氧反应而发光;(2)1.07V处析出的新鲜氧与鲁米诺阴离子反应而发光。     

Unsupported palladium nanoparticles for ethanol cyclic voltammetric sensing in alkaline media

Carbon-supported palladium nanostructures have had a recent rise in their use for ethanol oxidation applications. In this work, we present the use of unsupported palladium nanoparticles (PdNPs), synthesized by sodium borohydride chemical reduction method, for ethanol electrochemical sensing. The unsupported PdNPs were studied for ethanol oxidation in alkaline media by cyclic voltammetry, and additionally were characterized using transmission electron microscopy, and x-ray photoelectron spectroscopy. The performance of unsupported PdNP-modified glassy carbon electrodes for the electrochemical ethanol oxidation in 1.0 M potassium hydroxide (KOH) solution was studied by cyclic voltammetry. These electrochemical results demonstrated that the unsupported PdNPs have very promising catalytic activity towards the oxidation of ethanol in alkaline media with good detection performance in the concentration range of 2304 to 288 ppm (i.e., 50.00 to 6.25 mM). The detection limit and linear correlation coefficient were 49.3 ppm (1.10 mM) and 0.9998, respectively. The unsupported PdNP-modified glassy carbon electrodes presented good cyclic voltammetric stability for ethanol sensing application in alkaline media.     

Electrochemical corrosion resistance performance of sustainable resource-based nanoconducting polymer composites in alkaline medium

The corrosion resistance performance of poly (otoluidine) (POT)-dispersed castor oil-polyurethane, (COPU) nanocomposite coatings, POT/COPU, with three different compositions (i.e. 0.25, 0.5 and 1.0 wt%) in alkaline medium is studied. The coatings are applied on mild steel specimens by brushing. Corrosion resistance behaviour of these coatings is investigated using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS) and by weight loss. The morphological behaviour of corroded and uncorroded coated specimens is investigated by scanning electron microscopy (SEM). It is interesting to report that the presence of conducting polymer nanoparticles in POT/COPU coatings suppresses the saponification of COPU in an alkaline environment. These investigations show that the dispersion of POT in COPU remarkably improves the corrosion resistance performance of COPU in alkaline media. POT/COPU (1.0 wt%) coatings have potential as anticorrosive-coating materials in alkaline media at higher pH. These coatings have a higher resistance to alkaline medium in comparison to other compositions.     

Superoxide generation in alkaline dimethyl sulphoxide

The generation of superoxide (O₂) in alkaline dimethyl sulphoxide (DMSO) is investigated by using electron spin resonance and chemiluminescence for the detection of oxygen species. The concentration of superoxide in this system corresponds to the concentration of oxygen dissolved in DMSO. In tightly stoppered vessels, the superoxide is stable for more than 24 h; agitation of the mixture in open vessels rapidly decreases its concentration. The presence of hydroxyl, carbon-centred and superoxide radicals is demonstrated by spin trapping. Alkaline DMSO is not recommended for superoxide dismutase assays.     

A study on the electroanalytical performance of a bismuth film-coated and Nafion-coated glassy carbon electrode in alkaline solutions

Bismuth film electrodes are widely used for determination of heavy metal ions in acidic solutions, while alkaline solutions are rarely employed. We have compared the deposition of Bi(III) and Pb(II) on a Nafion-coated glassy carbon electrode in alkaline and acidic solutions. The results indicate that both Bi(III) and Pb(II) can be deposited in either alkaline or acidic solution, but the quantity of Pb(II) deposited in alkaline solution is less than that in acidic solution. The modified electrode was used to determine heavy metal ions in both alkaline and acidic solutions, and the results of the method agree well with those of atomic absorption spectroscopy.     

Bond structure in the alkaline ferric–tartrate system

The bond structure of the complex in the alkaline ferric–tartrate system (FeTNa) was examined and related to the cellulose-dissolving ability of the system. The subject of bonding was approached by magnetic susceptibility and absorption spectrophotometric techniques. The magnetic moment of the Fe(III) in the iron–tartrate system was found to depend on the pH of the system. With an iron molarity of 0.1 an iron/tartrate mole ratio of 1 : 3, and 2 moles of NaOH/mole of tartaric acid, a minimum magnetic moment of 3.9 BM was observed. In alkaline media the magnetic moment depended on the Fe(III) concentration and the iron/tartrate ratio. The Fe(III) in the cellulose–solvent FeTNa was found to be in a high–spin state (5.9 BM). With a large excess of tartrate, the absorption spectrum of the alkaline FeTNa was recorded and analyzed in terms of the Tanabe–Sugano determinants. Values of 13200 cm^?1 and 0.66 were obtained for the parameters Δ and β, respectively. In addition, it was shown that the Fe(III) in the cellulosesolvent FeTNa is coordinated with less than the maximum possible amount of tartrate. This tartrate deficiency is apparently responsible for the solvent properties of the system. From the use of glycerol as a model for cellulose, it appears that cellulose coordinates with the iron in the solvent FeTNa in much the same manner as does additional tartrate.     

Study on isohexenylnaphthazarins polymerization in alkaline media

The chiral pair alkannin and shikonin (A/S) and their isohexenylnaphthazarin (IHN) esters, which are naturally occurring hydroxynaphthoquinones (HNQ), are potent pharmaceutical substances with a wide spectrum of biological activity. The stability of A/S and their derivatives during process and storage is crucial to their use as drugs, cosmetics and food additives. The influence of alkaline media and of IHN esters hydrolysis was experimentally investigated on IHN polymerization by size exclusion chromatography (SEC). It was proved that during IHN esters hydrolysis, polymeric A/S and IHN are formed. An optimization of the hydrolysis conditions of IHN esters was also approached in terms of polymerization. Hydrolysis of IHN from a pure mixture of pigments proved preferable to that of preliminary root extracts by means of IHN polymerization, even for analytical determination; non-polar solvents are proposed for the extraction of IHN from roots, followed by hydrolysis, aiming to minimize the polymeric IHN and A/S formed. It was also proved that polymerization of IHN in alkaline media and during hydrolysis of IHN esters proceeds through the intermediate formation of semiquinones; after acidification, coupling of semiquinones with phenoxyl radicals results in polymeric IHN structures.