NaOH Medium Research Articles

Preparation of Pt/multiwalled carbon nanotubes modified Au electrodes via Pt–Cu co-electrodeposition/Cu stripping protocol for high-performance electrocatalytic oxidation of methanol

Pt nanoparticles well dispersed on multiwalled carbon nanotubes (MWCNTs) were prepared for high-performance electrocatalytic oxidation of methanol in both acidic and alkaline media via the co-electrodeposition/stripping (CS) protocol, namely, co-electrodeposition of Pt and Cu followed by electrochemical stripping of Cu, as examined by cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The Pt catalyst prepared by the CS protocol on MWCNTs (Pt cs/MWCNTs/Au) exhibited a specific electrocatalytic activity of 519 and 2210 A g −1 toward cyclic voltammetric electrooxidation (50 mV s −1) of methanol in 0.5 M CH 3OH + 0.5 M H 2SO 4 and 0.5 M CH 3OH + 1.0 M NaOH media, respectively, which are larger than those prepared by conventional electrodeposition from chloroplatinic acid on Au and MWCNTs/Au, as well as that by a CS protocol on Au. The Pt cs/MWCNTs/Au electrode also possessed the highest stability, which maintained 91% and 90% of its initial catalytic activity after 120-cycle CV in 0.5 M CH 3OH + 0.5 M H 2SO 4 and 0.5 M CH 3OH + 1.0 M NaOH, respectively. The electrode kinetics of methanol oxidation is also briefly discussed. The nanosubstrate-based CS protocol is simple, convenient and efficient, which is expected to find wide applications in film electrochemistry and electrocatalysis.

Kinetics and reactivities of ruthenium(III)- and osmium(VIII)-catalyzed oxidation of ornidazole with chloramine-T in acid and alkaline media: A mechanistic approach

Ornidazole is an antiparasitic drug having a wide spectrum of activity. Literature survey has revealed that no attention has been paid towards the oxidation of ornidazole with any oxidant from the kinetic and mechanistic view point. Also no one has examined the role of platinum group metal ions as catalysts in the oxidation of this drug. Such studies are of much use in understanding the mechanistic profile of ornidazole in redox reactions and provide an insight into the interaction of metal ions with the substrate in biological systems. For these reasons, the Ru(III)- and Os(VIII)-catalyzed kinetics of oxidation of ornidazole with chloramine-T have been studied in HCl and NaOH media, respectively at 313 K. The oxidation products and kinetic patterns were found to be different in acid and alkaline media. Under comparable experimental conditions, in Ru(III)-catalyzed oxidation the rate law is −d[CAT]/d t = k [CAT] o[ornidazole] o x [H +] − y [Ru(III)] z and it takes the form −d[CAT]/d t = k [CAT] o[ornidazole] o x [OH −] y [Os(VIII)][ArSO 2NH 2] − z for Os(VIII)-catalyzed reaction, where x, y and z are less than unity. In acid medium, 1-chloro-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one and in alkaline medium, 1-hydroxy-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one were characterized as the oxidation products of ornidazole by GC–MS analysis. The reactions were studied at different temperatures and the overall activation parameters have been computed. The solvent isotope effect was studied using D 2O. Under identical set of experimental conditions, the kinetics of Ru(III) catalyzed oxidation of ornidazole by CAT in acid medium have been compared with uncatalyzed reactions. The relative rates revealed that the catalyzed reactions are about 5-fold faster whereas in Os(VIII) catalyzed reactions, it is around 9 times. The catalytic constant ( K C ) has been calculated for both the catalysts at different temperatures and activation parameters with respect to each catalyst have been evaluated. The observed experimental results have been explained by plausible mechanisms. Related rate laws have been worked out.

A polyamidoamine dendrimer as a selective colorimetric and ratiometric fluorescent sensor for Li + cations in alkali media

In a DMF + NaOH medium, a polyamidoamine dendrimer having sixteen 1,8-naphthalimide fragments in its periphery, formed a complex only with Li + ions, detected by a colour change from red to yellow and by a significant increase in fluorescence intensity. The dendrimer can be used as a selective sensor for Li + ions in the presence of other alkali ions such as Na + or K +.

Oxidative decolorization of triphenylmethane dyes by chloramine-T in alkaline medium catalyzed by Pd(II): A comparative spectrophotomeric kinetic and mechanistic approach

Triphenylmethane dyes viz., p-rosaniline, crystal violet and ethyl violet (henceforth abbreviated as Dye) have been extensively used as colorants in textile industries. Effluents containing these dyes released by the industry causes significant environmental problems. Hence decolorization of dye effluents has acquired increasing attention. The oxidative decolorization of these dyes is of greater significance one understanding of their kinetic and mechanistic aspects in redox reactions is important. Consequently, Pd(II) catalyzed kinetics and oxidative decolorization of p-rosaniline, crystal violet and ethyl violet dyes by chloramine-T (CAT) in NaOH medium were studied spectrophotometrically. The oxidation reaction follows the identical kinetics for all the three dyes and obeys the rate law: rate = k[CAT] a [Dye] b [OH −] c [Pd(II)] d where a and b are unity, and c and d are less than unity. Addition of p-toluenesulfonamide, the reduction product of CAT, retards the rate and the order was found to be less than unity. The reaction rate increased with increasing ionic strength of the medium. Addition of chloride ions show negligible effect on the rate of reaction. Oxidation products were characterized by GC–MS analysis. Proton-inventory studies with ethyl violet as a probe have been made in H 2O–D 2O mixtures. Activation parameters and decomposition constants have been deduced. An isokinetic relation is observed with β = 423 K indicating enthalpy as a controlling factor. The rate of oxidation of triphenylmethane dyes follows the order: p-rosaniline > crystal violet > ethyl violet. This trend may be attributed to inductive effects of alkyl amino groups. Further, the kinetics of Pd(II)-catalyzed oxidation of these dyes have been compared with uncatalyzed reactions (in the absence of Pd(II) catalyst) and found that the catalyzed reactions are nearly four times faster. The catalytic constant ( K C) for Pd(II) was also calculated for each dye at different temperatures and the values of activation parameters with respect to the catalyst have been evaluated. Chlorite ion (OCl −) has been postulated as the reactive oxidizing species. The observed results have been explained by a general mechanism, and the related rate law has been obtained. Furthermore, the simple and elegant method developed for the decolorization of triphenylmethane dyes in the present work can be adopted for treating the aforesaid dyes present in industrial effluents to minimize the toxicity caused by these dyes.

Mechanistic aspects for the oxidation of sunset yellow dye by chloramine-T in presence of perchloric acid and in sodium hydroxide medium catalyzed by Os(VIII): A spectrophotometric kinetic approach

The kinetics of oxidation of sunset yellow (SY) by sodium- N-chloro- p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophotometrically in HClO 4 and NaOH media with Os(VIII) as a catalyst in the latter medium at 298 K and 303 K, respectively. In acid medium, the experimental rate law is −d[CAT]/d t = k[CAT] 0[SY] 0[HClO 4] −0.46. Alkali accelerates the rate of reaction and the rate law takes the form −d[CAT]/d t = k[CAT] 0[SY] 0[NaOH] 0.23[OsO 4] 0.84. The solvent isotope effect was studied using D 2O. Benzenesulfonic acid and 1,2-naphthoquinone-6-sulfonic acid were characterized as the oxidation products of SY. Under identical set of experimental conditions in alkaline medium, Os(VIII) catalyzed reaction is about seven-fold faster than the uncatalyzed reaction. Activation parameters for the overall reaction and also with respect to catalyst have been evaluated. The observed results have been explained by plausible mechanisms and the related rate laws have been deduced.

Ru(III), Os(VIII), Pd(II) and Pt(IV) catalysed oxidation of glycyl–glycine by sodium N‐chloro‐p‐toluenesulfonamide: comparative mechanistic aspects and kinetic modelling

AbstractThe Ru(III)/Os(VIII)/Pd(II)/Pt(IV)‐catalysed kinetics of oxidation of glycyl–glycine (Gly‐Gly) by sodium N‐chloro‐p‐ toluenesulfonamide (chloramine‐T; CAT) in NaOH medium has been investigated at 308 K. The stoichiometry and oxidation products in each case were found to be the same but their kinetic patterns observed are different. Under comparable experimental conditions, the oxidation‐kinetics and mechanistic behaviour of Gly‐Gly with CAT in NaOH medium is different for each catalyst and obeys the underlying rate laws: Rate = k [CAT]t [Gly‐Gly]0 [Ru(III)][OH−]x Rate = k [CAT]t[Gly‐Gly]x [Os(VIII)]y[OH−]z Rate = k [CAT]t[Gly‐Gly]x [Pd(II)][OH−]y Rate = k [CAT]t[Gly‐Gly]0 [Pt(IV)]x[OH−]y Here, ${\rm Ts} = {\rm CH}_3 {\rm C}_6 {\rm H}_4 {\rm SO}_{2^ -}$ and x, y, z < 1 in all the cases. The anion of CAT, CH3C6H4SO2NCl−, has been postulated as the common reactive oxidising species in all the cases. Under comparable experimental conditions, the relative ability of these catalysts towards oxidation of Gly‐Gly by CAT are in the order: Os(VIII) > Ru(III) > Pt(IV) > Pd(II). This trend may be attributed to the different d‐electronic configuration of the catalysts. Further, the rates of oxidation of all the four catalysed reactions have been compared with uncatalysed reactions, under identical experimental conditions. It was found that the catalysed reaction rates are 7‐ to 24‐fold faster. Based on the observed experimental results, detailed mechanistic interpretation and the related kinetic modelling have been worked out for each catalyst. Copyright © 2008 John Wiley & Sons, Ltd.

A novel route for the synthesis of processable conducting poly( m-aminophenol)

Polymerization of m-aminophenol (mAP) in aqueous NaOH solution was done chemically by using ammonium persulfate (APS) as an oxidative initiator. The product poly( m-aminophenol) (PmAP) was found to be highly soluble in aqueous sodium hydroxide, dimethyl sulfoxide (DMSO) and N, N-dimethyl formamide (DMF). From the intrinsic viscosity measurement, the optimum condition for the polymerization was established with 0.6 M NaOH medium with the ratio of monomer to oxidant as 1:1.5 (mol:mol). The polymer was characterized by FTIR and 1H NMR spectroscopy, elemental (CHNS) and thermogravimetric (TGA) analyses. From the spectroscopic analysis the structure of the polymer was found to resemble that of hydroxy polyaniline as the polymer contains free –OH groups attached to o/ m position in the phenyl ring. The elemental analysis of the polymer also confirmed the same. From TGA study, the polymer was found to be thermally stable. A freestanding film of poly( m-aminophenol) was cast in DMSO solution followed by solvent removal and drying of the film at 100 °C for 7–8 h in an oven. A dc conductivity of 4.8 × 10 −4 S cm −1 was obtained for the synthesized polymer film after doping with H 2SO 4 solution.

Mechanistic Investigations of Oxidation of Some Dipeptides by Sodium N‐chloro‐p‐toluenesulfonamide in Alkaline Medium:A Kinetic Study

AbstractThe kinetics of oxidation of five dipeptides (DPP) viz., glycylglycine (Gly‐Gly), L‐alanyl‐L‐alanine (Ala‐Ala), L‐valyl‐L‐valine (Val‐Val), L‐leucyl‐L‐leucine (Leu‐Leu) and phenylglycyl‐phenylglycine (Phg‐Phg) by sodium N‐chloro‐p‐toluenesulfonamide or chloramine‐T (CAT) in NaOH medium was studied at 308 K. The reactions follow identical kinetics for all the dipeptides, being first‐order dependence each on [CAT]o, [DPP]o and fractional‐order on [OH−]. Addition of p‐toluenesulfonamide or halide ions (Cl− or Br−) has no significant effect on the rate of reaction. The reaction rate was found to increase with increase in ionic strength of the medium. The solvent isotope effect was studied using D2O. The activation parameters for the reaction were computed from Arrhenius plots. Equilibrium and decomposition constants were evaluated. The oxidation products of the dipeptides were identified as their corresponding aldehydes. An isokinetic relationship was observed with β=352 K, indicating that enthalpy factors control the reaction rate. CH3C6H4SO2NCl− of the oxidant has been postulated as the reactive oxidizing species. Under comparable experimental conditions, the rate of oxidation of the dipeptides increases in the order:Phg‐Phg>Ala‐Ala>Val‐Val>Leu‐Leu>Gly‐Gly. The kinetics of oxidation of the dipeptides have also been compared with those of their corresponding monomer amino acids. The observed results have been explained by a plausible mechanism and the related rate law has been deduced.

Studies on the behavior of Co 2+ and Zn 2+ in the conversion from FeOOH to magnetite in NH 3 (NaOH)–Fe 2+, Co 2+–H 2O medium under hydrothermal conditions

Crystalline FeOOH and Zn(II) doped FeOOH samples were prepared by a co-precipitation method using ferrous sulphate heptahydrate, zinc sulphate heptahydrate, ammonia, 3% hydrogen peroxide at 80 °C and pH value 3.0. These samples were characterized by XRD and were also chemically analyzed. The XRD patterns of pure FeOOH matched with that of Zn(II) doped FeOOH sample and showed no shift in their d-values, which indicated that Zn 2+ ions were adsorbed on the surface of FeOOH or on the surface of the crystalline lattice, and were not captured into the ferrite lattice. Chemical analysis showed that the molar ratio of Zn(II)/Fe in Zn(II) doped FeOOH sample was only 0.038 when this ratio was 0.5 in an initial reaction solution. These samples were treated in ammoniacal or sodium hydroxide medium in the presence of ferrous sulphate or cobalt sulphate under hydrothermal conditions. The converted products were analyzed both for ferrous, total iron, cobalt and zinc. Characterization was carried out using instrumental techniques such as SEM, FT-IR, XRD and magnetization characterization. Though the XRD patterns of the converted products showed presence of only magnetite in the NH 3–Fe 2+, Co 2+–H 2O converted medium, the FT-IR spectra and chemical analysis showed an un-reacted FeOOH in the converted product. Even though, the saturation magnetization of this magnetite was higher to 97.489 emu g − 1 . Furthermore, higher temperature increased the concentration of Co 2+ captured into spinel structure. The conversion were restrained in NH 3 concentration of less than 12 g/L and more than 25 g/L. However, increasing of Fe 2+/Co 2+ ratio in the NH 3–Fe 2+, Co 2+–H 2O medium made no distinct difference in the introduction of Co 2+ into spinel structure when concentration of Fe 2+ was enough. Compared with Zn-free FeOOH, it was difficult for Zn-doped FeOOH to convert to magnetite in the NH 3 (NaOH)–Fe 2+–H 2O medium. Furthermore, alkali species were critical in the above conversion. The content of Zn 2+ which was out of Zn-doped FeOOH solid state and entered into the outer solution was more in the NH 3 medium than that of the NaOH medium, but conversion from Zn–FeOOH into magnetite was easy in the NaOH medium. The explanations of above facts were given in the text.

Synthesis of polystyrene nanoparticles with monodisperse size distribution and positive surface charge using metal stearates

Polystyrene (PS) nanospheres with a monodisperse size distribution, positive surface charge and high molecular weight were successfully synthesized using various types of metal stearates in an aqueous NaOH medium. The diameter of the PS nanospheres was controlled from 80 to 450 nm by changing the type of metal stearate. It was also found that controlling the NaOH concentration in solution was important for producing monodisperse PS nanoparticles. The nanospheres prepared with zinc stearate possessed a positive surface charge of 60 to 80 mV, confirming that PS particles were functionalized with metal stearates. It is believed that the metal stearates provide PS particles with not only colloidal stability but also a positive surface charge.

Oxidation of 2‐Phenylethylamine with N‐Bromosuccinimide in Acid and Alkaline Media: A Kinetic and Mechanistic Study

AbstractA kinetic study of oxidation of 2‐phenylethylamine (PEA), a bioactive compound, with potent oxidant, N‐bromosuccinimide (NBS) has been carried out in HCl and NaOH media at 313 K. The experimental rate laws obtained are: ‐d [NBS] /dt = k[NBS][PEA][H+] in hydrochloric acid medium and ‐d [NBS]/dt = k[NBS][PEA]x[OH−]y in alkaline medium where x and y are less than unity. Accelerating effect of [Cl−], and retardation of the added succinimide on the reaction rate have been observed in acid medium. Variation of ionic strength of the medium shows negligible effect on rate of reaction in both media. Decrease in dielectric permittivity of the medium decreased the rate in both media. The stoichiometry of the reaction was found to be 1:1 in acid medium and 1:2 in the case of alkaline medium. The oxidation products of PEA were identified as the corresponding aldehyde and nitrile in acid and alkaline medium, respectively. The reactions were studied at different temperatures and the activation parameters have been evaluated. The reaction constants involved in the proposed mechanisms were computed. The reaction was found to be faster in alkaline medium in comparison with the acid medium, which is attributed to the involvement of different oxidizing species. The proposed mechanisms and the derived rate laws are consistent with the observed experimental results.

Influence of co-solvents in the highly efficient selective monohydrolysis of a symmetric diester

The influence of the co-solvents in the selective monohydrolysis of a symmetric diester, in an aqueous NaOH medium at 0 °C, has been examined. The reactions were found to proceed through reaction media consisting of water with a small amount of a co-solvent and the starting symmetric diester. Slightly polar aprotic solvents that are slightly miscible with water, such as THF and acetonitrile, were found to be effective co-solvents.

Hydrogen Transport Conditions and Effects in Cathodically Polarized AF1410 Steel

Hydrogen permeation of AF1410 steel membranes due to cathodic polarization using the Devanathan and Starchurski double cell (DSDC) with 0.1M H2SO4 + 1 g/L Na2HAsO4·7H2O, and 0.1M NaOH media in the input and exit cells, respectively, under Galvanostatic conditions depended on the polarization current density, membrane thickness, and surface roughness. For a 0.35-mm-thick membrane, the steady-state hydrogen permeated using increasing polarization currents from 1.00 to 10.00 mA varied correspondingly from 0.6 × 10−5 (mol H/m2s) to 1.03 × 10−5 mol H/m2s, with accompanying transient rates or permeation rates of 1.07 × 10−4 A/m2s to 4.40 × 10−4 A/m2s. With a constant polarization current density of 20 A/m2, the steady-state permeated hydrogen was in the range of 1.00 × 10−5 (mol H/m2s) to 3.50 × 10−5 (mol H/m2s), for 0.30-mm and 0.09-mm-thick membranes, respectively. The breakthrough times decreased from 2130 to 300 seconds with decreasing membranes thickness from 0.30 to 0.09 mm. The formation of blisters was observed more on the input side surface than on the exit-side surface and occurred for polarization charging current densities greater than 30.0 A/m2. The tendency for blister formation increased with decreasing material’s surface roughness. Cracks accompanying blisters tended to form on both the input and exit-side surfaces only with continued charging following the attainment of steady-state permeation, though they were generally lower on the potentiostated exit side. The average effective permeation coefficient of hydrogen was determined to be 2.89 × 10−12 m2/s for membrane thicknesses ranging from 0.09 to 0.30 mm based on the slope method.

Ruthenium(III) – catalyzed oxidative cleavage of p-aminoazobenzene by chloramine-B in alkaline medium and uncatalyzed reaction in acid medium: spectrophotometric kinetic and mechanistic study

p-Aminoazobenzene (PAAB) is one of the important monoazo dyes and its oxidation kinetic study is of much use in understanding the mechanistic profile of PAAB in redox reactions. Consequently, the kinetics of oxidation of PAAB by sodium N-chlorobenzenesulfonamide or chloramine-B (CAB) in HClO4 medium and in NaOH medium catalyzed by ruthenium(III) chloride (RuIII) have been investigated at 298 K. U.v.–vis spectrophotometry was used as a basic analytical approach in this study. Under an identical set of experimental conditions, the reactions of PAAB–CAB in HClO4 medium were facile, but the reactions became too slow to be studied in alkaline medium and hence ruthenium(III) chloride has been used as a catalyst in alkaline medium. The stoichiometry (1:2) and oxidation products (nitrosobenzene and p-nitrosoaniline) are the same in both media, but the kinetic and mechanistic patterns were found to be different. The experimental rate laws obtained are: − d[CAB]/dt = k [CAB]0 [PAAB]0 [H+] in acid medium and − d[CAB]0/dt = k [CAB]0 [PAAB]0[OH−]x[RuIII]y in alkaline medium, where x and y are less than unity. The reaction was examined with reference to changes in (a) concentration of benzenesulfonamide, (b) concentration of added neutral salts, (c) ionic strength, (d) dielectric permitivity and (e) solvent isotope effect. The reaction was also studied at different temperatures and the overall activation parameters have been evaluated. The oxidation reaction fails to induce the polymerization of added acrylonitrile. C6H4SO2NHCl and C6H4SO2NCl− have been postulated as the reactive oxidizing species in acidic and alkaline media, respectively. It was found that the reactions are nearly 20 times faster in acid medium in comparison with alkaline medium. It was also observed that ruthenium(III) was an efficient catalyst for the facile oxidation of PAAB by CAB in alkaline medium by making the reaction go twelve-fold faster than the uncatalyzed reactions. The catalytic constant (KC) has been calculated at different temperatures and the values of activation parameters with respect to ruthenium(III) have also been evaluated in alkaline medium. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced.

Impedance Analysis and Electrochemical Measurements of A Direct Borohydride Fuel Cell Constructed with Ag Anode

The catalytic activity of the silver metal as regards to the oxidation of borohydride for fuel cell applications was investigated by cyclic voltammetry (CV), open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). It was observed that the oxidized Ag electrode leads to the six-electron oxidation of borohydride. According the CV results, the oxides formed upon the Ag surface have catalytic effect on the oxidation of borohydride. A DBFC was constructed using Ag powder as anode and Ni powder as cathode having Nafion-117 membrane producing a voltage of 0.52 V and a power density of 45 mW /cm2 at room temperature in a %10 NaBH4 in 6 M NaOH medium as anolyte and %3.5 H2O2 solution as an oxidant. The complex plane plots of the electrochemical impedance of Ag electrodes show an apparent inductive semicircle, indicating the presence of the reaction intermediate Ag(HO)2- . Decrease of charge transfer resistances (Rct) observed in Nyquist plots was due to fast kinetics of the Ag2O/Ag couple that Ag2O reduces Ag with NaBH4.

Os(VIII)-catalyzed and uncatalyzed oxidation of biotin by chloramine-T in alkaline medium: Comparative mechanistic aspects and kinetic modeling

Sodium N-chloro- p-toluenesulfonamide (chloramine-T or CAT) is the prominent member of aromatic sulfonyl haloamines and has received considerable attention as a mild oxidant for several organic compounds. d-Biotin, a member of the B-vitamin family, is an essential nutrient in human nutrition as is commonly referred to as Vitamin H. Controlled oxidation of biotin to biotin sulfoxide forms a very important synthetic route in biochemical reactions. Optimum conditions have been developed for the oxidation of biotin to biotin sulfoxide. Literature survey has revealed that no attention has been paid towards the controlled oxidation of biotin to biotin sulfoxide by N-haloamines from the kinetic and mechanistic view points. This prompted us to undertake the title investigation. The kinetics of Os(VIII) catalyzed and uncatalyzed oxidation of biotin by CAT have been studied in NaOH medium at 303 K under identical experimental conditions. The stoichiometry (1:1) and the oxidation product (biotin sulfoxide) are the same for Os(VIII) catalyzed and uncatalyzed reactions. Biotin sulfoxide was confirmed by GC–MS analysis. In Os(VIII) catalyzed oxidation, the rate law is −d[CAT]/dt = k[CAT][Os(VIII)]/[NaOH] but it takes the form −d[CAT]/dt = k[CAT][Biotin] x /[NaOH] − y for uncatalyzed reaction, where x and y are less than unity. The reaction was subjected to changes in: (a) concentration of added reduction product of CAT, p-toluenesulfonamide, (b) ionic strength, (c) dielectric permittivity and (d) halide ions effect in both the cases. Proton inventory studies made in a mixture of H 2O–D 2O indicated the participation of OH − ion in the formation of transition state. The reaction fails to initiate polymerization of acrylonitrile. Activation parameters for the composite reaction were deduced from Arrhenius plots. In case of uncatalyzed reactions, the reaction constants involved in the proposed scheme were deduced. Under the identical set of experimental conditions, the kinetics of Os(VIII) catalyzed oxidation of biotin by CAT in alkaline medium has been compared with uncatalyzed reactions, revealing that the catalyzed reactions are eight fold faster than the uncatalyzed reactions. Hence, Os(VIII) acts as an efficient catalyst for the oxidation of biotin by CAT in alkaline medium. The catalytic constant ( K C) has been calculated at different temperatures and the values of activation parameters with respect to catalyst have been evaluated from the plots of log K C versus 1/ T. Some spectroscopic evidence for the formation of 1:1 complex between oxidant and Os(VIII) has been obtained. CH 3C 6H 4SO 2NHCl has been postulated as the reactive oxidizing species in both the cases. The observed experimental results have been explained by plausible mechanisms and the related rate laws have been deduced for both catalyzed and uncatalyzed reactions.

A multisyringe flow-through sequential extraction system for on-line monitoring of orthophosphate in soils and sediments

A fully automated flow-through microcolumn fractionation system with on-line post-extraction derivatization is proposed for monitoring of orthophosphate in solid samples of environmental relevance. The system integrates dynamic sequential extraction using 1.0 mol l −1 NH 4Cl, 0.1 mol l −1 NaOH and 0.5 mol l −1 HCl as extractants according to the Hieltjes–Lijklema (HL) scheme for fractionation of phosphorus associated with different geological phases, and on-line processing of the extracts via the Molybdenum Blue (MB) reaction by exploiting multisyringe flow injection as the interface between the solid containing microcolumn and the flow-through detector. The proposed flow assembly, capitalizing on the features of the multicommutation concept, implies several advantages as compared to fractionation analysis in the batch mode in terms of saving of extractants and MB reagents, shortening of the operational times from days to hours, highly temporal resolution of the leaching process and the capability for immediate decision for stopping or proceeding with the ongoing extraction. Very importantly, accurate determination of the various orthophosphate pools is ensured by minimization of the hydrolysis of extracted organic phosphorus and condensed inorganic phosphates within the time frame of the assay. The potential of the novel system for accommodation of the harmonized protocol from the Standards, Measurement and Testing (SMT) Program of the Commission of the European Communities for inorganic phosphorus fractionation was also addressed. Under the optimized conditions, the lowest detectable concentration at the 3 σ level was ≤0.02 mg P l −1 for both the HL and SMT schemes regardless of the extracting media. The repeatability of the MB assay was better than 2.5% and the dynamic linear range extended up to 7.0 mg P l −1 in NH 4Cl and NaOH media and 15 mg P l −1 whenever HCl is utilized as extractant for both the HL and SMT protocols.

Corrosion and its inhibition in SA213-T22 TIG weldments used in power plants under neutral and alkaline environments

Failures of industrial boilers have been reported to be mainly due to water side corrosion and scaling. Boiler corrosion is due to highly alkaline or acidic conditions of the boiler water. The present work has been aimed at investigating the corrosion behaviour of T22 (2.25 Cr–1 Mo) boiler steel TIG weldments in neutral and alkaline media. The parent metal and weld root regions are chosen as regions of exposure for the study made at room temperature and at 100 °C. Electrochemical polarization technique such as Tafel line extrapolation (Tafel) was used to measure the corrosion current. Corrosion inhibition using thiourea at 100 ppm concentration was studied in these experiments. Micro-structural observation and surface characterization using SEM and XRD studies have been made on samples exposed at 100 °C. The results show that parent metal experiences higher corrosion rate than weld metal and thiourea as inhibitor is found unsuitable in NaOH medium.

Exhausted fluid catalytic cracking catalysts as raw materials for zeolite synthesis

The utilization of exhausted fluid catalytic cracking (FCC) catalysts as raw materials for the zeolite synthesis was analyzed. Samples of the catalysts directly released from FCC units and the corresponding impact grinding pretreated samples were used. Mechanical treatment was observed to decrease catalyst crystallinity and particle size. The catalyst reactivity was analyzed in terms of conversion in zeolite and product properties. Hydrothermal synthesis experiments in NaOH medium were performed. Catalysts conversion in A and X type zeolites was obtained for treated and not treated samples. In particular, high conversion in NaX type were achieved using the more siliceous catalyst, whereas grinding activation produces a decrease of particle size and Al/Si ratio of the zeolites obtained.

On the vibrational behaviour of cyanide adsorbed at Pt(1 1 1) and Pt(1 0 0) surfaces in alkaline solutions

This communication deals with the vibrational behaviour of cyanide adlayers formed on Pt(1 1 1) and Pt(1 0 0) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C–N stretching frequency in acidic electrolytes with quite a low uncertainty. Owing to the stability of the cyanide adlayer in alkaline solutions, experiments performed in NaOH medium are usually perturbed by the significant overlapping of the reference and the sample FTIR spectra. Deconvolution of the spectra was carried out assuming a Lorentz oscillator. The procedure allowed to confirm that two potential regions with different band centre frequency tuning coexist for Pt(1 1 1)–CN in perchloric acid medium. Conversely, in the alkaline electrolyte a single tuning rate for the band position was found for both surfaces studied. The lack of reorientation of the C–N molecular axis together with the occurrence of a certain screening effect of negatively charged hydroxyl anions on the electric field at the interface could be at the origin of the different behaviour displayed in both electrolytic media.