Green Synthesis of Silver Nanoparticle in Calotropis Procera flower extract and its application for Fe2+sensing in aqueous solution

The silver nanoparticles (AgNPs) was synthesized in Calotropis procera extract. The synthesized AgNPs were characterized by UV–vis spectoscopy, dynamic light scattering (DLS)and transmission electron microscopy (TEM). DLS and TEM analysis of the synthesized AgNPs clearly showed the nanoscale particle size distribution having spherical shaped morphology. The color change and spectral shift in absorption spectrum after addition of Fe2+ ion to AgNPs solution develop a simple and quick method for quantitative determination of Fe2+ from aqueous solution without any interference from excipients. The selective adsorption of Fe2+ ions over the nano particle surface and mechanism of binding was supported by Langmuir adsorption plot, zeta sizer and absorption titration results. The results suggest that the synthesized AgNPs to be used as an ideal, eco-friendly nano probe for selective and sensitive detection of Fe2+ ion in aqueous medium based on adsorption studies. The present method successfully applied for the quantitative analysis of Fe2+ ion in samples collected from local area having limit of detection 4.29 µg/mL. The method offers a simple, selective, economical approach for quantitative detection of Fe2+ in environmental samples without any pretreatment

Kinetics and mechanism of pyridinium chlorochromate oxidation of thallium(I)

307-310The oxidation of TI(I) by pyridinium chlorochromate has been studied in 2.0 mol dm-3 hydrochloric acid. The reaction exhibits total second order kinetics, first order in each reactant and it is catalysed by hydrogen and chloride ions. The active species have been found to be protonated pyridinium chlorochromate of the oxidant and TICl2- of the reductant respectively. Added products, TI(III) , and Mn(II) have no significant effect on the reaction. The protonation constant of the pyridinium chlorochromate has also been evaluated as 8.0×10-2 dm3 mol-1 from the [H+] dependence of the reaction. A plausible mechanism is proposed based on the experimental observations

Oxidation of tellurium(IV) by tetrabutylammonium tribromide

2048-2050The reaction between tetra butylammonium tribromide and tellurium(IV) has been studied in 50% (vlv) acetic acid under second order conditions. The overall order of reaction is found to be two, unity each in both the reactants. The reaction involves a direct two-electron transfer step since the test for the formation of free radicals due to single electron step was negative. The reaction is retarded by hydrogen ions due to protonation prior equilibria of the reductant, tellurium(IV). The active species of the reactants is found to be tribromide ion of the oxidant and HTeO3ˉ of the reductant. Considerable decrease in the entropy of activation of the reaction indicates formation of an ordered transition state between the two reactants analogous to that in alcohol oxidation by tetrabutylammonium tribromide ion

Outer-sphere electron transfer from platinum(II) to Keggin-type 12-tungstocobaltate( III) in the presence and absence of chloride ions

799-802  The reaction between Pt(II) and [COIIIW12O40]5- proceeds with two, one-electron steps involving formation of unstable Pt(III) followed by its reaction with another oxidant. The reaction rate is unaffected by the [H+] as there are no protonation equlibria involved with both the reactant s whereas, chloride ion accelerates the reaction and the reaction follows chloride independent and dependent paths leading to a two term rate law, rate= {k1 + Kk2 [Clˉ]} [Pt(II)] [CoIIIW12O40]5-.   The chloride ion dependent path is due to rapid substitution of chloride ion on PtCl42-. The products formed have been found to be PtCl4(aq) and PtCl62- in the absence and presence of chloride ion respectively. Increase in the ionic strength and decrease in the relative permittivity of the medium increase the rate of the reaction. This is due to the formation of an outer-sphere complex between the two reactants. The activation parameters in the presence and absence of chloride ions have also been determined and the values support the proposed mechanism

Kinetics and mechanism of uncatalyzed and selenium dioxide catalyzed oxidation of nicotinic acid hydrazide by bromate

70-76The uncatalyzed and selenium dioxide catalyzed oxidation of nicotinic acid hydrazide, (NIH) by bromate has been studied in hydrochloric acid medium. The –NH2 of hydrazoic moiety and pyridine nitrogen of the NIH forms protonated species which are involved in two ion pair complexes with the oxidant in prior equilibria. In case of uncatalyzed reaction the complex with the protonated hydrazoic moiety decomposes to give corresponding acyl diimide intermediate while that of the pyridine nitrogen decreases the rate of reaction. In presence of selenium dioxide as catalyst, the NIH reduces the catalyst to H2SeO2 species which is oxidized by the oxidant to complete its catalytic cycle. The product of the reaction is found to be nicotinic acid and there is no intervention of any free radicals. A rate law derived for both the reactions satisfy the kinetic data obtained and UV-spectrophotometer examination of the reaction mixture also support the mechanisms proposed

Kinetics and mechanism of oxidation of arsenous acid by Waugh-type enneamolybdomanganate(IV)

398-401The reaction between As(III) and Waugh-type enneamolybdomanganate(IV) has been studied in perchloric acid medium. The reaction follows a second order kinetics with an order of unity each on both the reactants and proceeds with a complimentary two-electron outer-sphere path. The reaction is accelerated by [H+] ions due to protonation equilibria of the oxidant. The first two protonation constants of the enneamolybdomanganate(IV) anion have been determined by pH metric titration and found to be 2.0 × 103 and 316 dm3 Mol-1. The product of reaction, enneamolybdomanganous(II) has been synthesized to study the effect of the added product. Both ammonium salts of enneamolybdomanganate(IV) and enneamolybdomanganous(II) have been characterized by FTIR and AAS. The reaction is unaffected by change in ionic strength and the free radical test is negative which suggests direct two-electron transfer from As(III) to oxidant. Di-protonated form of enneamolybdomanganate(IV) has been found to be active oxidant species. The solvent polarity and the thermodynamic parameters suggest the outer sphere mechanism

Kinetics and mechanism of oxidation of tellurium(IV) by pyridinium chlorochromate in aqueous hydrochloric acid

1268-1271The oxidation of tellurium(IV) by pyridinium chlorochromate has been studied in aqueous hydrochloric acid at 30°C. The reaction follows rate law( i),where <span style="font-size:15.0pt;mso-bidi-font-size: 9.0pt">K1, and K2 are the equilibrium constants of the protonation equilibria (ii) and the … </span

Chromium (VI) Oxidation of Thallium(I) in Aqueous Acetic Acid & Effect of Added Vanadium(V) on the Reaction

494-49

Kinetics and mechanism of oxidation of aliphatic alcohols by oxone catalyzed by Keggin type 12-tungstocobaltate(II)

1626-1630The oxidation of various aliphatic alcohols by ox one catalyzed by Kegin type [CoIIW12O40]6- has been studied in a buffer medium of pH = 4. The reaction proceeds by the oxidation of [CoIIW12O40]6- to [CoIIIW12O40]5- by oxone which then oxidizes the alcohol in a rate &nbsp;determining step generating alcohol free radical. The reaction is accelerated by increase in the pH of the solution due to the protonation equilibria of the oxidant. The reaction between oxone and [CoIIW12O40]6- has also studied and is found to proceed in two one-electron steps, involving formation HSO52- &nbsp;free radical in a slow first step followed by its reaction with reductant in a fast step. The reaction rate is inhibited by the [H+] due to protonation equili bria of HSO5- which is the active species. Decreasing the relative permittivity of the medium increases the rate of the reaction which is attributed to the formation of an outer-sphere complex between the reactants. The activation parameters determined for both the reactions support the proposed mechanisms

Analysis of Chromium(III) by a Kinetic Method

176-17