Persulfate Ions Research Articles

Effects of operational parameters on the decolorization of C.I. Reactive Red 198 in UV/TiO 2-based systems

The effects of pH, dye concentration, electron acceptor (hydrogen peroxide, persulfate and copper ions) and hydroxyl radical trap (ethanol) on the decolorization of C.I. Reactive Red 198 using a UV/TiO 2 system were determined. Decolorization rate increased as the concentration of persulfate ions added increased. The k values followed the order: pH 4 > pH 7 > pH 10 for the UV/TiO 2, UV/TiO 2/H 2O 2 and UV/TiO 2/Na 2S 2O 8 systems. Hydrogen peroxide, persulfate and copper ions trapped photogenerated electrons and inhibited the recombination of electron/hole pairs in UV/TiO 2, thereby accelerating decolorization rate; persulfate ions trapped photogenerated electrons and generated sulfate free radicals. The addition of ethanol inhibited decolorization, suggesting that the predominant decolorization pathway involves hydroxyl radicals and that direct oxidation by photogenerated holes is also significant.

Spectroelectrochemistry of hollow spherical CdSe quantum dot assemblies in water

The hollow spherical CdSe QD assemblies were synthesized via a sonochemical approach that utilizes β-cyclodextrin as a template reagent in aqueous solution. The hollow nanospheres have an average diameter of 70 nm and are found to consist of an assembly of monodispersed 5 nm sized CdSe quantum dots. Following an electrochemical reaction with persulfate ions, strong electrogenerated chemiluminescence (ECL) was observed from the CdSe nanoassemblies suspended in an aqueous solution of pH ⩽ 7.95. The study indicates that the morphology of the 70 nm nanoassembly plays an important role in generating the stable ECL since individually dispersed quantum dots did not exhibit any significant ECL. The unique ECL intensity and stability of the synthesized spherical nanoassemblies could allow for potential sensor applications of CdSe quantum dots in water.

Spectroscopic characterization of polyaniline formed in the presence of montmorillonite clay

This work shows the spectroscopic characterization of polyaniline–montmorillonite clay (PANI–MMT) composites prepared by polymerization of aniline in aqueous suspensions of montmorillonite clay and camphorsulfonic acid containing persulfate ions as oxidizing agent. X-ray diffraction, scanning electron microscopy, and X-ray absorption near Silicon K-edge data show that morphologies and structures of PANI–MMT nanocomposites depend on their relative amount. The electrical conductivity values of composites increase from 10−4 to 10−1S/cm−1 when PANI–MMT ratio increases, and percolation threshold is observed when polymer/clay mass ratio is changed. Resonance Raman, UV–VIS–NIR spectroscopy, electron spin resonance (EPR) and X-ray absorption near Nitrogen K-edge data confirm that PANI has emeraldine salt form for all PANI–MMT materials prepared.

Catalytic decomposition of organic anions in alkaline radioactive waste: II. oxidation of N-(2-Hydroxyethyl)ethylenediaminetriacetate

Decomposition of N-(2-hydroxyethyl)ethylenediam inetriacetate (HEDTA) in alkaline solutions containing H2O2, S2O 8 2− , and ClO− and under the action of ozone was studied titrimetrically. HEDTA decomposes in the presence of cobalt or copper salts at stepwise addition of H2O2. In the reaction between HEDTA and persulfate ion, an induction period was observed. It shortens with increasing alkali concentration, or temperature, or with decreasing the initial HEDTA concentration. Nitrite ion does not affect the complexone decomposition. The process is initiated by thermal dissociation of persulfate ions into radical ions followed by chain reaction. Hypochlorite ions effectively decompose HEDTA. Porducts of HEDTA decomposition are oxidized by ozone and persulfate mainly to oxalate and carbonate.

Catalytic decomposition of organic anions in alkaline radioactive waste: III. Oxidation of oxalate and glycolate

Decomposition of oxalate and glycolate ions in alkaline solutions under the action of O3, H2O2, and Na2S2O8 was studied spectrophotometrically and titrimetrically. At 20°C, ozone slowly decomposes oxalate in 0.05 M NaOH. In 1 M NaOH, heating at 90°C is required to oxidize oxalate with ozone. Glycolate is readily oxidized with ozone at 20°C in 0.05–1 M NaOH, predominantly into oxalate. Hydrogen peroxide is ineffective reagent for oxalate and glycolate decomposition. Persulfate oxidizes oxalate ion in 0.5–5 M NaOH at 90°C. The reaction of persulfate with glycolate proceeds at 50°C and higher temperatures and is characterized by an induction period, which shortens with increase in concentration of S2O82−, OH−, and temperature, or in the presence of AgNO3 and K4Fe(CN)6. Oxidation involves thermal dissociation of persulfate ions into radical ions followed by a chain reaction.

Efficient Photochemical Decomposition of Long-Chain Perfluorocarboxylic Acids by Means of an Aqueous/Liquid CO2 Biphasic System

Photochemical decomposition of persistent and bioaccumulative long-chain (C9-C11) perfluorocarboxylic acids (PFCAs) with persulfate ion (S2O8(2-)) in an aqueous/liquid CO2 biphasic system was examined to develop a technique to neutralize stationary sources of the long-chain PFCAs. The long-chain PFCAs, namely, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUA), which are used as emulsifying agents and as surface treatment agents in industry, are relatively insoluble in water but are soluble in liquid CO2; therefore, introduction of liquid CO2 to the aqueous photoreaction system reduces the interference of colloidal PFCA particles. When the biphasic system was used to decompose these PFCAs, the extent of reaction was 6.4-51 times as high as that achieved in the absence of CO2. In the biphasic system, PFNA, PFDA, and PFUA (33.5-33.6 micromol) in 25.0 mL of water were 100%, 100%, and 77.1% decomposed, respectively, after 12 h of irradiation with a 200-W xenon-mercury lamp; F- ions were produced as a major product, and short-chain PFCAs, which are less bioaccumulative than the original PFCAs, were minor products. All of the initial S2O8(2-) was transformed to SO42-. The system also efficiently decomposed PFCAs at lower concentrations (e.g., 4.28-16.7 micromol of PFDA in 25.0 mL) and was successfully applied to decompose PFNA in floor wax.

Kinetics of Technetium Reactions: XV. Tc(IV) Oxidation with Persulfate Ions in HClO4 Solution

Tc(IV) is oxidized with persulfate ions in HClO4 solution by reactions with both S2O 8 2− ion and product of its thermal decomposition, Caro acid, H2SO5. The reaction rate at 35°C and solution ionic strength µ = 1 is described by the equation d[Tc(IV)]/dt = k 1[Tc(IV)][S2O 8 2− ] + k 3[Tc(IV)][HSO 5 − ]/[H+], where k 1 = 0.88±0.04 l mol−1 min−1 and k 3 = 110±5 min−1. With increasing ionic strength to µ = 2, both rate constants decrease (k 1 = 0.58±0.08 l mol−1 min−1 and k 3 = 52±2 min−1 at 35°C). The activation energy of the overall reaction is 77.7±8.1 kJ mol−1. The mechanisms of both reactions are discussed.

Efficient Decomposition of Environmentally Persistent Perfluorocarboxylic Acids by Use of Persulfate as a Photochemical Oxidant

Photochemical decomposition of persistent perfluorocarboxylic acids (PFCAs) in water by use of persulfate ion (S2O8(2-)) was examined to develop a technique to neutralize stationary sources of PFCAs. Photolysis of S2O8(2-) produced highly oxidative sulfate radical anions (SO4-), which efficiently decomposed perfluorooctanoic acid (PFOA) and other PFCAs bearing C4-C8 perfluoroalkyl groups. The major products were F- and CO2; also, small amounts of PFCAs with shorter than initial chain lengths were detected in the reaction solution. PFOA at a concentration of 1.35 mM (typical of that in untreated wastewater after an emulsifying process in fluoropolymer manufacture) was completely decomposed by a photochemical system with 50 mM S2O8(2-) and 4 h of irradiation from a 200-W xenon-mercury lamp. The initial PFOA decomposition rate was 11 times higherthan with photolysis alone. All sulfur-containing species in the reaction solution were eventually transformed to sulfate ions by this method. This method was successfully applied to the decomposition of perfluorononanoic acid contained in a floor wax solution.

Palladized aluminum as a novel substrate for the non-electrolytic preparation of a Prussian Blue film modified electrode

A new type of Prussian Blue (PB) modified electrode is presented on the basis of a simple chemical modification of palladized aluminum surfaces. Electroless deposition of metallic palladium on the aluminum electrode (aluminum palladization) provides a suitable surface for the non-electrolytic deposition of PB, formulated as KFe III[Fe II(CN) 6], films from a solution of ferric ferricyanide. The PB films prepared in such a way are stable, thin, homogeneous and electrochemically active. The electrochemical behavior of the palladized aluminum-based PB modified electrode (PB/Pd-Al) has been investigated. The cyclic voltammetry of the PB/Pd-Al modified electrode exhibits two reversible redox couples resulting from Fe 3+/Fe 2+ and [Fe(CN) 6] 3−/[Fe(CN) 6] 4− transitions in the film. The effect of supporting electrolyte cations, pH and successive potential cycling on the electrochemical behavior and the stability of the modified electrode were investigated. The transfer coefficient ( α), rate constants of electron transfer ( k s) and apparent diffusion coefficients of hydrated potassium ion in the film ( D app) for each redox couple were also determined. The PB/Pd-Al modified electrode was used to electrocatalyze the reduction of persulfate ions.

Interaction of polyquaternary ammonium salt and persulfate

An interaction between poly(diallyldimethylammonium chloride) and ammonium persulfate in aqueous solutions has been detected and studied by methods of turbidimetry and viscometry. Investigations were carried out with the cationic polymer of different molecular weight. It was shown that association between low-molecular-weight polyquaternary ammonium salt polycations and persulfate anions was predominant over the chemical (redox) reaction with counterions Cl–. Appreciably stable interaction products (gels, suspensions, solids) were prepared by mixing aqueous solutions of poly(diallyldimethylammonium chloride) and ammonium persulfate. The phenomenon was associated with structural complementarity of both reagents and capacity of the divalent persulfate ions to bind two charged polymer groups by intra- and interchain bridges. Stoichiometry of complexes and their thermal stability in water were examined.

Promoted Dissociative Adsorption of Hydrogen Peroxide and Persulfate Ions and Electrochemical Oscillations: Caused by a Catalytic Effect of Adsorbed Bromine

Adsorbed bromine on Pt and Au electrodes acts as a catalyst for dissociative adsorption of and similar to adsorbed OH (and adsorbed iodine). This fact is revealed by analyses of newly found negative differential resistances and electrochemical oscillations, appearing in a potential region where the surface coverage of adsorbed bromine decreases steeply. The present result further supports the generality of a catalytic effect of adsorbed electronegative species such as OH, Br, and I on the dissociative adsorption of peroxides such as and © 2002 The Electrochemical Society. All rights reserved.

Electroluminescence from porous silicon in the cathodic reduction of persulfate ions: Degree of reversibility of the tuning effect

The temporal evolution of the spectra of cathodic electroluminescence from porous silicon in an electrolyte containing persulfate ions S2O 8 2− was studied in the galvanostatic mode. It was shown that irreversible changes in luminescence properties of porous silicon occur under cathodic polarization. These changes are manifested in a decrease in the signal intensity and a long-wavelength shift of the electroluminescence (EL) spectrum when the substrate potential remains virtually unchanged (pseudo-tuning). The irreversibility of the change in luminescence parameters is related to a concurrent electrochemical oxidation of the surface of porous silicon, which hinders the bipolar injection of carriers into luminescence-active crystallites. The results obtained suggest that the degradation phenomena observed under cathodic polarization are due to those same processes which are responsible for EL excitation, which casts doubt on the interpretation of the tuning effect, known in the literature, as a consequence of a purely electronic process in porous silicon.

Molecular Description of the Persulfate Ion Reduction on a Mercury Electrode

The polarization curves for the S2O82- electroreduction on a mercury electrode at high overvoltages and various concentrations of a surface-inactive supporting electrolyte are modeled within modern theory of charge transfer in polar media and quantum-chemical approaches. Based on an analysis of the reactant adsorption in terms of a cluster model, the conclusion is drawn that the persulfate ion is localized in the diffuse part of EDL. When calculated the current, it was assumed that the transfer of the first electron, accompanied by the bond cleavage, is the limiting stage of the total two-electron process. The integration if performed over the entire electron spectrum of the metallic electrode and an attempt is made to account for electrostatic and solvation effects on a molecular level. It is shown that the experimentally-studied overvoltage interval corresponds to the occurrence of the process near the activationless region. The increase in the current at high negative charges of the surface is due to an increase in the reaction layer thickness. This effect arises from a change in the ratio between contributions made by the reactants at the distance of closest approach and the species farther away.

Surface modification of low density polyethylene using accelerated decomposition of potassium persulfate and ceric ion induced acrylamide grafting

Surface modification of low density polyethylene using accelerated decomposition of potassium persulfate and ceric ion induced acrylamide grafting

Catalytic Decomposition of Organic Anions in Alkaline Radioactive Waste: 1. EDTA Oxidation

Decomposition of ethylenediaminetetraacetate in alkaline solutions with H2O2, Na2S2O8, NaClO, and NaBrO was studied titrimetrically. EDTA is oxidized in solutions heated above 60°C in the presence of cobalt salts at stepwise addition of excess H2O2. The reaction between persulfate and EDTA has an induction period decreasing with increasing NaOH concentration and temperature and with decreasing initial EDTA content or with adding AgNO3, K4Fe(CN)6, or NaNO2. The process involves thermal dissociation of the persulfate ions into radical ions and the subsequent development of a chain reaction. Hypochlorite ions oxidize EDTA in 0.5-5.0 M NaOH at 25-60°C. The process efficiency can be improved by fractional addition of the oxidant in the presence of Co(II) or Ni(II) salts. EDTA is oxidized in alkaline solutions with hypobromite ions only on heating to 95°C. Salts of Co(II), Ni(II), and Cu(II) accelerate the process.

Conducting Polyaniline/Calixarene Salts: Synthesis and Properties

Emeraldine base has been doped with the sulfonated calixarene host species, calix[4]-p-tetrasulfonic and calix[6]-p-hexasulfonic acid in water or DMSO solvents, yielding novel colloidal conducting emeraldine salts PAn.calix[4]SO3H and PAn.calix[6]SO3H. The colloidal polyaniline products were characterized by UV−vis and FTIR spectra, cyclic voltammetry, particle size analysis, and transmission electron microscopy. The polyelectrolyte dopants conferred enhanced stability on the emeraldine salts toward alkaline dedoping, with only partial conversion to emeraldine base occurring even at pH 14. The emeraldine salts could, however, be readily oxidized by persulfate ion at pH 2 to the pernigraniline salt forms, while oxidation at pH 12 generated pernigraniline base. Reduction at pH 12 using hydrazine hydrate yielded the fully reduced leucoemeraldine base.

Quantized electroluminescence from Q–CdS films immersed in aqueous electrolytes

Quantum dot electrodes (QDEs) have been constructed by deposition of Q–CdS particles onto indium–tin oxide substrates. Upon application of cathodic potentials to the electrodes in electrolytes containing persulfate ions (S 2O 8 2−), light emission is observed. The emission peak depends on the particle size, with electrolyte electroluminescence (EEL) being observed down to 478 nm (blue light) for CdS with a particle size of 3.6 nm.

Spectral Shifts of Electroluminescence from Porous n‐Si under Cathodic Bias

Spectral shifts of visible electroluminescence (EL) from cathodically biased n‐Si in electrolyte solution containing persulfate ions are described. The electrochemically etched n‐Si cathodes exhibit a blue shift of the EL with the increase of applied potential. It is explained that the blue shift is caused by the formation of an accumulation layer and the Fermi level pinning in the porous Si. A study of the EL as a function of time at a constant potential shows a red shift, which can be attributed to the bandgap lowering caused by the conversion of the predominant surface bonds Si‐H to Si‐Si. Electropolymerization of aniline on the porous Si surface enhanced the stability of the EL possibly due to the strengthening of the surface bonds.

Light-induced electroluminescence of porous silicon layers on p-Si in persulfate solution

Electroluminescence has been observed using the photostimulated reduction of persulfate ions at porous silicon layers grown on p−-Si substrates. Electrons were generated in the substrate by illumination from the ohmic contact side. The detection of visible electroluminescence shows that photogenerated electrons accumulate in the porous layer when the p− substrate is reverse biased. Voltage tuning of the electroluminescence spectrum was observed, but the tuning saturated when the reduction of persulfate became light limited. The tuning is attributed to the switching on of electroluminescence as electrons progressively populated particles of decreasing size, followed by switching off by Auger quenching when a second electron is captured before radiative decay occurs.

Study of the thermal decomposition of potassium persulfate by potentiometry and capillary electrophoresis

Two methods of analysis, potentiometry and capillary electrophoresis, were used to study the decomposition of potassium persulfate (KPS) in aqueous solutions. The experiments were carried out in a glass reactor equipped with continuous control of temperature and pH during the reaction. The effect of the pH on the decomposition of KPS was investigated. The rate of KPS decomposition in the presence of a variety of additives (surfactants, inhibitor, monomer-like molecules, and monomers), which are used in emulsion polymerization recipes, was also studied over the temperature range of interest. The rate of disappearance of the persulfate ion was greatly increased in the presence of hydroquinone, but changed very little in the presence of surfactants. © 1996 John Wiley & Sons, Inc.