Sulfate Radical Anion Research Articles

Theoretical and experimental studies of the spin trapping of inorganic radicals by 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 3. Sulfur dioxide, sulfite, and sulfate radical anions.

Radical forms of sulfur dioxide (SO(2)), sulfite (SO(3)(2-)), sulfate (SO(4)(2-)), and their conjugate acids are known to be generated in vivo through various chemical and biochemical pathways. Oxides of sulfur are environmentally pervasive compounds and are associated with a number of health problems. There is growing evidence that their toxicity may be mediated by their radical forms. Electron paramagnetic resonance (EPR) spin trapping using the commonly used spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), has been employed in the detection of SO(3)(•-) and SO(4)(•-). The thermochemistries of SO(2)(•-), SO(3)(•-), SO(4)(•-), and their respective conjugate acids addition to DMPO were predicted using density functional theory (DFT) at the PCM/B3LYP/6-31+G**//B3LYP/6-31G* level. No spin adduct was observed for SO(2)(•-) by EPR, but an S-centered adduct was observed for SO(3)(•-)and an O-centered adduct for SO(4)(•-). Determination of adducts as S- or O-centered was made via comparison based on qualitative trends of experimental hfcc's with theoretical values. The thermodynamics of the nonradical addition of SO(3)(2-) and HSO(3)(-) to DMPO followed by conversion to the corresponding radical adduct via the Forrester-Hepburn mechanism was also calculated. Adduct acidities and decomposition pathways were investigated as well, including an EPR experiment using H(2)(17)O to determine the site of hydrolysis of O-centered adducts. The mode of radical addition to DMPO is predicted to be governed by several factors, including spin population density, and geometries stabilized by hydrogen bonds. The thermodynamic data supports evidence for the radical addition pathway over the nucleophilic addition mechanism.

Efficient decomposition of perfluoroether carboxylic acids in water with a combination of persulfate oxidant and ultrasonic irradiation

The decomposition of perfluoroether carboxylic acids CF3OC2F4OCF2COOH, CF3OC2F4OC2F4OCF2COOH, CF3OC3F6COOH, C2F5OC2F4OCF2COOH, and C4F9OC2F4OC2F4OCF2COOH and perfluoroalkylether sulfonates C2F5OC2F4SO3− and C3F7OC2F4SO3− in water with a combination of persulfate oxidant and ultrasonic irradiation was investigated. In the absence of persulfate, the perfluoroether acids decomposed quite slowly. For example, the pseudo-first-order rate constants for the decomposition of perfluoroether carboxylic acids ranged from 2.03×10−2 to 3.34×10−2h−1. After 24h, 44.2–58.0% of the initial concentrations (ca. 50μM) of the substrates remained, and the F− yields were 27.7–59.7%. In contrast, the addition of persulfate dramatically accelerated the reactions. When 10mM persulfate was used, the pseudo-first-order rate constants for the decomposition of perfluoroether carboxylic acids were 2.5–3.9 times those in the absence of persulfate. However, the addition of persulfate did not enhance the decomposition of perfluoroalkylether sulfonates. Enhancement of the perfluoroether carboxylic acid decomposition can be explained by acceleration of substrate decarboxylation, induced by sulfate radical anions formed from the persulfate during ultrasonic irradiation.

Sulfate radical anion oxidation of diclofenac and sulfamethoxazole for water decontamination

This study aimed at investigating the reactivity of aniline-based pharmaceuticals with sulfate radical anion generated by the peroxymonosulfate (PMS)/Cobalt(II) system and by taking sulfamethoxazole and diclofenac as probe compounds. Transformation pathways were proposed for both pharmaceuticals relying on the identification of the main reaction intermediate products using liquid chromatography coupled to time of flight mass spectrometry. For diclofenac, the major transformation pathway led to the formation of a quinone imine derivative while for sulfamethoxazole a nitro derivative was obtained as the major intermediate. However, in both cases, oxidative reactions started with the formation of a N-centered radical probably through an one-electron transfer from the pharmaceutical to sulfate radical anion. This was followed by further multistep degradation involving decarboxylation, hydroxylation and bond cleavage reactions in route to mineralization. From a kinetic point of view, aniline-based pharmaceuticals quickly reacted with sulfate radical anion with second order kinetic rate constants in the 9–10×109M−1s−1 range. Sulfate radical-based technologies show promising results for the removal of these particular pharmaceuticals from wastewater treatment plant effluents mainly because of the higher selectivity of sulfate radical anion over hydroxyl radical, limiting radical scavenging by natural organic matter and allowing for higher abatement and mineralization rates.

Pulse radiolysis studies of functionally substituted imidazolium-based ionic liquids

The reactions of imidazolium-based ionic liquids having different substituent groups on the ring with hydrated electrons (e −aq ), hydroxyl radicals (•OH), and sulfate anion radicals (SO •−4 ) were investigated using nanosecond pulse radiolysis techniques. The spectra of these ionic liquids on reaction with eaq − all exhibited a similar peak at about 320 nm, and a typical peak for e −aq in aqueous ionic liquid solutions. The reaction rate constants for 1,3-disubstituted imidazolium-based ionic liquid hexafluorophosphates (BMIPF6) with eaq − were deduced to be 1010 L mol−1 s−1, however the values were lower for trisubstituted ionic liquids. For example, the rate constant for 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMIBF4) was 5.5×109 L mol−1 s−1. Imidazolium-based ionic liquids reacted with hydroxyl radicals via adducts to produce a mixture of isomeric OH adducts, and the pk a value of the OH adducts was deduced to be 8.4±0.4 for 1-butyl-3-methylimdazolium tetrafluoroborate (BMIBF4). Moreover, imidazolium cations were also oxidized by SO4 •− to produce bivalent cation radicals, which exhibit a peak at 320 nm, and these rate constants are of the same order of magnitude, i.e., 109 L mol−1 s−1, except that for 1-(2-hydroxyethyl)-3-methylimdazolium tetrafluoroborate with SO4 •− (k=2.8×108 L mol−1 s−1). Theoretical calculations were carried out to estimate the structures of the products of reduction by eaq −1 and the results were related to the experimental data.

Formation of reactive sulfite-derived free radicals by the activation of human neutrophils: An ESR study

The objective of this study was to determine the effect of (bi)sulfite (hydrated sulfur dioxide) on human neutrophils and the ability of these immune cells to produce reactive free radicals due to (bi)sulfite oxidation. Myeloperoxidase (MPO) is an abundant heme protein in neutrophils that catalyzes the formation of cytotoxic oxidants implicated in asthma and inflammatory disorders. In this study sulfite (•SO3−) and sulfate (SO4•−) anion radicals are characterized with the ESR spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in the reaction of (bi)sulfite oxidation by human MPO and human neutrophils via sulfite radical chain reaction chemistry. After treatment with (bi)sulfite, phorbol 12-myristate 13-acetate-stimulated neutrophils produced DMPO–sulfite anion radical, –superoxide, and –hydroxyl radical adducts. The last adduct probably resulted, in part, from the conversion of DMPO–sulfate to DMPO–hydroxyl radical adduct via a nucleophilic substitution reaction of the radical adduct. This anion radical (SO4•−) is highly reactive and, presumably, can oxidize target proteins to protein radicals, thereby initiating protein oxidation. Therefore, we propose that the potential toxicity of (bi)sulfite during pulmonary inflammation or lung-associated diseases such as asthma may be related to free radical formation.

Exploring the application of conjugated polymer nanoparticles in chemical sensing: detection of free radicals by a synergy between fluorescent nanoparticles of two conjugated polymers

Two classical conjugated polymers, poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), commonly used in organic optoelectronic devices are endowed with a new function for radical sensing. The synergetic effect between MEH-PPV and PFO nanoparticles (NPs) plays an important role in the detection of hydroxyl radicals and sulfate anion radicals. When exposed to free radicals, MEH-PPV NPs are subjected to attack by the radicals and undergo molecular structure changes. Thus, a strong-polarity shell can be formed on the radical treated MEH-PPV NPs. When such radical treated MEH-PPV NPs come into close contact with PFO NPs, a new phenomenon whereby PFO alters its fluorescence emission intensity of the 0–2 transition relative to the 0–0 transition band is observed. The relative intensity ratio of these two transition bands can serve as an index for the hydroxyl radical concentration. Therefore, radical detection can be realized by measuring the solid state fluorescence, which is highly desired in off-site laboratory determination since solid samples are more convenient for storage and transport than solutions. Our results can open a way for the application of conjugated polymer nanoparticles in chemical/biological sensing.

Sulfate radical anion as a new reagent for fast photochemical oxidation of proteins.

The focus is to expand the original design of fast photochemical oxidation of proteins (FPOP) and introduce SO(4)(-•), generated by 248 nm homolysis of low millimolar levels of persulfate, as a radical reactant in protein footprinting. FPOP is a chemical approach to footprinting proteins and protein complexes by "snapshot" reaction with free radicals. The radical used until now is the OH radical, and it provides a measure of residue-resolved solvent accessibility of the native protein. We show that FPOP can accommodate other reagents, increasing its versatility. The new persulfate FPOP system is a potent, nonspecific, and tunable footprinting method; 3-5 times less persulfate is needed to give the same global levels of modification as seen with OH radicals. Although solvent-exposed His and Tyr residues are more reactive with SO(4)(-•) than with (•)OH, oxidation of apomyoglobin and calmodulin shows that (•)OH probes smaller accessible areas than SO(4)(-•), with the possible exception of histidine. His64, an axial ligand in the heme-binding pocket of apomyoglobin, is substantially up-labeled by SO(4)(-•) relative to (•)OH. Nevertheless, the kinds of modification and residue selectivity for both reagent radicals are strikingly similar. Thus, the choice of these reagents relies on the physical properties, particularly the membrane permeability, of the radical precursors.

Catalytic activity of the SO 4[rad]− radical for photodegradation of the azo dye Cibacron Brilliant Yellow 3 and 3,4-dichlorophenol: Optimization by application of response surface methodology

Advanced oxidation processes (AOP) generate in situ active radicals with a high oxidation potential, allowing for the destruction of polluting agents through organic compound mineralization. The use of experimental design is a tool that allows adjustment of factors to obtain an optimal response in experimental analysis. We used multivariate analysis to optimize the process of organic removal from wastewater in a cylindrical reactor, using UV radiation (254 nm) and peroxodisulfate as an oxidant. We used 3,4-dichlorophenol and Cibacron Brillant Yellow 3 (CBY-3) as model organic compounds. Both of these compounds are characteristic polluting agents present in industrial wastewater. We used a factorial 2 n design to obtain the best experimental conditions to efficiently remove the compounds from the solution, using time and oxidant concentration as experimental variables. The initial concentration of both compounds was 100 ppm, and we obtained 90% dichlorophenol removal, with a rate constant of 0.0386 min −1. Degradation of azo dye was more efficient reaching 98%, with a rate constant of 0.0908 min −1. In both cases, the optimal time for reducing the maximum concentration was 60 min of irradiation. Total organic carbon (TOC) reduction was analyzed to determine the efficiency of the UV/K 2S 2O 8 process in mineralization, where we obtained 90% TOC reduction for both organic compounds. At the same time, the dye compound, CBY-3, whose organic structure is more complex, generated nitrate and chloride ions as mineralization products. The efficient mineralization of both compounds is based on the in situ formation of the strong oxidant sulfate anion radical ( E = 2.5–3.1 V).

Mechanism of Base Activation of Persulfate

Base is the most commonly used activator of persulfate for the treatment of contaminated groundwater by in situ chemical oxidation (ISCO). A mechanism for the base activation of persulfate is proposed involving the base-catalyzed hydrolysis of persulfate to hydroperoxide anion and sulfate followed by the reduction of another persulfate molecule by hydroperoxide. Reduction by hydroperoxide decomposes persulfate into sulfate radical and sulfate anion, and hydroperoxide is oxidized to superoxide. The base-catalyzed hydrolysis of persulfate was supported by kinetic analyses of persulfate decomposition at various base:persulfate molar ratios and an increased rate of persulfate decomposition in D(2)O vs H(2)O. Stoichiometric analyses confirmed that hydroperoxide reacts with persulfate in a 1:1 molar ratio. Addition of hydroperoxide to basic persulfate systems resulted in rapid decomposition of the hydroperoxide and persulfate and decomposition of the superoxide probe hexachloroethane. The presence of superoxide was confirmed with scavenging by Cu(II). Electron spin resonance spectroscopy confirmed the generation of sulfate radical, hydroxyl radical, and superoxide. The results of this research are consistent with the widespread reactivity reported for base-activated persulfate when it is used for ISCO.

Protein Radical Formation Resulting from Eosinophil Peroxidase-catalyzed Oxidation of Sulfite

Eosinophil peroxidase (EPO) is an abundant heme protein in eosinophils that catalyzes the formation of cytotoxic oxidants implicated in asthma, allergic inflammatory disorders, and cancer. It is known that some proteins with peroxidase activity (horseradish peroxidase and prostaglandin hydroperoxidase) can catalyze oxidation of bisulfite (hydrated sulfur dioxide), leading to the formation of sulfur trioxide anion radical ((.)SO(3)(-)). This free radical further reacts with oxygen to form peroxymonosulfate anion radical ((-)O(3)SOO(.)) and the very reactive sulfate anion radical (SO(4)()), which is nearly as strong an oxidant as the hydroxyl radical. However, the ability of EPO to generate reactive sulfur radicals has not yet been reported. Here we demonstrate that eosinophil peroxidase/H(2)O(2) is able to oxidize bisulfite, ultimately forming the sulfate anion radical (SO(4)()), and that these reactive intermediates can oxidize target proteins to protein radicals, thereby initiating protein oxidation. We used immuno-spin trapping and confocal microscopy to study protein oxidation by EPO/H(2)O(2) in the presence of bisulfite in a pure enzymatic system and in human promyelocytic leukemia HL-60 clone 15 cells, maturated to eosinophils. Polyclonal antiserum raised against the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) detected the presence of DMPO covalently attached to the proteins resulting from the DMPO trapping of protein free radicals. We found that sulfite oxidation mediated by EPO/H(2)O(2) induced the formation of radical-derived DMPO spin-trapped human serum albumin and, to a lesser extent, of DMPO-EPO. These studies suggest that EPO-dependent oxidative damage may play a role in tissue injury in bisulfite-exacerbated eosinophilic inflammatory disorders.

Photochemical decomposition of perfluorodecanoic acid in aqueous solution with VUV light irradiation

The photochemical decomposition of perfluorodecanoic acid (PFDeA) in water in the presence of persulfate ion (S 2O 8 2−) and sulfur ion (S 2−) was investigated under vacuum ultraviolet (VUV) light irradiation. PFDeA was decomposed under VUV light irradiation. With the addition of S 2O 8 2− or S 2−, the photo-decomposition and defluorination of PFDeA were enhanced significantly. Sulfate radical anion (SO 4 − ) generated from photolysis of S 2O 8 2− initiated PFDeA oxidation. While the S 2− ion, acting as a OH scavenger, enhanced the role of reduction pathway induced by aqueous electrons (e aq −). The shorter-chain perfluorocarboxylic acids (PFCAs), formed in a stepwise manner from longer-chain PFCAs, were identified as products by HPLC/MS.

Sonochemical oxidation of arsenic(III) to arsenic(V) using potassium peroxydisulfate as an oxidizing agent

The sonochemical oxidation of As(III) in the presence of peroxydisulfate ion (PDS) has been investigated. Sulfate anion radicals and OH radicals produced during acoustic cavitation readily oxidized As(III) to As(V) in an aqueous environment. The rate of oxidation of As(III) was remarkably high (∼10 times) with respect to the concentration of PDS. The As(III) oxidation was found to be independent of the initial pH of the solution in the range 3–8. It was relatively low at pH above 8, however, this could be circumvented by increasing the concentration of PDS. The presence of oxygen in solution played a significant role in the rate of oxidation of As(III). Around 40% oxidation of As(III) was observed in the absence of oxygen compared to 80% oxidation in the presence of dissolved oxygen (10 mg/L) over a sonication time of 5 min. The addition of humic acid (HA) retarded the oxidation rate of As(III), but the effect could be offset by using larger amounts of PDS. The effects of ultrasound intensity, and frequency on the rate of the oxidation of As(III) were also studied. The rate of the oxidation of As(III) was not significantly dependent on the acoustic power applied, for the concentrations of As(III) used in this study. At an ultrasound frequency of 211 kHz, the rate of oxidation of As(III) was lower than that observed at 20 kHz. It is concluded that the sonochemical treatment of As(III) solutions in the presence of PDS is a simple and viable technique for the oxidation of As(III) to As(V).

(Bi)sulfite Oxidation by Copper,Zinc-Superoxide Dismutase: Sulfite-Derived, Radical-Initiated Protein Radical Formation

BackgroundSulfur dioxide, formed during the combustion of fossil fuels, is a major air pollutant near large cities. Its two ionized forms in aqueous solution, sulfite and (bi)sulfite, are widely used as preservatives and antioxidants to prevent food and beverage spoilage. (Bi)sulfite can be oxidized by peroxidases to form the very reactive sulfur trioxide anion radical (•SO3−). This free radical further reacts with oxygen to form the peroxymonosulfate anion radical (−O3SOO•) and sulfate anion radical (SO4• −).ObjectiveTo explore the critical role of these radical intermediates in further oxidizing biomolecules, we examined the ability of copper,zinc-superoxide dismutase (Cu,Zn-SOD) to initiate this radical chain reaction, using human serum albumin (HSA) as a model target.MethodsWe used electron paramagnetic resonance, optical spectroscopy, oxygen uptake, and immuno-spin trapping to study the protein oxidations driven by sulfite-derived radicals.ResultsWe found that when Cu,Zn-SOD reacted with (bi)sulfite, •SO3− was produced, with the concomitant reduction of SOD-Cu(II) to SOD-Cu(I). Further, we demonstrated that sulfite oxidation mediated by Cu,Zn-SOD induced the formation of radical-derived 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin-trapped HSA radicals.ConclusionsThe present study suggests that protein oxidative damage resulting from (bi)sulfite oxidation promoted by Cu,Zn-SOD could be involved in oxidative damage and tissue injury in (bi)sulfite-exacerbated allergic reactions.

Rate constants and conversion ratios for aqueous‐phase reactions of SO with CnF2n+1C(O)O−(n= 4–7) at 298 K

AbstractKinetic data for aqueous‐phase reactions of sulfate anion radicals (SO) with perfluorocarboxylates (CnF2n+1C(O)O−) are needed to evaluate removal and transformation processes of CnF2n+1C(O)O−species in the environment, but rate constants for the reactions of SOwith CnF2n+1C(O)O−(kn) have been reported only for short‐chain CnF2n+1C(O)O−species (n= 1–3). Since CnF2n+1C(O)O−reacted with SOto form CmF2m+1C(O)O−(m<n), we determined relative rateskn−1/knfor the reactions of SOwith CnF2n+1C(O)O−(n= 4–7), along with conversion ratios for conversion of CnF2n+1C(O)O−into Cn−1F2n−1C(O)O−(αn) and into Cn−2F2n−3C(O)O−(βn) at 298 K. SOwas photolytically generated from S2Oby use of sunlamps (λ ≈ 310 nm). Even ifknandkn−1change with increasing ionic strength,kn−1/kncan be determined whenkn−1/knand αnremain almost constant during the reaction. The values ofkn/k1forn= 4–7 were nearly equal, and their average was 0.82 ± 0.04 (2σ). Conversion ratios of αnand βnwere mostly independent ofnforn= 4–7, and their averages were 0.77 ± 0.07 (2σ) and 0.13 ± 0.08, respectively. Branching ratios of reactions of a possible intermediate (CnF2n+1O•), reaction of CnF2n+1O•with H2O, and fission of the CC bond of CnF2n+1O•, seemed to determine αnand βn. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 735–747, 2009

A combined theoretical and experimental study on the oxidation of fulvic acid by the sulfate radical anion

The kinetics of the reaction of sulfate radicals with the IHSS Waskish peat fulvic acid in water was investigated in the temperature range from 289.2 to 305.2 K. The proposed mechanism considers the reversible binding of the sulfate radicals by the fulvic acid. The kinetic analysis of the data allows the determination of the thermodynamic parameters DeltaG degrees = -10.2 kcal mol(-1), DeltaH degrees = -16 kcal mol(-1) and DeltaS degrees = -20.3 cal K(-1) mol(-1) for the reversible association at 298.2 K. Theoretical (DFT) calculations performed with the Buffle model of the fulvic acids support the formation of H-bonded adducts between the inorganic radicals and the humic substances. The experimental enthalpy change compares well with the theoretical values found for some of the investigated adducts.

Radical intermediates generated in the reactions of l-arginine with hydroxyl radical and sulfate radical anion: A pulse radiolysis study

Reactions of l-arginine (Arg) with hydroxyl radical ( OH) and sulfate radical anion (SO 4 − ) were kinetically investigated by the pulse radiolysis technique. Hydrogen abstraction from Arg by OH afforded redox chemically oxidizing, neutral, and reducing carbon-centered Arg radicals. Kinetic properties of the radicals indicated that the reducing species might include the δ-C-centered Arg radical and CO 2 radical anion. Similar transient spectra were observed in the SO 4 − reaction with Arg, suggesting direct oxidation at the guanidino group is less likely.

Properties and Reactivity of the Adenosine Radical Generated by Radiation-Induced Oxidation in Aqueous Solution

The formation of oxidation products of DNA bases induced by hole injection into DNA duplexes is closely related to the characteristics of the radical species generated, especially those from purine bases possessing lower oxidation potentials than pyrimidines. To investigate the reactivities of adenosine base radicals generated from the radical cations of adenosine (Ado), we have conducted extensive pulse radiolysis and steady-state X-radiolysis investigations of Ado under the conditions generating oxidizing radical species such as the sulfate radical anion (SO(4)(-*)). Kinetic analysis of the transient absorption spectra demonstrated that the redox-neutral radical of adenosine [Ado(-H)(*)] decays via a homogeneous bimolecular reaction, recombines with an alkyl alcohol radical, or abstracts hydrogen from the phosphate ion, with rate constants of 2k = 4.2 x 10(8) M(-1) s(-1) and k = 6.4-8.5 x 10(8) and 10(3)-10(4) M(-1) s(-1), respectively. High-dose pulsed electron beam irradiation, which generates high concentrations of Ado(-H)(*) during the radiolysis, yielded 8-oxo-7,8-dihydroadenosine (8-oxo-Ado) with a G value of 0.018 x 10(-7) mol J(-1). It is thus proposed that the disproportionation of Ado(-H)(*) might lead to the formation of 8-oxo-Ado as a minor process, which is in addition to the widely accepted mechanism in which the addition of hydroxyl radical to Ado initiates its formation.

Carbon- and nitrogen-centered radicals produced from l-lysine by radiation-induced oxidation: A pulse radiolysis study

Radical species generated from the reactions of a basic amino acid, l-lysine (Lys), with hydroxyl radicals ( OH) and sulfate radical anion ( SO 4 - ) have been detected by the method of pulse radiolysis. On the basis of electron transfer reactivities toward tetranitromethane (TNM), it was demonstrated that reducing carbon-centered radicals are generated as a result of hydrogen abstraction from CH 2 of Lys with a G-value of 1.9 × 10 −7 mol J −1. On the other hand, direct oxidation of l-Lys by SO 4 - formed a transient species with different spectroscopic properties, most likely, the ε-N-centered Lys radical.

A pulse radiolysis study on the reactions of hydroxyl radical and sulfate radical anion with guanidine derivatives in aqueous solution

The reactions of hydroxyl radical ( OH) with guanidine, 1,1-dimethylguanidine, and 1-ethylguanidine have been investigated by the method of pulse radiolysis. The characteristic absorption observed in the OH reaction with guanidine under basic conditions was assigned to a nitrogen-centered radical. On the other hand, reducing carbon-centered radicals were generated in the OH reaction with 1,1-dimethylguanidine and 1-ethylguanidine over a pH range of 7–13, which may suggest that the primarily formed nitrogen-centered radicals at a high pH are converted into carbon-centered radicals by hydrogen atom shift. Similar transient species were also observed in the reaction of sulfate radical anion with the guanidine derivatives.

Photochemical Oxidation of Arsenic(III) to Arsenic(V) using Peroxydisulfate Ions as an Oxidizing Agent

The photochemical oxidation of arsenic, As(III), to the less toxic As(V) using peroxydisulfate ions (S2O8(2-)) as the oxidizing agent under UV light irradiation was investigated. The photochemical oxidation of As(III) to As(V) assisted using peroxydisulfate ions (KPS) proved to be a simple and efficient method, and the rate of oxidation for As(III) was exceptionally high in accordance with the concentration of KPS. In this study, the UV light intensity was of primary importance for the dissociation of the KPS in generating sulfate anion radicals (SO4(-*)). Upon intense UV light irradiation, very efficient oxidation was achieved due to the complete decomposition of KPS into SO4(-*) radicals which favor a higher reaction rate. Subsequent pH variation from 3 to 9 was seen to have no influence on the photolytic cleavage of KPS, and hence, the reaction was unaltered. There was also no significant effect from the continuous purging of oxygen or dissolved oxygen before the reaction as the air-equilibrated condition was found to be sufficient for efficient oxidation. However, the continuous purging of nitrogen substantially reduced the reaction rate (20%), confirming that the dissolved oxygen plays a role in this reaction, although at high concentrations of KPS, this situation was overcome. Humic acid was also found to have no detrimental effect on the reaction rate, even at 20 ppm concentration. The resultant SO4(2-) obtained in this studywas,thus, not considered a pollutant. Moreover, there was no need for a sensitizer or other metals with highly alkaline conditions that are normally used in conjunction with KPS. Natural solar light could also effectively oxidize As(III) at room temperature. This simple technique was, thus, considered a cost-effective and safe method for the oxidation of As(III) to As(V).