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1.
Chemosphere ; 248: 126000, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-32007774

RESUMO

Recently, the technology for the remediation of Cr(VI) pollutant via bisulfite has been found to be effective for fast elimination of co-contaminants especially in acidic solution, where free radicals (i.e., sulfate and/or hydroxyl radicals) are proposed to act as dominant oxidants. Here, it was demonstrated that high-valent Cr intermediate played a primary role in the Cr(VI)/bisulfite system through applying methyl phenyl sulfoxide (PMSO) as a probe. PMSO was effectively transformed in the Cr(VI)/bisulfite system with appreciable generation of methyl phenyl sulfone (PMSO2) product, while PMSO was oxidized by free radicals to hydroxylated and/or polymeric products rather than PMSO2. The involvement of high-valent Cr species was further supported by the formation of 18O-labeled PMSO2 in 18O labeling experiments, where the incorporation of 18O from solvent water H218O into PMSO2 was likely resulted from competitive oxygen exchange of Cr-oxo species with water. The relative contribution of high valent Cr species versus free radicals was evaluated based on the yield of PMSO2, which was dependent on the solution chemistry such as [Cr(VI)]:[bisulfite] ratio and dissolved oxygen. This work advances the understanding of chromium chemistry involved in the Cr(VI)/bisulfite system. These findings have important implications on the application of this "waste control by waste" technology for environmental decontamination.

2.
Chemosphere ; 235: 104-112, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31255750

RESUMO

In this study, the potential applicability of potassium permanganate (Mn(VII)) for anilines elimination was systematically investigated firstly, with a focus on the effect of manganese intermediates on the kinetics of anilines versus phenols. It was found that Mn(VII) could fairly oxidize anilines, where the second-order rate constants (kMn(VII)) values for anilines always decreased as pH increased from 5 to 9. This interesting pH-dependency was successfully described by the kinetic models proposed in literature to account for the unusual pH-rate profiles for phenols, where the formation of intermediates between Mn(VII) and phenols or anilines was likely involved. The effect of manganese products such as MnO2 and Mn(III) on the oxidation of anilines by Mn(VII) was demonstrated. Under slightly acidic conditions, the reactions of Mn(VII) with anilines displayed autocatalysis, suggesting a similar catalytic role of MnO2 formed in situ as compared to phenols. Several ligands (e.g., pyrophosphate) inhibited the formation of MnO2 colloids and lowered the oxidation rates of anilines by Mn(VII) at acidic pH, while these ligands greatly accelerated the kinetics of phenols under similar conditions. The contrasting effects of ligands might be mainly attributed to the different reactivity of ligand-stabilized Mn(III) formed in situ toward anilines vs phenols. The complex effect of humic acid was highly dependent on solution pH, possible due to the dual role of humic acid that it could act as a reductant (competitively consuming Mn(VII) and phenoxy or aniline radical) as well as a ligand (stabilizing manganese intermediates such as Mn(III) species) to affect Mn(VII) reactions.


Assuntos
Compostos de Anilina/química , Compostos de Manganês/química , Manganês/química , Óxidos/química , Permanganato de Potássio/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Compostos de Anilina/análise , Catálise , Substâncias Húmicas , Oxirredução , Fenóis
3.
Water Res ; 159: 454-463, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31125805

RESUMO

Aqueous aggregation kinetics of manganese oxides, the solid products formed during water treatment and subsurface remediation with permanganate, are crucial for its application. In this study, manganese oxides nanoparticles were in situ formed in a permanganate/(bi)sulfite system, which was found to have excellent oxidation ability. Aggregation kinetics of such manganese oxides (i.e., MnOx-1.5, MnOx-2.5 and MnOx-5; the number represents the molar ratio of (bi)sulfite to permanganate) were evaluated by employing time-resolved dynamic light scattering under various aquatic conditions. In NaNO3 solution, the stability of manganese oxides decreased in the order of MnOx-1.5 > MnOx-2.5 > MnOx-5, indicated by their critical coagulation concentrations (CCCs). X-ray photoelectron spectroscopy (XPS) and zeta potential measurements indicated that MnII/III were responsible for the decreased stability due to their charge neutralization effects. However, in Ca(NO3)2 solution, three manganese oxides had similar CCCs, probably due to the relatively great charge neutralization ability of Ca2+. Suwannee River fulvic acid (SRFA), through electrosteric interaction, suppressed the aggregation of MnOx-1.5 in Ca(NO3)2 solution, but had no such effect in NaNO3 solution. Comparatively, the stability of MnOx-5 was markedly enhanced with SRFA in NaNO3 solutions. It was proposed that Ca2+ and MnII/III could increase the adsorption of SRFA through charge neutralization and cation bridging. This study highlights the dual role, dependent on either presence or absence of SRFA, of Ca2+ and MnII/III in controlling the aggregation of manganese oxides nanoparticles.


Assuntos
Compostos de Manganês , Óxidos , Cinética , Oxirredução , Sulfitos
4.
Chemosphere ; 228: 602-610, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31059958

RESUMO

Recent studies have reported a novel advanced oxidation process (AOP) by combining permanganate (KMnO4) and peroxymonosulfate (PMS) for destruction of organic contaminants (i.e., acid orange 7, trichloroethylene, and benzene), where hydroxyl (•OH) and sulfate radicals (SO4•-) are proposed to be generated from PMS activation by amorphous manganese dioxide (MnO2) formed in situ from KMnO4 reduction. In this work, appreciable degradation of p-chlorobenzoic acid (p-CBA) was confirmed in KMnO4/PMS system, while KMnO4 or PMS alone showed inert reactivity toward p-CBA. Moreover, it was found that pre-synthesized amorphous MnO2 showed invalid PMS activation for p-CBA degradation, and pre-addition of inorganic or organic reducing agents to promote the formation of amorphous MnO2 showed negligible influence on p-CBA degradation as well. In these regards, a tentative mechanism for PMS activation by KMnO4 rather than its product MnO2 was proposed, involving the substitution of oxo atoms of KMnO4 by peroxo groups, subsequent reductive generation of peroxomanganese (VI) complexes, and intramolecular disproportionation of these complexes to generate radicals. Efficient degradation of p-CBA was achieved at acid or basic conditions with a maximum rate occurring at pH 3. The coexisting chloride anions showed suppressive effect on p-CBA degradation for scavenging SO4•- and •OH, while metal ions accelerated the degradation of p-CBA, possibly due to the cation bridging function between negatively-charged MnO4- and HSO5-. Hydroxylated intermediates of p-CBA were identified in KMnO4/PMS system. This work improved the fundamental understanding of a new class of AOPs by combining KMnO4 and PMS for environmental decontamination.


Assuntos
Compostos de Manganês/química , Óxidos/química , Peróxidos/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Concentração de Íons de Hidrogênio , Radical Hidroxila/química , Compostos Orgânicos/química , Oxirredução , Sulfatos
5.
Environ Sci Technol ; 53(7): 3689-3696, 2019 04 02.
Artigo em Inglês | MEDLINE | ID: mdl-30888798

RESUMO

Recently, it has been reported that the combination of permanganate (Mn(VII)) and bisulfite can lead to a rapid degradation of organic contaminants, where soluble Mn(III) is proposed to be responsible. Interestingly, in this work, we demonstrated the involvement of high-valent Mn-oxo species (possibly Mn(V)) as well as sulfate radical in the Mn(VII)/bisulfite system, by using methyl phenyl sulfoxide (PMSO) as a chemical probe. It was found that the combination of Mn(VII) and bisulfite resulted in appreciable degradation of PMSO under various conditions, while negligible PMSO was degraded by manganese dioxide (MnO2) in the presence of bisulfite under similar conditions. This result indicated that Mn(III) intermediate formed in situ in both Mn(VII)/bisulfite and MnO2/bisulfite systems as proposed in literature exhibited sluggish reactivity toward PMSO. In parallel, the formation of methyl phenyl sulfone (PMSO2) product in the Mn(VII)/bisulfite system was observed, suggesting the role of high-valent Mn-oxo species as an oxygen-atom donor in conversion of PMSO to PMSO2. Moreover, the yield of PMSO2 (i.e., mole of PMSO2 produced per mole of PMSO degraded) was quantified to be 20-100%, strongly depending on the [Mn(VII)]/[bisulfite] ratio as well as solution pH. The competitive contribution of sulfate radical, which oxidized PMSO to hydroxylated and/or polymeric products but not to PMSO2, accounted for the yield of PMSO2 less than 100%. This work advances the fundamental understanding of a novel class of oxidation technology based on the combination of Mn(VII) and bisulfite for environmental decontamination.


Assuntos
Manganês , Sulfatos , Compostos de Manganês , Oxirredução , Óxidos , Sulfitos
6.
Sci Total Environ ; 661: 670-677, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30684835

RESUMO

It is reported that methylparaben (MeP, a widely used phenolic preservative) and its major metabolite p­hydroxybenzoic acid (p-HBA) display estrogenic activity and are frequently detected in various environmental settings. Naturally occurring manganese dioxide (MnO2) plays an important role in attenuation of contaminants released into the environment, and the presence of iodide (I-) may affect these processes. In this work, it was found that both MeP and p-HBA displayed considerable reactivity towards MnO2 with their half-lives increased with decreasing MnO2 concentrations or increasing pH. The presence of I- obviously accelerated the transformation efficiency of MeP and p-HBA by MnO2 with stronger enhancement at higher I- concentrations or lower pH. Dimeric products (e.g., dimeric MeP or p-HBA) were generated from MeP/p-HBA treated by MnO2, and iodinated aromatic products (e.g., mono-/di-iodinated MeP/p-HBA) were additionally identified in the presence of I-. Higher concentrations of these iodinated aromatic products were generally formed at higher I- or lower MnO2 concentrations or lower pH. Ecotoxicity analysis showed that dimeric and iodinated aromatic products were more eco-toxic than parent MeP/p-HBA. This work shows that MnO2 may greatly affect the fate of MeP and p-HBA released into the environment, and the presence of I- can significantly affect these processes.

7.
Chemosphere ; 217: 402-410, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30439654

RESUMO

Recent studies have reported that permanganate (Mn(VII)) shows a good performance in treatment of phenolic compounds, and the presence of iodide (I-) may display a great impact on Mn(VII) oxidation with the formation of toxic iodinated aromatic products. In this work, transformation of bisphenol AF (BPAF) and bisphenol S (BPS) by Mn(VII) in the absence or presence of I- was studied. Mn(VII) showed considerable reactivity towards BPAF with apparent second-order rate constants (0.09-1.65 M-1s-1) higher than those of Mn(VII) with BPS (0.02-0.12 M-1s-1) reported in literature over the pH range of 5-9. The presence of I- apparently accelerated the transformation rates of BPAF and BPS by Mn(VII), and these results could be explained by the contribution of hypoiodous acid (HOI) in situ formed from Mn(VII) oxidation of I-. A kinetic model involving the competitive reactions (i.e., Mn(VII) with I- and bisphenols, HOI with Mn(VII) and bisphenols) well simulated BPAF/BPS transformation by Mn(VII) in the presence of I- under various conditions. Hydroxylated, bond-cleavage, and polymeric products were identified from BPAF/BPS oxidation by Mn(VII), and iodinated aromatic products (e.g., mono- and multi-iodinated BPAF/BPS) were additionally detected in the presence of I-. Reaction pathways involving Mn(VII) one-electron oxidation as well as HOI substitution of BPAF/BPS were proposed. Eco-toxicity analysis by ECOSAR showed that the toxicity of these products generally followed the order of polymeric and iodinated aromatic products > parent BPAF/BPS > hydroxylated products > bond-cleavage products.


Assuntos
Compostos Benzidrílicos/química , Iodetos/química , Compostos de Manganês/química , Óxidos/química , Fenóis/química , Cinética
8.
Environ Sci Technol ; 52(22): 13325-13335, 2018 11 20.
Artigo em Inglês | MEDLINE | ID: mdl-30346162

RESUMO

Many investigations focused on the capacity of ferrate for the oxidation of organic pollutant or adsorption of hazardous species, while little attention has been paid on the effect of ferrate resultant nanoparticles for the removal of organics. Removing organics could improve microbiological stability of treated water and control the formation of disinfection byproducts in following treatment procedures. Herein, we studied ferrate oxidation of p-arsanilic acid ( p-ASA), an extensively used organoarsenic feed additive. p-ASA was oxidized into As(V), p-aminophenol ( p-AP), and nitarsone in the reaction process. The released As(V) could be eliminated by in situ formed ferric (oxyhydr) oxides through surface adsorption, while p-AP can be further oxidized into 4,4'-(diazene-1,2-diyl) diphenol, p-nitrophenol, and NO3-. Nitarsone is resistant to ferrate oxidation, but mostly adsorbed (>85%) by ferrate resultant ferric (oxyhydr) oxides. Ferrate oxidation (ferrate/ p-ASA = 20:1) eliminated 18% of total organic carbon (TOC), while ferrate resultant particles removed 40% of TOC in the system. TOC removal efficiency is 1.6 to 38 times higher in ferrate treatment group than those in O3, HClO, and permanganate treatment groups. Besides ferrate oxidation, adsorption of organic pollutants with ferrate resultant nanoparticles could also be an effective method for water treatment and environmental remediation.


Assuntos
Nanopartículas , Poluentes Químicos da Água , Purificação da Água , Adsorção , Ferro , Oxirredução
9.
Water Res ; 147: 321-330, 2018 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-30317041

RESUMO

Roxarsone (ROX) is used in breeding industry to prevent infection by parasites, stimulate livestock growth and improve pigmentation of livestock meat. After being released into environment, ROX could be bio-degraded with the formation of carcinogenic inorganic arsenic (As) species. Here, ferrate oxidation of ROX was reported, in which we studied total-As removal, determined reaction kinetics, identified oxidation products, and proposed a reaction mechanism. It was found that the apparent second-order rate constant (kapp) of ferrate with ROX was 305 M-1s-1 at pH 7.0, 25 °C, and over 95% of total As was removed within 10 min when ferrate/ROX molar ratio was 20:1. Species-specific rate constants analysis showed that HFeO4- was the dominant species reacting with ROX. Ferrate initially attacked AsC bond of ROX and resulted in the formation of arsenate and 2-nitrohydroquinone. The arsenate was simultaneously removed by ferric nanoparticles formed in the reduction of ferrate, while 2-nitrohydroquinone was further oxidized into nitro-1,4-benzoquinone. These results suggest that ferrate treatment can be an effective method for the control of ROX in water treatment.


Assuntos
Arsênico , Nanopartículas , Roxarsona , Ferro , Oxirredução
10.
Water Res ; 145: 210-219, 2018 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-30142519

RESUMO

While fluoroquinolone (FQ) antibiotics are susceptible to degradation by sulfate and/or hydroxyl radicals formed in peroxymonosulfate (PMS) based advanced oxidation processes, here we report that unactivated PMS itself exhibits a specific high reactivity toward FQs for the first time. Reaction kinetics of PMS with two model FQs, ciprofloxacin (CF) and enrofloxacin (EF), showed a strong pH dependency with apparent second-order rate constants of 0.10-13.05 M-1s-1 for CF and 0.51-33.17 M-1s-1 for EF at pH 5-10. This pH dependency was well described by species-specific parallel reactions. On the basis of reaction kinetics and structure-activity assessment, the tertiary and secondary aliphatic N4 amines on the FQs' piperazine ring were proposed to be the main reaction sites. High performance liquid chromatography/electrospray ionization tandem mass analysis showed the formation of hydroxylated, N-oxide, and dealkylated products. Bacterial growth inhibition bioassays using Escherichia coli showed that oxidation products of FQs by PMS retained negligible antibacterial potency in comparison to parent FQs. Kinetic modeling using the rate constants estimated from pure water well predicted the oxidation kinetics of low levels of CF and EF by PMS in surface water. The degradation efficiency of FQs by PMS in surface water was slightly lower than that by ozone, comparable to that by ferrate, and much higher than that by permanganate. These results suggest that PMS is a promising oxidant for the treatment of FQs in water.


Assuntos
Antibacterianos , Poluentes Químicos da Água , Fluoroquinolonas , Cinética , Oxirredução , Peróxidos
11.
Water Res ; 143: 47-55, 2018 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-29940361

RESUMO

In this work, transformation of bisphenol A (BPA) alternatives bisphenol AF (BPAF) and bisphenol S (BPS) by manganese dioxide (MnO2) and the effect of iodide (I-) during these processes were investigated in comparison with BPA for the first time. These three bisphenols showed appreciable reactivity towards MnO2 with the half-lives of their loss following the order of BPA < BPAF < BPS under similar conditions, and a higher transformation efficiency was generally obtained at a lower pH. The presence of I- apparently accelerated the transformation of BPAF and BPS by MnO2 at pH ≤ 7 but negligibly affected BPA transformation over the pH range of 5-9. This discrepancy could be well explained by the relative contribution of hypoiodous acid (HOI) in situ formed from I- oxidation by MnO2. Polymers, hydroxylated derivatives, and bond-cleavage products were detected from BPAF and BPS treated by MnO2, where a series of reactions of BPAF/BPS radicals formed from one-electron oxidation of BPAF/BPS were likely involved, similar to the case of BPA reported in literature. A group of iodinated aromatic products were additionally identified from BPAF/BPS treated by MnO2 in the presence of I- (e.g., iodinated BPAF/BPS and iodinated BPAF/BPS dimers), and they could be further transformed. This study suggests that naturally occurring manganese oxides play a significant role in the attenuation of bisphenols released into the environment and the presence of I- can display a great effect on their transformation.


Assuntos
Compostos Benzidrílicos/química , Iodetos/química , Compostos de Manganês/química , Óxidos/química , Fenóis/química , Sulfonas/química , Poluentes Químicos da Água/química , Concentração de Íons de Hidrogênio , Oxirredução
12.
Environ Sci Technol ; 52(8): 4785-4793, 2018 04 17.
Artigo em Inglês | MEDLINE | ID: mdl-29584950

RESUMO

In previous studies, we interestingly found that several ligands (e.g., pyrophosphate, nitrilotriacetate, and humic acid) could significantly accelerate the oxidation rates of triclosan (TCS; the most widely used antimicrobial) by aqueous permanganate (Mn(VII)) especially at acid pH, which was ascribed to the contribution of ligand-stabilized Mn(III) (defined Mn(III)L) formed in situ as a potent oxidant. In this work, it was found that the oxidation of TCS by Mn(III)L resulted in the formation of dimers, as well as hydroxylated and quinone-like products, where TCS phenoxy radical was likely involved. This transformation pathway distinctly differed from that involved in Mn(VII) oxidation of TCS, where 2,4-dichlorophenol (DCP) was the major product with a high yield of ∼80%. Surprisingly, we found that the presence of various complexing ligands including pyrophosphate, nitrilotriacetate, and humic acid, as well as bisulfite slightly affected the yields of DCP, although they greatly enhanced the oxidation kinetics of TCS by Mn(VII). This result could not be reasonably explained by taking the contribution of Mn(III)L into account. Comparatively, the degradation of TCS by manganese dioxide (MnO2) was also greatly enhanced in the presence of these ligands with negligible formation of DCP, which could be rationalized by the contribution of Mn(III)L. In addition, it was demonstrated that DCP could not be generated from Mn(VII) oxidation of unstable phenoxy radical intermediates and stable oxidation products formed from TCS by Mn(III)L. These findings indicate that manganese intermediates other than Mn(III) are likely involved in the Mn(VII)/TCS/ligand systems responsible for the high yields of DCP product.


Assuntos
Triclosan , Substâncias Húmicas , Ligantes , Oxidantes , Oxirredução
13.
Water Res ; 138: 56-66, 2018 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-29573629

RESUMO

Recently, in situ chemical oxidation (ISCO) using peroxymonosulfate (PMS) for environmental decontamination has received increasing interest. In this study, oxidation kinetics and products of four steroid estrogens (i.e., estrone, 17ß-estradiol, estriol, and 17α-ethinylestradiol) by PMS under various conditions were investigated. PMS could fairly degrade steroid estrogens over the pH range of 7-10, and the degradation rate increased with the increase of solution pH. This pH-dependence was well described by parallel reactions between individual acid-base species of steroid estrogens (E and E-) and PMS (HSO5- and SO52-), where specific second-order rate constants for E- with HSO5- and SO52- were in the range of 2.11-5.58 M-1s-1 and 0.77-1.25 M-1s-1, respectively. Identification of oxidation products by liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometer showed that PMS readily oxidized the phenolic group of steroid estrogens, leading to the generation of hydroxylated and ring-opening products. The presence of bromide and chloride ions (Br- and Cl-) at environmentally relevant levels could greatly accelerate the degradation of steroid estrogens by PMS with the formation of halogenated aromatic products. This effect was quantitatively estimated by a kinetic model, where the formation of free bromine and chorine and their rapid electrophilic substitution with steroid estrogens were taken into consideration. Eco-toxicity of transformation products of 17α-ethinylestradiol by PMS treatment in the absence and presence of bromide and chloride was estimated by quantitative structure-activity relationship analysis using ECOSAR. These findings advance the understanding of ISCO using PMS.


Assuntos
Brometos/química , Cloretos/química , Congêneres do Estradiol/química , Estrogênios/química , Peróxidos/química , Poluentes Químicos da Água/química , Bromo/química , Cloro/química , Halogenação , Cinética , Modelos Químicos , Oxirredução , Fenóis/química
14.
Water Res ; 135: 75-84, 2018 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-29454924

RESUMO

This work investigated impacts of iodide (I-) on the transformation of the widely used phenolic preservative methylparaben (MeP) as well as 11 other phenolic compounds by potassium permanganate (KMnO4). It was found that KMnO4 showed a low reactivity towards MeP in the absence of I- with apparent second-order rate constants (kapp) ranging from 0.065 ±â€¯0.0071 to 1.0 ±â€¯0.1 M-1s-1 over the pH range of 5-9. The presence of I- remarkably enhanced the transformation rates of MeP by KMnO4 via the contribution of hypoiodous acid (HOI) in situ formed, which displayed several orders of magnitude higher reactivity towards MeP than KMnO4. This enhancing effect of I- was greatly influenced by solution conditions (e.g., I- or KMnO4 concentration or pH), which could be well simulated by a kinetic model involving competition reactions (i.e., KMnO4 with I-, KMnO4 with MeP, HOI with KMnO4, and HOI with MeP). Similar enhancing effect of I- on the transformation kinetics of 5 other selected phenols (i.e., p-hydroxybenzoic acid, phenol, and bromophenols) at pH 7 was also observed, but not in the cases of bisphenol A, triclosan, 4-n-nonylphenol, and cresols. This discrepancy could be well explained by the relative reactivity of KMnO4 towards phenols vs I-. Liquid chromatography-tandem mass spectrometry analysis showed that iodinated aromatic products and/or iodinated quinone-like product were generated in the cases where I- enhancing effect was observed. Evolution of iodinated aromatic products generated from MeP (10 µM) treated by KMnO4 (50-150 µM) in the presence of I- (5-15 µM) suggested that higher I- or moderate KMnO4 concentration or neutral pH promoted their formation. A similar enhancing effect of I- (1 µM) on the transformation of MeP (1 µM) by KMnO4 (12.6 µM) and formation of iodinated aromatic products were also observed in natural water. This work demonstrates an important role of I- in the transformation kinetics and product formation of phenolic compounds by KMnO4, which has great implications for future applications of KMnO4 in treatment of I--containing water.


Assuntos
Iodetos/química , Parabenos/química , Fenóis/química , Compostos Benzidrílicos/química , Halogenação , Concentração de Íons de Hidrogênio , Compostos de Iodo/química , Cinética , Modelos Químicos , Permanganato de Potássio/química , Triclosan/química , Poluentes Químicos da Água/química , Purificação da Água/métodos
15.
Water Res ; 131: 208-217, 2018 03 15.
Artigo em Inglês | MEDLINE | ID: mdl-29289922

RESUMO

Bisphenol S (BPS), as a main alternative of bisphenol A for the production of industrial and consumer products, is now frequently detected in aquatic environments. In this work, it was found that free chlorine could effectively degrade BPS over a wide pH range from 5 to 10 with apparent second-order rate constants of 7.6-435.3 M-1s-1. A total of eleven products including chlorinated BPS (i.e., mono/di/tri/tetrachloro-BPS), 4-hydroxybenzenesulfonic acid (BSA), chlorinated BSA (mono/dichloro-BSA), 4-chlorophenol (4CP), and two polymeric products were detected by high performance liquid chromatography and electrospray ionization-tandem quadrupole time-of-flight mass spectrometry. Two parallel transformation pathways were tentatively proposed: (i) BPS was attacked by stepwise chlorine electrophilic substitution with the formation of chlorinated BPS. (ii) BPS was oxidized by chlorine via electron transfer leading to the formation of BSA, 4CP and polymeric products. Humic acid (HA) significantly suppressed the degradation rates of BPS even taking chlorine consumption into account, while negligibly affected the products species. The inhibitory effect of HA was reasonably explained by a two-channel kinetic model. It was proposed that HA negligibly influenced pathway i while appreciably inhibited the degradation of BPS through pathway ii, where HA reversed BPS phenoxyl radical (formed via pathway ii) back to parent BPS.


Assuntos
Cloro/química , Substâncias Húmicas , Fenóis/química , Sulfonas/química , Poluentes Químicos da Água/química , Cromatografia Líquida de Alta Pressão , Halogenação , Concentração de Íons de Hidrogênio , Cinética , Oxirredução , Espectrometria de Massas por Ionização por Electrospray , Purificação da Água/métodos
16.
Water Res ; 125: 209-218, 2017 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-28863343

RESUMO

In this study, the kinetics of reactions of peroxymonosulfate (PMS) with ten model phenols (including phenol, methylphenols, methoxyphenols, and dihydroxybenzenes) were examined. The oxidation kinetics of these phenols by PMS except for catechol and resorcinol showed autocatalysis in alkaline conditions (pH 8.5 and 10), due to the contribution of singlet oxygen (1O2) produced from PMS activation by quinone intermediates formed from their phenolic parents. The oxidation rates of ortho- and meta-substituted methylphenols and methoxyphenols by PMS were much higher than their para-substituted counterparts under similar conditions. This was attributed to the relatively low yields of quinone intermediates from para-substituted phenols. SMX could be efficiently degraded by PMS in the presence of phenols which showed great autocatalysis when they individually reacted with PMS, and the addition of methanol in excess had negligible influence suggesting that 1O2 rather than hydroxyl radical and sulfate radical played an important role. Transformation of SMX by 1O2 underwent three pathways including hydroxylation of aniline ring, oxidation of aromatic amine group to generate nitro-SMX, and oxidative coupling to generate azo-SMX and hydroxylated azo-SMX. These results obtained in this work improve the understanding of in situ chemical oxidation using PMS for remediation of subsurface, where phenolic and quinonoid moieties are ubiquitous.


Assuntos
Benzoquinonas/química , Peróxidos/química , Fenóis/química , Oxigênio Singlete/química , Poluentes Químicos da Água/química , Radical Hidroxila , Cinética , Oxirredução , Sulfatos , Poluentes Químicos da Água/análise
18.
Environ Sci Technol ; 50(17): 9608-18, 2016 09 06.
Artigo em Inglês | MEDLINE | ID: mdl-27487036

RESUMO

In this work, it was found that the most widely used brominated flame retardant tetrabromobisphenol A (TBrBPA) could be transformed by free chlorine over a wide pH range from 5 to 10 with apparent second-order rate constants from 138 to 3210 M(-1)·s(-1). A total of eight products, including one quinone-like compound (i.e., 2,6-dibromoquinone), two dimers, and several simple halogenated phenols (e.g., 4-(2-hydroxyisopropyl)-2,6-dibromophenol, 2,6-dibromohydroquinone, and 2,4,6-tribromophenol), were detected by high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) using a novel precursor ion scan (PIS) approach. A tentative reaction pathway was proposed: chlorine initially oxidized TBrBPA leading to the formation of a phenoxy radical, and then this primary radical and its secondary intermediates (e.g., 2,6-dibromo-4-isopropylphenol carbocation) formed via beta-scission subsequently underwent substitution, dimerization, and oxidation reactions. Humic acid (HA) considerably inhibited the degradation rates of TBrBPA by chlorine even accounting for oxidant consumption. A similar inhibitory effect of HA was also observed in permanganate and ferrate oxidation. This inhibitory effect was possibly attributed to the fact that HA competitively reacted with the phenoxy radical of TBrBPA and reversed it back to parent TBrBPA. This study confirms that chlorine can transform phenolic compounds (e.g., TBrBPA) via electron transfer rather than the well-documented electrophilic substitution, which also have implications on the formation pathway of halo-benzoquinones during chlorine disinfection. These findings can improve the understanding of chlorine chemistry in water and wastewater treatment.


Assuntos
Retardadores de Chama , Substâncias Húmicas , Cloro/química , Espectrometria de Massas em Tandem , Água/química
19.
Environ Sci Technol ; 49(21): 12941-50, 2015 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-26452059

RESUMO

The reactions between peroxymonosulfate (PMS) and quinones were investigated for the first time in this work, where benzoquinone (BQ) was selected as a model quinone. It was demonstrated that BQ could efficiently activate PMS for the degradation of sulfamethoxazole (SMX; a frequently detected antibiotic in the environments), and the degradation rate increased with solution pH from 7 to 10. Interestingly, quenching studies suggested that neither hydroxyl radical (•OH) nor sulfate radical (SO4•-) was produced therein. Instead, the generation of singlet oxygen (1O2) was proved by using two chemical probes (i.e., 2,2,6,6-tetramethyl-4-piperidinol and 9,10-diphenylanthracene) with the appearance of 1O2 indicative products detected by electron paramagnetic resonance spectrometry and liquid chromatography mass spectrometry, respectively. A catalytic mechanism was proposed involving the formation of a dioxirane intermediate between PMS and BQ and the subsequent decomposition of this intermediate into 1O2. Accordingly, a kinetic model was developed, and it well described the experimental observation that the pH-dependent decomposition rate of PMS was first-order with respect to BQ. These findings have important implications for the development of novel nonradical oxidation processes based on PMS, because 1O2 as a moderately reactive electrophile may suffer less interference from background organic matters compared with nonselective •OH and SO4•-.


Assuntos
Benzoquinonas/química , Peróxidos/química , Catálise , Cromatografia Líquida/métodos , Espectroscopia de Ressonância de Spin Eletrônica , Concentração de Íons de Hidrogênio , Radical Hidroxila/química , Cinética , Espectrometria de Massas/métodos , Oxirredução , Sulfametoxazol/química , Sulfatos/química , Poluentes Químicos da Água/química , Purificação da Água/métodos
20.
Environ Sci Technol ; 49(19): 11764-71, 2015 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-26378975

RESUMO

In this study, it was, interestingly, found that 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), a widely used electron shuttle, could greatly accelerate the oxidation of substituted phenols by potassium permanganate (Mn(VII)) in aqueous solutions at pH 5-9. This was attributed to the fact that these substituted phenols could be readily oxidized by the stable radical cation (ABTS(•+)), which was quickly produced from the oxidation of ABTS by Mn(VII). The reaction of Mn(VII) with ABTS exhibited second-order kinetics, with stoichiometries of ∼5:1 at pH 5-6 and ∼3:1 at pH 7-9, and the rate constants varied negligibly from pH 5 to 9 (k = (9.44 ± 0.21) × 10(4) M(-1) s(-1)). Comparatively, the reaction of ABTS(•+) with phenol showed biphasic kinetics. The second-order rate constants for the reactions of ABTS(•+) with substituted phenols obtained in the initial phase were strongly affected by pH, and they were several orders of magnitude higher than those for the reactions of Mn(VII) with substituted phenols at each pH. Good Hammett-type correlations were found for the reactions of ABTS(•+) with undissociated (log(k) = 2.82-4.31σ) and dissociated phenols (log(k) = 7.29-5.90σ). The stoichiometries of (2.2 ± 0.06):1 (ABTS(•+) in excess) and (1.38 ± 0.18):1 (phenol in excess) were achieved in the reaction of ABTS(•+) with phenol, but they exhibited no pH dependency.


Assuntos
Benzotiazóis/química , Elétrons , Compostos de Manganês/química , Óxidos/química , Fenóis/química , Ácidos Sulfônicos/química , Água/química , Difosfatos/química , Concentração de Íons de Hidrogênio , Cinética , Manganês/química , Oxidantes/química , Oxirredução , Soluções , Termodinâmica
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