Ferrate (VI)-mediated transformation of diethyl phthalate (DEP) in soil: Kinetics, degradation mechanisms and theoretical calculation.

Diethyl phthalate (DEP), as a kind of universally used plasticizer, has aroused considerable public concern owing to its wide detection, environmental stability, and potential health risks. In this work, the highly efficient removal of DEP by ferrate (VI) (Fe(VI)) was systematically explored in soil environment. The effects of the oxidant dosages, soil types, as well as the presence of coexisting cations and anions in tested soil on DEP removal were evaluated. When the dosage of Fe(VI) was 20 mM, complete removal of DEP (50 µg/g) was achieved in the tested soil after 2 min of reaction. Furthermore, the removal rate of DEP was closely related to the soil types, and the degradation rates were decreased obviously in red soil (RS), black soil (BS) and paddy soil (PS), probably due to the acidic condition and high content of organic matters. Moreover, the presence of Ca2+, Mg2+ and Al3+ in soil can inhibit the removal of DEP by Fe(VI), while SO42- has an slightly promotion effect. Six oxidation intermediates were detected in the reaction process of DEP, product analysis revealed that the transformation of DEP was mainly through two pathways, including hydrolysis and hydroxylation reactions, which were probably mediated by oxygen atom transfer process of Fe(VI). Based on the frontier electron density theory calculation, two ester groups of DEP were prone to be attacked by Fe(VI), and the hydroxyl addition tended to occur at the para-position of one of the ester groups on the benzene ring. This study provides a novel approach for phthalate esters removal from soil using Fe(VI) oxidation and shows new insights into the oxidation mechanisms.

Oxidation of benzophenone-3 in aqueous solution by potassium permanganate: kinetics, degradation products, reaction pathways, and toxicity assessment.

Benzophenone-3 (BP-3) is used in a wide range of personal care products and plastics to resist ultraviolet light, which has aroused considerable public concern due to its endocrine-disrupting effects. In this work, we systematically investigated the chemical oxidation process of BP-3 by KMnO4. The influences of several factors, such as pH, oxidant dose, temperature, coexisting water constituents, and water matrices, on BP-3 degradation efficiency were evaluated. The removal rate of 10 µM BP-3 could reach 91.3% in 2 h under the conditions of pH = 8.0, [BP-3]0:[KMnO4]0 = 1:20, and T = 25 °C, with the observed rate constant (kobs) value of 0.0202 min-1. The presence of typical anions (Cl-, NO3-, SO42-) and HA could slightly increase BP-3 removal, while HCO3- caused a relatively significant promotion of BP-3 degradation. On the basis of mass spectrometry and theoretical calculations, hydroxylation, direct oxidation, and carbon-carbon bridge bond cleavage were mainly involved in the oxidation process. Toxicity assessment revealed that the acute and chronic toxicities were reduced significantly, which suggested KMnO4 is a promising technique for BP-3 removal.

Kinetics and reaction pathways for the transformation of 4-tert-butylphenol by ferrate(VI).

4-tert-butylphenol (4-tBP) is a phenolic endocrine disrupting chemical that has attracted great attention due to its wide occurrence, environmental persistence, and possible toxic effects. In this study, we systematically investigated the transformation of 4-tBP in ferrate (VI) oxidation process. The second-order reaction rate constant (kapp) of Fe(VI) with 4-tBP decreases with solution pH, and the kapp value was determined as 295 M-1·s-1 at pH 8.0. The removal efficiency of 4-tBP was slightly decreased by Mg2+ and HCO3-, while accelerated at varying degrees by the presence of Cu2+ and humic acid. Product analysis revealed that 4-tBP was mainly transformed into hydroxylation products, benzene-ring cleavage products, dimers and higher polymerization products via oxygen atom transfer, ring-opening of the benzene ring and radical coupling reaction. Furthermore, initial reactions of 4-tBP were rationalized by theoretical analysis of atom partial charges, frontier electron densities, and spin densities. Nearly complete removal of 4-tBP (20 µM) was achieved after 5 min of reaction in both ultrapure water and natural waters, demonstrating the feasibility of this Fe(VI) oxidation method in treating phenols-contaminated waters.

Enhanced oxidative degradation of decabromodiphenyl ether in soil by coupling Fenton-persulfate processes: Insights into degradation products and reaction mechanisms.

Decabromodiphenyl ether (BDE-209) has extreme hydrophobicity, which results in its significant accumulation in soil, sediments and other solid materials. In this work, an oxidation method coupling Fenton with persulfate (PS) was proposed for the effective degradation of BDE-209 adsorbed on solid surfaces. After adding 0.1 M PS to the Fenton system at 1.0 h, the removal rate of BDE-209 was significantly increased from 62.2% to 94.0%. The degradation of BDE-209 in various soil samples was also investigated by the coupling Fenton-PS method. Removal efficiency of 73.4-95.8% was obtained, suggesting that this coupling method was feasible in real application. According to the radical scavenging experiments, •OH dominated the overall reaction of BDE-209 in the coupling system. Meanwhile, the enhanced removal was attributed to the generation of SO4•- from the catalytic decomposition of PS. The calculated energy barriers for SO4•- attacking on the carbons were smaller than •OH initiated reactions, which further confirmed that SO4•- plays a role in the accelerated removal of BDE-209. The initial attack of BDE-209 by SO4•- generated the SO4•- adducts, which may undergo debromination or CO bond cleavage reaction together with subsequent hydroxyl substitution to form the primary product OH-Nona-BDEs and pentabromophenol. Under the successive attack of radicals, these primary products were further transformed into lower-brominated hydroxylation products and bromophenols via direct debromination and hydroxyl substitution reaction. This work provides an economical and effective method for treating BDE-209 contaminated soils and samples.

KMnO4-mediated reactions for hexachlorophene in aqueous solutions: Direct oxidation, self-coupling, and cross-coupling.

Hexachlorophene (HCP) is used in a range of general cleaning and disinfecting products and has received increased attention due to its damaging effect to the central nervous system in animals and its toxicity in humans. The chemical oxidation of HCP by KMnO4 was performed to systematically evaluate the effects of oxidant dose, pH, temperature, typical anions, humic acid (HA), and various matrices on HCP removal. The second-order rate constant for HCP was determined to be 4.83 × 104 M-1 s-1 at pH 7.0 and 25 °C. The presence of HA can inhibit the removal of HCP by KMnO4, while Cl-, NO3-, SO42-, PO43-, and CO32- have negligible effects. Degradation products analysis of the reaction, as well as theoretical calculations of HCP molecule and its phenoxy radical species, indicated that KMnO4 oxidation for HCP included a C-C bridge bond cleavage, hydroxylation, direct oxidation and self-coupling, and cross-coupling reactions. This study revealed that KMnO4 oxidation is an effective technique for eliminating HCP in real water and wastewater.