Presence Of Iodide Research Articles

Singlet oxygen is also involved in the formation of hypoiodous acid during the transformation of phenolic pollutants by peracetic acid in the presence of iodide

Peracetic acid (PAA) has been used as a disinfectant/oxidant in wastewater treatment. However, considering that the presence of iodide (I−) would induce the iodinated products in wastewater, the effect of I− on the transformation of phenolic pollutants by PAA was investigated. Herein, the presence of I− enhanced the transformation of phenolic pollutants (bisphenol S (BPS), bisphenol A (BPA), and p-hydroxybenzoic acid (p-HBA)) by PAA. Furthermore, hypoiodous acid (HOI) was reactive species in the PAA/I− system based on radical quenching experiments and electron spin resonance. In this system, PAA, together with 1O2 that was produced in PAA oxidized I− into HOI. Increasing PAA and I− dose promoted the transformation of phenolic pollutants but the promoting effect was less significant at higher dosage. The increase in H2O2 dose retarded the transformation of phenolic pollutants because of HOI being quenched by H2O2. In a wide range of pH (pH 4.0–10.0), the transformation of BPS, BPA, and p-HBA was pH-dependent and most effective at pH 7.0. The presence of chloride and bromide accelerated the transformation of phenolic pollutants by PAA/I− due to the formation of HOCl and HOBr. Furthermore, HOI substitution was the primary reaction pathway in the transformation of BPS, BPA, and p-HBA by PAA/I−. Finally, the transformation products of phenolic pollutants during the PAA/I− posed higher cytotoxicity compared to the parent pollutants. Overall, our findings improved the understanding of the chemical behavior of PAA in the presence of I− and suggested that the generation of iodinated products raised concerns for water safety.

Alkali Halide and MIBC Interaction at Typical Flotation Interfaces in Saline Water as Determined by Molecular Dynamics Simulations

The molecular structure of the liquid–vapor interfaces of aqueous solutions of alkali metal halides and methyl isobutyl carbinol (MIBC, (CH3)2CHCH2COCH3) is determined by using molecular dynamics simulations with polarizable force fields for the first time. The salts are chlorides, and iodides, some of which are found in raw and partially desalinated seawater increasingly used in flotation operations in regions affected by severe and prolonged drought. The density profiles at the interfaces show that all ions prefer the interface; however, with MIBC, non-polarizable ions, generally small ones, are increasingly pushed into the liquid bulk. A few ions of comparatively less ionic NaCl than KCl and CsCl, persist at the interface, consistent with spectroscopy observations. On the other hand, strongly polarizable ions such as I− always share the interface with MIBC. In the presence of chlorides, the frother chains at the interface stretch slightly more toward vapor than in freshwater; however, in the presence of iodides, the chains stretch so much that they become orthogonal to the interface, giving rise to a well-packed monolayer, which is the most effective configuration. The dominant water configurations at the interface are double donor and single donor, with hydrogen atoms pointing toward the liquid, consistent with studies with sum-frequency generation experiments and extensive ab initio simulations. This picture changes radically in the presence of MIBC and salts. Depending on the halide and MIBC concentration, the different molecular configurations at the interface lead to very different surface tensions. The structure and properties of these new salt-rich interfaces and their impact on the location and arrangement of frother molecules should serve the flotation practitioner, especially in the search for the best frother and dosing in poor-quality water.

Co-Extraction of Uranium and Mercury Using Ion Exchange from Cemented Radioactive Waste Sulfuric Leachate in Iodide Media

The production of medical isotopes in Chalk River Laboratories facilities (Chalk River, ON, Canada) has resulted in a large quantity of cemented radioactive waste (CRW) containing valuable elements such as uranium. From the perspective of recovering and ultimately recycling valuable elements from CRW, the solubilization of key constituents such as uranium, mercury, and cesium has been previously investigated using H2SO4/KI. However, to achieve recycling of these elements, separation must be performed as they are co-solubilized. In this study, the extraction of uranium and mercury by chelating resin Lewatit TP260 from surrogate cemented radioactive waste (SCRW) leaching solution in sulfuric media and in the presence of iodide was investigated. Extraction of U and Hg was assessed as a function of the concentration of KI (0.12 M to 0.24 M) used during the SCRW dissolution process. Continuous experiments showed that the Lewatit TP260 functional group, aminomethylphosphonic acid, had a high affinity for U. Mercury was also extracted onto the Lewatit TP260. However, the presence of iodide in the SCRW leaching solution increased the competition between the adsorbed mercury of the stationary phase and the iodide–mercury complexes of the mobile phase. Additionally, the reusability of the resin was tested through extraction and desorption cycles. Due to the presence of trivalent cation, the capacity of Lewatit TP260 for U and Hg decreases with the number of cycles.

UV/iodide advanced reduction process and biological treatments to ofloxacin photo-degradation and mineralization: influence parameters, kinetic, degradation pathway, energy consumption and toxicology

ABSTRACT The degradation of ofloxacin (OFL) by ultraviolet (UV) radiation in the presence of iodide was studied as an advanced reduction process (ARP), and followed resulting effluents were biodegraded for further mineralisation in the biological treatment. About 100% degradation of OFL was obtained under the selected condition (OFL: Iodide molar ratio of 2:1 and pH 9.0) after 20 min reaction time. In UV/Iodide ARP, the obtained range for reaction rate constant (k obs) and reaction rate (r obs) were from 0.311 to 0.039 min−1, and from 15.55 to 7.94 mg/L.min, respectively. The calculation of the energy consumption (using kinetic model) indicated with increasing OFL concentration from 50 to 200 mg L−1, the amount of energy consumption increases from 0.905 to 7.09 kW per cubic metre of treatment (also it was observed increase from 0.91 to 6.29 kW per cubic metre of treatment using IUPAC model). Intermediate (I) products and possible photodegradation pathways of OFL in the UV/Iodide ARP effluent were analysed after 30 min using GC-MS. Investigations showed after 30 min, most of the intermediates were converted to simple linear compounds such as acrylic acid (I6: C3H4O2), formic acid (I9: CH2O2) and acrylaldehyde (I10: C3H4O), that finally mineralised to CO2, H2O, NH4+ and NH3. Modified Kirby-Bauer disc diffusion test (applied to investigation of bacterial inhibition) was reduced from 33 mm (in initial concentration of OFL without treatment) to 9 mm (after 30 min of reaction). The UV/Iodide effluent reduced the COD by 40.9% after 30 min of reaction. When the biological reactor as post-treatment was operated at a concentration of MLSS 1000 mg L−1, the COD removal efficiency reached to 65.28% (121 to 42 mg L−1) within 11 h. However, by increasing the amount of MLSS to 3000 mg L−1, the COD removal efficiency reached to 84.09% (from 176 to 28 mg L−1) and at the 5000 mg L−1 of MLSS, the COD removal efficiency was 91.52% (from 236 to 20 mg L−1). It can be concluded from this study, although, the UV/Iodide ARP was very effective in breaking down OFL molecules, but it is not cost-effective due to the high time and cost of mineralisation. Therefore, application of the biological reactors as a post-treatment method after UV/Iodide ARP, due to cost-effective, environmentally friendly and the ability to degrade the intermediates produced can be useful.

Vapor transport growth of MnBi2Te4 and related compounds

Motivated by fine tuning of the magnetic and topological properties of MnBi2Te4 via defect engineering, in this work, we report the crystal growth of MnBi2Te4 and related compounds using vapor transport method and crystal characterization by measuring elemental ratio, magnetic and transport properties, and scanning tunneling microscopy. For the growth of MnBi2Te4 single crystals, I2, MnI2, MnCl2, TeCl4, and MoCl5 are all effective transport agents; chemical transportation occurs faster in the presence of iodides than chlorides. We further successfully grow MnSb2Te4, MnBi2−xSbxTe4, and Sb-doped MnBi4Te7 crystals. A small temperature gradient< 20∘C between the hot and cold ends of the growth ampoule is critical for the successful crystal growth of MnBi2Te4 and related compounds. Compared to flux grown crystals, vapor transported crystals tend to be Mn stoichiometric, and Sb-bearing compositions have more Mn/Sb site mixing. The vapor transport growth provides a new materials synthesis approach to fine tune the magnetic and topological properties of these intrinsic magnetic topological insulators where controlling defects is vital.

Highly selective colorimetric sensing for iodide in water based on a novel surface passivation of Ag nanoprisms

Because silver (Ag) nanoprisms with sharp edges are inherently unstable, it is very important to develop a facile method that can dramatically improve the chemical stability of Ag nanoprisms while maintaining their inherent properties, including their plasmonic properties. In the present work, we developed a novel surface passivation method based on a single-step water-based process and showed that it significantly improved the chemical stability of Ag nanoprisms. Specifically, tetramethylethylenediamine (TMEDA) was used as an organic capping ligand, and the TMEDA-treated Ag nanoprisms retained their triangular shape even when exposed to various strong etchants including bromide, chloride, and hydrogen peroxide. Only in the presence of iodide did the sharp corners of the nanoprisms become spontaneously etched, and this etching resulted in a dramatic change in their localized surface plasmon resonance (LSPR) properties. The extent of the change of the LSPR properties depended on the concentration of iodide; hence, aqueous solutions of the TMEDA-treated Ag nanoprisms with different concentrations of iodide showed different colors. Based on this relationship, a colorimetric sensing probe that can detect iodide in aqueous solutions was developed. The sensing probe exhibited very high selectivity for iodide and the ability to determine the concentration of iodide over a wide range of concentrations. In addition, the probe was found to provide significant advantages over previously developed systems for iodide analysis, including portability, ease of use, point-of-care analysis, and naked-eye detection.

Preconcentration and Determination of Palladium by Solvent-Free Microextraction and Flame Atomic Absorption Spectrometry (FAAS) in Environmental Samples

An alternative methodology based on the combination of microextraction with flame atomic absorption spectrometry (FAAS) is reported for the determination of Pd2+ in environmental samples. Cetyltrimethyl ammonium bromide (CTAB) was used as a cationic surfactant and a precipitating agent. The method involves the formation of a PdI4 2− complex with Pd2+ in the presence of iodide and CTAB causes PdI4 2− to precipitate. The method was performed using 0.01% (w/v) CTAB and 0.1% (w/v) KI in 35 mL 0.1% (v/v) nitric acid for the preconcentration of Pd2+. Under the optimized conditions, the calibration curve was linear between 20 and 170 μg L−1 with a correlation coefficient of 0.9964. The limit of detection and preconcentration factor were 2.4 µg L−1 and 35 for Pd2+. The results showed that this solvent-free microextraction is simple and sensitive for the preconcentration and determination of micrograms per liter of Pd2+ in seawater, stream water, and road dust with 94% to 103% spiked recoveries.

Phenol degradation in waters with high iodide level by layered double hydroxide-peroxodisulfate: Pathways and products

Recently, layered double hydroxide-peroxodisulfate (LDH-PDS) as an advanced oxidation system can effectively remove organics by the pathway of free radical. However, little has been known if there is a potential risk regarding the formation of high toxic iodine byproducts through another pathway when LDH-PDS is used in high iodide waters at coastal areas. Therefore, this study investigated phenol degradation pathways and transformation products to evaluate both removal mechanism and potential risk by LDH-PDS in high iodide waters. The results showed that in LDH-PDS system, with the degradation of PDS, phenol degraded till below detection limit in 1 hr in the presence of iodide, while PDS and phenol were hardly degraded in the absence of iodide, indicating iodide accelerated the transformation of PDS and the degradation of phenol. What is more, it reached the highest phenol removal efficiency under the condition of 100 mg/L LDH, 0.1 mmol/L PDS and 1.0 mmol/L iodide. In LDH-PDS system, iodide was rapidly oxidized by the highly active interlayer PDS, resulting in the formation of reactive iodine including hypoiodic acid, iodine and triiodide instead of free radicals, which contributed rapid degradation of phenol. However, unfortunately toxic iodophenols were detected. Specifically, 2-iodophenol and 4-iodophenol were formed firstly, afterwards 2,4-diiodophenol and 2,6-diiodophenol were produced, and finally iodophenols and diiodophenols gradually decreased and 2,4,6-Triiodophenol were produced. These results indicated that LDH-PDS should avoid to use in high iodide waters to prevent toxic iodine byproduct formation although iodide can accelerate phenol degradation.

Molecular insights into the role of genetic determinants of congenital hypothyroidism.

In our previous studies, we have demonstrated the association of certain variants of the thyroid-stimulating hormone receptor (TSHR), thyroid peroxidase (TPO), and thyroglobulin (TG) genes with congenital hypothyroidism. Herein, we explored the mechanistic basis for this association using different in silico tools. The mRNA 3'-untranslated region (3'-UTR) plays key roles in gene expression at the post-transcriptional level. In TSHR variants (rs2268477, rs7144481, and rs17630128), the binding affinity of microRNAs (miRs) (hsa-miR-154-5p, hsa-miR-376a-2-5p, hsa-miR-3935, hsa-miR-4280, and hsa-miR-6858-3p) to the 3'-UTR is disrupted, affecting post-transcriptional gene regulation. TPO and TG are the two key proteins necessary for the biosynthesis of thyroid hormones in the presence of iodide and H2O2. Reduced stability of these proteins leads to aberrant biosynthesis of thyroid hormones. Compared to the wild-type TPO protein, the p.S398T variant was found to exhibit less stability and significant rearrangements of intra-atomic bonds affecting the stoichiometry and substrate binding (binding energies, ΔG of wild-type vs. mutant: ‒15 vs. ‒13.8 kcal/mol; and dissociation constant, Kd of wild-type vs. mutant: 7.2E-12 vs. 7.0E-11 M). The missense mutations p.G653D and p.R1999W on the TG protein showed altered ΔG (0.24 kcal/mol and 0.79 kcal/mol, respectively). In conclusion, an in silico analysis of TSHR genetic variants in the 3'-UTR showed that they alter the binding affinities of different miRs. The TPO protein structure and mutant protein complex (p.S398T) are less stable, with potentially deleterious effects. A structural and energy analysis showed that TG mutations (p.G653D and p.R1999W) reduce the stability of the TG protein and affect its structure-functional relationship.

Mechanistic and kinetic understanding of micropollutant degradation by the UV/NH2Cl process in simulated drinking water

The UV/monochloramine (UV/NH2Cl) process has attracted increasing attention in water treatment, in which hydroxyl radicals (HO•), reactive chlorine species (RCS) and reactive nitrogen species (RNS) are produced. This study investigated the effects of water matrices including halides, natural organic matter (NOM), alkalinity and pH, on the degradation kinetic of a variety of micropollutants and radical chemistry in the UV/NH2Cl process. The presence of chloride blunted HO• and Cl• impacts, but enhanced Cl2•- effect on micropollutants reactive toward Cl2•-. The presence of 30 μM bromide led to an 82% decrease in the specific pseudo-first-order rate constants (k') by HO• (kHO•'), and significantly diminished RCS efficacy. Reactive bromine species (RBS) were formed in the presence of bromide, while the contribution could not compensate for the decrease of HO• and RCS due to their lower reactivity toward micropollutants. Iodide rapidly transformed to HOI via reacting with NH2Cl, which resulted in a 59% decrease of kHO•' and 12% ∼ 100% decreases of k' by reactive halogen species (RHS) and RNS (kRHS+RNS') for most micropollutants. Nevertheless, k' of phenolic compounds, such as paracetamol, bisphenol A and salbutamol, increased in the presence of iodide by 78%, 360% and 130%, respectively, due to the roles of HOI and reactive iodine species (RIS). Bicarbonate decreased the contributions of HO• and RCS, but enhanced that of CO3•- for micropollutants reactive toward CO3•-. The presence of 1 mg/L NOM scavenged over half the amount of HO•, and also consumed RCS and RNS, resulting in significantly decreased removal of micropollutants. High pH value witnessed enhanced degradation for those micropollutants reactive toward RCS and RNS through deprotonation. The degradation of most micropollutants was inhibited in real drinking water and in the coexistence of halides. This study provides a better understanding of radical chemistry in the UV/NH2Cl process under a practical water treatment condition.

Supramolecular hydrogelation via host-guest anion recognition: Lamellar hydrogel materials for the release of cationic cargo

Supramolecular hydrogelation via host-guest anion recognition: Lamellar hydrogel materials for the release of cationic cargo

Investigating the formation of iodinated aromatic disinfection by-products in chlorine/phenol/iodide system

Iodinated disinfection by-products (DBPs) have been attracting great attention due to their potential high toxicity to human health. Understanding of formation mechanisms and transformation process of iodinated aromatic DBPs during the chlorination of iodide-containing water is crucial. Phenol was therefore chosen as a representative of phenolic compounds to investigate the generation of iodinated aromatic DBPs in a chlorine/phenol/iodide system. The presence of iodide in water could enhance the removal of phenol by chlorine due to higher second order rate constants of HOI with phenol than that of HOCl with phenol. Fourteen kinds of iodinated aromatic DBPs were identified, which were generated from oxidation and electrophilic substitution of phenol by HOCl and HOI. Iodinated phenolic DBPs were sources of iodinated quinone DBPs and chlorinated/iodinated phenolic DBPs. Alkaline condition favored the formation of iodinated phenolic DBPs, while acid condition favored the production of iodinated quinone DBPs. Neutral condition might be the most suitable pH condition to control the formation of iodinated aromatic DBPs. The relative concentration of almost all iodinated aromatic DBPs first increased and then decreased with time, indicating iodinated aromatic DBPs might be further converted into halogenated aliphatic DBPs during the chlorination. This research provides a research basis for the removal of phenol in water.

New iodine-based electrochemical advanced oxidation system for water disinfection: Are disinfection by-products a concern?

A novel electrochemical Advanced Oxidation System (AOS) has been recently developed for water disinfection where iodide is used to generate active iodine species in-situ. However, the presence of iodide during water disinfection can lead to the formation of iodinated disinfection byproducts (I-DBPs), which have been shown to be more cyto- and genotoxic than their chlorinated and brominated analogs. In this study, the formation of DBPs was assessed in ultrapure water, river water and secondary wastewater effluents treated by the AOS. A comprehensive total organic halogen and target DBP analysis was used that included 25 unregulated DBPs, and the total organic halogen (TOX) quantified as total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). Ultrapure water disinfection only quantified iodoform (TIM) at a maximum concentration of 0.90 ± 0.05 µg/L. River water results show that TOI increase from 1.3 ± 0.3 µg/L before disinfection (t = 0) to a maximum of 3.5 ± 1.1 µg/L. TIM and bromodiiodomethane (BDIM) were the only targeted iodo-trihalomethanes (I-THMs) that were quantified with a maximum total I-THM concentration of 0.44 µg/L. Secondary wastewater effluent disinfection results show that TOI increased from 1.8 ± 0.3 µg/L (t = 0) to a maximum concentration of 35.3 ± 0.3 µg/L. Iodide and iodate were the main iodinated species exiting the AOS system with a iodine recovery of 94–101%. The results from this study show that the AOS formed low levels of iodinated DBPs in treated water sources that are comparable to the levels found in disinfected drinking water and wastewater.

Tripropyl Chitosan Iodide-Based Gel Polymer Electrolyte as Quasi Solid-State Dye Sensitized Solar Cells

Electrolyte as one of the major components in dye sensitized solar cells (DSSCs) plays an important role in dye regeneration and as the inner charge carrier transport between electrodes. Gel polymer electrolyte is a potential alternative to liquid electrolytes which suffer of leakage and solvent evaporation. In this present research, functionalization of chitosan by the quaternization reaction of chitosan with iodopropane forming tripropyl chitosan iodide is proposed for the preparation of gel polymer electrolyte. Tripropyl chitosan iodide was characterized by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Four different polymer electrolytes were tested at different compositions in presence of iodide/triiodide redox salt and imidazolium ionic liquid in DSSCs configurations. The results show that the gel polymer electrolyte containing the tripropyl chitosan iodide in presence of 1-propyl-3-methylimidazolium iodide ionic liquid showed better performance with power conversion efficiency of 0.415% as compared to the gel polymer electrolyte film without ionic liquid with power conversion efficiency of 0.075%. The results shown the synergistic effects of the polycationic tripropyl chitosan iodide with the ionic liquid 1-propyl-3-methylimidazolium iodide on the photovoltaic performance.

Synthesis, Structure, and Reactivity of 5-(Aryl)dibenzothiophenium Triflates.

A synthetic protocol for the preparation of 5‐(aryl)dibenzothiophenium salts starting from inexpensive dibenzothiophene S‐oxide and simple arenes is reported. The scope of the method regarding the nature of the arene is evaluated, intermediates along the reaction sequence have been trapped, and side‐reactions identified. In addition, the X‐ray structures of a complete set of these salts are reported and their reactivities studied. Specifically, chemoselective Suzuki coupling is observed at the dibenzothiophenium in the presence of iodides.

Synthesis, Structure, and Reactivity of 5‐(Aryl)dibenzothiophenium Triflates

AbstractA synthetic protocol for the preparation of 5‐(aryl)dibenzothiophenium salts starting from inexpensive dibenzothiophene S‐oxide and simple arenes is reported. The scope of the method regarding the nature of the arene is evaluated, intermediates along the reaction sequence have been trapped, and side‐reactions identified. In addition, the X‐ray structures of a complete set of these salts are reported and their reactivities studied. Specifically, chemoselective Suzuki coupling is observed at the dibenzothiophenium in the presence of iodides.

Halide-induced dissolution of lead(IV) oxide in frozen solution

The dark dissolution behavior of plattnerite (ß-PbO2) was investigated in frozen solutions containing halide ions and compared with those in aqueous solution. The amount of dissolved lead in the frozen solutions varied depending on the solution pH and the kind and concentration of halide ions. The presence of bromide and iodide ions enhanced the dissolution of lead in the aqueous phase, whereas the effect of chloride was insignificant. Compared with the aqueous phase dissolution, ß-PbO2 dissolution in the frozen solution was slightly enhanced in the presence of bromide but suppressed in the presence of iodide. Iodide ions seemed to be relatively more trapped in the bulk ice (ice-crystal lattice) than bromide ions, which might be related to the suppressed dissolution of lead oxide in the presence of iodide. The co-existence of bromide (or iodide) and chloride ions in the frozen solution enhanced the dissolution of lead, which seems to be enabled by an additional reaction pathway involving the formation of mixed halide radicals, whereas such kind of synergistic enhancements were not observed in aqueous solution. The halide-induced lead oxide dissolution in frozen solutions can be related to the behavior of lead ions found in various media of frozen environments.

Speciation of CdTe quantum dots and Te(IV) following oxidative degradation induced by iodide and headspace single-drop microextraction combined with graphite furnace atomic absorption spectrometry

A novel speciation method for tellurium present as CdTe quantum dots (CdTe QDs) and Te(IV) in natural waters combining hydride generation with headspace single drop microextraction (HS-SDME) and subsequent measurement by graphite furnace atomic absorption spectrometry has been developed. It was found that NaBH4 is only able to generate H2Te from Te(IV) and not from CdTe QDs. The presence of iodide at high concentration in the acidified sample causes the oxidation of CdTe to Te(IV), thus allowing the simultaneous hydride generation from both species. Furthermore, a gold-containing microdrop exposed to the headspace was found to be an efficient trapping agent for H2Te. Specifically, Au(III) in the drop is reduced by the H2 generated from NaBH4 decomposition forming gold nanoparticles, on which surface H2Te is trapped via catalytic decomposition. Experimental parameters influencing hydride generation, its transport to the headspace and trapping by the drop have been studied. Under optimal conditions, the proposed method yielded detection limits of 0.13 μg L−1 and 0.03 μg L−1 for Te(IV) and total Te [i.e., Te(IV) + CdTe QDs], respectively. Intra-day repeatability and inter-day reproducibility were lower than 4.2% (n = 3) and 9.5% for both measurements, respectively. The method was applied to the analysis of natural waters, namely superficial water, groundwater and lake water, obtaining good recoveries for both Te species.

Role of reactive oxygen species in As(III) oxidation by carbonate structural Fe(II): A surface-mediated pathway

Arsenite oxidation is commonly found during the removal of arsenite by iron minerals. The influencing factors and mechanisms of As(III) oxidation in reactive carbonate structural Fe(II) (CSF) suspensions were investigated in this study. Results showed that oxidation efficiency of As(III) was susceptible to CSF dosage, initial pH and dissolved oxygen (DO). It is interesting to note that the presence of iodide could conspicuously facilitate the oxidation efficiency of As(III) by accelerating Fe(III)/Fe(II) cycle. Scavenging experiments demonstrated that H2O2 and ·O2– were the crucial ROSs in the pH range of 5.0–9.0. Besides, the other predominant ROSs accounting for As(III) oxidation were Fe(IV) and surface-bound hydroxyl radical (·OH) in acid and neutral solutions while Fe(IV) became the main oxidant in alkaline solutions. Production of ROSs was attributed to the oxygenation of Fe2+ adsorbed on Fe(III) oxyhydroxides and complexed Fe(II) under neutral condition. No ROSs could be examined in the liquid phase, a surface-mediated mechanism was thus proposed: ROSs were generated on the surface of CSF while As(III) was adsorbed on the surface of CSF and then oxidized to As(V) by surface-bound ROSs. This study may shed light on molecular oxygen activation mechanism by carbonate structural Fe(II) during arsenite oxidation.

Oxidation of methylparaben (MeP) and p‑hydroxybenzoic acid (p-HBA) by manganese dioxide (MnO2) and effects of iodide: Efficiency, products, and toxicity

It is reported that methylparaben (MeP, a widely used phenolic preservative) and its major metabolite p‑hydroxybenzoic 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.