Revisiting the Electron Transfer Mechanisms in Ru(III)-Mediated Advanced Oxidation Processes with Peroxyacids and Ferrate(VI).

The potential of Ru(III)-mediated advanced oxidation processes has attracted attention due to the recyclable catalysis, high efficiency at circumneutral pHs, and robust resistance against background anions (e.g., phosphate). However, the reactive species in Ru(III)-peracetic acid (PAA) and Ru(III)-ferrate(VI) (FeO42-) systems have not been rigorously examined and were tentatively attributed to organic radicals (CH3C(O)O•/CH3C(O)OO•) and Fe(IV)/Ru(V), representing single electron transfer (SET) and double electron transfer (DET) mechanisms, respectively. Herein, the reaction mechanisms of both systems were investigated by chemical probes, stoichiometry, and electrochemical analysis, revealing different reaction pathways. The negligible contribution of hydroxyl (HO•) and organic (CH3C(O)O•/CH3C(O)OO•) radicals in the Ru(III)-PAA system clearly indicated a DET reaction via oxygen atom transfer (OAT) that produces Ru(V) as the only reactive species. Further, the Ru(III)-performic acid (PFA) system exhibited a similar OAT oxidation mechanism and efficiency. In contrast, the 1:2 stoichiometry and negligible Fe(IV) formation suggested the SET reaction between Ru(III) and ferrate(VI), generating Ru(IV), Ru(V), and Fe(V) as reactive species for micropollutant abatement. Despite the slower oxidation rate constant (kinetically modeled), Ru(V) could contribute comparably as Fe(V) to oxidation due to its higher steady-state concentration. These reaction mechanisms are distinctly different from the previous studies and provide new mechanistic insights into Ru chemistry and Ru(III)-based AOPs.

Mutual Effects and Uptake of Organic Contaminants and Nanoplastics by Lettuce in Co-Exposure.

Organic contaminants, such as pesticides and pharmaceuticals, are commonly found in agricultural systems. With the growing use of plastic products, micro- and nanoplastics (MNPs) are increasingly detected in these agricultural systems, necessitating research into their interactions and joint effects to truly understand their impact. Unfortunately, while there has been a long history of research into the uptake of organic pollutants by plants, similar research with MNPs is only beginning, and studies on their mutual effects and plant uptake are extremely rare. In this study, we examined the effects of three agriculturally relevant organic pollutants with distinctive hydrophobicity as measured by log KOW (trimethoprim: 0.91, atrazine: 2.61, and ibuprofen: 3.97) and 500 nm polystyrene nanoplastics on their uptake and accumulation by lettuce at two different salinity levels. Our results showed that nanoplastics increased the shoot concentration of ibuprofen by 77.4 and 309% in nonsaline and saline conditions, respectively. Alternatively, organic co-contaminants slightly lowered the PS NPs uptake in lettuce with a more pronounced decrease in saline water. These results underscore the impactful interactions of hydrophobic organic pollutants and increasing MNPs on a dynamic global environment.

Effects of ozone dose on brominated DBPs in subsequent chlor(am)ination: A comprehensive study of aliphatic, alicyclic and aromatic DBPs.

Ozone‒chlor(am)ine is a commonly used combination of disinfectants in drinking water treatment. Although there are quite a few studies on the formation of some individual DBPs in the ozone‒chlor(am)ine disinfection, an overall picture of the DBP formation in the combined disinfection is largely unavailable. In this study, the effects of ozone dose on the formation and speciation of organic brominated disinfection byproducts (DBPs) in subsequent chlorination, chloramination, or chlorination‒chloramination of simulated drinking water were investigated. High-molecular-weight, aliphatic, alicyclic and aromatic brominated DBPs were selectively detected and studied using a powerful precursor ion scan method with ultra performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (UPLC/ESI-tqMS). Two groups of unregulated yet relatively toxic DBPs, dihalonitromethanes and dihaloacetaldehydes, were detected by the UPLC/ESI-tqMS for the first time. With increasing ozone dose, the levels of high-molecular-weight (m/z 300-500) and alicyclic and aromatic brominated DBPs generally decreased, the levels of brominated aliphatic acids were slightly affected, and the levels of dihalonitromethanes and dihaloacetaldehydes generally increased in the subsequent disinfection processes. Despite different molecular compositions of the detected DBPs, increasing ozone dose generally shifted the formation of DBPs from chlorinated ones to brominated analogues in the subsequent disinfection processes. This study provided a comprehensive analysis of the impact of ozone dose on the DBP formation and speciation in subsequent chlor(am)ine disinfection.

Recent advances of polymeric nanoplatforms for cancer treatment: smart delivery systems (SDS), nanotheranostics and multidrug resistance (MDR) inhibition.

Nanotheranostics is a promising field that combines the benefits of diagnostic and treatment into a single nano-platform that not only administers treatment but also allows for real-time monitoring of therapeutic response, decreasing the possibility of under/over-drug dosing. Furthermore, developing smart delivery systems (SDSs) for cancer theranostics that can take advantage of various tumour microenvironment (TME) conditions (such as deformed tumour vasculature, various over-expressed receptor proteins, reduced pH, oxidative stress, and resulting elevated glutathione levels) can aid in achieving improved pharmacokinetics, higher tumour accumulation, enhanced antitumour efficacy, and/or decreased side effects and multidrug resistance (MDR) inhibition. Polymeric nanoparticles (PNPs) are being widely investigated in this regard due to their unique features such as small size, passive/active targeting possibility, better pharmaceutical kinetics and biological distribution, decreased adverse reactions of the established drugs, inherent inhibitory properties to MDR efflux pump proteins, as well as the feasibility of delivering numerous therapeutic substances in just one design. Hence in this review, we have primarily discussed PNPs based targeted and/or controlled SDSs in which we have elaborated upon different TME mediated nanotheranostic platforms (NTPs) including active/passive/magnetic targeting platforms along with pH/ROS/redox-responsive platforms. Besides, we have elucidated different imaging guided cancer therapeutic platforms based on four major cancer imaging techniques i.e., fluorescence/photo-acoustic/radionuclide/magnetic resonance imaging, Furthermore, we have deliberated some of the most recently developed PNPs based multimodal NTPs (by combining two or more imaging or therapy techniques on a single nanoplatform) in cancer theranostics. Moreover, we have provided a brief update on PNPs based NTP which are recently developed to overcome MDR for effective cancer treatment. Additionally, we have briefly discussed about the tissue biodistribution/tumour targeting efficiency of these nanoplatforms along with recent preclinical/clinical studies. Finally, we have elaborated on various limitations associated with PNPs based nanoplatforms.

Fate and distribution of orally-ingested CeO2-nanoparticles based on a mouse model: Implication for human health.

The use of nanoparticles in agrichemical formula and food products as additives has increased their chances of accumulation in humans via oral intake. Due to their potential toxicity, it is critical to understand their fate and distribution following oral intake. Cerium oxide nanoparticle (CeO2NP) is commonly used in agriculture and is highly stable in the environment. As such, it has been used as a model chemical to investigate nanoparticle's distribution and clearance. Based on their estimated human exposure levels, 0.15-0.75 mg/kg body weight/day of CeO2NPs with different sizes and surface charges (30-50 nm with negative charge and <25 nm with positive charge) were gavaged into C57BL/6 female mice daily. After 10-d, 50% of mice in each treatment were terminated, with the remaining being gavaged with 0.2 mL of deionized water daily for 7-d. Mouse organ tissues, blood, feces, and urine were collected at termination. At the tested levels, CeO2NPs displayed minimal overt toxicity to the mice, with their accumulation in various organs being negligible. Fecal discharge as the predominant clearance pathway took less than 7-d regardless of charges. Single particle inductively coupled plasma mass spectrometry analysis demonstrated minimal aggregation of CeO2NPs in the gastrointestinal tract. These findings suggest that nanoparticle additives >25 nm are unlikely to accumulate in mouse organ after oral intake, indicating limited impacts on human health.

Single atom catalyst-mediated generation of reactive species in water treatment.

Water is one of the most essential components in the sustainable development goals (SDGs) of the United Nations. With worsening global water scarcity, especially in some developing countries, water reuse is gaining increasing acceptance. A key challenge in water treatment by conventional treatment processes is the difficulty of treating low concentrations of pollutants (micromolar to nanomolar) in the presence of much higher levels of inorganic ions and natural organic matter (NOM) in water (or real water matrices). Advanced oxidation processes (AOPs) have emerged as an attractive treatment technology that generates reactive species with high redox potentials (E0) (e.g., hydroxyl radical (HO˙), singlet oxygen (1O2), sulfate radical (SO4˙-), and high-valent metals like iron(IV) (Fe(IV)), copper(III) (Cu(III)), and cobalt(IV) (Co(IV))). The use of single atom catalysts (SACs) in AOPs and water treatment technologies has appeared only recently. This review introduces the application of SACs in the activation of hydrogen peroxide and persulfate to produce reactive species in treatment processes. A significant part of the review is devoted to the mechanistic aspects of traditional AOPs and their comparison with those triggered by SACs. The radical species, SO4˙- and HO˙, which are produced in both traditional and SACs-activated AOPs, have higher redox potentials than non-radical species, 1O2 and high-valent metal species. However, SO4˙- and HO˙ radicals are non-selective and easily affected by components of water while non-radicals resist the impact of such constituents in water. Significantly, SACs with varying coordination environments and structures can be tuned to exclusively generate non-radical species to treat water with a complex matrix. Almost no influence of chloride, carbonate, phosphate, and NOM was observed on the performance of SACs in treating pollutants in water when nonradical species dominate. Therefore, the appropriately designed SACs represent game-changers in purifying water vs. AOPs with high efficiency and minimal interference from constituents of polluted water to meet the goals of water sustainability.

Visible light activation of ferrate(VI) by oxygen doped ZnIn2S4/black phosphorus nanolayered heterostructure: Accelerated oxidation of trimethoprim.

The increasing consumption of antibiotics and their subsequent release to wastewater or groundwater and ultimately to the water supply (or drinking water) has great concerns. This paper presents a visible light (VL) activated ferrate(VI) (FeVIO42-, Fe(VI)) system to degrade the selected antibiotic, trimethoprim (TMP), efficiently. An oxygen doped ZnIn2S4 nanosheet (O-ZIS) coupled with a black phosphorus (BP) heterostructure (O-ZIS/BP), is fabricated by a simple electrostatic self-assembly method. The O-ZIS/BP photocatalyst is comprehensively characterized by surface and analytical techniques, which show superior separation efficiency of the photoinduced charge carriers in the heterostructure. A VL-O-ZIS/BP-Fe(VI) system achieves more than 80% removal in 1.0 min and complete removal of TMP in 3.0 min. Comparatively, only ⁓7% and ⁓24% of TMP are degraded by O-ZIS/BP and Fe(VI) in 1.0 min, respectively. The degradation experiments using probe molecules of reactive species and electron paramagnetic resonance (EPR) measurements reveal involvement of superoxide (O2-•), hydroxyl radical (•OH), and iron(V)/iron (IV) (FeV/FeIV) species in the mechanism of TMP degradation. Oxidized products of TMP are identified and reaction pathways are given. Theoretical calculations predict the initial attack on the TMP molecule by the reactive species in the VL-O-ZIS/BP-Fe(VI) system. The activation of Fe(VI) by VL-heterostructure photocatalysts accelerates the degradation of antibiotics, demonstrating its potential for water depollution.

Overlooked Formation of Carbonate Radical Anions in the Oxidation of Iron(II) by Oxygen in the Presence of Bicarbonate.

Iron(II), (Fe(H2 O)6 2+ , (FeII ) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of FeII oxidation by dissolved molecular oxygen, O2 , under environmental conditions containing bicarbonate (HCO3 - ), which exists up to millimolar concentrations. In the absence and presence of HCO3 - , the formation of reactive oxygen species (O2 ⋅- , H2 O2 , and HO⋅) in FeII oxidation by O2 has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO3 ⋅- ) in the oxidation of FeII by O2 in the presence of bicarbonate, HCO3 - . The rate of the formation of CO3 ⋅- may be expressed as d[CO3 ⋅- ]/dt=[FeII [[O2 ][HCO3 - ]2 . The formation of reactive species was investigated using 1 H nuclear magnetic resonance (1 H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of FeII oxidation by O2 in the presence of bicarbonate and highlights the importance of considering the formation of CO3 ⋅- in the geochemical cycling of iron and carbon.

Enhanced Oxidation of Antibiotics by Ferrate Mediated with Natural Organic Matter: Role of Phenolic Moieties.

The increasing presence of antibiotics in water sources threatens public health and ecosystems. Various treatments have been previously applied to degrade antibiotics, yet their efficiency is commonly hindered by the presence of natural organic matter (NOM) in water. On the contrary, we show here that nine types of NOM and NOM model compounds improved the removal of trimethoprim and sulfamethoxazole by ferrate(VI) (FeVIO42-, Fe(VI)) under mild alkaline conditions. This is probably associated with the presence of phenolic moieties in NOMs, as suggested by first-order kinetics using NOM, phenol, and hydroquinone. Electron paramagnetic resonance reveals that NOM radicals are generated within milliseconds in the Fe(VI)-NOM system via single-electron transfer from NOM to Fe(VI) with the formation of Fe(V). The dominance of the Fe(V) reaction with antibiotics resulted in their enhanced removal despite concurrent reactions between Fe(V) and NOM moieties, the radicals, and water. Kinetic modeling considering Fe(V) explains the enhanced kinetics of antibiotics abatement at low phenol concentrations. Experiments with humic and fulvic acids of lake and river waters show similar results, thus supporting the enhanced abatement of antibiotics in real water situations.

Picolinic Acid-Mediated Catalysis of Mn(II) for Peracetic Acid Oxidation Processes: Formation of High-Valent Mn Species.

Metal-based advanced oxidation processes (AOPs) with peracetic acid (PAA) have been extensively studied to degrade micropollutants (MPs) in wastewater. Mn(II) is a commonly used homogeneous metal catalyst for oxidant activation, but it performs poorly with PAA. This study identifies that the biodegradable chelating ligand picolinic acid (PICA) can significantly mediate Mn(II) activation of PAA for accelerated MP degradation. Results show that, while Mn(II) alone has minimal reactivity toward PAA, the presence of PICA accelerates PAA loss by Mn(II). The PAA-Mn(II)-PICA system removes various MPs (methylene blue, bisphenol A, naproxen, sulfamethoxazole, carbamazepine, and trimethoprim) rapidly at neutral pH, achieving >60% removal within 10 min in clean and wastewater matrices. Coexistent H2O2 and acetic acid in PAA play a negligible role in rapid MP degradation. In-depth evaluation with scavengers and probe compounds (tert-butyl alcohol, methanol, methyl phenyl sulfoxide, and methyl phenyl sulfone) suggested that high-valent Mn species (Mn(V)) is a likely main reactive species leading to rapid MP degradation, whereas soluble Mn(III)-PICA and radicals (CH3C(O)O• and CH3C(O)OO•) are minor reactive species. This study broadens the mechanistic understanding of metal-based AOPs using PAA in combination with chelating agents and indicates the PAA-Mn(II)-PICA system as a novel AOP for wastewater treatment.

Insights into manganese(VII) enhanced oxidation of benzophenone-8 by ferrate(VI): Mechanism and transformation products.

Benzophenones (BPs) are commonly used as UV filters in cosmetics and plastics products and are potentially toxic to the environment. This paper presents kinetics and products of BPs oxidation by ferrate(VI) (FeO42-, Fe(VI)) promoted by permanganate (Mn(VII)) . Degradation of 10.0 µM 2,2'-dihydroxy-4-methoxybenzophenone (BP-8)were determined under different experimental conditions ([Mn(VII)] = 0.5-1.5 µM, [Fe(VI)] = 50-150 µM, and pH = 7.0-10.0). The addition of Mn(VII) traces to Fe(VI)-BP-8 solution enhanced kinetics and efficiency of the removal. Similar enhanced removals were also seen for other BPs (BP-1, BP-3, and BP-4) under optimized conditions. The second-order rate constants (k, M-1s-1) of the degradation of BPs showed positive relationship with the energy of the highest occupied orbital (EHOMO). The possible interaction between Mn(VII) and BP-8 and the enhanced generation of Fe(V)/Fe(IV) and •OH was proposed to facilitate the oxidation of the target benzophenone, supported by in-situ electrochemical measurements, theoretical calculations and reactive species quenching experiments. Thirteen oxidation products of BP-8 suggested hydroxylation, bond breaking, polymerization and carboxylation steps in the oxidation. Toxicity assessments by ECOSAR program showed that the oxidized intermediate products posed a tapering ecological risk during the degradation process. Overall, the addition of Mn(VII) could improve the oxidation efficiency of Fe(VI).

Reaction of FeaqII with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of FeaqIV and Carbonate Radical Anions.

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO5-, PMS) or peroxydisulfate (S2O82-, PDS) with Fe(H2O)62+ (FeaqII). This paper presents results on the kinetics and mechanisms of reactions between FeaqII and PMS or PDS in the absence and presence of bicarbonate (HCO3-) at different pH. In the absence of HCO3-, FeaqIV, rather than the commonly assumed SO4•-, is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO2) and phenyl methyl sulfone (PMSO2), respectively, confirming the generation of FeaqIV by the FeaqII-PMS/PDS systems without HCO3-. Significantly, in the presence of environmentally relevant concentrations of HCO3-, a carbonate radical anion (CO3•-) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of FeaqIV and CO3•- in the FeaqII-PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.

Ferrate(VI) mediated degradation of the potent cyanotoxin, cylindrospermopsin: Kinetics, products, and toxicity.

The presence of cylindrospermopsin (CYN), a potent cyanotoxin, in drinking water sources poses a tremendous risk to humans and the environment. Detailed kinetic studies herein demonstrate ferrate(VI) (FeVIO42-, Fe(VI)) mediated oxidation of CYN and the model compound 6-hydroxymethyl uracil (6-HOMU) lead to their effective degradation under neutral and alkaline solution pH. A transformation product analysis indicated oxidation of the uracil ring, which has functionality critical to the toxicity of CYN. The oxidative cleavage of the C5=C6 double bond resulted in fragmentation of the uracil ring. Amide hydrolysis is a contributing pathway leading to the fragmentation of the uracil ring. Under extended treatment, hydrolysis, and extensive oxidation lead to complete destruction of the uracil ring skeleton, resulting in the generation of a variety of products including nontoxic cylindrospermopsic acid. The ELISA biological activity of the CYN product mixtures produced during Fe(VI) treatment parallels the concentration of CYN. These results suggest the products do not possess ELISA biological activity at the concentrations produced during treatment. The Fe(VI) mediated degradation was also effective in the presence of humic acid and unaffected by the presence of common inorganic ions under our experimental conditions. The Fe(VI) remediation of CYN and uracil based toxins appears a promising drinking water treatment process.

Oxidation of Pharmaceuticals by Ferrate(VI)-Amino Acid Systems: Enhancement by Proline.

The occurrence of micropollutants in water threatens public health and ecology. Removal of micropollutants such as pharmaceuticals by a green oxidant, ferrate(VI) (FeVIO42-, Fe(VI)) can be accomplished. However, electron-deficient pharmaceuticals, such as carbamazepine (CBZ) showed a low removal rate by Fe(VI). This work investigates the activation of Fe(VI) by adding nine amino acids (AA) of different functionalities to accelerate the removal of CBZ in water under mild alkaline conditions. Among the studied amino acids, proline, a cyclic AA, had the highest removal of CBZ. The accelerated effect of proline was ascribed by demonstrating the involvement of highly reactive intermediate Fe(V) species, generated by one-electron transfer by the reaction of Fe(VI) with proline (i.e., Fe(VI) + proline → Fe(V) + proline•). The degradation kinetics of CBZ by a Fe(VI)-proline system was interpreted by kinetic modeling of the reactions involved that estimated the rate of the reaction of Fe(V) with CBZ as (1.03 ± 0.21) × 106 M-1 s-1, which was several orders of magnitude greater than that of Fe(VI) of 2.25 M-1 s-1. Overall, natural compounds such as amino acids may be applied to increase the removal efficiency of recalcitrant micropollutants by Fe(VI).

Phosphorous- and Boron-Doped Graphene-Based Nanomaterials for Energy-Related Applications.

Doping is a great strategy for tuning the characteristics of graphene-based nanomaterials. Phosphorous has a higher electronegativity as compared to carbon, whereas boron can induce p-type conductivity in graphene. This review provides insight into the different synthesis routes of phosphorous- and boron-doped graphene along with their applications in supercapacitors, lithium- ions batteries, and cells such as solar and fuel cells. The two major approaches for the synthesis, viz. direct and post-treatment methods, are discussed in detail. The former synthetic strategies include ball milling and chemical vapor discharge approaches, whereas self-assembly, thermal annealing, arc-discharge, wet chemical, and electrochemical erosion are representative post-treatment methods. The latter techniques keep the original graphene structure via more surface doping than substitutional doping. As a result, it is possible to preserve the features of the graphene while offering a straightforward handling technique that is more stable and controllable than direct techniques. This review also explains the latest progress in the prospective uses of graphene doped with phosphorous and boron for electronic devices, i.e., fuel and solar cells, supercapacitors, and batteries. Their novel energy-related applications will continue to be a promising area of study.

Development of a Novel LC-MS/MS Multi-Method for the Determination of Regulated and Emerging Food Contaminants Including Tenuazonic Acid, a Chromatographically Challenging Alternaria Toxin.

The regulation of food contaminants in the European Union (EU) is comprehensive, and there are several compounds in the register or being added to the recommendation list. Recently, European standard methods for analysis have also been issued. The quick analysis of different groups of analytes in one sample requires a number of methods and the simultaneous use of various instruments. The aim of the present study was to develop a method that could analyze several groups of food contaminants: in this case, 266 pesticides, 12 mycotoxins, 14 alkaloid toxins, and 3 Alternaria toxins. The main advantage of the herein described approach over other methods is the simultaneous analysis of tenuazonic acid (TEA) and other relevant food contaminants. The developed method unites the newly published standard methods such as EN 15662:2018, EN 17194:2019, EN 17256:2019, EN 17425:2021, EN 17521:2021, which describes the analysis of both regulated and emerging contaminants. The developed method is based on a QuEChERS sample preparation, followed by LC-MS/MS analysis under alkaline mobile phase conditions. The pH of the aqueous eluent was set to 8.3, which resulted in baseline separation among ergot alkaloids and their corresponding epimers, a symmetric chromatographic peak shape for analyzing TEA and fit-for-purpose sensitivity for MS/MS detection in both positive and negative ionization modes. Those compounds, which possess the corresponding isotopically labeled internal standards (ISTD), allowed for direct quantification by the developed method and no further confirmation was necessary. This was proven by satisfactory analyses of a number of quality control (QC), proficiency test (PT), and validation samples.

Bioavailability, phytotoxicity and plant uptake of per-and polyfluoroalkyl substances (PFAS): A review.

Per- and polyfluoroalkyl substances (PFAS) are a group of legacy and emerging contaminants containing at least one aliphatic perfluorocarbon moiety. They display rapid and extensive transport in the environment due to their generally high water-solubility and weak adsorption onto soil particles. Because of their widespread presence in the environment and known toxicity, PFAS has become a serious threat to the ecosystem and public health. Plants are an essential component of the ecosystem and their uptake and accumulation of PFAS affect the fate and transport of PFAS in the ecosystem and has strong implications for human health. It is therefore imperative to investigate the interactions of plants with PFAS. This review presents a detailed discussion on the mechanisms of the bioavailability and plant uptake of PFAS, and essential factors affecting these processes. The phytotoxic effects of PFAS at physiological, biochemical, and molecular level were also carefully reviewed. At the end, key research gaps were identified, and future research needs were proposed.

Particle-size distributions of environmentally persistent free radicals and oxidative potential of soils from a former gasworks site.

The formation of toxic by-products, such as environmentally persistent free radicals (EPFRs), is one of the causes for concern by polycyclic aromatic hydrocarbons (PAHs) in soils. However, the distribution of EPFRs in different soil fractions and their relative contribution to the oxidation potential (OP) have not been investigated. In the present paper, contaminated samples were obtained from the former gasworks sites and were fractionated into different size particles, which were analyzed for EPFRs, reactive oxygen species (ROS), and OP-assayed by dithiothreitol (DTT) (OPDTT). The results showed the highest concentration of EPFRs in the soil particle size with diameters <0.15 mm due to co-existence of PAHs and transition metals. ROS generation is in accordance with the size-specific distribution of EPFRs. Using the DTT assays, the redox activity of various size soil particles was examined, and found it was approximately 4- to 8-folds higher than that of un-contaminated samples and strongly associated with EPFRs, ROS, and PAHs. The obtained results advanced our knowledge on the EPFRs distribution in soil fractions at former MGP sites and emphasized the significance of PAH-EPFRs as a class of compounds to be considered in risk assessment of contaminated sites.

A Comparative Study on the Oxidation Mechanisms of Substituted Phenolic Pollutants by Ferrate(VI) through Experiments and Density Functional Theory Calculations.

In this work, the oxidation of five phenolic contaminants by ferrate(VI) was comparatively investigated to explore the possible reaction mechanisms by combined experimental results and theoretical calculations. The second-order rate constants were positively correlated with the energy of the highest occupied molecular orbital. Considering electronic effects of different substituents, the easy oxidation of phenols by ferrate(VI) could be ranked as the electron-donating group (-R) > weak electron-withdrawing group (-X) > strong electron-withdrawing group (-(C═O)-). The contributions of reactive species (Fe(VI), Fe(V)/(IV), and •OH) were determined, and Fe(VI) was found to dominate the reaction process. Four main reaction mechanisms including single-oxygen transfer (SOT), double-oxygen transfer (DOT), •OH attack, and electron-transfer-mediated coupling reaction were proposed for the ferrate(VI) oxidation process. According to density functional theory calculation results, the presence of -(C═O)- was more conducive for the occurrence of DOT and •OH attack reactions than -R and -X, while the tendency of SOT for different substituents was -R > -(C═O)- > -X and that of e--transfer reaction was -R > -X > -(C═O)-. Moreover, the DOT pathway was found in the oxidation of all four substituted phenols, indicating that it may be a common reaction mechanism during the ferrate(VI) oxidation of phenolic compounds.

Hierarchical Nanoflowers of MgFe2O4, Bentonite and B-,P- Co-Doped Graphene Oxide as Adsorbent and Photocatalyst: Optimization of Parameters by Box-Behnken Methodology.

In the present study, nanocomposites having hierarchical nanoflowers (HNFs) -like morphology were synthesized by ultra-sonication approach. HNFs were ternary composite of MgFe2O4 and bentonite with boron-, phosphorous- co-doped graphene oxide (BPGO). The HNFs were fully characterized using different analytical tools viz. X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersion spectroscopy, transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry and Mössbauer analysis. Transmission electron micrographs showed that chiffon-like BPGO nanosheets were wrapped on the MgFe2O4-bentonite surface, resulting in a porous flower-like morphology. The red-shift in XPS binding energies of HNFs as compared to MgFe2O4-bentoniteand BPGO revealed the presence of strong interactions between the two materials. Box-Behnken statistical methodology was employed to optimize adsorptive and photocatalytic parameters using Pb(II) and malathion as model pollutants, respectively. HNFs exhibited excellent adsorption ability for Pb(II) ions, with the Langmuir adsorption capacity of 654 mg g-1 at optimized pH 6.0 and 96% photocatalytic degradation of malathion at pH 9.0 as compared to MgFe2O4-bentonite and BPGO. Results obtained in this study clearly indicate that HNFs are promising nanocomposite for the removal of inorganic and organic contaminants from the aqueous solutions.