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Molecules (Basel, Switzerland) Jun 2022The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry,... (Review)
Review
The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years. Extensive research has been conducted on the subject of C-H bond functionalization by Pd catalysis with hypervalent iodine reagents as oxidants. Furthermore, the iodine(III) reagent is now often used as an arylating agent in Pd-catalyzed C-H arylation or Heck-type cross-coupling processes. In this article, the recent advances in palladium-catalyzed oxidative cross-coupling reactions employing hypervalent iodine reagents are reviewed in detail.
Topics: Catalysis; Indicators and Reagents; Iodides; Iodine; Oxidants; Oxidation-Reduction; Palladium
PubMed: 35745020
DOI: 10.3390/molecules27123900 -
Environmental Science & Technology Nov 2023Ozone is a commonly applied disinfectant and oxidant in drinking water and has more recently been implemented for enhanced municipal wastewater treatment for potable... (Review)
Review
Ozone is a commonly applied disinfectant and oxidant in drinking water and has more recently been implemented for enhanced municipal wastewater treatment for potable reuse and ecosystem protection. One drawback is the potential formation of bromate, a possible human carcinogen with a strict drinking water standard of 10 μg/L. The formation of bromate from bromide during ozonation is complex and involves reactions with both ozone and secondary oxidants formed from ozone decomposition, i.e., hydroxyl radical. The underlying mechanism has been elucidated over the past several decades, and the extent of many parallel reactions occurring with either ozone or hydroxyl radicals depends strongly on the concentration, type of dissolved organic matter (DOM), and carbonate. On the basis of mechanistic considerations, several approaches minimizing bromate formation during ozonation can be applied. Removal of bromate after ozonation is less feasible. We recommend that bromate control strategies be prioritized in the following order: (1) control bromide discharge at the source and ensure optimal ozone mass-transfer design to minimize bromate formation, (2) minimize bromate formation during ozonation by chemical control strategies, such as ammonium with or without chlorine addition or hydrogen peroxide addition, which interfere with specific bromate formation steps and/or mask bromide, (3) implement a pretreatment strategy to reduce bromide and/or DOM prior to ozonation, and (4) assess the suitability of ozonation altogether or utilize a downstream treatment process that may already be in place, such as reverse osmosis, for post-ozone bromate abatement. A one-size-fits-all approach to bromate control does not exist, and treatment objectives, such as disinfection and micropollutant abatement, must also be considered.
Topics: Humans; Bromates; Drinking Water; Bromides; Ecosystem; Ozone; Water Purification; Hydroxyl Radical; Oxidants; Water Pollutants, Chemical
PubMed: 37363871
DOI: 10.1021/acs.est.3c00538 -
Journal of Hazardous Materials May 2022The prevalence of organic micropollutants (OMPs) in aquatic environment has expedited scientific and regulatory efforts to retrofit existing wastewater treatment plants... (Review)
Review
The prevalence of organic micropollutants (OMPs) in aquatic environment has expedited scientific and regulatory efforts to retrofit existing wastewater treatment plants (WWTPs). The current strategy involves WWTPs upgrading with post-ozonation i.e., ozone (O) and/or peroxone process (O +HO). Still, ozone-based degradation of OMPs faces several challenges. For example, the degradation mechanism and kinetics of OMPs could largely be affected by water matrix compounds which include inorganic ions and natural organic matter (NOM). pH also plays a decisive role in determining the reactivity of the oxidants (O, HO, andHO), stability and speciation of matrix constituents and OMPs and thus susceptibility of OMPs to the reactions with oxidants. There have been reviews discussing the impact of matrix components on the degradation of OMPs by advanced oxidation processes (AOPs). Nevertheless, a review focusing on scavenging mechanisms, formation of secondary oxidants and their scavenging effects with a particular focus on ozonation and peroxone process is lacking. Therefore, in order to broaden the knowledge on this subject, the database 'Web of Science' was searched for the studies related to the 'matrix effect on the degradation of organic micropollutants by ozone based processes' over the time period of 2004-2021. The relevant literature was thoroughly reviewed and following conclusions were made: i) chloride has inhibitory effects if it exits at higher concentrations or as free chlorine i.e. HOCl/ClO. ii) The inhibitory effects of chloride, bromide, HOBr/OBr and HOCl/ClO are dominant in neutral and alkaline conditions and may result in the formation of secondary oxidants (e.g., chlorine atoms or free bromine), which in turn contribute to pollutant degradation or form undesired oxidation by-products such as BrO, ClO and halogenated organic products. ii) NOM may induce inhibitory or synergetic effects depending on the type, chemical properties and concentration of NOM. Therefore, more efforts are required to understand the importance of pH variation as well as the effects of water matrix on the reactivity of oxidants and subsequent degradation of OMPs.
Topics: Hydrogen Peroxide; Oxidants; Oxidation-Reduction; Ozone; Wastewater; Water; Water Pollutants, Chemical; Water Purification
PubMed: 35077976
DOI: 10.1016/j.jhazmat.2021.128189 -
ChemSusChem Oct 2022The dissolution of elemental noble metals (NMs) such as gold, platinum, palladium, and copper is necessary for their recycling but carries a high environmental burden...
The dissolution of elemental noble metals (NMs) such as gold, platinum, palladium, and copper is necessary for their recycling but carries a high environmental burden due to the use of strong acids and toxic reagents. Herein, a new approach was developed for the rapid dissolution of elemental NMs in organic solvents using mixtures of triphenylphosphine dichloride or oxalyl chloride and hydrogen peroxide, forming metal chloride salts directly. Almost quantitative dissolution of metallic Au, Pd, and Cu was observed within minutes at room temperature. For Pt, dissolution was achieved, albeit more slowly, using the chlorinating oxidant alone but was inhibited on addition of hydrogen peroxide. After leaching, transfer of Pt and Pd chloride salts from the organic phase into a 6 m HCl aqueous phase facilitated their separation by precipitation of Pt using a simple diamide ligand. In contrast, the retention of Au chloridometalate in the organic phase allowed its selective separation from Ni and Cu from a leachate solution obtained from electronic CPUs. This new approach has potential application in the hydrometallurgical leaching and purification of NMs from ores, spent catalysts, and electronic and nano-wastes.
Topics: Electronic Waste; Palladium; Copper; Chlorides; Platinum; Hydrogen Peroxide; Solubility; Ligands; Diamide; Salts; Recycling; Gold; Solvents; Oxidants
PubMed: 35929761
DOI: 10.1002/cssc.202201285 -
Water Research Aug 2022Manganese (Mn) oxide solids are ubiquitous in nature, acting as both electron donors and acceptors in diverse redox reactions in the environment. Reactions of Mn(III/IV)...
Manganese (Mn) oxide solids are ubiquitous in nature, acting as both electron donors and acceptors in diverse redox reactions in the environment. Reactions of Mn(III/IV) oxides with dissolved natural organic matter (DOM) are commonly described as reductive dissolutions that generate Mn(aq). In this study, we investigated the role of photochemical reactions of DOM in Mn(aq) oxidation and the resulting formation of Mn oxide solids. During the photolysis of DOM, reactive intermediates can be generated, including excited triplet state DOM (DOM*), hydroxyl radicals (OH), superoxide radicals (O), hydrogen peroxide, and singlet oxygen. Among these, we found that O radicals were mainly responsible for Mn oxidation. The solution pH controlled the formation of Mn oxide solids by affecting both Mn oxidation by O during photolysis of DOM and reductive dissolutions of Mn oxide solids by DOM. Further, with the addition of bromide ions (Br), reactions between DOM* and Br, together with reactions between OH and Br, can form reactive bromide radicals. The formed Br radicals also promoted Mn oxide formation. In DOM with more aromatic functional groups, more Mn was oxidized to Mn oxide solids. This enhanced oxidation could be the result of promoted pathways from charge-transfer state DOM (DOM) to O. These new observations advance our understanding of natural Mn oxidation and Mn(III/IV) oxide formation and highlight the underappreciated oxidative roles of DOM in the oxidation of metal ions in surface water illuminated by sunlight.
Topics: Bromides; Dissolved Organic Matter; Manganese Compounds; Oxides; Photolysis
PubMed: 35872522
DOI: 10.1016/j.watres.2022.118831 -
Chemosphere Sep 2023Manganese oxides (MnOx) are recognized as a strongest oxidant and adsorbent, of which composites have been proved to be effective in the removal of contaminants from... (Review)
Review
Manganese oxides (MnOx) are recognized as a strongest oxidant and adsorbent, of which composites have been proved to be effective in the removal of contaminants from wastewater. This review provides a comprehensive analysis of Mn biochemistry in water environment including Mn oxidation and Mn reduction. The recent research on the application of MnOx in the wastewater treatment was summarized, including the involvement of organic micropollutant degradation, the transformation of nitrogen and phosphorus, the fate of sulfur and the methane mitigation. In addition to the adsorption capacity, the Mn cycling mediated by Mn(II) oxidizing bacteria and Mn(IV) reducing bacteria is the driving force for the MnOx utilization. The common category, characteristics and functions of Mn microorganisms in recent studies were also reviewed. Finally, the discussion on the influence factors, microbial response, reaction mechanism and potential risk of MnOx application in pollutants' transformation were proposed, which might be the promising opportunities for the future investigation of MnOx application in wastewater treatment.
Topics: Manganese; Wastewater; Oxides; Manganese Compounds; Oxidation-Reduction; Bacteria
PubMed: 37327824
DOI: 10.1016/j.chemosphere.2023.139219 -
Current Protein & Peptide Science 2022Laccases and peroxidases have attracted great interest for industrial and environmental applications. These enzymes have a broad substrate range and a robust oxidizing...
AIM
Laccases and peroxidases have attracted great interest for industrial and environmental applications. These enzymes have a broad substrate range and a robust oxidizing ability. Moreover, using mediators or co-oxidants makes it possible to increase their catalytic activity and extend their substrate scope to more resistant chemical structures.
BACKGROUND
Fungal laccases and ligninolytic peroxidases, mainly lignin and manganese peroxidases, are the privileged oxidoreductases for bioremediation processes. Nonetheless, an increasing diversity of laccases and peroxidase-type enzymes has been proposed for environmental technologies.
OBJECTIVE
This article aims to provide an overview of these enzymes and compare their applicability in the degradation of organic pollutants.
METHODS
Fundamental properties of the proteins are covered and applications towards polycyclic aromatic hydrocarbons (PAHs) and pesticides are specially focused.
RESULTS
Laccases are multicopper oxidases initially studied for applications in the pulp and paper industry but able to oxidize a variety of environmentally concerning compounds. Relying on O, laccases do not require peroxides nor auxiliary agents, like Mn, although suitable redox mediators are needed to attack the more recalcitrant pollutants (e.g., PAHs). True and pseudo-peroxidases use a stronger oxidant (HO) and the redox chemistry at the heme site generates high potential species that allow the oxidation of dyes and some pesticides.
CONCLUSION
Lately, research efforts have been directed to enzyme discovery, testing with micropollutants, and improving biocatalysts' stability by immobilization and protein engineering. Further understanding of the effects of natural media components and solvents on the enzymes might lead to competitive enzymatic treatments of highly toxic media.
Topics: Laccase; Biodegradation, Environmental; Lignin; Environmental Pollutants; Peroxidase; Hemeproteins; Hydrogen Peroxide; Manganese; Peroxidases; Oxidation-Reduction; Polycyclic Aromatic Hydrocarbons; Heme; Pesticides; Coloring Agents; Oxidants; Solvents
PubMed: 35794739
DOI: 10.2174/1389203723666220704090416 -
Water Research Jan 2018Biodegradable organic matter (BOM), found in all surface waters, is a challenge for drinking water utilities because it can lead to distribution system bio-regrowth,... (Review)
Review
Biodegradable organic matter (BOM), found in all surface waters, is a challenge for drinking water utilities because it can lead to distribution system bio-regrowth, react to form disinfection by-products, or be a specific compound of concern. A critical review of BOM (occurrence and oxidant effects) and rapid-rate biofiltration performance (preozonation, backwashing with an oxidant, empty bed contact time (EBCT) and temperature) was carried out. An extensive literature data analysis (n = 100) found total organic carbon (TOC) in nonozonated water is comprised of 20% (median) biodegradable organic carbon (BDOC) and 3% (median) assimilable organic carbon (AOC). For ozonated waters (n = 103), these values increased to 30% (median) BDOC and 9% (median) AOC. For all operation conditions (n = 117), biofilters (12 min average EBCT) removed 12% (median) of the influent TOC with higher removals for ozonated waters, 15% (median), compared to nonozonated waters, 10% (median). As temperature increased from ≤10 °C to ≥20 °C, TOC removal increased from 10% to 17% (median). This review demonstrates biofiltration can be an efficient treatment technology to remove a portion of the BOM from the filter influent and should be optimized to achieve maximum removal.
Topics: Carbon; Disinfection; Drinking Water; Filtration; Organic Chemicals; Oxidants; Ozone; Water Purification
PubMed: 29107908
DOI: 10.1016/j.watres.2017.09.048 -
Water Research Apr 2023The fact that 94% of microplastics (MPs) ubiquitous in the environment are subject to natural weathering makes the aging study currently a research hotspot. This review... (Review)
Review
The fact that 94% of microplastics (MPs) ubiquitous in the environment are subject to natural weathering makes the aging study currently a research hotspot. This review summarized the physicochemical characteristics of MPs undergoing natural and artificial aging and evaluated current analytical methods used in aging studies. Besides, the differences in photoaging and aging induced by advanced oxidation processes (AOPs) were discussed, leading to a conclusion that AOPs composed of oxidant and ultraviolet (UV) irradiation can better facilitate the alteration of MPs compared to UV irradiation alone. In addition, the environmental behavior of aged MPs was outlined and their adsorption properties for organics and metals were highlighted as a result of combined effects of hydrophobic, π-π, diffusion, and hydrogen bond interaction. Furthermore, the mechanisms of photoaging and AOPs-initiated aging were analyzed, mainly the role of reactive oxygen species (ROS) and environmentally persistent free radicals (EPFRs). Finally, the applications of two-dimensional correlation spectroscopy (2D-COS) and three-dimensional fluorescence spectra using excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were discussed for the aging process analysis. This overview plays an important role in explaining the aging characteristics of MPs and provides a theoretical foundation for further investigations into their toxicity and removal.
Topics: Microplastics; Plastics; Skin Aging; Water Pollutants, Chemical; Oxidants
PubMed: 36774752
DOI: 10.1016/j.watres.2023.119628 -
Water Research Sep 2021Liquid sludge often contains odorous and toxic hydrogen sulfide and high levels of Fe compounds (e.g., iron sulfides), due to the extensive use of iron salts for...
Simultaneous removal of hydrogen sulfide, phosphate and emerging organic contaminants, and improvement of sludge dewaterability by oxidant dosing in sulfide-iron-laden sludge.
Liquid sludge often contains odorous and toxic hydrogen sulfide and high levels of Fe compounds (e.g., iron sulfides), due to the extensive use of iron salts for hydrogen sulfide control in sewers and for enhanced primary treatment and phosphate removal in wastewater treatment plants. We proposed and verified that dosing appropriate chemical oxidants in the sulfide-iron-laden sludge can be a simple and cost-effective strategy to remove hydrogen sulfide, phosphate, and emerging organic contaminants, and to improve sludge dewaterability simultaneously. Among the seven oxidants investigated, HO, ClO and NaClO were the more cost-effective oxidants than others to control hydrogen sulfide release from the liquid sludge. Dosing these three oxidants also improved sludge dewaterability and removed dissolved phosphate from the liquid sludge, with HO performing the best. Hydrogen sulfide was removed via both direct oxidation by the dosed oxidants and indirect oxidation by the Fe that was in-situ formed from oxidation of the Fe compounds in the sludge. The in-situ formed Fe also precipitated/adsorbed the soluble phosphate into the solid form (FePO). Fenton-like reactions occurred between HO and the Fe compounds in the sludge, and hydroxyl radicals (HO•) were generated. HO• oxidized hydrogen sulfide, destructed refractory organic emerging contaminants and sludge extracellular polymeric compounds (EPSs), and improved the sludge dewaterability. The formation of HO• can be enhanced by hydrogen sulfide and the sludge EPSs present in the sludge through providing more available Fe for the Fenton-like reactions. This study demonstrates the importance of selecting and dosing suitable oxidants to the sulfide-iron-laden sludge with due consideration for the multiple benefits in engineering practices. The same principles may be also used in formulating a dual oxidant-iron strategy to treat sulfide-iron-laden sewage, sludge, and sediments for simultaneous abatement of various pollutants.
Topics: Hydrogen Peroxide; Hydrogen Sulfide; Iron; Oxidants; Oxidation-Reduction; Phosphates; Sewage; Sulfides; Waste Disposal, Fluid
PubMed: 34418644
DOI: 10.1016/j.watres.2021.117557