Designing green oxidation catalysts for purifying environmental waters

Tetra-Amido Macrocyclic Ligand (TAML) at Silicon(IV): A Structurally Constrained, Water-Soluble Silicon Lewis Superacid

Tetracoordinate silicon species are typically tetrahedral, weak Lewis acids, and often sensitive to moisture. In this study, we present a tetra-amido macrocyclic ligand (TAML)-substituted Si(IV), isolated as its bis(pyridine) adduct. Due to structural constraint toward anti van't-Hof/Le Bel geometry, this compound exhibits Lewis superacidity and effectively catalyzes the hydroboration of pyridine. Kinetic and computational analyses of the catalytic cycle reveal that TAML-Si(IV) acts as a hydride transfer agent, and the hydrido silicate key intermediate is isolated. Notably, the Lewis acid is highly soluble (5 g/L) and long-term stable in water. Unlike previously described silicon-H2O adducts, the bound water becomes substantially acidified, reaching the Bro̷nsted superacidity range. A comparison of water affinity versus pKa lowering confirms our previous theory of the strength and the effect of Lewis acids. Overall, the compound's unlimited water compatibility and its mechanistically understood catalytic efficiency mark significant progress in applying structural constraint strategies for p-block element-based catalysis, while the acidification touches critical aspects of zeolite and silica surface chemistry.

Effects of a TAML catalyst on mice exposed during pregnancy and lactation

Tetra-amido macrocyclic ligands (TAMLs) are catalysts designed to mimic endogenous peroxidases that can degrade pollutants. Before TAMLs gain widespread use, it is first important to determine if they have endocrine disrupting properties. In this study, we evaluated the effects of the iron TAML, NT7, on hormone-sensitive outcomes in mice exposed during pregnancy and lactation, and on their litters prior to weaning. We administered NT7 at one of three doses to mice via drinking water prior to and then throughout pregnancy and lactation. Two hormonally active pharmaceuticals, ethinyl estradiol (EE2) and flutamide (FLUT), a known estrogen receptor agonist and androgen receptor antagonist, respectively, were also included. In the females, we measured pre- and post-parturition weight, length of pregnancy, organ weights at necropsy, and morphology of the mammary gland at the end of the lactational period. We also quantified maternal behaviors at three stages of lactation. For the offspring, we measured litter size, litter weights, and the achievement of other developmental milestones. We observed only one statistically significant effect of NT7, a decrease in the percentage of pups with ear opening at postnatal day 5. This contrasts with the numerous effects of EE2 on both the mother and the litter, as well as several modest effects of FLUT. The approach taken in this study could provide guidance for future studies that aim to evaluate novel compounds for endocrine disrupting properties.

The Mechanism of Formation of Active Fe-TAMLs Using HClO Enlightens Design for Maximizing Catalytic Activity at Environmentally Optimal, Circumneutral pH

Fe-TAML/peroxide catalysis provides simple, powerful, ultradilute approaches for removing micropollutants from water. The typically rate-determining interactions of H₂O₂ with Fe-TAMLs (rate constant k_I) are sharply pH-sensitive with rate maxima in the pH 9-10 window. Fe-TAML design or process design that shifts the maximum rates to the pH 6-8 window of most wastewaters would make micropollutant eliminations even more powerful. Here, we show how the different pH dependencies of the interactions of Fe-TAMLs with peroxide or hypochlorite to form active Fe-TAMLs (k_I step) illuminate why moving from H₂O₂ (pK_a, ca. 11.6) to hypochlorite (pK_a, 7.5) shifts the pH of the fastest catalysis to as low as 8.2. At pH 7, hypochlorite catalysis is 100-1000 times faster than H₂O₂ catalysis. The pH of maximum catalytic activity is also moderated by the pK_a's of the Fe-TAML axial water ligands, 8.8, 9.3, and 10.3, respectively, for [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NSO₂)₂CHMe}(H₂O)_n]^- (2) [n = 1-2], [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NCO)₂CF₂}(H₂O)_n]^- (1b), and [Fe{C₆H₄-1,2-(NCOCMe₂NCO)₂CMe₂}(H₂O)_n]^- (1a). The new bis(sulfonamido)-bis(carbonamido)-ligated 2 exhibits the lowest pK_a and delivers the largest hypochlorite over peroxide catalytic rate advantage. The fast Fe-TAML/hypochlorite catalysis is accompanied by slow noncatalytic oxidations of Orange II.

Porous Materials for Water Purification

Water pollution is a growing threat to humanity due to the pervasiveness of contaminants in water bodies. Significant efforts have been made to separate these hazardous components to purify polluted water through various methods. However, conventional remediation methods suffer from limitations such as low uptake capacity or selectivity, and current water quality standards cannot be met. Recently, advanced porous materials (APMs) have shown promise in improved segregation of contaminants compared to traditional porous materials in uptake capacity and selectivity. These materials feature merits of high surface area and versatile functionality, rendering them ideal platforms for the design of novel adsorbents. This Review summarizes the development and employment of APMs in a variety of water treatments accompanied by assessments of task-specific adsorption performance. Finally, we discuss our perspectives on future opportunities for APMs in water purification.

Generation of FeIV =O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron-N-C Catalyst

Generating Fe^IV =O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the Fe^IV =O generation pathway and oxidation behavior remain obscure. Employing an Fe-N-C catalyst with a typical Fe-N₄ moiety to activate peroxymonosulfate (PMS), we demonstrate that generating Fe^IV =O is mediated by an Fe-N-C-PMS* complex-a well-recognized nonradical species for induction of electron-transfer oxidation-and we determined that adjacent Fe sites with a specific Fe₁ -Fe₁ distance are required. After the Fe atoms with an Fe₁ -Fe₁ distance <4 Å are PMS-saturated, Fe-N-C-PMS* formed on Fe sites with an Fe₁ -Fe₁ distance of 4-5 Å can coordinate with the adjacent Fe^II -N₄ , forming an inter-complex with enhanced charge transfer to produce Fe^IV =O. Fe^IV =O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidation potential.

Enhanced Direct Electron Transfer Mediated Contaminant Degradation by Fe(IV) Using a Carbon Black-Supported Fe(III)-TAML Suspension Electrode System

Iron complexes of tetra-amido macrocyclic ligands (Fe-TAML) are recognized to be effective catalysts for the degradation of a wide range of organic contaminants in homogeneous conditions with the high valent Fe(IV) and Fe(V) species generated on activation of the Fe-TAML complex by hydrogen peroxide (H₂O₂) recognized to be powerful oxidants. Electrochemical activation of Fe-TAML would appear an attractive alternative to H₂O₂ activation, especially if the Fe-TAML complex could be attached to the anode, as this would enable formation of high valent iron species at the anode and, importantly, retention of the valuable Fe-TAML complex within the reaction system. In this work, we affix Fe-TAML to the surface of carbon black particles and apply this "suspension anode" process to oxidize selected target compounds via generation of high valent iron species. We show that the overpotential for Fe(IV) formation is 0.17 V lower than the potential required to generate Fe(IV) electrochemically in homogeneous solution and also show that the stability of the Fe(IV) species is enhanced considerably compared to the homogeneous Fe-TAML case. Application of the carbon black-supported Fe-TAML suspension anode reactor to degradation of oxalate and hydroquinone with an initial pH value of 3 resulted in oxidation rate constants that were up to three times higher than could be achieved by anodic oxidation in the absence of Fe-TAML and at energy consumptions per order of removal substantially lower than could be achieved by alternate technologies.

On TAML Catalyst Resting State Lifetimes: Kinetic, Mechanistic, and Theoretical Insight into Phosphate-Induced Demetalation of an Iron(III) Bis(sulfonamido)bis(amido)-TAML Catalyst

At ambient temperatures, neutral pH and ultralow concentrations (low nM), the bis(sulfonamido)bis(amido) oxidation catalyst [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NSO₂)₂CHMe}(OH₂)]^- (1) has been shown to catalyze the addition of an oxygen atom to microcystin-LR. This persistent bacterial toxin can contaminate surface waters and render drinking water sources unusable when nutrient concentrations favor cyanobacterial blooms. In mechanistic studies of this oxidation, while the pH was controlled with phosphate buffers, it became apparent that iron ejection from 1 becomes increasingly problematic with increasing [phosphate] (0.3-1.0 M); 1 is not noticeably impacted at low concentrations (0.01 M). At pH < 6.5 and [phosphate] ≥ 1.0 M, 1 decays quickly, losing iron from the macrocycle. Iron ejection is surprisingly mechanistically complex; the pseudo-first-order rate constant k_obs has an unusual dependence on the total phosphate concentration ([P_t]), k_obs = k₁[P_t] + k₂[P_t]², indicating two parallel pathways that are first and second order in [phosphate], respectively. The pH profiles in the 5.5-8.3 range for k₁ and k₂ are different: bell-shaped with a maximum of around pH 7 for k₁ and sigmoidal for k₂ with higher values at lower pH. Mechanistic proposals for the k₁ and k₂ pathways are detailed based on both the kinetic data and density functional theory analysis. The major difference between k₁ and k₂ is the involvement of different phosphate species, i.e., HPO₄^2- (k₁) and H₂PO₄^- (k₂); HPO₄^2- is less acidic but more nucleophilic, which favors intramolecular rate-limiting Fe-N bond cleavage. Instead, H₂PO₄^- acts intermolecularly, where the kinetics suggest that [H₄P₂O₈]^2- drives degradation.

Systematic Synthesis of Macrocycles Bearing up to Six 2,2'-Bipyridine Moieties through Self-Assembled Double Helix Structure

A new synthetic strategy for macrocycles bearing multiple coordination moieties was developed. A self-assembled double helix structure, composed of two linear strands bearing 2,2'-bipyridine units and Cu(I) ions, provided access to macrocycles bearing a defined number of 2,2'-bipyridine moieties and a defined ring size, via an olefin-metathesis reaction between two linear strands in the helix. The double helix structure improved the selectivity of the macrocycle synthesis by bringing the reaction points in close proximity even in the case of large macrocycles.

A mechanistic switch in C−H bond activation by elusive FeV(O)(TAML) reaction intermediate: A theoretical study

The divergent behavior of C−H bond oxidations of aliphatic substrates compared to those of aromatic substrates shown in Gupta's experiment was mechanistically studied herein by means of density functional theory calculations. Our calculations reveal that such difference is caused by different reaction mechanisms between two kinds of substrates (the aliphatic cyclohexane, 2,3-dimethylbutane and the aromatic toluene, ethylbenzene and cumene). For the aliphatic substrates, C−H oxidation by the oxidant FeV(O)(TAML) is a hydrogen atom transfer process; whereas for the aromatic substrates, C−H oxidation is a proton-coupled electron transfer (PCET) process with a proton transfer character on the transition state, that is, a proton-coupled electron transfer process holding a proton transfer-like transition state (PCET(PT)). This difference is caused by the strong π− π interactions between the tetra-anionic TAML ring and the phenyl ring of the aromatic substrates, which has a “pull” effect to make the electron transfer from substrates to the Fe=O moiety inefficient.

C-H Bond Cleavage by Bioinspired Nonheme Metal Complexes

The functionalization of C-H bonds is one of the most challenging transformations in synthetic chemistry. In biology, these processes are well-known and are achieved with a variety of metalloenzymes, many of which contain a single metal center within their active sites. The most well studied are those with Fe centers, and the emerging experimental data show that high-valent iron oxido species are the intermediates responsible for cleaving the C-H bond. This Forum Article describes the state of this field with an emphasis on nonheme Fe enzymes and current experimental results that provide insights into the properties that make these species capable of C-H bond cleavage. These parameters are also briefly considered in regard to manganese oxido complexes and Cu-containing metalloenzymes. Synthetic iron oxido complexes are discussed to highlight their utility as spectroscopic and mechanistic probes and reagents for C-H bond functionalization. Avenues for future research are also examined.

Detoxification of oil refining effluents by oxidation of naphthenic acids using TAML catalysts

The environmental problem stemming from toxic and recalcitrant naphthenic acids (NAs) present in effluents from the oil industry is well characterized. However, despite the numerous technologies evaluated for their destruction, their up-scaling potential remains low due to high implementation and running costs. Catalysts can help cutting costs by achieving more efficient reactions with shorter operating times and lower reagent requirements. Therefore, we have performed a laboratory investigation to assess iron-TAML (tetra-amido macrocyclic ligand) activators to catalyze the oxidation of NAs by activating hydrogen peroxide - considered environmentally friendly because it releases only water as by-product - under ultra-dilute conditions. We tested Fe-TAML/H₂O₂ systems on (i) model NAs and (ii) a complex mixture of NAs in oil refining wastewater (RWW) obtained from a refining site in Colombia. Given the need for cost-effective solutions, this preliminary study explores sub-stoichiometric H₂O₂ concentrations for NA mineralization in batch mode and, remarkably, delivers substantial removal of the starting NAs. Additionally, a 72-h semi-batch process in which Fe-TAML activators and hydrogen peroxide were added every 8 h achieved 90-95% removal when applied to model NAs (50 mg L^-1) and a 4-fold reduction in toxicity towards Aliivibrio fischeri when applied to RWW. Chemical characterization of treated RWW showed that Fe-TAML/H₂O₂ treatment (i) reduced the concentration of the highly toxic O₂ NAs, (ii) decreased cyclized constituents in the mixture, and (iii) preferentially degraded higher molecular weight species that are typically resistant to biodegradation. The experimental findings, together with the recent development of new TAML catalysts that are far more effective than the TAML catalysts deployed herein, constitute a foundation for cost-effective treatment of NA-contaminated wastewater.

Structure activity relationship study of N-doped ligand modified Fe(III)/H2O2 for degrading organic pollutants

The performance of Fe(III)/H₂O₂ was extremely enhanced by a novel N-doped ligand dipicolinamide (Dpa) for removing various organic pollutants. This dramatic enhancement of contaminants degradation in Fe(III)-Dpa/H₂O₂ system under pH≥ 7 was ascribed to the coordinating capacity of Dpa to form the dissolved Fe(III)-Dpa/Fe(II)-Dpa, and the reductive capacity of Dpa to maintain the concentration of Fe(II), which made Dpa improve the catalytic performance of Fe(III) nearly twice as much as Fe(II). Dpa has a strong complexing ability than Cit, NTA, and EDTA to maintain the catalytic activity of Fe(III) without light. The single crystal of Fe-Dpa was obtained to reveal its structure activity relationship. Fe-Dpa was composed of four bonds of Fe-N and two bonds of Fe-Cl. The Fe-Cl bonds were labile sites, which was easily experienced ligand exchange with H₂O₂, resulting Fe-H₂O₂ bonds to initiate degradation reaction. The remaining Fe-N bonds were effectively planar, which had a large delocalized π electrons flow domain, enhancing the production of multiple reactive species, including iron(IV/V)-oxo species, HO· and O₂^-·. An empirical kinetic model of Fe(III)-Dpa/H₂O₂ system was established. In addition, the evaluation results of the toxicity of Fe-Dpa to larval zebrafish and chinese cabbage displayed that Fe-Dpa possesses low toxicity.

Rapid destruction of triclosan by Iron(III)-Tetraamidomacrocyclic ligand/hydrogen peroxide system

Iron(III)-tetraamidomacrocyclic ligand (Fe(III)-TAML) activators can activate hydrogen peroxide to oxidize many kinds of organic pollutants. In this study, we investigated the degradation of triclosan, a widely used broad-spectrum bactericide, under the treatment of Fe(III)-TAML/H₂O₂ system at different pH conditions. We also studied the influence of natural organic matter (NOM) on the degradation process. Our results showed that complete removal of triclosan could be obtained within several minutes under the optimal conditions. The degradation of triclosan by Fe(III)-TAML/H₂O₂ system exhibited strong pH-dependence and the degradation rate increased with the increase in pH level from 7.0 to 10.0. When adding fulvic acid (FA) or humic acid (HA) in the reaction system, the degradation of triclosan could be suppressed slightly, and HA exhibited stronger inhibition than FA. Based on the analysis of reaction intermediates, phenoxyl radical reaction and ring open reaction were involved in the decomposition of triclosan. Significant inhibition of overall toxicity to Photobacterium phosphoreum further confirmed the high efficiency of Fe(III)-TAML/H₂O₂ system for the removal of antibiotic activities resulting from the parent triclosan molecule and its degradation products.

Designing Materials for Aqueous Catalysis: Ionic Liquid Gel and Silica Sphere Entrapped Iron-TAML Catalysts for Oxidative Degradation of Dyes

Materials have been developed that encapsulate a homogeneous catalyst and enable it to operate as a heterogeneous catalyst in water. A hydrophobic ionic liquid within the material was used to dissolve Fe-TAML and keep it from leaching into the aqueous phase. One-pot processes were used to entrap Fe-TAML in basic ionic liquid gels, and ionic liquid gel spheres structured via a modified Stöber synthesis forming SiO₂ particles of uniform size. Catalytic activity was demonstrated via the oxidative degradation of dyes. Fe-TAML entrapped in a basic ionic liquid gel exhibited consistent activity in five recycles. This discovery of heterogenized H₂O₂ activators prepared by sol-gel and Stöber processes opens new possibilities for the creation of engineered catalytic materials for water purification.

Redox Metal-Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes

Water oxidation catalysis stands out as one of the most important reactions to design practical devices for artificial photosynthesis. Use of late first-row transition metal (TM) complexes provides an excellent platform for the development of inexpensive catalysts with exquisite control on their electronic and structural features via ligand design. However, the difficult access to their high oxidation states and the general labile character of their metal-ligand bonds pose important challenges. Herein, we explore a copper complex (1^2-) featuring an extended, π-delocalized, tetra-amidate macrocyclic ligand (TAML) as water oxidation catalyst and compare its activity to analogous systems with lower π-delocalization (2^2- and 3^2-). Their characterization evidences a special metal-ligand cooperativity in accommodating the required oxidative equivalents using 1^2- that is absent in 2^2- and 3^2-. This consists of charge delocalization promoted by easy access to different electronic states at a narrow energy range, corresponding to either metal-centered or ligand-centered oxidations, which we identify as an essential factor to stabilize the accumulated oxidative charges. This translates into a significant improvement in the catalytic performance of 1^2- compared to 2^2- and 3^2- and leads to one of the most active and robust molecular complexes for water oxidation at neutral pH with a k_obs of 140 s^-1 at an overpotential of only 200 mV. In contrast, 2^2- degrades under oxidative conditions, which we associate to the impossibility of efficiently stabilizing several oxidative equivalents via charge delocalization, resulting in a highly reactive oxidized ligand. Finally, the acyclic structure of 3^2- prevents its use at neutral pH due to acidic demetalation, highlighting the importance of the macrocyclic stabilization.

Self-assembly of FeIII-TAML-based microstructures for rapid degradation of bisphenols

Iron(III)-tetraamidomacrocyclic ligand (Fe^III-TAML) activators have drawn great attentions due to the high reactivity to degrade organic pollutants. However, previous studies showed that the reactivity and stability of Fe^III-TAML were both strongly pH-dependent, which dramatically decrease at lower pH levels. Herein, Fe^III-TAML/DODMA (dimethyldioctadecylammonium chloride) microspheres with diameters ranging from 100 to 2000 nm were synthesized via a surfactant-assisted self-assembly technique. The newly synthesized Fe^III-TAML/DODMA composite exhibits superior reactivity compared to free Fe^III-TAML as indicated by the degradation of bisphenols (i.e., bisphenol A and its analogues) over a wide pH range (i.e., pH 4.5-10.0). Based on the adsorption results and quantitative structure-activity relationship (QSAR) models, the enhanced reactivity of Fe^III-TAML/DODMA is mainly ascribed to the hydrophobic sorption of bisphenols. Moreover, the enhanced ionization of the axial water molecule associated with Fe^III-TAML could further enhance the reactivity of synthesized microcomposites, which was confirmed by the results of infrared and Raman spectra. Furthermore, Fe^III-TAML/DODMA shows distinct acid-resistance as explained by the protection of the hydrophobic alkyl chains of DODMA. This novel method would provide a simple and effective strategy to expand the application of Fe^III-TAML in a wide pH range and render Fe^III-TAML/DODMA microstructure as a potential catalyst for treatment of bisphenol compounds.

Zero-Order Catalysis in TAML-Catalyzed Oxidation of Imidacloprid, a Neonicotinoid Pesticide

Bis-sulfonamide bis-amide TAML activator [Fe{4-NO₂ C₆ H₃ -1,2-(NCOCMe₂ NSO₂ )₂ CHMe}]^- (2) catalyzes oxidative degradation of the oxidation-resistant neonicotinoid insecticide, imidacloprid (IMI), by H₂ O₂ at pH 7 and 25 °C, whereas the tetrakis-amide TAML [Fe{4-NO₂ C₆ H₃ -1,2-(NCOCMe₂ NCO)₂ CF₂ }]^- (1), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra-low concentrations of both imidacloprid and 2, 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2. Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [2]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H₂ O₂ ]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [2]>[IMI]. A plausible mechanism of the TAML-catalyzed oxidations of imidacloprid is briefly discussed. Similar zero-order catalysis is presented for the oxidation of 3-methyl-4-nitrophenol by H₂ O₂ , catalyzed by the TAML analogue of 1 without a NO₂ -group in the aromatic ring.

Treatment of crude oil contaminated wastewater via an electrochemical reaction

A cost-effective and catalyst-free approach for the treatment of oil field formation water has been extensively explored in this work. ZnO NPs were synthesized via an electrochemical reaction using hydrogen peroxide as the electrolyte. The XRD and TEM analysis depicted the high purity and wurtzite hexagonal structure of ZnO NPs with an average size of 35 ± 5 nm. TGA data showed the thermal stability of the synthesized material up to 750 °C. The efficiency of the removal of hydrocarbons from formation water by the combination of electrochemical reaction and synthesized ZnO NPs was monitored by GC-MS and FTIR. GC-MS analysis revealed that out of 214 compounds (present in the untreated sample), a total of 131 compounds were adsorbed by ZnO NPs. Further, the absence of any compound in the chromatogram of the treated sample attests that the rest of the compounds were completely or partially degraded by electrochemical degradation reaction. Moreover, this technique overcomes some of the important drawbacks of the existing techniques in the area of electrochemical research, such as the generation of toxic byproducts, unwanted side reactions, and involvement of hazardous chemicals.

A novel electrochemical reaction was developed for the treatment of formation water and subsequently ZnO nanoparticles were synthesised in the in situ condition and further used as an adsorbing material for petroleum hydrocarbons.

Hydrogen Atom Abstraction by High-Valent Fe(OH) versus Mn(OH) Porphyrinoid Complexes: Mechanistic Insights from Experimental and Computational Studies

High-valent metal-hydroxide species have been implicated as key intermediates in hydroxylation chemistry catalyzed by heme monooxygenases such as the cytochrome P450s. However, in some classes of P450s, a bifurcation from the typical oxygen rebound pathway is observed, wherein the Fe^IV(OH)(porphyrin) species carries out a net hydrogen atom transfer reaction to form alkene metabolites. In this work, we examine the hydrogen atom transfer (HAT) reactivity of Fe^IV(OH)(ttppc) (1), ttppc = 5,10,15-tris(2,4,6-triphenyl)-phenyl corrole, toward substituted phenol derivatives. The iron hydroxide complex 1 reacts with a series of para-substituted 2,6-di-tert-butylphenol derivatives (4-X-2,6-DTBP; X = OMe, Me, Et, H, Ac), with second-order rate constants k₂ = 3.6(1)-1.21(3) × 10⁴ M^-1 s^-1 and yielding linear Hammett and Marcus plot correlations. It is concluded that the rate-determining step for O-H cleavage occurs through a concerted HAT mechanism, based on mechanistic analyses that include a KIE = 2.9(1) and DFT calculations. Comparison of the HAT reactivity of 1 to the analogous Mn complex, Mn^IV(OH)(ttppc), where only the central metal ion is different, indicates a faster HAT reaction and a steeper Hammett slope for 1. The O-H bond dissociation energy (BDE) of the M^III(HO-H) complexes were estimated from a kinetic analysis to be 85 and 89 kcal mol^-1 for Mn and Fe, respectively. These estimated BDEs are closely reproduced by DFT calculations and are discussed in the context of how they influence the overall H atom transfer reactivity.

Recent advances in metalloporphyrins for environmental and energy applications

Porphyrin-based chemistry has reached an unprecedented period of rapid development after decades of study. Due to attractive multifunctional properties, porphyrins and their analogues have emerged as multifunctional organometals for environmental and energy purposes. In particular, pioneer works have been conducted to explore their application in pollution abatement, energy conversion and storage and molecule recognition. This review summarizes recent advances of porphyrins chemistry, focusing on elucidating the nature of catalytic process. The Fenton-like redox chemistry and photo-excitability of porphyrins and their analogues are discussed, highlighting the generation of high-valent iron oxo porphyrin species. Finally, challenges in current research are identified and perspectives for future development in this area are presented.

Xenoestrogen interference with nongenomic signaling actions of physiological estrogens in endocrine cancer cells

Rapid nongenomic signaling by estrogens (Es), initiated near the cell membrane, provides new explanations for the potent actions of environmental chemicals that imperfectly mimic physiological Es. These pathways can affect tumor growth, stabilization, or shrinkage via a number of signaling streams such as activation/inactivation of mitogen-activated protein kinases and caspases, generation of second messengers, and phospho-triggering of cyclin instability. Though prostate cancers are better known for their responsiveness to androgen deprivation, ∼17% of late stage tumors regress in response to high dose natural or pharmaceutical Es; however, the mechanisms at the cellular level are not understood. More accurate recent measurements show that estradiol (E₂) levels decline in aging men, leading to the hypothesis that maintaining young male levels of E₂ may prevent the growth of prostate cancers. Major contributions to reducing prostate cancer cell numbers included low E₂ concentrations producing sustained ERK phospho-activation correlated with generation of reactive oxygen species causing cancer cell death, and phospho-activation of cyclin D1 triggering its rapid degradation by interrupting cell cycle progression. These therapeutic actions were stronger in early stage tumor cells (with higher membrane estrogen receptor levels), and E₂ was far more effective compared to diethylstilbestrol (the most frequently prescribed E treatment). Xenoestrogens (XEs) exacerbated the growth of prostate cancer cells, and as we know from previous studies in pituitary cancer cells, can interfere with the nongenomic signaling actions of endogenous Es. Therefore, nongenomic actions of physiological levels of E₂ may be important deterrents to the growth of prostate cancers, which could be undermined by the actions of XEs.

Self-Assembly of Mn(II)-Amidoximated PAN Polymeric Beads Complex as Reusable Catalysts for Efficient and Stable Heterogeneous Electro-Fenton Oxidation

A facile postsynthetic amidoxime modification method was reported on the preparation of transition-metal ions (Mn, Fe, and Co)-polyacrylonitrile (PAN) polymeric beads complex as reusable catalysts for efficient and stable heterogeneous electro-Fenton oxidation. Through one-step phase inversion, low-cost and chemically resistant polymeric PAN beads were fabricated on a large scale with controllable sizes and abundant porous structure. The postfunctionalization strategy led more active sites to be uniformly distributed into modified PAN beads owing to the favorable channel confined effect and chelate coordination. Compared with pure PAN beads, the modified composite catalysts exhibited remarkably higher activity and stability in electro-Fenton oxidation over wide pH range of 3-10 without any addition of H₂O₂. By analysis, the grafted amidoxime group was extremely beneficial for improving metal loading and binding force between active sites and organic supports, which accelerated the active sites autocatalytic cycle to promote H₂O₂ activation by means of excited electron transfer from composites' functional groups. The catalytic activity of Mn-amidoximated PAN evaluated by the turnover frequency was 15 times more than that of traditional iron oxide and very competitive to the reported metal-organic framework-based composites. Moreover, a strong metal and polymeric support interaction significantly enhanced the stabilization of active sites dispersed in porous matrix and solved the ever-present problem of metallic ions leaching to the greatest extent. The scalable introduction of functionalities into sophisticated structures after host framework synthesis will bring valuable insights to develop highly efficient and stable heterogeneous catalysts for green electrochemical oxidation in practical application.

Quantitative structure-activity relationship for the oxidation of aromatic organic contaminants in water by TAML/H2O2

Tetra-amido macrocyclic ligand (TAML) activator is a functional analog of peroxidase enzymes, which activates hydrogen peroxide (H₂O₂) to form high valence iron-oxo complexes that selectively degrade persistent aromatic organic contaminants (ACs) in water. Here, we develop quantitative structure-activity relationship (QSAR) models based on measured pseudo first-order kinetic rate coefficients (k_obs) of 29 ACs (e.g., phenols and pharmaceuticals) oxidized by TAML/H₂O₂ at neutral and basic pH values to gain mechanistic insight on the selectivity and pH dependence of TAML/H₂O₂ systems. These QSAR models infer that electron donating ability (E_HOMO) is the most important AC characteristic for TAML/H₂O₂ oxidation, pointing to a rate-limiting single-electron transfer (SET) mechanism. Oxidation rates at pH 7 also depend on AC reactive indices such as f_min^- and qH⁺, which respectively represent propensity for electrophilic attack and the most positive net atomic charge on hydrogen atoms. At pH 10, TAML/H₂O₂ is more reactive towards ACs with a lower hydrogen to carbon atoms ratio (#H:C), suggesting the significance of hydrogen atom abstraction. In addition, lnk_obs of 14 monosubstituted phenols is negatively correlated with Hammett constants (σ) and exhibits similar sensitivity to substituent effects as horseradish peroxidase. Although accurately predicting degradation rates of specific ACs in complex wastewater matrices could be difficult, these QSAR models are statistically robust and help predict both relative degradability and reaction mechanism for TAML/H₂O₂-based treatment processes.

Development of Fe(II) system based on N, N'-dipicolinamide for the oxidative removal of 4-chlorophenol

A novel catalyst system was investigated based on Fe-N, N'-dipicolinamide complex for the degradation of 4-chlorophenol (4-CP) by using hydrogen peroxide as an oxidant under mild alkaline conditions. This complex was stabilized by a ligand that assembles pyridyl and amide groups with a suitable linker. The optimization of the synthesized catalysts was evaluated in terms of the removal efficiency of 4-CP, by using Fe(II) and N, N'-1,2-phenyl-enedipyridine-2-carboxamide with a molar ratio of 1:1. The effects of reaction parameters on the oxidation of 4-CP were investigated by applying the selected catalyst with 4-CP removal rate of 99%. The results indicated that the pH and catalyst concentration could significantly affect the degradation rate of 4-CP. The mineralization level of 4-CP during the reaction was also examined, and almost 62.5% of 4-CP was absolutely mineralized into carbon dioxide and water. The preliminary analysis on the degradation mechanism indicate that the main active species are not hydroxyl radicals, and another kind of active species, called iron-oxo species, were proposed. This study explores a resultful linker between pyridyl and amide and presents a new method to expand the application of pH range of Fenton-like system.

Estrogenic activity of cylindrospermopsin and anatoxin-a and their oxidative products by FeIII-B*/H2O2

The cyanotoxins released into waters during cyanobacterial blooms can pose serious hazards to humans and animals. Apart from their toxicological mechanisms, cyanotoxins have been shown to be involved in estrogenic activity by in vivo and in vitro assays; however, there is limited information on the change in estrogenicity of cyanotoxins following chemical oxidation. In this study, the estrogenic activity of cylindrospermopsin (CYL) and anatoxin-a (ANA) at concentrations ranging from 2.4 × 10^-7 M to 2.4 × 10^-12 M (CYL) and 7.1 × 10^-6 M to 7.1 × 10^-11 M (ANA), and after treatment by the Fe^III-B*/H₂O₂ catalyst system, was investigated by the yeast estrogen screen (YES) assay. The results indicate that CYL and ANA acted as agonists in the YES assay (CYL logEC₅₀ = -8.901; ANA logEC₅₀ = -6.789), their binding affinity to estrogen receptors is associated with their intrinsic properties, including ring structures and toxicant properties. CYL and ANA were shown to simulate endocrine disrupting chemicals (EDCs) to modulate the 17β-estradiol-induced estrogenic activity, resulting in non-monotonic dose responses. The treated CYL showed a significantly altered estrogenicity compared to the untreated CYL (T₍₂₎ = 8.168, p ≤ .05), while the estrogenicity of the treated ANA was not significantly different to the untreated ANA (T₍₂₎ = 1.295, p > .05). Intermediate products generated from CYL and ANA oxidized by Fe^III-B*/H₂O₂ were identified using Q-Exactive Tandem Mass Spectrometry (LC-MS/MS). Treatment with Fe^III-B*/H₂O₂ yielded open-ring by-products which likely resulted in CYL's reduced binding affinity to estrogen receptors. The insignificant change in the estrogenicity of treated ANA was possibly a result of its multiple ring structure products, which were likely able to bind to estrogen receptors. The comparisons for the estrogenicity of these cyanotoxins before and after Fe^III-B*/H₂O₂ treatment suggest that the reductions in estrogenicity achieved by oxidation were dependent on the levels of cyanotoxins removed, as well as the estrogenicity of the degradation products. This is the first study on the change in the estrogenicity of CYL and ANA upon oxidation by Fe^III-B*/H₂O₂, a high activity catalyst system.

C-H activation and nucleophilic substitution in a photochemically generated high valent iron complex

The (photo) chemical oxidation of a (TAML)Fe^III complex using outer-sphere oxidants results in valence tautomerisation and C–H activation governed by exogenous anions.

The photochemical oxidation of a (TAML)Fe^III complex 1 using visible light generated Ru(bpy)₃³⁺ produces valence tautomers (TAML)Fe^IV (1⁺) and (TAML˙⁺)Fe^III (1-TAML˙⁺), depending on the exogenous anions. The presence of labile Cl^– or Br^– results in a ligand-based oxidation and stabilisation of a radical-cationic (TAML˙⁺)Fe^III complex, which subsequently leads to unprecedented C–H activation followed by nucleophilic substitution on the TAML aryl ring. In contrast, exogenous cyanide culminates in metal-based oxidation, yielding the first example of a crystallographically characterised S = 1 [(TAML)Fe^IV(CN)₂]^2– species. This is a rare report of an anion-dependent valence tautomerisation in photochemically accessed high valent (TAML)Fe systems with potential applications in the oxidation of pollutants, hydrocarbons, and water. Furthermore, the nucleophilic aromatic halogenation reaction mediated by (TAML˙⁺)Fe^III represents a novel domain for high-valent metal reactivity and highlights the possible intramolecular ligand or substrate modification pathways under highly oxidising conditions. Our findings therefore shine light on high-valent metal oxidants based on TAMLs and other potential non-innocent ligands and open new avenues for oxidation catalyst design.

Binding of oxime group to uranyl ion

Currently, the leading approach for extraction of uranium from seawater is selective sorption of UO2(2+) ions onto a poly(acrylamidoxime) fiber. Amidoxime functional groups are the most studied extractant moieties for this application, but are not perfectly selective, and understanding how these groups (and more generally the oxime groups) interact with UO2(2+) and competing ions in seawater is an important step in designing better extractants. We have started a new research programme aiming at in-depth studies of the uranyl-oxime/amidoxime interactions and we report here our first results which cover aspects of the coordination chemistry of 2-pyridyl ketoximes towards UO2(2+). Detailed synthetic investigations of various UO2(2+)/mepaoH and UO2(2+)/phpaoH reaction systems (mepaoH is methyl 2-pyridyl ketoxime and phpaoH is phenyl 2-pyridyl ketoxime) have provided access to the complexes [UO2(mepao)2(MeOH)2]{[UO2(NO3)(mepao)(MeOH)2]}2 (), [UO2(mepao)2(MeOH)2] (), [(UO2)2(O2)(O2CMe)2(mepaoH)2] () and [UO2(phpao)2(MeOH)2] (). The peroxido group in , which was isolated without the addition of external peroxide sources, probably arises from a bis(aquo)- and/or bis(hydroxido)-bridged diuranyl precursor in solution followed by photochemical oxidation of the bridging groups. The U(VI) atom in the [UO2(NO3)(mepao)(MeOH)2] molecules of () is surrounded by one nitrogen and seven oxygen atoms in a very distorted hexagonal bipyramidal geometry; two oxygen atoms from the terminal MeOH ligands, two oxygen atoms from the bidentate chelating nitrato group, and the oxygen and nitrogen atoms from the η(2) oximate group of the 1.110 (Harris notation) mepao(-) ligand define the equatorial plane. This plane consists of two terminal MeOH ligands and two η(2) oximate groups in the [UO2(mepao)2(MeOH)2] molecule () of . The structure of the [UO2(mepao)2(MeOH)2] molecule that is present in is very similar to the structure of the corresponding molecule in . The structure of the dinuclear molecule that is present in consists of two {UO2(O2CMe)(mepaoH)}(+) units bridged by a η(2):η(2):μ O2(2-) group. The equatorial plane of each uranyl site is composed of the pyridyl and oxime nitrogen atoms of a 1.011 mepaoH ligand, the oxygen atoms of an almost symmetrically coordinated bidentate chelating MeCO2(-) group and the two oxygen atoms of the peroxido groups. The core molecular structure of is similar to that of , the only difference being the presence of 1.110 phpao(-) ligands in the former instead of mepao(-) groups in the latter. The free pyridyl nitrogen atoms of mepao(-) and phpao(-) ligands of , and are acceptors of intramolecular H bonds from the ligated MeOH oxygen atoms. H-bonding and π-π stacking interactions build interesting supramolecular networks in the crystal structures of the four complexes. Compounds are the first structurally characterized uranyl complexes with 2-pyridyl aldoximes or ketoximes as ligands. IR data are discussed in terms of the coordination modes of the ligands in the complexes. (1)H NMR data in DMSO-d6 suggest that the complexes decompose in solution. The ESI(-) MS spectrum of dissolved in the NH4(O2CMe) buffer is indicative of the presence of [UO2(O2CMe)3](-), [UO2(O2CMe)2(phpao)](-), [UO2(O2CMe)(phpao)2](-) and [UO2(phpao)3](-) species. A common structural motif of the complexes containing the anionic mepao(-) (, ) and phpao(-) () ligands is that the deprotonated oximate group prefers to bind in the η(2) fashion forming a 3-membered chelating ring in spite of the presence of a pyridyl nitrogen atom, whose coordination would be expected to lead to 5- or 6-membered chelating rings.

Bis phenylene flattened 13-membered tetraamide macrocyclic ligand (TAML) for square planar cobalt(III)

The preparation, characterization, and evaluation of a cobalt(III) complex with 13-membered tetraamide macrocyclic ligand (TAML) is described. This is a square-planar (X-ray) S = 1 paramagnetic (¹H NMR) compound, which becomes an S = 0 diamagnetic octahedral species in excess d₅-pyridine. Its one-electron oxidation at an electrode is fully reversible with the lowest E _1/2 value (0.66 V vs SCE) among all investigated Co^III TAML complexes. The oxidation results in a neutral blue species which is consistent with a Co^III/radical-cation ligand. The ease of oxidation is likely due to the two benzene rings incorporated in the ligand structure (whereas there is just one in many other Co^III TAMLs). The oxidized neutral species are unexpectedly EPR silent, presumably due to the π-stacking aggregation. However, they display eight-line hyperfine patterns in the presence of excess of 4-tert-butylpyridine or 4-tert-butyl isonitrile. The EPR spectra are more consistent with the Co^III/radical-cation ligand formulation rather than with a Co^IV complex. Attempts to synthesize a similar vanadium complex under the same conditions as for cobalt using [V^VO(OCHMe₂)₃] were not successful. TAML-free decavanadate was isolated instead.

Targeting of High-Valent Iron-TAML Activators at Hydrocarbons and Beyond

TAML activators of peroxides are iron(III) complexes. The ligation by four deprotonated amide nitrogens in macrocyclic motifs is the signature of TAMLs where the macrocyclic structures vary considerably. TAML activators are exceptional functional replicas of the peroxidases and cytochrome P450 oxidizing enzymes. In water, they catalyze peroxide oxidation of a broad spectrum of compounds, many of which are micropollutants, compounds that produce undesired effects at low concentrations-as with the enzymes, peroxide is typically activated with near-quantitative efficiency. In nonaqueous solvents such as organic nitriles, the prototype TAML activator gave the structurally authenticated reactive iron(V)oxo units (Fe^VO), wherein the iron atom is two oxidation equivalents above the Fe^III resting state. The iron(V) state can be achieved through the intermediacy of iron(IV) species, which are usually μ-oxo-bridged dimers (Fe^IVFe^IV), and this allows for the reactivity of this potent reactive intermediate to be studied in stoichiometric processes. The present review is primarily focused at the mechanistic features of the oxidation by Fe^VO of hydrocarbons including cyclohexane. The main topic is preceded by a description of mechanisms of oxidation of thioanisoles by Fe^VO, because the associated studies provide valuable insight into the ability of Fe^VO to oxidize organic molecules. The review is opened by a summary of the interconversions between Fe^III, Fe^IVFe^IV, and Fe^VO species, since this information is crucial for interpreting the kinetic data. The highest reactivity in both reaction classes described belongs to Fe^VO. The resting state Fe^III is unreactive oxidatively. Intermediate reactivity is typically found for Fe^IVFe^IV; therefore, kinetic features for these species in interchange and oxidation processes are also reviewed. Examples of using TAML activators for C-H bond cleavage applied to fine organic synthesis conclude the review.

Electrochemical Formation of FeV (O) and Mechanism of Its Reaction with Water During O-O Bond Formation

A detailed electrochemical investigation of a series of iron complexes (biuret-modified tetraamido iron macrocycles Fe^III -bTAML), including the first electrochemical generation of Fe^V (O), and demonstration of their efficacy as homogeneous catalysts for electrochemical water oxidation (WO) in aqueous medium are reported. Spectroelectrochemical and mass spectral studies indicated Fe^V (O) as the active oxidant, formed due to two redox transitions, which were assigned as Fe^IV (O)/Fe^III (OH₂ ) and Fe^V (O)/Fe^IV (O). The spectral properties of both of these high-valent iron oxo species perfectly match those of their chemically synthesised versions, which were thoroughly characterised by several spectroscopic techniques. The O-O bond-formation step occurs by nucleophilic attack of H₂ O on Fe^V (O). A kinetic isotope effect of 3.2 indicates an atom-proton transfer (APT) mechanism. The reaction of chemically synthesised Fe^V (O) in CH₃ CN and water was directly probed by electrochemistry and was found to be first-order in water. The pK_a value of the buffer base plays a critical role in the rate-determining step by increasing the reaction rate several-fold. The electronic effect on redox potential, WO rates, and onset overpotential was studied by employing a series of iron complexes. The catalytic activity was enhanced by the presence of electron-withdrawing groups on the bTAML framework. Changing the substituents from OMe to NO₂ resulted in an eightfold increase in reaction rate, while the overpotential increased threefold.

Generation of reactive cobalt oxo oxamate radical species for biomimetic oxidation of contaminants

Bio-inspired formation of [Co^IVO˙]⁻ species: cobalt oxo radical intermediate was directly observed in ESI-MS.

A "Beheaded" TAML Activator: A Compromised Catalyst that Emphasizes the Linearity between Catalytic Activity and pKa

Studies of the new tetra-amido macrocyclic ligand (TAML) activator [Fe^III{(Me₂CNCOCMe₂NCO)₂CMe₂}OH₂]^- (4) in water in the pH range of 2-13 suggest its pseudo-octahedral geometry with two nonequivalent axial H₂O ligands and revealed (i) the anticipated basic drift of the first pK_a of water to 11.38 due to four electron-donating methyl groups alongside (ii) its counterintuitive enhanced resistance to acid-induced iron(III) ejection from the macrocycle. The catalytic activity of 4 in the oxidation of Orange II (S) by H₂O₂ in the pH range of 7-12 is significantly lower than that of previously reported TAML activators, though it follows the common rate law (v/[Fe^III] = k_Ik_II[H₂O₂][S]/(k_I[H₂O₂] + k_II[S]) and typical pH profiles for k_I and k_II. At pH 7 and 25 °C the rate constants k_I and k_II equal 0.63 ± 0.02 and 1.19 ± 0.03 M^-1 s^-1, respectively. With these new values for pK_a, k_I and k_II establishing new high and low limits, respectively, the rate constants k_I and k_II were correlated with pK_a values of all TAML activators. The relations log k = log k⁰ + α × pK_a were established with log k⁰ = 13 ± 2 and 20 ± 4 and α = -1.1 ± 0.2 and -1.8 ± 0.4 for k_I and k_II, respectively. Thus, the reactivity of TAML activators across four generations of catalysts is predictable through their pK_a values.

Mn(2+)-mediated homogeneous Fenton-like reaction of Fe(III)-NTA complex for efficient degradation of organic contaminants under neutral conditions

In this work, we report a novel Mn(2+)-mediated Fenton-like process based on Fe(III)-NTA complex that is super-efficient at circumneutral pH range. Kinetics experiments showed that the presence of Mn(2+) significantly enhanced the effectiveness of Fe(III)-NTA complex catalyzed Fenton-like reaction. The degradation rate constant of crotamiton (CRMT), a model compound, by the Fe(III)- NTA_Mn(2+) Fenton-like process was at least 1.6 orders of magnitude larger than that in the absence of Mn(2+). Other metal ions such as Ca(2+), Mg(2+), Co(2+) and Cu(2+) had no impacts or little inhibitory effect on the Fe(III)-NTA complex catalyzed Fenton-like reaction. The generation of hydroxyl radical (HO) and superoxide radical anion (O2(-)) in the Fe(III)-NTA_Mn(2+) Fenton-like process were suggested by radicals scavenging experiments. The degradation efficiency of CRMT was inhibited significantly (approximately 92%) by the addition of HO scavenger 2-propanol, while the addition of O2(-) scavenger chloroform resulted in 68% inhibition. Moreover, the results showed that other chelating agents such as EDTA- and s,s-EDDS-Fe(III) catalyzed Fenton-like reactions were also enhanced significantly by the presence of Mn(2+). The mechanism involves an enhanced generation of O2(-) from the reactions of Mn(2+)-chelates with H2O2, indirectly promoting the generation of HO by accelerating the reduction rate of Fe(III)-chelates to Fe(II)- chelates.

Minireview: Endocrine Disruptors: Past Lessons and Future Directions

Within the past few decades, the concept of endocrine-disrupting chemicals (EDCs) has risen from a position of total obscurity to become a focus of dialogue, debate, and concern among scientists, physicians, regulators, and the public. The emergence and development of this field of study has not always followed a smooth path, and researchers continue to wrestle with questions about the low-dose effects and nonmonotonic dose responses seen with EDCs, their biological mechanisms of action, the true pervasiveness of these chemicals in our environment and in our bodies, and the extent of their effects on human and wildlife health. This review chronicles the development of the unique, multidisciplinary field of endocrine disruption, highlighting what we have learned about the threat of EDCs and lessons that could be relevant to other fields. It also offers perspectives on the future of the field and opportunities to better protect human health.

TAML/H2O2 Oxidative Degradation of Metaldehyde: Pursuing Better Water Treatment for the Most Persistent Pollutants

The extremely persistent molluscicide, metaldehyde, widely used on farms and gardens, is often detected in drinking water sources of various countries at concentrations of regulatory concern. Metaldehyde contamination restricts treatment options. Conventional technologies for remediating dilute organics in drinking water, activated carbon, and ozone, are insufficiently effective against metaldehyde. Some treatment plants have resorted to effective, but more costly UV/H2O2. Here we have examined if TAML/H2O2 can decompose metaldehyde under laboratory conditions to guide development of a better real world option. TAML/H2O2 slowly degrades metaldehyde to acetaldehyde and acetic acid. Nuclear magnetic resonance spectroscopy ((1)H NMR) was used to monitor the degradation-the technique requires a high metaldehyde concentration (60 ppm). Within the pH range of 6.5-9, the reaction rate is greatest at pH 7. Under optimum conditions, one aliquot of TAML 1a (400 nM) catalyzed 5% degradation over 10 h with a turnover number of 40. Five sequential TAML aliquots (2 μM overall) effected a 31% removal over 60 h. TAML/H2O2 degraded metaldehyde steadily over many hours, highlighting an important long-service property. The observation of metaldehyde decomposition under mild conditions provides a further indication that TAML catalysis holds promise for advancing water treatment. These results have turned our attention to more aggressive TAML activators in development, which we expect will advance the observed technical performance.

The consortium of heterogeneous cobalt phthalocyanine catalyst and bicarbonate ion as a novel platform for contaminants elimination based on peroxymonosulfate activation

The design of catalytic oxidation processes with high efficiency has attracted considerable attention for a long while in environmental catalysis. In this work, a novel oxidation system, CFs-CoPc/PMS, was developed by coupling cellulosic fibers-bonded cobalt phthalocyanine (CFs-CoPc) with peroxymonosulfate (PMS). CFs-CoPc/PMS system could effectively decolorize azo dyes such as Acid Red 1 (AR1) with almost 100% decolorization efficiency in 35 min, suggesting that the CFs-CoPc/PMS system was a highly efficient oxidation process. In addition, bicarbonate ion (HCO3(-)) was further introduced to CFs-CoPc/PMS to construct a combined system, CFs-CoPc/PMS/HCO3(-). Remarkably, this system turned the negative effect of HCO3(-) observed in most reported Co/PMS systems into a positive one, which enhanced the AR1 decolorization with over 2-fold increase of the rate constant. The main factor responsible for the enhancement was high-valent cobalt-oxo intermediates (PcCo(IV)=O), which was presumably generated via the heterolytic cleavage of the PMS OO bond by CoPc-HCO3(-) complex. It is noteworthy that high-valent cobalt-oxo intermediates as the major active species is different from most reported mechanisms in Co/PMS systems, in which hydroxyl and sulfate radicals are recognized as the dominant active species. This study paves an avenue for developing highly efficient catalytic oxidation technology for wastewater remediation.