Efficient activation of ferrate(VI) by colloid manganese dioxide: Comprehensive elucidation of the surface-promoted mechanism

Layered clay confined single-atom catalyst for enhanced radical pathway to achieve ultrafast degradation of bisphenol A

Seeking a technically promising method and cost-effective material to synthesize carrier-supported single-atom catalysts has attracted on-going research interests to overcome the low productivity and high costs for their industrial application. Montmorillonite (MT), a natural silicate clay mineral, has specific two-dimensional layered structure, and could be an excellent carrier, which creates a unique microenvironment to enhance molecule adsorption and interfacial reactions within the single atoms, free radicals and pollutants in the heterogeneous catalytic system. We synthesized cobalt single-atom catalyst (Co-SAC) by ball milling MT and cobalt salt using surface and spatial confinement strategy. Co-SAC/MT catalyst was used to activate peroxymonosulfate for degrading emerging contaminants bisphenol A (BPA). Characterization results revealed that Co single atoms were confined in the interlayer of MT as Co-O6-Si. Co-SAC/MT catalyst demonstrated remarkable molecular interaction capabilities to shorten mass transfer distance of free radical diffusion to the target pollutants, enhance the utilization rate of free radicals, and thus improve the efficiency of oxidation reaction. The BPA solution was completely degraded in 3 min, with a mineralization rate of 75.7 % in 10 min. This study provides a simple and efficient method for the preparation of single-atom catalysts, which is expected to achieve large-scale production of single-atom catalysts.

Novel role of Silver(I) as electron shuttle for polymerization of chlorophenols by permanganate oxidation

Permanganate (Mn(VII)) oxidation is attracting increasing attention in the field of water treatment, however, it exhibits limited chemical oxygen demand (COD) removal due to its inability to completely destroy the structure of pollutants. This paper discovered the novel role of ionic silver as electron shuttle for regulation of chlorophenols (CPs) polymerization during Mn(VII) oxidation. The Mn(VII)-Ag(I) system displayed remarkable removal of CPs in real water bodies and facilitated polymerization to at least hexamerization for improved COD removal. The ring-closure reaction was proposed for the first time, potentially stabilizing chained oligomers and reducing their migration toxicity. Ag(I) plays a dual role to create the electron-deficient state of Mn(VII) and enhance the oxidation susceptibility of 2,4-DCP via complexation, which mediates the electron transfer to generate abundant phenoxyl radicals to initiate polymerization for the formation of filterable and settleable oligomers. Findings of this work would provide new inspirations for the development of highly-efficient, cost-effective and environment-friendly Mn(VII) oxidation technologies in removal of CPs-like contaminants.

Roles of iron (V) and iron (IV) species in ferrate-triggered oxidation of phenolic pollutants and their transformation induced by phenoxyl radical

Ferrate is a promising oxidizing agent for water treatment. Understanding the reaction characteristics and transformation mechanism of high-valent intermediate irons [Fe(V) and Fe(IV)] remains challenging. Here, we systematically investigated the roles of Fe(VI), Fe(V), and Fe(IV) species for acetaminophen oxidation using reaction kinetics, products, and stoichiometries. Acetaminophen reacts with Fe(VI) via one-electron transfer mechanism, to initiate a sequential conversion process of "Fe(VI)-Fe(V)-Fe(IV)-Fe(III)", with a stoichiometry [Δacetaminophen/Δferrate] up to 2.20:1. The stoichiometry decreased to 1.23:1 after adding pyrophosphate to sequester Fe(V) oxidation, higher than the Fe(VI)-contributed stoichiometry of 0.58:1, indicating the involvement of Fe(IV) species, not inhibited by pyrophosphate. Dimer yields and theoretical calculations demonstrated that the generated phenoxyl radical could reduce Fe(V) into Fe(IV) even in the presence of pyrophosphate, to achieve the sequential one-electron transfer process. For other phenols containing electron-donating substituents, their phenoxyl radicals could also induce the transformation of Fe(V) into Fe(IV). This organic radical-induced conversion could occur in the reaction of ferrate with natural organic matter, and enhance the effective removal of pollutants. This study highlights the interaction of phenoxyl radical with high-valent iron species, and offers new insights to guide future identification of high-valent iron species in ferrate oxidation.

VUV Activated Fe(VI) by Promoting the Generation of Intermediate Valent Iron and Hydroxyl Radicals

In this study, vacuum ultraviolet (VUV) was first proposed to activate ferrate (Fe(VI)) for degrading micropollutants (e.g., carbamazepine (CBZ)). Results indicated that VUV/Fe(VI) could significantly facilitate the CBZ degradation, and the removal efficiencies of VUV/Fe(VI) were 30.9-83.4% higher than those of Fe(VI) at pH = 7.0-9.0. Correspondingly, the degradation rate constants of VUV/Fe(VI) were 2.3-36.0-fold faster than those of Fe(VI). Free radical quenching and probe experiments revealed that the dominant active species of VUV/Fe(VI) were •OH and Fe(V)/Fe(IV), whose contribution ratios were 43.3 to 48.6% and 48.2 to 46.6%, respectively, at pH = 7.0-9.0. VUV combined with Fe(VI) not only effectively mitigated the weak oxidizing ability of Fe(VI) under alkaline conditions (especially pH = 9.0) but also attenuated the deteriorating effect of background constituents on Fe(VI). In different real waters (tap water, river water, WWTPs effluent), VUV/Fe(VI) retained a remarkably enhanced effect on CBZ degradation compared to Fe(VI). Moreover, VUV/Fe(VI) exhibited outstanding performance in the debasement of CBZ and sulfamethoxazole (SMX), as well as six other micropollutants, displaying broad-spectrum capability in degrading micropollutants. Overall, this study developed a novel oxidation process that was efficient and energy-saving for the rapid removal of micropollutants.

Ferrate (VI) oxidation of sulfamethoxazole enhanced by magnetized sludge-based biochar: Active sites regulation and degradation mechanism analysis

Developing non radical systems for antibiotic degradation is crucial for addressing the inefficiency of conventional radical systems. In this study, novel magnetic-modified sludge biochar (MASBC) was synthesized to significantly enhance the oxidative degradation of sulfamethoxazole (SMX) by ferrate (Fe (VI)). In the Fe (VI)/MASBC system, 90.46% of SMX at a concentration of 10 μM and 49.34% of the total organic carbon (TOC) could be removed under optimal conditions of 100 μM of Fe (VI) and 0.40 g/L of MASBC within 10 min. Furthermore, the Fe (VI)/MASBC system was demonstrated with broad-spectrum removal capability towards sulfonamides in single or mixture. Quenching experiments, EPR analyses, and electrochemical experiments revealed that direct electron transfer (DET) and •O2- were mainly responsible for the removal of SMX, with functional groups (e.g., -OH, C=O) and Fe-O (redox of Fe (III)/Fe (II)) acting as the active sites, while the probe experiments showed that Fe (IV)/Fe (V) made a minor contribution to the degradation of SMX. Benefiting from the DET, the Fe (VI)/MASBC system exhibited a wide pH adaptation range (e.g., from 5.0 to 10.0) and strong anti-interference ability. The N atoms and their neighboring atoms in SMX were the prior degradation sites, with the cleavage of bond and ring opening. The degradation products showed low or non-toxicity according to ECOSAR program assessment. The removal of SMX remained within a reasonable range of 71.33%-90.46% over five consecutive cycles. Also, the Fe (VI)/MASBC system was demonstrated to be effectively applied for successful SMX removal in various water matrices, including ultrapure water, tap water, lake water, Yangtze River water, and wastewater. Therefore, this study offered new insights into the mechanism of Fe (VI) oxidation and would contribute to the efficient treatment of organic pollutants.

Proton vs Electron: The Dual Role of Redox-Inactive Metal Ions in Permanganate Oxidation Kinetics

Redox-inactive metal-ion-driven modulation of the oxidation behavior of high-valent metal-oxo complex has garnered significant interest in biological and chemical synthesis; however, their role in permanganate (Mn(VII)) oxidation for the removal of organic pollutants has been largely neglected. Here, we uncover the impact of six metal ions (i.e., Ca2+, Mg2+, Ni2+, Zn2+, Al3+, and Sc3+) presenting in water environments on Mn(VII) activity. These ions uniformly boost the electron and oxygen transfer capabilities of Mn(VII) while impeding proton transfer, as evidenced by electrochemical tests, thioanisole probe analysis, and the kinetic isotope effect. The observed effects are intricately linked to the Lewis acidity of the metal ions. Further mechanistic insights reveal that Mn(VII) can interact with metal ions without direct reduction. Such interactions modify the electronic configuration of Mn(VII) and create an acidic microenvironment, thus increasing its electrophilicity and the energy barrier for the abstraction of proton from organic substrates. More importantly, the efficacy of Mn(VII) in removing phenolic pollutants is regulated by these ions through changing the driving force for proton and electron transfer, i.e., facilitated at pH > 4.5 and inhibited at lower pH. The contribution of active Mn intermediates is also discussed to reveal the oxidative mechanism of the metal ion/Mn(VII) system. These findings not only facilitate the rational design of Mn(VII) oxidation conditions in the presence of metal ions for water decontamination but also offer an alternative paradigm for enhancing electrophilic oxidation.

Pore modulation of single atomic Fe sites for ultrafast Fenton-like chemistry with amplified electron migration oxidation

The limited interaction between pollutants, oxidants, and the surface catalytic sites of single atom catalysts (SACs) restricts the water decontamination effectiveness. Confining catalytic sites within porous structures enables the localized enrichment of reactants for optimized reaction kinetics, while the specific regulatory mechanisms remain unclear. Herein, SACs with porous modification significantly improves the utilization of peroxymonosulfate (PMS) and pollutant degradation activity. Confining catalytic sites in porous structure effectively reduces the mass transfer distance between radicals (SO4•- and •OH) and pollutants, thereby improving reaction performance. Pore modulation changes the surface electronic structure, leading to a significant improvement in the electron migration process. The system shows significant potential in effectively oxidizing various common emerging pollutants, and exhibits robust resistance to interference from environmental matrices. Moreover, a quantitative evaluation using life cycle assessment (LCA) indicates that the pFe-SAC/PMS system showcases superior environmental importance and practicality.

Deciphering the Novel Picolinate-Mn(II)/peroxymonosulfate System for Sustainable Fenton-like Oxidation: Dominance of the Picolinate-Mn(IV)-peroxymonosulfate Complex

A highly efficient and sustainable water treatment system was developed herein by combining Mn(II), peroxymonosulfate (PMS), and biodegradable picolinic acid (PICA). The micropollutant elimination process underwent two phases: an initial slow degradation phase (0-10 min) followed by a rapid phase (10-20 min). Multiple evidence demonstrated that a PICA-Mn(IV) complex (PICA-Mn(IV)*) was generated, acting as a conductive bridge facilitating the electron transfer between PMS and micropollutants. Quantum chemical calculations revealed that PMS readily oxidized the PICA-Mn(II)* to PICA-Mn(IV)*. This intermediate then complexed with PMS to produce PICA-Mn(IV)-PMS*, elongating the O-O bond of PMS and increasing its oxidation capacity. The primary transformation mechanisms of typical micropollutants mediated by PICA-Mn(IV)-PMS* include oxidation, ring-opening, bond cleavage, and epoxidation reactions. The toxicity assessment results showed that most products were less toxic than the parent compounds. Moreover, the Mn(II)/PICA/PMS system showed resilience to water matrices and high efficiency in real water environments. Notably, PICA-Mn(IV)* exhibited greater stability and a longer lifespan than traditional reactive oxygen species, enabling repeated utilization. Overall, this study developed an innovative, sustainable, and selective oxidation system, i.e., Mn(II)/PICA/PMS, for rapid water decontamination, highlighting the critical role of in situ generated Mn(IV).

Ferrate(VI)-based oxidation for ultrafiltration membrane fouling mitigation in shale gas produced water pretreatment: Role of high-valent iron intermediates and hydroxyl radicals

Ultrafiltration (UF) is increasingly used in the pretreatment of shale gas produced water (SGPW), whereas severe membrane fouling hampers its actual operation. In this work, ferrate(VI)-based oxidation was proposed for membrane fouling alleviation in SGPW pretreatment, and the activation strategies of calcium peroxide (CaO2) and ultraviolet (UV) were selected for comparison. The findings indicated that UV/Fe(VI) was more effective in removing fluorescent components, and the concentration of dissolved organic carbon was reduced by 24.1 %. With pretreatments of CaO2/Fe(VI) and UV/Fe(VI), the terminal specific membrane flux was elevated from 0.196 to 0.385 and 0.512, and the total fouling resistance diminished by 52.7 % and 76.2 %, respectively. Interfacial free energy analysis indicated that the repulsive interactions between pollutants and membrane were notably enhanced by Fe(VI)-based oxidation, thereby delaying the deposition of cake layers on the membrane surface. Quenching and probe experiments revealed that high-valent iron intermediates (Fe(IV)/Fe(V)) played significant roles in both CaO2/Fe(VI) and UV/Fe(VI) processes. Besides, hydroxyl radicals (•OH) were also important reactive species in the UV/Fe(VI) treatment, and the synergistic effect of Fe(IV)/Fe(V) and •OH showed a positive influence on SGPW fouling mitigation. In general, these findings establish a theoretical underpinning for the application of Fe(VI)-based oxidation for UF membrane fouling mitigation in SGPW pretreatment.

Synchronously enhanced dual oxidation pathways via engineered Co-Nx/Co3O4 for high-efficiency degradation of versatile antibiotics

Developing efficient and eco-friendly technologies for treating the antibiotic wastewaters is crucial. At present, the catalysts with metal-nitrogen (M-Nx) coordination showed excellent Fenton-like performance but were always difficult to realize practical antibiotics degradation because of their complicated preparation methods and inferior stability. In this work, the Co-Nx configuration was facilely reconstructed on the surface of Co3O4 (Co-Nx/Co3O4), which exhibited superior catalytic activity and stability towards various antibiotics. DFT results indicated that stronger ETP oxidation will be triggered by the electron-donating pollutants since more electrons can be easily migrated from these pollutants to the Co-Nx/Co3O4/PMS complex. The Co-Nx/Co3O4/PMS system could maintain superior oxidation capacity, high catalytic stability and anti-interference due to (i) the strong nonradical ETP oxidation with superior degradation selectivity in Co-Nx/Co3O4/PMS system, and (ii) the synchronously enhanced radical oxidation with high populations of non-selective radicals generated via activating PMS by the Co-Nx/Co3O4. As a result, the synergies of synchronously enhanced dual oxidation pathways guaranteed the self-cleaning properties, maintaining 98 % of activity after eight cycles and stability across a wide pH range. Basically, these findings have significant implications for developing technologies for purifying antibiotic wastewater.

Homogeneous to heterogeneous redox mediator enhancing ferrate(VI) oxidation of sulfamethoxazole: Role of ferrate(VI) activation and electron shuttle

Ferrate (Fe(VI)) is a promising oxidant for water remediation, yet it has limited reactivity towards certain recalcitrant but important emerging contaminants, such as sulfamethoxazole. Here, this study demonstrates that nitroxide redox mediators, specifically 9-azabicyclo[3.3.1]nonasne N-oxyl (ABNO), can catalyze Fe(VI) reaction with sulfamethoxazole by functioning both as Fe(VI) activator and electron shuttle. The underlying mechanism is explained as: (i) Fe(VI) activation: a series of one-electron transfers between Fe(VI) and ABNO produces highly reactive Fe(V)/Fe(IV) and ABNO+; (ii) electron shuttle: the newly formed active ABNO+ reacts with the sulfamethoxazole, contributing to its removal. Concurrently, ABNOH is generated and subsequently converted back to ABNO by reactive species, thereby completing the redox cycle. The as-developed heterogeneous redox mediator, ABNO@SiO2, retained its catalytic properties and effectively catalyzed Fe(VI) to remove sulfamethoxazole at environmentally relevant pH levels.

Role of bipyridyl in enhancing ferrate oxidation toward micropollutants

Enhancing Fe(VI) oxidation ability by generating high-valent iron-oxo species (Fe(IV)/Fe(V)) has attracted continuous interest. This work for the first time reports the efficient activation of Fe(VI) by a well-known aza-aromatic chelating agent 2,2'-bipyridyl (BPY) for micropollutant degradation. The presence of BPY increased the degradation constants of six model compounds (i.e., sulfamethoxazole (SMX), diclofenac (DCF), atenolol (ATL), flumequine (FLU), 4-chlorophenol (4-CP), carbamazepine (CBZ)) with Fe(VI) by 2 - 6 folds compared to those by Fe(VI) alone at pH 8.0. Lines of evidence indicated the dominant role of Fe(IV)/Fe(V) intermediates. Density functional theory calculations suggested that the binding of Fe(III) to one or two BPY molecules initiated the oxidation of Fe(III) to Fe(IV) by Fe(VI), while Fe(VI) was reduced to Fe(V). The increased exposures of Fe(IV)/Fe(V) were experimentally verified by the pre-generated Fe(III) complex with BPY and using methyl phenyl sulfoxide as the probe compound. The presence of chloride and bicarbonate slightly affected model compound degradation by Fe(VI) in the presence of BPY, while a negative effect of humic acid was obtained under the same conditions. This work demonstrates the potential of N-donor heterocyclic ligand to activate Fe(VI) for micropollutant degradation, which is instructive for the Fe(VI)-based oxidation processes.

Mechanical energy triggered piezo-catalyzation of Bi2WO6 nanoplates on ferrate (Fe(VI)) oxidation in alkaline media: Performance and mechanism

Piezo-electricity, as a unique physical phenomenon, demonstrates high effectiveness in capturing the environmental mechanical energy into polarization charges, offering the possibility to activate the advanced oxidation processes via the electron pathway. However, information regarding the intensification of Fe(VI) through piezo-catalysis is limited. Therefore, our study is the first to apply Bi2WO6 nanoplates for piezo-catalyzation of Fe(VI) to enhance bisphenol A (BPA) degradation. Compared to Fe(VI) alone, the Fe(VI)/piezo/Bi2WO6 system exhibited excellent BPA removal ability, with the degradation rate increased by 32.6% at pH 9.0. Based on the experimental and theoretical results, Fe(VI), Fe(V), Fe(IV) and •OH were confirmed as reaction active species in the reaction, and the increased BPA removal mainly resulted from the enhanced formation of Fe(IV)/Fe(V) species. Additionally, effects of coexisting anions (e.g., Cl-, NO3-, SO42- and HCO3-), humic acid and different water matrixes (e.g., deionized water, tap water and lake water) on BPA degradation were studied. Results showed the Fe(VI)/piezo/Bi2WO6 system still maintained satisfactory BPA degradation efficiencies under these conditions, guaranteeing future practical applications in surface water treatment. Furthermore, the results of intermediates identification, ECOSAR calculation and cytotoxicity demonstrated that BPA degradation by Fe(VI)/piezo/Bi2WO6 posed a diminishing ecological risk. Overall, these findings provide a novel mechanical energy-driven piezo-catalytic approach for Fe(VI) activation, enabling highly efficient pollutant removal under alkaline condition.

Enhanced permanganate oxidation of phenolic pollutants by alumina and potential industrial application

In this study, we found that alumina (Al2O3) may improve the degradation of phenolic pollutants by KMnO4 oxidation. In KMnO4/Al2O3 system, the removal efficiency of 2,4-Dibromophenol (2,4-DBP) was increased by 26.5%, and the apparent activation energy was decreased from 44.5 kJ/mol to 30.9 kJ/mol. The mechanism of Al2O3-catalytic was elucidated by electrochemical processes, X-ray photoelectron spectroscopy (XPS) characterization and theoretical analysis that the oxidation potential of MnO4- was improved from 0.46 V to 0.49 V. The improvement was attributed to the formation of coordination bonds between the O atoms in MnO4- and the empty P orbitals of the Al atoms in Al2O3 crystal leading to the even-more electron deficient state of MnO4-. The excellent reusability of Al2O3, the good performance on degradation of 2,4-DBP in real water, the satisfactory degradation of fixed-bed reactor, and the enhanced removal of 6 other phenolic pollutants demonstrated that the KMnO4/Al2O3 system has satisfactory potential industrial application value. This study offers evidence for the improvement of highly-efficient MnO4- oxidation systems.

Understanding the Distance Effect of the Single-Atom Active Sites in Fenton-Like Reactions for Efficient Water Remediation

Emerging single-atom catalysts (SACs) are promising in water remediation through Fenton-like reactions. Despite the notable enhancement of catalytic activity through increasing the density of single-atom active sites, the performance improvement is not solely attributed to the increase in the number of active sites. The variation of catalytic behaviors stemming from the increased atomic density is particularly elusive and deserves an in-depth study. Herein, single-atom Fe catalysts (FeSA-CN) with different distances (dsite) between the adjacent single-atom Fe sites are constructed by controlling Fe loading. With the decrease in dsite value, remarkably enhanced catalytic activity of FeSA-CN is realized via the electron transfer regime with peroxymonosulfate (PMS) activation. The decrease in dsite value promotes electronic communication and further alters the electronic structure in favor of PMS activation. Moreover, the two adjacent single-atom Fe sites collectively adsorb PMS and achieve single-site desorption of the PMS decomposition products, maintaining continuous PMS activation and contaminant removal. Moreover, the FeSA-CN/PMS system exhibits excellent anti-interference performance for various aquatic systems and good durability in continuous-flow experiments, indicating its great potential for water treatment applications. This study provides an in-depth understanding of the distance effect of single-atom active sites on water remediation by designing densely populated SACs.

Insights into enhanced oxidation of benzophenone-type UV filters (BPs) by ferrate(VI)/ferrihydrite: Increased conversion of Fe(VI) to Fe(V)/Fe(IV)

In this work, the oxidation performance of a new ferrate(VI)/ferrihydrite (Fe(VI)/Fh) system was systematically explored to degrade efficiently six kinds of benzophenone-type UV filters (BPs). Fe(VI)/Fh system not only had a superior degradation capacity towards different BPs, but also exhibited higher reactivity over a pH range of 6.0-9.0. The second-order kinetic model successfully described the process of BP-4 degradation by heterogeneous Fh catalyzed Fe(VI) system (R2 = 0.93), and the presence of Fh could increase the BP-4 degradation rate by Fe(VI) by an order of magnitude (198 M-1·s-1 v.s. 14.2 M-1·s-1). Remarkably, there are higher utilization efficiency and potential of Fe(VI) in Fe(VI)/Fh system than in Fe(VI) alone system. Moreover, characterization and recycling experiments demonstrated that Fh achieved certain long-term running performance, and the residual Fe content of solution after clarifying process meet World Health Organization (WHO) guidelines for drinking water. The contributions of reactive species could be ranked as Fe(V)/Fe(IV) > Fe(VI) > •OH. Fe(IV)/Fe(V) were the dominant species for the enhanced removal in the Fe(VI)/Fh system, whose percentage contribution (72 %-36 %) were much higher than those in Fe(VI) alone system (5 %-17 %). However, the contribution of Fe(VI) in oxidizing BP-4 should not be underestimated (20 %-56 %). These findings reasonably exploit available Fh resources to reduce the relatively high cost of Fe(VI), which offers a proper strategies for efficient utilization of high-valent iron species and may be used as a highly-efficient and cost-effective BPs purification method.

Fe(IV)/Fe(V)-mediated polyferric sulfate/periodate system: A novel coagulant/oxidant strategy in promoting micropollutant abatement

Strategic modulation of the advanced oxidation processes for the selective oxidation of micropollutants has attracted accumulating attention in water decontamination. This study first reported the combination of the coagulant polyferric sulfate (PFS) and oxidant periodate (PI) to accomplish synergistic abatement of the antibiotic sulfamethoxazole (SMX). The oxidizing performance of SMX by this system was almost unaffected by coexisting water constituents, indicating the great promise of selective oxidation. Different from the current hydroxyl radicals (•OH)-mediated coagulant/oxidant systems (e.g., PFS/H2O2 and PFS/ozone), the dominance of high-valent Fe(IV)/Fe(V) intermediates was unambiguously verified in the PFS/PI treatment. The PFS colloids before and after the oxidation were characterized and the iron speciation was analyzed. The transformation of monomeric iron configurations (Fe(a)) to oligomeric iron configurations (Fe(b)) could maintain the homeostasis of surface-bound Fe(III) and Fe(II). The interaction mechanisms included the production of reactive species and dynamic reaction equilibrium for micropollutant degradation. Finally, the transformation pathways of SMX and carbamazepine (CMZ) in the PFS/PI system were postulated. Overall, this study provided a novel coagulant/oxidant strategy to achieve selective and sustainable water purification.

Fenton-like activity and pathway modulation via single-atom sites and pollutants comediates the electron transfer process

The studies on the origin of versatile oxidation pathways toward targeted pollutants in the single-atom catalysts (SACs)/peroxymonosulfate (PMS) systems were always associated with the coordination structures rather than the perspective of pollutant characteristics, and the analysis of mechanism commonality is lacking. In this work, a variety of single-atom catalysts (M-SACs, M: Fe, Co, and Cu) were fabricated via a pyrolysis process using lignin as the complexation agent and substrate precursor. Sixteen kinds of commonly detected pollutants in various references were selected, and their lnkobs values in M-SACs/PMS systems correlated well (R2 = 0.832 to 0.883) with their electrophilic indexes (reflecting the electron accepting/donating ability of the pollutants) as well as the energy gap (R2 = 0.801 to 0.840) between the pollutants and M-SACs/PMS complexes. Both the electron transfer process (ETP) and radical pathways can be significantly enhanced in the M-SACs/PMS systems, while radical oxidation was overwhelmed by the ETP oxidation toward the pollutants with lower electrophilic indexes. In contrast, pollutants with higher electrophilic indexes represented the weaker electron-donating capacity to the M-SACs/PMS complexes, which resulted in the weaker ETP oxidation accompanied with noticeable radical oxidation. In addition, the ETP oxidation in different M-SACs/PMS systems can be regulated via the energy gaps between the M-SACs/PMS complexes and pollutants. As a result, the Fenton-like activities in the M-SACs/PMS systems could be well modulated by the reaction pathways, which were determined by both electrophilic indexes of pollutants and single-atom sites. This work provided a strategy to establish PMS-based AOP systems with tunable oxidation capacities and pathways for high-efficiency organic decontamination.

Enhanced Fenton-like oxidation (Vis/Fe(III)/Peroxydisulfate): The role of iron species and the Fe(III)-LVF complex in levofloxacin degradation

Traditional Fenton and Fenton-like processes are affected by the sluggish kinetics of Fe(II) regeneration and Fe(III) accumulation. This research revealed that the degradation efficiency of pollutants was significantly increased by adding Fe(III) to the Vis/PS system. A mechanism is proposed in which photosensitivity pollutants can boost Fe(III) to produce Fe(II) under visible light irradiation. Intriguingly, Fe(III) rapidly combines with LVF in aqueous environments to form Fe(III)-LVF complexes. This research confirms that Fe(III)-pollutant complexes are generated. The proportion of complexes are calculated using mathematical models. Furthermore, the production of Fe(IV) is verified in the Vis/PS/Fe(III) system, which also plays a vital role in boosting LVF degradation. Overall, this study provides comprehensive insights into the degradation mechanism of micropollutants, involving hydroxyl radical (OH∙), Fe(IV), and Fe(III)-LVF complexes, providing an efficient and green strategy for contaminant removal during wastewater treatment.

Rational design of animal-derived biochar composite for peroxymonosulfate activation: Understanding the mechanism of singlet oxygen-mediated degradation of sulfamethoxazole

Animal-derived biochar are identified as a promising candidate for peroxymonosulfate (PMS) activation due to the abundant aromatics and oxygen-containing functional groups. The current investigation focuses on pig carcass-derived biochar (800-BA-PBC) by ball milling-assisted alkali activation. The results showed that 800-BA-PBC could effectively activate PMS and degraded 94.2% sulfamethoxazole (SMX, 10 mg/L) within 40 min. The reaction rate constant was found to be 47 times higher than that observed with PBC. The enhanced catalytic activity is mainly attributed to the increase in specific surface area, the increase content of oxygen-containing groups on the surface, and the formation of graphitic nitrogen. The quenching tests and electron paramagnetic resonance (EPR) analysis demonstrated that 1O2 is the main active species in the degradation of SMX. Moreover, the 800-BA-PBC + PMS system can maintain excellent degradation rate under different water quality, wide pH range, and the presence of different anions. The degradation pathways of SMX in the optimal system are also evaluated through intermediate identification and DFT calculation. These results indicate that the catalytic system has high anti-interference ability and practical application potential. This investigation provides new insight into the rational design of animal-derived biochar and develops a low-cost technology for the treatment of antibiotic containing wastewater.

Enhanced removal of phenolic compounds by ferrate(VI): Unveiling the Bi(III)-Bi(V) valence cycle with in situ formed bismuth hydroxide as catalyst

The use of 2-hydroxybenzophenone (2-HBP) in personal care products is of great concern due to its potential negative effects on the ecosystem and public health. This paper presents the degradation of 2-HBP by bismuth(III) (Bi3+)-ferrate(VI) (FeVIO42-, Fe(VI)) (Bi3+-Fe(VI) system). Experimental studies at different pH and dosages of Bi3+ and Fe(VI) showed that the Bi3+-Fe(VI) system increased the degradation rate and removal efficiency of 2-HBP compared to Fe(VI) alone. The in situ formed flake-like white flocculent precipitate of Bi(OH)3 showed catalytic performance through the Bi(III)-Bi(V)-Bi(III) valence cycle which was demonstrated through spectroscopic measurements. The hydrogen transfer-mediated reactions between Fe(VI) and Bi(OH)3 as well as subsequent formation of Bi(V) were supported by performing density functional theoretical (DFT) calculations. Seventeen identified transformation products of 2-HBP by Fe(VI) with and without Bi3+ revealed hydroxylation, bond breaking, carboxylation, and polymerization reaction pathways. Significantly, Bi3+ facilitated the polymerization reaction and the dioxygen transfer-mediated hydroxylation reaction pathways. The ions (anions and cations) and humic acids (HA) present in the Bi3+-Fe(VI) system had minimal influence on the removal efficiency of 2-HBP. Reusability tests and use of real water samples as well as toxicity assessments of transformation products unveiled the practical application aspect of the Bi3+-Fe(VI) system. Finally, the results showed that the system exhibits good removal efficiency for all 12 phenolic compounds, indicating theuniversality. The Bi3+-Fe(VI) system may be an easy-to-implement cost-effective method for the catalytic degradation of benzophenones by Fe(VI).

Iron(III)-(1,10-Phenanthroline) Complex Can Enhance Ferrate(VI) and Ferrate(V) Oxidation of Organic Contaminants via Mediating Electron Transfer

Recent research has primarily focused on the utilization of reductants as activators for Fe(VI) to generate high-valent iron species (Fe(IV)/Fe(V)) for the degradation of emerging organic contaminants (EOCs). However, a significant drawback of this approach arises from the reaction between reductants and ferrates, leading to a decrease in oxidation capacity. This study introduces a novel discovery that highlights the potential of the iron(III)-(1,10-phenanthroline) (Fe(III)-Phen) complex as an activator, effectively enhancing the degradation of EOCs by Fe(VI) and augmenting the overall oxidation capacity of Fe(VI). The degradation of EOCs in the Fe(VI)/Fe(III)-Phen system is facilitated through two mechanisms: a direct electron transfer (DET) process and electron shuttle action. The DET process involves the formation of a Phen-Fe(III)-Fe(VI)* complex, which exhibits a stronger oxidation ability than Fe(VI) alone and can accept electrons directly from EOCs. On the other hand, the electron shuttle process utilizes Fe(III)-Phen as a redox mediator to transfer electrons from EOCs to Fe(VI) through the Fe(IV)/Fe(III) or Fe(IV)/Fe(II)/Fe(III) cycle. Moreover, the Fe(III)-Phen complex can improve the utilization efficiency of Fe(V) by preventing its self-decay. This study's findings may present a viable option for utilizing an effective catalyst to enhance the oxidation of EOCs by Fe(VI) and Fe(V).

Enhanced Oxidation of Organic Compounds by the Ferrihydrite-Ferrate System: The Role of Intramolecular Electron Transfer and Intermediate Iron Species

Previous studies mostly held that the oxidation capacity of ferrate depends on the involvement of intermediate iron species (i.e., FeIV/FeV), however, the potential role of the metastable complex was disregarded in ferrate-based heterogeneous catalytic oxidation processes. Herein, we reported a complexation-mediated electron transfer mechanism in the ferrihydrite-ferrate system toward sulfamethoxazole (SMX) degradation. A synergy between intermediate FeIV/FeV oxidation and the intramolecular electron transfer step was proposed. Specifically, the conversion of phenyl methyl sulfoxide (PMSO) to methyl phenyl sulfone (PMSO2) suggested that FeIV/FeV was involved in the oxidation of SMX. Moreover, based on the in situ Raman test and chronopotentiometry analysis, the formation of the metastable complex of ferrihydrite/ferrate was found, which possesses higher oxidation potential than free ferrate and could achieve the preliminary oxidation of organics via the electron transfer step. In addition, the amino group of SMX could complex with ferrate, and the resulting metastable complex of ferrihydrite/ferrate would combine further with SMX molecules, leading to intramolecular electron transfer and SMX degradation. The ferrate loss experiments suggested that ferrihydrite could accelerate the decomposition of ferrate. Finally, the effects of pH value, anions, humic acid, and actual water on the degradation of SMX by ferrihydrite-ferrate were also revealed. Overall, ferrihydrite demonstrated high catalytic capacity, good reusability, and nontoxic performance for ferrate activation. The ferrihydrite-ferrate process may be a green and promising method for organic removal in wastewater treatment.

In Situ Regulation of MnO2 Structural Characteristics by Oxyanions to Boost Permanganate Autocatalysis for Phenol Removal

Oxyanions, a class of constituents naturally occurring in water, have been widely demonstrated to enhance permanganate (Mn(VII)) decontamination efficiency. However, the detailed mechanism remains ambiguous, mainly because the role of oxyanions in regulating the structural parameters of colloidal MnO2 to control the autocatalytic activity of Mn(VII) has received little attention. Herein, the origin of oxyanion-induced enhancement is systematically studied using theoretical calculations, electrochemical tests, and structure-activity relation analysis. Using bicarbonate (HCO3-) as an example, the results indicate that HCO3- can accelerate the degradation of phenol by Mn(VII) by improving its autocatalytic process. Specifically, HCO3- plays a significant role in regulating the structure of in situ produced MnO2 colloids, i.e., increasing the surface Mn(III)s content and restricting particle growth. These structural changes in MnO2 facilitate its strong binding to Mn(VII), thereby triggering interfacial electron transfer. The resultant surface-activated Mn(VII)* complexes demonstrate excellent degrading activity via directly seizing one electron from phenol. Further, other oxyanions with appropriate ionic potentials (i.e., borate, acetate, metasilicate, molybdate, and phosphate) exhibit favorable influences on the oxidative capability of Mn(VII) through an activation mechanism similar to that of HCO3-. These findings considerably improve our fundamental understanding of the oxidation behavior of Mn(VII) in actual water environments and provide a theoretical foundation for designing autocatalytically boosted Mn(VII) oxidation systems.

Fe(VI) activation system mediated by a solar-driven TiO2 nanotubes electrode for CLQ degradation: Performances, mechanisms and pathways

Ferrate (Fe(VI), FeO₄^2-) has been widely used in the degradation of micropollutants with the advantages of high redox potential, no secondary pollution and inhibition of disinfection byproducts. However, the low transformation of Fe(V) and/or Fe(IV) by Fe(VI) and incomplete mineralization of pollutants limit their application. In this work, we designed a photo electric cell with TiO₂ nanotubes (TNTs) and Pt serving as the anode and cathode to enhance the utilization of Fe(VI) (Fe(VI)-TNTs system). TNTs accelerated the generation of •OH via h_VB⁺ oxidation of OH^- and photogenerated electrons at Pt boosted the transformation of Fe(VI) to Fe(V) and/or Fe(IV), resulting in a 22.2 % enhancement of chloroquine (CLQ) removal compared to Fe(VI) alone. The results from EPR and quenching tests showed that Fe(VI), Fe(V), Fe(IV), •OH, O₂^•- and h_VB⁺ coexisted in the Fe(VI)-TNTs system, among which Fe(V) and Fe(IV) were testified as the primary reactive substances accounting for 59 % of CLQ removal. The performance tests and recycling tests demonstrated that the Fe(VI)-TNTs system maintained excellent performance in an authentic water environment. The plausible degradation pathway of CLQ oxidized in the Fe(VI)-TNTs system was proposed with nine identified oxidation products via N-C cleavage, electrophilic addition and carboxylation processes. Based on the ECOSAR calculation, the constructed reaction system allowed a decrease in acute and chronic toxicity. Our findings provide a highly efficient and cost-effective strategy to enhance Fe(VI) application for micropollutant degradation in the future.

Selective degradation of organic micropollutants by activation of peroxymonosulfate by Se@NC: Role of Se doping and nonradical pathway mechanism

In this study, Se@NC-x decorated with Se was successfully prepared via two-step calcination with zeolitic imidazole framework (ZIF) as a precursor. Mechanistic studies show that PMS would be adsorbed onto the surface of Se@NC-900 to form an active complex (Se@NC-900/PMS*), and the active Se@NC-900/PMS* could oxidize phenol by the rapid decomposition of PMS. Specifically, electrons are extracted by Se@NC-900/PMS* and then transferred to the surface of Se@NC-900, which can trigger the degradation of phenol. Notably, it is found that the local charge redistribution caused by the doping of Se can activate the catalytic potential of the intrinsically inert carbon skeleton through density flooding theory (DFT) calculations. The XLogP, ΔE, VIP, and E_{LUMO (Se@NC/PMS)-HOMO (pollutants)} and degradation rate constants of different micropollutants were correlated well linearly. This indicates that the Se@NC-900/PMS system has a great selectivity for the degradation of pollutants. Overall, these findings not only illustrate the role of Se in tuning the electronic structure of Se@NC-x to enhance the activation of PMS, but also bridge the gap in our knowledge about the physicochemical properties and degradation performance of Se@NC catalysts.

Permanganate activation with Mn oxides at different oxidation states: Insight into the surface-promoted electron transfer mechanism

The development of new strategies to improve the removal of organic pollutants with permanganate (KMnO₄) is a hot topic in water treatment. While Mn oxides have been extensively used in Advanced Oxidation Processes through an electron transfer mechanism, the field of KMnO₄ activation remains relatively unexplored. Interestingly, this study has discovered that Mn oxides with high oxidation states including γ-MnOOH, α-Mn₂O₃ and α-MnO₂, exhibited excellent performance to degrade phenols and antibiotics in the presence of KMnO₄. The MnO₄^- species initially formed stable complexes with the surface Mn(III/IV) species and showed an increased oxidation potential and electron transfer reactivity, caused by the electron-withdrawing capacity of the Mn species acting as Lewis acids. Conversely, for MnO and γ-Mn₃O₄ with Mn(II) species, they reacted with KMnO₄ to produce cMnO₂ with very low activity for phenol degradation. The direct electron transfer mechanism in α-MnO₂/KMnO₄ system was further confirmed through the inhibiting effect of acetonitrile and the galvanic oxidation process. Moreover, the adaptability and reusability of α-MnO₂ in complicated waters indicated its potential for application in water treatment. Overall, the findings shed light on the development of Mn-based catalysts for organic pollutants degradation via KMnO₄ activation and understanding of the surface-promoted mechanism.

Electrochemical activation of periodate with graphite electrodes for water decontamination: Excellent applicability and selective oxidation mechanism

Advanced oxidation technologies based on periodate (PI, IO₄^-) have garnered significant attention in water decontamination. In this work, we found that electrochemical activation using graphite electrodes (E-GP) can significantly accelerate the degradation of micropollutants by PI. The E-GP/PI system achieved almost complete removal of bisphenol A (BPA) within 15 min, exhibited unprecedented pH tolerance ranging from pH 3.0 to 9.0, and showed more than 90% BPA depletion after 20 h of continuous operation. Additionally, the E-GP/PI system can realize the stoichiometric transformation of PI into iodate, dramatically decreasing the formation of iodinated disinfection by-products. Mechanistic studies confirmed that singlet oxygen (¹O₂) is the primary reactive oxygen species in the E-GP/PI system. A comprehensive evaluation of the oxidation kinetics of ¹O₂ with 15 phenolic compounds revealed a dual descriptor model based on quantitative structure-activity relationship (QSAR) analysis. The model corroborates that pollutants exhibiting strong electron-donating capabilities and high pK_a values are more susceptible to attack by ¹O₂ through a proton transfer mechanism. The unique selectivity induced by ¹O₂ in the E-GP/PI system allows it to exhibit strong resistance to aqueous matrices. Thus, this study demonstrates a green system for the sustainable and effective elimination of pollutants, while providing mechanistic insights into the selective oxidation behaviour of ¹O₂.

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) (FeO₄^2-, 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 (E_HOMO). 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).

Ferrate(VI)/Periodate System: Synergistic and Rapid Oxidation of Micropollutants via Periodate/Iodate-Modulated Fe(IV)/Fe(V) Intermediates

The presence of organic micropollutants in water sources worldwide has created a need for the development of effective and selective oxidation methods in complex water matrices. This study is the first report of the combination of ferrate(VI) (Fe(VI)) and periodate (PI) for synergistic, rapid, and selective elimination of multiple micropollutants. This combined system was found to outperform other Fe(VI)/oxidant systems (e.g., H₂O₂, peroxydisulfate, and peroxymonosulfate) in rapid water decontamination. Scavenging, probing, and electron spin resonance experiments showed that high-valent Fe(IV)/Fe(V) intermediates, rather than hydroxyl radicals, superoxide radicals, singlet oxygen, and iodyl radicals, played a dominant role in the process. Further, the generation of Fe(IV)/Fe(V) was evidenced directly by the ⁵⁷Fe Mössbauer spectroscopic test. Surprisingly, the reactivity of PI toward Fe(VI) is rather low (0.8223 M^-1 s^-1) at pH 8.0, implying that PI was not acting as an activator. Besides, as the only iodine sink of PI, iodate also played an enhanced role in micropollutant abatement by Fe(VI) oxidation. Further experiments proved that PI and/or iodate might function as the Fe(IV)/Fe(V) ligands, causing the utilization efficiency of Fe(IV)/Fe(V) intermediates for pollutant oxidation to outcompete their auto-decomposition. Finally, the oxidized products and plausible transformation pathways of three different micropollutants by single Fe(VI) and Fe(VI)/PI oxidation were characterized and elucidated. Overall, this study proposed a novel selective oxidation strategy (i.e., Fe(VI)/PI system) that could efficiently eliminate water micropollutants and clarified the unexpected interactions between PI/iodate and Fe(VI) for accelerated oxidation.

Degradation kinetics and transformation pathway of methyl parathion by δ-MnO2/oxalic acid reaction system

Methyl parathion (MP) is a typical organophosphorus pesticide that is widely used worldwide, and hydrolysis, oxidation and reduction are the main abiotic degradation processes. Manganese dioxide (MnO₂) and organic acid can participate in various geochemical processes of pollutants, a reaction system was constructed to degrade MP using δ-MnO₂ and oxalic acid. The δ-MnO₂/oxalic acid reaction system could efficiently degrade MP, and the removal rate of MP (20 μM) reached 67.83% within 30 h under the optimized conditions (pH 5, [δ-MnO₂] = 2 mM, [oxalic acid] = 100 mM). MP was hydrolyzed by substitution reactions of S_N@P and S_N@C, and reduced by conversion of the nitro groups (-NO₂) in MP and its hydrolysates to amino groups (-NH₂). The primary active substance produced in the reaction system was the complexes dominated by Mn(III)-oxalic acid. This study provides a scientific basis for the degradation of organophosphorus pesticides using MnO₂ and an organic acid. The results have important theoretical significance and application value for pollution control and remediation of organophosphorus pesticides.

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).

Enhanced oxidation of organic contaminants by Mn(VII) in water

Studies that promote chemical oxidation by permanganate (MnO₄^-; Mn(VII)) as a viable technology for water treatment and environmental purification have been quickly accumulating over the past decades. Various methods to activate Mn(VII) have been proposed and their efficacy in destructing a wide range of emerging organic contaminants has been demonstrated. This article aims to present a state-of-art review on the development of Mn(VII) activation methods, including photoactivation, electrical activation, the addition of redox mediators, carbonaceous materials, and other chemical agents, with a particular focus on the potential activation mechanism and critical influencing factors. Different reaction mechanisms are involved in activated Mn(VII) oxidation processes, including the generation of reactive intermediates derived from Mn(VII) (e.g., Mn(III), Mn(V), and Mn(VI)) or activators (e.g., intermediates of redox mediators and Ru catalysts), reactive oxygen species (ROS) (e.g., •OH, O₂^•-, and ¹O₂), as well as electron transfer from organics to Mn(VII) via catalysts as the electron mediator. Except •OH that is generated as one of co-oxidants in UV/Mn(VII) process, other reactive species are relatively mild oxidants, which are more selective toward organic substrates and highly tolerant toward various water matrices (e.g., inorganic ions and natural organic matter) compared to strongly oxidizing radical species. Therefore, activated Mn(VII) oxidation processes show a good prospect for efficient removal of target contaminants in natural and complex environmental matrices. However, there are some disputes about the dominant reactive species generated in these processes, and their identification methods may be not appropriate, causing serious confusion in the mechanistic understanding. So, further efforts are still needed to fill the knowledge gap and also to address the application challenges of these technologies.

Novel solar-driven ferrate(VI) activation system for micropollutant degradation: Elucidating the role of Fe(IV) and Fe(V)

This paper presents a novel process of solar-ferrate(VI) [Fe(VI)] for micropollutant degradation. The solar-Fe(VI) process promoted micropollutant degradation compared with Fe(VI) alone and solar. The radical scavenging and probing experiment results suggested that Fe(V) and Fe(IV) but not reactive oxygen species were most likely involved in the solar-Fe(VI) process. Through building a kinetic model, Fe(IV) and Fe(V) were observed to play an equally significant role in the solar-Fe(VI) process. Afterward, the reaction mechanism of the photochemistry of Fe(VI) was elaborated. Fe(IV) formed from Fe(VI) photolysis and then decomposed to Fe(II) which reacted with Fe(VI) to form Fe(V). Furthermore, the effect of pH on carbamazepine (CBZ) degradation was studied and the quantum yields of Fe(VI) were determined, with (1.98 ± 0.16)× 10^-3 mol∙einstein^-1, (5.90 ± 0.27)× 10^-4 mol∙einstein^-1, and (1.66 ± 0.14)× 10^-4 mol∙einstein^-1 at pH 7.0, 8.0, and 9.0, respectively. Inorganic ions, including Cl^-, HCO₃^-, and Br^- displayed negligible influence on the CBZ degradation, whereas humic acid inhibited the CBZ degradation. Finally, the solar-Fe(VI) process exhibited good applicability in authentic waters and under different irradiation (natural sunlight, ultraviolet light, and visible light from solar cut-off emission). Overall, this study provides a new routine for efficient micropollutant elimination and reveals the photochemistry of Fe(VI).

Removal of microorganic pollutants in aquatic environment: The utilization of Fe(VI)

Microorganic pollutants (MOPs) in aquatic environment with low levels but high toxicity are harmful to ecosystem and human health. Fe(VI) has a dual-functional role in oxidation and coagulation, and can effectively remove MOPs, heavy metal, phosphate, particulates and colloids. Moreover, Fe(VI) can combine with traditional coagulants, or use as a pretreatment for membrane treatment because of its characters to generate nanoparticles by degradation in water. Based on the relevant toxicity experiments, Fe(VI) had been proved to be safe for the efficient treatment of MOPs. For better utilization of Fe(VI), its oxidation and coagulation mechanisms are summarized, and the knowledge about the control parameters, utilization methods, and toxicity effect for Fe(VI) application are reviewed in this paper. pH, different valences of iron, environmental substances, and other parameters are summarized in this study to clarify the important factors in the treatment of MOPs with Fe(VI). In the future study, aiming at cost reduction in Fe(VI) preparation, transportation and storage, enhancement of oxidation in the intermediate state, and better understanding the mechanism between interface and Fe(VI) oxidation will help promote the application of Fe(VI) in the removal of MOPs. This study offers guidelines for the application and development of Fe(VI) for the treatment of MOPs in aquatic environment.

Graphite (GP) induced activation of ferrate(VI) for degradation of micropollutants: The crucial reduction role of carbonyl groups on GP surface

The sluggish oxidation kinetics of ferrate (Fe(VI)) at neutral and slightly alkaline pH impedes its rapid abatement of micropollutants in practical application. This work discovers that graphite (GP), a metal-free carbonaceous material, can be a promising material to improve the reactivity of Fe(VI) in the pH range of 7.0 - 9.0. The performance of the GP/Fe(VI) process for sulfamethoxazole (SMX) removal was further evaluated via altering the dosages of Fe(VI), GP, and SMX. Probe analysis and quenching experiments identified Fe(IV) and Fe(V) as the primary active species responsible for the removal of organic compounds in the GP/Fe(VI) system. The detailed activation mechanism of GP is discussed via analyzing the surface chemical changes of GP exposed to Fe(VI). It is found that the carbonyl groups on GP surface execute a critical role in Fe(VI) activation. The GP/Fe(VI) system shows powerful anti-interference ability to environmental background substances. Therefore, the new oxidation process proposed in this work holds a great application prospect for contamination remediation. Finally, we discuss the underlying degradation pathways of SMX by the GP/Fe(VI) system. This study not only develops a promising system for the removal of micropollutants but also provides an in-depth insight into the activation mechanism of metal-free carbonaceous material in Fe(VI) oxidation process.