New Insights into Photo-Fenton Chemistry: The Overlooked Role of Excited IronIII Species.

Direct photoreduction of FeIII is a widely recognized route for accelerating FeIII/FeII cycle in photo-Fenton chemistry. However, most of the wavelengths covering the full spectral range are insufficient to supply enough photon energy for the direct reduction process. Herein, the hitherto neglected mechanism of FeIII reduction that the FeIII indirect reduction pathway initiated by light energy-dependent reactivity variation and reactive excited state (ES) was explored. Evolution of excited-state FeIII species (*FeIII) resulting from metal-centered charge excitation (MCCE) of FeIII is experimentally verified using pulsed laser femtosecond transient absorption spectroscopy with UV-vis detection and theoretically verified by quantum chemical calculation. Intense photoinduced intravalence charge transition was observed at λ = 380 and 466 nm, revealing quartet 4MCCE and doublet 2MCCE and their exponential processes. Light energy-dependent variation of *FeIII reactivity was kinetically certified by fitting the apparent rate constant of the radical-chain sequence of photo-Fenton reactions. Covalency is found to compensate for the intravalence charge separation following photoexcitation of the metal center in the MCCE state of Fenton photosensitizer. The *FeIII is established as a model, demonstrating the intravalence hole delocalization in the ES can be leveraged for photo-Fenton reaction or other photocatalytic schemes based on electron transfer chemistry.

High-valent metal-oxo species transformation and regulation by co-existing chloride: Reaction pathways and impacts on the generation of chlorinated by-products.

High-valent metal-oxo species (HMOS) have been extensively recognized in advanced oxidation processes (AOPs) owing to their high selectivity and high chemical utilization efficiency. However, the interactions between HMOS and halide ions in sewage wastewater are complicated, leading to ongoing debates on the intrinsic reactive species and impacts on remediation. Herein, we prepared three typical HMOS, including Fe(IV), Mn(V)-nitrilotriacetic acid complex (Mn(V)NTA) and Co(IV) through peroxymonosulfate (PMS) activation and comparatively studied their interactions with Cl- to reveal different reactive chlorine species (RCS) and the effects of HMOS types on RCS generation pathways. Our results show that the presence of Cl- alters the cleavage behavior of the peroxide OO bond in PMS and prohibits the generation of Fe(IV), spontaneously promoting SO4•- production and its subsequent transformation to secondary radicals like Cl• and Cl2•-. The generation and oxidation capacity of Mn(V)NTA was scarcely influenced by Cl-, while Cl- would substantially consume Co(IV) and promote HOCl generation through an oxygen-transfer reaction, evidenced by density functional theory (DFT) and deuterium oxide solvent exchange experiment. The two-electron-transfer standard redox potentials of Fe(IV), Mn(V)NTA and Co(IV) were calculated as 2.43, 2.55 and 2.85 V, respectively. Due to the different reactive species and pathways in the presence of Cl-, the amounts of chlorinated by-products followed the order of Co(II)/PMS > Fe(II)/PMS > Mn(II)NTA/PMS. Thus, this work renovates the knowledge of halide chemistry in HMOS-based systems and sheds light on the impact on the treatment of salinity-containing wastewater.

Mechanically treated Mn2O3 triggers peracetic acid activation for superior non-radical oxidation of micropollutants: Identification of reactive complexes.

This study used a simple mechanical ball milling strategy to significantly improve the ability of Mn2O3 to activate peracetic acid (PAA) for sustainable and efficient degradation of organic micropollutant (like bisphenol A, BPA). BPA was successfully removed and detoxified via PAA activation by the bm-Mn2O3 within 30 min under neutral environment, with the BPA degradation kinetic rate improved by 3.4 times. Satisfactory BPA removal efficiency can still be achieved over a wide pH range, in actual water and after reuse of bm-Mn2O3 for four cycles. The change in hydrophilicity of Mn2O3 after ball milling evidently elevated the affinity of Mn2O3 for binding to PAA, while the reduction in particle size exposed more active sites contributing partially to catalytic oxidation. Further analysis revealed that BPA oxidation in the ball mill-treated Mn2O3 (bm-Mn2O3)/PAA process mainly depends on the bm-Mn2O3-PAA complex (i.e., Mn(III)-OO(O)CCH3) mediated non-radical pathway rather than R-O• and Mn(IV). Especially, the existence of the Mn(III)-PAA complex was definitely verified by in situ Raman spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Simultaneously, density functional theory calculations determined that PAA adsorbs readily on manganese sites thereby favoring the formation of Mn(III)-OO(O)CCH3 complexes. This study advances an in-depth understanding of the underlying mechanisms involved in the manganese oxide-catalyzed activation of PAA for superior non-radical oxidation of micropollutants.

How Should We Activate Ferrate(VI)? Fe(IV) and Fe(V) Tell Different Stories about Fluoroquinolone Transformation and Toxicity Changes.

Many studies have investigated activation of ferrate (Fe(VI)) to produce reactive high-valent iron intermediates to enhance the oxidation of micropollutants. However, the differences in the risk of pollutant transformation caused by Fe(IV) and Fe(V) have not been taken seriously. In this study, Fe(VI)-alone, Fe3+/Fe(VI), and NaHCO3/Fe(VI) processes were used to oxidize fluoroquinolone antibiotics to explore the different effects of Fe(IV) and Fe(V) on product accumulation and toxicity changes. The contribution of Fe(IV) to levofloxacin degradation was 99.9% in the Fe3+/Fe(VI) process, and that of Fe(V) was 89.4% in the NaHCO3/Fe(VI) process. The cytotoxicity equivalents of levofloxacin decreased by 1.9 mg phenol/L in the Fe(IV)-dominant process while they significantly (p < 0.05) increased by 4.7 mg phenol/L in the Fe(V)-dominant process. The acute toxicity toward luminescent bacteria and the results for other fluoroquinolone antibiotics also showed that Fe(IV) reduced the toxicity and Fe(V) increased the toxicity. Density functional theory calculations showed that Fe(V) induced quinolone ring opening, which would increase the toxicity. Fe(IV) tended to oxidize the piperazine group, which reduced the toxicity. These results show the different-pollutant transformation caused by Fe(IV) and Fe(V). In future, the different risk outcomes during Fe(VI) activation should be taken seriously.

Fe-N co-doped biochar derived from biomass waste triggers peracetic acid activation for efficient water decontamination.

In this study, the porous carbon material (FeN-BC) with ultra-high catalytic activity was obtained from waste biomass through Fe-N co-doping. The prominent degradation rate (> 96.8%) of naproxen (NAP) was achieved over a wide pH range (pH 3.0-9.0) in FeN-BC/PAA system. Unlike previously reported iron-based peracetic acid (PAA) systems with •OH or RO• as the dominated reactive species, the degradation of contaminants was attributed to singlet oxygen (1O2) produced by organic radicals (RO•) decomposition, which was proved to be thermodynamically feasible and favorable by theoretical calculations. Combining the theoretical calculations, characteristic and experimental analysis, the synergistic effects of Fe and N were proposed and summarized as follows: i) promoted the formation of extensive defects and Fe0 species that facilitated electron transfer between FeN-BC and PAA and continuous Fe(II) generation; ii) modified the specific surface area (SSA) and the isoelectric point of FeN-BC in favor of PAA adsorption on the catalyst surface. This study provides a strategy for waste biomass reuse to construct a heterogeneous catalyst/PAA system for efficient water purification and reveals the synergistic effects of typical metal-heteroatom for PAA activation.

Origins of Selective Oxidation in Carbon-Based Nonradical Oxidation Processes toward Organic Pollutants: Quantitative Structure-Activity Relationships (QSARs).

Metal-free carbon material-mediated nonradical oxidation processes (C-NOPs) have emerged as a research hotspot due to their excellent performance in selectively eliminating organic pollutants in aqueous environments. However, the selective oxidation mechanisms of C-NOPs remain obscure due to the diversity of organic pollutants and nonradical active species. Herein, quantitative structure-activity relationship (QSAR) models were employed to unveil the origins of C-NOP selectivity toward organic pollutants in different oxidant systems. QSAR analysis based on adsorption and oxidation descriptors revealed that C-NOP selectivity depends on the oxidation potentials of organic pollutants rather than on adsorption interactions. However, the dominance of electronic effects in selective oxidation decreases with increasing structural complexity of organic pollutants. Moreover, the oxidation threshold solely depends on the inherent electronic nature of organic pollutants and not on the reactivity of nonradical active species. Notably, the accuracy of substituent descriptors (Hammett constants) and theoretical descriptors (e.g., highest occupied molecular orbital energy, ionization potential, and single-electron oxidation potential) is significantly influenced by the complexity and molecular state of organic pollutants. Overall, the study findings reveal the origins of organic pollutant-oriented selective oxidation and provide insight into the application of descriptors in QSAR analysis.

pH-dependent bisphenol A transformation and iodine disinfection byproduct generation by peracetic acid: Kinetic and mechanistic explorations.

Peracetic acid (PAA) is regarded as an environmentally friendly oxidant because of its low formation of toxic byproducts. However, this study revealed the potential risk of generating disinfection byproducts (DBPs) when treating iodine-containing wastewater with PAA. The transformation efficiency of bisphenol A (BPA), a commonly detected phenolic contaminant and a surrogate for phenolic moieties in dissolved organic matter, by PAA increased rapidly in the presence of I-, which was primarily attributed to the formation of active iodine (HOI/I2) in the system. Kinetic model simulations demonstrated that the second-order rate constant between PAA and HOI was 54.0 M-1 s-1 at pH 7.0, which was lower than the generation rate of HOI via the reaction between PAA and I-. Therefore, HOI can combine with BPA to produce iodine disinfection byproducts (I-DBPs). The transformation of BPA and the generation of I-DBPs in the I-/PAA system were highly pH-dependent. Specifically, acidic conditions were more favorable for BPA degradation because of the higher reaction rates of BPA and HOI. More iodinated aromatic products were detected after 5 min of the reaction under acidic and neutral conditions, resulting in higher toxicity towards E. coli. After 12 h of the reaction, more adsorbable organic iodine (AOI) was generated at alkaline conditions because HOI was not able to efficiency transform to IO3-. The presence of H2O2 in the PAA solution played a role in the reaction with HOI, particularly under alkaline conditions. This study significantly advances the understanding of the role of I- in BPA oxidation by PAA and provides a warning to further evaluate the potential environmental risk during the treatment of iodine-bearing wastewater with PAA.

Facilely Tuning the First-Shell Coordination Microenvironment in Iron Single-Atom for Fenton-like Chemistry toward Highly Efficient Wastewater Purification.

Precisely identifying the atomic structures in single-atom sites and establishing authentic structure-activity relationships for single-atom catalyst (SAC) coordination are significant challenges. Here, theoretical calculations first predicted the underlying catalytic activity of Fe-NxC4-x sites with diverse first-shell coordination environments. Substituting N with C to coordinate with the central Fe atom induces an inferior Fenton-like catalytic efficiency. Then, Fe-SACs carrying three configurations (Fe-N2C2, Fe-N3C1, and Fe-N4) fabricate facilely and demonstrate that optimized coordination environments of Fe-NxC4-x significantly promote the Fenton-like catalytic activity. Specifically, the reaction rate constant increases from 0.064 to 0.318 min-1 as the coordination number of Fe-N increases from 2 to 4, slightly influencing the nonradical reaction mechanism dominated by 1O2. In-depth theoretical calculations unveil that the modulated coordination environments of Fe-SACs from Fe-N2C2 to Fe-N4 optimize the d-band electronic structures and regulate the binding strength of peroxymonosulfate on Fe-NxC4-x sites, resulting in a reduced energy barrier and enhanced Fenton-like catalytic activity. The catalytic stability and the actual hospital sewage treatment capacity also showed strong coordination dependency. This strategy of local coordination engineering offers a vivid example of modulating SACs with well-regulated coordination environments, ultimately maximizing their catalytic efficiency.

Metal Borides as Excellent Co-Catalysts for Boosted and Long-Lasting Fenton-like Reaction: Dual Co-Catalytic Centers of Metal and Boron.

The continuous electron supply for oxidant decomposition-induced reactive oxygen species (ROS) generation is the main contributor for the long-standing micropollutant oxidation in the iron-based advanced oxidation processes (AOPs). Herein, as a new class of co-catalysts, metal borides with dual active sites and preeminent conductive performance can effectively overcome the inherent drawback of Fenton-like reactions by steadily donating electrons to inactive Fe(III). Among the metal borides, tungsten boride (WB) exhibits a significant co-catalytic performance run ahead of common heterogeneous co-catalysts and exceptionally high stability. Based on qualitative and semi-quantitative tests, the hydroxyl radical, sulfate radical, and iron(IV)-oxo complex are all produced in the WB/Fe(III)/PDS system and Fe(IV)-induced methyl phenyl sulfoxide decomposition is up to 72%. Moreover, the production efficiency of ROS and relative proportions of radical and nonradical pathways change with various experimental conditions (dosages of PDS, WB, and solution pH) and water matrices. The rate-determining step of Fe(II) regeneration is greatly accelerated resulting from the synergetic effect between exposed metallic reactive sites and nonmetallic boron with reductive properties of WB. In addition, the self-dissolution of surface tungsten oxide and boron oxide leads to a renovated surface for sustainable Fe(III) reduction in long-term operations. Our discovery provides an efficient and sustainable strategy in the field of enhanced AOPs for water remediation.

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.

Removal of Phenols by Highly Active Periodate on Carbon Nanotubes: A Mechanistic Investigation.

Carbon nanotubes (CNTs) and their derivatives have been widely exploited to activate various oxidants for environmental remediation. However, the intrinsic mechanism of CNTs-driven periodate (PI) activation remains ambiguous, which significantly impedes their scientific progress toward practical application. Here, we found that CNTs can strongly boost PI activation for the oxidation of various phenols. Reactive oxygen species analysis, in situ Raman characterization, galvanic oxidation process experiments, and electrochemical tests revealed that CNTs could activate PI to form high-potential metastable intermediates (CNTs-PI*) rather than produce free radicals and 1O2, thereby facilitating direct electron transfer from the pollutants to PI. Additionally, we analyzed quantitative structure-activity relationships between rate constants of phenols oxidation and double descriptors (e.g., Hammett constants and logarithm of the octanol-water partition coefficient). The adsorption of phenols on CNT surfaces and their electronic properties are critical factors affecting the oxidation process. Besides, in the CNTs/PI system, phenol adsorbed the CNT surfaces was oxidized by the CNTs-PI* complexes, and products were mainly generated via the coupling reaction of phenoxyl radical. Most of the products adsorbed and accumulated on the CNT surfaces realized phenol removal from the bulk solution. Such a unique non-mineralization removal process achieved an extremely high apparent electron utilization efficiency of 378%. The activity evaluation and theoretical calculations of CNT derivatives confirmed that the carbonyl/ketonic functional groups and double-vacancy defects of the CNTs were the primary active sites, where high-oxidation-potential CNTs-PI* were formed. Further, the PI species could achieve a stoichiometric decomposition into iodate, a safe sink of iodine species, without the generation of typical iodinated byproducts. Our discovery provides new mechanistic insight into CNTs-driven PI activation for the green future of environmental remediation.

Waste leather derived porous carbon boosted Fenton oxidation towards removal of diethyl phthalate: Mechanism and long-lasting performance.

The acceleration of Fe(III)/Fe(II) conversion in Fenton systems is the critical route to achieve the long-lasting generation of reactive oxygen species towards the oxidation of refractory contaminants. Here, we found that waste leather derived porous carbon materials (LPC), as a simple and readily available metal-free biochar material, can promote the Fe(III)/H2O2 system to generate hydroxyl radicals (•OH) for oxidizing a broad spectrum of contaminants. Results of characterizations, theoretical calculations, and electrochemical tests show that the surface carbonyl groups of LPC can provide electron for direct Fe(III) reduction. More importantly, the graphitic-N on surface of LPC can enhance the reactivity of Fe(III) for accelerating H2O2 induced Fe(III) reduction. The presence of LPC accelerates the Fe(III)/Fe(II) redox cycle in the Fe(III)/H2O2 system, sustainable Fenton chain reactions is thus initiated for long-lasting generation of hydroxyl radicals without adding Fe(II). The continuous flow mode that couples in-situ Fenton-like oxidation and LPC with excellent adsorption catalytic properties, anti-coexisting substances interference and reusability performance enables efficient, green and sustainable degradation of trace organic pollutants. Therefore, the application of metal-free carbon materials in Fenton-like system can solve its rate-limiting problem, reduce the production of iron sludge, achieve green Fenton chemistry, and facilitate the actual engineering application of economic and ecological methods to efficiently remove trace organic contaminants from actual water sources.

Efficient activation of ferrate by Ru(III): Insights into the major reactive species and the multiple roles of Ru(III).

Ferrate (Fe(VI)) has aroused great research interest in recent years due to its environmental benignancy and lower potential in disinfection by-product generation. However, the inevitable self-decomposition and lower reactivity under alkaline conditions severely restrict the utilization and decontamination efficiency of Fe(VI). Here, we discovered that Ru(III), a representative transition metal, could effectively activate Fe(VI) to degrade organic micropollutants, and its performance on Fe(VI) activation exceeded that of previously reported metal activators. The high-valent metal species (i.e., Fe(IV)/Fe(V) and high-valent Ru species) made a major contribution to SMX removal by Fe(VI)-Ru(III). Density functional theory calculations indicated the function of Ru(III) as a two-electron reductant, leading to the production of Ru(V) and Fe(IV) as the predominant active species. The characterization analyses proved that Ru species was deposited on ferric (hydr)oxides as Ru(III), indicating the possibility of Ru(III) as an electron shuttle with the rapid valence circulation between Ru(V) and Ru(III). This study not only develops an efficient way to activate Fe(VI) but also offers a thorough understanding of Fe(VI) activation induced by transition metals.

Identifying the evolution of primary oxidation mechanisms and pollutant degradation routes in the electro-cocatalytic Fenton-like systems.

Herein, electro-catalysis (EC) as the electron donor to accelerate the continuable Fe(III)/Fe(II) cycles in different inorganic peroxides (i.e., peroxymonosulfate (PMS), peroxydisulfate (PDS) and hydrogen peroxide (HP)) activation systems were established. These electro-cocatalytic Fenton-like systems exhibited an excellent degradation efficiency of sulfamethoxazole (SMX). A series of analytical and characterization methods including quenching experiments, probe experiments, and electron paramagnetic resonance spectrometry (EPR) were implemented to systematically sort out the source and yield of reactive oxygen species (ROS). A wide kind of ROS including hydroxyl radical (•OH), singlet oxygen (1O2), and sulfate radical (SO4•-), which contributed 38%, 37%, and 24% were produced in EC/Fe(III)/PMS system, respectively. •OH was the dominant ROS in both EC/Fe(III)/PDS and EC/Fe(III)/HP processes. According to the analysis of SMX degradation routes and biotoxicity, abundant degradation pathways were identified in EC/Fe(III)/PMS process and lower environmental impact was achieved in EC/Fe(III)/HP process. The diversiform ROS of EC/Fe(III)/PMS system makes it exhibit greater environmental adaptability in complex water matrixes and excellent low-energy consumption performance in many organic pollutants degradation. Continuous flow treatment experiments proved that the three systems have great sustainability and practical application prospect. This work provides a strong basis for constructing suitable systems to achieve different treatment requirements.

Efficient degradation of micropollutants in CoCaAl-LDO/peracetic acid (PAA) system: An organic radical dominant degradation process.

As a novel strategy, peracetic acid (PAA) based advanced oxidation processes (AOPs) are being used in micropollutant elimination due to their high oxidation and low toxicity. In this study, Co2Ca1Al1-LDO as a kind of layered double oxides (LDOs) was successfully synthesized, and it is the first time to apply Co2Ca1Al1-LDO for activating PAA. The Co2Ca1Al1-LDO/PAA system showed excellent removal efficiencies for various micropollutants with removal ratios ranging from 90.4% to 100% and k values from 0.087 min-1 to 0.298 min-1. In the degradation period, various reactive oxygen species (ROS) are involved in the system, while organic radicals (R-O•) with a high concentration of 5.52 × 10-13 M are the dominant ROS in the contaminants degradation process. Compared to other ROS, R-O• had the largest contribution ratio (more than 85%) to pollutant degradation. Further analysis demonstrated that C1, C2, C3, C4, C5, C6 and N11 concentrated on the aniline group of SMX are the main attack sites based on the density functional theory (DFT) results, which is consistent with the degradation products. The toxicity of contaminants was obviously reduced after removing in this system. Furthermore, Co2Ca1Al1-LDO showed good reusability and stability, and Co2Ca1Al1-LDO/PAA system had excellent removal ability in actual water bodies containing inorganic anions, showing good application potential. Importantly, this study explored the feasibility of applying LDO catalysts in PAA-based AOPs for micropollutants elimination, providing new insights for subsequent research.

Peracetic acid activation via the synergic effect of Co and Fe in CoFe-LDH for efficient degradation of pharmaceuticals in hospital wastewater.

As an oxidant, peracetic acid (PAA) is gradually applied in advanced oxidation processes (AOPs) for pollutants degradation due to its high oxidation and low toxicity. In this study, the prepared Co2Fe1-LDH showed excellent PAA activation ability for efficient degradation of various pharmaceuticals with a removal efficiency ranging from 82.3% to 100%. Taking sulfamethoxazole (SMX) as a model pharmaceutical, it's found that organic radical (R-O•) with high concentration of 5.27 × 10-13 M is the dominant ROS responsible for contaminants degradation. Further analysis demonstrated that bimetallic synergistic effect between Co and Fe can improve electron transfer ability of Co2Fe1-LDH, resulting in the accelerated conversion of Co from +3 to +2 valence state with a high reaction rate (4.3 × 101-1.483 × 102 M-1 s-1) in this system. Density functional theory (DFT) reveals that C1, C3, C5 and N11 with higher ƒ0 and ƒ-values concentrated on aniline group of SMX are the main attack sites, which is consistent with the results of degradation products. Besides, Co2Fe1-LDH/PAA system can effectively reduce biological toxicity after reaction, due to lower biotoxicity of degradation products and the carbon sources provided by PAA. In application, Co2Fe1-LDH/PAA system was capable of resisting the influence of water matrix and effectively removing pollutants in actual hospital wastewater. Importantly, this study comprehensively evaluated the ability of Co2Fe1-LDH/PAA system to remove organics and improve the biodegradability of actual hospital wastewater, providing guidance for application of PAA activation system.

Efficient wastewater disinfection by raised 1O2 yield through enhanced electron transfer and intersystem crossing via photocatalysis of peroxymonosulfate with CuS quantum dots modified MIL-101(Fe).

Peroxymonosulfate (PMS)-based photocatalysis is a promising alternative approach for wastewater disinfection. Singlet oxygen (1O2) is sensitive and efficient for bacterial inactivation. This study developed a 1O2-predominated PMS disinfection technique under visible light with CuS quantum dots (QDs) modified MIL-101(Fe) (CSQDs@MF). CuS QDs modification greatly enhanced the 1O2 quantum yield by 80% than that of MIL-101(Fe). Photoelectricity and photoluminescence tests demonstrated that both the enhanced electron transfer and energy transfer were responsible for improved 1O2 generation in Vis/PMS/CSQDs@MF system. The system took 60 min to inactivate 7.5-log E. coli, and it could be applied in a broad pH and dissolve oxygen range. Bacterial inactivation mechanism suggested that 1O2 attacked cell membrane first, then induced oxidative stress, up-regulated intracellular ROS level, eventually broke DNA strand. The system showed good disinfection performance on Gram-positive B. subtilis and fecal coliforms in practical wastewater, implying it is a promising alternative disinfection technology for wastewater treatment.

Removal of Bisphenol A via peroxymonosulfate activation over graphite carbon nitride supported NiCx nanoclusters catalyst: Synergistic oxidation of high-valent nickel-oxo species and singlet oxygen.

In this work, a g-C3N4 supported NiCx nanoclusters catalyst (NiCx-CN) was developed, and its performance in activating peroxymonosulfate (PMS) was evaluated. Mechanism investigation stated that although singlet oxygen (1O2) was formed in the catalytic process, its contribution to BPA elimination was weeny. Interestingly, through the experiment with dimethyl sulfoxide as the probe, it was considered that the high-valent nickel-oxo species (Ni&+=O), generated after the interaction of NiCx-CN and PMS, was the dominating reactive oxygen species (ROS). Theoretical calculations (DFT) implied that NiCx-CN might lose electrons to generate high-valent Ni, which was consistent with the detection of Ni3+ on the surface of the used NiCx-CN. Besides, the prepared NiCx-CN showed advantages in resisting the interference of inorganic anions. Meanwhile, three BPA degradation routes had been proposed based on the transformation intermediates. This study will establish a new protocol for PMS activation using heterogeneous Ni-based catalysts to efficiently degrade organic pollutants via a nonradical mechanism.

Introduction of oxygen vacancy to manganese ferrite by Co substitution for enhanced peracetic acid activation and 1O2 dominated tetracycline hydrochloride degradation under microwave irradiation.

High microwave-response cobalt-substituted manganese ferrite (CMFO-0.5) was successfully synthesized as a heterogeneous catalyst for efficient peracetic acid (PAA) activation and tetracycline hydrochloride (TCH) degradation with singlet oxygen (1O2) as the dominated reactive oxidized species (ROS). The removal efficiency of TCH could reach 98.16% within 6 min under microwave irradiation when the CMFO-0.5 was added at 20 mg/L. It's found that the Co substitution could produce the oxygen vacancies (OVs), improve the microwave (MW) absorbing performance and enhance the internal electron transfer efficiency of materials. The phenomenon why 1O2 as the dominated ROS rather than hydroxyl radical (•OH) and organic radicals (R-O•) would be explained by the following aspects: the oxygen adsorbed on the OVs can accept the electron transformed from PAA to form superoxide radical (•O2-), which will disproportionate to form 1O2; the energy generated by the non-thermal effect of MW can dissociate PAA to generate peroxy-group for 1O2 generation. Furthermore, the possible TCH degradation pathways were proposed based on DFT theory calculations and product identification, and the toxicity predictions of the degradation products were also performed by the Ecological Structure-Activity Relationship Model (ECOSAR) software. Additionally, the decrease of acute toxicity of treated TCH, excellent stability and strong resistance towards water matrix fully demonstrate the superiority of the proposed system for practical application in wastewater treatment.

Synchronous removal of pharmaceutical contaminants and inactivation of pathogenic microorganisms in real hospital wastewater by electro-peroxone process.

Herein, a highly efficient electro-peroxone (E-peroxone) process with graphite felt as ozone diffusion electrode (ODE) was developed for the synchronous removal of pharmaceutical contaminants and inactivation of pathogenic microorganisms in real hospital wastewater. Under optimal conditions, the total organic carbon (TOC) removal rate of real hospital wastewater could reach 93.9%. Importantly, 126 pharmaceutical compounds (antibiotics, antivirals, analgesics, antiepileptics, hormones, and others) were determined in hospital wastewater by using ultra performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS). 110 pharmaceutical compounds could be efficiently degraded in E-peroxone system. Concurrently, the microbial community analysis through high-throughput sequencing showed that E-peroxone process exhibited an excellent disinfection effect in real hospital wastewater. Escherichia coli as a bacterial indicator could be completely inactivated in E-peroxone process·H2O2 and hydroxyl radical (OH) were found in E-peroxone system based on the results of chemical probe experiments and electron paramagnetic resonance (EPR) analysis. The in-situ generation of H2O2 from cathodic oxygen reduction in ODE can react with ozone to produce OH, and realize high efficiencies for the elimination of pharmaceutical and sterilization. This work established a green and effective way without extra addition of chemical reagents for high-efficiency treatment of real hospital wastewater.