Phenyl Sulfoxide Research Articles

Successive β‐Glycosylations of Tiacumicinone: Formal Total Synthesis of Tiacumicin B and Access to a d‐Mannoside Analog

AbstractA formal total synthesis of the natural macrolide antibiotic tiacumicin B is described featuring successive and selective glycosylations of tiacumicinone. The challenging β‐facial selectivity of these key glycosylation steps was achieved by using noviosyl or rhamnosyl donors equipped with a phenyl sulfoxide leaving group and a 3‐O‐picoloyl group ensuring an efficient remote stereodirecting effect. Compared with our former total synthesis, this strategy enables us to save steps and gain access to new analogs. This was demonstrated by the replacement of the rhamnosidic moiety by a d‐mannose derivative.

Metal-Organic Frameworks as a Tunable Platform to Deconvolute Stereoelectronic Effects on the Catalytic Activity of Thioanisole Oxidation.

The local environment of a metal active site plays an important role in affecting the catalytic activity and selectivity. In recent studies, tailoring the behavior of a molybdenum-based active site via modulation of the first coordination sphere has led to improved thioanisole oxidation performance, but disentangling electronic effects from steric influences that arise from these modifications is nontrivial, especially in heterogeneous systems. To this end, the tunability of metal-organic frameworks (MOFs) makes them promising scaffolds for controlling the coordination sphere of a heterogeneous, catalytically active metal site while offering additional attractive features such as crystallinity and high porosity. Herein, we report a variety of MOF-supported Mo species, which were investigated for catalytic thioanisole oxidation to methyl phenyl sulfoxide and/or methyl phenyl sulfone using tert-butyl hydroperoxide (tBHP) as the oxidant. In particular, MOFs of contrasting node architectures were targeted, presenting a unique opportunity to investigate the stereoelectronic control of Mo active sites in a systematic manner. A Zr6-based MOF, NU-1000, was employed along with its sulfated analogue Zr6-based NU-1000-SO4 to anchor a dioxomolybdenum species, which enabled examination of support-mediated active site polarizability on catalytic performance. In addition, a MOF containing a mixed metal node, Mo-MFU-4l, was used to probe the stereoelectronic impact of an N-donor ligand environment on the catalytic activity of the transmetalated Mo center. Characterization techniques, including single crystal X-ray diffraction, were concomitantly used with reaction time course profiles to better comprehend the dynamics of different Mo active sites, thus correlating structural change with activity.

The selective oxidation of thioanisole to sulfoxide using a highly efficient electroenzymatic cascade system

Construction of an electroenzymatic cascade catalytic system based on a CPO-ILEMB@NMCNs-PEI biohybrid for selective oxidation of thioanisole to methyl phenyl sulfoxide with high catalytic activity.

Visible-Light-Responsive Polyoxometalate@Metal-Organic Frameworks Involving Ir Metalloligands for Highly Selective Photocatalytic Oxidation of Sulfides to Sulfoxide.

The synthesis of highly efficient visible-light-responsive photocatalysts is fundamental to solving the problems of low efficiency and poor selectivity in photocatalytic organic synthesis reactions. We synthesized a crystalline polyoxometalate @metal-organic framework material {Zn4 (H2 O)8 [Ir(ppy)2 (dcbpy)]4 [SiW12 O40 ]} ⋅ 4H2 O (Ir-SiW) by self-assembly of Ir metalloligands with POMs. The introduction of Ir metalloligands extends the light absorbing range to visible light, improving the efficient utilization of solar energy. The transfer of photogenerated electrons from Ir metalloligands to SiW12 was observed under visible light irradiation, which boosted the carrier separation efficiency. The synergistic effect of the two components increased the photocatalytic thioether oxidation activity, and the product methyl phenyl sulfoxide for 2.5 h under visible light irradiation (λ >400 nm) reached 99.5 %, which was higher than those of other POM-based photocatalysts. Meanwhile, the yield of methyl phenyl sulfoxide was still higher than 97 % after three cycles, demonstrating the high stability and reusability of Ir-SiW.

Enhanced phosphorus release from waste activated sludge triggered by ferrate/sulfite oxidation process: The overlooked role of high valent iron

Waste activated sludge is considered a promising resource for phosphorus recovery. Therefore, it’s of great significance to release phosphorus from sludge. Potassium ferrate (PF) is deemed to be a green oxidant, which has great potential in the field of sludge treatment. In this study, sulfite (Na2SO3) coupled with the PF oxidation process was proposed to improve phosphorus release from sludge. The analysis of extracellular polymeric substances (EPS) of sludge indicated that sludge flocs were destroyed and nutrients were released, the total phosphorus and organic phosphorus increased significantly to 33.26 mg/L and 20.16 mg/L (40 min), respectively. Proteins, polysaccharides, and total organic carbon were transformed from tightly bound EPS to soluble EPS. In addition, the dissolved organic matter in tightly bound EPS decreased sharply, while the tyrosine-like protein and soluble microbial by-product substances in loosely bound EPS and soluble EPS increased significantly. Ethanol quenching experiments suggested that free radicals have little effects on phosphorus release, while the existence of high valent iron was validated by a chemical probe method applying methyl phenyl sulfoxide (PMSO) as the probe molecule. Thus, it was speculated that high valent iron may be the active substance for phosphorus release. The coupled PF/Na2SO3 process produced multiple active species (reactive oxygen species and high valent iron) to destruct sludge, among which high-valent iron species were mainly responsible for phosphorus release. This study provides new insights into the improvement of phosphorus release from sludge by the PF/Na2SO3 coupled oxidation process.

Peroxygenase-Catalysed Sulfoxidations in Non-Aqueous Media.

Chiral sulfoxides are valuable building blocks in asymmetric synthesis. However, the biocatalytic synthesis of chiral sulfoxides is still challenged by low product titres. Herein, we report the use of peroxygenase as a catalyst for asymmetric sulfoxidation under non-aqueous conditions. Upon covalent immobilisation, the peroxygenase showed stability and activity under neat reaction conditions. A large variety of sulfides was converted into chiral sulfoxides in very high product concentration with moderate to satisfactory optical purity (e. g. 626 mM of (R)-methyl phenyl sulfoxide in approx. 89 % ee in 48 h). Further polishing of the ee value via cascading methionine reductase A (MsrA) gave>99 % ee of the sulfoxide. The robustness of the enzymes and high product titer is superior to the state-of-the-art methodologies. Gram-scale synthesis has been demonstrated. Overall, we demonstrated a practical and facile catalytic method to synthesize chiral sulfoxides.

Charge Separation to Facilitate The Conversion of Copper‐Phenylacetylide from Aggregation‐Induced Emission to Efficient Photocatalysis

AbstractAggregation‐induced emission (AIE) materials are considered promising photocatalyst candidates due to their robust light‐harvesting and efficient photoexcitation, if their photoexcited carriers can be separated effectively. Herein, by skillfully selecting multi‐alkynyl ligands instead of phenylacetylene to construct multi‐channel charge separation, copper‐phenylacetylide (CP‐1) with AIE properties is successfully transformed into efficient photocatalysts CP‐2P (copper‐1,4‐diethynylbenzene) and CP‐2M (copper‐1,3‐diethylnylbenzene). In these structures, the multi‐alkynyl ligands connects the copper‐ladder into multi‐dimensional metal‐organic frameworks with greatly reduced bandgap, enhances charge transfer and separation, and facilitated oxygen adsorption and activation. As a representative, CP‐2P has the best photocatalytic activity and stability for photocatalytic aerobic oxidation, such as thioanisole oxidation (conv. > 99%, methyl phenyl sulfoxide sel. ≧ 94%), benzyl alcohol oxidation (conv. > 99%, benzaldehyde sel. > 99%) and benzylamine oxidation (conv. > 99%, N‐benzylidene benzylamine sel. > 99%), which can be used for large‐scale sunlight‐driven organic photosynthesis. This work confirms the feasibility of controlled conversion of the conventional copper‐alkynyl from AIE material to efficient photocatalyst using charge separation strategy, which provides an important guidance for the rational design of new high‐efficiency photocatalyst.

Ligand Sulfur Oxidation State Progressively Alters Galectin-3-Ligand Complex Conformations To Induce Affinity-Influencing Hydrogen Bonds.

Galectins play biological roles in immune regulation and tumor progression. Ligands with high affinity for the shallow, hydrophilic galectin-3 ligand binding site rely primarily on a galactose core with appended aryltriazole moieties, making hydrophobic interactions and π-stacking. We designed and synthesized phenyl sulfone, sulfoxide, and sulfide-triazolyl thiogalactoside derivatives to create affinity-enhancing hydrogen bonds, hydrophobic and π-interactions. Crystal structures and thermodynamic analyses revealed that the sulfoxide and sulfone ligands form hydrogen bonds while retaining π-interactions, resulting in improved affinities and unique binding poses. The sulfoxide, bearing one hydrogen bond acceptor, leads to an affinity decrease compared to the sulfide, whereas the corresponding sulfone forms three hydrogen bonds, two directly with Asn and Arg side chains and one water-mediated to an Asp side chain, respectively, which alters the complex structure and increases affinity. These findings highlight that the sulfur oxidation state influences both the interaction thermodynamics and structure.

Reaction mechanism, degradation pathway and toxicity assessment of NH4+ enhanced potassium ferrate removal of levofloxacin

Considering that ammonium ion (NH4+) was widely distributed in natural water and many sewage, it was of great practical significance to study NH4+ enhanced potassium ferrate (Fe(VI)) to rapid removal of levofloxacin (LEV) from water. In this experiment, firstly, the reaction kinetic of NH4+ enhanced Fe(VI) removal of LEV was studied, and the results showed that the enhanced removal reaction conformed to the second-order kinetic equation. When pH ≤ 9, the second-order rate constant kapp was linearly related to NH4+ dosage, but when pH= 10, the above linear relationship was broken, and the slope of the fitting line would change toward a smaller trend. Subsequently, tert-butanol (TBA) and Methyl phenyl sulfoxide (PMSO) were used as probes for·OH and high-valent iron-based intermediate (Fe(V)/Fe(IV)) respectively, which further revealed the reaction mechanism that NH4+ enhanced Fe(VI) to remove LEV as follows: NH4+ could promote Fe(VI) to produce a large amount of Fe(V)/Fe(IV), thus accelerating the degradation of LEV. In addition, 10 degradation intermediates of LEV were identified by quadrupole time-of-flight tandem ultra-performance liquid chromatography mass spectrometer (Q-TOF LC-MS), and then combined with density functional theory (DFT) calculation, two possible degradation pathways were inferred. Through the luminescence inhibition experiment of Vibrio fischeri and the toxicity evaluation of ECOSAR, it could be concluded that in the process of NH4+ enhancing Fe(VI) to remove LEV, the toxicity of the solution showed a trend of increasing first and then decreasing, and its toxicity was effectively improved and reduced after full oxidation. Finally, the experiments in actual water showed that it was feasible to use NH4+ in actual water to enhance Fe(VI) for rapid removal of LEV.

Novel use of ferrous iron/peroxymonosulfate for high-performance seawater desalination pretreatment under harmful algal blooms

Marine harmful algae bloom (HAB) is a growing threat to desalination plants worldwide. This work proposes ferrous iron/peroxymonosulfate (Fe2+/PMS) as a novel pretreatment technology for seawater reverse osmosis (SWRO) under HAB. Herein, Fe2+/PMS achieved a significantly higher reduction of negative charge of algae-laden seawater as compared to conventional coagulation (i.e., coagulant is Fe3+), which thereby facilitated improved flocculation to remove algal cells, turbidity and algal organics matters (AOMs), and marine Ca2+ (∼430 mg/L) could partially contribute to the enhanced coagulation performance. A new understanding of the improved coagulation efficiency achieved with Fe2+/PMS in seawater has been proposed as compared to freshwater: seawater matrix (e.g., 504 mM Cl−) was demonstrated to significantly enhance the generation of high-valent iron (FeO2+) as the main reactive intermediate instead of the long-recognized Fe3+ and free radicals, as revealed by methyl phenyl sulfoxide (PMSO) probe, radicals scavenging analysis and electron spin resonance (ESR) spectra. This new mechanism is expected to provide valuable insights for the development of more novel oxidative seawater treatment technologies. Of note, while trade-off between particles and AOMs played an important role in membrane fouling reduction by different dosages of Fe2+/PMS, Fe2+/PMS with an optimal dosage of 0.1 mM/0.05 mM achieved an unprecedentedly higher reduction (95.26%) of modified fouling index (MFI) as compared to conventional coagulation (13.28%–42.36% with 0.1–0.2 mM of Fe3+). Optical-photothermal infrared spectromicroscopy with sub-micron spatial resolution was employed to analyze membrane foulants for the first time, and Fe2+/PMS was found to mainly cause reduced cake layer resistance, which was attributed to the collectively reduced concentration of algae cells, micro-particles with sizes from 2 to 10 µm, humic substances and biopolymers. Moreover, Fe2+/PMS resulted in lower dissolved Fe3+ (<0.027 mg/L) in ultrafiltration (UF) permeate, which would make it more reliable for SWRO operation as compared to conventional coagulation. When energy-intensive dissolved air flotation (DAF) was employed to withstand HAB, Fe2+/PMS outperformed it and was instrumental in achieving reduced MFI with 56.4% lower operational cost. In this context, Fe2+/PMS would facilitate a high-performance and low-cost pretreatment technology for seawater desalination plants under HAB.

Unraveling the contribution of Co(IV) and free radicals in Co2+-activated Peroxymonosulfate process: Reaction mechanism, degradation pathway, and DFT calculation

The Co2+ and Peroxymonosulfate (PMS) reaction is a highly regarded advanced oxidation process (AOP) that has been extensively researched. The consensus regarding the relative contribution of reactive species in the Co2+/PMS system under different pH conditions has not been established. In this study, quenching experiments and electron spin resonance (ESR) tests demonstrated the coexistence of Co(IV), sulfate radical (SO4•-), hydroxyl radical (•OH), and singlet oxygen (1O2), and there fell to CBZ degradation were Co(IV) > SO4•->•OH ≈ 1O2 in the optimal conditions, where almost 100% of CBZ was degraded in the Co2+/PMS system within 30 min. Furthermore, Cl− would suppress the formation of Co(IV), SO4•-, and •OH but enhance the yield of 1O2, thereby showing a trend of inhibiting CBZ degradation. The probe compound used in this study was Methyl Phenyl Sulfoxide (PMSO), while methyl phenyl sulfone (PMSO2) as the indicator of Co(IV), the generation efficiency of PMSO2 (η'[PMSO2]) increased with reaction time and reached 70%–98% at 40 min at all set pH values (3, 4, 6, and 8). These results suggest that Co(IV) played a significant role in the Co2+/PMS system and its importance became more pronounced as the reaction progressed. PMSO probe and SO4•- quantification experiments jointly revealed that Co(IV) had the greatest performance at pH 4, and compared to other pH values, SO4•- had the largest contribution in the initial stage of the reaction at pH 6. The Ecological Structure Activity Relationships (ECOSAR) software was utilized to predict the toxicity of the degradation by-products. Additionally, luminescent bacteria experiments were conducted to assess the acute toxicity of the reaction solution. The results of these experiments demonstrated that the Co2+/PMS process exhibited a remarkable ability to detoxify the solution.

Highly selective synthesis of surface FeIV=O with nanoscale zero-valent iron and chlorite for efficient oxygen transfer reactions

High-valent iron-oxo species (FeIV=O) has been a long-sought-after oxygen transfer reagent in biological and catalytic chemistry but suffers from a giant challenge in its gentle and selective synthesis. Herein, we propose a new strategy to synthesize surface FeIV=O (≡FeIV=O) on nanoscale zero-valent iron (nZVI) using chlorite (ClO2-) as the oxidant, which possesses an impressive ≡FeIV=O selectivity of 99%. ≡FeIV=O can be energetically formed from the ferrous (FeII) sites on nZVI through heterolytic Cl-O bond dissociation of ClO2- via a synergistic effect between electron-donating surface ≡FeII and proximal electron-withdrawing H2O, where H2O serves as a hydrogen-bond donor to the terminal O atom of the adsorbed ClO2- thereby prompting the polarization and cleavage of Cl-O bond for the oxidation of ≡FeII toward the final formation of ≡FeIV=O. With methyl phenyl sulfoxide (PMS16O) as the probe molecule, the isotopic labeling experiment manifests an exclusive 18O transfer from Cl18O2- to PMS16O18O mediated by ≡FeIV=18O. We then showcase the versatility of ≡FeIV=O as the oxygen transfer reagent in activating the C-H bond of methane for methanol production and facilitating selective triphenylphosphine oxide synthesis with triphenylphosphine. We believe that this new ≡FeIV=O synthesis strategy possesses great potential to drive oxygen transfer for efficient high-value-added chemical synthesis.

Selective abatement of electron-rich organic contaminants by trace complexed Mn(II)-catalyzed periodate via high-valent manganese–oxo species

Mn(II) is among the most efficient catalysts for the periodate (PI)-based oxidation process. In-situ formed colloidal MnO2 simultaneously serves as the catalyst and oxidant during the degradation of organic contaminants by PI. Here, it is revealed that the complexation of Mn(II) by ethylene diamine tetraacetic acid (EDTA) further enhances the performance of PI-based oxidation in the selective degradation of organic contaminants. As evidenced by methyl phenyl sulfoxide probing, 18O-isotope labeling, and mass spectroscopy, EDTA complexation modulates the reaction pathway between Mn(II) and PI, triggering the generation of high-valent manganese–oxo (MnV–oxo) as the dominant reactive species. PI mediates the single-electron oxidation of Mn(II) to Mn(III), which is stabilized by EDTA complexation and then further oxidized by PI via the oxygen-atom transfer step, ultimately producing the MnV–oxo species. Ligands analogous to EDTA, namely, [S,S]-ethylenediaminedisuccinic acid and L-glutamic acid N,N-diacetic acid, also enhances the Mn(II)/PI process and favors MnV–oxo as the dominant species. This study demonstrates that functional ligands can tune the efficiency and reaction pathways of Mn(II)-catalyzed peroxide and peroxyacid-based oxidation processes.

Fast degradation of atrazine by nZVI-Cu0/PMS: Re-evaluation and quantification of reactive species, generation pathways, and application feasibility.

Additive metal to zero-valent iron (ZVI) could enhance the reduction ability and the additive Cu0 was incorporated to ZVI to accelerate PMS activation with atrazine (ATZ) as target compound. The efficiencies of ATZ degradation and PMS decomposition climbed up firstly and then declined as Cu0 loading increased from 0.01 to 1.00wt% with the maximums at 0.10wt%. SO4•-, HO•, Fe(IV), O2•- and 1O2 were generated by nZVI-Cu0/PMS based on the results of electron paramagnetic resonance (EPR) and simultaneous degradation of nitrobenzene, ATZ, and methyl phenyl sulfoxide (PMSO). The rate constant of Fe(IV) and ATZ was estimated as 7×104 M-1∙s-1 via the variation of methyl phenyl sulfone (PMSO2)formation at different ATZ concentrations. However, Fe(IV) contributed negligibly to ATZ degradation due to the strong scavenging of Fe(IV) by PMS. SO4•- and HO• were the reactive species responsible for ATZ degradation and the yield ratio of SO4•- and HO• was about 8.70 at initial stage. Preliminary thermodynamic calculation on the possible activation ways revealed that the dominant production of SO4•- might originate from the atomic H reduction of PMS in the surface layer of nZVI-Cu0. Ten products of ATZ degradation were identified by HPLC/ESI/QTOF and the possible degradation pathways were analyzed combined with theoretical calculation on ATZ structure. The decrease of temperature or increase of solution pH led to the decline of ATZ degradation, as well as the individual addition of common ions (HCO3-, Cl-, SO42-, NH4+, NO3- and F-) and natural organic matters (NOM). In real water, ATZ was still efficiently degraded with the decontamination efficiency decreasing in the sequence of tap water > surface water > simulated wastewater > groundwater. For the treatment of ATZ-polluted continuous flow, nZVI-Cu0 in double-layer layout had a higher capacity than the single-layer mode. Meanwhile, the leaching TFe and TCu were limited. The results indicate nZVI-Cu0/PMS is applicable and the multiple-layer layout of nZVI-Cu0 is suggested for ATZ-polluted ground water and soil remediation.

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.

Nitrilotriacetic acid-assisted Mn(II) activated periodate for rapid and long-lasting degradation of carbamazepine: The importance of Mn(IV)-oxo species.

Periodate-based (PI, IO4-) oxidation processes for pollutant elimination have gained increased attention in recent years. This study shows that nitrilotriacetic acid (NTA) can assist trace Mn(II) in activating PI for fast and long-lasting degradation of carbamazepine (CBZ) (100% degradation in 2min). PI can oxidize Mn(II) to permanganate(MnO4-, Mn(VII)) in the presence of NTA, which indicates the important role of transient manganese-oxo species. 18O isotope labeling experiments using methyl phenyl sulfoxide (PMSO) as a probe further confirmed the formation of manganese-oxo species. The chemical stoichiometric relationship (PI consumption: PMSO2 generation) and theoretical calculation suggested that Mn(IV)-oxo-NTA species were the main reactive species. The NTA-chelated manganese facilitated direct oxygen transfer from PI to Mn(II)-NTA and prevented hydrolysis and agglomeration of transient manganese-oxo species. PI was transformed completely to stable and nontoxic iodate but not lower-valent toxic iodine species (i.e., HOI, I2, and I-). The degradation pathways and mechanisms of CBZ were investigated using mass spectrometry and density functional theory (DFT) calculation. This study provided a steady and highly efficient choice for the quick degradation of organic micropollutants and broadened the perspective on the evolution mechanism of manganese intermediates in the Mn(II)/NTA/PI system.

Degradation of dimethyl phthalate by morphology controlled β-MnO2 activated peroxymonosulfate: The overlooked roles of high-valent manganese species

Activated peroxymonosulfate (PMS) processes have emerged as an efficient advanced oxidation process to eliminate refractory organic pollutants in water. This study synthesized a novel spherical manganese oxide catalyst (0.4KBr-β-MnO2) via a simple KBr-guided approach to activate PMS for degrading dimethyl phthalate (DMP). The 0.4KBr-β-MnO2/PMS system enhanced DMP degradation under different water quality conditions, exhibiting an ultrahigh and stable catalytic activity, outperforming equivalent quantities of pristine β-MnO2 by 8.5 times. Mn(V) was the dominant reactive species that was revealed by the generation of methyl phenyl sulfone from methyl phenyl sulfoxide oxidation. The selectivity of Mn(V) was demonstrated by the negligible inhibitory effects of Inorganic anions. Theoretical calculations confirmed that Mn (V) was more prone to attack the CO bond of the side chain of DMP. This study revealed the indispensable roles of high-valent manganese species in DMP degradation by the 0.4KBr-β-MnO2/PMS system. The findings could provide insight into effective PMS activation by Mn-based catalysts to efficiently degrade pollutants in water via the high-valent manganese species.

The altered treatment efficiency of the bisulfite/permanganate process by chloride

Bisulfite-activated permanganate (S(IV)/Mn(VII)) process has proven to be a promising method for rapidly degrading micropollutants. Previous studies have shown that the treatment efficiency of the S(IV)/Mn(VII) process suffer from significant water matrix effects while the mechanism still remains unclear. This study systematically investigates the influence of chloride, which is a common water constituent, on the S(IV)/Mn(VII) process. Addition of chloride decreased the removal of methyl phenyl sulfoxide, phenol, benzoic acid and carbamazepine by the S(IV)/Mn(VII) process but increased dimethoxybenzene removal. The distribution of reactive species in the S(IV)/Mn(VII) process in the absence and presence of chloride was determined with relative rate method. The S(IV)/Mn(VII) process primarily relies on SO4•− and reactive manganese species (RMnS) for pollutant abatement while dosing chloride decreased the concentration of these reactive species. Reactive chlorine species (RCS), such as Cl2•– and ClO•, are formed through the reaction of SO4•– with chloride, and become more important at high concentrations of chloride. RMnS includes Mn(VI), Mn(V) and Mn(III), but none of these species are capable of oxidizing chloride. However, chloride retarded the consumption of bisulfite which reduced RMnS and RCS in turn. DOM inhibited pollutant removal by the S(IV)/Mn(VII) process while the impact mechanism was significantly altered by chloride. Additionally, the study observed a synergistic inhibition of DOM and chloride on the degradation of pollutants that are highly reactive towards Cl2•– and ClO•.

Activation of periodate by self-recycled Ru(III)/TiO2 for selective oxidation of aqueous organic pollutants: Essential role of homogeneous Ru(V)=O species

Recently, metal catalysts have received much attention in periodate (PI) activation for production of reactive oxygen species to efficiently degrade organic contaminants, yet activation efficiency is cumbered with their sluggish catalytic cycle. In the study, TiO2 supported Ru(III) catalysts (Ru(III)/TiO2, 0.45 wt% as Ru) were used to catalyze PI activation for oxidation of aqueous organic pollutants. Ru(III)/TiO2 exhibited comparable performance with homogeneous Ru(III) for phenol degradation via PI activation at initial pH = 4, 7 and 10. Moreover, the Ru(III)/TiO2-PI system showed high selectivity for degradation of electron-rich organic contaminants. In comparison, benzoic acid and ibuprofen were hardly oxidized in the system. Scavenging tests, H218O-isotope labeled methyl phenyl sulfoxide (PMSO) probe experiments, X-ray absorption near-edge structurespectra and Electron Spin Resonance analysis confirm formation of Ru(V) = O species as dominant oxidant in the process with little involvement of IO3, OH and O2−. The formed Ru(V) = O species were further confirmed to be water-soluble via analysis of Ru distribution between aqueous solution and TiO2surface. They can be reduced to Ru(III) species by reacting with organics, realizing the catalytic cycle of Ru(III) → Ru(V) = O → Ru(III) and self-recycle of Ru(III) onto TiO2surface. In addition, PI was decomposed in stoichiometry into IO3–without generation of undesired iodine species (i.e., HOI and I2). This study advances understandings of PI activation mechanism by heterogeneous Ru(III) catalysts, and also provides a promising oxidation technology for wastewater purification.

In-depth insights into Fe(III)-doped g-C3N4 activated peracetic acid: Intrinsic reactive species, catalytic mechanism and environmental application

In this study, we demonstrate that Fe(III)-doped g-C3N4 can efficiently activate peracetic acid (PAA) to degrade electron-rich pollutants (e.g., sulfamethoxazole, SMX) over a wide pH range (3−7). Almost ∼100% high-valent iron-oxo species (Fe(V)) was generated and acted as the dominant reactive species responsible for the micropollutants oxidation based on the analysis result of quenching experiments, 18O isotope-labeling examination and methyl phenyl sulfoxide (PMSO) probe method. Electrochemical testing (e.g., amperometric i−t and linear sweep voltammetry (LSV)) and density functional theory (DFT) calculations illustrated that the main active site Fe atom and PAA underwent electron transfer to form Fe(V) for attacking SMX. Linear free energy relationship (LFER) between the pseudo-first-order rates of different substituted phenols (SPs) and the Hammett constant σ+ depicted the electrophilic oxidation properties. The selective oxidation of Fe(V) endows the established system remarkable anti-interference capacity against water matrices, while the Fe(V) lead to the formation of iodinated disinfection by-products (I-DBPs) in the presence of I−. Fe(III)-doped g-C3N4/PAA system showed excellent degradation efficiency of aquaculture antibiotics. This study enriches the knowledge and research of high-valent iron-oxo species and provides a novel perspective for the activation of PAA via heterogeneous iron-based catalysts and practical environmental applications.