Production Of Cl Research Articles

Investigating Competing Inner‐ and Outer‐Sphere Electron‐Transfer Pathways in Copper Photoredox‐Catalyzed Atom‐Transfer Radical Additions: Closing the Cycle

AbstractThis integrated computational and experimental study comprehensively examines the viability of competing inner‐sphere electron transfer (ISET) and outer‐sphere electron transfer (OSET) processes in [Cu(dap)2]+‐mediated atom‐transfer radical additions (ATRA) of olefins and CF3SO2Cl that can deliver both R−SO2Cl and R−Cl products. Five sterically‐ and electronically‐varied representative alkenes were selected from which to explore and reconcile a range of experimentally observed outcomes. Findings are consistent with photoexcited [Cu(dap)2]+ initiating photoelectron transfer via ISET and the subsequent regeneration of the oxidized catalyst via ISET in the ground state to close the catalytic cycle and liberate products. R−SO2Cl/R−Cl product ratios appear to be primarily governed by the relative rates of direct catalyst regeneration {i.e., [Cu(dap)2SO2Cl]⋅++R⋅} and ligand exchange {i.e., [Cu(dap)2SO2Cl]⋅++Cl− }. Through this work, a more consistent and more complete conceptual framework has been developed to better understand this chemistry and how catalyst regeneration occurs. It is this important ground state process, which closes the catalytic cycle, and ultimately controls the enantioselectivity of ATRA reactions employing chiral copper photocatalysts.

In-situ complexation of Cu(II) with polyethyleneimine (PEI) triggers the enhanced formation of halonitromethanes, dichloroacetonitrile, and dichloroacetamide during UV/chlorine disinfection: Cu(I) contribution and Cl· sustainable production

The complexation of copper ions (Cu(II)) with coexisting organic ligands (e.g. polyethyleneimine (PEI)) in water may pose a new threat to water quality. This study revealed that the maxima concentrations of HNMs, DCAN, and DCAcAm from Cu(II)-PEI complex during UV/chlorine disinfection were 1.54, 2.00, and 1.25 times higher than those from PEI, and the maxima concentrations of HNMs, DCAN, and DCAcAm from Cu(II)-PEI complex during chlorination disinfection were 1.22, 1.31, and 1.10 times higher than those from PEI. Meanwhile, specific Cu(II) concentration (0.25 ∼ 3.0 mg L−1) and alkaline pH were more favorable for forming HNMs, DCAN, and DCAcAm during UV/chlorine disinfection, which were highly dependent on the involvement of HO· and Cl·. Cu(II)-PEI, an in-situ formed stable complex that permitted an efficient interconversion cycle of Cu(II)/Cu(I) via concurrent metal-to-ligand charge transfer and ligand-to-metal charge transfer. The analysis and comparison of extensive products provided solid evidence for the primary role of Cu(I) and the enhanced production of Cl· in increasing HNMs, DCAN, and DCAcAm productions, rather than only Cu(II) catalysis similar to that during chlorination. The new findings broaden the knowledge of the influence of in-situ formed Cu(II)-organic complexes on forming HNMs, DCAN, and DCAcAm during UV/chlorine disinfection.

Acidic chloride electrolyte mediates the high conversion ratio of CO2-to-C2H4 and direct production of Cl2

We design an efficient catalytic system for C2 and Cl2 formation by coupling CO2R and CER in an acidic environment. It can support C2H4 and Cl2 with 63% and 89% FEs at 700 mA cm−2. This provides a valuable reference for the development of the CO2RR.

Dissociative electron attachment to carbon tetrachloride probed by velocity map imaging.

Bond-breaking in CCl4via dissociative electron attachment (DEA) has been studied using a velocity map imaging (VMI) spectrometer. A number of effects related to the dissociation dynamics have been revealed. The near-zero eV s-wave electron attachment, which leads to the production of Cl- anions, is accompanied by a very efficient intramolecular vibrational redistribution. This is manifested by a small fraction of the excess energy being released in the form of the fragments' translation energy. A similar effect is observed for higher-lying electronic resonances with one exception: the resonance centered around 6.2 eV leads to the production of fast Cl2- fragments and their angular distribution is forward peaking. This behavior could not be explained with a single-electronic-state model in the axial recoil approximation and is most probably caused by bending dynamics initiated by a Jahn-Teller distortion of the transient anion. The CCl2- fragment has a reverse backward-peaking angular distribution, suggesting the presence of a long-distance electron hopping mechanism between the fragments.

Forecasting Model Accuracy Assessment in a Bottled Water Supply Chain

This study presents an accuracy assessment of various classical time series forecasting methods to determine the most accurate forecasting method for predicting demand of the 50cl product of a bottled water supply chain. The classical time series forecasting methods compared are the moving average, weighted moving average, exponential smoothing, adjusted exponential smoothing, linear trend line, Holt’s model, and Winter’s model. The Mean Absolute Percent Deviation (MAPD) value was determined for the various forecasting methods to find the forecasting method with the least MAPD and hence the highest forecasting accuracy. The tracking signal measure was also used to determine the forecasting models which were biased. The results showed that though the weighted moving average method began to underforecast demand in the final period, it had the lowest MAPD value of 2.25%, making it the forecasting method with the highest accuracy for predicting the 50cl bottled water demand. On the other hand, though the exponential smoothing forecasting method had the highest MAPD value of 3.43% and least accuracy for predicting the bottled water demand, its forecasts were consistently within the tracking signal control limits. This study will aid supply chain analysts in implementing accuracy assessment of classical time series forecasting models.

Nighttime NO emissions strongly suppress chlorine and nitrate radical formation during the winter in Delhi

Abstract. Atmospheric pollution in urban regions is highly influenced by oxidants due to their important role in the formation of secondary organic aerosol (SOA) and smog. These include the nitrate radical (NO3), which is typically considered a nighttime oxidant, and the chlorine radical (Cl), an extremely potent oxidant that can be released in the morning in chloride-rich environments as a result of nocturnal build-up of nitryl chloride (ClNO2). Chloride makes up a higher percentage of particulate matter in Delhi than has been observed anywhere else in the world, which results in Cl having an unusually strong influence in this city. Here, we present observations and model results revealing that atmospheric chemistry in Delhi exhibits an unusual diel cycle that is controlled by high concentrations of NO during the night. As a result of this, the formation of both NO3 and dinitrogen pentoxide (N2O5), a precursor of ClNO2 and thus Cl, are suppressed at night and increase to unusually high levels during the day. Our results indicate that a substantial reduction in nighttime NO has the potential to increase both nocturnal oxidation via NO3 and the production of Cl during the day.

Hydroxy esters atmospheric degradation: OH and Cl reactivity, products distribution and fate of the alkoxy radicals formed

Kinetic studies of the reaction of ethyl glycolate HOCH2C(O)OCH2CH3 with OH radicals (kOH) and Cl atoms (kCl) have been conducted by the relative method using a glass atmospheric reactor by “in situ” Fourier Transform Infrared (FTIR) and Gas Chromatography equipped with flame ionization detection by Solid Phase Micro Extraction (GC-FID/SPME) at room temperature and atmospheric pressure. The following relative rate coefficients were determined using several reference compounds and two different techniques: kEG + OH-FTIR = (4.36 ± 1.21) × 10−12; kEG + OH-GC-FID= (3.90 ± 0.74) × 10−12; and kEG + Cl-GC-FID= (6.40 ± 0.72) × 10−11 all values in units of cm3.molecule−1.s−1. Complementary product studies were performed under comparable conditions to the kinetic tests, in order to identify the reaction products and to postulate their tropospheric oxidation mechanisms. The reaction of OH radicals and Cl atoms with ethyl glycolate initiates via H-atom abstraction from alkyl groups of the molecule. Formic acid was positively identified as a reaction product by FTIR. On the other hand, formaldehyde, acetaldehyde, glycolic acid; and formic acid were identified by the GC-MS technique. The Structure–Activity Relationship, (SAR) calculations were also implemented to estimate the more favorable reaction pathways and compare them with the products identified. Tropospheric lifetimes of τOH = 34 h and τCl = 5.5 days were estimated to determine how these investigated reactions might affect the air quality. In this sense, average ozone production of [O3] = 0.75 and a Photochemical Ozone Creation Potential, POCP, of 38 were calculated for the hydroxyl ester studied.

Photocatalytic chlorine atom production on mineral dust–sea spray aerosols over the North Atlantic

Active chlorine in the atmosphere is poorly constrained and so is its role in the oxidation of the potent greenhouse gas methane, causing uncertainty in global methane budgets. We propose a photocatalytic mechanism for chlorine atom production that occurs when Sahara dust mixes with sea spray aerosol. The mechanism is validated by implementation in a global atmospheric model and thereby explaining the episodic, seasonal, and location-dependent 13C depletion in CO in air samples from Barbados [J.E. Mak, G. Kra, T. Sandomenico, P. Bergamaschi, J. Geophys. Res. Atmos. 108 (2003)], which remained unexplained for decades. The production of Cl can also explain the anomaly in the CO:ethane ratio found at Cape Verde [K. A. Read et al., J. Geophys. Res. Atmos. 114 (2009)], in addition to explaining the observation of elevated HOCl [M. J. Lawler et al., Atmos. Chem. Phys. 11, 7617-7628 (2011)]. Our model finds that 3.8 Tg(Cl) y-1 is produced over the North Atlantic, making it the dominant source of chlorine in the region; globally, chlorine production increases by 41%. The shift in the methane sink budget due to the increased role of Cl means that isotope-constrained top-down models fail to allocate 12 Tg y-1 (2% of total methane emissions) to 13C-depleted biological sources such as agriculture and wetlands. Since 2014, an increase in North African dust emissions has increased the 13C isotope of atmospheric CH4, thereby partially masking a much greater decline in this isotope, which has implications for the interpretation of the drivers behind the recent increase of methane in the atmosphere.

Adsorption and photocatalytic degradation of 2-chlorophenol in water: Evaluating the performance of TiO2/activated carbon vs. using a mixture of TiO2 and activated carbon

The work reported here compared between two photocatalytic degradation strategies of 2-chlorophenol (2-CP). The first strategy utilized titanium dioxide (TiO2) immobilized on activated carbons (AC) to produce TiO2/AC photocatalysts of various TiO2 loadings. Various immobilization techniques were used: chemical vapour deposition (CVD), direct air hydrolysis (DAH), high-temperature impregnation (HTI). In the first strategy, characterization, adsorption and photocatalytic degradation of 2-CP using TiO2/AC revealed that: 1) deposition of anatase TiO2 occurred in the micro pores of AC; 2) adsorption capacity decreased with increasing anatase TiO2 loading on TiO2/AC; 3) adsorption kinetics followed pseudo first order kinetics where 40 % of 2-CP was adsorbed; 4) photocatalytic degradation caused removal of all 2-CP and 80 % of total organic carbon (TOC), while no chloride ion (Cl−) was produced. In the second strategy, naked TiO2 (anatase) and mixtures of (anatase and AC) were involved to investigate the effect of presence of AC on degradation ability of anatase TiO2 towards 2-CP. The results showed that: 1) naked TiO2 (anatase) caused better degradation of 2-CP than TiO2/AC (Cl− was liberated; complete degradation of 2-CP occurred; some TOC remained in the suspension); 2) presence of AC with anatase TiO2 in the reaction mixture negatively affected Cl− production, but positively affected 2-CP and TOC disappearance; 3) when all 2-CP was adsorbed on AC, production of Cl− was inhibited but continued at a reduced rate. This might indicat that both dissolved and adsorbed 2-CP contributed to the degradation process.

Predicting demand in a bottled water supply chain using classical time series forecasting models

In this paper, various classical time series forecasting methods were compared to determine the forecasting method with the highest accuracy in predicting demand of the 50cl product of a bottled water supply chain. The classical time series forecasting methods compared are the moving average, weighted moving average, exponential smoothing, adjusted exponential smoothing, linear trend line, Holt’s model, and Winter’s model. These methods were evaluated to determine the method with the least Mean Absolute Deviation (MAD) value and hence the highest forecasting accuracy. From the results, the weighted moving average forecasting method had the lowest MAD value of 1,987, making it the forecasting method with the highest accuracy for predicting the 50cl bottled water demand. While the exponential smoothing forecasting method had the highest MAD value of 2,483, making it the forecasting method with the least accuracy for predicting the 50cl bottled water demand. This research provides a procedure for aiding supply chain analysts in implementing demand forecasting using classical time series forecasting models.

Synthesis, Characterization, and Biological Activity of Water-Soluble, Dual Anionic and Cationic Ruthenium–Arene Complexes Bearing Imidazol(in)ium-2-dithiocarboxylate Ligands

An efficient synthetic protocol was devised for the preparation of five cationic ruthenium-arene complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands from the [RuCl2(p-cymene)]2 dimer and 2 equiv of an NHC·CS2 zwitterion. The reactions proceeded cleanly and swiftly in dichloromethane at room temperature to afford the expected [RuCl(p-cymene)(S2C·NHC)]Cl products in quantitative yields. When the [RuCl2(p-cymene)]2 dimer was reacted with only 1 equiv of a dithiolate betaine under the same experimental conditions, a set of five bimetallic compounds with the generic formula [RuCl(p-cymene)(S2C·NHC)][RuCl3(p-cymene)] was obtained in quantitative yields. These novel, dual anionic and cationic ruthenium-arene complexes were fully characterized by various analytical techniques. NMR titrations showed that the chelation of the dithiocarboxylate ligands to afford [RuCl(p-cymene)(S2C·NHC)]+ cations was quantitative and irreversible. Conversely, the formation of the [RuCl3(p-cymene)]- anion was limited by an equilibrium, and this species readily dissociated into Cl- anions and the [RuCl2(p-cymene)]2 dimer. The position of the equilibrium was strongly influenced by the nature of the solvent and was rather insensitive to the temperature. Two monometallic and two bimetallic complexes cocrystallized with water, and their molecular structures were solved by X-ray diffraction analysis. Crystallography revealed the existence of strong interactions between the azolium ring protons of the cationic complexes and neighboring donor groups from the anions or the solvent. The various compounds under investigation were highly soluble in water. They were all strongly cytotoxic against K562 cancer cells. Furthermore, with a selectivity index of 32.1, the [RuCl(p-cymene)(S2C·SIDip)]Cl complex remarkably targeted the erythroleukemic cells vs mouse splenocytes.

Galerkin Approximations for the Solution of Fredholm Volterra Integral Equation of Second Kind

In this research, we have introduced Galerkin method for finding approximate solutions of Fredholm Volterra Integral Equation (FVIE) of 2nd kind, and this method shows the result in respect of the linear combinations of basis polynomials. Here, BF (product of Bernstein and Fibonacci polynomials), CH (product of Chebyshev and Hermite polynomials), CL (product of Chebyshev and Laguerre polynomials), FL (product of Fibonacci and Laguerre polynomials) and LLE (product of Legendre and Laguerre polynomials) polynomials are established and considered as basis function in Galerkin method. Also, we have tried to observe the behavior of all these approximate solutions finding from Galerkin method for different problems and then a comparison is shown using some standard error estimations. In addition, we observe the error graphs of numerical solutions in Galerkin method for different problems of FVIE of second kind. GANITJ. Bangladesh Math. Soc.41.1 (2021) 1–14

Observation and modelling of ozone-destructive halogen chemistry in a passively degassing volcanic plume

Abstract. Volcanoes emit halogens into the atmosphere that undergo complex chemical cycling in plumes and cause destruction of ozone. We present a case study of the Mount Etna plume in the summer of 2012, when the volcano was passively degassing, using aircraft observations and numerical simulations with a new 3D model “WRF-Chem Volcano” (WCV), incorporating volcanic emissions and multi-phase halogen chemistry. Measurements of SO2 – an indicator of plume intensity – and ozone were made in the plume a few tens of kilometres from Etna, revealing a strong negative correlation between ozone and SO2 levels. From these observations, using SO2 as a tracer species, we estimate a mean in-plume ozone loss rate of 1.3×10−5 molecules of O3 per second per molecule of SO2. This value is similar to observation-based estimates reported very close to Etna's vents, indicating continual ozone loss in the plume up to at least tens of kilometres downwind. The WCV model is run with nested grids to simulate the plume close to the volcano at 1 km resolution. The focus is on the early evolution of passively degassing plumes aged less than 1 h and up to tens of kilometres downwind. The model is able to reproduce the so-called “bromine explosion”: the daytime conversion of HBr into bromine radicals that continuously cycle in the plume. These forms include the radical BrO, a species whose ratio with SO2 is commonly measured in volcanic plumes as an indicator of halogen ozone-destroying chemistry. The species BrO is produced in the ambient-temperature chemistry, with in-plume BrO / SO2 ratios on the order of 10−4 mol/mol, similar to those observed previously in Etna plumes. Wind speed and time of day are identified as non-linear controls on this ratio. Sensitivity simulations confirm the importance of near-vent radical products from high-temperature chemistry in initiating the ambient-temperature plume halogen cycling. Heterogeneous reactions that activate bromine also activate a small fraction of the emitted chlorine; the resulting production of chlorine radical Cl strongly enhances the methane oxidation and hence the formation of formaldehyde (HCHO) in the plume. Modelled rates of ozone depletion are found to be similar to those derived from aircraft observations. Ozone destruction in the model is controlled by the processes that recycle bromine, with about three-quarters of this recycling occurring via reactions between halogen oxide radicals. Through sensitivity simulations, a relationship between the magnitude of halogen emissions and ozone loss is established. Volcanic halogen cycling profoundly impacts the overall plume chemistry in the model, notably hydrogen oxide radicals (HOx), nitrogen oxides (NOx), sulfur, and mercury chemistry. In the model, it depletes HOx within the plume, increasing the lifetime of SO2 and hence slowing sulfate aerosol formation. Halogen chemistry also promotes the conversion of NOx into nitric acid (HNO3). This, along with the displacement of nitrate out of background aerosols in the plume, results in enhanced HNO3 levels and an almost total depletion of NOx in the plume. The halogen–mercury model scheme is simple but includes newly identified photo-reductions of mercury halides. With this set-up, the mercury oxidation is found to be slow and in near-balance with the photo-reduction of the plume. Overall, the model findings demonstrate that halogen chemistry has to be considered for a complete understanding of sulfur, HOx, reactive nitrogen, and mercury chemistry and of the formation of sulfate particles in volcanic plumes.

Electrochemical degradation of tris(2-chloroethyl) phosphate by metal-oxide-coated Ti anodes: Kinetics, toxicity and mechanism

The current study presents a comprehensive and novel attempt to degrade aqueous tri(2-chloroethyl) phosphate (TCEP) by metal-oxide-coated Ti anodes for the first time. Six metal-oxide-coated Ti electrodes (Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2, Ti/SnO2-Sb/La-PbO2, Ti/SnO2-Sb/Ce-PbO2, Ti/SnO2-Sb/Ga-PbO2 and Ti/SnO2-Sb/Zr-PbO2) were prepared and characterized. Ti/SnO2-Sb/La-PbO2 showed the highest pseudo-first-order reaction rate constant (2.1 × 10−2 min−1) and lowest energy consumption (21.35 Wh L−1) in the degradation of 1 mg L−1 TCEP at 10 mA cm−2, mainly because of its highest oxygen evolution potential and OH production. Higher current density and neutral condition favored TCEP degradation, while the presence of Cl− or NO3− could suppress the degradation. In the electrochemical degradation of 10 mg L−1 TCEP, mineralization percentage of 48.0% (mineralization current efficiency of 0.30%) and PO43− release percentage of 72.7% were achieved at 150 min. By the attack of OH on the CO and CCl bonds in TCEP molecular structure, products of chloroethanol, Cl− and PO43− were released, with the major electrocatalytic degradation pathways of dechlorination and hydroxylation. Based on the results of flow cytometry, the relative toxicity to Escherichia coli effectively decreased to 4.93% in TCEP degradation. Compared with the UV-AOPs, electrochemical oxidation process is proved to be feasible and effective for mineralization and detoxification of TCEP in water.

UV/H2O2 oxidation of tri(2-chloroethyl) phosphate: Intermediate products, degradation pathway and toxicity evaluation

Tri(2-chloroethyl) phosphate (TCEP) with the initial concentration of 5 mg/L was degraded by UV/H2O2 oxidation process. The removal rate of TCEP in the UV/H2O2 system was 89.1% with the production of Cl− and PO43− of 0.23 and 0.64 mg/L. The removal rate of total organic carbon of the reaction was 48.8% and the pH reached 3.3 after the reaction. The oxidative degradation process of TCEP in the UV/H2O2 system obeyed the first order kinetic reaction with the apparent rate constant of 0.0025 min−1 (R2=0.9788). The intermediate products were isolated and identified by gas chromatography-mass spectrometer. The addition reaction of HO• and H2O and the oxidation reaction with H2O2 were found during the degradation pathway of 5 mg/L TCEP in the UV/H2O2 system. For the first time, environment risk was estimated via the “ecological structure activity relationships” program and acute and chronic toxicity changes of intermediate products were pointed out. The luminescence inhibition rate of photobacterium was used to evaluate the acute toxicity of intermediate products. The results showed that the toxicity of the intermediate products increased with the increase of reaction time, which may be due to the production of chlorine compounds. Some measures should be introduced to the UV/H2O2 system to remove the highly toxic Cl-containing compounds, such as a nanofiltration or reverse osmosis unit.

Numerical investigation of the effect of variation of gas mixture ratio on density distribution of etchant species (Br, Br+, Cl, Cl+, and H) in HBr/Cl2/Ar plasma discharge

A self-sustained fluid model is used to study the effect of variation of noble gas fraction (Ar) and variation of gas mixture ratio (HBr/Cl2/Ar) on density distribution of important etchant species (Br, Br+, Cl, Cl+, and H) in HBr/Cl2/Ar capacitive coupled plasma discharge that is being vastly used for dry etching of Si, GaAs, GaSb and other group III and IV semiconductor materials. A comprehensive set of 80 reactions in this plasma discharge is presented which contains electron impact reactions, neutral–neutral reactions, ion–ion reactions, and charge transfer reactions. Based on simulation results, it is found that densities of neutral species have normal distribution curve; density is higher at center of the reactor and decreases as we move towards electrode surface, while densities of charged species follow bimodal distribution in which peaks occur near electrodes. Furthermore, the addition of Ar in HBr/Cl2 causes electron density to increase which promotes ionization and dissociation. It was found that at constant supply of Cl2 gas, by increasing Ar fraction (HBr/Cl2/Ar from 80/10/10 to 10/10/80) densities of Br, Br+ and H will go down and at constant supply of Ar gas, raising Cl2 fraction in feedback gases (HBr/Cl2/Ar from 70/20/10 to 20/70/10) promoted the production of Cl and Cl+ while densities of Br, Br+, and H are dropped-off. Hence, densities and fluxes of important etchant species – for chemical vs. physical etching – can be controlled by tuning of mixture ratio.

3D hydrodynamic simulations of C ingestion into a convective O shell

ABSTRACT Interactions between convective shells in evolved massive stars have been linked to supernova impostors, to the production of the odd-Z elements Cl, K, and Sc, and they might also help generate the large-scale asphericities that are known to facilitate shock revival in supernova explosion models. We investigate the process of ingestion of C-shell material into a convective O-burning shell, including the hydrodynamic feedback from the nuclear burning of the ingested material. Our 3D hydrodynamic simulations span almost 3 dex in the total luminosity Ltot. All but one of the simulations reach a quasi-stationary state with the entrainment rate and convective velocity proportional to Ltot and $L_\mathrm{tot}^{1/3}$, respectively. Carbon burning provides $14\!-\!33{{\ \rm per\ cent}}$ of the total luminosity, depending on the set of reactions considered. Equivalent simulations done on 7683 and 11523 grids are in excellent quantitative agreement. The flow is dominated by a few large-scale convective cells. An instability leading to large-scale oscillations with Mach numbers in excess of 0.2 develops in an experimental run with the energy yield from C burning increased by a factor of 10. This run represents most closely the conditions expected in a violent O–C shell merger, which is a potential production site for odd-Z elements such as K and Sc and which may seed asymmetries in the supernova progenitor. 1D simulations may underestimate the energy generation from the burning of ingested material by as much as a factor 2 owing to their missing the effect of clumpiness of entrained material on the nuclear reaction rate.

In-situ chemical oxidation of chlorendic acid by persulfate: Elucidation of the roles of adsorption and oxidation on chlorendic acid removal

The oxidation of chlorendic acid (CA), a polychlorinated recalcitrant contaminant, by heat-, mineral-, and base-activated persulfate was investigated. In pH 3–12 homogeneous (i.e., solid-free) solutions, CA was oxidized by •OH and SO4•- radicals, resulting in a nearly stoichiometric production of Cl−. The rate constants for the reaction between these radicals and CA were measured at different temperatures by electron pulse radiolysis, and were found to be kOH = (8.71 ± 0.17) × 107 M−1s−1 and kSO4 = (6.57 ± 0.83) × 107 M−1s−1 at 24.5 °C for •OH and SO4•-, respectively. CA was oxidized at much slower rates in solutions containing iron oxyhydroxide or aquifer soils, partially due to the adsorption of CA on these solids. To gain further insight into the effect of solids during in-situ remediation of CA, the adsorption of CA onto iron (hydr)oxide, manganese dioxide, silica, alumina, and aquifer soils was investigated. The fraction of CA that was adsorbed on these materials increased as the solution pH decreased. Given that the solution pH can decrease dramatically in persulfate-based remedial systems, adsorption may reduce the ability of persulfate to oxidize CA. Overall, the results of this study provide important information about how persulfate can be used to remediate CA-contaminated sites. The results also indicate that the groundwater pH and geology of the subsurface can have a significant influence on the mobility of CA.

Autocatalytic Decomplexation of Cu(II)-EDTA and Simultaneous Removal of Aqueous Cu(II) by UV/Chlorine.

Traditional processes usually cannot enable efficient water decontamination from toxic heavy metals complexed with organic ligands. Herein, we first reported the removal of Cu(II)-EDTA by a UV/chlorine process, where the Cu(II)-EDTA degradation obeyed autocatalytic two-stage kinetics, and Cu(II) was simultaneously removed as CuO precipitate. The scavenging experiments and EPR analysis indicated that Cl• accounted for the Cu(II)-EDTA degradation at diffusion-controlled rate (∼1010 M-1 s-1). Mechanism study with mass spectrometry evidence of 11 key intermediates revealed that the Cu(II)-EDTA degradation by UV/chlorine was an autocatalytic successive decarboxylation process mediated by the Cu(II)/Cu(I) redox cycle. Under UV irradiation, Cu(I) was generated during the photolysis of the Cl•-attacked complexed Cu(II) via ligand-to-metal charge transfer (LMCT). Both free and organic ligand-complexed Cu(I) could form binary/ternary complexes with ClO-, which were oxidized back to Cu(II) via metal-to-ligand charge transfer (MLCT) with simultaneous production of Cl•, resulting in the autocatalytic effect on Cu(II)-EDTA removal. Effects of chlorine dosage and pH were examined, and the technological practicability was validated with authentic electroplating wastewater and other Cu(II)-organic complexes. This study shed light on a new mechanism of decomplexation by Cl• and broadened the applicability of the promising UV/chlorine process in water treatment.

An Alcohol Dehydrogenase from the Short-Chain Dehydrogenase/Reductase Family of Enzymes for the Lactonization of Hexane-1,6-diol.

Biocatalytic production of lactones, and in particular ϵ-caprolactone (CL), have gained increasing interest as a greener route to polymer building blocks, especially through the use of Baeyer-Villiger monooxygenases (BVMOs). Despite several advances in the field, BVMOs, however, still suffer several practical limitations. Alcohol dehydrogenase (ADH)-mediated lactonization of diols in turn has received far less attention and very few enzymes have been identified for the conversion of diols to lactones, with horse-liver ADH (HLADH) remaining the catalyst of choice. Screening of a diverse panel of ADHs, AaSDR-1, a member of the short-chain dehydrogenase/reductase family, was found to produce ϵ-caprolactone from hexane-1,6-diol. Moreover, cofactor regeneration by an NADH oxidase eliminated the requirement of co-substrates, yielding water as the sole by-product. Despite lower turnover frequencies as compared to HLADH, higher selectivity was found for the production of CL, with HLADH forming significant amounts of 6-hydroxyhexanoic acid and adipic acid through aldehyde dehydrogenation/oxidation of the gem-diol intermediates. Also, CL yield were shown to be dependent on buffer choice, as structural elucidation of a Tris adduct confirmed the buffer amine to react with aliphatic aldehydes forming a Schiff-base intermediate which through further ADH oxidation, forms a tricyclic acetal product.