Oxyanions Of Chlorine Research Articles

Equatorial Perturbation Driven Reaction Bifurcation in Non‐Heme Iron Complexes for Chlorite Oxidation

AbstractChlorine oxyanions have various applications, such as bleaching and oxidizers in rocket fuels. However, their high solubility in water and long environmental lifetimes have led to ecological concerns, especially regarding drinking water quality. This study focuses on the conversion of chlorite to chlorine dioxide, which is of significant interest as it exhibits superior antimicrobial activity and generates less harmful byproducts for water treatment. Two nonheme iron(II) complexes capable of producing chlorine dioxide from chlorite at room temperature and pH 5.0 are presented. These complexes oxidize chlorite through high‐valent iron (IV)‐oxo intermediates formed in‐situ. The study establishes second‐order rate constants for chlorite oxidation and investigates the effects and mechanisms involved by substituting a methyl group in the secondary coordination sphere of the FeIV(O)(N4Py) system. By employing kinetic analysis and spectroscopic investigations, the crucial elements for the reaction mechanism in chlorite oxidation are identified. These findings pave the way for future advancements in this field.

Investigation of black phosphorus anodic catalyst for electrolysis: Degradation of organics via a perchlorate-free oxidant activation

This study investigated the potential of a novel fabricated black phosphorus (BP) nanoparticle electrode as an alternative to noble metal-based catalysts for application in electrolysis. The BP electrode was compared with other conventional catalysts (boron-doped diamond (BDD) and a dimensional stable electrode (DSA)) under different electrolyte conditions for the generation of specific oxidants (e.g., OH•, HOCl, OCl−, SO4• -) in the bulk phase during electrolysis. In the presence of sulfate-based electrolyte, results on the electrochemical oxidation showed that the BP not only resulted in an 8-fold increase in the current efficiency compared to DSA, but also reduced energy consumptions by approximately 30-fold. Moreover, electrolysis using certain electrodes (i.e., BDD) under high current densities in the presence of chlorine-based electrolyte has been reported to be hazardous to the water system due to the generation of toxic chlorine oxyanions (i.e., perchlorate), which necessitates the operation of a post-treatment process. Likewise, application of the BDD electrode was confirmed to produce perchlorate under high current densities, while no by-product was generated by electrolysis with the BP electrode. Finally, multiple degradation pathways for selective water treatment was monitored under oxidation with the BP electrode. To the best of our knowledge, this study is the first to apply the novel fabricated BP electrode as the anodic catalyst for the treatment of a water system.

Characterization of oxyanions of chlorine by multipath titrimetric approach for drinking water quality control

The analysis of oxyanions, perchlorate, chlorate, chlorite and hypochlorite ions, is of interest, especially from the viewpoint of evaluating drinking water quality. Instrumental analyses are generally performed to quantify them, and require a standard solution of corresponding ions; however, no standard solutions characterized by a metrologically valid procedure have existed. In the present study, perchlorate, chlorate and chlorite ions were characterized by performing multipath titration techniques. This technique is an approach to determine the amount of substances in chemicals by employing different stoichiometric reactions. It has decreased the risk and the contribution of unknown biases that each measurement method has, and gives further reliable results than those based on a conventional single titration method. The comprehensive evaluation of the measurement uncertainties for these assays was carried out, resulting in the establishment of the measurement methodologies for oxyanion standards.

Adsorption of chlorine oxyanions, as water disinfectant by-products, on graphene flakes: A quantum chemical investigation

Chlorine oxyanions namely: hypochlorite ClO-, chlorite ClO2-, chlorate ClO3-, and perchlorate ClO4-, are considered to be harmful for public health since they are disinfectant by-products and are usually found in the disinfection process of drinking water treatment plants (DWTPs). The removal of these oxyanions is, therefore, an important demand. In the current work, the adsorption of chlorine oxyanions on some graphene flakes (Gr) such as coronene (C24H12), circumcoronene (C54H18), and circumcircumcoronene (C96H24), has been theoretically investigated. Favorable adequate (anion-π) interaction between the chlorine oxyanions and the electron-rich graphene flakes have been elucidated, where the stabilization largely originates from attractive electrostatic and dispersion effects. The exponential increase in the attractive electrostatic and dispersion components of the adsorption energies is found to be, in part, a consequence of a charge transfer contribution from the oxygen lone pairs of electrons of oxyanions (donors) to the low-lying π*-orbitals of graphene flakes (acceptors). This finding means that the favorable anion−π interaction between a chlorine oxyanion and a graphene surface is not purely non-covalent.

Unexpected favourable noncovalent interaction between chlorine oxyanions (ClOx−; x = 1–4) and benzene: Benchmarking DFT and SAPT methods with respect to CCSD(T)

The noncovalent interaction between chlorine oxyanions, namely: (hypochlorite (ClO−), chlorite (ClO2−), chlorate (ClO3−), and perchlorate (ClO4−), and benzene block is explicitly investigated and analyzed theoretically. The performance of a variety of DFT functionals and their dispersion-corrected DFT-D3 functionals as well as various wavefunction-based SAPT methods for the prediction of noncovalent interaction energies of C6H6–ClOx− (x = 1–4) complexes is justified in comparison with the benchmark CCSD(T)/CBS method. The results showed that benzene can form stable hydrogen-bond complexes of moderate strength with chlorine oxyanions. Moreover, the existence of favorable anion-π interactions between chlorine oxyanions and benzene π-system was demonstrated, which is predominantly attributed to attractive dispersion effects that depend on both the anion polarizability and the binding distance. It is worth mentioning that the origin of the binding energy in the studied complexes was found to be attributed in 68–74% to dispersion interaction. The sSAPT0/aVDZ method is found to perform qualitatively well for the prediction of the variation trends for the interaction energy components, compared to the computationally expensive, though provided the most accurate performance, SAPT2+(CCD)δMP2/aVTZ method. The D3-corrected DFT functionals showed good overall performance, particularly those of M06-2X, TPSS, PBE, and B3LYP.

Perchlorate ion standard solution: multipath titrimetric approach using three different stoichiometric reactions—towards the establishment of SI traceable chemical standards

Analyses of chloride ions, and oxyanions of chlorine named hypochlorite, chlorite, chlorate and perchlorate ions, are of interest especially in the fields of controlling water and food qualities. Some of them do not exist as a certified reference material characterized by a metrologically valid procedure, and the lack of the standards currently creates problems with the instrumental analyses. This paper describes an accurate multipath titrimetric determination technique for potassium perchlorate to establish the perchlorate ion standard solution as a certified reference material: acidimetric coulometric titration with cation exchange resin, oxidation-reduction gravimetric titration, and precipitation gravimetric titration. The gravimetric titrations and the coulometric titration are capable of ensuring the traceability of the mass fraction of perchlorate ions and cations in potassium perchlorate respectively to the International System of Units. The comprehensive evaluation of the uncertainties for potassium perchlorate assays was carried out, resulting in the establishment of the standard for perchlorate determinations.

Determination of chlorine species by capillary electrophoresis - mass spectrometry.

The applicability of CZE with mass spectrometric detection for the determination of four chlorine species, namely chloride and three stable chlorine oxyanions, was studied. The main aspects of the proper selection of BGE and sheath liquid for the CE-MS determinations of anions with high mobility were demonstrated, pointing out the importance of pH and the mobility of the anion in the BGE. The possibility of using uncoated fused silica capillary and common electrolytes for the separation was shown and the advantage of using extra pressure at the inlet capillary end was also presented. The linear range was found to be 1-100µg/mL for ClO3- and ClO4- , 5-500µg/mL for ClO2- , and 25-500µg/mL for Cl- , but the sensitivity can be greatly improved if larger sample volume is injected and electrostacking effect is utilized. The LOD for ClO3- in drinking water was 6ng/mL, when very large sample volume was injected (10000 mbar·s was applied).

Characterizing Isozymes of Chlorite Dismutase for Water Treatment.

This work investigated the potential for biocatalytic degradation of micropollutants, focusing on chlorine oxyanions as model contaminants, by mining biology to identify promising biocatalysts. Existing isozymes of chlorite dismutase (Cld) were characterized with respect to parameters relevant to this high volume, low-value product application: kinetic parameters, resistance to catalytic inactivation, and stability. Maximum reaction velocities (Vmax) were typically on the order of 104 μmol min-1 (μmol heme)-1. Substrate affinity (Km) values were on the order of 100 μM, except for the Cld from Candidatus Nitrospira defluvii (NdCld), which showed a significantly lower affinity for chlorite. NdCld also had the highest susceptibility to catalytic inactivation. In contrast, the Cld from Ideonella dechloratans was least susceptible to catalytic inactivation, with a maximum turnover number of approximately 150,000, more than sevenfold higher than other tested isozymes. Under non-reactive conditions, Cld was quite stable, retaining over 50% of activity after 30 days, and most samples retained activity even after 90–100 days. Overall, Cld from I. dechloratans was the most promising candidate for environmental applications, having high affinity and activity, a relatively low propensity for catalytic inactivation, and excellent stability.

Assessment of the impact of chloride on the formation of chlorinated by-products in the presence and absence of electrochemically activated sulfate

Boron-doped diamond anodes are widely used for electrochemical oxidation of contaminants, due to their excellent capability to form hydroxyl radicals as well as inorganic radicals such as chloride, phosphate, and sulfate radicals, electrogenerated when their corresponding anions are present in the influent water. Addition of sulfate increases the electrooxidation rates of organic pollutants at boron-doped diamond (BDD) anode. However, the effect of chloride on the electrooxidation is considered to be less straightforward. The anodic oxidation of chloride yields chlorine and hypochlorous acid/hypochlorite, besides chloride radicals, and may form toxic chlorine oxyanions at higher applied potentials. The present study investigates such implications of chloride ions to the electrooxidation of a natural organic matter surrogate, resorcinol, in the presence of sulfate. The presence of sulfate yielded up to eightfold enhancement in the removal of resorcinol and total organic carbon (TOC) at both acidic and neutral pH. Chloride addition to Na2SO4 inhibited the resorcinol oxidation and mineralization, whereas it enhanced resorcinol oxidation in NaNO3. However, sulfate inhibited the electrogeneration of chlorinated organics by ∼2–4 folds compared to nitrate at low chloride concentrations (i.e., [SO42−]:[Cl−]>1). Although increasing the pH from pH 2 to pH 7 yielded a two times lower amount of chlorinated organics, electrolysis in Na2SO4 anolyte enhanced the generation of undesired chlorate and perchlorate at both acidic and neutral pH.

Microbial respiration with chlorine oxyanions: diversity and physiological and biochemical properties of chlorate- and perchlorate-reducing microorganisms.

Chlorine oxyanions are valuable electron acceptors for microorganisms. Recent findings have shed light on the natural formation of chlorine oxyanions in the environment. These suggest a permanent introduction of respective compounds on Earth, long before their anthropogenic manufacture. Microorganisms that are able to grow by the reduction of chlorate and perchlorate are affiliated with phylogenetically diverse lineages, spanning from the Proteobacteria to the Firmicutes and archaeal microorganisms. Microbial reduction of chlorine oxyanions can be found in diverse environments and different environmental conditions (temperature, salinities, pH). It commonly involves the enzymes perchlorate reductase (Pcr) or chlorate reductase (Clr) and chlorite dismutase (Cld). Horizontal gene transfer seems to play an important role for the acquisition of functional genes. Novel and efficient Clds were isolated from microorganisms incapable of growing on chlorine oxyanions. Archaea seem to use a periplasmic Nar-type reductase (pNar) for perchlorate reduction and lack a functional Cld. Chlorite is possibly eliminated by alternative (abiotic) reactions. This was already demonstrated for Archaeoglobus fulgidus, which uses reduced sulfur compounds to detoxify chlorite. A broad biochemical diversity of the trait, its environmental dispersal, and the occurrence of relevant enzymes in diverse lineages may indicate early adaptations of life toward chlorine oxyanions on Earth.

Performance of Ti/Pt and Nb/BDD anodes for dechlorination of nitric acid and regeneration of silver(II) in a tubular reactor for the treatment of solid wastes in nuclear industry

One of the problems frequently encountered in the processing of nuclear fuels is the recovery of plutonium contained in various solid wastes. The difficulty is to make soluble the plutonium present as the refractory oxide PuO2. The dissolution of this oxide in nitric acid solutions is easily performed by means of silver(II) a strong oxidizing agent which is usually electrochemically generated on a platinum anode. However, certain solid residues that must be treated to separate actinides contain important quantities of chloride ions that require after dissolution in nitric acid a preliminary electrochemical step to be removed before introducing Ag(I) for Ag(II) electrogeneration. Research is conducted to find electrocatalytic materials being able to replace massive platinum in view to limit capital costs. In the present work a set-up including a two-compartment tubular reactor with recirculation of electrolytes was tested with anodes made of boron doped diamond coated niobium (Nb/BDD) and platinum coated titanium (Ti/Pt) grids for the removal of chlorides (up to 0.1 M) and for silver(II) regeneration. The study showed that these two anodes are effective for the removal of chlorides contained in 6 M HNO3 solution as gaseous chlorine, without producing the unwanted oxyanions of chlorine. Furthermore, the regeneration rate of silver(II) on Nb/BDD anode is approximately equal to that obtained on Ti/Pt anode for the same hydrodynamic conditions in the tubular reactor. Accordingly, dechlorination as well as silver(II) regeneration can be performed in the same reactor equipped either with a Nb/BDD or a Ti/Pt anode. Besides, the service life of Nb/BDD anodes estimated by accelerated life tests conducted in 6 M HNO3 can be considered as very satisfactory compared to that observed with Ti/Pt anodes.

Understanding Chlorite, Chlorate and Perchlorate Formation When Generating Hypochlorite Using Boron Doped Diamond Film Electrodes

This research used density functional theory for investigating reactions on boron doped diamond (BDD) film electrodes that contribute to unwanted byproduct formation during hypochlorite generation. Clusters containing 10 carbon atoms were used to simulate the diamond electrode surface. The simulations included reactions with hydrogen terminated surfaces, and with surface sites produced by anodic polarization, namely: ≡C•, =C•H, ≡C-O• and =CH-O•. The activation energies for oxidation of chlorine oxyanions via direct electron transfer and via reaction with hydroxyl radicals were calculated. Oxychlorine radicals (ClO•, ClO2 •, ClO3 •) were found to chemically adsorb to both secondary and tertiary carbon atoms on the BDD surface. These chemisorbed intermediates could react with hydroxyl radicals to regenerate the original chlorine oxyanion (ClO−, ClO2 −, ClO3 −), and produce ≡C-O• and =CH-O• sites on the BDD surface. The ≡C-O• and =CH-O• sites also reacted with oxychlorine radicals to form chemisorbed intermediates, which could then be converted to higher oxidation states (ClO2 −, ClO3 −, ClO4 −) via reaction with hydroxyl radicals.

Behavioral response of dissimilatory perchlorate-reducing bacteria to different electron acceptors

The response behavior of three dissimilatory perchlorate-reducing bacteria to different electron acceptors (nitrate, chlorate, and perchlorate) was investigated with two different assays. The observed response was species-specific, dependent on the prior growth conditions, and was inhibited by oxygen. We observed attraction toward nitrate when Dechloromonas aromatica strain RCB and Azospira suillum strain PS were grown with nitrate. When D. aromatica and Dechloromonas agitata strain CKB were grown with perchlorate, both responded to nitrate, chlorate, and perchlorate. When A. suillum was grown with perchlorate, the organism responded to chlorate and perchlorate but not nitrate. A gene replacement mutant in the perchlorate reductase subunit (pcrA) of D. aromatica resulted in a loss of the attraction response toward perchlorate but had no impact on the nitrate response. Washed-cell suspension studies revealed that the perchlorate grown cells of D. aromatica reduced both perchlorate and nitrate, while A. suillum cells reduced perchlorate only. Based on these observations, energy taxis was proposed as the underlying mechanism for the responses to (per)chlorate by D. aromatica. To the best of our knowledge, this study represents the first investigation of the response behavior of perchlorate-reducing bacteria to environmental stimuli. It clearly demonstrates attraction toward chlorine oxyanions and the unique ability of these organisms to distinguish structurally analogous compounds, nitrate, chlorate, and perchlorate and respond accordingly.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-009-2051-3) contains supplementary material, which is available to authorized users.

Ubiquity and diversity of dissimilatory (per)chlorate-reducing bacteria.

Environmental contamination with compounds containing oxyanions of chlorine, such as perchlorate or chlorate [(per)chlorate] or chlorine dioxide, has been a constantly growing problem over the last 100 years. Although the fact that microbes reduce these compounds has been recognized for more than 50 years, only six organisms which can obtain energy for growth by this metabolic process have been described. As part of a study to investigate the diversity and ubiquity of microorganisms involved in the microbial reduction of (per)chlorate, we enumerated the (per)chlorate-reducing bacteria (ClRB) in very diverse environments, including pristine and hydrocarbon-contaminated soils, aquatic sediments, paper mill waste sludges, and farm animal waste lagoons. In all of the environments tested, the acetate-oxidizing ClRB represented a significant population, whose size ranged from 2.31 x 10(3) to 2.4 x 10(6) cells per g of sample. In addition, we isolated 13 ClRB from these environments. All of these organisms could grow anaerobically by coupling complete oxidation of acetate to reduction of (per)chlorate. Chloride was the sole end product of this reductive metabolism. All of the isolates could also use oxygen as a sole electron acceptor, and most, but not all, could use nitrate. The alternative electron donors included simple volatile fatty acids, such as propionate, butyrate, or valerate, as well as simple organic acids, such as lactate or pyruvate. Oxidized-minus-reduced difference spectra of washed whole-cell suspensions of the isolates had absorbance maxima close to 425, 525, and 550 nm, which are characteristic of type c cytochromes. In addition, washed cell suspensions of all of the ClRB isolates could dismutate chlorite, an intermediate in the reductive metabolism of (per)chlorate, into chloride and molecular oxygen. Chlorite dismutation was a result of the activity of a single enzyme which in pure form had a specific activity of approximately 1,928 micromol of chlorite per mg of protein per min. Analyses of the 16S ribosomal DNA sequences of the organisms indicated that they all belonged to the alpha, beta, or gamma subclass of the Proteobacteria. Several were closely related to members of previously described genera that are not recognized for the ability to reduce (per)chlorate, such as the genera Pseudomonas and Azospirllum. However, many were not closely related to any previously described organism and represented new genera within the Proteobacteria. The results of this study significantly increase the limited number of microbial isolates that are known to be capable of dissimilatory (per)chlorate reduction and demonstrate the hitherto unrecognized phylogenetic diversity and ubiquity of the microorganisms that exhibit this type of metabolism.

Size, shape and charge effects in the partial molal volume, compressibility and electrostriction behaviour of sulphur and chlorine oxyanions in water

Ionic size, shape and charge effects in the interaction of a series of Cl and S oxyanions with water have been investigated by means of apparent molal volume and adiabatic compressibility measurements. Electrostriction volumes have been calculated from the partial molal volumes of the ions at infinite dilution using intrinsic ionic volumes evaluated by four methods which are critically compared. The evaluation of reliable intrinsic volumes of oxyanions with corrections for the dead-space in packing is shown to be a major problem in derivation of electrostriction volumes and in interpretation of the volumetric behaviour of oxyanions in solution.A relation between electrostriction volumes and compressibilities of ions is demonstrated and compared with the results of earlier a priori calculations. Both the compressibilities and partial molal volumes of the series of oxyanions and simple halide ions are almost linearly related to the respective standard entropies of solution of these ions.

The pitting corrosion of copper tubes in hot water

The electrode potential of copper tube used in hot water distribution system in buildings rises gradually with time of exposure and then attains to a critical value of pitting potential after a long incubation period. The process of potential rise proceeds in two stages. The first stage is the formation of a cuprous oxide layer in the potential range ≦ 60 mV(SCE) and the second stage is due to the reactions of chlorite ions accumulated in the cuprous oxide layer in the potential range > 60 mV(SCE). Oxyacids and oxyanions of chlorine formed in the water, to which chlorine gas or hypochlorite was added for sterilizing process, accelerate the formation of cuprous oxide layer in the first stage, and the reaction of chlorite ions increase the electrode potential of copper tube in the second stage.

Cl-LII,III fluorescent x-ray spectra measurement and analysis for the molecular orbital structure of ClO4−, ClO3−, and ClO2−

The chlorine LII, III low energy x-ray spectra from sodium perchlorate, chlorate and chlorite have been obtained using carbon Kα (277 eV) photon excitation and a lead myristate analyzing ’’crystal’’ (2d=80 A). X-ray induced decomposition was observed for each of these compounds. By taking repeated spectral scans, systematically distributed over six samples, it was possible to extrapolate to ’’zero-dose’’ Cl-LII, III spectra. A specially developed least-squares fitting program was applied to precisely determine the energy and strength of each spectral component which utilized the known collimation and crystal broadening functions and yielded energy resolutions of less than 1 eV. Broad low-energy satellite structures were observed for all the oxy-anions and for chloride (NaCl) and have been compared to similar satellites as measured in the Ar-LII, III spectrum. These structures were thus identified as resulting from multielectron processes. The other peaks in the Cl-LII, III spectra of the oxy-anions could be understood as corresponding to transitions from molecular orbitals with Cl 3s or 3d character. These results have demonstrated that 3d orbitals do play a definite role in the formation of chemical bonds in the oxy-anions of chlorine and that the importance of this role increases with the oxidation state of the chlorine. Satisfactory correlations have been obtained with the complementary Kβ x-ray emission and photoelectron spectra and with molecular orbital theory for the same anions.