Direct Chlorine Research Articles

Novel active chlorine based-mechanism for 1O2-dominated tetracycline hydrochloride electrocatalytic oxidation over N-doped MXene

Chloride ions (Cl−) as electrolyte contribute remarkably to electrocatalytic oxidation because of the by-production of active chlorine. Experiment and theoretical calculation were proposed to clarify the contribution of Cl− to TC degradation, the generation and contribution mechanism of active chlorine, and the mutual transformation of active species. DFT results showed the favorable adsorption and conversion of Cl− on Ti-N, Ti-O-N, and Ti-N-O sites of Ti3C2Tx@N-0.1, thereby facilitating the generation of active chlorine and improving the TC degradation. The limited effect of direct electrocatalytic degradation (leading to O2– and 1O2 accumulation) and active chlorine (e.g., HClO) oxidation was proved by quenching, EPR, and qualification test of active species. The secondary and dominant production of 1O2 from active chlorine conversion was greatly improved in Ti3C2Tx@N-0.1/electrocatalysis system and played a crucial role in TC removal. The mutual transformation of OH, O2–, and 1O2 from direct electrocatalysis and secondary active chlorine conversion also enriched the TC removal mechanism. This research provides novel insights into the influence of active chlorine on electrocatalytic oxidation and the underlying mechanism.

Mechanistic and kinetic aspects of florfenicol degradation by [rad]OH: Chloride moiety resistance

Antibiotic residues in aquatic environments can be effectively degraded by hydroxyl radical (OH)-based advanced oxidation processes (AOPs). However, the reaction kinetics and mechanisms have not been comprehensive determined due to the limitations of conventional competition kinetic methods and mass spectrometry-based product identification, as these methods fail to exclude interference from secondary radicals and are unable to capture unstable intermediates or transient species. In this study, these limitations were overcome using laser flash photolysis (LFP) and density functional theory (DFT) calculations, allowing accurate determination of the OH-initiated reaction kinetics and degradation mechanisms of florfenicol (FF), a model veterinary antibiotic compound that is frequently detected in the environment. Based on the LFP experiment results, the second order rate constant (k) between OH and FF was determined to be 1.96 × 109 M−1 s−1 by tracking the typical signal of (SCN)2−. Furthermore, DFT calculations revealed two distinct mechanisms for OH addition to the benzene ring and identified hydrogen atom abstraction (HAA) reaction from chiral carbons as being the most favorable initial reaction for OH. In addition, the destruction of chlorine moiety occurred via hydroxylation-chlorine abstraction, rather than direct chlorine abstraction or substitution reactions. The resistance of chlorine moiety to degradation during the initial oxidation process, resulted in the formation of chlorine-containing by-products. This study provided a novel approach to comprehensively investigate the mechanisms of emerging contaminants elimination during OH-based AOPs.

An Amiable Design of Cobalt Single Atoms as the Active Sites for Oxygen Evolution Reaction in Desalinated Seawater.

Green fuel from water splitting is hardcore for future generations, and the limited source of fresh water (<1%) is a bottleneck. Seawater cannot be used directly as a feedstock in current electrolyzer techniques. Until now single atom catalystswerereported by many synthetic strategies using notorious chemicals and harsh conditions. A cobalt single-atom (CoSA) intruding cobalt oxide ultrasmall nanoparticle (Co3 O4 USNP)-intercalated porous carbon (PC) (CoSA-Co3 O4 @PC) electrocatalystwassynthesized from the waste orange peel as a single feedstock (solvent/template). The extended X-ray absorption fine structure spectroscopy (EXAFS) and theoretical fitting reveal a clear picture of the coordination environment of the CoSA sites (CoSA-Co3 O4 and CoSA-N4 in PC). To impede the direct seawater corrosion and chlorine evolution the seawater has been desalinated (Dseawater) with minimal cost and the obtained PC is used as an adsorbent in this process. CoSA-Co3 O4 @PC shows high oxygen evolution reaction (OER) activity in transitional metal impurity-free (TMIF) 1M KOH and alkaline Dseawater. CoSA-Co3 O4 @PC exhibits mass activity that is 15 times higher than the commercial RuO2 . Theoretical interpretations suggest that the optimized CoSA sites in Co3 O4 USNPs reduce the energy barrier for alkaline water dissociation and simultaneously trigger an excellent OER followed by an adsorbate evolution mechanism (AEM).

Investigation of oxygen evolution reaction with 316 and 304 stainless-steel mesh electrodes in natural seawater electrolysis

Two commercially available stainless steel mesh substrates (316 SS and 304 SS) were evaluated as electrodes for oxygen evolution reaction (OER) in natural seawater electrolysis. The results show the 304 SS is less stable against corrosion under neutral (pH of 8.5) and low alkaline (0.1 M NaOH, pH of 12.8) seawater electrolytes because of the direct metal dissolution and chlorine evolution reaction (CER), and the 316 SS is superior to 304 SS in terms of electrocatalytic activity and resistance to corrosion under the same media. The performance of 304 SS is comparable to 316 SS under the high alkaline (1 M NaOH, pH of 13.7) seawater electrolyte, where the CER and metal dissolution are suppressed by OER. The overpotential for 304 and 316 SS is around 430 mV at 10 mA cm−2, and the Tafel slopes are below 50 mV dec−1 under the high alkaline (1 M NaOH) seawater electrolyte, showing promising performance. The poor resistance to corrosion of 304 SS is attributed to the low Mo content, and it is supposed that the stability of both 304 and 316 SS can be improved further with the addition of Mo content. This work expands on promising substrates for natural seawater electrolysis, with cost and performance advantages.

Revealing the mechanism of formation and transformation of chlorinated by‐products during electrolyzing synthetic urine using Ti/RuOx‐IrOx and BDD electrodes

AbstractIn this study, the mechanism of chlorinated by‐products (CBPs) formation and transformation during urine electrolysis was comparatively investigated with active and nonactive electrodes. It was found that nutrients removal and CBPs formation was dominated by the chlorine evolution on the active Ti/RuOx‐IrOx electrodes. CBPs formation was inhibited by the ammonia and urea chlorination and kept at a relatively low level before chlorination breakpoint. After the concentration of organic CBPs (OCBPs) increasingly reaching the maximum as a result of the peak concentration of free chlorine, most free chlorine transformed into inorganic chlorination by‐products (ICBPs) with the chlorate as the main species. In contrast, the formation of CBPs on boron‐doped diamond (BDD) electrodes was jointly dominated by the direct oxidation and chlorine mediated oxidation, which resulted in the complete degradation of OCBPs and the accumulation of ICBPs throughout the electrolysis. The organics with high molecular weight readily formed CBPs. Moreover, higher current density would accelerate the production of ICBPs on both electrodes, although it could mitigate OCBPs production at chlorination breakpoint for Ti/RuOx‐IrOx anodes. Separation of chloride ions and organics with high molecular weight from urine using nanofiltration was proposed to mitigate the production of CBPs.

Utilizing Spent Batteries to Fabricate Ni/ZnO-MnO2 Electrodes for Electrochemical Ammonia Oxidation

In this work, a novel Ni/ZnO-MnO2 electrode was fabricated by utilizing spent zinc-manganese batteries and then was applied to the electrochemical treatment of ammonia-containing wastewater. The obtained Ni/ZnO-MnO2 electrode was characterized by scanning electron microscopy, X-ray diffraction, and linear scanning voltammetry, suggesting that the fabricated electrode had a flower-like structure and showed high oxygen evolution potential and electrochemical activity. The electrochemical performance of the ZnO-MnO2 electrode in regard to ammonia removal and product selectivity was then investigated with different operating factors (i.e., electrolyte concentration, initial pH value, current density, and Cl− concentration), and the results indicated that the ammonia removal efficiency could reach 100% with a N2 selectivity of 91.8% under optimal conditions. Additionally, the mechanism of ammonia oxidation was proposed by cyclic voltammetry tests and active radical measurements, showing that ammonia was mainly oxidized via direct electron transfer, hydroxyl radicals, and active chlorine. Finally, the ZnO-MnO2 electrode was equipped for the treatment of actual pharmaceutical wastewater, results for which showed that ammonia could be completely removed with a current efficiency of 26.2% and an energy consumption of 52.7 kWh/kg N. Thus, the ZnO-MnO2 electrode prepared by recycling spent batteries is a promising anode for wastewater treatment.

Risk factors for recurrent positive results of the nucleic acid amplification test for COVID-19 patients: a retrospective study

Positive retests of COVID-19 represent a public health concern because of the increased risk of transmission. This study explored whether factors other than the nucleic acid amplification test (NAAT) contribute to positive retest results. Patients with COVID-19 admitted to the Guanggu district of the Hubei Maternal and Child Health Hospital between February 17 and March 28, 2020, were retrospectively included. The patients were grouped into the negative (n = 133) and positive (n = 51) retest groups. The results showed that the proportion of patients presenting with cough was higher (P < 0.001) and the proportion of patients with dyspnea was lower (P = 0.018) in the positive than in the negative retest group. The positive retest group showed shorter durations between symptom onset and hospitalization (P < 0.001) and symptom onset and the first positive NAAT (P = 0.033). The positive retest group had higher basophil counts (P = 0.023) and direct bilirubin (P = 0.032) and chlorine concentrations (P = 0.023) but lower potassium concentrations (P = 0.001) than the negative retest group. Multivariable regression analysis showed that coughing (OR = 7.59, 95% CI 2.28–25.32, P = 0.001) and serum chloride concentrations (OR = 1.38, 95% CI 1.08–1.77, P = 0.010) were independently associated with a positive retest result. Coughing and serum chloride concentrations were independent risk factors for positive NAAT retest results. Patients with a hospital stay of < 2 weeks or a short incubation period should stay in isolation and be monitored to reduce transmission. These results could help identify patients who require closer surveillance.

Stabilizer for the catalytic system of the direct chlorine processing of ethylene to 1,2-dichlorethane

Article is devoted to the research of the influence of the sodium salt of perfluoro sulfonic acid, as a stabilizer, on the catalytic activity of iron chloride and sodium chloride in the reaction of direct chlorination of ethylene to 1,2- dychloroethane. During research authors found that increase of stabilizer concentration up to 4% mas. had no significant impact on the

Mechanistic aspects of the gas-phase reactions of halobenzenes with bare lanthanide cations: a combined experimental/theoretical investigation.

The gas-phase reactions of chlorobenzene with all atomic lanthanide cations Ln(+) (except Pm(+) ) have been investigated by using Fourier transform ion cyclotron resonance mass spectrometry in conjunction with density functional theory calculations. According to the latter, a direct chlorine transfer to the lanthanide cation, which has been observed previously for fluorine abstraction from fluorobenzene, is not operative for the C6 H5 Cl/Ln(+) couples; rather, chlorine transfer proceeds through an initial coordination of the lanthanide cation to the aromatic ring of the substrate. Both, the product distribution and the chlorine abstraction efficiencies are affected by the bond dissociation energy (BDE(Ln(+) Cl)) as well as the promotion energies of Ln(+) to attain a 4f(n) 5d(1) 6s(1) configuration. In addition, mechanistic aspects of some CH and CC bond activations are presented. Where appropriate, comparison with the previously studied C6 H5 F/Ln(+) systems is made.

Catalytic formation of 2,3,3,3-tetrafluoropropene from 2-chloro-3,3,3-trifluoropropene at fluorinated chromia: A study of reaction pathways

The catalytic gas phase reaction between CF3CClCH2 with HF yielding CF3CFCH2 was investigated regarding the reaction pathways involved. Different from the reaction under liquid phase (homogenous) conditions, in heterogeneous phase CF3CClCH2 does not add HF forming the saturated intermediate CF3CFClCH3 but undergoes direct Cl/F exchange at the starting olefin molecule resulting directly in the formation of CF3CFCH2. This might be caused mainly by the fact that under heterogeneous gas phase conditions higher temperatures are needed as compared to liquid phase conditions thus suppressing the formation of kinetically less stable CF3CFClCH3 under these conditions. Since for all the reaction steps involved in this complex reaction system the Gibbs free reaction enthalpy values are close to zero [1], the selectivity towards several reaction products is strongly dependent on the reaction parameters, e.g. temperature, pressure and molar ratio of the reactants. Based on the catalytic data obtained for fluorinated chromia as catalyst, a reaction path distinguishing direct chlorine against fluorine exchange versus hydrofluorination/dehydrochlorination is proposed.

The mechanistic study of the hydroxyl radical reaction with trans-2-chlorovinyldichloroarsine.

The trans-2-chlorovinyldichloroarsine (Lewisite) was produced and handled during WWI and WWII as chemical warfare agents. It was very difficult to explore its chemical characterization by experiments ways. The quantum chemical calculations proved to be a precise and harmless method for the toxicological system. In this paper, the gas phase reaction mechanisms of OH radical with trans-2-chlorovinyldichloroarsine (lewisite) were studied by second-order Møller-Plesset perturbation theory (MP2) method. The geometries of reactants, products, complexes, and transition states were optimized at the MP2/6-311++G(d,p) level. To gain more accurate mechanistic knowledge, the single-point energies were calculated using G3 and CCSD(T) method. This reaction exhibited three mechanisms, namely, direct hydrogen abstraction, direct chlorine abstraction, and addition/elimination. Multichannel Rice-Ramsperger-Kassel-Marcus theory and transition-state theory have been carried out for overall and individual rate constants over a wide range of temperatures and pressures. The computational results indicated that addition/elimination reaction is more favorable than direct hydrogen abstraction and direct chlorine abstraction. The major products for the total reaction are AsCl2 and CHClCH2O generated via C(2)-addition/elimination.

Development of a vaporization system for direct determination of chlorine in petroleum coke by ICP-MS

An electrothermal vaporization system (ETV) was developed for direct chlorine (Cl) determination in petroleum coke by inductively coupled plasma mass spectrometry (ICP-MS). The ETV system consists of a high power lamp enclosed in glass chamber equipped with solenoid valves. The system is controlled by a printed circuit board and software developed in LabVIEW environment. The temperature and heating time were optimized. Solenoid valves were used to control the flow of Ar (carrier gas) during pyrolysis and vaporization steps. Pyrolysis and vaporization temperatures were set at 350°C and 900°C, respectively; while the Ar flow rate was 1.20lmin−1 and the plasma power 1300W. Up to 5mg of petroleum coke sample can be analyzed. Calibration was carried out by standard addition whereas a certified reference material of coal (SARM 19) was used for that purpose. The relative standard deviation was lower than 9% (n=4) and the limit of quantification (10s) of Cl was 3.5μgg−1. Results obtained for chlorine in petroleum coke sample were in agreement with those obtained using other validated methods for Cl determination. The time of analysis (approximately 2min per sample), risk of contamination, analyte losses and waste generation are drastically reduced in comparison with techniques that require sample digestion for chlorine determination.

Direct chlorine determination in crude oils by energy dispersive X-ray fluorescence spectrometry: An improved method based on a proper strategy for sample homogenization and calibration with inorganic standards

Official guidelines to perform chlorine determination in crude oil are (i) American Society for Testing and Materials (ASTM) D6470, which is based on the extraction of water from the oil and subsequent determination of the chloride by potentiometry, (ii) ASTM D3230, that measures the conductivity of a solution of crude oil in a mixture of organic solvents and (iii) US Environmental Protection Agency (EPA) 9075 that uses energy dispersive X-ray fluorescence spectrometry to quantify chlorine and it is applicable for the range from 200 μg g − 1 to percent levels of the analyte. The goal of this work is to propose method to quantify lower amounts of chlorine in crude oil using energy dispersive X-ray fluorescence spectrometry using a simple calibration strategy. Sample homogenization procedure was carefully studied in order to enable accurate results. The calibration curve was made with standards prepared by diluting aqueous NaCl standard in glycerin. The method presented a linear response that covers the range from 8 to at least 100 μg g − 1 of chlorine. Chlorine in crude oil samples from Campos Basin – Brazil were quantified by the proposed method and by potentiometry after extraction of chlorine from the oil. Results achieved using both methods were statistically the same at 95% confidence level.

Direct Compound-Specific Stable Chlorine Isotope Analysis of Organic Compounds with Quadrupole GC/MS Using Standard Isotope Bracketing

A method has been developed for the direct determination of the stable chlorine isotope composition (delta(37)Cl) of organochlorines that eliminates sample preparation, achieves precision comparable to earlier techniques while improving the sensitivity, and makes use of benchtop gas chromatography-quadrupole mass spectrometry instruments (GCqMS). The method is based on the use of multiple injections (n = 8-10) of the sample, bracketed by a molecularly identical isotopic standard with known delta(37)Cl, determined using off-line thermal ionization mass spectrometry (TIMS). Mass traces of two isotopologues differing by one chlorine isotope were used to calculate delta(37)Cl values. Optimization of mass spectrometry and peak integration parameters as well as method validation was achieved using tetrachloroethene (PCE), p,p'-dichlorodiphenyltrichloroethane (DDT), and pentachlorophenol (PCP), spanning a delta(37)Cl range of -5.5 to +3.2 per thousand vs SMOC. Injecting 1.6-1100 pmol resulted in standard deviations (1sigma) of 0.6-1.3 per thousand, and the delta(37)Cl results agreed with values independently measured with TIMS. The method was tested by determining the Rayleigh fractionation during evaporation of pure liquid PCE, resulting in a chlorine isotopic enrichment factor of epsilon(Cl) = -1.1 +/- 0.4 per thousand. Furthermore, position-specific delta(37)Cl analysis based on analysis of DDT mass fragments was evaluated. The GCqMS-delta(37)Cl method offers a simplified yet sensitive approach for compound-specific chlorine isotope analysis.

Optimization of the intermittent chlorine injection (ICI) method for seawater desalination RO plants

The major trouble in the RO method of seawater desalination is biological fouling (biofouling) by microorganism multiplication. By carrying out direct chlorine sterilization of the RO membrane with an intermittent chlorine injection (ICI) method, biofouling trouble is eliminated. In this work, change of characteristics of a cellulose triacetate (CTA) membrane in the case of chlorine injection to seawater containing heavy metals was established quantitatively by experiments and development of a performance prediction formula for the CTA membrane. In addition, the validity of the performance prediction formula was verified by comparing with the actual performance change in the desalination plants. Finally, optimization of ICI condition was attained by using this newly established prediction formula.

Elimination of biological fouling in seawater reverse osmosis desalination plants

The main trouble in the RO method of seawater desalination is biological fouling (bio-fouling) from microorganism growth. In this work, the growth rate of microorganisms in the Red Sea and sterilization by chlorine injection were measured and quantified. Furthermore, actual demonstration of RO pilot tests using cellulose tri-acetate (CTA) RO membranes with chlorine resistance was performed in RO plants where bio-fouling actually occurred. By carrying out direct chlorine sterilization of the RO membrane with an intermittent chlorine injection method, bio-fouling was eliminated. The combination of the CTA membrane and chlorine injection successfully prevented increases of differential pressure and stabilized product water quantity and quality.

Photocatalytic Removal of Pesticide Dichlorvos from Indoor Air: A Study of Reaction Parameters, Intermediates and Mineralization

This paper presents for the first time the investigation of TiO2 photocatalysis for the removal of pesticides in gas phase. Dichlorvos was used as a model pesticide, and experiments were carried out using both static and dynamic reaction systems to explore the different aspects of the process. Thus, adsorption, reaction kinetics, and the influence of several operational parameters such as relative humidity (RH), inlet concentration, flow rate, and association of TiO2 with activated carbon (AC) were all examined in detail. Furthermore, a special attention was devoted to the analysis of reaction products by means of various analytical techniques such as Fourier transform infrared spectroscopy, automated thermal desorption technique coupled to gas chromatography-mass spectrometry instrument, gas chromatography equipped with a pulse discharge helium photoionization detector, and ion chromatography. The results showed an immediate and total removal of dichlorvos at ppbv levels (50-350 ppbv) along with a high mineralization extent (50-85%) into harmless final products (CO2, HCl, PO43-). Moreover, RH was found to significantly affectthe mineralization extent and the formation of reaction intermediates. On the basis of identification data, direct charge transfer and chlorine radical (Cl*) attack were shown to play a key role in the reaction mechanism at low RH, whereas at high RH, HO* radicals were the predominant active species.

Trichloroethene Degradation by UV/H2O2 Advanced Oxidation Process: Product Study and Kinetic Modeling

The broadband UV irradiation of 1.1 mM trichloroethene (TCE) aqueous solution in the presence of 10.4 mM H2O2 resulted in formic, oxalic, dichloroacetic (DCA), and monochloroacetic (MCA) acids, as organic byproducts. The organic chlorine was converted completely to chloride ion as a final product. TCE and its degradation products were completely mineralized in 30 min, under a volume-averaged UV-C irradiant power of 35.7 W/L from a 1 kW medium-pressure mercury vapor arc lamp. TCE degraded primarily through hydroxyl radical-induced reactions and onlyto a low extentthrough direct UV photolysis and chlorine atom-induced chain reactions. The experimental patterns of TCE, H2O2, and detected reaction products combined with the literature information on radical reactions in the aqueous phase were used to postulate a degradation mechanism and to develop a kinetic model to predict the TCE decay, formation and degradation of byproducts, and pH and oxygen profiles. The agreement between the model calculations and the experimental data is satisfactory.

Theoretical study of the dechlorination reaction pathways of octachlorodibenzo-p-dioxin.

The dechlorination reaction pathways of 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD) by the hydrogen atom are investigated by the density-functional theory B3PW91 method. The dechlorination reactions have large exothermicity and small activation energies. The activation energies (approximately 5 kcal/mol) of the sigma-complex formation due to the hydrogen addition are lower than those (approximately 9 kcal/mol) of the direct chlorine abstraction. It is suggested that the sigma-complex plays an important role in the reactions, although it has scarcely been shown in previous studies of the dechlorination of dioxins. The sigma-complex formation is favored at low temperatures and the chlorine abstraction is favored at high temperatures. Furthermore, it is found that the lateral positions have a marginal preference over the longitudinal positions. The dechlorination of OCDD by the hydrogen atom is thus not likely to result in a dominant formation of the laterally substituted toxic congeners.

Theoretical study on chlorine and hydrogen shift in cycloheptatriene and cyclopentadiene derivatives.

The transition structures (TSs) for chlorine 1,7-shift and 1,5-shift in 1,7,7-trichlorocycloheptatriene (1) and those of chlorine 1,5-shifts in 1,5,5-trichlorocyclopentadiene (3) and 1,2,5-trichloro-1,3-pentadiene (5) derivatives have been located with density functional theory (DFT) at the Becke3LYP/6-311G [and Becke3LYP/6-311+G] level. The calculational results were compared with those for corresponding hydrogen shifts in nonsubstituted molecules (cycloheptatriene (2), cyclopentadiene (4), and 1,3-pentadiene (6)). The following points were clarified: (1) The activation energy (Delta E(++)) for chlorine 1,7-shift in 1 was evaluated to be only +50.1 [+49.2] kJ/mol, which is smaller than that (+69.9 [+68.3]) for a 1,5-shift, supporting the theory that the conversion between two equivalent A and A' proceeds through a TS for direct chlorine 1,7-shift (Figure 1), rather than through a TS for a 1,5-shift (Figure 2). (2) The considerable amount of charge separation between a migrating chlorine atom (Cl(m)) and a seven-membered ring (-0.53 and +0.47 for Merz-Singh-Kollman scheme) occurs in a chlorine 1,7-shift, which is in good contrast to the result that the migrating hydrogen atom (H(m)) for a 1,7-shift in cycloheptatriene (2) carries almost no charge (Figure 3). This large charge separation can stabilize the TS for the chlorine 1,7-shift pathway. (3) The Delta E(++) values for suprafacial hydrogen 1,7-shift in 2 are quite large (+288.0 [+284.8] kJ/mol), much larger than that (+166.8 [+167.0]) for a 1,5-shift in 4 which is orbital symmetrically allowed (Figure 3). The calculation suggests that the chlorine 1,7-shift in 1 occurs easily at room temperature (actually observed experimentally) by proceeding via concerted suprafacial 1,7-shift through the zwitterionic TS with the significant assistance of Coulomb interaction between charged fragments (negatively charged chlorine atom and positively charged tropylium ring), rather than via a suprafacial 1,5-sigmatropic pathway. Other cases studied in this paper showed usual results predicted by orbital symmetrical consideration.