Decomposition Of Trichloroethylene Research Articles

A multiple Kirkendall strategy for converting nanosized zero-valent iron to highly active Fenton-like catalyst for organics degradation

Nanosized zero-valent iron (nZVI) is a promising persulfate (PS) activator, however, its structurally dense oxide shell seriously inhibited electrons transfer for O-O bond cleavage of PS. Herein, we introduced sulfidation and phosphorus-doped biochar for breaking the pristine oxide shell with formation of FeS and FePO4-containing mixed shell. In this case, the faster diffusion rate of iron atoms compared to shell components triggered multiple Kirkendall effects, causing inward fluxion of vacancies with further coalescing into radial nanocracks. Exemplified by trichloroethylene (TCE) removal, such a unique "lemon-slice-like" nanocrack structure favored fast outward transfer of electrons and ferrous ions across the mixed shell to PS activation for high-efficient generation and utilization of reactive species, as evidenced by effective dechlorination (90.6%) and mineralization (85.4%) of TCE. [Formula: see text] contributed most to TCE decomposition, moreover, the SnZVI@PBC gradually became electron-deficient and thus extracted electrons from TCE with achieving nonradical-based degradation. Compared to nZVI/PS process, the SnZVI@PBC/PS system could significantly reduce catalyst dosage (87.5%) and PS amount (68.8%) to achieve nearly complete TCE degradation, and was anti-interference, stable, and pH-universal. This study advanced mechanistic understandings of multiple Kirkendall effects-triggered nanocrack formation on nZVI with corresponding rational design of Fenton-like catalysts for organics degradation.

Efficient Production of Segmented Carbon Nanofibers via Catalytic Decomposition of Trichloroethylene over Ni-W Catalyst.

The catalytic utilization of chlorine-organic wastes remains of extreme importance from an ecological point of view. Depending on the molecular structure of the chlorine-substituted hydrocarbon (presence of unsaturated bonds, intermolecular chlorine-to-hydrogen ratio), the features of its catalytic decomposition can be significantly different. Often, 1,2-dichloroethane is used as a model substrate. In the present work, the catalytic decomposition of trichloroethylene (C2HCl3) over microdispersed 100Ni and 96Ni-4W with the formation of carbon nanofibers (CNF) was studied. Catalysts were obtained by a co-precipitation of complex salts followed by reductive thermolysis. The disintegration of the initial bulk alloy driven by its interaction with the reaction mixture C2HCl3/H2/Ar entails the formation of submicron active particles. It has been established that the optimal activity of the pristine Ni catalyst and the 96Ni-4W alloy is provided in temperature ranges of 500-650 °C and 475-725 °C, respectively. The maximum yield of CNF for 2 h of reaction was 63 g/gcat for 100Ni and 112 g/gcat for 96Ni-4W catalyst. Longevity tests showed that nickel undergoes fast deactivation (after 3 h), whereas the 96Ni-4W catalyst remains active for 7 h of interaction. The effects of the catalyst's composition and the reaction temperature upon the structural and morphological characteristics of synthesized carbon nanofibers were investigated by X-ray diffraction analysis, Raman spectroscopy, and electron microscopies. The initial stages of the carbon erosion process were precisely examined by transmission electron microscopy coupled with elemental mapping. The segmented structure of CNF was found to be prevailing in a range of 500-650 °C. The textural parameters of carbon product (SBET and Vpore) were shown to reach maximum values (374 m2/g and 0.71 cm3/g, respectively) at the reaction temperature of 550 °C.

Cometabolic decomposition of trichloroethylene by recombinant hydroxyquinol 1,2-dioxygenase

Trichloroethylene (TCE) is known to microbially decomposed by a cometabolic process. In this study, a dioxygenase for the ring cleavage of benzenetriols was used to catalyze the cometabolic oxidation of TCE. Hydroxyquinol 1,2-dioxygenase (HQD) was obtained in vitro using a recombinant technique, and its catalytic function and products in the TCE cometabolic transformation were identified. The HQD (CphA-I) was cloned from Pseudarthrobacter chlorophenolicus A6, overexpressed, and purified using Ni2+-nitrilotriacetic acid (Ni2+-NTA) affinity chromatography, and soluble form of enzymes with 34 kDa protein size were effectively achieved with a high expression rate (4,177 μg/mL). TCE was effectively decomposed by CphA-I, and the specific activity was 5.1 U/mg-protein. The Hill equation was found to describe well the kinetics of TCE decomposition by CphA-I, which were determined as: vmax = 1.06 mM/min, KM = 1.44 mM, and nH = 2.41. This indicates that CphA-I has at least three cooperative binding sites for TCE decomposition, further accentuating the high affinity between the enzyme and the substrate. Glyoxylate and chloral hydrate were identified as the primary decomposition products from TCE cometabolic oxidation. This suggested that CphA-I exhibited a cometabolism catalytic function similar to those of methane monooxygenase and toluene dioxygenase. These results are expected to provide fundamental information for the enzymatic remediation of organic contaminants.

Cometabolic Decomposition of Trichloroethylene by Recombinant Hydroxyquinol 1,2-Dioxygenase

Cometabolic Decomposition of Trichloroethylene by Recombinant Hydroxyquinol 1,2-Dioxygenase

Plasma degradation of trichloroethylene: process optimization and reaction mechanism analysis

In this study, a multi-pin-to-plate negative corona discharge reactor was employed to degrade the hazardous compound trichloroethylene (TCE). The response surface methodology was applied to examine the influence of various process factors (relative humidity (RH), gas flow rate, and discharge power) on the TCE decomposition process, with regard to the TCE removal efficiency, CO2 and CO selectivities. The variance analysis was used to estimate the significance of the single process factors and their interactions. It has been proved that the discharge power had the most influential impact on the TCE removal efficiency, CO2 and CO selectivities and subsequently the gas flow rate, and finally RH. Under the optimal conditions with 20.83% RH, 2 W discharge power and 0.5 l min–1 gas flow rate, the optimal TCE removal efficiency (86.05%), CO2 selectivity (8.62%), and CO selectivity (15.14%) were achieved. In addition, a possible TCE decomposition pathway was proposed based on the investigation of byproducts identified in the exhaust gas of the non-thermal plasma reactor. This work paves the way for control of chlorinated volatile organic compounds.

Post plasma-catalysis for trichloroethylene decomposition over CeO2 catalyst: Synergistic effect and stability test

This study is devoted to investigate the opportunities of a plasma-catalytic system with CeO2 downstream (i.e. PPC-Post Plasma-catalysis) for the abatement of trichloroethylene (TCE), a typical chlorinated VOC, from dry air. A multi-pin-to-plate negative DC corona/glow discharge is used and showed poor COx selectivity despite having high abatement efficiency due to the formation of oxygenated intermediates such as phosgene, dichloroacetylchloride (DCAC) and trichloroacetaldehyde (TCAA), when operated alone. Nonetheless, NTP enables catalyst activation at lower temperature. As a result, suppression of unwanted chlorinated by-products as well as high COx selectivity at lower energy cost have been achieved, proving that this plasma-catalysis route shows great potential as air pollution control technology for low concentrated VOC air streams. Special attention is given to the effect of catalyst temperature, the role of ozone in the plasma–catalytic TCE abatement and the possible synergy between NTP and catalysis. Also, a long term test to evaluate the stability of CeO2 catalyst has also been successfully performed.

Photocatalytic degradation of trichloroethylene over BiOCl under UV irradiation

In this study, BiOCl samples were synthesized under different pH values and characterized by XRD, SEM, UV‐vis DRS, BET, photoelectrochemical measurement and PL. The photocatalytic performances of the as‐prepared samples were evaluated through the decomposition of trichloroethylene (TCE) under UV irradiation. The influences of several parameters such as solution pH and common inorganic anions on TCE removal were investigated. Results indicated that BiOCl‐0.6 exhibited better photocatalytic performance than BiOCl‐6.0 because of its higher migration ability of photo‐induced carrier. The photocatalytic degradation of TCE over BiOCl‐0.6 followed pseudo first‐order kinetics and appeared to be more efficient in acidic solution than in alkaline. TCE was almost completely dechlorinated in 120 minutes. The inhibiting effect of naturally occurring anions was in the order of HCO3‐ >SO42‐ >NO3‐, while Cl‐ exhibited a dual effect. Moreover, BiOCl‐0.6 exhibited superior reusability after three cycles of repetition tests.

Physicochemical Study of Gamma-irradiated mono azo dye in aqueous Solutions as liquid dosimeter

AQUEOUS solutions of pH indicator (mono azo dye) Amacid Yellow M (AYM) dye were titrated by different concentrations of (H+) resulting from irradiation decomposition of trichloroethylene (ClHC=CCl2) (TCE) solution for possible use as an monitoring device (label) for gamma radiation. The titrated solutions were readout spectrophotometrically. These solutions can be used qualitatively as routine indicators in the 0.5–5 kGy range because they have stable change in color for (AYM) from yellow to red at 540 nm depending on irradiated trichloroethylene [H+]. The effective dose range exceeds in this technique due to avoiding direct exposure of dye to gamma radiation, utilizing back titration technique followed by color measurements using spectrophotometer. Moreover, the useful measuring range was found to be 5kGy. The solutions can be used qualitatively as routine indicators in the range of 0.5 to 2kGy. Further calculations such as rate of reaction (r) and kinetic constant (k) have been assigned.

CrOx/TiO2촉매의 결정성과 TCE 산화반응 활성

Titania-supported chromium oxides with different loadings have been embarked in catalytic oxidation of trichloroethylene (TCE) to inquire association of the formation of crystalline <TEX>$Cr_2O_3$</TEX> with catalytic performances. A better activity in the oxidative TCE decomposition at chosen temperatures was represented when chromium oxides (<TEX>$CrO_x$</TEX>) had been dispersed on pure anatase-type <TEX>$TiO_2$</TEX> (DT51D) rather than on phase-mixed and sulfur-contained ones such as P25 and DT51. The extent of TCE oxidation at temperatures below <TEX>$350^{\circ}C$</TEX> was a strong function of <TEX>$CrO_x$</TEX> content in <TEX>$CrO_x$</TEX>/DT51D <TEX>$TiO_2$</TEX>, and a noticeable point was that the catalyst has two optimal <TEX>$CrO_x$</TEX> loadings in which the lowest <TEX>$T_{50}$</TEX> and <TEX>$T_{90}$</TEX> values were measured for the TCE oxidation. This behavior in the activity with respect to <TEX>$CrO_x$</TEX> amounts could be associated with the formation of crystalline <TEX>$Cr_2O_3$</TEX> on the support surface, that is less active for the oxidation reaction, and an easier mobility of the surface oxygen existing in noncrystalline <TEX>$CrO_x$</TEX> species with higher oxidation states, such as <TEX>$Cr_2O_8$</TEX> and <TEX>$CrO_3$</TEX>.

In-situ Decomposition of Trichloroethylene Using Electrochemical Treatment Method

Trichloroethylene (TCE) has an excellent degreasing capacity, so it is often used as a solvent for dry cleaning, and is still used for removing grease from metallic parts and so on. However, its inappropriate handling caused contamination of soil. Recently, its toxicity and carcinogenicity to humans have been concerned. By these reasons, it is highly required to remediate the contaminated soils. In the present study, the possibility of application of electrochemical treatment method to the in-situ decomposition of TCE is examined because in-situ remediation is expected to be simple and inexpensive. The experiment in the aqueous systems was conducted as a basic examination. As a result of comparing experimental values under various stirring speeds with the theoretical value calculated from mass transfer coefficient, it turned out that TCE transferring from bulk to the electrode surface is accelerated by the radicals in the boundary film near the electrode surface. Hence the TCE decomposition rate is affected by the radical formation rate or radical concentration in the boundary film. In the experiment with the soils, the TCE decomposition rate was much smaller than that in the aqueous systems. Moreover, the influence of the voltage was not observed. Therefore, it turned out that the movement of TCE in the aqueous phase near the electrode surface was the rate-controlling step in the soils. Under the condition, the TCE decomposition rate was not affected by the particle size. Consequently, it turned out TCE is not transported by bulk flow but is mostly transfered by molecular diffusion in the soil.

Photocatalytic Decomposition of low-concentrated Trichloroethylene and Tetrachloroethylene in Water

The photocatalytic decomposition of trichloroethylene (TCE) and tetrachloroethylene (PCE)in water was studied. TCE and PCE were present in water at very low concentrations of about 15 μg/dm3. Thisconcentration level corresponds to the one occasionally occurring in groundwater. Results of this researchconfirmed usefulness of the photocatalytic process for successful removal of low-concentrated TCE and PCEfrom water. Removal of trichloroethylene and tetrachloroethylene from water can be achieved by applicationof the photocatalytic process over titanium dioxide. It was confirmed that both suspended and immobilizedmodes of the photocatalytic process give comparable results. Therefore it is recommended to employ theimmobilized system as more beneficial from the economical point of view. Presented studies revealed that very low amounts of TCE and PCE can be removed from water using the photocatalytic process. This methodcould be than applied for purification of groundwater occasionally polluted with the small amounts of TCEand PCE.

Synergistic Effects of Fenton’s Reaction and the Sonochemical Reaction on the Decomposition of Trichloroethylene in Water

Synergistic Effects of Fenton’s Reaction and the Sonochemical Reaction on the Decomposition of Trichloroethylene in Water

Investigation of Humidity Effect on Atmospheric Plasma Decomposition of Toxic Gas With Direct Optical Measurement of OH Radicals

Plasma application for environment improvement is desirable. In order to improve the efficiency of toxic gas decomposition by plasma, it is worthwhile to clarify the behavior of radicals in nonthermal plasma. Although previous studies have revealed the behavior of radical densities and temperatures in atmospheric discharge, they are not yet connected to apprehension or simulation of practical toxic gas decomposition by atmospheric plasma. In this study, the coaxial dielectric barrier discharge cylinder reactor is prepared, where the radical behavior and the toxic gas decomposition efficiency can be measured altogether. The density of OH radical is directly measured by laser-induced fluorescence, and trichloroethylene (TCE) decomposition efficiency is also investigated in the same reactor. TCE decomposition efficiency is suppressed as background humidity increases. On another front, OH density measurement in ac barrier discharge indicates that OH density is about 2-4 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in time and spatial average and saturated with increasing humidity. From the saturation pattern, the initial OH density is estimated to be about the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in streamer site. In addition, TCE addition in background reduces OH density, which indicates that OH reacts with TCE. The reason for the suppression of decomposition efficiency with increasing humidity is estimated as a consequence of O radical reduction by water-originated particles.

Air trichloroethylene oxidation in a corona plasma-catalytic reactor

The oxidative decomposition of trichloroethylene (TCE; 300 ppm) by non-thermal corona plasma was investigated in dry air at atmospheric pressure and room temperature, both in the absence and presence of catalysts including MnO x, CoO x. The catalysts were synthesized by a co-precipitation method. The morphology and structure of the catalysts were characterized by BET surface area measurement and Fourier Transform Infrared (FTIR) methods. Decomposition of TCE and distribution of products were evaluated by a gas chromatograph (GC) and an FTIR. In the absence of the catalyst, TCE removal is increased with increases in the applied voltage and current intensity. Higher TCE removal and CO 2 selectivity is observed in presence of the corona and catalysts, as compared to those with the plasma alone. The results show that MnO x and CoO x catalysts can dissociate the in-plasma produced ozone to oxygen radicals, which enhances the TCE decomposition.

Plasma-catalysis of low TCE concentration in air using LaMnO3+δ as catalyst

The oxidative decomposition of trichloroethylene (TCE; 500–600ppmv) was investigated in synthetic (dry air) and humid air (RH=18%) with NTP (non thermal plasma) at atmospheric pressure, both in the absence and presence of lanthanum manganite catalyst at 150°C. In the absence of catalyst, TCE removal is enhanced with humidity (RH=18%) while O3 production is decreased. However, whatever the carrier gas the carbon mass balances are poor amounting to 25–30% due to the presence of polychlorinated by-products such as phosgene, dichloroacetyl chloride (DCAC) and trichloroacetaldehyde (TCAD). In the presence of catalyst, the TCE conversion significantly increased as compared to that of the plasma alone system. The perovskite catalyst can dissociate the in plasma produced ozone to oxygen radicals that decompose TCE. In dry air, the carbon mass balance keep rather poor (35% – 460J/L) due to the structural transformation of the catalyst with chlorine. In dry air, an optimum temperature of the catalytic reactor is found to be 100°C resulting from a compromise between catalyst deactivation and enhancement of the catalytic reactions. However, water remarkably promotes the carbon mass balance (75% – 460J/L) due to the beneficial role of water which acts as a chlorine scavenger at the surface of the catalyst, therefore retarding the perovskite degradation.

Polymer material-supported titania nanofibers with different polyvinylpyrrolidone to TiO2 ratios for degradation of vaporous trichloroethylene

Polymer-supported TiO2 nanofibers with different polyvinylpyrrolidone (PVP)-to-TiO2 (PT) ratios were synthesized and their photocatalytic efficiencies were examined for the decomposition of trichloroethylene (TCE). The spectral results of the TiO2 nanofibers confirmed the presence of TiO2 crystal phases in the nanofibers. The TiO2 nanofiber with the highest PT ratio of 1:1.3 showed the highest TCE decomposition (94%), followed by TiO2 nanofibers with PT ratios of 1:0.7 (91%), 1:0.35 (88%), and 1:0.1 (84%). The conditions of low input concentration and humidity were suggested for the optimal decomposition of TCE. Consequently, the TiO2 nanofiber webs could be used effectively to decompose TCE.

Effect of the structural change of an iron–iron oxide mixture on the decomposition of trichloroethylene

The effect of the structure of a mixture of industrially produced iron and iron oxide on the decomposition of trichloroethylene (TCE) was investigated by gas chromatography, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffractometry, and 57Fe-Mossbauer spectroscopy. The concentration of 10 mg L−1 TCE aqueous solution decreased to 0.41, 0.52, 0.26, and 0.09 mg L−1 when stirred for 7 days with iron–iron oxide mixtures having mass ratios of 2:8, 3:7, 4:6, and 5:5, respectively. The Mossbauer spectra of the mixtures after leaching were composed of two sextets with respective isomer shifts (δ) and internal magnetic fields (H) of 0.29±0.01 mm s−1 and 48.8±0.1 T, and 0.64±0.01 mm s−1 and 45.5±0.1 T, attributed to the Fe3+ species in tetrahedral (Td) and the Fe2+ and Fe3+ mixed species (Fe2.5+) in octahedral (Oh) sites, respectively. Mossbauer spectra of a 3:7 mass ratio iron–iron oxide mixture showed a gradual decrease in the absorption area (A) of zero valent iron (Fe0) from 40.6. to 12.6, 13.2, 3.8 2.8, and 1.0±0.5 % and an increase in A of Fe3O4 from 31.8 to 59.4, 71.4, 93.2, 95.6, and 98.0±0.5 % after leaching with 10 mg L−1 TCE aqueous solution for 1, 2, 3, 7, and 10 days, respectively. Consistent values of the first-order rate constant were calculated as 0.32 day−1 for Fe0 oxidation, 0.34 day−1 for Fe3O4 production, and 0.30 day−1 for TCE decomposition, which indicates that the oxidation of Fe0 was the rate-controlling factor for Fe3O4 production and TCE decomposition. It is concluded from the experimental results that an iron–iron oxide mixture is very effective for the decomposition of TCE.

Highly organic natural media as permeable reactive barriers: TCE partitioning and anaerobic degradation profile in eucalyptus mulch and compost

Batch and column experiments were conducted with eucalyptus mulch and commercial compost to evaluate suitability of highly organic natural media to support anaerobic decomposition of trichloroethylene (TCE) in groundwater. Experimental data for TCE and its dechlorination byproducts were analyzed with Hydrus-1D model to estimate the partitioning and kinetic parameters for the sequential dechlorination reactions during TCE decomposition. The highly organic natural media allowed development of a bioactive zone capable of decomposing TCE under anaerobic conditions. The first order TCE biodecomposition reaction rates were 0.23 and 1.2d−1 in eucalyptus mulch and compost media, respectively. The retardation factors in the eucalyptus mulch and compost columns for TCE were 35 and 301, respectively. The results showed that natural organic soil amendments can effectively support the anaerobic bioactive zone for remediation of TCE contaminated groundwater. The natural organic media are effective environmentally sustainable materials for use in permeable reactive barriers.

Influence of pH and Dissolved Fe Ion Concentration on Decomposition of Trichloroethylene with Fenton's Reaction Using Iron Powder

Influence of pH and Dissolved Fe Ion Concentration on Decomposition of Trichloroethylene with Fenton's Reaction Using Iron Powder

Comparison of the Effects of Fluidized-Bed and Fixed-Bed Reactors in Microwave-Assisted Catalytic Decomposition of TCE by Hydrogen

Trichloroethylene (TCE) decomposition by hydrogen with microwave heating under different reaction systems was investigated. The activities of a series of catalysts for microwave-assisted TCE hydrodechlorination were tested through the fixed-bed and the fluidized-bed reactor systems. This study found that the different reaction system is suitable for different catalyst type. And there is an interactive relationship between the catalyst type and the reaction bed type.