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Query: EC:3.4.23.17 (PCE)
 1,301 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The influence of residual cosolvent on the partitioning tracer technique for estimating a nonaqueous phase liquid (NAPL) saturation in porous media was investigated. Batch equilibrium and column miscible displacement tests were used to evaluate the influence of residual alcohol cosolvents in the aqueous phase on partitioning and transport of alcohol tracers through sandy soil columns containing tetrachloroethylene (PCE). As the volume fraction of cosolvent alcohol (f(c)) increased ( f(c) < or = 0.1; 10 vol %), partition coefficients (K(nc)) for the alcohol tracers linearly decreased for residual cosolvent ethanol, linearly increased for residual cosolvent tert-butyl alcohol, and did not exhibit an evident change for residual cosolvent 2-propanol. These observations are consistent with measured changes in solubility (S(c)) of the alcohol tracers over the same range (f(c) < or = 0.1) of these residual cosolvent alcohols. Column miscible displacement tests using ethanol as a residual cosolvent ( f(c) < or = 0.1) exhibited earlier partitioning tracer breakthrough leading to an underestimation of NAPL saturation (S(n)) when constant, cosolvent-free partitioning coefficients were assumed. The underestimation magnitude increased with higher initial residual cosolvent alcohol in the columns. The S(n) underestimates were not significant but were 1-10% lower than the actual S(n) (0.18). The estimated partition coefficients based on column tests with residual cosolvent (K(col)) were consistently less than those based on batch tests. Column tests with low (0.5%) and high (15%) S(n) revealed that the residual cosolvent alcohol effect was different depending on the amount of NAPL in the column. Using ethanol for a cosolvent (10%) and 2,4-dimethyl-3-pentanol as a partitioning tracer, the S(n) values were underestimated by about 17% and 5%, respectively, in the low and high NAPL saturation columns.
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PMID:Residual alcohol influence on NAPL saturation estimates based on partitioning tracers. 1273 48

This study reports on a surfactant-based flood for tetrachloroethylene (PCE) removal from a control test cell at the Dover National Test Site. The surfactant formulation (sodium dihexyl sulfosuccinate (Aerosol-MA or AMA), isopropanol and calcium chloride) was able to achieve a high concentration of PCE in swollen micelles (supersolubilization) without vertical PCE migration. The hydraulic system included eight screened wells that were operated in both vertical circulation and line drive configurations. After 10 pore volumes of flushing, the overall PCE removal was 68% (65% of which corresponded to the surfactant flooding alone). In addition, the residual PCE saturation was reduced from 0.7% to 0.2%, and the concentration of PCE in the groundwater was reduced from 37-190 mg/L before the flushing to 7.3 mg/L after flooding. Recycling the surfactant solution reduced the required surfactant mass (and thus cost, and waste) by 90%. Close to 80% of the total PCE removal was obtained during the first five pore volumes which were operated in an upward vertical circulation flow scheme. No free oil phase was observed during the test. Further analysis of multilevel sampler data suggests that most of the trapped oil remaining in the cell was likely localized in secluded regions of the aquifer, which helps explain the lower PCE groundwater concentration after remedial activities. In summary, this field study demonstrated the feasibility of surfactant-enhanced remediation to reduce the mass in the source zone and significantly reduce the PCE aqueous concentration and therefore the risk associated with the contaminant plume.
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PMID:Field demonstration of surfactant-enhanced solubilization of DNAPL at Dover Air Force Base, Delaware. 1623 35

The ability of modified Fenton reactions to promote simultaneous chemical and biological oxidation in an artificially contaminated soil was studied in batch laboratory slurry reactors. Tetrachloroethene (PCE) and oxalate (OA) were used to distinguish chemical oxidation from aerobic heterotrophic metabolism. PCE was mineralized by Fenton reactions, but OA was not oxidized. Indigenous soil microorganisms did not degrade added PCE aerobically but readily assimilated OA. Fenton reactions were promoted at the natural soil pH (7.6) by adding H2O2 and Fe(III), with nitrilotriacetic acid (NTA) as a chelator, at a constant molar ratio of H2O2/Fe(III)/NTA of 50:1:1. The *OH-mediated mineralization of PCE was demonstrated by adding 2-propanol (an *OH scavenger), which inhibited PCE oxidation. In subsequent dosing studies, PCE oxidation served as an indicator of Fenton reactions, while OA assimilation, dissolved oxygen (DO) concentration, and heterotrophic plate counts were indicators of aerobic microbial activity. Increasing Fenton doses to 20 times that required to achieve 95% PCE oxidation only delayed OA assimilation by 500 min and reduced plate counts by 1.5 log units g(-1) soil. Results show that aerobic metabolism can coexist with Fenton oxidation in soils.
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PMID:Effect of Fenton reagent dose on coexisting chemical and microbial oxidation in soil. 1668 23

The use of calcium peroxide (CaO2) powder as a source of H2O2 to promote modified Fenton (MF) chemistry was studied. First, the rate of production and yield of H2O2 from CaO2 dissolving in water at pH 6-9, and 12-13 (i.e., unbuffered CaO2) was measured. The rate of CaO2 dissolution increased as pH decreased, from 62 h for complete dissolution at pH 12-13 to only 4h at pH 6. The yield of H2O2 also increased with decreasing pH, from zero at pH 12-13 to 82% at pH 6. The ability of CaO2 to promote MF oxidation of PCE was demonstrated with a hydroxyl radical (OH) scavenger (2-propanol) at pH 8. The scavenger inhibited PCE oxidation, but 97% of the PCE was oxidized without it. Release of Cl(-) showed that PCE was mineralized. Finally, PCE oxidation was compared with liquid H2O2 (pH 7) and with CaO2 (pH 6, 7, 8, 9). Liquid H2O2 showed the lowest efficiency (mol H2O2 consumed/mol PCE oxidized) and the greatest temperature increase, disproportionation to O2, and PCE volatilization. CaO2 was a more efficient oxidant than liquid H2O2 at all pH values because it only releases H2O2 upon dissolution, reducing the loss to O2 and volatilization. CaO2 performed optimally at pH 8.
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PMID:Calcium peroxide (CaO2) for use in modified Fenton chemistry. 1780 64

Inner-sphere (nonradical) and outer-sphere (radical-based) mechanisms have been suggested for cobalamin-mediated dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE). In this study, the role of free vinyl radicals was investigated using deuterated radical traps: d(8)-isopropanol and d(8)-tetrahydrofuran. For both substrates, addition of trap resulted in production of deuterated dechlorination products, and higher concentrations of trap resulted in increased amounts of deuterated products. However, only a finite proportion of the products were trappable: 8% of the PCE-derived products and 86% of the TCE-derived products result from free radicals. The data show that the reaction does not proceed solely by either an inner-sphere or an outer-sphere mechanism and led to the hypothesis that caged radical intermediates were involved in the mechanism. The untrappable fraction of products are hypothesized to result from in-cage reactions. This hypothesis was investigated using d(5)-glycerol as a radical trap and viscogen. Although increased viscosity resulted in decreased formation of free-radical-derived products, consistent with the cage hypothesis, these data were inconclusive. The role of d(8)-isopropanol in enhancing the production of radicals in this system via an acetone ketyl radical chain mechanism was also investigated, and no evidence for such an effect was found.
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PMID:Reconciling disparate models of the involvement of vinyl radicals in cobalamin-mediated dechlorination reactions. 1994 73

In this study, the effects of reducing agents on the degradation of tetrachloroethene (PCE) were investigated in the Fe(II)/Fe(III) catalyzed sodium percarbonate (SPC) system. The addition of reducing agents, including hydroxylamine hydrochloride, sodium sulfite, ascorbic acid and sodium ascorbate, accelerated the Fe(III)/Fe(II) redox cycle, leading to a relatively steady Fe(II) concentration and higher production of free radicals. This, in turn, resulted in enhanced PCE oxidation by SPC, with almost complete PCE removal obtained for appropriate Fe and SPC concentrations. The chemical probe tests, using nitrobenzene and carbon tetrachloride, demonstrated that HO was the predominant radical in the system and that O2(-) played a minor role, which was further confirmed by the results of electron spin resonance measurements. PCE degradation decreased significantly with the addition of isopropanol, a HO scavenger, supporting the hypothesis that HO was primarily responsible for PCE degradation. It is noteworthy that Cl(-) release was slightly delayed in the first 20 min, indicating that intermediate products were produced. However, these intermediates were further degraded, resulting in the complete conversion of PCE to CO2. In conclusion, the use of reducing agents to enhance Fe(II)/Fe(III) catalyzed SPC oxidation appears to be a promising approach for the rapid degradation of organic contaminants in groundwater.
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PMID:Enhancement effects of reducing agents on the degradation of tetrachloroethene in the Fe(II)/Fe(III) catalyzed percarbonate system. 2625 94

The quality of the perovskite layer plays a key role in the performance of perovskite solar cells (PSCs). In this work, we demonstrate a facile way to improve the quality of perovskite films by using a MAI/IPA solution to post-treat the perovskite material after the film formation. XRD, SEM and AFM show that an optimal, uniform, dense and highly crystalline perovskite film is achieved after the post-treatment. The transient photocurrent and transient photovoltage also confirm that the devices after the post-treatment have both the outstanding ability of charge extraction and suppressed charge recombination. By using the post-treatment, a maximum PCE of 19.08%, which is 12% higher than that of the control device, is obtained with a Jsc of 23.12 mA cm-2, a Voc of 1.08 V and an FF of 76.03%. The results show that the MAI/IPA solution post-treatment after the perovskite film formation is a facile way to improve the film quality and the PSC performance.
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PMID:Performance enhancement of perovskite solar cells via material quality improvement assisted by MAI/IPA solution post-treatment. 3093 49

Interfacial modification of the perovskite surface with octocrylene (2-ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate, OCT) is capable of enhancing humidity stability and passivating the defects of perovskite films. In this study, octocrylene can be attached to the surface of the perovskite, and the carbonyl group (C[double bond, length as m-dash]O) in octocrylene achieved excellent passivation through the Lewis base electron passivation of Pb2+ ions. By increasing the concentration of the octocrylene/IPA solution, the modified device exhibited an optimal PCE of 20.54% and a steady state output PCE of 19.75%. This study shows that the introduction of octocrylene in the preparation of perovskite could effectively enhance the performance of perovskite solar cells.
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PMID:Interfacial modification by multifunctional octocrylene for high efficiency and stable planar perovskite solar cells. 3242 58

5-Ammonium valeric acid iodide (AVAI) has been widely known as a stabilizer to enhance the stability of MAPbI3 perovskite, but its role and function is still under exploration. The typical 2D perovskites of AVA2PbI4 have been proposed as the capping layer for stabilization. Here, a novel AVA-MA mixed-cation perovskite of AVAMAPbI4 is found to show a more even and compact coverage than the typical 2D perovskite of AVA2PbI4. A simple post-treatment on MAPbI3 films by using AVAI isopropanol solution can fabricate such a mixed-cation 2D perovskite capping layer on the MAPbI3 sample. This AVAMAPbI4 capping layer effectively passivates surface defects of MAPbI3 perovskite films and reduces the charge-carrier recombination, enabling AVAI-MAPbI3 perovskite films to exhibit improved stability against thermal and moisture stress. Finally, the AVAI-MAPbI3-based perovskite solar cells also show an enhanced photovoltaic performance with a champion PCE up to 20.05% with enhanced stability.
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PMID:5-Ammonium Valeric Acid Iodide to Stabilize MAPbI3 via a Mixed-Cation Perovskite with Reduced Dimension. 3293 Dec 81