Vaishnavi Sarathy - Academia.edu (original) (raw)

Papers by Vaishnavi Sarathy

Research paper thumbnail of FINAL REPORT Prospects for Remediation of 1 , 2 , 3-Trichloropropane by Natural and Engineered Abiotic Degradation Reactions SERDP Project ER-1457 AUGUST 2010

1,2,3-trichloropropane (TCP) is a contaminant of DOD concern mainly due to it use in solvent form... more 1,2,3-trichloropropane (TCP) is a contaminant of DOD concern mainly due to it use in solvent formulations for paint and varnish removal, cleaning and degreasing, etc. Compared with other chlorinated solvents, TCP is similarly mobile, exceptionally persistent, and relatively toxic, suggesting that TCP will pose clean-up challenges that are similar, but in some respects more difficult. While TCP is characteristically recalcitrant, to both abiotic (and biotic) degradation pathways, potentially beneficial transformations of TCP are possible by hydrolysis, elimination, reduction, and oxidation. The goal of this project was to provide a detailed, quantitative characterization of these pathways of TCP degradation in water or soil.

Research paper thumbnail of Engineered remediation and natural attenuation of halogenated alkanes (carbon tetrachloride and 1,2,3-trichloropropane) a study of contaminant reactivity and reductant morphology

.................................................................................................... more ................................................................................................................................................................ix 1 Fate and Redox Chemistry of Chlorinated Aliphatics in Groundwater .............................................1 Abstract ..............................................................................................................................................................

Research paper thumbnail of Aging of Iron Nanoparticles in Water: Effects on Structure and Reactivity

We studied the aging of Fe0-core/oxide-shell nanoparticles in water with a focus on changes in (i... more We studied the aging of Fe0-core/oxide-shell nanoparticles in water with a focus on changes in (i) the composition and structure of the particles (by XRD, TEM, XPS, and bulk Fe0 content), and (ii) the reactivity of the particles (by carbon tetrachloride reaction kinetics, electrochemical corrosion potentials, and H2 production rates). The results show that nano-Fe0 become more reactive between 0 and ~2 days exposure to water, and then gradually it loses reactivity over the next few hundred days. The behavior of unaged nano-Fe0 in our laboratory experiments may be similar to that in field-scale applications for source-zone treatment due to the short reaction times involved. However, nano-Fe0 that has been aged in water for >3 days acquires properties that are relatively stable over weeks or even months.

Research paper thumbnail of Passivation and Depassivation of Iron/Iron Oxide Nanoparticles

Research paper thumbnail of Prospects for Remediation of 1,2,3-Trichloropropane by Natural and Engineered Abiotic Degradation Reactions

Public reporting burden for the collection of information is estimated to average 1 hour per resp... more Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Research paper thumbnail of Copper complexation by dissolved organic matter from surface water and wastewater effluent

Ecotoxicology and Environmental Safety, Jul 31, 2005

Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been ex... more Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been extensively studied with respect to complexation with copper, unlike natural organic matter (NOM). Acid-base and copper titrations were conducted on both types of organic matter. Experimental copper complexation data were compared to predictions from the Windermere Humic Aqueous Model (WHAM) Version VI. We found that NOM and WWOM have ligands with similar proton binding, but the copper binding of WWOM is not well predicted by WHAM especially at low copper concentrations because the concentrations of ligands that are most important at the low copper concentrations (below 10(-6) M) were found to be about 15 times higher in the WWOM. Consideration of sulfide present in the wastewater effluent does not fully explain this deviation. Due to the possibility that there exist nonhumics like biological macromolecules in WWOM, it may need to be considered as an alternative ligand to humics in toxicity and speciation predicting models like the biotic ligand model (BLM).

Research paper thumbnail of Chemistry of metallic iron nanoparticles

Research paper thumbnail of Effects of Particle Size on the Kinetics of Degradation of Contaminants

Research paper thumbnail of Degradation of Reduction by Iron and Zinc

Research paper thumbnail of Environmental Applications of Zerovalent Metals: Iron vs. Zinc

ACS Symposium Series, 2010

ABSTRACT A review. The reactivity of particulate zero-valent metals in soln. is affected by the m... more ABSTRACT A review. The reactivity of particulate zero-valent metals in soln. is affected by the metal type (e.g., Fe vs. Zn), particle size (nano vs. micro), surface conditions (passivation by coatings of oxides), and soln. conditions (including the type and concn. of oxidants). Comparing the reactivity of various types of Fe0 and Zn0 with CCl4 (CCl4) shows that the intended effect of properties engineered to give enhanced reactivity can be obscured by effects of environmental factors. In this case, rates of CCl4 redn. by Zn0 are more strongly affected by soln. chem. than particle size or surface morphol. Under favorable conditions, however, Zn0 reduces CCl4 more rapidly-and more completely-than Fe0, regardless of particle size. The suitability of nano-sized Zn0 for environmental remediation applications is uncertain. [on SciFinder(R)]

Research paper thumbnail of Nanosize effects on the kinetics of contaminant reduction by iron and iron oxides

Research paper thumbnail of Effect of aging on the structure and reactivity of nanoparticles of iron/iron oxides

ABSTRACT The short- and long-term aging of a nanosized iron, which is produced by redn. of iron o... more ABSTRACT The short- and long-term aging of a nanosized iron, which is produced by redn. of iron oxide in a H2 atm., in anoxic water and the resulting effects on the chem. of the oxide-shell and reactivity of the particles with carbon tetrachloride (CT) are presented. [on SciFinder(R)]

Research paper thumbnail of Synthesis, Characterization, and Properties of Zero-Valent Iron Nanoparticles

This chapter provides an overview of synthesis, characterization and property measurements techni... more This chapter provides an overview of synthesis, characterization and property measurements techniques important for making understanding the nature of zero valent iron nanoparticles. The chemical reactivity of nanometer-sized materials can be quite different from that of either bulk forms of a material or the individual atoms and molecules that comprise it. Advances in our ability to synthesize, visualize, characterize and

Research paper thumbnail of ChemInform Abstract: Synthesis, Characterization, and Properties of Zero-valent Iron Nanoparticles

ChemInform, 2013

A new series of novel chalcones (III) is synthesized and transformed into chromenone derivatives ... more A new series of novel chalcones (III) is synthesized and transformed into chromenone derivatives (IV) and (V) via oxidative cyclization reactions.

Research paper thumbnail of Aging of Iron Nanoparticles in Aqueous Solution: Effects on Structure and Reactivity

Journal of Physical Chemistry C, 2008

Research paper thumbnail of Characterization challenges for nanomaterials

Surface and Interface Analysis, 2008

Nanostructured materials are increasingly subject to nearly every type of chemical and physical a... more Nanostructured materials are increasingly subject to nearly every type of chemical and physical analysis possible. Due to their small sizes, there is a significant focus on tools with high spatial resolution. It is also natural to characterize nanomaterials using tools designed to analyze surfaces, because of their high surface area. Regardless of the approach, nanostructured materials present a variety of obstacles to adequate, useful, and needed analysis. Case studies of measurements on ceria and iron metal-core/oxide-shell nanoparticles are used to introduce some of the issues that frequently need to be addressed during analysis of nanostructured materials. We use a combination of tools for routine analysis including X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and x-ray diffraction (XRD) and apply several other methods as needed to obtain essential information. The examples provide an introduction to other issues and complications associated with the analysis of nanostructured materials including particle stability, probe effects, environmental effects, specimen handling, surface coating, contamination, and time.

Research paper thumbnail of Recovery of iron/iron oxide nanoparticles from solution: comparison of methods and their effects

Journal of Nanoparticle Research, 2011

Most methods currently being used to recover Fe 0-core/oxide-shell nanoparticles from solutions (... more Most methods currently being used to recover Fe 0-core/oxide-shell nanoparticles from solutions (including the solvents they are synthesized or stored in) are potentially problematic because they may alter the particle composition (e.g., depositing salts formed from solutes) or leave the particles prone to transformations during subsequent storage and handling (e.g., due to residual moisture). In this study, several methods for recovery of nanoparticles from aqueous solution were studied to determine how they affect the structure and reactivity of the recovered materials. Simple washing of the nanoparticles during vacuum filtration (i.e., ''flash drying'') can leave up to *17 wt% residual moisture. Modeling calculations suggest this moisture is mostly capillary or matric water held between particles and particle aggregates, which can be removed by drying for short periods at relative vapor pressures below 0.9. Flash drying followed by vacuum drying, all under N 2 , leaves no detectable residue from precipitation of solutes (detectable by X-ray photoelectron spectroscopy, XPS), no significant changes in overall particle composition or structure (determined by transmission electron microscopy, TEM), and negligible residual moisture (by thermogravimetric analysis, TGA). While this improved flash-drying protocol may be the preferred method for recovering nanoparticles for many purposes, we found that Fe 0-core/oxide-shell nanoparticles still exhibit gradual aging during storage when characterized electrochemically with voltammetry.

Research paper thumbnail of Characterization and Properties of Metallic Iron Nanoparticles:  Spectroscopy, Electrochemistry, and Kinetics

Environmental Science & Technology, 2005

Research paper thumbnail of Degradation of 1,2,3-Trichloropropane (TCP): Hydrolysis, Elimination, and Reduction by Iron and Zinc

Environmental Science & Technology, 2010

1,2,3-Trichloropropane (TCP) is an emerging contaminant because of increased recognition of its o... more 1,2,3-Trichloropropane (TCP) is an emerging contaminant because of increased recognition of its occurrence in groundwater, potential carcinogenicity, and resistance to natural attenuation. The physical and chemical properties of TCP make it difficult to remediate, with all conventional options being relatively slow or inefficient. Treatments that result in alkaline conditions (e.g., permeable reactive barriers containing zerovalent iron) favor base-catalyzed hydrolysis of TCP, but high temperature (e.g., conditions of in situ thermal remediation) is necessary for this reaction to be significant. Common reductants (sulfide, ferrous iron adsorbed to iron oxides, and most forms of construction-grade or nano-Fe(0)) produce insignificant rates of reductive dechlorination of TCP. Quantifiable rates of TCP reduction were obtained with several types of activated nano-Fe(0), but the surface area normalized rate contants (k(SA)) for these reactions were lower than is generally considered useful for in situ remediation applications (10(-4) L m(-2) h(-1)). Much faster rates of degradation of TCP were obtained with granular Zn(0), (k(SA) = 10(-3) - 10(-2) L m(-2) h(-1)) and potentially problematic dechlorination intermediates (1,2- or 1,3-dichloropropane, 3-chloro-1-propene) were not detected. The advantages of Zn(0) over Fe(0) are somewhat peculiar to TCP and may suggest a practical application for Zn(0) even though it has not found favor for remediation of contamination with other chlorinated solvents.

Research paper thumbnail of Copper complexation by dissolved organic matter from surface water and wastewater effluent

Ecotoxicology and Environmental Safety, 2005

Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been ex... more Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been extensively studied with respect to complexation with copper, unlike natural organic matter (NOM). Acid-base and copper titrations were conducted on both types of organic matter. Experimental copper complexation data were compared to predictions from the Windermere Humic Aqueous Model (WHAM) Version VI. We found that NOM and WWOM have ligands with similar proton binding, but the copper binding of WWOM is not well predicted by WHAM especially at low copper concentrations because the concentrations of ligands that are most important at the low copper concentrations (below 10(-6) M) were found to be about 15 times higher in the WWOM. Consideration of sulfide present in the wastewater effluent does not fully explain this deviation. Due to the possibility that there exist nonhumics like biological macromolecules in WWOM, it may need to be considered as an alternative ligand to humics in toxicity and speciation predicting models like the biotic ligand model (BLM).

Research paper thumbnail of FINAL REPORT Prospects for Remediation of 1 , 2 , 3-Trichloropropane by Natural and Engineered Abiotic Degradation Reactions SERDP Project ER-1457 AUGUST 2010

1,2,3-trichloropropane (TCP) is a contaminant of DOD concern mainly due to it use in solvent form... more 1,2,3-trichloropropane (TCP) is a contaminant of DOD concern mainly due to it use in solvent formulations for paint and varnish removal, cleaning and degreasing, etc. Compared with other chlorinated solvents, TCP is similarly mobile, exceptionally persistent, and relatively toxic, suggesting that TCP will pose clean-up challenges that are similar, but in some respects more difficult. While TCP is characteristically recalcitrant, to both abiotic (and biotic) degradation pathways, potentially beneficial transformations of TCP are possible by hydrolysis, elimination, reduction, and oxidation. The goal of this project was to provide a detailed, quantitative characterization of these pathways of TCP degradation in water or soil.

Research paper thumbnail of Engineered remediation and natural attenuation of halogenated alkanes (carbon tetrachloride and 1,2,3-trichloropropane) a study of contaminant reactivity and reductant morphology

.................................................................................................... more ................................................................................................................................................................ix 1 Fate and Redox Chemistry of Chlorinated Aliphatics in Groundwater .............................................1 Abstract ..............................................................................................................................................................

Research paper thumbnail of Aging of Iron Nanoparticles in Water: Effects on Structure and Reactivity

We studied the aging of Fe0-core/oxide-shell nanoparticles in water with a focus on changes in (i... more We studied the aging of Fe0-core/oxide-shell nanoparticles in water with a focus on changes in (i) the composition and structure of the particles (by XRD, TEM, XPS, and bulk Fe0 content), and (ii) the reactivity of the particles (by carbon tetrachloride reaction kinetics, electrochemical corrosion potentials, and H2 production rates). The results show that nano-Fe0 become more reactive between 0 and ~2 days exposure to water, and then gradually it loses reactivity over the next few hundred days. The behavior of unaged nano-Fe0 in our laboratory experiments may be similar to that in field-scale applications for source-zone treatment due to the short reaction times involved. However, nano-Fe0 that has been aged in water for >3 days acquires properties that are relatively stable over weeks or even months.

Research paper thumbnail of Passivation and Depassivation of Iron/Iron Oxide Nanoparticles

Research paper thumbnail of Prospects for Remediation of 1,2,3-Trichloropropane by Natural and Engineered Abiotic Degradation Reactions

Public reporting burden for the collection of information is estimated to average 1 hour per resp... more Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Research paper thumbnail of Copper complexation by dissolved organic matter from surface water and wastewater effluent

Ecotoxicology and Environmental Safety, Jul 31, 2005

Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been ex... more Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been extensively studied with respect to complexation with copper, unlike natural organic matter (NOM). Acid-base and copper titrations were conducted on both types of organic matter. Experimental copper complexation data were compared to predictions from the Windermere Humic Aqueous Model (WHAM) Version VI. We found that NOM and WWOM have ligands with similar proton binding, but the copper binding of WWOM is not well predicted by WHAM especially at low copper concentrations because the concentrations of ligands that are most important at the low copper concentrations (below 10(-6) M) were found to be about 15 times higher in the WWOM. Consideration of sulfide present in the wastewater effluent does not fully explain this deviation. Due to the possibility that there exist nonhumics like biological macromolecules in WWOM, it may need to be considered as an alternative ligand to humics in toxicity and speciation predicting models like the biotic ligand model (BLM).

Research paper thumbnail of Chemistry of metallic iron nanoparticles

Research paper thumbnail of Effects of Particle Size on the Kinetics of Degradation of Contaminants

Research paper thumbnail of Degradation of Reduction by Iron and Zinc

Research paper thumbnail of Environmental Applications of Zerovalent Metals: Iron vs. Zinc

ACS Symposium Series, 2010

ABSTRACT A review. The reactivity of particulate zero-valent metals in soln. is affected by the m... more ABSTRACT A review. The reactivity of particulate zero-valent metals in soln. is affected by the metal type (e.g., Fe vs. Zn), particle size (nano vs. micro), surface conditions (passivation by coatings of oxides), and soln. conditions (including the type and concn. of oxidants). Comparing the reactivity of various types of Fe0 and Zn0 with CCl4 (CCl4) shows that the intended effect of properties engineered to give enhanced reactivity can be obscured by effects of environmental factors. In this case, rates of CCl4 redn. by Zn0 are more strongly affected by soln. chem. than particle size or surface morphol. Under favorable conditions, however, Zn0 reduces CCl4 more rapidly-and more completely-than Fe0, regardless of particle size. The suitability of nano-sized Zn0 for environmental remediation applications is uncertain. [on SciFinder(R)]

Research paper thumbnail of Nanosize effects on the kinetics of contaminant reduction by iron and iron oxides

Research paper thumbnail of Effect of aging on the structure and reactivity of nanoparticles of iron/iron oxides

ABSTRACT The short- and long-term aging of a nanosized iron, which is produced by redn. of iron o... more ABSTRACT The short- and long-term aging of a nanosized iron, which is produced by redn. of iron oxide in a H2 atm., in anoxic water and the resulting effects on the chem. of the oxide-shell and reactivity of the particles with carbon tetrachloride (CT) are presented. [on SciFinder(R)]

Research paper thumbnail of Synthesis, Characterization, and Properties of Zero-Valent Iron Nanoparticles

This chapter provides an overview of synthesis, characterization and property measurements techni... more This chapter provides an overview of synthesis, characterization and property measurements techniques important for making understanding the nature of zero valent iron nanoparticles. The chemical reactivity of nanometer-sized materials can be quite different from that of either bulk forms of a material or the individual atoms and molecules that comprise it. Advances in our ability to synthesize, visualize, characterize and

Research paper thumbnail of ChemInform Abstract: Synthesis, Characterization, and Properties of Zero-valent Iron Nanoparticles

ChemInform, 2013

A new series of novel chalcones (III) is synthesized and transformed into chromenone derivatives ... more A new series of novel chalcones (III) is synthesized and transformed into chromenone derivatives (IV) and (V) via oxidative cyclization reactions.

Research paper thumbnail of Aging of Iron Nanoparticles in Aqueous Solution: Effects on Structure and Reactivity

Journal of Physical Chemistry C, 2008

Research paper thumbnail of Characterization challenges for nanomaterials

Surface and Interface Analysis, 2008

Nanostructured materials are increasingly subject to nearly every type of chemical and physical a... more Nanostructured materials are increasingly subject to nearly every type of chemical and physical analysis possible. Due to their small sizes, there is a significant focus on tools with high spatial resolution. It is also natural to characterize nanomaterials using tools designed to analyze surfaces, because of their high surface area. Regardless of the approach, nanostructured materials present a variety of obstacles to adequate, useful, and needed analysis. Case studies of measurements on ceria and iron metal-core/oxide-shell nanoparticles are used to introduce some of the issues that frequently need to be addressed during analysis of nanostructured materials. We use a combination of tools for routine analysis including X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and x-ray diffraction (XRD) and apply several other methods as needed to obtain essential information. The examples provide an introduction to other issues and complications associated with the analysis of nanostructured materials including particle stability, probe effects, environmental effects, specimen handling, surface coating, contamination, and time.

Research paper thumbnail of Recovery of iron/iron oxide nanoparticles from solution: comparison of methods and their effects

Journal of Nanoparticle Research, 2011

Most methods currently being used to recover Fe 0-core/oxide-shell nanoparticles from solutions (... more Most methods currently being used to recover Fe 0-core/oxide-shell nanoparticles from solutions (including the solvents they are synthesized or stored in) are potentially problematic because they may alter the particle composition (e.g., depositing salts formed from solutes) or leave the particles prone to transformations during subsequent storage and handling (e.g., due to residual moisture). In this study, several methods for recovery of nanoparticles from aqueous solution were studied to determine how they affect the structure and reactivity of the recovered materials. Simple washing of the nanoparticles during vacuum filtration (i.e., ''flash drying'') can leave up to *17 wt% residual moisture. Modeling calculations suggest this moisture is mostly capillary or matric water held between particles and particle aggregates, which can be removed by drying for short periods at relative vapor pressures below 0.9. Flash drying followed by vacuum drying, all under N 2 , leaves no detectable residue from precipitation of solutes (detectable by X-ray photoelectron spectroscopy, XPS), no significant changes in overall particle composition or structure (determined by transmission electron microscopy, TEM), and negligible residual moisture (by thermogravimetric analysis, TGA). While this improved flash-drying protocol may be the preferred method for recovering nanoparticles for many purposes, we found that Fe 0-core/oxide-shell nanoparticles still exhibit gradual aging during storage when characterized electrochemically with voltammetry.

Research paper thumbnail of Characterization and Properties of Metallic Iron Nanoparticles:  Spectroscopy, Electrochemistry, and Kinetics

Environmental Science & Technology, 2005

Research paper thumbnail of Degradation of 1,2,3-Trichloropropane (TCP): Hydrolysis, Elimination, and Reduction by Iron and Zinc

Environmental Science & Technology, 2010

1,2,3-Trichloropropane (TCP) is an emerging contaminant because of increased recognition of its o... more 1,2,3-Trichloropropane (TCP) is an emerging contaminant because of increased recognition of its occurrence in groundwater, potential carcinogenicity, and resistance to natural attenuation. The physical and chemical properties of TCP make it difficult to remediate, with all conventional options being relatively slow or inefficient. Treatments that result in alkaline conditions (e.g., permeable reactive barriers containing zerovalent iron) favor base-catalyzed hydrolysis of TCP, but high temperature (e.g., conditions of in situ thermal remediation) is necessary for this reaction to be significant. Common reductants (sulfide, ferrous iron adsorbed to iron oxides, and most forms of construction-grade or nano-Fe(0)) produce insignificant rates of reductive dechlorination of TCP. Quantifiable rates of TCP reduction were obtained with several types of activated nano-Fe(0), but the surface area normalized rate contants (k(SA)) for these reactions were lower than is generally considered useful for in situ remediation applications (10(-4) L m(-2) h(-1)). Much faster rates of degradation of TCP were obtained with granular Zn(0), (k(SA) = 10(-3) - 10(-2) L m(-2) h(-1)) and potentially problematic dechlorination intermediates (1,2- or 1,3-dichloropropane, 3-chloro-1-propene) were not detected. The advantages of Zn(0) over Fe(0) are somewhat peculiar to TCP and may suggest a practical application for Zn(0) even though it has not found favor for remediation of contamination with other chlorinated solvents.

Research paper thumbnail of Copper complexation by dissolved organic matter from surface water and wastewater effluent

Ecotoxicology and Environmental Safety, 2005

Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been ex... more Organic matter from wastewater treatment plants (wastewater organic matter, WWOM) has not been extensively studied with respect to complexation with copper, unlike natural organic matter (NOM). Acid-base and copper titrations were conducted on both types of organic matter. Experimental copper complexation data were compared to predictions from the Windermere Humic Aqueous Model (WHAM) Version VI. We found that NOM and WWOM have ligands with similar proton binding, but the copper binding of WWOM is not well predicted by WHAM especially at low copper concentrations because the concentrations of ligands that are most important at the low copper concentrations (below 10(-6) M) were found to be about 15 times higher in the WWOM. Consideration of sulfide present in the wastewater effluent does not fully explain this deviation. Due to the possibility that there exist nonhumics like biological macromolecules in WWOM, it may need to be considered as an alternative ligand to humics in toxicity and speciation predicting models like the biotic ligand model (BLM).