Carbon nanotube synthesis and detection : limiting the environmental impact of novel technologies

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2009Driven by commercial promise, the carbon nanotube (CNT) industry is growing rapidly, yet little is known about the potential environmental impacts of these novel materials. In particular, there are no methods to detect CNTs in environmental matrices (e.g., sediment) and thus, there is no way to study their transport or gauge ecological exposure. Thermal methods were developed to quantify CNTs in coastal sediments down to 10 ug per sample, which is sufficient to for CNTs in laboratory air, but not sufficient to measure contemporary levels of CNTs in the environment (which were estimated to be present at pg g-1 sediment levels using a dynamic mass balance model). In addition to the CNTs themselves, potential impacts of CNT production were assessed by monitoring emissions from a representative synthesis. An ethene-fed chemical vapor deposition process generated several compounds of environmental concern, including the greenhouse gas, methane, the hazardous pollutants, benzene and 1,3-butadiene, and toxic polycyclic aromatic hydrocarbons. By identifying critical CNT precursors (alkynes), I delivered these compounds without thermal pre-treatment and achieved rapid CNT growth. This approach reduced carbonaceous emissions by more than an order of magnitude, and lowered initial feedstock requirements and energetic demands by at least 20%, without sacrificing CNT yield.National Science Foundation (NSF) Graduate Research Fellowship Program, NSF OCE-0221181, the Seaver Institute, the Martin Family Society of Fellows for Sustainability, Arunas and Pam Chesonis through MIT’s Earth System Initiative, and the WHOI Ocean Ventures Fund

Sol-gel-platform optical sensors for oxygen gas : sensor development and investigation of probe partitioning in sol-gel matrices

I have developed gas sensors that respond rapidly and noticeably to changes in oxygen concentration by doping fluorescent complexes into gas-permeable sol-gel materials. Ruthenium (II) 4,7-diphenyl-1,10- phenanthroline, Ru(dpp)32+, responds to variations in ambient oxygen concentrations through marked changes in its fluorescence intensity. I investigated the response of Ru(dpp)32+ to oxygen in solution, in aerogels (sol gels dried under ambient conditions) and in aerogels (sol gels dried using supercritical conditions). Aerogels have particularly high porosity and low density, which allows for rapid diffusion of gases into the material. The aerogel sensor responds reversibly to changes in ambient oxygen concentration within 10 s, as compared to 50 s for Ru(dpp)32+ in a aerogel and a 69-min. response time in solution. These rapid, reversible systems have potential for use as switches, and future work will focus on evaluating their use as quantitative oxygen sensors. In addition, I have conducted fluorescence lifetime measurements to monitor probe partitioning within the aerogels and aerogels, in order to ascertain whether there are fundamental differences in the microenvironments experienced by the probes in the two types of sol gels. I have found that the probes exist in two distinct microenvironments (presumably, within the silicate matrix and along the pore-matrix interface region) within both types of sol-gel materials. This indicates that probe partitioning likely occurs early on in the sol-gelation process

Polyparameter linear free energy relationship for wood char–water sorption coefficients of organic sorbates

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Environmental Toxicology and Chemistry 34 (2015): 1464-1471, doi:10.1002/etc.2951.Black carbons (BCs), including soots, chars, activated carbons, and engineered nanocarbons, have different surface properties, but we do not know to what extent these affect their sorbent properties. To evaluate this for an environmentally ubiquitous form of BC, biomass char, we probed the surface of a well-studied wood char using 14 sorbates exhibiting diverse functional groups and then fit the data with a polyparameter linear free energy relationship (ppLFER) to assess the importance of the various possible sorbate-char surface interactions. Sorption from water to water-wet char evolved with the sorbate's degree of surface saturation and depended on only a few sorbate parameters: log Kd(L/kg) = [(4.03 ± 0.14) + (-0.15 ± 0.04) log ai)] V + [(-0.28 ± 0.04) log ai)] S + (-5.20 ± 0.21) B where ai is the aqueous saturation of the sorbate i, V is McGowan’s characteristic volume, S reflects polarity, and B represents the electron-donation basicity. As generally observed for activated carbon, the sorbate’s size encouraged sorption from water to the char, while its electron donation/proton acceptance discouraged sorption from water. However, the magnitude and saturation dependence differed significantly from what has been seen for activated carbons, presumably reflecting the unique surface chemistries of these two BC materials and suggesting BC-specific sorption coefficients will yield more accurate assessments of contaminant mobility and bioavailability and evaluation of a site's response to remediation.This material is based upon work supported by the U.S. Army Corps of Engineering, Humphreys Engineer Center Support Activity under Contract No. W912HQ-10-C-0005 awarded as part of the SERDP program.2016-05-1

Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of American 112 (2015): 13184-13189, doi: 10.1073/pnas.1511474112 .Hundreds of organic chemicals are utilized during natural gas extraction via high volume hydraulic fracturing (HVHF). However, it is unclear if these chemicals, injected into deep shale horizons, reach shallow groundwater aquifers and impact local water quality, either from deep underground injection sites or from the surface or shallow subsurface. Here, we report detectable levels of organic compounds in shallow groundwater samples from private residential wells overlying the Marcellus Shale in northeastern Pennsylvania. Analyses of purgeable and extractable organic compounds from 64 groundwater samples revealed trace levels of volatile organic compounds, well below the Environmental Protection Agency’s maximum contaminant levels, and low levels of both gasoline range (GRO; 0-8 ppb) and diesel range organic compounds (DRO; 0-157 ppb). A compound-specific analysis revealed the presence of bis(2-ethylhexyl)phthalate, which is a disclosed HVHF additive, that was notably absent in a representative geogenic water sample and field blanks. Pairing these analyses with 1) inorganic chemical fingerprinting of deep saline groundwater, 2) characteristic noble gas isotopes, and 3) spatial relationships between active shale gas extraction wells and wells with disclosed environmental health and safety (EHS) violations, we differentiate between a chemical signature associated with naturally occurring saline groundwater and a one associated with alternative anthropogenic routes from the surface (e.g., accidental spills or leaks). The data support a transport mechanism of DRO to groundwater via accidental release of fracturing fluid chemicals derived from the surface rather than subsurface flow of these fluids from the underlying shale formation.The authors thank Duke University’s Pratt School of Engineering and the National Science Foundation’s CBET Grant Number 1336702 and NSF EAGER (EAR-1249255) for financial support.2016-04-1

Vertically aligned carbon nanotubes: production and applications for environmental sustainability

Carbon nanomaterials play an essential role in resolving the increasingly urgent energy and environmental crises. A unique type of carbon nanotubes (CNTs), vertically aligned CNTs (VACNTs) possess the intrinsic, extraordinary nanoscale properties (mechanical, electrical, and thermal) of individual CNTs, but present them in a hierarchical and anisotropic morphology, which holds promise to transform a diverse set of practical environmental application processes from water filtration to energy storage. Nevertheless, the potential environmental impacts beholden to their synthetic methodology might reduce the net sustainability benefits of this advanced material, where environmental impacts of the synthesis may be reduced or offset by the lifetime benefits of the proposed technologies. Aiming to provide a holistic view of the robust development of VACNT-enabled environmental technologies, this critical review assesses recent advances in their production routes and applications, both with a focus on environmental objective optimization. In particular, sustainable production of VACNTs, VACNT-based functional composite materials, and their environmental engineering applications based on different functional mechanisms (i.e., sorption, catalysis, and separation) are thoroughly featured. Finally, we illustrate VACNTs as an example to explore strategies to co-optimize their environmental benefits and costs, which could potentially impact the way all other emerging materials are designed for environmental sustainability purposes.National Science Foundation (U.S.) (Award 1552993)United States. Environmental Protection Agency (Grant RD83558001

Natural Aerogels with Interesting Environmental Features: C-Sequestration and Pesticides Trapping

International audienceThis chapter discusses the emerging and promising field of environmental applications of aerogels. Due to their large pore volume, specific surface area, and diverse range of tailorable solid-phase and surface chemistries, aerogel materials are interesting candidates for addressing many challenging environmental remediation objectives. Herein we review the use of silicate, nonsilicate, and allophane-clay-based aerogels in several challenging environmental remediation applications including the removal of air pollutants, water remediation, oil spill reclamation, heavy metal capture, CO2 sequestration, trapping of pesticides, immobilization of nuclear waste, and capture of orbital space debris

Waste Containment Ponds Are a Major Source of Secondary Organic Aerosol Precursors from Oil Sands Operations

Copyright © 2020 American Chemical Society. The surface mining and bitumen extraction of oil sands (OS) generates over one million barrels of heavy oil each day in the Alberta Oil Sands Region of Canada. Recent observations suggest that emissions from OS development contribute to secondary organic aerosol (SOA) formation, but the chemical composition, mass fluxes, and sources of those emissions are poorly delineated. Here, we simulated OS extraction and used comprehensive two-dimensional gas chromatography to quantify and characterize direct air emissions, bitumen froth, residual wastewater, and tailings components, ultimately enabling fate modeling of over 1500 chromatographic features simultaneously. During the non-ice cover season, tailings ponds emissions contributed 15000-72000 metric tonnes of hydrocarbon SOA precursors, translating to 3000-13000 tonnes of SOA, whereas direct emissions during the extraction process itself were notably smaller (960 ± 500 tonnes SOA yr-1). These results suggest that tailings pond waste management practices should be targeted to reduce environmental emissions

Halogenation Chemistry of Hydraulic Fracturing Additives under Highly Saline Simulated Subsurface Conditions

Unconventional natural gas extraction via hydraulic fracturing coupled with horizontal drilling (HDHF) has generated disruptive growth in the domestic energy sector. Field analyses of residual HDHF fluids have detected halogenated species, potentially the product of unexplored reactions between authigenic halides and HDHF additives. Utilizing a custom high-pressure reactor system, we simultaneously screened 12 frequently disclosed, functionally diverse HDHF additives to uncover transformation chemistry. One emergent pathway, the halogenation of cinnamaldehyde in the presence of ammonium persulfate, demonstrated the potential for oxidative breakers to react with halides to yield reactive halogen species. Halogenated product formation, product distribution, and kinetics were evaluated with respect to shale well subsurface condition, linking transformation risk to measurable well-dependent characteristics (e.g., halide compositions, well temperatures, and pH). In a representative flowback brine, the brominated product dominated on a molar percent basis (6 ± 2%, as normalized by initial cinnamaldehyde loading) over chlorinated (1.4 ± 0.4%) and iodinated forms (2.5 ± 0.9%), reflecting relative halide abundance and propensity for oxidation. This work demonstrates that relevant subsurface reactions between natural brines and hydraulic fracturing additives can result in the unintended formation of halogenated products