Grantee Research Project Results
Final Report: Photochemical and Fungal Transformations of Carbon Nanotubes in the Environment
EPA Grant Number: R834858Title: Photochemical and Fungal Transformations of Carbon Nanotubes in the Environment
Investigators: Jafvert, Chad T. , Fairbrother, D. Howard , Filley, Timothy
Institution: Purdue University , The Johns Hopkins University
EPA Project Officer: Hahn, Intaek
Project Period: August 15, 2010 through August 14, 2013
Project Amount: $600,000
RFA: Increasing Scientific Data on the Fate, Transport and Behavior of Engineered Nanomaterials in Selected Environmental and Biological Matrices (2010) RFA Text | Recipients Lists
Research Category: Chemical Safety for Sustainability
Objective:
We proposed that due to their size, any transformation of carbon nanotubes (CNTs) in the environment is likely dominated by abiotic oxidative and extracellular microbial processes. Consequently, in this study we investigated the photochemical and fungal mediated transformations that occur to colloidal and solid phase CNTs. Our goal was to identify transformation products, reaction kinetics, and reaction mechanisms. The plan also was to study transformation of CNTs in polymer composites, and determine if and under what conditions CNTs are released from composites as a result of exposure to light. The capacity of fungi to use CNTs as a carbon source for metabolism and growth was investigated. Our objectives are based on two overarching hypotheses: (1) Photochemical and fungal transformations of CNTs will occur and proceed via oxidative processes with important consequences for their overall persistence in the environment, and (2) that the rate of these reactions will depend on CNT physicochemical properties (e.g. surface properties), environmental conditions (e.g., pH, fungi type), and CNT form (e.g., colloids or immobilized in polymers).
Summary/Accomplishments (Outputs/Outcomes):
Photochemical Studies With Functionalized SWCNTs: We examined the production of reactive oxygen species (ROS) as a function of SWCNT functionalization. Aqueous colloidal dispersions of carboxylated (SWCNT-COOH) and PEG-functionalized single-walled CNTS were found to generated ROS, including singlet oxygen (1O2), superoxide anion (O2.-), and hydroxyl radicals (×OH) in light within the solar spectrum (λ = 300-410 nm). Additional studies analyzed carbon-13 content of headspace CO2 above solar light irradiated carboxylated CNTs, indicating that within 30 days of irradiation, over 2.5 percent of the nanotube carbon had been mineralized by direct photolysis.
Photochemistry Studies With Unfunctionalized SWCNTs: Unfunctionalized single walled carbon nanotubes (SWCNTs) are much less reactive under sunlight than functionalized SWCNTs. With surfactant added as a dispersing agent, unfunctionalized SWCNTs produced no measurable ROS within 60 hrs of irradiation, whereas functionalized SWCNTS produced measurable ROS in less than 5 hours, as detected using the same ROS scavengers. As a result, indirect photochemical reactions involving these materials was investigated. It is well known that very low (» 10-15 M) concentrations of hydroxyl radicals occur in many natural waters due to photochemical reactions involving humic acids and other naturally occurring aqueous substances. As a result, we have used solar irradiation of hydrogen peroxide as a way to produce low steady-state concentrations of hydroxyl radicals to study indirect photochemical reactions of unfunctionalized SWCNTs in water. In most of the experiments, aqueous suspensions containing sodium dodecylsulfate (used as a dispersant) were irradiated, following the reactions by UV/Vis, Raman, and near infrared fluorescence (NIRF) spectrometry, and TEM imaging. Within several days, UV/Vis absorbance bands decreased, the Raman I(D) band increased relative to the I(G) band, and fluorescence signals for (6,5) and (8,4) chiralities (the dominate chiralities contained in the SG-65 mixture) faded. This indicated loss in characteristic properties of the unfunctionalized nanotubes, due to reaction with hydroxyl radicals. Additional experiments without surfactant present also indicated the decrease in the fluorescence signals of SG-65 sample photolyzed with hydrogen peroxide after 68 and 93 days.
Dark Reactions Involving SWCNTs With Biological Reducing Agents: ROS-induced DNA damage is suspected to be responsible for the cytotoxicity of carbon nanotubes (CNTs) from both in vivo and in vitro experiments, but the mechanism for ROS generation under CNTs-mediated conditions had not yet elucidated, especially for light-independent redox reactions. Originating from the concept that CNTs could catalyze redox reactions and promote electron-transfer reactions of biomolecules, we hypothesized that CNTs can act as electron shuttles that transfer electrons from electron donors to aqueous molecular oxygen, thereby generating ROS (i.e., O2.-, H2O2, OH) in the absence of light. With milligram per liter suspensions of SWCNT-COOH at pH 7 containing NADH (0.05-0.4 mM) as the electron donor, the catalytic oxidation of NADH to NAD+ over time was verified. Upon addition of Nitro Blue Tetrazolium salts (NBT) as a probe, the production of O2.-was confirmed. For this same system, addition of a hydroxyl radical scavenger (p-chlorobenzoic acid) indicated that subsequence formation of measurable hydroxyl radical did not occur within the same time period (20 hrs). As a result, a modified DPD - horseradish peroxidase (HRP) assay was used to measure potential accumulation of H2O2. Indeed, an increase in absorbance at 551 nm over time occurred due to stable DPD.+ formation, indicating accumulation of H2O2 during the oxidation of NADH. DNA electrophoresis results confirmed that significant DNA cleavage occurred by the build-up of nicked supercoiled DNA (pBR 322), despite our inability to measure hydroxyl radical, the species thought responsible of pBR 322 cleavage.
Photochemical Reactions of Oxidized MWCNTs Exposed to UV (254 nm) Irradiation: Oxidized multiwalled CNTs (O-MWCNTs) were suspended under a variety of solution conditions of pH, ionic strength, and O2 concentration. These CNTs were then exposed to UVC irradiation in a photochemical reactor to examine the effects of these solution conditions and light intensity as a function of irradiation time. Chemical and physical changes resulting from UV exposure were characterized using a combination of UV-Vis, DLS, XPS, Raman, and TEM. A common phenomenon that was observed at all solution conditions examined was UV-induced aggregation. Over the course of irradiation, the O-MWCNTs begin to aggregate until the flocculates reach a size large enough to become visible to our eyes. Once the particle size is large enough, the particles settle to the bottom of the vessel.
Photodegradation of Multiwalled Carbon Nanotube/Polymer Nanocomposite Under 350 nm Irradiation: Nanocomposites of polystyrene (PS) and pristine multi-walled carbon nanotubes (p-MWCNTs) were prepared by solution blending in tetrahydrofuran. Characterization of the nanocomposite was performed by SEM and XPS to confirm that the nanoparticles are well dispersed in the polymer matrix. Once the CNT/polymer nanocomposites had been made they were exposed to the effects of hydroxyl radicals generated by exposing hydrogen peroxide (H2O2) to 350 nm light.
Fungi Related Studies: A study was completed to test the enzymatic response of cultured saprotrophic white-rot fungi Trametes versicolor and Phlebia tremellosa various SWCNTs under different media conditions. The nanomaterials used in this study represent a range of SWCNTs synthesized by the same method, and include unpurified (AP-SWCNT), purified and unfunctionalized (P2-SWCNT), and purified and carboxylated (P3-SWCNT) SWCNTs. Figure 13 illustrates how the unpurified AP-SWCNT and carboxylated P3-SWCNT promoted significant changes in the activity of oxidative enzymes, laccase and perocidaes, of both white-rot fungi in this study. The addition of the purified but unfunctionalized P2-SWCNT did not significantly alter enzyme activity. Analysis of residual metals released by SWCNT into media found significant catalyst leaching from unpurified tubes and subsequent fungal uptake, but at levels below those toxic to fungi. Movement of catalytic metal into growth media was not significantly affected by media composition. These results demonstrate that the enzymatic response of saprotrophic fungi exposed to carbon nanomaterials is complex, depending not only on SWCNT surface chemistry but also media composition and fungal species.
Journal Articles on this Report : 11 Displayed | Download in RIS Format
Other project views: | All 31 publications | 11 publications in selected types | All 11 journal articles |
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Berry TD, Filley TR, Blanchette RA. Oxidative enzymatic response of white-rot fungi to single-walled carbon nanotubes. Environmental Pollution 2014;193:197-204. |
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Berry TD, Clavijo AP, Zhao Y, Jafvert CT, Turco RF, Filley TR. Soil microbial response to photo-degraded C60 fullerenes. Environmental Pollution 2016;211:338-345. |
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Berry TD, Filley TR, Clavijo AP, Gray MB, Turco R. Degradation and microbial uptake of C-60 fullerols in contrasting agricultural soils. Environmental Science & Technology 2017;51(3):1387-1394. |
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Bitter JL, Yang J, BeigzadahMilani S, Jafvert CT, Fairbrother DH. Transformations of oxidized multiwalled carbon nanotubes exposed to UVC (254 nm) irradiation. Environmental Science:Nano 2014;1(4):324-337. |
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Chen C-Y, Jafvert CT. The role of surface functionalization in the solar light-induced production of reactive oxygen species by single-walled carbon nanotubes in water. Carbon 2011;49(15):5099-5106. |
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Dawson D, Salice C, Dacko N, Kurian A. A Model of Culex quinquefasciatus Abundance Constructed Using Routine Surveillance and Treatment Data in Tarrant County, Texas. JOURNAL OF THE AMERICAN MOSAUITO CONTROL ASSOCIATION 2019;35(1):1-10 |
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Hou W-C, BeigzadahMilani S, Jafvert CT, Zepp RG. Photoreactivity of unfunctionalized single-walled carbon nanotubes involving hydroxyl radical: chiral dependency and surface coating effect. Environmental Science & Technology 2014;48(7):3875-3882. |
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Hsieh H-S, Jafvert CT. Reactive oxygen species generation and dispersant-dependent electron transfer through single-walled carbon nanotubes in water. Carbon 2015;89:361-371. |
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Hsieh H-S, Wu R, Jafvert CT. Light-independent reactive oxygen species (ROS) formation through electron transfer from carboxylated single-walled carbon nanotubes in water. Environmental Science & Technology 2014;48(19):11330-11336. |
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Zhao Y, Jafvert CT. Environmental photochemistry of single layered graphene oxide in water. Environmental Science: Nano 2015;2:136-142. |
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Zhao Y, Hsieh H, Wang M, Jafvert C. Light-independent redox reactions of graphene oxide in water: Electron transfer from NADH through graphene oxide to molecular oxygen, producing reactive oxygen species. CARBON 2017;123:216-222 |
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Supplemental Keywords:
Nanotechnology, environmental fate, photochemistry, mineralization, solar light, nanomaterials, nanotubes, functionalized carbon nanotubes, reactive oxygen species, nanomaterial characterization, DNA cleavage, toxicityProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.