Grantee Research Project Results

The present research was originally proposed to investigate the impact of natural organic matter (NOM) on the transport, bioavailability and toxicity of C₆₀ fullerene. During the investigation, solar irradiation, another important environmental factor, was found to greatly alter the physicochemical properties of fullerene nanoparticles (nC₆₀), and strongly influence their stability and transport behaviors. Meanwhile, a number of studies on carbon nanomaterials show that much of the previously observed toxicity of nC₆₀ is attributed to the organic solvents used in nC₆₀ suspension preparation or their derivatives; CNTs were found to show stronger toxicity than nC₆₀. Due to chemical similarity between C₆₀ and CNTs, CNTs were hypothesized to undergo similar photochemical transformation. Therefore, we adjusted our focus to investigating the role of sunlight and NOM and expanded our scope of research to include CNTs. The new overarching objective of this investigation is to determine the role of sunlight and NOM in fate, transport and toxicity of carbon based nanomaterials including nC₆₀ and carbon nanotubes in surface and ground waters.

 

Specifically, the project had three sub-objectives: 1) to investigate the photochemical transformation of nC₆₀ and CNTs under sunlight and its impact on the physicochemical properties of nC₆₀ and CNTs in realistic aqueous environments; 2) to determine the effect of photochemical transformation and NOM on the transport behaviors (i.e., aggregation and deposition) of nC₆₀ and CNTs in surface water and ground water solution conditions; and 3) to determine the impact of photochemical transformation on the toxicity of nC₆₀ and CNTs.

Summary of Findings and Accomplishments

 

Over the past 4 years, we conducted extensive investigation following our proposed research approach. In this final report, we summarize the major findings of the research and present them according to the three sub-objectives proposed. Implications of this investigation will be discussed in a separate section.

 

Task 1: Photochemical transformation of fullerene nanoparticles and carbon nanotubes under environmentally relevant conditions

 

Our investigation reveals that photochemical transformation of aqueous fullerene nanoparticles (nC₆₀) and carbon nanotubes occur at significant rates under UVA irradiation at intensity similar to that in sunlight. The transformation processes are mainly mediated by the self-generated reactive oxygen species (ROS), resulting in changes of surface chemistry of nC₆₀ and CNTs depending on their initial surface oxidation state.

 

Photochemical transformation of aqueous nC₆₀ under environmentally relevant conditions

 

UV lamps emitting light between 300 and 400 nm (peak at 350 nm) were used to simulate the UVA component in the solar spectrum. The irradiation intensity was set to be 2 mW/cm², which was comparable to the UVA intensity at the ground level on a sunny day in Houston, TX.

 

(1)  Photochemical transformation products and kinetics of nC₆₀

The particle size (measured by dynamic light scattering [DLS]) and morphology (measured by transmission electron microscope [TEM]) remained unchanged over 21 days of UVA irradiation, suggesting negligible release of soluble phototransformation products from the nanoparticle surface. In addition, total organic carbon (TOC) concentration of the sample remained unchanged, suggesting that there was no mineralization of C₆₀. However, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy results revealed oxygen-containing functional groups on the transformed nC₆₀, and the photochemical reaction products had structures similar to that of fullerol (C₆₀(OH)_x) (Figures 1 and 2). XPS analysis with argon etching suggested that only the C₆₀ molecules on nC₆₀ particle surface were oxidized, while the core of nC₆₀ remained intact (Figure 1).

 

Photochemical transformation of nC₆₀ and carboxylated multiwalled CNTs (COOH-MWCNTs) occurs at significant rates under UVA irradiation at intensity similar to that in sunlight.

The transformation is caused by photogenerated reactive oxygen species (ROS) and leads to oxygenation or decarboxylation of the nanocarbon surface depending on its initial surface oxidation state.

Surface oxidation of nC₆₀ occurs under UVA irradiation in the presence of oxygen, resulting in intermediate products similar to fullerol. The photochemical oxidation reaction initially is limited only to the surface of the nC₆₀ nanoparticles; while long-term exposure can potentially lead to its degradation and mineralization.

UVA irradiation reduces the surface oxygen concentration of COOH-MWCNTs mainly through ·OH-mediated reactions. ·OH initially reacts with the carboxylated carbonaceous fragments on CNT surface, resulting in their destruction or exfoliation. Further reaction between ·OH and the graphitic sidewall leads to formation of defects including functional groups and holes.

The presence of NOM hinders the phototransformation of nC₆₀ due to light screening and ROS scavenging.

• The environmental transport of CNs is strongly affected by their surface chemistry, the concentration and properties of NOM, and the ionic concentration and composition of water.
• In electrolyte solutions without the presence of NOM, mobility of CNs is mainly decided by their surface chemistry, especially the oxygen-containing functional groups.
• Surface oxidation induced by UVA irradiation hinders nC₆₀ aggregation and deposition on silica surface in NaCl solutions because of the increased negative surface charge and hydrophilicity; it enhances nC₆₀ aggregation in CaCl₂ solutions because of specific interactions of Ca²⁺ with the negatively charged oxygen-containing functional groups on UV-irradiated nC₆₀ surface.
• The colloidal stability of COOH-MWCNTs correlated well with the abundance of surface carboxyl groups. COOH-MWCNTs with more surface carboxyl groups have higher surface charge and consequently higher stability.
• UVA irradiation reduces the surface carboxyl concentration of COOH-MWCNTs, leading to increased aggregation and deposition on a silica surface in NaCl solutions. However, the surface potential and colloidal stability of COOH-MWCNTs remain unchanged in CaCl₂ solutions after UVA irradiation.
• Dissolved humic acid, once adsorbed onto nC₆₀ surface, hinders its deposition mainly through steric hindrance forces. The extent of this effect depends on the properties and amount of humic acid adsorbed, which is a function of ionic strength and humic acid concentration. Humic acid has limited adsorption on UVA-irradiated nC₆₀ and is expected to play a less important role in its stability.
• Humic acid immobilized onto the silica surface can potentially enhance or hinder nC₆₀ deposition, depending on the complex interplay of DLVO and non-DLVO interactions such as electrostatic interaction, steric hindrance, and hydrogen bonding as well as humic acid molecular conformation.

• MWCNTs are more toxic to the bacterium Escherichia coli than COOH-MWCNTs because of their higher bioavailability and oxidative capacity.
• UVA irradiation enhances the oxidative capacity of COOH-MWCNTs.

References:

1. Hou, W. C.; Jafvert, C. T., Photochemistry of Aqueous C(60) Clusters: Evidence of (1)O(2) Formation and its Role in Mediating C(60) Phototransformation. Environ. Sci. Technol. 2009, 43, (14), 5257-5262.
2. Chen, C. Y.; Jafvert, C. T., 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.
3. Latch, D. E.; McNeill, K., Microheterogeneity of singlet oxygen distributions in irradiated humic acid solutions. Science 2006, 311, (5768), 1743-1747.
4. Hassett, J. P., Chemistry - Dissolved natural organic matter as a microreactor. Science 2006, 311, (5768), 1723-1724.
5. Dukovic, G.; White, B. E.; Zhou, Z. Y.; Wang, F.; Jockusch, S.; Steigerwald, M. L.; Heinz, T. F.; Friesner, R. A.; Turro, N. J.; Brus, L. E., Reversible surface oxidation and efficient luminescence quenching in semiconductor single-wall carbon nanotubes. J. Am. Chem. Soc. 2004, 126, (46), 15269-15276.
6. Chan, S. P.; Chen, G.; Gong, X. G.; Liu, Z. F., Oxidation of carbon nanotubes by singlet O-2. Phys. Rev. Lett. 2003, 90, (8).
7. Alvarez, N. T.; Kittrell, C.; Schmidt, H. K.; Hauge, R. H.; Engel, P. S.; Tour, J. M., Selective Photochemical Functionalization of Surfactant-Dispersed Single Wall Carbon Nanotubes in Water. J. Am. Chem. Soc. 2008, 130, (43), 14227-14233.
8. Zhao, Y.; Allen, B. L.; Star, A., Enzymatic Degradation of Multiwalled Carbon Nanotubes. J. Phys. Chem. A 2011, 115, (34), 9536-9544.
9. Salzmann, C. G.; Llewellyn, S. A.; Tobias, G.; Ward, M. A. H.; Huh, Y.; Green, M. L. H., The role of carboxylated carbonaceous fragments in the functionalization and spectroscopy of a single-walled carbon-nanotube material. Adv. Mater. 2007, 19, (6), 883-+.
10. Reber, J. F.; Meier, K., PHOTOCHEMICAL PRODUCTION OF HYDROGEN WITH ZINC-SULFIDE SUSPENSIONS. J. Phys. Chem. 1984, 88, (24), 5903-5913.
11. Kang, S.; Mauter, M. S.; Elimelech, M., Microbial Cytotoxicity of Carbon-Based Nanomaterials: Implications for River Water and Wastewater Effluent. Environ. Sci. Technol. 2009, 43, (7), 2648-2653.
12. Kang, S.; Pinault, M.; Pfefferle, L. D.; Elimelech, M., Single-walled carbon nanotubes exhibit strong antimicrobial activity. Langmuir 2007, 23, (17), 8670-8673.
13. Kang, S.; Herzberg, M.; Rodrigues, D. F.; Elimelech, M., Antibacterial effects of carbon nanotubes: Size does matter. Langmuir 2008, 24, (13), 6409-6413.
14. Liu, S. B.; Wei, L.; Hao, L.; Fang, N.; Chang, M. W.; Xu, R.; Yang, Y. H.; Chen, Y., Sharper and Faster "Nano Darts" Kill More Bacteria: A Study of Antibacterial Activity of Individually Dispersed Pristine Single-Walled Carbon Nanotube. ACS Nano 2009, 3, (12), 3891-3902.
15. Kang, S.; Mauter, M. S.; Elimelech, M., Physicochemical determinants of multiwalled carbon nanotube bacterial cytotoxicity. Environ. Sci. Technol. 2008, 42, (19), 7528-7534.
16. Vecitis, C. D.; Zodrow, K. R.; Kang, S.; Elimelech, M., Electronic-Structure-Dependent Bacterial Cytotoxicity of Single-Walled Carbon Nanotubes. ACS Nano 2010, 4, (9), 5471-5479.
17. Yang, C. N.; Mamouni, J.; Tang, Y. A.; Yang, L. J., Antimicrobial Activity of Single-Walled Carbon Nanotubes: Length Effect. Langmuir 2010, 26, (20), 16013-16019.

Journal Articles on this Report : 5 Displayed | Download in RIS Format

Publications Views

Other project views:	All 13 publications	5 publications in selected types	All 5 journal articles

Publications

Type	Citation	Project	Document Sources
Journal Article	Hwang YS, Qu X, Li Q. The role of photochemical transformations in the aggregation and deposition of carboxylated multiwall carbon nanotubes suspended in water. Carbon 2013;55:81-89.	R834093 (2009) R834093 (2010) R834093 (Final)	Abstract: ScienceDirect-Abstract Exit
Journal Article	Qu X, Hwang YS, Alvarez PJJ, Bouchard D, Li Q. UV irradiation and humic acid mediate aggregation of aqueous fullerene (nC60) nanoparticles. Environmental Science & Technology 2010;44(20):7821-7826.	R834093 (2009) R834093 (Final)	Abstract from PubMed Full-text: ResearchGate-Abstract & Full Text Exit Abstract: ACS-Abstract Exit Other: ResearchGate-Full Text PDF Exit
Journal Article	Qu X, Alvarez PJJ, Li Q. Impact of sunlight and humic acid on the deposition kinetics of aqueous fullerene nanoparticles (nC60). Environmental Science & Technology 2012;46(24):13455-13462.	R834093 (2009) R834093 (2010) R834093 (Final)	Abstract from PubMed Full-text: Research Gate-Abstract & Full Text Exit Abstract: ACS-Abstract Exit Other: Research Gate-Full Text PDF Exit
Journal Article	Qu X, Alvarez PJJ, Li Q. Applications of nanotechnology in water and wastewater treatment. Water Research 2013;47(12):3931-3946.	R834093 (Final)	Abstract from PubMed Full-text: ScienceDirect-Full Text HTML Exit Abstract: ScienceDirect-Abstract Exit Other: ScienceDirect-Full Text PDF Exit
Journal Article	Hwang YS, Li Q. Characterizing photochemical transformation of aqueous nC60 under environmentally relevant conditions. Environmental Science & Technology 2010;44(8):3008-3013.	R834093 (Final)	Abstract from PubMed Full-text: ResearchGate-Abstract & Full Text (prepublication) Exit Abstract: ACS-Abstract Exit Other: ResearchGate-Full Text PDF (prepublication) Exit

Supplemental Keywords:

fullerene nanoparticles, carbon nanotubes, nanomaterials, natural organic matter, UVA, sunlight, irradiation, transport, fate, bioavailability, toxicity, photochemical transformation, aggregation, deposition, stability, ROS, reactive oxygen species, MWCNTs, SWCNTs, Health, Scientific Discipline, Water, Health Risk Assessment, Risk Assessments, Environmental Chemistry, Engineering, Chemistry, & Physics, Biochemistry, Drinking Water, community water system, toxicity, toxicokinetics, epidemelogy, nanomaterials, water quality, human exposure, engineered nanomaterials, drinking water system, drinking water contaminants, fate and transport, ambient particle health effects, nanotechnology, other - risk assessment, cellular responses, human health effects, human health risk, particle exposure, biochemical research

Relevant Websites:

Progress and Final Reports:

Original Abstract

2009 Progress Report

2010 Progress Report