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NIOSH Program Portfolio

 

Manufacturing

NORA Manufacturing Sector Strategic Goals

927Z6RU - Determination of diameter distribution for carbon nanotubes by Raman Spectroscopy

Start Date: 10/1/2006
End Date: 9/30/2009

Principal Investigator (PI)
Name: Madalina Chirila
Phone: 304-285-5948
E-mail: dwx9@cdc.gov
Organization: NIOSH
Sub-Unit: HELD
Funded By: NIOSH

Primary Goal Addressed
5.0

Secondary Goal Addressed
None


Attributed to Manufacturing
100%

Project Description

Short Summary

The goal of this project is to use Raman spectroscopy for evaluating the diameter distribution of the carbon nanotubes and dispersion grade. This study will form part of NIOSH Nanotechnology research initiative program to characterize the physical and chemical properties of nanoaerosols in support of Manufacturing Sector Strategic Goal #5. Even though carbon nanotubes are used in end products, their physical properties are still under investigation and little is known about their toxicity. By measuring direct on filter Raman spectra from aerosol samples with several laser lines, a broad diameter distribution can be determined. The results from these studies will allow us to estimate a relative population of carbon nanotubes species and the possible state of agglomeration of the carbon nanotubes.



Description

The purpose of the project is to determine the morphology of airborne carbon nanotubes deposited on Mica and stainless steel substrates. To obtain this information we will be using the Raman bands in the 200 cm-1 region, called radial breathing mode (RBM). The frequency of the RBM is directly linked to the reciprocal of the nanotube diameter. In the case of an isolated SWCNT this relation is ? ? 248/dt. However, non isolated SWCNTs are subject to inter-tube interactions which increase the frequency of the RBM and the relationship changes to ? ? 12.5 + 223.5/dt. From the RBM Raman band peak positions we will determine the distribution of tubes diameters and from the intensity of these bands we will calculate the percentage of nanotubes with a certain diameter. To accomplish this goal we will collect Raman spectra from the same CNT sample, using: eleven different excitation wavelengths from an argon ion laser.

We also aim to determine whether or not ultrasonication in surfactant of carbon nanotubes can be used to produce individual, isolated carbon nanotubes. In powder or solutions CNTs form bundles. These bundles are conglomerates of nanotubes that are tightly bound by an estimated 500 eV/µm of tube length. We are interested to design a method of monitoring the process of de-bundling and isolation of individual nanotubes from a bundle. The method consists in comparing the Raman spectra taken with the same excitation wavelength from a dry sample and from solution sample. First sample is the dry CNT deposited on Mica substrate, which we call "as received". The second sample would be CNT mixed with surfactant and ultrasonicated. We call this sample "sonicated". In a first attempt to design this method we have used sodium dodecyl sulfate (SDS) but other surfactants like DPPC and pluronic will be tested. We will also test different concentrations of surfactant and different times for sonication and powers of sonication in order to determine the best parameters to produce isolated CNT. After sonication we will centrifuge the solution and use the top as a new sample called "centrifuged". The top of the solution should contain more isolated CNT than the bottom, since isolated CNT are lighter then bundles. To prove the presence of isolated tubes we will collect photoluminescence (PL) spectra. The existence of PL peaks is a clear indication of isolated CNT since bundled tubes can not produce photoluminescence because the binding energy between them is weakening the process. To validate the results from Raman, combined experiments of TEM and AFM will be performed on the same samples.



Objectives

Objectives:

• Obtain the Raman spectra from the air generated samples prepared at NYU, using three different laser excitations.

• Determine the size distribution of the single-wall carbon nanotubes from Raman spectra by converting the Raman shift frequency to diameter by using empirical equation. For this procedure it is necessary to conduct a literature search to find the latest results in the field.

• Prepare aliquots of carbon nanotubes with different types of surfactant in order to study the efficiency of the surfactant to de-bundle the carbon nanotubes. For this procedure use biological compatible surfactants. We intend to use DPPC, pluronic, and tween20 for this study.

• Sonicate and collect PL spectra from the aliquots of CNT and surfactants. The efficiency of de-bundling will be asses from the PL experimental results.

• Achieve a standard operational procedure for efficiency of de-bundling.



Evaluation:

• Internal review of standard operational procedure

• Peer review of publication



Mission Relevance

According to the Institute of Occupational Medicine in 2004 there were approximately 2000 people employed in the university/research sectors and new nanoparticle companies in activities in which they may potentially be exposed to nanoparticles in some form. Around 100,000 individuals may potentially be exposed to fine powders through various powder handling processes, including the pharmaceutical industry. A maximum of 500 workers are considered to potentially be exposed to nanoparticles through existing ultrafine, manufacturing processes, mostly the manufacture of carbon black and carbon nanotubes. It is predicted that the number of people in the university/research sector, and in new nanoparticle companies may double over the next five years. Based on occupational hygiene aspects of nanoparticles production there are four main groups of nanoparticle production processes: gas-phase, vapor deposition, colloidal, and attrition, all of which may potentially result in exposure by inhalation, dermal, or ingestion routes.

Although impressive from a physical-chemical viewpoint, the novel properties of nanomaterials raise concerns about adverse effects on biological systems. There is almost unanimous opinion in the scientific world that the full potential of nanotechnology requires attention to safety issues. Nanomaterials from quantum dots, fullerenes, nanofibers and nanotubes are already manufactured in a controlled manner and used in a variety of end products like electronics, gas sensors, tires, sporting goods, scratch-resistant coatings, cosmetics, etc. The possible pathogenic potential of single wall carbon nanotubes (SWCNTs) is starting to be explored. For example, one report (Shvedova et al., 2005) of acute inflammation with early onset progressive fibrosis and granulomas in mice exposed to SWCNTs demonstrated two distinct pathologies from a single kind of exposure. One was associated with SWCNTs bundles, and the other was thought to be associated with dispersed SWCNTs. Warheit in 2003, showed that recent experimental studies in rats indicate that inhaled carbon black particles may produce significant lung toxicity and that the toxicity potential increases with the decreasing particle size and increasing surface area. The materials proposed for study in this project are single wall carbon nanotubes (SWCNTs), multiwall carbon nanotubes (MWCNTs), and carbon black (CB).

The goal of this proposal is to develop a method to determine the diameter distribution and the dispersion of carbon nanotubes (CNT) in various forms: powder, air samples, suspended in aqueous solution, and mixture of CNT and surfactant. Based on these measurements, we will estimate the relative population of CNT in a sample. This study seeks to provide a methodology to qualitatively and quantitatively determine a biologically-relevant metric of exposure associated with CNT material. We will address this issue by using Raman spectroscopy combined with photoluminescence (PL) along with TEM (transmission electron microscopy) and AFM (atomic force microscopy). This would constitute an important step in obtaining quantitative analysis of the level of CNT in order to assess risks and determine hazards in working places were CNT are manufactured or used for fabrication of other products.

Sectors:

100% Manufacturing Sector:

Strategic Goal 5: "Reduce the number of respiratory conditions and diseases due to exposure in the manufacturing sector" (09PPMNFSG5).

Cross-Sector Health Outcome:

100% Respiratory Diseases

Strategic Goal 5: "Prevent respiratory and other diseases potentially resulting from occupational exposures to nanomaterials" (09PPRDRSG5).

Intermediate Goal 5.1 (09PPRDRIG5.1): determine the potential respiratory toxicities of nanomaterials.
Activity/Output Goal 5.1.1 (09PPRDRAOG5.1.1): perform basic in vitro and in vivo toxicology studies to evaluate for respiratory toxicity of nanoparticles and, if present, to characterize nanoparticles characteristics and mechanisms of action underlying toxic effects.

Other Cross-Sector:
50% Exposure Assessment
Strategic Goal 2: "Develop or improve specific methods and tools to assess worker exposures to critical occupational agents and stressors" (09PPEXASG1)

Intermediate Goal 2.11 (09PPEXAIG2.11): Address critical exposure assessment needs in emerging areas such as nanotechnology for application of new approaches to both new and traditional industrial processes, and for emerging initiatives to substitute alternative (e.g., ostensibly more safe) chemical process in areas where hazards have been identified.
Activity/Output 2.11.1 (09PPEXAAOG2.11): Development of exposure assessment tools to characterize and evaluate the exposure to these emerging areas.

50% Nanotechnology
Strategic Goal 1 (09PPNANSG1). Determine if nanoparticles and nanomaterials pose risks for work-related injuries and illnesses.
Intermediate Goal 5.1 (09PPNANIG5.1) Extend existing measurement methods. Evaluate current methods for measuring airborne mass concentrations of respirable particles in the workplace and determine whether these mass-based methods can be used as an interim approach for measuring nanomaterials in the workplace and to maintain continuity with historical methods.

Strategic Goal 4: "Enhance global workplace safety and health through national and international collaborations on nanotechnology research and guidance" (09PPNANSG4).
Intermediate Goal 2.1 (09PPNANIG2.1) Key factors and mechanisms: systematically investigate the physical and chemical properties of particles that influence their toxicity (e.g., size, shape, surface area, solubility, chemical properties, and trace components).

This project is 100% allocated to manufacture sector because as a new emerging technology, the manufacturing of carbon nanotubes is the most active sector.



Page last updated: June 3, 2011
Page last reviewed: May 23, 2011
Content Source: National Institute for Occupational Safety and Health (NIOSH) Office of the Director

 

NIOSH Program:

Manufacturing