Abstract
ABSTRACTCarbon nanotubes (CNTs) are cylindrical molecules of carbon with diverse commercial applications. CNTs are also lightweight, easily airborne, and have been shown to be released during various phases of production and use. Therefore, as global CNT production increases, so do concerns that CNTs could pose a safety threat to those who are exposed to them. This makes it imperative to fully understand CNT release scenarios to make accurate risk assessments and to implement effective control measures. However, the current suite of direct-reading and off-line instrumentation used to monitor the release of CNTs in workplaces lack high chemical specificity, which complicates risk assessments when the sampling and/or measurements are performed at a single site where multiple CNT types are handled in the presence of naturally occurring background particles, or dust. Herein, we demonstrate the utility of Raman spectroscopy to unequivocally identify whether particulate matter collected from a multi-user analytical balance workstation comprised CNTs, as well as, whether the contamination included CNTs that were synthesized by a Ni/Y-catalyzed electric-arc method or a Co/Mo-catalyzed chemical vapor deposition method. Identifying the exact CNT type generated a more accurate risk assessment by knowing the metallic impurities involved, and it also led to the identification of the users who handled these CNTs, a review of their handling techniques, and an improved protocol for safely weighing CNTs.
Highlights
Carbon nanotubes (CNTs) are an allotrope of carbon that come in two basic varieties
The primary intentions behind this standard operating procedure (SOP) are to describe methods to handle lightweight carbon nanomaterial (CNM) in order to minimize the contamination of non-vented workplace areas with CNMs and the exposure of personnel to CNMs, to properly clean CNM contamination, to properly dispose of CNM waste, and to provide recommendations for suitable personal protective equipment (PPE) that should be used during these operations.[13,25,38,50,51]
The first step in using microprobe Raman spectroscopy to analyze particulate matter collected from this analytical balance workstation was the evaluation of the 633-nm Raman spectrum of the filter paper used to collect the particulate matter, in this case, quartz fiber filter (QFF) papers approved by the U.S EPA for use with air-collection devices and personnel exposure badges
Summary
Carbon nanotubes (CNTs) are an allotrope of carbon that come in two basic varieties. The first is a single-walled CNT (SWCNT) that can be represented as a graphene sheet of sp2hybridized carbon atoms seamlessly wrapped into a cylindrical tube. The most commonly used off-line instruments for assessing the release of CNTs include thermal-optical (TO) detectors that can measure elemental and organic carbons,(31,33,41) laser induced breakdown spectrometers (LIBSs) that can identify metal-containing CNTs,(32) and most notably, a scanning or transmission electron microscope (SEM/TEM) with an energy-dispersive x-ray (EDX) analyzer that can detect all elements in a sample between atomic numbers 4 and 92.(26–34,40–42) all of these direct-reading and off-line instruments lack high chemical specificity for nanostructured carbons This can complicate risk assessments especially when the sampling and/or measurements are performed at a site where multiple carbon nanomaterial (CNM) types are handled in the presence of naturally-occurring background particles, or dust – a complex mixture of plant pollen, mammalian hair and skin cells, textile and paper fibers, minerals from the soil, vehicle emissions, and potentially many other inorganic and organic materials.[29,34,36,37,38,43]
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