Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating
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The concerns regarding potential environmental release and ecological risks of multi-walled carbon nanotubes (MWCNTs) rise with their increased production and use. As a result, there is the need for an analytical method to determine the environmental concentration of MWCNTs. Although several methods have been demonstrated for the quantification of well-characterized MWCNTs, applying these methods to field samples is still a challenge due to interferences from unknown characteristics of MWCNTs and environmental media. To bridge this gap, a recently developed microwave-induced heating method was investigated for the quantification of MWCNTs in field samples. Our results indicated that the microwave response of MWCNTs was independent of the sources, length, and diameter of MWCNTs; however, the aggregated MWCNTs were not able to convert the microwave energy to heat, making the method inapplicable. Thus, a pre-treatment process for dispersing bundled MWCNTs in field samples was crucial for the use of the microwave method. In the present paper, a two-step pre-treatment procedure was proposed: the aggregated MWCNTs loaded environmental samples were first exposed to high temperature (500 °C) and then dispersed by using an acetone-surfactant solution. A validation study was performed to evaluate the effectiveness of the pre-treatment process, showing that an 80–120% recovery range of true MWCNT loading successfully covered the microwave-measured MWCNT mass.
KeywordsMicrowave induced heating method Quantification MWCNTs Aggregation Environmental sample Pre-treatment
This project was supported, in part, by an appointment in the Research Participation Program at the Office of the Research and Development (ORD), EPA administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the DOE and EPA. This manuscript was subjected to EPA internal reviews and quality assurance approval. The research results presented in this paper do not necessarily reflect the views of the Agency or its policy. Mention of trade names or products does not constitute endorsement or recommendation for use. The authors would like to thank Dr. Raghuraman Venkatapathy for valuable comments on the manuscript and Mr. Phillip Cluxton for technical and laboratory support.
This research was funded and conducted by the National Risk Management Research Laboratory of U.S. Environmental Protection Agency (EPA), Cincinnati, Ohio.
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