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Abstract

Hua B., J. Yang, J. Zheng and B. Deng. 2008. Characterization and dissolution of metal impurities in multi-walled carbon nanotubes. JEMREST 5:92-98.

Carbon nanotubes (CNT) containing heavy metal impurities from the remnant of the catalysts such as iron (Fe), nickel (Ni), and chromium (Cr) have been reported toxic to aquatic life and are, therefore, of environmental concern. Understanding the mechanisms of CNT toxicity to aquatic organisms is critical for assessing their potential environmental impacts. This study was conducted to characterize these metals and evaluate their dissolution kinetics from multi-walled carbon nanotubes (MWCNT). Characterization by scanning microscopy and microprobe (SEM-EDS) indicated that Ni, Fe, and Cr were major metal impurities of the MWCNT. Extraction study by 3.5 M HNO3 showed that on a per gram CNT basis, 3.78 mg Ni and 0.779 mg Fe were extractable, while by deionized water, only 1.12 mg Ni and 0.00634 mg Fe were extracted. In both cases, extractable Cr was below the detection limit of 0.001 mg g-1. Burning of MWCNT at 950°C followed by 3.5 M HNO3 extraction resulted in 7.42 mg Ni and 2.31 mg Fe g-1. Results demonstrate that about 49% of Ni, 66% of Fe, and 100% of Cr may reside inside MWCNT and are non-extractable or non-releasable to the aqueous phase.