Plata D L, Gschwend P M, Reddy C M
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
Nanotechnology. 2008 May 7;19(18):185706. doi: 10.1088/0957-4484/19/18/185706. Epub 2008 Apr 2.
Commercially available single-walled carbon nanotubes (SWCNTs) contain large percentages of metal and carbonaceous impurities. These fractions influence the SWCNT physical properties and performance, yet their chemical compositions are not well defined. This lack of information also precludes accurate environmental risk assessments for specific SWCNT stocks, which emerging local legislation requires of nanomaterial manufacturers. To address these needs, we measured the elemental, molecular, and stable carbon isotope compositions of commercially available SWCNTs. As expected, catalytic metals occurred at per cent levels (1.3-29%), but purified materials also contained unexpected metals (e.g., Cu, Pb at 0.1-0.3 ppt). Nitrogen contents (up to 0.48%) were typically greater in arc-produced SWCNTs than in those derived from chemical vapor deposition. Toluene-extractable materials contributed less than 5% of the total mass of the SWCNTs. Internal standard losses during dichloromethane extractions suggested that metals are available for reductive dehalogenation reactions, ultimately resulting in the degradation of aromatic internal standards. The carbon isotope content of the extracted material suggested that SWCNTs acquired much of their carbonaceous contamination from their storage environment. Some of the SWCNTs, themselves, were highly depleted in (13)C relative to petroleum-derived chemicals. The distinct carbon isotopic signatures and unique metal 'fingerprints' may be useful as environmental tracers allowing assessment of SWCNT sources to the environment.
市售的单壁碳纳米管（SWCNT）含有大量的金属和碳质杂质。这些组分影响SWCNT的物理性质和性能，但其化学成分尚未明确界定。这种信息的缺乏也妨碍了针对特定SWCNT库存进行准确的环境风险评估，而新兴的地方法规要求纳米材料制造商进行此类评估。为满足这些需求，我们测量了市售SWCNT的元素、分子和稳定碳同位素组成。正如预期的那样，催化金属的含量为百分之几（1.3 - 29%），但纯化后的材料也含有意外的金属（例如，铜、铅的含量为0.1 - 0.3 ppt）。电弧法制备的SWCNT中的氮含量（高达0.48%）通常高于化学气相沉积法制备的SWCNT。可被甲苯萃取的物质占SWCNT总质量的比例不到5%。二氯甲烷萃取过程中的内标损失表明，金属可参与还原脱卤反应，最终导致芳香族内标的降解。萃取物的碳同位素含量表明，SWCNT的大部分碳质污染物来自其储存环境。相对于石油衍生化学品，一些SWCNT本身的¹³C含量极低。独特的碳同位素特征和独特的金属“指纹”可能有助于作为环境示踪剂，用于评估SWCNT进入环境的来源。
