USEPA Office of Research and Development, National Exposure Research Laboratory, 960 College Station Road, Athens, Georgia 30605, United States.
Environ Sci Technol. 2012 Apr 17;46(8):4458-65. doi: 10.1021/es204618v. Epub 2012 Apr 3.
Little is known about how low levels of surfactants can affect the colloidal stability of single-walled carbon nanotubes (SWNTs) and how surfactant-wrapping of SWNTs can impact ecological exposures in aqueous systems. In this study, SWNTs were suspended in water with sodium dodecylsulfate (SDS) as a surface-active dispersing agent. The effect of SDS concentration on SWNT suspension stability was investigated with time-resolved dynamic light scattering (TRDLS) initial aggregation studies utilizing both monovalent (Na(+)) and divalent (Ca(2+)) cations. The critical coagulation concentration (CCC) values increased with SDS concentration for the Na(+) treatments, but the Ca(2+) treatments were less sensitive to SDS concentration changes. Longer term stability studies with SDS concentrations orders of magnitude below the SDS critical micelle concentration demonstrated that SWNTs remained suspended for over six weeks in a surface water. Transport studies in a freshwater sediment similarly showed a SDS concentration-dependent mobility of SDS-wrapped SWNTs in that SWNTs showed a relatively greater retention at lower SDS concentrations (0.001%-0.05% w/v) than at a higher SDS concentration (0.1%). It is hypothesized that the stability and mobility of SWNT suspensions is directly related to the surface coverage of SDS on the SWNT surface that simultaneously increases electrosteric repulsion and decreases surface chemical heterogeneity. Overall, these studies demonstrate that low levels of surfactant are effective in stabilizing and mobilizing SWNTs in environmental media.
关于表面活性剂低浓度如何影响单壁碳纳米管 (SWNTs) 的胶体稳定性，以及 SWNTs 的表面活性剂包裹如何影响水系统中的生态暴露，目前知之甚少。在这项研究中，SWNTs 悬浮在含有十二烷基硫酸钠 (SDS) 的水中，SDS 是一种具有表面活性的分散剂。利用单价 (Na(+)) 和二价 (Ca(2+)) 阳离子，通过时间分辨动态光散射 (TRDLS) 初始聚集研究，考察了 SDS 浓度对 SWNT 悬浮液稳定性的影响。对于 Na(+) 处理，CCC 值随 SDS 浓度的增加而增加，但 Ca(2+) 处理对 SDS 浓度变化的敏感性较低。在 SDS 临界胶束浓度 orders of magnitude 以下的 SDS 浓度下进行的更长期稳定性研究表明，SWNTs 在地表水中可保持悬浮状态超过六周。在淡水沉积物中的传输研究同样表明，SDS 包裹的 SWNTs 的迁移率与 SDS 浓度有关，即与较高的 SDS 浓度 (0.1%) 相比，SWNTs 在较低的 SDS 浓度 (0.001%-0.05% w/v) 下具有相对更大的保留率。据推测，SWNT 悬浮液的稳定性和迁移率与 SDS 在 SWNT 表面的覆盖度直接相关，这同时增加了电动排斥力并降低了表面化学异质性。总的来说，这些研究表明，低水平的表面活性剂可有效稳定和迁移环境介质中的 SWNTs。
