National Research Council Research Associate, 960 College Station Road, Athens, Georgia 30605, United States.
U.S. Environmental Protection Agency Office of Research and Development, National Exposure Research Laboratory, 960 College Station Road, Athens, Georgia 30605, United States.
Environ Sci Technol. 2016 Sep 6;50(17):9214-22. doi: 10.1021/acs.est.6b01536. Epub 2016 Aug 16.
Sodium dodecyl sulfate (SDS) facilitates multiwalled carbon nanotube (MWCNT) debundling and enhances nanotube stability in the aqueous environment by adsorbing on the nanotube surfaces, thereby increasing repulsive electrostatic forces and steric effects. The resulting SDS-wrapped MWCNTs are utilized in industrial applications and have been widely employed in environmental studies. In the present study, MWCNTs adsorbed SDS during ultrasonication to form stable MWCNTs suspensions. Desorption of SDS from MWCNTs surfaces was then investigated as a function of Suwannee River Humic Acid (SRHA) and background electrolyte concentrations. Due to hydrophobic effects and π-π interactions, MWCNTs exhibit higher affinity for SRHA than SDS. In the presence of SRHA, SDS adsorbed on MWCNTs was displaced. Cations (Na(+), Ca(2+)) decreased SDS desorption from MWCNTs due to charge screening effects. Interestingly, the presence of the divalent calcium cation facilitated multilayered SRHA adsorption on MWCNTs through bridging effects, while monovalent sodium reduced SRHA adsorption. Results of the present study suggest that properties of MWCNTs wrapped with commercial surfactants will be altered when these materials are released to surface waters and the surfactant coating will be displaced by natural organic matter (NOM). Changes on their surfaces will significantly affect MWCNTs fate in aquatic environments.
十二烷基硫酸钠（SDS）通过吸附在纳米管表面，促进多壁碳纳米管（MWCNT）的解缠和提高纳米管在水相环境中的稳定性，从而增加斥力静电和空间位阻效应。得到的 SDS 包裹的 MWCNT 被应用于工业应用，并已广泛应用于环境研究。在本研究中，MWCNT 在超声过程中吸附 SDS 以形成稳定的 MWCNT 悬浮液。然后研究了 SDS 从 MWCNT 表面的解吸作为苏万尼河腐殖酸（SRHA）和背景电解质浓度的函数。由于疏水效应和π-π相互作用，MWCNT 对 SRHA 的亲和力高于 SDS。在 SRHA 的存在下，MWCNT 上吸附的 SDS 被取代。由于电荷屏蔽效应，阳离子（Na(+)、Ca(2+)) 降低了 SDS 从 MWCNT 上的解吸。有趣的是，二价钙离子的存在通过桥接作用促进了多层 SRHA 在 MWCNT 上的吸附，而单价钠离子则减少了 SRHA 的吸附。本研究的结果表明，当这些材料释放到地表水中时，商业表面活性剂包裹的 MWCNT 的性质将发生变化，并且表面活性剂涂层将被天然有机物（NOM）取代。它们表面的变化将显著影响 MWCNT 在水生环境中的命运。
