Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, People's Republic of China.
Environ Sci Technol. 2012 Apr 3;46(7):3891-7. doi: 10.1021/es204657k. Epub 2012 Mar 16.
Suspension of the pristine and COOH-substituted multi-walled carbon nanotubes (P- and C-MWCNTs) with different outer diameters (ODs) by humic acids (HAs) from a peat soil was examined. Under shaking condition, MWCNTs were not suspended within 5 d. Without HAs, C-MWCNTs were slightly suspended by sonication within 16 h, but no suspension was observed for the pristine ones (P-MWCNTs). HAs greatly enhanced suspension of both P- and C-MWCNTs. The suspension enhancement was attributed to HA sorption, which increased electrostatic repulsion and steric hindrance between individual MWCNTs. Introduction of O-containing hydrophilic moieties to MWCNTs via HA sorption enhanced the interactions of their surfaces with water through H-bonding. Suspending capability of various MWCNTs on suspended mass concentration basis by four HAs showed inconsistent orders with the increasing or decreasing trend of their ODs. However, the suspended surface area concentrations of both P- and C-MWCNTs by individual HAs consistently followed an order of P8 > P30 > P50, and C8 > C30 > C50 (P and C, respectively, refer to P- and C-MWCNTs, and the numbers represent their ODs). These data implied that MWCNTs with smaller OD could be more strongly suspended by a given HA relative to those with larger OD under sonication condition.
采用腐殖酸（HA）悬浮法研究了不同外径（OD）的原始和羧基化多壁碳纳米管（P-MWCNTs 和 C-MWCNTs）的悬浮稳定性。在振荡条件下，MWCNTs 在 5 天内未悬浮。无 HA 时，C-MWCNTs 在 16 小时内通过超声处理略有悬浮，但 P-MWCNTs 无悬浮。HA 极大地增强了 P-和 C-MWCNTs 的悬浮稳定性。悬浮增强归因于 HA 吸附，这增加了 MWCNTs 之间的静电排斥和空间位阻。通过 HA 吸附向 MWCNTs 中引入含氧亲水性基团，通过氢键增强了它们表面与水的相互作用。基于悬浮质量浓度，四种 HA 对各种 MWCNTs 的悬浮能力表现出不一致的顺序，与其 OD 的增加或减少趋势有关。然而，在超声处理条件下，每种 HA 悬浮的 P-MWCNTs 和 C-MWCNTs 的悬浮表面积浓度均遵循 P8>C8、P30>C30、P50>C50 的顺序（P 和 C 分别代表 P-MWCNTs 和 C-MWCNTs，数字代表它们的 OD）。这些数据表明，在超声处理条件下，与具有较大 OD 的 MWCNTs 相比，给定 HA 可以更强烈地悬浮具有较小 OD 的 MWCNTs。
