Suspending Multi-Walled Carbon Nanotubes by Humic Acids from a Peat Soil

Abstract

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.

Multi-walled carbon nanotube dispersion by the adsorbed humic acids with different chemical structures

“…3, MWCNT suspension increased with increasing Q e , but suspension was below the detection limit (<0.5 mg/L) without HAs, indicating that adsorption of HAs on the MWCNTs was vital for suspending MWCNTs. This result has universally been observed in the literature (Smith et al, 2012;Zhou et al, 2012). The coating of MWCNTs by HA (or surfactants) can decrease MWCNT hydrophobicity (Hyung et al, 2007;Chappell et al, 2009) (Table 1) while increasing MWCNT electrostatic repulsion (Jiang et al, 2003;Chen et al, 2004;Zhou et al, 2012) (as suggested by the negative charge in Fig.…”

“…It has also been found that, as a whole, for a single DOM, there is a good correlation between the amount of DOM adsorbed and the amount of CNTs suspended. This may explain why in some cases suspended CNTs increase with increasing DOM concentration (Smith et al, 2012;Zhou et al, 2012), but when different DOMs are compared, higher DOM adsorption by CNTs does not always result in an increase in the amount of CNT suspended (Chappell et al, 2009). Based on the above discussion, it can be hypothesized that the chemical nature of the DOM plays an important role in dispersing and suspending CNTs.…”

“…It has been reported that CNTs with smaller outer diameters (Zhou et al, 2012) or shorter in length (Schwyzer et al, 2011) are more easily suspended by DOM; however, the preference of largediameter MWCNTs in stable suspension was also reported (Schwyzer et al, 2012;Yang et al, 2013). With regard to DOM, it has been reported that 1) hydrophilic (polar) DOMs suspended CNTs more effectively (Chappell et al, 2009;Lin et al, 2013), 2) both hydrophilic and hydrophobic fractions of DOM play important roles in suspending CNTs (Hyung et al, 2007).…”

A Review of the Properties and Processes Determining the Fate of Engineered Nanomaterials in the Aquatic Environment

“…Increase of DOM concentration decreased the aggregate growth rate due to a decrease in the hematite surface available for interaction with the MWCNTs. In many studies DOM has been found to increase the colloid stability of MWCNTs (Hyung et al, 2007;Lin et al, 2010;Petersen et al, 2011;Smith et al, 2012;Zhou et al, 2012), probably by steric repulsion of the macromolecules associated with the MWCNTs.…”

Double walled carbon nanotubes promote the overproduction of extracellular protein-like polymers in Nitzschia palea: An adhesive response for an adaptive issue

“…On the one hand, NOM can occupy hydrophobic areas that are inherent to DWCNTs, limiting interaction between DWCNTs and EPS [64]. On the other hand, NOM could promote the interaction between DWCNTs and EPS through forming different bonds such as electrostatic, hydrophobic, p-p and hydrogenbond interactions [17,63] with both DWCNTs and EPS [17,50].…”