Co-transport of multi-walled carbon nanotubes and sodium dodecylbenzenesulfonate in chemically heterogeneous porous media

Authors: ZHANG, MIAOYUE - SUN YAT-SEN UNIVERSITY; Bradford, Scott; SIMUNEK, JIRKA - UNIVERSITY OF CALIFORNIA; VEREECKEN, HARRY - AGROSPHERE INSTITUTE; KLUMPP, ERWIN - AGROSPHERE INSTITUTE

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2019
Publication Date: 2/1/2019
Citation: Zhang, M., Bradford, S.A., Simunek, J., Vereecken, H., Klumpp, E. 2019. Co-transport of multi-walled carbon nanotubes and sodium dodecylbenzenesulfonate in chemically heterogeneous porous media. Environmental Pollution. 247:907-916. https://doi.org/10.1016/j.envpol.2019.01.106.
DOI: https://doi.org/10.1016/j.envpol.2019.01.106

Interpretive Summary: Multi-walled carbon nanotubes (MWCNTs) are increasingly used in commercial applications, and will be released into the environment with detergents in sewer and wastewater discharges. Studies were conducted to better understand the influence of a negatively charged detergent on the transport of MWCNTs in sand with different surface charges. The negatively charged detergent adsorbed onto the surfaces of the sand and especially MWCNTs. This surface modification greatly enhanced the transport of MWCNTs in the sand. The fate of other colloids may similarly be enhanced by adsorbed detergents, which could potentially be exploited for remediation operations or inadvertently increase the risk of colloid contamination. These findings will be of potential interest to scientists, engineers, public health officials, and government regulators concerned with predicting the fate of nanoparticles and colloids in the environment.

Technical Abstract: Multi-walled carbon nanotubes (MWCNTs) are increasing used in commercial applications and may be released into the environment with anionic surfactants, such as sodium dodecylbenzenesulfonate (SDBS), in sewer discharge. Little research has examined the transport, retention, and remobilization of MWCNTs in the presence or absence of SDBS in porous media with controlled chemical heterogeneity, and batch and column scale studies were therefore undertaken to address this gap in knowledge. The adsorption isotherms of SDBS on quartz sand (QS), goethite coated quartz sand (GQS), and MWCNTs were determined. Adsorption of SDBS (MWCNTs'»'GQS'>'QS) decreased zeta potentials for these materials, and produced a charge reversal for goethite. Transport of MWCNTs (5'mg'L-1) dramatically decreased with an increase in the fraction of GQS from 0 to 0.1 in the absence of SDBS. Conversely, co-injection of SDBS (10 and 50'mg'L-1) and MWCNTs radically increased the transport of MWCNTs when the GQS fraction was 0, 0.1, and 0.3, especially at a higher SDBS concentration, and altered the shape of retention profile. Mathematical modeling revealed that competitive blocking was not the dominant mechanism for the SDBS enhancement of MWCNT transport. Rather, SDBS sorption increased MWCNT transport by increasing electrostatic and/or steric interactions, or creating reversible interactions on rough surfaces. Sequential injection of pulses of MWCNTs and SDBS in sand (0.1 GQS fraction) indicated that SDBS could mobilize some of retained MWCNTs from the top to deeper sand layers, but only a small amount of released MWCNTs were recovered in the effluent. SDBS therefore had a much smaller influence on MWCNT transport in sequential injection than in co-injection, presumably because of a greater energy barrier to MWCNT release than retention. This research sheds novel insight on the roles of competitive blocking, chemical heterogeneity and nanoscale roughness, and injection sequence on MWCNT retention and release.