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

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 À1) 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 À1) 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.

Significance of Non-DLVO Interactions on the Co-Transport of Functionalized Multiwalled Carbon Nanotubes and Soil Nanoparticles in Porous Media

“…A stainless-steel column with 3 cm inner diameter and 12 cm length was uniformly wet packed with purified quartz sand (QS, median grain size of 240 μm). , Approximately 30 pore volumes (PVs) of background electrolyte solution (1 mM KCl) were injected at a constant Darcy velocity of 0.71–0.72 cm min –1 to equilibrate the column before initiating an experiment.…”

“…CNTs have been employed in numerous commercial applications and as adsorbents for environmental remediation and water treatment, − which will eventually result in their release into the subsurface . Current studies have investigated the transport behavior of CNTs in porous media under various physical and chemical conditions, including ionic strength (IS), water content, porous medium grain size, input concentration of CNTs, surfactants, and organic matter. − However, information on the co-transport of CNTs and soil colloids or soil nanoparticles (SNPs), as well as interactions of CNTs with soil colloids or SNPs is still limited.…”

New guidelines for testing “Deep eutectic solvents” toxicity and their effects on the environment and living beings

“…However, there is a concern about the importance of assessing risks of environmental pollutants obtained in those processes (Nilsen et al, 2019;Vita et al, 2018). Thus, several recent works address new guidelines and approaches to optimize the assessment of the quite recently environmental risks in both, terrestrial and aquatic environments (Song et al, 2018;Zhang et al, 2019;Shiyuan et al 2019). This work contributes to the knowledge of assessing risks of environmental pollutants, as it is the case of DESs as potential environmental contaminants.…”

Biosurfactant-mediated mobility of graphene oxide nanoparticles in saturated porous media

“…50 Finally, the steric effect induced by the deposited surfactant molecules also contributed to saponin's enhancement of GO transport. 66,75,78…”