Abstract
Ageing is the inevitable fate of carbon nanotubes (CNTs) in natural environments. However, the ageing-induced changes in the mobility of CNTs are still poorly understood. In this study, we investigated the migration of CNTs with different ageing degrees in saturated quartz sand using ultrapure water, fresh water and seawater as background solutions. Ageing could change the physicochemical properties of CNTs, leading to less hydrophobicity, lower hydrodynamic diameter, more negative charge and higher dispersity. As a result, aged CNTs exhibited a higher migration ability than pristine CNTs. Furthermore, DLVO theory and XDLVO theory were applied to explore the interaction between CNTs and between CNTs and quartz sand, respectively. Electrostatic repulsion is the primary force, and the total force is also repulsion and increases with ageing, which is favorable for CNTs to migrate in quartz sand. In fresh water and seawater, high ionic strength reduced the electrostatic repulsion, as well as hydrodynamic diameters and negative charges, and thus ageing exhibited a weaker enhancement on CNTs migration than that in ultrapure water. This work is useful to better understand the migration of aged CNTs and is of great significance to reveal the fate of carbon nanomaterials in nature.
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