Separation of dispersed carbon nanotubes from water: Effect of pH and surfactants on the aggregation at oil/water interface

• Oil/water interface aggregation (OWIA) was proposed for the decontamination of CNTs.
• Tuning pH or adding cationic surfactant can cause the OWIA of dispersed CNTs.
• CNTs in water can be reduced to a safe value of less than 1 mg/L.
• Interactions of surfactants with CNTs were elucidated schematically.

With the extensive use of carbon nanotubes (CNTs), the environmental health risk raised by this nanomaterial is concerned. Dispersed CNTs in aqueous suspension greatly increase the possibility of human and ecological exposures, but little attention has been paid to the decontamination/remediation of CNT pollution. In this study, an oil/water interface aggregation (OWIA) method was proposed for the decontamination of CNTs aqueous suspension. Tuning the water pH to suitable ranges (⩽1.8 or ⩾13.2) or adding cationic surfactant CTAB (0.075–1 mM) can cause the aggregation of CNTs at the oil/water interface, which allows the subsequent separation of CNTs from the liquids. Through the OWIA process, more than 99% of the CNTs were removed from water, and the remnant CNTs in water were less than 1 mg/L. Adding surfactant or extreme pHs may change the charged status of CNTs’ surface, and induced the aggregation of CNTs when the repulsion force between individual CNTs diminished. The cationic surfactant CTAB molecules have different interaction models with dispersed CNTs, depending on the concentrations of CTAB. This study provides a feasible approach for future decontamination of CNTs or other nanoparticles from aqueous environments.

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