  We experimentally demonstrate the formation of salt aggregations with
unexpectedly high concentration inside multi-walled carbon nanotubes (CNTs)
soaked only in dilute salt solutions and even in solutions containing only
traces of salts. This finding suggests the blocking of fluid across CNTs by the
salt aggregations when CNTs are soaked in a dilute salt solution with the
concentration of seawater or even lower, which may open new avenues for the
development of novel CNT-based desalination techniques. The high salt
accumulation of CNTs also provides a new CNT-based strategy for the
collection/extraction of noble metal salts in solutions containing traces of
noble metal salts. Theoretical analyses reveal that this high salt accumulation
inside CNTs can be mainly attributed to the strong hydrated cation-pi
interactions of hydrated cations and pi electrons in the aromatic rings of
CNTs.
