Cu²⁺ sequestration by amine-functionalized silica nanotubes.

A novel method for Cu(2+) sequestration in Cu(2+) aqueous solution has been demonstrated using amine-functionalized double-walled silica nanotubes (DWSNTs). Herein, the precipitation method and the adsorption method are combined to remove Cu(2+) in the Cu(2+) aqueous solution. Primary (1°), secondary (2°), tertiary (3°), di-, tri-amines are immobilized on the surface of DWSNT as the adsorption site. The results show that the Cu(2+) adsorption amount on the amine-functionalized DWSNTs is in the following order: tri-amine>di-amine>1° amine>2° amine>3° amine. The complexed Cu(2+)s with the amine-functionalized DWSNTs become Cu(OH)2 crystals due to the reaction with OH(-)s dissociated from water. Thus, the amine-functionalized DWSNTs show the superior sequestration capacity of Cu(2+) in the Cu(2+) aqueous solution owing to the Cu(OH)2 crystals growth on them. FT-IR, FEG-SEM, HR-TEM, and XRD studies demonstrate the mechanism of the Cu(2+) adsorption and the Cu(OH)2 crystals growth. The crystallization-technique of the heavy metal ion on the amine-functionalized DWSNTs is also expected to have potential applications such as the facile synthesis of nano- and microparticles, and the metal catalyst supporter.