Coumarin-anchored halloysite nanotubes for highly selective detection and removal of Zn(II)

Abstract Development of a facile tool for selective detection and separation of heavy metals present in aqueous media is a demanding challenge in the chemosensing field. In this study, a natural product, halloysite nanotube (HNT), which shows excellent dispersibility in water, was selected as the scaffold to demonstrate simultaneous detection and removal of Zn ions from aqueous solution. For this purpose, HNTs were rationally integrated with coumarin moieties. The nanocomposite was prepared by treating amino-functionalized HNTs with 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde (1) to give the C N bond in the spacer resulting in the formation of the Zn2+-sensitive chemosensor (CHNTs). The successful modification was confirmed by FTIR, XPS, solid-state NMR, TG and TEM analyses. The free CHNTs showed a weak fluorescence signal, while a remarkable “turn on” behavior can be observed upon exposure to Zn2+ ions of the concentration as low as 1 × 10−6 M. In addition, CHNTs displayed excellent selectivity toward Zn2+ ions over other metal cations. Moreover, the selective removal of Zn2+ ions from an aqueous solution containing various metal ions was achieved by precipitation. The as-prepared CHNTs showing high efficiency and selectivity on the detection and separation of Zn2+ will pave the way towards novel approaches for the remediation of heavy metal pollution.