Luminescent Sensing, Selective Extraction and Recovery of Cu²⁺ from Aqueous Environment by a Novel Turn-on...

A novel luminescent hydrazone ligand was synthesized via 1:1 condensation reaction of 9-anthracene aldehyde and 2-hydrazinobenzoic acid followed by its characterization with the help of absorption, emission, FTIR, NMR and mass studies. It was investigated as a reversible, ratiometric and turn-on luminescent chemosensor for Cu²⁺ in aqueous environment. The receptor shows a prominent color change in presence of Cu²⁺ from yellow to reddish brown in DMSO-H₂O (2:1) medium. Upon addition of Cu²⁺, a remarkable increment in emission intensity (Φ = 0.091, 11 fold) was observed probably due to intra-ligand charge transfer transition (ILCT). Interestingly, this sensor is capable to extract Cu²⁺ selectively from aqueous mixture of metal ions using dichloromethane solvent with the increased extraction efficiency from 85% (L:Cu²⁺, 1:1) to 95% (L:Cu²⁺, 2:1) in the pH range of 6.5-10.0. The extraction behavior of Cu²⁺ was monitored with the help of UV-Vis spectroscopy and a readily-usable smartphone to capture the RGB data which may be helpful as a field based analysis tool. In presence of Cu²⁺ (1.0 × 10^-5 M), no significant interference was observed after addition of 5-fold excess of other metal ions (Zn²⁺, Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Ni²⁺, Hg²⁺, Sn²⁺, Al³⁺, Cr³⁺, Mn²⁺) in DMSO-H₂O (2:1) medium. Moreover, the ligand was regenerated (> 98%) by adjusting the pH upto 4 cycles and showed a good recyclability and reusability which might be helpful to extract Cu²⁺ efficiently from aqueous medium.