Synthesis And Study Of Colorimetric Chemosensor For Metal Ions

The novel, easily available Salicylaldehyde bis-Schiff based colourimetric chemosensors 2-[(2,4-dihydroxyphenyl)methylene]hydrazone (L1), 2,2'-[1,2-ethanediylbis(nitrilomethy lidyne)]bis[5-(diethylamino)-Phenol (L2) and the new coumarin based colorimetric nickel chemosensor 7-hydroxycoumarin-3 (2-pyridyl)methylene)amine (L3) have been investigated in this work. The structures of these compounds were characterized by mass spectrometry, NMR and elemental analysis. L1 exhibits highly selective and sensitive recognition toward Cu²⁺ in aqueous solution via a naked eye colour change from colourless to yellow and toward Al³⁺ via a significant fluorescent enhancement in ethanol over a wide range of tested metal ions. L2 exhibits highly selective and sensitive recognition toward Mn²⁺ in pure aqueous solution over a wide range of tested metal ions with a clear naked eye color change from colorless to red. In addition, it could detect Mn²⁺ down to 10-6M by naked eye and work over a wide pH range. The coumarin based colorimetric nickel sensor L3 with high selectivity and sensitivity toward Ni²⁺ ion was reported. The absorption maximum of L3 shows a large red shift from 341 nm to 540 nm in the presence of Ni²⁺ ion, and the resulted color change from colorless to pink upon addition of Ni²⁺ is very easily observed by the naked eye, while other metal ions, such as Zn²⁺, Cd²⁺, Cu²⁺ et al. do not induce such a change. By the'naked eye', the detection limit of Ni²⁺ is as low as 0.5μM in solution.Functional films have been fabricated from UV cured material membranes containing L1-L3 as Cu²⁺, Mn²⁺, Ni²⁺ ions colorimetric film sensor. The membrane exhibits good senseitive with linear colorimetric response in the concentration range of 1.0×10^-4 to 1.0×10^-3, but always needs a long response time.To improve the water soluble of organic chemosensors, a new water-soluble allylamine N-Vinylbutyrolactam copolymer P(AH-co-NVP) (P0) grafting L2 moietie on the side chains was prepared conveniently through Mannich reaction. The color of the solution of which could be fastly changed by Fe³⁺ ions at the concentration as low as 2.0×10^–6 mol/L in diluted solutions. Moreover, no interference were observed from other anions, including Cu²⁺, Ag²⁺, Al³⁺ et al., making P0 as a novel, sensitive and selective Fe³⁺ probe.New chemosensing materials based on NVP-co-GMA-g-N2H4 polymer (P1) are prepared for the Cu²⁺ detection in water. The designed polymer was found to exhibit selective colorimetric sensing behavior toward Cu²⁺ ions with a clear naked eye color change from colorless to yellow over other representative metal ions such as K+, Fe³⁺, Cu²⁺, Al³⁺ et al. ions. And then, Bis-NVP-co-GMA-g-N2H4 hydrogel (P2) are also be synthesized for situ monitoring and its potential for reuse. Research indicates that color of this functional gel will be changed from colorless to light pink, then to dark yellow after soaked in different Cu²⁺ ions and other common metal ions can not cause this transformation. These optical changes are appreciable enough to be seen even by the naked eye for the polymer P1 aqueous solution and P2 gel.