Equilibrium and kinetics for temperature swing adsorption of a target metal on molecular imprinted thermosensitive gel adsorbents

A novel thermosensitive gel adsorbent, which adsorbs and/or desorbs a specific heavy metal, as a function of gel shrinking/swelling by temperature swing was developed. The gel, a copolymer of N-isopropylacrylamide as a thermosensitive component, 4-(vinylbenzyl)ethylenediamine (VBEDA) as a chelating agent, and cross-linker, was prepared by copolymerization by means of a molecular imprinting technique using Cu(II) ion as a template. Equilibria and kinetics for the adsorption/desorption for a temperature swing of 307/283 K were investigated. Adsorption equilibria, expressed as the Langmuir isotherms, indicated that one Cu molecule is strongly coordinated to two VBEDA groups at 307 K and weakly coordinated to one VBEDA group at 283 K. The rates of adsorption and desorption were dominantly expressed with the diffusion equation within the gel and were evaluated in terms of effective diffusivity. The equilibria and kinetics data shows the thermosensitive reconstruction/destruction of an adsorption site composed of two VBEDA groups.