Novel hexamethylene diamine-functionalized macroporous copolymer for chromium removal from aqueous solutions

Abstract

Macroporous copolymers of poly[(glycidyl methacrylate)-co-(ethylene glycol dimethacrylate)] (PGME) with various crosslinker (ethylene glycol dimethacrylate) concentrations and porosity parameters and additionally functionalized with hexamethylene diamine (PGME-HD) were tested as potential Cr(VI) oxyanion sorbents from aqueous solutions. Kinetics of Cr(VI) sorption was investigated in the temperature range 298-343 K and the results were fitted to chemical reaction and particle diffusion models. The Cr(VI) sorption obeys the pseudo-second-order model with definite influence of pore diffusion. A temperature rise promotes chromium removal, with a maximum experimental uptake capacity of 4.21 mmol g(-1) at 343 K for the sample with the highest amino group concentration. Equilibrium data were analysed with Langmuir, Freundlich and Temkin adsorption isotherm models. Thermodynamic parameters, i.e. Gibbs free energy (G(0)), enthalpy (H-0) and entropy change (S-0) and activation energy of sorption (E-a), were calculated. The Cr(VI) adsorption onto PGME-HD was found to be spontaneous and endothermic, with increased randomness in the system. Desorption experiments show that chromium anion sorption was reversible and the PGME-HD sample GMA 60 HD was easily regenerated with 0.1 mol L-1 NaOH up to 90% recovery in the fourth sorption/desorption cycle. In the fifth cycle, a substantial sorption loss of 37% was observed.