Studies on the Complexation of 3d Transition Metal Ions with NR/PEO Block Copolymer in Aqueous Medium

Abstract

Polyethylene oxide (PEO) was chemically linked to natural rubber (NR) segments to form a block copolymer (BC), which proved to be a suitable material for complexing with selected first row transition metal ions in aqueous solution through batch adsorption method under noncompetitive mode. Optimum conditions for sorption were found to be 20 mmol/L initial concentration, pH at 6, ambient temperature, and 24 h. The order of decreasing adsorption capacity obtained is Mn(II) > Co(II) > Zn(II) > Ni(II) > Cu(II) > Fe(III). Freundlich isotherm shows the best fit indicating that the adsorption is of heterogeneous in nature. The complexation follows pseudo second‐order kinetics. Exothermic character of the complexation was confirmed by thermodynamic study. For all metal ions, the standard free energy change values are negative for the different temperatures studied, which confirms the spontaneous character of the process. At ambient temperature, the free energy change lies between −2.35 and − 7.83 kJ/mol for all complexes. Values of activation energy for all the metal ion complexation is within the range 11–25 kJ/mol, which indicates chemical interaction via activated physico–chemical adsorption. Variation in stability constant of the complexes also follows the same order as given above. POLYM. ENG. SCI., 60:661–672, 2020. © 2020 Society of Plastics Engineers