Pullulan based hydrogels for the removal of various metal ions from aqueous solutions

Abstract

Pullulan-graft-poly(acrylic acid) (pullulan-g-poly(AA)) and pullulan-graft-poly(acrylic acid-co-acrylamide) (pullulan-g-poly(AA-co-AAm)) hydrogels were synthesized by free radical solution polymerization. Fourier Transform Infrared Spectroscopy, Thermal Gravimetric Analysis and Scanning Electron Microscopy were used to further understand the formation and the characteristics of the hydrogels. Additionally, the hydrogels’ swelling capacities and swelling kinetics were investigated. Pullulan-g-poly(AA-co-AAm) was found to have the highest swelling capacity with 461% after optimization. Metal ion adsorption and desorption abilities and the reusability properties of the hydrogels were examined, and both of the prepared hydrogels were found to be efficient adsorbents of cadmium(II), copper(II), mercury(II), nickel(II) and zinc(II) ions. The most adequate hydrogel was found to be pullulan-g-poly(AA-co-AAm) for the adsorption of cadmium(II) ions with 169.79 mg/g followed by pullulan-g-poly(AA) hydrogel for the adsorption of cadmium(II) ions with 137.76 mg/g. The desorption tests were conducted by using hydrochloric acid and the hydrogel with the best desorption ability was found to be pullulan-g-poly(AA) hydrogel with 76% for the desorption of Cd(II) ions. The adsorption-desorption cycles were repeated 3 times and the hydrogel that has the best reusability was found to be pullulan-g-poly(AA-co-AAm) with 169.79 mg/g, 124.78 mg/g and 115.34 mg/g for the adsorption of Cd(II) ions in the first, second and third cycles, respectively. All of the synthesized hydrogels were found to be good candidates for the adsorption and desorption of Cd(II), and Cu(II) ions; and pullulan-g-poly(AA-co-AAm) was able to adsorb and desorb Hg(II) ions for at least three times.