Pullulan based porous semi-IPN hydrogel: Synthesis, characterization and its application in the removal of mercury from aqueous solution

Abstract

A pullulan-graft-polyacrylamide semi-IPN hydrogel was prepared by free radical polymerization and became porous by the incorporation of calcium carbonate and a subsequent acid treatment. The product was characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, and optical microscopy to confirm the formation of porous hydrogels. In addition, the effect of several variables such as monomer, crosslinker, initiator and porogen concentration on swelling ratio and porosity of hydrogels was explored. The maximum porosity and swelling capacity in the optimized conditions were found to be 96.5% and 3089%, respectively. The prepared hydrogel was utilized as a selective adsorbent of Hg(II) ions from an aqueous solution with fast and high removal efficiency. The mercury sorption capacity under non-buffered conditions is achieved 8.6 mmol/g in the first 90 min via colorimetric method. The mechanism of adsorption was well presented using a pseudo-second-order kinetic model. Furthermore, the isothermal adsorption equilibrium data were fitted to Freundlich model. Finally, the mercury-loaded hydrogel was regenerated without losing its original activity and stability.