A Comparative Study on Heavy Metal Removal Capacity of Different Hydrogels through Electrostatic Interactions and Ion-Exchange Mechanisms

Abstract

The use of hydrogel materials as adsorbents for heavy metal ions removal has grabbed the attention of several researchers due to its high removal capacity and generatability, thus providing both operational and economic efficiency. The design phase of fabricating the hydrogel material is a very critical step. A full knowledge of the effect of different potential functional groups and their interactions together can surely save resources and time. This study evaluates the removal capacity of different hydrogels whose functional groups remove via ion-exchange versus electrostatic interactions. The removal of Poly(2-Acrylamido-2-Methylpropane Sulphonic Acid) (PAMPS) was compared to that of sodium polyacrylate (NA-PA) hydrogels, which remove metals through electrostatic attraction and ion exchange respectively. It was found that the removal capacity of PAMPS, which has two anionic functional groups, is almost as good as one salt group available for ion exchange, reaching up to 92% and 87% respectively. A semi-interpenetrating network (IPN) based on both hydrogels showed slightly decreased removal capacity, almost to 80%, which was interpreted due to the loss of some active sites due to the inevitable attraction between PAMPS’s anionic functional groups and Na-PA’s salt group. The obtained results encourage the use of hydrogel materials with salt groups employing ion-exchange mechanism.