Role of Ionic Moieties in Hydrogel Networks to Remove Heavy Metal Ions from Water

A variety of methods for removing heavy metal ions from wastewater have been developed but because of their low efficiency, further production of toxic sludge or other waste materials, high expense, and lengthy procedures, limited progress has been achieved to date. Polymeric hydrogel has been attracting particular attention for the effective removal of heavy metal ions from wastewater. Here, ionogenic polymeric hydrogels were prepared by free-radical copolymerization of a neutral acrylamide (AAm) monomer with an ionic comonomer in the presence of a suitable initiator and a cross-linker. Different types of ionic comonomers such as strongly acidic: 2-acrylamido-2-methylpropane sulfonic acid, weakly acidic: acrylic acid (AAc), and zwitterionic: 2-methacryloyloxy ethyl dimethyl-3-sulfopropyl ammonium hydroxide with varying amounts were incorporated into the poly(AAm) networks to fabricate the hydrogels. The heavy metal ions (Fe³⁺, Cr³⁺, and Hg²⁺) removal capacity of the fabricated hydrogels from an aqueous solution via electrostatic interactions, coordination bond formation, and a diffusion process was compared and contrasted. The poly(AAm) hydrogel containing weakly acidic AAc groups shows excellent removal capacity of heavy metal ions. The release and recovery of heavy metal ions from the hydrogel samples are also impressive. The compressive strength of hydrogels was found to be significantly high after incorporating heavy metal ions that will increase their potential applications in different sectors.