A graphene-based porous composite hydrogel for efficient heavy metal ions removal from wastewater

Abstract

A graphene-enhanced supramolecular hydrogel containing poly(acrylic acid)(PAA) and poly(4-vinylpyridine) (P4VP) was fabricated for the wastewater remediation. In this work, P4VP brushes were grown from functionalized graphene oxide (GO) through surface-initiated atom transfer radical polymerization. Then, the P4VP-grafted GO (i.e., GO-g-P4VP) was integrated into PAA matrix to form GO-g-P4VP@PAA hydrogel as a highly efficient adsorbent for extraction of toxic metal ions from wastewater. Due to the introduction of GO-g-P4VP, the GO-g-P4VP@PAA composite hydrogel exhibited good compressive strength, and a special interconnected 3D porous network was formed in the hydrogel. The effect of pH, initial heavy metal ion concentration, contact time, and adsorbent dosage regarding the adsorption capacity and removal efficiency of Pb2+ and Cd2+ on the hydrogel was examined. Under appropriate conditions, the GO-g-P4VP@PAA hydrogel can achieve maximum adsorption capacities of 257.28 mg/g for Pb2+, 175.79 mg/g for Cd2+. The adsorption kinetics of Pb2+ and Cd2+ on the GO-g-P4VP@PAA hydrogel followed a pseudo-second order model and the adsorption isotherms were more consistent with the Langmuir isotherm model. In addition, the GO-g-P4VP@PAA hydrogel exhibited good reusability. After five cycles, the removal efficiency of both Pb2+ and Cd2+ still remained above 80 %. These results demonstrate the GO-g-P4VP@PAA hydrogel serves as a desirable adsorbent in removal of heavy metal cations from wastewater.