Graphene Oxide-regulated Hydrogel Membrane for Extreme Heavy Metal Recovery: The Role of Size Exclusion and Ultralong Three-dimensional Channel Adsorption

Abstract

The efficient recovery of heavy metals through nanofiltration from typical wastewater sources, such as electroplating and mining, has emerged as a crucial solution for environmental protection and sustainable development. However, traditional nanofiltration membranes encounter significant challenges in heavy metal recovery, primarily due to the relatively low hydrated diameters of these metal ions. In this study, an interpenetrating polymer network (IPN) hydrogel membrane regulated by graphene oxide (GO) was developed, which features considerably longer hydrogel channels than conventional ultrathin membranes. Experimental results indicated that the IPN/GO membrane achieved over 90% recovery efficiencies for ions including Cu 2+ , Ni 2+ , Cd 2+ , Pb 2+ , and Zn 2+ , and reached nearly complete recovery of these ions when feed solution pre-adjusted to a pH of 11. By employing time-of-flight secondary ion mass spectrometry to analyze the spatial distribution of heavy metals within the IPN/GO membrane, we observed a substantial presence of heavy metal ions on the membrane surface and in the hydrogel channels. Moreover, a series of characterizations and calculations demonstrated that the IPN/GO membrane possessed enhanced hydrophilicity, uniform pore size, and extensive strong negative charge channels, facilitating the efficient recovery of heavy metal ions via size exclusion and Donnan adsorption, while maintaining high water molecule permeability. This research offers comprehensive insights into the mechanisms underlying heavy metal recovery by using hydrogel membranes.