Nanometric Graphene Oxide Framework Membranes with Enhanced Heavy Metal Removal via Nanofiltration

A novel dual-modification strategy, including (1) the cross-linking and construction of a GO framework by ethylenediamine (EDA) and (2) the amine-enrichment modification by hyperbranched polyethylenimine (HPEI), has been proposed to design stable and highly charged GO framework membranes with the GO selective layer thickness of 70 nm for effective heave metal removal via nanofiltration (NF). Results from sonication experiments and positron annihilation spectroscopy confirmed that EDA cross-linking not only enhanced structural stability but also enlarged the nanochannels among the laminated GO nanosheets for higher water permeability. HPEI 60K was found to be the most effective post-treatment agent that resulted in GO framework membranes with a higher surface charge and lower transport resistance. The newly developed membrane exhibited a high pure water permeability of 5.01 L m^-2 h^-1 bar^-1 and comparably high rejections toward Mg²⁺, Pb²⁺, Ni²⁺, Cd²⁺, and Zn²⁺. These results have demonstrated the great potential of GO framework materials in wastewater treatment and may provide insights for the design and fabrication of the next generation two-dimensional (2D)-based NF membranes.