Layer-by-layer construction of graphene oxide (GO) framework composite membranes for highly efficient heavy metal removal

In this study, an ultrathin graphene oxide (GO) framework layer was successfully deposited on a modified Torlon^® hollow fiber support via a layer-by-layer (LbL) approach, enabling the composite membrane with superior nanofiltration (NF) performance. To molecularly design the GO framework, the substrate layer was firstly cross-linked with polyethylenimine (HPEI), followed by repeating the GO and ethylenediamine (EDA) deposition cycles and then an amine-enrichment modification by HPEI. The combination of the GO framework layer and the Torlon^® support can not only effectively seal the defects of the composite membrane with a narrow pore size distribution but also reduce the polymer consumption for the fabrication of traditional integrally skinned NF membranes. The GO/Torlon^® composite membrane has rejections higher than 95% towards Pb²⁺, Ni²⁺, and Zn²⁺ with a superior water permeability of 4.7 L m^-2 h^-1 bar^-1. The membrane also exhibits excellent long-term performance stability during a 150-h NF test. Thus, the newly developed membrane has great potential for heavy metal removal. This study may provide useful insights on the fabrication of new generation 2-dimensional (2D) NF membranes.