Enhancing polysulfone nanocomposite membrane heavy-metal-removal performance using an amine-functionalized separation layer with 3D nanonetworks

Two-dimensional (2D) hexagonal boron nitride (h-BN) nanosheet is a promising nanomaterial that may be used in the removal of heavy metals from wastewater. However, its large-scale production presents challenges related to time consumption, low yield and high cost. Herein, a novel and simple strategy is proposed to achieve the effective exfoliation of bulk h-BN during the membrane fabrication by intercalating with amino groupfunctionalized carbon nanotubes (CNT-NH) and an amphiphilic sodium styrene-maleic anhydride copolymer (SMANa). Significantly, an organic/inorganic 3D nanonetwork was formed in the dope solution, which stemmed from combined intercalation and hydrogen bonding, and then segregated onto the surface during the phase inversion. Subsequently, an amine-functionalized separation layer with 3D nanonetworks was constructed on the membrane surface by crosslinking polyethyleneimine (PEI) and glutaraldehyde (GA). The optimized membrane exhibited extremely high rejections of Cu2+ (99.6%), Pd2+ (98.6%), Ni2+ (98.4%) and Cd2+ (98.5%), together with a high permeate flux (30-40 L/m(2).h.bar) at 0.1 MPa, during the simulated filtration of wastewater containing various heavy metal ions. Results on membrane surface chemical composition, zeta potential and molecular weight cut off (MWCO) indicate that the separation mechanism stems from a synergistic effect between electrostatic repulsion and size sieving.