Three-dimensionally assembled polyelectrolyte multilayers-functionalized silica nanowire membrane for highly-efficient adsorptive separation of copper ions from water

High-performance materials for heavy metal ion removal are highly demanded in environmental treatment. Membrane adsorption has the advantages of being easy to operate and avoiding secondary pollution. It remains challenging to prepare adsorption membranes with both high removal rate and high permeability. Here, we present a novel strategy for preparing poly(acrylic acid) (PAA) and polyethyleneimine (PEI) multilayer-assembled silica nanowires (SiO₂ NWs) membrane with abundant, multiple functional groups on a highly porous network for Cu(II) capture. The SiO₂ NWs in the hybrid membranes serve as a rigid 3D framework to improve membrane porosity and water flux, while the polyelectrolyte multilayers assembled on the SiO₂ NWs provide abundant, highly accessible adsorption sites for Cu(II) uptake. The adsorption capacity of the membranes can be tuned by changing the dosage of the assembled SiO₂ NWs and the PAA/PEI pair layers. The maximum adsorption capacity of the active polyelectrolyte layer for SiO₂ NWs@(PAA/PEI)₄ composite membrane was 272.5 mg/g toward Cu(II), outperforming the counterpart (PAA/PEI)₄ membrane (97.5 mg/g) after removal of the SiO₂ NWs framework. The hybrid membrane shows excellent adsorption performance for the removal of low concentrations of Cu(II) in a dynamic adsorption mode, and the removal rate is maintained at above 90 % after eight recycles.