Construction of high performance thin-film nanocomposite nanofiltration membrane by incorporation of hydrophobic MOF-derived nanocages

In this study, hydrophobic nanofillers (ODA-h-NCs) were firstly synthesized through surface modification of MOF-derived nanocages by octadecylamine (ODA). ODA-h-NCs were then incorporated into poly(piperazine-amide) (PA) active layer to fabricate thin-film nanocomposite (TFN) nanofiltration membranes. The effects of ODA-h-NCs dosage on PA’s properties were characterized and the membrane performances on salt rejections were evaluated. Finally, the TFN nanofiltration membrane with the optimal nanoparticle doping amount was chosen. The experimental results show that the water permeance of the constructed TFN nanofiltration membrane reaches 8.97 L/(m2·h·bar) with 95.8% Na2SO4 rejection when ODA-h-NCs concentration is 0.0075 wt%, which is 1.7 times that of pristine membrane. It is also testified that the prepared TFN nanofiltration membrane possesses good stability through 50-h filtration test. Although the introduction of hydrophobic ODA-h-NCs increases the PA layer thickness, ODA-h-NCs decrease the crosslinking degree of PA layer by inhibiting the piperazine diffusion rate and pathway, their unique porous nanocage structure and large surface area provide additional transport path for water molecules, which equips TFN nanofiltration membrane with higher water flux.