A thin film nanocomposite membrane with pre-immobilized UiO-66-NH₂ toward enhanced nanofiltration performance

A facile controlled interfacial polymerization strategy was proposed for the synthesis of novel thin film nanocomposite (TFN) membranes for enhanced nanofiltration performance. UiO-66 nanoparticles were aminated and pre-immobilized onto a polymer substrate via polydopamine (PDA) coating to achieve a continuous and defect-free polyamide dense layer. The mediation of the PDA coating could not only enhance the structural stability of TFN nanofiltration membranes, but also improve the dispersion and anchorage of UiO-66-NH₂, thus closely fixing the position of UiO-66-NH₂ nanoparticles on the polymer substrate. Moreover, since the amino group (-NH₂) further reacted with PDA via Michael addition or Schiff base reaction, the in situ mutual reaction reduced the nanoparticle losses significantly during the draining off of the monomer solution in the fabrication process, which effectively cut down the actual dosage. The results showed that the PDA interlayer could induce the tight attachment of the PA layer to the support, enhancing the structural stability of TFN membranes. Furthermore, the dosage of UiO-66-NH₂ in the as-prepared TFN membranes could also be decreased to as low as 0.01 w/v%, which was nearly a 10-20-fold reduction in the required amount of UiO-66-NH₂ for the synthesis. The fabricated TFN/UiO-66-NH₂ membranes exhibited very high water permeance and competitive salt rejections in cross-flow nanofiltration, which shows the huge potential for the application of novel TFN membranes with controlled nanoparticle incorporation in industrial separation.