New Insights into the Role of an Interlayer for the Fabrication of Highly Selective and Permeable Thin-Film Composite Nanofiltration Membrane

A triple-layered TFC nanofiltration (NF) membrane consisting of a polyamide (PA) top layer covered on a poly(ether sulfone) microfiltration membrane with a carbon nanotube (CNT) interlayer was fabricated via interfacial polymerization. The structure and properties of the PA active layer could be finely tailored by tuning the interfacial properties and pore structure of the CNT interlayer, including its surface pore size and thickness, thus improving its NF performance. This TFC NF membrane exhibited a high divalent salt rejection (the rejection of Na₂SO₄ and MgSO₄ solution >98.3%) and dye rejection (the rejection of methyl violet (MV) >99.5%) with a high pure water flux of around 21 L m^-2 h^-1 bar^-1. Excitingly, this membrane also showed excellent selectivity to both mono/divalent salt ion (the selectivity of Cl^-/SO₄^2- is as high as 85.5) and NaCl/dye solution (the selectivity of NaCl/MV is more than 123.5), which are much higher than most of other commercial and reported NF membranes. Moreover, this membrane also showed a good separation performance and long-term stability during a continuous NF process for a salt/dye mixture solution. This triple-layered TFC NF membrane showed a great promise for applications in both wastewater treatment and dyes recycling.