Corolliform morphology thin film composite polyamide membrane constructed via Tröger's base PIM for enhancing nanofiltration separation performances

In this study, a kind of Tröger's base (TB) polymer of intrinsic microporosity (PIM) was proposed to adjust both the micro-structure and macro-performance of the thin film composite (TFC) polyamide nanofiltration (NF) membrane. First, a rigidly-contorted Tröger's base (TB) diamine monomer — 2,8-diamino-4,10-dimethyl-6H,12H-5,11-methanodibenzo [1,5]-diazocine (TBDA) was synthesized (Yield: 90.2 %), and then was incorporated with piperazine (PIP) to react with trimesoyl chloride (TMC) monomer via the coupling of phase inversion and interfacial polymerization for constructing the TB-PIM-based polyamide (PA) selective separation layer. Especially, the NF membrane (TFC-TBDA/PIP) fabricated with 1/1 of TBDA/PIP and 0.075 (w/v) % TMC exhibited particular “corolla-like” morphology with high microporosity, thinner selective layer <55 nm. Under neutral condition, this membrane surface also is more negatively charged. These features further endowed this membrane superior permeability and selectivity. It showed about 2-fold water flux (87.67 L·m−2·h−1) of the conventional NF membrane (TFC-PIP) without sacrificing the multivalent sulfate salt rejections of Na2SO4 and MgSO4, and meanwhile the MgSO4 rejection was about 4.3 times as much as MgCl2. Moreover, the XPS results also revealed that there was nearly no chemical structure change of TB-PIM-based polyamide after acid soaking. Therefore, this study provides an effective way to fabricate the high-performance TFC nanofiltration membrane.