Wholly-Tröger's base with strong rigidity-based polyamide loose nanofiltration membranes with excellent permeance, precise dye/salt selectivity, and durability under strongly acidic conditions

A novel Tröger's base-based diamine monomer-4,4′-(6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)dianiline (DAPTB) was designed and prepared. • The novel DAPTB decorated polyamide thin film composite nanofiltration (TFC NF) membrane was fabricated. • The M DAPTB-TMC NF membrane showed a water flux that was 4.54 times higher than that of the M PIP-TMC membrane, and precise dye/salt selectivity. • The M DAPTB-TMC NF membrane showed excellent durability under strong acidic environments. • The rejection for EBT still remained over 99% after 63 days of static soaking in 20 wt% H 2 SO 4 solution. For efficient dye/salt separation, particularly under strongly acidic conditions, the limited acid stability of traditional polypiperazine-amide thin film composite nanofiltration membrane (M PIP-TMC TFC NF) poses a significant challenge, as the piperazine-amide bonds are susceptible to hydrolysis, resulting in pronounced performance deterioration. Optimizing the chemical composition of loose NF membranes offers a promising strategy to overcome this limitation by simultaneously enhancing selectivity and permeance. In this study, a novel kind of wholly Tröger's base-based diamine monomer was developed and a Tröger's base-based polyamide TFC NF membrane was successfully fabricated through sequential non-solvent induced phase separation (NIPs) method and in situ interfacial polymerization (IP) reaction. Compared with the conventional M PIP-TMC NF membrane, the novel diamine monomer 4,4′-( 6H,12H -5,11-methanodibenzo[b,f][1,5]diazocine-2,8-diyl)dianiline (DAPTB) which decorated with linear, rigid, and twisted structure endowed the obtained M DAPTB-TMC NF membrane with a more loosely packed separation layer. Meanwhile, the M DAPTB-TMC NF membrane showed high water permeability of 26.15 L·m −2 ·h −1 ·bar −1 , which was 4.54 times higher than M PIP-TMC membrane. Furthermore, the membrane achieved exceptional rejections including 99.8% for eriochrome black T (EBT), and 99.2% for congo red (CR), accompanied by low Na₂SO₄ rejections of approximately 7.17% and 1.01%, respectively. Especially, the M DAPTB-TMC membrane demonstrated outstanding acid resistance, maintaining a high EBT rejection of 99.5% and a stable permeance even after 60 days of immersion in 20 wt% H₂SO₄, demonstrating the great potential for NF separation applications in the strong acidic conditions in the future. Download: Download high-res image (335KB) Download: Download full-size image