Tailoring polyamide loose nanofiltration membrane with 4-aminobenzoylhydrazine for efficient dye/salt separation: the differential N-site reactivity modulation in interfacial polymerization

Exploring novel aqueous monomers to construct loose nanofiltration (LNF) membranes with excellent permeability and dye/salt selectivity is still needed for recovering resources in textile wastewater. In this study, a novel strategy for exploiting the differential N-site reactivities in 4-aminobenzoylhydrazine (4ABH) was proposed to precisely modulate the structure of the polyamide (PA) layer, thereby fabricating unique LNF membranes. The nucleophilic reactivities of 4ABH monomer and their effect on the PA layer formation were studied via density functional theory (DFT) and molecular dynamics simulation (MDS), which provided theoretical guidance for understanding the formation mechanism of LNF membranes. Based on the differential nucleophilic reactivities of N-sites in 4ABH (-NH₂ > -NH 2 of -NH-NH₂ > -NH- of -NH-NH₂), the proportion of large cavities within the PA cross-linked networks increased, and then the compact cross-linked structure emerged as the monomer concentration increased. The experimental result demonstrated that the optimized 4ABH/TMC LNF membrane exhibited a high water permeability of 45.03 L·m -2 ·h -1 ·bar -1 , while maintaining excellent rejection for methyl blue (MB) (95.18%), eriochrome black T (EBT) (99.24%) and congo red (CR) (99.64%) with a low salt rejection for Na₂SO₄ (24.37%), MgSO 4 (7.03%), NaCl (6.79%), and MgCl 2 (3.29%). Moreover, the membrane achieved a selectivity factor of 239.00 for CR/NaCl in dye/salt mixture solutions and showed robust stability and fouling resistance in continuous filtration tests. The strategy explored in this work provided a new insight into selecting suitable aqueous monomers for preparing the unique LNF membranes with excellent permeability and dye/salt selectivity.