Porous organic polymer embedded thin-film nanocomposite membranes for enhanced nanofiltration performance

Porous organic polymers have been considered promising for the design of high performing membranes, mainly because of their superior surface area, intrinsic mesoporous structure and good polymer affinity. In this study, hierarchical o-hydroxyazo porous organic polymers (o-POPs) and piperazine (PIP) monomers were incorporated into the casting solution, followed by phase inversion to prepare PIP-containing polymeric substrates. The o-POPs modified thin film nanocomposite (TFN) membranes were fabricated by interfacial polymerization (IP) with trimesoyl chloride (TMC). The incorporated o-POPs could locally enrich PIP in substrates and impede its diffusion towards the organic interface during IP reaction through hydrogen bonding and physical obstruction, leading to the formation of a crumpled membrane surface. The enhancement of surface roughness and hydrophilicity endowed the TFN membranes with a signally elevated water permeance while maintaining a comparable solute rejection. The optimal TFN membrane with the o-POP content of 0.3 wt% displayed a remarkable water permeance of 29.6 L m⁻² h⁻¹ bar⁻¹, a high Na₂SO₄ rejection of 94.9%, and an efficient removal of reactive dyes (e.g., reactive black 5 and reactive orange 16, >98.2%), which makes o-POP functionalized TFN membranes competitive for NF applications in water treatment.