Constructing multi-functional hydroxyapatite interlayer for the fabrication of high-performance polyamide nanofiltration membranes

Polyamide (PA) nanofiltration (NF) membranes are widely used in precious separation field, but balancing permeability and selectivity remains a significant challenge due to the conventional uncontrolled interfacial polymerization (IP) process. This study reports a synthetic nano-hydroxyapatite (HA) multi-functional interlayer constructing strategy via vacuum-assisted, to modulate and quantify the IP reaction process for enhance the perm-selectivity of PA NF membranes. Combined macroscopic characterization and molecular dynamics simulations reveal a dual function of the HA interlayer: (i) HA modulates the diffusion dynamics of the aqueous-phase monomer piperazine via synergistic H-bonding and water-mediated long-range electrostatic interactions, and (ii) enhances interfacial compatibility by forming strong covalent bond between its surface reactive groups and the PA separation layer. Benefiting from these modulated mechanisms, a structurally optimized separation layer was successfully fabricated. Compared with the pristine PA membrane, the optimal PA-HA3 membrane exhibited an approximately 3-fold increase in pure water permeance (32.40 L·m −2 ·h −1 ·bar −1 ) while maintaining a Na 2 SO 4 rejection of 99.1%, along with well long-term stability. This work not only proposes a novel strategy of HA multifunctional interlayer for high-performance NF membrane fabrication but also provides new mechanistic insights and a theoretical framework for the quantifiable design of IP process and structural optimization of separation membranes.