Nanofiller-confined spatial fluctuation in monomer diffusion synthesizing ultrafast reverse osmosis membranes driven by hydrogen-bonding networks

Thin-film composite (TFC) reverse osmosis (RO) membranes encounter a significant trade-off between water permeability and selectivity. This study presents a mechanism to address this limitation by altering the structure of the polyamide (PA) layer. By incorporating layered double hydroxides (LDH) and sodium lignosulfonate (SL), we establish differential diffusion resistances during interfacial polymerization (IP). This approach facilitates the diffusion of m-phenylenediamine (MPD) across the interface while concurrently inhibiting it in the bulk phase, thereby inducing spatial fluctuations in monomer diffusion. The resulting heterogeneous polymerization dynamics yield a thin, highly wrinkled PA layer that promotes ultrafast water transport. Moreover, the hydrophilic sulfonic groups (-SO₃^-) present on the LDH nanosheets form a robust hydrogen-bonding network with water, further enhancing transport efficiency. The optimized membrane attains a water permeance of 4.00 LMH·bar^-1 and a NaCl rejection rate of 99.4%, surpassing most current TFC/TFN RO membranes. This research offers insights into the control of the polymerization process, contributing to the design of next-generation RO membranes.