Nanocolloidal-confined interface polymerization for the preparation of high-permeance nanofiltration membrane

Polyamide membranes prepared through interfacial polymerization (IP) hold substantial promise for nanofiltration applications. Nevertheless, the problems of uneven accumulation of aqueous monomers at the interface and uncontrollable rapid reaction rates usually lead to the non-uniform distribution of pore sizes and a relatively large thickness of the polyamide separation layer, thereby limiting the comprehensive separation performance of nanofiltration membranes. Modification of the diffusion–reaction process during IP can effectively regulate the structure and performance of the polyamide separation layer. In this work, we put forward a novel nanocolloidal-confined IP method for preparing polyamide membranes by incorporating piperazine (PIP)-based nanocolloidals to regulate the diffusion and distribution of aqueous-phase amine monomers. Firstly, the PIP-based nanocolloidals are pre-synthesized via the reversible reaction between PIP and 2,4,6-Triformylphloroglucinol (TP). Subsequently, these nanocolloidals are accumulated on the polyacrylonitrile (PAN) membrane to facilitate the subsequent interfacial polymerization with trimesoyl chloride (TMC). During this process, TP functions as a PIP coupling agent, ensuring the uniform distribution and enrichment of PIP at the interface. Moreover, it also serves as a PIP sustained-release agent (through the reversible decomposition of oligomers) to control the diffusion–reaction rate of the interfacial polymerization. The nanofiltration membrane thus prepared exhibits a polyamide separation layer that is characterized by fewer defects, a loose structure, and an ultrathin nature. It achieves a high permeance of 34.13 L m −2  h −1  bar −1 (nearly four times the increase compared to conventional membranes) and a high sulfate rejection rate of approximately 98.6 %. Additionally, due to the stable pore structure of the polyamide separation layer, the nanofiltration membrane demonstrates durable separation performance. The membrane was applied to 30 h continuous nanofiltration at an operating pressure of 4 bar, while the rejection rate only experienced a slight decline yielding a high level above 95 %. This work offers a promising solution for the development of high-performance membranes customized for wastewater desalination, fulfilling a crucial requirement in the field of seawater desalination.