A “grab-and-throw” access for monomer diffusion in interfacial polymerization process for high-efficiency polyamide membrane in water purification

The surface structures of polyamide (PA) layer are closely related to the monomers diffusion during interfacial polymerization (IP) process and is one of the significant issues affecting nanofiltration separation performance. However, nanofiltration membrane prepared by the conventional interfacial polymerization method usually has a relatively smooth surface, which limits the effective filtration area leading to low water permeation. Effective strategies to control monomer diffusion also need to be developed. To solve these problems, carbon disulfide (CS 2 ) is inferred as an additive to form piperazine n-dithiocarbonate (PIP-CS 2 ) in aqueous phase, which can reversibly protonate piperazine (PIP) into PIP-CS 2 - anion and PIP-H + cation. Due to the amphiphilic piperazine part, PIP-CS 2 and PIP-CS 2 - /PIP-H + ion pair tend to gather at water-oil interface offering a special “grab-and-throw” access for free PIP monomer. In this way, the diffusion of PIP monomer is well-controlled to fabricate an ordered nanoscale hollow surface of polyamide layer. The exceptional surface structure significantly affects the properties of nanofiltration membrane. the pure water flux enlarged from 6.53 to 17.65 L m −1  h −1 bar −1 . Na 2 SO 4 rejection was maintained at more than 98 %. the separation coefficient of Cl − and SO 4 2− enhanced from 19.14 to 54.80. This work provided a novel and effective way to increase the flux and adjust the surface structure and cross-linking degree in nanofiltration membrane production.