Large Area Self‐Assembled Ultrathin Polyimine Nanofilms Formed at the Liquid–Liquid Interface Used for Molecular Separation

Abstract

Separation membranes with higher molecular weight cut‐offs are needed to separate ions and small molecules from a mixed feed. The molecular sieving phenomenon can be utilized to separate smaller species with well‐defined dimensions from a mixture. Here, the formation of freestanding polyimine nanofilms with thicknesses down to ≈14 nm synthesized via self‐assembly of pre‐synthesized imine oligomers is reported. Nanofilms are fabricated at the water–xylene interface followed by reversible condensation of polymerization according to the Pieranski theory. Polyimine nanofilm composite membranes are made via transferring the freestanding nanofilm onto ultrafiltration supports. High water permeance of 49.5 L m‐2 h−1 bar−1 is achieved with a complete rejection of brilliant blue‐R (BBR; molecular weight = 825 g mol−1) and no more than 10% rejection of monovalent and divalent salts. However, for a mixed feed of BBR dye and monovalent salt, the salt rejection is increased to ≈18%. Membranes are also capable of separating small dyes (e.g., methyl orange; MO; molecular weight = 327 g mol−1) from a mixed feed of BBR and MO. Considering a thickness of ≈14 nm and its separation efficiency, the present membrane has significance in separation processes.

Pore engineering of ultrathin covalent organic framework membranes for organic solvent nanofiltration and molecular sieving

“…31 The TFP-DHF membrane showed a remarkably high solvent ux in the application of organic solvent nanoltration. The performance was much better not only than those of conventional OSN membranes built on exible amorphous polymers, [32][33][34][35][36][37][38] but also than those of membranes built on rigid microporous polymers. 39 However, to meet the growing demands for precise molecular sieving it is also critical to rationally tune the pore size.…”

Ultraselective and Highly Permeable Polyamide Nanofilms for Ionic and Molecular Nanofiltration

“…[ 7 ] Extensive research work has been conducted to increase the energy efficiency in the separation processes by reducing the thickness of the separation layer and thereby increasing the permeance of the membranes. [ 8–11 ] However, exceedingly high retention of specific ions and dissolved solutes is always imperative to achieve high efficiency [ 1,2,5,12 ] in the separation process. Thus, designing high‐specification nanofiltration membranes with performance beyond the permeance–selectivity upper‐bound of polymer membranes [ 13,14 ] is of primary importance to achieve both high selectivity and high permeance.…”

“…Thus, designing high‐specification nanofiltration membranes with performance beyond the permeance–selectivity upper‐bound of polymer membranes [ 13,14 ] is of primary importance to achieve both high selectivity and high permeance. Additionally, the solvent stability of the high‐specification membranes [ 9,10 ] would be beneficial for their applications in many complex separation processes involving nonaqueous feed.…”

Supramolecular fabrication of hyperbranched polyethyleneimine toward nanofiltration membrane for efficient wastewater purification

“…[16][17][18][19][20] In particular, more attention has been focused on polymeric separation membranes owing to their superiorities, including low cost, environmentally benign, and energy-efficient. [21][22][23][24] Interfacial polymerization is considered one of the most valuable manners to manufacture polymeric separation membranes. [25][26] During the preparation process, the monomers were dissolved in immiscible liquids (such as water and cyclohexane) and then reached with each other to form a nanofiltration layer.…”