Extreme pH‐Resistant, Highly Cation‐Selective Poly(Quaternary Ammonium) Membranes Fabricated via Menshutkin Reaction‐Based Interfacial Polymerization

Abstract

Membrane-based separation technologies have attracted significant interest from various industries owing to their high process efficiency. However, the wider applications of conventional polyamide (PA) thin-film composite (TFC) membranes are limited by their poor pH stability and low cation selectivity, necessitating the development of membranes with advanced chemistries. Herein, an extreme pH-resistant, highly cation-selective TFC membrane is fabricated by synthesizing a crosslinked poly(quaternary ammonium) (PQA) selective layer on a polyethylene support via Menshutkin reaction-based interfacial polymerization (Men-IP). The Men-IP process produces a thin, densely crosslinked, and positively charged PQA permselective layer without hydrolysisprone functional groups. The fabricated PQA membrane features a highly selective molecular density that significantly exceeds those of previously reported membranes with non-PA chemistries. Moreover, the PQA membrane exhibits remarkably high rejection (>90%) and selectivity for divalent cations owing to the exceptionally strong positive charge imparted by its abundant cationic QA groups. More importantly, the PQA membrane displays ultrahigh pH stability under both extremely acidic (1.5 m H 2 SO 4 ) and alkaline (5 m NaOH) conditions for 28 days. No other membrane reported in the literature demonstrates such excellent pH stability. This strategy opens a new route for fabricating highly selective membranes that can be used in harsh pH environments.

Positively Charged Polyamine Nanofiltration Membrane for Precise Ion–Ion Separation

“…The water permeance, MgCl 2 rejection, and S Li,Mg of the PEI-TBB composite membrane were also compared with polyamide-based NF membranes reported in the literature. ,− The PEI-TBB composite membrane achieved a comparable water permeance of 4.2 L·m –2 ·h –1 ·bar –1 , a high MgCl 2 rejection of 94.7%, and a superior S Li,Mg of 16.7 (Figure D, Table S4).…”

Dually Charged Acid Stable Tight Polyamine Composite Nanofiltration Membranes with Low Molecular Weight Amine Molecules for MgCl2 Rejection

“…To date, researchers have developed sulfonamide, 6 polyurea, 7 polyamine, 8 polyelectrolytes, 9 and other kinds of ARNFMs. 10,11 But most of the reported ARNFMs and the commercial ARNFMs with high selectivity are all suffering from the low membrane permeability mainly due to lamination of the membrane structure, 12,13 which limits the further application of ARNFMs in real acidic wastewater treatment. How to obtain an ARNFM with high performance via a facile method is the crucial issue in the current research.…”

“…19 Thus, ARNFMs with large MWCOs would exhibit poor separation performance in a high salt concentration solution because of the electrostatic shield effect. 11 Moreover, most of multivalent metal ions would interact with the acid group anion in an acidic environment (e.g., Mn 2+ → MnSO weakens the electrostatic effect of the membrane on metal ions (most NF membranes are positively charged at pH < 3) and hence leads to poor rejection rates for metal salts of these ARNFMs with large MWCOs. Therefore, developing ARNFMs with high membrane permeability as well as low MWCOs is of importance.…”

“…Nanofiltration (NF) has been proposed as an alternative and attractive approach for acidic wastewater treatment, benefiting from the high rejection rates for divalent and multivalent salts in acid through the electrostatic effect and size exclusion effect. − However, the traditional NF membranes cannot maintain efficient rejection for metal salts in acidic solutions (pH < 2) for a long time. , Therefore, the development of ARNFMs is becoming more and more important. To date, researchers have developed sulfonamide, polyurea, polyamine, polyelectrolytes, and other kinds of ARNFMs. , But most of the reported ARNFMs and the commercial ARNFMs with high selectivity are all suffering from the low membrane permeability mainly due to lamination of the membrane structure, , which limits the further application of ARNFMs in real acidic wastewater treatment. How to obtain an ARNFM with high performance via a facile method is the crucial issue in the current research .…”

“Clickable” Interfacial Polymerization of Polythioether Ultrathin Membranes for Ion Separation

“…Methodologically, interfacial polymerization (IP) in an immiscible two-liquid-phase system initiates an ingenious way to fabricate such ultrathin membranes for ion separation. , It is the restricted reaction area and controllable diffusion of reactive monomers that make the membrane thin but defect-free. , In particular, polyamide (PA) ultrathin membranes enjoy a high reputation owing to their superior performances in both nanofiltration and reverse osmosis processes. − A typical PA membrane derives from the Schotten–Baumann-type condensation polymerization between amine and acyl chloride precursors at the water–oil interface. , However, decades of technological improvements almost focused on perfecting PA-type membranes, − other reaction types potentially occurring at the interface attracted scant attention. The variety of ultrathin membranes by IP for ion separation outside the PA world − is therefore very limited.…”