Ultraselective and Highly Permeable Polyamide Nanofilms for Ionic and Molecular Nanofiltration

Abstract

Membranes with ultrahigh ion selectivity and high liquid permeance are needed to produce high-quality product water with increased recovery and process efficiency in water desalination. The narrow pore size distribution and controlled surface charge in the separation layer of nanofiltration membranes significantly improve the ion selectivity through molecular sieving and Donnan exclusion of co-ions. Here, the ultraselective and yet highly water permeable polyamide nanofilm composite nanofiltration membranes developed by precisely controlling the kinetics of the interfacial polymerization reaction by maintaining the stoichiometric equilibrium at the interface is reported. The kinetically favorable stoichiometric equilibrium condition prohibits the formation of aggregate pores in the nanofilm and leads to the formation of narrow network pores with a high surface negative charge. Nanofilms are designed with a controlled degree of crosslinking and made as thin as ≈7 nm to achieve increased water permeance. The ultraselective membranes exhibit up to 99.99% rejection of divalent salt (Na 2 SO 4) and demonstrate monovalent to divalent ion selectivity of >4000. The selectivity of these nanofilm composite membranes is beyond the permeance-selectivity upper-bound line of the state-of-the-art nanofiltration membranes and one to two orders of magnitude higher than the commercially available membranes with pure water permeances of up to 23 L m −2 h −1 bar −1. The fabrication process is scalable for membrane manufacturing.

Electrostatic-modulated interfacial polymerization toward ultra-permselective nanofiltration membranes

“…This abnormal NaCl concentration effect is because of the co-ion competition effect between Cl − and SO 4 2− facilitating the transport of Cl − ( Luo and Wan, 2013 ). From the practical perspective of resource reuse, high SO 4 2− rejection along with high Cl − permeation counts more than the single metric of Cl − /SO 4 2− selectivity ( Hao et al., 2020 ; Sarkar et al., 2020 ; Zhu et al., 2018 ). Conclusively, the unprecedented ionic separation performance endows the eIP-3 membrane with great promise for brine refinement and salt reclamation applications ( Sarkar et al., 2020 ).…”

Membrane Materials for Selective Ion Separations at the Water–Energy Nexus

“…As a result, the membrane can differentiate between species more precisely than conventional polyamide membranes (Figure 3c), with recent work reporting selectivity over 4000 between SO 4 2− and Cl − ions in nanofiltration. [ 67 ]…”

Covalent Organic Framework Membranes for Efficient Chemicals Separation

“…[135] In addition, the carboxyl-functionalized COF (COF-COOH) that bears a much higher affinity with PA layer has also been incorporated into the TFN membrane for efficient forward osmosis (FO) desalination. [136] However, most of COFs particles with a much larger size (1-3 μm) [67] maybe fail to match with PA active layers with thicknesses of 7-300 nm, [137] resulting in compromised selectivity. Therefore, Xu and coworkers adopted COF (TpPa-2) nanosheets as additives to prepare TFN membranes which showed improved H 2 O/NaCl selectivity and water permeance (Figure 17a).…”