Positively charged membranes with fine-tuned nanopores for ultrafast and high-precision cation separation

Abstract

There is significant interest in high-performance positively charged membranes that enable the fast and high-precision separation of various cationic substances for purifying water and recovering precious metals. This study demonstrates...

Nanofiltration Membranes Modified with a Clustered Multiquaternary Ammonium-Based Ionic Liquid for Improved Magnesium/Lithium Separation

“…For the DABIL membrane, the net effect of decreased size exclusion due to the loose and enlarged membrane pore structure is counterbalanced by the enhanced surface charge density due to the dense multication charged groups. Recent studies have revealed that the interactions between the surface QA groups and Cl – ions are stronger than the interactions between the surface carboxyl groups and the Na + ions . Therefore, the Cl – ions experience stronger electrostatic attraction and are permeated faster through the membrane conducing to the observed low rejection of LiCl than NaCl rejection.…”

“…Simulated brine solutions containing a mixture of aqueous LiCl and MgCl 2 solutions with total concentrations ranging from 1 to 10 g L –1 were used to determine the membrane ion selectivity. The LiCl/MgCl 2 selectivity (S Li + /Mg 2+ ) was calculated using the salt concentrations measured from the rejection experiment using eq where C ion,f is the ion concentration in the feed solutions, and C ion,p is the ion concentration in the permeate solutions.…”

“…Polyamide thin-film composite (TFC) membranes typically prepared by an interfacial polymerization (IP) method based on the diffusion–reaction process are widely applied in reverse osmosis, nanofiltration (NF), and other water treatment applications because of their simple preparation and good separation. In particular, positively charged TFC NF membranes have the capacity to effect high-performance separation of various cationic substances for the recovery of high-value metal ions. − However, they are characterized by narrow pores and confined transport modes, which limits their performance, while weak surface charges affect their ion selectivity . Considering that the separation performance of typical TFC NF membranes is mainly dependent on the structural properties of the polyamide selective layer, several polyamide layer modification strategies have been explored to tune and improve the performance of TFC NF membranes.…”

“…4−6 However, they are characterized by narrow pores and confined transport modes, which limits their performance, while weak surface charges affect their ion selectivity. 6 Considering that the separation performance of typical TFC NF membranes is mainly dependent on the structural properties of the polyamide selective layer, several polyamide layer modification strategies have been explored to tune and improve the performance of TFC NF membranes. Some of the approaches include using nanofillers and hydrophilic additives, 7 decreasing the thickness of the membranes 8 or increasing the membrane filtration areas.…”

“…Correspondingly, the design of new electrolyte monomers containing multication side chains and strong positively charged moieties is particularly desirable, not only to achieve improved ion selectivity with high water permeability but also to unravel the surface modification approaches and promote further applications for sustainable water purification. Herein, we designed and synthesized N 1 -(6-aminohexyl)-N 1 ,N 1 ,N 6 ,N 6 ,N 6 -pentamethylhexane-1,6-diaminium bromide ionic liquid (denoted as DABIL) monomer, containing two quaternary ammonium (QA) cations on long flexible hexyl spacers as a strong electrolyte modifier for the polyamide matrix to develop NF membranes for lithium separation. This is the first time to utilize the chemical structure of the DABIL monomer containing multication charged moieties for the surface modification of NF membranes to improve ion selectivity by Donnan's effect.…”