Efficient Ion Sieving in Covalent Organic Framework Membranes with Sub‐2‐Nanometer Channels

Abstract

Membranes of sub‐2‐nanometer channels show high ion transport rates, but it remains a great challenge to design such membranes with desirable ion selectivities for ion separation applications. Here, covalent organic framework (COF) membranes with a channel size of ≈1.4 nm and abundant hydrogen bonding sites, exhibiting efficient ion sieving properties are demonstrated. The COF membranes have high monovalent cation permeation rates of 0.1–0.2 mol m−2 h−1 and extremely low multivalent cation permeabilities, leading to high monovalent over divalent ion selectivities for K+/Mg2+ of ≈765, Na+/Mg2+ of ≈680, and Li+/Mg2+ of ≈217. Experimental measurements and theoretical simulations reveal that the hydrogen bonding interaction between hydrated cations and the COF channel wall governs the high selectivity, and divalent cations transport through the channel needs to overcome higher energy barriers than monovalent cations. These findings provide an effective strategy for developing sub‐2‐nanometer sized membranes with specific interaction sites for high‐efficiency ionic separation.

The Preparation of High-Performance and Stable MXene Nanofiltration Membranes with MXene Embedded in the Organic Phase

“…It presented that the prepared Ti3C2Tx had abundant oxygen-containing and fluorine-containing functional groups, which made Ti3C2Tx have a higher negative charge [19]. At the same time, the abundant functional groups were conducive to the formation of hydrogen bonds between the nanosheets and hydrated ions, and hydrogen bonds had potential advantages in improving the desalination performance of the membrane [20].…”

“…It presented that the prepared Ti 3 C 2 T x had abundant oxygen-containing and fluorine-containing functional groups, which made Ti 3 C 2 T x have a higher negative charge [19]. At the same time, the abundant functional groups were conducive to the formation of hydrogen bonds between the nanosheets and hydrated ions, and hydrogen bonds had potential advantages in improving the desalination performance of the membrane [20]. As shown in Figure 2a, the characteristic peak (002) of generated Ti3C2Tx after etching moved from 9.6° to 7.7°, and the (104) peak basically disappeared, indicating that Ti3AlC2 was well been etched.…”

“…This might be attributed to the increase in the crosslinking degree of interfacial polymerization, making the effective pore size of the membrane smaller and increasing the ions' rejection. In addition, the interlayer channels in the MXene membrane might have had hydrogen bonding sites, which had a hydrogen bonding effect with hydrated ions for hindering hydrated ions rapidly pass through the membrane [20]. The pure water flux of the membrane was presented in Figure 8a.…”

Angstrom-scale ion channels towards single-ion selectivity

“…For 3D PIM-based ion channel membranes, they show a moderate K + /Mg 2+ selectivity of B50 and a moderate K + permeate rate. Besides, 3D COF membranes with relatively large pores, such as TpBDMe 2 173 membranes of 1.4 nm pores and COF-EB 1 BD 1 174 membranes of 2 nm, achieve a high K + /Mg 2+ selectivity of B765 and a good Na + /Mg 2+ cation selectivity of 827, respectively. High mono-/di-valent anion selectivity (i.e., Cl À /SO 4…”

A Review of Advancing Two-Dimensional Material Membranes for Ultrafast and Highly Selective Liquid Separation

“…Besides, nanoscale membranes with specific interaction sites can also be constructed by tuning the channel wall chemistry for efficient ion separation. Sheng et al [44] constructed ultrathin nanoporous COF membranes with one-dimensional channels and abundant hydrogen bonding sites on porous substrates by interfacial growth. 1,3,5-Triformylphloroglucinol (Tp) and 2,6-dimethylbenzidine (BDMe 2 ) formed a TpBDMe 2 membrane with a pore size of about 1.4 nm at the interface of dichloromethane and water (Figure 3c-e).…”