Precisely Tunable Ion Sieving with an Al₁₃–Ti₃C₂T_x Lamellar Membrane by Controlling Interlayer Spacing

Abstract

Two-dimensional (2D) membranes exhibit exceptional properties in molecular separation and transport, which reveals their potential use in various applications. However, ion sieving with 2D membranes is severely restrained due to intercalation-induced swelling.Here, we describe how to efficiently stabilize the lamellar architecture using Keggin Al 13 polycations as pillars in a Ti 3 C 2 T x membrane. More importantly, interlayer spacing can be easily adjusted with angstrom precision over a wide range (2.7−11.2 Å) to achieve selective and tunable ion sieving. A membrane with narrow d-spacing demonstrated enhanced selectivity for monovalent ions. When applied in a forward osmosis desalination process, this membrane exhibited high NaCl exclusion (99%) with a fast water flux (0.30 L m −2 h −1 bar −1 ). A membrane with wide d-spacing showed notable selectivity, which was dependent on the cation valence. When it was applied to acid recovery from iron-based industrial wastewater, the membrane showed good H + /Fe 2+ selectivity, which makes it a promising substitute for traditional polymeric membranes. Thus, we introduce a possible route to construct 2D membranes with appropriate structures to satisfy different ion-sieving requirements in diverse environment-, resource-, and energy-related applications. KEYWORDS: Ti 3 C 2 T x membrane, interlayer spacing, Al 13 Keggin ions, tunable ion sieving, desalination

Precise Sub-Angstrom Ion Separation Using Conjugated Microporous Polymer Membranes

“…The ion selectivity of the membrane is also impressive (Figure c). The selectivity performance of the CMP@100-20c membrane surpasses those of existing intrinsic microporosity (PIMs), graphene-oxide (GO), carbides and/or nitrides of transition metals (Ti 3 C 2 T x ) membranes, commercialized Nafion 212 membrane, − and Nafion 211 membrane (Figure S19). The selectivity of K + /Al 3+ was 134, K + /[Fe­(CN) 6 ] 3– was 436, and Mg 2+ /[Fe­(CN) 6 ] 3– was 261.…”

“…(c) K + permeation rate vs K + /Al 3+ (red edge) or K + /Fe­(CN) 6 3– (blue edge) selectivity for CMP@100-20c membrane in the concentration-driven process. Typical ion separation data of state-of-the-art ion-sieving membranes such as polymers of intrinsic microporosity (PIMs), graphene-oxide (GO), carbides and/or nitrides of transition metals (Ti 3 C 2 T x ) membranes, and commercialized Nafion membrane that are reported in the literature − are included. (d) Ion-sieving performance monitored by current–voltage ( I – V ) measurements.…”

Super-assembly of freestanding graphene oxide-aramid fiber membrane with T-mode subnanochannels for sensitive ion transport

“…17 To achieve precise ion sieving, an Al 13 –Ti 3 C 2 T x lamellar membrane with an adjustable interlayer spacing in angstrom-scale precision over a wide range (2.7–11.2 Å) was applied to achieve selective ion sieving. 18 GO membranes, as a member of 2D membranes, have inspired scientists to study their transport properties and mechanisms owing to their abundant water-transport pathways through assembled GO laminates. 19 In addition, GO membranes bearing well-aligned interlayer nanochannels and well-defined physicochemical properties 20 promise fast proton transport 21 and energy conversion.…”

Designing Biomimic Two-Dimensional Ionic Transport Channels for Efficient Ion Sieving

“…Compared with the conventional technologies, membrane-based technology has been a clean, reliable, and affordable method of ion sieving. , Extensive research has been devoted to imitating advanced membranes with artificial ion channels. − For instance, Liu and co-workers developed a track-UV technique to produce a high density of uniformly sized nanopores in polymer films for fast ion sieving. , Shen and collaborators presented target ion-controlled multilayer membranes with ion exchange sites for efficient ion extraction. , Wang and colleagues reported ultrathin metal organic framework membranes with pore structures composed of sub-nanometer-sized windows and nanometer-sized cavities for selective ion separation . Emerging two-dimensional (2D) laminar membranes with numerous well-defined 2D nanochannels approaching the ionic scale are highly desirable for constructing artificial ion channels. − Exemplified by graphene oxide (GO) membranes, flexibly tunable 2D interlayer spaces can readily serve as fast and selective nanochannels for ion transport. − However, the compromise between permeability and selectivity limits the ion sieving performance of GO membranes . For example, a GO membrane with a relatively large interlayer spacing enables an ultrafast K + transport rate reaching 2.0 mol m –2 h –1 but negligible K + /Mg 2+ selectivity of just ∼1, whereas a GO membrane with a relatively narrow interlayer spacing exhibits K + /Mg 2+ selectivity up to ∼2000 but a very low K + transport rate of ∼0.007 mol m –2 h –1 …”