Ternary Heterostructure Membranes with Two-Dimensional Tunable Channels for Highly Selective Ion Separation

Abstract

Selective ion separation from brines is pivotal for attaining high-purity lithium, a critical nonrenewable resource. Conventional methods encounter substantial challenges, driving the quest for streamlined, efficient, and swift approaches. Here, we present a graphene oxide (GO)-based ternary heterostructure membrane with a unique design. By utilizing Zn2+-induced confinement synthesis in a two-dimensional (2D) space, we incorporated two-dimensional zeolitic imidazolate framework-8 (ZIF-8) and zinc alginate (ZA) polymers precisely within layers of the GO membrane, creating tunable interlayer channels with a ternary heterostructure. The pivotal design lies in ion insertion into the two-dimensional (2D) membrane layers, achieving meticulous modulation of layer spacing based on ion hydration radius. Notably, the ensuing layer spacing within the hybrid ionic intercalation membrane occupies an intermediary realm, positioned astutely between small-sized hydrated ionic intercalation membrane spacing and their more extensive counterparts. This deliberate configuration accelerates the swift passage of diminutive hydrated ions while simultaneously impeding the movement of bulkier ions within the brine medium. The outcome is remarkable selectivity, demonstrated by the partitioning of K+/Li+ = 20.9, Na+/K+ = 31.2, and Li+/Mg2+ = 9.5 ion pairs. The ZIF-8/GO heterostructure significantly contributes to the selectivity, while the mechanical robustness and stability, improved by the ZA/GO heterostructure, further support its practical applicability. This report reports an advanced membrane design, offering promising prospects for lithium extraction and various ion separation processes.

Unipolar Ionic Diode Nanofluidic Membranes Enabled by Stepped Mesochannels for Enhanced Salinity Gradient Energy Harvesting

“…Over the past few decades, advances in nanofabrication and synthesis have greatly facilitated the research on nanofluidics, − which can manipulate ion flows at length scales of <100 nm. In nanofluidic ion channels, dominant intermolecular forces, such as steric interactions, hydration, van der Waals, and electrostatic interactions, endow them with unique selective mass transport capabilities. − These properties make nanofluidic ion channel membranes promising in various applications, including water purification, − energy conversion, − molecular sensing, , and resource recovery. , Among them, the nanofluidic energy harvesting of salinity gradients has experienced considerable research interest in recent years due to its high energy conversion efficiency and power density. − Fundamental studies on single-pore nanofluidic membranes have shown that nanofluidic membranes promise to achieve an ultrahigh power output. − For example, a single-layered MoS 2 sheet with a single nanopore has achieved an output power density of 10 6 W/m 2 , which is several magnitudes higher than conventional ion-exchange membranes . Nevertheless, to scale up these single-nanopore devices for practical use, two major hurdles need to be overcome.…”

“…7−9 These properties make nanofluidic ion channel membranes promising in various applications, including water purification, 10−12 energy conversion, 13−15 molecular sensing, 16,17 and resource recovery. 18,19 Among them, the nanofluidic energy harvesting of salinity gradients has experienced considerable research interest in recent years due to its high energy conversion efficiency and power density. 20−22 Fundamental studies on single-pore nanofluidic membranes have shown that nanofluidic membranes promise to achieve an ultrahigh power output.…”

Designing biomimetic two-dimensional channels for uranium separation from seawater

“… 19 In scenarios involving mixed ion systems, the determination of the GO membrane's interlayer spacing hinges upon the initial entry of metal ions into the interlayer space. 35 However, the flexible nature of materials such as GO implies that the size screening effect alone fails to comprehensively account for all observed separation phenomena. Consequently, it is imperative to posit the existence of an alternative separation mechanism beyond the confines of the size screening effect.…”