Regularly channeled MXene membranes for ionic and molecular separation
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Regularly channeled MXene membranes for ionic and molecular separation Jingchong Liu, Nü Wang (✉) Key Laboratory of Bioinspired Smart Interfacial Science and Technology of Ministry of Education, Beijing Key Laboratory of Bioinspired Energy Materials and Devices, School of Chemistry, Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100191, China
© Higher Education Press 2020
Membrane-based separation technologies, compared with other traditional separation operations such as evaporation, extraction, precipitation and distillation, have the merits of low energy consumption, small land footprint and high efficiency and have, therefore, attracted wide attention in past decades [1,2]. Laminar membranes formed by twodimensional (2D) nanosheet stacking showed high flexibility in adjusting the subnanoscale interlayer spacing to allow the unhindered transport of small ions or molecules, demonstrating high separation performance and economic applicability [3]. Graphene oxide (GO) membranes have been applied in seawater desalination, gas separation, nanofiltration, and ultrafiltration [4,5]. However, the intrinsic flexibility of GO nanosheets may lead to the formation of random laminar structures if stacked into membranes, which limits their selectivity [6,7]. Therefore, the fabrication of nanoconfined highly ordered separation membranes with regular 2D nanochannels is the key to efficient and stable separation capability. Recently, Wang et al. reported that, compared to flexible GO nanosheets, rigid Ti3C2Tx MXene nanosheets could be employed as promising building blocks to construct regular and straight channels without curling [6]. MXene, as a vibrant family of 2D materials, was first reported by Naguib et al. at Drexel University in 2011 [8]. It has a formula of Mn+ 1XnTx, where M is an early transition metal, X is carbon and/or nitrogen, and n ranges from 1 to 3. Tx generally refers to ‒H, ‒O, or ‒F, because the synthesis of MXene usually involves etching the interlayer A element (from groups IIIA and IVA) from the precursor Mn+1AXn phase with HF solution. Ti3C2Tx is the most extensively investigated MXene among more than 30 Received April 24, 2020; accepted June 3, 2020 E-mail: [email protected]
candidates. It can be assembled into 2D laminar membranes via several methods, including solvent-evaporationinduced self-assembly, and vacuum filtrating the Ti3C2Tx aqueous or organic dispersions (Fig. 1). The ordered and straight nanochannels in the prepared MXene membrane endowed it with precise molecular rejection for molecules larger than approximately 2 nm and unparalleled permeations of 2300 and 5000 L$m–2$h–1$bar–1 [6] for water and organics, such as acetone and acetonitrile. This ultrahigh permeation of MXene membranes could be attributed to the regular and straight interlayer nanochannels, which produced uninterrupted and steady water-bonded flow. For other laminar membranes with irregular nanochannels, the large disturbance in water-bonded flow caused relatively low wat
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