Carbon Nanomembranes with sub-nanometer channels:
2D materials for water purification
Physics of Supramolecular Systems and Surfaces,
Bielefeld University, 33615 Bielefeld, Germany
Clean water is a global challenge, and membrane filtration is a key technology to achieve it. There are growing research efforts to explore the use of 2D carbon materials as nanoconduits for molecular transport and separation . Here, I report on carbon nanomembranes (CNMs) with sub-nanometer channels that prove to be excellent water filters, combining a high selectivity with an exceptionally high water permeance. The CNMs are fabricated via the cross-linking of terphenyl self-assembled monolayers , resulting in a ~1.2 nm thick membrane perforated by channels with diameters below ~0.7 nm and areal densities of ~1018 m−2. When tested as filter membranes, it was found that the CNMs efficiently block the passage of most gases and liquids. However, water passes through with an exceptionally high permeance of ~1.0×10−4 mol·m−2·s−1·Pa−1 . This suggests that water fast and cooperatively translocates through a channel with a rate of ~66 molecules·s−1·Pa−1. As the fabrication of CNMs is scalable, this finding can open new paths towards the use of 2D materials in water purification.
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Advanced Nanocarbon Materials for Solar Energy Conversion Schemes
Dirk M. Guldi
Department of Chemistry and Pharmacy 7 Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universitaet Erlangen-Nuernberg, Egerlandstr. 3, 91058 Erlangen, Germany
Carbon is the key to many technological applications that have become indispensable in our daily life. Altering the periodic binding motifs in networks of sp3-, sp2-, and sp-hybridized C-atoms is the conceptual starting point for a wide palette of carbon allotropes. To this end, the past two decades have served as a test-bed for measuring the physico-chemical properties of low-dimensional carbon with the advent of fullerenes (0D), followed in chronological order by carbon nanotubes (1D), carbon nanohorns, and, most recently, by graphene (2D). These species are now poised for use in catalysis.
Expanding global needs for energy have led to a significant effort to develop alternatives to fossil fuels. While alternative sources for energy are already in use, they comprise a small percentage of the energy demands needed to carry us through the 21st century. No single source will solve the global needs, but the development of photocatalysis has vast potential as a point-of-use power source.
I report on our efforts regarding a unifying strategy to use the unprecedented charge transfer chemistry of 0D fullerenes, the ballistic conductance of 1D carbon nanotubes, and the high mobility of charge carriers in 2D graphene, together in a groundbreaking approach to solving a far-reaching challenge, that is, the efficient use of the abundant light energy around us. For example, hybrid materials based on nanocarbons and metaloxides are the ideal design for realizing breakthroughs in high photon conversion efficiencies suitable for the catalysis of water.
Topochemistry and Delamination of Layered Topological Insulators
Prof. Dr. Michael Ruck, Faculty of Chemistry and Food Chemistry, TU Dresden, Germany
A topological insulator (TI) is a quantum material that provides fast and dissipation-free transport of information at room temperature.[1, 2] This recommends them as ultimate materials for spintronics and quantum computing close to the atomic limit of nanoelectronics. The TI has a narrow band in the bulk, but a topologically protected metallic surface state. This special surface state is based on symmetry and the spin-orbit coupling generated hybridization of states on both sides of the band gap. Electrons in topologically protected surface states are sheltered against scattering by impurities and their spin is locked to their propagation direction. Still, the number of well characterized TIs is rather limited, and many of them are not suitable for industrial use. Moreover, thin layers are required for technological application.
Layers of Bi2Te3, the most prominent TI, were obtained by mechanical exfoliation as well as by gas-phase deposition. However, none of these methods was able to provide larger amounts of good quality 2D materials at reasonable costs. In contrast, lithium intercalation and solution processing of Bi2Te3 led to stable suspensions of exfoliated layers, which could be processed further. In the past years, our group succeeded in contributing to five families of compounds that show TI properties: (A) Bi14Rh3I9 and variants thereof,[5, 6] (B) BinTeX (n = 1, 2, 3; X = Br, I), (C) Bi2nMnTe3n+1 (n = 1, 2, 3), (D) QXTe (Q = Ga, In; X = Ge, Sn), and (E) Bi4X4 (X = Br, I).[12, 13] The families A to D have layered crystal structures with certain contrast in the strength and type of chemical bonding, which is a necessity for the exfoliation of individual functional layers. We managed to swell and chemically exfoliate Bi14Rh3I9 and Bi2TeI down to packages of few layers. Electron diffraction patterns indicate that the topological non-trivial RhBi4] and the TeBiI] layers, i.e. the 2D TIs, chemically survive the procedure. GaGeTe was successfully exfoliated by another group. We studied underlying topochemistry also on chemically and structurally related metallic and superconducting compounds.[15, 16]
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"2D polymers: Synthesis in single crystals and on water"
Dieter Schlüter, ETH Zürich
Two-dimensional materials (2DM) are sheet-like entities and of great interest for their manifold properties. Famous representatives are graphene, boronitride or molybdenum disulfide. 2DMs are often provided by nature or are obtained under harsh conditions. Such conditions exclude the synthetic arsenal of organic chemistry to be used for rational sheet creation, sheet structure variation and sheet engineering on a molecular level.
Recently it was shown that covalent monolayer sheets can be accessed at room temperature by genuine two-dimensional polymerization of organic monomers applying simple protocols. They include spreading of monomers at an air/water interface into long-range ordered reactive monolayer packings or crystallizing them into layered single crystals, followed by light-induced growth reactions. These growth reactions result in macroscopic sheets of considerable mechanical strength, whose structures resemble molecular fishing nets (2D polymers).
The contribution addresses strategic, synthetic and analytical issues and provides a view into future.
Recommended reading: M. Servalli, H. C. Öttinger, A. D. Schlüter, Physics Today 2018, 72(5), 41.