報(bào) 告 人：Prof. Thomas Heine

報(bào)告時(shí)間：2019年5月9日（周四）下午2:30

報(bào)告地點(diǎn)：化學(xué)樓一號(hào)會(huì)議室

邀 請(qǐng) 人：楊利明研究員

報(bào)告摘要：

In this lecture, I will cover two topics. In the first, I will present our design and development concept for new 2D materials. In the second, I will present our efforts on hydrogen isotope separation.

The discovery of graphene initiated an immense research effort in the field of two-dimensional (2D) crystals. Graphene shows extraordinary high stability, intriguing electronic, including topological, properties, and chemical inertness. Soon it was clear that 2D crystals can be formed from virtually all layered materials by top-down (exfoliation…), but also bottom-up (chemical vapor deposition…) approaches. The family of 2D materials contains a lot of remarkable phenomena, for example 2D semiconductors that get metallic when the number of layers is increased, 2D topological insulators, and 2D metals.

It is somewhat less known that graphene represents also the prototype 2D polymer. 2D polymers (also 2D covalent-organic frameworks – 2D COFs) are a rather new family of synthetic 2D crystals where molecular units are stitched together with strong bonds. This offers a regular crystal lattice and thus materials comprising all collective phenomena that are known from solid state physics, however, with a much richer diversity due to the essentially infinite number of molecules that can be considered. A recent breakthrough was the discovery of chemical coupling reactions that achieve full conjugation between the constituting molecules, which is the precondition for the formation of 2D semiconductors with ballistic transport properties.

For the 2D polymers I will to focus on structural diversity: while mathematically, 11 tilings are possible in two-dimensions (the so-called Kepler nets), nature offers much less structural diversity in crystalline 2D materials. By picking suitable molecular building units we can form lattices with structural topologies that impose, in turn, electronic topologies. One of the examples that I will highlight is the kagome structure, which produces both Dirac points and flat bands.

In the second part of the lecture I will discuss the importance of nuclear quantum effects of adsorbed dihydrogen and its exploitation for hydrogen isotope separation. I will discuss the concept of kinetic quantum sieving and its first application in metal-organic framework (MOF) MFU-4. While quantum sieving works well at low temperature, real-world application would be realistic only if isotope separation at temperatures above 77 K (liquid nitrogen) are possible. I will demonstrate that this is the case if we exploit strong adsorption sites in MOFs with undercoordinated metal centers, such as CPO-27(Co) and Cu(I)-MFU-4l. I will also give recent results on hydrogen isotope separation in the interstitial space of layered materials h-BN and MoS₂.