Prof. Yongjae Lee [Yonsei University, South Korea]

[Yonsei University, South Korea]

Title: High-pressure chemistry of zeolites and MOFs; need for high-resolution XRD at low-to-intermediate pressure range

Time: 10:00 - 11:30, August 26

Place: Conference Room 201, Building 6, HPSTAR (Shanghai)

Abstract:

Zeolites and MOFs (Metal-Organic Framework materials) are an important class of technological materials in designing chemical reactions, exchange, and absorption in molecular and nanometer scales. While an ever-expanding variety of zeolites and MOFs with a wide range of nanopore topology is available, it is desirable to have a way to tailor a given nanopore via controlling both the coordination-inclusion chemistry within and distortion/relaxation of the nanopore. Pressure can be used as a clean and safe variable to extend both the structural and chemical diversity of a nanopore as many of the nanoporous materials are vulnerable to temperature-treatment. One of the surpassed chemical and structural features observed under pressure in nanoporous materials is pressure-induced hydration and accompanying volume expansion in a small-pore zeolite natrolite (Na16Al16Si24O80x16H2O).1 This has now been established to be a systematic structural property of this class of small-pore zeolite. Depending on the type of cations within the zeolitic nanopores (Li, Ag, K, Rb, Cs, Ca, Sr, Pb, Cd), the degree of volume contraction is controlled from 5% up to -21% in the pressure range of 0.4 – 3.0 GPa.2 These systematic high-pressure investigations of nanoporous materials require the use of high-resolution powder diffraction setup to unveil in unprecedented details the varying degrees of structural and chemical changes occurring in the low-to-intermediate pressure range. Another example to demonstrate the unique role of pressure in mediating chemical and structural changes in nanoporous materials is the pressure-driven exchange of the guest molecules in MIL-47(V).3 ‘Spring-like’ motions of the nanopores are coupled to the replacement of the existing TPA template molecules to methanol used as pressure-transmitting medium in the pressure range of 0.3 – 2 GPa. Such an efficient role of pressure to induce hitherto unknown changes in nanoporous materials leads us to design some model cases of pressure-driven applications. A novel procedure to exchange and sequestrate important radionuclides such as Cs and I under industrially-achievable pressure and temperature will be shown.4 Another pressure-driven application is to control the chemical selectivity of a nanopore to trap nominally non-absorbable gas molecules. We have recently succeeded in pressure-induced insertion of Xe into a small-pore zeolite. Intriguingly, Xe absorption into the zeolitic nanopores occurs irreversibly at moderate pressure and temperature conditions and mediates charge disproportionation reaction within the nanopores.5 This result sheds new insight into the ‘Missing Xenon’ problem to be seen as a subsurface process and demonstrates that there are still many new things to discover in the low-to-intermediate pressure regime.

1. Lee et. al., JACS (2002) 124, 5466; Lee et. al., Nature (2002) 420, 485.

2. Lee et. al., Chemistry - A European Journal (2013) 19, 10876.

3. Lee et. al., (in preparation)

4. Lee et. al., (submitted)

5. Lee et. al., Nature Chemistry (Advance Online Publication)

Biography of the speaker:

Professor Yongjae Lee is from the department of Earth System Sciences College of Science, Yonsei University, Seoul, South Korea. Professor Lee has been dedicated in the high-pressure research for many years with multiple high quality paper published in the world.