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Scientists have successfully produced molecular sieve membranes that are thinner than cicada's wings

2019/06/26 09:31
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On dec 12, a team led by Yang weishen and li yanshuo of dalian institute of chemical physics, Chinese academy of sciences, successfully prepared for the first time a molecular sieve membrane composed of one-nanometer-thick nanoplates, which is only one thousandth of the thickness of a cicada's wing. The thickness of conventional molecular sieve film is more than 10 times that of cicada. The nanosheet is not only extremely thin, but also has highly structured "sieve holes" that can accurately screen hydrogen and carbon dioxide molecules with a size difference of only 0.04 nanometers, thus effectively trapping the latter. The permeation flux and separation selectivity of the nanosheet molecular sieve membrane far exceed all the hydrogen/carbon dioxide separation membranes reported in the literature, and it is the only membrane material that can meet the requirements of carbon dioxide precombustion capture application. The study was published in the journal Science on December 12 (10.1126/science.1254227).

The separation of hydrogen and carbon dioxide is a key step in clean energy and carbon dioxide capture, and the use of selective membrane materials to separate the two at the molecular level has long been an industry dream. For conventional membrane materials, there is a trade-off between osmotic flux and separation selectivity. Therefore, how to improve the osmotic flux and separation selectivity of the membrane is an important challenge in academia.

Professor y. Lin, deputy editor of membrane science magazine and A famous inorganic membrane scientist in the United States, commented that the research result is A major advance in membrane science. Professor j. Caro, A famous German molecular sieve membrane and membrane catalysis scientist, evaluated that this study was A ground-breaking work in the field of molecular sieve membrane. Professor t. Tsuru, chairman of the Japanese membrane association and A famous microporous membrane scientist, commented that this study developed A new generation of molecular sieve membrane.

How to effectively reduce the membrane thickness is the key to improve the permeability flux of the separation membrane. The key to improve the selectivity of membrane is how to construct molecular scale channels in membrane. Dalian institute of chemical physics, Chinese academy of sciences, the team will get extensive research of zeolite a imidazole ester skeleton (Zeolitic Imidazolate Frameworks, ZIFs), ZIF - 7, nanoparticles (zinc (bim) 2, bim = benzimidazolate) for water treatment, get excellent stability of two-dimensional layered framework matrix material (Zn2 (bim) 4), methanol and normal propyl alcohol as dispersing agent, combined with ultra-low power wet ball mill and ultrasonic dispersing technology, It is the first time to obtain Metal Organic framework (MOFs) nano-plates with single molecular layer thickness (~ 1nm) in the world. On this basis, ultra-thin molecular sieve membrane was obtained by thermal assembly. The hydrogen/carbon dioxide separation coefficient of the nanosheet molecular sieve membrane reached more than 200, and the hydrogen permeability reached more than 2000 GPUs (1CPU=1 × 10-6 cm3/cm2• SEC •cmHg, STP), which was much higher than the hydrogen/carbon dioxide separation performance of organic and inorganic membranes reported so far. The stability of the nanosheet molecular sieve membrane was tested for up to 400 hours under different temperature and temperature conditions (room temperature to 200 oC) and hydrothermal conditions (150 oC), and the membrane performance remained unchanged.

In recent years, two-dimensional layered porous materials are becoming a hotspot in the field of low-dimensional materials and nanopores. The abundant orifice structure and adjustable surface properties of two-dimensional MOFs provide an important platform for the directional design and synthesis of MOFs nanosheet molecular sieve films. This work demonstrates for the first time an important application of two-dimensional layered MOFs in the field of ultra-thin molecular sieve membranes. The prepared nanosheet molecular sieve membrane is expected to play a practical role in integrated coal gasification combined cycle (IGCC) system and realize pre-combustion capture of carbon dioxide.

The research was funded by the national natural science foundation of China and the key deployment program of the Chinese academy of sciences.

By li yanshuo and liu wansheng