On December 12, a research team led by researcher Yang Weishen and researcher Li Yanshuo of Dalian Institute of Chemical Physics, Chinese Academy of Sciences, successfully prepared a molecular sieve membrane composed of 1 nanometer thick nanosheets for the first time. Its thickness is only 1‰ of the thickness of cicada wings, far "thinner than cicada wings". The thickness of the regular molecular sieve membrane is more than ten times the thickness of the cicada wing. The nanosheets are not only extremely thin, but also have highly regular channels like "mesh", which 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 capture before combustion. The results of the study were published December 12 in Science (Science)(10.1126/science.1254227).

The separation of hydrogen and carbon dioxide is a key step in clean energy and carbon dioxide capture. Using selective membrane materials to achieve the separation of the two at the molecular level is a long-term dream of the industry. For regular membrane materials, there is a trade-off relationship between permeation flux and separation selectivity. Therefore, how to simultaneously improve the permeation flux and separation selectivity of separation membranes is an important challenge for academia.

Professor Lin yuesheng (Y. Lin), deputy editor-in-chief of membrane science and a famous inorganic membrane scientist in the United States, commented that the research result is an important progress in the field of membrane science (A major advance in membrane science); Professor Carlo (J. Caro), a famous German scientist on molecular sieve membrane and membrane catalysis, commented that the research is a pioneering work in the field of molecular sieve membrane (A ground-breaking work); Chairman of Japan Membrane Association, professor T. Tsuru, a famous microporous membrane scientist, evaluated the research and developed a new generation (A new generation) molecular sieve membrane.

To improve the permeation flux of separation membrane, the key is how to effectively reduce the membrane thickness; to improve the selectivity of separation membrane, the key is how to build molecular scale channels in the membrane. The research team of Dalian Institute of Chemical Physics, Chinese Academy of Sciences hydrothermally treated a widely studied zeolite imidazole ester framework (Zeolitic Imidazolate Frameworks, ZIFs),ZIF-7 nanoparticles,(Zn(bim)2, bim = benzimidazolate) to obtain a two-dimensional layered framework precursor material (Zn2(bim)4) with excellent stability, using methanol and n-propanol as dispersants, combined with ultra-low power wet ball milling and ultrasonic dispersion technology, metal organic framework (Metal Organic Frameworks, MOFs) nanosheets with monolayer thickness (~ 1nm) were successfully obtained for the first time in the world. On this basis, the ultra-thin molecular sieve membrane was obtained by thermal assembly method. The hydrogen/carbon dioxide separation coefficient of the nanosheet molecular sieve membrane is more than 200, and the hydrogen permeability is more than 2000 GPUs (1CPU = 1 × 10-6 cm3/cm2 • sec • cmHg,STP), which is much higher than the hydrogen/carbon dioxide separation performance of organic and inorganic membranes reported so far. The nanosheet molecular sieve membrane was tested for stability for up to 400 hours under different 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 research hotspot in the field of low-dimensional materials and nanoporous materials. The rich pore structure and adjustable surface properties of two-dimensional MOFs materials provide an important platform for the directional design and synthesis of MOFs nanosheet molecular sieve membranes. This work is the first to demonstrate the 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 the integrated coal gasification combined cycle (IGCC) system, and realize the capture of carbon dioxide before combustion.

The research was supported by the National Natural Science Foundation of China and the key deployment project of the Chinese Academy of Sciences.

Author: Li Yanshuo and Liu Wansheng Source: Science Network