Scientists have successfully fabricated a molecular sieve membrane “thinner than a cicada’s wing.”

　　On December 12, a research team led by Researchers Yang Weishen and Li Yanshuo at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, successfully fabricated for the first time a molecular sieve membrane composed of nanosheets just 1 nanometer thick—only one-thousandth the thickness of a cicada’s wing, making it far “thinner than a cicada’s wing.” By contrast, conventional molecular sieve membranes are more than ten times as thick. These nanosheets are not only extremely thin but also feature highly ordered channels resembling “sieve pores,” enabling precise separation of hydrogen and carbon dioxide molecules whose size difference is merely 0.04 nanometers, thereby effectively retaining the latter. The resulting nanosheet‑based molecular sieve membrane exhibits permeation flux and selectivity that surpass all previously reported hydrogen–carbon dioxide separation membranes, and it is the only material documented to meet the performance requirements for pre‑combustion carbon capture. The findings were published on December 12 in the journal Science (10.1126/science.1254227).

　　The separation of hydrogen and carbon dioxide is a critical step in clean energy technologies and carbon capture. Achieving molecular-level separation of these two gases using selective membrane materials has long been an aspiration of the industrial sector. For conventional membrane materials, there is an inherent trade-off between permeation flux and separation selectivity. Consequently, simultaneously enhancing both the permeation flux and the separation selectivity of separation membranes remains a major challenge for the scientific community.

　　Professor Y. Lin, Associate Editor of the journal “Membrane Science” and a renowned U.S. inorganic membrane scientist, described the research findings as a major advance in the field of membrane science; Professor J. Caro, a distinguished German expert in molecular sieve membranes and membrane catalysis, hailed the study as a groundbreaking contribution to the molecular sieve membrane domain; and Professor T. Tsuru, President of the Japan Membrane Society and a leading authority on microporous membranes, commended the work for pioneering a new generation of molecular sieve membranes.

　　To enhance the permeation flux of separation membranes, the key lies in effectively reducing membrane thickness; to improve their selectivity, the critical challenge is constructing molecular‑scale pores within the membrane. A research team at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, subjected ZIF‑7 nanoparticles—derived from the widely studied zeolitic imidazolate frameworks (ZIFs), with the composition Zn(bim)₂, where bim = benzimidazolate—to hydrothermal treatment, yielding a highly stable two‑dimensional layered framework precursor, Zn₂(bim)₄. Using methanol and n‑propanol as dispersants, and combining ultra‑low‑power wet ball milling with ultrasonic dispersion, they achieved, for the first time internationally, the exfoliation of metal–organic framework (MOF) nanosheets with a single‑molecule‑layer thickness (~1 nm). Building on this, they fabricated ultrathin molecular sieve membranes via thermal assembly. The resulting nanosheet‑based molecular sieve membrane exhibits a hydrogen/carbon dioxide separation factor exceeding 200 and a hydrogen permeance of more than 2,000 GPUs (1 CPU = 1 × 10⁻⁶ cm³/cm²·sec·cmHg, STP), far surpassing the hydrogen/carbon dioxide separation performance reported to date for both organic and inorganic membranes. Furthermore, this nanosheet molecular sieve membrane underwent stability testing under varying temperature cycles (from room temperature to 200 °C) and hydrothermal conditions (150 °C) for up to 400 hours, during which its performance remained unchanged.

　　In recent years, two-dimensional layered porous materials have emerged as a research hotspot in the fields of low-dimensional materials and nanoporous materials. The rich pore‑opening architectures and tunable surface properties of 2D MOFs provide an important platform for the targeted design and synthesis of MOF nanosheet‑based molecular sieve membranes. This work represents the first demonstration of the significant applications of 2D layered MOFs in the realm of ultrathin molecular sieve membranes. The resulting nanosheet‑based molecular sieve membranes hold promise for practical deployment in integrated gasification combined cycle (IGCC) systems, enabling pre‑combustion capture of carbon dioxide.

　　This research was supported by the National Natural Science Foundation of China and a key project funded by the Chinese Academy of Sciences.

　　Author: Li Yanshuo, Liu Wansheng Source: ScienceNet