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Molecular Sieve

Molecular sieve is a kind of aluminosilicate compound with cubic lattice. Its molecular formula is MO·Al2O3·xSiO2·yH2O, M stands for K, Ca, Na and so on. The pore of molecular sieve can adsorb molecules smaller than their diameter into the interior of the cavity, and has the preferential adsorption ability to the polar molecule and the unsaturated molecule, thus can separate molecules with different polarity degree, saturation degree, molecular size, and boiling point.

Pore selectivity of molecular sievesFigure 1. Pore selectivity of molecular sieves

Applications:

  • Hygroscopic agent: The molecular sieve is extremely hygroscopic and is the only available high temperature adsorbent. Direct exposure to air during storage should be prevented due to the hygroscopicity of molecular sieves. The zeolite stored for a long time or absorbing moisture can be regenerated and reused before use. Gases for drying in industrial production are: air, hydrogen, oxygen, nitrogen, argon, etc.
  • Catalyst: Molecular sieve crystal has the advantages of uniform pore structure, large surface area and high surface polarity. These structural properties make molecular sieve not only an excellent adsorbent, but also a good catalyst and catalyst carrier. Molecular sieves are acidic catalysts, which are regulated by different Si-Al ratios, and the surface acidity of molecular sieves directly affects their catalytic activity. Since the molecular sieve structure has uniform internal pores, the selectivity of the catalyst reaction often depends on the size of the molecule and pore size.
  • Photoelectric and energy storage materials: The morphology control of molecular sieve material, and its application in high-tech fields such as photoelectricity, microelectric level, and sensors will also become the focus of molecular sieve research. The morphology control of molecular sieve materials includes molecular sieve nanoparticles, molecular sieve large crystals, molecular sieve fibers and membranes. Molecular sieves have spacious pores, for example, carbon or Pd light storage materials can be manufactured in-situ in their pores to increase the ease of handling and surface area of these energy storage materials. When their energy is slowly released to achieve the effect of transferring energy, they may become a new generation of environmentally friendly energy storage materials in the future.
  • Optical materials: The unique microporous system of molecular sieves has shown potential application prospects in semiconductors, molecular wires, molecular photodiodes and other fields, especially in nanoscale optical and microelectronic technologies, thus becoming a field of microporous materials research hotspots.

Classification:

  • Natural molecular sieve: Most of the natural zeolites are produced by the reaction of volcanic tuff and tuff sedimentary rocks in the ocean or lake environment. More than 1,000 zeolite ores have been discovered, 35 of which are more important. Clinoptilolite, mordenite, erionite and chabazite are commonly seen.
  • Artificial molecular sieve: Because natural zeolite is limited by resources, people began to use a large number of synthetic zeolites, which are often classified according to different crystal structures.

References:

  1. M.G. Buonomenna, W. Yave and G. Golemme. Some approaches for high performance polymer based membranes for gas separation: block copolymers, carbon molecular sieves and mixed matrix membranes [J]. RSC Adv., 2012, 2, 10745-10773.
  2. Shilun Qiu, Ming Xue and Guangshan Zhu. Metal–organic framework membranes: from synthesis to separation application [J]. Chem. Soc. Rev., 2014, 43, 6116-6140.
  3. Jing Wang, Junyong Zhu, Yatao Zhang, Jindun Liu and Bart Van der Bruggen. Nanoscale tailor-made membranes for precise and rapid molecular sieve separation [J]. Nanoscale, 2017, 9, 2942-2957.

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