Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents and catalysts. Zeolites have a porous structure that can accommodate a wide variety of molecules. Zeolites occur naturally but are also produced industrially on a large scale. Earlier, zeolites came in 3D or 2D structures. But zeolites in a nanotubular (1D) shape have been discovered by researchers at the Georgia Institute of Technology, Stockholm University, and Penn State University.
“A discovery like this is one of the most exciting parts of our research,” said Sankar Nair, principal investigator, and professor in the School of Chemical & Biomolecular Engineering at Georgia Tech. “We’re increasingly used to doing research that has a predetermined application at the end of it, so this is a reminder that fundamental discoveries in materials science are also exciting and important.”
Zeolites are the aluminosilicate members of the family of microporous solids known as “molecular sieves”. A molecular sieve is a material with pores of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. Since the principal raw materials used to manufacture zeolites are silica and alumina, which are among the most abundant mineral components on earth, the potential to supply zeolites is virtually unlimited. Most material testing labs are equipped to evaluate all the raw materials used in such studies.
The research team at Georgia Tech were designing syntheses to assemble 2D zeolite materials. However, the results indicated that a new type of assembly process was occurring at the material testing lab. One such case led to a novel 1D zeolite material that had a tube-like structure with perforated porous walls. This 1D material, termed a zeolitic nanotube, was unlike any zeolite ever synthesized or discovered in nature previously. Nanotubes generally have solid walls, but a low-dimensional version of zeolites now introduces porosity into such structures.
“Zeolite nanotubes could be used to make entirely new types of nanoscale components that can control the transport of mass or heat or charge, not only down the length of the tube the pipe, but also in and out through the perforated walls,” said Nair.
To resolve the detailed arrangement of the atoms in the zeolite nanotube the Georgia Tech researchers teamed up with zeolite crystallography experts at Stockholm University and Penn State. They found that the nanotube walls had a unique arrangement of atoms that are not known in 3D or 2D zeolites. This same arrangement is also responsible for forcing the zeolite to form as a 1D tube rather than a 2D or 3D material.
“This is the first example of a new class of nanotubes, and its unique and well-defined structure provides exciting ideas and opportunities to design zeolite nanomaterials,” said Tom Willhammar, co-investigator and researcher at Stockholm University. “Through further work, we hope that different zeolitic nanotubes could be obtained with variations in pore size, shape and chemistry.”
The researchers see potential for many practical applications, “The unique structural attributes of these materials will allow for an array of potential applications in membrane separations, catalysis, sensing, and in energy devices where mass or energy transport are crucial,” said Christopher W. Jones, co-principal investigator and professor at Georgia Tech. “The materials may have unique mechanical properties, as well, finding applications in composite materials, as carbon nanotubes have done. At this stage, the sky’s the limit, and we hope researchers will look for creative ways to deploy these materials for the benefit of humanity.”
Akshay Korde, Byunghyun Min, Elina Kapaca, Omar Knio, Iman Nezam, Ziyuan Wang, Johannes Leisen, Xinyang Yin, Xueyi Zhang, David S. Sholl, Xiaodong Zou, Tom Willhammar, Christopher W. Jones, Sankar Nair. Single-walled zeolitic nanotubes. Science, 2022; 375 (6576): 62 DOI: 10.1126/science.abg3793.