Zeolites
Zeolites are materials that are traditionally used as absorbents, catalysts and as a filter for several decades. Zeolites are micro porous crystalline alumino silicates and widely used in petrochemistry and fine-chemical synthesis because strong acid sites within their uniform micro pores enable size- and shape-selective catalysis. In spite of this there have been substantial challenges in processing zeolitic materials into extended sheets that remain intact.
Zeolite nanosheets
Efforts to create zeolite nanosheets which are very small sieves to separate molecules from one another have proved rather fruitless as the processes used so far tend to result in the creation of holes in the sheet that are too large to capture the desire molecules. The result of blending the two layered zeolites silicate and its other component by melting them together is a nanocomposite that has two unique kinds of nanosheets. When making zeolites, the polystyrene in the mix is removed and this results in bent or curled sheets, which won’t work because it causes grouping or bunching which results in the development of holes that isn’t of the desired size. . Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation).
Researchers at University of Minnesota have produced zeolites which results in deformed structures in the framework leading to holes in the material that are larger than the pores needed to capture whatever is being filtered.
The researchers used sound waves in the water soluble liquid toluene and a centrifuge and obtained flaky crystal type flat nanosheets having the right amount of thickness (2.6 and 3.4nm). The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes. The nanosheets were used to coat an anodised alumina membrane and a rough alpha-alumina support to produce zeolite membranes. Subsequent calcination gave smooth, well packed overlapping layers. The coated structures which were hydro thermally treated had reduced the space between the nanosheets and were highly effective at separating xylene isomers. Good performance was also observed for helium-hydrogen and helium-nitrogen mixtures.
Applications
The resultant product can be used to separate molecules as a sieve or as a membrane barrier in both research and industrial applications and the same process can be used to create other types of zeolites.
Thin zeolite films are attractive for a wide range of application. They can be used for making molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Zeolites nanosheets could potentially be used for a wide range of applications such as sieves that can separate molecules based on their size and catalytic membranes. zeolite nanosheets that are only 2nm thick renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion.