Session: Nanoscience:

Aluminum nanocrystals have drawn increasing interest due to their promising optical properties and the low cost of aluminum. The synthesis of aluminum nanocrystals using titanium catalysts has progressed rapidly in recent years, with several developments towards understanding the growth mechanism and improved size and shape control. This work demonstrates a novel system of catalysts, formed by the reaction of two previously studied catalysts with each other, titanium isopropoxide (TIP) and either Tebbe’s reagent or its analogue, bis(cyclopentadienyl)titanium(III) chloride (Cp₂TiCl). The catalyst structures are characterized using EPR, NMR, and IR spectroscopies, indicating that they are a family of bridged molecules that has had little previous study. The newly formed catalysts retain the same reactive titanium centers of the parent molecules, combined through Ti-O-Ti bridges. However, both show significantly different activity in Al nanocrystal synthesis, with faster reaction kinetics and altered shape control compared to Tebbe’s reagent alone. Whereas TIP produces large cuboctahedra, and both Tebbe’s reagent and Cp₂TiCl produce large cubes, the new catalysts can be tuned to favor either cubes or octahedra by the choice of parent molecule. The size of the particles is also tunable in size (50 nm to 150 nm) through temperature control. In addition to being the first demonstrated synthesis of {111} faceted nano-Al (octahedra), this new system of catalysts represents a modular system where the reactivity can be tuned by substituting different component molecules into the di-titanium catalyst itself, or by modifying the specific ligands of each Ti-centered molecular component. This modular strategy can dramatically expand the available library of catalysts for Al NC synthesis.

Professor Naomi Halas

Stanley C. Moore Professor of Electrical and Computer Engineering, Professor of Chemistry, Rice University

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