Achieving the Full Phase Space of Inorganic Natural Products and Beyond in Nanocrystal Synthesis

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Nature, through geology, has created an inspiring array of crystals with a wide range of properties (color, porosity, and mechanical strength, etc.). The unique properties of different types of crystals are a result of not only their chemical compositions, but also the precise and specific arrangement of the constituent atoms. As nanosized crystals (of dimensions of only about 1/1000 times the width of a strand of hair), these diverse properties could lead to applications as far reaching as earth abundant and active industrial catalysts, new cancer treatments, magnetic storage media, better batteries, and inexpensive and efficient solar panels. Before any of this is possible, the routes to synthesize these crystals at the nanoscale must first be discovered because the extreme conditions of geology cannot be easily replicated in the chemistry laboratory or industrial facilities. The research group of Professor Janet Macdonald at Vanderbilt University seeks to understand how the precise placements of atoms in nano-sized rocks can be controlled. Experiments are designed to interrogate what happens to organic molecules and metal atoms when they react and how to control the precise placement of atoms in these nano-sized rocks. The ultimate goal is to make all the phases of crystals that geology does, and possibly be able to design and prepare crystals with new phases. The project also examines how the surfaces of small pieces of iron oxide pigments bind to granite surfaces in the remarkably durable rock paintings of the Anishinaabe, an indigenous people of the United States and Canada. The goal here is to rediscover the lost technique for rock art and return it to the Anishinaabe. The project supports the training of researchers in high school, undergraduate and graduate student levels. Established and new connections encourage Anishinaabe researchers to take part in the research. Specifically, this project uses libraries of organic molecules that contain sulfur and selenium atoms as precursors to obtain the diverse crystals made of these materials. A wide, sweeping and systematic study of the phase-controlled synthesis of iron, cobalt, nickel and copper chalcogenide nanocrystals is being performed. Libraries of organochalcogenides are employed to separate the roles of kinetic rates from the decomposition mechanisms in phase-determination. Organic reaction products are identified to decipher the mechanisms of decomposition of the organochalcogenides on the metals and deduce the impact of these mechanisms on phase control. In a second aim, organoselenol and diselenide chemistry facilitates polytypic selection in the transition metal chalcogenides. In situ solution 1H and 77Se NMR spectroscopy of nanocrystal reactions are used to understand how the organochalcogenide chemistry influences the polytypism in nanocrystal synthesis. In the final thrust, adherence of hematite pigments to silica is studied under varied application conditions precisely controlled using laboratory chemicals. Translation of these studies to naturally sourced materials follows.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.