Size and Shape of Small Crystals Affect Surface Chemistry and Consolidation. Rational Synthetic Methods

Kansas State University, Manhattan KS

Investigators

Abstract

The proposed research aims to develop a deeper understanding of two powerful synthetic methods. First, a Modified Aerogel Process (MAP) will be challenged. Remarkable solvent effects that have been encountered will be scientifically assessed. Equilibria set up during the hydrolysis step will be probed by changes in the Lewis acidity of metal ions employed (e.g. magnesium (2+) vs zinc 2+)). Changes in dehydration procedures (vacuum vs gas flow) will also be assessed. In this work zinc oxide (ZnO), zirconium dioxide (ZrO2), magnesium oxide (MgO), and calcium oxide (CaO) will serve as models. In a second phase of this work, adsorption behavior of different crystal shapes will be assessed with carefully worked out standardized procedures. The effect of crystal shape on nanocrystal consolidation will also be studied. A second synthetic approach, Solvated Metal Atom/Molecule Dispersion (vapor deposition into cold solvents followed by controlled aggregation) will be analyzed. In this work nanocrystals of selected sulfides, selenides, and halides will be studied (zinc sulfide (ZnS), cadmium sulfide (CdS_, cadmium selinide (CdSe), lead sulfide (PbS), lithium fluoride (LiF), magnesium fluoride (MgF2), magnesium chloride (MgCl2), and tin sulfide (SnS). The underlying theme will be to develop understanding and predictability for these powerful synthetic methods that are scalable. In addition, the broad array to techniques, opportunities for creative input and opportunities for presentation of results will allow excellent training for students in laboratory setting that has always accepted and encouraged a highly diverse mixture of me and women. Evidence is accumulating that common mineral-like substances, when produced in very small crystalline form (nanocrystals), have very different shapes compared to larger crystals. This difference has profound effects on the ability of these fine powdery substances to adsorb toxic chemicals. In fact, nanocrystals have been shown to be extremely good at adsorbing and detoxifying many air pollutants toxic industrial chemicals, chemical warfare agents, and bacteria. However, the methods to produce these useful nanocrystals are mostly "alchemical" in nature. Better understanding is needed in order to probe two important synthetic methods by studying different solvents, temperatures, concentrations of reagents, and other key features. The underlying theme of the work will be to develop scientific understanding and predictability for scalable production of these interesting and useful nanocrystalline materials. In addition, the broad array of scientific techniques to be employed, opportunities for creative input, and opportunities for presentation of scientific findings will allow excellent training of students in a laboratory setting that has always encouraged a highly diverse mixture of men and women.