Halide Mediated Phase-Selective Synthesis of Tin Oxide Nanomaterials

• Julia Higgs, Chemistry, University of Delaware

• Emil Hernandez-Pagan, Department of Chemistry and Biochemistry, University of Delaware

Metal oxide nanoparticles are of great interest for both fundamental studies and applications. Amongst this class of materials, tin oxides have received considerable attention due to their optoelectrical, sensing, and and catalytic properties. These properties are dependent on the composition (i.e. phase) and crystal structure of the tin oxide. However, despite the promising applications, the colloidal synthesis of tin oxides remains under-developed compared to other post-transition metal oxides. In particular, synthesis methods that afford control over the phase are highly desired. Recent work from our research group demonstrated that varying the metal halide precursor can achieve such control in the synthesis of manganese and tin chalcogenide nanocrystals. Motivated by these findings, this work investigates the extension of halide-directed phase control in the colloidal synthesis of tin oxide nanoparticles. Initial efforts focused on systematic variation of the tin halide precursors while holding all other parameters constant. Subsequently studies varying the reaction temperature and time were employed to obtain insights into the reaction pathway. To determine the crystal structure and morphology, the particles were characterized using powder X-ray diffraction and transmission electron microscopy (TEM), respectively. We found that SnI2 favors the formation of cassiterite SnO2 , whereas the use of SnF2 , SnCl2 or SnBr2 yielded romarchite SnO. The insights gained from these studies could potentially  be extended to achieve structure/phase control in other materials systems and enable the discovery of new metastable structures.