We have synthesized small, monodisperse, spherical nanocrystals of Co(III)OOH (size 3.3�0.9 nm) by photolyzing aqueous solutions of [Co(NH3)5Cl]Cl2 at 350 nm. A mechanistic investigation shows that neither Co(H2O)3+ nor Co(H2O)2+ are reactive intermediates. The decomposition of [Co(NH3)5Cl]Cl2 proceeds both photochemically at room temperature and thermally at 80�C; however, crystals produced thermally exhibit sizes up to 250 nm, and are composed of crystalline rod formations surrounded by amorphous regions. Thermogravimetric analysis shows that the smaller, photochemically prepared CoOOH nanocrystals exhibit a phase transition to Co3O4 at 210�C, while the larger, thermally prepared CoOOH crystals undergo the same transition at 250�C. We heated dry samples of nanocrystalline CoOOH to produce small Co3O4 (size 5�1 nm) nanocrystals of similar spherical morphology. We characterized the electronic structure and density of states of CoOOH computationally, using the Vienna Ab-initio Simulation Package. Low-temperature photochemical nanocrystal syntheses could allow isolation of doped nanocrystals and other unstable phases.

Photochemical vs. thermal synthesis of cobalt(III) oxyhydroxide nanocrystals

243rd National Meeting (2012)

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