Evolution of Nanoscale SnO2 Grains, Flakes, and Plates into Versatile Particles and Films through Crystal Growth in Aqueous Solutions

Hierarchically structured porous particles and films consisting of nanocrystalline SnO 2 were spontaneously grown by gradual oxidation of tin(II) in a simple aqueous system at a low temperature. The nanoscale shape and macroscopically assembled architecture of SnO 2 crystallites were totally controlled by preparation conditions for crystal growth. Spherical and prickly particles exhibiting a high specific surface area in the range of 120−230 m 2 /g were produced by organized growth of nanoscale SnO 2 grains and flakes, respectively. Porous SnO 2 films consisting of the nanograins and nanoflakes were directly grown on a glass substrate through heterogeneous nucleation promoted by addition of urea. Cellular aggregates and films composed of platy subunits were constructed in the solutions under an oxygen-deficient condition. Amorphous and monoxide phases contained in as-deposited particles and films were easily transformed into SnO 2 crystals without deformation of the macroscopic architecture by subsequent hydrothermal treatment at 150 °C in water and calcination at 500 °C in air, respectively. The easy-to-handle nanocrystalline SnO 2 with hierarchical and porous architectures would be utilized for various practical applications.