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 SnO2 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 SnO2 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 SnO2 grains and flakes, respectively. Porous SnO2 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 SnO2 crystals without deformation of the macroscopic architecture by subsequent hydrothermal treatment at 150 degrees C in water and calcination at 500 degrees C in air, respectively. The easyto-handle nanocrystalline SnO2 with hierarchical and porous architectures would be utilized for various practical applications.