Solvothermal synthesis and enhanced photo-electrochemical performance of hierarchically structured strontium titanate...

Homogeneous powders of almost spherical particles of SrTiO₃ with diameters of about 1 μm and large surface areas of up to 186 m² g^-1 were obtained from a facile one-pot solvothermal synthesis. Thorough characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), (high-resolution) transmission electron microscopy, and nitrogen physisorption measurements revealed the hierarchical architecture of the particles down to the scale of a few nanometers. In contrast to SrTiO₃ samples obtained by high-temperature solid-state reaction, the particles are neither agglomerated nor sintered above the micrometer scale. The samples exhibit enhanced photoelectrochemical properties in a 1.0 M KOH aqueous solution compared to their bulk counterpart. The formation mechanism of the SrTiO₃ particles was systematically investigated on the basis of a series of XRD and SEM studies of the products obtained at different reaction temperatures and times. The growth of the hierarchically structured SrTiO₃ particles mainly includes two stages: an intermediately formed amorphous TiO₂ hydrate transforms in a subsequent step into the final SrTiO₃ product. The latter step is a morphology-conserving transformation (pseudomorphosis). Further study indicates that ethylene glycol plays a dominant role in the formation of the hierarchical structures. SrTiO₃ particles of polyhedral shapes with smooth surfaces are obtained when ethylene glycol is substituted by the strongly hydrated basic ionic liquid (IL) tetrabutylammonium hydroxide (TBAH) as the solvent.