Microwave-Assisted Synthesis of SrTiO₃ Nanocuboids without TiCl₄

Strontium titanate (STO) nanocuboids are a novel support for Pt nanoparticle catalysts (Pt/STO). The first of many steps in commercializing Pt/STO will be developing a scalable, environmentally sustainable, and cost-effective STO nanocuboid synthesis. Herein, Sr-Ti-OH mixtures are synthesized from various Sr²⁺ and Ti⁴⁺ reagents and treated by convection- and microwave-assisted heating to obtain STO nanoparticles. These experiments clarify how phase composition of the prehydrothermal Sr-Ti-OH mixture and choice of heating method affect final nanoparticle morphology. In Sr-Ti-OH mixtures synthesized with TiCl₄, STO is the most stable phase and precipitates prior to heating, while titania sol-gels are the most stable phase when other Ti⁴⁺ sources are used. STO nanocrystals always form when Sr-Ti-OH mixtures are treated by convection heating, though nanocuboids are only observed if STO precipitates from the Sr-Ti-OH mixture. Microwave-assisted hydrothermal treatment more rapidly heats the precursor solution, and thus, STO nanocuboids can form from a variety of Sr-Ti-OH mixtures regardless of mixture composition. Two microwave syntheses of STO nanocuboids are reported: one which uses TiCl₄ as a Ti⁴⁺ source, and another that uses titanium(IV) bis(ammonium lactato) dihydroxide ([NH₄CH₃CH(O)CO₂]₂Ti(OH)₂), a water-stable Ti⁴⁺ complex.