Microwave-Assisted Synthesis of SrTiO3 Nanocuboids without TiCl4

Abstract

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.