Synthesis-dependent surface acidity and structure of SrTiO₃ nanoparticles

Chemisorption of pyridine and atmospheric CO₂ followed by means of visible Raman and DRIFT spectroscopy were employed to investigate the surface acidity and structure of as-prepared SrTiO₃ (STO) samples synthesized using three different approaches, solid-state reaction, molten salt, and sol-precipitation-hydrothermal treatment. Samples prepared via solid-state reaction consisted of irregularly shaped polycrystalline grains with a BET surface area of ∼2 m²/g, whereas those obtained via molten salt synthesis and sol-precipitation-hydrothermal treatment were single-crystalline nanocubes with the {100} faces primarily exposed and BET surface areas of ∼10 and 20 m²/g, respectively. Pyridine and atmospheric CO ₂ chemisorption demonstrated that the differences in surface acidity between samples synthesized using different approaches are rather slight with a mixture of SrO-based and TiO-based terminations observed in all cases. In contrast, the typology of surface carbonate species arising from the reactive adsorption of atmospheric CO₂ varied significantly between samples, indicating the atomic structure of STO surfaces depends strongly on the synthetic method employed. The presence of coordinatively unsaturated Ti ⁴⁺ acid centers and highly nucleophilic O^2- anions is particularly relevant in the perspective of employing morphology-controlled perovskite nanoparticles as supports in catalytic applications such as the oxidation of hydrocarbons.