The Power of Ionic Liquids: Crystal Facet Engineering of SrTiO₃ Nanoparticles for Tailored Photocatalytic Applications

Abstract Sonochemical synthesis of nano‐sized SrTiO₃ carried out at close to room temperature, in ionic liquids (ILs) allows the tuning of particle size and particle morphology, that is, tracht and habitus, as well as particle aggregation via the choice of the ionic liquids (ILs) as the reaction medium. The nanoparticles demonstrate high performance for photocatalytic water splitting and photodecomposition of organic material. To this end bis(trifluoromethanesulfonyl)amide ([Tf₂N]⁻)‐based ILs with cations of different properties with respect to specific interactions with the target material are investigated. Isolated, 15 ± 1 nm sized nano‐spheres of SrTiO₃ are observed to form in [C₃mimOH][Tf₂N] ([C₃mimOH]⁺ = 1‐(3‐hydroxypropyl)‐3‐methylimidazolium). Aggregation of small sized nanoparticles are observed to around 250 ± 100 nm large cube‐like formations in [C₄mim][Tf₂N] ([C₄mim]⁺ = 1‐butyl‐3‐methylimidazolium), raspberry‐like in [C₄Py][Tf₂N] ([C₄Py]⁺ butylpyridinium), and ball‐like in [P₆₆₆₁₄][Tf₂N] ([P₆₆₆₁₄]⁺ tetradecyltrihexyl phosphonium). Importantly, the different materials show different performance as photocatalysts. SrTiO₃ prepared in [C₄mim][Tf₂N] shows the highest photocatalytic activity for H₂ evolution (1115.4 µmol h⁻¹) when using 0.025 wt% Rh as the co‐catalyst, whereas the material prepared in [C₃mimOH][Tf₂N] shows the highest activity for the photocatalytic degradation of methylene blue (88%) under UV irradiation. The different photocatalytic activities can be correlated with the different crystal surface facets expressed in the respective nanosized SrTiO₃ material, {110} for material obtained from [C₄mim][Tf₂N], and {100} for material from [C₃mimOH][Tf₂N]. First‐principles density functional theory (DFT) calculations are used to support the experimental findings.