Microwave-Assisted Synthesis of Perovskite SrSnO3 Nanocrystals in Ionic Liquids for Photocatalytic Applications

Abstract

Nanosized SrSnO₃ photocatalysts have been successfully synthesized by microwave synthesis in various ionic liquids (ILs) followed by a heat treatment process to optimize the materials' crystallinity. The influence of the ILs with various cations such as 1-butyl-3-methylimidazolium ([C₄mim]⁺), 6-bis(3-methylimidazolium-1-yl)hexane ([C₆(mim)₂]²⁺), butylpyridinium ([C₄Py]⁺), and tetradecyltrihexylphosphonium ([P₆₆₆₁₄]⁺) and bis(trifluoromethanesulfonyl)amide ([Tf₂N]^-) as the anion on the structure, crystallization, and morphology of the products was investigated. The samples were characterized by X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), surface area analysis by gas adsorption, X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-vis spectroscopy, and Raman and IR spectroscopy. According to structure characterization by XRD and Raman spectroscopy all samples crystallized phase-pure in the orthorhombic GdFeO₃ perovskite structure type. SEM reveals that, on the basis of the IL, the obtained SrSnO₃ nanoparticles exhibit different morphologies and sizes. Rod-shaped particles are formed in [C₄mim][Tf₂N], [C₆(mim)₂][Tf₂N]₂, and [P₆₆₆₁₄][Tf₂N]. However, the particle dimensions and size distribution vary depending on the IL and range from quite thin and long needlelike particles with a narrow size distribution obtained in [P₆₆₆₁₄][Tf₂N] to relatively larger particles with a broader size distribution obtained in [C₆(mim)₂][Tf₂N]₂. In contrast, in [C₄Py][Tf₂N] nanospheres with a diameter of about 50 nm form. For these particles the highest photocatalytic activity was observed. Our investigations indicate that the improved photocatalytic activity of this material results from the synergistic effect of the relatively large surface area associated with nanosize and an appropriate energy band structure.