Ni/SrTiO₃ Nanoparticles for Photodegradation of Methylene Blue

Dyes are routinely used in the textile and pharmaceutical industries, causing serious environmental issues by decreasing water quality. Photocatalysts are used for dye degradation, and different acting mechanisms may occur during the photodegradation process. In this study, Ni nanoparticles were heated to selected temperatures up to 500 °C under an ambient atmosphere and subsequently supported on SrTiO3. The samples were characterized by X-ray diffraction, small-angle X-ray scattering, transmission electron microscopy, X-ray photoelectron spectroscopy, Mott–Schottky, in situ X-ray absorption spectroscopy (XAS), and in situ time-resolved XAS at the Ni K edge during thermal treatment. In addition to improving the photodegradation of methylene blue compared with SrTiO3 alone, there was a direct association between the Ni oxidation state and the atomic mechanism of photodegradation. Thermal treatments of Ni nanoparticles up to 300 °C induce surface reconstruction of SrTiO3 during the photodegradation reaction and can dissociate H2O molecules into OH• radicals, which act as oxidizing agents of methylene blue dye. Conversely, thermal treatment of Ni nanoparticles at 500 °C allows the fabrication of a NiO/SrTiO3 heterojunction, which promotes efficient methylene blue degradation due to improved electron–hole pair separation. Controlling the acting mechanism of photocatalysts could pave the way for the research of photocatalysts with improved photodegradation activity.