TiO2/SrTiO3 and SrTiO3 microspheres decorated with Rh, Ru or Pt nanoparticles: Highly UV–vis responsible photoactivity and mechanism

Abstract A series of TiO2/SrTiO3 and SrTiO3 microspheres decorated by Rh, Ru or Pt NPs were prepared by facile hydrothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) with energy-dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), photoluminescence spectrometry (PL), Fourier transform infrared (FT-IR) and Raman spectra and diffuse reflectance spectroscopy (DRS). The formation mechanism of TiO2/SrTiO3 and SrTiO3 microspheres was proposed and the photocatalytic properties of the samples were characterized using phenol as the pollutant under the UV–vis and light irradiation. The gas chromatography-mass spectrometry was employed to detect organic intermediates to establish degradation pathway of isotopically labeled (1-13C) phenol. The role of the active species in the process of the degradation was evaluated using different types of active species scavengers as well as hydroxyl radical test with coumarin were also carried out. The PL spectra indicate that the formation of TiO2/SrTiO3 and SrTiO3 decreased the recombination rate of photogenerated carriers. The obtained results revealed that the samples showed an enhanced photocatalytic activity for the degradation of organic pollutant. The SrTiO3/Rh(0.05) photocatalyst showed a higher photodegradation rate under UV–vis and Vis light (3.6 and 1.2 μmol dm−3 min−1, respectively) compared to the unmodified SrTiO3 (0.6 and 0.2 μmol dm−3 min−1, respectively). The active species trapping experiments indicated that under UV–vis as well as Vis illumination O 2 - are the main active species in the degradation process. The main by-products detected in phenol oxidation were catechol, hydroquinone, malonic, fumaric and maleic acid. Moreover, GC–MS results indicated the formation of isotopically labeled and unlabeled maleic acid which could be generated by two different pathways: trough decomposition of catechol and hydroquinone at the same time.