Journal
APPLIED SURFACE SCIENCE
Volume 456, Issue -, Pages 676-693Publisher
ELSEVIER
DOI: 10.1016/j.apsusc.2018.06.067
Keywords
Ultra-trace concentrations (ppm); Anatase to rutile transition (ART); Photocatalytic degradation; Hydroxyl (center dot OH-) and oxygen (center dot O-) radicals; Anatase-rutile heterojunction
Categories
Funding
- National Basic Research Program of China [2011CB933300]
- National Science Fund for Distinguished Young Scholars [50125309]
- National Natural Science Foundation of China [51272184, 91433203]
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A series of novel photocatalysts were synthesized by incorporating tungsten (W6(+)) ions in to the lattice of pure anatase TiO2 nanoparticles with ultra-trace concentrations (ppm) such as 10 ppm, 50 ppm, 90 ppm and 120 ppm using a simple one-step hydrothermal method under identical conditions. X-ray diffraction (XRD) studies, revealed a spectacular structural phase transformation from anatase to ruffle on doping and associated morphological changes are seen by scanning electron microscopy (SEM). The phase transformation is promoted with the increase of W concentration up to 50 ppm and inhibited thereafter. Microstructural lattice distortions due to the presence of W6(+) ions are monitored by high-resolution transmission electron microscopy (HR-TEM). The valence band X-ray photoelectron spectra (XPS), Ultraviolet photoelectron spectra (UPS) and UV-Vis absorption studies confirm the reduction of band gap for W doped TiO2 mixed phase nanoparticles. The doping causes an enhanced visible light absorption. Room temperature photoluminescence (PL) spectroscopy ensures an oxygen vacancy mediated phase transformation. The photocatalytic performances of the W doped TiO2 catalysts are evaluated for the degradation of Rhodamine B (RhB), Methylene blue (MB) and Methyl orange (MO) aqueous solutions under visible-light irradiation. The efficiency of photocatalytic degradation of the dyes gradually increased with the content of W6+ ions (fill 50 ppm) and then decreased which is consistent with the structural and optical studies. The control experiments, showed possible oxidative species, are hydroxyl (center dot OH-) and oxygen (center dot O-2(-)) radicals while the earlier plays a dominant role. The resuability tests performed for five cycles demonstrate high stability and reusability of the photocatalysts. A possible synergistic mechanism based on the impurity energy levels of W6(+) ions, oxygen vacancies and anatase-rutile heterojunction for the enhancement of the photocatalytic activity under visible-light irradiation is proposed.
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