A new type of cobalt-deposited titanate nanotubes for enhanced photocatalytic degradation of phenanthrene

We prepared and characterized a new type of photocatalyst, referred to as cobalt-deposited titanate nanotubes, using TiO2 (P25) as the precursor through a two-step process (hydrothermal reaction at 150 degrees C followed by calcination at 600 degrees C). The optimal catalyst (Co-TNTs-600) was obtained at a Co loading of 2.26 wt.% and calcination temperature of 600 degrees C. The catalyst can effectively catalyze photodegradation of phenanthrene (a model polycyclic aromatic hydrocarbon) under simulated solar light. The pseudo first-order rate constant was determined to be 0.39 h(-1), which is about 10 times that of the conventional photocatalyst TiO2. TEM, XRD and XPS analyses indicate that Co-TNTs-600 is a composite nanomaterial containing titanate, anatase and CoO crystals. The hydrothermal treatment converts TiO2 into tubular, multilayered titanate nanotubes, allowing for incorporation Co(II) ions on the matrices. The subsequent calcination partially transforms titanate into anatase and the adsorbed Co2+ ions into CoO. UV-vis DRS spectra suggest that the absorption edge of Co-TNTs-600 shifts to the visible light region compared to P25 and un-calcined TNTs, and the new catalyst displays a narrower optical energy band of 2.8 eV compared to 3.2 eV for P25 and 3.4 eV for TNTs. The incorporated CoO acts as an electron transfer mediator, which prevents the recombination of hole-electron pairs created mainly by anatase under solar irradiation. In addition, Co-TNTs-600 exhibits good reusability and can be gravity-separated and reused in multiple cycles of operations for phenanthrene photodegradation. This new catalyst appears promising for catalyzing photodegradation of persistent polycyclic aromatic hydrocarbons. (C) 2016 Elsevier B.V. All rights reserved.