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

• A new photocatalyst of Co-doped titanate nanotubes is prepared and characterized.
• The catalyst is a composite nanomaterial consisting of anatase, titanate and CoO.
• The catalyst offers 10 times faster photodegradation rate over conventional TiO2.
• The catalyst has a lower band gap (2.8 eV) and improved response to visible light.
• CoO and anatase facilitate production of e-h pairs and impede recombination thereof.

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 °C followed by calcination at 600 °C). The optimal catalyst (Co-TNTs-600) was obtained at a Co loading of 2.26 wt.% and calcination temperature of 600 °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.

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