Reusable Platinum-Deposited Anatase/Hexa-Titanate Nanotubes: Roles of Reduced and Oxidized Platinum on Enhanced Solar-Light-Driven Photocatalytic Activity

A new class of photocatalysts, referred to as Pt(0)- or Pt(IV)-deposited anatase/hexa-titanate nanotubes (Pt(0)-TNTs-600 and Pt(IV)-TNTs-600), were prepared through a three-step process: hydrothermal conversion of commercial TiO2 to titanate nanotubes and subsequent deposition of Pt and calcination. At the optimal Pt dosage (0.1 wt %) and calcination temperature (600 °C), Pt(0)-TNTs-600 showed the highest photocatalytic activity for degrading phenanthrene. The apparent pseudo-first order rate constant (k1) was determined to be 0.12 h–1, which was ∼2 and 3 times of that for Pt(IV)-TNTs-600 and P25. TEM, XRD, FTIR, and XPS analyses indicate that Pt(0)-TNTs-600 is a composite of anatase and hexa-titanate with metallic Pt deposited, where Pt facilitates transport of photogenerated electrons, thus inhibiting recombination of the electron–hole pairs. Moreover, DRS UV–vis analysis revealed a narrower optical energy gap of materials, resulting in enhanced absorbance in the visible region. The new photocatalyst could also produce more reactive oxygen species, i.e. ·OH, than the P25 and pristine TNTs. The material can be reused in multiple cycles of water treatment operations (with almost no activity loss after six consecutive cycles). The new photocatalyst appears promising for efficient photodegradation of a host of organic pollutants in water under solar light.