Rapid photo- and photo-Fenton-like catalytic removals of malachite green in aqueous solution on undoped and doped TiO₂ nanotubes

Abstract

Undoped and Fe-doped TiO₂ nanotubes with Fe content of 0–3.86 at.% were fabricated by hydrothermally treating sol–gel-derived undoped and Fe-doped TiO₂ nanoparticles in NaOH aqueous solution. The Fe doping narrowed the optical band gap of the nanotubes from 3.17 to ~2.76 eV as the increase in Fe-doping content from 0 to 3.86 at.%. The nanotubes showed a large specific surface area of ~274–303 m² g⁻¹, which increased as the increase of Fe content. The sunlight-excited degradation experiments of malachite green in the water indicated that the nanotubes had a high photocatalytic activity. The Fe doping further enhanced the photocatalytic activity of the nanotubes, increased as increasing Fe-doping content. Moreover, the photodegradation of the dye became more fast as H₂O₂ was used, showing remarkable Fenton-like photocatalytic activity. This Fenton-like reaction also enhanced as increasing Fe content. An optimal H₂O₂ dosage was also observed. The quasi-kinetic first-order rate constant of the photodegradation of the malachite green aqueous solution with the concentrations of 1 × 10⁻⁶ and 1×10⁻⁵ mol l⁻¹ were in the range of ~1.61–2.03 and ~0.41–0.65 min⁻¹, respectively. These constants further increased to ~2.81–3.51 and ~1.71–2.04 min⁻¹ as the H₂O₂ with a concentration of 10 ml l⁻¹ is used.

Keywords:

• Semiconductors
• Nanotubes
• Photocatalytic properties
• Fenton-like reaction