Mineralization of malachite green dye over visible light responsive bismuth doped TiO2–ZrO2 ferromagnetic nanocomposites

Abstract

We report enhanced visible light photocatalytic activity for ferromagnetic Bi doped (1% by atomic weight) TiO₂–ZrO₂ nanocomposites for the degradation of malachite green in aqueous solution. X-ray diffraction, Raman and High resolution Transmission electron microscopy (HRTEM) analysis indicate the presence of monoclinic ZrO₂ and anatase TiO₂ in the composite sample. The particle size of the nanocomposite is ∼20 nm. A significant absorption of visible light is observed for the doped TiO₂ composite as compared to P25 and undoped TiO₂–ZrO₂. The photocatalytic activity of different concentrations of the TiO₂–ZrO₂ nanocomposite for the degradation of malachite green follows the order: 98% TiO₂–2% ZrO₂ < 80% TiO₂–20% ZrO₂ < 90% TiO₂–10% ZrO₂. The Bi doped TiO₂–ZrO₂ (90% TiO₂–10% ZrO₂) composite shows a still higher activity as compared to the undoped composite and commercial P25. TOC analysis exhibited 88% mineralization of malachite green over Bi doped TiO₂–ZrO₂ (90% TiO₂–10% ZrO₂). The enhanced photocatalytic activity of the doped TiO₂–ZrO₂ composite is attributed to improved visible light absorption and efficient separation of photogenerated charge carriers. The composite samples are found to be photo-stable and the photocatalytic activity remains almost the same for four cycles of degradation experiments. Testing with different quenchers suggest that hydroxyl radicals, holes and superoxide radicals play a considerable role in the photodegradation of malachite green. It is noteworthy that the Bi doped TiO₂–ZrO₂ nanocomposite exhibits defect induced room temperature ferromagnetism.