Photocatalytic degradation of Orange G using TiO₂/Fe₃O₄ nanocomposites

Titanium dioxide (TiO₂) is one among the best photocatalysts used in commercial applications. However, its large intrinsic bandgap (~ 3.23 eV) limits its photocatalytic application only to the ultraviolet (UV) region that is only 4% of the solar spectrum. The recombination of photogenerated electron–hole pairs reduces the quantum efficiency and photocatalytic activity. The visible region allows us to use 43% of the solar spectrum. Therefore, to extend the photocatalytic activity of TiO₂ to visible light spectrum, its bandgap must be decreased that suppresses the recombination reactions. This can be achieved by coupling of semiconductor metal oxides having different bandgap values with TiO₂ for the efficient use in the visible light region. In this work, magnetite (Fe₃O₄) nanoparticles were synthesized by a modified co-precipitation method, and it was used to prepare a TiO₂/Fe₃O₄ nanocomposite with three different ratios (0.2/0.8, 0.5/0.5, and 0.8/0.2). The obtained nanocomposite was characterized using X-ray diffraction, Raman and ultraviolet–visible spectroscopies, and scanning electron microscopy fitted with scanning transmission electron microscopy to understand the various properties such as crystallinity, optical properties, and morphology of the nanocomposites. We noticed that the crystallite size of TiO₂ in the nanocomposite, as well as the bandgap energy of the nanocomposite, decreases with the increasing Fe₃O₄ content. The degradation of Orange G with Fe₃O₄, TiO_2, and nanocomposites with three different ratios was studied in a solar simulator under different exposure times. Our studies show that (TiO₂)_0.2(Fe₃O₄)_0.8 nanocomposite having small crystallite size and bandgap gives the best photocatalytic activity under visible light among other ratios.