Highly efficient visible-driven reduction of Cr(VI) by a novel black TiO₂ photocatalyst

Finding a facile and practical method to produce black TiO₂ remains a challenge. Bismuth-vanadium co-doped black TiO₂ (BVBT) was synthesized as a visible light driven photocatalyst by a simple one-pot hydrothermal method. The synthesized BVBT was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-Vis DRS). The light absorption of the synthesized Bi-V co-coped black TiO₂ nanoparticles was significantly improved in the visible and infrared regions. The XRD patterns indicated that the black TiO₂ contained mixed phases of brookite, anatase, and rutile of TiO₂. This was further confirmed by Raman spectroscopy. The photocatalytic activity of the sample was evaluated by reduction of hexavalent chromium (Cr(VI)) under visible light irradiation. Among investigated hole (h⁺) scavengers, ethylenediaminetetraacetic acid (EDTA) led to the highest reduction of Cr(VI) with a molar ratio of 1:5 (EDTA:Cr(VI)). The results indicated that the Bi-V co-coped black TiO₂ nanocomposite can reduce 94% of 1 mg/L of Cr(VI) within 20 min irradiation time (pH 3 and catalyst dose of 1 g/L). Introducing a simple method to synthesize black TiO₂ which has absorption in the visible and infrared region can open up new applications.