Synthesis of rutile TiO2 nanowires by thermal oxidation of titanium in the presence of KOH and their ability to photoreduce Cr(VI) ions

Abstract Rutile TiO2 nanowires were fabricated by thermal oxidation of titanium foil in the presence of potassium hydroxide, KOH. The fabrication process consisted of two parts; first as to deposit and liquefy KOH into droplets, done at 400 °C for 10 min, followed by ramping the furnace to a desired oxidation temperature (500–800 °C) for oxide growth. The presence of KOH was found to be beneficial in the formation of “shells” that induced anisotropic TiO2 growth (hence nanowires were observed under scanning electron microscope) as oppose to compact, planar oxide. Nevertheless, there exist a temperature window in which the anisotropic growth can be achieved: 550–750 °C. Above or below this temperature range, the oxide is compact without any noticeable nanostructures. Within the temperature window, the nanowires grown were dense with length of 500–600 nm and diameter averaged at 50 nm. The TiO2 nanowires were then used as catalyst to reduce Cr(VI) to Cr(III) in aqueous solution at pH 2.10 mg/L of Cr(VI) was able to be reduced completely within 90 min under ultra violet (UV) irradiation on TiO2 nanowires fabricated at 750 °C.