Enhanced photocatalytic properties of TiO2 nanotube arrays with Cr2O3 nanoparticles under visible light

In this work we report the photocatalytic properties of TiO2 nanotubes (NTs) with Cr2O3 nanoparticles (NPs) to improve the visible light activity of the composite. The TiO2 NTs with ∼100 nm diameters and ∼8 µm lengths were fabricated by means of anodization technique with an organic formamide-based electrolyte at an applied voltage of ∼35 V. The Cr2O3 NPs of 5 ∼ 10 nm in diameter were formed on the outer walls of the NTs by dipping the NTs into a liquid solution including Cr-oxide precursors. The NT arrays with NPs showed visible-light absorption properties that were superior to those of NTs without NPs. That Cr impurities within the TiO2 NTs originating from the NPs formed on the surfaces of the TiO2 NT arrays are believed to provide donor levels of Cr3+ ions located deep in the forbidden band gap of the TiO2 NTs and superior absorption properties under visible light up to ∼600 nm. The impurity levels also act as fast recombination sites for electrons and holes formed by photon excitation.