Journal of Catalysis 252 (2007) 296–302 www.elsevier.com/locate/jcat Highly visible-light active C- and V-doped TiO 2 for degradation of acetaldehyde Xiangxin Yang a , Chundi Cao a , Keith Hohn a , Larry Erickson a , Ronaldo Maghirang b , Dambar Hamal c , Kenneth Klabunde c,∗ a Department of Chemical Engineering, Kansas State University, Manhattan, KS 66506, USA b Department of Biological & Agricultural Engineering, Kansas State University, Manhattan, KS 66506, USA c Department of Chemistry, Kansas State University, Manhattan, KS 66506, USA Received 25 July 2007; revised 19 September 2007; accepted 20 September 2007 Available online 30 October 2007 Abstract C-doped and C- and V-doped TiO 2 photocatalysts were prepared by a sol–gel process. Both catalysts showed high activity for the degradation of acetaldehyde under visible irradiation (>420 nm). The co-doped TiO 2 catalysts also were highly active in the dark; 2.0% V-containing co-doped TiO 2 had the highest activity, comparable with the activity under visible light irradiation. The catalysts were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), and N 2 adsorption–desorption. The results suggest that vanadium ions were introduced both on the surface and into the bulk of TiO 2 . A free electron, induced by the formation of V 5+ in the sublayers of TiO 2 during calcination at 500 ◦ C in air, was delocalized and promoted into the conduction band by thermal energy and further transferred to O 2 , generating a superoxide radical anion (O · − 2 ) that is responsible for degradation of acetaldehyde in the dark. In addition to functioning as a photosensitizer that shifts the optical response of TiO 2 from the ultraviolet (UV) to the visible light region, the doped elemental carbon increased the surface area and improved the dispersion of vanadium.  2007 Elsevier Inc. All rights reserved. Keywords: Visible light; Carbon; Vanadium; TiO 2 ; Photocatalyst 1. Introduction Photocatalytic degradation and complete mineralization of toxic organic compounds in water, soil, and air in the presence of semiconductor powders have received much attention over the last two decades [1–4]. A semiconductor is characterized by a filled valence band and an empty conduction band. When it is irradiated with light of sufficient energy corresponding to or exceeding its band gap, an electron is promoted into the conduc- tion band, leaving a hole in the valence band. The electrons and holes are good reductants and powerful oxidants, respectively, and they can initiate redox reactions on the semiconductor sur- face [2]. TiO 2 is considered the most promising photocatalyst due to its high efficiency, chemical stability, nontoxicity, and * Corresponding author. Fax: +1 785 532 6666. E-mail address: kenjk@ksu.edu (K. Klabunde). relative cost. However, the use of TiO 2 is impaired by its wide band gap (3.2 eV), which requires ultraviolet irradiation for photocatalytic activation (λ< 387 nm) [5–7]. UV light ac- counts for only about 5% of solar energy; visible light, 45% [8]. The shift of the optical response of TiO 2 from UV to the visible spectral range will have a profound positive effect on the effi- cient use of solar energy in photocatalytic reactions [9]. Thus, much effort has been directed toward the development of visi- ble light-active photocatalysts. One approach to synthesizing visible light active photocat- alysts is the substitution of Ti by V, Cr, Mn, Ni, or Fe. Anpo et al. [7] modified TiO 2 catalysts by bombarding them with high-energy metal ions. The metal ion-implanted TiO 2 showed a large absorption shift toward the visible light region, and the V ion had the highest effectiveness in the red shift. Klosek and Raftery [10] synthesized V-doped, supported TiO 2 photocata- lysts that were quite active using visible light (396–450 nm). Wu and Chen [11] reported that V-doped TiO 2 acquired the 0021-9517/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2007.09.014