Applied Catalysis A: General 443–444 (2012) 96–102 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General jo u r n al hom epage: www.elsevier.com/locate/apcata Enhanced photocatalytic activity of multi-doped TiO 2 for the degradation of methyl orange A. Charanpahari a , S.S. Umare a,∗∗ , S.P. Gokhale b , V. Sudarsan c , B. Sreedhar d , R. Sasikala c,∗ a Chemistry Department, Visvesvaraya National Institute of Technology, Nagpur 440010, India b Physical and Material Chemistry Division, National Chemical Laboratory, Pune 411008, India c Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India d Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500607, India a r t i c l e i n f o Article history: Received 16 May 2012 Received in revised form 11 July 2012 Accepted 23 July 2012 Available online 3 August 2012 Keywords: Gd N S doped TiO2 Photocatalyst Photodegradation Methyl orange Fluorescence lifetime a b s t r a c t We report the synergistic effect of dopants like Gd, N and S in enhancing the photocatalytic activity of TiO 2 . Nanosized TiO 2 doped at both cationic and anionic sites by Gd, N and S exhibited increased photocatalytic activity compared to TiO 2 doped with either Gd or N and S. All the doped TiO 2 existed as anatase phase and no separate phase due to Gd 2 O 3 was seen up to a Gd concentration of 2%. The particle size as seen from the transmission electron micrograph was ∼25 nm. The optical absorption property of TiO 2 was improved by doping and redshift of the absorption edge is seen for all doped samples compared to pristine TiO 2 . The red shift of the absorption edge was the highest for the multiple ion-doped sample. Presence of bonded N and S in TiO 2 was detected by X-ray photoelectron spectroscopy. Fluorescence lifetime studies indicated an enhanced lifetime for the charge carriers in the doped system compared to pristine TiO 2 . Photocatalytic activity study showed that the multi-doped sample has the highest activity for the degradation of methyl orange compared to Gd-TiO 2 , NS-TiO 2 and pristine TiO 2 . The enhanced photocatalytic activity of the multi-doped TiO 2 is attributed to factors such as improved optical absorption property and improved lifetime of the charge carriers. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Photocatalytic degradation of organic pollutants using solar radiation is a potential method to control the environmental pollu- tion as solar energy is renewable. For harnessing the solar radiation effectively, suitable semiconductors are to be developed, which is a major task. As solar radiation contains around 40% visible light, semiconductors with a bandgap less than 3 eV are to be developed to make the process efficient. Most of the present photocatalysts work efficiently with UV radiation, which is ∼3% of the solar radi- ation. TiO 2 is a widely studied photocatalyst which requires UV radiation for its excitation as its band gap is 3.2 eV. Several modifi- cations of TiO 2 have been attempted like doping with cations like Fe, Sn, Ce, etc. [1–3] or doping with anions like N, S, etc. [4–6] or co-doping of both cations and anions [7–9]. In most of the cases, an improved optical absorption and enhanced photocatalytic activity has been reported. ∗ Corresponding author. Tel.: +91 22 25590289; fax: +91 22 25505151. ∗∗ Corresponding author. Tel.: +91 712 2801316; fax: +91 712 2223230. E-mail addresses: ssumare@chm.vnit.ac.in (S.S. Umare), sasikala@barc.gov.in (R. Sasikala). TiO 2 doped with lanthanide ions have been reported as effi- cient systems for photodegradation of organic compounds present in water. The advantage of using these ions is that they have the ability to form complexes with Lewis bases like amines, aldehydes, alcohols and thiols due to the interaction of the f orbitals of the lan- thanides with the functional groups of the organic compounds [10]. This can lead to the increased adsorption of the organic pollutants on the surface of the photocatalyst resulting in enhanced photocat- alytic activity. It has been reported that TiO 2 doped with La 3+ , Ce 3+ , Er 3+ , Pr 3+ , Gd 3+ , Nd 3+ or Sm 3+ exhibited enhanced photodegrada- tion of nitrite ions [11]. The increase in photocatalytic activity is due to the increased optical absorption property, higher adsorption of reactants and increase in the rate of interfacial transfer of electrons. TiO 2 doped at both cationic and anionic sites form another class of catalysts, which are reported to have higher photocatalytic activ- ity than that of TiO 2 doped with single ions. Nitrogen and Gd doped TiO 2 showed improved photocatalytic activity compared to pristine TiO 2 , Gd or N doped TiO 2 [12]. The high activity was attributed to high adsorption activity, high crystallinity, red shift in absorption edge and strong absorption in the visible light region of N and Gd co-doped titania sample. When Fe 3+ and N were co-doped in TiO 2 , enhanced decolorization of the dye wastewater was observed com- pared to pure TiO 2 and the enhanced activity was correlated with the improved optical absorption property of the co-doped sample 0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2012.07.032