Applied Catalysis B: Environmental 162 (2015) 310–318 Contents lists available at ScienceDirect Applied Catalysis B: Environmental j ourna l h omepa ge: www.elsevier.com/locate/apcatb Nitrogen-doped, metal-modified rutile titanium dioxide as photocatalysts for water remediation D. Dolat a,∗ , S. Mozia a , R.J. Wróbel a , D. Moszy ´ nski a , B. Ohtani b , N. Guskos c , A.W. Morawski a a Institute of Chemical and Environment Engineering, West Pomeranian University of Technology, Szczecin, ul. Pułaskiego 10, 70-310 Szczecin, Poland b Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan c Institute of Physics, West Pomeranian University of Technology, Szczecin, Al. Piastów 48, 70-311 Szczecin, Poland a r t i c l e i n f o Article history: Received 11 February 2014 Received in revised form 26 June 2014 Accepted 1 July 2014 Available online 8 July 2014 Keywords: Photocatalysis Rutile-TiO2 co-modification a b s t r a c t A comparison study of metal (Fe, Co, or Ni) – modification, nitrogen – doping of rutile titanium dioxide via impregnation followed by calcination method is presented. The aim of this study was to obtain a highly photoactive rutile titanium dioxide and to establish the origin of its photoactivity with reference to the influence of the physicochemical properties of the modified materials and the type of the applied metal. Moreover, the properties of the co-modified photocatalysts were compared to those of the single (metal or nitrogen) modified materials. For this purpose highly advanced analytical methods such as SEM with EDS, XPS, EPR–AFMR, XRD, ICP–OES, UV–vis/DR, N 2 adsorption/desorption at 77 K and elemental analysis were employed. We have proved that a proper modification of rutile may lead to obtaining highly visible and/or UV light active materials. It has been revealed that the metal applied for rutile titanium dioxide modification plays a crucial role in its photocatalytic performance. In case of visible light the Fe > Ni > Co order and in case of UV light activity the Ni > Fe > Co order, for both single-modified and co-modified materials, is followed. Moreover, it was proven that the co-modified samples exhibited significantly higher activity than the single-modified rutile. An effort has been made in order to shed light on this new, unexplored area of titanium dioxide modification and application. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide is undoubtedly the most studied semiconduc- tor for photocatalytic water and air remediation due to its high stability, fine optical properties and availability [1,2]. Nevertheless, despite many advantages of this material, its commercial appli- cation is still limited. The main obstacles to be overcome before titanium dioxide can be successfully used for solar light applica- tions are: (1) Wide band gap of 3.2 eV and 3.0 eV for anatase and rutile TiO 2 , respectively, which implies application of, additionally to solar, UV light irradiation source [3,4]; (2) Rapid electron–hole pairs recombination [5,6] resulting in low electron concentration in conduction band of TiO 2 , which diminishes the photocatalytic efficiency of the semiconductor [7]. In order to overcome these difficulties the researchers employed numerous modification methods among which the non-metal doping [8,9] as well as transition metal-doping [10] seem to be the ∗ Corresponding author. Tel.: +0048914494277; fax: +0048914494686. E-mail addresses: ddolat@zut.edu.pl, dianadolat@wp.pl (D. Dolat). most promising for TiO 2 band-gap narrowing, whereas titanium dioxide modification with metals [11], graphene [12,13] or semi- conductors coupling [14,15] are mainly used in order to inhibit electron/hole pairs recombination rate. Among non-metals, it is nitrogen, which attracts the most attention. Starting from the paper by Asahi et al. [16], every year numerous publications considering this subject are published [17]. The significantly higher interest in nitrogen in regard to other non-metals arises from the fact that nitrogen can be relatively easily incorporated in TiO 2 structure [18]. Moreover, the position of newly formed, after nitrogen-doping, energy state above the valence band of TiO 2 possesses sufficiently high oxidation potential for water contaminants photodegradation [19] which is not always the case for carbon, sulfur or fluorine- doped TiO 2 [17]. Theoretical studies discuss different influence of titanium dioxide N-doping on anatase and rutile form of TiO 2 [20]. Di Valentin et al. [21] claim that whereas the position of the valence band of N-doped anatase increases by 0.14 eV or 0.73 eV for sub- stitutional and interstitial doping, respectively, the valence band position of N-doped rutile decreases by 0.03 eV and the position of the rutile conduction band increases by 0.05 eV, resulting in higher band gap energy than for pure rutile (3.08 eV for N-doped vs. 3.0 eV http://dx.doi.org/10.1016/j.apcatb.2014.07.001 0926-3373/© 2014 Elsevier B.V. All rights reserved.