Hydrothermal synthesis, structure and photocatalytic activity of PF-co-doped TiO 2 László Kőrösi a,n , Mirko Prato b , Alice Scarpellini b , Andreas Riedinger b,c , János Kovács d,e , Monika Kus f , Vera Meynen f , Szilvia Papp a a Department of Biotechnology, Nanophage Therapy Center, Enviroinvest Corporation, Kertváros u. 2, H-7632 Pécs, Hungary b Department of Nanochemistry, Istituto Italiano di Tecnologia, via Morego 30,16163 Genova, Italy c Optical Materials Engineering Laboratory, ETH Zurich, 8092 Zurich, Switzerland d Department of Geology & Meteorology, University of Pécs, Ifjúság u. 6, H-7624 Pécs, Hungary e Environmental Analytical & Geoanalytical Research Group, Szentágothai Research Centre, University of Pécs, Ifjúság u. 20, H-7624 Pécs, Hungary f Laboratory of Adsorption and Catalysis, Department of Chemistry, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium article info Keywords: Nanostructures Crystal growth Electron microscopy X-ray photoelectron spectroscopy Photocatalysis abstract A series of PF-co-doped titanium dioxide (PF-TiO 2 ) samples with various PF contents were synthesized hydrothermally at 250 1C and systematically investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. For the PF-co- doping of TiO 2 , hexafluorophosphoric acid (HPF 6 ) was used. Increasing HPF 6 concentration did not decrease the crystallinity of the synthesized samples, but the dopant concentra- tion strongly influenced the size and morphology of the PF-TiO 2 nanoparticles. The undoped TiO 2 consisted of polymorphic and polydisperse nanoparticles, whereas smaller, predominantly spherical particles were observed for the PF-TiO 2 samples. Diffuse reflectance UV–vis spectroscopy revealed that PF-TiO 2 exhibited a slightly higher band gap energy than that of undoped TiO 2 . Despite this blue-shift in absorption edge, the photocatalytic activity of PF-TiO 2 was higher than that of undoped TiO 2 even under visible light irradiation. The effects of the dopant concentration on the structure and photo- catalytic activity are discussed in detail. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction The relevant literature data from the past decade indi- cate that TiO 2 (or its derivatives) is still one of the most promising metal oxide photocatalysts. This is mainly due to the fact that TiO 2 has a higher photocatalytic activity than those of other metal oxides. In addition, it is nontoxic and photostable. As a result of its wide band gap (  3.2 eV for anatase), its superior photocatalytic activity can be observed only when TiO 2 is excited by UV light. Since its applications are limited to UV light, this disadvantageous feature has stimulated intensive research aimed at the development of visible light-driven photocatalysts (sec- ond-generation photocatalysts). The band gap narrowing of TiO 2 can be achieved by its doping with metal or nonmetal elements [1,2]. In most cases, doping with transition metals results in a band gap narrowing, but simultaneously it can also give rise to a decrease in photocatalytic activity [3]. For example, Nagaveni et al. [4] reported that the doping of TiO 2 with metal ions (W, V, Ce, Zr, Fe and Cu) reduced the degradation of 4-nitrophenol under both UV and visible light irradiations, indicating that metal doping can induce the formation of recombination centers on TiO 2 . Other results have shown that the photo- activity of metal ion-doped TiO 2 depends on numerous Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing http://dx.doi.org/10.1016/j.mssp.2014.10.033 1369-8001/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author at: Department of Biotechnology, Nanophage Therapy Center, Enviroinvest Corporation, Kertváros u. 2, H-7632, Pécs, Hungary. Tel.: þ36 72 526894; fax: þ36 72 551041. E-mail address: ltkorosi@gmail.com (L. Kőrösi). Materials Science in Semiconductor Processing 30 (2015) 442–450