Sol–gel synthesis and photocatalytic activity of B and Zr co-doped TiO 2 Derya Kapusuz a,n , Jongee Park b , Abdullah Ozturk a a Department of Metallurgical and Materials Engineering, METU, 06800 Ankara, Turkey b Department of Metallurgical and Materials Engineering, Atilim University, 06836 Ankara, Turkey article info Article history: Received 10 August 2012 Received in revised form 22 February 2013 Accepted 26 February 2013 Available online 6 March 2013 Keywords: A. Oxides B. Sol-gel growth abstract Effects of boron (B) and/or zirconium (Zr) doping on photocatalytic activity of sol–gel derived titania (TiO 2 ) powders were investigated. A conventional, non-hydrous sol–gel technique was applied to synthesize the B, Zr doped/co-doped TiO 2 powders. Doping was made at molar ratios of Ti/B ¼1 and Ti/Zr ¼10. Sol–gel derived xero-gels were calcined at 500 1C for 3 h. The crystal chemistry and the morphology of the undoped and B, Zr doped/co-doped TiO 2 nanoparticles were investigated using X-ray diffractometer and scanning electron microscope. Nano-scale (9–46 nm) TiO 2 crystallites were obtained after calcination. Doping and co-doping decreased the crystallite size. Photocatalytic activity was measured through the degradation of methylene blue (MB) under 1 h UV-irradiation using a UV–vis spectrophotometer. Results revealed that B doping into anatase caused the formation of oxygen vacancies, whereas Zr addition caused Ti substitution. Both B and Zr ions had a profound effect on the particle morphology and photocatalytic activity of TiO 2 . The photocatalytic activity of B and Zr doped TiO 2 particles increased from 27% to 77% and 57%, respectively. The best activity (88.5%) was achieved by co-doping. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Recently, TiO 2 nanoparticles have attracted great interest for the degradation of organic and inorganic pollutants and toxics in environmental purification owing to their high efficiency, low cost, and long term stability upon commercial use [1,2]. Many investigations have been performed to improve the photocatalytic properties of TiO 2 since the discovery of photocatalyst TiO 2 by Fujishima and Honda in 1972 [2]. Anatase phase of TiO 2 exhibits better chemical and photon characteristics due to its good absorbability and lower electron–hole recombination rate than those of rutile [3]. However, its large band gap (3–3.2 eV) limits the light interaction only to ultraviolet (UV) light. This accounts for only 5% of solar energy [4–6]. Thus, many studies have been performed to extend the spectral response of anatase to visible light and to enhance its photocatalytic activity. Doping and co- doping with metals and non-metals have been shown to be among the most effective strategies to improve the photocatalytic performance of TiO 2 [7–12]. Asahi et al. [5] studied the effect of N doping into TiO 2 and achieved longer wavelength photo- absorption than 400 nm. In this respect, B–N co-doping has been found to be one of the most efficient ways of increasing photo- catalytic activity in visible region [13]. B doping is of interest because it shifts the light absorption to visible range [7]. On the other hand, the doping of metal atoms possibly causes the formation of new phases dispersed into TiO 2 , temporarily trapping the photogenerated charge carriers and inhibiting the recombination of photoinduced electron–hole pairs when the electron–hole pairs migrate from the inside of the photocatalyst to the surface [14]. Since each method has different advantages, novel attempts include the investigation of optimum compositions of co-doping into TiO 2 to earn from their synergetic effects. Unfortunately, especially for B doped TiO 2 , conflicting results have been reported on structural evolution of TiO 2 in literature. Geng et al. [15] stated that B atoms can be added into TiO 2 lattice either as interstitial atoms or at the O sites. This substitution at O sites causes a decrease in the band gap. Conversely, Chen et al. [16] stated that B atoms were interstitially present in the lattice forming a Ti–B–O structure. Non-metal doping like B tends to increase the photocatalytic activity to visible region. However, the behavior of B atoms in TiO 2 lattice is still vague. In addition, metal dopings such as Ga 3 þ , Cr 3 þ , Sb 5 þ , and V 5 þ were reported to reduce the photo- catalytic activity since both trivalent and pentavalent ions act as recombination centers for photogenerated charge carriers [17]. However, Zr doping may enhance the photocatalytic efficiency as compared to undoped TiO 2 . TiO 2 and ZrO 2 both belong to the same group, 4A elements, and both oxides are n-type semicon- ductors [18]. It is envisaged that Zr doping causes O defects and/ or Ti 4 þ to Zr 4 þ exchange and hence enhances the photoactivity. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jpcs Journal of Physics and Chemistry of Solids 0022-3697/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jpcs.2013.02.022 n Corresponding author. Tel.: þ90 312 210 59 23; fax: þ90 312 210 25 18. E-mail addresses: dkapusuz@metu.edu.tr, dkapusuz@live.com (D. Kapusuz). Journal of Physics and Chemistry of Solids 74 (2013) 1026–1031