Catalysis Today 225 (2014) 80–89 Contents lists available at ScienceDirect Catalysis Today j our nal homep ag e: www.elsevier.com/locate/cattod Ti 3+ self-doped TiO 2-x anatase nanoparticles via oxidation of TiH 2 in H 2 O 2 Xin Liu a , Hui Xu a , Lauren R. Grabstanowicz b , Shanmin Gao a,b,∗ , Zaizhu Lou c , Wenjun Wang c , Baibiao huang c , Ying Dai c , Tao Xu b,∗∗ a College of Chemistry and Materials Science, Ludong University, Yantai 264025, Shandong, PR China b Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA c State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, PR China a r t i c l e i n f o Article history: Received 16 May 2013 Received in revised form 29 August 2013 Accepted 30 August 2013 Available online 22 October 2013 Keywords: Ti 3+ self-doped TiO2 Visible light photocatalytic TiH2 Interface ion diffusion-redox reaction a b s t r a c t Anatase phase Ti 3+ self-doped TiO 2-x nanoparticles (NPs) has been successfully synthesized by a simple interface ion diffusion-redox reaction using TiH 2 and H 2 O 2 as precursors. The structure, crystallinity, morphology and other properties of the samples were characterized by X-ray diffraction (XRD), trans- mission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The chemical states of Ti in the samples were confirmed by X-ray photoelectron spectra (XPS). Electron spin resonance (ESR) spectra confirm the presence of high concentration of Ti 3+ in the bulk and surface of the as-prepared substoichiometric TiO 2-x NPs. Composition of the samples was also analyzed by energy dispersive X-ray spectra (EDX) and the results indicate the exist of oxygen vacancies. UV–vis diffuse reflectance spectroscopy (UV–vis DRS) showed that Ti 3+ self-doped TiO 2-x NPs have a strong absorp- tion between 400 and 800 nm. The formation mechanism of the Ti 3+ self-doped TiO 2-x NPs was also discussed. Methylene blue (MB) solutions were used as model wastewater to evaluate the visible-light photocatalytic activity of the samples. Under visible light radiation, the samples exhibit excellent ability in the photocatalytic degradation of MB and splitting of water to produce H 2 . The most active Ti 3+ self- doped TiO 2-x NPs obtained at 500 ◦ C exhibits 68-fold enhancement for the visible light decomposition of MB in comparison to commercial P25 TiO 2 . The samples also show an excellent cyclic stability of the photocatalytic activity of degrading MB. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Among numerous photocatalytic materials, the excellent stabil- ity, nontoxicity and photoactivity of TiO 2 has attracted considerable attentions for its potential use in environmental purification and hydrogen generation [1,2]. However, the implementation of pris- tine TiO 2 for as photocatalysts is largely impeded due to its large band gap (∼3.2 eV) that only sensible to UV fraction of solar light and the rapid electron–hole recombine at the defect-induced traps inside the lattice before reaching the external surface reactive sites [3,4]. To enhance the photocatalytic efficiency, current efforts are focusing on narrowing the band gap to harvest the visible photons and increasing the charge separation efficiency [5,6]. ∗ Corresponding author at: College of Chemistry and Materials, Science Ludong University, Yantai 264025, PR China. Tel.: +86 535 6672176; fax: +86 535 6697667. ∗∗ Corresponding author at: Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA. Tel.: +1 815 753 6357; fax: +1 815 753 4802. E-mail addresses: gaosm@ustc.edu (S. Gao), txu@niu.edu (T. Xu). To extend the light response of TiO 2 to the visible region, many band gap engineering methods have been reported, including doping of metal ions and non-metals [7–9], noble metal deposition [10,11], composite semiconductors [12,13], and surface sensitiza- tion [14,15]. However, these approaches such as the metal ion or non-metal doping can act as the recombination centers of charge carrier, which is a critical factor for the photocatalytic activity [16]. Recent theoretical and experimental studies show rapidly increasing interests in nonstoichiometric titanium suboxides (TiO 2-x ) for environmental purification, water splitting, fuel cells, gas-adsorption and solar battery [17]. The presence of Ti 3+ in nonstoichiometric TiO 2-x improves the wet stability due to the water molecules can be easily incorporated at an oxygen vacancy- containing surface and electronic conductivity, which is important for photocatalysis activity [18,19]. The oxygen vacancy (O V ) state residing between the valence band and conduction band is sug- gested to induce visible light activity [20]. According to the electrode potential (TiO 2+ /Ti 3+ , ϕ  A = 0.1 V), the generated Ti 3+ is very easily oxidized to Ti 4+ in the air (O 2 /H 2 O, ϕ  A = 1.23 V). However, to date, the reported reductive methods to pro- duce TiO 2-x mainly rely on difficult reaction conditions including 0920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cattod.2013.08.025