TiO 2 Modified by e-Beam Irradiation Bull. Korean Chem. Soc. 2013, Vol. 34, No. 5 1397 http://dx.doi.org/10.5012/bkcs.2013.34.5.1397 Enhanced Photocatalytic Activity of TiO 2 Modified by e-Beam Irradiation Moon Su Kim, Won Jun Jo, Dowon Lee, Sung-Hyeon Baeck, * Joong Hyeock Shin, † and Byung Cheol Lee † Department of Chemical Engineering, Inha University, Incheon 402-751, Korea. * E-mail: shbaeck@inha.ac.kr † Korea Atomic Energy Research Institute, Daejeon 305-353, Korea Received August 21, 2012, Accepted February 8, 2013 The influence of electron beam irradiation on photocatalytic activity of TiO2 thin films was investigated. TiO2 thin films were prepared by anodization of Ti foil, and they were then subjected to an 1 MeV electron beam. Changes in physical properties and photocatalytic activity of TiO2 before and after e-beam irradiation were investigated. The crystallinity of the synthesized materials was investigated by X-ray diffraction, and the oxidation states of both titanium and oxygen were determined by X-ray photoelectron spectroscopy (XPS). The density of donor (Nd) and flat band potential (Efb) were investigated by Mott-Schottky analysis, and photo- current was measured under a 1kW Xenon lamp illumination. After e-beam irradiation, significant change of Ti oxidation state was observed. Ti 3+ /Ti 4+ ratio increased mainly due to the surface reduction by electron, and photocurrent was observed to increase with e-beam irradiation. Key Words : Photoelectrochemical cell, e-beam, TiO 2 , Hydrogen, Anodizing Introduction Photocatalytic reactions are considered as one of the most promising routes for solar energy conversion. 1 Among the photocatalytic materials, TiO 2 has been known as the most effective photocatalyst, and has been widely applied in the decomposition of VOC’s and energy conversion. 2,3 How- ever, poor photon absorption of TiO 2 (due to a wide band gap of 3.2 eV) limits its applications in solar energy con- version. 4 To improve photocatalytic activity of TiO 2 , several modification approaches have been proposed, including doping metal on the surface of TiO 2 , synthesis of nano- structured TiO 2 , and synthesis of mixed metal oxides. It has been well known that surface composition and structure of TiO 2 greatly influence on photocatalytic activities. 5-8 In recent years, impurity doping has been widely performed by chemical and physical methods in order to enhance photo- catalytic activity under visible light irradiation. It has been also reported that ion implantation of transition metals such as V, Cr, Co, Mn, Fe and Ni, makes the absorption edge shift to the visible region, resulting in enhanced photocatalytic activity of TiO 2 in the visible region. 9 Synthesis of mixed metal oxides has been tried to change the band structure and increase surface area. 10,11 Electron beam (e-beam) irradiation was known as an effective method to improve the stability and performance of electrodes by varying the chemical and physical properties of materials. It has been reported that surface morphology, oxidation state, optical properties, and electrochemical pro- perties can be modified by e-beam irradiation. 12,13 In this study, the influence of e-beam irradiation on the photocatalytic properties of TiO 2 was investigated. An anodizing method was employed to fabricate TiO 2 thin films, because it is very simple and the reproducibility is very good. e-Beam was then irradiated on the surface of anodized TiO 2 thin films. The photocatalytic properties of e- beam irradiated TiO 2 thin films were investigated by photo- current measurement in a photoelectrochemical cell, and changes of physical and chemical properties before and after e-beam irradiation were also examined. Experimental Preparation TiO 2 /Ti Electrodes. Titanium foils (Aldrich, 15 × 15 × 0.127 mm, 99.7%) were cleaned in CHCl 3 , and then etched for 30s in a dilute Kroll’s acid (4% w/w HF, 30%w/w HCl). After etching Ti foil, it was rinsed in distilled water and acetone. The titanium foils were then subjected to anodic oxidation with constant current (125 mA/cm 2 , Find Power DC power supply H-220D) in 1 M H 2 SO 4 using Pt plate as a counter electrode. 14 The TiO 2 /Ti foil samples were irradiated by an e-beam of the constant energy of 1 MeV (ELV4 type electron accele- rator). The e-beam irradiation was carried out with various doses (0.5 to 2 MGy) under ambient atmosphere at room temperature. Characterization of e-beam Treated TiO 2 . Crystallinity of synthesized samples was examined by X-Ray diffraction analysis (XRD, Rigaku MAX 2200V). The surface characteri- zation was studied by Atomic force microscopy (AFM, NS4A) and X-ray photoelectron spectroscopy (XPS, Thermo K-Alpha). All the photoelectrochemical measurements were carried out in a 0.1 M NaOH solution at room temperature in a conventional three-electrode cell. In a photoelectrochemical cell, 1 cm 2 of anodized TiO 2 , sealed with Teflon was ex- posed to electrolyte. A platinum plate and Ag/AgCl were used as a counter electrode and reference electrode, respec- tively. In order to investigate the density of donor (N d ) and flat band potential (E fb ), Mott-Schottky analysis was carried out