Characterization and activity of visible-light driven TiO 2 photocatalyst doped with tungsten T. Putta, M. C. Lu and J. Anotai ABSTRACT T. Putta National Center of Excellence for Environmental and Hazardous Waste Management, Chulalongkorn University, Bangkok 10130, Thailand E-mail: Thapanun_tam@hotmail.com M. C. Lu Department of Environmental Resources Management, Chia-Nan University of Pharmacy and Science, Tainan 717, Taiwan E-mail: mmclu@mail.chna.edu.tw J. Anotai (corresponding author) National Center of Excellence for Environmental and Hazardous Waste Management, Department of Environmental Engineering, Faculty of Engineering, King Mongkut’s University of technology Thonburi, Bangkok 10140, Thailand E-mail: jin.ano@kmutt.ac.th This research aimed to expand the activity of TiO 2 down to the visible light region by modifying the sol-gel conditions and doping with tungsten. The optimum conditions for calcination temperature, acid type, and heating rate were 2008C, HNO 3 , and 18C/min, respectively. The undoped TiO 2 synthesized under these conditions could significantly absorb the visible light whereas the commercial Degussa P-25 could not. The absorptivity decreased sequentially as the wavelength increased from 400 to 700 nm. Within 6 h of 2-W blue-light illumination, 23% of 0.1 mM 2-chlorophenol was removed. The XRD result showed that the crystalline was anatase phase. The visible-light absorption property of the TiO 2 became even better when doped with tungsten. At the optimum W to TiO 2 ratio of 0.5%, the degradation of 0.1 mM 2-chlorophenol increased to 53% indicating a higher photocatalytic activity. Both crystalline and amorphous TiO 2 could exhibit the photocatalytic activity under the visible light region. Key words | 2-chlorophenol, photocatalysis, titanium dioxide, visible light INTRODUCTION Semiconductor photocatalysis was proven to be a high efficient process for environmental remediation, air- purification, deodorizing, sterilization, self-cleaning and water treatment (Hoffmann et al. 1995; Chang et al. 2005). TiO 2 is the most preferable photocatalyst because of its physical and chemical stability and non-toxicity. However, it is facing with two major limitations in real practice. Firstly, TiO 2 requires UV of the wavelength shorter than 380 nm, whose energy exceeds the band gap of 3.2 eV of the anatase crystalline phase. Hence, it can utilize a very small fraction of sunlight, only 3% of total solar energy (Yang et al. 2006; Murakami et al. 2008; Stengl et al. 2008; Wang et al. 2009). Secondly, ordinary TiO 2 has a high recombination rate of electron-hole pairs because it has wide band gap energy leading to a low charge transfer rate on semicon- ductor surface. Several techniques have been found to improve the visible light absorptivity of the TiO 2 including doping with non-metals (such as S, N, P) (Huang et al. 2006; Sun et al. 2008; Xu et al. 2008), doping with transition metals (such as W, V) (Wu et al. 2005), doping with noble metals (such as Au, Ag, Pt) (Zhang et al. 2006; Chen et al. 2007; Higashimoto et al. 2008), and coupling TiO 2 with other semiconductors (Kumar & Jain 2001). In this paper, the sol-gel method was used to synthesize the W-doped TiO 2 (W/TiO 2 ) and its photocatalytic activity in aqueous phase under visible-light irradiation was determined using 2-chlorophenol (2-CP) as the target compound. 2-CP is an important biorefractory and toxic chemical commonly present in water and wastewater due to its wide applications as a biocide, lubricant, and solvent. It is also produced as an intermediate in the manufacture of pesticides, dyestuffs and preservatives or generated during the chlorination of effluents containing phenolic compounds. 2-CP can adver- sely impact the ecosystem, either directly or indirectly, and is a suspected carcinogenic agent. As a result, 2-CP has been listed as the priority pollutant by the US Environmental doi: 10.2166/wst.2010.410 2128 Q IWA Publishing 2010 Water Science & Technology—WST | 62.9 | 2010 Downloaded from https://iwaponline.com/wst/article-pdf/62/9/2128/446925/2128.pdf by guest on 07 July 2020