JOURNAL OF ENVIRONMENTAL SCIENCES ISSN 1001-0742 CN 11-2629/X www.jesc.ac.cn Available online at www.sciencedirect.com Journal of Environmental Sciences 2012, 24(6) 1125–1132 Photocatalytic degradation of paraquat using nano-sized Cu-TiO 2 /SBA-15 under UV and visible light Maurice G. Sorolla II 1 , Maria Lourdes Dalida 1 , Pongtanawat Khemthong 2 , Nurak Grisdanurak 3, ∗ 1. Department of Chemical Engineering, College of Engineering, University of the Philippines, Diliman 1101, Quezon City, Philippines. E-mail: mauricesorolla@yahoo.com 2. National Nanotechnology Center, National Science and Technology Development Agency, Klong Luang, Pathumthani 12120, Thailand 3. Department of Chemical Engineering, NCE for Environmental and Hazardous Waste Management, Faculty of Engineering, Thammasat University, Pathumthani 12120, Thailand Received 01 July 2011; revised 12 November 2011; accepted 29 November 2011 Abstract Photocatalytic degradation of paraquat using mesoporous-assembled Cu-TiO 2 /SBA15 under UV and visible light was investigated. The catalyst was synthesized by impregnation of Cu-TiO 2 colloids onto SBA-15. The colloids of Cu-TiO 2 were prepared via sol- gel method while the mesoporous support was prepared using hydrothermal technique. The catalyst was characterized using X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV diffuse reflectance spectroscopy, Zeta potential and X-ray adsorption spectroscopy. Results from characterizations showed that Cu doped TiO 2 had a small crystalline size and was well- dispersed on SBA-15. The inclusion of SBA-15 significantly enhanced the photocatalytic activity of the catalyst. Among the three types of undoped catalyst in this study (P25, TiO 2 , TiO 2 /SBA-15), TiO 2 /SBA-15 yielded the highest degradation of paraquat for all pH under UV illumination. Meanwhile 2 wt.% Cu-TiO 2 /SBA-15 yielded the highest activity under visible light. Key words: paraquat; photocatalysis; titania; SBA-15; copper-doped DOI: 10.1016/S1001-0742(11)60874-7 Introduction Herbicides, such as paraquat, are one of the sources of chemical pollutants released into the water stream, soil as well as groundwater. Paraquat [1,1 ′ -dimethyl-4,4 ′ - bipyridinium dichloride] is known to display some harmful effects on humans such as damage to the digestive system, kidneys and lungs (M´ egarbane, 2003). Although it is prohibited by European Union (Court of first instance in Case T-229/04 Sweden 2007), paraquat is still used in developing countries in Southeast Asia such as Philippines and Thailand. Because of its known toxicity, degradation and removal of paraquat in wastewater have been a matter of paramount importance. Photocatalytic degradation of paraquat using titania (TiO 2 ) under UV light has been studied extensively (Lee et al., 2002; Moctezuma et al., 1999; Florˆ encio et al., 2004; Tennakone and Kottegod, 1996). However, there is no study yet about paraquat degradation using surface- modified TiO 2 to markedly enhance its surface area. Commercial ultra fine powders of TiO 2 , such as P25, show a low adsorption capacity due to their low surface area. To overcome this drawback, incorporation of mesoporous support such as SBA-15 was implemented in this research. * Corresponding author. E-mail: gnurak@engr.tu.ac.th In addition, photocatalytic degradation of paraquat has not yet been investigated under visible light. For this study, copper was used as the metal dopant to shift the photo- catalytic activity towards the visible range. Furthermore, persulfate was also used to enhance the photocatalytic activity of the catalyst under the visible region. This research aims to degrade paraquat under UV and visible light using Cu-TiO 2 /SBA-15 photocatalyst. The catalyst was synthesized by subsequent addition of Cu- TiO 2 colloids onto SBA-15. The colloids of Cu-TiO 2 were prepared via sol-gel method while the mesoporous support was prepared using hydrothermal technique. Char- acterization was done using X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, UV diffuse reflectance spectroscopy, Zeta potential and X- ray adsorption spectroscopy. Finally, the influence of initial solution pH and dopant loading were investigated. 1 Materials and methods 1.1 Synthesis SBA-15 was synthesized hydrothermally according to Meynen (2009) using triblock copolymer P123 (EO 20 PO 70 EO 20 , Sigma-Aldrich, USA) as structure directing agent and tetraethyl orthosilicate (TEOS, 98%,