Pt-CdS/TiO 2 nanotube catalyst for photocatalytic reduction of CO 2 with water under visible light irradiation
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Pt-CdS/TiO 2 nanotube catalyst for photocatalytic reduction of CO 2 with water under visible light irradiation Jian Yuan, Chuanzhao Zhang, Caolong Li, Mingxia Chen, Wenfeng Shangguan Research Center for Combustion and Environmental Technology, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. ABSTRACT Titanate nanotube (TNT) was prepared by alkaline hydrothermal method starting from TiO 2 (P25), and then CdS-TNT was prepared for visible light harvesting by immersing TNT in Cd(CH 3 COO) 2 and then (NH 2 ) 2 CS aqueous solutions subsequently and heat treated at special temperature. After loading with Pt, photocatalytic reduction of gas phase CO 2 with water vapor was carried out under UV-VIS and visible light irradiation. The results showed that the main reaction products were CH 4 , C 2 H 4 , C 2 H 6 and H 2 , which were online characterized by gas chromatography when the flow rate of 5000 ppm CO 2 is 0.35 ml/min. The hydrogenation process also realized under visible light illumination for Pt-CdS/TNT and producted 0.44 μmol/min CH 4 . The maximum yield of methane reached about 130 μmol/min when Pt-CdS/TNT was irradiated with UV-Vis light. The time profile for production yield increased steadily with time up to about 6-7 h, then a decrease of the reaction rate occurred. It is suggested that the adsorption of intermediate products CO, O 2 etc. on Pt and the oxidation of Pt might be the reasons for the photocatalytic reaction deterioration. INTRODUCTION The greenhouse effect has become a threat to the living environment of mankind. CO 2 is the primary greenhouse gas which is released mainly by the burning of fossil fuels and the expanded human activity. At the same time, CO 2 is also a nontoxic, cheap, and highly functional carbon source. The conversion of CO 2 at room temperature and atmospheric pressure using solar light is a highly challenging and promising approach to close the CO 2 cycle, and to develop photosynthesis mimetic processes [1-3]. As the most appropriate candidate for photocatalytic processes, TiO 2 is also the most commonly used catalyst for the investigation of photocatalytic hydrogenation of CO 2 [4]. Recently, one-dimensional nano-materials, including oxide nano-tubes, have attracted extensive attention due to their nano-tubular morphologies and high surface areas. Yu et al [5] presented the photocatalytic activity of titania nanotube supported Pt catalyst for the CO 2 hydrogenation toward methane production. Using nitrogen-doped titania nanotube arrays loaded with both Cu and Pt nanoparticles, Varghese and co-workers [6] obtained a hydrocarbon production rate of 111 ppmcm-2h-1 under outdoor global sunlight. Moreover, various simple semiconductors such as ZnO, SnO 2 , WO 3 , Fe 3 O 4 , CdS, and ZnS have been employed in assorted manners for this purpose. However, all the processes yielded only low carbon dioxide conversion rates, while the intrinsic idea of photocatalytic conversion of carbon dioxide and water (liquid/vapor) into hydrocarbon fuels is appealing. It is known that CdS has a
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