Photocatalytic reforming of formic acid with simultaneous hydrogen production under visible light over CdS sensitized Na
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Photocatalytic reforming of formic acid with simultaneous hydrogen production under visible light over CdS sensitized Na2Ti2O4(OH)2 Wendong Tang, Dengwei Jing and Liejin Guo1 1 State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, 710049, P. R. China ABSTRACT The present work reports the renewable hydrogen production by an anaerobic photocatalytic reforming of formic acid over CdS sensitized Na2Ti2O4(OH)2 nanotubes. the Na2Ti2O4(OH)2 nanotube was prepared and charactered by X-ray diffraction, UV-visible absorption, transmission electron microscopy, etc. The activity of the catalyst in formic acid was investigated. The greatest photocatalytic reforming activity of formic acid occurs as the formic acid initial concentration is 20 v.%. A probable mechanism for the photocatalytic reforming process was proposed and discussed. INTRODUCTION The depletion of fossil fuel reserves and the pollution caused by increasing energy demands make hydrogen an attractive alternative energy source. Splitting water using sunlight with photocatalysts is a promising approach to produce hydrogen [1-3]. Numerous oxide [4-6] and sulfide [7-9] semiconductors have been developed since Fujishima and Honda had reported the photoelectrocatalytic production of hydrogen from water on the TiO2 semiconductor electrode [10]. However, the energy conversion efficiency from solar to hydrogen by photocatalytic water-decomposition is still low, mainly due to the rapid recombination of photogenerated electron/hole pairs [11]. During the process of photocatalytic reaction, electron donors as sacrificial agents were used to react irreversibly with the photogenerated holes, which prevented the recombination of electron/hole resulting in higher efficiency [12, 13]. A large variety of organic compounds have been used as electron donors for photocatalytic hydrogen production, including alcohols [14, 15] and polyalcohols [16, 17], sugars [18, 19] and organic acids [20], as well as aliphatic and aromatic compounds [21]. These compounds are satisfactory hole scavengers and undergo a relatively rapid and irreversible oxidation. This not only reduces the cost of the photocatalytic hydrogen production, but also degrades the organic pollutants effectively, achieving the dual goals of hydrogen production and pollution control. Pt/TiO2 is the most reported photocatalyst to produce hydrogen in organic sacrificial system [12, 14, 17, 20, 22-25]. The major disadvantage of this photocatalyst is its inability to utilize visible light and the high cost of the doped noble metals. In this paper, narrow gap semiconductor CdS was used to sensitize the wide gap semiconductor Na2Ti2O4(OH)2 nanotube, in order to make it responsible to visible light. Na2Ti2O4(OH)2 nanotube, existing in TiOx state[26], is easier to separate and transport the electron because of its one-dimensional nanostructure. And Na2Ti2O4(OH)2 nanotube also has a strong physical and chemical adsorption capacity of the organic molecules, due to its large surface area a
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