Eosin Y-sensitized ZnO/TiO 2 for efficient visible light photocatalytic hydrogen evolution
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Eosin Y-sensitized ZnO/TiO2 for efficient visible light photocatalytic hydrogen evolution Haipei Liu, Dengwei Jing，Liejin Guo﹡ State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R. China ABSTRACT In this work a series of Eosin Y-ZnO(x%)/TiO2 were prepared. ZnO well dispersed on the surface of TiO2, which improves the adsorption of Eosin Y and the excited electron to transfer to the conduction band of TiO2. Therefore the visible light activity of 0.2%Pt-Eosin Y-ZnO(x%)/TiO2 is much higher than that of the 0.2%Pt-Eosin Y-TiO2 and 0.2%Pt-Eosin Y-ZnO. The 0.2%Pt-Eosin YZnO(1.5%)/TiO2 has the highest visible light activity among the catalysts coupled with various ZnO amount, whose activity is increased by a factor of 3.5 compared to that of 0.2%Pt-Eosin Y-TiO2. It is proposed that, 0.2%Pt-Eosin Y-ZnO(1.5%)/TiO2 has the optimal trapping sites of carriers and thickness of the space-charge layer on the TiO2 particle surface, so these factors result a more efficient charge separation, an increased lifetime of the charge carriers, and the enhanced of hydrogen production . INTRODUCTION Hydrogen is considered to be an ideal energy carrier for future [1]. However, renewable energy contributes only 5% of commercial hydrogen production via water electrolysis while 95% hydrogen is mainly derived from fossil fuel [2]. Alternatively, photocatalytic water splitting by solar energy has been considered as one of the most promising routes for renewable hydrogen production [3]. TiO2 has been widely used as a photocatalyst [4] due to its relatively high photocatalytic activity, biological and chemical stability, low cost, non-toxic and long time stability. However, TiO2 absorbs only a small portion of solar spectrum in the UV region with low quantum efficiency due to its wide band gap (ca. 3.2 eV). Hence, the development of photocatalyst that can effectively harvest the visible light in the sunlight is in dispensable for the photocatalytic hydrogen production. Dye sensitization proved to be one of the possible methods for dealing with this issue [5]. Some dyes have been proved to be efficient sensitizers for hydrogen evolution over Pt/TiO2, such as Eosin Y [6], merocyanine [7], Ru(bpy)32+ [8] and coumarin [9]. And the prevenient literatures have reported that coupled semiconductor photocatalystes was a novel approach to achieve a more efficient charge separation, an increased lifetime of the charge carriers, and an enhanced interfacial charge transfer to adsorbed substrates. At the same time, their physical and optical properties are greatly modified. Recently, coupled photocatalyst ZnO/TiO2 has also been studied extensively [10-11]. In the present study, we used ZnO/TiO2 as a matrix to prepare a high active dye-sensitizention (Esion Y) photocatalyst. The activity of EosinY-sensitized ZnO/TiO2 for hydrogen evolution increases notably compared to that of the sensitized TiO2. The effects of the nitrogen doping for the prepared sensitization catalys
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