Photocatalytic properties of MIn(WO 4 ) 2 (M = Li, Na, and K)
- PDF / 245,676 Bytes
- 7 Pages / 585 x 783 pts Page_size
- 1 Downloads / 185 Views
Jinhua Ye Photocatalytic Ecomaterials Center, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0047, Japan
Zhigang Zoua) Ecomaterials and Renewable Energy Research Center, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, People’s Republic of China (Received 29 January 2006; accepted 7 December 2006)
MIn(WO4)2 (M ⳱ Li, Na, and K) with InO6 and WO6 octahedra were synthesized via a conventional solid-state reaction method. The photophysical and photocatalytic properties were studied. Compared with WO3, which is unable to evolve H2 from an aqueous CH3OH solution under illumination, the three materials can evolve H2 and O2 from aqueous solutions with CH3OH and AgNO3 sacrificial reagents, respectively. The activity order of photocatalytic H2 evolution is NaIn(WO4)2 > LiIn(WO4)2 > KIn(WO4)2 under irradiation ( > 200 nm). Under irradiation ( > 300 nm), however, LiIn(WO4)2 has a high activity for photocatalytic H2 evolution over NaIn(WO4)2. It is also noteworthy that LiIn(WO4)2 and NaIn(WO4)2 exhibit the ability to split pure water. The results suggest that the bottoms of the conduction bands in these photocatalysts are raised to meet the potential requirements of photocatalytic H2 evolution.
I. INTRODUCTION
Recently, more and more attention has been paid to photocatalytic water splitting by using solar energy.1–6 Generally, a reaction of photocatalytic water splitting involves the following steps: (i) generation of photoinduced electron-hole pairs in the semiconductor photocatalyst, (ii) migration of the photogenerated carriers to the semiconductor surface, and (iii) redox reaction of the photogenerated electrons and holes with water (or sacrificial reagents). The generation and migration of photoinduced electron-hole pairs are associated with the electronic structure of the photocatalyst. Therefore, the electronic structure of the material often plays a decisive role in the photocatalytic properties. Modulating the electronic structures of the photocatalysts may improve the photocatalytic properties, and has thus attracted much attention recently.7–10 Besides, it is an efficient way to develop new photocatalysts. It is well known that tungsten oxide is a catalyst for photocatalytic O2 evolution, but not for photocatalytic H2 a)
Address all correspondence to this author. e-mail: [email protected]. DOI: 10.1557/JMR.2007.0111 958
J. Mater. Res., Vol. 22, No. 4, Apr 2007 http://journals.cambridge.org Downloaded: 09 Oct 2014
evolution.11,12 In general, the basic requirements for the reactions of photocatalytic water splitting are that the potential on the bottom of the conduction band (CB) is more negative than the reduction potential of H+/H2, and that the potential on the top of the valence band (VB) is more positive than the oxidation potential of O2/H2O. Tungsten oxide is unable to evolve H2 because the bottom of the CB is more positive than the H+/H2 potential. Some efforts have been made to adjust the electronic structures of tungstates, such as AgInW2O8,
Data Loading...
