Molybdenum polyoxometalate impregnated amino- functionalized mesoporous silica thin films as multifunctional materials f
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Molybdenum polyoxometalate (PMo)/silica mesoporous composite thin films, which can be applied as multifunctional materials for photochromic and electrochemical applications, were prepared by impregnating PMo into amino-functionalized mesoporous silica thin films. The composite thin films possess excellent reversible photochromic properties and change from colorless to blue under ultraviolet (UV) irradiation. It is shown in the study that intervalence charge transfer and ligand-to-metal charge transfer are the main reasons for photochromism. After UV irradiation, the charge transfer occurs by the reduction of heteropolyanions accompanying the formation of heteropolyblues with multivalence Mo (+6, +5), and the bleaching process of composite thin films is closely related to the presence of oxygen. Moreover, the composite thin films deposited on the indium tin oxide (ITO) substrate can be used as the electrode and have many advantages, including simple fabrication, fast response, and good stability. The modified ITO electrode retains the electrochemical properties of PMo, can catalyze the electroreduction of the BrO3−, and may be used as the current sensor for the BrO3−.
I. INTRODUCTION
Surfactant-templated mesoprous silica thin films with uniform pore sizes, high surface areas, and excellent thermal stability have received much attention because of their applications in optical and electronic devices, such as lasers,1,2 sensors,3–5 and photochromic films.6–8 In most cases, mesoporous silica thin films are synthesized by spontaneous formation at air–solution, 9–11 air– solid,12,13 or solution–solution14 interfaces and evaporation-induced self-assembly (EISA)15,16 via a spin- or dipcoating process. Better homogeneity and optical quality can be obtained through the EISA process. By simply changing the ratio of surfactant to the silica precursor, a large variety of mesoporous thin films have been obtained using the EISA approach, including lamellar,15,17,18 hexagonal,15,17–22 and cubic15,18,20–22 structures. Although ordered mesoporous silica thin films show their advantages in high surface areas, uniform pore sizes, periodic nanocage structures, and topological perfection, the properties of the pure mesoporous silica framework do not satisfy the request for practical applications. Therefore, the functionalized mesoporous thin a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0028 18
J. Mater. Res., Vol. 23, No. 1, Jan 2008 http://journals.cambridge.org Downloaded: 09 Jun 2014
films will attract growing interest, for reasons other than the optimization synthesis and the exploration for new types of mesoporous thin films. Recently, some research groups have reported that functionalized mesoporous thin films accommodate optically,4–8,23–25 electrochemically,26–29 magnetically,30,31 and biologically32 active molecules in their pores to form host–guest complexes by wetness impregnation and electrodeposition; thus, the resulting nanocomposites exhibit effective optical, electron
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