Controlled anisotropic growth of Ag nanoparticles on oil-decorated TiO 2 films with photocatalytic reduction method
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–TiO2 hybrids are useful in various applications, such as photocatalysis, solar energy conversion, and biosensoring. In this study, oil-decorated TiO2 films were used to induce the formation of Ag nanoplates in AgNO3 solution via a photocatalytic method. Ag nanoplates in the products can be controlled by changing the oil-decoration time of films or changing the AgNO3 concentration of the solution. Oil decoration was found to be necessary in the formation of Ag nanoplates, and a critical concentration of AgNO3 solution was needed. The oil layer on the TiO2 films was demonstrated to play a role in the prevention of the reoxidation of the Ag atoms, and a growth model was proposed to interpret the formation of Ag nanoplates on the oil-decorated TiO2 films.
I. INTRODUCTION
TiO2 is the most promising material in the field of photocatalysis because of its superior photocatalytic activity, chemical stability, low cost, and nontoxicity. As such, its performances in the photodegradation of chemical pollutants and solar energy conversion have been extensively studied in the past decades, and its practical application has been seriously considered. 1,2 TiO2 assembled with noble metal nanocomposite particulates has received much attention, because such a hybrid can effectively separate the charges and redshift the absorption to visible light via plasmonic resonance on the metal nanoparticle.3–5 For example, Awazu et al. combined TiO2 and Ag core/SiO2-shell nanoparticles in a heterostructure and the photocatalytic activity was enhanced by a factor of 7 under near-ultraviolet (UV) irradiation.4 TiO2 assisted by the localized surface plasmonic resonance (LSPR) of Ag NPs is promising in applications such as photocatalysis,3–5 solar cells,6,7 reversible imaging,8 and LSPR sensors.9 Many methods have been used to assemble metal nanoparticles (NPs) onto a solid surface, and some of the top-to-down lithographic methods (e.g., electron-beam lithography, nanoprint lithography, and nanosphere lithography) have been used to control the growth of metal NPs. The photocatalytic reduction method is a cost-effective and facile method to synthesize Ag NPs on TiO2 film. Under UV irradiation, Ag NPs are directly grown on the TiO2 film by reducing Ag1 ions in AgNO3 solution. However, the as-grown Ag NPs on TiO2 films a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.283 J. Mater. Res., Vol. 29, No. 21, Nov 14, 2014
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are often sphere-like, and an effective method is still needed for controlling the formation of anisotropic Ag NPs with the photocatalytic reduction method. It is well known that LSPR gives rise to absorption and scattering of light at specific wave lengths, which depends on the particle size, shape, orientation, interparticle spacing, and dielectric environment.10–13 A controlled anisotropic growth of Ag NPs on TiO2 films is expected in tuning the optical response of the Ag–TiO2 hybrid films. Moreover, the growth behavior of the Ag NPs on TiO2 fi
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