Visible Light Semiconductor Photo-Catalysis Enhanced by Ag Nanoparticle Plasmon Resonance

Tuesday, November 9, 2010: 3:36 PM
151 F Room (Salt Palace Convention Center)
David B. Ingram, Phillip Christopher and Suljo Linic, Department of Chemical Engineering, University of Michigan, Ann Arbor, MI

The efficient conversion of solar energy into useful chemical energy, for example through processes such as water splitting and CO2 reduction, is of critical importance for the development of sustainable, long-term solutions to society's energy problems. These and other photochemical processes require the development of novel photo-catalysts that can efficiently make use of the solar spectrum.

TiO2 has been studied extensively as a promising photo-catalyst because it is abundant, cheap and stable under reaction conditions. TiO2 absorbs ultraviolet (UV) light, creating electron/hole (e/h) pairs, which can perform redox half-reactions for a range of photochemical processes. However, UV accounts for only a small portion of the solar spectrum. Shifting the band gap of TiO2 to lower energy (e.g., by adding various dopants) allows for absorption in the visible spectrum, which represents ~50% of the solar spectrum. The result is a material that shows photo-catalytic activity upon illumination with visible light. However, the absorption efficiency of the doped materials in the visible region is inherently low, which leads to low visible photo-reaction rates.

In this contribution we show that the photocatalytic activity of visible light active nitrogen-doped TiO2 can be significantly enhanced by the addition of optically active Ag nanostructures of targeted size and shape to form composite metal/semiconductor photocatalysts. The observed activity enhancement is attributed to the radiative decay of Ag surface plasmon resonance (SPR) states, increasing the steady-state concentration of e/h pairs in N-TiO2, thereby increasing the reaction rate. The ability to predictably tune the Ag SPR by controlling particle shape and size allows for the rational design of optimized metal/semiconductor composite photocatalysts and photo-electro-catalysts wherein the overlap of the metal nanostructure SPR, semiconductor band gap, and energy of the light source is maximized.

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