Invited Paper SE-WeM5
Structuring Highly Active, Nano-scale Photocatalytic Films using Reactive Sputtering

Wednesday, October 17, 2007, 9:20 am, Room 617

Since Fujishima and Honda developed the photoelectrochemical cell for H₂O splitting in 1972, heterogeneous photocatalysis has attracted much attention. TiO₂ is among the most extensively studied semiconductor photocatalysts. It is chemically and biologically inert, photocatalytically stable, commercially available, and inexpensive. In the past three 30 years, most of the effort in the photocatalytic field has been focused on energy and environmental applications, which require materials with the following properties: (1) hindered charge recombination and improved photocatalytic efficiency; (2) targeted reactivity and selectivity that match band energies to the desired reaction, and (3) extended photoresponse into the visible light region. Masakazu Anpo first introduced the notion of "second-generation" TiO₂ photocatalysts, which can absorb visible light and also operate effectively as photocatalysts. We hypothesize that the solid-solid interface in TiO₂-based nanocomposites is key to overcoming these three challenges and are a promising candidates for 2nd-generation photocatalysts. Recent findings in our laboratory and others throughout the world reveal a number of surprising insights as to why TiO₂ nanocomposites tend to display higher photoactivity than pure-phases and point to the critical role of the solid-solid interface as the location of catalytic "hot spots". Yet, efforts to probe the role of the solid-solid interface in photocatalytic activity are stymied by an inability to synthesize under sufficiently controlled conditions and in sufficient quantities the "interface", which would then allow structural characterization and functional interrogation. Advances in photocatalyst synthesis using sputtering technologies promise to revolutionize our ability to engineer the solid-solid interface at the molecular level and thus, to fabricate photoactive nanostructured composite materials having high densities of "defects" designed for energy harvesting and storage. We prepare highly active TiO₂ nanocomposites using chemical and physical methods in our laboratory. By varying key fabrication conditions (target power, substrate bias, oxygen partial pressure, and deposition angle) in reactive DC magnetron sputtering, we synthesize TiO₂ thin films with different microstructures. This paper will report the synthesis and characterization of photocatalytic films and their use to generate solar fuels and oxidize gas phase contaminants.