(514f) Enhancement of Visible Light Absorption of Ordered Mesoporous Titanium (Ti3+) and Nitrogen Doped Titanium Dioxide Thin Films for Solar Energy Conversion

The optical and electronic properties of TiO₂ thin films provide tremendous opportunities in several applications including photocatalysis, photovoltaics and photconductors for energy production. The primary challenge of using TiO₂ thin film for solar energy conversion is its inability to absorb the visible light of the solar spectrum due to its high band gap. In this study, visible light responsive cubic ordered mesoporous titanium (Ti³⁺) and nitrogen codoped TiO₂ thin films (Ti³⁺-N-TiO₂) are prepared by a surfactant templated sol-gel method. Hydrazine is used as a nitrogen source as well as a reducing agent to form Ti³⁺ in TiO₂. To prepare the films, cubic ordered mesoporous TiO₂ thin films are first prepared using Pluronic F127 as the template and TiCl₄ as the precursor. After aging and calcination, the films are dipped into hydrazine hydrate to induce nitrogen doping / reduction, followed by annealing at low temperature. After doping, the films are confirmed to have an accessible, well-ordered cubic mesopore structure by XRD and SEM analyses.  XPS analysis shows that Ti³⁺ and both interstitial and substitutional nitrogen are present in the doped films.  The Ti³⁺-N-TiO₂ has a narrower band gap than pure TiO₂, and as a result, the Ti³⁺-N-TiO₂ films show better visible-light photocatalytic activity than undoped TiO₂ for both the degradation of methylene blue in aqueous solution and hydrogen generation by water splitting. The effects of materials synthesis conditions on the doping process and photocatalytic activity will be discussed.