Surface-area-controlled synthesis of porous TiO₂ thin films for gas-sensing applications

Surface-area-controlled porous TiO₂ thin films were prepared via a simple sol-gel chemical route, and their gas-sensing properties were thoroughly investigated in the presence of typical oxidizing NO₂ gas. The surface area of TiO₂ thin films was controlled by developing porous TiO₂ networked by means of controlling the TiO₂-to-TTIP (titanium isopropoxide, C₁₂H₂₈O₄Ti) molar ratio, where TiO₂ nanoparticles of size ∼20 nm were used. The sensor's response was found to depend on the surface area of the TiO₂ thin films. The porous TiO₂ thin-film sensor with greater surface area was more sensitive than those of TiO₂ thin films with lesser surface area. The improved sensing ability was ascribed to the porous network formed within the thin films by TiO₂ sol. Our results show that surface area is a key parameter for obtaining superior gas-sensing performance; this provides important guidelines for preparing and using porous thin films for gas-sensing applications.