Self-Cleaning Organic Vapor Sensor Based on a Nanoporous TiO₂ Interferometer

Porous thin films of TiO(2) are prepared and their use as chemical sensors for organic vapor analytes is investigated. Thin-film optical interference (Fabry-Perot) fringes in the reflectance spectrum are monitored using Reflectometric Interference Fourier Transform Spectroscopy (RIFTS). Three analytes are employed to probe the sensitivity of the porous TiO(2)-based sensors as a function of analyte vapor pressure: dodecane, isopropyl alcohol (IPA), and pentane. Measured lower limits of detection (3, 30, and 11, 000 ppmv for dodecane, IPA, and pentane, respectively) track the saturation vapor pressures (P(sat)) of the analytes (0.134, 45, and 513 Torr at 25°C for dodecane, IPA, and pentane, respectively); the analyte with the lowest value of P(sat) shows the lowest LLOD. Recovery of the sensor after a saturation dose of analyte is also dependent on P(sat): the sensor displays good recovery from pentane and IPA, and sluggish and incomplete recovery from dodecane. However, irradiation of the porous TiO(2) sensor with UV light in the presence of air accelerates recovery, and this process is attributed to photo-catalyzed oxidation of the analyte at the TiO(2) surface.