posted on 2012-08-22, 00:00authored byFengxia Liang, Timothy
L. Kelly, Lin-bao Luo, Hui Li, Michael J. Sailor, Yang Yang Li
Porous thin films of TiO2 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 TiO2–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 (Psat) 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 Psat shows the lowest LLOD. Recovery of the sensor after
a saturation dose of analyte is also dependent on Psat: the sensor displays good recovery from pentane and
IPA, and sluggish and incomplete recovery from dodecane. However,
irradiation of the porous TiO2 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 TiO2 surface.