A porous glass-based ozone sensing chip impregnated with potassium iodide and α-cyclodextrin

A chemical sensing chip for gaseous ozone (O3) has been fabricated by impregnating a porous glass sheet (8 mm square and 1 mm thick) with potassium iodide (KI) and α-cyclodextrin. The latter suppresses volatilization of iodine formed by the reaction of KI with O3. When passively exposed to air containing a sub-ppm level of O3 at a relative humidity (RH) of 90%, this chip changes from colorless to pale yellow, with an absorption peak at 360 nm. A plot of change in absorbance at this wavelength against the total O3 exposure yields a good linear relationship passing through the origin. From the slope of the plot, the detection limit is estimated to be several ppb, assuming an exposure interval of 1 h. Upon exposure at lower RH values of 50-70%, the chip turns reddish brown and absorbs over the range of 420 to 550 nm, although its absorption maximum remains at 360 nm. Absorption in the visible region under these conditions was found to be transient and thus unsuitable for measuring O3, although this visible absorption could be readily shifted to 360 nm by applying higher RH values, such as 90%. From these results, it is concluded that hourly variations of ambient O3 concentration can be measured by observing the absorbance of the chip at 360 nm, in conjunction with conditioning of the chip at 90% RH following the exposure interval.