Development and performance evaluation of ozone detection paper using azo dye orange I: Effect of pH

A highly sensitive sensing paper that uses the reaction of ozone with azo dye orange I has been developed for ambient ozone monitoring. This reaction results in reaction products, without absorption in visible region, on paper that can be determined by measuring the reflectance spectrum of the paper. The combination of a cellulose sheet, a humectant (glycerol), an alkali (sodium hydroxide) and orange I is needed to achieve a sensitive sensing paper. We found that the pH of the immersion solution used for preparing the sensing paper had a strong influence on the paper's responsivity to ozone. Ozone detection papers that were made using acidic or neutral immersed solutions were not faded by ozone exposure, whereas those made using a strong alkaline immersion solution were faded by ozone exposure and the color of the paper faded completely at an ozone exposure of about 400 ppb × h. We considered an orange I reaction site for ozone using UV–vis spectrum measurements and molecular orbital calculation by comparing experimental results for both orange I and its isomer orange II. It was estimated that the hydrazone form of orange I in alkaline condition would be sensitive to ozone.