In-situ Calibration of the Hydroperoxyl Radical Using an Immobilized
TiO₂ Photocatalyst in the Atmosphere

摘要

The present study is the first report of utilizing TiO₂ photocatalyst to analytically calibrate the hydroperoxyl radical (HO₂^·). An in-situ calibration method of HO₂^· is proposed for air monitoring by using an 2-methyl-6-(p-methoxyphenyl)- 3,7-dihydroimidazo-[1,2-a]pyrazin-3-one (MCLA)-chemiluminescence (CL) technique. In this method, HO₂^· (pK_a = 4.80) is produced by the ultraviolet (UV) photolysis of immobilized TiO₂ using a constant flow rate of air equilibrated water, in which HO₂^· is controlled by using various lengths of knotted tubing reactor (KTR). The principle of the proposed calibration is based on the experimentally determined halflife (t_1/2) of HO₂^· and its empirically observed pH-dependent rate constant, kobs, at a given pH. The concentration of HO₂^·/O₂^·? is increased as pH increases. This pH dependence is due to the different disproportionative reactivities between HO₂^·/O₂^·? and HO₂^·/O₂^·?. Experimental results indicate the practical feasibility of the approach, producing very promising method.