In-situ Calibration of the Hydroperoxyl Radical Using an Immobilized TiO₂Photocatalyst in the Atmosphere

Abstract

The present study is the first report of utilizing TiO 2 photocatalyst to analytically calibrate the hydroperoxyl radical (HO 2 ·). An in-situ calibration method of HO 2 · is proposed for air monitoring by using an 2-methyl-6-(pmethoxyphenyl)-3,7-dihydroimidazo-[1,2-a]pyrazin-3-one (MCLA)-chemiluminescence (CL) technique. In this method, HO 2 · (pK a = 4.80) is produced by the ultraviolet (UV) photolysis of immobilized TiO 2 using a constant flow rate of air equilibrated water, in which HO 2 · 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 HO 2 · and its empirically observed pH-dependent rate constant, k obs , at a given pH. . Experimental results indicate the practical feasibility of the approach, producing very promising method.