Experimental evidence of the mobility of hydroperoxyl/superoxide anion radicals from the illuminated TiO2 interface into the aqueous phase

Abstract

The understanding of behaviors of hydroperoxyl/superoxide anion radicals (HO2·/O2-·) generated from a photoirradiated TiO2 surface is essential to improve the efficiency of TiO2 photocatalytic reactions by decreasing the recombination of photoinduced electron-hole (e--h+) pairs. In contrast with previous studies, we found that HO2·/O2-· generated on the surface of illuminated TiO2 particles are mobile. HO2·/O2-· formed by the photocatalysis of TiO2 particles immobilized onto the inner surface of a coil-quartz tube were forced under a continuous flow through a knotted tubing reactor (KTR) and into the aqueous phase completely separated from the TiO2 particles, and were measured by a chemiluminescence (CL) technique using 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (MCLA) as the reagent. The initial concentration of the HO2·/O2-· stream entering the KTR was determined by its half-life (98 s) at pH 5.8. We suggests that the efficiency of TiO2 photocatalytic reactions may be further improved by utilizing the mobility of HO2·/O2-·.