Experimental Evidence of the Mobility of Hydroperoxyl/Superoxide Anion Radicals from the Illuminated TiO2 Interface into the Aqueous Phase

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 ‑ · . KCI Citation Count: 14