Detection of Hydroxyl Radicals in Catalytic Ozonation by Using ESR Spectroscopy

Generation of hydroxyl radical (middotOH), one of the major reactive species in the ozonation of water, was directly measured with an electron spin resonance (ESR) spectroscopy. Hydroxyl radical in ozonated water was trapped with 5,5-dimethyl-pyrrolidine-1-oxyl (DMPO) as a stable radical, DMPO-OH, and the amount of DMPO-OH was measured with an ESR spectrometer. The ESR signal of DMPO-OH increased with increasing ozone dosage when ozone dosage below 5 mgO₃/mgTOC, whereas the signal of it decreased with increasing ozone dosage when ozone dosage above 5 mgO₃/mgTOC.