Analysis of hydroxyl radical generated in electrolyzed strong acid aqueous solution by electron spin resonance spectroscopy

A hydoxyl radical, which acts as an active oxygen radical, has been investigated in an electrolyzed strong acid aqueous solution by electron spin resonance spectroscopy. The hydroxyl radical is detected as two different spin adducts of 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) and N-[(1-oxido-4-pyridinio) methylene]-t-butylamine N-oxide. The amount of DMPO-OH spin adduct has not been changed for ca, 10 days in sealed bottles. The DMPO-OH spin adduct is gradually increased after DMPO addition into the solution where sodium sulfate is used as an electrolysis promoting reagent instead of sodium chloride. It is suggested that the hydroxyl radical is produced from a precursor like a peroxodisulfate ion, which is derived from the sulfate. The amount of generated hydroxyl radical can be controlled by current density and sulfate concentration in the supplied water, where sodium chloride is used in general as the promoting reagent.