EPR Measurement of Hydroxyl Radicals and Rate Constant of n-Hexadecane Photocatalytic Degradation

Abstract

Abstract: Spin trapping technique was used to detect the free radicals formed upon light irradiation of TiO₂ in aqueous solutions. 5,5-dimethylpyrroline-N-oxide(DMPO) was used as a spin trapper. The Electron paramagnetic resonance( EPR) signal obtained 1 min after reaction initiated by 180 W mercury lamp irradiation with a mixture of 1 g/L TiO₂, 0.05 mol/L DMPO in phosphate buffer(pH=7.4) gave the 1/2/2/1 quartet with hyperfine splittings of a N=a H=1.49×10^-3 T, g=2.005 0, which were typical peaks of DMPO-OH. A model was used to speculate on the free radical mechanisms of n-hexadecane photodegradation by TiO₂ in aqueous solutions. The intensity increased with increase of the irradiation time and the steady state was achieved at 1 min light irradiation. By employing the known rate constant for the reaction of hydroxyl radicals(HO ·) with the DMPO, the rate constant k=5.0×10¹¹ mol^-1·L·s^-1 for the reaction of hydroxyl radicals with n-hexadecane could be obtained. In conclusions, TiO₂ photocatalytic reaction proceeded in a free radical mechanism.

Key words: Photocatalytic degradation, Hydroxyl radicals, EPR, Nano TiO₂, n-Hexadecane

CLC Number:

O643.1

TrendMD:

ZHONG Ping, KONG Ling-Ren, LIU Guang-Ming, SUI Yun-Xia . EPR Measurement of Hydroxyl Radicals and Rate Constant of n-Hexadecane Photocatalytic Degradation[J]. Chem. J. Chinese Universities, 2002, 23(12): 2313.

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EPR Measurement of Hydroxyl Radicals and Rate Constant of n-Hexadecane Photocatalytic Degradation

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