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.
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] Chemical Journal of Chinese Universities, 2002,V23(12): 2313-2316