正十六烷光催化降解的羟自由基测定及其反应速率常数

以5,5-二甲基-1-吡咯啉-N-氧化物(DMPO)为自旋捕集剂,采用电子顺磁共振(EPR)方法,在光照的TiO₂磷酸缓冲水溶液(pH=7.4)中检测到羟自由基的自旋加合物(DMPO-OH),其强度随光照时间增加而加大.在1min时达到稳态,此时DMPO-OH的产生和猝灭达到平衡.根据已知的羟自由基(HO·)与DMPO结合的速率常数k0,推导出纳米级TiO₂光催化生成羟自由基氧化正十六烷(n-C_{16H34)的速率常数k=5.0×10¹¹mol^-1·L·s^-1.}

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

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.