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采用脉冲辐解技术,以羟基自由基和硫酸根自由基作为氧化剂,研究了9,10-菲醌(PhQ)在水溶液中的单电子氧化行为,获取了瞬态产物的吸收光谱和有关动力学数据。在中性pH条件下,PhQ 与羟基自由基以(1.5±0.2)×1010 dm3·mol-1·s-1的速率反应,生成一个初级瞬态产物。该瞬态产物的吸收光谱呈现出位于370nm的吸收峰和在较长波长下的一个宽吸收带。进一步实验观察到,随着短波长区初级吸收的衰减,可见光区的吸收同步增加,在400nm处形成最大吸收峰,并产生以500nm为中心的宽吸收带,表明次级瞬态产物的形成。PH9.9条件下得到的结果与中性pH的一致。降低pH至2—4,尽管初始瞬态吸收谱也呈现出位于370nm的最大吸收峰,但伴随着初始吸收的哀减,没有观察到可见区域吸收的增加。在中性pH条件下,硫酸根自由基与PhQ反应的速率常数测定为(4.0±0.6)×109dm3·mol-1·s-1,生成的瞬态吸收谱与氢氧自由基反应得到的次级吸收谱一致,呈现以400nm和500nm为中心的两个吸收带。基于光谱的相似性和动力学分析,以及羟基自由基和硫酸根自由基的特性,本工作推断反应机理如下:PhQ羟基自由基反应首先生成OH加成产物,OH加成产物脱水生成阳离子自由基:阳离子自由基办可通过硫酸根自由基的氧化直接产生。
The single-electron oxidation of 9,10-phenanthrenequinone (PhQ) in aqueous solution was studied by using pulsed radiolysis technology with hydroxyl radical and sulfate radical as oxidant. The absorption spectra and related kinetics of transient products were obtained data. At neutral pH, PhQ reacts with hydroxyl radicals at a rate of (1.5 ± 0.2) × 1010 dm3 · mol-1 · s-1 to form a primary transient product. The absorption spectrum of this transient product shows an absorption peak at 370 nm and a broad absorption band at longer wavelengths. Further experiments showed that with the attenuation of the primary absorption in the short wavelength region, the absorption in the visible region increased synchronously, the maximum absorption peak was formed at 400 nm and a broad absorption band centered at 500 nm was generated, indicating the formation of secondary transient products. The results obtained at pH 9.9 are consistent with the neutral pH. Lowering the pH to 2-4, although the initial transient absorption spectrum also showed the maximum absorption at 370 nm, no increase in absorption in the visible region was observed with the initial absorption wail. Under neutral pH, the rate constant of the sulfate radical reaction with PhQ was determined to be (4.0 ± 0.6) × 109dm3 · mol-1 · s-1. The resulting transient absorption spectrum reacted with hydroxyl radical The absorption spectra are consistent, showing two absorption bands centered at 400 nm and 500 nm. Based on the similarity and kinetic analysis of the spectra and the characteristics of hydroxyl radical and sulfate radical, the reaction mechanism is deduced as follows: The OH radical reaction of PhQ radical first generates OH addition product, and the OH addition product is dehydrated to generate cationic radical Cationic free radicals can be directly generated by the oxidation of sulfate radicals.