摘要
用ESR方法研究了硫化镉超微粒子表面被不同浓度的过剩硫离子S^(2-)改性后对其光诱导电子转移及底物的氧化还原反应进程的影响.结果表明,在较高浓度下光还原反应易于进行.若所用底物的氧化还原电位E0为负值,在无过剩S^(2-)存在及低浓度S^(2-)环境中不发生光还原反应,但却可在高浓度S^(2-)环境发生反应; 若底物的E0为正值,则在无硫离子及较低硫离子浓度下能够发生的光氧化反应,在高浓度时则被完全抑止.这是由于表面过剩S^(2-)的作用,改变了底物的氧化还原电位与半导体超细微粒带隙间的匹配关系.根据Langmuir 等温吸附模型,进一步导出了修饰物的浓度c与平带电位负移值间的关系表达式ΔEfb=ΔKc/(1＋Kc).可以合理解释修饰物S^(2-)的浓度越高,Efb负移越大,越有利于光还原反应的实验事实.因此根据需要,适当地选择修饰物并控制浓度,使带隙位置与底物氧化还原电位间能有合适的匹配,有助于调节光化学反应的选择性与方向.
The influence of S2- ion and its concentration upon the photoinduced electron transfer and red-ox reaction of substrates on the surface of modified US colloid have been studied by means of ESR technique. The experimental results show that the existence of S2- ion with high concentration is advantageous to the interfacial photoreduction reaction and may restrain the photooxidation reaction. If the red-ox potential E-0 of the substrate is negative, photoreduction reaction is impossible to occur in the system with low concentration of S2- ion, but it can take place as the concentration of S2- ion is sufficient high; when E-0 of the substrate is positive, photooxidation reaction can be prohibited entirely under condition of high S2- ion concentration, even though it is able to occur while the concentration of S2- ion is low. Due to the strong interaction of S2- ion with the surface of US superfine particles, negative shift in flat potential E-fb of US leads to a change of gap position, and then to a variation in match relation between the red-ox potential E-0 of the substrate and the position of conducton band to valence band in semiconductor particles. According to Langmuir's adsorption isotherm model, a formula expressing the relation between the concentration c of modification compound and the negative shift A Efb in flat potential was derived: DeltaE(fb) = DeltaE(fb)(m) Kc/(1 + Kc), By using this formula, experiment facts may be explained rationally, the higher the concentration, the greater the amount of negative shift DeltaE(fb), and thus the more favourable to photoreduction reaction. Therefore, by choosing suitable modification substance and adjusting its concentration, the selection, direction as well as the mechanism of interfacial photoreaction can be controlled effectively.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2001年第9期781-787,共7页
Acta Physico-Chimica Sinica
基金
国家基础研究发展规划项目(G1998010100)
国家自然科学基金资助项目(No:39890390).
