通过硫化镉量子点的连续质子耦合单电子转移将硝基苯光催化转化为苯胺,Journal of the American Chemical Society

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通过硫化镉量子点的连续质子耦合单电子转移将硝基苯光催化转化为苯胺
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2016-01-29 , DOI: 10.1021/jacs.5b11353
Stephen C. Jensen ₁ , Stephanie Bettis Homan ₁ , Emily A. Weiss ₁

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本文描述了使用硫化镉量子点 (CdS QD) 作为可见光光催化剂，通过六个连续的光诱导质子耦合电子转移将硝基苯还原为苯胺。在 pH 3.6-4.3 下，光子还原电子的内量子产率在 54 小时光照下为 37.1%，催化剂活性没有明显降低。通过瞬态吸收监测 QD 激子表明，对于催化循环的每一步，牺牲还原剂 3-巯基丙酸在约 5 ps 内清除激子空穴以形成 QD(•-)；电子转移到硝基苯或中间体亚硝基苯和苯羟胺然后发生在纳秒时间尺度上。单电子转移反应的速率常数与相应的质子耦合电子转移的驱动力相关。该结果表明但并未证明电子转移而非质子转移是这些反应的限速器。QD 分子系统的核磁共振分析表明，光产物苯胺未质子化，通过吸附到 QD 催化剂的表面作为毒物。在酸性 pH 下进行反应不仅会促进苯胺解吸，还会增加质子化中间体的可能性；后一种效应可能确保质子的募集不受速率限制。QD 分子系统的核磁共振分析表明，光产物苯胺未质子化，通过吸附到 QD 催化剂的表面作为毒物。在酸性 pH 下进行反应不仅会促进苯胺解吸，还会增加质子化中间体的可能性；后一种效应可能确保质子的募集不受速率限制。QD 分子系统的核磁共振分析表明，光产物苯胺未质子化，通过吸附到 QD 催化剂的表面作为毒物。在酸性 pH 下进行反应不仅会促进苯胺解吸，还会增加质子化中间体的可能性；后一种效应可能确保质子的募集不受速率限制。

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Photocatalytic Conversion of Nitrobenzene to Aniline through Sequential Proton-Coupled One-Electron Transfers from a Cadmium Sulfide Quantum Dot

This paper describes the use of cadmium sulfide quantum dots (CdS QDs) as visible-light photocatalysts for the reduction of nitrobenzene to aniline through six sequential photoinduced, proton-coupled electron transfers. At pH 3.6-4.3, the internal quantum yield of photons-to-reducing electrons is 37.1% over 54 h of illumination, with no apparent decrease in catalyst activity. Monitoring of the QD exciton by transient absorption reveals that, for each step in the catalytic cycle, the sacrificial reductant, 3-mercaptopropionic acid, scavenges the excitonic hole in ∼5 ps to form QD(•-); electron transfer to nitrobenzene or the intermediates nitrosobenzene and phenylhydroxylamine then occurs on the nanosecond time scale. The rate constants for the single-electron transfer reactions are correlated with the driving forces for the corresponding proton-coupled electron transfers. This result suggests, but does not prove, that electron transfer, not proton transfer, is rate-limiting for these reactions. Nuclear magnetic resonance analysis of the QD-molecule systems shows that the photoproduct aniline, left unprotonated, serves as a poison for the QD catalyst by adsorbing to its surface. Performing the reaction at an acidic pH not only encourages aniline to desorb but also increases the probability of protonated intermediates; the latter effect probably ensures that recruitment of protons is not rate-limiting.

更新日期：2016-01-29

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