Macpherson Stuart, Lawson Takashi, Abfalterer Anna, Andrich Paolo, Lage Ava, Reisner Erwin, Euser Tijmen G, Stranks Samuel D, Gentleman Alexander S
Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, U.K.
Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, U.K.
ACS Catal. 2024 Jul 26;14(16):12006-12015. doi: 10.1021/acscatal.4c02327. eCollection 2024 Aug 16.
Carbon nanodots (CNDs) are nanosized light-harvesters emerging as next-generation photosensitizers in photocatalytic reactions. Despite their ever-increasing potential applications, the intricacies underlying their photoexcited charge carrier dynamics are yet to be elucidated. In this study, nitrogen-doped graphitic CNDs (NgCNDs) are selectively excited in the presence of methyl viologen (MV, redox mediator) and different electron donors (EDs), namely ascorbic acid (AA) and ethylenediaminetetraacetic acid (EDTA). The consequent formation of the methyl viologen radical cation (MV) is investigated, and the excited charge carrier dynamics of the photocatalytic system are understood on a 0.1 ps-1 ms time range, providing spectroscopic evidence of oxidative or reductive quenching mechanisms experienced by optically excited NgCNDs (NgCNDs*) depending on the ED implemented. In the presence of AA, NgCNDs* undergo oxidative quenching by MV to form MV, which is short-lived due to dehydroascorbic acid, a product of photoinduced hole quenching of oxidized NgCNDs. The EDTA-mediated reductive quenching of NgCNDs* is observed to be at least 2 orders of magnitude slower due to screening by EDTA-MV complexes, but the MV population is stable due to the irreversibly oxidized EDTA preventing a back reaction. In general, our methodology provides a distinct solution with which to study charge transfer dynamics in photocatalytic systems on an extended time range spanning 10 orders of magnitude. This approach generates a mechanistic understanding to select and develop suitable EDs to promote photocatalytic reactions.
碳纳米点（CNDs）是一种纳米级的光捕获剂，正成为光催化反应中的下一代光敏剂。尽管其潜在应用不断增加，但其光激发电荷载流子动力学背后的复杂机制仍有待阐明。在本研究中，氮掺杂石墨碳纳米点（NgCNDs）在甲基紫精（MV，氧化还原介质）和不同电子供体（EDs），即抗坏血酸（AA）和乙二胺四乙酸（EDTA）存在的情况下被选择性激发。研究了由此形成的甲基紫精自由基阳离子（MV），并在0.1皮秒至1毫秒的时间范围内了解了光催化系统的激发电荷载流子动力学，提供了光学激发的NgCNDs（NgCNDs*）根据所使用的ED经历氧化或还原猝灭机制的光谱证据。在AA存在下，NgCNDs通过MV进行氧化猝灭形成MV，由于脱氢抗坏血酸（氧化的NgCNDs光致空穴猝灭的产物），MV寿命较短。由于EDTA-MV络合物的屏蔽作用，观察到EDTA介导的NgCNDs的还原猝灭至少慢2个数量级，但由于不可逆氧化的EDTA阻止了逆反应，MV群体是稳定的。一般来说，我们的方法提供了一种独特的解决方案，用于在跨越10个数量级的扩展时间范围内研究光催化系统中的电荷转移动力学。这种方法产生了一种机理理解，以选择和开发合适的EDs来促进光催化反应。
