Subedi Pradeep, Parajuli Suman, Alpuche-Aviles Mario A
Department of Chemistry, University of Nevada, Reno, NV, United States.
Front Chem. 2021 Sep 10;9:733642. doi: 10.3389/fchem.2021.733642. eCollection 2021.
We demonstrate that colloidal quantum dots of CdSe and CdSe/ZnS are detected during the photooxidation of MeOH, under broad spectrum illumination (250 mW/cm). The stepwise photocurrent vs. time response corresponds to single entities adsorbing to the Pt electrode surface irreversibly. The adsorption/desorption of the QDs and the nature of the single entities is discussed. In suspensions, the QDs behave differently depending on the solvent used to suspend the materials. For MeOH, CdSe is not as stable as CdSe/ZnS under constant illumination. The photocurrent expected for single QDs is discussed. The value of the observed photocurrents, > 1 pA is due to the formation of agglomerates consistent with the collision frequency and suspension stability. The observed frequency of collisions for the stepwise photocurrents is smaller than the diffusion-limited cases expected for single QDs colliding with the electrode surface. Dynamic light scattering and scanning electron microscopy studies support the detection of aggregates. The results indicate that the ZnS layer on the CdSe/ZnS material facilitates the detection of single entities by increasing the stability of the nanomaterial. The rate of hole transfer from the QD aggregates to MeOH outcompetes the dissolution of the CdSe core under certain conditions of electron injection to the Pt electrode and in colloidal suspensions of CdSe/ZnS.
我们证明，在宽光谱照明（250 mW/cm）下，甲醇光氧化过程中可检测到CdSe和CdSe/ZnS的胶体量子点。逐步光电流与时间的响应对应于单个实体不可逆地吸附到铂电极表面。讨论了量子点的吸附/解吸以及单个实体的性质。在悬浮液中，量子点的行为因用于悬浮材料的溶剂而异。对于甲醇，在持续光照下CdSe不如CdSe/ZnS稳定。讨论了单个量子点预期的光电流。观察到的光电流值>1 pA是由于形成了与碰撞频率和悬浮稳定性一致的团聚体。观察到的逐步光电流的碰撞频率小于单个量子点与电极表面碰撞预期的扩散限制情况。动态光散射和扫描电子显微镜研究支持了聚集体的检测。结果表明，CdSe/ZnS材料上的ZnS层通过提高纳米材料的稳定性促进了单个实体的检测。在向铂电极注入电子的某些条件下以及在CdSe/ZnS的胶体悬浮液中，从量子点聚集体到甲醇的空穴转移速率超过了CdSe核的溶解速率。
