Carbon dots on photoactive semiconductor nanomaterials have represented an effective strategy for enhancing their photoelectrochemical (PEC) activity. By carefully designing and manipulating a carbon dot/support composite, a high photocurrent could be obtained. Currently, there is not much fundamental understanding of how the interaction between such materials can facilitate the reaction process. This hinders the wide applicability of PEC devices. To address this need of improving the fundamental understanding of the carbon dots/semiconductor nanocomposite, we have taken the TiO₂ case as a model semiconductor system with nitrogen-doped carbon dots (NCDs). We present here with in-depth investigation of the structural hybridization and energy transitions in the NCDs/TiO₂ photoelectrode via high-resolution scanning transmission microscopy (HR-STEM), electron energy loss spectroscopy (EELS), UV–vis absorption, electrochemical impedance spectroscopy (EIS), Mott–Schottky (M–S), time-correlated single-photon counting (TCSPC), and ultraviolet photoelectron spectroscopy (UPS), which shed some light on the charge-transfer process at the carbon dots and TiO₂ interface. We show that N doping in carbon dots can effectively prolong the carrier lifetime, and the hybridization of NCDs and TiO₂ is able not only to extend TiO₂ light response into the visible range but also to form a heterojunction at the NCDs/TiO₂ interface with a properly aligned band structure that allows a spatial separation of the charges. This work is arguably the first to report the direct probing of the band positions of the carbon dot–TiO₂ nanoparticle composite in a PEC system for understanding the energy-transfer mechanism, demonstrating the favorable role of NCDs in the photocurrent response of TiO₂ for the water oxidation process. This study reveals the importance of combining structural, photophysical, and electrochemical experiments to develop a comprehensive understanding of the nanoscale charge-transfer processes between the carbon dots and their catalyst supports.

中文翻译：

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氮掺杂碳点/ TiO ₂纳米粒子复合材料的光电化学水氧化

光敏半导体纳米材料上的碳点代表了一种增强其光电化学（PEC）活性的有效策略。通过仔细设计和处理碳点/载体复合材料，可以获得高光电流。目前，关于这些材料之间的相互作用如何促进反应过程的了解还很少。这阻碍了PEC设备的广泛应用。为了满足改善对碳点/半导体纳米复合材料的基本理解的需求，我们将TiO ₂外壳作为具有氮掺杂碳点（NCD）的模型半导体系统。我们在此对NCDs / TiO ₂中的结构杂化和能量跃迁进行深入研究通过高分辨率扫描透射显微镜（HR-STEM），电子能量损失谱（EELS），紫外可见吸收，电化学阻抗谱（EIS），莫特-肖特基（MS），与时间相关的单光子计数的光电极（TCSPC）和紫外光电子能谱（UPS），这为碳点和TiO ₂界面的电荷转移过程提供了一些启示。我们表明碳点中的N掺杂可以有效地延长载流子寿命，并且NCD和TiO ₂的杂交不仅能够将TiO _2的光响应扩展到可见光范围内，而且还可以在NCDs / TiO ₂上形成异质结与适当对准的能带结构相交界面，该带结构允许电荷的空间分离。这项工作可以说是第一个报告的直接探测碳点二氧化钛的带位置的₂在PEC系统粒子复合体为了解能量传递装置，展示以TiO2光电流响应非传染性疾病的有利作用，₂对水的氧化过程。这项研究揭示了结合结构，光物理和电化学实验以发展对碳点及其催化剂载体之间纳米级电荷转移过程的全面理解的重要性。