Understanding photocatalyzed redox interactions between Fe(III)–(oxyhydr)oxide mineral nanoparticles and adsorbed chromophoric organic matter is critical for accurately predicting bioavailable iron fluxes in the euphotic zone of natural aquatic systems, and for improving the effectiveness of nano-iron-based water purification systems. However, the electron transfer processes that underpin photoreductive dissolution at particle/organic/solution interfaces occur on ultrafast timescales and thus remain difficult to probe. Here we report an ultrafast transient absorption spectroscopy (TAS) study of suspensions of hematite nanoplatelets (HNPs) sensitized by adsorbed rhodamine B (RhB) dye as a function of solution media and pH. The TAS results indicate a substantially longer fluorescence lifetime of RhB adsorbed on HNPs across a wide range of pH conditions, consistent with transient photoinduced electron transfer to the oxide with recombination kinetics controlled by electron migration back to the interface via small polaron hopping. Normalization of the observed kinetics to the measured surface loading of RhB at different pH values shows that the recombination rates are insensitive to environmental variables, likely controlled instead by particle properties that determine small polaron diffusion behavior.

中文翻译：

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有机发色团与赤铁矿纳米粒子之间的光催化电子交换及固态电荷传输的作用

了解 Fe( III ) 之间的光催化氧化还原相互作用)–(羟基)氧化物矿物纳米颗粒和吸附的发色有机物对于准确预测天然水生系统透光区的生物可利用铁通量以及提高纳米铁基水净化系统的有效性至关重要。然而，在粒子/有机物/溶液界面处支持光还原溶解的电子转移过程发生在超快的时间尺度上，因此仍然难以探测。在这里，我们报告了由吸附的罗丹明 B (RhB) 染料敏化的赤铁矿纳米血小板 (HNPs) 悬浮液的超快瞬态吸收光谱 (TAS) 研究，该研究是溶液介质​​和 pH 值的函数。TAS 结果表明，在广泛的 pH 条件下，吸附在 HNP 上的 RhB 的荧光寿命显着延长，通过小极化子跳跃。将观察到的动力学标准化为在不同 pH 值下测量的 RhB 表面负载表明重组率对环境变量不敏感，可能由决定小极化子扩散行为的粒子特性控制。