Shimizu K, Tschulik K, Compton R G
Department of Chemistry , Physical and Theoretical Chemistry Laboratory , Oxford University , South Parks Road , Oxford , OX1 3QZ , UK . Email:
Nano-Electrochemistry - Center for Electrochemical Sciences , Faculty of Chemistry and Biochemistry , Ruhr-University Bochum , D-44780 Bochum , Germany.
Chem Sci. 2016 Feb 1;7(2):1408-1414. doi: 10.1039/c5sc03678j. Epub 2015 Nov 18.
In spite of their natural and technological importance, the intrinsic electrochemical properties of hematite (α-FeO) nanoparticles are not well understood. In particular, particle agglomeration, the presence of surface impurities, and/or inadequate proton concentrations are major obstacles to uncover the fundamental redox activities of minerals in solution. These are particularly problematic when samples are characterized in common electrochemical analyses such as cyclic voltammetry in which nanoparticles are immobilized on a stationary electrode. In this work, the intrinsic reaction kinetics and thermodynamics of individual hematite nanoparticles are investigated by particle impact chronoamperometry. The particle radius derived from the integrated area of spikes recorded in a chronoamperogram is in excellent agreement with electron microscopy results, indicating that the method provides a quantitative analysis of the reduction of the nanoparticles to the ferrous ion. A key finding is that the suspended individual nanoparticles undergo electrochemical reduction at potentials much more positive than those immobilized on a stationary electrode. The critical importance of the solid/water interface on nanoparticle activity is further illustrated by a kinetic model. It is found that the first electron transfer process is the rate determining step of the reductive dissolution of hematite nanoparticles, while the overall process is strongly affected by the interfacial proton concentration. This article highlights the effects of the interfacial proton and ferrous ion concentrations on the reductive dissolution of hematite nanoparticles and provides a highly effective method that can be readily applied to study a wide range of other mineral nanoparticles.
尽管赤铁矿（α-Fe₂O₃）纳米颗粒具有天然和技术上的重要性，但其本征电化学性质尚未得到充分理解。特别是，颗粒团聚、表面杂质的存在和/或质子浓度不足是揭示矿物在溶液中基本氧化还原活性的主要障碍。当在常见的电化学分析（如循环伏安法）中对样品进行表征时，这些问题尤为突出，在循环伏安法中，纳米颗粒固定在固定电极上。在这项工作中，通过颗粒碰撞计时电流法研究了单个赤铁矿纳米颗粒的本征反应动力学和热力学。从计时电流图中记录的尖峰积分面积得出的颗粒半径与电子显微镜结果非常吻合，表明该方法提供了对纳米颗粒还原为亚铁离子的定量分析。一个关键发现是，悬浮的单个纳米颗粒在比固定在固定电极上的纳米颗粒更正的电位下发生电化学还原。动力学模型进一步说明了固/水界面对纳米颗粒活性的至关重要性。研究发现，第一个电子转移过程是赤铁矿纳米颗粒还原溶解的速率决定步骤，而整个过程受到界面质子浓度的强烈影响。本文强调了界面质子和亚铁离子浓度对赤铁矿纳米颗粒还原溶解的影响，并提供了一种高效方法，该方法可轻松应用于研究广泛的其他矿物纳米颗粒。
