Issue 2, 2016

Exploring the mineral–water interface: reduction and reaction kinetics of single hematite (α-Fe2O3) nanoparticles

Abstract

In spite of their natural and technological importance, the intrinsic electrochemical properties of hematite (α-Fe2O3) 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.

Graphical abstract: Exploring the mineral–water interface: reduction and reaction kinetics of single hematite (α-Fe2O3) nanoparticles

Article information

Article type
Edge Article
Submitted
28 Sep 2015
Accepted
17 Nov 2015
First published
18 Nov 2015
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2016,7, 1408-1414

Author version available

Exploring the mineral–water interface: reduction and reaction kinetics of single hematite (α-Fe2O3) nanoparticles

K. Shimizu, K. Tschulik and R. G. Compton, Chem. Sci., 2016, 7, 1408 DOI: 10.1039/C5SC03678J

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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