The influence of radiolytically-formed Reactive Oxygen Species in mineral transformation in Liquid-Phase Transmission Electron Microscopy
Liquid phase transmission electron microscopy (LPTEM) allows in situ observations of the dynamic behaviour of materials in liquids with both high spatial resolution and temporal resolution. One of the main drawbacks of this technique comes from the interaction of the incident electron with the water molecules constituting the solvent of the liquid cell. The water molecules initially decompose into reactive species such as hydrated electron eh−, hydrogen radical H•, hydroxyl radical OH•, or hydrogen gas H2. All of these species diffuse to the surrounding liquid and can lead to further reactions with water molecules or with the target sample.
This project aims at following the electron beam induced dissolution of goethite minerals to better assess the potential radiation damages involved with the in-situ imaging of iron oxide and understand associated kinetics.
Figure 1: STEM micrograph of goethite irradiated in water with an electron flux of 385 e-Å-2 s-1
The influence of environmentally relevant concentrations of Reactive Oxygen Species on mineral transformations
In surface environments, many chemical species are present in very low abundance and are thus considered insignificant in many biogeochemical processes. However, for some of these species, their low concentrations are solely due to their rapid rates of production and simultaneous consumption. These species are thus transient and short-lived but they can play a crucial effect in many global biogeochemical element cycles.
Reactive oxygen species (ROS) are among the most reactive transient species present in a wide range of environments. Theyinclude radical species such as superoxide O2·-, hydroxyl OH· and hydroperoxyl HO2· radicals as well as non-radical species like hydrogen peroxide H2O2, singlet oxygen 1O2, and ozone O3. All of these species are produced through both abiotic and biogenic reaction pathways. As a result, an increasing number of studies report ROS concentrations in natural waters ranging from 10-18 to 10-12 M for hydroxylradical, 10-12 to 10-9 M for superoxide anion, and 10-10 to 10-7 M for hydrogen peroxide.
This project aims at unraveling the influence of environmentally relevant concentration of ROS is investigated on magnetite minerals FeIIFeIII2O4 transformation into maghemite FeIII2O3. Magnetite is a mixed-valent iron mineral, and thus it cangreatly influence the cycle of metals and organic carbon. It plays an important role the regulating the mobility, toxicity, and redox transformation of organic and inorganic pollutants in terrestrial environments through its redox control.