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Liquid Phase Electron Microscopy of Magnetite

Periodic Reporting for period 1 - LPEMM (Liquid Phase Electron Microscopy of Magnetite)

Reporting period: 2017-03-01 to 2019-02-28

Nature, through evolution, has achieved exquisite control over the nucleation and growth of organic and inorganic materials, creating highly functional, complex and hybrid materials with exceptional properties, such as bones and sea shells. In this process called biomineralization, the pathway of formation is controlled in order to build complex materials in ambient aqueous conditions. If, as chemists, we are ever able to achieve this kind of control over the fabrication of materials it will come from a deep understanding of the pathway-dependent mechanisms involved in the nucleation and growth of hierarchical and hybrid structures. Among researchers in the materials sciences, calls have been made for a change in our trial and error based ‘Edisonian approach’ and to develop and use ‘in situ characterization techniques’ that will improve our understanding to the level where we can truly design complex functional materials form the bottom up using sustainable environmentally friendly methods.
LPEMM address these challenges using Liquid-Phase Electron Microscopy (LP-EM) a technique pioneered at TU/e, in collaboration with DENSsolutions (Delft-NL) and FEI company (Eindhoven-NL). It provides unique insight into nucleation and growth processes in liquids, by the direct real-time observation of nanoscale structure and dynamics in a liquid environment. In a recent review in Science, it was argued that LP-EM can solve the ‘grand challenges in materials science and self-assembly,’ particularly in relation to biomineral formation. LP-EM has already revolutionized our understanding of nanoparticle formation in liquids; however, so far research has mainly focused on simple one or two component systems in simple solvents. In order for LP-EM to contribute to the wider materials science community, we need a platform to analyse the formation of pathway-dependent materials in a series of increasingly complex environments.
LPEMM’s objective are: 1) Develop and optimize LP-EM protocols for imaging magnetite and ferrihydrite (the precursor to magnetite). 2) Determine the effect of reduction, pH, confinement and surface nucleation on the pathway of magnetite formation using LP-EM.
Fe3O4 has 2:1 stoichiometric ratio of Fe3+ and Fe+2 ions. In magnetotactic bacteria, formation occurs through the reduction of a ferrihydrite-like Fe3+ precursor, where the reduction rate, pH and iron uptake are controlled inside a confined environment, magnetosomes (1). In this project, the formation of magnetite is studied by LPEM in a series of increasingly complex but controlled environments. The aim is to determine the effect of reduction, pH, confinement and surface nucleation on the pathway of magnetite formation while developing new LPEM protocols for imagining optimization. First, plasma cleaned liquid cell TEM chips are sealed inside the liquid cell holder. FeCl is flown into the sealed liquid cell holder. N2 gas and subsequently, NaOH are flown to adjust the pH to 13, creating the ferrihydrite precursor inside the cell. The reduction to magnetite is then initiated by the electron beam.

Experiments have been conducted with a range of iron and hydroxide concentrations as well as the electron dose rate. Currently > 11 experimental variations have been tried with multiple repeats. In many cases we are able to form particles and observe their growth in-situ. Imaging and diffraction analysis after disassembly of the cell indicates the formation of crystalline iron oxide particles. In several cases we observe particles aligning, a behavior which appears to be linked with crystal formation. The in-situ data shows the dynamics of these particles during formation. Detailed analysis will provide insight into the relationship between particle size, morphology and their ability to self-organize.
The far reaching goal of LPEMM is to provide new insights into the formation of magnetite to allow its controlled formation under desirable synthetic conditions.
In this program we have already begun to make the first in-situ observations which show how the effects of reduction, solution conditions and confinement should allow us to manipulate the structure of magnetite particles and consequently their magnetic properties. Progress towards control over magnetite formation under environmental conditions could improve the cost effectiveness of the water purification process enabling its wider use around the world.
Furthermore, the goal of LPEMM is to further the use of liquid phase electron microscopy (LPEM) as a central tool in materials chemistry. In this program we have introduced LPEM into the masters course ‘Natural vs. Synthetic Materials’ at TU/e, presented LPEM movies at outreach programs such as, TU/e ‘Teachers Day’ and TU/e Science Festival Day and organized international meetings on LPEM including, The Royal Microscopical Society Microscopy Characterisation of organic-inorganic Interfaces 2018 and Liquid Phase Electron Microscopy 2017, Eindhoven, NL, 2017. The program has also been strongly connected to industry, work has been presented at ThermoFisher Scientific, DENSsolution and SABIC.
TEM images (a&d) and electron diffraction (b&d) of iron oxide particles made inside the liquid cell
Schematic approach of the work outlined in LPEMM