| Autor: |
LaGrow AP; Biophysics Group, Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK. ntk.thanh@ucl.ac.uk., Besenhard MO; Department of Chemical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK. a.gavriilidis@ucl.ac.uk., Hodzic A; Central European Research Infrastructure Consortium, CERIC-ERIC, Trieste, Italy., Sergides A; Biophysics Group, Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK. ntk.thanh@ucl.ac.uk., Bogart LK; UCL Healthcare Biomagnetics Laboratories, University College London, 21 Albemarle Street, London, W1S 4BS, UK., Gavriilidis A; Department of Chemical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK. a.gavriilidis@ucl.ac.uk., Thanh NTK; Biophysics Group, Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK. ntk.thanh@ucl.ac.uk. |
| Abstrakt: |
Co-precipitation is the most ubiquitous method for forming iron oxide nanoparticles. For a typical co-precipitation synthesis, the pH of a ferrous and/or ferric ion solution is increased via the addition of a base. The latter can be added either slowly (a steady addition over either minutes or hours) or fast (a one-time addition) resulting in an abrupt increase in the pH. However, understanding the mechanism of particle formation is still lacking, which limits the reproducibility of the co-precipitation reaction due to intermediate phases still being present in the final product. In this work, we study in detail a co-precipitation synthesis with an abrupt increase in pH via the addition of sodium carbonate. Fast and reproducible mixing at defined precursor and base solution temperatures was achieved utilising a flow reactor. Transmission electron microscopy, electron diffraction and room temperature 57Fe Mössbauer spectroscopy showed a distinct transition from an amorphous ferrihydrite phase to a mixture of magnetite-maghemite (Fe3O4/γ-Fe2O3). Synchrotron X-ray diffraction revealed the initial formation of crystalline iron hydroxide carbonate (green rust) plates occurring before the Fe3O4/γ-Fe2O3 appeared. The ferrihydrite particles increase in size over time as the proportion of iron hydroxide carbonate plates are re-dissolved into solution, until the ferrihydrite particles crystallise into Fe3O4/γ-Fe2O3. |
