期刊
NANOSCALE
卷 11, 期 14, 页码 6620-6628出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c9nr00531e
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资金
- EPSRC [EP/M015157/1]
- EPSRC CDT for the Advanced Characterisation of Materials [EP/L015277/1]
- AOARD [FA2386-17-1-4042]
- CERIC ERIC internal research project: Nano Analytics in Pharmaceutics
- EPSRC [EP/M015157/1] Funding Source: UKRI
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 Fe-57 Mossbauer spectroscopy showed a distinct transition from an amorphous ferrihydrite phase to a mixture of magnetite-maghemite ((FeO4)-O-3/gamma-Fe2O3). Synchrotron X-ray diffraction revealed the initial formation of crystalline iron hydroxide carbonate (green rust) plates occurring before the Fe3O4/gamma-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/gamma-Fe2O3.
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