Abstract
In the synthesis of surface-modified nanocrystals (NCs), a simple and green chemistry approach to reduce liquid waste, particularly a solventless process, has been desired. In this study, we applied the supercritical CO2 technology, which is an excellent solventless process, to the synthesis of surface-modified iron oxide NCs. The synthesis was performed at 30.0 ± 0.8 MPa of CO2, 18 h and 100 °C, where iron(iii) acetylacetonate, pure water and decanoic acid were used as starting materials. As a result, the supercritical CO2 medium gave the NCs of α-Fe2O3 and γ-Fe2O3 with unimodal size distribution, where the mean size was 7.8 ± 2.0 nm. In addition, they were self-assembled on the TEM substrate and the mean nearest-neighbor spacing was close to the chain length of decanoic acid. Furthermore, FT-IR and TG analyses indicate that decanoic acid chemically attaches to the surface of iron oxide NCs that are dispersed in cyclohexane. These results suggest that the supercritical CO2 medium could be the new appealing reaction field to fabricate densely modified NCs without liquid waste.
Highlights
IntroductionSurface-modi ed metal oxide nanocrystals (NCs) have attracted considerable interest in recent years.[1]
Wet-based methods cause a large amount of liquid waste for the synthesis and washing,[9–11] where the disposal and the regeneration cost of them is known as the critical issue
These results clearly indicate that the addition of water to the supercritical CO2 medium accelerated the particle formation
Summary
Surface-modi ed metal oxide nanocrystals (NCs) have attracted considerable interest in recent years.[1]. Surface modi cation at the synthesis stage allows the inhibition of aggregation and the control of the size and shape of NCs that strongly affects their physicochemical properties.[6,7]. These appealing effects of surface modi cation have promoted the research on the direct-synthesis methods for surfacemodi ed NCs.[7–10]. The synthesis in supercritical carbon dioxide (CO2) can be new appealing candidate to fabricate surface-modi ed NCs. Supercritical CO2 has unique properties such as high solubility of the metal organic precursor[13]
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