Various-Shaped Uniform Mn3O4 Nanocrystals Synthesized at Low Temperature in Air Atmosphere

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• 作者：Taekyung Yu ; Jaewon Moon ; Jinkyung Park ; Yong Il Park ; Hyon Bin Na ; Byung Hyo Kim ; In Chan Song ; Woo Kyung Moon ; Taeghwan Hyeon
• 刊名：Chemistry of Materials
• 出版年：2009
• 出版时间：June 9, 2009
• 年：2009
• 卷：21
• 期：11
• 页码：2272-2279
• 全文大小：509K
• 年卷期：v.21,no.11(June 9, 2009)
• ISSN：1520-5002

文摘

We report a novel and facile method for the synthesis of manganese oxide (Mn₃O₄) nanocrystals with various sizes and shapes. Mn₃O₄ nanocrystals were synthesized via a reaction of manganese(II) acetate with water in xylene in the presence of surfactants at the temperature of as low as 90 °C in air atmosphere. Structural characterizations revealed that the synthesized nanocrystals were tetragonal Mn₃O₄ structure and that they were highly crystalline in spite of the low reaction temperature. The size and shape of the nanocrystals were readily controlled by varying the experimental conditions such as precursors, surfactants, and injection temperature of water. Nanoplates with a thickness of 5 nm and side dimensions of 9, 15, and 22 nm were synthesized using oleylamine as the surfactant. When carboxylic acid was used as the cosurfactant along with oleylamine, spherical nanocrystals were obtained with sizes of 5.5, 6.2, 7.2, 8.5, and 15 nm. Interesting anisotropic nanostructures including nanowires and nanokites were also prepared by changing the injection temperature of water. Mechanistic studies revealed that in situ generated manganese hydroxide (Mn(OH)₂) mainly contributes to the nucleation, whereas the manganese−oleylamine complex contributes to the shape-controlled growth process. The current procedure can be readily applicable to large-scale synthesis because of their facile and mild reaction conditions including low reaction temperature and air environment and the use of nontoxic and inexpensive reagents. For example, under optimized reaction conditions, we were able to synthesize as much as 4.5 g of 15 nm sized Mn₃O₄ nanoplates using a 1 L reactor. Water-dispersible 9 nm sized Mn₃O₄ nanoplates exhibited specific relaxivity (r₁) value of 0.13 mM⁻¹ s⁻¹, demonstrating the potential application of the nanocrystals to T₁ contrast agent for magnetic resonance imaging (MRI).