Hematite nanocubes with a broad size distribution have been synthesized by the decomposition of an iron−oleate complex under hydrothermal conditions, which was prepared from the reaction of iron chloride and sodium oleate. Well-defined assembly of uniform nanocubes with an average size of 15 nm can be obtained after a simple size-selection process. The molar ratio of iron chloride to sodium oleate and hydrothermal temperature had a crucial influence on the morphology of hematite nanopaticles in the synthesis. The blocking temperature of hematite nanocubes was ca. 80 K with an external field of 100 Oe, and they were superparamagnetic at room temperature. A cyclohexane-dispersed colloidal solution of hematite nanocubes showed a strong shape-dependent adsorption peak at 230 nm in the UV−vis spectrum. This synthesis approach is expected to become a general method for the preparation of other uniform nanoparticles with unique shapes such as cobalt and nickel oxides and so on.

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