We developed a versatile method using alkylamines (octylamine and isobutylamine) as structure-directing agents for synthesis of various 1D transition metal oxides in aqueous solution. In this report, 1D iron and copper oxide precursors (for simplicity, we have denoted them as pre-Fe2O3 and pre-CuO) and ZnO were prepared. After calcination and reduction, the 1D nanostructure of pre-Fe2O3 can be easily converted to 1D α-Fe2O3 and 1D Fe3O4, successively. The aspect ratio of the 1D nanostructures increases with the reaction time. XRD, TEM, in situ TEM, and TGA were used to characterize the samples. Results showed that after calcination at temperatures higher than 300 °C, the as-prepared 1D pre-Fe2O3, which was polycrystalline, transformed into 1D single-crystalline α-Fe2O3. A mechanism of assembling and “packing” along a certain direction for the growth of the 1D nanostructure was confirmed.

Copper oxide with various morphologies was synthesized by the hydrolysis of Cu(ac)2 with urea under mild hydrothermal conditions. In the synthesis, a series of organic amines with one or two amine groups (monoamine and diamine), including isobutylamine, octylamine (OLA), dodecylamine, octadecylamine (monoamines), ethylenediamine dihydrochloride, and hexamethylenediamine (diamines), was used as the "structure-directing agent". The monoamines led to the formation of one-dimensional (1D) aggregates of the copper oxide precursor particles (Pre-CuO), while the diamines led to the formation of two-dimensional (2D) aggregates. In both cases, the shorter carbon-chain amine molecules showed a stronger structure-directing function than that of the longer carbon-chain amine molecules. Next, in a series of syntheses, OLA was selected for further study, and the experimental parameters were systematically manipulated. When the hydrolysis was adjusted to a very slow rate by coupling the hydrolysis reaction with an esterification reaction, 1D aggregates of Pre-CuO were formed; when the hydrolysis rate was in the middle range, spherical Pre-CuO architectures composed of smaller linear aggregates were formed. However, under the high hydrolysis rates achieved by increasing the precipitation agent (urea) or by conducting the reaction at high temperatures (>/=120 degrees C), only Pre-CuO nanoparticles with a featureless morphology were formed. The formed spherical Pre-CuO architectures can be converted to a porous structure (CuOx) after removing the OLA molecules via calcination. Compared to the 1D and 2D aggregates, this porous architecture is highly thermally stable and did not collapse even after calcination at 500 degrees C. Preliminary results showed that the porous structure can be used both as a catalyst support and as a catalyst for the oxidation of CO at low temperatures.