Fabrication of Co3O4 hierarchically superhydrophobic boat-like hollow cages at the silicon surface

By employing a simple bottom-up method for the first time and using ideas learned from nature, especially from the lotus leaf, we fabricated unique Co3O4 hierarchical boat-like hollow cages about 30 mu m in length and 8 mu m in width at the middle constituted of many nanorods and nanoparticles. The various morphologies of the products can be tailored from nanoparticles to nanorods and to microcages by tuning the concentration of Co(NO3)(2)center dot 6H(2)O. We believe that ammonia employed in this method plays not only the role of ligand to ensure the oxidation of Co2+ to Co3+ but also helps with the variation of concentration for the final morphologies. The products, which might be used as catalysts and microreactors, show superhydrophobic properties after chemical modification with poly(dimethylsiloxane) vinyl-terminated (PDMSVT) compound. It is confirmed that the synergic effect of the surface morphology and the surface free energy contribute to this unique surface water repellence.