Self-generation of tiered surfactant superstructures for one-pot synthesis of Co3O4 nanocubes and their closeand non-close-packed organizations

Self-generation of ionic organic capping from nonionic surfactant polyoxyethylene (20) sorbitan trioleate (Tween-85) has been realized for the controlled synthesis of single crystalline Co3O4 quantum dots (3.0-5.7 nm) in cubic morphology from related layered hydroxide precursors at 80-95 degreesC. With chemical modification of hydrophobic functional groups on the surface Of Co3O4 nanocubes; furthermore, various nanocube-containing micellar superstructures can be further assembled through hydrophobic interactions between Tween-85 molecules and the surface coating under "one-pot" conditions. In particular, square arrangements, spherical domains, and line-assemblies of the prepared Co3O4 nanocubes and their inter-transformations have been attained for the first time by manipulating intersurfactant-interactions. Hydrolysis of Tween-85 and the resultant tiered surfactant superstructures have been investigated with FTIR/UV-vis/EA/TGA/DTA/XPS methods, and the capping species has been identified to be alkylated oleic carboxylate anions derived from Tween-85. Pronounced quantum confinement effects have been observed with the prepared Co3O4 nanocubes, and the optical band gap energies determined are 3.95 and 2.13 eV, respectively, for O2- --> Co2+ --> and O2- --> Co3+ charge-transfer processes.