Self-Generation of Tiered Surfactant Superstructures for One-Pot Synthesis of Co3O4 Nanocubes and Their Close- and Non-Close-Packed Organizations

Abstract

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 Co(3)O(4) quantum dots (3.0-5.7 nm) in cubic morphology from related layered hydroxide precursors at 80-95 degrees C. With chemical modification of hydrophobic functional groups on the surface of Co(3)O(4) 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 Co(3)O(4) 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 Co(3)O(4) nanocubes, and the optical band gap energies determined are 3.95 and 2.13 eV, respectively, for O(2-)--> Co(2+) and O(2-)--> Co(3+) charge-transfer processes.