Controlled Synthesis of Co₃O₄Nanoparticles through Oriented Aggregation

Monodispersed 5-nm Co 3 O 4 nanocrystals are prepared by thermal decomposition, in long carbon chain alcohols, of the intermediate product Co(NO 3 ) 2 ·7C 6 H 13 OH, which is first obtained through the reaction of Co(NO 3 ) 2 ·6H 2 O with n -hexanol. A designed addition of water into the reaction system causes an oriented aggregation of the primary nanocrystals resulting in spherical mesoporous-like nanostructures from tens to several hundred nanometers. IR, XRD, UV−visible, and 1 H NMR analysis techniques are applied to determine the intermediate product, and the thermal-decomposition mechanism is identified through gas chromatography-mass spectrum analysis. XRD, TEM, HRTEM, SAED, and TG/MS are used to characterize the oriented aggregating nanostructures. The binder effect of water molecules on the oriented aggregation of the building blocks and the capping effect of the alcohols on the particle surface during the process are discussed.