Effect of cetyltrimethylammonium bromide on the morphology of self assembled water soluble MnO2 nano-composites

Self-assembled water soluble MnO2 nano-composites have been synthesized by a facile one-step chemical reduction method at room temperature for the first time. MnO4−, tri-ethyl amine (TEA) and cetyltrimethylammonium bromide (CTAB) were acted as a reducing-, oxidizing-, and shape directing-agents, respectively. Stoichiometry, kinetics, and morphology of resulting colloidal particles were determined by using UV-visible spectrophotometric and transmission electron microscopic techniques. TEM images show that the MnO2 nanoparticles are self aggregated and/or adsorbed in an un-symmetric manner with a horizontal axis of 108 nm and longitudinal axis of 126 nm. CTAB increases the absorbance of MnO4− solution, alters the morphology of MnO2 particles from nano-composites to nano-sheets and inhibits the TEA oxidation rates. The lamellar δ-MnO2 nano-sheets are single crystals and formed from two types of building blocks, i.e., nano-wires and nano-particles. The role of inorganic salts (NaCl, NaNO3 and Na2SO4) on the formation kinetics of MnO2 has also been studied and discussed.