Thesis (M.Sc.)--Chulalongkorn University, 2008

Mn-doped layered lithium cobalt oxides, LiCo₁₋ₓMnₓO₂ (x = 0.0 - 1.0), were synthesized by citric acid-assisted sol-gel method (CAS). Characterized by X-ray diffraction (XRD), the single-phased LiCo₁₋ₓMnₓO₂ (LCMx) was observed for Mn doping up to x = 0.2 using the calcinations temperature of 700 oC for 6 h. The Mn doping apparently led to the reduction of crystallite size. The single-phased oxides were converted into proton-exchanged HCMx by stirring LCMx powders in acid solution for 24 h. The colloidal suspensions of single-phased LCMx (x = 0.0, 0.1, and 0.2) were obtained by exfoliation in tetrabutylammonium hydroxide (TBAOH) using ultrasound irradiation. The optimum condition for preparing the stable colloid was using the mole ratio of TBA/HCMx = 1.0 and the ultrasonic processor with the setting at 125 W for 30 min. Transmission electron microscopy (TEM) was used to reveal the dispersion of the layer oxide particles by the exfoliation process. The solid parts in a colloidal suspension were characterized as the mixture of oxide nanoparticles and exfoliated oxide nanosheets. Multilayer thin films of Mn-doped layered oxides and poly(diallyldimethylammonium) (PDAD) ions were successfully deposited layer-by layer (LBL) onto substrates by dipping coat technique. The optimum condition for thin film preparation was using 10 mM PDAD solution containing 0.5 M NaCl and dipping time at 10 min. FT-IR spectrum indicated the presence of PDAD on the attained composite films. UV-Vis absorption spectroscopy, Atomic force microscope (AFM) and XRD analysis were used to indicate the LBL growth of the thin films.