Thesis (M.Eng.)--Chulalongkorn University, 2007

Gold nanoparticle is a nanomaterial drawing many research attentions because it could exhibit distinctive properties, which are different from its bulk. Optical property is the most interesting aspect because it is strongly dependence on size of gold nanoparticles which could be controlled by many parameters. Though gold nanoparticles could be synthesized by various methods, liquid-phase reduction method is recognized as one of the most potential method because it consumes less energy and uses simple apparatus. Hence this research sets its aim at investigating the dependence of gold nanoparticle size on the molar ratio of precursor and reducing agent, total concentration of precursors, reaction temperature, sonication power and pH. Based on our experimental results, size of gold nanoparticle was strongly dependent on the molar ratio of precursor (HAuCl[subscript 4]) to reducing agent (Na[subscript 3]C[subscript 6]H[subscript 5]O[subscript 7]), total concentration of precursors and reaction temperature while sonication power could provide insignificant effect on the size of gold nanoparticles. Moreover, size and stability of gold nanoparticles could be controlled by adjusting pH of solution. Regarding to electrical property, gold nanoparticle is another alternative for using as ozone sensor. In this research, it was experimentally found that adsorption of ozone molecules on gold nanoparticles film caused a change of electrical resistance of gold nanoparticles.