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

Photocatalytic titanium dioxide (TiO₂) was synthesized by using an acid-catalyzed sol-gel process with titanium n-butoxide as the precursor. This synthetic TiO₂ responded to the visible light and its crystal structure was dominated by anatase. Several factors including the alcohol/acid type, calcinations temperature, light wavelength, and pH were examined for their impacts on the photocatalytic activity of the synthetic TiO₂ by using aniline as a target compound in aqueous suspension solution under visible light irradiation by using light-emitting diodes (blue, green, yellow, or red light). Photocatalytic activity of the synthetic TiO₂ under blue light illumination was detected whereas no photoreaction was observed for the commercial Degussa P-25 TiO₂ under the similar conditions. In addition, this photo-activity was more pronouncing under the blue than green, yellow, and red light, respectively, which was corresponding very well with its adsorption spectrum. As the initial concentration of aniline increased from 0.047 to 0.80 mM, the degradation efficiency of aniline for 4-hour irradiation with 1 g L⁻¹ TiO₂ decreased from 72 to 18%. The reaction rate was sufficiently explained by a non-linear second-order rate expression according to the Langmuir-Hinshelwood kinetic model. The value of the adsorption equilibrium constant was 15.89 mM⁻¹ and the second-order rate constant was 9.96 x 10⁻⁴ mM⁻¹ min⁻¹. Between pH 4 to 10, the optimum pH for the photocatalysis of aniline was 7.