Study On Synthesis And Modification With Doping Of Nano-sized TiO₂

The objective of this study is to synthesize nano-particle TiO₂ catalyst using titanium tetrabutoxide by modified sol-gel method and hydrothermal crystallization in organic solvents, and different content of metal ions (Fe³⁺, Eu³⁺, Dy³⁺, Nd³⁺ and Tb³) doping TiO₂ was prepared by modified sol-gel method. All samples were characterized by XRD, BET, SEM, TEM and TG/DTG/DSC method. Their photocatalytic activity were studied by photodegradation of methyl orange in aqueous solutions.First, the central composite design (CCD) method of second-order response surface model was used to investigate the effects of four different factors(the molar ratio of CH₃COOH/Ti(OC₄H₉)₄, velocity of stir, reaction time and calcination temperature) on the properties of the nano-sized photocatalyst TiO₂. The aim of this part is to determine the optimum processing parameters for TiO₂ produced via modified sol-gel method. The finding of the study showed that the optimum conditions of modified sol-gel method are obtained with the molar ratio 1:4:4 between titanium alkoxide of precursor, ethanol and acetic acid. The mixture must be stirred at ca. 400rpm in bath for 6h at 25℃. These conditions produced a better catalyst for methyl orange photocatalytic degradation after calcined at 500℃. SEM and TEM observed that the particle size was 10-30nm. XRD phase analysis showed that the sample was a mixture of anatase (89%) and rutile (11%).Then nano-sized titanium oxide was synthesized by hydrolysis of titanium alkoxide in toluene with water that was dissolved from the gas phase at high temperatures. TiO₂ particle was prepared by hydrothermal crystallization in organic solvents which are always crystallized in the anatase structure with particle size ranging from 10 to 20nm and BET surface area of 61.41m²/g after calcining at 550℃. This particle showed the highest activity in the photocatalytic degradation of methyl orange and high thermal stability. Finally, the modified sol-gel method was utilized to process Fe³⁺, Eu³⁺, Dy³⁺, Nd³⁺ and Tb³⁺ doped TiO₂ powders with doping element concentrations of 0.25, 0.5, 1, 2.5, 5 and 10 mol%. XRD, SEM, TEM and BET measurement results showed that the BET surface area of metal ions doped TiO₂ was more than that of pure TiO₂ because of the particle size reduced. Photocatalysis experimental results found that photocatalysis activity of doped TiO₂ calcined at 500℃was highest with optimal doping concentration of metal ions. Moreover, the applications of PL spectra in TiO₂ with doping metal ions, viz. the inherent relationships between the PL intensity and photocatalytic activity are revealed on the basis of PL attributes, demonstrating that the PL spectra can reflect some important information such as surface defects and oxygen vacancies, surface states, photo-induced charge carrier separation and recombination processes in nano-sized TiO₂.