Synthesis and characterization of metal-doped TiO2 nanobead prepared by using hydrothermal method

Abstract

Titanium dioxide (TiO2) is a ceramic material that is chemically stable, harmless and is used in many fields due to its effective redox reaction. The photocatalyst industry uses sunlight as a light source that consists of 5 % ultraviolet, 43 % visible light, and 52 % infrared region. TiO2 has photoactivity even with the low energy of ultraviolet, but the ultraviolet of sunlight has a limitation, so it is necessary to improve the characteristics of TiO2. Therefore, this thesis was aimed to enhance the photocatalytic effect by increasing the surface area and lowering the bandgap energy of TiO2 to have photoactivity in the visible region. TiO2 nanoparticles were synthesized by the sol-gel and hydrothermal methods and as the calcination temperature increased, the crystallinity increased so that the photocatalytic effect was enhanced. Methylene blue degradation was performed to measure the photolysis effect. TiO2 calcined at 600 °C decomposed 62.79 % of methylene blue, indicating the highest photocatalytic effect among the nanoparticle samples. In order to increase the surface area of TiO2 nanoparticles, various kinds of acids were added to synthesize nanobeads. Sulfuric acid did not form bead shape, but TiO2 with hydrochloric acid and nitric acid were made of nanobeads. pH 3 and pH 7 with nitric acid had a larger surface area and pore size than pH 3 and pH 7 with hydrochloric acid, and the methylene blue decomposition effect was better. Sample by pH 3 nitric acid had a surface area of 42.2399 m2/g and a pore size of 19.2778 nm, and TiO2 had more anatase structure at lower pH, leading to the highest photocatalytic effect. The metal doping to TiO2 increased the photocatalytic effect of TiO2 by lowering the bandgap energy. TiO2 nanobeads were doped with vanadium, iron, and nickel at molar ratios of 1 %, 5 %, and 10 % with Ti. Analysis indicated that the bandgaps of the TiO2 nanobead samples were reduced by doped with metals. TiO2 nanobeads doped with vanadium at 1 % had a bandgap energy of 3.07 eV and indicated the highest photocatalytic effect of 69.25 %. Through this study, vanadium-doped TiO2 nanobeads had the highest photolysis efficiency, which had the photoactivity in the visible region and exhibited high photocatalytic properties. As a result, vanadium-doped TiO2 nanobeads are expected to appear positive performance once they apply for photocatalyst, air cleaner filter, electronic material and sensor field.