Characterization and photocatalytic performance evaluation of TiO2 according to various synthesis methods

Abstract

Titanium dioxide (TiO2) is a very useful functional material widely applied to photocatalysts, optical materials, dye-sensitized solar cells, lithium-ion batteries, and superhydrophobic materials. TiO2 has three types of crystal phase anatase, rutile and brookite and has a large redox power. TiO2 is mainly used as a photocatalyst to absorb the wavelength in the ultraviolet region activate the catalytic activity. Photocatalysts can be applied to energy fields such as removal of organic pollutants, deodorization, suppression of formation of carcinogenic substances, wastewater treatment, SOX and NOX removal and Water decomposition for hydrogen fuel generation. Moreover, the application of photocatalysts can be used not only to decompose harmful substances but also to convert harmful ingredients into useful ingredients. TiO2 has unique physical and chemical properties that it is difficult to control the size because particles tend to aggregate. To enhance the photocatalytic performance of TiO2 in aqueous conditions, the experiments of increasing the possibility of contact between the photocatalysis and pollutants were conducted, such as control of the specific surface area of TiO2 and preparation of TiO2 composites with silica having high specific surface area. The silica having a high specific surface area was synthesized from rice husk that is biomass thrown away after threshing rice. Rice husk is one of biomass that is biomass is an environmentally friendly energy resource. It is also highly commercial value because of easily obtained in countries where rice is a staple food. Rice husk silica has the advantages of low cost, economical and eco-friendly raw materials. Rice husk silica (RHS) used the Taguchi method to optimize the variables controlling the specific surface area (appropriate pH, aging time, amount of rice husk ash) and synthesized rice husk silica with large specific surface area (655.26 m2/g) via sol-gel method. The purpose of this thesis was improvement of photocatalytic activity, which was conducted by control the particle size and shape of TiO2, synthesis of black TiO2 with property to absorb even visible light and preparation of composites of TiO2 with rice husk silica having a high specific surface area. Photocatalyst generally is wide-ranging about the destruction of both organic and inorganic compounds, but this thesis was focused on organic compounds. In the process of synthesizing TiO2 nanoparticles, the yield and the conditions of the reflux process were optimized and TiO2 was synthesized using the sol-gel method. The synthesized TiO2 nanoparticles were confirmed for structural properties by XRD and HR-TEM analysis, dispersibility was observed through zeta potential and the specific surface area was confirmed by BET analysis The samples were set as TiO2 calcined from 200 to 900 ℃ (T200 ~T900), Black TiO2 by reduction of the surface through calcination at 200℃ under hydrogen atmosphere (TBlack200), and TiO2/RHS composites. T200 had the lowest zeta potential of -40.005 mV with appearance high dispersity in the aqueous phase and the second-largest a specific surface area of 258.64 m2/g. The TiO2/RHS composites had the largest specific surface area as 355.26 m2/g. The photolysis performance of the TBlack200 was the highest until the first 30 minutes by UV equipment, and after then the decomposition value of T200 was higher. Comparing with commercial product P25, the photocatalytic performance of T200 was better than P25 for about 100 minutes. When using photocatalyst for a short time, T200 was brought economical advantage because it was synthesized at lower temperatures than other TiO2 relatively and had the potential better photocatalytic efficiency than commercial P25. In addition to the field of photocatalyst, it has the potential to apply in various fields such as electronic materials and sensors.