Abstract:
The development of visible-light active TiO2 photocatalysts has attracted more attention in recent years due to its various applications in energy and environment related fields. Non-metal doping is one of the most effective techniques for the improvement of photocatalytic activity of TiO2 under visible light, especially with nitrogen doping. Doping method is very important factor for the synthesis nitrogen doped TiO2 which may influence the state of nitrogen in TiO2 and its efficiency in the visible-light absorption. Therefore, it is necessary to modify the conventional impregnation method by using ultrasonic-assisted. The objective of this thesis was to improve the visible-light activity of titanium dioxide catalysts by nitrogen doping using ultrasonic-assisted impregnation method. The effect of parameters such as ultrasonic power density and ultrasonic time on the properties and photocatalytic activity of TiO2 were examined. The results showed that nitrogen doping by ultrasonic-assisted impregnation method with both high and low power density induced the increasing of oxygen vacancy and decreasing of band gap energy of TiO2. The increasing of ultrasonic time leads to increase amount of interstitial nitrogen atoms within TiO2 lattice which resulted in enhanced visible light absorption compared with undoped TiO2 but not much effect on band gap narrowing. The optimal oxygen vacancy quantity and band gap narrowing could promote the photocatalytic performance. However, the results found that the catalysts prepared by ultrasonic-assisted impregnation method with both high and low power density exhibited clearly higher visible-light photocatalytic activity than undoped TiO2. The optimal condition for the preparation of nitrogen doped TiO2 using ultrasonic-assisted impregnation method with low power density was 90 min ultrasonic time and one with high power density was 30-60 min ultrasonic time,
that showed the highest photocatalytic activity under visible-light for degradation of methylene blue, which can reach 80% within 3 hours.