Effects of particle size of TiO₂ on photocatalytic degradation of methylene blue in aqueous suspensions

The influence of particle size of TiO₂ on the photocatalytic degradation of methylene blue (MB) in a suspended aqueous solution has been studied. The results suggested that the adsorption rate and adsorbability of MB on suspended TiO₂ particles increased as the particle sizes of TiO₂ decreased. Photocatalytic activity of TiO₂ also increased as the particle size of TiO₂ became smaller, especially when the particle size is less than 30 nm. The half-life (t_0.5) of the photocatalytic degradation of MB also decreased as the particle sizes of TiO₂ decreased. The first-order reaction rate constant for photodegradation of MB increased as the particle size of TiO₂ decreased. The initial degradation rate of MB in a suspended model was higher than that of a fixed-bed model. This will overcome the difficulty of preparation of ultrafine TiO₂ catalyst particles. Once the problem of separation of fine TiO₂ particles is solved, a TiO₂ suspended photoreactor could be provided on an industrial basis.