Phase control and photocatalytic properties of nano-sized titania particles by gas-phase pyrolysis of TiCl_4

摘要

Nanometer size titania particles smaller than 60 nm were prepared by gas-phase pyrolysis of TiCU.The rutile content of nano-sized titania particles was controlled by changing the preparation temperature from 700 to 1100 deg C.It was found that mixed-phase titania nanoparticles containing about 11% of rutile,which were prepared at 810 deg C,showed higher photoactivity than that of as-prepared pure anatase one as well as Degussa P25.Pure anatase titania nanoparticles prepared at 700 deg C had much lower photoactivity compared with Degussa P25 or lab-made other samples which have some rutile phase since they have low crystallinity.So,the anatase titania nanoparticles prepared at 700 deg C was thermally post-treated in order to improve the crystallinity.As a result,the photoactivity was improved as the post-treatment temperature increases up to 800 deg C by which no significant rutile phase was formed.However,the improved photoactivity of pure anatase nanoparticles by the post-treatment was still smaller than all lab-made others which were not post-treated and had some rutile phase.From this result,it was concluded that the post heat treatment of pure anatase nanoparticles obtained by the gas-phase reaction at a low temperature is not helpful to prepare high photoactive titania nanoparticles.So,when titania nanoparticles are prepared by a gas-phase synthetic route,the direct preparation of high crystalline nanoparticles at high reaction temperature is recommended to obtain high photoactivity as long as no significant rutile phase is formed.