Controlled facile synthesis and photocatalytic activity of ultrafine high crystallinity TiO2 nanocrystals with tunable anatase/rutile ratios

Graphical abstract: - Highlights: • We devised a facile route for the controllable synthesis of TiO2 nanocrystals. • The anatase/rutile ratios can be tunable by sample adjusting aging time. • The well-crystallized TiO2 nanocrystals exhibit higher photocatalytic activities. - Abstract: The superfine high crystallinity TiO2 nanocrystals with tunable anatase/rutile ratios have been synthesized in an ethanol aqueous solution of HCl and sodium dodecylbenzene sulfonate (DBS) by a "low temperature dissolution–reprecipitation process" (LTDRP) and solvethermal treatment composite method. The effect of the synthesis parameters on the crystal structure, crystal size and the photocatalytic properties of the TiO2 nanocrystallines were investigated. The growth and aggregation of TiO2 nanocrystallines can be inhibited, and the high crystallinity spherical nanoparticles with small size are generated in the presence of DBS. The ratios of anatase and rutile can be easily controlled by sample adjusting aging time. The pure phase anatase is obtained by solvethermal treatment without aging process, the contents and the crystallite size of rutile are increased with increase of the aging time and only rutile exists while aging time is 16 h or more. The well-crystallized TiO2 nanocrystals exhibit higher photocatalytic activities. Their high photocatalytic activities could be attributed to high crystallinity, small crystal size (approximately 5 nm for anatase and 8 to 15 nm for rutile), the synergistic effect between anatase and rutile and strong electron-withdrawing characteristic of the sulfoacid radical of DBS