TiO
2 photocatalysts with predetermined phase composition (anatase-to-rutile ratio) have been prepared from strongly acidic aqueous HCl/TiCl
4 mixtures with 0.1 M ≤ [HCl]
TOT ≤ 5 M and 0.05 M ≤ [TiCl
4]
TOT ≤ 3 M (where the subscript TOT denotes total or analytical concentration). During the syntheses, TiCl
4 was added to a cold-HCl solution. The initially precipitate free reaction mixture was boiled, resulting in the formation of large amount of solid, nanocrystalline (particle size 4–12 nm) TiO
2 particles with large specific surface area (up to
![not, vert, similar not, vert, similar](http://www.sciencedirect.com/scidirimg/entities/223c.gif)
240 m
2/g). We found from the XRD patterns that at constant [HCl]
TOT, the anatase content of the crystallized solid systematically increases with decreasing [TiCl
4]
TOT, while at constant [TiCl
4]
TOT, the rutile content was found to systematically increase with increasing [HCl]
TOT. Thus the phase composition of the photocatalysts prepared was possible to be fine-tuned with the aid of these two simple initial parameters. The photocatalytic activity of the as-prepared catalysts was found to strongly correlate with the phase composition. In phenol decomposition the samples’ photocatalytic performance gradually and significantly increases with their anatase content: photocatalysts containing only anatase as crystalline phase were up to three times more efficient than rutile ones. Interestingly, in salicylic acid decomposition, rutile-only catalysts were found to show no activity at all, but some of our catalysts (both anatase-only and rutile–anatase mixtures) at pH
![not, vert, similar not, vert, similar](http://www.sciencedirect.com/scidirimg/entities/223c.gif)
3 (but not at pH
![not, vert, similar not, vert, similar](http://www.sciencedirect.com/scidirimg/entities/223c.gif)
7) displayed photocatalytic activity commensurable to that of Degussa P25. This can be explained in terms of the efficient surface chemisorption of salicylate ion on large specific surface area TiO
2 particles in acidic solutions.