Crystal structure is one of the most influential features of an individual TiO2 compound on photocatalytic activity, especially the composition between the most two abundant phases – anatase and rutile. Although anatase structure is considerably acceptable as the highest photoactive phase, many reactions have been facilitated much better with the rutile form, and occasionally mixed phases with the certain composition shows the highest performance on particular reactions.  However, the principle on the synergistic effect of anatase/rutile is still unclear and debatable. The solid experimental evidences are therefore urgently required in order to clarify the question ‘which phenomena do govern the overall observed improved photoactivity of anatase/rutile composites?’.
In this research, two series of mesoporous TiO2 nanoparticles with tunable anatase-rutile percentage has been hydrothermally synthesized by a simple approach based on novel Ti(III)-peroxide system at relatively low temperature (≤ 200°C). Phase-tuned materials (anatase/rutile) were carefully characterized, compared, and discussed based on several photocatalytic tests, including water oxidation and reduction, hydrogen peroxide reduction.  It appeared, that the optimal, ‘universal’ phase composition does not exists, but strongly depends on the reaction type – high contents of rutile or anatase should be considered for H2O2 reduction and water oxidation, respectively, while methanol-assisted water reduction requires moderate contents of both polymorphs. Presented data show that a synergistic effect observed usually for anatase/rutile composites can result from both, intrinsic and extrinsic factors, which are related to its physicochemical properties and performed redox reactions, respectively.