Synthesis of triphasic, biphasic, and monophasic TiO2 nanocrystals and their photocatalytic degradation mechanisms

Abstract

The preparation of the triphasic (anatase/rutile/brookite), biphasic (anatase/brookite), and monophasic (anatase) TiO2 nanocrystals from peroxotitanium complex (PTC) as precursor by the hydrothermal method was reported in this work. The experimental results indicated that a large window for tuning the phase compositions was achieved by varying the HCl/PTC ratio due to the high stability of PTC. Moreover, the growth mechanism and microstructure evolution of the obtained TiO2 nanocrystals were discussed. The liquid-phase photocatalytic degradation of phenol under UV illumination was used as a model reaction to evaluate the photocatalytic activity of the synthesized materials. The photocatalytic activity is as follows: anatase/brookite biphase > anatase monophase > anatase/rutile/brookite triphase TiO2 nanocrystals. The possible photodegradation mechanism was studied by the examination of active species such as ·OH, photogenerated electrons and holes through adding their scavengers such as methanol, t-BuOH, and K2S2O8. Although the anatase/rutile/brookite triphase TiO2 nanocrystals samples show the most effective separation ability of photo-induced electron–hole pairs, the anatase/brookite biphase TiO2 nanocrystals samples exhibited the highest photocatalytic activity, which can be attributed to effective formation of the activated radicals.