Preparation of the anatase phase TiO2 nanocrystallites using subcritical water as the solvent and evaluation of their photocatalytic properties under visible light irradiation

Anatase phase TiO2 nanocrystallites are prepared using subcritical water and Rhodamine B (RB) as the solvent and the model pollutant, respectively, to test the photocatalytic activity of the obtained TiO2 nanocrystallites. The experimental results indicate that the prepared products exhibit better photocatalytic properties than those of commercial P25. The sample characterization results also indicate that the anatase phase TiO2 nanocrystallites are generated in the hydrolysis process and that the crystallinity is remarkably increased after calcination. The crystallite sizes of the anatase nanocrystallites are investigated and the interactions between the factors are evaluated using response surface methodology. The optimal conditions for the preparation process are obtained as follows: hydrolysis temperature of 603 K, calcination temperature of 953 K, calcination time of 60 min and solution pressure of 13 MPa. The practical experiments under the optimal condition are carried out in triplicate, and the average crystallite size is 21.38 nm. The photodegradation kinetics is discussed using the Langmuir-Hinshelwood (LH) model. The results show that LH model is feasible in describing RB degradation.