How Phase Composition Influences Optoelectronic and Photocatalytic Properties of TiO2

In the present study the ratio of rutile and anatase phases in sol-gel-synthesized TiO2 was varied by calcination at temperatures ranging from 500 to 900 degrees C. Changes in opto-electronic properties were analyzed by time-resolved microwave conductance measurements (TRMC) and evaluated by comparison of the photocatalytic activity. The presence of rutile improves the charge separation efficiency by trapping of positive charges at the rutile surface, as derived from the increased levels of conductivity and electron lifetimes. These phenomena result in a decrease in the effective hole concentration at the anatase surface, the TiO2 surface with the highest intrinsic reactivity, when in contact with. rutile. Indeed, the presence of rutile results in inferior performance in the degradation of methylene blue and cyclohexane-selective photocatalytic oxidation. The negative effect of the presence of rutile can be compensated by improved morphological properties of the anatase phase, such as those present in P25. A novel structure-activity relationship is proposed and discussed.