TiO2 faceted nanocrystals on the nanofibers: Homojunction TiO2 based Z-scheme photocatalyst for air purification

Although high energy TiO2 nanocrystals (HE-TiO2-NCs) with exposed (0 0 1) facets shows superior photoreactivity in oxidation of organic pollutants, they are suffering from the problem of hard to be collected in recycling use. In this paper, high photoreactive HE-TiO2-NCs decorated TiO2 nanofibers (TiO2-NFs) were fabricated by electrospinning the mixture of TiOF2 cubes and tetrabutyl titanate (TBT) followed by calcination. We systematically studied the dependence of calcination temperature on microstructure and photocatalytic property toward acetone oxidation. It was found that heat treatment of the TiOF2 embedded TiO2 nanofibers results in the formation of HE-TiO2-NCs decorated TiO2-NFs (HE-TiO2-NCs/TiO2-NFs). The addition of TiOF2 not only improves the crystallization, but also prevents the anatase-to-rutile phase transformation of TiO2-NFs, and 600 degrees C-calcined HE-TiO2-NCs/TiO2-NFs sample (TF600) shows the highest photoreactivity under UV irradiation with an acetone oxidation rate of 97.2 ppmh(-1), 4.2 times higher than pristine TiO2-NFs sample (T600) that was prepared under similar conditions but without the addition of TiOF2. TF600 sample also exhibits increased visible photoreactivity in oxidation of NO when compared with T600 sample. The enhanced photoreactivity of HE-TiO2-NCs/TiO2-NFs was attributed to the combined effects of fluoride-induced enhancement of crystallization, formation of oxygen vacancy (Vo) and the production of a direct Z-scheme homojunction between HE-TiO2-NCs and TiO2-NFs.