Fabrication of TiO₂(B)/Anatase Heterophase Junctions at High Temperature via Stabilizing the Surface of TiO₂(B) for Enhanced Photocatalytic Activity

In recent years, TiO2(B) has been widely used in photocatalysis, electrocatalysis, and lithium-ion batteries due to its unique crystal structure. However, as a metastable phase semiconductor, TiO2(B) is prone to transform into the stable anatase or rutile phase at high temperature. Therefore, the low crystallinity of TiO2(B) was usually formed at low temperature. Both of the above two concerns restrict its application in photocatalysis. In this research, we found that an appropriate amount of HF could inhibit the phase transformation process from TiO2(B) to anatase. XRD patterns and Raman spectra showed that when 0.3 wt % HF was added prior to the calcination, a large amount of TiO2(B) could be maintained even at 750 °C. Thus, the sample with TiO2(B)/anatase heterophase junction structure was obtained at high temperature, which exhibited the enhanced photocatalytic activity both for pollution degradation and hydrogen production. The phase transformation mechanism was finally revealed by DFT calculations. It was demonstrated that the F anions adsorbed on the surface of TiO2(B) could efficiently decrease the surface energy from 0.63 J/m2 for the clean surface to −0.22 J/m2 for the F anions adsorbed surface, which was the internal factor for the retarded phase transformation process and promoted the fabrication of heterophase junction at high temperature