Modification of TiO2 with hBN: high temperature anatase phase stabilisation and photocatalytic degradation of 1,4-dioxane

This paper examines the modification of anatase TiO2 with hexagonal boron nitride (hBN) and the impact this coupling has on the temperature of the anatase to rutile phase transition and photocatalytic activity. All samples were 100% anatase when calcined up to 500 °C. At 600 °C, all BN-modified samples contain mixed rutile and anatase phases, with 8% and 16% BN–TiO2 showing the highest anatase contents of 64.4% and 65.5% respectively. The control sample converted fully to rutile at 600 °C while the BN modified sample converted to rutile only at 650 °C. In addition to TiO2 phase composition, XRD also showed the presence of bulk boron nitride peaks, with the peak at 26° indicating the graphite-like hBN structure. Density functional theory calculations of hBN-rings adsorbed at the anatase (101) surface show strong binding at the interface; new interfacial bonds are formed with key interfacial features being formation of B–O–Ti and N–Ti bonds. Models of extended hBN sheets at the anatase (101) surface show that formation of B–O and N–Ti bonds along the edge of the hBN sheet anchor it to the anatase surface. 16% BN–TiO2 at 500 °C showed a significant increase in the photocatalytic degradation of 1,4-dioxane when compared with pure anatase TiO2 at 500 °C. This arises from the effect of hBN on anatase. The computed density of states (DOS) plots show that interfacing anatase with BN results in a red shift in the TiO2 energy gap; N-p states extend the valence band maximum (VBM) to higher energies. This facilitates transitions from high lying N-p states to the Ti-d conduction band. A simple photoexcited state model shows separation of electrons and holes onto TiO2 and BN, respectively, which promotes the photocatalytic activity.