Effects of the calcination temperature on the photoactivity of B- and F-doped or codoped TiO2 in formic acid degradation

In the framework of a large systematic investigation on the effects of doping TiO2 with first raw p-block elements of the Period Table, we discuss here the results obtained with a series of TiO2 photocatalysts doped or co-doped with boron and fluorine, prepared by sol-gel synthesis and calcined at 500 °C or at 700 °C. The photocatalytic activity of such materials in the oxidative decomposition of formic acid is related to their surface and structural properties, determined by BET, XRPD and Uv-vis absorption analyses. The photoactivity of singly doped or codoped TiO2 full anatase materials calcined at 500 °C appears to increase with their specific surface area and to be not related to electronic structure modifications due to the presence of the dopants. The photoactivity increase observed upon B-doping TiO2, which leads to B2O3 surface segregation, may thus simply result from their increased surface area, the presence of B2O3 having negligible effects on photoactivity. Highly crystalline F-doped or BF-codoped TiO2 materials calcined at 700 °C exhibit the highest photoactivity, essentially due to the retarded anatase into rutile transformation intrinsic of fluorine-doped materials.