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.