Bipyramidal anatase TiO 2 nanoparticles, a highly efficient photocatalyst? Towards a better understanding of the reactivity

Anatase nanoparticles with shape controlled bipyramidal morphology (TiO2-A-bipy) exhibited mainly {101} facets were synthesized through the sol–gel method and then used for the photodegradation of three model pollutants – Rhodamine B, phenol and formic acid – under UV-A radiation exposure. These titania samples exhibit better photocatalytic efficiency than the commercial TiO2-P25 reference for the dye degradation while this one demonstrates a higher activity for both phenol and formic acid. Moreover, supplementary washings of the particles significantly enhanced their photocatalytic efficiency in any case. To better understand these differences in term of photoactivity and the role of the TiO2 surface according to the nature of the targeted organic pollutant, various characterization techniques such as XRD, TEM and N2-sorption were used. Their surface properties were studied by FT-IR, TRMC and EPR. The presence of more acidic sites on TiO2-A-bipy surface could explain the faster degradation of the dye molecule through surface-mediated reactions. On the other side, a better generation and separation dynamic of photogenerated charges for TiO2-P25 could account for its higher photocatalytic efficiency for both formic acid and phenol degradation. This study shows that even if a quick test of dye degradation is mostly used in literature to confirm the efficiency of a photocatalyst, further investigation is often needed.