Enhanced photocatalytic activity of single-phase, nanocomposite and physically mixed TiO2 polymorphs

• Various polymorphs of TiO2 were synthesized.
• Treatment of BPA using heterogeneous photocatalytic oxidation process.
• Among TiO2 polymorphs anatase phase shows the highest activity for BPA oxidation.
• Enhanced activity of physically mixed anatase and rutile nanoparticles is observed.

In this study, testing of TiO2 polymorphs (anatase, rutile, brookite) and their mixtures (anatase/rutile, anatase/TiO2-B) in heterogeneous photocatalytic oxidation process was conducted at ambient conditions in a batch slurry reactor. The efficiency of bare TiO2 catalysts was evaluated based on the degree of bisphenol A (BPA) removal, which is a well-known endocrine disrupting compound (EDC). The obtained results indisputably show that BPA removal is strongly affected by catalyst morphology, crystallite size, structure and specific surface area. Detailed interpretation of catalyst properties combined with BPA removal rates leads to the conclusion that photocatalytic oxidation is the most prominent either by using pure anatase particles or high surface area anatase/TiO2-B nanocomposite. However, the highest extent of mineralization was observed in the presence of high specific surface area nanotubular anatase/TiO2-B nanocomposite. Interestingly, when anatase and rutile particles were physically mixed, an additional beneficial effect on BPA degradation was observed. Interpretation of the obtained results shows that a synergistic effect between the respective phases takes place, and consequently enhances the overall activity. This phenomenon was explained by the proposed mechanism of overall hydroxyl radicals concentration increment due to transfer of OH formed on the surface of anatase particles (via H2O oxidation with photogenerated holes in the valence band) to rutile particles.

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