Immobilization of hydrothermally produced TiO2 with different phase composition for photocatalytic degradation of phenol

Hydrothermally produced TiO₂ powders with different phase composition (anatase, rutile and mixed phase) were immobilized on glass fibers and tested in the phenol mineralization process. Both H₂O₂ and O₂ were used as oxygen donors, and their performances were compared with those of the same TiO₂ samples as slurries.The catalytic properties of the immobilized different crystalline phases, rutile and anatase, show the same trend as the slurry samples: pure rutile displays the highest catalytic efficiency in the presence of H₂O₂, while samples containing anatase improve the photodegradation efficacy with O₂. It was suggested that the stability of the photogenerated electron–hole couple allows high activity of rutile in the presence of H₂O₂, while the relevant oxygen chemisorption on anatase causes high catalytic activity in the presence of O₂. A four parameters kinetics model shows that both reaction steps, the phenol degradation and the mineralization of the intermediates, are photoactivated by TiO₂.Photoactivity of the coated glass fibers is generally lower than that of slurries, even if their efficiencies are almost comparable when the oxidation is performed by H₂O₂, while much lower when the oxygen donor is O₂. As a matter of fact, the morphology of immobilized catalysts shows the presence of chestnut burr aggregates of large rutile crystalline rods on the glass fiber, which are much less compact than the aggregates of small anatase particles. This preserves rutile surface area from the coarsening effects; thus, when rutile is the more active species, as in the presence of H₂O₂, the photocatalytic activity is less affected by immobilization.