Interaction of anatase and rutile TiO2 particles in aqueous photooxidation

The interaction of anatase and rutile titanias was studied with various combinations of TiO2 catalysts having different particle sizes and impurity contents by photodecomposition of phenol and formic acid. The reactivity of commercial Ishihara ST-series anatase titanias (95 % TiO2) increased with the increase of primary particle size (ST-01, 7 nm; ST-21, 20 nm; ST-41, 200 nm) and the decrease of surface area. Light extinction coefficients of the ST-series anatase TiO2’s at the wavelength of 365 nm were about 1 order of magnitude lower than that of Kemira (KE) rutile TiO2 having a surface area of 52 m2/g. Different interactions between anatase and rutile titanias were observed with the mixtures of the ST-series anatase TiO2’s and KE rutile TiO2. When the irradiation field was dominated by the KE in the mixtures, these interactions inverted completely the order of activities of the ST-series catalysts in phenol photooxidation. The impurity distribution in particles of the Ishihara ST-series TiO2 catalysts was proposed to explain the above phenomena. The different interactions between anatase and rutile TiO2 particles were related to their relative Fermi levels prior to their contacting each other. Different interactions between Hombikat UV-100 anatase TiO2 (HK, 99 % TiO2) and rutile-phase TiO2 made from HK (HK R) by heating were observed in phenol and formic acid photodegradations. The change of interaction between HK and HK R was explained by the stronger hydrolyzation and weaker agglomeration of TiO2 particles at lower pH values. The experiments done showed that the synergistic effect between anatase and rutile in Degussa P25 was not universal and it was related to the relative Fermi levels of anatase and rutile particles and the particle shape